ICSV 14 Cairns • Australia 9-12 July , 2007 1 INVESTIGATION OF TORSIONAL VIBRATION CHARACTERISTICS OF MARINE DIESEL ENGINE CRANKSHAFT SYSTEM
Evaluation of the torsional vibration characteristics of a crankshaft system is indispensable to the development of marine diesel engines. It influences the selection or decision about shafting components such as the flywheel, torsional damper, generator and even modification of the crankshaft itself. In this paper, experimental and analytical investigations of torsional vibration were carried out for a newly developed marine diesel engine. The measurements were performed on various system changes e.g. engine with and without torsional damper, tuning wheel and coupling of dynamometer or generator. Based on the measurement results, analytical models were tuned to achieve better reliability. Meanwhile the sensitivity of parameters–inertia, stiffness and damping on the free vibration and torsional response-were assessed quantitatively and qualitatively. Dynamic stresses in the highly stressed area of the crankshaft were also measured under actual operating conditions with telemetry equipment. The safety factor against fatigue was evaluated with the measured stresses and compared with the analyzed ones and showed good agreement with each other.
Validated Analytical Modeling of Eccentricity and Dynamic Displacement in Diesel Engines with Flexible Crankshaft
In spite of the fact that the flexibility of the crankshaft of diesel engines exhibits notable nonlinearities, analytical modeling of such nonlinearities is not yet realized. The present study thus analytically models the effect of eccentricity on flexible crankshaft and piston secondary motion. The eccentricity of the crankshaft is modeled as the summation of the hydrodynamic eccentricity and the dynamic mass eccentricity of the crankshaft. The study also models the absolute value of the vibrational dynamic displacement of the center of the crankshaft. The paper proves that such dynamic displacement of the center of the crankshaft is sensitive to the changes in its independent variables. It was found that the most influential parameters on the dynamic displacement of the center of the crankshaft due to vibration are the natural frequency and the eccentricity of the crankshaft. The modeling of the dynamic displacement in a flexible crankshaft was validated using a case study based on the eccentricity of the crankshaft showing a relative error of 4%, which is less than the relative error in the CMEM and GT-Power. Furthermore, the analytical modeling of the dynamic displacement in the flexible crankshaft was validated using another case study based on fatigue analysis of the crankshaft showing a relative error of 9%, which is less than that the relative error in Newman’s model of diesel engine fuel consumption and Lansky’s model of diesel engine cylinders. The paper also presents a proposed approach of fatigue failure analysis for vehicular dynamic components and presents a proposed nanostructure of crankshafts for improving such fatigue performance. The developed models would help develop efficient diesel engines and help prolong their service life.
Rates of Change of Eigenvalues, With Reference to Buckling and Vibration Problems
There are many problems in practice, particularly in the fields of buckling and vibration, where the required end result is a curve showing the relation between the eigenvalue and one or more of the basic parameters of the physical system. For example, the curve relating the buckling stress and side ratio of a rectangular plate, with some specified set of edge conditions, under uni-axial compression may be required. Or the problem may be the buckling of a rectangular plate of given proportions, under combined compression and shear, and the determination of the relation between the two types of load at buckling. Alternatively, the effect on the frequency of vibration of varying a concentrated mass, or the stiffness of an elastic constraint at a given point in an elastic system may be required.