A ship – ice – water interaction model is established using smoothed-particle hydrodynamics (SPH) to predict the ice breaking resistance of the icebreaker in the Yellow River effectively. This method includes the numerical process of the constitutive equation, yield criterion, and the coupling model in SPH. The ice breaking resistance is determined under different conditions. The numerical results of the ice breaking resistance agree with the empirical formula results. Results show that the prediction accuracy of ice resistance is less than 17.6% compared with the empirical formula in the level ice. The method can also be extended to predict the floe motion and ice breaking resistance in actual river channels. The validation against the empirical formula indicates that the proposed ship – ice – water SPH method can predict the ice breaking resistance of icebreakers in actual rivers effectively. The predicted ice breaking resistance is analyzed under different conditions. The ice breaking resistance increases with increasing bending strength and ice thickness, and the latter is the most important factor influencing ice resistance.

A fully Lagrangian algorithm for numerical simulation of fluid-elastic structure interaction (FSI) problems is developed based on the Smoothed Particle Hydrodynamics (SPH) method. The developed method corresponds to incompressible fluid flows and elastic structures. Divergence-free (projection based) incompressible SPH (ISPH) is used for the fluid phase, while the equations of motion for structural dynamics are solved using Total Lagrangian SPH (TLSPH) method. The temporal pressure noise can occur at the free surface and fluid-solid interfaces due to errors associated with the truncated kernels. A FSI particle shifting scheme is implemented to produce sufficiently homogeneous particle distributions to enable stable, accurate, converged solutions without noise in the pressure field. The coupled algorithm, with the addition of proposed particle shifting scheme, is able to provide the possibility of simultaneous integration of governing equations for all particles, regardless of their material type. This remedy without need for tuning a new parameter, resolves the unphysical discontinuity beneath the interface of fluid-solid media. The coupled ISPH-TLSPH scheme is used to simulate several benchmark test cases of hydro-elastic problems. The method is validated by comparison of the presented results with experiments and numerical simulations from other researchers.

Using linear water wave theory, three-dimensional problems concerning the interaction of waves with spherical structures in a fluid which contains a three-layer fluid consisting of a layer of finite depth bounded above by freshwater of finite depth with free surface and below by an infinite layer of water of greater density are considered. In such a situation time-harmonic waves with a given frequency can propagate with three wavenumbers. The sphere is submerged in either of the three layers. Each problem is reduced to an infinite system of linear equations by employing the method of multipoles and the system of equations is solved numerically by standard technique. The hydrodynamic forces (vertical and horizontal forces) are obtained and depicted graphically against the wavenumber. When the density ratio of the upper and middle layer is made to approximately one, curves for vertical and horizontal forces almost coincide with the corresponding curves for the case of a two-layer fluid with a free surface. This means that in the limit, the density ratio of the upper and middle layer goes to approximately one, the solution agrees with the solution for the case of a two-layer fluid with a free surface.

Oblique surface waves incident on a fixed vertical porous membrane of various geometric configurations is analyzed here. The mixed boundary value problem is modified into easily resolvable problems by using a connection. These problems are reduced to that of solving a couple of integral equations. These integral equations are solved by a one-term or a two-term Galerkin method. The method involves a basis functions consists of simple polynomials multiplied with a suitable weight functions induced by the barrier. Coefficient of reflection and total wave energy are numerically evaluated and analyzed against various wave parameters. Enhanced reflection is found for all the four barrier configurations.

This study investigates the roll decay of a fishing vessel by experiments and computational fluid dynamics (CFD) simulations. A fishing vessel roll decay is tested experimentally for different initial roll angles. The roll decay is also simulated numerically by CFD simulations and is validated against the experimental results. It shows that the roll damping could be obtained by CFD with high level of accuracy. The linear and nonlinear damping terms are extracted from the CFD roll decay results and are used in a potential-based solver. In this way we are using a hybrid solver that benefits the accuracy of the CFD results in terms of roll damping estimation and the fast computations of the potential-based solver at the same time. This hybrid method is used for reproducing the free roll decays at Fn=0 and also in analyzing some cases in waves. The experiments, CFD and the hybrid parts are described in detail. It is shown that the suggested method is capable of doing the simulations in a very short time with high level of accuracy. This strategy could be used for many seakeeping analyses.

Indonesian offshore and coastal areas are vulnerable to swells from Roaring Forties and cyclone disasters. However, the understanding of the characteristics and propagation mechanisms of local disastrous waves is insufficient, posing a threat to the construction, maintenance, and protection of coastal structures. This study establishes a multiple nested wave model based on the third-generation wave model WAVEWATCHⅢ. This model includes sole forcing of Roaring Forties and combined forcing of Roaring Forties and cyclone Ernie to simulate the influence of disastrous waves under the Roaring Forties and tropical cyclones in the Indonesian offshore zone and coasts. The following results are obtained. The Indonesian offshore is prevailed by relatively stable southern to southwestern dominant swells and small wind waves under the impacts of the Roaring Forties without cyclone winds. Long propagating swells originated from the Roaring Forties dominate in nearshore coastal waters with deformed directions and strength because of the shoaling effect.

In the last two decades, the exploitation of marine renewable energies (70% of the globe is made up of oceans), especially wave energy, has attracted great interest, not only for their high potential, but also for their high energy density. The development of wave energy is suitable for countries or regions with extensive coastline and high waves approaching the shore. This paper focuses on the study of wave potential and wave energy distribution in the Casablanca-Mohammedia nearshore area (Moroccan Atlantic coast) in order to identify prospective wave energy hotspots. To achieve this purpose, the offshore wave potential was firstly estimated from a 20 years wave data provided by ECMWF (European Center for Medium range Weather Forecasts). In the second step, a numerical modeling of the wave propagation in the study area was performed using the SWAN model jointly with WAVEWATCHIII. The performance of the model to simulate accurately the wave field was evaluated in a real situation characterized by large waves. The model then was applied to determine the patterns of wave field in the Casablanca-Mohammedia nearshore area for a typical wave conditions (winter, summer and storm). The results of this study show the abundance of wave energy in the region with an average annual wave potential of about 22 kW/m. A seasonal variability of the wave resource was demonstrated, with values five times higher in winter than in summer. In addition, a major hotspot site was identified that should be considered when studying WEC implementation. This hotspot is located at the southern edge of the Casablanca-Mohammedia coast, near the coastal area of Sidi Rahal.

As autonomous underwater vehicles (AUVs) merely adopt the inductive obstacle avoidance mechanism to avoid collisions with underwater obstacles, path planners for underwater robots should consider the poor search efficiency and inadequate collision-avoidance ability. To overcome these problems, a specific two-player path planner based on an improved algorithm is designed. First, by combing the artificial attractive field (AAF) of artificial potential field (APF) approach with the random rapidly exploring tree (RRT) algorithm, an improved AAF-RRT algorithm with a changing attractive force proportional to the Euler distance between the point to be extended and the goal point is proposed. Second, a two-layer path planner is designed with path smoothing, which combines global planning and local planning. Finally, as verified by the simulations, the improved AAF-RRT algorithm has the strongest searching ability and the ability to cross the narrow passage among the studied three algorithms, which are the basic RRT algorithm, the common AAF-RRT algorithm, and the improved AAF-RRT algorithm. Moreover, the two-layer path planner can plan a global and optimal path for AUVs if a sudden obstacle is added to the simulation environment.

A dual-baffled rectangular tank with different configurations is proposed to reduce the sloshing effect, and design optimization is conducted through numerical simulations with open-source software, namely OpenFOAM, based on the computational fluid dynamic model. A series of physical experiments in the dual-baffled rectangular tank is performed for model validation and design optimization with the measured water surface elevation distributions along the tank. The optimization uses the calculated maximum horizontal force exerted on the tank and entropy generation (EG) as the criterion. Results show that the dual-baffle configuration positioned at the tank center is more effective in reducing the sloshing than that of the single baffle when the relative baffle height and initial water depth ratio (H_b/H_w, where H_b and H_w represent baffle height and static water depth, respectively) are larger than 0.5. However, such an effect then diminishes when the ratio is larger than 0.75. The effect of the dual-baffle configuration on the sway motion under the condition of different motion amplitudes and frequencies is also evaluated. The results show that the reduction in the maximum horizontal force is almost the same for dual- and single-baffled configurations and reaches the minimum when the sway motion amplitude is near 0.03 m. The dual-baffled configuration for the angular frequency of the sway motion is more effective than the single-baffled in reducing the sloshing at the low angular frequencies but is only less effective at high angular frequencies. Furthermore, the optimal baffle inclination angle is 85° when the inclined straight and curved baffles are used, and curved baffles can successfully decrease the horizontal force exerted on the tank and EG.

The Sagar Island, located north of the Bay of Bengal, intercepts the flow in the Hoogly estuary that comprises a network of several estuarine distributaries and creeks, which is considered to be one of the largest estuarine systems in the world. The Hooghly River experiences a tidal range in the order of about 4 m, due to which the tide-generated currents drive the sediments which are continuously set in motion. The temple, Kapil Muni (21°38’15.35"N, 88°4’30.56"E) is located on the south-western side of Sagar Island, where an annual religious festival and rituals with about a million pilgrims is conducted. The pertinent erosion problem at a rate of about 5 m/year is prevalent at the site has considerably reduced the beach width, thereby, resulting in reduced space for religious as well as recreational activities along the coast. A novel cross-section for the proposed submerged reef using geosynthetic materials is designed considering the different sitespecific, environmental, and socio-economic conditions. The submerged reef can effectively be devised to redistribute the current circulation pattern and trap the sediment for beach restoration. The performance of such a structure depends on its geometrical and structural characteristics, the location of the reef (i. e.) the water depth at the toe, distance from the coastline, wave-structure interaction, sediment transport and local morpho dynamics. The aforesaid criteria were optimized using a numerical model which predicted the average residual velocity in the site to be in the order of about 1 m/s. Owing to logistical constraints geosynthetic materials had to be employed. The detailed design of such a system arrived through numerical modelling and field measurements are presented and discussed in this paper.

Based on the three-dimensional Reynolds-averaged Navier-Stokes equation with the closure of renormalization group k-ε turbulence model and volume of fluid method, a wave-breakwater interaction numerical flume was developed to examine the wave-structure interaction of the porous I-type composite (PITC) breakwater. The transmission and reflection coefficients of the breakwater at different wave steepness H/L are quantitatively analyzed, and the wave-dissipating performance of the breakwater is compared. By changing the submerged depth of the breakwater, the velocity field, and vorticity field in the wave propagation process are analyzed, and the optimal working water depth of the new breakwater is explored. The results show that the vertical wave force on the PITC breakwater is greater than the horizontal wave force. In addition, during the wave dissipation process, the transverse baffle provided by the new breakwater destroys the trajectory of the water particle. In the interior of the wave-breaking chamber, the water that enters from the gap of the permeable plate mixes with the water entering through the bottom hole. The turbulence created by this process further dissipates the wave energy. The relative submergence depth of h/d has a great influence on the hydrodynamic characteristics. When the relative depth is large, most of the wave energy enters the breakwater, the wave energy dissipation of the breakwater is large, and the wave-absorbing effect is good. These research results provide important referential data for the study of permeable plate breakwaters.

In this study, a one-dimensional simulation was performed to evaluate the performance of in-cylinder combustion to control NO x emissions on a four-stroke, six-cylinder marine medium-speed diesel engine. Reducing the combustion temperature is an important in-cylinder measure to decrease NO_x emissions of marine diesel engines. The Miller cycle is an effective method used to reduce the maximum combustion temperature in a cylinder and accordingly decrease NO_x emissions. Therefore, the authors of this study designed seven different early intake valve closing (EIVC) Miller cycles for the original engine, and analyzed the cycle effects on combustions and emissions in high-load conditions. The results indicate that the temperature in the cylinder was significantly reduced, whereas fuel consumption was almost unchanged. When the IVC was properly advanced, the ignition delay period increased and the premixed combustion accelerated, but the in-cylinder average pressure, temperature and NO_x emissions in the cylinder were lower than the original engine. However, closing the intake valve too early led to high fuel consumption. In addition, the NO_x emissions, in-cylinder temperature, and heat release rate remarkably increased. Therefore, the optimal timing of the EIVC varied with different loads. The higher the load was, the earlier the best advance angle appeared. Therefore, the Miller cycle is an effective method for in-engine NO_x purification and does not entail significant cost.