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Body Force

*Body Force, <option>
<element set name>, grav, <mag>, <dir1, dir2, dir3>

This command defines a body force acting on the volumes of 3D elements (or areas in 2D) within the specified <element set name>. All sub-arguments are mandatory.

Arguments

  • <option>

    Specifies how the load is applied over time. The following options are available:

    • instant: The full load is applied instantaneously at the beginning of the step.

    • ramp: The load increases linearly with time from 0 % at the start to 100 % at the end of the step.

    • Amplitude = <amplitude name>: Applies the load according to a predefined amplitude function.

  • <element set name>

    The name of the element set to which the body force should be applied.

  • grav

    A fixed keyword indicating that a gravity-type body force is to be applied, defined as the vector
    \(\boldsymbol{g} = (g_1, g_2, g_3)^T\).

  • <mag>

    The magnitude of the gravitational acceleration \(g = \|\boldsymbol{g}\|\), specified in units of L/T² (e.g. m/s²).

  • <dir1, dir2, dir3>

    A direction vector defining the direction of the gravity load: \(\hat{\boldsymbol{g}} = \boldsymbol{g} / \|\boldsymbol{g}\|\).

Example

To define a gravitational force of 9.81 m/s² acting in the negative z-direction on all elements in a 3D Cartesian coordinate system (with the z-axis pointing upwards), use:

\[ \boldsymbol{g} = \begin{bmatrix} 0 \\ 0 \\ -9.81 \end{bmatrix} = 9.81 \cdot \begin{bmatrix} 0 \\ 0 \\ -1 \end{bmatrix} \]

The corresponding numgeo command is:

*Body Force, instant
all, grav, 9.81, 0, 0, -1