Science method

NVH - Science method

Explore the latest questions and answers in NVH, and find NVH experts.
Questions related to NVH
  • asked a question related to NVH
Question
1 answer
Can anyone share the details about Brake wire brush noise ?
How the test has to be conducted to capture the wire brush noise, frequency range etc., ?
Relevant answer
Answer
  • asked a question related to NVH
Question
5 answers
I already made the experimental setup of impedance tube for the same construction. Do I have to validate it?
Relevant answer
Answer
did you di it?
  • asked a question related to NVH
Question
2 answers
How the NVH performance products affects the sales performance (Improvement)???
Kindly provide me the reference.
Thanks
Relevant answer
Answer
Hello,
Could you be more specific on what kind of products you would like information?
As part of an electric motor manufacturer company, NVH is often a customer request and can be more or less significant. It can happen than not fulfilling this customer request leads to no further industrialization after a prototype phase. As a result, your question is very hard to answer, NVH not being the sole parameter of success.
Best,
Guillaume
  • asked a question related to NVH
Question
4 answers
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.
Relevant answer
Answer
(close enough) symmetric structures will give you similar/same frequencies. Circular or square cross sections for example. It can also differ which shape you get as the first or second, or the result can even be a linear combination of those 2 shapes, based on the computer you are running on. So those are very likely 2 distinct modes, which you should keep.
  • asked a question related to NVH
Question
9 answers
What are the open source software available for the analysis of noise vibration and harshness?
Relevant answer
Answer
If your interest lies in CAE, then Code Aster can analyze sound/vibration.
  • asked a question related to NVH
Question
4 answers
the international regulations on NVH
Relevant answer
Answer
  • asked a question related to NVH
Question
3 answers
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.
Relevant answer
Answer
This is a new term to me. I have done eigenvalue analysis in rotor dynamics both analytically and experimentally, and never come across this term. I would be interested to learn if it is something new. As for estimating eigenvalues; you amy simply proceed using one of the following: (1) one can just formulate the generalized eigenvalue problem and use MATLAB eigenvalue solver; or (2) model your brake using ANSYS (use rotordynamics module if you want to account for rotation) then solve eigenvalue in ANSYS, or (3) experimentally by roving hammer excitations and measuring the FRF using a frequency analyzer with modal analysis software to obtain frequencies and mode shape.    .   
  • asked a question related to NVH
Question
4 answers
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?
Best Regards,
David
Relevant answer
Answer
Hi David
Debugging software always is dog's work.
Suggestions on simple things to compare are
  • RMS (1s) values computed from raw time signals to ensure signals have similar energy content.
  • Autospectrum, verify that frequencies and amplitudes are identitical. Check Autospectrum with Amplitude shown as Peak, RMS, Pk-Pk etc.
  • A good overview of long time series often is to use Amplitude histograms and to look at Kurtosis.
Where possible, try and swap data between systems, i.e. get test data to act as simulation data and vice versa. If this works, use a simple calibrator signal of 1 g at fixed and known frequency as first signal to test AMESim.
If I should venture a guess, test systems use fixed sampling rates as the measurement HW uses fixed clock frequency. A simulation system may use different time steps because of numerical efficiency and this difference in time stepping may complicate post processing.
Have fun
Claes
  • asked a question related to NVH
Question
9 answers
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?
  1. Can I assume every harmonic belong to a noise generated by a gear having the same meshing frequency?
  2. Then, what are those harmonics which don't match with any gear order?
  3. An irrelevant question - Does excess PCD runout of a gear cause whine? How to prove if that is the major cause?
Relevant answer
Answer
May I ask you in which condition was the vehicle transmission tested? I mean, on the road, on a test rig with full transmission enabled, with clutch detached, etc.
Can you do synchronous averaging on the microphone time traces?
Sorry if I put questions instead of answers, but I hope it helped in defining more the topic.
My regards,
Alessandro
  • asked a question related to NVH
Question
7 answers
I need some good materials on TVD and their applications to automotive driveline NVH control.
Thanks.
Relevant answer
Answer
Happy new year David!
Please have a look at the works of Prof. Paul Sas: https://www.researchgate.net/profile/Paul_Sas/publications
My best regards,
Alessandro
  • asked a question related to NVH
Question
7 answers
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.
Relevant answer
Answer
Hi Praneeth,
The book by Matthew Harrison "Vehicle Refinement: Controlling Noise and Vibration in Road Vehicles" is a good place to start. It covers the entire aspect of automobile NVH.
Regards,
David
  • asked a question related to NVH
Question
17 answers
Hallo Group
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
Pratik
Relevant answer
Answer
Hi
Your measurements are amplitude only. You need phase as well, i.e. either you use amplitude/phase or real/imaginary.
I suggest the following reading order. The material is old but still the best available. Skip the parts you already know.
Sincerely
Claes
  • asked a question related to NVH
Question
3 answers
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?
Relevant answer
Answer
Hi Allesandro
I believe I must complicate your world a bit more. :)
You measure mobility (receptance or accelerance) rather than impedance.This is a common mistake, in fact the Impedance standardization group had to switch name to mobility standardization. 
Why? Well, if you set up the impedance matrix, i.e. forced displacement input, you must block motion at all other positions and there measure blocked force. This can only be done in special test stands and with some limitations at that.
See Figures 3 & 4 here & try the same for mobility and the difference is obvious
Next, I used to be a big fan of impedance heads until I learned that impedance heads are riddled with measurement errors. The reason lies in the force cell being situated in between your measurement object and the accelerometer.
If the measurement object stiffness is higher than that of the force cell, the accelerometer response will not move in phase with the measurement object and your FRF is in error. As most FRFs have anti.resonances, and stiffness if very high at anti-resonance, this error in your drive point FRF will be notable.
Incidentally, this is a unique way to identify the difference, ;), between the FRFs where the FRF with the accelerometer placed close to the drive point will be the correct one.
When checking things, I find that it is very useful to rely on a no-excuses-accepted case. One such is a rectangular, say 10mm thick, 40 mm wide and 1+ m long steel beam. You can simulate this case using simple Euler Bernoulli beam theory and make very accurate free-free measurements on this case. In any case, this is what Mike and I did when we were working on 6 dof mobility measurements a while back in time. https://www.researchgate.net/publication/256801180_Direct_measurement_of_moment_mobility_Part_I_A_theoretical_study?ev=prf_pub
Over2Jo
Claes
  • asked a question related to NVH
Question
5 answers
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)  
Relevant answer
Answer
Hi
Exhaust/Intake noise is part of regular NVH design for motors, so is sound radiated from block vibration and structure-borne sound emitted from motor supports. 
Apart from combustion noise, you will find mechanical sources like unbalance, rattling and gear whine.
If you are into flow and asking whether it is the flow, the answer is that flow and kinetic pressure are not major contributors to NVH. It usually is the elastic part of the pressure, i.e. the sound that matters for NVH.
Sincerely
Claes
  • asked a question related to NVH
Question
5 answers
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.
Relevant answer
Answer
I was thinking for a long time of using what so called a smart resonator.
that automatically changes its size based on excitation, i made a literature research about that and found some people used a mechanical way, but i am thinking of using an electric way .. we can discuss it in details if you like the idea
  • asked a question related to NVH
Question
9 answers
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?
Relevant answer
Answer
Hallo Christian, I do not think your suggestion fits the problem.. As I understood Vinicius wants to measure gears inside the gearbox.. and there space is more than tight!
Regards
L
  • asked a question related to NVH
Question
6 answers
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.)
Relevant answer
Answer
Hello Sidharath! Usually, in silencer simulations, the easiest approach is based on the 1-D linear equations (continuity and momentum) under the assumption of isoentropic process and harmonic time dependence of all the variables. Under these hypotheses the above equations can be """easily""" (!) solved in each part constituting the silencer, and eventually they can by combined by using a product between the transfer matrices of the elements. The TM of the entire muffler is given by the product of the TMs of all the components, and the Transmission loss of the muffler can be expressed as a function of the global TM (at each frequency).
I'm not very sure about Ricardo Wave but GT-Power allows to perform linear-calculations. Anyways, the most used acoustic tool of GT-Power is the one based on non-linear equations solved through a time domain approach. The equations are no more linear and there's no more harmonic dependence of the variables. So the complexity in that case is higher, but the program can exploit the time-domain formulation used for the fluid-dynamic simulations of the manifolds (which is he main goal of the software).
GT-power also uses some "hybrid" 0D-1D elements (flow splits) to fill the expansion chambers. My suggestion is: pay attention when you simulate short chambers with big diameters.....
In conclusion, if you want to program a little tool to simulate simple silencer configurations, then you should definitely use the 1D linear approach. One of the best gurus in this field is Munjal, and his book is a sort of Bible for the acousticians (no offense for the other guys)! Good luck and let us know about your simulations!