## General Mechanical

#### How to assign boundary conditions for this physical problem to calculate the static deflections?

• arv2995
Subscriber

I wish to know the boundary conditions for this physical problem to calculate the static deflection of the shaft in lateral direction at various locations .

I have to do the structural analysis and check the static deflection of a shaft. The following is the arrangement of the system. The shaft is supported with 2 bearings. It also has 2 rotors at its 2 ends. I wish to apply the boundary conditions in ANSYS Structural so that the solver does not gives errors.

If we consider each bearing it has 2 reaction forces and 2 moments as unknowns, each. The values of reaction force and moment are already known calculated through another type of analysis. Can we use these values as boundary conditions?

Kindly help me with this problem.

• Ashish Khemka
Ansys Employee

You can model the bearings using cylindrical support and the weight of the compressor rotor and turbine can be modeled at the shaft ends using point mass. Cylindrical support will allow you to constrain the radial, axial and tangential motion.

Regards Ashish Khemka

• arv2995
Subscriber
Hello Ashish
As for the rotor of compressor and turbines I do not have to create the point masses as I already have the actual 3D geometry with me to which I am assigning conditions. I have given Moment of inertia and material properties to various parts of the geometry.
Also, I will try using the Cylindrical support. But I do not want to constrain the axial motion at the points of the 2 bearings as they are radial bearings and not axial bearings. Is there any other way I can achieve that?

• Ashish Khemka
Ansys Employee

How is the motion of the shaft constrained in the axial direction? Something must be keeping the shaft in place.
Regards Ashish Khemka

• arv2995
Subscriber
Hi
There is an axial bearing near the compressor side. But I have not taken it for consideration here as I want lateral displacements.
• Ashish Khemka
Ansys Employee

You can use a longitudinal spring (low stiffness) and can see the axial deformation.

Regards Ashish Khemka