About maxwell material

[khunglongkhelua]

Dear Vesna

I am using the maxwell material to model my damper. I have a question regard to the parameter K, C for the damper.

uniaxialMaterial Maxwell $matTag $K $C $a $L
$matTag integer tag identifying material
$K Elastic stiffness of linear spring (to model elastic stiffness of viscous damper)
$C Viscous parameter of damper
$a Viscous damper exponent
$L Viscous damper length

What is the relationship between the viscous parameter to the force? Is it F = C(v)^ alpha or stress = C(strain-rate)^alpha.
And for the parameter K, in the example http://opensees.berkeley.edu/wiki/index ... l_Material it is (kN/mm) but I did some examples and K seems to be the modulus of elasticity stress = K* strain, not force = K*displacement.

And do you have any example people model damper by maxwell material besides this example . http://opensees.berkeley.edu/wiki/index ... l_Material
I am looking forward to your reply.
Thanks a lot.

[vesna]

Maxwell material defines a force(F)-velocity(v) relationship of the form: F = K*u + C*v**a
// K: axial stiffness of a damper
// C: Velocity constant of a damper
// Alpha: Exponent of velocity of a damper
// L: Length of the Damper

This is a very recent material and the example you mentioned is the only one we have so far.

[khunglongkhelua]

Dear vesna

Can you tell me where can I see the equations Dr. Dimitrios G. Lignos used for his Maxwell material ? I still have trouble to understand his example http://opensees.berkeley.edu/wiki/index ... l_Material.

My second question is in his example, what are these codes for ?

set LoadPat 1
# Unit Load Pattern in X direction
pattern Plain $LoadPat "Linear" {

# nd FX

load 2 0.01 0.0 0.0

}

Thanks a lot

[khunglongkhelua]

And in your previous post, you said that F = K*u + C*v**a

I thought the Maxwell Material is a linear spring and nonlinear dashpot in series hence F = ku = cv**alpha ? Please reply me as soon as possible. Thanks a lot.

[vesna]

You can find equations that Dimitrios used for his model in the source code:
Here is a header file: http://opensees.berkeley.edu/WebSVN/fil ... FMaxwell.h
Here is a cpp file: http://opensees.berkeley.edu/WebSVN/fil ... axwell.cpp

The part of the code you showed defines a linear load pattern that applies reference load of 0.01 in the global X direction at node 2. You can find the syntax for definition of a load pattern here: http://opensees.berkeley.edu/wiki/index ... in_Pattern.

[khunglongkhelua]

Dear vesna

Thanks for your help. I understand about the syntax of a load pattern, I just don't understand why we have to do that, I erased these lines and the program still runs normally .