2012 ANSYS, Inc. March 28, 2013 1 Release 14.5

14.5 Release

Workshop 4A Modal Analysis (Plate with a Hole)

ANSYS Mechanical Linear and Nonlinear Dynamics

2012 ANSYS, Inc. March 28, 2013 2 Release 14.5

Workshop 4A - Goals

Our goal is to determine the first 10 natural frequencies and mode shapes for the plate with the hole shown.

The plate is made of Aluminum.

Assume the plate is fully constrained at the hole.

As if the plate is tightly bolted down at the hole.

Fixed Center

2012 ANSYS, Inc. March 28, 2013 3 Release 14.5

Workshop 4A Project Schematic

From the project schematic, insert a new Modal system.

Import the Geometry file

plate.iges

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Workshop 4A - Preprocessing Edit the Engineering Data cell.

add Aluminum Alloy from the General Materials library to Engineering Data

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Workshop 4A - Preprocessing Return to the Project

Edit the Model cell to open the Mechanical application

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Workshop 4A Units In Mechanical, set the following units system:

in, lbm, lbf, F, s, V, A Degrees RPM

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Workshop 4A - Preprocessing Set the plate thickness to 0.1 in

Set the plate material assignment to Aluminum Alloy

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Workshop 4A - Environment Constrain the center hole.

highlight the Modal Branch to >Insert>Fixed Supports.

Switch to edge selection mode as necessary

Use Box Select, or drag single-select LMB around the hole to pick all applicable edge segments (4 edges)..

Click Apply in the Details window Reorient model as necessary throughout.

9

8

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Workshop 4A Modal Solution Check the Details of Modal Analysis Settings.

set Max Modes to Find to 10 set Calculate Stress Yes set Calculate Strain Yes

If you just want frequencies and shapes, you dont need to calculate stress or strain. It will save a little time to skip those calculations.

Solve the Modal analysis.

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Workshop 4A - Results After the modal solution is completed, review the modal shapes for each frequency.

Click on the Modal Solution Branch in the Tree. Then LMB on the top of the Frequency Column in the Tabular Data region, and >RMB>Create Mode Shape Results

This will automatically insert Total Deformation objects in the Tree for all modes solved.

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Workshop 4A - Results

To get an overall view of the Modal results step thru (LMB) the Total Deformation result objects for each mode.

You can also Animate (Play & Stop) the mode from the Timeline window.

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Workshop 4A - Comments Remember:

Displacements reported with mode shapes are relative and do not reflect the actual max magnitudes of the displacements. The actual magnitudes will depend on the energy input to the system (depends on forcing function).

Sometimes it is challenging to visualize the true mode shape from a simple contour plot.

Try the Vector Display instead. Adjust the Vector Scale slider as desired.

You can also animate the vector plot too.

Contour

Plot.

Difficult to

determine

deformation

directions

Vector

Plot

Arrows may

be more

intuitive in

some cases.