# Modal analysis of an automobile

• slnavimechsit
In summary, The DMX valve represents the amplitude of vibration. The lower the DMX value, the lower the amplitude of vibration. Can I conclude that the region with minimum displacement value as safe region (low vibration)?Yes, the peak displacement amplitude. Not the maximum acceleration, not the maximum velocity.
slnavimechsit
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

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.

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.

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.

## 1. What is modal analysis of an automobile?

Modal analysis of an automobile is a technique used to study the natural frequencies and mode shapes of an automobile's structure. It involves measuring and analyzing the vibrations of the vehicle in order to identify its dynamic characteristics.

## 2. Why is modal analysis important for automobiles?

Modal analysis is important for automobiles because it helps engineers understand how the vehicle will respond to various road conditions and external forces. It also allows for the identification of potential design flaws or weaknesses in the structure, which can then be corrected to improve the vehicle's performance and safety.

## 3. How is modal analysis performed on an automobile?

Modal analysis is typically performed using specialized equipment such as accelerometers, strain gauges, and data acquisition systems. These instruments are attached to various points on the vehicle's structure, and the resulting data is analyzed using software to determine the natural frequencies and mode shapes.

## 4. What are the benefits of modal analysis for automobile manufacturers?

Modal analysis provides automobile manufacturers with valuable information about the dynamic behavior of their vehicles, which can be used to improve the design and performance of future models. It can also help to reduce production costs by identifying potential issues early on in the design process.

## 5. Can modal analysis be used to improve the ride and comfort of an automobile?

Yes, modal analysis can be used to improve the ride and comfort of an automobile. By understanding the natural frequencies and mode shapes of the vehicle's structure, engineers can make adjustments to reduce unwanted vibrations and improve the overall driving experience for passengers.

• Mechanical Engineering
Replies
6
Views
1K
• Mechanical Engineering
Replies
3
Views
648
• Mechanical Engineering
Replies
4
Views
1K
• Mechanical Engineering
Replies
1
Views
2K
• Mechanical Engineering
Replies
3
Views
1K
• Mechanical Engineering
Replies
4
Views
1K
• Classical Physics
Replies
8
Views
1K
• Mechanical Engineering
Replies
1
Views
2K
• Differential Equations
Replies
1
Views
1K
• Mechanical Engineering
Replies
1
Views
1K