Page 185 - Pipelines and Risers

158 Chapter I1

large. Only a fraction of the kinetic energy of the trawl board is absorbed by the steel pipe
locally.

A Level-2 analysis is shown in Figure. 11.1. The notations used in this figure is defined as
below:

Trawl Board
- m, and m are the added mass and steel mass of the trawl board
- and ki are the trawl board out-of-plane and in-plane stiffness

Coating and Steel Shell
- hl represents the coating stiffness
- h2 denotes possible effect the coating has on the steel shell stiffness
- k, is the local shell stiffness of the steel pipeline

Pipe and Support
- m, is the effective mass of the pipe including hydrodynamic added mass
- kpb is the effective bending stiffness of the pipe
- hs is the effective soil stiffness acting on the pipe

--
Trawl Board -- coating and Steel Shell -- Pipe and Support w

Figure 11.1 Physical Model (Mass-Spring System) for Simulation of Impact Between Trawl Board and
Pipeline.

The local indentation curve including both steel pipe and insulation coating can be obtained
by finite element analyses using Static Local Shell Model. The steel pipe should be modeled
using geometrical and material nonlinear elements. Large deflection should be considered but
small strain theory might be applied. The sophistication of the elements for insulation coating
shall largely depend on the availability of the material properties from the insulationcoating
manufacturer.