Hi, I have to do frequency respons
Hi, I have to do frequency respons
(OP)
Hi,
I have to do frequency response analysis for automotive frames and cradles. Before starting the analysis I have some questions. Can any body please answer my questions?
My questions.
1) What is frequency response analysis ?
2) what is Low frequency and High frequency responses.
3) When and why we have to do the frequency response analysis for the automotive structures ?
Please answer my questions.
Thanks
Kamalakar Rao
I have to do frequency response analysis for automotive frames and cradles. Before starting the analysis I have some questions. Can any body please answer my questions?
My questions.
1) What is frequency response analysis ?
2) what is Low frequency and High frequency responses.
3) When and why we have to do the frequency response analysis for the automotive structures ?
Please answer my questions.
Thanks
Kamalakar Rao





RE: Hi, I have to do frequency respons
frequency response analysis is, give one sinusoidal input, find the output, usually, for linear system, the frequency is same as the input, find the gain of magnitude and phase shift. I think there are many experiment equiment can do that.
the find the natural frequency of the automobile and reduce the vibration of the automobile by passive or active method, or maybe for control purpose.
RE: Hi, I have to do frequency respons
Additionally, resonances affect the ability of the fasteners within the vehicle to do their job of holding things together. Too much vibration and things shake apart and start buzzing and rattling.
TTFN
RE: Hi, I have to do frequency respons
I wanted to know some more information about frequency reposnse ana;ysis.
To my knowledge, there are three methods in frequency response.They are
1) Displacement appraoch
2) Velocity approach
3) Acceleration approach
My question is which of these approaches, we need to follow ? To be more clear,
When do we do displacement, velocity or acceleartion responses required. Also, when some body is talking about the Low frequecny response ( say about 0-200 Hz) of the vehicle, why that low frequency responce required ?
When we have to study the high frequency response ( say 200-600 Hz)of the structures? Can you please answer my questions? I think, I am clear in asking the questions.
Thanks
Kamalakar
RE: Hi, I have to do frequency respons
LF response (more typically 1-40 Hz) affects durability, shake, ride comfort, handling and so on. There are also some nois eproblems that can be caused by these low frequencies.
40 Hz+ gives noise problems, and on the body at least, local issues such as booms being amplified by specific panels.
Cheers
Greg Locock
RE: Hi, I have to do frequency respons
Michael
RE: Hi, I have to do frequency respons
A starting place would be "Theory of Vibration" by William T. Thomson.
RE: Hi, I have to do frequency respons
Thanks for response. I have another question? If we look for acceleartion response, and plot the acceleartion Vs Frequency graph, How can we use this information? To be more clear, suppose if I get the peak response (acceleration ) in the rane of say 150-200 Hz, How this information can be used?
Sasank
RE: Hi, I have to do frequency respons
In such cases, you need to evaluate the likelihood of getting such a stimulus and whether there is a problem with having such a high response. In many cases, such responses are unacceptable because the vibration level or noise becomes too high, or ultimately, the system will shake itself apart.
TTFN
RE: Hi, I have to do frequency respons
If you are at an early stage of the design then you won't be able to test for these effects, you'll just have to rely on the noise predictions from the computer models (good luck) and the prior experience of the design people, who will nominate 'do not exceed levels' for compliances. A typical requirement for an engine mount bracket is that it should have no local modes at less than (max firing frequency *1.15) and a dynamic stiffness of 10 times that of the engine mount over the same frequency range. There is some redundancy in that spec, and it assumes that you know what your engine mounts will look like. Later on in the program you can drop your point mobilities into a noise path analysis and see if they are important.
Your noise and vibration people should also be building a modal alignment chart showing you where you can have the modes for major subsystem, graphed against the typical causes of excitation.
Cheers
Greg Locock
RE: Hi, I have to do frequency respons
RE: Hi, I have to do frequency respons
Here is my question
1. for what kind of applications FFT analysers are used?
2. Can I use it for vbrations in bearings. If so what is the mounting procedure for accelerometers?
3. What way can we use a FFT for preventive maintenance and condiotion monitoring.
4. What r the things that we can interpret from a signature of a frequency responce?
Thks