Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces. The subject of this paper is the 3-DOF modeling of roll, heave, and pitch motions of such a wing in the presence of surface waves and other ground non-uniformities. The potential-flow extreme-ground-effect theory is applied for calculating unsteady pressure distribution under the wing which defines instantaneous lift force and moments. Dynamic simulations of a selected ram wing configuration are carried out in the presence of surface waves of various headings and wavelengths, as well as for transient flights over a ground obstacle. The largest amplitudes of the vehicle motions are observed in beam waves when the periods of the encounter are long. Nonlinear effects are more pronounced for pitch angles than for roll and heave. The present method can be adapted for modeling of air-supported lifting surfaces on fast marine vehicles.

Nowadays, several stern devices are attracting a great deal of attention. The control surface is an effective apparatus for improving the hydrodynamic performance of planing hulls and is considered an important element in the design of planing hulls. Control surfaces produce forces and a pitching moment due to the pressure distribution that they cause, which can be used to change the running state of high-speed marine boats. This work elaborates a new study to evaluate the hydrodynamic performance of a planing boat with a trim tab and an interceptor, and optimizes them by using an optimization algorithm. The trim tab and the interceptor have been used to optimize the running trim and motion control of semi-planing and planing boats at various speeds and sea conditions for many years. In this paper, the usage of trim tab is mathematically verified and experimental equations are utilized to optimize the performance of a planing boat at a specificd trim angle by using an optimization algorithm. The genetic algorithm (GA) is one of the most useful optimizing methods and is used in this study. The planing boat equations were programmed according to Savitsky’s equations and then analyzed in the framework of the GA-based optimization for performance improvement of theplaning hull. The optimal design of trim tab and interceptor for planing boat can be considered a multiobjective problem. The input data of GA include different parameters, such as speed, longitudinal center of gravity, and deadrise angle. We can extract the best range of forecasting the planing boat longitudinal center of gravity, the angle of the trim, and the least drag force at the best trim angle of the boat.

The aim of the present work is to assess the offshore wave energy potential along the Atlantic coast of Morocco. Research works of this paper focus on the identification of the most energetic sites for wave energy converters (WECs) deployment. For this purpose, 11 sites have been explored; all of them are located at more than 40m depth on the Moroccan Atlantic coast. The wave power at each site is computed on the basis of wave data records in terms of significant wave height and energy period provided by the Wave Watch three (WW3) model. Results indicate that the coast sites located between latitudes 30° 30’ N and 33° N are the most energetic with an annual average wave power estimated at about 30 kW·m^-1, whereas, in the other sites, the wave power is significantly lower. Moreover, the study of the monthly and seasonal temporal variability is found to be uniform in the powerful sites with values four times greater in winter than in summer. The directional investigation on the significant wave height has shown that for almost all the powerful sites, the incoming waves have a dominant sector ranging between Northern (N) and Western-Northern-Western (WNW) directions.

A two-dimensional numerical Computational Fluid Dynamics (CFD) model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wave energy converter (WEC) under regular wave conditions. The convergence study of mesh size and time step is performed to ensure that wave height and motion response are sufficiently accurate. Wave height results reveal that the attenuation of wave height along the wave tank is less than 5% only if the suitable mesh size and time step are selected. The model proposed in this work is verified against published experimental and numerical models. The effects of mechanical damping, wave height, wave frequency, and water depth on the motion response, power generation, and energy conversion efficiency of the flap-type WEC are investigated. The selection of the appropriate mechanical damping of the WEC is crucial for the optimal extraction of wave power. The optimal mechanical damping can be readily predicted by using potential flow theory. It can then be verified by applying CFD numerical results. In addition, the motion response and the energy conversion efficiency of the WEC decrease as the incident wave height increases because the strengthened nonlinear effect of waves intensifies energy loss. Moreover, the energy conversion efficiency of the WEC decreases with increasing water depth and remains constant as the water depth reaches a critical value. Therefore, the selection of the optimal parameters during the design process is necessary to ensure that the WEC exhibits the maximum energy conversion efficiency.

Elastic critical buckling load of a column depends on various parameters, such as boundary conditions, material, and crosssection geometry. The main purpose of this work is to present a new method for investigating the buckling load of tapered columns subjected to axial force. The proposed method is based on modified buckling mode shape of tapered structure and perturbation theory. The mode shape of the damaged structure can be expressed as a linear combination of mode shapes of the intact structure. Variations in length in piecewise form can be positive or negative. The method can be used for single-span and continuous columns. Comparison of results with those of finite element and Timoshenko methods shows the high accuracy and efficiency of the proposed method for detecting buckling load.

Coastal defenses such as the breakwaters are important structures to maintain the navigation conditions in a harbor. The estimation of their hydrodynamic characteristics is conventionally done using physical models, subjecting to higher costs and prolonged procedures. Soft computing methods prove to be useful tools, in cases where the data availability from physical models is limited. The present paper employs adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) models to the data obtained from physical model studies to develop a novel methodology to predict the reflection coefficient (K_r) of seaside perforated semicircular breakwaters under low wave heights, for which no physical model data is available. The prediction was done using the input parameters viz., incident wave height (H_i), wave period (T), center-to-center spacing of perforations (S), diameter of perforations (D), radius of semicircular caisson (R), water depth (d), and semicircular breakwater structure height (h_s). The study shows the prediction below the available data range of wave heights is possible by ANFIS and ANN models. However, the ANFIS performed better with R²=0.9775 and the error reduced in comparison with the ANN model with R²=0.9751. Study includes conventional data segregation and prediction using ANN and ANFIS.

In marine engineering, appendages such as fin stabilizers and/or T-foils are made to rotate and to reduce the motion of ships. Research on the hydrodynamics of ships fitted with active appendages has significantly improved the design and control of such ships. However, most studies focus on fixed rather than rotating appendages, thereby ignoring the hydrodynamic unsteadiness of active appendages. To enhance the reliability and precision of the numerical simulations, we propose the use of overlapping grids for simulating advanced catamarans fitted with a pair of rotating T-foils under each bow. The fundamental purpose of the overlapping grid technique is to realize information exchange via regional overlap sharing in each subdomain of the computing domain, instead of using the method of boundary sharing, thus greatly alleviating the difficulty of generating the subdomain grid; moreover, the technique guarantees the quality of the subdomain grid. Within the main computational domain, a subdomain was allocated to accommodate the T-foil. Overlapping meshes near the interface between the two domains enable information flow during the simulation; the overlapping grids are updated at every iteration step because the subdomain rotates. The instantaneous trim and sinkage responses of the catamaran to the T-foil rotation were reproduced. From the moment the active T-foil stopped moving, there was no change in the ship’s sailing attitude, indicating that the response was in real time. By comparing with EFD data, the numerical results showed reasonable agreement, indicating the feasibility and effectiveness of the technique in simulating the hydrodynamics of ships fitted with active appendages.

The CO₂ emission reduction policy of the International Maritime Organization (IMO) recommends that the operation of ships, managed by maritime transport companies, should be energy-efficient. An evaluation method that can determine how successfully a ship implements the energy efficiency plan is proposed in this study. To develop this method, the measures required for energy-efficient ship operations according to the Ship Energy Efficiency Management Plan (SEEMP) operational guidelines were selected. The weights of the selected measures, which indicate how they contribute to the energy-efficient operation of a ship, were derived using a survey based on the analytic hierarchy process (AHP) method. Consequently, using these measures and their weights, a new evaluation method was proposed. This evaluation method was applied to shipping companies in South Korea, and their ship operation energy efficiency indices were derived and compared. This evaluation method will be useful to the government and shipping companies in assessing the energy efficiency of ship operations.

This paper describes an analytical investigation into synchrophasing, a vibration control strategy on a machinery installation in which two rotational machines are attached to a beam-like raft by discrete resilient isolators. Forces and moments introduced by sources are considered, which effectively represent a practical engineering system. Adjusting the relative phase angle between the machines has been theoretically demonstrated to greatly reduce the cost function, which is defined as the sum of velocity squares of attaching points on the raft at each frequency of interest. The effect of the position of the machine is also investigated. Results show that altering the position of the secondary source may cause a slight change to the mode shape of the composite system and therefore change the optimum phase between the two machines. Although the analysis is based on a one-dimensional Euler-Bernoulli beam and each machine is considered as a rigid-body, a key principle can be derived from the results. However, the factors that can influence the synchrophasing control performance would become coupled and highly complicated. This condition has to be considered in practice.

In response to the development of deep-sea oil and gas resources, which require a high degree of cooperation by crude oil transportation equipment, a new type of ship known as the cargo transfer vessel (CTV) has been developed. To provide a theoretical reference for the design and equipment of the CTV’s dynamic positioning system, in this paper, we take the new deepwater CTVas the study object and theoretically and numerically analyze its operation, wind load, current load, wave load, and navigational resistance in a range of Brazilian sea conditions with respect to its positioning and towing modes. We confirm that our proposed method can successfully calculate the total environmental load of the CTVand that the CTV is able to operate normally under the designed sea conditions.

A dynamic model of a remotely operated vehicle (ROV) is developed. The hydrodynamic damping coefficients are estimated using a semi-predictive approach and computational fluid dynamic software ANSYS-CFX^TM and WAMIT^TM. A sliding-mode controller (SMC) is then designed for the ROV model. The controller is subsequently robustified against modeling uncertainties, disturbances, and measurement errors. It is shown that when the system is subjected to bounded uncertainties, the SMC will preserve stability and tracking response. The paper ends with simulation results for a variety of conditions such as disturbances and parametric uncertainties.

Obstacle avoidance becomes a very challenging task for an autonomous underwater vehicle (AUV) in an unknown underwater environment during exploration process. Successful control in such case may be achieved using the model-based classical control techniques like PID and MPC but it required an accurate mathematical model of AUV and may fail due to parametric uncertainties, disturbance, or plant model mismatch. On the other hand, model-free reinforcement learning (RL) algorithm can be designed using actual behavior of AUV plant in an unknown environment and the learned control may not get affected by model uncertainties like a classical control approach. Unlike model-based control model-free RL based controller does not require to manually tune controller with the changing environment. A standard RL based one-step Q-learning based control can be utilized for obstacle avoidance but it has tendency to explore all possible actions at given state which may increase number of collision. Hence a modified Q-learning based control approach is proposed to deal with these problems in unknown environment. Furthermore, function approximation is utilized using neural network (NN) to overcome the continuous states and large statespace problems which arise in RL-based controller design. The proposed modified Q-learning algorithm is validated using MATLAB simulations by comparing it with standard Q-learning algorithm for single obstacle avoidance. Also, the same algorithm is utilized to deal with multiple obstacle avoidance problems.

The galvanic corrosion behavior of the metal combinations 15CDV6/MDN138 and 15CDV6/MDN250, with 1:1 area ratio, has been studied in natural seawater using the open well facility of CECRI’s Offshore Platform at Tuticorin for a year. The open circuit potentials of MDN138, MDN250, and 15CDV6 of the individual metal, the galvanic potential and galvanic current of the couples 15CDV6/MDN138 and 15CDV6/MDN250, were periodically monitored throughout the study period. The calcareous deposits on MDN138 and MDN250 in galvanic contact with 15CDV6 were analyzed using XRD. The electrochemical behavior of MDN138, MDN250, and 15CDV6 in seawater was studied using an electrochemical work station. The surface characteristics of MDN138 and MDN250 in galvanic contact with 15CDV6 have been examined with a scanning electron microscope. The results of the study reveal that the galvanic protection offered by 15CDV6 to MDN250 and MDN138 in natural seawater amounts to 93% and 98%, respectively, implying that the galvanic protection offered by 15CDV6 is continuous and effective, which has been further evinced from the adherent nature of the calcareous deposit film comprising compounds such as CaCO3 (calcite, aragonite, and vaterite), MgCO3 (magnesite), Mg(OH)2 (brucite), and MgO (brucite).