Mechanical APDL Structural Analysis Guide

5.3.4. Apply the Loads

You are now ready to apply loads for the analysis. The loads shown in Table 2.5: Loads Applicable in a
Static Analysis (p. 16) are also applicable to a transient dynamic analysis. In addition to these, you can
apply acceleration loads in a transient analysis (see DOF Constraints in the Basic Analysis Guide for more
information).

Except for inertia loads, velocity loads, and acceleration loads, you can define loads either on the solid
model (keypoints, lines, and areas) or on the finite element model (nodes and elements). In an analysis,
loads can be applied, removed, operated on, or deleted. For a general discussion of solid-model loads
versus finite-element loads, see Loading in the Basic Analysis Guide.

You can also apply time-dependent boundary conditions by defining a one-dimensional table (TABLE
type arra y parameter). See Applying Loads Using TABLE Type Array Parameters (p. 17).

Note

It is recommended that you use acceleration input to define support motion when applicable

(using the tabular arra y parameter definition on the D,,ACC or ACEL command). A displacement

input (D,,U command) is likely to show numerical noise, because it implies a discontinuity

in acceleration in the simulation. In this case, numerical damping (GAMMA on

the TINTP command) can be used to improve the acceleration and force results.

5.3.5. Save the Load Configuration for the Current Load Step

As described in Establish Initial Conditions (p. 110), you need to apply loads and save the load configur-
ation to a load step file for each corner of the load-versus-time curve. You may also want to have an
additional load step that ext ends past the last time point on the curve to capture the response of the
structure after the transient loading.
Command(s):LSWRITE
GUI: Main Menu> Solution> Load Step Opts> Write LS File

5.3.6. Repeat Steps 3-6 for Each Load Step

For each load step that you want to define for a full transient dynamic analysis, you need to repeat
steps 3-6.That is, for each load step, reset any desired solution controls and options, apply loads, and
write the load configuration to a file.

For each load step, you can reset any of these load step options:TIMINT,TINTP,ALPHAD,BETAD,
MP,ALPD,MP,BETD,TIME,KBC,NSUBST,DELTIM,AUTOTS,NEQIT,CNVTOL,PRED,LNSRCH,CRPLIM,
NCNV,CUTCONTROL,OUTPR,OUTRES,ERESX, and RESCONTROL.

An example load step file is shown below:

TIME, ...! Time at the end of 1st transient load step

Loads ...! Load values at above time

KBC, ...! Stepped or ramped loads

LSWRITE! Write load data to load step file

TIME, ...! Time at the end of 2nd transient load step

Loads ...! Load values at above time

KBC, ...! Stepped or ramped loads

LSWRITE! Write load data to load step file

TIME, ...! Time at the end of 3rd transient load step

Loads ...! Load values at above time

KBC, ...! Stepped or ramped loads

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Performing a Full Transient Dynamic Analysis