• 한국공간구조학회논문집
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• 제20권1호
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• pp.69-77
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• 2020

In this paper, the mean and fluctuating pressure coefficients derived from the results of wind tunnel tests on closed and open dome roofs were analyzed. The distribution characteristics of the fluctuating pressure according to the opening ratio and the height change were discussed. The analysis results showed that when the roof is open, the overall wind pressure decreases due to the open space, but more fluctuation occurred than the closed dome roof.

• 산업기술연구
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• 제20권A호
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• pp.185-194
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• 2000

In this work we measured the total pressure of the aqueous solutions and the methanol-water solutions dissolved with inorganic salts, at $25^{\circ}C$. In organic electrolytes used in this work were $K_2SO_4$ and $(NH_4)_2SO_4$. Using the measured vapour pressures the activity coefficient of solvents and the mean ionic activity coefficient were obtained through thermodynamic relations. The activity coefficients of solvent and the mean ionic activity coefficirnt obtained in this work were fitted with Macedo's model and Acard's model. Both two models were good agreeable to the vapor pressure and the mean ionic activity coefficient for the electroyte aqueous solutions. For electrolyte /methanol/water solutions, Macedo's model had much deviation from experimental data, while Acard's model showed a good agreement with experimental data.

• Journal of Mechanical Science and Technology
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• 제15권1호
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• pp.81-87
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• 2001

Cyclic variability limits the range of operating conditions of spark ignition engines, especially under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by pressure parameters, combustion related parameters, and flame-front related parameters. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle.

• Wind and Structures
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• 제30권2호
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• pp.199-210
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• 2020

Building wind pressure coefficient transiting test is a new method to test the building wind pressure coefficient by using the wind generated by a moving vehicle, which is susceptible to natural wind and other factors. In this paper, the Commonwealth Advisory Aeronautical Research Council standard model with a scale ratio of 1:300 is used as the test object, and the wind pressure coefficient transiting test is repeated under different natural wind conditions to study the influence of natural wind. Natural wind is measured by an ultrasonic anemometer at a fixed location. All building wind pressure coefficient transiting tests meet the test conditions, and the vehicle's driving speed is 72 km/h. The mean wind pressure coefficient, the fluctuating wind pressure coefficient, and the correlation coefficient of wind pressure are used to describe the influence of natural wind on the building wind pressure coefficient transiting test qualitatively and quantitatively. Some rules, which can also help subsequent transiting tests, are also summarized.

• 대한기계학회논문집B
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• 제24권5호
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• pp.709-717
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• 2000

Cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by the pressure parameters, combustion parameters, and flame front parameters. The coefficient of variation in indicated mean effective pressure ($COV_{IMEP}$) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle driveability problems usually result when $COV_{IMEP}$ exceeds about 10%. For analysis of the cyclic variability in SI engines at idling, the results show that cyclic variability by the $COV_{IMEP}$ or the coefficient of variation in maximum pressure can be explained and may be consequently reduced by the help of the optimum spark timings.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.59-66
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• 2001

This experimental study is to investigate the flow characteristics of the multi-hole nozzle used in the fuel injection system of a heavy-duty diesel engine. A multi-hole diesel nozzle with a 2-spring nozzle holder was used in this study and without changing the total orifice exit area, its hole number varied from 3($d_n$=0.42mm) to 8($d_n$=0.25mm). The injection pressure and needle lift were measured and Bosch type injection rates measurement system was used. The discharge flowrates of each orifice in the multi-hole nozzle changed by the flow conditions inside the nozzle sac hole. In case that pump speed and injection quantity were low, the orifice located in the vertex of nozzle tip had a great deal of injection quantity compared with that of others. As the increment of multi-hole number, the injection duration and the mean injection pressure decrease. The mean and peak injection rates, however, increase. Actually, the mean flow coefficient(${C_d}_{(mean)}$) increases, too. The flow coefficient of the multi 8 hole was evaluated as Cd(mean)=0.74 and that is the maximum value among the examined conditions.

• Wind and Structures
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• 제37권6호
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• pp.425-444
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• 2023

This study is to investigate the effect of interference between two C-shaped high-rise buildings by computational fluid dynamics (CFD), focusing on the variation of the local pressure coefficient (C_P) and the mean pressure coefficient (C_PMEAN). Sixteen building position cases are considered for the present study. These cases were based on the position and height of the interference building (IB). The pressure coefficient (C_P) is calculated on the principal building (PB) and is compared with an isolated building identical in shape and size. The interference effect on PB has also been presented in reference for the interference factor (IF). According to the findings, the maximum force coefficient on the PB is 0.971 and it is 10.97% more than the isolated PB when IB is located at position 2b (two times the width of the building), and the interfering height of 13H/15 mm. The moment coefficient on PB is 1.27, which is 27.36% less than the isolated case in which IB pushed 2b to 3b in the y direction with 750 mm height. In most of the cases, because of the shielding effect of the IB, the value of force coefficient (C_F) on PB has been reduced. On the face of the PB, there are also considerable differences in the mean pressure coefficient C_PMEAN. When IB was positioned at a location of 2b in Y direction and an interfering height of 13H/15 mm, the maximum C_PMEAN (1.58) was observed on the leeward face of PB.

• 한국분무공학회지
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• 제2권1호
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• pp.46-51
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• 1997

In this study, spray characteristics of the pressure swirl atomizer have teen investigated. Four atomizers with the different orifice diameter and five tangential ports with the different inlet number were fabricated. For the purpose of the measurement of the mean drop sine, Malvern particle sizer was used. And also discharge coefficient was measured and spray cone angle was measured by using shadow graphy method. As a result when the injection pressure was increased, mean drop size was decreased. And the dominant factor which influence on the spray characteristics of pressure swirl atomizer was orifice diameter.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1151-1158
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• 2000

Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper was to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. To analyse the cyclic variation in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. The burn rate analysis program was used here and the burn parameters were used to determine the variations in the input parameter-i. e., fuel, air, and residual mass. In this study, we investigated the relationship of indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, burn angles, and lowest normalized value (LNV) in a spark ignition engine in a view of cyclic variations.

• Wind and Structures
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• 제26권2호
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• pp.99-114
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• 2018

Due to shortage of land and architectural aesthetics, sometimes the buildings are constructed as unconventional in plan. The wind force acts differently according to the plan shape of the building. So, it is of utter importance to study wind force or, more specifically wind pressure on an unconventional plan shaped tall building. To address this issue, this paper demonstrates a comprehensive study on mean pressure coefficient of 'E' plan shaped tall building. This study has been carried out experimentally and numerically by wind tunnel test and computational fluid dynamics (CFD) simulation respectively. Mean wind pressures on all the faces of the building are predicted using wind tunnel test and CFD simulation varying wind incidence angles from $0^{\circ}$ to $180^{\circ}$ at an interval of $30^{\circ}$. The accuracy of the numerically predicted results are measured by comparing results predicted by CFD with experimental results and it seems to have a good agreement with wind tunnel results. Besides wind pressures, wind flow patterns are also obtained by CFD for all the wind incidence angles. These flow patterns predict the behavior of pressure variation on the different faces of the building. For better comparison of the results, pressure contours on all the faces are also predicted by both the methods. Finally, polynomial expressions as the sine and cosine function of wind angle are proposed for obtaining mean wind pressure coefficient on all the faces using Fourier series expansion. The accuracy of the fitted expansions are measured by sum square error, $R^2$ value and root mean square error.