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4.6. Sample Harmonic Response Analysis (GUI Method) In this sample problem, you will determine the harmonic response of a two-mass-spring system. 4.6.1. Problem Description Determine the response amplitude (X i ) and phase angle ( i ) for each mass (m i ) of the system shown below when excited by a harmonic force (F 1 sin t) acting on mass m 1 . 4.6.2. Problem Specifications Material properties for this problem are: m 1 = m 2 = 0.5 lb-sec 2 /in k 1 = k 2 = k c = 200 lb/in Loading for this problem is: F 1 = 200 lb The spring lengths are arbitrarily selected and are used only to define the spring direction. Two master degrees of freedom are selected at the masses in the spring direction. A frequency range from zero to 7.5 Hz with a solution at 7.5/30 = 0.25 Hz intervals is chosen to give an adequate response curve. POST26 is used to get an amplitude versus frequency display. 4.6.3. Problem Diagram Figure 4.4. Two-Mass-Spring-System Diagram Sample Harmonic Response Analysis (GUI Method) 4.6.3.1. Set the Analysis Title 1. Choose menu path Utility Menu>File>Change Title . 2. Type the text "Harmonic Response of Two-Mass-Spring System" and click on OK. 4.6.3.2. Define the Element Types 1. Choose menu path Main Menu>Preprocessor>Element Type> Add/Edit/Delete . 2. Click on Add. The Library of Element Types dialog box appears. 3. Scroll down the list on the left to "Combination" and select it. 4. Click once on "Spring-damper 14" in the list on the right. 5. Click on Apply. 6. Scroll up the list on the left to "Structural Mass" and select it. 7. Click once on "3D mass 21" in the list on the right. 8. Click on OK. The Library of Element Types dialog box closes. Sample Harmonic Response Analysis (GUI Method)

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9. Click on Close in the Element Types dialog box. 4.6.3.3. Define the Real Constants 1. Choose menu path Main Menu>Preprocessor>Real Constants . 2. Click on Add. The Element Type for Real Constants dialog box appears.
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