• Journal of Advanced Marine Engineering and Technology
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• v.11 no.2
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• pp.51-60
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• 1987

Recently, the problem of the axial vibration for the marine diesel engine shafting has become important due to the increased exciting forces resulting from high supercharging and large output, and the reduced natural frequencies resulting from long stroke and show speed. The effects of the axial vibration on the propulsion shafting induce cracks of the connecting point of crankpin and crankarm, the severe wear of thrust bearing, the fatigue failure of each fixing bolt and jointed parts, the hull and local hull vibrations, and also the wear and the noise due to intense hammering phenomena of thrust collar. Therefore, each classification society requires the calculation of natural frequencies and their amplitudes and also measurements of the forced damped axial vibration. At present, the technical and theoretical level is at the stage of estimating the resonant points and their maximum displacements, but the estimated displacements of the resonant points are not so reliable as the torsional one. In this study, induced stresses and amplitudes of the forced damped axial vibration are calculated. For this purpose, the equation of forced axial vibration with damping for the propulsion shafting is derived and its steady-state response is calculated by the mechanical impedance method. A computer program for above calculations is developed. The measured values are analyzed and the calculated results are compared with the measured ones. They show fairly good agreements and the reliability of developed program is confirmed.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.482-492
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• 2004

Recently. the market trend for marine diesel engine has involved the lower running speeds. larger stroke/bore ratio and higher combustion pressure. Consequently, because of the flexible engine shafting system due to the larger mass. inertia and the more elasticity, the complicated coupled torsional-axial vibrations have occurred in the operating speed range. Also, the vibrations act as an excitation on the hull-structural vibration. To predict the vibration behavior with more accuracy and reliability. many studies have proposed the several kinds of method to calculate the stiffness matrix of crankshaft. However, most of these methods have a weak point to spend much time on three dimensional modeling and meshing work for crankshaft. Therefore. in this work. the stiffness matrix for the crankthrow is calculated using the energy method (Influence Coefficient Method, ICM) with the each mass having 6 degree of freedom. Its effectiveness is verified through the comparison with the stiffness matrix obtained by using the finite element method (FEM) and measured results for actual ships propulsion system.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.149-153
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• 2005

Marine Propulsion shafting system coupled with medium diesel engine forms multi-degree torsional vibration system which consist of many inertia masses such as crank, flywheel, propeller and sometimes gear system is adopted additionally for the purpose of improving propeller's propulsion efficiency or connecting with PTO/PTI. The periodic excitation torques generated by combustion pressure in cylinder and reciprocating masses induce various kinds of vibrations in this shafting system. If the frequency of this excitation torques is equal to the natural frequency of the shafting, the amplitude of the torsional vibration increases steeply and the damage of crankshaft or gears may be occurred by that. This frequency is called critical speed. When making a plan for shafting system, it is important for this frequency to be expected exactly and not to be in commonly used speed. For this reason, this paper introduces the experimental equipment for torsional vibration of marine propulsion shafting system and describes the theoretic and the experimental methods to look for natural frequencies.

• Journal of Advanced Marine Engineering and Technology
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• v.8 no.1
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• pp.37-48
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• 1984

For the designing propulsion shafting of ship, shaft diameters are usually calculated according to the Society's rules and other scantlings such as a shaft length, coupling and taper parts, etc., are decided according to calculated diameters. And then, the torsional vibration, the lateral vibration and shaft alignment should be reviewed to check whether the resonance points of torsional or lateral vibration appear within the normal operating speed range and the shaft alignment is reasonable. If the results of calculations are unsatisfactory, this process should be repeated until the final condition is determined and the process of this work takes much time to carry out. To simplify the above tedious processes, authors have developed a computer program to fulfill the above design processes at once. This program takes aim at reducing the manual calculating work associated with the propulsion shafting of ship. To confirm the availability of developed computer program, several propulsion shaftings which are driven by diesel engines, have been analysed. The results calculated by authors developed computer program show comparatively good agreements with those of the actual propulsion shafting.

• Special Issue of the Society of Naval Architects of Korea
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• 2005.06a
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• pp.134-137
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• 2005

Recently, in VLCC, shafting system is stiffer due to large engine power whereas hull structure is more flexible due to scantling optimization, which can be suffered from alignment damage by incompatibility between shafting and hull, In this study, shafting system without stern tube forward bush was adapted for less sensitive system against external factors. Also, shaft alignment analysis was considered with hull deflection at various ship loading conditions and stern tube after bush of long journal bearing was evaluated by static squeezing pressure and dynamic oil film pressure with sloping control. Whirling vibration was also reviewed to avoid resonance with propeller blade order. So, reliable shafting design for VLCC could be achieved through optimized alignment analysis for the system without stern tube forward bush.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.12
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• pp.1168-1175
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• 2010

Excessive torsional vibrations from marine engine shafting systems can be reduced by using torsional vibration dampers. But in order to be tuned effectively, the dampers should be designed through the optimum design procedure. In this paper, the procedure to get the optimum values of system parameters of spring-viscous dampers using effective modal mass of inertia and stiffness is suggested and the damping is determined by the exact algebra optimization method. The validity of the suggested method is confirmed through the application to a 1800 kW four cycle diesel engine and generator system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.776-785
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• 2006

Ship builder's requirement for a higher power output rating has lead to the development of super large two stroke low speed diesel engines. Usually a large-sized bore ranging from 8-14 cylinders, this engine group is capable of delivering power output of more than 100,000 bhp at maximum continuous rating. Other positive aspects of this engine type include higher thermal efficiency, reliability, durability and mobility. This all playa vital role in meeting the propulsion requirement of vessels, specifically for large container ships, of which speed is a primary concern to become more competitive. Consequently, this also resulted in the modification of engine parameters and new component designs to meet the consequential higher mean effective pressure and higher maximum combustion pressure. Even though the fundamental excitation mechanism unchanged, torsional vibration stresses in the propulsion shafting are subsequently perceived to be higher. As such, one important viewpoint in the initial engine design is the resulting vibration characteristic expected to prevail on the propulsion shafting system(PSS). This paper investigated the torsional vibration characteristics of these super large engines. For the two node torsional vibration with a nodal point on the crankshaft, a tuning damper is necessary to reduce the torsional stresses on the crankshaft. Hence, the tuning torsional vibration damper design and compatibility to the shafting system was similarly reviewed and analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.376-381
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• 2009

The increasing needs for higher cargo capacity in the container vessels' fleet has led to ship builder's demand for higher power output rating engine to meet the propulsion requirement, thus, leading to the development of super large two stroke low speed diesel engines. This large sized bore engines with more than 12 cylinders are capable of delivering power output up to more than 100,000 bhp at maximum continuous rating. The thrust variation force due to axial vibration occurring in propulsion shafting of these ships are transmitted to ship structure via thrust bearing. This force may vibrate the super structure of ship in the fore-aft direction and the fatigue strength of crank shaft can be decreased by additional bending stress increase in crank shaft pin and journal. In this paper, the axial vibration of propulsion shafting system on the 14RT-flex96C super large diesel engine with 14 cylinders is identified by theoretical analysis and vibration measurement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1166-1176
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• 2011

The prospect in opening the arctic trade transportation route on a year-round basis offers vast opportunity of exploring untapped resources and shortened navigational routes. In addition, the environment's remoteness and lack of technical experiences remains a big challenge for the maritime industry. With this, engine designers and makers are continually investigating, specifically optimizing propulsion shafting system design, to meet the environmental and technical challenges of the region. The International Association of Classification Society, specifically machinery requirements for polar class ships(IACS UR13), embodies the propulsion shafting design requirements for ice class vessels. However, the necessity to upgrade the various features of the unified rules in meeting current polar requirements is acknowledged by IACS and other classification societies. For the polar class propulsion shafting system, it is perceived that the main source of excitation will be the propeller - ice load interaction. The milling - and the impact load, in addition to the load cases interpreted by IACS, contribute greatly to the overall characteristic of the system and due considerations are given during the propulsion design stage. This paper will expound on the excitation load estimation factors affecting the dynamic response of the different propulsion shafting system design. It is anticipated that detailed understanding of these factors will have a significant role during propulsion shafting design in the future.