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.

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 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.

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.

The hydrodynamic performance of a three-dimensional finite-length rotating cylinder is studied by means of a physical tank and numerical simulation. First, according to the identified influencing factors, a hydrodynamic performance test of the rotating cylinder was carried out in a circulating water tank. In order to explore the changing law of hydrodynamic performance with these factors, a particle image velocimetry device was used to monitor the flow field. Subsequently, a computational field dynamics numerical simulation method was used to simulate the flow field, followed by an analysis of the effects of speed ratio, Reynolds number, and aspect ratio on the flow field. The results show that the lift coefficient and drag coefficient of the cylinder increase first and then decrease with the increase of the rotational speed ratio. The trend of numerical simulation and experimental results is similar.

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.

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.

Ice crossings have been used for several reasons. First, due to the active development of the Arctic shelf, supplies and minerals are provided and transferred on special transports on the surface of ice covers. Second, ice crossings across rivers are used to reduce the length of transport routes. Traditional methods of increasing the load bearing capacity of ice are ice freezing from above, ice freezing from below, and ice strengthening through a wooden copepod flooring. Practical experience shows that the physical and mechanical properties of ice covers are unreliable and changeable in time and strongly depend on various external factors. Therefore, ice covers should be strengthened through alternative methods. Thus, predicting the bearing capacity of ice crossings and exploring methods for their strengthening are important. In this study, we consider the results of experimental and numerical studies on the bearing and deformation capacity of ice beams upon destruction from pure bending. Under pure bending, ice breaks down in the ice crossing when transports move along it. Tests were carried out with a specified reinforcement scheme. The results of the model experiments were compared with numerical calculations in the ANSYS software package. Experiments on ice beams reinforced with various composite materials were also performed. Destruction of samples in all cases occurred as a result of the formation of extensive cracks in the ice caused by the bending moment in the middle of the beam span. Based on the experimental and numerical research results, the use of a surface reinforcement in ice with various materials can increase the bearing capacity from 65% to 99% for this reinforcement scheme.

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.

In general, submerged pipes passing over the sedimentary bed of seas are installed for transmitting oil and gas to coastal regions. The stability of submerged pipes can be threatened with waves and coastal flows occurring at coastal regions. In this study, for the first time, the adaptive neuro-fuzzy inference system (ANFIS) is optimized using the particle swarm optimization (PSO) algorithm, and a meta-heuristic artificial intelligence model is developed for simulating the scour pattern around submerged pipes located in sedimentary beds. Afterward, six ANFIS-PSO models are developed by means of parameters affecting the scour depth. Then, the superior model is detected through sensitivity analysis. This model has the function of all input parameters. The calculated correlation coefficient and scatter index for this model are 0.993 and 0.047, respectively. The ratio of the pipe distance from the sedimentary bed to the submerged pipe diameter is introduced as the most effective input parameter. PSO significantly improves the performance of the ANFIS model. Approximately 36% of the scour depths simulated using the ANFIS model have an error less than 5%, whereas the value for ANFIS-PSO is roughly 72%.

As a core part of subsea production systems, subsea control modules (SCMs) are costly, difficult, and expensive to install and inconvenient to use in underwater maintenance. Therefore, performance and function tests must be carried out before launching SCMs. This study developed a testing device and an SCM test by investigating SCMs and their underwater. The testing device includes four parts:a hydraulic station, an SCM test stand, a signal generating device, and an electronic test unit. First, the basic indices of the testing device were determined from the performance and working parameters of the SCM. Second, the design scheme of the testing device for the SCM was tentatively proposed, and each testing device was designed. Finally, a practical measurement of the SCM, in combination with the hydraulic station, SCM test stand, signal generator, electronic unit, and highpressure water tank, was carried out according to the test requirements. The measurement mainly involved equipment inspection before testing and an experimental test for the SCM. The validity and feasibility of the testing device and method were simultaneously verified through an association test.

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.

Optimization procedures are required to minimize the amount of fuel consumption and exhaust emissions from marine engines. This study discusses the procedures to optimize the performance of any marine engine implemented in a 0D/1D numerical model in order to achieve lower values of exhaust emissions. From that point, an extension of previous simulation researches is presented to calculate the amount of SO_x emissions from two marine diesel engines along their load diagrams based on the percentage of sulfur in the marine fuel used. The variations of SO_x emissions are computed in g/kW·h and in parts per million (ppm) as functions of the optimized parameters:brake specific fuel consumption and the amount of air-fuel ratio respectively. Then, a surrogate model-based response surface methodology is used to generate polynomial equations to estimate the amount of SO_x emissions as functions of engine speed and load. These developed non-dimensional equations can be further used directly to assess the value of SO_x emissions for different percentages of sulfur of the selected or similar engines to be used in different marine applications.

In power production, gas turbines are commonly used components that generate high amount of energy depending on size and weight. They function as integral parts of helicopters, aircrafts, trains, ships, electrical generators, and tanks. Notably, many researchers are focusing on the design, operation, and maintenance of gas turbines. The focal point of this paper is a DEMATEL approach based on fuzzy sets, with the attempt to use these fuzzy sets explicitly. Using this approach, the cause-effect diagram of gas turbine failures expressed in the literature is generated and aimed to create a perspective for operators. The results of the study show that, "connecting shaft has been broken between turbine and gear box" selected the most important cause factor and "sufficient pressure fuel does not come for fuel pump" is selected the most important effect factor, according to the experts.

Acoustic scattering as the perturbation of an incident acoustic field from an arbitrary object is a critical part of the targetrecognition process in synthetic aperture sonar (SAS) systems. The complexity of scattering models strongly depends on the size and structure of the scattered surface. In accurate scattering models including numerical models, the computational cost significantly increases with the object complexity. In this paper, an efficient model is proposed to calculate the acoustic scattering from underwater objects with less computational cost and time compared with numerical models, especially in 3D space. The proposed model, called texture element method (TEM), uses statistical and structural information of the target surface texture by employing non-uniform elements described with local binary pattern (LBP) descriptors by solving the Helmholtz integral equation. The proposed model is compared with two other well-known models, one numerical and other analytical, and the results show excellent agreement between them while the proposed model requires fewer elements. This demonstrates the ability of the proposed model to work with arbitrary targets in different SAS systems with better computational time and cost, enabling the proposed model to be applied in real environment.