Analyses |
 
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Analyses |
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The base of the vertical riser is fixed in all degrees of freedom. The upper ends of the jumper hoses are attached to the vessel. The initial position of the vessel is specified with an undisplaced orientation of 90° to the global Y-axis in the YZ plane. The vessel RAOs are also specified.
The contact regions on the jumper hoses are defined in terms of element sets. When defining contact regions, it is important to specify reasonable data to prevent excessive runtimes, by ensuring that the program is not checking for contact between points that will never approach.
Depending on whether or not clashing is being modelled, a relatively high contact stiffness is specified (100 kN/m) or an insignificant one (specification of a token stiffness facilitates clearance computations for comparison purposes even though contact is effectively ignored).
The boundary conditions remain unchanged and are carried through automatically from the initial static analysis. Since vessel boundary conditions and RAO data have previously been input, dynamic motions are automatically applied with the onset of wave loading.
Where clashing effects are not being modelled, a fixed time step of 0.25s is used throughout the analysis. For the analysis which includes clashing, a variable time step is specified, and this allows the interaction between the jumper hoses to be accurately captured. Flexcom continually monitors the relative velocity of approaching lines, allowing the time step to be gradually reduced in anticipation of contact. Once the lines have separated after impact, the time step begins to increase again. This approach facilitates a robust and accurate contact model, while also ensuring an efficient simulation overall.