Simulating unconstrained structures using Fictitious Support

A free body is a structure capable of motion without internal stress. It has one or more rigid-body degrees of freedom. The Inertia Relief option, located on the Parameters page of the Create Solution or Edit Solution dialog box, is an advanced option that allows you to simulate these unconstrained structures in a static analysis. Typical applications of inertia relief include modeling an aircraft in flight, an automobile on a test track, or a satellite in space.

When you use the Inertia Relief option in a SOL 103 – Response Dynamics solution, a Fictitious Support is required. If rigid-body motion is possible in the model, you must define these degrees of freedom as a reference system. The solver calculates displacements relative to the motion of the support points. The element stresses and forces are independent of any valid set of supports.

This object corresponds to the SUPORT bulk data entry in Simcenter Nastran. For theoretical information, see Rigid Body Supports and Description of Inertia Relief Using PARAM,INREL,-1 in the Simcenter Nastran User's Guide. For a discussion of how to properly support a model, see Modeling Considerations for Using SUPORT in the Basic Dynamic Analysis User's Guide.

Where do I find it?

• Choose Home tab→Loads and Conditions group→Fictitious Support .

• In the Simulation Navigator→right-click Simulation Objects→New Simulation Object→Fictitious Support.

How do I

Define rigid-body mode tolerance for Simcenter Nastran

Define Response Dynamics result types

Define the frequency range and number of modes to solve

Filter out modes according to their modal effective mass fraction

Import results and event data from I-deas

Learn more

Defining the Simcenter Nastran solution

Efficiency through restart analysis

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Simulating unconstrained structures using Fictitious Support, Simcenter 3D 2021.1 Series

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