Free span development and self-lowering of pipelines

The paper describes the numerical program, PIPESIN, that simulates the behavior of a pipeline placed on an erodible seabed. PIPEline Seabed INteraction from installation until a stable pipeline seabed configuration has occurred is simulated in the time domain including all important physical processes. The program is the result of the joint research project, ``Free Span Development and Self-lowering of Offshore Pipelines`` sponsored by EU and a group of companies and carried out by the Danish Hydraulic Institute and Delft Hydraulics. The basic modules of PIPESIN are described. The description of the scouring processes has been based on and verified through physical model tests carried out as part of the research project. The program simulates a section of the pipeline (typically 500 m) in the time domain, the main input being time series of the waves and current. The main results include predictions of the onset of free spans, their length distribution, their variation in time, and the lowering of the pipeline as function of time.