Modelling of multi-bodies in close proximity under water waves—Fluid forces on floating bodies

2011 ◽  
Vol 38 (13) ◽  
pp. 1403-1416 ◽  
Author(s):  
Lin Lu ◽  
Bin Teng ◽  
Liang Sun ◽  
Bing Chen
Keyword(s):  
Water Waves ◽  
Floating Bodies ◽  
Fluid Forces ◽  
Close Proximity

Effective Power and Speed Loss of Underwater Vehicles in Close Proximity to Regular Waves

2017 ◽  
Author(s):  
Stefan Daum ◽  
Martin Greve ◽  
Renato Skejic
Keyword(s):  
Free Surface ◽  
Deep Water ◽  
Water Waves ◽  
Underwater Vehicles ◽  
Total Resistance ◽  
Wave Load ◽  
Regular Waves ◽  
Effective Power ◽  
Close Proximity ◽  
Deep Water Waves

The present study is focused on performance issues of underwater vehicles near the free surface and gives insight into the analysis of a speed loss in regular deep water waves. Predictions of the speed loss are based on the evaluation of the total resistance and effective power in calm water and preselected regular wave fields w.r.t. the non-dimensional wave to body length ratio. It has been assumed that the water is sufficiently deep and that the vehicle is operating in a range of small to moderate Froude numbers by moving forward on a straight-line course with a defined encounter angle of incident regular waves. A modified version of the Doctors & Days [1] method as presented in Skejic and Jullumstrø [2] is used for the determination of the total resistance and consequently the effective power. In particular, the wave-making resistance is estimated by using different approaches covering simplified methods, i.e. Michell’s thin ship theory with the inclusion of viscosity effects Tuck [3] and Lazauskas [4] as well as boundary element methods, i.e. 3D Rankine source calculations according to Hess and Smith [5]. These methods are based on the linear potential fluid flow and are compared to fully viscous finite volume methods for selected geometries. The wave resistance models are verified and validated by published data of a prolate spheroid and one appropriate axisymmetric submarine model. Added resistance in regular deep water waves is obtained through evaluation of the surge mean second-order wave load. For this purpose, two different theoretical models based on potential flow theory are used: Loukakis and Sclavounos [6] and Salvesen et. al. [7]. The considered theories cover the whole range of important wavelengths for an underwater vehicle advancing in close proximity to the free surface. Comparisons between the outlined wave load theories and available theoretical and experimental data were carried out for a submerged submarine and a horizontal cylinder. Finally, the effective power and speed loss are discussed from a submarine operational point of view where the mentioned parameters directly influence mission requirements in a seaway. All presented results are carried out from the perspective of accuracy and efficiency within common engineering practice. By concluding current investigations in regular waves an outlook will be drawn to the application of advancing underwater vehicles in more realistic sea conditions.

scholarly journals Generalized eigenfunction method for floating bodies

2011 ◽  
Vol 667 ◽  
pp. 544-554 ◽  
Author(s):  
COLM J. FITZGERALD ◽  
MICHAEL H. MEYLAN
Keyword(s):  
Time Domain ◽  
Water Waves ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Two Dimensions ◽  
Floating Body ◽  
Floating Bodies ◽  
Abstract Wave Equation ◽  
Generalized Eigenfunction ◽  
The Time Domain

We consider the time domain problem of a floating body in two dimensions, constrained to move in heave and pitch only, subject to the linear equations of water waves. We show that using the acceleration potential, we can write the equations of motion as an abstract wave equation. From this we derive a generalized eigenfunction solution in which the time domain problem is solved using the frequency-domain solutions. We present numerical results for two simple cases and compare our results with an alternative time domain method.

Gap Resonance of Fixed Floating Multi Caissons

2019 ◽  
Author(s):  
Limin Chen ◽  
Guanghua He ◽  
Harry B. Bingham ◽  
Yanlin Shao
Keyword(s):  
Free Surface ◽  
Water Waves ◽  
Offshore Structures ◽  
Wave Number ◽  
Wave Forces ◽  
Wave Runup ◽  
Floating Bodies ◽  
Constrained Interpolation ◽  
Gap Resonance ◽  
Narrow Gaps

Abstract Generally, numerous marine and offshore structures are composed of a number of modules which introduce narrow gaps between the multi-modules arranged side by side. The interaction between water waves and floating structures excites complex wave runup in the gaps and wave forces on the adjacent modules. In this study, free surface oscillations in twin narrow gaps between identical floating rectangular boxes are investigated by establishing a 2D viscous flow numerical wave tank based on a Constrained Interpolation Profile (CIP) method. The Tangent of Hyperbola for INterface Capturing (THINC) method is employed to capture the free surface. The rigid floating bodies are treated by a Virtual Particle Method (VPM). The incident waves are generated by an internal wave maker. For the fixed module cases, the computational results of wave height in narrow gaps are found in good coincidence with the available experimental measurements, especially for the resonant frequencies. The wave forces on the floating bodies are calculated numerically. The characteristic response of wave forces on the leading and rear bodies are consistent with the free surface elevations in the corresponding narrow gaps. With shallow draft, the gap resonance occurs at higher wave number.

scholarly journals Trapped modes around freely floating bodies in a two-layer fluid channel

2014 ◽  
Vol 470 (2170) ◽  
pp. 20140396 ◽  
Author(s):  
Filipe S. Cal ◽  
Gonçalo A. S. Dias ◽  
Juha H. Videman
Keyword(s):  
Spectral Problem ◽  
Water Waves ◽  
Adjoint Operator ◽  
Trapped Modes ◽  
Floating Bodies ◽  
Floating Structures ◽  
Nonlinear Spectral Problem ◽  
Time Harmonic ◽  
Fluid Channel ◽  
Elimination Scheme

Unlike the trapping of time-harmonic water waves by fixed obstacles, the oscillation of freely floating structures gives rise to a complex nonlinear spectral problem. Still, through a convenient elimination scheme the system simplifies to a linear spectral problem for a self-adjoint operator in a Hilbert space. Under symmetry assumptions on the geometry of the fluid domain, we present conditions guaranteeing the existence of trapped modes in a two-layer fluid channel. Numerous examples of floating bodies supporting trapped modes are given.

Nonlinear-wave effects on fixed and floating bodies

1982 ◽  
Vol 120 ◽  
pp. 267-281 ◽  
Author(s):  
Michael De St Q. Isaacson
Keyword(s):  
Initial Conditions ◽  
Integral Equation Method ◽  
Ocean Waves ◽  
Floating Bodies ◽  
Time Step ◽  
Fluid Forces ◽  
Time Stepping ◽  
Transient Problem ◽  
Wave Effects ◽  
Incident Waves

A numerical method for calculating the interaction of steep (nonlinear) ocean waves with large fixed or floating structures of arbitrary shape is described. The interaction is treated as a transient problem with known initial conditions corresponding to still water in the vicinity of the structure and a prescribed incident waveform approaching it. The development of the flow, together with the associated fluid forces and structural motions, are obtained by a time-stepping procedure in which the flow at each time step is calculated by an integral-equation method based on Green's theorem. A few results are presented for two reference situations and these serve to illustrate the effects of nonlinearities in the incident waves.

Numerical Study of the Motions in Shallow Water Waves of Floating Bodies Elastically Linked to Bottom

2009 ◽  
Author(s):  
Marcio Michiharu Tsukamoto ◽  
Liang-Yee Cheng ◽  
Kazuo Nishimoto
Keyword(s):  
Shallow Water ◽  
Water Waves ◽  
Large Amplitude ◽  
Numerical Study ◽  
Numerical Approach ◽  
Floating Bodies ◽  
Restoring Force ◽  
Hydrodynamic Loads ◽  
Elastic Links ◽  
Analytical Approaches

The motion of floating bodies linked elastically to the bottom of seas and waterways is of great interest in the analysis of the wave suppressing devices, such as wave breakers, and the behaviors of the floating structures, such as buoys and tension leg platforms (TLP). For the modeling of the dynamics, the coupling between the hydrodynamic loads due to waves and the restoring forces due to the elastic link must be considered. In some simpler cases, the analytical approaches are available. However, in case of large amplitude waves and floating bodies with complex geometries, the analytical solutions do not give accurate results. In the present study, a numerical model based on MPS (moving particle semi-implicit method) for the hydrodynamic loads coupled with the Hook’s Law for the restoring force is adopted to analyze the motion of floating bodies with one or several elastic links to the bottom of shallow water under large amplitude waves. Initially, the results of 2D numerical simulation of simple oscillating buoys are compared with the analytical and experimental ones to validate the numerical approach. After that, the approach is applied to the study of the shallow water wave supressing devices. Heave, surge and pitching motions of the floaters are assessed as well as the hydrodynamic coefficients to show the effect of the elastic links in the nonlinear wave hydrodynamics.

Theoretical and numerical investigations of wave resonance between two floating bodies in close proximity

2017 ◽  
Vol 29 (5) ◽  
pp. 805-816 ◽  
Author(s):  
Lei Tan ◽  
Guo-qiang Tang ◽  
Zhong-bing Zhou ◽  
Liang Cheng ◽  
Xiaobo Chen ◽  
...  
Keyword(s):  
Floating Bodies ◽  
Numerical Investigations ◽  
Wave Resonance ◽  
Close Proximity

Diffraction of solitary water waves around three-dimensional floating bodies

1990 ◽  
Vol 6 (1) ◽  
pp. 1-8
Author(s):  
Liu Yingzhong ◽  
Zhu Dexiang ◽  
Miao Guoping
Keyword(s):  
Water Waves ◽  
Three Dimensional ◽  
Floating Bodies

scholarly journals A Novel Method for Estimating Wave Energy Converter Performance in Variable Bathymetry Regions and Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2092 ◽  
Author(s):  
Kostas Belibassakis ◽  
Markos Bonovas ◽  
Eugen Rusu
Keyword(s):  
Wave Field ◽  
Wave Energy ◽  
Water Waves ◽  
Bottom Topography ◽  
Wave Energy Converter ◽  
Diffraction Radiation ◽  
Floating Bodies ◽  
Energy Converter ◽  
Coupled Mode ◽  
Energy Absorbers

A numerical model is presented for the estimation of Wave Energy Converter (WEC) performance in variable bathymetry regions, taking into account the interaction of the floating units with the bottom topography. The proposed method is based on a coupled-mode model for the propagation of the water waves over the general bottom topography, in combination with a Boundary Element Method for the treatment of the diffraction/radiation problems and the evaluation of the flow details on the local scale of the energy absorbers. An important feature of the present method is that it is free of mild bottom slope assumptions and restrictions and it is able to resolve the 3D wave field all over the water column, in variable bathymetry regions including the interactions of floating bodies of general shape. Numerical results are presented concerning the wave field and the power output of a single device in inhomogeneous environment, focusing on the effect of the shape of the floater. Extensions of the method to treat the WEC arrays in variable bathymetry regions are also presented and discussed.

Drift Motion of Floating Bodies Under the Action of Green Water

2021 ◽  
Author(s):  
Sasan Tavakoli ◽  
Luofeng Huang ◽  
Alexander V. Babanin
Keyword(s):  
Numerical Simulations ◽  
Water Waves ◽  
The Body ◽  
Green Water ◽  
Floating Body ◽  
Floating Bodies ◽  
Drift Motion ◽  
Upper Deck ◽  
Steep Waves ◽  
The Impact

Abstract Numerical simulations are peformed to model the dynamic motions of a free floating body exposed to water waves. The solid body has low freeboard and draft, and its upper deck can be washed by the steep waves. Thus, the green water phenomenon occurs as large waves interact with the floating body. The aim of the research is to improve the understanding of the green water emerging above the upper deck of a floating plate. A thin floating body with barriers is also modeled. For the case of the body equipped with barriers, no green water occurs. Green water has been seen to affect the wave field and the dynamic motions of the plate. It is observed that when water can wash the upper surface of the floating object, drift speed is slightly decreased as a proportion of the energy of waves is dissipated above the body. Water waves are seen to impact the upper surface of the thin floating body as the green water flows over its upper deck. Furthermore, water is seen to impact the plate as its front edge re-enters the water. The first water impact only occurs when the floating body is not equipped with any barrier. By sampling the numerical simulations, it is observed that the non-dimensional value of the impact pressure, resulting from the green water, is larger for the case of smaller wavelength.

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