Power train mount - Modal kinetic energy calculation 2

[elogesh]

Hi,

would like to calculate the modal kinetic energy of Power train mount suspension modes based on FEA modal results.
Power train System built as 6-dof model and hence there are totally 6 modes (Bounce, lateral, longitudinal, roll, yaw,pitch).

80% participation of individual modes ensures decoupling between the modes and also would like to have coupling between bounce and pitch mode.

How can we calculate the modal kinetic energy values from modal data?

In this regard, following paper was referred ,

paws.kettering.edu/~amazzei/s41p03.pdf

If you need additional information in this regard, kindly let us know.

Regards,
Elogesh

 

[GregLocock]

Well, from first principle the KE is sigma 1/2 m v^2 for all inertias and directions. That is for one body it is

1/2*m*(vx^2+vy^2+vz^2)+1/2*Ixx*rotvx^2...

where rrotx is the roattional angular velocity of that mode about that principal axis, NOT the circular frequency.

Why make it any harder than that?

obviously vx=dx*w*j and you are probably about to look at the PE of each elastomer to do some sort of Rayleigh thing, where PE= 1/2*k*x^2...



Cheers

Greg Locock


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[MikeyP]

Hmmm...

The reference you quote does not calculate what I would call modal kinetic energy.

It calculates how the KE of a given mode is proportionally distributed between the physical coordinates. Because we are looking at this proportionally then the fraction of the KE that is in each direction will be

Mx^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )
My^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )
Mz^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )
Ixx rotx^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )
Iyy roty^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )
Izz rotz^2 / ( M(x^2 + y^2 + z^2) + Ixx rotx^2 + Iyy roty^2 + Izz rotz^2 )

Where x, y, z, rotx, roty and rotz are the values of the mode shape in those directions

M

--
Dr Michael F Platten

 

[GregLocock]

I'd add that any of these ideal processes for finding powertrain mount stiffnesses stumbles in the real world where we use hydromounts with tunable dynamic stiffnesses. When you combine this with real life variations in mounting point impedances, and the different transfer functions from each mount to the response location (eg driver's ear), and the practical importance of cancellation, and the fact that mount tuning doesn't just affect the noise and vibration boys, it all gets a bit hard.



Cheers

Greg Locock


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