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This paper presents a theoretical and numerical analysis based on a model of mangrove forests incorporating stems and roots to determine the nearshore wave angle and wave height for one-dimensional (1-D) and two-dimensional (2-D) problems. The shallow water equations are solved using the two-step Lax-Wendroff method. The resulting wave height and wave direction vectors are displayed and analyzed to assess the impact of mangrove effects on various bathymetries, including constant, sloping, and parabolic profiles. This procedure is also applied to actual bathymetric data obtained from the Hatiya channel to analyze the influence of mangrove forests and shoreline geometry on the amplitude and wave directionality of nearshore waves. The obtained numerical results demonstrate that both coastal geometry and vegetation exhibit non-linear characteristics in wave behavior. Furthermore, these factors significantly contribute to the directionality and attenuation of nearshore waves. • Mangrove models studied for nearshore wave angle and height via theoretical and numerical methods. • Wave vectors explore mangrove impact on various bathymetries: constant, sloping, parabolic, real. • Numerical results show nonlinear wave behavior due to coastal geometry and vegetation. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical and numerical analysis based on a model of mangrove forests incorporating stems and roots to determine the nearshore wave angle and wave height for one-dimensional (1-D) and two-dimensional (2-D) problems. The shallow water equations are solved using the two-step Lax-Wendroff method. The resulting wave height and wave direction vectors are displayed and analyzed to assess the impact of mangrove effects on various bathymetries, including constant, sloping, and parabolic profiles. This procedure is also applied to actual bathymetric data obtained from the Hatiya channel to analyze the influence of mangrove forests and shoreline geometry on the amplitude and wave directionality of nearshore waves. The obtained numerical results demonstrate that both coastal geometry and vegetation exhibit non-linear characteristics in wave behavior. Furthermore, these factors significantly contribute to the directionality and attenuation of nearshore waves. • Mangrove models studied for nearshore wave angle and height via theoretical and numerical methods. • Wave vectors explore mangrove impact on various bathymetries: constant, sloping, parabolic, real. • Numerical results show nonlinear wave behavior due to coastal geometry and vegetation. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a mathematical method for producing hard-chine ship hulls based on a set of numerical parameters that are directly related to the geometric features of the hull and uniquely define a hull form for this type of ship. The term planing hull is used generically to describe the majority of hard-chine boats being built today. This paper is focused on un-stepped, single-chine hulls. B-spline curves and surfaces were combined with constraints on the significant ship curves to produce the final hull design. The hard-chine hull geometry was modeled by decomposing the surface geometry into boundary curves, which were defined by design constraints or parameters. In planing hull design, these control curves are the center, chine and sheer lines, as well as their geometric features including position, slope and, in the case of the chine, enclosed area and centroid. These geometric parameters have physical, hydrodynamic and stability implications from the design point of view. The proposed method utilizes 2D orthogonal projections of the control curves and then produces 3D definitions using B-spline fitting of the 3D data points. The fitting considers maximum deviation from the curve to the data points and is based on an original selection of the parameterization. A net of B-spline curves (stations) is then created to match the previously defined 3D boundaries. A final set of lofting surfaces of the previous B-spline curves produces the hull surface. [Copyright &y& Elsevier]

In this paper, mathematical models for obtaining the parameter A of the potential function, which describes the equilibrium beach profile, were generated. The aim of the research was to analyse the most important variables related to the equilibrium beach profile, so that the models are used only those variables that are easy to obtain. On the other hand, the sensitivity of the models must be taken into account, since small changes in variables can cause significant deviations in the models results. For this reason, a detailed research of the sensitivity of the studied models in relation to the different variables has been performed. The parameters considered for the evaluation and selection of the optimal model are: the volume error, the Pearson coefficient ( R 2 ), the relative mean square error (MSE/Var), the mean error ( ϵ ) and the relative percentage error ( δ ) and the model stability under changes in the input variables of up to 20% by a Monte Carlo simulation. The best models have been validated using data corresponding to beaches from outside the area where the dataset has been collected. [ABSTRACT FROM AUTHOR]

The symmetric distortions of a containership in large amplitude waves are analyzed by means of numerical methods and are compared with experimental results. The study is part of a ISSC–ITTC benchmark study which was intended to analyze the accuracy of the numerical methods and the uncertainty involved with the predictions of the ship responses. In this paper the numerical calculations are carried out by means of a body nonlinear time domain method. The time domain code is coupled with a finite element model and the ship hull is modeled as a non-uniform Timoshenko beam. The experiments were conducted in a wave tank with an aluminum back bone and the flexible responses of the ship were measured. The ship was tested in regular waves of moderate to large amplitude to analyze the effect of nonlinear springing. Even though a slight discrepancy is found between the numerical and the experimental vertical motions in large amplitude waves, the numerical vertical bending moments are in reasonably good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The gas explosions in offshore installations are known to be very severe according to their geometries and environmental conditions such as leak locations and wind directions, and the dynamic responses of structures caused by blast loads depend on the load profile. To minimize the damage from these critical accidents, the study of the dynamic response of structural members subjected to gas explosion loads must be conducted. In this paper, a numerical model based on time-history data is proposed where we consider the negative phase pressure; in this data, considerable negative phase pressures were observed in gas explosion analysis results. The idealized model was used to characterize the dynamic response under the explosion loading. Also, the structural responses of various structural models were thoroughly investigated using the finite element method [ABSTRACT FROM AUTHOR]

This paper examines the optimum power output of a pitching-surge point absorber wave energy converter in irregular wave climates. A mathematical model based on frequency domain is used as the first step to estimate the hydrodynamic parameters of the device and its potential power output in realistic sea waves. The numerical results predict that the point absorber energy converter has the potential to absorb more energy than what is contained in its own geometrical width. The optimum power of the device is then obtained from wave tank experiments in irregular wave climates. The comparison of numerical and experimental results demonstrates that the frequency domain method based on linear theory will lead to an overestimation of the energy absorption for this device. The frequency domain method provides an upper estimate for wave energy absorption due to the non-linear, viscous effects and constrained amplitude of device oscillation. However, comparison of the performance of the device with other point absorber wave energy converters shows that this wave energy converter is one of the most efficient in terms of absorbing wave energy. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a numerical model for analyzing the course stability of a towed ship in uniform and constant wind. The effects of an unstable towed ship and a stable towed ship were recorded using numerical analysis at various angles and velocities of wind. The stability investigation of the ship towing system was discussed using the linear analysis, where a tug''s motion was assumed to be given. When the tug and the towed ship''s motions were coupled through a towline as a proper model of the ship towing system, their dynamic interactions during towing was then captured using towing trajectories and analyzed using nonlinear time-domain simulation. With increasing wind velocity, the simulation results revealed that the towing instability of the unstable towed ship was recovered in the range of beam to quartering winds; however, the towing stability of the stable towed ship in head and following winds gradually degraded. It should be noted that this towing instability might have resulted in the impulsive towline tension and could led to serious towing accident e.g. towline breakage or collisions. [Copyright &y& Elsevier]

Abstract: A two-dimensional SPH–FEM model is proposed to investigate its application in the fluid–structure interaction (FSI) problem. The fluid model is based on the theory of Smoothed Particle Hydrodynamics (SPH) and the structural dynamics employ a large-deformation Finite Element Method (FEM). This paper describes the basics of both SPH and FEM models and presents the development of a loosely coupled SPH–FEM model. Validation results of two benchmark FSI problems are illustrated. The first test case is flow in a sloshing tank interacting with an elastic body (Souto-Iglesias et al., 2008) and the second one is dam-break flow through an elastic gate (Antoci et al., 2007). The results obtained with the SPH–FEM model show good agreement with published experimental results and suggest that the SPH–FEM model is a viable and effective numerical tool for FSI problems. [Copyright &y& Elsevier]

Abstract: This study reports on energy efficiency optimization regarding bottom trawls. Efficient fishing gear uses up only a small amount of energy per fish caught. Drag and mouth area during trawling operations affect energy efficiency. Drag causes the energy consumption and the trawl mouth area impacts the quantity of fish caught, hence an energy efficient gear has a low ratio drag on the mouth area. A novel numerical optimization technique using spatial fish distribution is presented in this work. The tool is based on a FEM mechanical model for trawls which consist mostly of netting panels sewn together. This tool is adapted to minimize an objective function namely the drag-to-mouth area ratio. This technique consists in modifying the design of all the panels of the trawl. In this paper the modifications are constant and quantified in terms of mesh number. Moreover the trawl mouth area takes into account the presence of fish within a given depth with respect to sea bottom and the value of the depth is adapted to the fish species of interest. Trawl design optimization with two uniform fish distributions at a given depth (6m and 3m above the sea bed) and one linear distribution at 6m above the sea bed are compared. The application of this tool when designing a bottom trawl for research vessels leads to an energy economy ranging from 16% to 52% under certain assumptions. [Copyright &y& Elsevier]

Abstract: The penetration behavior and trajectory of drag anchors in seabed soils is not only a complicated engineering problem, but also an interesting topic with lots of scientific meanings. Nearly all the previous methods that are capable of predicting the trajectory of drag anchors need a numerical incremental computation. Based on a kinematic model and mathematical derivations, a theoretical framework for predicting the trajectory of drag anchors is established. The concepts put forward and described in detail in the paper are not only necessary for the theoretical framework but also meaningful to further understanding of the engineering problem due to clear physical background. A comparative study has proved the effectiveness and veracity of the kinematic model and theoretical framework for predicting the trajectory. The proposed model and developed drag equations, which combine the anchor, the drag line and the anchor handling vessel being an interactional system, may provide a new angle of view to understand the anchor behaviors in soils, and be valuable for deterministic and theoretical analysis of drag anchors. [Copyright &y& Elsevier]

Abstract: This paper considers arrays of wave energy devices consisting of oscillating rigid bodies undergoing optimum displacements in regular waves. A previously published identity concerning the directional behaviour of the interaction factor, q (which characterises an important effect of the array configuration in the context of point absorber theory), is shown to be valid under more general conditions. In fact, this identity is shown to be a consequence of a more fundamental result. Boundary element hydrodynamic calculations carried out on simple three-member arrays are shown to be consistent with these theoretical proofs. Some aspects of the behaviour of the arrays are also investigated. [Copyright &y& Elsevier]

Abstract: Structural systems will normally fail as a consequence of a chain of different components failure es. In this paper, fatigue reliability of fixed offshore platforms is investigated by analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, it is divided into a finite number of sub-scenarios. All combinations of time sequences are generated for a given sequence of failures, using a specially developed program. In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. A large number of sub-scenarios should be analyzed, therefore implementing time consuming traditional methods for evaluating fatigue reliability may be unrealistic, and a simplified and accurate method is required. Herein, an “Artificial transfer function” is used to calculate the cumulative fatigue degradation in components. The preciseness of the proposed method is evaluated using a numerical model, and then, it is used to calculate the occurrence probability of each sub-scenario. Based on the calculated values, probability of occurrence is obtained for each scenario, and finally, the failure probability of entire system is calculated. The proposed method can be used in inspection planning and evaluating the life extension of existing offshore platforms. [Copyright &y& Elsevier]

Abstract: In this paper, a vertically integrated shallow water model is developed. The model includes air bubbles to investigate air bubble effect (sensitivity) on water level due to a tropical storm along the coastal region of Bangladesh. The shallow water equations are solved using doubly nested conditionally stable finite difference schemes for incorporating coastal bending and offshore islands with considerable accuracy in the numerical schemes. A fine mesh scheme has been nested into a coarse mesh scheme in the region of our study. In the fine mesh scheme, all the major islands are incorporated through proper stair step representation. For the existence of so many small and big islands between Barisal and Chittagong and also for high bending of the coastline along the Meghna estuary, a very fine mesh scheme is again nested into the fine mesh scheme. The developed model was then applied to simulate water levels due to surges associated with the cyclones April 1991 and AILA along the coast of Bangladesh. The increases in water levels due to air bubbles were found to be around 2–12% with respect to the reference void fraction 10–70%. [Copyright &y& Elsevier]

Abstract: The paper presents the results of the application of a new hybrid URANS–LES method for the investigations of the ship wake behind the tanker KVLCC2. The switching between URANS and LES models is based on the ratio between the turbulence scale and the cell size of the mesh. Ship resistance, fields of the axial velocity and turbulent kinetic energy in the propeller plane are calculated and compared with measurements. Much attention is paid to the analysis of the unsteady velocities, their PDF distributions and spectra. Numerical analysis shows that the instantaneous velocities deviate substantially from their mean values which are usually used as the estimated velocities in modern engineering methodologies. The thrust variation in the unsteady wake is more than twice as large as that in the time averaged (frozen) wake. The results of the present study point out that the unsteadiness in the wake behind full ships can be very large and should be taken into account when propulsion and unsteady loadings are determined. [Copyright &y& Elsevier]

Abstract: Geo-hazard assessment of the potential damage to a pipeline caused by a submarine landslide requires a quantitative model to evaluate the impact forces on the pipeline. In contrast with typical geotechnical problems, the strain rate within the fast moving, flow-like submarine landslide is typically far higher, which will lead to enhancement of the soil strength and therefore result in larger impact forces. Generally, there are two possible predictive frameworks for strain-rate dependence: a fluid dynamics framework and a geotechnical framework. By comparison of common rheological models adopted in these two different approaches, a unified additive power-law model, a normalised form of the Herschel–Bulkley model from fluid mechanics, is explored in this paper. This model has been used in conjunction with a large deformation finite element approach to investigate the undrained limiting loads on a cylinder moving steadily through inertia-less soft rate-dependent material, in order to quantify the strain-rate effects. The flow mechanism and the effects of the shear-thinning index and Oldroyd number on the shear zones are explored. The calculated resistance factors are compared with the drag coefficients obtained from computational fluid dynamics analysis. The average rate of strain experienced by the soil flowing past the cylinder is estimated for a given flow velocity and an expression in the form of a conventional bearing capacity equation, but with shear strength linked directly to the normalised flow velocity, is proposed to predict the magnitude of the viscous force exerted by the debris flow. [Copyright &y& Elsevier]

Abstract: Phase control may substantially increase the power absorption in point-absorber wave energy converters. This study deals with validation of dynamic models and latching control algorithms for an oscillating water column (OWC) inside a fixed vertical tube of small circular cross-section by small-scale testing. The paper describes experimental and numerical results for the system''s dynamics, using simple and practical latching control techniques that do not require the prediction of waves or wave forces, and which will be relevant to any type of point-absorbing devices. In the experimental set-up, the upper end of the tube was equipped with an outlet duct and a shut-off valve, which could be controlled to give a latching of the inner free surface movement. The pressure drop through the open valve is used as a simplified measure of the energy extraction. The control was realized by using the real-time measurement signals for the inner and outer surface displacement. A mathematical model of the system was established and applied in numerical simulation. In the case the OWC''s diameter is much smaller than the wavelength and the wave amplitude much smaller than the draft, the free surface movement inside the tube can be described as an oscillating weightless piston. For this hydrodynamic problem an analytical solution is known. In addition, the mathematical model includes the effects of viscous flow losses, the air compressibility inside the chamber and the pressure drop across the valve. Experimental results were used to calibrate some of the model parameters, and the total model was formulated as a coupled system of six non-linear, first-order differential equations. Time-domain integration was used to simulate the system in order to test the control strategies and compare with experimental results. [Copyright &y& Elsevier]

Abstract: In this paper, a numerical model based on the potential flow theory is established to simulate the interaction of a gas bubble with a nearby wall. The time-integration boundary integral method is used to solve the dynamics of a gas bubble. With this method the numerical calculations show an excellent agreement with the experimental data. Employing the numerical code based on the presented algorithm, the dynamics of a gas bubble close to a rigid wall is investigated systematically, especially the relationship between various characteristic parameters and the Bjerknes effect due to the presence of a nearby wall. It is found that Blake''s criterion, which is usually used to predict the direction of the bubble jet, has a great degree of accuracy for the bubble relatively far away from the wall and bubble near a wall, there is a significant error, attributed to its simplifications and assumptions. Further studies show that an oblique jet will be formed when a bubble close to an inclined wall collapses, direction and width of which have a close relationship with the characteristic parameters used to characterize the bubble. For the bubble near a horizontal wall, a liquid jet pointing directly to the wall is developed generally when the Bjerknes attraction and buoyancy are in the same direction; and at the same time, if the Bjerknes attraction is in the opposite direction of buoyancy, the direction of the jet will depend on a criterion. Then the interaction of gas bubble between complicated walls of some a submarine is also studied, which shows the most dangerous induced loading condition of structure in water, and the evidently effects of bubble jet on loading. The special phenomena mentioned above have a great significance for the further study on the interaction of the bubble with its boundaries. [Copyright &y& Elsevier]