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Operation |
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When you want to perform a wake interference analysis with Flexcom, you model the upstream and downstream structures in the normal fashion, and indicate to Flexcom that you want to model wake interference by specifying appropriate wake interference data.
The two structures may be defined in separate models or combined in a single model (note that is not possible to model a situation where one structure is downstream of another and upstream of a third). Using separate models is appropriate where the two structures are independent (other than being hydrodynamically coupled) or stand-alone, for example top-tensioned drilling and production risers operating in close proximity on a drilling vessel or production unit. The use of a combined model is appropriate where the two components are not structurally independent, for example in the case of two jumper hoses in the same hybrid riser system.
If the upstream and downstream structures are being analysed separately, you need to perform a static analysis of the upstream riser subject to current loading before you can proceed to modelling the downstream structure. You inform Flexcom the name of the analysis with current of this structure. If both structures are defined in the same model, you specify the wake interference data when you are performing the static analysis of both structures subject to current loading. Regardless of which modelling strategy you use, the conduct of the wake interference analysis of the downstream structure is the same. At each iteration at each solution time, Flexcom computes a reduced current velocity profile at the downstream structure based on the configuration of both structures and the selected wake model (Huse’s, Blevins’ or user-defined). Obviously this can change from iteration to iteration depending on the results from the previous iteration, but eventually a converged static solution is achieved. Once this has been completed for all solution times, the analysis terminates in the usual way.
•*WAKE UPSTREAM is used to specify the composition of the upstream structure in terms of element sets, for use in wake interference calculations. The keyword also selects the wake interference model to be used, and defines associated data to characterise the wake field.
•*WAKE DOWNSTREAM is used to specify the composition of the downstream structure in terms of element sets for use in wake interference calculations. The keyword also facilitates the (optional) definition of lift coefficients in the case of a User-Defined wake interference model.