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 methods of force analysis, where each object is considered as a separate entity. When analyzing such objects, they are always influenced by forces and moments from neighboring objects. These interactions lead to deformation and motion caused by the resultant force and moment. This approach is highly compatible with computer simulations, as each unit can be treated independently. By establishing explicit equations for each unit and applying Newton’s second law along with various constitutive relations, differential equations are solved iteratively. When combined with animation technology, this method provides a visual and intuitive representation of how mechanical parameters—such as stress fields, displacement fields, and velocity fields—evolve over time. Moreover, DEM is not restricted by the number of objects within the system, making it particularly suitable for complex multi-body dynamics.
In the case of journal bearings and rotor-casing interactions, the constitutive forces are similar: both are simplified into pairs of normal and tangential spring-damper systems, along with a tangential sliding friction model. Notably, the spring-damper system (Ks-Cs) and the sliding friction mechanism work in tandem. When the tangential force between two units exceeds the frictional resistance, relative sliding occurs, activating the sliding friction device while deactivating the spring-damper. Conversely, if the tangential force remains below the friction limit, the spring-damper takes effect, and the sliding friction device remains inactive. Additionally, the interaction between the journal and the bearing is modeled as continuous when the minimum oil film thickness is greater than or equal to zero or above a specific threshold. This ensures that the contact remains intact under certain operational conditions, contributing to a more accurate dynamic representation of the rotor system.
U-Bolt, namely horseback bolt. It is a non-standard part. It is named because of its U-shape. It has threads at both ends and can be combined with nuts. It is mainly used to fix tubular objects such as water pipes or sheet objects such as car leaf springs. Because it fixes objects in the same way as people ride on a horse, it is called horseback bolt.
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