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.
Experimental study on ground vibration of blasting the boulder with tandem shaped charging warhead
Hazardous effects of blasting the boulder with the new breaking-blasting equipment-tandem shaped charging warhead are mainly air shock wave, seismic wave and blast slung shot. Blast-induced ground vibration is one of the inevitable effects and may cause substantial damage to nearby structures. Started from the formation process and mechanism of ground vibration to study the seismic wave, the research attained curve of vibration velocity of monitoring points by TC-4850 and carried out differential and fast Fourier transform analysis of the curve. And the results concluded that blasting vibration with tandem shaped charging warhead mainly comes from prime charge; the attenuation law can be predicted by Sadev’s Formula. Explosion vibration frequency range is 20-150 Hz, while with the increase of distance from the blasting center, blasting vibration intensity attenuates rapidly, vibration duration increases and vibration frequency gradually reduces. Compared with general rock blasting, its attenuation rate of blasting vibration is faster with higher frequency and smaller impact on buildings, but the harm effects should not be ignored for the special application environment.