• Journal of Advanced Marine Engineering and Technology
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• v.15 no.2
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• pp.44-52
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• 1991

The crankshaft system of engine is a complex vibratory object and its vibration modes are consisted of torsional, axial and their coupled vibration. Among them, the torsional vibration causes engine noise as well as serious fatigue faillures of crankshaft. If the troules of noises and crankshaft strength are forecasted by torsional vibration calculation in the design atage of crankshaft, the torsional damper is adopted as the final countermeasure. In this paper, some computer program to calculate crankshaft torsional vibration of engine are developed and with developed programs, an efficient rubber-viscous damper for automobile and with developed programs, an efficient rubber-viscous damper for automobile engine is designed and manufactured, and then it is fitted on the actual automobile engine to confirm its calculated efficiency. By comparing the measured result (with damper and without damper) with the calculated one, the reliability of developed computer programs and the performances of manufactured damper are confirmed.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.05a
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• pp.60-71
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• 2000

When the crankshaft of Diesel engine has more than 3 throws which are arranged in a different plane its vibration induces coupled motions especially the coupled torsional and axial vibration. Nowadays the torsional vibration which is influenced rather weak than axial one can be theoretically calculated fairly accurately but theoretical calculation results of the axial vibration which is influenced strongly from torsional vibration is not so good. To get accurate calculation results of axial vibration coupled axial-torsional vibration must be treated. in this investigation coupled effects of vibration of Diesel engine propulsion shafting are analyzed theoretically and some more simple calculation methods are also studied. On this first report effects of coupling on natural frequencies and their modes are mainly studied setting the each mass in 4 degrees of freedom. later this problem may be studied again by setting each mass as 6 degrees of freedom.

• Journal of Advanced Marine Engineering and Technology
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• v.7 no.2
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• pp.22-28
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• 1983

In former papers which were published already, authors had derived calculation formulae for the axial stiffness and the radial force conversion factor of crankshaft. In this paper, crankthrow axial stiffness and radial force conversion factors of actual engines are calculated by these theoretical formulae and then their characteristics are investigated. As the results, the axial stiffness and the radial force conversion factor of the latest super-long stroke engine are smaller than those of old-type engines. The influence of the former brings down the resonance speed of engine and the latter reduces the exciting force of axial vibration, but as the harmonic component of axial vibration force becomes rather strong, its effect of reducing is considerably canceled. In conclusion, as the latest super-long stroke engine is seemed to be liable to axial vibration of crankshafat, it is recommend that, in the design stage of propulsion shaft, its axial vibration condition must be more carefully checked.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.173-179
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• 2001

The torsional or axial critical vibration of the order coinciding with the number of propeller blades is simultaneously excited by the harmonic tangential or radial forces acting on the crank shaft and by the harmonic of the same order from the propeller. The exciting torque of propeller is relatively small comparing with that of crank side, but the exciting force of propeller rather larger than that of crank shaft. With this situation, the exciting force of propeller cannot neglect if the axial vibration of propulsion shafting is calculated. With the propeller in its optimal angular position, i.e. its excitation effect opposed to that of the engine, the stresses at the critical revolution will largely cancel themselves out. In this paper, a method of optimizing the angular propeller position with regard to torsional and axial vibration is studied. The optimal relative angle is determined theoretically by calculation results of coupled torsional-axial vibration.

• Bulletin of the Society of Naval Architects of Korea
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• v.7 no.2
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• pp.61-70
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• 1970

Since there has been no analytical method to calculate principal dimensions of the axial vibration damper of marine diesel engine shaftings in design state, it has often happened to install the axial vibration damper after the ship's trial trip. In this paper a method to calculate the coefficient of equivalent damping of the axial vibration damper is introduced and with this value one can calculate fairy accurate vibrating amplitudes of the crankshaft that is fitted with an axial vibration damper, by using author's matrix methods.[1][2][3][4] A comparison of the calculated amplitudes with measured ones is shown and its result is fairy good, except values of the case where the damper nozzle is almost closed.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.3
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• pp.563-572
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• 2001

With the results of calculation for natural frequencies the reponses of forced coupled vibration of propulsion shafting system were investigated by the modal analysis method. For the forced vibration response analysis, the axial exciting forces, the axial damper/detuner, propeller exciting forces and damping coefficients were extensively considered. As the conclusion of this study, some items are cleared as follows.-The torsional vibration amplitudes are not influenced by the radial excitation forces of the crank shaft. -The axial vibration amplitudes are influenced by the tangential exciting forces as well as the radial exciting forces of the crank shaft. The increase of the amplitudes is observed in the speed range at the neighbourhood of any torsional critical speed. 1The closer the torsional and axial critical speed. the larger coupling effect becomes. -The axial exciting force of propeller is relatively strong comparing with axial exciting forces of cylinder gas pressure and oscillating inertia of reciprocating mechanism. Therefore, the following conclusions are obtained. -Torsional vibration calculation with the classical one dimensional model is still valid. -The influence of torsional excitation at each crank upon the axial vibration is improtant. especially in the neighbourhood of a torsional critical speed. That means that the calculation of axial vibration with the classical one dimensional model is inaccurate in most of cases.

• Journal of Advanced Marine Engineering and Technology
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• v.5 no.1
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• pp.34-51
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• 1981

Lately, due to increasing engine output by high supercharging, heavy crankshaft and propeller mass, as well as long strokes attended with the reduced crankshaft axial stiffness, the critical crankshaft axial vibration has frequently appeared in maneuvering range of the engine. Some investigators have developed calculating methods of natural frequencies and resonant amplitudes for crankshaft axial vibrations. But their reliabilities are uncertain as the estimated crankshaft axial stiffness are incorrect. The calculating procedure of these natural frequencies is practically analogous to the classical calculation of torsional vibration frequencies, except for an important difference due to the relationship of the axial stiffness of a crank and the angle between the crank and other, especially the adjacent, cranks. In this paper, 6 calculation formulae of crankshaft axial stiffness already published and a theoretically- developed one by authors are checked by comparing their calculating results with those measured values of one model crankshafat and three full-scale actual crankshafts. Also, the calculating methods of the crankshaft axial free vibration are investigated and their computer programs are developed. Finally, those developed computer programs are applied to calculating one model crankshaft and two full-scale actual crankshafts of ship's propulsion engines and their calculated results are compared with those measured values.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.3
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• pp.94-106
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• 1986

Since the oil shock of '70s the engine makers have developed new types of diesel engine with low fuel consumption. There is an obvious tendency towards the use of poorer quality fuels, such as the residual oil from chemical processes of refinery. The shaft driving generators is also widely adopted on behalf of the auxiliary diesel engines, which are driving on the expensive diesel oil and have high fuel oil consumption rates, and some mania propulsion diesel engines are equipped with reduction gear systems to get better propulsive efficiency by slower propeller revolutions. The propulsion shafting system equipped with the shaft driving generator or the geared diesel engine shafting system has flexible couplings, and it requires extensive investigations of the torsional vibration and torque fluctuation in order to ensure the acceptable operation range in service. The characteristics of misfiring must be especially examined for the high viscosity fuels to be used. Both torsional vibration and fluctuating torque resulted from misfiring, should be examined for thier effects on the flexible coupling and propulsion shafting system. This paper is to investigate and solve the above mentioned problems which must be predicted on the design-stage of marine propulsion shafting system. A computer program is developed to calculate the indicated diagram, fluctating torque and torsional vibration for both normal and misfiring conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.10 no.2
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• pp.146-155
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• 1986

Until recently, the calculation of torsional vibration for the marine diesel engine shafting has been performed only for vibratory stresses of resonant points and vibratory stresses for other engine speeds are determined by the estimation. With the advent of energy-saving engines which have a long stroke and a small number of cylinders, the first major critical torsional vibration of the propulsion shaft appears ordinarily near the MCR speed of engine and the flank of its vibratory stress exceeds now and then the limit stress defined by the rules of Classification Society. In order to know the above condition in the design stage of propulsion shafting, it is necessary to calculate the forced torsional vibration with the damping of propulsion shafting for all orders and to synthesize its calculated results according to their phase angles. In this study, the forced torsional vibrations with the damping of propulsion shafting are calculated for several orders by mechanical impedance method, and their results are synthesized. A computer program for above calculations are developed and some test-runs of the developed program are performed for propulsion shaftings of actual ships. The results of calculations are compared with measured values and also with those of the modal analysis method. They show fairly good agreements and the developed program is checked up on its reliability.

• Journal of Advanced Marine Engineering and Technology
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• v.9 no.4
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• pp.307-316
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• 1985

Nowadays, the natural frequencies and their relative amplitudes of torsional vibration for the marine diesel engine shafting are usually calculated by the Holzer method and also its resonant amplitudes are estimated by the energy method, that is, by equating the exciting energy to the damping one. Therefore, the forced vibration amplitudes out of the resonant points can not be calculated by the above-mentioned method. And so, the reasonable barred-ranges of torsional vibration can not be set and also the flank of resonant point which locates near the calculation limit can not be estimated. For such problems, the equation of forced vibration with damping must be solved directly and these results can be utilized to derive the synthesized torsional vibration of the marine diesel engine propulsion shafting. In this study, the equation of forced vibration with damping for the marine diesel engine propulsion shafting is derived and its steady-state vibration is calculated by the mechanical impedance method. For numerical calculation of the actual propulsion shafting a computer program is developed. In order to prove the reliability of this program, an actual ship's propulsion shafting whose torsional vibration was measured is analyzed and the calculated propulsion shafting whose torsional vibration was measured is analyzed and the calculated results are compared with the measured ones. And also, they are compared with the calculated results which were obtained by the modal analysis.