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Item type:Publication, Access status: without files , Hydroelastic potential flow solver suited for nonlinear wave dynamics in ice-covered watersThe aim of this paper is to introduce a fully nonlinear numerical finite element solver for the simulation of nonlinear wave processes in the presence of a solid ice sheet. In this study, solid ice cover referred to the size of the ice sheet and denoted that the length of the ice sheet was many times larger than the longest relevant wavelength. The complexity of the ice sheet characteristics was assumed to be homogeneous, isotropic and in the linear elastic plate regime so that the deformation process could be modeled by the Kirchhoff–Love plate ansatz. The method presented was verified and validated for different ice dimensions and wave scenarios. At the beginning, the implementation of the flexural rigidity to the free surface boundary condition was verified by comparing the analytical wave-ice dispersion relation to simulation results with small amplitude regular waves and varying ice dimensions. Afterwards, the general applicability was validated by means of wave-ice experiments. The experiments were performed in the ice tank at Hamburg Ship Model Basin HSVA comprising regular waves and transient wave groups.Publicationtype: Journal Article51 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Phase-suppressed hydrodynamics of solitons on constant-background plane wave(2020-11-11); ; ; ; Soliton and breather solutions of the nonlinear Schrödinger equation (NLSE) are known to model localized structures in nonlinear dispersive media such as on the water surface. One of the conditions for an accurate propagation of such exact solutions is the proper generation of the exact initial phase-shift profile in the carrier wave, as defined by the NLSE envelope at a specific time or location. Here, we show experimentally the significance of such initial exact phase excitation during the hydrodynamic propagation of localized envelope solitons and breathers, which modulate a plane wave of constant amplitude (finite background). Using the example of stationary black solitons in intermediate water depth and pulsating Peregrine breathers in deep water, we show how these localized envelopes disintegrate while they evolve over a significant long distance when the initial phase shift is zero. By setting the envelope phases to zero, the dark solitons will disintegrate into two gray-type solitons and dispersive elements. In the case of the doubly localized Peregrine breather the maximal amplification is considerably retarded; however, locally, the shape of the maximal focused wave measured together with the respective signature phase-shift are almost identical to the exact analytical Peregrine characterization at its maximal compression location. The experiments, conducted in large-scaled shallow-water as well as deep-water wave facilities, are in very good agreement with NLSE simulations for all cases.Publicationtype: Journal Article43 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Investigation of nonlinear wave-ice interaction using parameter study and numerical simulation(American Society of Mechanical Engineers (ASME), 2020-04); ; ; ; This paper investigates the question of the existence of nonlinear wave-ice interaction with the focus on nonlinear wave propagation and dispersion of waves. The scope of this investigation is to provide a better understanding of ice and wave conditions required to observe nonlinear wave effects under level ice. Direct numerical simulations of nonlinear waves in solid ice are performed within the weakly nonlinear Schrödinger equation (NLSE) framework, using the theoretical findings from Liu and Mollo-Christensen’s 1988 paper. Systematic variations of wave and ice parameters address the impact of the mechanical ice properties and ice thickness on traveling waves of certain wave lengths. The impacts of parameter characteristics on nonlinear focusing and wave dynamics, as well as possible constraints regarding physical consistency, are discussed. It is presented that nonlinear focusing in level ice occurs theoretically. Hereby, distinctive areas of validity with respect to nonlinear wave focusing are identified within the parameter study, which strongly depends on the material properties of the level ice. The results obtained in the parameter study are subsequently used to investigate wave focusing under level ice. Therefore, an exact solution of the NLSE, the Peregrine breather, is utilized. The analytical solution for level ice is compared to the open water solution and accompanied by direct numerical simulations. These investigations show that nonlinear wave focusing can be predicted under level ice for certain parameters. In addition, the agreement of the direct simulations and the analytic solution verifies the numerical approach for nonlinear waves in solid ice.Publicationtype: Journal ArticleScopus© Citations 3 357 466 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the deterministic prediction of water waves(Multidisciplinary Digital Publishing Institute (MDPI), 2020-01-07); ; ; ; This paper discusses the potential of deterministic wave prediction as one basic module for decision support of offshore operations. Therefore, methods of different complexity - the linear wave solution, the non-linear Schrödinger equation (NLSE) of two different orders and the high-order spectral method (HOSM) - are presented in terms of applicability and limitations of use. For this purpose, irregular sea states with varying parameters are addressed by numerical simulations as well as model tests in the controlled environment of a seakeeping basin. The irregular sea state investigations focuses on JONSWAP spectra with varying wave steepness and enhancement factor. In addition, the influence of the propagation distance as well as the forecast horizon is discussed. For the evaluation of the accuracy of the prediction, the surface similarity parameter is used, allowing an exact, quantitative validation of the results. Based on the results, the pros and cons of the different deterministic wave prediction methods are discussed. In conclusion, this paper shows that the classical NLSE is not applicable for deterministic wave prediction of arbitrary irregular sea states compared to the linear solution. However, the application of the exact linear dispersion operator within the linear dispersive part of the NLSE increased the accuracy of the prediction for small wave steepness significantly. In addition, it is shown that non-linear deterministic wave prediction based on second-order NLSE as well as HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance, with the HOSM providing a high accuracy over a wider range of applications.Publicationtype: Journal ArticleScopus© Citations 42 573 270 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical study on nonlinear wave-ice-interaction(American Society of Mechanical Engineers (ASME), 2019-06); ; ; ; This paper investigates the fundamental question of nonlinear wave-ice interaction under level ice focusing on nonlinear wave propagation and dispersion of waves. Therefore, numerical investigations are performed to verify theoretically if nonlinearity takes place under level ice and if this can lead to intense wave events far away from the ice edge in order to provide an explanation for observed real-world ice break-ups. Therefore, nonlinear wave-ice interaction as well as the impact of the ice characteristics on this interaction will be investigated. The direct numerical simulations of the nonlinear wave propagation under solid ice are performed within the Nonlinear Schrödinger Equation (NLSE) framework. The Peregrine breather solution is applied to represent exact solutions of the NLSE for a nonlinear wave group. The application of such a nonlinear wave group is predestined for the verification of occurring nonlinear wave-wave interaction below the ice sheet. For the definition of wave and ice parameters in the simulation setup, the results of the presented parameter study are used. The parameters are analyzed regarding relevant characteristics of nonlinear wave-ice interaction and wave propagation. By assuming constraints with respect to physical consistency, the parameter range for the NLSE simulations can be narrowed. The scope of this investigation is to provide a better understanding of the ice conditions required to observe nonlinear wave effects under level ice.Publicationtype: Conference Paper308 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Directional soliton and breather beamsSolitons and breathers are nonlinear modes that exist in a wide range of physical systems. They are fundamental solutions of a number of nonlinear wave evolution equations, including the unidirectional nonlinear Schrödinger equation (NLSE). We report the observation of slanted solitons and breathers propagating at an angle with respect to the direction of propagation of the wave field. As the coherence is diagonal, the scale in the crest direction becomes finite; consequently, beam dynamics form. Spatiotemporal measurements of the water surface elevation are obtained by stereo-reconstructing the positions of the floating markers placed on a regular lattice and recorded with two synchronized high-speed cameras. Experimental results, based on the predictions obtained from the (2D + 1) hyperbolic NLSE equation, are in excellent agreement with the theory. Our study proves the existence of such unique and coherent wave packets and has serious implications for practical applications in optical sciences and physical oceanography. Moreover, unstable wave fields in this geometry may explain the formation of directional large-amplitude rogue waves with a finite crest length within a wide range of nonlinear dispersive media, such as Bose-Einstein condensates, solids, plasma, hydrodynamics, and optics.Publicationtype: Journal ArticleScopus© Citations 23 280 262 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Peregrine breathers as design waves for wave-structure interaction(2016-12-01); ; ; ; This paper introduces the Peregrine breather solution of the nonlinear Schrödinger-type equation as an innovative design wave. The major benefits are the potential to generate abnormal waves of certain frequency up to physically possible wave heights, the symmetrical abnormal wave shape and the availability of an analytical solution. The characteristics of Peregrine breathers as well as their impact on marine structures were investigated. To evaluate the applicability of the Peregrine breather solution as design wave, wave-structure investigations with a LNG carrier were performed in a set of Peregrine breathers at certain frequencies. The investigations comprised model tests as well as numerical simulations. For the purpose of comparison, a real-world abnormal wave reproduction was additionally investigated allowing the evaluation of breather-type abnormal waves regarding the applicability as design wave. Therefore, the famous ‘New Year Wave’, an abnormal wave recorded in the North Sea at the Draupner jacket platform on January 1st, 1995, was selected.Publicationtype: Journal Article93 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Observation of dispersive shock waves developing from initial depressions in shallow waterWe investigate surface gravity waves in a shallow water tank, in the limit of long wavelengths. We report the observation of non-stationary dispersive shock waves rapidly expanding over a 90 m flume. They are excited by means of a wave maker that allows us to launch a controlled smooth (single well) depression with respect to the unperturbed surface of the still water, a case that contains no solitons. The dynamics of the shock waves are observed at different levels of nonlinearity equivalent to a different relative smallness of the dispersive effect. The observed undulatory behavior is found to be in good agreement with the dynamics described in terms of a Korteweg–de Vries equation with evolution in space, though in the most nonlinear cases the description turns out to be improved over the quasi linear trailing edge of the shock by modeling the evolution in terms of the integro-differential (nonlocal) Whitham equation.Publicationtype: Journal Article94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental observation and theoretical description of multisoliton fission in shallow water(American Physical Society (APS), 2016-09-28); ; ; ; We observe the dispersive breaking of cosine-type long waves [Phys. Rev. Lett. 15, 240 (1965)] in shallow water, characterizing the highly nonlinear "multisoliton" fission over variable conditions. We provide new insight into the interpretation of the results by analyzing the data in terms of the periodic inverse scattering transform for the Korteweg-de Vries equation. In a wide range of dispersion and nonlinearity, the data compare favorably with our analytical estimate, based on a rigorous WKB approach, of the number of emerging solitons. We are also able to observe experimentally the universal Fermi-Pasta-Ulam recurrence in the regime of moderately weak dispersion.Publicationtype: Journal Article158 131 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Deterministic non-linear wave forecast and motion prediction for short-term offshore operationsThis paper presents a time-domain decision support system based on deterministic, non-linear wave forecast and motion prediction for short-term offshore operations. The system consists of three individual constituents: sea state registrations, non-linear wave forecast and motion prediction. Surface elevation snapshots taken continuously by a ship board radar at great distance ahead the operational area are preprocessed by the wave monitoring system WaMoS II1 and used as input for the wave forecast tool. The non-linear wave propagation is modelled by applying the Higher Order Spectral Method (HOSM), which offers high accuracy and fast calculation time at once. The predicted surface elevation at the location of operation are used for the evaluation of the corresponding offshore structure response. For this purpose, Impulse Response Functions are implemented, which enable the fast determination of the response in time domain. The focus of the present study lies on the evaluation of the non-linear wave forecast and motion prediction part of the proposed decision support system. For illustrating the efficiency of the process, an offshore crane operation is investigated. The accuracy of the predicted (future) surface elevation as well as response of the multi-body problem is evaluated against model tests in the controlled environment of a seakeeping basin.Publicationtype: Conference Paper65