Mechanical APDL Structural Analysis Guide

11.Review the Results (p. 118)

5.3.1. Build the Model

See Building the Model in the Basic Analysis Guide. For further details, see the Modeling and Meshing
Guide.

5.3.1.1. Points to Remember

Keep the following points in mind when building a model for a full transient dynamic analysis:

• You can use both linear and nonlinear elements.


• Both Young's modulus (EX) (or stiffness in some form) and density (DENS) (or mass in some form)
  must be defined. Material properties may be linear or nonlinear, isotropic or orthotropic, and constant
  or temperature-dependent.


• You can define damping using element damping, material damping and/or proportional damping
  ratios. For more details about damping definition, see Damping (p. 2).

Some comments on mesh density:

• The mesh should be fine enough to resolve the highest mode shape of interest.


• Regions where stresses or strains are of interest require a relatively finer mesh than regions where
  only displacements are of interest.


• If you want to include nonlinearities, the mesh should be able to capture the effects of the nonlinear-
  ities. For example, plasticity requires a reasonable integration point density (and therefore a fine
  element mesh) in areas with high plastic deformation gradients.


• If you are interested in wave propagation effects (for example, a bar dropped exactly on its end), the
  mesh should be fine enough to resolve the wave. A general guideline is to have at least 20 elements
  per wavelength along the direction of the wave.

5.3.2. Establish Initial Conditions

Before you can perform a full transient dynamic analysis on a model, you need to understand how to
establish initial conditions and use load steps.

A transient analysis, by definition, involves loads that are functions of time. T o specify such loads, you
need to divide the load-versus-time curve into suitable load steps. Each "corner" on the load-time curve
may be one load step, as shown in Figure 5.1: Examples of Load-Versus-Time Curves (p. 111).

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Transient Dynamic Analysis