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Hello Spongebob, I thank you once again for your response. In my task, I have to evaluate damping co-efficients. For this purpose, I did an experiment with the aim of extracting first 6modes and resp modal parameters. All this is done to evaluate damping coefficients. So, now I am with 6...

Hello spongebob, Thanks for your reply. Yeah, literature suggests that. As its known that damping ratio should be constant for particulary mode ( irrespecitve of the measurement points). That means, at all measurement points we should have same damping ratio. If we use the formula, D=1/2T...

Hello Greg locock, Thanks for the reply. I couldn't understand the answer for my 2nd query. As per the calculations which I peformed, I am with varying coefficients (varying with the modes). Which means, mode1 has one set of coefficients and likewise for other modes. Regards

Dear members, I request you to please confirm the number of modes ( if possible with approximate modal frequencies) in the picture which can be found at http://rapidshare.com/files/59768133/trans.png.html That curve is in between transmissibility ratio (acceleration ratios) and the excitation...

Dear members, In our present task, we have to evaluate Rayleigh damping coefficients. --> Could anyone suggest how they can be evaluated? --> Do Rayleigh damping co-efficients vary with modes? Suggestions are most welcome. Regards

Hello dear members, Thank you very much for suggestions. As we can't proceed again with experiments, we have to use this transmissibility ratio data,(acceleration of the structure/accelration of the shaker)to determine damping ratios. --> Calculation of Damping ratios from the transmissibility...

Thanks for the responses. Theoretically, D ( damping ratio) has to increase with the increase of modes. This is deduced from D=C/Cc. Where Cc is the Critical Damping and is proportial to Sqrt(mk). Here m is the modal mass pariticipation. This decreases with the increase of modes. Consequently...

Hello Greg, Thanks for the response. I came across certain formula to calculate damping ratio from the transmissibility curves and it's T=1/(2/*D) Where T is the transmissibility ratio and D is the damping ratio and this formula is appplicable if D<0.1. Please someone confirm whether I can use...

Hello dear members, I am bit newbie to the Exp Modal Analysis. Recently, we conducted several experiments and we were with certain transmissibility ratio data along with the frequency. After maknig transmissibility ratio vs frequency charts, I was able to determine peaks in the chart. Now, the...

As damping is one of the natural charactarestics of your structure under analysis, the kind of domain matters nothing here. Whether it's time domain or frequency domain, damping remains same. As told before, because of the mathematical ease, viscous damping is considered as a representative...

Hello friends, I am in damn need of the best possible method for finding noise reulting from vibrations. i.e for noise calculations, transient vibration results are the inputs. My postprocessor supports Sigma1, Rayleigh, Helmholtz (all based on Rayleigh intergrals) & Indirect Boundary Element...

In continuation to the previous post.. To consider only the structural damping, it's requird to find other damping model values. i.e structural damping = overall damping value - (material damping values+ etc) But, depending on your structure and type of application, type of energy dissipation...

Well, literature tells that there are several kinds of damping models. Among them to carry out FEA calculatins, viscous damping has been chosen so that its energy dissipation per cycle of osciallation is equal to that of original damping present in the structure. Thus, for the ease of...

Hello Members, Can any one comment on the test rigs which I would like to use for my present project. File is loaded in rapidshare.com and is available at http://rapidshare.com/files/20851929/Test_Rigs.doc Regards,

Hello GregLocock, Thanks for the response. I am a newbie to all this stuff. I need some elaborate explanation on this. Can you suggest any relevant literature regarding this. regards

Thanks to one and all for their valuable suggestions. I will get back if I face any difficulties during experimentation. Before that, I would like to know ---any method of selecting points over the structure. ( random or any mathematical method etc..) ---number of points required to get better...

Thank you very much for immediate response.. It's very clear about the methodology and its usage limits. Now, I have one more question regarding the test rig which I am going to use. Test rig consists of SPEAKER as an harmonic excitor. Can I replace the conventially used hammer/shaker with the...

Hello 271828(Structural) " I have another specimen that has the first two frequencies of 7.8 Hz and 8.0 Hz and half-power works fine for it because it has a damping ratio of about 0.2% of critical, so the modes are well separated even though they're only 0.2 Hz apart." Could you kindly explain...

If that's the case, is there any other better method of exciation in this case.

Dear members, I am very glad to receive your responses. I got some idea on the method to use. Can any one suggest on the test equipment which I explained before? --Speaker as exciting source-- --FRF defined as the ratio of velocity just above the surface of the structure to the sound pressure...