• Title/Summary/Keyword: Long tunnel

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Wake effects of an upstream bridge on aerodynamic characteristics of a downstream bridge

  • Chen, Zhenhua;Lin, Zhenyun;Tang, Haojun;Li, Yongle;Wang, Bin
    • Wind and Structures
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    • v.29 no.6
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    • pp.417-430
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    • 2019
  • To study the wake influence of an upstream bridge on the wind-resistance performance of a downstream bridge, two adjacent long-span cable-stayed bridges are taken as examples. Based on wind tunnel tests, the static aerodynamic coefficients and the dynamic response of the downstream bridge are measured in the wake of the upstream one. Considering different horizontal and vertical distances, the flutter derivatives of the downstream bridge at different angles of attack are extracted by Computational Fluid Dynamics (CFD) simulations and discussed, and the change in critical flutter state is further studied. The results show that a train passing through the downstream bridge could significantly increase the lift coefficient of the bridge which has the same direction with the gravity of the train, leading to possible vertical deformation and vibration. In the wake of the upstream bridge, the change in lift coefficient of the downstream bridge is reduced, but the dynamic response seems to be strong. The effect of aerodynamic interference on flutter stability is related to the horizontal and vertical distances between the two adjacent bridges as well as the attack angle of incoming flow. At large angles of attack, the aerodynamic condition around the downstream girder which may drive the bridge to torsional flutter instability is weakened by the wake of the upstream bridge, and the critical flutter wind speed increases at this situation.

Thermohydromechanical Stability Study on the Joint Characteristics and Depth Variations in the Region of an Underground Radwaste Repository (절리 발달 특성 및 심도 변화에 의한 방사성폐기물 처분장 주변영역에서의 열수리역학적 안정성 연구)

  • Kim, Jhinwung;Daeseok Bae;Park, Chongwon
    • Tunnel and Underground Space
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    • v.13 no.2
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    • pp.153-168
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    • 2003
  • The objective of this present study is to understand long term(500 years) thermohydromechanical interaction behavior in the vicinity of a repository cavern on the joint location and repository depth variations. The model includes a saturated discontinuous granitic rock mass, PWR spent nuclear fuel in a disposal canister surrounded with compacted bentonite inside a deposition hole, and mixed bentonite backfilled in the rest of the space within a repository cavern. It is assumed that two joint sets exist within the model. Joint set 1 includes joints of 56$^{\circ}$ dip angle, spaced at 20 m, and joint set 2 is in the perpendicular direction to joint set 1 and includes joints of 34$^{\circ}$ dip angle, spaced at 20 m. In order to understand the behavior change on the joint location variations, 5 different models of 500m in depth are analyzed, and additional 3 different models of 1000 m in depth are analyzed to understand the effect of depth variation.

Analysis of Benchmark Test Model for Evaluation of Damage Characteristics of Rock Mass near Radioactive Waste Repository (방사성폐기물 처분장 주변 암반의 손상 특성 고찰을 위한 벤치마크 시험 모델 해석)

  • Lee, Hee-Suk
    • Tunnel and Underground Space
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    • v.17 no.1 s.66
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    • pp.32-42
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    • 2007
  • Severe damage can occur around deposition holes due to complex interaction of thermo-hydro-mechanical (THM) loading during the long term operation of high level radioactive waste repository. Many candidate sites for repository are located in crystalline rock mass, therefore mechanism of damage follows the form of brittle fracture and failure. This paper briefly introduces major outcomes from 15 years international collaborative project, DECOVALEX, and presents major study results for current ongoing benchmark test study from DECOVALEX-THMC, to evaluate the effect of THM loading to rock mass in excavation damaged zone (EDZ) near deposition holes. Through benchmark test model by simplifying THM loading to boundary loading obtained numerical results are compared, and discrete fracture interaction after up to 1 million years operation is discussed.

Determination of Boil-Off gas Ratio for the Design of Underground LNG Storage System in Rock Cavern (암반동굴식 지하 LNG 저장 시스템 설계를 위한 기화율의 산정)

  • Chung, So-Keul;Lee, Hee-Suk;Jeong, Woo-Cheol;Park, Eui-Seob
    • Tunnel and Underground Space
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    • v.17 no.1 s.66
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    • pp.56-65
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    • 2007
  • A new underground LNG storage concept in the rock mass has been developed by combining underground cavern construction and new ice-ring harrier technologies with the conventional cryogenic insulation system. Technical feasibility of the storage system has been verified through construction and operation of the pilot storage cavern and a full-scale project is expected to start in the near future. One of the most important issues in the LNG storage system is the operational efficiency of the storage to minimize heat loss during a long period of operation due to the cryogenic heat transfer. This paper presents several important results of heat transfer and coupled hydro-thermal analyses by a finite element code Temp/W and Seep/W. A series of heat transfer analyses for full-scale caverns were performed to determine design parameters such as boil-off gas ratio (BOR), insulation thickness and pillar width. The result of the coupled hydro-mechanical analysis showed that BOR for underground storage system remains at about 0.04 %/day during the early stage of the operation. This value could be even much lower when the discontinuities in the rock masses are taken into consideration.

Development of an Optimized Prediction System of Round Trip Occurrence using Genetic Algorithm (유전자알고리즘을 활용한 최적화된 라운드트립 발생 예측 시스템 개발)

  • Lee, Seung Soo;Seo, Jong Won;Kim, Kwang Yeom;Shin, Hyu-Soung
    • Tunnel and Underground Space
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    • v.25 no.6
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    • pp.534-542
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    • 2015
  • Round trip activity occurs discretely due to the abrasion of drill bit in the deep drilling project. Round trip has great impact on the drilling performance because it takes more time to change a drill bit as the depth goes deeper. Therefore, a reliable prediction technology of the round trip should be secured for feasibility analysis and effective management of the drilling project. Lee et al. (2013) developed the TOSA (round trip occurrence simulation algorithm) which can analyze the depth and timing of round trip occurrence at each abrasion state of bit. However, TOSA has weakness that it takes long time for simulation because the number of simulation increase exponentially as increasing the number of simulation section. This study developed the TOSA based round trip performance prediction module using genetic algorithm for simulating in a short time and verified simulation results.

Half-turned Truncal Switch Operation for Transposition of Great Arteries, Ventricular Septal Defect and Pulmonic Stenosis (폐동맥 협착과 심실 중격 결손을 동반한 대혈관 전위에서 시행한 반회전 동맥간 전환술)

  • Lim Hong Gook;Hwang Seong Wook;Lee Cheul;Kim Chong Whan;Kim Jun Seok;Lee Chang-Ha
    • Journal of Chest Surgery
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    • v.39 no.2 s.259
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    • pp.145-149
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    • 2006
  • The surgical management of patients with transposition of the great arteries, ventricular septal defect, and pulmonary stenosis remains a challenge. The Rastelli operation or Lecompte operation is the preferred surgical procedure, but its long-term results are not optimal because of a warped left ventricular outflow tract through a space-occupied intraventricular tunnel and a contrived right ventricular outflow tract. We performed a half-turned truncal switch operation as an alternative surgical procedure in a 3-year-old boy (weighing 9.6 kg) with this anomaly. Postoperative echocardiography showed laminar flow through straight and nonobstructive aortic and pulmonary ventricular outflow tracts.

Stability Assessment on the Final Pit Slope in S Limestone Mine (S 석회석광산에서의 최종 잔벽사면의 안정성 평가)

  • Sun, Woo-Choon;Lee, Yun-Su;Kim, Hyun-Woo;Lee, Byung-Joo
    • Tunnel and Underground Space
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    • v.23 no.2
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    • pp.99-109
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    • 2013
  • The slopes of open-pit mine are typically designed without considering the reinforcement and support method due to the economical efficiency. However, the long-term stability of final pit slope is needed in some case, therefore the appropriate measures that can improve the stability are required. In this study, the field survey and laboratory test were carried out in S limestone mine. The stability assessment of final pit slope was performed through the stereographic projection method, SMR, and numerical analysis. And countermeasures for stabilization were proposed. The results of analysis show that full scale of slope failure is not expected but the failures of bench slope scale are likely to occur. In oder to increase the stability of bench slope, we suggested the remedial methods as follows: excavating the final pit slope by pre-splitting blasting, placing the wide berm in the intermediate bench slope and installing the horizontal drainage hole in the place of local ground water runoff.

Experimental Study on the Aerodynamic Characteristics of the Ducted fan for the Propulsion of a Small UAV (소형 무인항공기 추진용 덕티드팬의 공력특성에 대한 실험적 연구)

  • Ryu, Min-Hyoung;Cho, Lee-Sang;Cho, Jin-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.5
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    • pp.413-422
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    • 2012
  • The ducted fan for a small UAV propulsion can reconnoiter and observe in a town and a small area, it has better thrust efficiency and a long endurance than propeller. Thrust characteristics of hover and for ward flight condition for the ducted fan UAV is important issue to improve a endurance. The unsteady 3-dimensional flow fields of the ducted fan UAV is essential to stable flight. In this paper, to verify the design results of the ducted fan and to investigate a stable aeronautical characteristic, the thrust performance and the unsteady 3-dimensional flow fields are measured. Thrust characteristics for the hovering and the forward flight conditions are measured by the 6-components balance system in the subsonic wind tunnel. The unsteady 3-dimensional flow fields are analyzed by using a stationary $45^{\circ}$ slanted hot-wire technique. The swirl velocity is almost removed behind the stator blades. Therefore, the thrust performance of the ducted fan is improved and the flight stability is maintained.

A Study on the Performance Evaluation System of Conventional(ASSM) Road Tunnels (재래식(ASSM) 도로터널의 성능평가 체계 연구)

  • Park, Kwang-Rim;Chung, Jee-Seung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.4
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    • pp.27-36
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    • 2018
  • Although the current evaluation system has been revised four times since it was revised in 1996, it is insufficient to utilize it as a basis for predicting the performance degradation from the long-term viewpoint and prioritization decision for the budget input due to the evaluation system limited to securing the structural safety. Therefore, this study proposes a new evaluation system suitable for the performance evaluation of conventional (ASSM) tunnels among the various types of existing road tunnels using Delphi technique and AHP technique. Since the existing evaluation systems and evaluation items in domestic and overseas are limited in scope of evaluation criteria, the survey was conducted in conjunction with closed questionnaires on existing items and open questionnaires for eliciting new items. The validity of the questionnaire results were verified and the performance evaluation factors suitable for conventional (ASSM) tunnels were derived. After calculating weighted value of the derived evaluation item using AHP technique, a new evaluation system is proposed to meet the characteristics of the ASSM tunnel, so that they can be used as reference materials for revising and supplementing detailed guidelines of performance evaluation in the future.

An Experimental Study on Load Bearing Capacity of Lattice Girder as a Steel Support in Tunnelling (터널 지보재로서 격자지보의 하중지지력에 관한 실험적 연구)

  • 유충식;배규진
    • Geotechnical Engineering
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    • v.13 no.4
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    • pp.163-176
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    • 1997
  • It has long been recognized that the H-beam steel rib has many shortcomings when used as a steel support in tunneling. One of the major shortcomings is the shotcrete shadow created behind H-beam flange which eventually reduces the load bearing capacity of shotcrete shell. In many European countries, plate girder as the H-beam steel rib has been replaced by lattice girder which has many advantages over the H-beam steel rib. Successful application of the lattice girder as a steel support requires a thorough investigation on the load bearing capacity of the lattice girder. Therefore, laboratory bending and compression tests were conducted on lattice girders with the aim of investigating the load bearing capacity of the lattice girders. The results of tests show that the load bearing capacity of laIn twice girders is higher than that of H-beams, which indicates that the lattice girder can be effectively used as a support in tunneling.

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