Incorrect Reaction for Unit Displacement
Incorrect Reaction for Unit Displacement
(OP)
Hi
I am modelling a lumped mass model of the outer shell of a Nuclear Containment Structure given in a research paper.It is a hollow cylinder with a dome placed on top.
To find out the total lateral stiffness, I applied a Unit displacement at the topmost node of the structure and checked the total reaction of the structure which is coming out to be less than the given value. I am doing a linear static general analysis in ABAQUS with concrete as the material.
I can't figure out what is causing the issue. Please help!
I am modelling a lumped mass model of the outer shell of a Nuclear Containment Structure given in a research paper.It is a hollow cylinder with a dome placed on top.
To find out the total lateral stiffness, I applied a Unit displacement at the topmost node of the structure and checked the total reaction of the structure which is coming out to be less than the given value. I am doing a linear static general analysis in ABAQUS with concrete as the material.
I can't figure out what is causing the issue. Please help!





RE: Incorrect Reaction for Unit Displacement
RE: Incorrect Reaction for Unit Displacement
Thank you!
RE: Incorrect Reaction for Unit Displacement
If it is a static model, the density is irrelevant unless you are considering the self weight. Regarding the poisons ratio, assuming that the vessel is concrete, are you trying to model it in a cracked state?
RE: Incorrect Reaction for Unit Displacement
I appreciate your effort to help me and I apologize for unsatisfactory information. I am new to this forum and I will improve upon this.
By shell, I meant to describe that I am only considering the outer concrete surface and not the internal components of the containment structure. I did not mean it as a shell element.
I am referring to the uncracked state. The paper gives the E as 29.16Gpa and G as 14.58Gpa and says nothing about the poissons ratio so I used the formula E=2G(1+v) to calculate it as 0. I gave it a mesh size of 1.165m and gave an ENCASTRE boundary at the base of the structure and a Unit Displacement boundary condition in the X direction at the top. I checked RF1 at the end of the Static General step which is about 50% less than what it should be. I have attached the input model for your reference.
http://link.springer.com/article/10.1007%2Fs11803-... is the link of the paper. If needed I can attach the PDF.
Thank you so much for your time.
RE: Incorrect Reaction for Unit Displacement
RE: Incorrect Reaction for Unit Displacement
I haven't tried shell elements as the paper mentions the use of solid elements for the analysis.
I used the tet mesh with a "free" orientation and reduced the mesh size a little more to about 0.9 which did result in a higher reaction than before but still about 25% less than what it should be. I used the C3D4H element in the mesh.
I will try iterating the mesh size to see if the value of RF1 reaches the level I want it to.
Do you have any other suggestion bkal?
Many thanks for your inputs.
RE: Incorrect Reaction for Unit Displacement
if you can use section force(sf) output for whole model in field output
then after run job in visiualization module use cut free body to observe the section force component in each increment.
good luck
RE: Incorrect Reaction for Unit Displacement
I tried iterating the mesh size. I found that as I increase the global mesh seed, the reaction force increases. I suppose this follows from the logic that a larger mesh size makes for a stiffer surface whereas a lower mesh size makes the surface more flexible. Even though now I am getting the reaction RF1 that I wanted but I don't know if I can trust this as when I checked the warnings, it said that there are several elements distorted.
Please help!
RE: Incorrect Reaction for Unit Displacement
RE: Incorrect Reaction for Unit Displacement
Use C3D8I or C3D20R elements or use at least 4 elements through thickness with C3D8R elements.