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A theoretical approach was applied to study the vibration of simple-supported submerged horizontal plate. The derived analytical solution was used to determine natural frequencies for a horizontal plate vibrating in fluid. The investigations were conducted for a very wide range of material density and elasticity modulus covering all materials used in engineering practice. Analysis shows that plate vibration frequency decreases with increasing plate width and draft, and decreases with decreasing plate thickness. Moreover, the results show that a substantial effect on vibration of submerged plate has mass of water above plate. The results also show that plate vibration frequency decreases with increasing plate material density and decreases with decreasing elasticity modulus. The dominant factors affecting the vibration of the submerged plate are the plate width, the plate thickness, and elasticity modulus. For moderate and low values of elasticity modulus, vibration frequency is becoming lower than frequency of water waves. This is very important because wave frequencies overlap with the natural plate vibration frequencies, which may lead to resonance and failure of a structure. The problem is that the overlap of plate vibration frequencies and wave frequencies occurs for very wide range of wave and plate parameters. Laboratory experiments confirm theoretical results. [ABSTRACT FROM AUTHOR]

The horizontal elements of maritime structures are susceptible to both wave impact and resulting vibrations. These vibrations can lead to a partial or complete failure of structures and require detailed investigations. To address this issue, laboratory experiments were conducted in a wave flume. The aim of this study was to investigate the problem of standing wave impact underneath a horizontal deck. The main focus was on the effect of the wave-induced vertical forces on the global response of the structure. The physical model of the deck was installed above a still water level in front of a vertical barrier. The model was supported by a system of strings and springs. The mechanical system had one degree of freedom corresponding to a small rotational displacement around rear deck edge. Among other physical parameters, the impact pressure generated under the structure due to wave impact was measured. The high sampling frequency of the data acquisition system allowed to capture momentary slamming pressure. The systems of accelerometers and displacement gauges were installed to measure induced vibrations. Thorough analysis of the influence of wave parameters and the deck clearance on the structure response was performed based on the measurements. The rapid slamming force increase, recorded at the moment of impact is not revealed in the dynamic response of the plate. [ABSTRACT FROM AUTHOR]

The paper presents the results of the research focused on linear and nonlinear wave generation and propagation in a deepwater towing tank equipped with a single flap-type wavemaker of variable draft. The problem of wave generation and propagation has been theoretically formulated and solved by applying an analytical method; linear and nonlinear solutions were obtained. The linear solution has been verified experimentally. The laboratory experiments confirmed that a linear model can be applied to predict the generation and propagation of water waves of low steepness. However, according to the analysis, the discrepancies between wave profiles predicted by applying the linear and nonlinear models rapidly increases with increasing wave steepness. Additionally, the secondary phenomena which occur in the towing tank, including: disintegration of wave profile, wave reflections from the beach and wave damping, were analyzed. Knowledge on the nonlinear processes and phenomena is essential for modeling the environmental conditions during tests carried out to secure the safety of the naval and offshore constructions. The theoretical formulation was derived and the solution was obtained by the Institute of Hydroengineering of the Polish Academy of Sciences IBW PAN while the experimental research was carried out in Ship Hydromechanics Division of the Ship Design and Research Centre CTO S.A. [ABSTRACT FROM AUTHOR]

Abstract An efficient semi-analytical solution to the problem of nonlinear water waves propagating at a constant depth is derived using parallel computing techniques. The approach is based on the assumptions of an irrotational flow of an inviscid and incompressible fluid. Velocity potential and free-surface displacement functions are represented in a form based on Fourier series satisfying a formulated initial boundary-value problem by a proper selection of time-dependent coefficients. The eigenfunction expansions are resolved by means of a Fast Fourier Transform technique and a higher-order time-stepping procedure to provide an efficient spectral collocation method of computation of wave-induced free-surface flows. The application of the Fourier transform qualifies the semi-analytical algorithm for efficient parallelization. Hence, the numerical model performance is improved using the computing capabilities of a GPU. The derived semi-analytical approach is easy to implement and may be straightforwardly extended to cover the generation of waves in a flume or a basin. The ability of the model to reproduce nonlinear phenomena is demonstrated in simulations of two- and three-dimensional instabilities of a modulated Stokes wave. The model can be used to solve standard as well as complex wave problems in large computational domains considerably faster than its CPU-based counterpart. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to study the kinematics of water particles and mass transport of wave-induced flow generated in a closed flume. A semi-analytical pseudo-spectral solution to the problem of mechanically generated nonlinear water waves propagating at a constant depth is derived under the potential flow assumptions. Velocity potential and free-surface displacement functions are represented in a form based on Fourier series. The eigenfunction expansions are resolved by means of a Fast Fourier Transform technique and a higher order time-stepping procedure. The derived nonlinear solution of the wavemaker problem is based on Taylor series representation of the free-surface and wavemaker boundary conditions expanded up to an arbitrary truncation order. This technique is employed to study the evolution of a velocity field and particle trajectories under regular gravity waves generated in a wave flume. The instantaneous velocity fields are integrated in time to calculate the particle trajectories and time-averaged spatial distribution of Lagrangian and Eulerian mean velocities. The theoretical results are compared with the available experimental data. A good agreement is observed, which confirms the applicability of the presented theory to the problems of transport processes associated with the propagation of water waves and their generation in the flume. [ABSTRACT FROM AUTHOR]

The problem of a solitary wave attack on a vertical seawall is investigated by applying two approaches. The first is a semi-analytical method in which the Euler equations of motion are solved under the assumption of a potential flow by employing an approach based on the fast Fourier transform technique and a numerical time-stepping scheme. The second approach employed to analyse the problem considered is the smoothed particle hydrodynamics (SPH) method, in which the equations are solved in the Lagrangian coordinates. The two methods are used to simulate solitary wave propagation in water of uniform depth, followed by a wave impact on a vertical wall. The simulations focus on the determination of the maximum run-up of the wave on the wall, the calculation of pressures exerted by water on the structure, and the evaluation of water velocities in the vicinity of the structure. The predictions of the two approaches are compared to identify wave regimes for which both methods give satisfactory results. The results of numerical simulations have shown that both proposed methods predict practically the same free-surface profiles for waves of small and moderate amplitudes. For higher waves, some discrepancies between the results of the two methods occur. The two models results have been also compared with empirical data known from the literature, showing good agreement with experimental measurements in terms of the maximum wave run-up and the wave crest residence time at a wall. [ABSTRACT FROM AUTHOR]

Theoretical investigations supported by a series of original laboratory experiments are conducted to study a wave-induced vertical mixing process. The derived semi-analytical solution is very efficient and is applied to predict the effects of water waves on the temperature changes and the evolution of temperature profiles. The results indicate that waves increase a mixing process. The rate of change of the temperature is higher when waves contributed to mixing process and this process increases with increasing the wavelength to water depth ratio. The analysis indicates that for typical ocean waves the contribution of water waves to mixing may be several orders of magnitude higher than a corresponding contribution arising from the classical diffusion process. This implies a need to conduct more theoretical studies and experimental investigation on the effect of water waves on mixing processes. A series of original laboratory experiments were conducted in the insulated wave flume to verify the derived model. The comparisons show a reasonable agreement between predicted and measured temperature profiles. A reasonable agreement between theoretical results and experimental data is observed for the whole considered range of initial temperature distributions. The comparisons indicate that the model is applicable even to cases when gradients in temperature distributions over water depth are fairly high. [ABSTRACT FROM AUTHOR]

A theoretical approach is applied to investigate wave-induced mixing. The problem is formulated to describe evolution of temperature in a layer of fluid and is solved by applying eigenfunction expansions. The derived semi-analytical solution is applied to predict temperature changes and evolution of temperature profiles due to mechanically generated waves in a closed flume. The results show that water waves modify the temperature distribution in space and time. The analysis shows that the changes occur in the whole layer of fluid. The results indicate that time is a more important factor in a process of wave-induced mixing than expected. Mixing processes depend on a wave height. The rate of change of temperature distribution is more pronounced for higher waves. Another important parameter in mixing processes is the wavelength. The mixing effects are more distinct for deep water waves. The sensitivity analysis implies a need to conduct more theoretical studies and experimental investigations on wave-induced mixing. the model is verified in the course of the original laboratory experiments that were conducted in the insulated flume. A reasonable agreement between predicted and measured temperature profiles proves the applicability of the present approach even for relatively high gradients of temperature distribution over water depth. • An original theoretical approach to the problem of wave-induced mixing is derived. • The analytical model is applied to predict the effect of wave-induced mixing. • Novel laboratory experiments are conducted to verify theoretical results. • The experimental data confirm theoretical results even for high waves. • The effect of wave-induced mixing is more pronounced for deep water waves. [ABSTRACT FROM AUTHOR]

Based on the potential flow theory, a second-order Higher-Order Boundary Element Method model is developed to simulate hydrodynamic loads and pressure on a stationary cylindrical-type oscillating water column (OWC) wave energy converter. Quadratic pneumatic damping and additional viscous damping are introduced to simulate the effects of the power take-off and the viscous dissipation inside the chamber, respectively. The proposed model is verified against a carefully instrumented scaled experiment. The effects of the chamber geometry and the wave environment on the hydrodynamic loads of the OWC device are then explored using the validated model. The resonance excited by the second-order wave component is observed with the fundamental frequency being half of the natural frequency. This resembles a sloshing mode and leads to a significant increase in hydrodynamic pressure and surge force as well as pitch moment. The effects of the second-order waves cannot be ignored under the action of the low-frequency long waves. In addition, the surge force and the pitch moment are not sensitive to the variation in the orifice opening ratios, while the heave force increases with the opening ratio at a resonant heave frequency. • Nonlinear wave dynamic on a stationary cylindrical-type OWC device was investigated. • A second-order time-domain HOBEM model for OWC dynamics was developed. • A second-order sloshing resonance is observed inside the OWC chamber. • The effects of the opening ratio on the OWC device are discussed. [ABSTRACT FROM AUTHOR]