Hi

I am trying to carry out fatigue analysis of tubesheet (with tubes) of a heat exchanger. There are 2500 tubes in a quarter. As per my information there are 2 ways to model tubes

1. model a small portion of tubes using solid elements and model rest of the portion as beam element

2. convert the tubes into equivalent solid cylinders 

I am not sure about the applicability of second approach for calculating fatigue life. 

As far as first method is concerned,I have modelled the tubes but I am not able to give  constraints equations to all the solid-beam tubes. Is there any short method to apply constraints equations ?

If anyone knows any other method I would be grateful to know it.