General Mechanical

General Mechanical

PSD analysis

    • vgiordano3
      Subscriber

      Hello everyone. I'm having some difficulties performing a PSD analysis in Ansys APDL. I have a steel structure and a steel box, joined toghether with 4 brackets. This structure performed a vibrational test according to the MIL-STD-810. The PSD spectrum is the following (blue one) with 176lbs of weight on the box:

      I modeled the structure in Ansys with the spectrum analysis, but I'm having trouble with the mode combination.

      Here's the code.

      fini
      /clear
       
      !PARTE DICHIARATIVA
      !DIMENSIONI
      h=0.76 !Altezza telaio
      l=1.41 !Lunghezza telaio
      w=0.8 !Larghezza telaio
      wcer=0.020 !Spessore cerniere
      lc1=0.30575 !Dimensione 1 su x cassetta
      lcc1=0.32575 !Dimensione 1 su x nervatura N
      lc2=1.1065 !DImensione 2 su x cassetta
      lcc2=1.0865 !Dimensione 2 su x nervatura N
      ls1=0.273 !Dimensione 1 su x staffa
      ls2=1.137 !Dimensione 2 su x staffa
      hc1=0.18075 !Dimensione 1 su y cassetta
      hcc1=0.20075 !Dimensione 1 su y cassetta
      hc2=0.67925 !Dimensione 2 su y cassetta
      hcc2=0.65925 !Dimensione 2 su y nervatura N
      hs1=0.622 !Dimensione 1 su y staffa
      hs2=0.522 !Dimensione 2 su y staffa
      wc1=0.16575 !Dimensione 1 su z cassetta
      wc2=0.66425 !Dimensione 2 su z cassetta
      tc=1.5e-3 !Spessore lamiera cassetta
      bh=30e-3 !Dimensione 1 sezione staffa
      bb=6e-3 !Dimensione 2 sezione staffa
       
      h1=0.515 !Altezza posiz staffa UPN160
      h2=0.415 !Altezza fissaggio traversa
      w1=0.29 !Posizione su z traversa sup 1
      w2=0.49 !Posizione su z traversa sup 2
      w3=0.54 !Posizione su z traversa sup 3
       
      !DATI DELLE CERNIERE/CHIUSURE
      !LUNGO X
      lunghezzacer=0.135
      lcera1=lc1+0.1
      lcera2=lcera1+0.1
      lcerb2=lc2-0.1
      lcerb1=lcerb2-0.1
      lcerc1=lc1+0.040
      lcerc2=lcerc1+lunghezzacer
      lcerd1=lc1+((lc2-lc1)/2)-(lunghezzacer/2)
      lcerd2=lcerd1+lunghezzacer
      lcere2=lc2-0.040
      lcere1=lcere2-0.135
      !LUNGO Y
      hcer2=hcc2-0.01
      hcer1=hcc1+0.01
       
      !DATI COPERCHIO
      lcop1=lcc1+0.01
      lcop2=lcc2-0.01
      hcop1=hcc1+0.01
      hcop2=hcc2-0.01
       
      !DATI DEL TUBOLARE QUADRATO
      wh1=40e-3
      th1=4e-3
       
      !DATI DEL UPN160
      wu1=65e-3
      wu2=160e-3
      tu1=10.5e-3
      tu2=7.5e-3
       
      !PARAMETRI DEL MATERIALE
      E=210e+9 !Modulo di young acciaio
      ni=0.3 !Coefficiente di Poisson acciaio 
      !e AISI304
      rho=7850 !Densità acciaio
      E1=196e+9 !Modulo di young AISI304
      rho1=7910 !Densità AISI304
       
      rho2=3500 !Densità ABS
      E2=70e+6 !Modulo di young ABS
      ni2=0.37 !Coefficiente di Poisson ABS
       
      /prep7
      !Spigoli telaio
      k,1 $ k,2,l $ k,3,l,,w $ k,4,,,w
      k,5,,h $ k,6,l,h $ k,7,l,h,w $ k,8,,h,w
      k,9,,h1 $ k,10,l,h1 $ k,11,,h,w1 $ k,12,l,h,w1
      k,13,,h,w2 $ k,14,l,h,w2 $ k,15,,h,w3
      k,16,l,h,w3 $ k,17,,h2
       
      !Spigoli cassetta
      k,18,lc1,hc1,wc1 $ k,19,lc2,hc1,wc1
      k,20,lc2,hc1,wc2 $ k,21,lc1,hc1,wc2
      k,22,lc1,hc2,wc1 $ k,23,lc2,hc2,wc1
      k,24,lc2,hc2,wc2 $ k,25,lc1,hc2,wc2
       
      !Spigoli staffe
      k,27,lc1,h,w1 $ k,28,lc1,hs1,w1 $ k,29,lc1,hs2,w1
       
      k,31,lc1,h,w3 $ k,32,lc1,hs1,w3 $ k,33,lc1,hs2,w3
       
      k,35,lc2,h,w1 $ k,36,lc2,hs1,w1 $ k,37,lc2,hs2,w1
       
      k,39,lc2,h,w3 $ k,40,lc2,hs1,w3 $ k,41,lc2,hs2,w3
       
      k,42,lcc1,hcc2,wc2 $ k,43,lcc1,hcc1,wc2
       
      k,44,lcc2,hcc2,wc2 $ k,45,lcc2,hcc1,wc2
       
      !KEYPOINT CERNIERE/CHIUSURE
      k,56,lcera1,hcc2,wc2 $ k,57,lcera2,hcc2,wc2
      k,58,lcera2,hcer2,wc2 $ k,59,lcera1,hcer2,wc2
       
      k,60,lcerb1,hcc2,wc2 $ k,61,lcerb2,hcc2,wc2
      k,62,lcerb2,hcer2,wc2 $ k,63,lcerb1,hcer2,wc2
       
      k,64,lcerc1,hcer1,wc2 $ k,65,lcerc2,hcer1,wc2
      k,66,lcerc2,hcc1,wc2 $ k,67,lcerc1,hcc1,wc2
       
      k,68,lcerd1,hcer1,wc2 $ k,69,lcerd2,hcer1,wc2
      k,70,lcerd2,hcc1,wc2 $ k,71,lcerd1,hcc1,wc2
       
      k,72,lcere1,hcer1,wc2 $ k,73,lcere2,hcer1,wc2
      k,74,lcere2,hcc1,wc2 $ k,75,lcere1,hcc1,wc2
       
      !KEYPOINT COPERCHIO
      k,76,lcop1,hcop2,wc2 $ k,77,lcop2,hcop2,wc2
      k,78,lcop2,hcop1,wc2 $ k,79,lcop1,hcop1,wc2
      !Rinforzo coperchio
      k,80,lcop1,hcop2,wc2-0.01 $ k,81,lcop2,hcop2,wc2-0.01
      k,82,lcop2,hcop1,wc2-0.01 $ k,83,lcop1,hcop1,wc2-0.01
       
      !Ritti
      l,1,17 $ l,17,9 $ l,9,5 $ l,2,10 
      l,10,6 $ l,3,7 $ l,4,8
       
      !Traversi e longheroni
      l,1,2 $ l,2,3 $ l,3,4 $ l,4,1
      l,5,6 $ l,6,12 $ l,12,14 $ l,14,16 $ l,16,7
      l,7,8 $ l,8,15 $ l,15,13 $ l,13,11 $ l,11,5
      l,11,27 $ l,27,35 $ l,35,12
      l,13,14 $ l,15,31 $ l,31,39 $ l,39,16
       
      !Montante
      l,9,10
       
      !Traverse oblique
      l,17,2 $ l,1,8 $ l,6,3
       
      !Staffe
      l,27,28 $ l,28,29
      l,31,32 $ l,32,33
      l,35,36 $ l,36,37
      l,39,40 $ l,40,41
       
      !Aree relative alla cassetta
      a,18,22,28,29 !A1
      a,22,25,32,28 !A2
      a,28,32,33,29  !A3
      a,21,33,32,25 !A4
      a,18,29,33,21  !A5
      a,18,22,23,19 !A6
      a,18,19,20,21  !A7
      a,22,23,24,25 !A8
      a,19,37,36,23  !A9
      a,23,36,40,24 !A10
      a,36,37,41,40  !A11
      a,20,24,40,41 !A12
      a,19,20,41,37 !A13
       
      !Aree rinforzi cassetta
      a,25,42,43,21 !A14
      a,24,25,42,56,57,60,61,44 !A15
      a,24,44,45,20 !A16
      a,20,21,43,67,66,71,70,75,74,45 !A17
       
      !Aree cerinere
      a,56,57,58,59 !A18 
      a,60,61,62,63 !A19
      a,64,65,66,67 !A20
      a,68,69,70,71 !A21
      a,72,73,74,75 !A22
       
      !Area coperchio
      a,76,59,58,63,62,77,78,73,72,69,68,65,64,79 !A23
      !Aree rinforzo coperchio
      a,76,59,58,63,62,77,81,80 !A24
      a,77,81,82,78 !A25
      a,82,83,79,64,65,68,69,72,73,78 !A26
      a,76,79,83,80 !A27
       
      !Tipologia elementi,materiali e sezioni
      et,1,beam188,,,3 !Beam 188 con f.f. cubica
      mp,ex,1,E !Modulo Young material 1
      mp,nuxy,1,ni !Coeff poisson material 1
      mp,dens,1,rho !Densità material 1
      sectype,1,beam,hrec,tubquad !Sezione tubolare quad
      secdata,wh1,wh1,th1,th1,th1,th1 !Dati sezione tubolare quad
      sectype,2,beam,chan,upn160 !Sezione upn160
      secdata,wu1,wu1,wu2,tu1,tu1,tu2 !Dati sezione upn 160
      sectype,3,beam,rect,staffa !Sezione staffe
      secdata,bb,bh !Dati sezione staffe
      et,2,shell63 !Shell163 cassetta
      mp,ex,2,E1 !Modulo Young material 2
      mp,nuxy,2,ni !Coeff Poisson material 2
      mp,dens,2,rho1 !Densità material 2
      r,1,tc !Spessore dello shell
      et,3,shell63 !Shell163
      r,2,ws !Spessore dello Shell delle staffe
      et,4,shell63 !Shell163 cerniere
      r,3,wcer !Spessore cerniere
      mp,ex,3,E2 !Modulo di Young material 3 ABS
      mp,nuxy,ni2 !Coeff di Poisson material 3 ABS
      mp,dens,3,rho2 !Densità ABS
       
      !Meshing
       
      !Mesh telaio
      esize,0.05
      lsel,r,line,,1,28
      latt,1,,1,,,,1
      lmesh,all
      lsel,all
       
      lsel,r,line,,30,32
      latt,1,,1,,,,1
      lmesh,all
      lsel,all
       
      lsel,r,line,,29
      k,1000,,-1e+12
      latt,1,,1,,1000,,2
      lmesh,all
      lsel,all
       
      !Mesh staffe
      esize,0.02
      lsel,r,line,,33,40
      latt,1,,1,,,,3
      lmesh,all
      lsel,all
       
      !Mesh cassetta
      asel,s,area,,1,17
      type,2
      mat,2
      allsel,all
       
      asel,s,area,,23,27
      type,2
      mat,2
      allsel,all
       
      !Mesh chiusure
      asel,s,area,,18,19
      type,4
      mat,3
      allsel,all
       
      !Mesh cerniere in alluminio
      asel,s,area,,20,22
      type,4
      mat,2
      allsel,all
      amesh,all
       
      /eshape,1,1
      eplo
       
       
      !vincoli
      ksel,r,kp,,1,4,1
      nslk,r,n,all
      d,all,all
      allsel,all
       
      !ANALISI MODALE
       
      /solu
      antype,modal
      modopt,lanb,all,10,500
      mxpand,,,,yes,,,
      save
      solve
      finish
       
      !VIBRAZIONE LONGITUDINALE (LUNGO X)
       
      !ANALISI SPETTRALE PSD
       
      /solu
      antype,spectrum,new
      spopt,psd,,yes
      sed,1.0,0.0,0.0
      !DEFINIZIONE SPETTRO DI RISPOSTA DELLA STRUTTURA
      psdunit,1,accg,9.81
      spfreq,1,10,40,500
      spval,1,,0.078,0.078,0.0078
      pfact,1,base
      !psdgraph
      psdres,acel
      save
      solve
      finish
       
       
      ! COMBINAZIONE DEI MODI
      /solu
      antype,spectr
      psdcom,0,244
      solve
      finish
       
      !/post26
      !store,psd,244
      !nsol,
      !rpsd
      !plvar
       
      Can someone help me find the problem?
      Thank you!
       
    • Chandra Sekaran
      Ansys Employee

      You seem to be mixing up commands used for PSD analysis (SPOPT,PSD) and multipoint response spectrum analysis (SPOPT,MPRS). Commands like SED or SPFREQ, SPVAL are used for MPRS.  For PSD you specify the direction of excitation by giving a UNIT displacement to the nodes that are fixed in the modal analysis (e.g you select nodes fixed in X direction, then specify ux=1 to indicate that these nodes are to be excited in X direction). You also use PSDFRQ and PSDVAL commands to specify the input spectra. 

    • vgiordano3
      Subscriber

      Thank you a lot!

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