Seabed Contact Modelling |
 
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Seabed Contact Modelling |
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Elastic seabed contact is modelled via a direct augmentation of the global stiffness matrix (as opposed to using boundary conditions as in the rigid seabed case) at appropriate locations. Incorporation of some degree of elasticity is typically beneficial when modelling situations of intermittent contact, as the stiffness terms tend to cushion any impact between the structure and the seabed.
The elastic seabed contact algorithm also provides further options for modelling Lateral Resistance to horizontal motion, vertical resistance within a Suction Zone, or non-linear elastic contact via the Embedment facility.
Rigid seabed contact is modelled in Flexcom by checking the positions of all nodes at every iteration. If a node is found to have penetrated the seabed, it is brought back to the mudline, and a boundary condition is applied in the direction normal to the surface to prevent further penetration.
Where there is a large amount of intermittent seabed contact, using a rigid seabed may require relatively small time-steps in order to accurately capture the intermittent impact and avoid high frequency noise, possibly leading to protracted simulation run-times. In such circumstances, it may be beneficial to invoke the elastic seabed option instead, and select a reasonable value of contact stiffness.
Rigid seabed contact is also further complicated by issues of Seabed Penetration, Negative Contact Reactions and the application of Global Boundary Conditions. In summary, the elastic seabed contact model is the preferred option, except in cases of exceptionally high contact stiffness.