• Journal of Power System Engineering
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• v.19 no.6
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• pp.60-67
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• 2015

While designing and operating machines, it is very important to understand the dynamic characteristic of the machines. Authors developed the Sylvester-transfer stiffness coefficient method in order to analyze effectively the free vibration of machines or structures. The Sylvester-transfer stiffness coefficient method was derived from the combination of the Sylvester's inertia theorem and the transfer stiffness coefficient method. In this paper, the authors formulate the computational algorithm for flexural free vibration analysis of axisymmetric annular plate using the Sylvester-transfer stiffness coefficient method. To confirm the usefulness of the Sylvester-transfer stiffness coefficient method, the natural frequencies and modes for two computational models computed using the Sylvester-transfer stiffness coefficient method are compared with those computed using the exact solution and the finite element method.

• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.2
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• pp.3-12
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• 1975

As for two dimensional added mass coefficients for straight framed hull forms in a free surface of an ideal fluid, theoretical calculations by F.M. Lewis, vertical, K. Wendel, J.H. Hwang, and etc. are available; vertical modes of rectangular and triangle sections by Lewis, vertical, horizontal and torsional models of rectangular and triangle section by Wendel, and systematical calculations for vertical modes of single chine forms by Hwang. In this paper, employing the conformal transformation by which a unit circle and its exterior region can conformally mapped to a polygon and its exterior region, the author calculated two dimensional added inertia coefficients systematically for straight framed sections with single chine in horizontal and torsional modes of vibrations. As the results, it was found that sloping side angle is an important factor measuring the magnitude of two dimensional added inertia coefficient for a set of given values of the sectional area coefficient and the beam-draft ratio. To grasp it cleary in physical sense, pressure distributions are investigated for some typical section contours. The numerical results are presented graphically in the form of two dimensional added sectional area coefficients with beam-draft ratios and sloping side angles as parameters, so that the data may conveniently utilized for estimation of the added inertia coefficients based on a three parameter technique.

• Bulletin of the Society of Naval Architects of Korea
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• v.7 no.2
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• pp.3-18
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• 1970

An investigation was made for the added mass moment of inertia induced by the rotational motion of the cylinder with hull section on water in order to obtain the information to estimate the natural frequency of the torsional vibration of ships. The special consideration to the effect of the draught upon the added mass moment of inertia is taken into account in the study. In this paper, the general expression for the added mass coefficients of moment of inertia of arbitary two dimensional forms induced by the torsional vibration, was derived by the author. Hence, the coefficients for these forms are represented as functions of parameters, the section area coefficient and draft beam ratio, from which the added mass coefficients for arbitrary forms can be obtained. The result was shown in a chart for estimation of the added mass moment of inertia induced by the torsional vibration, as first trial, for the convenience of practical use.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1556-1570
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• 2016

In the process of virtual inertia control (VIC), the frequency regulation capability of the directly-driven wind turbine with permanent-magnet synchronous generator (D-PMSG) on wind farm is related to its rotor kinetic energy and capacity margin. This paper proposes the method for assessing the D-PMSG frequency regulation capability and defining its coefficient according to the operating state of wind power generators. In addition, the calculating method of parameters in VIC is also discussed according to the principles of primary frequency regulation and inertia response of synchronous generators. Then, by introducing the capability coefficient into the proportion-differential virtual inertia control (PD-VIC) for power coordination, a coordinated virtual inertia control (C-VIC) strategy is developed, with the consideration of the difference in frequency regulation capability between wind power generators. The proposed control method can not only give full play to the frequency regulation capability of wind power generators, decrease the movements of the pitch angle control system but also bring some self-coordination capability to different wind power generators thus to avoid a secondary drop in system frequency. The simulations and experiments prove the proposed method to be effective and practicable.

• Bulletin of the Society of Naval Architects of Korea
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• v.11 no.2
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• pp.7-14
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• 1974

Hydrodynamic moments produced by the rolling oscillation on the free surface and the associated swaying force were exactly calculated by Ursell-Tasai method for the cylinders with Kim's chine form sections($a_1,\;a_7$). The coefficient of the added moment of inertia $K_{\varphi^{\tau}}$, the progressive wave height ratio $\bar{A}$, the coefficient of swaying forces $K_{RS}$, ${\alpha}_{RS}$ of rolling oscillations are shown in the several figures. The results of the computation were compared with those of lewis form sections. It is concluded that the effect of the section form on the added moment of inertia is significant for the cylinder with the section of same beam-draft ratio and sectional area coefficient, on the other hand, a little effect appears on the wave damping.

• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.1
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• pp.91-93
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• 1975

• Journal of the korean Society of Automotive Engineers
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• v.4 no.1
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• pp.20-30
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• 1982

Recent diesel engine has achieved high speed running comparable to that of gasoline engine as a speed improvement effort. Consequently, torsional vibration of high-speed diesel engine induced vibration nosise, reduced horsepower and the like. Viscous damper which is thought to be effective in curtailing the torsional vibration was studied over a wide range of speed. In this investigation, a water cooling, 4-cycle high-speed diesel engine(Msx. 3500 rpm)was used for the study. Theoretical analysis was made by assuming the engine to be an ideal equivalent system(length, moment of inertia) i. e. the multi-degree of freedom equivalent torsional vibration system with damper was analyzed. In the analysis, the inertia moment of suitable damper for this experiment was calculated by varying the relative damping coefficient of damper of engine for each damper. Furthermore, in the torsional vibration experiment, the torsional vibration amplitude of the crankshaft system was measured when the engine was equipped with dampers of different moments of inertia and also when the engine was equipped without dampers. The experimental results were compared with the analytical values and were found to be satisfied. The results of this investigation are summarized below; (1) It was found that for the engine equipped with dampers, the torsional vibration amplitude was reduced to about one third of those without dampers. (2) The optimum value of inertia moment of viscous damper for the engine was found to be about Id=1.05(kg.cm.s$^{2}$) (3) The optimum damping coefficient and the ratio of moment of inertia for the engine were found to be about Ca= 850(kg.cm.s), Rd=0.509, respectively (b1 dapmper).

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.1
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• pp.33-38
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• 2016

The turbocharger is an essential component to realize the engine down-sizing. The moment of inertia of turbocharger rotor is an important parameter with respect to acceleration performance of the vehicle. It can be calculated from the CAD software based the geometry data and the material properties. But the accurate value of the inertia of turbocharger rotor must be measured through the experimental method. In this study, the measurement of moment of inertia of turbocharger rotor for 2.0 L spark-ignition engine was carried out. First, an experimental equipment using a trifilar method was designed and fabricated. Some optical devices, that is, photo sensor, counter, convex lens, etc, were used to increase the accuracy of the measurement. Second, error sensitivity for the equipment was analyzed. The error of period time and the radius can give big affects to the accuracy of the moment of inertia. When the amount of error of these two were each 1.0 %, maximum error of the moment of inertia was under 3.0 %. Third, the calibration for the equipment was performed using a calibration rotor which has similar shape to turbine rotor but simple. Calculated value from CAD software and measured one for the calibration rotor were compared. The total error of the equipment and the measurement is about 1.3 %. This result shows that the equipment can give the good result with resonable accuracy. Finally the moment of inertia of the turbine rotor and compressor wheel were measured. The coefficient of variations, the ratio of standard deviation to mean value, were reasonably small at 0.57 % and 0.73 % respectively. Therefore this equipment is suitable for the measurement of the moment of inertia of the turbine rotor and compressor wheel.

• Journal of the Korean Society of Industry Convergence
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• v.15 no.1
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• pp.13-19
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• 2012

Due to a low stiffness of cranktrain and a failure experience from a history within short development time, a viscous torsional vibration damper was applied in order to reduce the torsional vibration and keep the high reliability for the durability of cranktrain system in the direct injection diesel engine. As an improvement of the crankshaft stiffness by increasing the diameter of main and pin journal, a rubber type damper could be considered. In this study, the control factors of rubber damper, the moment of inertia ring, stiffness of damper and damping coefficient of ring, were investigated by DFSS method through the analysis work and the measurement in the real engine condition.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.740-748
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• 1998

The inertia friction properties of C/C composites manufactured by the processes of pressure and at-mospheric carbonizaton with a commerciallized and two kinds of modified coal-tar pitch as a matrix pre-cursor were investigated. The modifications of a pitch such as the introduction of mesophase and the ad-dition of sulphur into a raw pitch were not effective for a impregnation efficiency conducted in a vacuum and at the same time in a pressure of 5kg/cm2 due to the increase of the pitch viscosity. There was not a difference in the densification increment between the pitch modifications however it was revealed that a pressure carbonization was more advantageous than an atmospheric in the densification and the formation of anisotropic carbon matrix. The friction and wear propertis of C/C having higher degree of matrix cry-stallization higher density and hardness of friction surface showed superiority. As the braking energy was increased the friction coefficients were decreased and reached almost same level at the high kinetic energy of 99.6kJ. The wear trends at 99.6kJ were different from the behaviors of friction ceofficient under the same energy in which an oxidation wear is being considered along with a mechnical wear although the wear rates were almost similar to the friction coefficient at the low energy.