유압관로에서 비정상 압력측압공의 동특성에 관한 연구

나기대,유영태,김지환 조선대학교 에너지.자원신기술연구소 2000 에너지·자원신기술연구소 논문지 Vol.22 No.2

In this study, the analysis of the dynamics characteristics and performance investigation of the pressure measurement in the hydraulic pipe. The exact solution of the frequency response is obtained by using the complicated transfer function. The discrepancy with the exact and the approximate is small, so the approximation solution is adopted to compare the experimental result with the theoretical analysis. The pressure measurement in the hydraulic pipe is caused by length of capillary and according to the end volume size. The experimental and calculate result show that characteristic of the pressure .measurement in the hydraulic pipe varies with the length of capillary and volume size. Therefore present theoretical formulation and experimental result can be used generally in designing and performance evaluation of all the hydraulic pressure measurement in the hydraulic pipe

마그네슘합금 부품의 제조기술

나영기,임창동,신광선 한국주조공학회 2002 한국주조공학회지 Vol.22 No.3

경계조건변화에 따른 동력전달관로의 동특성

나기대,유영태,김지환 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.6

Design for a quiet operation of fluid power system requires the understanding of noise and vibration characteristics of the system. It's not easy to analyze noise problem in hydraulic cylinder used in typical actuator Because they've got complex fluid dynamics. One of the fundamental problems associated with the hydraulic system is the pulsating flow in pipe lines, which can e tackled by the analysis under simplifying assumptions. The present study focuses on theoretic analysis and experimental study on the dynamics of laminar pulsating flow in a circular pipe. We analyze the propagation characteristics of the pressure pulse within a hydraulic pipe line taking into account the pulsating flow frequency variation. We also measure instantaneous pressure pulses within pipe line to identify the transfer functions. We conduct series of experiments to investigate the propagation characteristics of pressure pulse for various pressure of pulsating flow. The working fluid of the present study is ISO VG46 and the temperature ranges from 20 to 60℃ with normal pressure at 4000kPa. The flow rate is measured by using an ultrasonic flow meter. Pressures at fixed upstream and downstream positions are measured concurrently. The electric signals of the pressure sensor are stored and analyzed using a system analyzer(PKE 983 series). The frequency is varied in the range of 10~500Hz. The Reynolds number is kept below 2,000. In the present study, boundary condition was varied by installing a surge tank and an orifice at the end of pipe. Experimental and theoretical results were compared each other under various boundary conditions.

정사각 덕트의 출구 영역에서 속도분포에 대한 실험적 연구

유영태,모양우,나기대,임인호 朝鮮大學校 機械技術硏究所 2002 機械技術硏究 Vol.5 No.2

A numerical simulation has been performed with the non-linear turbulence model proposed by Speziale(1987) coupled with the k-ε equations coming from the renormalization group theory(RNG) derived by Yakhot et al(1992). The fully developed turbulent flow through a straight square duct, involing secondary motion is simulated. This paper represent computations of the interaction between measurement and numerical computation of turbulent flow on velocity distribution of outlet region in a square duct. RNG turbulent model was adapted and compared with the experimental data and the result of Standard k-ε turbulent model. The predictions obtained with the RNG k-ε model show improvements when compared with the Standard k-ε model. Mean velocity, turbulence kinetic energy and Reynolds shear stresses are in quantitiative agreement with the experimental data. We feel that the RNG k-ε model suggested in this paper can be a useful turbulence model for practical engineering

유압관로의 주파수변화 따른 압력전파특성

유영태,나기대,김지환 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.2

In this paper, an oil hydraulic pipeline is terminated by both rotary sinusoidal flow generator at upstream and oriffice at down stream. The pulsating pressure wave form, generated by the rotary sinusoidal flow generator, is measured by pressure sensor. In the analysis of this paper, a component of the fundamental frequency is obtained by using Laplace transformation. The experimental and analytical results make clear that (1) viscosity is significant role in hydraulic pipe. (2) When pulsating frequency is matched with the natural frequency, resonance frequency occurred periodically. According to the study proposed here, dynamic pressure in a circular oil pipe is expressed in propagation of pressure wave with respect to frequency and Bessel function. The resonance frequency is 108Hz at oil temperature 20℃ in this study. The abrupt change of gain value id due to effect of resonance frequency. The results of experiment are compared with the calculated results, and agreement of both results is fairly good.

유압관로의 임피던스 전달특성

유영태,나기대,모양우,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

Design for quite operation of fluid power system requires t h understanding of noise and vibration characteristics of t h system This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation characteristics of pressure ripple in automotive power steering hydraulic pipe with dynamic response of hydraulic pipe line is examined.

원위부 신세뇨관성 산증에서 산-염기 운반체의 결손

김혜영,한진석,이정상,김현리,김진,이중건,이서진,김근호,진호준,전은실,주권욱,나기영,정우경,오지은,엄재호,궁성수 대한신장학회 2000 Kidney Research and Clinical Practice Vol.19 No.5

The purpose of this study was to elucidate whether the molecular defect of acid-base transporters in renal tubules is related to the functional defect of urinary acidification in distal renal tubular acidosis(RTA). We performed NH₄Cl, furosemide, or bicarbonate loading test to evaluate renal acidification function, and immunohistochemistry using antibodies to H^+ -ATPase, Cl^-/HCO₃^- exchanger(band-3 protein), and Na^+/K^+ -ATPase in kidney tissue in 6 patients with RTA and renal cell carcinoma patients as normal controls. Kidney tissue was obtained either by percutaneous needle biopsy(RTA) or nephrectomy(NC). The results were as follows; 1) In all six RTA patients, proton secretory defect of distal acidification was shown by a failure to lower the urine pH after NHC1 loading or furosemide test or abnormally low urine-blood pCO₂ difference during bicarbonate loading. In two patients with RTA, proximal acidification defect was combined, which was demonstrated by increased fractional excretion of bicarbonate. 2) In mal control, intense H^+ -ATPase and band-3 protein staining was observed in collecting ducts. 3) In distal RTA patients, H6+ -ATPase and band-3 protein staining was not demonstrable or markedly decreased in the intercalated cells of distal nephron. 4) In two patients who had both proximal and distal RTA, H^+ -ATPase staining was markedly decreased in the brush border of proximal tubules as well as the distal nephron. In conclusion, the defect of acid-base transporters in renal tubule was related with the functional defect of urinary acidification in distal RTA.

원심압축기의 선회실속특성에 관한 연구

모양우,나기대,유영태,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

In the present study, the performance characteristics and the number of stall cell during rotating stall of a centrifugal air compressor were experimentally investigated. Rotating stall in the vaneless diffuser were investigated by measuring unsteady pressure fluctuations at several different diffuser radius using a high frequency pressure transducer. The number of stall cell and their rotational speeds are distinctive features of the rotating stall phenomenon. The present study is mainly forced on the analysis for the stall cell number and its propagation speed unstable operating region of the compressor. The interpretation method of visualization is based on the pressure distribution in the circumference pressure fields while plotting the pressure and its harmonics variations in time in polar coordinates. To obtain the visualize the existence rotating stall, auto-correlation function and the frequency spectra of the pressure fluctuations were measured at rh-2 = 1.52. When the flow coefficient is lower than 0.150, the static pressure at impeller inlet is higher than that at inlet duct of the Compressor. And the flow coefficient is lower than 0.086, several stall cell groups of discrete frequencies are observed.

유압관로의 비정상유동에 따른 임피던스 전달특성

모양우,유영태,나기대,김지환 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.6

Design for quite operation of fluid power system requires the understanding of noise and vibration characteristics of the system. This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation of pressure ripple in automotive power steering hydraulic pipe line is examined. Also, a mathematical model of hydraulic pipe is proposed to support a design of the hydraulic circuit. and the impedance characteristics of pressure ripple is analyzed. It is experimentally shown that power steering hydraulic pipe attenuates pressure ripple with high frequency.

연속파형 Nd:YAG 레이저에 의한 인코넬 600의 용접 공정변수의 연구

배신철,유영태,송성욱,신호준,나기대 朝鮮大學校 機械技術硏究所 2004 機械技術硏究 Vol.7 No.1

The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. Welding characteristics of Inconel 600 Alloy using a continuous wave Nd:YAG laser are experimentally investigated. The major process parameters studied in the present laser welding experiment were position of focus, laser power, travel speed. The gap and offset maintained as small as possible. Optical microscope were used to investigate the microstructures of the welded zone. The follow conclusions can be drawn the laser power and travel speed have a pronounced effect the fusion zone size and shape.