LEAST INERTIA APPROACH TO LOW-SPEED MARINE DIESEL PROPULSION SHAFTING OPTIMUM DESIGN

In this study, a novel approach to the low-speed marine diesel propulsion shafting design is proposed and examined. The proposed approach is based on the shafting least inertia principle, in which the design task is formulated and solved as a constrained nonlinear optimization problem. The core of the approach is a cost function, which is defined as a weighted sum of the shafting, turning wheel, and tuning wheel inertias, because it is a suitable proxy of the propulsion shafting material and production costs. The constraint set is composed of the three mandatory constraints, where the crankshaft, intermediate shaft, and propeller shaft torsional vibration stresses should be lower than the corresponding stress limits, as well as a few additional constraints that help ensure that the plant behavior complies with applicable regulatory and operational requirements. For optimization purposes, a Recursive Quadratic Programming method is utilized, while the shafting torsional vibration response is determined using a standard vibration analysis program with slight modifications. Numerical experiments have shown that fast convergence can be achieved. Compared to the classically obtained solution, the proposed approach provided more than 8 % reduction in cost function as well as significantly reduced design time.