Learning Forum

[vgiordano3]

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]

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]

Thank you a lot!