General Mechanical

General Mechanical

Vibroacoustic – precise formula for determining the EDPC from stored energies

    • O_Plata
      Subscriber

      Wer are calculating some vibroacoustics problems, requiring precise control of energy lost (dissipated) due to damping. The inquiry concerns the ANSYS internal algorithms allowing the determination of energy-dissipated-per-cycle (EDPC) in harmonic analyses.

      The benchmark is very simple. It consists in rectangular plate, loaded symetrically in in-plane axial ("X") direction. The boundary conditions eliminate any possible movement but that along X asis. Therefore, it is a quasi-1D situation. On the other hand, we did not want to use beam elements, as the real problem at stake requires shells.

      The main part of the benchmark macro is as follows:

      XA=3.0

      YA=1.0

      THICK=0.005

      /prep7

      RECT,0,XA,0,YA

      ET,1,SHELL181

      MP,EX,1,2e11

      MP,NUXY,1,0.3

      MP,DENS,1,7800

      SECTYPE,1,SHELL

      SECDATA,THICK

      ESIZE,YA/2

      AMESH,all

      NSEL,S,LOC,X,0

      D,all,all,0

      ALLS

      D,all,UZ,0

      D,all,ROTX,0

      D,all,ROTY,0

      D,all,UY,0

      ....

      /solu

      ANTYP,HARMIC

      ....

      DMPRAT,0.05

      KBC,1            

      freqstart=400

      freqend=500

      freqstep=5


      *DO,given_frequency,freqstart,freqend,freqstep

      HARF,given_frequency

      N1=NODE(XA,YA/2,0)

      F,N1,FX,-F1AMP

      ALLS

      SOLVE

      ..... postprocess of energies ....:

      SET, (imaginary or real)

      ETABLE, (kind of energy)

      SSUM

      *GET .... SSUM, ITEM,....

      *ENDDO

      We have determined the natural frequency of the plate associated with its "spring-like" behaviour (~450 Hz), and studied its response around that resonance. At each frequency, the various energies (TENE, SENE, KENE, AENE) are stored (ETABLE,... and summed in all elements. Both the real and imaginary parts are taken separately into account.

      The plot of energies is as follows:

    • HuiLiu
      Ansys Employee
      Hi, looks like your question is related to the formula that are from conference papers, it would be best to reach out to the authors to find out the details of these formula, and decide the one that's best to describe the specific physics you are trying to simulate. If you have some further questions regarding usage of the product, we will be happy to address them.n
    • BenjaminStarling
      Subscriber
      Hi O_Plata,nThe driving point approach is correct. However there are errors in your understanding the energy approach which has led to the discrepancy you see.nThere is only 1 form of energy, SENE=KENE, with thermal energy (TENE) being 0 as this is not a thermal analysis. The KENE and SENE are equivalent with any kinetic energy being stored as elastic potential energy (SENE) when the velocity is 0. Therefore, look at one energy result, SENE or KENE.nYou need to combine the real and imaginary components of the SENE across the frequency domain in a SRSS fashion. This is essentially an amplitude result which can be requested in the mechanical postprocessing environment. Once you have done this you will see that the energy approach matches the driving point approach.nn
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