• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1172-1176
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• 2009

In the present study, natural convection over a heat sink with a horizontal circular base and rectangular fins was numerically analyzed. To calculate natural convection heat transfer, the assumptions of ideal gas and laminar flow were made for air. Flow patterns around the heat sink were chimney-like. The resultant temperature distribution on the circular base appeared almost uniform. Parametric studies were performed to compare the effects of fin length, fin height, the ideal number of fins, and heat flux on the average temperature of a heat sink and the average heat transfer coefficient from the heat sink array. Correlation to predict the average Nusselt number was presented.

• 한국자원식물학회지
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• 제11권3호
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• pp.264-271
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• 1998

This study was conducted to investigate morphological characteristics of Korean local garlic varieties and to define the genetic variability and the correlations amongthe characters associated with yield. The plant height, the leaf sheath diameter, the nubmer of leaves, and bulb weight were significantly increased in the garlic plants from heavier seed bulbs. The proportation of six clove bulbs was more than 60% in Seosan variety and this was not realted with the number of cloves in seed bulb. While more than 70% bulbs in Jeoksung and Danyang varieties cultivated in paddy field were composed of 6 or 7 cloves, majority of the bulbs of Euisung and Danyang varieties cultivated in upland were composed of bulbs with 7 cloves or more. The highest genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were observed in bulb weight. GCV and PCV also showed high value in leaf sheath diameter. Thus, there is a greater scope for selection of these characters. The small difference between PCV and GCV values in plant height indicates that the environmental influence would be limited in this character. High heritability was observed of plant height (56.76%) and bulb weight (45.95%). And the weight per bulb (34.24%) exhibited highest genitic advance followed by leaf sheath diameter (18.8%) and plant height (9.61%), and those would be the ideal characters for selelction.

• Wind and Structures
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• 제28권3호
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• pp.155-170
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• 2019

This paper presents a novel test method for the galloping of iced conductor using wind generated by a moving vehicle which can produce relative wind field. The theoretical formula of transiting test is developed based on theoretical derivation and field test. The test devices of transiting test method for aerodynamic coefficient and galloping of an iced conductor are designed and assembled, respectively. The test method is then used to measure the aerodynamic coefficient and galloping of iced conductor which has been performed in the relevant literatures. Experimental results reveal that the theoretical formula of transiting test method for aerodynamic coefficient of iced conductor is accurate. Moreover, the driving wind speed measured by Pitot tube pressure sensors, as well as the lift and drag forces measured by dynamometer in the transiting test are stable and accurate. Vehicle vibration slightly influences the aerodynamic coefficients of the transiting test during driving in ideal conditions. Results of transiting test show that the tendencies of the aerodynamic coefficient curve are generally consistent with those of the wind tunnel tests in related studies. Meanwhile, the galloping is fairly consistent with that obtained through the wind tunnel test in the related literature. These studies validate the feasibility and effectiveness of the transiting test method. The present study on the transiting test method provides a novel testing method for research on the wind-resistance of iced conductor.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.495-509
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• 2019

The objective of this study is to analyze the compressibility effects of multiphase cavitating flow during the water-entry process. For this purpose, the water-entry of a projectile at transonic speed is investigated computationally. A temperature-adjusted Tait equation is used to describe the compressibility effects in water, and air and vapor are treated as ideal gases. First, the computational methodology is validated by comparing the simulation results with the experimental measurements of drag coefficient and the theoretical results of cavity shape. Second, based on the computational methodology, the hydrodynamic characteristics of flow are investigated. After analyzing the cavitating flow in compressible and incompressible fluids, the characteristics under compressible conditions are focused upon. The results show that the compressibility effects play a significant role in the development of cavitation and the pressure inside the cavity. More specifically, the drag coefficient and cavity size tend to be larger in the compressible case than those in the incompressible case. Furthermore, the influence of entry velocities on the hydrodynamic characteristics is investigated to provide an insight into the compressibility effects on cavitating flow. The results show that the drag coefficient and the impact pressure vary with the entry velocity, and the prediction formulas for drag coefficient and impact pressure are established respectively in the present study.

• 대한설비공학회지:설비저널
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• 제5권1호
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• pp.19-24
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• 1976

An ideal heat pump system was optimized by considering the coefficient of performance and the size of condenser and evaporator as two competing objectives. Thermodynamic limitations were included as natural constraints. Experimental data for compressor performance were utilized in evaluating the system behavior. With a varying weighting factor between the two competing objectives the optimum deiogn parameters were presented in a graphical form.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 전자세라믹스 센서 및 박막재료 반도체재료 일렉트렛트 및 응용기술
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• pp.134-138
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• 2000

The physical, electrical and piezoresitive characteristics of CrN(chromiun nitride) thin-films on silicon substrates have been investigated for use as strain gauges. The thin-film depositions have been carried out by DC reactive magnetron sputtering in an argon-nitrogen atmosphere(Ar-(5~25 %)$N_2$). The deposited CrN thin-films with thickness of $3500{\AA}$nd annealing conditions($300^{\circ}C$, 48 hr) in Ar-10 % $N_2$ deposition atmosphere have been selected as the ideal piezoresistive material for the strain gauges. Under optimum conditions, the CrN thin-films for the strain gauges is obtained a high electrical resistivity, $\rho=1147.65\;{\mu}{\Omega}cm$, a low temperature coefficient of resistance, TCR=-186 ppm/$^{\circ}C$ and a high temporal stability with a good longitudinal gauge factor, GF=11.17.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.135-141
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• 2000

The physical, electrical and piezoresitive characteristics of CrN(chromiun nitride) thin-films on silicon substrates have been investigated for use as strain gauges. The thin-film depositions have been carried out by OC reactive magnetron sputtering in an argon-nitrogen atmosphere(Ar-(5~25 %)$N_2$). The deposited CrN thin-films with thickness of $3500{\AA}$ and annealing conditions($300^{\circ}C$, 48 hr) in Ar-10 % $N_2$ deposition atmosphere have been selected as the ideal piezoresistive material for the strain gauges. Under optimum conditions, the CrN thin-films for the strain gauges is obtained a high electrical resistivity, $\rho=1147.65\;{\mu}{\Omega}cm$, a low temperature coefficient of resistance, TCR=-186 ppm/$^{\circ}C$ and a high temporal stability with a good longitudinal gauge factor, GF=11.17.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1466-1474
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• 1997

In order to design and develop a spark ignition engine, many studies must be preceded about the characteristics of thermal flow. For measurement of transient wall temperature thin film thermocouples of Bendersky type were manufactured and these probes were fixed into the wall of combustion chamber. Surface wall temperatures were measured in experiments of various engine speeds. Transient heat fluxes were calculated from the wall temperature measurements. Pressure was measured from combustion chamber using pressure transducer and gas temperatures were calculated using the state equation of ideal gas. And instantaneous heat transfer coefficients were obtained. It will be the basic data for the formulae of instantaneous heat transfer coefficients.

• 설비공학논문집
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• 제7권1호
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• pp.150-160
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• 1995

A Finkelstein adiabatic analysis is performed for Stirling refrigerator with real gas properties of helium. The mass balance and the energy balance equations are formulated into the form that is convenient for incorporating an available computer code of the helium properties. The differential equations are solved numerically. The calculated coefficient of performance(COP) and the pressure variation are compared with the results obtained when helium is assumed to be an ideal gas. The relative errors in COP are presented as functions of the refrigeration temperature and the maximum cycle pressure.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.443-454
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• 2016

This study focus to make 8 legs robot based on Jansen's mechanism. In the process of making, we found GL(Ground length),GAC(Ground Angle Coefficient) and the height difference of tract and compare Several models with M.Sketch to find link's Length ratio Optimised simple walking and crossing of obstacles. In the process, our team Analyzed the difference ideal tract (Jansen holy number model's track) contrived by Jansen and our final model tract. As a result, we found optimal link's length ratio to over the obstacles and some features that our model differ from Jansen holy number model. It means that optimal link's length ratio depends on certain circumstances, perfect length ratio is nonexistent.