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Analyses and Scripts

Creating and Running a Forced Vibration Analysis

1.	From the Vibration menu, point to Test, and then select Vibration Analysis.

2.	Select New Vibration Analysis.

3.	Create your analysis as described in the dialog box help for Perform Vibration Analysis, being sure to select Forced Vibration Analysis.

4.	Optionally select Create Multi-Run Script and following the instructions in Create Vibration Multi-Run Script.

5.	Select OK.

6.	Adams/Vibration performs a forced vibration analysis. The process runs quickly. If no error messages appear, you can assume the vibration analysis completed correctly. If you receive error messages, correct the problem, and rerun your analysis.

 

Note:

You cannot combine vibration actuators of the non-PSD-type with PSD-type vibration actuators in the same vibration analysis.

Creating and Running a Normal Modes Analysis

1.	From the Vibration menu, point to Test, and then select Vibration Analysis.

2.	Select New Vibration Analysis.

3.	Create your analysis as described in the dialog box help for Perform Vibration Analysis, being sure to select Normal Modes Analysis.

4.	Optionally, select Create Multi-Run Script and follow the instructions in Create Vibration Multi-Run Script.

5.	Select OK.

Adams/Vibration performs a normal modes analysis. The process runs quickly. If no error messages appear, you can assume the vibration analysis completed correctly. If you receive error messages, correct the problem, and rerun your analysis.

Modifying Existing Analyses

1.	From the Vibration menu, point to Test, and then select Vibration Analysis.

2.	Select Vibration Analysis.

3.	In the corresponding text box, enter the name of your existing vibration analysis.

4.	Make changes as necessary.

5.	Select OK to run your analysis.

Vibration Analysis Calculation Methods

Vibration analysis is a frequency domain simulation of Adams models. This simulation can be a normal modes analysis in which the Eigenvalues and mode shapes for the model are computed. The frequency domain simulation can also be a forced response analysis using the input and output channels along with the vibration actuators.

•	Frequency Response

•	Modal Coordinates

•	Power Spectral Density (PSD)

•	Transfer Function

Frequency Response

Frequency response is the magnitude and phase response produced by a given input channel, at a given omega, for a given output channel.

For frequency response computation, the linearized model is represented as:

sx(s) = Ax(s) + Bu(s)

y(s) = Cx(s) + Du(s)

where:

•	s is the Laplace variable

•	A, B, C, and D are state matrices for the linearized model

The system transfer function can be represented as:

where:

•	H(s) is the transfer function for the model

•	I is the identity matrix of dimension equal to the number of system states

For a given vibration analysis, the system frequency response is given as:

Modal Coordinates

Modal coordinates are states in the frequency domain solution associated with a specific mode. Modes most active in a frequency response can be identified from the modal coordinates. The modal coordinates are computed as:

Power Spectral Density (PSD)

PSD of output channels for given input PSDs is given as:

where:  

•	p(s) is the matrix of power spectral density

•	H*(s) is the complex conjugate transpose of H(s)

•	U(s) is the matrix of input spectral density

The matrix of input spectral densities is a diagonal matrix with the vibration actuator PSDs on the diagonal locations. Off-diagonal locations of this matrix are populated with cross-correlation PSD specification.

For example, for a model with two input channels with actuators of type PSD:

where:  

•	U1(s) is the PSD of input channel 1

•	U2(s) is the PSD of input channel 2

•	U12(s) is the cross correlation PSD of input channel 1 to input channel 2

•	U21(s) is U12(s)

Transfer Function

Transfer function is a basic property of a model, and is computed as the magnitude and phase response at a given output channel for a given input channel with a unit swept sine vibration actuator.

For frequency response computation, the linearized model is represented as:

sx(s) = Ax(s) + Bu(s)

y(s) = Cx(s) + Du(s)

where:  

•	s is the Laplace variable

•	A, B, C and D are state matrices for the linearized model

The system transfer function can be represented as:

where:  

•	H(s) is the transfer function for the model

•	I is the identity matrix of dimension equal to the number of system states

Creating a Multi-Run Script

You can create a simulation script that you can use during multi-run simulations (such as design studies, design of experiments, and so on).

To create a multi-run script:

1.	Perform one of the following:

• From the Vibration menu, point to Test, and then select Create Multi-Run Script.

• From the Vibration menu, point to Test, and then select Vibration Analysis. In the Perform Vibration Analysis dialog box, select Create Multi-Run Script.

2.	Complete the dialog box as described in Create Vibration Multi-Run Script.

3.	Select OK.

Specifying Solver Settings

You can specify the default solver options for your simulation.

To specify the solver settings:

1.	From the Vibration menu, point to Test, and then select Solver Settings.

2.	Complete the dialog box as described in Solver Settings - Solver Executable.

3.	Select OK.