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1

A side-hinged paddle wavemaker

Sulisz W., Zdolska A.

Archives of Mechanics

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2023

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Vol. 75, nr 1-2

213--242

EN

Theoretical investigations were conducted to study the generation of transient nonlinear water waves by a novel side-hinged paddle wavemaker. A 3D nonlinear solution was derived in a semi-analytical form by applying eigenfunction expansions and FFT. The solution was applied to study the features of nonlinear waves generated by a side-hinged paddle wavemaker. The results show that nonlinear terms in the free-surface boundary conditions and in the kinematic wavemaker boundary condition imply the modification of wave profiles so that wave troughs are flattered and crests are getting steeper and interaction effects between waves in a wave train increase. Moreover, these terms imply the modification of a wave spectrum. A train of originally very narrow-banded waves changes its one-peak spectrum to a multi-peak one. Theoretical results are in a fairly good agreement with experimental data. A reasonable agreement is observed between predicted and measured time series of free-surface elevations and the amplitudes of the corresponding Fourier series. The investigations show that a side-hinged paddle wavemaker is an attractive wave generation system. Simple and reliable boundary condition at the paddle enables verification of advanced 3D nonlinear models and accurate physical modeling of many phenomena where high accuracy of incoming wave properties are important.

2

Impact of nonlinear standing waves underneath a deck

Majewski D., Sulisz W.

Archives of Civil Engineering

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2020

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Vol. 66, nr 4

79--96

EN

A theoretical approach was applied to investigate the impact of nonlinear standing waves underneath a horizontal deck. A solution was achieved by applying a boundary element method. The model was applied to predict impact pressure underneath a deck. The results show that the wave impact is a very complex momentary process. The influence of initial boundary conditions, wave parameters and deck clearance on impact pressure are analysed. The analysis shows that purely sinusoidal waves of very small amplitude may cause an impact pressure several orders of magnitude higher than a pressure arising from typical applications of a linear wave theory. The analysis shows that all these non-intuitive outcomes arise from the complexity of a wave impact process and its enormous sensitivity to initial conditions what indicates serious difficulties in a reliable prediction of a wave impact for complex wave fields or other structures. Laboratory experiments were conducted to validate theoretical results.

PL

Zbadano proces uderzenia nieliniowych, stojących fal wodnych w spód poziomego pokładu. Wykorzystano podejście teoretyczne, którego rozwiązanie opiera się na Metodzie Elementów Brzegowych. Za pomocą modelu wyznaczono ciśnienia generowane uderzeniem fal wodnych. Wyniki wskazują na to, że proces jest bardzo złożony i ma charakter impulsowy. Analizowano wpływ początkowych warunków brzegowych, parametrów fali oraz wysokości zawieszenia pokładu nad powierzchnią spokoju na generowane ciśnienia. Wyniki pokazują, że nawet fale sinusoidalne, o małej amplitudzie mogą wywołać ciśnienia kilkukrotnie większe niż ciśnienia wynikające z typowych zastosowań teorii liniowej falowania. Pokazują również, że często nieintuicyjne wnioski wynikają ze złożoności procesu uderzenia fali i jego dużej czułości na początkowe warunki brzegowe. Wskazuje to na poważne trudności w wiarygodnym modelowaniu procesu uderzenia dla złożonych pól falowych oraz skomplikowanych układów geometrycznych budowli. Przeprowadzono również pomiary laboratoryjne w celu uzyskania danych do walidacji modelu numerycznego. Opracowany model zapewnia wyniki z dokładnością umożliwiającą zastosowanie go w zadaniach inżynierskich.

3

Impact pressure distribution on a monopile structure excited by irregular breaking wave

Veic D., Sulisz W.

Polish Maritime Research

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2018

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S 1

29--35

EN

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.

4

Reflection and transmission of nonlinear water waves at a semi-submerged dock

Sulisz W.

Archives of Mechanics

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2013

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Vol. 65, nr 3

237--260

EN

A theoretical approach is applied to predict reflection and transmission of nonlinear water waves at a semi-submerged dock. The solution was achieved analytically and by the method of matched eigenfunction expansions. The results show that the dock geometry has a significant effect on the nonlinear components of wave reflection and transmission. The reflection and transmission of nonlinear waves simultaneously increase with increasing dock width for shallow water waves and decrease with increasing dock width for intermediate- and deep-water waves, which is an interesting outcome. A similar simultaneous increase or decrease of nonlinear wave reflection and transmission was observed for the changes of the dock draft. Moreover, the solution reveals that nonlinear wave components may provide a significant contribution to the wave field for a wide range of wave parameters. The nonlinear components of wave reflection and transmission may exceed many times the amplitudes of the corresponding second-order Stokes waves as well as the amplitudes of the corresponding linear components. This phenomenon occurs within the commonly accepted range of the applicability of the second-order wave theory and implies a need to include scattered nonlinear wave components in the analysis of many problems of practical importance, including sediment transport, for which second-order waves have been shown to be the main driving force. Laboratory experiments were conducted to verify nonlinear wave field components. Theoretical results are in reasonable agreement with experimental data.

5

Modeling of the propagation and evolution of nonlinear waves in a wave train

Sulisz W., Paprota M.

Archives of Mechanics

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2011

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Vol. 63, nr 3

311-311

EN

A theoretical approach is applied to predict the propagation and evolution of nonlinear water waves in a wave train. A semi-analytical solution was derived by applying an eigenfunction expansion method. The solution is applied to study the evolution of nonlinear waves in a wave train and the formation of freak waves. The analysis focuses on the changes of wave profile and wave spectrum due to the interaction of wave components in a wave train. The results indicate that for waves of very low steepness, the changes of wave profile and wave spectrum are of secondary importance and weakly nonlinear wave theories can be applied to describe wave propagation in a wave train. For waves of low and moderate steepness, the nonlinear terms in the free-surface boundary conditions are becoming more and more important and weakly nonlinear wave theories cannot be applied to describe substantial changes in wave profile. A train of basically sinusoidal waves may drastically change its form within a relatively short distance from its original position and freak waves are often formed. The interaction between waves in a wave train and significant wave evolution has substantial effects on a wave spectrum. A train of initially very narrow-banded spectrum changes its simple one-peak spectrum to a broad-banded and often multi-peak spectrum in a fairly short period of time. The analysis shows that these phenomena cannot be described properly by the nonlinear Schrödinger equation or its modifications. 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, even for complex changes of long wave trains.