Hi Rana,

Okay, but if you want to study the dynamics of a mass and spring system, and you are idealizing the mass to a point mass and are idealizing the springs to linear elastic springs, then the dynamic response is the textbook case of a Mass-Spring system. I can write the equation of motion for that, or I can build a model to simulate the response and let ANSYS numerically calculate the response.

You might want to compare the textbook Mass-Spring system to the response of a more complex system to draw analogies, or to make a 1 DOF representation of a complex system. In that case, it doesn't matter if you replace the convective mass of water with a rigid solid body, it is an idealization of the system to a 1 DOF system.

Regards,

Peter