Dynamic Analysis User Guide – A comprehensive user guide for Simcenter Femap and Nastran users

May 24, 2019

Vibration analysis is a huge topic and is easily the second most common type of FEA analysis after basic static stress analysis. Within the field of vibration analysis, the most common type of analysis is that based on the linear behavior of the structure or system during its operation. That is, its stress/strain response is linear and when a load is removed, the structure returns to its original position in a stress/strain free condition.

Although this might sound a bit restrictive, it actually covers a huge swath of structures from automobiles, planes, ships, satellites, electrical circuit boards, and consumer goods. If one needs to consider a nonlinear response of the structure during operation, there exist codes such as LS-DYNA that can solve for the complete nonlinear vibration response. But that is not simple or basic and is left for another seminar sometime in the future.

We’ve compiled all of our seminars and white papers from over the years into this one comprehensive document on vibration analysis.

PDF of Dynamic Analysis User Guide - Simcenter Femap User Guide (12 MB PDF)

TABLE OF CONTENTS

INTRODUCTION TO LINEAR DYNAMICS (SIMCENTER NASTRAN)
1. some examples of linear vibration analysis (predictive)
2. eigenvalue or normal modes analysis (gotta have mass)
FOUNDATIONS OF FREQUENCY ANALYSIS
1. baby’s first beam model.
  1. here’s your modal analysis checklist
  2. setting up the model for normal modes with mass participation
  3. interpreting results based on orthogonality and mass participation
  4. symmetry and frequency analysis
  5. significance of strain energy for frequency analysis
STANDARD NORMAL MODES ANALYSIS
1. model setup
2. natural frequency results and interpretation
  1. mass participation
MODAL FREQUENCY ANALYSIS
1. running a modal frequency analysis in Simcenter Femap and Simcenter Nastran
INTRODUCTION TO RANDOM VIBRATION
1. the psd function
2. the nx nastran method
3. psd units
EXAMPLE 1: PSD ANALYSIS OF PCB WITH TWO HEAVY ELECTRICAL COMPONENTS
EXAMPLE 2: CANTILEVER BEAM
1. problem definition
2. analytical solution
3. defining the system damping
4. creating the psd function
5. creating the modal frequency table/setting up the load set options for dynamic analysis
6. loading & constraining the model
7. specifying groups for nodal and elemental output
8. creating an analysis set – simple psd
9. interpreting the output
10. positive crossings
11. fatigue analysis using rms stress and positive crossings
12. fatigue analysis – time to failure
EXAMPLE 3: SOLID MESHED BEAM
1. analytical solution
2. psd function input
3. psd stress results
4. comparing miles’ approximation and psd results
DIRECT TRANSIENT ANALYSIS.
QUESTIONS AND ANSWERS ABOUT FREQUENCY ANALYSIS
BEING AN EXPERT: VIBRATION IS ABOUT MASS AND CONSTRAINTS
1. check fo6 for mass summation and know what you know
2. ground check if you are doing aerospace quality work
RANDOM VIBRATION CONCLUSION
INTRODUCTION TO RESPONSE SPECTRUM ANALYSIS
1. the accelerogram
2. creating a response spectrum
3. nx nastran method
RESPONSE SPECTRUM ANALYSIS EXAMPLE: CANTILEVER BEAM
1. problem definition
2. analytical solution
3. step 1: creating the fe model
4. step 2: defining the response spectrum
5. step 3: creating interpolation table
6. step 4: creating a modal damping function
7. step 5 creating the excitation node
8. step 6: constraining the model
9. step 7: setting up the analysis
10. post processing the results
11. results comparison
EXTRA CREDIT: SOLID MESHED BEAM
APPENDIX
1. flow chart from nx nastran theoretical manual
2. creating modal frequency table
3. autocorrelation function
4. multiple excitation spectrums
5. why we do a psd analysis

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