# Overall energy input in random vehicle vibration tests

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• Roy1984
In summary, the conversation discussed the calculation of overall energy input in random vehicle vibration tests. The speaker wanted to compare different power spectral density levels, but was unsure how to calculate the energy input per mass for each test. They mentioned using the Grms value, but were unsure about its accuracy and how to convert it to the correct unit for energy per mass. They also mentioned that they only needed a proportionate value for comparison purposes.
Roy1984
Hello Everyone

I have got a question concerning the calculation of the overall energy input in random vehicle vibration tests.

I have got different power spectral density levels for different random vehicle vibration tests and would like to compare them with each other concerning the overall energy input of the different tests. What I'm aware of is the following: The energy input definitely depends on the mass that is placed on a "shaker" for such a vibration test. Therefore I guess it would make sense to calculate an energy per mass for these different tests.

Besides the power spectral density levels, I already know the Grms value for the different levels. What I now would like to calculate is the energy-per-mass-input when such a test is performed for a certain time. So just comparing the Grms values doesn't do the trick, since I want to compare different tests with different running times and different power spectral density levels (and therefore different Grms values).

Here are some of the levels I would like to compare:

I hope anyone can help me on that subject. Thanks in advance.

Regards,
Roy

What I can add so far, or what I have tried before is the following (which didn't help me a lot):

Energy or work is defined as follows (units in [ ] ):
W = F*s = [N]*[m]

with:
[N] = [kg * m/s^2]

work follows:
W = [kg * m^2/s^2]

So work "W" per mass "m" is:
W/m = [m^2/s^2]

Now my problem is that I don't have a clue how I should calculate the input energy of such a power spectral density spectrum as shown above.

To my understanding the Grms value should be the relevant value. (https://en.wikipedia.org/wiki/Random_vibration: The root mean square acceleration (Grms) is the square root of the area under the ASD curve in the frequency domain. The Grms value is typically used to express the overall energy of a particular random vibration event and is a statistical value used in mechanical engineering for structural design and analysis purposes.)

But when I just multiply the Grms [m/s^2] value with the duration time of the test, the resulting unit is [m/s]. Which is not the unit [m^2/s^2] derived above for work per mass...

By the way: I don't necessarily need an exact value for the energy input per mass. What would be sufficient is a value I can claim to be proportional to the energy input, so I can compare different spectrums with each other.

Last edited:

## 1. What is the purpose of measuring overall energy input in random vehicle vibration tests?

The purpose of measuring overall energy input is to evaluate the structural integrity and durability of a vehicle when subjected to random vibrations, which closely mimic real-world road conditions. This measurement helps engineers identify potential weak spots and improve the design of the vehicle to ensure its safety and reliability.

## 2. How is overall energy input measured in vehicle vibration tests?

Overall energy input is typically measured using an accelerometer, which is a sensor that measures the acceleration of the vehicle in multiple directions. The data collected by the accelerometer is then processed to calculate the overall energy input in terms of root-mean-square (RMS) acceleration, which provides a measure of the total energy absorbed by the vehicle during the test.

## 3. What factors affect the overall energy input in random vehicle vibration tests?

Several factors can affect the overall energy input in vehicle vibration tests, including the amplitude and frequency of the vibrations, the weight and stiffness of the vehicle, and the type of road surface being simulated. Other factors such as the vehicle's suspension and shock absorbers can also impact the overall energy input.

## 4. How does the overall energy input relate to the ride comfort of a vehicle?

The overall energy input can have a significant impact on the ride comfort of a vehicle. Higher levels of energy input can result in a rougher and more uncomfortable ride for passengers. Therefore, it is essential for engineers to carefully measure and analyze the overall energy input to ensure that the vehicle provides a comfortable and smooth ride for its occupants.

## 5. Can the overall energy input be used to compare different vehicle designs?

Yes, the overall energy input can be used to compare different vehicle designs. Engineers can use this measurement to evaluate the effectiveness of design changes and improvements in reducing the overall energy input and improving the vehicle's durability and ride comfort. It can also be used to compare the performance of different vehicles and identify areas for improvement.

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