"力学体系" can be translated into English as "mechanical system" or "dynamics system" (though "mechanical system" is more commonly used and straightforward in this context).
Mechanical system refers to a collection of physical bodies and their interactions governed by the principles of mechanics.
Dynamics system (less commonly used for this specific meaning) typically emphasizes the study of motion and forces but can sometimes be used more broadly in contexts related to dynamic behavior, though "mechanical system" is more precise for "力学体系".
For most contexts, especially in engineering and physics, "mechanical system" is the preferred and most accurate translation.