• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.173-176
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• 2007

The characteristics of the tool system give many effects into the costs and qualities for the finished components. This study proposes a new method for manufacturing of high manufacturing productivity, production process reduction and low cost through back pressure forming. The Lock-up hub is manufactured through many processes, such as upsetting($1^{st}$ Forming), piercing, direct extrusion($2^{nd}$ Forming), final sizing process($3^{rd}$ Forming). In this study, process design for closed-die forging of a Lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of Lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.716-724
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• 1990

Oblique impinging plane jets were investigated experimentally and numerically at Reynolds number 21000. The inclination angle was varied from 90.deg.(normal to the impinging plate) to 60.deg.. The distance H between the nozzle exit and the stagnation point on the impinging plate was fixed at H/D=8. The working fluid was air. The mean velocity components and turbulent quantities were measured by a hot-wire anemometer. And the static pressure distributions on the impinging plate were measured by a Pitot tube. In numerical computation, the governing partial differential equations of elliptic type were solved with conventional k-.epsilon. turbulence model. The measurements show that, after impingement, the jet half width alone the wall increases in both directions, and that similarity for each turbulent quantity such as Reynolds shear stress or turbulent kinetic energy is revealed in the wall jet region. The computed results show some deviation from experimental data in the impingement region, where streamline curvature is significant. However, the computed results agree qualitatively well with measurements.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.5
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• pp.605-612
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• 1994

The methods to determine the hydrodynamic coefficients for the fixed type artificial reefs which were constructed to control ecological system in coastal waters are compared and discussed by model test results. To calculate the wave forces, least square method show good agreement with the experimental results and more stability than maximum force component method or Fourier decomposition method. This modified least square method of weighting the square of measured force turned out to be the most feasible method for maximum force. Using the feasible method, hydrodynamic characteristics for artificial reefs on uniform slopes offshore and breaking zone were studied. They were properly related to Keulegan-Carpenter's number and found larger than previous results. Wave force coefficients for artificial reefs around breaking zone were distributed from 1.5 to 2.5, and the mean value was 2.0. Drag force components were more in evidence than inertia force in maximum force which is important parameter to evaluate stability for high-permeability structures. A formula for the calculation of the maximum force for artificial reefs design is proposed, using structural dimension, water particle velocity and Keulegan-Carpenter's number.

• Journal of the Korean institute of surface engineering
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• v.39 no.6
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• pp.295-301
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• 2006

Hard chrome plating has been used in surface hard coating over 50 years both for applying hard coating and re-building of worn components. Hard chrome plating solution and mist pollute environment with very toxic $Cr^{6+}$(hex-Cr) known as carcinogen which causes lung cancer, High velocity oxy-fuel (HVOF) thermal spray coatings of WC base cermet and Co-alloy powders are the most promising candidates for the replacement of the traditional hard chrome plating. Surface properties, wear, and friction behaviors of micron size Co-alloy (T800) and micron size WC-l2Co (WC-Co) have been studied for the application as hard coatings. The temperature dependence of wear and friction behaviors of T800 and WC-Co have been investigated at the temperature of $25^{\circ}C$ and $538^{\circ}C$ for the application to high speed spindle.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.57.1-57.1
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• 2014

We present the preliminary results of CO outflow survey toward the 56 Very Low Luminosity Object (VeLLO) candidates at CO J=2-1 and J=3-2 transitions with two radio telescopes of the Caltech Submillimeter Observatory (CSO) and the Atacama Submillimeter Telescope Experiment (ASTE). The survey is aimed to understand the origin of the formation of low-mass stars or substellar objects. The VeLLO is a very faint (${\leq}0.1$ $L_{\odot}$) object deeply embedded in dense molecular clouds and believed to be a proto-brown dwarf which will be a brown dwarf or a faint protostar which has just formed with little mass accretion or which is in quiescent stage of episodic accretion. The candidates were searched for over all nearby ($d{\leq}450$ pc) Gould belt clouds and listed in a new catalogue of the VeLLO candidates by Kim et al. (2014 submitted). To diagnose present status and future fate of the VeLLOs, we conducted a systematic observation for the CO molecular outflows of the 56 VeLLOs to infer how accretion is being made around the VeLLOs. We found 17 VeLLO candidates either having a prominent wing in line profiles or showing bipolar intensity distribution of high velocity components. We will discuss the physical properties of these CO outflows and the identity of the VeLLO candidates.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.773-778
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• 2001

In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in SF$_{6}$ and SF$_{6}$-Ar mixtures have described. The ionization and attachment coefficients in pure SF$_{6}$ and SF$_{6}$-Ar mixtures have been calculated over the range of 10$_{6}$ molecule and for Ar atom proposed by other authors. The transport coefficients for electrons in (0.2%)SF$_{6}$-Ar and (0.5%)SF$_{6}$-Ar mixtures were measured by time-of-flight method, and the electron energy distribution function and the parameters of the velocity and the diffusion were determined by the variation of the collision cross-sections with energy. The results obtained in this work will provide valuable information on the fundamental haviors of electrons in weakly ionized gases and the role of electron attachment in the choice of better gases and unitary gas dielectrics or electro negative components in dielectric gas mixtures. gas mixtures.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.71-78
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• 2002

All modem, aerospace gas turbines must operate with hot stage gas temperature several hundreds of degrees hotter than the melting temperatures of the materials used in their construction. Complicated cooling schemes need to be employed in the combustor walls and In the high pressure turbine stages. Internal passages are cast or machined into the hot sections of aero-gas turbine engines and air from the compressor is used for cooling. In many cases, the cooling system is engineered to utilize jets of high velocity air, which impinge on the internal surfaces of the components. They are divided by Impinging cooling method and Vortex cooling method. Specially, Research of new cooling system(Vortex cooling method) that overcome inefficiency of film cooling and limitation of space. The focus of new cooling system that improve greatly cooling efficiency using quantity's cooling air which is less is set in surface heat transfer elevation. Therefore, In this study, the numerical analysis have been performed for characteristic of flow and thermal in the swirl chamber and compared with the flow field measurement by LDV. especially, for understanding of high heat transfer efficiency in vicinity of wall. we considered flow structure and mechanism of vortex and heat transfer characteristic in variation of Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3041-3053
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• 1995

Cylindrical chokes are used widely as components of hydraulic equipments. The dynamic characteristics between flowrate and pressure drop through the cylindrical chokes were discussed by the frequency characteristics of the chokes. It was assumed no pressure recovery occurred near the downstream of the choke. The pulsating jetflow from the outlet of cylindrical chokes show very complex behaviours which are quite different from the steady jet flow but it's not clarified quantitatively. In order to utilize the chokes as a flowmeter, it is indispensable to discuss the estimation of the dynamics of pressure drop in the downstream jetflow region of cylindrical chokes. In this experimental study, it is clarified that the reattachment length depended on pressure wave is compared with it depended on velocity wave. A pulsating flow is verified by visualization method. In the present study, the flow characteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristic parameters of the ratios of inertia(.PHI.$_{t,1}$) and viscous(.PHI.$_{z,1}$) term to pressure term are introduced to describe the flow pattern of laminar pulsating flow. flow.low.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.623-631
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• 2000

Hot-wire measurements were carried out on the developing turbulent flows subject to plane rate of strain in a rotating curved duct. The cross-section of the curved duct varies from 100mm${\times}$50mm rectangular shape at the bend inlet gradually to the 50mm${\times}$100mm rectangular shape at the bend outlet. Experimental setup consists of the test section of $90^{\circ}$ curved duct, rotating disc of 1.95m diameter, Ag-Ni precision slip ring, automatic traversing mechanism, variable speed motor, centrifugal blower, orifice flowmeter and hot-wire anemometer. Data signals from the rotating curved duct are transmitted through the slip ring to the computer which is located at the outside of the rotating disc. 3-dimensional velocity and 6 Reynold stresses components were obtained from the fluctuating and mean voltage measured by the slant type hot-wire probe rotating into 6 orientations. We investigate the effects of Coriolis and centrifugal forces on the turbulence structure.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.1
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• pp.14-28
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• 2000

The frequency response characteristics of a condenser were numerically studied for the control of refrigeration and air conditioning systems. The important parameters, such as the refrigerant flow rate, refrigerant temperature, air velocity, and air temperature at the condenser inlet, were analyzed. Superheated vapor, two phase, and subcooled liquid domain in condenser can be described by using the energy balance equation and the mass balance equation in refrigerant and tube wall, the basic equation for describing the dynamic characteristics of condenser can be derived. The transfer function for describing dynamic response of the condenser to disturbances can be obtained from using linearizations and Laplace transformations of the equation. From this transfer function, analytical investigation which affects the frequency responses of condenser has been made. Block diagrams were made based on the analytic transfer function; dynamic responses were evaluated in Bode diagrams on the frequency response. Through this study, it became possible that the information about the dynamic characteristics of air-cooled condenser is offered. The results may be used for determining the optimum design parameters in actual components and entire systems. Also, the mathematical models, frequency response may be used to help understanding, evaluate optimum design parameters, design control systems and determine on setting the best controller for the refrigeration and air-conditioning systems.