• International Journal of High-Rise Buildings
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• 제8권4호
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• pp.283-290
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• 2019

Corner cut, corner chamfered or a building shape change are adopted in the design of tall buildings to achieve aerodynamic superiority as well as response reduction. Kikuchi et.al pointed out that large negative peak external pressures can appear near the inside corner of set-back low rise buildings. It is therefore necessary to pay attention to facade design around steps in building surfaces. Peak wind pressures for corner cut or corner chamfered configurations are given in the AIJ code. However, they cannot be applied where there are many variations of vertical and horizontal steps. There has been no previous systematic research on peak wind pressures around steps in building surfaces. In this study, detailed phenomenon of peak wind pressures around steps in buildings are investigated focusing on vertical and horizontal distances from the building's corner.

• Journal of the Korean Society of Industry Convergence
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• 제24권1호
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• pp.45-51
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• 2021

The purpose of this study is to suggest the optimal shape for a local air ventilation system for fume removal, which is operated in a zinc galvanizing factory, and to propose the improvement plan for a ventilation system used in a zinc galvanizing factory through flow analysis. A part of the air sprayed by an air curtain goes out. It will be necessary to research the position of an air curtain, its spray angles, and its nozzle shape. In addition, additional research needs to be conducted on the shape of the fan installed before a hood in order to make it easy to induce fume. In a local air ventilation system, air is inhaled from the outside. The higher an inlet negative pressure is, the easier fume is removed. It was found that it was necessary to install an appropriate hole in the wall on the back of a push nozzle in order to reduce an inlet negative pressure.

• The Journal of Korea Robotics Society
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• 제18권4호
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• pp.456-462
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• 2023

In recent years, the use of robot arms has increased rapidly in both industrial and service applications. Unlike production sites, where only one type of gripper is used for productivity, service sites often use a tool changer to replace fingered grippers or vacuum grippers to cover various objects to be grasped. To this end, a tool changer-based pneumatic grasping system was developed in this study. In order to simultaneously use a positive pressure-based pneumatic gripper and a negative pressure-based vacuum gripper, a small vane pump capable of generating positive and negative pressures depending on the direction of rotation was developed. Experiments with actual prototypes have shown that the pneumatic system based on the developed vane pump can effectively realize both pneumatic grippers and vacuum grippers.

• The Korean Journal of Physiology
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• 제27권1호
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• pp.37-49
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• 1993

Ventilatory responses to inhaled $CO_2$ were measured during continuous negative pressure breathing (CNPB) in awake dogs. End expiratory lung volume (EELV) decreased linearly with pressure level during CNPB (correlation coefficient= 0.81, p<0.005) during air breathing. When CNPB was applied during 5% $CO_2$ inhalation, the decrease in EELV was not significantly different (p<0.5) from that during air breathing. As a result of a lowered EELV, tidal volume ($V_T$) significantly decreased by 22% and breathing frequency ($f_B$) increased by 68% in the steady state during air breathing (p<0.0001). These responses were similar during 5% $CO_2$ inhalation, thus the $CO_2$ response curve measured during CNPB shifted upward without a change in sensitivity (p>0.05). These results indicate additive effects of CNPB and $CO_2$ inhalation. The degree of hyperventilation during CNPB at eupnea was estimated to be 63% of that during control ventilation and was significantly greater than zero (p<0.0001), which suggests an alveolar hyperventilation due to CNPB. These results suggest that the mechanical alterations associated with n decrease in lung volume could play an important role in ventilatory control independently of chemical regulation of breathing. Thus, exercise hyperpnea, which is associated with a lowered functional residual capacity (FRC), may in part be explained by this mechanical stimulation of breathing.

• Journal of Ocean Engineering and Technology
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• 제20권5호
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• pp.49-56
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• 2006

In this thesis, centrifuge model experiments and numerical analyses were carried out to investigate the behavior of an excavated slope in soft clay ground. Centrifuge model tests were performed with various slopes for the excavated ground, such as 1:1.5 and 1:2. Pore pressuresthe model ground were measured to find their effects on the stability of the excavated slope. These experiments showed that the model with 1:2.5 maintained its stability within a short period of time and failed gradually. Therefore, anexcavated slope of soft soil with this slope might maintain stable conditions within a certain time. The mode1 with a 1:3 slope was observed to maintain a very stable condition, showing insignificant deformation in the ground after being excavated. Numerical analyses with PLAXIS, a commerciallyavailable software implemented with the finite element numerical technique, were performed to find the pore pressure distribution within the ground mass and the deformation of the soil. From the results of numerical analysis, a negative pore pressure was developed after the excavation and thus the stability of the slope was maintained. The safety factor for slope failure was found to decrease with time because of the dissipation of negative pore pressure with time.

• The Transactions of the Korean Institute of Electrical Engineers P
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• 제58권4호
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• pp.516-520
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• 2009

Atmosphere Plasmas of Gas Discharge (APGD) have been used in plasma sources for material processing such as etching, deposition, surface modification, etc. This study is to investigate and understand the fundamental plasma discharge properties. Especially, $SF_6/N_2$ mixed gas would be used in power transformer, GIS (Gas insulated switchgear) and so on. In this paper, we developed a one dimensional fluid simulation model with capacitively coupled plasma chamber at the atmosphere pressure (760 [Torr]). 38 kinds of $SF_6/N_2$ plasma particles which are an electron, two positive ions (${SF_5}^+$, ${N_2}^+$), five negative ions (${SF_6}^-$, ${SF_5}^-$, ${SF_4}^-$, ${F_2}^-$, ${F_1}^-$), thirty excitation and vibrational particles for $N_2$ were considered in this computation. The $N_2$ gases of 20%, 50%, 80% were mixed in $SF_6$ gas. As the amount of $N_2$ gas was increased, the properties of electro-negative plasma moved toward the electro-positive plasma.

• Proceedings of the KSME Conference
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.465-471
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제13권1호
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• pp.85-93
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• 2000

In this paper, the predischarge propagation processes of SF\ulcorner gas stressed by impulse voltages under nonuniform electric field perturbed by a needle protrusion are described. The statistical and formative time-lags and the time interval between leader pulses were investigated on the basis of the predischarge current measured in the gas pressure range of 0.1~0.5 MPa. The predischarge current is closely related to the waveform, amplitude and polarity of applied votages, the gas pressure and the gap geometry. Both the positive and negative predischarge processes in nonuniform electric field develop in a regime of stepwise leader propagation leading to electrical breakdown. The mean of the time interval between leader pulses gives about a factor of 10 higher for the negative than for the positive leader current puls-es. According as the gas pressure increases, the statistical time-lag was almost unchangeable, but the formative time-lag was gradually decreased.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.431-438
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• 2009

A Large Eddy Simulation (LES) of the flow in an inducer is carried out under flow rate oscillations. The present study focuses on the dynamic response of the backflow and the unsteady pressure performance to the flow rate fluctuations under non-cavitation conditions. The amplitude of angular momentum fluctuation evaluated by LES is larger than that evaluated by RANS. However, the phase delay of backflow is nearly the same as RANS calculation. The pressure performance curve exhibits a closed curve caused by the inertia effect associated with the flow rate fluctuations. Compared with simplified one dimensional evaluation of the inertia component, the component obtained by LES is smaller. The negative slope of averaged performance curve becomes larger under unsteady conditions. From the conservations of angular momentum and energy, an expression useful for the evaluation of unsteady pressure rise was obtained. The examination of each term of this expression show that the apparent decrease of inertia effects is caused by the response delay of Euler's head and that the increase of negative slope is caused by the delay of inertial term associated with the delay of backflow response. These results are qualitatively confirmed by experiments.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제24권7호
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• pp.976-983
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angle of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder due to the presence of a ground plate nearby.