# Boundary conditions for a grid tube under combined loading

• Vigardo
In summary, the individual is seeking advice on how to model the linear buckling behavior of a cylinder using ANSYS Mechanical. They are specifically asking for guidance on setting up the boundary conditions to keep the ends rigid while allowing for motion under combined loading. The individual has tried using the CERIG command but encountered confusing results, with the buckling modes under combined loading being the same as those under pure axial compression. They believe they have correctly selected master and slave nodes, and the results from the initial static analysis seem satisfactory. They are looking for any comments or suggestions on what could be done differently.
Vigardo
Dear experts,

I´m trying to model in ANSYS Mechanical (v14.5) the linear buckling behavior of a cylinder made of BEAM4 elements under combined loading (axial compression and bending moment) applied at the ends.

How should I set up the boundary conditions of a cylinder to keep rigid the ends while allowing their motion under both compressive force and moment?

After rigidifying one end of a cylinder made of BEAM4 elements with the CERIG command (CERIG,P) I´ve found confusing results: the buckling modes under combined loading are equal to the modes obtained only under pure axial compression. All nodes from the other end were fully clamped. I think that I successfully selected master and slave nodes and that the results from the initial static analysis seem ok, i.e. the moment applied at the master node node leads to some curvature and the axial force to some compression while the end nodes keep rigid.

What am I doing wrong? Any comments would be highly appreciated.

Thanks a lot in advance!

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

## 1. What are boundary conditions for a grid tube under combined loading?

Boundary conditions for a grid tube refer to the set of constraints that are applied at the boundaries of the tube in order to accurately model its behavior under combined loading, which includes both axial and lateral forces.

## 2. Why are boundary conditions important for a grid tube under combined loading?

Boundary conditions are crucial for accurately predicting the behavior of a grid tube under combined loading because they define the limits of the tube's movement and deformation, and thus affect the overall structural integrity and stability of the tube.

## 3. How are boundary conditions determined for a grid tube under combined loading?

The boundary conditions for a grid tube under combined loading are typically determined through a combination of experimental testing and numerical simulations. This involves subjecting the tube to different load configurations and measuring its response, which is then used to calibrate the boundary conditions in the simulation model.

## 4. What are some common boundary conditions used for a grid tube under combined loading?

Some common boundary conditions for a grid tube under combined loading include fixed supports at the ends of the tube, which prevent translation and rotation, and prescribed displacements or loads at specific points along the tube's boundaries.

## 5. How do boundary conditions affect the results of a grid tube under combined loading analysis?

The choice and accuracy of boundary conditions can significantly impact the results of a grid tube under combined loading analysis. Incorrect or incomplete boundary conditions can lead to inaccurate predictions of the tube's behavior and potentially compromise the safety and reliability of the structure.

• Mechanical Engineering
Replies
2
Views
2K
• Mechanical Engineering
Replies
1
Views
4K
• Mechanical Engineering
Replies
1
Views
2K
• Mechanical Engineering
Replies
23
Views
36K