## 1 Introduction  
The research of shipboard equipment anti-shock performance can be divided into two methods: shock tests and calculations. The cost of underwater explosion trials on a real ship is very expensive, the preparation period is very long, and it faces huge pressure from the public opinion on marine environmental protection [1]. The aim of calculation method is to calculate the impact environment of shipboard equipment through the mathematical and mechanical models to obtain the equipment dynamic characteristics and predict its anti-shock performance. This method is cheap in cost, short in time, and easy to repeat. Diesel engines are commonly used power equipment on ships. The external impact strength is often much greater than the impact load generated by the diesel engine. As a machine with multiple moving parts and complex contact relationships between moving parts, the diesel engine should be investigated for an appropriate calculation method [2, 3, 4, 5]. The anti-shock analysis of diesel engines mostly uses the time-domain calculation method. Diesel engines contain a variety of moving parts such as crankshafts, connecting rods, and pistons, and the external shocks generally last long. In order to reduce the number of calculations, the multi-body dynamics method is generally used. The crankshaft, connecting rod, and engine block are important parts of diesel engines. The calculation of the strength of these parts under external impact is an important content of diesel engine anti-shock performance research. From the works of the researchers, the crankshaft is greatly affected by external shocks, but the strength of the connecting rod is in safe range under the impact [6; 7; 8; 9]. [PERSON] analyzed the shafting dynamics of a certain type of 16V240 diesel engine in an explosion shock environment. It was found that the dynamic stress of the crankshaft is not greatly increased after impact and does not exceed the static yield limit of the crankshaft material with a large safety margin [10]. [PERSON] et al. performed dynamic calculations on a large 16-cylinder V-type diesel engine assembly model under impact. From the calculation results, the maximum stress of each component is increased by dozens of MPa when the vertical impact is applied to the diesel engine in the running state, which does not exceed the yield limit of each material [11]. [PERSON] et al. calculated the shock response of the TBD234V6 diesel engine. The block stress far exceeds the safety limit. The vertical relative deformation between both ends of the first main journal reaches 0.2 mm, which exceeds the range of the main bearing clearance. It is inferred that the lubricating oil film of the first main bearing will be damaged. Under the shock, the threads of diesel engine bolts cannot bear the impact load, and the bolts will separate, even bend or shear [12]. [PERSON] et al. took a certain type of diesel generator as the research object and established a rigid-flexible multi-body dynamics model of the diesel engine, synchronous motor, common base, and vibration isolator. The stress of the crankshaft under normal operating conditions and external impact conditions does not exceed the yield limit of the crankshaft material [13]. In the underwater explosion test of a real ship, it was observed that the engine foot fasteners of the diesel engine were damaged by the impact, and the phenomenon was researched by calculations [14; 15]. [PERSON] simulated the shock resistance of a TBD234V6 diesel generator set. According to the calculation results, when a diesel engine is in the static state, the maximum stress of the diesel engine foot does not exceed the yield limit of the material in external impact [16]. Researchers have studied the overall impact response of external shocks on diesel engines and the weak position of diesel engine under external shocks [17; 18]. [PERSON] obtained the maximum stress and weak position of a 16 VPA6 diesel engine through calculation in an external shock environment.