Transient - Contact Analysis in Ansys

[dimikallio]

Hi all!

I am trying to solve a transient contact analysis in Ansys 14.0

The problem is a Bouncing Rectangle problem. That's the procedure I use:

/Prep7

k,1,-30,0,0
k,2,30,0,0
k,3,-30,30,0
k,4,0,30,0
Create->Areas->Arbitrary->Through Keypoints !Create the ground

k,50,-20,30,0
k,70,-20,45,0
k,80,0,45,0
Create->Areas->Arbitrary->Through Keypoints !Create the foundation

k,500,-10,95,0
k,600,0,95,0
k,700,-10,105,0
k,800,0,105,0
Create->Areas->Arbitrary->Through Keypoints !Create the bouncing rectangle

Element Type->
Type1->Plane183 (Stress with thickness) rectangle
Type2->Plane183 (Stress with thickness) foundation
Type3->Plane183 (Stress with thickness) ground

Real Constants

Set1->Plane183 (Thickness=10)
Set2->Plane183 (Thickness=10)
Set3->Plane183 (Thickness=10)

Add Materrial Properties
Material 1 (rectangle)
EX=4400 ksi
Poisson Ratio=0.25
Bilinear : Yield Stress=4, Tangent=220
Material 2 (foundation)
EX=5100 ksi
Poisson Ratio=0.25
Bilinear : Yield Stress=6, Tangent=255
Material 3 (ground)
EX=5500 ksi
Poisson Ratio=0.25
Bilinear : Yield Stress=8, Tangent=280

Glue Areas (foundation & Ground)

Meshing: Edge Length=2 for all

Contact Pair (surface to surface): Using Contact Wizard: Target=Area of Foundation, Contact=Area of Rectangle

Create Component: Based on Material Type : Rectangle

Solution

-Type=transient (No lumped mass approach)
-Large Transiend Displacement
-Automatic Stepping=off
TIMINT,off
-Time=0.0002
-Time step size=0.0001
-Rayleigh Damping:Stiffness Matrix Multiplies=0.0002
-Component (Rectangle) Acceleration=386.4
-Force Convergence=0.00001
-Apply->Displacement->Nodes->Select all->All DOFs
Solve
-Delete->Displacement->Nodes->Select all->All DOFs
-Apply->Displacement->Lines->(Fix foundation and Ground)
-Timint,on
-Time=3
-Automatic time stepping=on
-Initial time step size=0.02 with min 0.0002 and max 0.02
-Reset force convergence tolerance
-Save results for every time step
Solve

That's all I do

The questions I have are:
-Do I need to define any initial stiffness for the contact or I just should let the program calcualate it according to the material properties I am defining>
-When I define global gravity for the whole system, the rectangle falls down w/o even getting in contact with the foundation!
-When I plot the displacement and velocity everything looks fine. However, in the animation I did the rectangle does not get in touch! in all the impacts that take place!So, the forces I get are wrong!Should I do anything extra to correct that!?
-I want to solve also a problem that the contact and the target surfaces are in both surfaces (symmetric contact pair) because the material properties I use are not much different for the rectangle and the foundation! So, should I have the target rigid or I can just use flexible to flexible?
-Sometimes, I have convergence problems. Should I change any of the contact default options to correct that? (ICONT, CNOF,close gap,exclude everything,gap and offset,penalty of augmented method, contact stiffness etc). I tried to change some of them but I didn't find any difference in the solution. And ansys doesn't provide any recommendations about all these...

Thank you!

 

[Navin A S]

</code>This looks like a challenging problem. I'm not sure I have all the answers, but here are some suggestions that may help you.Do I need to define any initial stiffness for the contact or I just should let the program calcualate it according to the material properties I am defining?No, you don't need to define any initial stiffness. Ansys should be able to calculate the appropriate stiffness based on the material properties you've defined.When I define global gravity for the whole system, the rectangle falls down w/o even getting in contact with the foundation!Gravity should not affect the contact. If the rectangle is falling down without contacting the foundation, you may need to adjust the geometry of the rectangle or the foundation to ensure they make contact.When I plot the displacement and velocity everything looks fine. However, in the animation I did the rectangle does not get in touch! in all the impacts that take place!So, the forces I get are wrong!Should I do anything extra to correct that!?If the forces are wrong, then there may be an issue with either the geometry or the material properties. Make sure that the geometry is set up correctly and that the material properties are accurate. You may also need to adjust the contact parameters to ensure that the contact is modeled correctly.I want to solve also a problem that the contact and the target surfaces are in both surfaces (symmetric contact pair) because the material properties I use are not much different for the rectangle and the foundation! So, should I have the target rigid or I can just use flexible to flexible?It depends on the application. If you want to model the contact accurately, then you should use a flexible to flexible contact. If you only want to approximate the contact, then a rigid to flexible contact may be sufficient.Sometimes, I have convergence problems. Should I change any of the contact default options to correct that? (ICONT, CNOF,close gap,exclude everything,gap and offset,penalty of augmented method, contact stiffness etc). I tried to change some of them but I didn't find any difference in the solution. And ansys doesn't provide any recommendations about all these...If you're having convergence issues, then you may need to adjust some of the contact parameters. Start by adjusting the contact stiffness and then adjust the other parameters if