Abstract: As a critical component of offshore fracturing vessel diesel engines, the crankshaft is prone to vibration due to long-term high-speed operation and mass imbalance caused by manufacturing tolerances, both of which can compromise engine reliability. This study established a finite element model of the crankshaft, taking the firing condition of the second cylinder as the working scenario, to systematically investigate its static and dynamic characteristics. Modal analysis was conducted to determine the first six natural frequencies and their associated mode shapes. This revealed that low-order modes could cause significant deformation under resonance conditions. Furthermore, harmonic response and random vibration analyses were performed to identify regions of dynamic response and stress concentration under external loads. The results of the topology-based lightweight design indicate that the mass of the crankshaft was reduced from 37.7 kg to 19.3 kg (a weight reduction of approximately 48.8%), while the first natural frequency increased from 545.36 Hz to 560.32 Hz (a rise of 10.3%). This effectively avoids resonance and mitigates the risk of failure. This study provides theoretical guidance and an engineering reference for optimising the structure, lightweight design, and enhancing its vibration reliability in the context of crankshafts in offshore fracturing vessel diesel engines.

Key words: crankshaft, random vibration, mode analysis, topology optimization, dynamic characteristics