Transient Torsional Vibration Response due to Ice Impact Torque Excitation on Marine Diesel Engine Propulsion Shafting

Abstract

In recent years, there has been an increasing demand to apply the new IACS(International Association of Classification Societies) standards for ice and polar-classed ships. For ice-class vessel propulsion system, the ice impact torque design criterion is defined as a periodic harmonic function in relation to the number of the propeller blades. However, irregular or transient ice impact torque is assumed to occur likely in actual circumstances rather than these periodic loadings. In this paper, the reliability and torsional vibration characteristics of a comparatively large six-cylinder marine diesel engine for propulsion shafting system was examined and reviewed in accordance with current regulations. In this particular, the transient ice impact torque and excessive vibratory torque originating from diesel engine were interpreted and the resonant points identified through theoretical analysis.Several floating ice impacts were carried out to evaluate torque responses using the calculation method of classification rule requirement. The Newmark method was used for the transient response analysis of the whole system.

Coupled vibration characteristics of marine shafting with complex change of inclination under ice loads

“…In engineering practice, although the calculated value of torque are within the normal range in frequency domain, it may exceed the instantaneous allowable value at a certain moment. 29 taken as that the propeller take to rotate 1 deg, and the loads are applied at the 720th time steps. After a total of 4000 sub-steps are calculated, the time-domain curves of torque can be obtained as shown in Figure 11(a), (c), and (e).…”

“…In engineering practice, although the calculated value of torque are within the normal range in frequency domain, it may exceed the instantaneous allowable value at a certain moment. 29 So the calculations of transient torsional vibration induced by ice loads have become mandatory since January 2011 in DNV specifications. According to three different conditions as shown in Table 1, the transient torque of driven shaft at speed ω = 3600 deg / s with inclination angles of 1 deg are calculated, in which the calculation time step is taken as that the propeller take to rotate 1 deg, and the loads are applied at the 720th time steps.…”