Seabed Penetration |
 
|
Seabed Penetration |
|
Checking for seabed contact with a rigid seabed takes place prior to the solution of the equations of motion. On the other hand, the determination of convergence criteria takes place just after the equations have been solved. A situation can occasionally occur where Flexcom deems convergence to have been achieved, but in fact one or more nodes have penetrated the seabed and would have boundary conditions applied if a further iteration were to occur. This can sometimes lead to unreasonable moments or stresses being reported.
In this case you can use the Rigid Surface Threshold Penetration entry to prevent this occurring. If you input any threshold value, it is an instruction to Flexcom to check all nodes for seabed penetration as part of the convergence checking after solving the equations of motion. Furthermore, if a node has penetrated the seabed to a depth greater than the threshold you specify here, then convergence cannot be deemed to have been achieved, regardless of the maximum convergence measure calculated in the normal fashion. The rationale for specifying a threshold is to prevent unnecessary iterating in the case for example of infinitesimal penetrations.
•*TOLERANCE is used to define the analysis convergence tolerance measure and related data, including the Rigid Surface Threshold Penetration input.