• Proceedings of the KSME Conference
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• 2005.11a
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• pp.98.1-98.1
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• 2005

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.114-120
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• 2000

Friction forces of piston rings for a typical SI engine were independently measured while excluding the effects of cylinder pressure, oil starvation and piston secondary motion using a floating liner system. Friction patterns, represented by the measured friction forces, were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(mid-stroke and dead centers). The modes were identified on the Stribeck diagram of the dimensionless bearing parameter and friction coefficients which were evaluated at the mid-stroke and at the dead centers. And the frictional modes were estimated to the full operation range. The compression rings behave in the mode where hydrodynamic lubrication is dominant at the mid-stroke and mixed lubrication is dominant at the dead centers under steady operating conditions. However, the oil control ring behave in the mode where mixed lubrication is dominant throughout the entire stroke.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.56-64
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• 2000

A friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was carefully designed to control the effect of the piston secondary motion and the temperature of cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner, was measured under the condition of flooded oil supply. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(midstroke and dead centers). The modes could be identified on the Stribeck diagram of the friction coefficients and the dimensionless number of ㎼/p, where the friction coefficients are evaluated at near the midstroke and dead centers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.107-110
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• 2009

Combustion oscillations are caused by a coupling between acoustic waves and unsteady heat release. They can be eliminated using passive controller such as a helmholtz resonator. But, helmholtz resonator is normally only effective over a narrow frequency range. In this work, helmholtz resonator is applied for reducing the combustion oscillations and we vary the helmholtz resonator volume using piston in oder to tune in the wide range of operating conditions. As the result, it is found that the dominant combustion oscillations can be reduced by optimizing the size of resonator volume. Also, from these results, we investigate feasibility of actively tuned passive control

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.291-298
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• 2013

In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.1-8
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• 1999

This paper experimentally investigates the steady shear behaviors of electro-rheological(ER) fluids under flow mode at high pressure level. As for the ER fluid to be tested, two types of ER fluids are employed; water-based ER fluids (ERF 1, ERF 2) and water-free ER fluid(ERF 3). The water-based ER fluids are composed inhousingly, and the concentrations of dispersed particles are 20 wt% and 30 wt% for ERF 1 and ERF 2, respectively. To generate the flow mode at high pressure, an experimental apparatus operated by two-way hydraulic cylinder is constructed and utilized. The pressure difference is measured by the pressure sensor, while the flow rate is calculated using the measured data of the displacement sensor(LVDT). Consequently, the shear stress and shear rate are distilled by incorporating the measured data; the pressure difference and the flow rate.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.3
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• pp.209-217
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• 2013

This paper presents an optimal design of a magnetorheological(MR) fluid-based mount(MR mount) that can be used for to vibration control in diesel engines of ships. In this work, a mount that uses mixed-modes(squeeze mode, flow mode, and shear mode) is proposed and designed. To determine the actuating damping force of the MR mount required for efficient vibration control, the excitation force from a diesel engine is analyzed. In this analysis, a model of a V-type engine is considered. The relationship between the velocity and pressure of gas in terms of the torque acting on the piston is derived. Subsequently, by integrating the field-dependent rheological properties of commercially available MR fluid with the excitation force, the appropriate size of the MR mount is designed. In addition, to achieve the maximum actuating force under geometric constraints, design optimization is undertaken using the ANSYS parametric design language software. Through magnetic density analysis, optimal design parameters such as the bottom gap and radius of coil are determined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.93-99
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• 2012

This paper presents an optimal design of magnetorheological (MR) fluid based mount (MR mount in short) which can be applicable to vibration control of diesel engine of ship. In this work, a mixed - mode including squeeze mode, flow mode and shear mode is proposed and designed. In order to determine actuating damping force of MR mount required for efficient vibration control, excitation force from diesel engine is analyzed. In this analysis, a model of V-type engine is considered and the relationship between velocity and pressure of gas in torque of the piston is derived. Subsequently, by integrating the field-dependent rheological properties of commercially available MR fluid with the excitation force an appropriate size of MR mount is designed. In addition, in order to achieve maximum actuating force with geometric constraints design optimization is undertaken using ANSYS software. Through the magnetic density analysis, optimal design parameters such as bottom gap and radius of coil are determined.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.36-46
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• 2011

A two-dimensional floating body with a moon pool under forced heave motion, including a piston mode, is numerically simulated. A dynamic CFD simulation is carried out to thoroughly investigate the flow field around a two-dimensional moon pool over various heaving frequencies. The numerical results are compared with experimental results and a linear potential program by Faltinsen et al. (2007). The effects of vortex shedding and viscosity are investigated by changing the corner shapes of the floating body and solving the Euler equation, respectively. The flow fields, including the velocity, vorticity, and pressure fields, are discussed to understand and determine the mechanisms of wave elevation, damping, and sway force.

• Composites Research
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• v.15 no.3
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• pp.52-61
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• 2002

For the aerothermoelastic analysis of cylindrical piezolaminated shells, geometrically nonlinear finite elements based on the multi-field layerwise theory hale been developed. Applying a Han Krumhaar's supersonic piston theory, supersonic flutter analyses are performed for the cylindrical piezolaminted shells subject to thermal stresses and deformations. The possibility to increase flutter boundary and reduce thermoelastic deformations of piezolaminated panels is examined using piezoelectric actuations. Results show that active piezoelectric actuations can effectively increase the critical aerodynamic pressure by retarding the coalescence of flutter modes and compensating thermal stresses.