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Offsets components

The Offset tab defines a list of individual offsets applied to Floaters that may be used to define combined environments from the Combination Matrix tab.

Warning

Offsets are prescribed quasi-static displacements that apply to Floater components only.

Note

The type of prescribed displacements that may be defined within the tab does not cover all types of imposed displacements available within the Imposed Displacements component and is limited to certain predefined types for the sake of simplicity.

The Offset tab includes 2 sheets labeled Offsets list and Quasi-static evolution.

Offsets list data sheet

The Offset List sheet includes the following items:

  • Number of offsets: The number of offset components must be set with the spin box located in the upper right corner of the tab. You may either use the up/down arrows to setup the number of offsets, or input any value using your keyboard and then pressing the ENTER key. Pressing the ENTER key confirms the number of individual components to be included and generates the main offset data table with appropriate number of rows.

  • Insert new offsets: Pressing this button inserts a new row in the main offset data table.

  • Remove selected offsets: Pressing this button deletes the selected rows from the main offset data table.

  • Offsets data table: This table is used to define the offset data. This table includes 8 columns, as follows:

    • Name: This assigns names that will be used to refer to the offset components in the Combination matrix tab.

    • Object: Used to select the Floater to which the offset will apply. Each cell in this column contains a drop-down list filled in with the names of all floaters components available in the model.

    • Location: Used to select the point on the floater at which the offset will apply. Each cell in this column contains a drop-down list filled in with the list of points including the COG and all fairleads/hang-off points defined in the floater component.

    Note

    Selecting a fairlead or hang-off point instead of the COG allows applying rotations (e.g. yaw) about the turret axis for turret moored vessels.

    • Heading (deg): Defines the heading of the horizontal displacement with respect to the global X-axis.

    • Amplitude (m): Defines the amplitude of the horizontal displacement.

    • Yaw (deg): Used to define the yaw angle, i.e. the rotation about the local Z-axis.

    • Heel (deg): Used to define the heel angle, i.e. the rotation about the local X-axis.

    • Trim (deg): Used to define the roll angle, i.e. the rotation about the local Y-axis.

Quasi-static evolution data sheet

The Quasi-static evolution tab is used to set an evolution law (i.e. the ratio of displacement applied as a function of the quasi-static load step) that will be common to all offsets.

  • "Linear" means that the offset is applied progressively with a linear ramp between the first quasi-static step (i.e. no displacement at step 0)and the last quasi-static step (i.e. complete displacement at the last quasi-static step).

  • "User defined" allows selecting the rate of offset amplitude that is considered as a function of the quasi-static step.

Offset data restrictions

Types of displacement allowed within the Offsets tab are limited to the following:

  • Displacements imposed to Floaters components only (does not include displacements imposed to other types of structural components such as Lines, Buoys, Rigid Bodies, etc.)

  • Incremental displacements only (does not include Sinusoidal, Uniform acceleration and Time-dependant displacements types)

  • Horizontal displacements combined with heel, trim and yaw motion.

  • The incremental quasi-static evolution is similar for the horizontal displacement and the heel, trim and yaw rotations, i.e. the same displacement ratio table is used for all sub-loadings.

The above restrictions allow a simpler definition of each offsets within a simple table.

An example of Offset tab is shown below: