Research on Numerical Calculation Methods for Modelling the Dynamics of Diesel Engine Crankshaft System Substructures

The complex structure of a diesel engine crankshaft, combined with diverse and dynamically changing loads, leads to the interaction of torsional, bending, and longitudinal vibrations. These complexities present challenges in achieving comprehensive and efficient dynamic modelling and analysis. This paper presents a dynamic modelling and numerical computation method for the crankshaft system based on the substructure dynamic model to address this. Specifically, the primary degrees of freedom (DOFs) of the crankshaft system are transformed through coupling between master and slave node DOFs and DOF condensation. A numerical method for free vibration analysis is developed using Cholesky decomposition and Jacobi iteration, while a dynamic response is computed based on the Newmark-β implicit integration algorithm. Additionally, an adaptive step-size control strategy based on the energy gradient criterion was proposed by introducing a dynamic relaxation factor, significantly enhancing computational efficiency. The study further examines the influence of primary DOF selection, coupling region size between master and finite element nodes, bearing support stiffness, and integration step size on the dynamic response. Numerical case studies demonstrate that the substructure model, with fewer DOFs, accurately characterizes the dynamic behaviour of the crankshaft by appropriately selecting primary DOFs and computational parameters, thereby enabling efficient dynamic analysis.