• 제목/요약/키워드: GRID

Search Result 9,493, Processing Time 0.032 seconds

A Study on the Stability Analysis of the Bank Revetment at Urban Streams in Flood Times (홍수시 도시하천의 호안 안정성 분석에 관한 연구)

  • Kim, Chul;Park, Nam-Hee
    • Journal of the Korean Society of Hazard Mitigation
    • /
    • v.10 no.6
    • /
    • pp.139-145
    • /
    • 2010
  • Recently, close-to-nature stream improvement works have been carried out in urban streams, where eco-friendly bank revetment methods have been adopted. These bank revetment methods are vulnerable to be damaged or washed away by floods compared to the traditional methods which use concrete materials. Damage analysis methods on the urban streams by the floods of severe rain storm are presented. The analysis methods are the graph-using method and the grid method, which are derived from the survey results at Gwangju stream. Damage analysis grid which is intersected velocity grid and material strength grid is the highest correlation with the damage survey grid. The biggest damage on the bank revetments have been occurred around the crossing structures. Big damages have also been occurred in the connection of low water revetment and the terrace land, and around the structures in the terrace land of the stream.

Effective resource selection and mobility management scheme in mobile grid computing (모바일 그리드 컴퓨팅에서 효율적인 자원 확보와 이동성 관리 기법)

  • Lee, Dae-Won
    • The Journal of Korean Association of Computer Education
    • /
    • v.13 no.1
    • /
    • pp.53-64
    • /
    • 2010
  • In this paper, we tried to enable a mobile device as a resource to access to mobile grid networks. By advanced Internet techniques, the use of mobile devices has been rapidly increased. Some researches in mobile grid computing tried to combine grid computing with mobile devices. However, according to intrinsic properties of mobile environments, mobile devices have many considerations, such as mobility management, disconnected operation, device heterogeneity, service discovery, resource sharing, security, and so on. To solve these problems, there are two trends for mobile grid computing: a proxy-based mobile grid architecture and an agent-based mobile grid architecture. We focus on a proxy-based mobile grid architecture with IP-paging, which can easily manage idle mobile devices and grid resource status information. Also, we use SIP(Session Initiation Protocol)to support mobility management, mobile grid services. We manage variation of mobile device state and power by paging cache. Finally, using the candidate set and the reservation set of resources, we perform task migration. The performance evaluation by simulation, shows improvement of efficiency and stability during execution.

  • PDF

A Study on Optical Characteristic of Nano Metal Grid Polarizer Film with Different Deposition Thicknes (나노 금속 격자형 편광필름 제작에서 증착 두께에 따른 광 특성 연구)

  • Kim, Jiwon;Cho, Sanguk;Jeong, Myung Yung
    • Journal of the Microelectronics and Packaging Society
    • /
    • v.22 no.1
    • /
    • pp.63-67
    • /
    • 2015
  • In this study, we demonstrate the change of optical characteristic by thickness of metal deposition on nano metal grid polarizer film fabrication. Nano metal grid polarizer film consists of aluminium grid polarizer layer on PET (Polyethylene phthalate) substrate. We aim at metal grid layer formation for the large nano wire grid polarizer fabrication. we draw process conditions of the nano metal grid polarizer film fabrication to improve transmittance and extinction ratio and Nano wire grid polarizer film (NWGP) film is fabricated with 140 nm pitch, 70 nm width, and 70 nm depth of metal grid on optimum design conditions. As a result, we get high optical properties of nano wire grid polarizer which is the maximum transmittance of 80% and the extinction ratio of $10^6$ at 600 nm wavelength respectively.

Simulations of the Dynamic Load in a Francis Runner based on measurements of Grid Frequency Variations

  • Ellingsen, Rakel;Storli, Pal-Tore
    • International Journal of Fluid Machinery and Systems
    • /
    • v.8 no.2
    • /
    • pp.102-112
    • /
    • 2015
  • In the Nordic grid, a trend observed the recent years is the increase in grid frequency variations, which means the frequency is outside the normal range (49.9-50.1 Hz) more often. Variations in the grid frequency leads to changes in the speed of rotation of all the turbines connected to the grid, since the speed of rotation is closely related to the grid frequency for synchronous generators. When the speed of rotation changes, this implies that the net torque acting on the rotating masses are changed, and the material of the turbine runners must withstand these changes in torque. Frequency variations thus leads to torque oscillations in the turbine, which become dynamical loads that the runner must be able to withstand. Several new Francis runners have recently experienced cracks in the runner blades due to fatigue, obviously due to the runner design not taking into account the actual loads on the runner. In this paper, the torque oscillations and dynamic loads due to the variations in grid frequency are simulated in a 1D MATLAB program, and measured grid frequency is used as input to the simulation program. The maximum increase and decrease in the grid frequency over a 440 seconds interval have been investigated, in addition to an extreme event where the frequency decreased far below the normal range within a few seconds. The dynamic loading originating from grid frequency variations is qualitatively found by a constructed variable $T_{stress}$, and for the simulations presented here the variations in $T_{stress}$ are found to be around 3 % of the mean value, which is a relatively small dynamic load. The important thing to remember is that these dynamic loads come in addition to all other dynamic loads, like rotor-stator interaction and draft tube surges, and should be included in the design process, if not found to be negligible.

A Compensation of the Grid Current Unbalance and Distortion caused by the Grid Voltage Unbalance and Distortion in 3-Phase Bi-Directional DC to AC Inverter (3상 양방향 인버터의 계통전압 불평형 및 왜곡에 의한 계통전류 불평형 및 왜곡 보상)

  • Yang, Seung-Dae;Kim, Seung-Min;Choi, Ju-Yeop;Choy, Ick;Song, Seung-Ho;Lee, Sang-Cheol;Lee, Dong-Ha
    • The Transactions of the Korean Institute of Power Electronics
    • /
    • v.18 no.2
    • /
    • pp.161-168
    • /
    • 2013
  • This paper presents an algorithm of a compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it suggest simple method to solve the problem. Simulation and experiment is used to validate the proposed algorithm.

A Study on the Optimal Resource Configuration Considering Load Characteristics of Electric Vehicles in Micro Grid Environment (전기자동차 부하 특성을 고려한 마이크로그리드의 최적 전원 구성에 관한 연구)

  • Hwang, Sung-Wook;Chae, Woo-Kyu;Lee, Hak-Ju;Yun, Sang-Yun;Kim, Jung-Hoon
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.64 no.2
    • /
    • pp.228-231
    • /
    • 2015
  • In power system research fields, one of current key issues is the construction and commercialization of micro grid site which is called green island, carbon zero island, energy independent island, building micro grid, etc. and various affiliated technologies have been being vigorously developed to realize. In addition, various researches about electric vehicles (EVs) are in progress and it is expected to penetrate rapidly with the next a few years. Some new load models should be developed integrating with electric vehicle loads because the EVs' deployment could cause the change of load composition rate on power system planning and operations. EVs are also resources for micro grid as well as distributed generation and demand response so that various supply and demand side resources should be considered for micro grid researches. In this paper, the load composition rate of residential sectors is prospected considering the deployment of EVs and the resource configuration of micro grid is optimized based on net present cost. In the optimization, the load patten of case studies includes EV's charging characteristics and various cases are simulated comparing micro grid environment and normal condition. HOMER is used to compare various cases and economic effects.

COARSE GRID LARGE-EDDY SIMULATION OF FLOW OVER A HEAVY VEHICLE (화물차 주위 유동의 성긴 격자 큰에디모사)

  • Lee, S.;Kim, M.;You, D.;Kim, J.J.;Lee, S.J.
    • Journal of computational fluids engineering
    • /
    • v.21 no.1
    • /
    • pp.30-35
    • /
    • 2016
  • In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.

Studios in Selected Grid Ratio of Objective Thickness on X-ray Exposure (X선촬영시(X線撮影時) 피사체(被寫體) 두께에 따른 격자비(格子比) 선정(選定)에 관한 연구(硏究))

  • Yoon, Chul-Ho;Chu, Sung-Shil;Huh, Joon
    • Journal of radiological science and technology
    • /
    • v.5 no.1
    • /
    • pp.21-34
    • /
    • 1982
  • When unattenuated x-ray radiation passes through the object it is transmitted and scattered from objectes and impinging on the film. During this process certain radiation is absorbed within the object and others transmitted in reduced scattering. The scattering radiation influence upon radiation image quality, confining x-ray beam which means scattering radiation produce increased fog on x-ray film image and as a consequence decrease contrast and less detail of the film there for the elimination of fog and for absorbing scattered radiation, the grid has been used between the object and the film in order to rid of scattering rays. Using grid is good method for the qualification of the better image as well as in using air gap technique. The grid is easy to manipulate and promote good efficiency which is defined by ICRU and JIS. It is the purpose to study for eliminating scattered radiation from the tissue equivalent acryl phantom using grid, we have studied and evaluated the grid permeability about the x-ray exposure, the selection of grid ratio according to phantom thickness, on x-ray exposure are performed as follows. 1. The penetrating ratio of primary x-ray is remarkably decreased by increasing of the grid ratio, but it is almost not influenced in KVP difference and phantom thickness. 2. The scattered radiation is proportionaly increased by thickness of the phantom, having nothing to do with grid ratios. 3. The relative between the penetration rate of primary and secondary x-ray is improved by increasing grid ratio, and decreased by phantom thickness, and slightly decreased by high tube voltage. 4. The grid of 5:1 and 10:1 ratio are adequate to the phantom of 10cm and 15cm thickness, respectively.

  • PDF

A selective effect of grid and window net in the shrimp beam trawl fishery (새우조망 어업에서 그리드와 윈도우 네트의 선택효과)

  • JANG, Choong-Sik;CHO, Youn-Hyoung;AN, Young-Su
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.51 no.3
    • /
    • pp.375-386
    • /
    • 2015
  • The study aims at a selective effect of the Grid and Window net in the shrimp beam trawl. The experimental trawling of the Proto type, Grid type and Grid and Window net type was performed in a sea area of Geo-je and Tong-yeong from Mar, 2006 to Apr, 2010. The obtained results are as follows; Catch per unit area (Number) of the Proto type net and Grid type net were $0.18/m^2$, $0.23/m^2$, respectively. The Grid type demonstrated 2.4% lower bycatch rate than the proto type (6.6% vs 4.2%, respectively). In addition, in terms of total weight, the bycatch rate of Grid type was 7.6% lower than the proto type (50.2% vs 42.6%, respectively). In the comparison of shrimp catch, the Proto type demonstrated better haul outcome ($0.02case/m^2$) than the Grid & Window type ($0.02case/m^2$). The Grid & Window net type demonstrated 16.4% lower bycatch rate than the Proto type (32.2% vs 48.6%, respectively). In addition, in terms of total weight, the bycatch rate of Grid & Window net type was 8.3% lower than the Proto type (85.9% vs 94.2% respectively).

Design of Modified Slip-Mode Frequency Shift Islanding Detection Method for Power Quality Improvement (Slip-Mode Frequency Shift 단독운전 검출 기법의 정상상태 전력 품질 개선)

  • Kim, Dong-Uk;Kim, Sungmin
    • Journal of IKEEE
    • /
    • v.22 no.3
    • /
    • pp.539-547
    • /
    • 2018
  • Grid-connected inverter is required to cut off the power supplied to the grid at the islanding condition, immediately. For this reason, an islanding detection is an indispensable function for grid-connected distributed generation system. Slip-Mode frequency Shift (SMS) islanding detection method is very popular method to determine the grid state. SMS method supplies the reactive power to the load according to the grid frequency. In the islanding condition of grid, this injected reactive power pulls out the grid frequency from the allowable range, then the inverter system can detect the islanding condition of the grid. The SMS method can detect the islanding state well and does not generate any harmonics of the grid current. However, the reactive power would be generated and the power quality is reduced even though the grid is not islanding condition, but normal condition. In this paper, a modified SMS method is proposed to remove the reactive power in the normal condition. The performance of the proposed method is evaluated by 600W single phase inverter experimental results.