• 한국산학기술학회논문지
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• 제12권1호
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• pp.19-25
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• 2011

최근의 차량 연비는 환경 규제 및 고가의 연료 가격으로 인하여 중요한 문제로 대두되었다. 연비 향상을 위한 기술 개발은 엔진, 파워트레인 등 차량의 많은 구성품들의 성능을 개선하였다. 따라서 연비는 많이 향상 되었으나 연비 측정은 현재도 주어진 모드(LA-4, FTP-75 등)에서 컴퓨터 모의시험 및 다이나모에서 수행한다. 본 논문에서는 실제 도로의 연비 향상 방안을 도출하기 위하여 약 213Km 영동고속도로를 제안하는 3가지 다른 알고리즘으로 모의 주행하였다. 이를 위해 GPS 수신 데이터 중에서 거리와 고도 데이터를 추출하여 각 구간의 경사도, 주행저항을 계산, 알고리즘에 따른 속도 프로파일을 약 213Km 전 구간에 대해서 완성하였다. 이 속도 프로파일로 컴퓨터를 이용한 AVL Cruise 프로그램으로 모의 주행하여 연비를 산출하고 Eco-driving 방안을 제안한다.

• 한국지반공학회지:지반
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• 제14권2호
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• pp.67-78
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• 1998

마이크로터널링은 비교적 연약한 사질토 지반을 통과하는 소규모의 터널을 시공할 때 적용하는 공법으로, 터널 시작 위치에서 일련의 짧은 원형 콘크리트 관을 유압으로 밀어서 전구간을 관통하는 공법이다. 미국 뉴욕의 JFK공항의 활주로에서는 활주로 하부를 통과하는 전력구의 설치를 위하여 이러한 마이l터널링 공법을 시도하였다. 마이크로터널링 공법에서는 콘크리트관을 전진시키기 위해 강력한 유압으로 벤토나이트를 분출하는데, 이로 인하여 활주로 하부의 지반이 교란될 가능성이 있었기에 본 연구에서는 터널시공으로 인한 교란의 정도를 평가하기 위하여 SASW 기법과 크로스흘 시험을 수행하였다. 구조물 비파괴 건전도 기법인 SASW 기법으로는 활주로 기층 부위의 지반강성 변화 정도를 평가하였고, 크로스흘 시험으로는 활주로 인접 지반의 깊이별 5파속도 변화를 조사하였다. 또한, JFK 공항 부지에서 결정한 5파 속도-N 치의 부지특유 관계식을 통하여 5파 속도를 N치로 변환함으로써 지반강성의 변화를 지반강도 변화의 측면으로도 지반교란의 정도를 파악하였다.

• 한국지반공학회논문집
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• 제30권4호
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• pp.101-106
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• 2014

관입시험은 한정된 범위에서 1차원적 정보를 얻을 수 있으나, N치는 다양한 지반설계정수와 실험적으로 연관되어 있다. 탄성파를 이용한 비파괴 검사는 역산 과정을 통해 비용 및 시간에 효율적으로 2차원 및 3차원 물성에 대한 지도를 얻을 수 있으며, N치와 탄성파 속도는 간극비, 포화도, 유효응력 등에 의해 좌우된다. 따라서 N치와 탄성파 속도간의 경험적 관계들이 제안되어 왔다. 본 연구는 다양한 간극비와 포화도를 갖는 주문진사에 대해 정지토압조건에서 탄성파를 실험적으로 측정하였다. 그 결과 하중 조건이 간극비 및 포화도에 비하여 가장 영향을 주는 요소로 나타났으며, 간극비와 포화도는 응력-속도 관계의 경향에 영향을 주었다. 각 영향인자간의 관계를 다중회귀분석을 통해 상관식으로 나타내었다.

• 천문학회지
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• 제41권6호
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• pp.163-172
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• 2008

Using the spectral data in the 3700 to $10050{\AA}$ wavelength range secured with the Hamilton Echelle Spectrograph (HES) at the Lick observatory, we have investigated the expansion velocities and the physical conditions of the elliptical planetary nebula NGC 6803. Various forbidden and permitted lines, e.g. HI, HeI, HeII, [OIII], [NII], [ArIII], and [SII], indicate complicated but systematic physical conditions variation: electron temperatures $T_{\varepsilon}\;{\sim}\;9000$ - 11000 K and electron number densities $N_{\varepsilon}\;{\sim}\;2000$ - $9000\;cm^{-3}$. The line profile analysis of these ions also indicates the systematic change or the acceleration of the expansion velocities in the range of 10 - $22\;km\;s^{-1}$. We show that the velocity gradient and physical condition found in various ions are closely related to the prolate ellipsoidal structure of NGC 6803. The expansion velocity and the ionic abundance of $O^{2+}$ were derived based on the OII and [OIII] lines. In spite of the discrepancy of ionic abundances derived by the two cases and their line profiles, the expansion velocities of them agree well. We find that the ratios of the red to blue line component of the HeII & OII lines are different from those of the [OIII] or other forbidden lines that indicates a possible involvement of emission of HeII & OII lines. This subtle difference and the different physical condition of the lines are likely to be caused by the elongated geometry and the latitude dependence of the emission zone.

• 대한기계학회논문집B
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• 제26권11호
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• pp.1613-1621
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• 2002

An electromagnetic flowmeter(EMF) essentially averages the velocity distribution over the pipe cross- sectional area, and the measured value is dependent on the velocity profiles. In this study, installation effects of 90$^{\circ}$long elbow(KS B 1522, ISO 3419) on the EMF characteristics was investigated. A commercial EMF was adopted and the distribution of magnetic field in the electrodes cross section was measured. In the experiment, the national flow standard system, of which measurement uncertainty was evaluated in accordance with ISO 17025 recommendation, was used fur characterization of EMF. The leading line has 150D long straight pipe to established a fully developed flow before entering into the elbow and the elbow was installed downstream of it. then the flowmeter was tested within 50 D from the elbow. The installation effects of the flowmeter were investigated by varying the mean velocity(Reynolds No.)in pipe section, the locations and the direction of electrodes plane.($\phi$) From the experimental results, we find the optimal conditions to get most accurate measurements. Generally, the deviations from the calibration value were less than 0.5 % in farther than 10D distance from the elbow and the direction of electrode plane. $\phi$ = 90$^{\circ}$yielded the smallest measurement deviation. These characteristics were shown consistently in turbulent region regardless of the mean Reynolds number.

• 대한기계학회논문집B
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• 제25권6호
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• pp.786-798
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• 2001

This paper describes the phenomena of wake-induced transition of the boundary layers on a NACA0012 airfoil using measured phase-averaged data. Especially, the phase-averaged wall shear stresses are reasonably evaluated using the principle of Computational Preston Tube Method. Due to the passing wake, the turbulent patch is generated in the laminar boundary layer on the airfoil and the boundary layer becomes temporarily transitional. The patches propagate downstream with less speed than free-stream velocity and merge with each other at further down stream station, and the boundary layer becomes more transitional. The generation of turbulent patch at the leading edge of the airfoil mainly depends on velocity defects and turbulent intensity profiles of passing wakes. However, the growth and merging of turbulent patches depend on local streamwise pressure gradients as well as characteristics of turbulent patches. In this transition process, the present experimental data show very similar features to the previous numerical and experimental studies. It is confirmed that the two phase-averaged mean velocity dips appear in the outer region of transitional boundary layer for each passing cycle. Relatively high values of the phase-averaged turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall.

• 동력기계공학회지
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• 제5권2호
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• pp.22-29
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• 2001

This paper represents axial mean velocity, turbulent kinetic energy and swirl number based on momentum flux measured in the X-Y plane and Y-Z plane respectively of a cone type gas swirl burner by using X-probe from the hot-wire anemometer system. This experiment is carried out at flow rates 350 and $450{\ell}/min$ respectively, which are equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of a subsonic wind tunnel. Axial mean velocities and turbulent kinetic energies show that their maximum values exist centering around narrow slits situated radially on the edge of and in the forefront of a burner until $X/R{\fallingdotseq}1.5$, but they have a peculiar shape like a starfish diffusing and developing into inward and outward of a burner by means of the mixing between flows ejected from narrow slits, an inclination baffle plate and swirl vanes respectively according to downstream regions. Moreover, they show a relatively large value in the inner region of 0.5$S_m$ obtained by integration of velocity profiles shows a characteristic that has an inflection point composing of the maximum and minimum value until X/R<3, but shows close agreement with the geometric swirl number after a distance of X/R=3.

• Steel and Composite Structures
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• 제36권5호
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• pp.603-615
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• 2020

The present manuscript focuses on the flow and heat transfer of the dusty fluid along exponentially stretching cylinder. Enormous attempts are made for fluid flow along cylinder but the study of fluid behavior along exponentially stretching cylinder is discussed lately. Using appropriate transformations, the governing partial differential equations are converted to non-dimensional ordinary differential equations. The transformed equations are solved numerically using Shooting technique with Runge-Kutta method. The influence of the physical parameters on the velocity and temperature profiles as well as the skin fraction coefficient and the local Nusselt number are examined in detail. The essential observations are as the fluid velocity decreases but temperature grows with rise in particle interaction parameter, and both the fluid velocity and temperature fall with increase in mass concentration parameter, Reynold number, Particle interaction parameter for temperature and the Prandtl number.

• 한국전산유체공학회지
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• 제18권4호
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• pp.1-8
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• 2013

The performance of small-size impellers with ruled surfaces was investigated for flank milling over a wide speed range, using computational fluid dynamics analyses and gas bench tests. An impeller with a ruled surface was designed, manufactured, and tested to evaluate the effects of blade loading, the backsweep angle, and the relative velocity distribution on the compressor performance. The simulations and tests were completed using the same compressor cover with identical inlet and outlet channels to accurately compare the performance of the abovementioned impeller with a commercial impeller containing sculptured blades. Both impellers have the same number of blades, number of splitters, and shroud meridional profiles. The backsweep angles of the blades on the ruled impeller were selected to work with the same pinched diffuser as for a sculptured impeller. The inlet-to-exit relative velocity diffusion ratio and the blade loading were provided to maximize the flow rate and to minimize the surge flow rate. The design flow rate, rpm, were selected same for both impellers. Test results showed that for the compressor stage with a ruled impeller, the efficiency was increased by 0.32% with an extended surge margin without a reduction in the pressure ratio as compared to the impeller with the sculptured design. It was concluded that an increased relative velocity diffusion coupled with a large backsweep angle was an effective way to improve the compressor stage efficiency. Additionally, an appropriate blade loading distribution was important for achieving a wide operating range and higher efficiency.

• 대한기계학회논문집B
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• 제25권5호
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• pp.722-730
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• 2001

The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.