The Discrete Element Method (DEM) differs from the finite element method, which is based on the principle of minimum potential energy variation. Instead, DEM is grounded in Newton’s second law, making it fundamentally rooted in classical mechanics. Its conceptual foundation can be traced back to ancient approaches of force analysis, where any object is treated as an isolated entity. In this framework, each object is influenced by forces and moments exerted by its neighboring objects. These combined forces and moments lead to deformation and motion. This approach is well-suited for computational implementation, as each discrete unit can be modeled individually. By formulating explicit equations for each unit and applying Newton’s second law along with various constitutive relations, differential equations are solved through iterative calculations. When integrated with animation technology, DEM provides a clear and visual representation of how mechanical parameters—such as stress fields, displacement fields, and velocity fields—evolve over time. Importantly, this method is not constrained by the number of objects in the system, making it highly flexible for complex simulations.
In the context of rotor systems, the interaction between the journal and the bearing, as well as the rotor and the casing, follows a similar constitutive relationship. Both are simplified into pairs of normal and tangential spring-damper elements, along with a tangential sliding friction model. Notably, the spring-damper (Ks-Cs) and the sliding friction mechanism are combined. When the tangential force between two units exceeds the maximum static friction, relative sliding occurs, activating the sliding friction device while deactivating the spring-damper. If the tangential force is below the friction threshold, the spring-damper takes effect, and the sliding friction remains inactive. Additionally, the behavior of the journal and bearing unit is considered continuous when the minimum oil film thickness is greater than or equal to zero or above a specific threshold, ensuring smooth operation under normal conditions. This detailed mechanical model enables accurate simulation of dynamic interactions within the rotor system.
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