Hi, I am designing a wave energy converter, which has one degree of freedom - heaving motion. Meaning it will move only in vertical direction. My system can be considered as a Mass Spring Damper system. Thus my equation of motion is: F=Fh+Fe Where, Fe= Excitation force (Wave force) F=m*a (mass times acceleration) Fh= -m(a)*a - b(hyd)*v - k*x (hydromechanical load) m(a) - added mass b(hyd) - damping coefficient v - velocity k - spring coefficient x - distance However, I also want to add a power extracting device to my system, which can be considered a generator. I have read many papers and they usually add a external damping force to enable power extraction. Fb(ext)=-b(ext)*v Thus my new equation of motion would be: F=Fh+Fb(ext)+Fe And finally my question. I would like to understand the physical meaning behind the external damping force. Does it mean that it is just a resistance (load) applied to the system to enable power extraction?