• 대한기계학회논문집
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• 제7권2호
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• pp.193-203
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• 1983

The mixed convective heat transfer problems are characterized by the relatively significant contribution of buoyancy force to the transport processes of momentum and heat. Past analytical studies on this kind of problems have been carried out by employing either the conventional R-.epsilon. turbulence model which includes constant turbulent Prandtl number .sigma.$_{+}$ 1 or an extended R-.epsilon. turbulence model which takes account of the buoyancy effect in appropriate length scale equations. But in the latter case, the temperature variance .the+a.$^{2}$ over bar is approximated by a model under local equilibrium condition and the time scale ratio between velocity and temperature is assumed to be constant. These approximation is known to break down when the buoyancy effect is dominant. The present study is aimed at development of new computational turbulence closure level which can be applied to this rather complex turbulent process. The temperature variance is obtained directly by solving its dynamic transport equation and the time scale ratio which is variable in space is computed by a solution of a dynamic equation for the rate of scalar dissipation .epsilon.$_{\thetod}$ It was found that the computational results are in good agreement with available experimental data of wide range of unstable conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권6호
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• pp.2824-2837
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• 2019

Container technologies are widely used in infrastructures to deploy and manage applications in cloud computing environment. As containers are light-weight software, the cluster of cloud applications can easily scale up or down to provide Internet-based services. Container-based applications can well deal with fluctuate workloads by dynamically adjusting physical resources. Current works of scheduling applications often construct applications' performance models with collected historical training data, but these works with static models cannot self-adjust physical resources to meet the dynamic requirements of cloud computing. Thus, we propose a self-adaptive automatic container scheduling framework AutoScale for cloud applications, which uses a feedback-based approach to adjust physical resources by extending, contracting and migrating containers. First, a queue-based performance model for cloud applications is proposed to correlate performance and workloads. Second, a fuzzy Kalman filter is used to adjust the performance model's parameters to accurately predict applications' response time. Third, extension, contraction and migration strategies based on predicted response time are designed to schedule containers at runtime. Furthermore, we have implemented a framework AutoScale with container scheduling strategies. By comparing with current approaches in an experiment environment deployed with typical applications, we observe that AutoScale has advantages in predicting response time, and scheduling containers to guarantee that response time keeps stable in fluctuant workloads.

• 수산해양기술연구
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• 제51권1호
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• pp.146-153
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• 2015

A model net experiment of the gape net for anchovy in Jindo, Jeollanam-do was carried out to investigate the net shape and hydrodynamic resistance using circulating water channel. The model net was made 1/33 down scale by Tauti's similarity method and the range of experimental current speed was from 0.5 knot to 3.5 knot (increasing 0.5 knot interval). The net mouth height in 0.5 knot of the minimum experiment current speed was shown 26.0 cm (full-scale conversion value 8.58 m). The net mouth height and mouth area in 1.5 knot of the same current speed with a gape net fishing ground were shown 20.0 cm (full-scale conversion value : 6.60 m) and about $507.9cm^2$ (full-scale conversion value : $55.31m^2$). The net mouth height and area were decreased with increase the experimental current speed. The hydrodynamic resistance of the model net in 1.5 knot current speed was shown 1.11 kgf and the value of full-scale conversion by Tauti's method was shown 3.996 ton.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.705-706
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• 2008

When heat generated inside a large factory building is not discharged due to a stagnant flow, the working environment of workers becomes worse and the cooling of high-temperature products such as hot-rolling coils is delayed. To investigate the natural ventilation inside a large factory building, experimental studies were carried out using wind-tunnel tests. The scale-down factory building models were placed in an atmospheric boundary layer (ABL) and the mean and fluctuating velocity fields were measured using a particle image velocimetry (PIV) technique. For the prototype factory model, the outdoor air is only entrained into the factory building through the one-third open windward wall, and stagnant flow is formed in the rear part of the target area. In order to improve the indoor ventilation environment of the factory building, three different louver-type ventilators were attached at the upper one-third open windward wall of the factory model. Among the three louver ventilators tested in this study, the ventilator model #3 with the outer louver (${\theta}_o$ = 90$^{\circ}$) and the inner louver (${\theta}_i$ = -70$^{\circ}$) was found to improve the natural ventilation inside the factory building model effectively. The flow rate of the entrained air was increased with aligning the outer louver blades with the oncoming wind and guiding the entrained air down to the ground surface with elongated inner louver blades.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 A
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• pp.219-221
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• 1999

HVDC(High Voltage Direct Current) transmission system was constructed between Cheju island and mainland Haenam and has been operating commercially since 1998. But research activities in this area are not so much. That is caused by the facts that HVDC is large scale system and it is not so easy to implement and to test. Though such simulation tools as RTDS(Real Time Digital Simulator) and EMTDC can be useful, these have limitations for actual control and protective system design. Therefore scaled-down HVDC model was developed for the purpose of researches at operating technique, control and protection methods. The design of this model was based on real Cheju-Haenam HVDC system. And additionally faults simulator such as ground fault, short-circuit and change of impedance in transmission line is equipped for analysis of these faults. Control system of the model was implemented fully digitally. So it is very easy for the researchers to develope control and protection algorithm and to test the performance.

• 한국농공학회논문집
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• 제59권2호
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• pp.49-55
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• 2017

Recently climate change and urbananization have been increased surface runoff, resulting in flooding. Retention basins have been constructed to control urban flooding by reducing peak flow rate. Recently, the retention basin plays a role in controlling combined sewer overflows (CSOs) as well as urban flooding. In this study, the retention basin with a rotatable bucket was suggested and scale down experiments was performed for the optimum design of the retention basin. Scaled down model was produced using a 3D printer after it was designed as law of similarity. Two times for operating a rotary bucket is required to sweep out the sediments deposited on the bottom of the basin. Optimized dimensions for the retention basin were width of 5 m, height of 5 m, bucket radius of 0.5 m, and bottom slope of 5.0 %. It can be concluded that the results obtained from this study can be used to design the retention basin with a rotatable bucket which does not require energy to operate.

• International Journal of Automotive Technology
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• 제7권5호
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• pp.609-618
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• 2006

This paper presents the lateral control of an autonomous vehicle by using a look-ahead sensing system. In look-ahead sensing by an absolute positioning system, a reference lane, constructed by straight lanes or circular lanes, was switched by a segment switching algorithm. To cope with sensor noise and modeling uncertainty, a robust LMI-based $H_{\infty}$ lateral controller was designed by the feedback of lateral offset and yaw angle error at the vehicle look-ahead. In order to verify the safety and the performance of lateral control, a scaled-down vehicle was developed and the location of the vehicle was detected by using an ultrasonic local positioning system. In the mechatronic scaled-down vehicle, the lateral model and parameters are verified and estimated by a J-turn test. For the lane change and reference lane tracking, the lateral controllers are used experimentally. The experimental results show that the $H_{\infty}$ controller is robust and has better performance compared with look-down sensing.

• Steel and Composite Structures
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• 제1권2호
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• pp.187-200
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• 2001

Most of the portal frames are designed these days by the application of plastic analysis, with the normal assumption being made that the column bases are pinned. However, the couple produced by the compression action of the inner column flange and the tension in the holding down bolts will inevitably generate some moment resistance and rotational stiffness. Full-scale portal frame tests conducted during a previous research program had suggested that this moment can be as much as 20% of the moment of resistance of the column. The size of this moment of resistance is particularly important for the design of the tensile capacity of the holding down bolts and also the bearing resistance of the foundation. The present research program is aiming at defining this moment of resistance in simple design terms so that it could be included in the design of the frame. The investigation also included the study of the semi-rigid behaviour of the column base/foundation, which, to a certain extent, affects the overall loading capacity and stiffness of the portal frames. A series of column bases with various details were tested and were used to calibrate a finite element model which is able to simulate the action of the holding down bolts, the effect of the concrete foundation and the deformation of the base plate.

• 해양환경안전학회지
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• 제29권5호
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• pp.479-487
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• 2023

최근 지구 온난화의 영향으로 태풍의 파괴력이 증가함에 따라 부유식 해상풍력발전기의 막대한 유실과 붕괴에 대한 우려가 깊어지고 있다. 부유식 해상풍력발전기의 안전한 운영을 위해 새로운 형태의 탈착형 계류 시스템 개발이 요구되고 있다. 본 연구에서 고려한 새로운 반잠수식 계류 풀리는 기존의 탈착형 계류 장치에 비해 계류 라인으로 부유식 해상풍력 터빈을 보다 쉽게 탈부착할 수 있도록 고안되었다. 8MW급 부유식 해상풍력발전기에 적용 가능한 반잠수식 계류 풀리의 초기 설계에 대한 구조적 안전성을 검토하기 위해 3D 프린터를 이용하여 축소구조모형을 제작하고, 이 모형에 대한 구조시험을 수행하였다. 축소 모형의 구조시험을 위해 3D 프린팅에 사용된 ABS 소재의 인장 시편을 제작하고 인장시험을 수행하여 소재의 물성을 평가하였다. 인장시험에서 얻은 재료 특성과 축소모형 구조 시험과 동일한 하중 및 경계 조건을 적용하여 반잠수식 계류 풀리의 유한요소해석을 수행하였다. 유한요소해석을 통해 반잠수식 계류 풀리의 구조적 취약 부분을 검토하였다. 반잠수식 계류 풀리의 주요 하중조건을 고려하여 구조모형시험을 수행하였으며, 재료의 최대인장응력 이상이 발생하는 위치에 대해 유한요소해석과 시험 결과를 비교하였다. 유한요소해석과 모형시험의 결과로부터 작동조건에서는 Body와 Wheel의 연결부 구조가 취약한 것으로 파악되었고, 계류조건에서는 Body와 Chain stopper의 연결부 구조가 취약한 것으로 검토되었다. 축소모형 구조시험에서 나타난 SMP의 구조 취약부는 구조해석의 결과와 일치하는 것으로 나타났다. 연구 결과를 통해 반잠수식 계류 풀리의 초기 설계에 대한 구조적 안전성을 실험적으로 검증할 수 있었다. 또한, 본 연구 결과는 상세설계 단계에서 반잠수식 계류 풀리의 구조 강도를 향상시키는데 유용하게 활용될 수 있을 것으로 판단된다.

• Journal of information and communication convergence engineering
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• 제10권2호
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• pp.194-199
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• 2012

This paper proposes a novel scheme of a gray scale fingerprint image for a high-accuracy capacitive sensor chip. The conventional grayscale image scheme uses a digital-to-analog converter (DAC) of a large-scale layout or charge-pump circuit with high power consumption and complexity by a global clock signal. A modified capacitive detection circuit for the charge sharing scheme is proposed, which uses a down literal circuit (DLC) with a floating-gate metal-oxide semiconductor transistor (FGMOS) based on a neuron model. The detection circuit is designed and simulated in a 3.3 V, 0.35 ${\mu}m$ standard CMOS process. Because the proposed circuit does not need a comparator and peripheral circuits, the pixel layout size can be reduced and the image resolution can be improved.