Page 129 - Marine Structural Design

Chapter 6 offshore Structural Analysis 105

6.2.3 Design Brief

A Design Brief document lists the procedures to be adopted in’the initial stages of the design
process as follows:
Analysis Models
A general description of models to be utilized, including the description of:
Global analysis model(s)
Local analysis model(s)
Load cases to be analyzed
Analysis Procedures
A general description of analytical procedures to be utilized including a description of the
procedures to be adopted with respect to:
The evaluation of temporary conditions
The consideration of accidental events
The evaluation of fatigue actions
Air gap evaluation
The establishment of dynamic responses (including methodology, factors, and relevant
parameters)
The inclusion of ‘built-in’ stresses
The consideration of local responses (e.g. those resulting from mooring and riser actions,
ballast distribution in tanks as given in the operating manual etc.)
. Consideration of structural redundancy
Structural Evaluation
A general description of the evaluation process including:
Description of procedures to be completed when considering global and local responses
Description of fatigue evaluation procedures (including use of design fatigue factors, SN-
curves, basis for stress concentration factors (SCFs), etc.)
Description of procedures to be completed during the code check

6.3 Use of Finite Element Analysis

6.3.1 Introduction
Basic Ideas Behind FEM
The finite element method is a powerful computational tool that has been widely used in the
design of complex marine structures over the decades. The basic idea behind the finite element
method is to divide the structure, into a large number of finite elements. These elements may
be one, two or three-dimensional. The finite element model may be in the form of a truss of
members connected at nodal points, or a detailed assembly of elements representing an entire
structure, or a particularly complex and critical component of the structure.