• Title/Summary/Keyword: Numerical Loss

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COUPLING LOSS ANALYSIS OF SUPERCONDUCTING WIRE (다심 초전도 선재의 결합손실 해석)

  • Lee, J.K.;Hahn, S.Y.
    • Proceedings of the KIEE Conference
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    • 1991.11a
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    • pp.119-121
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    • 1991
  • Multifilamentary superconducting wires exposed to an alternating field generate the coupling loss and hysteresis loss. The geometric shapes of multifilamentary superconducting wire are very complicate, and loss generating mechanism is too. In this paper, coupling loss of superconducting wire in case of twelve filament is calculated by two dimensional numerical analysis, and compared with value of conventional formulus. The basic idea of this calculating method is potential difference of external transverse field.

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A Study on Numerical Analysis of the AC Loss in a Single-layer Superconducting Cable Sample (단층 초전도케이블 샘플에서 교류손실의 수치해석에 대한 연구)

  • Li, Zhu-Yong;Ma, Yong-Hu;Ryu, Kyung-Woo;Hwang, Si-Dole
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.22 no.7
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    • pp.606-611
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    • 2009
  • AC loss is one of the important factors for commercialization of a high temperature superconducting (HTS) cable from an economic point of view. But AC loss characteristics of the HTS-cable are not elucidated completely because of its complex structure. As an earlier stage of analyzing the AC loss in the 22.9 kV/50 MVA, 100m HTS-cable system of Korea Electric Power Corporation (KEPCO) which is now in collaboration with us, a two-dimensional (2D) numerical model, which takes into account the nonlinear conductivity properties of a high temperature superconductor, has been developed. In order to examine our 2D model, we have prepared several single-layer cable samples whose AC losses are sufficiently reliable due to their simple structure. The AC losses of the samples were experimentally investigated and then compared with our 2D model. The results show that the numerically calculated AC losses are not in good agreement with the measured ones for the cylindrical cable and deca-cable samples with low critical current density. However, the numerically calculated and measured AC losses are relatively in good agreement for the deca-cable and hex-cable samples with high critical current density, although the difference between these two loss data in the deca-cable sample tends to increase in the low current region.

Study on Numerical Model of Leakage Flow at Gap between Compartments in a Building (건축물 구획실간 틈새에서의 누설유동에 대한 수치모델 연구)

  • Kim, Jung-Yup;Kim, Ji-Seok
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.25 no.10
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    • pp.562-567
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    • 2013
  • 1D-numerical analysis of the network algorithm with the orifice equation for the relationship between pressure difference and flowrate has been mostly used to analyse leakage flow at the gap. In this study, a 3D-numerical method applying momentum loss model to the gap region in the computational domain is represented to reflect effectively the effect of leakage flow by determining the proportion of pressure difference to air passage velocity. While the 3D-numerical method is verified through the computation of the two compartments model, the numerical analysis of the stack effect in a building stairway is performed. As the temperature of air outside drops, the pressure in the upper stairway and leakage flowrate through the gap in the door rise. The change of gap area does not have an effect on pressure in the stairway for the analysis conditions.

Numerical analysis of tunnelling-induced ground movements (터널굴착으로 발생한 지반거동에 대한 수치해석적 분석)

  • Son, Moo-Rak;Yun, Jong-Cheol
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.11 no.3
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    • pp.229-242
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    • 2009
  • Numerical analysis has been performed to estimate maximum settlement, maximum horizontal displacement and total settlement volume at the ground surface due to tunnel excavation varying ground condition, tunnel depth and diameter, and construction condition (volume loss at excavation face). The maximum surface settlement from the numerical analysis has been compared with the maximum settlement at tunnel crown considering ground condition, tunnel depth and diameter, and construction condition, and it has been also compared with the maximum horizontal displacement. In addition, the volume loss ($V_L$) at tunnel excavation face has been compared with the total surface settlement volume ($V_s$) with the variation of ground condition, tunnel depth, and tunnel diameter. The results from the numerical analysis have been compared with field measurements to confirm the applicability and validity of the results and by this comparison it is believed that the numerical results in this study can be utilized practically in analyzing the ground movements due to tunnel excavation.

A study on numerical modeling method considering gap parameter and backfill grouting of the shield TBM tunnel (쉴드 TBM 터널의 gap parameter와 뒤채움재를 고려한 수치모델링 방법에 대한 연구)

  • You, Kwang-Ho;Kim, Young-Jin
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.19 no.5
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    • pp.799-812
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    • 2017
  • Backfill grouting and realistic convergence distribution were not properly considered in previous studies on 2D numerical analysis of a shield TBM tunnel. In this study, a modeling method was suggested to cope with this problem by considering a realistic convergence distribution and proper properties of backfill grouting. To this end, the influence of gap parameter and depth of rock cover on volume loss and composed of ground volume loss around tunnel excavation and surface volume loss were analyzed with a single layer of weathered soil. As a result, most of surface settlements were occurred immediately after excavation. Additional, as depth of rock cover and gap parameter increased, the influence range of surface settlement curves obtained from 2D numerical analyses became broader than a suggested theoretical equation. Therefore, it is inferred that gap parameter should be applied based on load distribution ratio and the property of backfill grouting properly considered for the estimation of the precise behavior of a shield TBM tunnel in 2D numerical analysis.

Friction loss of multi-purpose stormwater tunnel simulated by Flow 3D (Flow 3D를 이용한 다목적 수로 터널의 마찰 손실 산정)

  • Lee, Du Han;Kim, Jung Hwan;Chung, Gunhui
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.3
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    • pp.14-21
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    • 2017
  • The extreme floods recently are have been attributed global warming, The development of a canal tunnel to prevent floods by making a bypass or undercurrent to flood discharge in a major flooding area is required because urban flooding in heavy rainfall occurs frequently, increasing the impermeability according to lack of capacity in sewage to urbanization by the existing urban basin. In this study, a numerical simulation was performed to support design standards for a multi-purpose waterway tunnel combined road tunnel of canal tunnel. The numerical simulation showed that the size of the friction loss occurring in the tunnel section of the same channel occurred more than the theoretically calculated frictional loss derived from the numerical simulations. This is probably due to the additional frictional loss caused by the change in the flow structure due to the geometry of the pipe when the shape of the channel is non-circular. The increase in friction loss was more pronounced in the laminar flow than in the turbulent flow. Depending on the shape of the conduit, the friction loss should be adjusted for accurate flow calculations. This result can provide the basin information about the design of flood by a pass conduit.

A Theory of Nonlinear Grinding Chatter Due to Loss of Contact between Grinding Wheel and Workpiece (接觸 離脫 現象 에 의한 非線型 硏削 채터의 解析 理論)

  • 김옥현;김성청;임영호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.6
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    • pp.706-713
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    • 1985
  • It is clear that when the amplitude of grinding chatter increases enough the contact between grinding wheel and workpiece cannot be sustained and the loss of contact occurs during a period of grinding chatter. In this paper the behavior of nonlinear grinding chatter due to the loss of contact has been studied. A nonlinear grinding chatter loop is developed where the loss of contact is considered as a nonlinear element of asymmetrical gain. The analysis is carried out in the time domain by numerical simulation and also in the complex domain by use of describing function method. The results show that two typical patterns of nonlinear grinding chatter can originate from the nonlinearity. One is an irregular chatter frequency at starting stage decreases to the natural frequency of grinding structure while the chatter amplitude increases and decreases repeatedly. The other is a limit cycle chatter of which the amplitude and frequency converge to constant and remain. This nonlinear behavior of grinding chatter has been well analyzed by the describing function method and confirmed by the numerical simulation.

A Numerical Analysis of the Reverse Heat Loss Method for a Refrigerator (냉장고 역열손실 방법의 수치해석적 분석에 관한 연구)

  • Ha, Ji-Soo;Shim, Jae-Sung
    • Journal of Energy Engineering
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    • v.20 no.4
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    • pp.303-308
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    • 2011
  • The present study has been carried out to predict the heat transfer characteristics of reverse heat loss method for a residential refrigerator by using numerical analysis and corresponding experiment. From the measured values of temperature and heat input, one can conclude that, the temperature inside the refrigerator has a nearly linear relationship with heat input. The effect of gasket heat loss was examined with the change of thermal conductivity of gasket region. The appropriate thermal conductivity of gasket region was acquired from the comparison of heat losses with the experimental result and numerical analysis. The result of calculated heat losses had accuracy within 1.8% error with the experimental result. With the selected thermal conductivity of gasket region, the effectiveness of reverse heat loss method was examined with the change of thermal conductivity of vacuum insulation panel.

Investigation on the Change of Ammonia Dissociation for Satellite Thruster According to the Catalyst Loss (위성추력기에서 촉매유실에 따른 암모니아 해리도 변화에 대한 연구)

  • Hwang, Chang-Hwan;Lee, Sung-Nam;Baek, Seung-Wook;Kim, Su-Kyum;Yu, Myoung-Jong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.11a
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    • pp.218-222
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    • 2011
  • During the development of the iridium catalyst for domestic production, the catalyst failure, loss, sintering phenomena are observed by high pressure and temperature. By these abnormal failure of catalyst bed, the performance of thruster is degraded. To figure out the detail phenomena on the damaged catalyst bed, a numerical analysis code is developed by assuming the catalyst bed as an one dimensional porous media. The numerical analysis code is validated with experiment data. Thereby, resulting physical phenomena are examined by considering the variation of catalyst bed characteristics incurred by catalyst granule failure. Through these numerical analyses we figure out the effect of the catalyst loss on the decomposition of hydrazine and ammonia.

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Numerical Investigation on Frictional Pressure Loss in a Perfect Square Micro Channel with Roughness and Particles

  • Han Dong-Hyouck;Lee Kyu-Jung
    • Journal of Mechanical Science and Technology
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    • v.20 no.8
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    • pp.1266-1274
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    • 2006
  • A numerical study is performed to investigate the effect of inner surface roughness and micro-particles on adiabatic single phase frictional pressure drop in a perfect square micro channel. With the variation of particles sizes (0.1 to $1{\mu}m$) and occupied volume ratio (0.01 to 10%) by particles, the Eulerian multi-phase model is applied to a $100{\mu}m$ hydraulic diameter perfect square micro channel in laminar flow region. Frictional pressure loss is affected significantly by particle size than occupied volume ratio by particles. The particle properties like density and coefficient of restitution are investigated with various particle materials and the density of particle is found as an influential factor. Roughness effect on pressure drop in the micro channel is investigated with the consideration of roughness height, pitch, and distribution. Additionally, the combination effect by particles and surface roughness are simulated. The pressure loss in microchannel with 2.5% relative roughness surface can be increased more than 20% by the addition of $0.5{\mu}m$ diameter particles.