• Title/Summary/Keyword: Waveguide below cutoff (WBC)

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Evaluation of Local Loss Coefficients for Different Waveguide-Below-Cutoff (WBC) Arrays of Electromagnetic Pulse (EMP) Shied in Buildings (도파관 배열에 의한 국부저항계수 산정)

  • Pang, Seung Ki;Chae, Young Tae
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.7
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    • pp.366-372
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    • 2017
  • The objective of this study was to characterize Waveguide-Blow-Cutoff (WBC) array for Electromagnetic Pulse (EMP) shield in air duct or water pipe, the typical pathway of pulse in indoor space with critical electronic device. A numerical investigation with three different WBC designs (circular, rectangular, and hexagonal or honeycomb) was conducted to satisfy recommended shielding effectiveness (SE) levels from 80 dB to 140 dB. Pressure drop between upstream and downstream of EMP shields based on WBC arrays was also investigated to understand air flow feature in air duct of HVAC system. Results showed that honeycomb geometry outperformed other shapes in terms of reducing the depth of EMP shield, thus providing better air flow in duct path with lower local loss coefficient in HVAC system under SE requirements.

Design Guideline of Waveguide-Below-Cutoff Array for Electromagnetic Pulse Shielding (EMP 차폐 도파관의 형상 결정 가이드라인 작성)

  • Pang, Seung-Ki;Kim, Jae-Hun;Yook, Jong-Gwan;Kim, Yuna;Kim, Sangin
    • Journal of Energy Engineering
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    • v.25 no.1
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    • pp.86-91
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    • 2016
  • Convenient design guideline for Waveguide-below-cutoff (WBC) array is proposed to obtain the minimum waveguide length for electromagnetic pulse (EMP) shielding. The analysis includes circular, rectangular, and hexagonal WBC, determine the total length of the waveguide. When the unit side of rectangular WBC and the diagonal line of hexagonal WBC are given as 30 mm, the length of hexagonal WBC is 5 mm shorter than rectangular case with shielding effectiveness (SE) 80 dB. The length difference is deepened with SE of 100 dB, which shows approximately 30 mm shorter length for hexagonal case than others. In addition, hexagonal WBC requires much shorter length than circular WBC. In conclusion, hexagonal case is the most effective with respect to flow velocity and pressure loss for equivalent SE.

A Design Optimization on Coupling Joint between Exhaust Chimney of Electricity Generator and Electromagnetic Pulse (EMP) Shield (EMP 차폐를 위한 비상발전기 연도의 최적 형상 결정)

  • Pang, Seung-Ki;Kim, Jae-Hun
    • Journal of Energy Engineering
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    • v.24 no.4
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    • pp.159-165
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    • 2015
  • The article presents a parametric study on geometrical design optimization for coupling the joint between a large exhaust air chimney and electromagnetic pulse (EMP) shield for gas turbine electricity generator. We conducted computational fluid dynamics (CFD) simulations on hydraulic diameters of waveguide below cutoff(WBC) ranges 800mm~1025mm, the connection distance ranges 150~450mm, and exhaust gas flow velocities at 15, 20, and 25m/s. The results show that the diameter of main chimney, connection distance, and exhaust gas velocity had impacts on flow stream at the EMP shield. To provide a fully developed stream line at three different flow velocity cases, the WBC diameter and distance of connection should be larger than 1050mm and longer than 300mm, respectively.

Evaluation of Air Flow Characteristics in accordance with Types of Waveguide-Below-Cutoff (WBC) Arrays and Their Shielding Effectiveness of Electromagnetic Pulse (EMP) (EMP 차폐를 위한 도파관 형상과 SE에 따른 유동 특성 평가)

  • Pang, Seung-Ki;Ahn, Hye-Rin;Yook, Jong-Gwan
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.12 no.3
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    • pp.1-8
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    • 2016
  • In this study, we evaluated the flow characteristics of various types of waveguide-below-cutoff (WBC) arrays and their shielding effectiveness (SE) of electromagnetic pulses (EMP) based on computational fluid dynamics (CFD). Three types of waveguides were selected for analysis: (1) grid type, (2) honeycomb type, and (3) multi-layer types (2-ply, 4-ply, 6-ply, and 8-ply). To analyze the air flow characteristics, the flow velocities in the longitudinal center of the WBC and the differential pressures between the WBC array inlet and outlet were evaluated. Consequently, we derive the following conclusions: (1) despite an increase in the inlet velocity, the pressure drop of the 6-ply multi-layer type did not significantly increase as compared to that of other types of waveguides (waveguide thickness of 0.1 mm, SE of 100 dB); (2) the grid and honeycomb type had the fastest flow rate of 17.5 m/s, which is approximately 2.5 m/s faster than that at the inlet (waveguide thickness of 1 mm, module size of 30 mm); and (3) the average pressure drop of the grid type waveguide is the lowest in the overall model, whereas that of the 8-ply is the highest (waveguide thickness of 1 mm, module size of 30 mm, and SE of 80, 100 dB).

Electromagnetic Pulse (EMP) Shielding Effectiveness of Waveguide-Below-Cutoff (WBC) Arrays Installed in Generator Exhaust Chimney and its Effects on Gas Velocity (도파관 배열이 설치된 비상발전기 연도의 유속 예측 및 EMP 차폐평가)

  • Pang, Seung-Ki;Kim, Jae-Hun;Yook, Jong-Gwan;Kim, Yuna;Kim, Sangin;Kim, Suk-Bong
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.12 no.1
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    • pp.1-6
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    • 2016
  • Characteristics of exhaust from chimney of electricity generator are analyzed based on CFD when Waveguide-Below-Cutoff (WBC) array is installed in order to achieve the certain level of electromagnetic pulse (EMP) shielding. The main purpose is prediction of average and maximum velocity of exhaust. The results reveal that: 1) When the specification of waveguide is given as 80-diameter, 400-length, and the gap of 20 mm, the shielding effectiveness (SE) is 140dB. The average and maximum velocity of exhaust in the chimney with WBC Array can be represented as exponential functions. 2) As the number of WBC increases, the velocity in the chimney dwindles. 3) Under the situation that WBC with 80 mm diameter is located at intervals of 20 mm, the average velocity can be approximated by $25.5344{\times}e^{(-0.0098{\times}N_{WBC})}$ with input velocity of 15 m/s. In addition, the determination coefficient is 0.915, which is sufficiently high.

Analysis on Shielding Effectiveness of Electromagnetic Wave in Fire Pipes (물이 채워진 소화 배관의 전파 차폐도 해석)

  • Kim, Yoon-Jeung
    • Fire Science and Engineering
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    • v.30 no.4
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    • pp.94-102
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    • 2016
  • When establishing shielding facilities for EMP protection, WBC effect is used to protect fire pipes and honeycomb cells are inserted into the fire pipes to improve the shielding effectiveness. At this point, the smaller unit cell of honeycombs becomes, the more likely it interrupts the flow of water, which ends up clogging the fire pipes with sediment. To prevent this phenomenon, I would suggest a design method due to the pilarization loss of water molecules that contributes to increasing the size of honeycomb cells and remaining thin-walled sufficient for required shielding effectiveness.

Evaluation of Flow Characteristics in Water Supply Pipes Shielding Electromagnetic Pulse of 100 dB with Concentric and Eccentric Reducers (Concentric Reducer와 Eccentric Reducer를 사용한 EMP 차폐 100dB급 급수관의 유동특성 평가)

  • Pang, Seung-Ki;Ahn, Hye-Rin
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.13 no.1
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    • pp.1-6
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    • 2017
  • In this paper, the flow characteristics of water in the water supply pipes of a WBC array were evaluated. We simulated the flow velocities and pressures for a standard pipe, an expansion pipe with a concentric reducer, and an expansion pipe with an eccentric reducer using computational fluid dynamics. In the case of the standard pipe, when the inlet flow velocities were 0.5 m/s and 2.0 m/s, the maximum flow velocities at the center of the WBC array were 0.54 m/s and 2.74 m/s, respectively, which were the greatest values among those of all the pipe models considered. In the case of the expansion pipe, the maximum flow velocities at the center of the WBC array were almost the same under the same conditions regardless of the type of reducer. The pressure losses in the pipe due to the concentric and eccentric reducers were found to be (165.09 ${\times}$ inlet $velocity^{1.6677}$) and (210.98 ${\times}$ inlet $velocity^{1.6478}$), respectively. The coefficient of determination at this time was greater than 0.99 and was the same for both the models. As a simulation result, it was found that in order to reduce the pressure loss when pipe with WBC array is connected with a conventional pipe, diameter of the pipe with WBC array at that section should be enlarged by one step, and then connected to the conventional pipe with a concentric reducer.

Design Optimization for Air Ducts and Fluid Pipes at Electromagnetic Pulse(EMP) Shield in Highly Secured Facilities (EMP 방호시설의 덕트 및 배관 최적 설계 방안)

  • Pang, Seung-Ki;Kim, Jae-Hoon
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.10 no.4
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    • pp.15-24
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    • 2014
  • This study conducted a computational fluid dynamics(CFD) analysis to find an appropriate diameter or sectional area of air ducts and fluid pipes which have an electromagnetic pulse(EMP) shied to protect indoor electronic devices in special buildings like military fortifications. The result shows that the optimized outdoor air intake size can be defined with either the ratio of the maximum air velocity in the supply duct to the air intake size, or the shape ratio of indoor supply diffuser to the outdoor air intake. In the case of water channel, the fluid velocity at EMP shield with the identical size of the pipe, decreases by 25% in average due to the resistance of the shield. The enlargement of diameter at the shield, 2 step, improves the fluid flow. It illustrated that the diameter of downstream pipe size is 1step larger than the upstream for providing the design flow rate. The shield increases friction and resistance, in the case of oil pipe, so the average flow velocity at the middle of the shield increase by 50% in average. In consideration of the fluid viscosity, the oil pipe should be enlarged 4 or 5 step from the typical design configuration. Therefore, the fluid channel size for air, water, and oil, should be reconsidered by the engineering approach when EMP shield is placed in the middle of channel.