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Transferring parent model state for restart analyses |
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Transferring parent model state for restart analyses |
If no data changes have been made between a restart analysis and its parent model, then all the state from the parent model is transferred into the child before the restart analysis is performed. This means that the restart picks up from exactly where the parent analysis left off, just like extending an existing simulation. Examples of such state include friction target positions, hysteretic bending history, vessel added mass and damping convolution integrals etc.
If data changes have been made, then OrcaFlex will still attempt to transfer any relevant state from the parent model. However, in practice, certain data changes may either render the parent state redundant or else be completely incompatible. In such cases, OrcaFlex will either:
Which policy is adopted depends upon the particular aspect of the model in question and the nature of the data that has changed.
| Note: | When we talk about data changes in this topic we obviously mean data whose values have been modified. But additionally we refer to data whose values have not been modified, but that have been marked as changed using the always mark selected items as changed item on the popup menu. |
For line seabed friction in a static restart, the treatment depends upon the line statics seabed friction policy. For line seabed friction in a dynamic restart, friction target positions are loaded from the parent simulation.
For other friction models (shape friction, line contact friction, supports friction), if the appropriate friction coefficient is non-zero, then OrcaFlex will attempt to load the friction target positions from the parent simulation. Failing this, it will initialise the restart analysis such that the friction target positions are equal to the contact positions at the start of the restart.
So long as key data are not changed in the restart, OrcaFlex will be able to load the friction target positions from the parent simulation. In a number of circumstances, however, data changes can make it impossible to load the target friction positions. For example:
Winches operate in two broad control modes: length-controlled and tension-controlled. In a restart, the winch state transferred is dictated by the control mode specified in the restart:
In a static restart, if the winch control value data is modified, then state is not transferred and the specified value is used in the restart analysis.
Hysteresis model state will be transferred from the parent simulation to the restart whenever the stiffness data is unchanged. If the stiffness data is changed in the restart, then the state is not transferred, and the hysteresis model is restarted as it would be in an initial analysis.
When the depressurised static model for line bending is selected, the depressurised model is always applied during static analysis (both for initial static analyses, and restarted static analyses). If you do not want this behaviour over a restart (e.g. you only want it in the initial static analysis) then you can change to the pressurised static model in the restart and hysteresis model state will be transferred.
The convolution integral used for frequency dependent added mass and damping loads is calculated using the history of vessel velocity. This history of velocity is transferred to the restart provided that statics is disabled for the restart, and that no data that impacts the convolution integral evaluation has been changed. These data are:
If any of this data is changed in the restart then the convolution integral is re-initialised with an empty velocity history.
For objects using the static position (interpolated) wave calculation method, the object's position at the end of the static analysis is used to determine the wave kinematics observed by the object. For a dynamic restart (i.e. a restart with statics disabled) the static position is transferred from the parent simulation and used in the restart for calculating the wave kinematics observed by the object.
In some circumstances, due to data changes, the static position cannot be transferred from the parent simulation, and the position at the start of the dynamic restart is used in its place.
In a simular vein, when using sea state RAOs that are interpolated on direction and period only (known informally as 2D interpolation), the interpolation is based on the static position of the object. Again, this static position will be transferred if no data changes have been made that would invalidate it.
Data changes that invalidate transferring static position include changes to:
When the line statics VIV method is set to either SHEAR7 or VIVA, the line's drag coefficients are calculated by the VIV program. These drag coefficients are calculated during the static analysis, and then used during subsequent dynamics. The drag coefficients will be re-calculated in a restart analysis, if and only if statics is enabled in the restart analysis.
Many externals functions are defined from the instantaneous state of the simulation. For externals functions of this nature, there is therefore no state to transfer for restart analyses. However, some external functions do depend on historical state. These are the external functions that respond to the eaStoreStateCreate action (for native external functions) or implement the StoreState method (for Python external functions).
For a dynamic restart (i.e. a restart with statics disabled) the external function state will usually be transferred from the parent simulation, and passed to the external function in the restart analysis. The state will not be transferred if any of the external function data (source, script, file name, function name or initial value) has changed.