WS2-1 WORKSHOP 2 NORMAL MODES ANALYSIS OF A 2 DOF STRUCTURE NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation

WS2-2 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation

WS2-3 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation NORMAL MODES ANALYSIS OF A 2 DOF STRUCTURE n Problem Description u The purpose of this exercise is to study the Normal Modes of a simple 2 degree of freedom mass-spring structure. The structure is formed with 3 springs, each with spring constant value of The two end nodes of the springs are constrained while the middle nodes are attached with 0D masses. u User will submit this model to MSC.Nastran for a normal modes analysis and observe the two eigenvalues and eigenvectors.

WS2-4 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation NORMAL MODES ANALYSIS OF A 2 DOF STRUCTURE n Problem Description (cont.) Node IDNode Coordinate 1[0,0,0] 2[1,0,0] 3[2,0,0] 4[3,0,0] Table WS Figure WS2-1

WS2-5 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation NORMAL MODES ANALYSIS OF A 2 DOF STRUCTURE n Suggested Exercise Steps 1. Create the nodes according to the values given in Table WS Connect the nodes with bar elements. 3. Create 2 point elements to the two middle nodes. 4. Assign a spring properties to the bar elements with spring constant of Assign mass properties to the point elements. 6. Create the boundary conditions. 7. Submit the model to MSC.Nastran for analysis. 8. Attach the.XDB results file. 9. Post Process results – Create an animation of the mode shapes.

WS2-6 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation CREATE NEW DATABASE Create a new database called ws2.db. a.File / New. b.Enter ws2 as the file name. c.Click OK. d.Choose Default Tolerance. e.Select MSC.Nastran as the Analysis Code. f.Select Structural as the Analysis Type. g.Click OK. a b c d e f g

WS2-7 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 1. Elements: Create / Node / Edit Create 4 nodes using coordinates shown in Table WS2-1. a.Elements: Create / Node / Edit. b.Uncheck Associate with Geometry option. c.Uncheck Auto Execute d.Enter coordinate listed in Table WS2-1. e.Click Apply. f.Click on the Node Size icon to show the nodes. a b c e d e

WS2-8 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 2. Elements: Create / Element / Edit Create 3 bar elements to connect the nodes together. a.Elements: Create / Element / Edit. b.Select Bar in the Shape pull down menu. c.Pick the nodes from the screen to create 3 bar elements. You do not need to press apply if Auto Execute is checked a b c

WS2-9 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 3. Elements: Create / Element / Edit Create a point element at the two middle nodes. a.Select Point in the Shape pull down menu. b.Select the two middle nodes. If Auto Execute is checked, Apply does not need to be clicked. a b

WS2-10 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 4. Properties: Create / 1D / Spring Assign the Spring Element Properties to the bar elements. a.Properties: Create / 1D / Spring. b.Enter spring for the Property Set Name. c.Click on Input Properties button. d.Enter 1000 for the Spring Constant. e.Select UX from the pull down menu for Dof at Node 1 and Node 2. f.Click OK. g.Click in the Select Members box, and select Bar Element selection tool from menu. Select all the bar elements. h.Click Add. i.Click Apply. a b c g h i d e f g

WS2-11 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 5. Properties: Create / 0D / Mass Assign the Mass Element Properties to the point elements. a.Properties: Create / 0D / Mass. b.Enter m1 for the Property Set Name. c.Select Lumped option. d.Click on Input Properties button. e.Enter 20 for the Mass. f.Click OK. g.Click in the Select Members box, and select Point Element selection tool from the menu. Select the Point element on the left. h.Click Add. i.Click Apply. a b d g h i e f g c

WS2-12 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 5. Properties: Create / 0D / Mass (Cont.) Assign the Mass Element Properties to the point elements (cont.). a.Enter m2 for the Property Set Name. b.Click on Input Properties button. c.Enter 40 for the Mass. d.Click OK. e.Click in the Select Members box, and select Point Element selection tool from menu. Select the Point element on the right. f.Click Add. g.Click Apply. a b e f g c d e

WS2-13 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 6. Loads/BCs: Create / Displacement / Nodal Create the boundary condition. a.Loads/BCs: Create / Displacement / Nodal. b.Enter fixed for the New Set Name. c.Click on the Input Data button. d.Enter for Translations and for Rotations. e.Click OK. f.Click on Select Application Region. g.Change the Geometry Filter to FEM. h.Select the 2 nodes at the end. i.Click Add, and click OK. j.Click Apply. a b c d e f g h i j i

WS2-14 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 6. Loads/BCs: Create / Displacement / Nodal (Cont.)

WS2-15 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 6. Loads/BCs: Create / Displacement / Nodal (Cont.) Create the boundary condition (cont.). a.Loads/BCs: Create / Displacement / Nodal. b.Enter make_1d for the New Set Name. c.Click on the Input Data button. d.Enter for Translations and for Rotations. e.Click OK. f.Click on Select Application Region. g.Change the Geometry Filter to FEM. h.Select the 2 nodes in the middle. i.Click Add, and click OK. j.Click Apply. a b c d e f g h i j i

WS2-16 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 6. Loads/BCs: Create / Displacement / Nodal (Cont.)

WS2-17 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 7. Analysis: Analyze / Entire Model / Full Run Submit the model for analysis. a.Analysis: Analyze / Entire Model / Full Run. b.Enter mass2_k3_ex for the Job Name. c.Click on Solution Type. d.Select NORMAL MODES. e.Click on Solution Parameters button. f.Make sure the value for Wt.-Mass Conversion is 1.0. g.Click OK. h.Click OK. a b c d e h g f

WS2-18 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 7. Analysis: Analyze / Entire Model / Full Run (Cont.) Submit the model for analysis (cont.). a.Click on Subcases. b.Select Default in the Available Subcases field. c.Click on Subcase Parameters button. d.Change the Number of Desired Roots to 2. e.Click OK. f.Click Apply to apply the changes made to the Default subcase. g.Click Cancel to exit the Subcases menu. h.Click Apply to submit the model to Nastran for analysis. a b c f e d h g

WS2-19 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 8. Analysis: Access Results / Attach XDB / Result Entities Attach the XDB result file. a.Analysis: Access Results / Attach XDB / Result Entities. b.Click on Select Result File. c.Select mass2_k3_ex.xdb. d.Click OK. e.Click Apply. a b c d e

WS2-20 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 9. Results: Create / Deformation Create a Deformation of the first mode. a.Results: Create / Deformation. b.Select the Mode 1. c.Select Eigenvector, Translational in the Select Deformation Result box. d.Click on the Display Attribute icon. e.Increase the thickness of the Line Width using the pull down menu. f.Click Apply. g.Increase the node size by typing node_ size(30) in the Command Line. Hit Enter. b c d e a f g

WS2-21 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 9. Results: Create / Deformation (Cont.) Create an animation of the mode shape. a.Preferences / Graphics b.Make sure the Hardware Rendering option is checked. c.Click Apply. d.Click Cancel. e.Return to the Create / Deformation form, and click on the Animation Option icon. f.Select 2D option in the Animation Graphics field. g.Check the Animate box. h.Click Apply. b c d e a f g h

WS2-22 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Step 9. Results: Create / Deformation (Cont.)

WS2-23 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation Summary Summary of Frequencies and Modes for project _______________ ModeFreq (Hz) Description

WS2-24 NAS122, Workshop 2, August 2005 Copyright 2005 MSC.Software Corporation