Cannot Plot Beam 3 Displacement Information 1

[seymours2571]

Hello,

I am new to Ansys so forgive me if I am asking a stupid question. The problem I am having is that I cannot plot the UY beam deflections. The end rotations can be plotted and match exactly with theory, but for some reason the displacement data within the results does not seem to be present. I would like to graph it across the beam element, but for now I would settle with just getting some results.

My model consists of a single beam modeled with two nodes 24 inches appart. I am using the BEAM 3 element and applying to concentrated moments at both nodes (i.e. M1=-M and M2=+M).

Not sure what the deal is. Would appreciate any help anyone can offer.

Thanks,

Steve

 

[Drej]

Not sure I completely understand your model. Guess that your beam axis is along the global X-axis, but you haven't mentioned how the beam is constrained along X or Y. When you say "displacement data within the results doesn't appear to be present" what does this mean exactly?

Cheers,

-- drej --

 

[seymours2571]

Thanks for the quick response Drej.

Here is a better explination of the model. Single beam element. Node 1 is located at 0,0,0 Node 2 is located at 24,0,0. Beam element 3 is the element type. UX and UZ are constrained at both nodes 1 and 2, MZ at nodes 1 and 2 are unconstrained.

Loading consists of a negative moment applied to node 1 and a equal but positive moment applied to node 2.

After solving the problem, I plot the nodal solutions for the rotations. The values at nodes 1 and 2 are correct with theory and the plot shows the distribution of the rotation throughout the beam element from node 1 to node 2 (i.e. left to right).

However, when I try to plot the nodal solution for the vertical displacement throught the beam element (i.e. UY) Ansys does not indicate an answer or I am not aquiring the results for UY correctly.

Thanks,

steve

 

[Drej]

Steve - First of all do away with your UZ constraint, that DOF is not active anyway. Secondly, you're not seeing any reasonable UY displacements because your model is probably in rigid body motion (so the displacement of the whole body will be enormous) since there is NO constraint in the Y-direction. If you were to check warnings in the output it would indicate this. You have to constrain your model such that it doesn't just fly off in space - there is nothing stopping the beam from flying off in the Y-direction at the moment.

Cheers,

-- drej --

 

[seymours2571]

Sorry Drej, typo on the UZ. I actually do have both nodes constrained in both the UX and UY.

What is stumping me is why I can get a nodal plot through the beam element showing the rotational displacement (about the z axis) and can't create a nodal plot of the UY disp.

 

[Drej]

If you have a single element with just two nodes, and you constrain all of the available DOF of that element, what would be the response? Zero. Beam3 is a linear (first order) beam - it does not have midside nodes - hence nor does it have its solution integrated across the width of the beam. Remember also that UY (displacement) is a nodal quantity, thus, if you have no nodes for results, you have no results! The only solution available therefore is the rotation at the ends. You need more than just a single element for this problem. Would suggest you try with 3 elements to start, check the displacement, then re-mesh with 6 elements, check the displacement again. If there is very ilttle change between the two results (~5%), then your model has converged. Do that and the problem is solved.

Cheers,

-- drej --

 

[seymours2571]

Drej,

Thanks a million for the insight. I see it know. I went back through the Ansys theory and looked at the shape function equation itself. I guess I had a momentary lapse of stupidity.

Thanks again for your help.


Steve