Learning Forum

[ankitdv98]

Hello everyone,

I am working on structural analysis of turbine and i have to study the response under rotation, for now i have considered a small disk mounted on shaft supported on two bearings

• Bearings i have provided on edges of steps in the shaft and providing stiffness (K11 & K22 = 1E+06 N/mm)


• At the end faces i have provided remote displacements (only rotation allowed about the longitudinal axis)


• and RPM to both bodies i am providing for centrifugal load

Can anyone check whether i am applying correct boundary conditions means my model is correct or not or it need any changes, model screenshot also attached.

configuration i am working on also attached.

 

As per configuration, right end of shaft would be coupled to generator so only rotation about longitudinal axis & rest constrained seems fine but at left end should i allow translations as well.

Also why does it give deflection in all directions when only standard earth gravity is applied although values are very very small? Since under the influence of gravity it should bend only in Y(downward) direction.

 Please anyone check the model and suggest if any changes needed

Thanks

 

 

 

[ankitdv98]

Model:

[BenjaminStarling]

Hello,

Typically you would constrain the longitudinal direction at the end of the shaft that is connected to something that is fixed to ground (the generator). You may also constrain the other two translations at this end of the shaft but it is not always that simple. In reality constraining translations and bending is acheived across the couplings and bearings.

In your model as currently configured, the bearings will be doing nothing. The translations and bending rotations are constrained at the end of the shafts, therefore the only degree of freedom left is the desired rotation of the shaft, of which bearings offer no stiffness to.

Consider releasing all degrees of freedom at the shaft ends, other than the longitudinal translation at the generator end.

Then include other constraints incrementally to see their effect. For instance, couplings on the generator/motor end can be very stiff able to transfer bending rotations, but they can also be built with flexibilty between components.

Regarding your small displacements in directions other than Y. This is normal, although they should be very small, orders of magnitude smaller than the y displacement.