• Journal of KIISE:Computing Practices and Letters
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• v.7 no.6
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• pp.641-652
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• 2001

Most of current internet auction systems are single auction server program that partly automates the function of the conventional auction house. So these systems do not provide sufficient independence, distribution and parallelism between the functions of the conventional auction house. In these suction systems, only some of suction management facilities are automated by the server program, but still users need to execute a repetitive task to monitor the dynamic progress of a certain auction, decide the proper bid price, and submit the bid. Another problem is that they support only the single auctions such as English suction and Dutch auction, but they do not support the double auctions that are superior to the single auction in terms of speed, efficiency, and the fair distribution of profit. In this paper, we present are design and implement of an agent-based continuous double auction system, called CoDABot, in order to overcome the limitations of current auction systems. CoDABot supports the continuous double auction, provides various bidding agents for users to select, and has been implemented with a multi-agent system to realize more independent, and parallel subsystems.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1139-1147
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• 2000

This paper describes that the size of inactive zone can be directly applied to design multiblade fan/scroll system. From the experimental studies using a five hole pitot tube and smoke test, it is found that the size of inactive zone has linear relations with the mean velocity of impeller inlet and cut-off angle gives a great influences to the fan efficiency. For the practical design, a function related with geometric parameters(i.e. inner radius, cord length, cut-off clearance and cut-off angle) of fan/scroll system is suggested. By using these formulas, the size and distribution of inactive zone can be predicted without the measurements through the full domain, it can be possible to use them to know the efficiency improvement for new model designed.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.233-239
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• 2000

Investigation results are presented fur the shaft end displacements due to the elastic deformation of the casing and support in double suction centrifugal pump. Suction and discharge nozzles of the pump are subject to external piping loads and, in API 610, maximum values of their components are specified. This means that each nozzle can be subject to various combinations of loading conditions. Considering upper and lower criteria of each load, we must perform for the 4,096 load cases, and assign the direction and range of the loads. So, this paper develops an efficient procedure(Compliance Coefficient Method) to calculate the shaft end displacements(＠ coupling) to determine whether satisfying the pump's standard. Also, we analyzed the effects of the casing and support thickness on shaft end displacements.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.10
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• pp.993-1001
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• 2001

Experimental investigation on the performance of dual-evaporator refrigeration system with an ejector has been carried out. In this study, a hydrofluorocarbon (HFC) refrigerant R134a is chosen as a working fluid. The condenser and two-evaporators are made as concentric double pipes with counter-flow type heat exchangers. Experiments were performed by changing the inlet and outlet temperatures of secondary fluids entering condenser, high-pressure evaporator and low-pressure evaporator at test conditions keeping a constant compressor speed. When the external conditions (inlet temperatures of secondary fluid entering condenser and one evaporator) are fixed, results show that coefficient of performance (COP) increases as the inlet temperature of the other evaporator rises. It is also shown that the COP decreases as the mass flaw rate ratio of suction fluid to motive fluid increases. The COP of dual-evaporator refrigeration system with an ejector is superior to that of a single-evaporator vapor compression system by 3 to 6%.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.4
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• pp.201-210
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• 2002

Experimental investigation on the performance of dual-evaporator refrigeration system with an ejector has been carried out. In this study, a hydrofluorocarbon (HFC) refrigerant R134a is chosen as a working fluid. The condenser and two-evaporators are made as concentric double pipes with counter-flow type heat exchangers. Experiments were peformed by changing the inlet and outlet temperatures of secondary fluids entering condenser, high-pressure evaporator and low-pressure evaporator at test conditions keeping a constant compressor speed. When the external conditions (inlet temperatures of secondary fluid entering condenser and one of the evaporators) are fixed, results show that coefficient of performance (COP) increases as the inlet temperature of the other evaporator rises. It is also shown that the COP decreases as the mass flow rate ratio of suction fluid to motive fluid increases. The COP of dual-evapo-rator refrigeration system with an ejector is superior to that of a single-evaporator vapor compression system by 3 to 6%.

• Journal of Energy Engineering
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• v.9 no.2
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• pp.89-94
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• 2000

양흡입 펌프 회전차 내부 유동특성을 수치적으로 고찰하였다. 수치계산은 설계점과 2개의 탈설계점에서 이루어졌으며, Patankar에 의해 제시된 SIMPLE 알고리즘을 이용하였다. 설계점에서는 양 회전차 채널 내부에서 대칭 형상을 갖는 이차유동 특성을 발견하였지만, 탈설계점에서는 비대칭 유동특성을 발견하였다. 수치해석 결과로는 유량감소에 따라 양흡입 펌프 회전차 채널내부의 이차유동 특성이 달라진다는 사실을 고찰하였다. 또한 양흡입 펌프 회전차 단면에는 모퉁이 와류가 존재함을 알 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.1
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• pp.69-76
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• 1989

This paper presents a method of the optimum design for rotating shaft of centrifugal pump. That is, the object is to optimize the system in stability at the operating speed, unbalance response in the vicinity of the rotor critical speed, leakage flow of the seals. The objective function is composed of these three elements and is minimized by changing seal cleareance, diamoters, and lengths. A typical double suction centrifugal pump is analyzed and its objective function is presented. Then the optimum dimensions of seals are obtained, and vibration characteristics at both initial and optimum conditions are investigated.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.643-646
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• 2002

Experimental study was conducted to reveal the flow mechanism under rotating stall in an axial flow fan. For this study unsteady pressure was measured using high frequency pressure transducers mounted on the casing wall of rotor passage and total pressure fields were measured at the rotor upstream and downstream. The measured pressure signal was analyzed by Wavelet Transform and Double Phase Locked Averaging Technique. From the result of unsteady pressure field of the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail. The pressure field was also analyzed in terms of the pressure distribution along pressure side and suction side of blade tip. From the result of total pressure fields at inlet and outlet of the rotor, the useful information on the characteristics of the stall cell in radial direction was provided.

• Horticultural Science & Technology
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• v.19 no.2
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• pp.179-185
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• 2001

Throughout the world, physical and chemical analyses of horticultural substrates are carried out in many different ways at the different laboratories. In Europe, standardization in properties and analytical methods of horticultural substrates has been a topic over the last decades. As a result, the CEN methods as European standard methods for the physical and chemical analyses were introduced and the final draft was reported in 1999 by CEN(Committee for European Standardization). Dry matter and moisture content are analyzed after drying samples at $103^{\circ}C$. Laboratory compacted bulk density is analyzed by determining the weight of sample compacted in the test cylinder with constant volume. Dry bulk density, particle density, total pore space, water volume, air volume and volume shrinkage are determined by saturating, draining and drying the sample using double rings and a sand suction table. pH and EC are analyzed by 1:5(sample:distilled water) extraction method on the basis of volume. Organic matter and ash content are determined after drying and combusting the samples. Now, CEN methods are being regarded almost as European standard methods. Further study needs to be carried out for universal applicability of the CEN methods to all the substrates.

• Geomechanics and Engineering
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• v.23 no.4
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• pp.301-311
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• 2020

In this study, shear strength behavior of fine-grained soils was investigated under unsaturated conditions. The samples in the unsaturated state were subjected to a net normal stress (σ-u_a) of 40 kPa and different matric suctions (u_a-u_w) of 50, 100 and 150 kPa. The matric suction values applied in the triaxial tests were selected according to the bubbling pressures determined from the SWC curves. The study was carried out on prepared re-constituted cylindrical samples by uniaxial consolidation of soil slurries. First, consolidated drained (CD) triaxial compression tests were performed on the saturated samples and the cohesion and angle of internal friction were determined. After that, drained triaxial compression tests under matric suctions were performed on the unsaturated samples. In order to obtain unsaturated test results, cohesion and internal friction angle values of saturated samples were used. The nonlinear surface representing the shear strength surface was approximated consisting of two planes (double planar surface). The reason for the nonlinear behavior of some soils is that the amount of sand content contained in it is relatively high and the bubbling pressure/permanent water content value is relatively low.