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Dynamic motion components

The Dynamic Motion tab defines a list of individual dynamic motions applied to any structural model components (such as Lines, Floaters; Rigid Bodies, Buoys, etc.) that may be used to define combined environments from the Combination matrix tab.

Warning

Dynamic Motions can only be accounted for within dynamic analyses in the time-domain. These dynamic loads are not accounted for within dynamic analyses in the frequency-domain.

The Dynamic Motion tab includes the following items:

  • Number of motions: The number of Dynamic Motion 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 Dynamic Motions, 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 Dynamic Motion data table with appropriate number of rows.

  • Insert new motion: Pressing this button inserts a new row in the main Dynamic Motion data table.

  • Remove selected motion: Pressing this button deletes the selected rows from the main Dynamic Motion data table.

  • Dynamic Motion data table: This table is used to define the Dynamic Motion data. This table includes 6 columns, as follows:

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

    • Object: Used to select the structural model component to which the Dynamic Motion will apply. Each cell in this column contains a drop-down list filled in with the names of all structural components available in the model (including lines, floaters, rigid bodies, buoys, etc.).

    • Location: Used to select the point on the structural component at which the Dynamic Motion will apply. Each cell in this column contains a drop-down list filled in with the list of points that is available with the selected structural model component (e.g. including the COG and all fairleads/hang-off points for Rigid bodies, Buoys and Floaters, and including all primary connection points for Lines).

    Warning

    Dynamic Motion would have no effect on the structural component in case this latter is left "free" (i.e. with no boundary condition applied to the node) or if the node is assigned a "fully blocked" boundary condition. The user interface does not raise any warning message in case the node to which the loads apply is not assigned an appropriate boundary condition.

  • Motion type: This selects whether the Dynamic Motion must be defined through "Displacement" or "Actual position" motion types.

    • "Displacement" motion type: this refers to motion relative to the position of the node at the initial time of the dynamic analysis. Motion data must then be specified relative to the coordinates of the node at the start of the dynamic analysis (i.e. the 6 displacement components at time zero must then all be zero). Rotation components are specified through Euler angles, i.e. roll, pitch and yaw angles.

    Note

    This motion type is defined in the LOG file with the *GMOVE2 keyword.

    • "Actual position" motion type: this refers to motion specified through the actual coordinates of the node expressed in the global XYZ coordinates system (i.e. the 6 displacement components at time zero may be non zero). Rotation components are specified through pseudo-rotation components, i.e. pseudo-rotations about the global X, Y and Z-axes.

    Note

    This motion type is defined in the LOG file with the *GMOVE3 keyword.

    Note

    Motion from any dynamic analysis may be automatically post-processed and saved along the appropriate file format by the FE engine by adding the *SAVEMOT keyword in the LOG file. This instructs the FE engine to create a text-based file in the analysis folder, which contains the actual position of selected nodes. In this file, the X, Y and Z coordinates are expressed in (m), and the X, Y and Z pseudo- rotations are expressed in (rad).

    Warning

    Pseudo-rotation components are not identical to standard roll, pitch and yaw angles. Pseudo-rotations are specific to DeepLines FE engine and conveniently allow modelling rotation matrices through the Rodrigues equation, as detailed in the theory section. Defining prescribed motion through actual position motion types then requires that the primary motion was recorded from another dynamic analysis.

  • File: Path and name of the external data file providing the time-history of the dynamic motion along the 6 degrees of freedom. The path could either be defined by typing the text or by browsing to the file after clicking the button placed on the right-hand side of the cells.

    The content of the file depends on the selected motion type, as follows:

    • The file format for "Displacement" motion types is shown below. The number of lines in the file is not limited.

    T0 DX DY DZ ROLL PITCH YAW
    T1 DX DY DZ ROLL PITCH YAW
    T2 DX DY DZ ROLL PITCH YAW
    TN DX DY DZ ROLL PITCH YAW

    where:

    T0, T1, ... are times values at which the displacement is defined

    DX DY DZ are the displacement along the X, Y and Z axes relative to the position of the node at the start of the dynamic analysis (in m). These components must then all be zero at time zero.

    ROLL PITCH YAW are Euler angles components relative to initial time (in rad). These components must all be zero at time zero.

    • The file format for "Actual position" motion types is shown below. The number of lines in the file is not limited.

    T0 X Y Z RX RY RZ
    T1 X Y Z RX RY RZ
    T2 X Y Z RX RY RZ
    TN X Y Z RX RY RZ

    where:

    T0, T1, ... are times values at which the actual position is defined

    X Y Z are the actual coordinates of the node expressed in the global XYZ coordinates system (in m).

    RX RY RZ are pseudo-rotations about the global X, Y and Z-axes (in rad)

Note

Motion data specified in the external text-based file are interpolated over the time through spline functions. Small time-steps may then be required to avoid spurious acceleration peaks.

Note

Incremental quasi-static displacements are ignored with the "Actual position" motion type. Actual position motion automatically forces the coordinates of the node at the last step of the quasi-static analysis to be similar to the coordinates specified defined in the first row of the external file.

An example of Dynamic Loads tab is shown below: