Research On Torsional Vibration Of Marine Low Speed Diesel Engine’s Shafting And Its Characteristics In Ice Area

The torsional vibration of marine propulsion shafting has been studied for more than a century. Increased torsional vibration can cause the fracture of crankshaft, intermediate shaft and propeller shaft as well as gear wear, excessive noise and other issues, which will affect ship’s sailing safety. Furthermore, as the passage in the Arctic opens, the demand for ice-class vessels is increasing. Considering the ice impact, the propulsion shafting’s torsional vibration state becomes more complicated due to propeller-ice interaction, which will pose a great challenge to ship propulsion shafting system. Thus, studying on torsional vibration of marine diesel engine and its characteristics in ice area has a great significance on the development of Arctic shipping and international economy. In this paper, the theory of torsional vibration is studied and integrated. Analytical work is done on various factors of torsional vibration and several calculation methods of torsional vibration are compared. In the meantime, based on MATLAB GUI development platform, a torsional vibration calculation(TVC) software for ship propulsion shafting is developed, and verified through the TVC of 6S70MC-C marine diesel engine. Lastly, the paper theoretically researched the ice strengthening of propulsion shafting’s torsional vibration. Then, combined with the aforesaid TVC software, it focuses on the 6S70MC-C marine diesel engine and analyses the torsional vibration characteristics of marine low-speed diesel engine’s shaft line with ice impact.The content of the paper is involved with the establishment of equivalent system, comparison between Holzer method and System matrix method of free torsional vibration, discussion about calculation of harmonic coefficients and damping, development of TVC software, research on the torsional vibration calculation of marine low-speed diesel engine in ice area, etc. Through calculating and verifying, it is proved that the system matrix method and dynamic amplification coefficient method are of good accuracy and practical significance to be programmed and used in the computer calculation. By analyzing the current materials, reasonable proposal and discussion are put forward to the calculation of four-blade propeller ice torque excitation and the relationship of the designed ice block torque VS. engine speed. In the end, aiming at the 6S70MC-C marine diesel engine with four-blade propeller, the torsional vibration with ice impact is calculated in frequency domain. According to the results, the case of one-blade ice impact in 90 degrees makes the greatest effect on shaft’s torsional vibration. At the time of blade order resonance, the torsional stresses of intermediate shaft and propeller shaft increase a lot, which put the shaft line in a dangerous situation.