Spring force calculation in PSD analysis

[ScottMf]

I am doing a simple PSD analysis on a 2 spring 2 mass system (spring attached to floor, attached to mass, attached to spring, attached to mass). When I compare the force ansys gives for spring 1 it is equal to the spring constant times sigma 1 (the average displacement of mass 1) as expected, when calculating the force on spring 2, however, it is not just K2*(sigma1-sigma2) which makes sense because it assumes the two masses are in phase. The question is then how ansys calculates this force; does it compute the force sequentially during the calculation and thus take into account the phase of the two masses, or does it use some other method to compute this force?

Thanks,
Scott