how to get the external force from presribed BC.s in N-R method?

ying · Jul 12, 2001

I am doing the non-linear viscoelastic problem by Newton-Raphson method.

And I am now trying to test the code by a bar, one end is constrained
while the other is under prescribed displacement u=at, where a is a constant.

The questions are:

1. how to get reaction forces acted at the two ends by the prescribed displacements?

2. for r=p-f, should the applied load be 0 or be the reactions due to the BC.s at the
two ends?

3.Do I need to modify the jacobin stiffness matrix for the essential BC.s during
each iteration?

thanks a lot!

ying

brad · Jul 17, 2001

I'll answer what I think your questions are. If I've misunderstood what you're asking, please clarify.
1. After you solve for u and u' vectors, this becomes "simple" tensor algebra. Multiply your "stiffness" matrices (I'm using the term generically wrt the viscoelastic contribution) by your u and u' vectors to solve for the reactions (I am presuming no inertial effects here--hence quasi-static).
2. There is no "applied load" in your case. I take "applied load" to mean that F(t) is explicitly defined a priori. In your case, F(t) is an unknown, hence a reaction force. For both ends, F(t) should be expected to be non-zero for most t (although it could approach zero as time goes to infinity, depending on your model). Both ends should be equal in magnitude and opposite in direction.
3.Yes.

Brad

brad · Jul 18, 2001

Let me correct my own mistake before somebody else does.
In (quasi-static) viscoelastic analysis, u' does not enter into the equation (answer to #1). You only solve for the u vector.
Long day yesterday. The mind misfired.

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

how to get the external force from presribed BC.s in N-R method?

ying

Mechanical

Recommended for you

brad

Mechanical

brad

Mechanical

Similar threads

Part and Inventory Search

Sponsor