Introduction |
 
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Introduction |
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This example considers the deployment of landing string through a marine riser. The simulation is performed in a series of separate stages, considering different lengths of landing string deployed, in conjunction with various degrees of lateral vessel offset. The following points are noteworthy:
•The model is heavily parameterised, making extensive use of Parameters and Equations. In addition to being QA friendly, the template file readily accommodates any changes which may need to be made subsequently. For example, the number of riser joints is parameterised (e.g. setting RJ1_N = 8 means that the riser stack-up contains 8 riser joints of 'type 1'. So it's very easy to alter the number of joints present in the stack-up.
•Explicit units are assigned to every base/independent parameter in the model. Not only does this provide clarity to an engineer reading the keyword data, it also ensures consistency of units when defining secondary/dependent parameters. Metric units are used throughout this model, but it is also possible to mix units subsequently if you wish (e.g. by defining a wall thickness in inches).
•Each riser joint is modelled in detail, including its bare, buoyant and flange sections. To achieve this effect, line section groups are used to model Repeating Sub-Sections. These subsections are then used to automatically assemble the riser joint stack-up with relatively little effort required from the user.
•Pipe-in-pipe is used to model the interaction between the marine riser and landing string, in terms of both contact modelling and hydrodynamic forces.
•Separate Parameters are used to define to the number of landing string joints present within the marine riser and the horizontal vessel offset. The initial model has 4 landing string joints included, corresponding to 56m of landing string. It is gradually lowered into the marine riser, by incrementally adding 4 new joints each time, until finally there are 32 joints present, corresponding to 448m of landing string. Lateral vessel offsets of up to 12m are considered, in increasing increments of 2m from the mean vessel position on station. Keyword Based Variations are used to define all the required parameters, as this facility is ideally suited to parameters which vary in fixed increments. The combinations input is used to control the names and locations of generated keyword files. In this case, a separate folder is established for every landing string deployment stage, and individual file names within each folder reflect the various vessel offset cases considered.
•Summary Postprocessing is used to examine flex joint angles, effective tension and bending moment, for every individual simulation. After each individual analysis has completed, Flexcom produces a text-based Summary Output File for visual inspection, but more importantly it also creates a Summary Database File, which is effectively a binary version of the same data, for subsequent collation. Landing string deployment length and vessel offset are also defined as key parameters which uniquely identify each individual simulation.
•The Summary Postprocessing Collation facility subsequently assembles all the output data into a single Summary Collation Spreadsheet. It also presents the data graphically in the form of 3-dimensional Summary Collation Plots.