• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.244-249
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• 1997

The enclosure with a small opened area is extensively used in power plants to reduce the propagating noise from transformers. The radiation impedance associated with the location and width of the opened area, and the geometric configurations of internal acoustic field is very important to determine the basic acoustic characteristics of this partial enclosure. In this study, two-dimensional rectangular chambers with opened areas are investigated to examine the acoustic properties of the enclosure. The mode expansions of the physical variables defined on boundary surfaces are introduced to derive a simple algebraic equation. The acoustic characteristics can be easily predicted by this analytical approach, and the results well agree with physical grounds. Physical concepts as results of this work will be helpful to use the partial enclosure as a noise control element.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1288-1300
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• 1994

Mathematical modeling and numerical calculation on the flow and thermal characteristics induced by fire in a partial enclosure are performed. The solution procedures include the Shvab-Zeldovich approximation for the physical transport equations, low Reynolds number k-.epsilon. model for the turbulent fluid flow and Discrete Ordinate method(DOM) to calculate the radiative heat transfer. PMMA(Polymethylmethacrylate) is adopted as a solid fuel. Two different cases are considered : combustions with and without gas radiation occuring in a open cavity for variable pyrolyzing location of PMMA. When the fire source is located at the left-wall, the flow region of flame gas is limited at the left-wall and ceiling and recirculation region of inlet gas is formulated at neat the floor. In case of neglecting the radiative heat transfer, more large flame size and higher temperature is predicted. It is essential to consider the radiative heat transfer for analysis of fire phenomenon.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.87-88
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• 2007

An acoustic total or partial enclosure is widely used to reduce the sound pressure level propagating from a noise source. However, the performance of the acoustic enclosure is decreased by its inherent limitations such as temperature rise or acoustic pressure build-up inside the enclosed acoustic field. In this reason, an acoustic enclosure consisting of a silencer and absobent panels with acoustic resonators is studied to reduce the transmitted noise from a transformer. Large sound-attenuation is expected by applying the enclosure to the large transformers in a substation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.786-789
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• 2005

An acoustic total or partial enclosure is widely used to reduce the sound pressure level propagating from a noise source. However, the performance of the acoustic enclosure is decreased by its inherent limitations such as temperature rise or acoustic pressure build up inside the enclosed acoustic field. In general, a silencer is installed to overcome these limitations, for large amount of air can be exchanged through the silencers. In this reason, a parallel baffle type duct silencer with acoustic resonators is studied to reduce the transmitted noise from a transformer. In this silencer, the high frequency components of the transmitted noise over 360Hz are effectively absorbed by the parallel baffles and the other ones, 120 and 240 Hz, are reduced due to the presence of Helmholtz resonators. Large sound attenuation is achieved by applying the sound resonating barrier to the large transformers in a substation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.528-537
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• 1995

Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.287-297
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• 1995

In this study, the geometry consists of a two-dimensional rectangular enclosure with localized heating from below. The size and the location of the heater on the floor has been varied, and one of the vertical walls remains at a low temperature simulating a cold window. The governing equations for momentum, energy and continuity, which are coupled with turbulent equations have been solved using a finite volume method. A low Reynolds number $k-{\varepsilon}$ model has been incorporated to solve the turbulent kinetic energy and the dissipation rate. The heat transfer characteristics and the thermal environmental characteristics of the room have been obtained for various system parameters in a room with a partially heated floor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2999-3007
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• 1994

The unsteady numerical simulations have been presented for the laminar natural convection in a partially open compartment. Computations were performed within the domain of the compartment in order to show the thermal radiation and the partially opening effects on the flow fields and heat transfer characteristics. The results were shown for different Planck numbers(0.05~5) and opening ratios(0.25~0.75) being fixed with Ra=$10^5$ and Pr=0.71. Considering the flow which is buoyancy driven from the heated wall, and the buoyancy is not much affected by the further outside region from the opening, the numerical computations have been performed without an outer region by the particular boundary treatments on the flow velocity and temperature at the different partial openings. The confined numerical domain reduced the CPU time and the memory of computer. P-1 approximation of radiative transfer equation was employed with Marshak type boundary conditions along with the pseudo-black body approximation at the partial openings. The numerical results clearly show that the natural convective flow and heat transfer are much affected by increase of thermal radiation particularly from the initial state. When thermal radiation is not much affecting the flow ($PL{\le}1$), it was found that thermal radiation effects are almost negligible.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1659-1661
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• 2003

Recently, diagnostic techniques have been investigated to defect a partial discharge in high voltage electrical equipment. We have studied the characteristics of the acoustic partial discharge originating from the electrical defects in cubicle GIS(C-GIS). An acoustic emission(AE) sensor is used on the enclosure to detect partial discharge source because the sensor is sensitive to stress waves in its frequency range that may not be from a partial discharge source. AE signal is analyzed with phase-magnitude-frequency number(${\Phi}$-V-n) and pulse per second(PPS). Experience result has shown that the omitted acoustic signal has phase dependency and phase shift characteristic according to increase with applied voltage. These result will be helpful to the pattern recognition of the acoustic partial discharge in a C-GIS.

• Journal of information and communication convergence engineering
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• v.21 no.3
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• pp.233-238
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• 2023

This study presents a method for identifying partial discharge defects in an eco-friendly gas insulated system using a backpropagation algorithm. Four partial discharge (PD) electrode systems, namely, a free-moving particle, protrusion on the conductor, protrusion on the enclosure, and voids, were designed to simulate PD defects that can occur during the operation of eco-friendly gas-insulated switchgear. The PD signals were measured using an ultrahigh-frequency sensor as a nonconventional method based on IEC 62478. To identify the types of PD defects, the PD parameters of single PD pulses in the time and frequency domains and the phase-resolved partial discharge patterns were extracted, and a back-propagation algorithm in the artificial neural network was designed using a virtual instrument based on LabVIEW. The backpropagation algorithm proposed in this paper has an accuracy rate of over 90% for identifying the types of PD defects, and the result is expected to be used as a reference database for asset management and maintenance work for eco-friendly gas-insulated power equipment.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.77-93
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• 1997

The natural convection and combined heat transfer induced by fire in a rectangular enclosure is numerically studied. The model for this numerical analysis is partially opened, it is divided by a vertical baffle projecting from ceiling. The solution procedure Includes the standard k- $\varepsilon$ model for turbulent flow and the discrete ordinates method (DOM ) is used for the calculation of radiative heat transfer equation. In this study, numerical simulation on the combined naturnal convection and radiation is carried out in a partial enclosure filled with absorbed-emitted gray media, but is not considered scattering problem. The velocity vectors, streamlines, and isothermal lines are compared the results of pure convection with those of the combined convection-radiation, the combined heat transfer. Comparing the results of pure convection with those of the combined convection-radiation, the combined heat transfer analysis shows the stronger circulation than those of the pure convection. Three different locations of heat source are considered to observe the effect of heat source location on the heat transfer phenomena. As the results, the circulation and the heat transfer In the left region from heating block are much more influenced than those in the right region. It is also founded that the radiation effect cannot be neglected in analyzing the building in fire.