General Mechanical

Boundary condition

• andimens13
Subscriber

Please I am analysing an electrical cabinet using shell elements. The cabinet is mounted on top of an existing cabinet via 4 vertically oriented bolts at 4 corners, this one per corner. I had to change the geometry to mid-surfaces on spaceclaim before. However when I apply my fixed support at the bottom holes where the bolts are to be inserted in real life? I am getting huge stress values. I think this is more of stress singularity. Will I be right to apply the fixed support at the bottom of the cabinet instead of the hole edges at the corners of the cabinet. Will I be over simplifying the situation by doing that? I am suppose to apply 1g vertical, 1g lateral and 1g longitudinal acceleration on the cabinet to check for equivalent stress and deformation any where on the cabinet.

• peteroznewman
Subscriber

Inserting an image of your geometry will give us better understanding of your model to make suggestions.

Does the bottom of the bottom cabinet have four feet that are bolted to the floor?  If so, those four feet could be Fixed Supports.

How are you modeling the bolted connection between the top and bottom cabinets? There are several methods. A good method is to use a beam to represent each bolt at each corner. The reference end of the beam is scoped to the hole in the top of the bottom cabinet, the mobile end of the beam is scoped to the hole in the bottom of the top cabinet.

I don't understand why you would get a huge stress value. Again, an image would help.

• andimens13
Subscriber

The cabinet itself is been analysed as a stand alone equipment see attcahed image for clarity. I first inserted beam elements at the fixing holes at the bottom and assigned fixed support at the vertexes, stresses were quite high. so i have decided to do the bolt calcs via classical calculation.

• peteroznewman
Subscriber

1) Avoid using Vertices as fixed supports because that can generate high stresses. Why would you not use the edge of the circular hole on the bottom of the bottom cabinet as the fixed support?

2) Even if there is a high stress on the vertices on the bottom side of the bottom cabinet, that won't affect the Beam Probe values of axial force and shear force going through the beams connecting the top cabinet to the top of the bottom cabinet.

It would be helpful if you would label holes on the image of the bottom cabinet. I don't know if I am looking at the top, the bottom or the side of the cabinet.