Development of a Computer Program for Three Dimensional Analysis of Zero Speed First Order Wave Body Interaction in Frequency Domain

2013 ◽  
Author(s):  
Amitava Guha ◽  
Jeffrey Falzarano
Keyword(s):  
Computer Program ◽  
Green’S Function ◽  
Frequency Domain ◽  
Green's Function ◽  
Early Stage ◽  
Diffraction Problem ◽  
Offshore Structures ◽  
Wave Radiation ◽  
Numerical Implementation ◽  
Strip Theory

Evaluation of motion characteristics of ships and offshore structures at the early stage of design as well as during operation at the site is very important. Strip theory based programs and 3D panel method based programs are the most popular tools used in industry for vessel motion analysis. These programs use different variations of the Green’s function or Rankine sources to formulate the boundary element problem which solves the water wave radiation and diffraction problem in the frequency domain or the time domain. This study presents the development of a 3D frequency domain Green’s function method in infinite water depth for predicting hydrodynamic coefficients, wave induced forces and motions. The complete theory and its numerical implementation are discussed in detail. An in house application has been developed to verify the numerical implementation and facilitate further development of the program towards higher order methods, inclusion of forward speed effects, finite depth Green function, hydro elasticity, etc. The results were successfully compared and validated with analytical results where available and the industry standard computer program for simple structures such as floating hemisphere, cylinder and box barge as well as complex structures such as ship, spar and a tension leg platform.

Comparative Study of Seakeeping Analysis Results From Various Methods

2011 ◽  
Author(s):  
Sharad S. Dhavalikar
Keyword(s):  
Green’S Function ◽  
Frequency Domain ◽  
Green's Function ◽  
Time Domain ◽  
Scalar Potential ◽  
Design Stage ◽  
Advantages And Disadvantages ◽  
Frequency Domain Methods ◽  
Strip Theory ◽  
Seakeeping Analysis

Over the years many methods are evolved for computing ship motions and loads, i.e. seakeeping analysis. All of these methods are known as potential flow methods where fluid is assumed to be irrotational. In these methods velocity vector is represented as a gradient of scalar potential phi (φ) known as velocity potential. One of the oldest methods is strip theory method where ship is descretized into number of 2D strips. Other methods are panel methods where entire hull is descretized into number of panels. These are also known as Green’s function methods. Various formulations of Green’s function do exist. In a recent development Green’s function methods are extended to Rankine Panel method (RPM) where free surface in the vicinity of vessel is panelized for computations. In RPM Green’s function computations are made easy. Again these methods are divided into frequency domain and time domain. Time domain methods take into account various nonlinearities which generally cannot be handled by frequency domain methods. For zero and non-zero forward speed of the vessel different formulations exist. All these methods have their own advantages and disadvantages. Hence, it is very important in the initial design stage to decide on method of seakeeping analysis. Here an attempt is made to compare the results of seakeeping analysis using various tools based on various seakeeping methods.

Elastodynamic Green’s Function for Laminated Anisotropic Circular Cylinders

1999 ◽  
Vol 66 (3) ◽  
pp. 665-674 ◽  
Author(s):  
W. Zhuang ◽  
A. H. Shah ◽  
S. B. Dong
Keyword(s):  
Green’S Function ◽  
Cross Section ◽  
Green's Function ◽  
Material Properties ◽  
Integral Transform ◽  
Circular Cylinders ◽  
Element Formulation ◽  
System Of Equations ◽  
Numerical Implementation ◽  
Cylindrically Anisotropic

The construction of a steady-state Green’s function for a laminated anisotropic circular cylinder is presented herein. The cylinder’s profile through its depth consists of any number of perfectly bonded, uniform thickness concentric cylindrical layers, with each able of having its own distinct elastic cylindrically anisotropic properties. Green’s function is predicated on the superposition of numerically generated modal solutions from a system of equations based on a semi-analytical finite element formulation. Two methods are proposed for its construction, both relying on the same set of eigendata. One is by means of an integral transform. The other may be viewed as the forced vibration of a cylinder with cylindrically monotropic properties under symmetry/antisymmetry conditions on the cross section containing the source load. The second method, being more restrictive with respect to material properties, was intended primarily as a cross-check of the integral transform version of Green’s function. Numerical implementation details are discussed in terms of two example thickness profiles to show the essential keys for the convergence and accuracy of Green’s function.

Sign in / Sign up

Export Citation Format

Share Document