• 한국자동차공학회논문집
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• 제14권1호
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• pp.17-24
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• 2006

This study was performed to figure out spray behavior and fuel atomization characteristics of a piezo-driven injector and a solenoid-driven injector in the common-rail injection system under the same design parameters and test conditions. The process of spray injection was visualized by using the spray visualization system composed of a Nd:YAG laser and an ICCD camera. The atomization characteristics were investigated in terms of axial mean velocity, Sauter mean diameter(SMD) and droplet distributions obtained from a phase Doppler particle analyzer system. Compared with solenoid-driven injector, the piezo-driven injector has short injection delay and reaches quickly to the maximum injection value. Spray tip penetration shows some difference, however, spray angle of piezo-driven injector is wider than that of solenoid-driven injector. Sauter mean diameter of piezo-driven type injector is smaller than that of solenoid-driven type.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.139-148
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• 2016

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

• 화약ㆍ발파
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• 제38권1호
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• pp.23-29
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• 2020

발파나 충격과 관련된 연구에서 충격센서를 이용한 하중 및 진동의 계측이 널리 사용되고 있다. 하지만 대부분의 충격센서는 고가이며 외부로부터의 손상에 대해 보호할 필요성이 존재한다. 본 연구에서는 충격센서의 외부 구조적 변화에 따른 계측 대상 매질로부터 입사되는 하중정보의 왜곡현상을 보정할 수 있는 방법에 대해 고찰하였다. 홉킨슨 압력봉 시스템을 이용해 충격센서로 전달되는 충격가속도를 산출하였으며, 이와 동시에 충격진동의 감쇠를 야기하는 센서 홀더를 고안 및 적용하여 센서의 출력 값에 대한 비교분석을 수행하였다. 결과적으로 센서에 적용된 외부 구조적 변화가 센서의 진동운동 자체를 왜곡시키는 비선형 거동이 아닌 경우 본 방법을 통한 충격센서 보정기술이 합리적으로 작용할 수 있을 것으로 판단하였다.

• 한국대기환경학회지
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• 제15권2호
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• pp.191-199
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• 1999

This study evaluated the availability as an alternative adsorbent which is cheaper and more efficient than CuO/${\gamma}$-$Al_2O_3$ which have been studing vigorously to remove $SO_2$. Five adsorbents (CuO/${\gamma}$-$Al_2O_3$, Iron ore, Slag, LD slag, $Fe_2O_3$) was employed in a fixed bed reactor. $SO_2$ breakthrough curves were obtained as a function of temperature, initial gas velocity and particle size. Saturation capacities calculated by the numerical integration of breakthrough curves of $SO_2$ increased with increasing reaction temperature. $SO_2$ breakthrough curve equation of $Fe_2O_3$ for this system can be expressed as Kr=3,914,000 exp(-37,329.86/RT). By means of the breakthrough curve, the influence of bed height on breakthrough time was also estimated.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1993년도 학술발표집 지반진동 영향평가
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• pp.55-72
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• 1993

동다짐은 무거운 다짐추를 고공에서 낙하시켜 낙하시 지반에 가하는 충격을 이용하여 지반을 개량하는 공법으로서, 시공시 발생하는 진동에 의하여 주변 구조물매 피해가 유발될 수도 있다. 본 연구는 쓰레기 매립지반에서 동다짐을 시공할시 수행된 진동 측정자료들을 분석하였으며 그 결과 다음과 같은 사실들을 확인할 수 있었다. \circled1 동다짐시 발생하는 진동의 입자속도는 Longitudinal, vertical, Transversal 방향순으로 그 크기가 크며, 체감을 또한 Lcugitudinal, Vertical, Transversal 방향순으로 큰 것으로 나타났다. \circled2동다짐시 발생하는 진동의 탁훨 진동수는 7-9 Hz내외이다. \circled3구조물에 인접한 동다짐은 다짐추의 낙하고를 저하시켜 충격에너지를 감소시켰으며, 이를 이용하여 구조물께 대한 피해를 애방할 수 있었다. \circled4사무기기는 켜놓은 상태가 꺼놓은 상태보다 진동에 대하여 약하므로 사무기기에 대한 진동피해를 줄이기 위하여는 비 업무시간을 이용하여 사무실에 10m까지 인접하여 동다짐을 실시할 수 있었다.

• 자원리싸이클링
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• 제10권6호
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• pp.35-42
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• 2001

Air table을 이용해서, 입상플라스틱 혼합물로부터 PVC를 제거 분리하는 연구를 행하였다. Air table상에서 플라스틱이 어떠한 운동을 하는가 연구하고, PVC 10%와 PE 90%의 인공흔합물을 가지고 선별 분리시험을 행하였다. 이 연구로부터 선별 최적조건은, 9.2 Hz의 Frequency, 1.05 m/sec의 바람속도, 7.5 End-slope, 1 side-slope, 450 g/min의 Feeding speed 등이었다 PE-PVC 흔합물에서 99.96%의 PE를 98.9% 얻을 수 있었고, 88.7%의 PVC를 99.6% 얻을 수 있었다.

• 대한조선학회논문집
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• 제49권5호
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• pp.410-415
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• 2012

An experimental study is carried out to investigate the near-wake characteristics of a NACA 0018 foil with a flat plate. Two-frame grey-level cross correlation PIV method is used to measure the local flow characteristic around a pitch damping foil to control the vertical motion of high speed crafts in a circulating water channel. The analysis also includes angles of attack 10 and 20 degrees respectively. Reynolds number $Re{\fallingdotseq}3.5{\times}10^4$ based on the chord length(C=100mm) of NACA0018 has been applied during the whole experiments. The distance between the foil and the flat plate is D/C=0.5, 1.0 and 1.5 respectively. The channel effect according as the distance between the foil and the flat plate has a close relation with the velocity distributions around the foil. In the wake of 20-degree of attack, the complex turbulent flow and a thick boundary layer are formed due to the processes of vortex generation and dissipation.

• 한국수산과학회지
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• 제27권5호
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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.

• 설비공학논문집
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• 제15권10호
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• pp.835-842
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• 2003

A three dimensional numerical analysis has been conducted for a stoker type incinerator which has the capacity of 1.5 ton/hr. The objective of the present study is to predict the effects of swirl induced by secondary air and to find an optimal operating condition of the incinerator. In this study, combustion characteristics such as distributions of temperature, velocity and concentration of each species have been examined with various injection types of secondary air and with different flow rates of secondary air in the incinerator. It is found that the secondary air injection on the combustion process makes the path of fluid particle longer in the combustor and enhances the mixing between air and combustion gas by arousing a swirl. Therefore, the injection type of secondary air can be an important key in the design process of incinerator.

• 한국유체기계학회 논문집
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• 제9권1호
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• pp.9-18
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• 2006

In the range of very low specific speed ($n_s<0.25$, non-dimensional), the performance of a centrifugal pump is much different from that of a centrifugal pump of normal ns and the efficiency of the pump drops rapidly with the decrease of $n_s$. In order to examine the reason of unstable performance characteristics of the very low $n_s$- centrifugal pump, the internal flow of the pump with a semi-open impeller is measured by a PTV(Particle Tracking Velocimetry) system. The purpose of this study is to make clear the internal flow characteristics and to obtain basic knowledge of the pump performance. The results show that the leakage flow through tip clearance give a strong effect on the flow pattern of impeller passage. A large vortex in the impeller passage and a strong reverse flow at impeller outlet are formed in the range of small flow rates, and the vortex and the reverse flow together reduce the absolute tangential velocity at the impeller outlet and cause the performance instability.