• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.111-121
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter d$_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0-3.0MPa, 4.0-2.0MPa, 2.0-4.0MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter do shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability of swirl-controlled rotor-bearing system.

• Tribology and Lubricants
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• v.13 no.3
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• pp.63-72
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter $d_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0~3.0 MPa, 4.0~2.0 MPa, 2.0~4.0 MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter $d_0$ shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial effects on the magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability control of swirl-controlled rotor-bearing system.

• Journal of ILASS-Korea
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• v.10 no.3
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• pp.29-37
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• 2005

The spray and acoustic characteristics of a gas/liquid swirl coaxial injector are studied experimentally. The self-pulsation is defined as a pressure and flow rate oscillations by a time-delayed feedback between liquid and gas phase. Self-pulsation has strong influences on atomization and mixing processes and accompanies painful screams. So. the spray and acoustic characteristics are investigated. Spray patterns are observed by shadow photography technique in order to determine the onset of self-pulsation. And self-pulsation boundary with Injection conditions and recess length is get. To measure the frequency of the spray oscillation. oscillation of the laser intensity which passes through spray is analyzed by Fast Fourier Transform. For acoustic tests, a PULSE System was used. Acoustic characteristics of a swirl coaxial injector are investigated according to the injection conditions. such as the pressure drop or the liquid and gas phase. and injector geometries. such as recess length and gap size between the inner and outer injector. Front the experimental results. the increase of recess length leads to the rapid increase of the sound pressure level. And as the pressure drop of the liquid phase increases. the frequency of the self?pulsation shifts to the higher frequency. The frequency of spray oscillations is the same as that of the acoustic fields by self-pulsation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.20-23
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• 2011

The spray and atomization characteristics of swirl coaxial injectors which use gas methane and LOx as propellants are investigated experimentally with a recess length variation. Mass distribution and spray angle are measured by a patternator and droplet size to find atomization characteristics are measured by GSV(Global Size and Velocity) system. As a result, when the liquid sprayed, the spray angle decreased and the atomization characteristic was improved with the recess length increase. When the gas and liquid injected simultaneously, the spray angle was decreased and the atomization characteristic was improved comparing to only the liquid injection.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.3
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• pp.82-87
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• 1998

In order to provide a manufacturing system with efficiency and flexibility to cope with the changes in shop floor status, the integration of process planning and operations scheduling is required. In this paper, an integrated system of process planning and operations scheduling based on the concept of process net model and genetic algorithm is suggested. The process net model includes the alternative process plans. The integrated system is applied for prismatic parts.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.286-292
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• 2011

In order to design a shear coaxial injector of solid particles for underwater propulsion system, basic experiments on gas-liquid shear coaxial injector are necessary. In the gas-liquid coaxial injector self-pulsation usually occurs with an intense scream. When self-pulsation occurs, mass flow rate oscillation and intense scream are detected by the interactions between the liquid and gas phase. Self-pulsation must be suppressed since this oscillation may cause combustion instabilities. Considerable research has been conducted on self-pulsation characteristics, but these researches are conducted in swirl coaxial injector. The main objective of this research is to understand the characteristics of self-pulsation in shear coaxial injector and reveal the mechanism of the phenomenon. Toward this object, self-pulsation frequency and spray patterns are measured by laser diagnostics and indirect photography. The self-pulsation characteristics of shear coaxial injector are studied with various injection conditions, such as the pressure drop of liquid and gas phase, and recess ratio. It was found that the frequency of the self-pulsation is proportional to the liquid and gas Reynolds number, and proportional to the L/d.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.6
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• pp.38-48
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• 1993

A recessed n-p Juction diode with the self-aligned sturcture is proposed and fabricated by using the polysilicon as an n$^{+}$ diffusion source. The diode structure can be applicable to the emitter-base formation of high performance bipolar divice and the n$^{+}$ polysilicone mitter has an important effect on the device characteristics. The considered parameters for the polysilicon formation are the deposition condition. As$^{+}$ dose for the doping of the polysilicon and the annealing condition using RTP system. The vertical depth profiles of the fabricated diode are obtained by SIMS and the electrical characteristics are analyzed in terms of the ideality factor of diode (n), contact resistance and reverse leakage current. In addition, n$^{+}$-p junction diodes are formed by using the amorphous silicon (of combination of amorphous and polysiliocn) instead of polysilicon and their characteristics are compared with those of the standard sample. The As$^{+}$ dose for the formation of good junction is about 1~2${\times}10^{16}cm^{2}$ at given RTA conditions (1100.deg. C, 10sec).

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.108-119
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• 2020

Dynamic pressure sensor used in liquid rocket engine combustor and gas turbine is recess-mounted usually because it should work in high temperature environment. Although recess-mounted method can protect it from combustion gas in high temperature, tube resonance occurs in a tube-cavity system. To reduce it, the infinite tube probe(ITP) was introduced in this study. The ITP model suggested in previous literature was validated with experimental data and frequency response characteristics were analyzed. Guidelines for designing the ITP were suggested as frequency response profiles varied with geometric information and physical properties using this model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.985-990
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• 1995

Recently, the development of high speed and high precision NC-lathe for piston head machining is needed for the complexity and diversity of the piston head shape used in automobile reciprocating engine. THe piston head has many complex shapes in the aspect of fuel economy, such as ovality, profile, double ovality and recess. Among them, for the maching of the over shape of 0.1~1mm the cutting tool should move periodically symchronized with the rotation of piston workpiece. The cutting tool feeed system must have high positioning accuracy for the precise machining, high speed for the fast maching and high dynamic stiffness for the cutting force. The linear brushless DC motor is used for satisfying these coditions. The ballbush guide and supporting guide using turcite is used for the guidance of the feed drive system. Linear encoder, digital servo ampllifer and controller are used for driving the motor. THis paper presents the design and simulation of the new tool feed system for noncircular machining.

• Journal of the Korea Safety Management & Science
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• v.15 no.4
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• pp.113-121
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• 2013

The rate that women's EMTs(emergency medical technicians) in fire department occupy is increasing, but my general plan is aimed at suggesting the improving plan for the working environment of women's EMTs paying attention to the duty stresses of increasing women's EMTs, because improvement for the working environment of women's EMTs is being proceeded slowly. I suggested my improving plan for solving the working stress on the basis of a survey of the Recognition against women's EMTs as follows. Firstly, I suggested that physical strength of women's EMTs should be managed well continually via program establishment and a defined evaluation not only by employing a professional person in charge for physical strength in firehouse, but also by replenishing the suitable number for the urgent mobilization. Secondly, I suggested that the suitable number for the urgent mobilization should be increased to 3 including an ambulance driver. Thirdly, I suggested necessity such as the fruitful education and the creation of circumstances that can focus on education for improving participation rate, development of various new educational program, incentive program and penalty. finally, I suggested the fact that is related to the actual re-amendment of the concerned law and ordinance such as not only the smooth treatment of penalty for a traffic signal violation of ambulance and the legal remedy system due to aggravation of a patient's condition during a first-aid course, but also workshop and meeting among the periodical EMTs and administration of special therapy program and sufficient recess.