Questions related to NVH
I already made the experimental setup of impedance tube for the same construction. Do I have to validate it?
When I perform Normal Mode analysis for certain components in Abaqus , I often come across repeated frequency/mode shapes. Say like 998.2Hz, 998.6Hz,1532.8Hz,1533.3Hz....so on . I would like to know to skip or delete those repeats mode shapes . This repeated mode cause increase in output file (.odb) .
PS: My loadstep will Lancoz method(for eigen value extraction),mass normalisation, and specify frequency range only.
I am working on a Brake NVH problem. On searching for methods to accurately predict eigen frequencies for rotary machines, I came across this term.
Two time series data (1. Engine RPM wrt time and 2. Seat Acceleration wrt time) were analyzed using LMS Testlab and LMS AMESim post processing tools. It was observed that the order plot of acceleration wrt rpm obtained from both softwares using the same window type and trend removal option do not match. Further investigations reveals that using the same sampling frequency in AMESim and Testlab produced a result that have similar trends with Testlab result. However, the accelerations amplitudes have significant deviation from Testlab results.
What other parameters should be checked to obtain same results from Testlab and AMESim?
Presently there is a gear whine noise issue in a vehicle transmission. Our NVH team captured the noise signal using a microphone and then did an FFT of the signal and gave us a frequency plot. What exactly can I take out of it?
- Can I assume every harmonic belong to a noise generated by a gear having the same meshing frequency?
- Then, what are those harmonics which don't match with any gear order?
- An irrelevant question - Does excess PCD runout of a gear cause whine? How to prove if that is the major cause?
I'm a Mechanical Engineering student passionate in automobiles. I would like to the explore the NVH Domain in automobiles. But because of lack of knowledge on the subject, I'm confused about where to start with.
Please suggest me some standard books which are good to start with and gain expertise in NVH, their analysis and control methods in automobiles.
I am new to NVH simulation.
I have a component tested for vibration. From the test involved measuring Frequency response function (Mobility)FRF on 6 points on the modell. So I have plots of FRF values at Six points on the modell. Using this I want to calibrate My FEM model. What are techniques to callibrate such modell. I have come across Modal assurance criterion (MAC) and Model updating technique. can you enlighten me about such method.
Thanks and Regards
When a coarse set of SIMO FRF is available, the driving point is just one. But when the FRF are estimated very close to each other in spatial domain, and might be very similar and all with PI-constrained phase or one sided imaginary part (apart from little measurement errors), how can we discriminate the best/true driving point FRF?
Looking for NVH test experts who can shed some light on the underlying root cause for Vibration and Harshness (at the engine level only, rather than at the vehicle level)
In Indian market fuel economy is important. Will removal of muffler affect the back pressure and engine design, thereby increasing fuel economy.
I did simple analysis of a theoretical muffler approximated to a car size, and predicted the values of Sound Pressure Level and reduction in SPL.
I study the dynamics of automotive powertrains, and for me it is very important to measure torsional vibrations. However, we have a huge observability problem, because we want to measure what is happening to gears inside the gearbox, so it is not possible to use optical sensors or decoders. Today we use proximity sensors and the number of teeth of some gears to do so, although it provides poor frequency resolution for low speeds and does not allow one to measure negative speeds. Does any one know a better device to do so?
I am trying to develop a simple 1-D formulation for the transmission loss of a reactive muffler, the expansion, rentry lengths of inlet and outlet and perforations effects. I have the equations for their individual transmission loss, but baffle or separation in the muffler I am not able to account for. Can anyone share their ideas on how to achieve it, and also how to combine all these individual acoustic elements to get the complete effect? (Transfer matrix method might be used to combine the effects, but I don't know exactly how to use it, so please share your thoughts on TMM also.)