• Journal of the Society of Naval Architects of Korea
• /
• v.53 no.3
• /
• pp.201-209
• /
• 2016

Supercavitation is a technology that reduces frictional resistance of an underwater vehicle by surrounding it with bubbles. Supercavity is divided into natural supercavity and ventilated supercavity which is formed by artificially supplying gas. Planing forces are present when a section of the underwater vehicle goes outside of the cavitation region in the supercavity condition. Planing often leads to an unstable flight because it acts vertically on the body suddenly. In this paper, a relationship between the ventilation rate and the cavitation number is determined. Based on the relationship, desired cavitation number which can avoid to planing is determined and then ventilation controller is designed. The performance of the ventilation controller is verified with a depth change controller using the cavitator. Simulation results show that the ventilation controller can minimize the planing force and moment.

• Agricultural and Biosystems Engineering
• /
• v.1 no.2
• /
• pp.73-80
• /
• 2000

Aerodynamics in a naturally ventilated multi-span greenhouse with plants was analyzed numerically by the computational fluid dynamics (CFD) simulation. To investigate the potential application of CFD techniques to greenhouse design and analysis, the numerical results of the CFD model were compared with the results of a steady-state mass and energy balance numerical model. Assuming the results of the mass and energy balance model as the standard, reasonably good agreement was obtained between the natural ventilation rates computed by the CFD numerical model and the mass and energy balance model. The steady-state CFD model during a sunny day showed negative errors as high as 15% in the morning and comparable positive errors in the afternoon. Such errors assumed to be due to heat storage in the floor, benches, and greenhouse structure. For a west wind of 2.5 m s$^{-1}$ , the internal nonporous shading screens that opened to the east were predicted to have a 15.6% better air exchange rate than opened to the west. It was generally predicted that the presence of nonporous internal shading screens significantly reduced natural ventilation if the horizontal opening of the screen for each span was smaller that the effective roof vent opening.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.67-70
• /
• 2008

As a part of the project on road tunnel fire safety system development, Quantitative Risk Assessment program was developed. In this study, We carried out Quantitative Risk Assessment with this program by using a factor of cross passage interval, warning announcement time and congestion ratio etc for 1km tunnel with natural ventilation. In the case of 250m below of cross passage interval, Risk value due to warning announcement time was a slightly changed. but if cross passage interval is more than 250m, expected fatalities in the same HRR(heat release rate) was sharp increased. As a result, Quantitative Risk Assessment program which was developed in this research project is possible to risk assessment with ventilation type, cross passage for evacuation and detection system response property etc. hereafter, this program look forward to use as a tool for road tunnel performance based design.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.3
• /
• pp.247-253
• /
• 2002

In this study, reduced-scale experiments were conducted to analyze smoke movement in tunnel fire with roof vent. The 1/20 scale experiments were carried out under the Froude scaling using gasoline pool fire ranging from 7.3 to 15.4 cm in diameter with total heat release rate from 1.0 to 8.46kw. In case of 1 m high vent, smoke front reached to the tunnel exit at about 16 sec delayed with ventilation. The delay time grew longer with the vent height. The temperature after the vent was lower than that without the vent. The exit temperature declined maximum of $20^{\circ}C$ after passing the vent. It was confirmed that the thickness of smoke layer was maintained uniformly under the 25% height of the tunnel through the visualized smoke now by a laser sheet and the digital camcorder.

• Journal of Environmental Impact Assessment
• /
• v.31 no.5
• /
• pp.334-342
• /
• 2022

The stringent air environment conservation act forced to build an indoor dome for coal storage. However, it causes some problems due to accumulation of fly ash and harmful substances inside. To solve this problem, this study analyzed the pattern of internal airflow and the amount of ventilation for an indoor coal yard. Overall, the airflow inside the indoor coal yard tended to move to the southwest facing the mountain. In addition, sea-breeze was blowing from the northern louver window facing the sea, where airflow was flowing in. The total flow rate flowing into the indoor coal yard was 918,691 m³/h, and the number of natural ventilation per hour was 0.6 times. Therefore, it is proposed to install a forced ventilation device at the location where internal air flow is concentrated.

• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.121-126
• /
• 2001

In this study, reduced-scale experiments were conducted to understand smoke movements in tunnel fires with the natural ventilation. The 1/20 scale experiments were conducted under the Froude scaling since the smoke movement in tunnels is governed by buoyancy force. Six cases of experiments(pool diameter is 6.5cm, 7.3cm, 8.3cm, 10cm, l2.5cm and l5.4cm), in which vertical vents positioned 1m from the fire source symmetrically, were conducted in order to evaluate the effect of the vent on smoke movement. In case of heat release rate under 2MW, smoke front reached to the tunnel exit about 20 see delayed with ventilation and the smoke velocity was proportional to the power of the heat release rate. Temperature after the vent was lower than without vent. In case of l5.4cm pool, the temperature difference was about $50^{\circ}C$. It was confirmed that the thickness of smoke layer was maintained uniformly under the 35% height of tunnel through the visualized smoke flow by a laser sheet and the digital camcoder.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.29 no.2
• /
• pp.74-81
• /
• 2017

In this study, the combined-type diffuser developed by the Authors, in a previous study, was applied to a residential space. The performance of a ventilation and thermal environment, created by the use of a combined-type diffuser was compared to the pan-type diffuser widely used in apartment houses. In cooling conditions, because of the relatively high air flow rate of ceiling cassette-type air conditioners, the characteristics of airflow distribution in a room were governed by the air conditioner's airflow. In heating conditions, because of the low air flow rate of the diffuser, the characteristics of airflow distribution were governed by the buoyancy effect created by cold external walls and a hot floor. In terms of the Air Diffusion Performance Index (ADPI), which is a thermal environmental index, the result of a combined-type diffuser was greater than a pan-type diffuser in both of cooling and heating conditions. Consequently, the combined-type diffuser showed equal or superior ventilation and thermal environment performance compared to a pan-type diffuser.

• Tunnel and Underground Space
• /
• v.27 no.1
• /
• pp.1-11
• /
• 2017

Most of the local limestone mines are developed as large-opening underground mines, while mine ventilation is heavily dependent on the natural ventilation and auxiliary systems, rather than the mechanical ventilation system using main fans. The current auxiliary ventilation system with fan and ducting requires optimization since enhanced deployment of diesel equipment demands higher airflow rate and the associated cost is expected to be too excessive for the local mine operators. This paper aims at optimizing the fan capacity for the working site ventilation through comparing the fan pressure in the mine airway and the ventilation efficiency of an axial-flow fan and a propeller fan developed in this study.

• Journal of Bio-Environment Control
• /
• v.23 no.3
• /
• pp.181-191
• /
• 2014

Modern commercial greenhouse requires the use of advanced climate control system to improve crop production and to reduce energy consumption. As an alternative to classical sensor-based control method, this paper introduces a model-based control method that consists of two models: the predictive model and the evaluation model. As a first step, this paper presents straightforward models to predict the effect of natural ventilation in a greenhouse according to meteorological factors, such as outdoor air temperature, soil temperature, solar radiation and mean wind speed, and structural factor, opening rate of roof ventilators. A multiple regression analysis was conducted to develop the predictive models on the basis of data obtained by computational fluid dynamics (CFD) simulations. The output of the models are air temperature drops due to ventilation at 9 sub-volumes in the greenhouse and individual volumetric ventilation rate through 6 roof ventilators, and showed a good agreement with the CFD-computed results. The resulting predictive models have an advantage of ensuring quick and reasonable predictions and thereby can be used as a part of a real-time model-based control system for a naturally ventilated greenhouse to predict the implications of alternative control operation.

• Journal of Microbiology and Biotechnology
• /
• v.17 no.10
• /
• pp.1622-1628
• /
• 2007

We characterized the efficacy of an electrostatic precipitator (ESP) air-cleaner in reducing the concentration of Serratia marcescens in an enclosed space. We used an experimental room ($4.5{\times}3{\times}2.9\;m$) in which electrostatic air-cleaners were located. Two air-cleaners enhanced the equivalent ventilation rates in the chamber by about 3.3 air changes per hour (ACH) over the 2 ACH provided by the mechanical ventilation system. Natural die-off of the organisms provided an additional equivalent of 3 ACH, so that the total ventilation rate with the ESP air-ccleaners was 8.3 ACH. We also examined whether the ESP air-cleaners altered the deposition of Serratia marcescens aerosols on the experimental room surfaces. We did not find any significant differences in the number of colony forming units recovered from surfaces with and without the air-cleaners. We installed UV lights inside the ESPs and determined if UV light, in addition to electrical fields, increased the efficacy of the ESPs. The presence of UV light inside the ESP reduced S. marcescens aerosols by approximately 2 ACH. Finally, a box model indicates that the efficiency of the air-cleaner increases for both biological and nonbiological particles at ventilation rates of 0.2-1, which are typical for residential settings.