The finite element method for solving the linear floating body hydrodynamic problem is considered with a hierarchy of boundary damper options for modelling the far field. The computer program is validated using two simple examples for which added mass and damping coefficients are computed over a wide range of frequencies. The program is applied to the ISSC TLP, being a typical practical example for which a large scatter in numerical results is reported in the literature. © 1995.

P. Krishnankutty

Department of Ocean Engineering

Chiruvai P. Vendhan

finite element analysis

OFFSHORE PLATFORMS-TENSION LEG

Radiation

WAVE DIFFRACTION

Boundary value problems

Computer software

Damping

Diffraction

finite element method

Frequencies

Hydrodynamics

three dimensional

Water waves

Added mass

DIFFRACTION RADIATION PROBLEM

FLOATING BODY

RADIATION DAMPER

WAVE STRUCTURE INTERACTION

OFFSHORE STRUCTURES

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Three-dimensional finite element analysis of the diffraction-radiation problem of hydrodynamically compact structures

Marine Structures

Design of floating structures exposed to water waves often requires nonlinear analysis because of high wave steepness and large body motion. In this context, Mixed Eulerian-Lagrangian (MEL) methods for nonlinear water wave problems based on the potential flow theory have been studied extensively. Here, the Laplace equation with Dirichlet boundary condition on the free surface is solved using the boundary integral method, and a time integration method is used to find the particle displacements and velocity potential on the free surface. Finite element methods based on the MEL formulation have been developed in the 90s. Several researchers have pursued this approach, addressing the various challenges thrown open, such as velocity computation, pressure computation on moving surfaces, remeshing of the computational domain, smoothing and imposition of radiation condition. Apart from these, the implementation of the FE model in particular involves several computational issues such as element property computation, solution of large banded matrix equations, and efficient organization of computer storage, all of which are crucial for the computational tool to become successful. A study of these aspects constitutes the primary focus of the present work. The authors have recently developed a 3-D FE model employing the MEL formulation, which has been applied to predict waves in a flume and basin. The fluid domain is discretized using 20-node hexahedral elements. The free surface equations are solved in the time domain employing the three-point Adams-Bashforth method. Validation of the numerical model and relative computation times for salient steps in the FE model are discussed in the paper. Copyright © 2012 by ASME.

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE

Finite element analysis of nonlinear water wave-body interaction- computational issues

In a domain method of solution of exterior scalar wave equation, the radiation condition needs to be imposed on a truncation boundary of the modelling domain. The Bayliss, Gunzberger and Turkel (BGT) boundary dampers of first- and second-orders, which require a circular cylindrical truncation boundary in the diffraction-radiation problem of water waves, have been particularly successful in this task. However, for an elongated body, an elliptic cylindrical truncation boundary has the potential to reduce the modelling domain and hence the computational effort. Grote and Keller [On non-reflecting boundary conditions. Journal of Computational Physics 1995; 122: 231-243] proposed extension of the first- and second-order BGT dampers for the elliptic radiation boundary and used these conditions to the acoustic scattering by an elliptic scatterer using the finite difference method. In this paper, these conditions are implemented for the problem of diffraction of water waves using the finite element method. Also, it is shown that the proposed extension works well only for head-on wave incidence. To remedy this, two new elliptic dampers are proposed, one for beam-on incidence and the other for general wave incidence. The performance of all the three dampers is studied using a numerical example of diffraction by an elliptic cylinder. Copyright © 2001 John Wiley & Sons, Ltd.

International Journal for Numerical Methods in Fluids

Absorbing boundary condition on elliptic boundary for finite element analysis of water wave diffraction by large elongated bodies

International Journal for Numerical Methods in Engineering

Direct evaluation of singular integrals in elastoplastic analysis by the boundary element method

Journal of Waterway, Port, Coastal, and Ocean Engineering

FEM Solution of 3‐D Wave Interference Problems

The effectiveness of dampers for the analysis of exterior scalar wave diffraction by cylinders and ellipsoids

Applied Ocean Research

The applied dynamics of ocean surface waves

Journal of Fluid Mechanics

The wave forces acting on a floating hemisphere undergoing forced periodic oscillations