Page 138 - Pipelines and Risers
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On-bottom Stabiliw 111
8.4 Special Purpose Program for Stability Analysis
8.4.1 General
There are several analysis methods available on which to base pipeline stability design. Three
different methods are used by pipeline industry:
1) Dynamic analysis
2) Generalized stability analysis
3) Simplified stability analysis
The choice of the above analysis methods is dependent on the degree of detail required in
results of the design analysis.
1) Dynamic analysis involves a full dynamic simulation of a pipeline resting on the seabed,
including modeling of soil resistance, hydrodynamic forces, boundary conditions and
dynamic response. It may be used for detailed analysis of critical areas along a pipeline, such
as pipeline crossings, riser connections etc. where a high level of detail is required on pipeline
response or for reanalysis of a critical existing line.
Software: PONDUS and AGA (1993) Software
2) The Generalized stability analysis is based on a set of non-dimensional stability curves,
which have been derived from a series of runs with a dynamic response model.
Software: PIPE
3) The Simplified stability analysis is based on a quasi-static balance of forces acting on the
pipe, but has been calibrated with results from the generalized stability analysis. The method
generally gives pipe weights that form a conservative envelope of those obtained from the
generalized stability analysis.
SOFTWARE: Purpose made spreadsheets (EXCEL, LOTUS 1-2-3)
A short description of the two computer programs, PONDUS and PIPE, are given below.
8.4.2 PONDUS
PONDUS is a computer model, which computes the dynamic response of a pipeline on the
seabottom due to wave and current excitation in the time domain. The response of the pipeline
is non-linear due to non-linear hydrodynamic forces and non-linear interaction between the
pipe and soil.
A 100 meter long pipeline section subjected to wave and current loading is modeled. The
pipeline is unconstrained at its free ends to simulate an infinitely long pipeline resting on a
flat seabed. The purpose of this model is to determine pipeline stability in terms of
