In the present paper a vibrational differential equation governing on a rigid beam on viscoelastic foundation has been investigated. The nonlinear differential equation governing on this vibrating system is solved by a simple and innovative approach, which has been called Akbari-Ganji’s method (AGM). AGM is a very suitable computational process and is usable for solving various nonlinear differential equations. Moreover, using AGM which solving a set of algebraic equations, complicated nonlinear equations can easily be solved without any mathematical operations. Also, the damping ratio and energy lost per cycle for three cycles have been investigated. Furthermore, comparisons have been made between the obtained results by numerical method (Runk45) and AGM. Results showed the high accuracy of AGM. The results also showed that by increasing the amount of initial amplitude of vibration (A), the value of damping ratio will be increased, and the energy lost per cycle decreases by increasing the number of cycle. It is concluded that AGM is a reliable and precise approach for solving differential equations. On the other hand, it is better to say that AGM is able to solve linear and nonlinear differential equations directly in most of the situations. This means that the final solution can be obtained without any dimensionless procedure. Therefore, AGM can be considered as a significant progress in nonlinear sciences.

Due to the dissimilar scaling issues, the conventional experimental method of FOWTs can hardly be used directly to validate the full-scale global dynamic responses accurately. Therefore, it is of absolute necessity to find a more accurate, economic and efficient approach, which can be utilized to predict the full-scale global dynamic responses of FOWTs. In this paper, a literature review of experimental-numerical methodologies and challenges for FOWTs is made. Several key challenges in the conventional basin experiment issues are discussed, including scaling issues; coupling effects between aero-hydro and structural dynamic responses; blade pitch control strategies; experimental facilities and calibration methods. Several basin experiments, industrial projects and numerical codes are summarized to demonstrate the progress of hybrid experimental methods. Besides, time delay in hardware-in-the-loop challenges is concluded to emphasize their significant role in real-time hybrid approaches. It is of great use to comprehend these methodologies and challenges, which can help some future researchers to make a footstone for proposing a more efficient and functional hybrid basin experimental and numerical method.

In continuation of the extensive studies carried out to update the corrosion map of India, in this study, the degradation of mild steel by air pollutants was studied at 16 different locations from Nagore to Ammanichatram along the east coast of Tamilnadu, India over a period of two years. The weight loss study showed that the mild steel corrosion was more at Nagapattinam site, when compared to Ammanichatram and Maravakadu sites. A linear regression analysis of the experimental data was attempted to predict the mechanism of the corrosion. The composition of the corrosion products formed on the mild steel surfaces was identified by XRD technique. The corrosion rate values obtained are discussed in the light of the weathering parameters, atmospheric pollutants such as salt content & SO2 levels in the atmosphere, corrosion products formed on the mild steel surfaces.

This paper presents a simulator model of a marine diesel engine based on physical, semi-physical, mathematical and thermodynamic equations, which allows fast predictive simulations. The whole engine system is divided into several functional blocks: cooling, lubrication, air, injection, combustion and emissions. The sub-models and dynamic characteristics of individual blocks are established according to engine working principles equations and experimental data collected from a marine diesel engine test bench for SIMB Company under the reference 6M26SRP1. The overall engine system dynamics is expressed as a set of simultaneous algebraic and differential equations using sub-blocks and S-Functions of Matlab/Simulink. The simulation of this model, implemented on Matlab/Simulink has been validated and can be used to obtain engine performance, pressure, temperature, efficiency, heat release, crank angle, fuel rate, emissions at different sub-blocks. The simulator will be used, in future work, to study the engine performance in faulty conditions, and can be used to assist marine engineers in fault diagnosis and estimation (FDI) as well as designers to predict the behavior of the cooling system, lubrication system, injection system, combustion, emissions, in order to optimize the dimensions of different components. This program is a platform for fault simulator, to investigate the impact on sub-blocks engine’s output of changing values for faults parameters such as: faulty fuel injector, leaky cylinder, worn fuel pump, broken piston rings, a dirty turbocharger, dirty air filter, dirty air cooler, air leakage, water leakage, oil leakage and contamination, fouling of heat exchanger, pumps wear, failure of injectors (and many others).

This paper presents a comprehensive review and analysis of ship hull cleaning technologies. Various cleaning methods and devices applied to dry-dock cleaning and underwater cleaning are introduced in detail, including rotary brushes, high-pressure and cavitation water jet technology, ultrasonic technology, and laser cleaning technology. The application of underwater robot technology in ship cleaning not only frees divers from engaging in heavy work but also creates safe and efficient industrial products. Damage to the underlying coating of the ship caused by the underwater cleaning operation can be minimized by optimizing the working process of the underwater cleaning robot. With regard to the adhesion technology mainly used in underwater robots, an overview of recent developments in permanent magnet and electromagnetic adhesion, negative pressure force adhesion, thrust force adhesion, and biologically inspired adhesion is provided. Through the analysis and comparison of current underwater robot products, this paper predicts that major changes in the application of artificial intelligence and multirobot cooperation, as well as optimization and combination of various technologies in underwater cleaning robots, could be expected to further lead to breakthroughs in developing next-generation robots for underwater cleaning.

The wind-assisted propulsion system is becoming one of the most popular and efficient ways to reduce both fuel consumption and carbon dioxide emission from the ships. In this study, several analyses have been carried out on a model of bulk carrier fitted with five rigid sails with a 180° rotating mechanism for maximum usage of wind power and a telescopic reefing mechanism for folding it during berthing. The stability of the ship has been verified through the calculations of initial stability, static stability, and dynamic stability through the fulfillment of the weather criterion using MAXSURF software. The structural analysis of the sail was carried out in ANSYS static structural module. Several flow simulations were carried out in ANSYS fluent module to predict the thrusts produced by the sails at different apparent wind angles, which would in turn reduce the thrust required from the propeller. In this way, the brake horse powers required for different sail arrangements were analyzed to find out a guideline for this wind propulsion system to generate better powering performances. To consider drift and yaw effect on propulsion system, an MMG mathematical model–based simulation was carried out for different drift angles of motion of the ship considering hard sail–based wind loads. Through these analyses, it has been found out that the hard sail–based wind-assisted propulsion system in some cases have produced a reduction of more than 30% brake power in straight ahead motion and around 20% reduction in case of drifting ships compared to the model having no sails.

In this study, a series of numerical calculations are carried out in ANSYS Workbench based on the unidirectional fluid-solid coupling theory. Using the DTMB 4119 propeller as the research object, a numerical simulation is set up to analyze the open water performance of the propeller, and the equivalent stress distribution of the propeller acting in the flow field and the axial strain of the blade are analyzed. The results show that FLUENT calculations can provide accurate and reliable calculations of the hydrodynamic load for the propeller structure. The maximum equivalent stress was observed in the blade near the hub, and the tip position of the blade had the largest stress. With the increase in speed, the stress and deformation showed a decreasing trend.

Structural integrity has remained a challenge for design and analysis of wave energy devices. A difficulty in assessment of the structural integrity is often laid in the accurate determination of the wave-induced loads on the wave energy devices and the repones of the structure. Decoupled hydroelastic response of a submerged, oscillating wave energy device to extreme nonlinear wave loads is studied here. The submerged wave energy device consists of an oscillating horizontal disc attached to a direct-drive power take-off system. The structural frame of the wave energy device is fixed on the seafloor in shallow water. Several extreme wave conditions are considered in this study. The nonlinear wave loads on members of the submerged structure are obtained by use of the level I Green-Naghdi equations and Morison’s equation for cylindrical members. Distribution of Von Mises stresses and the elastic response of the structure to the extreme wave loads are determined by use of a finite element method. The decoupled hydroelastic analysis of the structure is carried out for devices built by four different materials, namely stainless steel, concrete, aluminium alloy, and titanium alloy. The elastic response of these devices is studied and results are compared with each other. Points of maximum stress and deformations are determined and the structural integrity under the extreme conditions is assessed. It is shown that the proposed approaches provide invaluable information about the structural integrity of wave energy devices.

Liquid sloshing is a common phenomenon in the transportation of liquid-cargo tanks. Liquid waves lead to fluctuating forces on the tank walls. If these fluctuations are not predicted or controlled, for example, by using baffles, they can lead to large forces and momentums. The volume of fluid (VOF) two-phase numerical model in OpenFOAM open-source software has been widely used to model the liquid sloshing. However, a big challenge for modeling the sloshing phenomenon is selecting a suitable turbulence model. Therefore, in the present study, different turbulence models were studied to determine their sloshing phenomenon prediction accuracies. The predictions of these models were validated using experimental data. The turbulence models were ranked by their mean error in predicting the free surface behaviors. The renormalization group (RNG) k-ε and the standard k-ω models were found to be the best and worst turbulence models for modeling the sloshing phenomena, respectively; moreover, the SST k-ω model and v2-f k-ε results were very close to the RNG k-ε model result.

In the Lagrangian meshless (particle) methods, such as the smoothed particle hydrodynamics (SPH), moving particle semi-implicit (MPS) method and meshless local Petrov-Galerkin method based on Rankine source solution (MLPG_R), the Laplacian discretisation is often required in order to solve the governing equations and/or estimate physical quantities (such as the viscous stresses). In some meshless applications, the Laplacians are also needed as stabilisation operators to enhance the pressure calculation. The particles in the Lagrangian methods move following the material velocity, yielding a disordered (random) particle distribution even though they may be distributed uniformly in the initial state. Different schemes have been developed for a direct estimation of second derivatives using finite difference, kernel integrations and weighted/moving least square method. Some of the schemes suffer from a poor convergent rate. Some have a better convergent rate but require inversions of high order matrices, yielding high computational costs. This paper presents a quadric semi-analytical finite-difference interpolation (QSFDI) scheme, which can achieve the same degree of the convergent rate as the best schemes available to date but requires the inversion of significant lower-order matrices, i.e. 3×3 for 3D cases, compared with 6×6 or 10×10 in the schemes with the best convergent rate. Systematic patch tests have been carried out for either estimating the Laplacian of given functions or solving Poisson’s equations. The convergence, accuracy and robustness of the present schemes are compared with the existing schemes. It will show that the present scheme requires considerably less computational time to achieve the same accuracy as the best schemes available in literatures, particularly for estimating the Laplacian of given functions.

High-speed planing crafts have successfully evolved through developments in the last several decades. Classical approaches such as inviscid potential flow-based methods and the empirically based Savitsky method provide general understanding for practical design. However, sometimes such analyses suffer inaccuracies since the air-water interface effects, especially in the transition phase, are not fully accounted for. Hence, understanding the behaviour at the transition speed is of fundamental importance for the designer. The fluid forces in planing hulls are dominated by phenomena such as flow separation at various discontinuities viz., knuckles, chines and transom, with resultant spray generation. In such cases, the application of potential theory at high speeds introduces limitations. This paper investigates the simulation of modelling of the pre-planing behaviour with a view to capturing the air-water interface effects, with validations through experiments to compare the drag, dynamic trim and wetted surface area. The paper also brings out the merits of gridding strategies to obtain reliable results especially with regard to spray generation due to the air-water interface effects. The verification and validation studies serve to authenticate the use of the multi-gridding strategies on the basis of comparisons with simulations using model tests. It emerges from the study that overset/chimera grids give better results compared with single unstructured hexahedral grids. Two overset methods are investigated to obtain reliable estimation of the dynamic trim and drag, and their ability to capture the spray resulting from the air-water interaction. The results demonstrate very close simulation of the actual flow kinematics at steady-speed conditions in terms of spray at the air-water interface, drag at the pre-planing and full planing range and dynamic trim angles.

Resistance prediction of ships using computational fluid dynamics has gained popularity over the years because of its high accuracy and low cost. This paper conducts numerical estimations of the ship resistance and motion of a Japan bulk carrier model using SHIP_Motion, a Reynolds-averaged Navier-Stokes (RaNS)-based solver, and HydroSTAR, a commercial potential flow (PF)-based solver. The RaNS solver uses an overset-structured mesh and discretizes the flow field using the finite volume method, while the PF-based solver applies the three-dimensional panel method. In the calm water test, the total drag coefficient, sinkage, and trim were predicted using the RaNS solver following mesh dependency analysis, and the results were compared with the available experimental data. Next, calm water resistance was investigated for a range of Froude numbers. The added resistance in short-wave cases was simulated using both RaNS and PF solvers, and the results were compared. The PF solver showed better agreement with the RaNS solver for predicting motion responses than for predicting added resistance. While the added resistance results could not be directly validated because of the absence of experimental data, considering the previous accuracy of the RaNS solver in added resistance prediction and general added resistance profile of similar hull forms (bulk carriers), the prediction results could be concluded to be reliable.

With the rapid development of marine renewable energy technologies, the demand to mitigate the fluctuation of variable generators with energy storage technologies continues to increase. Offshore compressed air energy storage (OCAES) is a novel flexible-scale energy storage technology that is suitable for marine renewable energy storage in coastal cities, islands, offshore platforms, and offshore renewable energy farms. For deep-water applications, a marine riser is necessary for connecting floating platforms and subsea systems. Thus, the response characteristics of marine risers are of great importance for the stability and safety of the entire OCAES system. In this study, numerical models of two kinds of flexible risers, namely, catenary riser and lazy wave riser, are established in OrcaFlex software. The static and dynamic characteristics of the catenary and the lazy wave risers are analyzed under different environment conditions and internal pressure levels. A sensitivity analysis of the main parameters affecting the lazy wave riser is also conducted. Results show that the structure of the lazy wave riser is more complex than the catenary riser; nevertheless, the former presents better response performance.

The probability distributions of wave characteristics from three groups of sampled ocean data with different significant wave heights have been analyzed using two transformation functions estimated by non-parametric and parametric methods. The marginal wave characteristic distribution and the joint density of wave properties have been calculated using the two transformations, with the results and accuracy of both transformations presented here. The two transformations deviate slightly between each other for the calculation of the crest and trough height marginal wave distributions, as well as the joint densities of wave amplitude with other wave properties. The transformation methods for the calculation of the wave crest and trough height distributions are shown to provide good agreement with real ocean data. Our work will help in the determination of the most appropriate transformation procedure for the prediction of extreme values.

Elastic acoustic scattering is important for buried target detection and identification. For elastic spherical objects, studies have shown that a series of narrowband energetic arrivals follow the first specular one. However, in practice, the elastic echo is rather weak because of the acoustic absorption, propagation loss, and reverberation, which makes it difficult to extract elastic scattering features, especially for buried targets. To remove the interference and enhance the elastic scattering, the de-chirping method was adopted here to address the target scattering echo when a linear frequency modulation (LFM) signal is transmitted. The parameters of the incident signal were known. With the de-chirping operation, a target echo was transformed into a cluster of narrowband signals, and the elastic components could be extracted with a band-pass filter and then recovered by remodulation. The simulation results indicate the feasibility of the elastic scattering extraction and recovery. The experimental result demonstrates that the interference was removed and the elastic scattering was visibly enhanced after de-chirping, which facilitates the subsequent resonance feature extraction for target classification and recognition.

API RP2AWSD is a design code in practice for design of jacket platforms in the Persian Gulf but is based on the Gulf of Mexico environmental condition. So for the sake of using this code for the Persian Gulf, it is better to perform a calibration based on this specific region. Analysis and design of jacket platforms based on API code are performed in a static manner and dynamic analysis is not recommended for such structures. Regarding the fact that the real behavior of the offshore jacket platforms is a dynamic behavior, so in this research, dynamic analysis for an offshore jacket platform in the Persian Gulf under extreme environmental condition is performed using random time domain method. Therefore, a new constructed offshore jacket platform in the Persian Gulf is selected and analyzed. Fifteen, 1-h storm, simulations for the water surface elevation is produced to capture the statistical properties of extreme sea condition. Time series of base shear and overturning moment are derived from both dynamic and static responses. By calculating the maximum dynamic amplification factor (DAF) from each simulation and fitting the collected data to Weibull distribution, the most probable maximum extreme (MPME) value for the DAF is achieved. Results show that a realistic value for DAF for this specific platform is 1.06, which is a notable value and is recommended to take into practice in design of fixed jacket platform in the Persian Gulf.

This article presents a numerical study of the forces induced by hydrodynamic impact, that is, the impact of a part of the bottom of the hull on the water surface. The prediction of these efforts is often based on numerical simulations to determine the shock intensity of a structure on the surface of a weakly compressible fluid (for example, water). The short duration of the impact is also investigated in this work. This phenomenon occurs especially when a ship encounters a harsh and difficult sea conditions. Under such conditions, it is important to know how to predict the hydrodynamic forces applied to the structure to correctly optimize the ship elements during its design stage or to prevent possible damage. Indeed, various factors such as speed of the ship and height of the swell can cause the hull to partially emerge and then fall violently onto the water surface, which is referred to by naval personnel as tossing or slamming causing vibrations, stresses, and fatigue to the structural elements of the ship. In this work, we present an example of phenomenon modeling and then a numerical study of the different geometries (dihedron) that play a role in different sections of the bow. Then, we compare our present results with the theoretical and experimental results of other researchers in the field. The average interval impact time for a dihedral model corresponding to the section of the chosen ship and other experimental and theoretical data is in good agreement with the experimental and theoretical measurements.

A method of reliability analysis based on a direct strength calculation employing the von Mises stress failure criterion is presented here. The short term strain distributions of ship hull structural components are identified through the statistical analysis of the wave-induced strain history and the long term distributions by the weighted summation of the short term strain distributions. The wave-induced long term strain distribution is combined with the still water strain. The extreme strain distribution of the response strain is obtained by statistical analysis of the combined strains. The limit state function of the reliability analysis is based on the von Mises stress failure criterion, including the related uncertainties due to the quality of the material and model uncertainty. The reliability index is calculated using FORM and sensitivity analysis of each variable that has effects on the reliability is also discussed.

Terrain matching accuracy and real-time performance are affected by local underwater terrain features and structure of matching surface. To solve the extraction problem of local terrain features for underwater terrain-aided navigation (UTAN), real-time data model and selection method of beams are proposed. Then, an improved structure of terrain storage is constructed, and a fast interpolation strategy based on index is proposed, which can greatly improve the terrain interpolation-reconstruction speed. Finally, for the influences of tide, an elimination method of reference depth deviation is proposed, which can reduce the reference depth errors caused by tidal changes. As the simulation test shows, the proposed method can meet the requirements of real-time performance and effectiveness. Furthermore, the extraction time is considerably reduced, which makes the method suitable for the extraction of local terrain features for UTAN.

The inclining experiment is the only regulatory tool to assess ship stability. This experiment is a time consuming process for both real-life tests and ship model experiments. The difficulty is mainly due to a bias in the measurement of heel angle. Nowadays, digital inclinometers are available, but they are expensive. In this study, the use of a smartphone application is presented for ship inclination and rolling-period tests. The idea consists of using accelerometer and gyroscope sensors built into the current smartphones for the measurements. Therefore, some experiments are carried out on an example trawler model to exhibit the uses and advantages of this method. The obtained results are in good agreement with those provided from the pendulum method and natural roll-period test. This application is new, easy, and more accurately assesses metacentric height during the inclining and rolling-period tests.

Subsea development is moving constantly toward simplification, digitalization, and cost-out strategies because the exploration and production of hydrocarbons are moving toward deeper and remote sea water areas. Usage of all-electric subsea technology instead of hydraulic technology is growing and will be the future of subsea systems due to the former’s environmental and functional advantages and reduced costs. The benefits of all-electric subsea systems are health, safety, and environment (HSE) and improved reliability, flexibility, and functionality compared with traditional hydraulic-electrical systems. Existing electrohydraulic technology for a typical subsea system, hydraulic and electric actuators, and subsea manifold valves including valve types and selection philosophy have been reviewed in this paper. Some major worldwide oil companies such as Equinor and Schlumberger have successful experiences with subsea electric actuators. Considering the benefits of all-electric technology especially in terms of cost and HSE, as well as successful experiences of two major oil companies, further research in this area is warranted. One of the gaps in existing reviewed literature is the effect of using all-electric actuators for manifold valves. Thus, three main questions related to electric actuator selection, requirement of safety integrity level (SIL), and effect of using electric actuators on manifold valve selection have been addressed and answered. Forty hydraulic actuated manifold valves from nine past subsea projects in different parts of the world, mainly Africa and Australia, have been selected for the analysis of all-electric actuators. Results show that 93% of the valves require spring-return electric actuators, whereas 7% can be operated with conventional electric actuators without any spring. The manifold valves do not require SIL certification because they are not connected to an emergency shut down system. Introducing the electric actuators to the manifold valve will not change the valve selection philosophy.

In order to introduce clean environment and sustainable energy to traditional coastal fishing community, the objective of this study is to encourage the Indonesian traditional coastal fishing community to use green and renewable energy in their fishing activities. Introducing solar power as the main source of energy for fish-attracting lights and boat propulsion can reduce the use of fossil fuels, and sustain clean and healthy environment. As the world’s largest archipelago, Indonesia accounts for a high percentage of traditional fishing communities spread out along its islands. This fishing communities use various traditional fishing boats, and platforms. The fishing platforms are usually made of bamboo and placed on top of supporting structures on the seabed. Diesel electric generators are used to obtain electricity needed for lighting to attract the fish at night, and as the source of power for lifting the fishing net. The structure and fuel used are neither environmentally friendly nor clean; thus, an innovation is introduced. Traditional fishing practices using a fishing platform were studied, including the common size of the platform and the power needed for the fishing light. Based on the gathered information, this study proposes a catamaran vessel with a special top structure designed for fish lifting outfitting, and equipped with photovoltaic solar cells as the energy source for the fishing lights and vessel propulsion. Through this innovative break through, the vessel can be moved to the shore and will not be a threat to ship navigation and the environment. Furthemore, powered by clean and sustainable energy, the vessel can be directed to the best fishing ground.

As the energy supply problem worsens, the development and utilization of marine renewable energy have become a research hotspot. The development of wave energy is moving from the near shore to the distant sea. The power-generation efficiency of a single two-floating-body wave-energy converter is relatively low. To fully utilize wave energy and improve the wave-energy capture rate of a fixed sea area, arranging a two-floating-body wave-energy converter array is necessary. This paper first introduces the basic theory of multi-floating flow field, time-domain calculation method, and influence factor of the waveenergy converter array. Then, the development of AQWA software in Fortran language considers the effect of power takeoff. A calculation method based on ANSYS-AQWA is proposed to simulate the motion of the oscillating-buoy two-floating-body wave-energy converter. The results are compared with the experimental results from the National Renewable Energy Laboratory. Finally, the ANSYS-AQWA method is used to study the power characteristics of simple and complex arrays of wave-energy converters. The average power generation of simple arrays is largest at 0°, and the average power generation of complex arrays does not change with the wave direction. Optimal layout spacing exists for the simple and complex arrays. These findings can serve as a valuable reference for the large-scale array layout of wave-energy converters in the future.

Optimization analysis and computational fluid dynamics (CFDs) have been applied simultaneously, in which a parametric model plays an important role in finding the optimal solution. However, it is difficult to create a parametric model for a complex shape with irregular curves, such as a submarine hull form. In this study, the cubic Bezier curve and curve-plane intersection method are used to generate a solid model of a parametric submarine hull form taking three input parameters into account: nose radius, tail radius, and length-height hull ratio (L/H). Application program interface (API) scripting is also used to write code in the ANSYS DesignModeler. The results show that the submarine shape can be generated with some variation of the input parameters. An example is given that shows how the proposed method can be applied successfully to a hull resistance optimization case. The parametric design of the middle submarine type was chosen to be modified. First, the original submarine model was analyzed, in advance, using CFD. Then, using the response surface graph, some candidate optimal designs with a minimum hull resistance coefficient were obtained. Further, the optimization method in goal-driven optimization (GDO) was implemented to find the submarine hull form with the minimum hull resistance coefficient (C_t). The minimum C_t was obtained. The calculated difference in C_t values between the initial submarine and the optimum submarine is around 0.26%, with the C_t of the initial submarine and the optimum submarine being 0.001 508 26 and 0.001 504 29, respectively. The results show that the optimum submarine hull form shows a higher nose radius (r_n) and higher L/H than those of the initial submarine shape, while the radius of the tail (r_t) is smaller than that of the initial shape.

Swarm robotics in maritime engineering is a promising approach characterized by large numbers of relatively small and inexpensive autonomous aquatic crafts (AACs) to monitor marine environments. Compared with a single, large aquatic manned or unmanned surface vehicle, a highly distributed aquatic swarm system with several AACs features advantages in numerous real-world maritime missions, and its natural potential is qualified for new classes of tasks that uniformly feature low cost and high efficiency through time. This article develops an inexpensive AAC based on an embedded-system companion computer and open-source autopilot, providing a verification platform for education and research on swarm algorithm on water surfaces. A topology communication network, including an inner communication network to exchange information among AACs and an external communication network for monitoring the state of the AAC Swarm System (AACSS), was designed based on the topology built into the Xbee units for the AACSS. In the emergence control network, the transmitter and receiver were coupled to distribute or recover the AAC. The swarm motion behaviors in AAC were resolved into the capabilities of go-to-waypoint and path following, which can be accomplished by two uncoupled controllers:speed controller and heading controller. The good performance of velocity and heading controllers in go-to-waypoint was proven in a series of simulations. Path following was achieved by tracking a set of ordered waypoints in the go-to-waypoint. Finally, a sea trial conducted at the China National Deep Sea Center successfully demonstrated the motion capability of the AAC. The sea trial results showed that the AAC is suited to carry out environmental monitoring tasks by efficiently covering the desired path, allowing for redundancy in the data collection process and tolerating the individual AACs’ path-following offset caused by winds and waves.

Using a discretized finite difference method, a numerical model was developed to study the interaction of regular waves with a perforated breakwater. Considering a non-viscous, non-rotational fluid, the governing equations of Laplacian velocity potential were developed, and specific conditions for every single boundary were defined. The final developed model was evaluated based on an existing experimental result. The evaluated model was used to simulate the condition for various wave periods from 0.6 to 2 s. The reflection coefficient and transmission coefficient of waves were examined with different breakwater porosities, wave steepnesses, and angular frequencies. The results show that the developed model can suitably present the effect of the structural and hydraulic parameters on the reflection and transmission coefficients. It was also found that with the increase in wave steepness, the reflection coefficient increased logarithmically, while the transmission coefficient decreased logarithmically.

One of the new methods for powering low-power electronic devices at sea is a wave energy harvesting system. In this method, piezoelectric material is employed to convert the mechanical energy of sea waves into electrical energy. The advantage of this method is based on avoiding a battery charging system. Studies have been done on energy harvesting from sea waves, however, considering energy harvesting with random JONSWAP wave theory, then determining the optimum values of energy harvested is new. This paper does that by implementing the JONSWAP wave model, calculating produced power, and realistically showing that output power is decreased in comparison with the more simple Airy wave model. In addition, parameters of the energy harvester system are optimized using a simulated annealing algorithm, yielding increased produced power.

This paper presents a constructive design of new controllers that force underactuated ships under constant or slow time-varying sea loads to asymptotically track a parameterized reference path, that guarantees the distance from the ship to the reference path always be within a specified value. The control design is based on a global exponential disturbance observer, a transformation of the ship dynamics to an almost spherical form, an interpretation of the tracking errors in an earth-fixed frame, an introduction of dynamic variables to compensate for relaxation of the reference path generation, p-times differentiable step functions, and backstepping and Lyapunov’s direct methods. The effectiveness of the proposed results is illustrated through simulations.

In this paper we have investigated the reflection and the transmission of a system of two symmetric circular-arc-shaped thin porous plates submerged in deep water within the context of linear theory. The hypersingular integral equation technique has been used to analyze the problem mathematically. The integral equations are formulated by applying Green’s integral theorem to the fundamental potential function and the scattered potential function into a suitable fluid region, and then using the boundary condition on the porous plate surface. These are solved approximately using an expansion-cum-collocation method where the behaviour of the potential functions at the tips of the plates have been used. This method ultimately produces a very good numerical approximation for the reflection and the transmission coefficients and hydrodynamic force components. The numerical results are depicted graphically against the wave number for a variety of layouts of the arc. Some results are compared with known results for similar configurations of dual rigid plate systems available in the literature with good agreement.

In this paper we study the problem of generation of surface waves produced due to a) rolling of the plate and b) presence of a line source in front of a fixed vertical plate. The amplitudes of radiated waves at large distance from the plate, in both cases, are obtained by a suitable application of Green’s integral theorem. These are then studied graphically for various values of the ice cover parameter.

Underwater acoustic channels pose a great difficulty for the development of high speed communication due to highly limited band-width as well as hostile multipath interference. Enlightened by rapid progress of multiple-input multiple-output (MIMO) technologies in wireless communication scenarios, MIMO systems offer a potential solution by enabling multiple spatially parallel communication channels to improve communication performance as well as capacity. For MIMO acoustic communications, deep sea channels offer substantial spatial diversity among multiple channels that can be exploited to address simultaneous multipath and co-channel interference. At the same time, there are increasing requirements for high speed underwater communication in very shallow water area (for example, a depth less than 10 m). In this paper, a space-time multichannel adaptive receiver consisting of multiple decision feedback equalizers (DFE) is adopted as the receiver for a very shallow water MIMO acoustic communication system. The performance of multichannel DFE receivers with relatively small number of receiving elements are analyzed and compared with that of the multichannel time reversal receiver to evaluate the impact of limited spatial diversity on multi-channel equalization and time reversal processing. The results of sea trials in a very shallow water channel are presented to demonstrate the feasibility of very shallow water MIMO acoustic communication.

Underwater terrain-aided navigation is used to complement the traditional inertial navigation employed by autonomous underwater vehicles during lengthy missions. It can provide fixed estimations by matching real-time depth data with a digital terrain map. This study presents the concept of using image processing techniques in the underwater terrain matching process. A traditional gray-scale histogram of an image is enriched by incorporation with spatial information in pixels. Edge corner pixels are then defined and used to construct an edge corner histogram, which employs as a template to scan the digital terrain map and estimate the fixes of the vehicle by searching the correlation peak. Simulations are performed to investigate the robustness of the proposed method, particularly in relation to its sensitivity to background noise, the scale of real-time images, and the travel direction of the vehicle. At an image resolution of 1 m²/pixel, the accuracy of localization is more than 10 meters.

Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm’s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.

The present work focused on corrosion inhibition of AA6063 type Al-Mg-Si alloy in sodium chloride (NaCl) solution with a silicon carbide inhibitor, using the potentiodynamic electrochemical method. The aluminium alloy surface morphology was examined, in the as-received and as-corroded in the un-inhibited state, with scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS). The results obtained via linear polarization indicated a high corrosion potential for the unprotected as-received alloy. Equally, inhibition efficiency as high as 98.82% at 10.0 g/v silicon carbide addition was obtained with increased polarization resistance (R_p), while the current density reduced significantly for inhibited samples compared to the un-inhibited aluminium alloy. The adsorption mechanism of the inhibitor aluminium alloy follows the Langmuir adsorption isotherm. This shows that the corrosion rate of aluminium alloy with silicon carbide in NaCl environment decreased significantly with addition of the inhibitor.

The main goal of this paper is to investigate sound scattering from the sea surface, by Kuo’s small perturbation method (SPM), in the Persian Gulf’s environmental conditions. Accordingly, the SPM method is reviewed, then it is demonstrated how it can accurately model sound scattering from the sea surface. Since in Kuo’s approach, the effects of surface roughness and sub-surface bubble plumes on incident sounds can be studied separately, it is possible to investigate the importance of each mechanism in various scattering regimes. To conduct this study, wind and wave information reported by Arzanah station as well as some numerical atmospheric models for the Persian Gulf are presented and applied to examine sound scattering from the sea surface in the Persian Gulf region. Plots of scattering strength by Kuo’s SPM method versus grazing angle for various frequencies, wave heights, and wind speeds are presented. The calculated scattering strength by the SPM method for various frequencies and wind speeds are compared against the results of critical sea tests 7 (CST-7). The favorable agreement achieved for sound scattering in the Persian Gulf region is indicative of the fact that the SPM method can quite accurately model and predict sound scattering from the sea surface.

Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flowinduced vibration. The obtained successes were based on solutions of design problems considered in the framework of ideal fluid theory with their following validation by towing tank tests. However, various aspects of the interaction of ventilated cavities with the viscous flows around the ship hulls remain unclear, whereas there is usually no possibility to simultaneously keep the full-scale Froude number and cavitation number in the test facilities. So, the further progress of the application of ventilated cavitation substantially depends on the ability of computational tools to predict this interaction. This paper briefly describes the state-of-the-art computation of ventilated cavitation and points out the most challenging unsolved problems that appeared in the model tests (prediction of air demand by cavities, ventilation effect on ship drag, on hydrofoil lift, and on the propagation of shock waves in cavities).

Power generation is one of the most essential functions of any plant for continuous functioning without any interruption. A marine power plant (MPP) is the same section. In the present paper, the authors have tried to find the various reliability characteristics of an MPP. A marine power plant which is a composition of two generators and in which one of them is located at the stern and another at the bow, both associated to the main switchboard (MSB). The distribution switchboards (DSB) receive power from the MSB through cables and their respective junctions. Given that arrangement, a working based transition state diagram has been generated. With the help of the Markov process, a number of intro-differential equations are formed and solved by Laplace transform. Various reliability characteristics are calculated and discussed with the help of graphs.

A subsea flowline jumper (FJ) is a basic connected component for the wet oil tree, subsea pipeline and riser base, and it plays an irreplaceable role in the subsea production system. During the installation of FJ, collisions often happen between FJ and other equipment, which may cause serious damage. Besides, as the operating water depth increases, the demand for the installation equipments, such as the crane and winch, will increase. The research of deepwater FJ installation in China is still in the primary stage, thus an installation method for the deepwater FJ is proposed in this paper. Finite element models of a typical M-shaped FJ installation system are built to simulate the installation procedures. Analysis results show that the installation steps designed are feasible and valid for the deepwater FJ. In order to ensure the safety of the installation process, the collision-sensitive analysis for the FJ is conducted, and results show that it is necessary to set the pick up speed at a proper value, in order to avoid collision in the installation process. Besides, the mechanical characteristics of FJ during the installation are investigated under a range of environmental conditions and it is found that the maximum stress of the FJ always happens at its central position. The basic requirements for the installation equipment are also obtained through the analysis of the main installation steps.

The scattering of plane surface waves by bottom undulations in channel flow consisting of two layers is investigated by assuming that the bed of the channel is composed of porous material. The upper surface of the fluid is bounded by a rigid lid and the channel is unbounded in the horizontal directions. There exists only one wave mode corresponding to an internal wave. For small undulations, a simplified perturbation analysis is used to obtain first order reflection and transmission coefficients in terms of integrals involving the shape function describing the bottom. For sinusoidal bottom undulations and exponentially decaying bottom topography, the first order coefficients are computed. In the case of sinusoidal bottom the first order transmission coefficient is found to vanish identically. The numerical results are depicted graphically in a number of figures.

The research performed in this paper was carried out to investigate the computational procedure to design seakeeping optimized ship hull form. To reach the optimized hull form, four stages should be done, which consists of: generate alternative hull form, seakeeping calculations, objective functions and optimization techniques. There are many parameters that may be determined in ship hull form optimization. This paper deals with developed strip theory for determining the seakeeping performance, genetic algorithm (GA) as optimization method, high order equations for curve fitting of the hull form and finally reaching to the minimum bow vertical motion in regular head waves. The Wigley hull is selected as an initial hull and carried to be optimized. Two cases are considered. For the first case, the only form coefficients of the hull (CB, CM, CW, CP) are changed and main dimensions (L, B, T) are fixed. In the second case both hull form and main dimensions are varied simultaneously. Finally, optimized hull form and its seakeeping performances are presented. The results of optimization procedure demonstrate that the optimized hull forms yield a reduction in vertical motion and acceleration.

The numerical simulation of wake and free-surface flow around ships is a complex topic that involves multiple tasks: the generation of an optimal computational grid and the development of numerical algorithms capable to predict the flow field around a hull. In this paper, a numerical framework is developed aimed at high-resolution CFD simulations of turbulent, free-surface flows around ship hulls. The framework consists in the concatenation of “tools”, partly available in the open-source finite volume library OpenFOAM?. A novel, flexible mesh-generation algorithm is presented, capable of producing high-quality computational grids for free-surface ship hydrodynamics. The numerical frame work is used to solve some benchmark problems, providing results that are in excellent agreement with the experimental measures.

The hydroelastic response of very large floating structures (VLFS) under the action of ocean waves is analysed considering the small amplitude wave theory. The very large floating structure is modelled as a floating thick elastic plate based on TimoshenkoMindlin plate theory, and the analysis for the hydroelastic response is performed considering different edge boundary conditions. The numerical study is performed to analyse the wave reflection and transmission characteristics of the floating plate under the influence of different support conditions using eigenfunction expansion method along with the orthogonal mode-coupling relation in the case of finite water depth. Further, the analysis is extended for shallow water depth, and the continuity of energy and mass flux is applied along the edges of the plate to obtain the solution for the problem. The hydroelastic behaviour in terms of reflection and transmission coefficients, plate deflection, strain, bending moment and shear force of the floating thick elastic plate with support conditions is analysed and compared for finite and shallow water depth. The study reveals an interesting aspect in the analysis of thick floating elastic plate with support condition due to the presence of the rotary inertia and transverse shear deformation. The present study will be helpful for the design and analysis of the VLFS in the case of finite and shallow water depth.

This paper describes the characteristics of liquefied natural gas (LNG) carriers briefly. The LNG carrier includes power plant selection, vapor treatment, liquid cargo tank type, etc. Two parameters—fuel substitution rate and recovery of boil of gas (BOG) volume to energy efficiency design index (EEDI) formula are added, and EEDI formula of LNG carriers is established based on ship EEDI formula. Then, based on steam turbine propulsion device of LNG carriers, mathematical models of LNG carriers’ reference line value are established in this paper. By verification, the EEDI formula of LNG carriers described in this paper can provide a reference for LNG carrier EEDI calculation and green shipbuilding.

This paper proposes a new method for ship recognition and classification using sound produced and radiated underwater. To do so, a three-step procedure is proposed. First, the preprocessing operations are utilized to reduce noise effects and provide signal for feature extraction. Second, a binary image, made from frequency spectrum of signal segmentation, is formed to extract effective features. Third, a neural classifier is designed to classify the signals. Two approaches, the proposed method and the fractal-based method are compared and tested on real data. The comparative results indicated better recognition ability and more robust performance of the proposed method than the fractal-based method. Therefore, the proposed method could improve the recognition accuracy of underwater acoustic targets.

The galvanic corrosion behaviour of aluminium 3004 - ? brass with different area ratios was studied in the tropical marine atmosphere at Tuticorin harbour over a period of 426 days. The area ratios, viz. AAluminium:A? brass, studied were 0.125, 0.25, 0.5, 1, 2, 4 and 8. The galvanic corrosion behaviour of the metals was studied in terms of the relative increase in the corrosion rate of aluminium due to galvanic coupling with ? brass, the relative decrease in the corrosion rate of ? brass due to galvanic coupling with aluminium, and the susceptibility of aluminium to pitting owing to galvanic coupling with ? brass. The galvanic potential and galvanic current of the system were monitored. Pits of different dimensions ranging from mild etchings to perforations were experienced on the borders and the surfaces of the interface of aluminium in contact with ? brass. The corrosion products resulting from galvanic corrosion were analysed using XRD and the pitting on aluminium as a result of galvanic corrosion was highlighted in terms of pit depth, size and density of pit, using a high resolution microscope. The most favourable area ratio of aluminium - ? brass in marine atmosphere in terms of gravimetric corrosion rate is 8:1 and the most unfavourable area ratio of aluminium - ? brass is 1:4.

As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics (CFD). A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Turbulence model plays a significant role in the complex flows’ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox (2006) k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition’s behavior.

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.

The effect of a guide vane installed at the elbow on flow-induced noise and vibration is investigated in the range of Reynolds numbers from 1.70?105 to 6.81?105, and the position of guide vane is determined by publications. The turbulent flow in the piping elbow is simulated with large eddy simulation (LES). Following this, a hybrid method of combining LES and Lighthill’s acoustic analogy theory is used to simulate the hydrodynamic noise and sound sources are solved as volume sources in code Actran. In addition, the flow-induced vibration of the piping elbow is investigated based on a fluid-structure interaction (FSI) code. The LES results indicate that the range of vortex zone in the elbow without the guide vane is larger than the case with the guide vane, and the guide vane is effective in reducing flow-induced noise and vibration in the 90° piping elbow at different Reynolds numbers.

An LES simulation of flow over an accumulator unit of an underwater compressed air energy storage facility was conducted. The accumulator unit consists of three touching underwater balloons arranged in a floral configuration. The structure of the flow was examined via three dimensional iso surfaces of the Q criterion. Vortical cores were observed on the leeward surface of the balloons. The swirling tube flows generated by these vortical cores were depicted through three dimensional path lines. The flow dynamics were visualized via time series snapshots of two dimensional vorticity contours perpendicular to the flow direction; revealing the turbulent swinging motions of the aforementioned shedding-swirling tube flows. The time history of the hydrodynamic loading was presented in terms of lift and drag coefficients. Drag coefficient of each individual balloon in the floral configuration was smaller than that of a single balloon. It was found that the total drag coefficient of the floral unit of three touching balloons, i.e. summation of the drag coefficients of the balloons, is not too much larger than that of a single balloon whereas it provides three times the storage capacity. In addition to its practical significance in designing appropriate foundation and supports, the instantaneous hydrodynamic loading was used to determine the frequency of the turbulent swirling-swinging motions of the shedding vortex tubes; the Strouhal number was found to be larger than that of a single sphere at the same Reynolds number.

To simulate the dynamic responses of the multibody system with a floating base when the upper parts spread with a certain sequence and relative speed, the homogeneous matrix method is employed to model and simulate a four-body system with a floating base and the motions are analyzed when the upper parts are spread sequentially or synchronously. The rolling, swaying and heaving temporal variations are obtained when the multibody system is under the conditions of the static water along with the wave loads and the mean wind loads or the single pulse wind loads, respectively. The moment variations of each joint under the single pulse wind load are also gained. The numerical results showed that the swaying of the floating base is almost not influenced by the spreading time or form when the upper parts spread sequentially or synchronously, while the rolling and the heaving mainly depend on the spreading time and forms. The swaying and heaving motions are influenced significantly by the mean wind loads. The single pulse wind load also has influences on the dynamic responses. The torque of joint 3 and joint 4 in the single pulse wind environment may be twice that in the windless environment when the system spreads with 60 s duration.