Numerical investigations of gap resonance excited by focused transient wave groups

2020 ◽  
Vol 212 ◽  
pp. 107628 ◽  
Author(s):  
Junliang Gao ◽  
Hongzhou Chen ◽  
Jun Zang ◽  
Lifen Chen ◽  
Gang Wang ◽  
...  
Keyword(s):  
Transient Wave ◽  
Wave Groups ◽  
Numerical Investigations ◽  
Gap Resonance

Development of a CFD Model to Simulate Three-Dimensional Gap Resonance Applicable to FLNG Side-by-Side Offloading

2017 ◽  
Author(s):  
Hongchao Wang ◽  
Scott Draper ◽  
Wenhua Zhao ◽  
Hugh Wolgamot ◽  
Liang Cheng
Keyword(s):  
Numerical Model ◽  
Three Dimensional ◽  
Domain Size ◽  
Cfd Model ◽  
Transient Wave ◽  
Wave Groups ◽  
Mesh Topology ◽  
Gap Resonance ◽  
Viscous Losses ◽  
Computational Fluid Dynamics Cfd

This paper addresses the process of establishing a numerical model to accurately reproduce experimental results presented by Zhao et al. (2017) of three-dimensional (3D) gap resonance between two fixed ship-shaped boxes. The ship-shaped boxes were arranged in a side-by-side configuration to represent FLNG offloading and were subjected to NewWave-type transient wave groups. To develop the numerical model we employ the open-source Computational Fluid Dynamics (CFD) package OpenFOAM and systematically optimize mesh topology and size, domain size and boundary conditions. CFD is necessary for this problem to accurately reproduce the viscous losses and non-linear free surface effects that are observed in the experiments. The incident transient wave group used in the experiment is regenerated using various iterative schemes. The results show satisfactory agreements between the target and regenerated waves.

Extreme runup events around a ship-shaped floating production, storage and offloading vessel in transient wave groups

2021 ◽  
Vol 911 ◽  
Author(s):  
L.F. Chen ◽  
P.H. Taylor ◽  
D.Z. Ning ◽  
P.W. Cong ◽  
H. Wolgamot ◽  
...  
Keyword(s):  
Transient Wave ◽  
Wave Groups

Abstract

Development of a Computational Fluid Dynamics Model to Simulate Three-Dimensional Gap Resonance Driven by Surface Waves

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Hongchao Wang ◽  
Scott Draper ◽  
Wenhua Zhao ◽  
Hugh Wolgamot ◽  
Liang Cheng
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Computational Cost ◽  
Three Dimensional ◽  
Domain Size ◽  
Experimental Results ◽  
Mode Shapes ◽  
Transient Wave ◽  
Mesh Topology ◽  
Gap Resonance

This paper expounds the process of successfully establishing a computational fluid dynamics (CFD) model to accurately reproduce experimental results of three-dimensional (3D) gap resonance between two fixed ship-shaped boxes. The ship-shaped boxes with round bilges were arranged in a side-by-side configuration to represent a floating liquefied natural gas offloading scenario and were subjected to NewWave-type transient wave groups. We employ the open-source CFD package openfoam to develop the numerical model. Three-dimensional gap resonance differs from its two-dimensional (2D) counterpart in allowing spatial structure along the gap and hence multiple modes can easily be excited in the gap by waves of moderate spectral bandwidth. In terms of numerical setup and computational cost, a 3D simulation is much more challenging than a 2D simulation and requires careful selection of relevant parameters. In this respect, the mesh topology and size, domain size and boundary conditions are systematically optimized. It is shown that to accurately reproduce the experimental results in this case, the cell size must be adequate to resolve both the undisturbed incident waves and near-wall boundary layer. By using a linear iterative method, the NewWave-type transient wave group used in the experiment is accurately recreated in the numerical wave tank (NWT). Numerical results including time series of gap responses, resonant amplitudes and frequencies, and mode shapes show excellent agreement with experimental data.

Resolving wave and laminar boundary layer scales for gap resonance problems

2019 ◽  
Vol 866 ◽  
pp. 759-775 ◽  
Author(s):  
H. Wang ◽  
H. A. Wolgamot ◽  
S. Draper ◽  
W. Zhao ◽  
P. H. Taylor ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Second Harmonic ◽  
Critical Role ◽  
Harmonic Excitation ◽  
Resonant System ◽  
Primary Interest ◽  
Wave Groups ◽  
Laminar Boundary Layers ◽  
Gap Resonance ◽  
Free Surface Oscillations

Free surface oscillations in a narrow gap between elongated parallel bodies are studied numerically. As this represents both a highly resonant system and an arrangement of relevance to offshore operations, the nature of the damping is of primary interest, and has a critical role in determining the response. Previous experimental work has suggested that the damping could be attributed to laminar boundary layers; here our numerical wave tank successfully resolves both wave and boundary layer scales to provide strong numerical evidence in support of this conclusion. The simulations follow the experiments in using wave groups so that the computation is tractable, and both linear and second harmonic excitation of the gap are demonstrated.

CFD Analysis of Deck Impact in Irregular Waves: Wave Representation by Transient Wave Groups

2011 ◽  
Author(s):  
O̸ystein Lande ◽  
Thomas B. Johannessen
Keyword(s):  
Wave Field ◽  
Irregular Waves ◽  
Computational Domain ◽  
Cfd Analysis ◽  
Wave Group ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Wave Induced ◽  
Random Background

Analysis of wave structure interaction problems are increasingly handled by employing CFD methods such as the well known Volume-of-Fluid (VoF) method. In particular for the problem of deck impact on fixed structures with slender substructures, CFD methods have been used extensively in the last few years. For this case, the initial conditions have usually been treated as regular waves in an undisturbed wave field which may be given accurately as input. As CFD analyses become more widely available and are used for more complex problems it is also necessary to consider the problem of irregular waves in a CFD context. Irregular waves provide a closer description of the sea surface than regular waves and are also the chief source of statistical variability in the wave induced loading level. In general, it is not feasible to run a long simulation of an irregular seastate in a CFD analysis today since this would require very long simulation times and also a very large computational domain and sophisticated absorbing boundary conditions to avoid build-up of reflections in the domain. The present paper is concerned with the use of a single transient wave group to represent a large event in an irregular wave group. It is well known that the autocovariance function of the wave spectrum is proportional to the mean shape of a large wave in a Gaussian wave field. The transient nature of such a wave ensures that a relatively small wave is generated at the upwave boundary and dissipated at the downwave boundary compared with the wave in the centre of the domain. Furthermore, a transient wave may be embedded in a random background if it is believed that the random background is important for the load level. The present paper describes the method of generating transient wave groups in a CFD analysis of wave in deck impact. The evolution of transient wave groups is first studied and compared with experimental measurements in order to verify that nonlinear transient waves can be calculated accurately using the present CFD code. Vertical wave induced loads on a large deck is then investigated for different undisturbed wave velocities and deck inundations.

Application of Focusing Wave Groups in Model Testing Practice

2014 ◽  
Author(s):  
Christian Schmittner ◽  
Joris Brouwer ◽  
Janou Hennig
Keyword(s):  
Hydrodynamic Model ◽  
Transfer Functions ◽  
Theoretical Description ◽  
Model Testing ◽  
Historical Background ◽  
Irregular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Floating Structures

For hydrodynamic model testing different types of model waves are applied, where the most common ones are regular (monochromatic) and irregular (multichromatic) waves. In addition to these wave types the application of focusing wave groups, which are also often denoted as wave packages or transient wave packets, can give insight into aspects that cannot be assessed by the conventional model waves. This paper describes the different applications of focusing wave groups for hydrodynamic model testing. The paper starts with the historical background, followed by a theoretical description and the generation procedure. The main part of the paper is dedicated to the practical application of focusing wave groups in the basin. Items that will be described are a) the derivation of transfer functions for floating structures and for anti-roll tanks b) the determination of hydraulic and electrical transfer function of wave makers c) the verification of position and calibration of wave probes in the basin d) the generation of extreme wave events e) the assessment of reflection coefficient of beaches f) the investigation of non-linear aspects of transfer functions. Finally, characteristics of the analysis of focusing waves are introduced and compared to conventional methods based on regular and irregular waves.

Numerical investigation of harbor oscillations induced by focused transient wave groups

2020 ◽  
Vol 158 ◽  
pp. 103670 ◽  
Author(s):  
Junliang Gao ◽  
Xiaozhou Ma ◽  
Jun Zang ◽  
Guohai Dong ◽  
Xiaojian Ma ◽  
...  
Keyword(s):  
Numerical Investigation ◽  
Transient Wave ◽  
Wave Groups ◽  
Harbor Oscillations

scholarly journals Note on the Application of Transient Wave Packets for Wave–Ice Interaction Experiments

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1699
Author(s):  
Marco Klein ◽  
Moritz Hartmann ◽  
Franz von Bock und von Bock und Polach
Keyword(s):  
Amplitude Spectrum ◽  
Wave Structure ◽  
Wave Dispersion ◽  
Wide Frequency Range ◽  
Single Test ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Efficient Alternative

This paper presents the transient wave packet (TWP) technique as an efficient method for wave–ice interaction experiments. TWPs are deterministic wave groups, where both the amplitude spectrum and the associated phases are tailor-made and manipulated, being well established for efficient wave–structure interaction experiments. One major benefit of TWPs is the possibility to determine the response amplitude operator (RAO) of a structure in a single test run compared to the classical approach by investigating regular waves of different wave lengths. Thus, applying TWPs for wave–ice interaction offers the determination of the RAO of the ice at specific locations. In this context, the determination of RAO means that the ice characteristics in terms of wave damping over a wide frequency range are obtained. Besides this, the wave dispersion of the underlying wave components of the TWP can be additionally investigated between the specific locations with the same single test run. For the purpose of this study, experiments in an ice tank, capable of generating tailored waves, were performed with a solid ice sheet. Besides the generation of one TWP, regular waves of different wave lengths were generated as a reference to validate the TWP results for specific wave periods. It is shown that the TWP technique is not only applicable for wave–ice interaction investigations, but is also an efficient alternative to investigations with regular waves.

scholarly journals Gap resonance and higher harmonics driven by focused transient wave groups

2017 ◽  
Vol 812 ◽  
pp. 905-939 ◽  
Author(s):  
W. Zhao ◽  
H. A. Wolgamot ◽  
P. H. Taylor ◽  
R. Eatock Taylor
Keyword(s):  
Incident Wave ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Transient Wave ◽  
Sea State ◽  
Wave Groups ◽  
Wave Basin ◽  
Higher Harmonic ◽  
Harmonic Components ◽  
Quadratic Coupling

The first and higher harmonic components of the resonant fluid response in the gap between two identical fixed rectangular boxes are experimentally investigated in a wave basin. Gap response is excited by transient wave groups (being based on scaled versions of the autocorrelation function of sea-state spectra, representing NewWaves, the average shape of large waves in a sea state). Several different wave groups with different maximum surface elevations, spectral peak frequencies and bandwidths are used, while the bilge shape of the boxes and approach angle of the waves are also varied. Unlike a simple regular wave, it is complicated to separate the harmonic components for a transient wave group due to nonlinear wave–wave and wave–structure interactions. A four-phase combination methodology is used to separate the first four harmonic components, and this also allows higher harmonic components to be isolated with simple digital frequency filtering. Harmonic components up to 14th order in the incident wave amplitude have been extracted. It is shown that for an incident group with appropriate frequency content, the linear gap response may be substantially smaller than the second harmonic component, which is strongly driven via quadratic coupling of the linear terms from the incident wave and occurs in the gap resonant modes. Double frequency excitation may have important practical implications for offshore operations. Fourth and zeroth (long-wave) harmonics in the gap are further driven via quadratic coupling of the second harmonic itself. Linear damping coefficients for the first few modes of the gap resonant response are derived from measured time series using a numerical fit and shown to be higher than those from linear diffraction calculations.

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