measirung excitation forces
measirung excitation forces
(OP)
Hello,
I would like to ask if someone has an experiences how to measure excitation forces, for example: Imagine that you have an electric engine mounted on the structure and you need to measure the excitation forces from engine applied on the structure - what will be the best procedure? how to get "clean" forces (not including structure eigen-frequency responses)?
thank you for your answer!
I would like to ask if someone has an experiences how to measure excitation forces, for example: Imagine that you have an electric engine mounted on the structure and you need to measure the excitation forces from engine applied on the structure - what will be the best procedure? how to get "clean" forces (not including structure eigen-frequency responses)?
thank you for your answer!





RE: measirung excitation forces
TTFN
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RE: measirung excitation forces
There are three axis dynamical force sensors which can be fixed between the both structures (see Kistler for instance)
But if you can not afford to buy these sensors, then you can asses the coupling using substructuring method.
In this case, the coupling force is given by
F=V^2/(Y1+Y2) where Y is the mobility i.e. FRF.
So you need to have at least an impact hammer to do this.
RE: measirung excitation forces
A relatively easy approach would be to add a known imbalance to your motor and measure the structure's vibration, and then compare it with the original value, if you are worried about balance forces.
Cheers
Greg Locock
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RE: measirung excitation forces
Using your mobility and velocity based approach, wouldn't you miss the energy corresponding to rotation around the three axes? I wonder in which cases this might still be a fair approximation?
RE: measirung excitation forces
It's a technological problem that obliges us to do this assumption.
RE: measirung excitation forces
Walt
RE: measirung excitation forces
Under this hypothese,measurement of translation acceleration includes the effect of rotation. The torsional vibration can be seen as hidden variable...
RE: measirung excitation forces
For better imagination I created a simple image,. the motor (black) is mounted on bigger plastic part (red) in four locations.
The problem is that we need a "clean" forces from measuring (not including red structures eigen resonances) but we don't know how to measure that.
Let's say that our budget is unlimited so If anyone can tell us how to measure this problem and what equipment we should use? this is the picture (hand drawn in paint)
RE: measirung excitation forces
Cause it's very trembling...
Anyway, your issue is just the basic source-isolator-receiver problem.
It seems that you assume that the isolator is a structural element with distributed mass and elasticity.
You should then consider your model in terms of impedance(Z) and determine the Force Transmissibility: Fr/F=1/(1+Zs/ZI+Zs/Zr)
RE: measirung excitation forces
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: measirung excitation forces
Don't you rather mean 3 dof instead of 6 dof.. (but maybe you wanted to make a joke and then it was very funny)
RE: measirung excitation forces
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: measirung excitation forces
Could you please reveal your scoop?
RE: measirung excitation forces
obviously
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: measirung excitation forces
=====================================
(2B)+(2B)' ?
RE: measirung excitation forces
The only problem is that Rx Ry and Rz are not measurable. All the dificulty is here.
I thought that greg knew a sensor able to measure the rotations.
RE: measirung excitation forces
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?