Solution Criteria Automation |
 
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Solution Criteria Automation |
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Flexcom allows you to specify desired values of critical solution parameters, and the program automatically adjusts the model configuration to satisfy the specified criteria. For example, you could specify the maximum allowable bending moment in the touchdown zone for an SCR, or the desired hang-off angle at the vessel connection. You also have control over how the model is to be adjusted, for example using a vessel offset or a change in line length. The increased automation provided by this new feature will expedite model set-up and improve engineering productivity.
Note that criteria apply to static analyses only. Required criteria may be specified in an initial static analysis, or in any subsequent static restart analysis. Automation on solution parameters is not possible in a dynamic simulation.
The inputs are defined in terms of a criterion type (i.e. a solution parameter), a criterion monitor (i.e. a particular region of interest), a target value and, optionally an allowable tolerance on the target.
Most of the criteria types represent standard program outputs, but a small number require further elaboration. The full list of accepted criteria is as follows.
1.Axial Stress.
2.Axial Strain.
3.Bending Stress.
4.Bending Strain.
5.Bending Moment.
6.Hangoff Angle. This is the angle in degrees that the specified element is required to make with the global x-axis. Note that unlike many of the other criteria types, a single element (rather than a set of elements) is used to monitor the hang-off angle.
7.Support Reaction. This is the contact reaction force at a guide surface. Note that unlike many of the other criteria types, the name of a guide surface (as opposed to a set of elements) is used to monitor the contact reaction.
8.Seabed Contact. This is the reaction at a node or nodes due to contact with the seabed. Note that unlike many of the other criteria types, a single node, or set of nodes (as opposed to a set of elements) is used to monitor the seabed contact reaction.
9.Tension.
10.Von Mises Stress.
You have control over how the requested criteria are to be achieved. For example, the adjustment variable may be a node, a vessel, or an element set. In the case of a node or vessel adjustment, Flexcom moves the selected node or vessel along a line parallel to the designated vector as it attempts to satisfy the specified criteria. Regarding the selected vector, Flexcom initially applies motion in a positive sense with respect to the vector, so the vector should ideally be set up such that it tends to aid criteria convergence if possible. In any case, Flexcom will immediately switch to motion in a negative sense if criteria divergence is exhibited in the first iteration. In the case of an element set length adjustment, Flexcom will adjust the length of the selected element set as it attempts to satisfy the specified criteria. The initial change in length may be positive or negative – Flexcom automatically estimates the direction most likely to aid criteria convergence.
Multiple criteria may be specified in a single analysis. If this is the case, the order in which the criteria are specified determines the priority. Specifically, Flexcom will attempt to satisfy the first criteria, and only proceed to the second and subsequent criteria after the first has been satisfied. While multiple criteria may be specified, only one parameter can be iterated upon in order to satisfy the specified criteria.
The solution parameters should only be varied if Flexcom is finding it difficult to attain a configuration which satisfies the specified criteria. The default values are adequate for the majority of analyses. For example, you may wish to reduce the Min Adjustment to ensure convergence if you have specified a very small deviation tolerance for your criterion. The minimum adjustment defaults to 0.1m or 0.328ft (or 0.1 degrees for angular adjustments), and the maximum adjustment defaults to 50m or 164.042ft (or 10 degrees for angular adjustments), depending on the unit system being used. Note also that there is no need to specify the time step under the *TIME keyword because the number of solution steps is automatically governed by the Max Iterations input.
•*CRITERIA is used to specify certain criteria that need to be satisfied in a static analysis, and to define how the model is to be adjusted to satisfy the desired criteria.
•*PRINT is used to request additional printed output to the main output file. Specifically, the OUTPUT=CRITERIA option is used to request additional information regarding solution convergence towards specified criteria.
If you would like to see an example of how these keywords are used in practice, refer to B01 - Steel Catenary Riser.