• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.87-93
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• 1998

Pressure ripples of hydraulic vane pump results from flow ripples due to pump geometry and reverse flow through the discharge port due to compressibility of fluid and result in vibration and noise of connected hydraulic elements. In a balanced type vane pump, cam ring curve is important factor to influence the flow ripples. Therefore, to reduce the flow ripple, it has been required that optimal selection of seal region by proper design of cam ring and each port position, and notches for preventing the excessive reverse flow. This paper has been performed analytical study of compression characteristics with major design parameter in side plate and cam ring. and examined into the role of notch and radius reduction ratio.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.12a
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• pp.85-91
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• 1993

Air-Lubricated tilting pad journal bearing that has high stability is analyzed by using the direct method, and this bearing is usually used to need high precision. The pressure that supports the shaft is occured by the differences between the shaft and pads radii of curvatures. So the characteristics of load capacity for their variable values is important. In this paper the load capacity is compared with some of the eccentricity ratio values. The large load oapacity comes form large eccentricity ratio, high bearing number and high preload. But if the preload becomes too high, the shaft comes into contact with the pads. Stiffness and damping coefficients are compared with some of the preload, too. The coefficients decreased along compressibility number with constant load.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.82-85
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• 1999

Permanent magnets of Nd-Fe-B group have kept a key post in the permanent magnet market and used in various parts. Tube Process is a process to produce permanent magnets using a deformable tube for denslfication of powder magnets. Advantage claimed for this process is that it can accomplish both densification and anisotropication in one step forming. In this paper. the simulation has been carried out for a full Tube Process in a closed Qe considering the compressibility of material, arbitrary curved shape and deformable body contact between Nd-Fe-B powder magnet and copper tube. The results show that the analysis of Tube Process is applicable with great help in the stage of preform design.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.20-24
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• 2011

In this paper, numerical simulation of cavitation flow for modified NACA66 hydrofoil was made by using the multi-phase RANS equation based on pseudo-compressibility. The Homogeneous mixture model comprised of the mixture continuity, mixture momentum and liquid volume fraction equations was utilized. A vertex-centered finite-volume method was used in conjunction 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing The Spalart-Allmaras one equation model was employed for the closure of turbulence. Reasonable agreements were obtained between the calculation results and the experiment for pressure coefficients on the hydrofoil surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.2 s.245
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• pp.105-111
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• 2006

This paper describes a Neural Network based PID control scheme for pneumatic NC axes. Pneumatic systems have inherent nonlinearities such as compressibility of air and nonlinear frictions present in cylinder. The conventional PID controller is limited in some applications where the affection of nonlinear factor is dominant. A self-excited oscillation method is applied to derive the dynamic design parameters of linear model. The gains of PID controller are determined using a self tuning scheme. The experiments of a trajectory tracking control using the proposed control scheme are performed and a significant reduction in tracking error is achieved by comparing with those of a PID control.

• Transactions of The Korea Fluid Power Systems Society
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• v.1 no.1
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• pp.17-22
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• 2004

The goal of this paper is to improve the position control performance of pneumatic rotary actuator with variable brake using Magneto-Rheological Fluid. The air compressibility and the lack of damping of the pneumatic actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. In this study, a variable rotary brake comprising Magneto-Rheological Fluid is equipped to the joint of a pneumatic manipulator. Experiments of step response have proved that the transient response of the manipulator could be improved compared with that of the conventional control algorithm by using a phase plane switching control algorithm.

• Journal of Drive and Control
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• v.12 no.4
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• pp.21-27
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• 2015

The accurate position control of pneumatic driving apparatus is considered in this paper. In pneumatically actuated positioning systems, accurate positioning as an electrical servo has been known to be difficult because of the friction force and compressibility of the air. For good control performance of the pneumatic system, an actuator mounted with externally pressurized air bearings is produced to compensate for friction force. For the controller design, the governing equation of the pneumatic driving apparatus is derived. In order to reduce the nonlinear characteristics of the control valve, linearized control input is derived from the relation between the effective area of the valve and the control input. The experimental results are presented to show the results of the improved position control of the pneumatic driving apparatus.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.851-852
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• 2006

The introduction of ceramic particulate into metallic powder will unavoidably lower the compressibility and formability of the mixed powder. In this study, warm compaction, which is a simple and low cost technique to produce high density PM parts, was introduced in preparing composite. The aim of this paper is to prepare the warm compacted NbC particulate reinforced Fe-based composite, then study its tribological behavior and application in the valve-guide cup. A 15 wt.% NbC reinforced iron-based composite was prepared. It possesses a relative density of 98%, a tensile strength of 515 MPa, a hardness of HRC 58 and a remarkable tribological behavior.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.702-703
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• 2006

The particle size distribution and shape are among the important parameters for characterisation of quality of metal powders. Specific material properties such as ability to flow, reactivity as well as compressibility and its hardening potentials hence the most important characteristics of sintered metals - are determined by the size distribution and shape. The correct particle size distribution and particle shape information are the key to best product quality in atomisation processes of aluminium, milling of pure metals and other processes. This paper presents state-of-the-art technology for characterization of particle size distribution and shape.

• Journal of KSNVE
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• v.4 no.2
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• pp.209-219
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• 1994

Classical method calculates the resonance frequency of Helmholtz resonator by postulating that there is a moving mass in neck and a stiffness which expresses the compressibility of cavity. This has been widely accepted as reasonable to determine the resonant frequency, provided that the wave length of interest is longer that any length scale of resonater. Nevertheless, it has been often recognized that this classical method sometimes does not well predict the resonant frequency. This paper decribes the way in which the dynamics of resonator very often does care about the detail geometries of resonator; location of the neck, diameter ratio of the neck to that of cavitty, length of resonator compared with that of neck, etc. This rather unexpected observations have been proved theoretically; 3 dimensional analysis of acoustic wave equation, as well as experimentally by comparing the resonant frequencies, transmission loss, and insertion loss of resonator.