Spring and Damper

k.manoj · Post by **k.manoj** » Wed Oct 24, 2007 2:02 am

Dear Dr. Silvia,

Are there elements representing spring and damper properties. Is it possible to model a link element with gap property
combined with spring and damper (Kelvin-Voigt element) in OpenSees.

silvia · Post by **silvia** » Wed Oct 24, 2007 7:36 am

you can try some of those elements that we do have (i'd use a zero-length element for a spring).
see the user manual:
http://opensees.berkeley.edu/OpenSees/m ... index.html

zhenxinli1999 · Post by **zhenxinli1999** » Sat Nov 03, 2007 1:12 am

Can zero-length element be used for two different joints?
In the OpenSees manual: Zero-length elements connect two points at the same coordinate.

silvia · Post by **silvia** » Sat Nov 03, 2007 7:11 am

the two nodes have to be at the same location.
otherwise, use a truss element.

zhenxinli1999 · Post by **zhenxinli1999** » Sat Nov 03, 2007 8:37 am

element zeroLength 35 54 11 -mat 2 -dir 3
This command is only for link relation of traslation along globle z axe. So I want to know the link relation of translation along globle X, Z axes or rotaion about globle X, Y, Z axes. fix or free?
Section Aggregator 1 2 Vy 5 Mz
The same question for section Aggregator. such as P, Vz is how to define.

silvia · Post by **silvia** » Sun Nov 04, 2007 8:08 am

you need to provide those constraints independently.

zhenxinli1999 · Post by **zhenxinli1999** » Mon Nov 05, 2007 12:10 am

If I didn't define the other constraints, the link relation of system default is what? fix or free?
I think it's free through some examples.
Is it right for all elements?

silvia · Post by **silvia** » Mon Nov 05, 2007 7:06 am

yes, it is unconnected.
be careful, you may get a singular stiffness matrix.

zhenxinli1999 · Post by **zhenxinli1999** » Mon Nov 05, 2007 6:33 pm

Thank you for reply
If I use a small elastic stiffness to define the link relation in a direction, is it the same result with no defined relation?

silvia · Post by **silvia** » Tue Nov 06, 2007 12:00 am

it is better to leave the constraints free if that's what you want.

zhenxinli1999 · Post by **zhenxinli1999** » Wed Nov 28, 2007 9:45 am

When I use the truss element to simulate the longitudinal friction hystereticrelation and the transversal friction hysteretic relation. THe OpenSees give warning for the following commands. Is there something wrong?
equalDOF 183 41 3 4 6
uniaxialMaterial Elastic 1 1.0e10
uniaxialMaterial Steel01 2 331.2 165600 0.1
uniaxialMaterial Steel01 3 1188.62 594310 0.1
section Uniaxial 2 2 Vy
section Uniaxial 3 3 Vz
section Aggregator 10 1 P 2 Vy 3 Vz
element truss 1 183 41 10
When I use the following commands, no warning appears, but transversal direction is fixed, not for hysteretic relation.
equalDOF 183 41 2 3 4 6
uniaxialMaterial Elastic 1 1.0e10
uniaxialMaterial Steel01 2 331.2 165600 0.1
uniaxialMaterial Steel01 3 1188.62 594310 0.1
section Uniaxial 2 2 Vy
section Uniaxial 3 3 Vz
section Aggregator 10 1 P 2 Vy 3 Vz
element truss 1 183 41 10

silvia · Post by **silvia** » Wed Nov 28, 2007 11:12 am

what kind of warning?

zhenxinli1999 · Post by **zhenxinli1999** » Wed Nov 28, 2007 9:23 pm

UmfpackGenLinDOE:setSize - n 1760 nnz 30470 IVal 609400
UMD2FA: matrix is singular. Only 1759 pivots found
WARNING UmfpackGeLinSolveCurrentStep<> -theLinearSysofEqn failed in solve<>
StaticAnalysis:: analyze<> - the Algorithm failed at iteration: 0 with at load factor 0.05
analyze failed, returned:-3 error flag
When the last line appears it means the result is unbelievable, right?

silvia · Post by **silvia** » Thu Nov 29, 2007 7:39 am

it means your stiffness matrix is singular -- you have not assigned any flexural stiffness to your section/elements.

zhenxinli1999 · Post by **zhenxinli1999** » Thu Nov 29, 2007 7:14 pm

I want to simulate the longitudinal and transversal friction hysteresis energy of bridge bearings. So I don't assign any flexural stiffness.
equalDOF 183 41 2 3 4 6
uniaxialMaterial Elastic 1 1.0e10
uniaxialMaterial Steel01 2 331.2 165600 0.1
section Uniaxial 2 2 Vy
section Aggregator 10 1 P 2 Vy
element truss 1 183 41 10
If I only simulate the longitudinal that's ok.
If I use the Zero-length Element that's ok.