Vessel data: Externally calculated primary motion

Externally calculated primary motion enables you to impose a motion on the vessel that is calculated programmatically in your own external function. Typically the calculation will be based on values of variables which change as the simulation proceeds – if not, it may be preferable to use a time history to impose an entirely pre-calculated motion.

To use externally-calculated primary motion:

On the calculation page of the vessel data form, set the primary motion to be externally calculated.
In the external functions section of the variable data form, set up a variable data source that has the details of your external function.
On the primary motion page of the vessel data form, set the externally calculated primary motion to the external function variable data source that you have set up, and set the origin to the coordinates (in vessel axes) of the point on the vessel whose motion your external function specifies.

Unlike most standard external functions, the externally calculated primary motion external function returns multiple values per call: position, orientation, velocity, angular velocity, acceleration and angular acceleration. These values are returned in a TExternallyCalculatedImposedMotionStructValue struct, documented in full in the OrcFxAPI help.

Note:

If the imposed motion consistent with solver option is checked (implicit integration scheme only), then only the position and orientation values are needed. The returned velocity, angular velocity, acceleration and angular acceleration values will be ignored, and instead will be determined by the solver.