Loads and Constraints

The loads and constraints discussed within this section are applicable specifically to nonlinear analyses. Additional loads and constraints are covered in the Loads and Constraints section under General Information (Applicable to Multiple Analysis Types).

Important: Also, please refer to the information under the General Considerations heading and the Application of Loads and Constraints at Duplicate Vertices heading on the General Loads and Constraints page.

Loads

Loads in a nonlinear analysis can vary over the duration of the analysis. This is controlled by load curves. Most loads are assigned to a load curve. Multiple loads can follow the same load curve, and in most cases, individual loads can be assigned to different load curves. See the list below.

Also, some element types can be used to create loads. Truss elements and beam elements have preloads which are not assigned to a load curve. Actuator elements can be used to control the distance between two nodes; the actuator elements in each part can be assigned to different load curves.

Load curves can be created using two methods. First, the Load Curve Editor can be accessed directly from the load dialog. Second, the Load Curves tab in the Analysis Parameters dialog can be used.

Click the link to the load that you need more information about.

Loads	Load Curve
Beam Preloads	Add an initial load to beam elements to create preload and pre-stress.
Centrifugal Loads	Entire model follows the centrifugal load assigned to one load curve.
Distributed Loads	Different distributed loads can be assigned to different load curves.
Forces	Different forces can be assigned to different load curves.
Gravity or Acceleration	Entire model follows gravity assigned to one load curve.
Hydrostatic Pressure	Pressure on different surfaces can be assigned to different load curves.
Initial Velocity	Velocities are not assigned to a load curve.
Lumped Masses	Masses are not assigned to a load curve.
Moments	Different moments can be assigned to different load curves.
Prescribed Displacement	Different displacements can be assigned to different load curves.
Pressures or Tractions	Pressure on different surfaces can be assigned to different load curves.
Probes	Not exactly a load, but a marker to a node in the model which affects other loads.
Remote Loads and Constraints	Load curve based on type of load applied.
Temperatures	All temperatures follow one load curve.
Variable Loads	Pressure on different surfaces can be assigned to different load curves.
Voltages	All voltages follow one load curve.

Note:

The MES Riks analysis does not use any loads other than nodal forces and moments.
Natural Frequency (Modal) with Nonlinear Materials does not use any loads other than lumped masses.

Constraints

Constraints are constant throughout the analysis. Naturally, the impact planes and surface-to-surface contact affect the model only when the parts are in contact. Otherwise, the input values are constant throughout the entire analysis.

Tip: Prescribed displacements can be used in place of boundary conditions when the node needs to be released at some time. The prescribed displacement can be given a death time to release the node.