Finite element analysis of crankshaft vibration

• Main Author: Chua, Yi Xing.
• Other Authors: Sellakkutti Rajendran
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics
• Online Access: http://hdl.handle.net/10356/53602
• Institution: Nanyang Technological University

This Final Year Project deals with the free vibration analysis of a reciprocating engine crankshaft. The mechanical failure of crankshafts is commonly due to fatigue caused by vibration at resonant frequency. A proper study of natural frequencies can help avoid such catastrophe. The ANSYS Mechanical APDL, a finite element software, is used to carry out modal analysis. The geometric models for the crankshaft, connecting rod and piston are constructed in SolidWorks and imported into ANSYS. Initially, the natural frequencies and mode shapes of the bare crankshaft with rigid supports at the journals are determined. The first six modes are free rigid body modes and the corresponding natural frequencies are zero. Next, the support stiffness at the journals is modeled by spring elements and the effect of the bearing stiffness on the natural frequencies and mode shapes are studied. An interesting observation from this study is that the increment of bearing stiffness has little effect on the natural frequency of the torsional mode. However, it is observed that the bending modes are sensitive to the bearing stiffness. Finally, the modal analysis is carried out on the crankshaft assembly to study the effect of the inertia of piston and connecting rod on the natural frequencies and mode shapes. The crankshaft assembly consists of the crankshaft, connecting rod and piston corresponding to the top dead center position. Appropriate boundary conditions are applied to suppress the rigid body motion. This study shows that the inertia of the piston and connecting rod reduces the natural frequency of the crankshaft.