Mechanical APDL Structural Analysis Guide

3.3. Building the Model for a Modal Analysis

When building your model with the intention of performing a modal analysis, the following conditions
apply:

• Only linear behavior is valid in a modal analysis.

If you specify nonlinear elements, Mechanical APDL treats them as linear. For example, if you include

contact elements, their stiffnesses are calculated based on their initial status and never change. For

a prestressed modal analysis, the program assumes that the initial status of the contact elements is

the status at the completion of the static prestress analysis.

• Material properties can be linear, isotropic or orthotropic, and constant or temperature-dependent.

Define both Young's modulus (EX) (or stiffness in some form) and density (DENS) (or mass in some

form). Mechanical APDL ignores nonlinear properties.

• If applying element damping, define the required real constants for the specific element type (COMBIN14,
  COMBIN37, and so on). For more details about damping definition, see Damping (p. 2).

3.4. Applying Loads and Obtaining the Solution

In this step, you define the analysis type and options, apply loads, specify load step options, and begin
the finite element solution for the natural frequencies, as follows:

3.4.1. Enter the Solution Processor

3.4.2. Define Analysis Type and Options.

3.4.3. Apply Loads

3.4.4. Specify Load Step Options

3.4.5. Solve

3.4.6. Participation Factor Table Output

3.4.7. Exit the Solution Processor

3.4.1. Enter the Solution Processor

1. Enter the solution processor.
   Command(s):/SOLU
   GUI: Main Menu> Solution

3.4.2. Define Analysis Type and Options

After you have entered the solution processor, you define the analysis type and analysis options.
Mechanical APDL offers the options listed in Table 3.1: Analysis Types and Options (p. 40) for a modal
analysis. Each of the options is explained in detail below.

Table 3.1: Analysis Types and Options

Com- GUI Path

mand

Option

Main Menu> Solution> Analysis Type> New

Analysis

New Analysis ANTYPE

Main Menu> Solution> Analysis Type> New

Analysis> Modal

Analysis Type: Modal (see Note ANTYPE

below)

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Modal Analysis