A gravity or acceleration load applies an acceleration value to any part that has a mass density defined. The acceleration can be applied along any direction.
In the case of Linear analyses (Static Stress, Modal with Load Stiffening, and Critical Buckling) and Flow through Porous Media analysis, the acceleration value is constant. For Nonlinear analyses (MES and Static Stress with Nonlinear Materials) and Fluid Flow analyses (Steady, Unsteady, and Open Channel Flow), the acceleration is controlled by a load curve and can be increased gradually and/or otherwise varied over time.
Apply Gravity/Acceleration
To apply a gravity or acceleration load to a model, right-click the Gravity/Acceleration heading under the Analysis Type heading in the tree view and select the Edit command. Note that the text of this command will be gray before gravity is activated and defined. However, it is not grayed-out. That is, the heading is still right-clickable and the Edit command is available. The heading text becomes black once gravity is set up.
To apply the acceleration due to gravity on Earth, press the Set for standard gravity button. The standard value for the acceleration of gravity is applied in the units of the model. To apply a different acceleration magnitude, specify this in the Acceleration due to body force field. Next, use the X multiplier, Y multiplier, and Z multiplier fields to define the vector along which the acceleration is applied. Specifying a value in only one of these fields applies the acceleration in that direction. Specifying values in more than one of these fields applies the acceleration along an arbitrary vector. The value in the Acceleration due to body force field is multiplied by the values in these three fields before it is applied to the model in that direction.
The X, Y, and Z multiplier values are not normalized to a unit vector, as they are for many other types of loads. Consider the following two examples:
- If you wish to apply standard gravity at a 45° angle between the +X and -Z directions, click the Set for standard gravity button, set the X multiplier to 0.707107 and set the Z multiplier to -0.707107. Tip: cos (45°) = 0.707107
The resultant vector is 1.0 and is in the desired direction.
- If you wish to simultaneously apply a 3g acceleration in the -Y direction and a 5g acceleration in the -Z direction, click the Set for standard gravity button, set the Y multiplier to -3, and set the Z multiplier to -5.
In the case of Nonlinear or Fluid Flow analyses (Steady, Unsteady, and Open Channel Flow), choose the load curve that will control the gravity/acceleration load using the available pull-down list. The load curve must be previously defined and the model saved in order for it to appear in this list.
When gravity is applied to the model, an arrow appears on the model showing the direction of the gravity load in both the FEA Editor and the Results environment. The gravity arrow can be shown in the display area at either of these locations:
- At the center of the box that encloses the model. If parts are hidden, shown, deactivated, or activated; the location of the arrow updates when the model is enclosed (View
Navigate Enclose). - Super-imposed on the mini-axis. Use the
Options Graphics Mini-axis Include gravity (when applied) check box to control where the gravity arrow appears at.
In the FEA Editor, the gravity arrow itself can also be shown or hidden by right-clicking on the Gravity/Acceleration entry in the tree view which is located underneath the Analysis Type entry.