Modal analysis of an automobile

Click For Summary

Discussion Overview

The discussion focuses on the modal analysis of an automobile, specifically aiming to identify a safe region within the vehicle where vibration levels are low. Participants explore concepts related to modal analysis, boundary conditions, and the implications of displacement values on vibration safety.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the meaning of the DMX valve, questioning whether it represents the amplitude of vibration and if regions with minimum displacement values can be considered safe.
  • Another participant confirms that the DMX valve indicates peak displacement amplitude, distinguishing it from maximum acceleration and velocity.
  • A suggestion is made that the most stable location in the vehicle may be low down on the mid-line, near the driver's seat.
  • A participant expresses uncertainty about their modal analysis process, particularly regarding the boundary conditions of fixing the tires and the implications of calculating frequency based on the motor's rated RPM while the vehicle is stationary.
  • Concerns are raised about the clarity of the modal analysis approach, noting the existence of various modes in a vehicle, including rigid body and bending modes, and how nodal points may vary across these modes.
  • Another participant elaborates on their process of running modal analysis in ANSYS, calculating natural frequencies, and concluding that areas with lower DMX values are safer for sensitive electronics, while also mentioning guidance received about the presence of translation modes only.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the modal analysis process and the implications of the results. There is no consensus on the best approach to determining safe regions for electronics based on modal analysis outcomes.

Contextual Notes

Participants highlight limitations in their understanding of the modal analysis process, including assumptions about boundary conditions and the types of modes present in the vehicle. There are unresolved questions regarding the validity of the methods used and the interpretation of results.

slnavimechsit
Messages
4
Reaction score
0
hi.
I need to locate a safe region in an automotive, where vibration level is very low.

i have done modal analysis of that vehicle. In the result i got DMX valve. which is maximum deflection value. what does it actually represent?
Does it means the amplitude of vibration.
Can i conclude that the region with minimum displacement value as safe region (low vibration)

thanks and regards
naveen
 
Engineering news on Phys.org
Welcome to PF.
slnavimechsit said:
Does it means the amplitude of vibration.
Yes, the peak displacement amplitude. Not the maximum acceleration, not the maximum velocity.

My guess is that the most stable place will be low down on the mid-line of the vehicle, half way between the front and rear wheels. That is, next to where the driver's seat is usually mounted.
 
Baluncore said:
Welcome to PF.

Yes, the peak displacement amplitude. Not the maximum acceleration, not the maximum velocity.

My guess is that the most stable place will be low down on the mid-line of the vehicle, half way between the front and rear wheels. That is, next to where the driver's seat is usually mounted.

Thank you for your reply and useful information.

I have one more doubt.

While doing modal analysis, I am asked to fix the tires (Boundary condition). That automotive is electric. So from specification sheet i got RPM(Rated revolution). from which i calculated frequency. I got mode shapes upto that frequency.

Is the process I followed, right?

Because, as tires are fixed vehicle can't move.
and motor can't run at so much speed(rated revolution) when vehicle is stationary.

If this process is wrong how can i proceed?
 
It's not really that clear what you are doing. So it's hard to give any advice.

There are many, many modes from a vehicle:
Vehicle rigid body (translation and rotation modes)
Vehicle bending modes
Powertrain rigid modes (generally based on mounting bushes)
Powertrain bending modes

So a nodal point for one mode, might sit on a massive peak of another mode.
 
  • Like
Likes   Reactions: 1 person
xxChrisxx said:
It's not really that clear what you are doing. So it's hard to give any advice.

There are many, many modes from a vehicle:
Vehicle rigid body (translation and rotation modes)
Vehicle bending modes
Powertrain rigid modes (generally based on mounting bushes)
Powertrain bending modes

So a nodal point for one mode, might sit on a massive peak of another mode.

To be clear:

problem statement: I have one manually operated electric vehicle. I need to automate it. For which i need to add many sensitive on-board electronics to it. My work is to locate safe region for these electronics.

What I have done: I created the model and run modal analysis in ANSYS. As it is electric vehicle and motor rated rpm is 3480, i calculated frequency as w=(N/60)=(3480/60)=58hz

I gave frequency range between 0 to 58 and got around 13 natural frequencies and mode shapes.
Finally I am concluding that in all these mode shapes, where ever DMX value is lower, will be the safe area for those electronics.

My guide told me that there will be only translation modes are present but no rotational modes. he told me the reason but I don't remember as of now.
 

Similar threads

Vibration and Modal Analysis: Adding massless springs to a shaft
  • · Replies 6 ·
Replies
6
Views
2K
Modal Analysis for Safe Region in Automotive Vibrations
  • · Replies 1 ·
Replies
1
Views
3K
Random Vibration Fatigue Analysis
  • · Replies 4 ·
Replies
4
Views
3K
Vibrations, Modal Analysis and Mechanical Systems
  • · Replies 5 ·
Replies
5
Views
3K
Experimental Modal Analysis using FDD?
  • · Replies 3 ·
Replies
3
Views
2K
Buckling and modal FEA of a submarine structure
  • · Replies 4 ·
Replies
4
Views
3K
Rotor Analysis -- Big deformation problem
  • · Replies 4 ·
Replies
4
Views
2K
Why Does My Axial Fan Wobble at Certain Frequencies?
  • · Replies 1 ·
Replies
1
Views
2K
Graduate What is the purpose of modal analysis?
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad What is the Purpose of Modal Analysis in Mechanical Systems?
  • · Replies 1 ·
Replies
1
Views
2K