WHAT is it:
Dynamic Analysis constitutes Harmonic, Transient, and Random Vibrations.
WHEN to use:
If an external load depends on the frequency, varies with time or if its non deterministic i.e random.
WHY do we need:
Static Analysis gives us a rough idea of the behavior of the structure. However we shouldn’t neglect the fact that all structures are exposed to operating conditions that are dynamic in nature. The stress level obtained in a dynamic loading is much smaller and closer to the actual stress undergone by the structure in the real time application. Dynamic analysis is of extreme importance when the excitation frequency of the applied load coincides with the natural frequency of the structure to avoid Resonance. Response of the system when subjected to impulsive load/random vibrations can be carefully evaluated. If a non-linear material is used in such an analysis, it leads to Non-linear Dynamic Analysis. After an excellent description of non-linear analysis in the previous tech blog entry, we will focus on Linear Dynamic Analysis.
HOW to apply:
HARMONIC ANALYSIS
- Define Material Properties.
- Specify Restraints (Operating Conditions).
- Apply Harmonic Analysis properties as shown below.
- Run the Analysis.
- Predict the results.
IMPACT LOADING
- Define Material Properties.
- Specify Restraints (Operating Conditions).
- Apply Impact load properties as shown below.
- Run the Analysis.
- Predict the results.
RANDOM LOADING
- Define Material Properties.
- Specify Restraints (Operating Conditions).
- Apply PSD data as shown below.
- Run the Analysis.
- Predict the results.
SUMMARY:
To get the results of any type of analysis is like half battle won. The real challenge is to analyze and interpret the results correctly and correlating to physical test or to its application in the real world. Never expect an even distribution of stress across a symmetrical structure under dynamic loading. The first few natural frequencies are of primary concern and a careful study should be done by plotting the results with the response plot. Avoid resonance by varying the frequency either by adding or removing the material from the structure. Never forget to plug in the damping in the system else the results have little value. Mass Participation factor is also critical for the validity of the results.
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