Page 453 - Pipelines and Risers

420 Chapter 22

- Frequency domain analysis

Static analysis
The static analysis is based on a complete non-linear formulation. To reduce computer time
there has been implemented a pre-processor based on catenary theory.
The analysis is used for establishing a pipe configuration for a specified set of conditions.
The results from the static analysis are listed below:
- Nodal point co-ordinates
- Curvature at nodal points
- Axial forces
- Bending moment
- Shearforces
- Torsion

Static parameter variation analysis
The purpose of this analysis is to determine the riser sensitivity to support vessel position,
external forces and current variations.
The results available are for the same parameters as for static analysis.

Dynamic time domain analyses including eigenvalue analysis
The purpose of this analysis is to determine the influence of support vessel motion and direct
wave induced loads on the system.
The results from the eigenvalue analysis are the systems eigenfrequencies and eigenvectors.
The results from the dynamic analysis are time series of a selected Iimited number of response
parameters, as listed in static analysis.

Results from RlFLEX (SINTEF, 1998)
The results from the above analyses are stored in separate files for subsequent post
processing, such as plots or calculation. Some of the more interesting output are listed below:

Plots
- System geometry
- Force variation along lines
- Pipe wall forces
- Geometry during variation of parameters

- Response time series
- Vessel motion transfer function
- Animation of the dynamic behavior of the complete system including support vessel and
exciting waves