A marine engine torsion vibration measuring method and its implementation based on FPGA

The torsion vibration in a marine engine shaft-gear system is a major cause of its main shaft fracture. In order to avoid such damage, monitoring and forecasting of the torsion vibration strength in the engine shaft-gear system is needed. Although some methods for torsion vibration measurement have been presented in the literature, there is a need for improving both the measuring accuracy and the efficiency of hardware implementations. We present a new accurate measurement method of monitoring and forecasting the vibration amplitude in real time, and solving the problem of interfacing it with a small computer. First, under a constant main shaft velocity, a theoretical expression is derived which can be used to calculate the torsion vibration amplitude in the main shaft-gear system exactly, at the time of shaft-pulse occurrence, according to a pulse-fill-in principle. This expression leads to (i) a recursive algorithm for obtaining the torsion vibration data of the main shaft-gear system, and (ii) to an expression for calculating the average main shaft velocity. Errors of the algorithm are discussed. Finally, an FPGA-based hardware circuit is designed to implement the algorithm, and its performance is simulated and evaluated by using SystemView, a dynamical system analysis tool. Our results show that experimental data fit the theoretical results very well.