Ice-induced structural vibration generally decreases with an increase in structural width at the waterline. Definitions of wide/narrow ice-resistant conical structures, according to ice-induced vibration, are directly related to structure width, sea ice parameters, and clearing modes of broken ice. This paper proposes three clearing modes for broken ice acting on conical structures: complete clearing, temporary ice pile up, and ice pile up. In this paper, sea ice clearing modes and the formation requirements of dynamic ice force are analyzed to explore criteria determining wide/narrow ice-resistant conical structures. According to the direct measurement data of typical prototype structures, quantitative criteria of the ratio of a cone width at waterline (D) to sea ice thickness (h) is proposed. If the ratio is less than 30 (narrow conical structure), broken ice is completely cleared and a dynamic ice force is produced; however, if the ratio is larger than 50 (wide conical structure), the front stacking of broken ice or dynamic ice force will not occur.

To simulate the FPSO-iceberg collision process more accurately, an elastic-plastic iceberg material model considering temperature gradient effects is proposed and applied. The model behaves linearly elastic until it reaches the ‘Tsai-Wu’ yield surfaces, which are a series of concentric elliptical curves of different sizes. Decreasing temperature results in a large yield surface. Failure criteria, based on the influence of accumulated plastic strain and hydrostatic pressure, are built into the model. Based on published experimental data on the relationship between depth and temperature in icebergs, three typical iceberg temperature profiles are proposed. According to these, ice elements located at different depths have different temperatures. The model is incorporated into LS-DYNA using a user-defined subroutine and applied to a simulation of FPSO collisions with different types of icebergs. Simulated area-pressure curves are compared with design codes to validate the iceberg model. The influence of iceberg shape and temperature on the collision process is analyzed. It is indicated that FPSO structural damage not only depends on the relative strength between the iceberg and the structure, but also depends on the local shape of the iceberg.

Owing to the increase in unprecedented accidents with new root causes in almost all operational areas, the importance of risk management has dramatically risen. Risk assessment, one of the most significant aspects of risk management, has a substantial impact on the system-safety level of organizations, industries, and operations. If the causes of all kinds of failure and the interactions between them are considered, effective risk assessment can be highly accurate. A combination of traditional risk assessment approaches and modern scientific probability methods can help in realizing better quantitative risk assessment methods. Most researchers face the problem of minimal field data with respect to the probability and frequency of each failure. Because of this limitation in the availability of epistemic knowledge, it is important to conduct epistemic estimations by applying the Bayesian theory for identifying plausible outcomes. In this paper, we propose an algorithm and demonstrate its application in a case study for a light-weight lifting operation in the Persian Gulf of Iran. First, we identify potential accident scenarios and present them in an event tree format. Next, excluding human error, we use the event tree to roughly estimate the prior probability of other hazard-promoting factors using a minimal amount of field data. We then use the Success Likelihood Index Method (SLIM) to calculate the probability of human error. On the basis of the proposed event tree, we use the Bayesian network of the provided scenarios to compensate for the lack of data. Finally, we determine the resulting probability of each event based on its evidence in the epistemic estimation format by building on two Bayesian network types: the probability of hazard promotion factors and the Bayesian theory. The study results indicate that despite the lack of available information on the operation of floating objects, a satisfactory result can be achieved using epistemic data.

The offshore pipeline network in the U.S. Gulf of Mexico is the largest and most transparent system in the world. A review of deepwater projects in the region provides insight into construction cost and installation methods and the evolution of contract strategies. Pipeline projects are identified as export systems, infield flowline systems, and combined export and infield systems, and three dozen deepwater pipeline installations from 1980-2014 are described based on Offshore Technology Conference (OTC) and Society of Petroleum Engineers (SPE) industry publications and press release data. Export lines and infield flowlines are equally represented and many projects used a combination of J-lay, S-lay and reel methods with rigid steel, flexible line, and pipe-in-pipe systems. The average 2014 inflation-adjusted cost for pipeline projects based on OTC/SPE publications was $2.76 million/mi and ranged from $520 000/mi to $12.94 million/mi. High cost pipelines tend to be short segments or specialized pipeline. Excluding the two cost endpoints, the majority of projects ranged from $1 to $6million/mi. The average inflation-adjusted cost to install deepwater pipelines in the U.S. Gulf of Mexico based on available public data is estimated at $3.1 million/mi.

This work details the simulation of tsunami waves generated by seaquakes in the Manila Trench and their effect on fixed oil and gas jacket platforms in waters offshore North Borneo. For this study, a four-leg livingquarter jacket platform located in a water depth of 63m is modelled in SACS v5.3. Malaysia has traditionally been perceived to be safe from the hazards of earthquakes and tsunamis. Local design practices tend to neglect tsunami waves and include no such provisions. In 2004, a 9.3M_w seaquake occurred off the northwest coast of Aceh, which generated tsunami waves that caused destruction in Malaysiatotalling US$ 25 million and 68 deaths. This event prompted an awareness of the need to study the reliability of fixed offshore platforms scattered throughout Malaysian waters. In this paper, we present a review ofresearch on the seismicity of the Manila Trench, which is perceived to be high risk for Southeast Asia. From the tsunami numerical model TUNA-M2, we extract computer-simulated tsunami waves at prescribed grid points in the vicinity of the platformsin the region. Using wave heights as input, we simulate the tsunami using SACS v5.3structural analysis software of offshore platforms,which is widely accepted by the industry. We employ the nonlinear solitary wave theory in our tsunami loading calculationsfor the platforms, and formulatea platform-specific risk quantification system. We then perform an intensive structural sensitivity analysis and derive a corresponding platform-specific riskrating model.

In this study, the coupled heave-pitch motion equations of a spar platform were established by considering 1st-order and 2nd-order random wave loads and the effects of time-varying displacement volume and transient wave elevation. We generated random wave loads based on frequency-domain wave load transfer functions and the Joint North Sea Wave Project (JONSWAP) wave spectrum, designed program codes to solve the motion equations, and then simulated the coupled heave-pitch motion responses of the platform in the time domain. We then calculated and compared the motion responses in different sea conditions and separately investigated the effects of 2nd-order random wave loads and transient wave elevation. The results show that the coupled heave-pitch motion responses of the platform are primarily dominated by wave height and the characteristic wave period, the latter of which has a greater impact. 2nd-order mean wave loads mainly affect the average heave value. The platform’s pitch increases after the 2nd-order low frequency wave loads are taken into account. The platform’s heave is underestimated if the transient wave elevation term in the motion equations is neglected.

Tendons vertically moor Tension-Leg Platforms (TLPs), thus, a deep understanding of physical tendon stresses requires the determination of the total axial deformation of the tendons, which is a combination of the heave, pitch, and surging responses. The vertical motion of the lateral sides of the TLP is coupled with surge and constitutes a portion of the pitch motion. Tendons are connected to the sides of the TLP; hence, the total displacement of the lateral sides is related to the total deformation of the tendons and the total axial stress. Therefore, investigating the total vertical response at the sides of the TLP is essential. The coupling between various degrees of freedom is not considered in the Response Amplitude Operator (RAO). Therefore, in frequency domain analysis, the estimated vertical RAO is incomplete. Also, in the time domain, only the heave motion at the center of TLP is typically studied; this problem needs to be addressed. In this paper, we investigate the portion of the pitch motion in the vertical response at the sides of the TLP in both the frequency and time domains. Numerical results demonstrate a significant effect of the pitch motion in the vertical motion of the edges of the TLP in some period ranges.

The development of robust damage detection methods for offshore structures is crucial to prevent catastrophes caused by structural failures. In this research, we developed an Improved Modal Strain Energy (IMSE) method for detecting damage in offshore platform structures based on a traditional modal strain energy method (the Stubbs index method). The most significant difference from the Stubbs index method was the application of modal frequencies. The goal was to improve the robustness of the traditional method. To demonstrate the effectiveness and practicality of the proposed IMSE method, both numerical and experimental studies were conducted for different damage scenarios using a jacket platform structure. The results demonstrated the effectiveness of the IMSE method in damage location when only limited, spatially incomplete, and noise-polluted modal data is available. Comparative studies showed that the IMSE index outperformed the Stubbs index and exhibited stronger robustness, confirming the superiority of the proposed approach.

Offshore jacket-type platforms are attached to the seabed by long batter piles. In this paper, results from a finite element analysis, verified against experimental data, are used to study the effect of the pile’s inclination angle, and its interaction with the geometrical properties of the pile and the geotechnical characteristics of the surrounding soil on the behavior of the inclined piles supporting the jacket platforms. Results show that the inclination angle is one of the main parameters affecting the behavior of an offshore pile. We investigated the effect of the inclination angle on the maximum von Mises stress, maximum von Mises elastic strain, maximum displacement vector sum, maximum displacement in the horizontal direction, and maximum displacement in the vertical direction. Results indicate that the pile’s operationally optimal degree of inclination is approximately 5°. By exceeding this value, the instability in the surrounding soil under applied loads grows extensively in all the geotechnical properties considered. Cohesive soils tend to display poorer results compared to grained soils.

The dynamic responses of any floating platform are dependent on the mass, stiffness and damping characteristics of the body as well as mooring system. Therefore, it is very essential to study the effect of individual contributions to the system that can finally help to economise their cost. This paper focuses on the effect of mooring stiffness on the responses of a truss spar platform, obtained by different grouping of lines. The study is part of our present researches on mooring systems which include the effect of line pretension, diameter and azimuth angles. The platform is modelled as a rigid body with three degrees-of-freedom and its motions are analyzed in time-domain using the implicit Newmark Beta technique. The mooring lines restoring force-excursion relationship is evaluated using a quasi-static approach. It is observed that the mooring system with lines arranged in less number of groups exhibits better performance in terms of the restoring forces as well as mean position of platform. However, the dynamic motions of platform remain unaffected for different line groups.

This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.

In order to provide a theoretical guide for choosing the material for the hawsers for the FPSO side-by-side offloading system, which is moored by the yoke system, the 3D potential flow theory and full coupled time-domain analysis are presented to study the dynamic response of the offloading system. The MingZhu FPSO offloading system in the field BZ25-1 is simulated here; and four different characteristic fiber ropes are used as the material for the hawsers. To acquire an accurate hawser line tension, the polynomial fitting method is used to calculate the nonlinear stiffness of the hawsers. By comparing the hawser lines’ tension and the relative motion between the FPSO and the shuttle tanker, a suitable material for the hawser lines is chosen and discussed in this paper. The results indicate that the nonlinear stiffness characteristic of the fiber rope has a small effect on the relative motion of the vessels, but the hawser lines’ tension is greatly influenced by the different characteristics of the fiber ropes. The hawser lines’ tension with nonlinear stiffness is in accordance with the one with the upper and lower bound linear stiffness, which proves this method of fitting the fiber ropes’ nonlinear stiffness is reasonable and reliable.

This paper focuses on the research of a semi-submersible platform equipped with a DP-assisted mooring system. Based on the working principles of the DP-assisted mooring system and the model of the platform motion, a time domain simulation program is applied to analyze the impact, in the case of one line failure, on the platform motion, power consumption of the thrusters and the tension of the mooring lines. The results show that, under the 10-year wind dominant, a one line failure will have little impact on the tension of the mooring lines. When the failure line is windward, the power consumption will increase greatly with a weakened position of accuracy. However when the failure line is leeward, the power consumption will be reduced with a partly strengthened position of accuracy.

The extending of a cantilever and transverse moving of a drilling floor enable the jack-up to operate in several well positions after the Jack-up has pitched. The cantilever allowable load nephogram is the critical reference which can evaluate the jack-up’s drilling ability, design the cantilever structure and instruct a jack-up manager to make the operations safe. The intent of this paper is to explore the interrelationships between the cantilever position, drilling floor and the loads including wind force, the stand set-back weight etc., through analyzing the structure and load characteristics of the x-type cantilever and the simplified mechanics model with the restriction of the maximum moment capacity of the cantilever single side beam. Referring to several typical position designs load values, the cantilever allowable load nephogram is obtained by using the suitable interpolation method. The paper gives a method for cantilever allowable load design, which is proved reliable and effective by the calculation example.

The subsea dynamic riser base（SDRB）is an important piece of equipment for the floating production platform mooring system.One end is connected to the rigid pipeline, carrying a rigid pipeline thermal expansion load and the other end is connected to a flexible riser, carrying the dynamic load of the flexible riser, so its function is a transition connection between the flexible riser and the rigid pipeline which fixes the flexible riser on the seabed. On the other hand，as a typical subsea product, the design will satisfythe requirements of the standards for subsea products. By studying the stress analysisphilosophy of the topside piping and subsea pipeline, a physical model and procedure for piping stress analysis of the SDRB have been established.The conditions of the adverse design load have been considered, and a combination of the static load from the rigid pipeline and the dynamic load flexibility has also been optimized. And a comparative analysis between the AMSE, DNV and API standards for piping stress with the checking rules has been done.Because theSDRB belongs to the subsea pipeline terminal product, the use of DNV standards to check its process piping stress is recommended. Finally, the process piping stress of the SDRB has been calculated, and the results show that the jacket pipe and the carrier pipe stress of the SDRB process piping satisfy the DNV standards as a whole.The bulkhead cannot be accurately simulated by the AutoPIPE software which uses the FEA software ANSYS inthe detailed analysis, but the checking results will still meet the requirements of the DNV standards.

In order to assess the possible collision effect, a numerical simulation for the upper module and spar platform docking at the speed of 0.2 m/s was conducted by using the software ANSYS/LS-DYNA, and the time history of the collision force, energy absorption and structural deformation during the collision was described. The purpose was to ensure that the platform was safely put into operation. Furthermore, this paper analyzes different initial velocities and angles on the Von Mises stress and collision resultant force during the docking collision. The results of this paper showed that the docking could be conducted with higher security. The data in this paper can provide useful references for the determination of the upper module’s offshore hoisting scheme and practical construction by contrasting the numerical simulation results of the parameters on the docking collision.

This paper studies the current available options for floating production platforms in developing deepwater oil fields and the potential development models of future oil and gas exploration in the South China Sea. A detailed review of current deepwater platforms worldwide was performed through the examples of industry projects, and the pros and cons of each platform are discussed. Four types of platforms are currently used for the deepwater development: tension leg platform, Spar, semi-submersible platform, and the floating production system offloading. Among these, the TLP and Spar can be used for dry tree applications, and have gained popularity in recent years. The dry tree application enables the extension of the drilling application for fixed platforms into floating systems, and greatly reduces the cost and complexity of the subsea operation. Newly built wet tree semi-submersible production platforms for ultra deepwater are also getting their application, mainly due to the much needed payload for deepwater making the conversion of the old drilling semi-submersible platforms impossible. These platforms have been used in different fields around the world for different environments; each has its own advantages and disadvantages. There are many challenges with the successful use of these floating platforms. A lot of lessons have been learned and extensive experience accumulated through the many project applications. Key technologies are being reviewed for the successful use of floating platforms for field development, and potential future development needs are being discussed. Some of the technologies and experience of platform applications can be well used for the development of the South China Sea oil and gas field.

The chain/wire rope/chain combination is a common choice for mooring offshore floating platforms. However, data of the drag coefficients of chain links are rather limited, resulting in uncertainties with the calculations of the drag force, and hence the damping of the mooring system. In this paper, the importance of the selection of the drag coefficient is first investigated. The computational fluid dynamics (CFD) method is then used to determine the drag coefficients of a studless chain under steady flows. Numerical model validation is first completed by simulating a smooth circular cylinder under steady flows. In particular, the performance of different turbulence models is assessed through the comparisons between the calculations and the experimental results. The large eddy simulation (LES) model is finally selected for the simulation of steady flows past a chain. The effects of the Reynolds number on the drag coefficient of a stud-less chain is also studied. The results show that the calculated drag coefficients of a stud-less chain are fairly consistent with the available experimental data.

The research purpose of this paper is to estimate the impacts of the parameters of the guide plate on the vertical motion characteristics of the moonpool fluid. With the volume of fluid (VOF) method, three-dimensional models of the moonpool fluid motions of the truss spar platform are established. Simulation results are then presented for the moonpool forced oscillation by employing the dynamic mesh method and user-defined functions in FLUENT. The motions of the moonpool fluid and the loads on the guide plates are obtained for both cases of square-ring and crisscross. The results show that the shape and area of the guide plate at the bottom of the moonpool have a significant impact on the physical parameters of the moonpool, including the load on the moonpool guide plate, motion form of the moonpool fluid and the mass flow rate.

The solution for the Duffing equation in a nonlinear vibration problem is studied in this paper. Clearly, in the case of the perturb parameter being a larger value, the traditional perturbation method is no longer valid but the Homotopy Perturbation Method (HPM) is applicable usually. HPM is used to solve the weak and strong nonlinear differential equations for finding the perturbed frequency of the response. The obtained frequencies via HPM and the approximate method have good accordance for weak and strong nonlinear differential equations. Additionally, the calculated responses by use of the approximate method are compared with the responses obtained from the Numerical method in the time history of the response and phase plane. The results represent good accordance between them.

Global strength is a significant item for floating production storage and offloading (FPSO) design, and steel weight plays an important role in the building costs of FPSO. It is the main task to consider and combine these two aspects by optimizing hull dimensions. There are many optional methods for the global strength analysis. A common method is to use the ABS FPSO Eagle software to analyze the global strength including the rule check and direct strength analysis. And the same method can be adopted for the FPSO hull optimization by changing the depth. After calculation and optimization, the results are compared and analyzed. The results can be used as a reference for the future design or quotation purpose.

As a novel type of foundation in beach and shallow sea, the bucket structure is especially suitable for complex conditions such as soft clay ground and the worse types of sea environments. In this paper, the bearing capacity of a multi-bucket structure is studied by experiments with a single bucket and four-bucket foundation in a saturated sand layer. Based on the experimental data and numerical analysis results, the bearing capacity behavior and the bucket group effect are compared and analyzed. Furthermore, some influential factors, such as the soil type, the ratio of length to diameter L/D, the ratio of the bucket spacing to the bucket diameter S/D, and the bucket number are introduced and their effects on the multi-bucket structural capacity are investigated. The vertical static capacity adjustment factor is introduced to evaluate the bucket group effects of the multi-bucket foundation.

This paper discusses the numerical modeling of the dynamic coupled analysis of the floating platform and mooring/risers using the asynchronous coupling algorithm with the purpose to improve the computational efficiency when multiple lines are connected to the platform. The numerical model of the platform motion simulation in wave is presented. Additionally, how the asynchronous coupling algorithm is implemented during the dynamic coupling analysis is introduced. Through a comparison of the numerical results of our developed model with commercial software for a SPAR platform, the developed numerical model is checked and validated.

The main challenge for container ports is the planning required for berthing container ships while docked in port. Growth of containerization is creating problems for ports and container terminals as they reach their capacity limits of various resources which increasingly leads to traffic and port congestion. Good planning and management of container terminal operations reduces waiting time for liner ships. Reducing the waiting time improves the terminal’s productivity and decreases the port difficulties. Two important keys to reducing waiting time with berth allocation are determining suitable access channel depths and increasing the number of berths which in this paper are studied and analyzed as practical solutions. Simulation based analysis is the only way to understand how various resources interact with each other and how they are affected in the berthing time of ships. We used the Enterprise Dynamics software to produce simulation models due to the complexity and nature of the problems. We further present case study for berth allocation simulation of the biggest container terminal in Iran and the optimum access channel depth and the number of berths are obtained from simulation results. The results show a significant reduction in the waiting time for container ships and can be useful for major functions in operations and development of container ship terminals.

For studying the dynamic performance of subsea umbilical cable laying system and achieving the goal of cable tension and laying speed control, the rigid finite element method is used to discrete and transform the system into a rigid-flexible coupling multi-body system which consists of rigid elements and spring-damping elements. The mathematical model of subsea umbilical cable laying system kinematic chain is presented with the second order Lagrange equation in the joint coordinate system, and dynamic modeling and simulation is performed with ADAMS. The dynamic analysis is conducted assuming the following three statuses: ideal laying, practical laying under wave disturbance, and practical laying with tension compensation. Results show that motion disturbances of the laying budge under sea waves, especially with heaving and pitching, will cause relatively serious fluctuations in cable tension and laying speed. Tension compensation, i.e., active back tension torque control can restrict continuous tension increasing or decreasing effectively and rapidly, thus avoiding cable breach or buckling.

For a large floating vessel in waves, radiation damping is not an accurate prediction of the degree of roll unlike other degrees of freedom motion. Therefore, to get the knowledge of roll motion performance of deepwater pipelay crane vessels and to keep the vessel working safety, the paper presents the relationship between a series of dimensionless roll damping coefficients and the roll response amplitude operator (RAO). By using two kinds of empirical data, the roll damping is estimated in the calculation flow. After getting the roll damping coefficient from the model test, a prediction of roll motion in regular waves is evaluated. According to the wave condition in the working region, short term statistics of roll motion are presented under different wave parameters. Moreover, the relationship between the maximal roll response level to peak spectral wave period and the roll damping coefficient is investigated. Results may provide some reference to design and improve this kind of vessel.

A pipe model with a mass ratio (mass/displaced mass) of 4.30 was tested to investigate the vortex-induced vibrations of submarine pipeline spans near the seabed. The pipe model was designed as a bending stiffness-dominated beam. The gap ratios (gap to diameter ratio) at the pipe ends were 4.0, 6.0, and 8.0. The flow velocity was systematically varied in the 0–16.71 nondimensional velocity range based on the first natural frequency. The mode transition between the first and the second mode as the flow velocity increases was investigated. At various transition flow velocities, the research indicates that the peak frequencies with respect to displacement are not identical along the pipe, nor the frequencies associated with the peak of the amplitude spectra for the first four modes as well. The mode transition is associated with a continuous change in the amplitude, but there’s a jump in frequency, and a gradual process along the pipe length.

Secure storage yard is one of the optimal core goals of container transportation; thus, making the necessary storage arrangements has become the most crucial part of the container terminal management systems (CTMS). This paper investigates a random hybrid stacking algorithm (RHSA) for outbound containers that randomly enter the yard. In the first stage of RHSA, the distribution among blocks was analyzed with respect to the utilization ratio. In the second stage, the optimization of bay configuration was carried out by using the hybrid genetic algorithm. Moreover, an experiment was performed to test the RHSA. The results show that the explored algorithm is useful to increase the efficiency.

In order to study the influence of parameters on durability of marine concrete structures, the parameter’s sensitivity analysis was studied in this paper. With the Fick’s 2nd law of diffusion and the deterministic sensitivity analysis method (DSA), the sensitivity factors of apparent surface chloride content, apparent chloride diffusion coefficient and its time dependent attenuation factor were analyzed. The results of the analysis show that the impact of design variables on concrete durability was different. The values of sensitivity factor of chloride diffusion coefficient and its time dependent attenuation factor were higher than others. Relative less error in chloride diffusion coefficient and its time dependent attenuation coefficient induces a bigger error in concrete durability design and life prediction. According to probability sensitivity analysis (PSA), the influence of mean value and variance of concrete durability design variables on the durability failure probability was studied. The results of the study provide quantitative measures of the importance of concrete durability design and life prediction variables. It was concluded that the chloride diffusion coefficient and its time dependent attenuation factor have more influence on the reliability of marine concrete structural durability. In durability design and life prediction of marine concrete structures, it was very important to reduce the measure and statistic error of durability design variables.

The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In efforts to fulfill this task, concept of the minimum rank perturbation theory has been utilized. The present article introduces a promising methodology to select frequency points effectively. To achieve this goal, modal strain energy ratio of each member was evaluated at different natural frequencies of structure in order to identify the sensitive frequency domain for damage detection. The proposed methodology opens up the possibility of much greater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology.

This paper presents a design of boundary controllers implemented at the top end for global stabilization of a marine riser in a three dimensional space under environmental loadings. Based on the energy approach, nonlinear partial differential equations of motion, including bending-bending and longitudinal-bending couplings for the risers are derived. The couplings cause mutual effects between the three independent directions in the riser’s motions, and make it difficult to minimize its vibrations. The Lyapunov direct method is employed to design the boundary controller. It is shown that the proposed boundary controllers can effectively reduce the riser’s vibration. Stability analysis of the closed-loop system is performed using the Lyapunov direct method. Numerical simulations illustrate the results.

Offshore observation platforms are required to have great ability to resist waves when they are operating at sea. Investigation on the motion characteristics of the platforms in the sea can provide significant reference values during the platform design procedure. In this paper, a series of numerical simulation on the interaction of a triple-hulled offshore observation platform with different incident waves is carried out. All of the simulations are implemented utilizing our own solver naoe-FOAM-SJTU, which is based and developed on the open source tools of OpenFOAM. Duration curves of motion characteristics and loads acting on the platform are obtained, and a comparison between the results of the amplitude in different incident waves is presented. The results show that the solver is competent in the simulation of motion response of platforms in waves.

Experimental and theoretical studies of drag embedment plate anchors recently carried out in Tianjin University are summarized in this research paper, which involve a series of important topics relevant to the study of drag anchors. The techniques for measuring the trajectory and movement direction of drag anchors in soils, the techniques for measuring the moving embedment point and reverse catenary shape of the embedded drag line, the penetration mechanism and kinematic behavior of drag anchors, the ultimate embedment depth of drag anchors, the movement direction of the anchor with an arbitrary fluke section, the reverse catenary properties of the embedded drag line, the interactional properties between drag anchor and installation line, the kinematic model of drag anchors in seabed soils, and the analytical method for predicting the anchor trajectory in soils will all be examined. The present work remarkably reduces the uncertainties in design and analysis of drag embedment plate anchors, and is beneficial to improving the application of this new type of drag anchor in offshore engineering.

Risk analysis of key systems have become a growing topic late of because of the development of offshore structures. Equipment failures of offloading system and fire accidents were analyzed based on the floating production, storage and offloading (FPSO) features. Fault tree analysis (FTA), and failure modes and effects analysis (FMEA) methods were examined based on information already researched on modules of relex reliability studio (RRS). Equipment failures were also analyzed qualitatively by establishing a fault tree and Boolean structure function based on the shortage of failure cases, statistical data, and risk control measures examined. Failure modes of fire accident were classified according to the different areas of fire occurrences during the FMEA process, using risk priority number (RPN) methods to evaluate their severity rank. The qualitative analysis of FTA gave the basic insight of forming the failure modes of FPSO offloading, and the fire FMEA gave the priorities and suggested processes. The research has practical importance for the security analysis problems of FPSO.

Numerical simulations of wind turbine blade-tower interaction by using the open source OpenFOAM tools coupled with arbitrary mesh interface (AMI) method were presented. The governing equations were the unsteady Reynolds-averaged Navier-Stokes (RANS) which were solved by the pimpleDyMFoam solver, and the AMI method was employed to handle mesh movements. The National Renewable Energy Laboratory (NREL) phase VI wind turbine in upwind configuration was selected for numerical tests with different incoming wind speeds (5, 10, 15, and 25 m/s) at a fixed blade pitch and constant rotational speed. Detailed numerical results of vortex structure, time histories of thrust, and pressure distribution on the blade and tower were presented. The findings show that the wind turbine tower has little effect on the whole aerodynamic performance of an upwind wind turbine, while the rotating rotor will induce an obvious cyclic drop in the front pressure of the tower. Also, strong interaction of blade tip vortices with separation from the tower was observed.

Transportation of tension leg platform (TLP) structures for a long distance has always been associated with the use of a heavy semi-transport vessel. The requirements of this type of vessel are always special, and their availability is limited. To prepare for the future development of South China Sea deepwater projects, the China Offshore Oil Engineering Corporation has recently built a heavy lift transport vessel–Hai Yang Shi You 278. This semi-submersible vessel has a displacement capacity of 50k DWT, and a breath of 42 meters. Understanding the vessel’s applicability and preparing it for use in future deepwater projects are becoming imminent needs. This paper reviews the current critical issues associated with TLP transportation and performs detailed analysis of the designed TLP during load-out and transportation. The newly built COOEC transportation vessel HYSY 278 was applied to dry transport of the TLP structure from the COOEC fabrication yard in Qingdao to an oil field in South China Sea. The entire process included the load-out of the TLP structure from the landsite of the fabrication yard, the offloading and float-on of the platform from the vessel, the dry transport of the TLP over a long distance, and the final offloading of the platform. Both hydrodynamic and structure analysis were performed to evaluate the behavior of the transport vessel and TLP structure. Special attention was paid to critical areas associated with the use of this new vessel, along with any potential limitations. The results demonstrate that HYSY 278 can effectively be used for transporting the structure with proper arrangement and well-prepared operation. The procedure and details were presented on the basis of the study results. Special attention was also given to discussion on future use based on the results from the analysis.

The method for design and analysis of a buoyancy tank riser tensioner system (BTRTS) was put forward in this paper, taking the free standing hybrid riser’s top buoyancy tank as an example. The design procedure was discussed and was also illustrated in a flowchart, after a short description of the global arrangement, structure configuration, and the function of different types of buoyancy tanks (BT). The objective of this paper is to describe a way of developing a BT with minimal hydro force, maximal net lift, and no redundancy of compartments. The method of determining the main dimensions of the BT, namely the length and the outer diameter, was outlined. A series of investigations was conducted for a West Africa FSHR BT design, and the effect of the ratio of the length to the outer diameter (L/D) on the hydrodynamics and the weight of the BT was discussed. The methodology of designing the internal structure of the BT was presented. The effects of the number of compartments and the dimension of the inner stem on the BT weight and strength were compared. The relationship between inner structure and the number one index of the BT as well as the riser’s top tension factor (TTF) were illustrated for normal operating conditions and conditions with one or more compartments (or inner stem) damaged. A design instance was given in this paper, when L/D is 4–6, the BT weight and the drag force are compromised. When the BT is divided into 10 compartments, the riser TTF will reach the maximum value, and the ratio of the stem OD to shell OD is about 0.3. A global strength analysis method of the BT and the main load case matrix was also included in the paper, together with the local strength analysis of the buoyancy tank’s pad-eye assembly.

This paper researches how to apply the advanced control technology of model predictive control (MPC) to the design of the dynamic positioning system (DPS) of a semi-submersible platform. First, a linear low-frequency motion model with three degrees of freedom was established in the context of a semi-submersible platform. Second, a model predictive controller was designed based on a model which took the constraints of the system into account. Third, simulation was carried out to demonstrate the feasibility of the controller. The results show that the model predictive controller has good performance and good at dealing with the constraints of the system.

The development of offshore wind farms was originally carried out in shallow water areas with fixed (seabed mounted) structures. However, countries with limited shallow water areas require innovative floating platforms to deploy wind turbines offshore in order to harness wind energy to generate electricity in deep seas. The performances of motion and mooring system dynamics are vital to designing a cost effective and durable floating platform. This paper describes a numerical model to simulate dynamic behavior of a new semi-submersible type floating offshore wind turbine (FOWT) system. The wind turbine was modeled as a wind block with a certain thrust coefficient, and the hydrodynamics and mooring system dynamics of the platform were calculated by SESAM software. The effect of change in environmental conditions on the dynamic response of the system under wave and wind loading was examined. The results indicate that the semi-submersible concept has excellent performance and SESAM could be an effective tool for floating wind turbine design and analysis.

The jack-up unit is one of the best drilling platforms in offshore oil fields with water depth shallower than 150 meters. As the most pivotal component of the jack-up unit, the leg system can directly affect the global performance of a jack-up unit. Investigation shows that there are three kinds of leg structure forms in the world now: the reverse K, X, and mixing types. In order to clarify the advantage and defects of each one, as well as their effect on the global performance of the jack-up unit, this paper commenced to study performance targets of a deepwater jack-up unit with different leg systems (X type, reverse K type, and mixing type). In this paper a typical leg scantling dimension and identical external loads were selected, detailed finite element snalysis (FEA) models were built to simulate the jack-up unit’s structural behavior, and the multi-point constraint (MPC) element together with the spring element was used to deal with the boundary condition. Finally, the above problems were solved by comparative analysis of their main performance targets (including ultimate static strength, dynamic response, and weight).

As a kind of clean and renewable energy, tidal current energy is becoming increasingly popular all over the world with the shortage of energy and environmental problems becoming more and more severe. A floating tidal current power station is a typical type of tidal current power transformers which can sustain the loads of wind, waves, and current, and even the extreme situation of a typhoon. Therefore, the mooring system must be reliable enough to keep the station operating normally and to survive in extreme situations. The power station examined in this paper was installed at a depth of 40 m. A 44 mm-diameter R4-RQ4 chain was chosen, with a 2 147 kN minimum break strength and 50 kN pretension. Common studless link chain was used in this paper. Based on the Miner fatigue cumulative damage rule, S-N curves of chains, and MOSES software, a highly reliable mooring system was designed and analyzed. The calculation results show that the mooring system designed is reliable throughout a 10-year period. It can completely meet the design requirements of American Petroleum institution (API). Therefore, the presented research is significant for advancing the design of this kind of power station.

Mooring systems play an important role for semi-submersible rigs that drill in deepwater. A detailed analysis was carried out on the mooring of a semi-submersible rig that conducted a trial well drilling at a deepwater location in the South China Sea in 2009. The rig was 30 years old and had a shallow platform with a designed maximum operating water depth of 457 m. Following the mooring analysis, a mooring design was given that requires upgrading of the rig’s original mooring system. The upgrade included several innovations, such as installing eight larger anchors, i.e. replacing the original anchors and inserting an additional 600 m of steel wires with the existing chains. All this was done to enhance the mooring capability of the rig in order for the rig to be held in position to conduct drilling at a water depth of 476 m. The overall duration of the drilling was 50 days and the upgraded mooring system proved to be efficient in achieving the goal of keeping the rig stationary while it was drilling the trial well in the South China Sea. This successful campaign demonstrates that an older semi-submersible rig can take on drilling in deep water after careful design and proper upgrading and modification to the original mooring system.

At present, equivalent water depth truncated mooring system optimization design is regarded as the priority of hybrid model testing for deep sea platforms, and will replace the full depth system test in the future. Compared with the full depth system, the working depth and span are smaller in the truncated one, and the other characteristics maintain more consistency as well. In this paper, an inner turret moored floating production storage & offloading system (FPSO) which works at a water depth of 320m, was selected to be a research example while the truncated water depth was 80m. Furthermore, an improved non-dominated sorting genetic algorithm (INSGA-II) was selected to optimally calculate the equivalent water depth truncated system, considering the stress condition of the total mooring system in both the horizontal and vertical directions, as well as the static characteristic similarity of the representative single mooring line. The results of numerical calculations indicate that the mathematical model is feasible, and the optimization method is fast and effective.

Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In this paper, the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program. The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation. The vegetative parameters, along with the width of the green belt, its position from the reference line, the diameter of the individual stems as well as the spacing between them, and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem. The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number (KC) was discussed in this paper. It has been shown that when vegetal patches are present in front of structure, the forces could be limited to within F*?1, by a percentile of 92%, 90%, 55%, and 96%, respectively for gap ratios of 0.0, 0.5, 1.0, and 1.5. The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.

Mooring system plays an important role in station keeping of floating offshore structures. Coupled analysis on mooring-buoy interactions has been increasingly studied in recent years. At present, chains and wire ropes are widely used in offshore engineering practice. On the basis of mooring line statics, an explicit formulation of single mooring chain/wire rope stiffness coefficients and mooring stiffness matrix of the mooring system were derived in this article, taking into account the horizontal restoring force, vertical restoring force and their coupling terms. The nonlinearity of mooring stiffness was analyzed, and the influences of various parameters, such as material, displacement, pre-tension and water depth, were investigated. Finally some application cases of the mooring stiffness in hydrodynamic calculation were presented. Data shows that this kind of stiffness can reckon in linear and nonlinear forces of mooring system. Also, the stiffness can be used in hydrodynamic analysis to get the eigenfrequency of slow drift motions.

The cylindrical shell is one of the main structural parts in ocean engineering structures. These cylinders are mostly of medium length, which means that the radius of the cross section is significantly smaller than the length of the cylindrical shell. From the viewpoint of the shell theory, they belong to the mid-long cylindrical shell category. To solve mechanical problems on this kind of structure, especially a cracked cylindrical shell, analysis based on shell theory is necessary. At present the generally used solving system for the mid-long cylindrical shell is too complicated, difficult to solve, and inapplicable to engineering. This paper introduced the Sanders’ mid-long cylindrical shell theory which reduces the difficulty of the solution process, and will be suitable for solving problems with complicated boundary conditions. On this basis, the engineering applications of this theory were discussed in conjunction with the problem of a mid-long cylindrical shell having a circumferential crack. The solution process is simple, and the closed form solution can usually be found. In practical engineering applications, it gives satisfactory precision.

The basic configuration of a new type of subsea pipeline connector was proposed based on the press-fitting principle, and a parametric finite element model was created using APDL language in ANSYS. Combining the finite element model and optimization technology, the dimension optimization aiming at obtaining the minimum loading force and the optimum sealing performance was designed by the zero order optimization method. Experiments of the optimized connector were carried out. The results indicate that the optimum structural design significantly improved the indicators of the minimum loading force and sealing performance of the connector.

A jack-up platform, with its particular structure, showed obvious dynamic characteristics under complex environmental loads in extreme conditions. In this paper, taking a simplified 3-D finite element dynamic model in extreme storm conditions as research object, a transient dynamic analysis method was proposed, which was under both regular and irregular wave loads. The steps of dynamic analysis under extreme conditions were illustrated with an applied case, and the dynamic amplification factor (DAF) was calculated for each response parameter of base shear, overturning moment and hull sway. Finally, the structural response results of dynamic and static were compared and analyzed. The results indicated that the static strength analysis of the Jack-up Platforms was not enough under the dynamic loads including wave and current, further dynamic response analysis considering both computational efficiency and accuracy was necessary.

Bundled hybrid offset riser (BHOR) global strength analysis, which is more complex than single line offset riser global strength analysis, was carried out in this paper. At first, the equivalent theory is used to deal with BHOR, and then its global strength in manifold cases was analyzed, along with the use of a three-dimensional nonlinear time domain finite element program. So the max bending stress, max circumferential stress, and max axial stress in the BHOR bundle main section (BMS) were obtained, and the values of these three stresses in each riser were obtained through the “stress distribution method”. Finally, the Max Von Mises stress in each riser was given and a check was made whether or not they met the demand. This paper provides a reference for strength analysis of the bundled hybrid offset riser and some other bundled pipelines.

Considering the static stability and the change of the displacement volume, including the influences of higher order nonlinear terms and the instantaneous wave surface, the nonlinear coupled heave-pitch motion was established in stochastic waves. The responses of heave-pitch coupling motion for the Truss Spar platform were investigated. It was found that, when the characteristic frequency of a stochastic wave is close to the natural heave frequency, the large amplitude pitch motion is induced under the parametric-forced excitation, which is called the Mathieu instability. It was observed that the heave mode energy is transferred to pitch mode when the heave motion amplitude exceeds a certain extent. In addition, the probability of internal resonant heave-pitch motion is greatly reduced while the characteristic wave frequency is away from the natural heave frequency.

The mechanical performance of a flexible riser is more outstanding than other risers in violent environmental conditions. Based on the lumped mass method, a steep wave flexible riser configuration attached to a Floating Production Storage and Offloading (FPSO) has been applied to a global analysis in order to acquire the static and dynamic behavior of the flexible riser. The riser was divided into a series of straight massless line segments with a node at each end. Only the axial and torsional properties of the line were modeled, while the mass, weight, and buoyancy were all lumped to the nodes. Four different buoyancy module lengths have been made to demonstrate the importance of mode selection, so as to confirm the optimum buoyancy module length. The results in the sensitivity study show that the flexible riser is not very sensitive to the ocean current, and the buoyancy module can reduce the Von Mises stress and improve the mechanical performance of the flexible riser. Shorter buoyancy module length can reduce the riser effective tension in a specific range of the buoyancy module length when other parameters are constant, but it can also increase the maximum curvature of the riser. As a result, all kinds of the riser performances should be taken into account in order to select the most appropriate buoyancy module length.

In the exploitation of ocean oil and gas, many offshore structures may be damaged due to the severe environment, so an effective method of diagnosing structural damage is urgently needed to locate the damage and evaluate its severity. Genetic algorithms have become some of the most important global optimization tools and been widely used in many fields in recent years because of their simple operation and strong robustness. Based on the natural frequencies and mode shapes of the structure, the damage diagnosis of a jacket offshore platform is attributed to an optimization problem and studied by using a genetic algorithm. According to the principle that the structural stiffness of a certain direction can be greatly affected only when the brace bar in the corresponding direction is damaged, an improved objective function was proposed in this paper targeting measurement noise and the characteristics of modal identification for offshore platforms. This function can be used as fitness function of a genetic algorithm, and both numerical simulation and physical model test results show that the improved method may locate the structural damage and evaluate the severity of a jacket offshore platform satisfactorily while improving the robustness of evolutionary searching and the reliability of damage diagnosis.

In order to improve the safety properties of an offloading system with side-by-side (SBS) mooring in which the FPSO is moored by a yoke system in the field of BZ25-1, it is necessary to analyze those properties. According to the experience of similar projects, tow strategies of different offloading arrangements were discussed by using the 3-D radiation/diffraction theory and quasi-static time domain method to assess their respective safety properties. Through the safety assessment analysis of different arrangement comparisons, various ways to improve the safety properties of offloading systems with side-by-side mooring were verified by analyzing the tension in the mooring lines and the fender deflection. Through comparison it can be concluded that by enlarging the key factors properly, including the size of the fenders and the hawsers as well as the number of hawsers, a better safety performance can be achieved.

The South China Sea contains tremendous oil and gas resources in deepwater areas. However, one of the keys for deepwater exploration, the investigation of deepwater floating platforms, is very inadequate. In this paper, the authors studied and compared the hydrodynamics and global motion behaviors of typical deepwater platforms in the South China Sea environment. The hydrodynamic models of three main types of floating platforms, e.g. the Semi-submersible, tension leg platform (TLP), and Truss Spar, which could potentially be utilized in the South China Sea, were established by using the 3-D potential theory. Additionally, some important considerations which significantly influence the hydrodynamics were given. The RAOs in frequency domains as well as global motions in time domains under time-varying wind, random waves, and current in 100-y, 10-y, and 1-y return period environment conditions were predicted, compared, and analyzed. The results indicate that the heave and especially the pitch motion of the TLP are favorable. The heave response of the Truss Spar is perfect and comparable with that of the TLP when the peak period of random waves is low. However, the pitch motion of Truss Spar is extraordinarily larger than that of Semi-submersible and TLP.

This paper proposes the finite element simplified fatigue analysis method for fatigue evaluation of the composite non-tubular joint structure of an offshore jacket subjected to wave loads. The skirt pile sleeve of the offshore jacket, which had been in service, was taken as an example of the non-tubular joint structure. SACS software was used for global analysis of multi-directional wave loads for the jacket platform, and ALGOR software was used to build a finite element model, perform finite element analysis, post-process stress results for acquiring the stress range, and perform fatigue evaluation. The analysis results indicate that the extreme stress range is within the allowable stress range and meets the requirements of DNV code. That means the simplified fatigue analysis method is effective and can be used in fatigue design for the non-tubular joint structure of an offshore jacket.

This research proposes a new offshore wind energy generation system that uses a tension leg platform (TLP) and describes experiments performed on a TLP type wind turbine in both waves and wind. The following conclusions can be made from the results of this research. 1) In the case of coexisting wave-wind fields, the wind effect stabilizes the pitch motion. 2) The wind effect decreases vibration of the mooring lines when waves and wind coexist. In particular, the springing (2nd or 3rd order force) also decreases in this field. 3) It can be estimated that the reduction in the rate of generation of electrical power can be up to about 6% as a result of the heel angle. In addition, the annual amount of electricity generated was estimated along with the utilization factor based on the experimental results.

Flexible risers and steel catenary risers often provide unique riser solutions for today’s deepwater field development. Accurate analysis of these slender structures, in which there are high-speed HP/HT internal flows, is critical to ensure personnel and asset safety. In this study, a special global coordinate-based FEM rod model was adopted to identify and quantify the effects of internal flow and hydrostatic pressure on both flexible and deepwater steel catenary risers, with emphasis on the latter. By incorporating internal flow induced forces into the model, it was found that the internal flow contributes a new term to the effective tension expression. For flexible risers in shallow water, internal flow and hydrostatic pressure made virtually no change to effective tension by merely altering the riser wall tension. In deep water the internal pressure wielded a dominant role in governing the riser effective tension and furthering the static configuration, while the effect of inflow velocity was negligible. With respect to the riser seabed interaction, both the seabed support and friction effect were considered, with the former modeled by a nonlinear quadratic spring, allowing for a consistent derivation of the tangent stiffness matrix. The presented application examples show that the nonlinear quadratic spring is, when using the catenary solution as an initial static profile, an efficient way to model the quasi-Winkler-type elastic seabed foundation in this finite element scheme.

The wave force exerted on vertical piles of offshore structures is the main criterion in designing them. In structures with more than one large pile, the influence of piles on each other is one of the most important issues being concerned in past researches. An efficient method for determining the interaction of piles is introduced in present research. First the wave force is calculated by the exact method using the diffraction theory, then in the finite difference numerical method the force is calculated by adding the velocity potentials of each pile and integration of pressure on their surface. The results showed that the ratio of the wave force on each of the double piles to a single pile has a damped oscillation around unity in which the amplitude of oscillation decreases with the increase in the spacing parameter. Also different wave incident directions and diffraction parameters were used and the results showed that the numerical solution has acceptable accuracy when the diffraction parameter is larger than unity.

The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens. The blades are the key components of offshore wind turbines, and their dynamic characteristics directly determine the effectiveness of offshore wind turbines. With different rotating speeds and blade length, the rotating blades generate various centrifugal stiffening effects. To directly analyze the centrifugal stiffening effect of blades, the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade, including the centrifugal stiffening effect and the axial force calculation formula. The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates. The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed, and then the fundamental frequency correction formula was built based on the rotating speed and the blade length. The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results. The error of calculation results between them is less than 0.5%.

The authors analyzed requirements for a new deepwater platform, from conceptual design to hydrodynamic analysis. The design incorporated Deep Draft Multi-Spar (DDMS) that allowed easy fabrication, reduced costs, and provided favorable motion performance. It also provided a dry tree system and other benefits. The conceptual design process included dimension estimation, general arrangements, weight estimation, weight distribution, stability analysis, etc. A high order boundary element method based on potential theory and the modified Morison equation was used to predict the hydrodynamic and viscous effects of this new concept platform. The response amplitude operators (RAOs) were acquired and compared with those of a typical Truss Spar. The response of the platform to the JONSWAP spectra of 3 different extreme ocean conditions was analyzed to evaluate the seakeeping ability of the new concept. The results revealed favorable motion performance due to all the degrees of freedom available.

This paper addresses the need for systematic evaluation of the station keeping systems of deepwater drilling semi-submersibles. Based on the selected drilling semi-submersible configuration, the mooring systems were analyzed and designed for a range of water depths using different mooring line materials. These were steel wire rope, polyester rope and HMPE (high modulus poly ethylene). The mooring analysis was carried out using the advanced fully coupled time domain analysis method in the computer software package HARP. Diffraction analysis was first applied to solve the hydrodynamic properties of the vessel and then the motion equations of the complete dynamic system including the drilling rig, the mooring lines and risers were developed and solved in the time domain. Applying the advanced analysis method, a matrix of mooring systems was developed for operating in water depths of 1 000 m, 1 500 m, and 2 000 m using various mooring materials. The development of mooring systems was conducted in accordance with the commonly adopted mooring design code, API RP 2SK and API RP 2SM. Fresh attempts were then made to comparatively evaluate the mooring system’s characteristics and global performance. Useful results have been obtained in terms of mooring materials, water depths, and key parameters of mooring configurations. The results provide in-depth insight for the design and operation of deepwater mooring systems in the South China Sea environment.

Experiments were conducted to study characteristics of flow when flow is fluctuating. The experimental results showed a phase difference between the flow rate and the pressure drop fluctuations. This phase difference between the fluctuating flow rate and pressure drop was analyzed for laminar flow. Analysis showed that the phase difference changes with the period of the flow fluctuation, the pipe radius, the density and the dynamic viscosity of the liquid. Fluctuating pipe flow was then numerically simulated. Results of the numerical simulation were compared with theoretical values and experimental results. It was shown that, when the flow rate fluctuates with time as a sine wave, the pressure drop fluctuates with the same periodicity, and there is a phase difference between them.

The spatial distribution of the energy flux, bottom boundary layer (BBL) energy dissipation, surface elevation amplitude and current magnitude of the major semidiurnal tidal constituents in the Bering Sea are examined in detail. These distributions are obtained from the results of a three-dimensional numerical simulation model (POM). Compared with observation data from seven stations, the root mean square errors of tidal height are 2.6 cm and 1.2 cm for M2 and N2 respectively, and those of phase-lag are 21.8° and 15.8° respectively. The majority of the tidal energy flux off the deep basin is along the shelf edge, although some of this flux crosses the shelf edge, especially in the southeast of the shelf break. The total M2 energy dissipation in the Bering Sea is 30.43 GW, which is about 10 times of that of N2 and S2. The semidiurnal tidal energy enters mainly to the Bering Sea by Samalga Pass, Amukta Pass and Seguam Pass, accounting more than 60% of the total energy entering the Being Sea from the Pacific.

In this paper, two novel numerical computation methods are introduced which have been recently developed at Research Institute for Applied Mechanics ( RIAM ), Kyushu University, for strongly nonlinear wave-body interaction problems, such as ship motions in rough seas and resulting green-water impact on deck. The first method is the CIP-based Cartesian grid method, in which the free surface flow is treated as a multi-phase flow which is solved using a Cartesian grid. The second method is the MPS method, which is a so-called particle method and hence no grid is used. The features and calculation procedures of these numerical methods are described. One validation computation against a newly conducted experiment on a dam break problem, which is also described in this paper, is presented.

Breaking waves can have tremendous destructive impact on vertical walls, yet they are poorly understood. By using particle imaging velocimetry (PIV) technology and high-precision pressure transducers, actual breaking wave loads on vertical walls were studied. By simultaneously comparing the flow field structure and wave pressure, the mechanisms of breaking wave pressure could be analyzed. The probability distribution of the peak value of the first impact of a breaking wave was investigated. The results showed that the impact pressure p is mainly distributed in the range of 0.25-2.75 , with the greatest possible probability at = 0.75.

To solve the dimensional limitations of physical models in tests, an equivalent water depth truncated design for a classical SPAR working in 913 m water was investigated. The water depth was reduced to 736m and then to 552m. As this was done, the mooring line lengths, EA value, and mass per meter were adjusted. Truncation rules and formulas for parameters and truncation factors were proposed. SPAR static characteristics were made to be consistent with those at full water depth. Then further time-domain coupled analysis was carried out for the SPAR when the mooring system experienced waves. The mooring lines were simulated by quasi-static method. Global responses and mooring line forces were found to agree well with test results for a prototype at that water depth. The truncation method proved to be robust and reliable.

Wind power has made rapid progress and should gain significance as an energy resource, given growing interest in renewable energy and clean energy. Offshore wind energy resources have attracted significant attention, as, compared with land-based wind energy resources, offshore wind energy resources are more promising candidates for development. Sea winds are generally stronger and more reliable and with improvements in technology, the sea has become a hot spot for new designs and installation methods for wind turbines. In the present paper, based on experience building offshore wind farms, recommended foundation styles have been examined. Furthermore, wave effects have been investigated. The split installation and overall installation have been illustrated. Methods appropriate when installing a small number of turbines as well as those useful when installing large numbers of turbines were analyzed. This investigation of installation methods for wind turbines should provide practical technical guidance for their installation.

Problems experienced during Floating Production, Storage and Offloading (FPSO) tandem offloading operations were investigated. The aim of this research was to improve the reliability of such systems, and it needed a means to assess them. Time-domain simulation and analysis of offloading systems was performed using the multi-body mooring software ARIANE 7.0. Hydrodynamic interaction between the vessels was considered. The responses of the offloading system in different loading cases, different parameters of offloading hawsers and the effects of challenging environmental conditions were calculated. There was a focus on the problems of relative motion between the two bodies and its effects on the intensity of hawser forces. Minimum relative distance, maximum relative headings and maximum tension in the hawsers of offloading systems were obtained by time-domain analysis. The time-domain analysis was effective and comparative study can be used to optimize parameters of the system and extend operating limits.

Simulation of the flow and deposition from a laboratory turbidity current, in which dense mixtures of sediment move down a narrow, sloping channel and flow into a large tank. SSIIM CFD software is used to model 3-D flow and deposition. SSIIM predicts the height of the accumulated mound to within 25% of experimental values, and the volume of the mound to 20%~50%, depending on the concentration of sediment and slope of the channel. The SSIIM predictions were consistently lower than experimental values. In simulations with initial sediment volumetric concentrations greater than 14%, SSIIM dumped some of the sediment load at the entry gate into the channel, which was not the case with the experimental runs. This is likely due to the fact that the fall velocity of sediment particles in SSIIM does not vary with sediment concentration. Further simulations of deposition from turbidity currents should be attempted when more complete experimental results are available, but it appears for now that SSIIM can be used to give approximate estimates of turbidity current deposition.

In the Pearl River Delta (PRD), there is severe competition between container ports, particularly those in Hong Kong, Shenzhen, and Guangzhou, for collecting international maritime container cargo. In addition, the second phase of the Nansha terminal in Guangzhou’s port and the first phase of the Da Chang Bay container terminal in Shenzhen opened last year. Under these circumstances, there is an increasing need to quantitatively measure the impact these infrastructure investments have on regional cargo flows. The analysis should include the effects of container terminal construction, berth deepening, and access road construction. The authors have been developing a model for international cargo simulation (MICS) which can simulate the movement of cargo. The volume of origin-destination (OD) container cargo in the East Asian region was used as an input, in order to evaluate the effects of international freight transportation policies. This paper focuses on the PRD area and, by incorporating a more detailed network, evaluates the impact of several infrastructure investment projects on freight movement.

An inevitable consequence of the development of the offshore petroleum industry is the eventual obsolescence of large offshore structures. Proper methods for removal of decommissioned offshore platforms are becoming an important topic that the oil and gas industry must pay increasing attention to. While removing sections from a decommissioned jacket platform, the stability of the remaining parts is critical. The jacket danger indices Dσ and Ds defined in this paper are very useful for analyzing the safety of any procedure planned for disassembling a jacket platform. The safest piles cutting sequence can be determined easily by comparing every column of Dσ and Ds or simply analyzing the figures of every row of Dσ and Ds.

This paper analyzes the motion performance and mooring system of deepwater semi-submersible drilling unit in the district of the South China Sea using the MOSES procedure system. After the 3-D panel model of the unit was built, the 3-D diffraction-radiation theory was used to obtain the hydrodynamic loads on the wet surfaces and the response amplitude operators (RAO) of the unit. According to the environmental data, the short-term motion response to motion performance of the unit is predicted by the spectral method. Then a time-domain calculation was done to analyze the motion of the unit with its mooring system. The research results can be a reference for the model test of unit.

The present status of self-elevating drilling units was analysed. Based on statistics of the main dimensions of self-elevating drilling units, a mathematical model was established using stepwise return procedures and a back-propagation neural network. Analysis of examples of calculations showed that the mathematical model is applicable and reliable. The model is useful for mastering the essential variations of the main dimensions of self-elevating drilling units and can be used for technical and economic analysis as well as in conceptual designs of drilling units.

This paper introduces the recent highly significant activity of China Oilfield Services Ltd. (COSL) in the South China Sea, where COSL conducted pretrial drilling in June of 2008. The paper discusses some key research and new practices which led to the fabrication of related equipment which was evaluated in the trial. The market for deepwater drilling in the world has grown over the past 10 years but there are few drilling vessels or platforms suitable for drilling in deepwater or super deepwater. China needs equipment capable of deepwater drilling operations. COSL has some semisubmersible platforms, but they are only considered suitable for operations in water depths less than 475 m. An enabling technology, referred to as an artificial seabed, has been under development by COSL since 2004, and it applies the research results and experiences of many experts in deepwater drilling. COSL hopes this technology will allow drilling to depths of approximately 1 000~1 500 m with its current platforms. The paper presents research progress and improvements in fabrication and necessary upgrades to equipment for extending deepwater drilling. The pretrial well was executed at a water depth of nearly 500 m. COSL will drill the trial well around 2009 at the same location in the South China Sea.

Floating production storage and offloading (FPSO) vessels offer a cost-effective field development solution, especially in deepwater areas lacking an adequate pipeline network. Most FPSOs are permanently moored, i.e. the complete system is designed to withstand any kind of extreme environment at the field location. FPSOs that can be quickly disconnected from their moorings and risers have also been designed and deployed. The key feature of this type of disconnectable FPSO is that it can be disconnect and so avoid dangerous environmental conditions such as icebergs, hurricanes in the Gulf of Mexico and typhoons in the South China Sea. In this paper, the concept of disconnectable FPSOs for deepwater field development is presented. Key technologies and their engineering analyses are highlighted. The merits and demerits of disconnectable vs permanent FPSOs are then evaluated. The paper concludes that both permanent and disconnectable FPSOs are versatile floating systems and their selection depends on safety, technological, cost and operational considerations.

Spans occur when a pipeline is laid on a rough undulating seabed or when upheaval buckling occurs due to constrained thermal expansion. This not only results in static and dynamic loads on the flowline at span sections, but also generates vortex induced vibration (VIV), which can lead to fatigue issues. The phenomenon, if not predicted and controlled properly, will negatively affect pipeline integrity, leading to expensive remediation and intervention work. Span analysis can be complicated by: long span lengths, a large number of spans caused by a rough seabed, and multi-span interactions. In addition, the complexity can be more onerous and challenging when soil uncertainty, concrete degradation and unknown residual lay tension are considered in the analysis. This paper describes the latest developments and a ‘state-of-the-art’ finite element analysis program that has been developed to simulate the span response of a flowline under complex boundary and loading conditions. Both VIV and direct wave loading are captured in the analysis and the results are sequentially used for the ultimate limit state (ULS) check and fatigue life calculation.

The general layout of 6th generation semi-submersible drilling platforms is the main factor impacting the efficiency of their drilling operations. This paper provides a compound/integrated algorithm based on process flow that is aimed at improving efficiency, while giving attention to stability and safety at the same time. The paper describes the process flow of dual drilling centers and a hierarchical division of rigs based on the different modes of transportation of various drilling support systems. The general layout-centripetal overall arrangement spatially was determined based on drilling efficiency. We derived our modules according to drilling functionality; the modules became our basic layout units. We applied different layout algorithm to mark out the upper and lower decks. That is, the upper deck was designed based on the lowest transportation cost while the lower deck’s calculations were based on the best-fit scope. Storage configurations in columns and pontoons were also considered for the layout design. Finally the center of gravity was taken into consideration and the general layout was adjusted accordingly, to result in an optimal center of gravity. The methodology of the general layout can provide a reference for implementation of domestic designs of semi-submersible rigs.

The concepts of floating structure plays a very important role in deepwater projects; and the design of the floating structure is one of the most important tasks in the project. The importance of the floating structure in offshore projects can be demonstrated in the following several areas: the substantial dynamic structure responses due to wave loading and current loading; the limited motion requirements of risers in deep water; and the increasing difficulty of installation for different components of the system. Three major technical aspects have to be considered, i.e. the strength of structure, the fatigue resistance capacity of the system, and local and global stability of the structure. This paper reviews the current design practice of floating structures, evaluates the main tasks during the design and associated major technical requirements, and addresses the major technical challenges encountered during the design. As a close-out of the paper, the authors discuss some potential future developments in the design of floating structures.

Stress response of a tension leg platform (TLP) in extreme environments was investigated in this paper. A location on one of the gussets was selected as the object point, where directional stresses were numerically simulated and also experimentally verified by a strain gage. Environmental loading and the platform’s structural strength were analyzed in accordance with industrial standards, utilizing linear wave theory and the finite element method (FEM). The fast Fourier transform technique was used to calculate the stress response amplitude operators (RAO) from the records of measurements. A comparison was performed between the stress RAO of the numerical simulation and that of the actual measurements. The results indicated that the stress RAO of the numerical simulation fitted well with measured data at specified wave headings with different periods.

The methodology to obtain the non-linear roll damping from decay tests is very old. It has been proposed by Froude in the 19th century and used from then on. Behind it there is a quadratic model for the damping and a subsequent equivalent linearization. Probably all model basin in the world follows this approach to assess the damping from a decay test. This is well documented and so is the methods to get the p1-p2 coefficients. This is very general in the sense that in principle, it could be applied to any kind of hull. However, it has become clear that for hull with a flat bottom such as a very large crude carrier (VLCC), this approach may lead to confusing results such as negative p2. Faced with this, the work presents a completely new idea. Avoiding the polynomial approximation, the basic attitude is to devise two regions from the decaying test response. The first, called the large amplitude response region yields a larger damping, probably due to the large bilge keel vortices that are attracted to the hull flat bottom. The second is the small amplitude response region where the vortices are not attracted to the bottom but travels approximately 45? sidewise. These observations has led to a new approach called the bi-linear approach as discussed in the work after analyzing several (many) model test results. In fact, a new modified bi-linear approach is ultimately proposed after the understanding of a transition region instead of a transition angle.

During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional loads on vortex-induced vibration (VIV) response is investigated. On the basis of the Hamilton principle, a differential equation was derived to describe the motion of a pinned-pinned tensioned spanning pipeline conveying fluid. The VIV response was calculated according to DNV-RP-F105 under different functional loads. The results showed that functional loads influence free spanning pipeline VIV response by changing the natural frequency. Internal flow velocity was found less important for VIV response than other functional load factors, such as effective axial force, because the speed in reality is not high enough to be significant. The research may provide a reference for sensitivity studies of the effect of functional loads on allowable free span lengths.

In recent years, numerous exploration activities of oil and gas industry have been conducted in ultra deep water. The global offshore industry is building systems today for drilling in even deeper water, progressively using new technologies, and significantly extending existing technologies. This is the general trend in the offshore oil and gas industry. So the technology of ultra-deepwater risers, which is the main tool in drilling oil, is more and more standard. This paper manly focuses on the global analysis of the drilling risers. And it is divided into two parts, operability analysis and hang-off analysis that are used to check the design of the riser. In this paper, the rotation angle and stress of the riser in the drilling mode are calculated to determine the operability envelop. The number of the buoyancy modules has been determined and according to the API standard, all the worked out values have been checked out. From all the above, it is concluded that the operability envelop is relatively small under harsh condition and the number of the buoyancy modules is a little large. And above all, the design of this riser is successful.

Steel catenary risers (SCR) have become an enabling technology for deepwater environments. A comprehensive review was conducted on recent research that examined interactions between deepwater steel catenary risers and soft clay seabeds. This included the STRIDE (steel risers in deepwater environments) and CARISIMA (catenary riser soil interaction model for global riser analysis) joint jndustry jrogram’s test data as well as information from existing papers.

A quantitative risk assessment (QRA) based on leak detection criteria (LDC) for the design of a proposed subsea oil export pipeline is presented in this paper. The objective of this QRA/LDC study was to determine if current leak detection methodologies were sufficient, based on QRA results, while excluding the use of statistical leak detection; if not, an appropriate LDC for the leak detection system would need to be established. The famous UK PARLOC database was used for the calculation of pipeline failure rates, and the software POSVCM from MMS was used for oil spill simulations. QRA results revealed that the installation of a statistically based leak detection system (LDS) can significantly reduce time to leak detection, thereby mitigating the consequences of leakage. A sound LDC has been defined based on QRA study results and comments from various LDS vendors to assist the emergency response team (ERT) to quickly identify and locate leakage and employ the most effective measures to contain damage.

This paper describes the model test and the virtual simulation respectively for the VLCC class FPSO hookup, as well as addresses their different applications to the mating operation between the FPSO and the soft yoke mooring system (SYMS) in extremely shallow water. The scope of the model test and the virtual simulation covers various installation stages including a series of positioning trials, positioning keeping and temporary mooring to the pre-installed SYMS mooring tower, pendulum mating, and yoke ballasting to storm-safe. The model test is to accurately verify bollard pull capacity to keep the FPSO in position and assess motion responses and mooring loads for the FPSO and installation vessels during various installation stages. The virtual simulation is to provide a virtual-reality environment, thus realistically replicating the hookup operation at the Simulation Test Center (STC) facility and identifying any deficiencies in key installation personnel, execution plan, or operation procedures. The methodologies of the model test and the virtual simulation addressed here can be easily extended to the deepwater applications such as positioning and installation operations of various floating systems.

Based on relevant in-service experience, this paper discusses how risks associated with station-keeping systems can be controlled through adequate design criteria, inspection, repair and maintenance practice, as well as quality assurance and control of the engineering processes. Particular focus must be placed on quantitative design for system robustness. The application of structural reliability analysis to quantify safety is briefly reviewed. In particular it was emphasized that reliability predictions based on normal uncertainties and variability yielded lower failure rates than those experienced for predictions of hulls and catenary mooring systems; gross errors in design, fabrication and operation were responsible. For this reason the broad safety management approach mentioned above was proposed. Moreover, it was found that this approach needed to be supported by a quantitative risk assessment. Finally, the challenges in dealing with the effects of human factors in risk management are outlined, along with means to deal with them in a qualitative manner, by the so-called barrier method to limit risk.

The immersion of large-scale tunnel elements is one of the most important working procedures in the construction of an underwater immersed tunnel. To investigate the dynamic characteristics of tunnel element in the process of immersion, based on the twin-barge immersing operation method, the frequency-domain analysis of the tunnel element motions under wave actions was made. The linear wave diffraction theory and the three-dimensional source distribution method were applied to calculate the wave loads and motion responses of the tunnel element under different incident wave conditions. In the study, movement of the two barges in the water was assumed to be small and was ignored. Cable tension was computed by the static method. On the basis of the above theories, a computer program was made, and two cases were taken to check the validity of the program. The results showed that wave loads acting on the immersed tunnel element are relatively large near the water surface, and they decrease with the increase of immersing depth of the tunnel element. Wave loads first increase, then decrease, with the increase of wave period. The motion responses of the tunnel element are also generally large near the water surface and decrease as the immersing depth increases.

In the process of designing self-elevating drilling unit, it is important, yet complicated, to use comparison and filtering to select the optimum scheme from the feasible ones. In this research, an index system and methodology for the evaluation of self-elevating drilling unit was proposed. Based on this, a multi-objective combinatorial optimization model was developed, using the improved grey relation Analysis (GRA), in which the analytic hierarchy process (AHP) was used to determine the weights of the evaluating indices. It considered the connections within the indices, reflecting the objective nature of things, and also considered the subjective interests of ship owners and the needs of designers. The evaluation index system and evaluation method can be used in the selection of an optimal scheme and advanced assessment. A case study shows the index system and evaluation method are scientific, reasonable, and easy to put into practice. At the same time, such an evaluation index system and evaluation method will be helpful for making decisions for other mobile platforms.

A new method that uses time-domain response data under random loading is proposed for detecting damage to the structural elements of offshore platforms. In our study, a time series model with a fitting order was first constructed using the time-domain of noise data. A sensitivity matrix consisting of the first differential of the autoregressive coefficients of the time series models with respect to the stiffness of structural elements was then obtained based on time-domain response data. Locations and severity of damage may then be estimated by solving the damage vector whose components express the degrees of damage to the structural elements. A unique aspect of this detection method is that it requires acceleration history data from only one or a few sensors. This makes it feasible for a limited array of sensors to obtain sufficient data. The efficiency and reliability of the proposed method was demonstrated by applying it to a simplified offshore platform with damage to one element. Numerical simulations show that the use of a few sensors’ acceleration history data, when compared with recorded levels of noise, is capable of detecting damage efficiently. An increase in the number of sensors helps improve the diagnosis success rate.

In order to more accurately examine developing trends in gross cargo throughput, we have modeled the probability distribution of cargo throughput. Gross cargo throughput is determined by the time spent by cargo ships in the port and the operating efficiency of handling equipment. Gross cargo throughput is the sum of all compound variables determining each aspect of cargo throughput for every cargo ship arriving at the port. Probability distribution was determined using the Wald equation. The results show that the variability of gross cargo throughput primarily depends on the different times required by different cargo ships arriving at the port. This model overcomes the shortcoming of previous models: inability to accurately determine the probability of a specific value of future gross cargo throughput. Our proposed model of cargo throughput depends on the relationship between time required by a cargo ship arriving at the port and the operational capacity of handling equipment at the port. At the same time, key factors affecting gross cargo throughput are analyzed. In order to test the efficiency of the model, the cargo volume of a port in Shandong Province was used as an example. In the case study the actual results matched our theoretical analysis.