Practical flow-representations for arbitrary singularity-distributions in ship and offshore hydrodynamics, with applications to steady ship waves and wave diffraction-radiation by offshore structures

2020 ◽  
Vol 83 ◽  
pp. 24-41 ◽  
Author(s):  
Jiayi He ◽  
Huiyu Wu ◽  
Ren-Chuan Zhu ◽  
Chen-Jun Yang ◽  
Francis Noblesse
Keyword(s):  
Wave Diffraction ◽  
Offshore Structures ◽  
Diffraction Radiation ◽  
Ship Waves

Irregular Frequency Removal and Convergence in Higher-Order BEM for Wave Diffraction/Radiation Analysis

2019 ◽  
Author(s):  
Tomoaki Utsunomiya
Keyword(s):  
Free Surface ◽  
Wave Diffraction ◽  
Higher Order ◽  
The Body ◽  
Diffraction Radiation ◽  
First Order ◽  
Irregular Frequency ◽  
Intersection Line ◽  
Order Quantities ◽  
Drift Forces

Abstract Higher-order boundary element method (HOBEM) for wave diffraction/radiation analysis is a powerful tool for its applicability to a general (curved) geometry. Inspired by the paper which examined the convergence of BIE code with constant panels (Martic, et al., 2018; OMAE2018-77999), the convergence characteristics of HOBEM with quadrilateral panels have been examined. Here, the effect of removal of irregular frequencies is particularly focused as discussed by Martic, et al. (2018). The irregular frequency removal has been made by the rigid-lid method which is applicable to HOBEM, where the intersection line between the body-surface and the free-surface should be carefully handled. The results show that for first order quantities the convergence is quite good for both cases with/without irregular frequency removal (except where the irregular frequencies affect for the case without irregular frequency removal). For mean drift forces, the convergence becomes poor particularly for the case without irregular frequency removal. The convergence characteristics are examined and some discussions are made.

Hydrodynamic Interactions of the Truncated Porous Vertical Circular Cylinder With Water Waves

2018 ◽  
Author(s):  
Charaf Ouled Housseine ◽  
Sime Malenica ◽  
Guillaume De Hauteclocque ◽  
Xiao-Bo Chen
Keyword(s):  
Circular Cylinder ◽  
Porous Body ◽  
Wave Diffraction ◽  
Water Waves ◽  
Expansion Method ◽  
Integral Equation Method ◽  
Boundary Integral ◽  
Diffraction Radiation ◽  
Linear Potential ◽  
Eigenfunction Expansion Method

Wave diffraction-radiation by a porous body is investigated here. Linear potential flow theory is used and the associated Boundary Value Problem (BVP) is formulated in frequency domain within a linear porosity condition. First, a semi-analytical solution for a truncated porous circular cylinder is developed using the dedicated eigenfunction expansion method. Then the general case of wave diffraction-radiation by a porous body with an arbitrary shape is discussed and solved through Boundary Integral Equation Method (BIEM). The main goal of these developments is to adapt the existing diffraction-radiation code (HYDROSTAR) for that type of applications. Thus the present study of the porous cylinder consists a validation work of (BIEM) numerical implementation. Excellent agreement between analytical and numerical results is observed. Porosity influence on wave exciting forces, added mass and damping is also investigated.

Optimization of Offshore Structures Based on Linear Analysis of Wave-Body Interaction

2008 ◽  
Author(s):  
Lothar Birk ◽  
Gu¨nther F. Clauss
Keyword(s):  
Rational Design ◽  
User Interaction ◽  
Offshore Structures ◽  
Design Tool ◽  
Integrated System ◽  
Diffraction Radiation ◽  
Hydrodynamic Analysis ◽  
Automated Generation ◽  
Wide Range ◽  
Hull Design

This paper discusses new developments in automated hull shape optimization spearheaded by the authors. The use of the linear diffraction-radiation panel code WAMIT® as a design tool is highlighted. Early optimization results yielded bodies with extreme shapes. A series of studies has been performed comparing model test data and numerical computations. The presented comparisons reinforce the numerical results. The authors connected the reliable hydrodynamic analysis provided by WAMIT® with a newly developed parametric hull design methodology. This allows the automated generation of hull shapes without requiring user interaction. Single- and multi-objective optimization algorithms are available to solve a wide range of nonlinear programming problems. The integrated system optimizes hulls by minimizing motions and forces in waves. This is especially important for innovative systems when prior design experience is missing. The results of an optimization run provide a wealth of information which can be utilized to support rational design decisions.

Numerical Evaluation of Free-Surface Green Functions

1994 ◽  
Vol 38 (03) ◽  
pp. 193-202
Author(s):  
B. Ponizy ◽  
F. Noblesse ◽  
M. Ba ◽  
M. Guilbaud
Keyword(s):  
Coordinate Transformation ◽  
Near Field ◽  
Finite Domain ◽  
Diffraction Radiation ◽  
Green Functions ◽  
Offshore Structure ◽  
Local Flow ◽  
Ship Waves ◽  
Function Transformation ◽  
Singular Functions

A very simple and efficient method for computing the nonoscillatory near-field terms in the expressions for the Green functions, and their gradients, for wave diffraction/radiation by an offshore structure and steady ship waves in deep water is presented. The Green functions are decomposed into three terms corresponding to simple (Rankine) singularities, wave fields, and nonoscillatory near-field (local) flow components. The method which is presented for approximating the latter nonoscillatory near-field components is based on the use of a coordinate-transformation and a function-transformation. The coordinate-transformation maps the unbounded domain of definition of the Green function into a finite domain (unit square or cube) of transformed coordinates. The function-transformation expresses the near-field components, which are singular at the origin, in terms of functions that are regular everywhere. Proper coordinate and function transformations reduce the problem of approximating singular functions in unbounded domains into that of approximating smoothly varying functions within finite domains. The latter task can be accomplished in a number of ways, including the use of linear table interpolation presented in the study.

Numerical analysis of the effects on a floating structure induced by ship waves

2011 ◽  
Vol 55 (02) ◽  
pp. 124-134
Author(s):  
L. Sun ◽  
G.H Dong ◽  
Y. P. Zhao ◽  
C. F. Liu
Keyword(s):  
Time Domain ◽  
Equation Of Motion ◽  
Offshore Structures ◽  
Floating Body ◽  
Kutta Method ◽  
Floating Structure ◽  
Ship Waves ◽  
Runge Kutta Method ◽  
Frequency Domain Methods ◽  
The Time Domain

Ship-generated waves can make bad effects on offshore structures. A numerical model is presented for evaluating the forces exerted on a nearby floating structure by ship generated waves. The ship waves were modeled using Michell thin-ship theory (Wigley waves), the forces were computed using a boundary element method in the time domain, and the motions of the offshore structures were evaluated using the equation of motion of the floating body, and predicted using the fourth-order Runge-Kutta method. The numerical method was validated by comparing its results to those of frequency-domain methods reported in the literature. It was then applied to calculate the force of ship waves on a floating box. The ship's speed, dimensions, and distance were varied. The numerical results indicate some useful rules for varying these factors.

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