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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.