Create rotational spring at beam ends
Create rotational spring at beam ends
(OP)
Hi,
I want to model a beam and find it's natural frequency. At the end of the beam I want to add a rotational spring. Therefore I define a double node at the same coordinates and use Combin 14 (Also tried combin7). I used the D command on the node that only connects to the Combin element and coupled the UX and UY of both coincedent nodes.
This however doesn't seem to work. Using the Combin 7 element there is no influence of the rotational stiffness. When using combin 14 I need to use the D command on both nodes, otherwise it gives rigid body movement
Is this the correct element and am I using it correctly
Any help is greatly apreciated
Here the input file
FINISH
/CLEAR,START
/BATCH
! /COM,ANSYS RELEASE 8.1A1 UP20040609 15:01:53 10/27/2004
!*
/NOPR
/PMETH,OFF,0
KEYW,PR_SET,1
KEYW,PR_STRUC,1
/GO
/PREP7
!Parameters in in standaard eenheden
Blength=10 !in meter
Bmass=10
Bnodes=51
massa=100 !in kg
Emodulus=2.1e5 !in N/mm2
Akom=1000e4 !in mm4
Hoogte=200 !in mm
RotatiestijfheidLinks=1e10 !in Nm/rad
RotatiestijfheidRechts=1e10 !in Nm/rad
!Omrekenen naar SI-eenheden
rekEmodulus = Emodulus*1e6
rekAkom = Akom/1e12
rekHoogte =Hoogte/1000
rekOpp = 1
ET,1,BEAM3
ET,2,COMBIN7
ET,3,COMBIN14,0,6
KEYOPT,1,6,0
KEYOPT,1,9,9
KEYOPT,1,10,0
R,1,rekOpp,rekAkom,rekHoogte,0,0,massa
!R,2, , , ,RotatiestijfheidLinks
!R,3, , , ,RotatiestijfheidRechts
R,4, RotatiestijfheidLinks
R,5, RotatiestijfheidRechts
MP,EX,1,rekEmodulus
MP,PRXY,1,0.3
TYPE,1
MAT,1
REAL,1
!Creeer knopen
*DO,teller,1,Bnodes,1
N,teller,(teller-1)*Blength/(Bnodes-1),0
*ENDDO
!Dubbele knopen tbv veer
N,Bnodes+1,0,0
N,Bnodes+2,Blength,0
!Hulpknopen tbv combin7 element
!N,Bnodes+3,0,0,1
!N,Bnodes+4,Blength,0,1
!Balkelementen
*DO,ecurrent,1,Bnodes-1,1
EN,ecurrent,ecurrent,ecurrent+1
*ENDDO
!Combin14 elementen
TYPE,3
REAL,4
EN,Bnodes,Bnodes+1,1
REAL,5
EN,Bnodes+1,Bnodes+2,Bnodes
!Koppelen van translatie vrijheidsgraden in de dubbele knopen
CP,1,UX,Bnodes+1,1
CP,2,UY,Bnodes+1,1
CP,3,UX,Bnodes+2,Bnodes
CP,4,UY,Bnodes+2,Bnodes
!CP,5,ROTZ,Bnodes+1,1
!CP,6,ROTZ,Bnodes+2,Bnodes
!D, 1, UX, 0, , Bnodes, Bnodes-1, UY
D, Bnodes+1, UX, 0, , , , UY,ROTZ
D, Bnodes+2, UX, 0, , , , UY,ROTZ
!Rvw knopen aan balkelement. Het lijkt me niet dat deze vastgezet moeten worden, maar wanneer dit niet gebeurd is
!het resultaat een verticale translatie. Het vastzetten zou met het CP commando moeten zijn verzorgd.
!D, 1, UX, 0, , , , UY
!D, Bnodes, UX, 0, , , , UY
FINISH
/SOL
ANTYPE,2
MODOPT,LANB,5
EQSLV,SPAR
MXPAND,5, , ,0
LUMPM,0
PSTRES,0
SOLVE
FINISH
/POST1
SET,1,1
/DSCALE,ALL,AUTO
/VIEW,1,1,1,1
/ANG,1
/PNUM,NODE,1
/PSYMB,DOT,1
/PBC,ALL,,1
PLDI, ,
ANMODE,20,0.1, ,0
FINISH
I want to model a beam and find it's natural frequency. At the end of the beam I want to add a rotational spring. Therefore I define a double node at the same coordinates and use Combin 14 (Also tried combin7). I used the D command on the node that only connects to the Combin element and coupled the UX and UY of both coincedent nodes.
This however doesn't seem to work. Using the Combin 7 element there is no influence of the rotational stiffness. When using combin 14 I need to use the D command on both nodes, otherwise it gives rigid body movement
Is this the correct element and am I using it correctly
Any help is greatly apreciated
Here the input file
FINISH
/CLEAR,START
/BATCH
! /COM,ANSYS RELEASE 8.1A1 UP20040609 15:01:53 10/27/2004
!*
/NOPR
/PMETH,OFF,0
KEYW,PR_SET,1
KEYW,PR_STRUC,1
/GO
/PREP7
!Parameters in in standaard eenheden
Blength=10 !in meter
Bmass=10
Bnodes=51
massa=100 !in kg
Emodulus=2.1e5 !in N/mm2
Akom=1000e4 !in mm4
Hoogte=200 !in mm
RotatiestijfheidLinks=1e10 !in Nm/rad
RotatiestijfheidRechts=1e10 !in Nm/rad
!Omrekenen naar SI-eenheden
rekEmodulus = Emodulus*1e6
rekAkom = Akom/1e12
rekHoogte =Hoogte/1000
rekOpp = 1
ET,1,BEAM3
ET,2,COMBIN7
ET,3,COMBIN14,0,6
KEYOPT,1,6,0
KEYOPT,1,9,9
KEYOPT,1,10,0
R,1,rekOpp,rekAkom,rekHoogte,0,0,massa
!R,2, , , ,RotatiestijfheidLinks
!R,3, , , ,RotatiestijfheidRechts
R,4, RotatiestijfheidLinks
R,5, RotatiestijfheidRechts
MP,EX,1,rekEmodulus
MP,PRXY,1,0.3
TYPE,1
MAT,1
REAL,1
!Creeer knopen
*DO,teller,1,Bnodes,1
N,teller,(teller-1)*Blength/(Bnodes-1),0
*ENDDO
!Dubbele knopen tbv veer
N,Bnodes+1,0,0
N,Bnodes+2,Blength,0
!Hulpknopen tbv combin7 element
!N,Bnodes+3,0,0,1
!N,Bnodes+4,Blength,0,1
!Balkelementen
*DO,ecurrent,1,Bnodes-1,1
EN,ecurrent,ecurrent,ecurrent+1
*ENDDO
!Combin14 elementen
TYPE,3
REAL,4
EN,Bnodes,Bnodes+1,1
REAL,5
EN,Bnodes+1,Bnodes+2,Bnodes
!Koppelen van translatie vrijheidsgraden in de dubbele knopen
CP,1,UX,Bnodes+1,1
CP,2,UY,Bnodes+1,1
CP,3,UX,Bnodes+2,Bnodes
CP,4,UY,Bnodes+2,Bnodes
!CP,5,ROTZ,Bnodes+1,1
!CP,6,ROTZ,Bnodes+2,Bnodes
!D, 1, UX, 0, , Bnodes, Bnodes-1, UY
D, Bnodes+1, UX, 0, , , , UY,ROTZ
D, Bnodes+2, UX, 0, , , , UY,ROTZ
!Rvw knopen aan balkelement. Het lijkt me niet dat deze vastgezet moeten worden, maar wanneer dit niet gebeurd is
!het resultaat een verticale translatie. Het vastzetten zou met het CP commando moeten zijn verzorgd.
!D, 1, UX, 0, , , , UY
!D, Bnodes, UX, 0, , , , UY
FINISH
/SOL
ANTYPE,2
MODOPT,LANB,5
EQSLV,SPAR
MXPAND,5, , ,0
LUMPM,0
PSTRES,0
SOLVE
FINISH
/POST1
SET,1,1
/DSCALE,ALL,AUTO
/VIEW,1,1,1,1
/ANG,1
/PNUM,NODE,1
/PSYMB,DOT,1
/PBC,ALL,,1
PLDI, ,
ANMODE,20,0.1, ,0
FINISH





RE: Create rotational spring at beam ends
RE: Create rotational spring at beam ends
I'll try and describe it.
At the beam ends I want to restrict in a certain amount the free rotation, so when the beam-end rotates, a moment, proportional to the rotation is created.
RE: Create rotational spring at beam ends
I think you need KEYOPT(3) = 1 for the combin14 (KEYOPT,3,3,1 in your input deck OR ET,3,COMBIN14,0,0,1), hopefully it will be clear (and a lot easier than me trying to explain) if you look at the help file for combin14. If KEYOPT(2) is zero, the length of the spring-damper element must not be zero, i.e., nodes I and J should not be coincident, since the node locations determine the spring orientation. Hence, go to a 3D beam but constrain all the Z-DOF and rotations, and make the spring nodes non-coincident. Don't forget to ground (apply constraint to) the spring nodes!
Good luck,
-- drej --
RE: Create rotational spring at beam ends
Thanx for your answer. Though it didn't prove to be giving the correct geometry it put me on the track of checking the DOF. I use COMBIN14 with KEYOPT(2)=6, which results in a spring with only the ROTZ DOF. It also requires the nodes to be at the same coordinates.
Because it only has the ROTZ DOF it can't use the info that the UX and UY DOF are set to be 0 (fixed), and so the coupling doesn't work.
By only fixing the ROTZ for node 1(only Combin14) and the UY and UX for node 2(Connection node between Combin14 and Beam) it works great.