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Oh, and here is the last one but with the TMD tuned to 7 Hz So you get less attenuation, but over a bigger frequency range. Units used throughout are any self consistent set, so N/m, N/m/s and kg in SI

Just a quick look at TMDs, which came up elsewhere. In this case I am looking at the normal automotive case, where a large body is excited directly by a force, and we then bolt on a TMD. Typical example is the harmonic damper on the crankshaft, used to suppress torsional vibrations, and bending...

As i said we do an rpm sweep, which makes it obvious if it is resonance or a forced response. You can measure TVs with a TV analyser (surprise) - a toothed wheel on the nose of the crank, a pickup, and an FM demodulator, which turns your pulse train into a usable signal. An F to V box would...

Welcome to the world of experimental modal analysis! Simplest way with what you have already is to mount two accelerometers. Move one around and plot the ratio of the amplitude at 87 Hz to the reference fixed accelerometer. Hopefully you'll get a ) shape along the length of the unit. That isn't...

You get 2 answers because I can't find out if it is a 2 stroke or a 4 stroke! 4stroke Nope, firing frequency for a V16 4 stroke at 1500 rpm is 200 hz, which doesn't solve your problem admittedly. So you've got 3.5 order. Wow, that is odd. Also odd is the absence of ANY firing order vibration...

Yes, I can't see why on the basis of that data you'd choose 0.030. However, if buildings are designed to 33 Hz and don't tend to fall down then I suppose you could argue it is sufficient. You'd probably get a better response on the structural engineering forum where people design earthquake...

It's a rule of thumb for the upper limit of signal from an earthquake. Like most rules of thumb it works until it doesn't. On hard rock you can see 100 Hz. So on this graph 33 Hz is a period of 0.030 s, so yes there's nothing much going on between 0 and 0.030, but it seems a pretty arbitrary...

The finer the fibre the more the attenuation. That's because there's more surface area to slow the airflow.

I don't think you are necessarily wrong. The structure is responding to the frequency content of your pules, not the pulse itself. So if it has a resonance at 1/4*1000/4.8 Hz say then that would give that effect. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376...

Roughly speaking 0.1% for homogenous steel parts, 0.3% for cast iron, more for bolted assemblies, much more for complete items. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

You've assumed E in your stiffness example, which has to be measured (well OK you can calculate it if you measure some other stuff instead). No there isn't a way of calculating damping for a structure, that I know of. If you have a large discrete damper in the system (eg TV damper) then yes you...

I can't see any advantage in doing that in linear FEA, but I can't see it is a problem either. I'm used to people extracting the first x hundred modes, or all modes up to 3 times the frequency range of interest. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376...

I'm guessing you are doing linear FEA? "Since 10 Hz is the starting frequency, the initial displacement at all nodes would be zero, x(t)=0x(t) = 0x(t)=0. By solving this, we get the response for this frequency. Now, when the solver moves to 11 Hz, will it assume the initial displacement is zero...

Hmm. Are you following in someone's footsteps with this approach? If not, you have taken a very brave route. Sorry I have no simulation experience with sloshing apart from a demo of an open source particle modelling software, possibly called Euler. "other query was how to find natural...

Well, you are working to a standard, you have done the test, and it fails. So, either the standard gives you a let-out clause, or your test is wrong, or your structure needs redesigning. Unvalidated FEA is just pretty pictures on a screen. Cheers Greg Locock New here? Try reading these, they...

I suggest you synthesise data showing your 50 events, and another with say just 20 and see what the difference in the spectrum is. I think you'll be disappointed. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

Have you looked at the mode shapes? Have you done a real life modal analysis on a similar skid? Cheers Greg Locock New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

500 Hz or so? Yes that is a ridiculously high modal density in that 20% bandwidth for a supposedly rigid structure about the size of a car. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

Sand. Scattered on the horizontal disc, with a tiny shaker at each resonant frequency frequency it showed the mode shape nicely. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

Nice catch. Ah, I remember a similar issue. I was looking a the mode shapes of a brake rotor, I couldn't get a good mode shape using a normal accelerometer, as the mass of the accelerometer forced the repsonse to be nodal wherever it was mounted. The wavy mode shape just rotated around to...