Ok, so we're running a compressor rig powered by an air turbine that keeps breaking. I've been asked to review the rotordynamics for the entire system. Prior to my employment, the compressor shaft itself was evaluated, however they want the effect of the turbine and the spline couplings to be included in the model. My question is if anyone has any experience in this, or even a paper on the topic. I googled and found what seems to be a decent paper titled Effect of coulomb spline on rotor dynamic response Which SHOULD be available on the NASA technical report server, but the entire site is down. I also found a paper titled DDM Rotordynamic Design Sensitivity Analysis of an APU Turbogenerator Having a Spline Connection but unfortunately that paper didn't indicate (probably purposely) how the actual connection was modeled. So, I have two approaches. The first is a Transfer-Matrix method using a program such as Dyrobes (XLRotor, etc). This assumes that everything is a cone/cylinder and computes everything analytically. In that case, I will need to define a "bearing" stiffness/damping value to connect the shafts. The second approach is finite element using ANSYS. In this case I would connect the two shafts using....? I'm guess it would have to be contact elements. I would assume that coupling equations would be "too stiff". Either way, I'm sure that a damping value would need to somehow be input. So, I will stop rambling thanks for the help.