Modal Analysis using Ansys Workbench
Modal Analysis using Ansys Workbench :
AIM:
- What is modal analysis?
- Purpose of modal analysis
- Types
- How to do model analysis?
- Conclusion
Analysis
- What is modal analysis?
Modal analysis look for natural frequency and normal mode of a structure.Natural frequency and modes are some of the important factors of a structure, they determine how the structure will respond .
- Purpose of modal analysis
By knowing naturing frequencies of a component we can design them to avoid specific ranges to prevent resonance.In this way we can design from car components, buildings, blades and any other component to prevent faliure of the structure.
- Types
Here three types of model analysis will discuss three types of model analysis-
1. Free free model analysis(models which are free to move like drones , boats , aeroplanes etc)
2. Models which have fixed boundary condition
3. prestressed model analysis(models which have an initial stress condition)
- How to do model analysis?
1. Free free model analysis:
First drag and drop modal
open designmodular by double click on geometry and we will design a rough structure for visualization.
Close designmodular and open model
Before going to model we can choose material of the model by clicking on engineering data.
Choose engineering data sources by right click
Then choose material
Then open project- geometry-solid and we can assign any material that we have added to the library
Then we can mesh the geometry and can assign sizing option
We can assign boundary conditions like fixed support, thermal condition , displacement etc by right click on model
We can see any solution from deformation, stress, strain etc by right click on solution
After assigning boundary conditions and preffered solutions right click on solution and click on solve
In tabular graph right click- select all - create mode shape results and in solution rigth click - evaluate all
Here we have choosen 16 modes from analytical settings.
What are modes?
Modes are the state of the model in a certain frequency by which we can find whether the model will be excited by force at this frequency in a certain direction.
Modes are the result of numbers of degrees of freedom in a certain model as there may be millions of DOF in a complex structure so there may be millions of modes.
so How we will find that how much mode we require to get satisfactory results.
As this is a free-free structure its first 6 freqency are zero or nrerer to zero.
In solution information we can see the participation factor and effective mass.
Participation factor and effective mass are both same in definaiton but different in mathematical notation resulting in to determine which frequency in what direction can lead to more excitation.
These are larger participation factor and effective masses - so in this frequencies and in that certain direction the body will be much more excited.
Now how will we find How to determine number of modes?
when ratio of effective mass and total mass is nearer to one that number of modes should be taken.
Video: Total deformation 16:https://www.youtube.com/watch?v=qJtjy9D1UHs
2. Models which have fixed boundary condition
We draw a simple beam.
After meshing we have taken fixed support here
After solving the model previously described
Results:
We can see maximum participation factor in x direction 1071.7hz and in z direction 905.47, so that the excitation is more in that frequency in that directions.
video:https://www.youtube.com/watch?v=0a_f_px0hbM
3.prestressed model analysis
For this case first we have to calculate stress for the geometry first and then its calculated stifness will be added to the modular stifness during model anlysis.
our first calculation may be linear or non-linear but model analysis will be always linear.
We first taking stating structure and fading modal to its solution.
We have taken a simple rectangular beam
Boundary conditions :
zero temperature with environment temperature 22 degree
Then we calculated normal stress in first solution
Total deformation of the first mode in second solution
Now we take parametric of - first solution normal stress- average
Thermal condition and Total deformation frequency
It had taken Thermal condition as input and normal stress and total deformation frequency as output.so varying the temperature we can get different outputs.
From this chart we can see that with increase in temperature normal stress decrease(compressive stress increase) and frequency increase.
Video :prestressed_model
Conclusion:
In this way we can conclude that modal analysis is a very important thing in structural analysis through which we can came to know in which direction and how much frequency the structure will have more excitation and it will also help us to safely build our products by eliminating the errors of being failed.
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