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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]

A semi-analytical solution to an advection–diffusion equation is coupled with a nonlinear wavemaker model to investigate the effect of strong nonlinearity on wave-induced mixing. The comparisons with weakly nonlinear model predictions reveal that in the case of waves of higher steepness, enhanced mixing affects the subsurface layer of the water column. A fully nonlinear model captures the neglected higher-order terms from a weakly nonlinear solution and provides a reliable estimation of the time-mean velocity field. The corrected wave-induced mass-transport velocity leads to improved estimates of subsurface mixing intensity and ocean surface temperature. [ABSTRACT FROM AUTHOR]

The problem of the interaction of waves with a serpent-type wave energy converter was investigated, and a novel 3D analytical solution was derived. The optimal parameters of the energy converter were derived for the first time from wave energy principles. The results show that the wave power captured by the device increases with increasing wave lengths until a maximum and then decreases. The efficiency increases with decreasing stiffness of the device in shallow and intermediate waters. In deep water, the efficiency increases with increasing stiffness until a local maximum and then decreases. Moreover, the efficiency increases with the increasing mass of the device in shallow and intermediate waters. In deep water, the efficiency of a converter decreases with the increasing mass of the device. An original approach to determine the optimal parameters of a device for given wave conditions was derived. The derived analytical formula shows that the top efficiency level of power capturing cannot exceed 50%. This is the theoretical maximum for this type of converter. The power take-off optimization analysis also identifies the spectrum of wave conditions for which the efficiency of the generator is close to the maximum. A series of laboratory experiments were conducted in a hydraulic laboratory to verify the model. The comparisons of the recorded data with the analytical solution show a very good agreement. [ABSTRACT FROM AUTHOR]

Significant wave height is the most important parameter in feasibility studies and the design of wave energy converters. In this study, the novel nested artificial neural networks were developed and applied to predict significant wave height at twenty selected locations of the North Sea. A nested artificial neural network applies nonlinear machine learning models as transfer functions in the neurons of networks. Two input parameters comprising wind speed and wind direction were implemented to train the derived models. The results show that the derived nonlinear machine learning models are about 18.39% more accurate than the linear regression technique. The statistical indices confirm that the nested artificial neural network may increases the accuracy of traditional models by up to 34%. Among all applied models, the nested artificial neural network developed based on the integration of particle swarm optimization algorithm and adaptive neuro-fuzzy inference system, with RMSE = 0.525m and R 2 = 0.84, provides the most accurate prediction of wave heights. The high accuracy of the results indicates that if computational time is not a very critical factor for users, then the application of nested artificial neural networks may be recommended for the modeling of wave parameters and other complex problems. [ABSTRACT FROM AUTHOR]

Significant wave height (H s) is a critical parameter in the design, operation, and maintenance of nearshore and offshore wind and wave farms. In this study, the original pyramid neural network (PNN) was introduced and applied to predict H s for North Sea renewable energy farms. The performance of PNN was compared with state-of-the-art algorithms. The results show that the machine learning (ML) models trained by the network datasets can accurately predict Hs at any point of nearshore or offshore energy farms, significantly reducing wave monitoring costs. The PNN models predict H s with high accuracy. The results predicted by PNN, with SRMSE of 0.256 and R 2 of 0.873, are more accurate than the corresponding results obtained by the deep neural network (DNN) model, which show that PNNs with their far simpler structures and lower number of parameters are attractive alternatives for complex and time-consuming DNN models. The ensemble of regular models, with SRMSE of 0.247, is ranked as the most accurate method. The results also show that the applied state-of-the-art algorithms including MLR, SNN, DNN, ANFIS, and SVR models predict non-physical negative values of H s. The PNNs developed in this study predict H s with positive values. Moreover, the analysis shows that the scatter of the results obtained by the derived nonlinear models is less pronounced than the scatter of corresponding results obtained by other methods. The results also show that to evaluate the performance of nonlinear ML methods for large datasets, the analysis of standard statistical indices is not sufficient. For large datasets standard statistical indices provide inadequate or insufficient information and additional calculations, and statistical analysis are required. • The pyramid neural network (PNN) was introduced. • The performance of PNN was analyzed in predicting significant wave height (H s) for North Sea renewable energy farms. • The PNN with fewer unknown parameters has the potential to deliver results even superior to those of a deep neural network. • Even the trained models can predict the H s of neighboring farms. [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 boiling point rise (BPR) is a critical parameter in the operation and optimal design of a multi-stage flash desalination system. Accurate prediction of BPR would increase the efficiency of freshwater production. In this study, original aggregated random intelligent approach (ARIA) models is developed to enhance the prediction of BPR. The ARIA algorithms, similar to a random forest (RF) technique, combine a set of models trained on different subsets of data in an ensemble structure. Five ARIA-type models were developed based on shallow neural network (SNN), deep neural network (DNN), support vector regression (SVR), classification and regression decision tree (CART), and adaptive neuro-fuzzy inference system (ANFIS). Synthesis index (SI) and visual graphs were used to rank models. Results show that the developed ARIA models are far more accurate than their regular counterparts. The ARIAs increase the prediction efficiency of regular modes by up to 25.04 %. The ARIA-ANFIS with the lowest root mean square error (RMSE) of 0.027 °C outperformed other models and regression equations. The developed ARIA-ANFIS decreases the error of corresponding RF prediction by 69.66 % (RMSE = 0.089 °C), which is a significant achievement because RF is a widely recognized model and numerous studies underline the high accuracies of RF applications. • Novel aggregated random intelligent approach (ARIA) is developed. • Several ARIA models were used to enhance the prediction of boiling point rise (BPR) of multi-stage flash desalination system. • The accuracy of ARIAs was compared with their regular counterparts. • The application of ARIAs for the modeling of other complex scientific and engineering problems is recommended. [ABSTRACT FROM AUTHOR]

In this study novel clustered machine learning (CML) models were developed by applying different base learners including multi linear regression (MLR), adaptive neuro-fuzzy inference system (ANFIS), classification and regression trees (CART), least-squares boosting (LSBoost), and random forest (RF) to predict scour profile induced by the jet of a propeller. Moreover, the results of CML models were compared with regular ML algorithms. The results show that the tree-based ensemble models, RF and LSBoost, are more accurate than CART. The ANIFS has the worst performance compared with other regular nonlinear methods, RMSE = 17.414 mm. The performance of MLR is also weak, RMSE = 35.63 mm and R2 = 0.088. However, the implementation of CML drastically increases the performance of MLR, RMSE = 15.053 mm, and R2 = 0.871. The CANFIS with RMSE = 8.757 mm, R2 = 0.976, and SI = 0 is ranked as the most accurate model. The results show that CLM enhances the performance of regular ML by up to 59.90%. The application of clustered ML is recommended for other complex problems. Finally, the results show that the derived models trained by other datasets very well predict measured scour profiles which datasets were not used in the training process. • Novel clustered machine learning (CML) models are developed. • Several CML models were used to predict scour profile induced by the jet of a propeller. • The performance of CML were compared with regular models. • The results show that CLM drastically enhances the performance of regular ML. [ABSTRACT FROM AUTHOR]

A numerical model is derived to investigate the effect of breaking wave shape on impact load on a monopile structure. The derived model combines potential flow model with a Navier-Stokes/VOF solution. The analysis indicates that the breaking wave impact on a monopile structure results in an extremely rapid increase of pressure to high amplitudes. The peak impact pressure occurs in the region below the overturning wave jet. The breaking wave impact leads to extremely high slamming forces. It is observed that the slamming coefficient corresponding to the peak impact force approaches 2π. The area directly affected by the impact force is much higher than the impact area considered in engineering practice. Moreover, the analysis shows that the vertical load distribution is far more realistic than a rectangular shape distribution commonly applied in engineering practice. The results also show that the parameters of the rectangular shape distribution applied in engineering practice are complex function of the breaking wave shape and cannot be uniquely defined beforehand. This is because the vertical load distribution strongly depends on breaking wave shape and it is difficult to uniquely approximate such a complex load distribution by a rectangle. The derived results are compared with experimental data from laboratory experiments on irregular breaking wave loads on a monopile structure. Numerical results are in reasonable agreement with experimental data. [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]

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]

Laboratory experiments were conducted to investigate the interaction of gravity waves with a semi-submerged rectangular cylinder of elastic bottom. Laboratory investigations were conducted for a wide range of wave parameters and a structure of different drafts. The analysis of results focuses on wave transmission at the structure, wave-induced pressures excreted on the plate, plate deflections, etc. The results shows that the nonlinear pressure and plate deflection components arising from the interaction of incoming waves with the structure are often significant. The results show that the nonlinear components often exceed their linear counterparts even for waves of low steepness. This is an original and surprising outcome of significant practical importance as the large nonlinear pressure and plate deflection components may spark a resonance. The problem is serious because plate natural vibration frequencies are often lower than the frequency of fundamental waves or their nonlinear components and the vibration of a plate may be amplified by incoming waves or their nonlinear products. The occurrence of a resonance amplified by incoming waves may lead to the failure of a structure. This outcome is of significant practical importance because it may occur for a wide range of wave parameters. • Waves have substantial effects on the vibration of the elastic elements of submerged structures. • Wave-induced pressure and plate deflection co mponents are often significant. • Nonlinear components often exceed their linear counterparts even for waves of low steepness. • Large nonlinear pressure and plate deflection components spark resonance. [ABSTRACT FROM AUTHOR]

The problem of impact pressure distribution on a monopole structure excited by irregular breaking waves is investigated. The analysis is performed by applying a numerical model that combines potential flow model with a Navier-Stokes/VOF solution. The temporal pressure distribution is analysed for two breaking wave cases characterized by the significant difference in the steepness of the wave front. The peak impact pressures are observed in the region below the overturning wave jet where the pressure increases rapidly resulting in a peak value of the slamming coefficient equal to Cs=2π. The vertical load distribution provided by the derived model is more realistic than a rectangular shape distribution applied in engineering practice. This is because the vertical load distribution strongly depends on breaking wave shape and it is difficult to uniquely approximate such a load distribution by a rectangle. [ABSTRACT FROM AUTHOR]

An original method is proposed to extract drift velocity induced by waves propagating in a wave flume. The particle image velocimetry technique is employed to measure velocity fields under regular gravity waves propagating at a constant depth. Based on the measurements, the Eulerian mean current velocity is determined. The instantaneous velocity fields are integrated to calculate particle trajectories and the Lagrangian time-averaged vertical distribution of mass-transport velocity. The Stokes drift velocity is determined by subtracting the Eulerian mean current from the Lagrangian mass-transport velocity. The results are in good agreement with theoretical second-order irrotational solution and confirm applicability of the weakly nonlinear solution for calculating transport processes associated with propagating ocean waves. [ABSTRACT FROM AUTHOR]

Freak waves are unique phenomena that appear unexpectedly on the ocean surface. These waves are not only a danger to fishermen and yachtsmen, but are also capable of damaging large vessels and offshore and coastal structures. The available field measurements that provide insight into the origin and physics of freak waves are very limited. The main objective of the present study was to analyze a unique set of wave data comprising 19,025 wind-wave records from the southern Baltic Sea to provide information on the occurrence, parameters, and prevailing conditions of the formation of freak waves. The complex nature of freak waves was investigated by obtaining spectral and statistical parameters of freak-wave-prone sea states using a wide set of tools. The study revealed a large number of freak-type waves, including waves over 12 m high. The study indicates that these hazardous waves may even exceed 20 m during severe storms in the Baltic Sea. Multi-point wind-wave measurements are needed to provide more information about the physics of freak waves and to eventually develop a prediction or warning system to avoid casualties. [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 describe the diffraction of water waves by a structure in a channel of arbitrary configuration. The solution was achieved by applying the three-dimensional (3D) boundary element method and is valid for a structure of arbitrary shape. The derived model was applied to analyze the effect of the structure geometry and the configuration of the channel on diffracted wave field and on generalized wave-load components. The results show that the wave field in the channel and wave loads on a structure strongly depend on wavelength and the geometry of the structure. The far-field wave amplitudes and wave load components oscillate with increasing wave number, and for selected wave frequencies, the incoming waves are fully transmitted and forces on the structure simultaneously vanish. This result is of practical importance. The oscillations depend primarily on the length of the structure and are associated with the formation of partially standing waves in the subdomain along the structure, which affect wave reflection in the main channel and wave loads on the structure. The effect of the draft and width of the structure on the oscillations is very limited. However, the draft and width of a structure has a substantial effect on the magnitude of wave reflection and transmission, especially for narrow channels. Moreover, the draft and width of a structure has a substantial effect on wave-load components. The analysis of the results indicates that it is difficult to simplify a theoretical description because, even for a channel of a constant depth and ideal vertical walls, once a structure is present in the channel, the problem needs to be described by 3D formulation, which complicates the solution. Theoretical results are in reasonable agreement with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: The problem of wave propagation and wave damping in a channel with side porous mattresses of arbitrary shape protruding from the walls is studied. The solution was achieved by applying 3-D boundary element method and was employed to study wave field in the channel and to analyze the effect of the geometry of the mattresses and physical and hydraulic properties of porous material on wave damping. The results show that wave damping in the channel strongly depends on wave parameters, especially, on the wave number. Wave reflection and transmission decrease with increasing the wave number. The results also show that the wave field in the channel strongly depends on the geometry of the mattresses as well as on physical and hydraulic properties of porous material used to build these wave dampers. The geometry of the mattresses and physical and hydraulic properties of porous material have a moderate effect on wave reflection and a significant effect on wave transmission. The results show that wave transmission down the channel decreases with increasing the length and thickness of the mattresses. Moreover, wave transmission decreases with increasing the porosity and damping properties of porous media used to build the mattresses. The analysis shows that porous mattresses protruding from the channel walls are very efficient in damping water waves propagating down the channel and may be built in channels to reduce high waves and achieve desired wave conditions. Theoretical results are in reasonable agreement with experimental data. [Copyright &y& Elsevier]

Abstract: A semi-analytical nonlinear wavemaker model is derived to predict the generation and propagation of transient nonlinear waves in a wave flume. The solution is very efficient and is achieved by applying eigenfunction expansions and FFT. The model is applied to study the effect of the wavemaker and its motion on the generation and propagation of nonlinear waves. The results indicate that the linear wavemaker theory may be applied to predict only the generation of waves of low steepness for which the nonlinear terms in the kinematic wavemaker boundary condition and free-surface boundary conditions are of secondary importance. For waves of moderate steepness and steep waves these nonlinear terms have substantial effects on wave profile and wave spectrum just after the wavemaker. A wave spectrum corresponding to a sinusoidally moving wavemaker possesses a multi-peak form with substantial nonlinear components, which disturbs or may even exclude physical modeling in wave flumes. The analysis shows that the widely recognized weakly nonlinear wavemaker theory may only be applied to describe the generation and propagation of waves of low steepness. This is subject to further restrictions in shallow and deep waters because the kinematic wavemaker boundary condition as well as the nonlinear interaction of wave components and the evolution of wave energy spectrum is not properly described by weakly nonlinear wavemaker theory. Laboratory experiments were conducted in a wave flume to verify the nonlinear wavemaker model. The comparisons show a reasonable agreement between predicted and measured free-surface elevation and the corresponding amplitudes of Fourier series. A reasonable agreement between theoretical results and experimental data is observed even for fairly steep waves. [Copyright &y& Elsevier]

A three-dimensional numerical solution was developed to determine the wave field in a narrow channel with side porous caves. The solution was achieved by applying the boundary element method. The model was applied to determine the effect of the geometry of caves and the physical and hydraulic properties of the porous material in the caves on the wave field in the channel. The results show that the cave geometry and the physical and hydraulic properties of porous material in the cave have a significant effect on the wave field in a channel. Wave transmission down the channel usually decreases with increasing cave length and cave width and decreases with increasing porosity. Moreover, wave transmission usually decreases with increasing wave-damping properties for porous material of low damping properties and increases with increasing wave-damping properties for porous material of high damping properties. A reduction of wave transmission down the channel, often substantial, can usually be achieved by increasing the porosity and increasing the wave-damping properties of the porous material. The results and additional analysis show that a reasonable wave transmission level can be achieved even for fairly short porous caves and that the model can be applied to select an optimal cave system for any prespecified conditions. Theoretical results are found to be in reasonable agreement with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical approach is applied to predict the propagation and transformation of nonlinear water waves. A semi-analytical solution was derived by applying an eigenfunction expansion method. The solution is applied to analyze the effect of wave frequencies and wave steepness on the propagation of nonlinear waves. The main attention is paid to the wave profile, the wave energy spectrum, and the changes of wave profile and energy spectrum due to the interaction of wave components in a wave train. The results show that for waves of low steepness the nonlinear wave effects and effects associated with the interaction of water waves in a wave train are of secondary importance. For waves of moderate steepness and steep waves the effects associated with the interactions between waves in a wave train are becoming significant and a train of initially sinusoidal waves may drastically change its form within a short distance from its original position. The evolution of wave components has substantial effects on the wave spectrum. A train of initially very narrow-banded waves changes its one-peak spectrum to a multi-peak one in a fairly short period of time. Laboratory experiments were conducted in a wave flume to verify theoretical approaches. The free-surface elevation recorded by a system of wave gauges was compared with the results provided by the semi-analytical solution. Theoretical results are in a fairly good agreement with experimental data. A reasonable agreement between theoretical results and experimental data is observed often even for relatively steep waves. [Copyright &y& Elsevier]

A 3D numerical solution was derived to determine the wave field in a physical wave tank equipped with a porous wave absorber of variable width and draft. The solution was achieved by applying the boundary element method. The model was applied to analyze the effect of the geometry and material of wave absorbers on wave reflection to eventually equip a wave tank with a proper wave absorber. The results show that absorber geometry has a complex, often surprising and nonintuitive effect on wave reflection. A more pronounced effect on wave reflection possesses physical and hydraulic properties of the material used to build a wave absorber. A reduction of wave reflection can usually be achieved by increasing absorber length and simultaneously decreasing its slope, and often a reduction of wave reflection can be achieved by increasing absorber draft or width. Moreover, a reduction of wave reflection, often substantial, can be achieved by increasing porosity and the damping coefficient. The results and additional analysis show that a reasonable wave reflection level can already be achieved for fairly short absorbers, and the model can be applied to select an optimal wave absorber for any prespecified conditions. Theoretical results are in reasonable agreement with experimental data. [ABSTRACT FROM AUTHOR]

The analytical solution to the problem of the diffraction of second-order surface waves by a horizontal rectangular cylinder founded on a low rubble base was derived. The solution is based on the assumption that the pressure underneath the cylinder is linearly dependent on the horizontal space coordinate. The approach is basically valid for a small rubble base height to cylinder beam ratio and is recommended especially for cylinders founded on low and very low rubble bases for which other methods are difficult to apply. The solution was applied to investigate wave loads on a cylinder founded on a low rubble base. The results show that low rubble bases have significant effect on a nonlinear wave load on a cylinder. In general, the load increases with increasing cylinder width and increases with decreasing rubble base height. This implies that even thin rubble bases have to be included in the analysis of wave loads on a founded cylinder. Moreover, the results show that the nonlinear component of wave load is a dominant contribution to the wave load for a wide range of wave frequency. Laboratory experiments were conducted to verify theoretical results. The second-order component of vertical force and the vertical force correct up to second-order were compared with corresponding experimental data. The comparison show a fairly good agreement for both amplitudes and phases. [Copyright &y& Elsevier]

Provides information on a study that presents a solution to the diffraction problem for second-order surface waves by a horizontal rectangular cylinder founded on a rubble base. Statement of problem; Results; Summary.

Solves the problem of the interaction of linear waves with composite breakwater and determines wave reflection, transmission and wave loads on a caisson founded on a multilayered rubble base. Satisfactory description of damping by the Darcy damping law; Agreement between theoretical results and experimental data.

The effect of permeability on the stability of homogeneous and multilayered rubble bases is investigated. The approach consists of theoretical modeling of the interaction of water waves with a caisson-type breakwater and its rubble foundation, and then employing predicted flow fields in a stability model to determine the required stone size. The permeability is shown to have significant effect on the stability. The results indicate that the stability increases with increasing the rubble-base permeability at intermediate water depths, and increases with decreasing the rubble-base permeability in shallow water. The armor-layer permeability has little effect on the stability at intermediate water depths, but in shallow water the permeability of the armor layer has little effect on the stability only for rubble bases of low core permeability. The significant effect of permeability on the stability implies a need for including permeability effects in hydraulic modeling. An analysis or scaling of experimental data without taking the effect of permeability into account may lead to confusing conclusions or just incorrect results, which is demonstrated on the basis of the laboratory results commonly applied in design. [ABSTRACT FROM AUTHOR]

Wave-induced inundation in coastal zones is a serious problem for residents. Accurate prediction of wave run-up height is a complex phenomenon in coastal engineering. In this study, several machine learning (ML) models are developed to simulate wave run-up height. The developed methods are based on optimization techniques employing the group method of data handling (GMDH). The invasive weed optimization (IWO), firefly algorithm (FA), teaching–learning-based optimization (TLBO), harmony search (HS), and differential evolution (DE) meta-heuristic optimization algorithms are embedded with the GMDH to yield better feasible optimization. Preliminary results indicate that the developed ML models are robust tools for modeling the wave run-up height. All ML models' accuracies are higher than empirical relations. The obtained results show that employing heuristic methods enhances the accuracy of the standard GMDH model. As such, the FA, IWO, DE, TLBO, and HS improve the RMSE criterion of the standard GMDH by the rate of 47.5%, 44.7%, 24.1%, 41.1%, and 34.3%, respectively. The GMDH-FA and GMDH-IWO are recommended for applications in coastal engineering. [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]

• A new methodology is derived to determine sediment particle velocities over a sandy rippled bed. • The analysis shows that the derived method nearly perfectly predict observed wave-induced sediment particle velocity. • The results indicate that the ANFIS and CART methods are more accurate than regression equations. • SPBO as a training method is more accurate and PSO. The physics and quantification of sediment transport are still a challenge for scientists and engineers. Measurements of wave-induced sediment velocities may be conducted only in selected laboratories and require weeks of pre-tests and a very experienced team. In this study, student psychology-based optimization (SPBO) algorithm was applied to develop new integrated machine learning methods for the determination of wave-induced non-cohesive sediment particle velocities over a rippled bed by incorporating the outcome of particle image velocimetry. Easily measurable data comprising sediment characteristics, bedform details, and hydrodynamic conditions were used to train the machine learning models. The developed techniques determine well the sediment particle horizontal velocity over a horizontal profile. The analysis shows that the derived models nearly perfectly predict observed data. The proposed methodology provides insight into the physics of sediment processes and may also be applied to interpret measurement data and verify sediment transport models. [ABSTRACT FROM AUTHOR]

Mixing induced by nonbreaking surface waves was investigated in a wave tank by measuring the thermal destratification rate of the water column. One experiment without waves and four experiments with waves of amplitudes ranging from 1.0 to 1.5 cm and wavelength from 30 to 75 cm were conducted. Water temperature variations at depths from 4 to 12 cm below the surface were measured. In the layer from 4 to 7 cm, the originally dense isothermal lines disperse soon after the waves are generated, whereas the vertical gradient from 9 to 12 cm is maintained for a relatively long time. The time span, during which the water temperature becomes well mixed, changes from about 20 h for the case with no waves to tens of minutes for the case with waves, and it decreases with increasing wave amplitude and wavelength. A one-dimensional diffusion numerical model with wave-induced mixing parameterization shows consistent results with the measurement. The study demonstrates that the mixing induced by nonbreaking waves may add an important contribution to the vertical mixing process in the upper ocean and suggests a way to parameterize wave-induced mixing in numerical ocean models. [ABSTRACT FROM AUTHOR]

The present study aimed to predict the maximum seasonal wave height by new integrative data driven methods. For this purpose, two data-driven techniques, that are, the Adaptive Neuro-Fuzzy Inference System (ANFIS) and the Support Vector Regression (SVR), were applied, and a BWO algorithm was used as an integrated method (ANFIS-BWO and SVR-BWO). In addition, the Particle Swarm Optimization (PSO) algorithm was used as a method integrated with SVR and ANFIS (SVR-PSO and ANFIS-PSO) to compare the performance of the newly developed methods (ANFIS-BWO and SVR-BWO). The wave data were collected in different seasons by a buoy station deployed in the southern Baltic Sea by the Institute of Hydro-Engineering of the Polish Academy of Sciences. Seasonal simulations were performed to investigate the effect of seasons on the maximum wave height. The wave data constituted an unevenly spaced time series. The maximum wave height was modeled using the maximum wave height period (T max), the significant wave height (H s), the significant wave period (T s), and time steps (Δt). The results showed that the application of BWO and PSO algorithms increased the accuracy of ANFIS and SVR by about 18.45%. Moreover, the results show that PSO increased the accuracy of ANFIS and SVR by about 17.98% and 21.59%, respectively. The results of different runs indicated that the BWO is more stable to reach the global solution than PSO. The results also show that show that SVR-BWO is the most accurate model. • The obtained results indicated that the BWO and PSO algorithms increased the accuracy of ANFIS and SVR. • The results indicate that the BWO acted better in SVR than the PSO. • The performance of the models was poorer in summer than in the other seasons. • The models can predict the maximum wave height for winter more accurately than other seasons. [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]

The paper presents the experimental test setup and measurement method of hydrodynamic force generated on the rotating cylinder (rotor) under uniform flow including the free surface effect. The experimental test setup was a unique construction installed in the flume tank equipped with advanced flow generating and measuring systems. The test setup consisted of a bearing mounted platform with rotor drive and sensors measuring the hydrodynamic force. The low length to diameter ratio cylinders were selected as models of bow rotor rudders of a shallow draft river barge. The rotor dynamics was tested for the rotational speeds up to 550 rpm and water current velocity up to 0.85 m/s. The low aspect ratio of the cylinder and free surface effect had significant impacts on the phenomena influencing the generated hydrodynamic force. The effects of the rotor length to diameter ratio, rotational velocity to flow velocity ratio, and the Reynolds number on the lift force were analyzed. The validation of the computational model against experimental results is presented. The results show a similar trend of results for the simulation and experiment. [ABSTRACT FROM AUTHOR]

A breakwater consisting of three pontoon-type wave energy converters equipped with Power Take-Off (PTO) systems to extract wave energy from pitch and heave motions is proposed. The proposed integrated system has the potential to reduce the cost of the wave energy conversion system by sharing the essential infrastructure with the floating breakwater. In the model, the eigenfunction expansion matching method and technique of variables separation are used. The effects of the geometrical parameters (including pontoon width, draft and spacing) on the hydrodynamic performance characterized by the wave energy conversion efficiency, transmission and reflection coefficients are investigated, respectively. It is found that the effective bandwidth (transmission coefficient K T < 0.5 and hydrodynamic efficiency C w > 0.3) and the peak efficiency are enhanced when the pitch and heave motions are considered simultaneously, compared with the single DoF motion system. The effective bandwidth increases with the decrease of width and draft of the front pontoon. And the variation of pontoon spacing affects significantly the distribution of the efficiency due to the Bragg-type reflection. Additionally, it is found that the variation of the geometrical parameters of the front pontoon on wave transmission is limited by changing the geometrical parameters of the front pontoon only. • Hydrodynamics of triple dual-DoF-motion pontoons is analytically investigated. • Hydrodynamic efficiency is enhanced when pontoons allowed both pitch and heave motions, compared with single DOF motion. • The smaller the width and draft of front pontoon, the larger the effective bandwidth. • The distribution of efficiency with wave frequency is obviously affected by the pontoon spacing. [ABSTRACT FROM AUTHOR]