• 제목/요약/키워드: hydraulic conditions

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대칭 적층 복합재 연소관의 탄성파 전파에 관한 실험적 연구 (An Experimental Study on Elastic Wave Propagation in a Symmetrically Filament-Wound Composite Motor Case)

  • 송성진;최지웅
    • 비파괴검사학회지
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    • 제18권3호
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    • pp.191-204
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    • 1998
  • 복합재 연소관의 수압/AE 시험의 성공적 수행을 위한 핵심 과제중의 하나는 수압으로 인해 방출되어 연소관을 통해 전파하는 탄성파의 특성을 분석함으로써 수압/AE 시험시 감지해야할 탄성파의 최적 성분을 결정하는 것이다. 이러한 문제를 해결하기 위해 본 연구에서는 대칭 적층 구조를 갖는 복합재 연소관에 광대역 초음파를 발진시키고 전파방항과 거리를 변화시킨 105지점에서 광대역 음향방출 센서를 이용하여 복합재 내를 전파한 탄성파를 수신하고, 그 특성(주파수, 전파거리, 전파속도)을 분석하였다. 이와 같은 실험을 내부가 비어 있는 연소관과 내부를 물로 채우고 수압을 가한 연소관에 대해 반복 수행함으로써, 수압이 탄성파의 전파특성에 미치는 영향을 분석하고, 이를 바탕으로 수압/AE 시험시 검출할 탄성파의 최적 성분을 결정하였다.

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Factors affecting particle breakage of calcareous soil retrieved from South China Sea

  • Wang, Xinzhi;Shan, Huagang;Wu, Yang;Meng, Qingshan;Zhu, Changqi
    • Geomechanics and Engineering
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    • 제22권2호
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    • pp.173-185
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    • 2020
  • Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

도심지 강우 특성을 고려한 투수성 보도블록의 배수 특성 (Characteristics of Drainage Pervious Block Considering Urban Rainfall)

  • 서다와;윤태섭;염광수;정상섬;문성호
    • 한국지반공학회논문집
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    • 제31권1호
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    • pp.53-64
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    • 2015
  • 본 연구는 도심지 내 집중 강우 특성을 고려한 투수성 보도블록의 배수 특성을 알아보기 위하여 2 가지 골재크기에 대하여 강도, 투수성, 증발 및 배수실험을 실시하였다. 강도의 경우 골재크기와 무관하게 한국산업표준(KS) 규격을 만족시킨 반면, 작은 골재로 구성된 투수성 보도블록의 경우 단위시간당 유량이 작은 경우에도 표면유출이 발생하였다. 큰 골재는 초기 우수조건에서의 배수는 원활한 반면 일정시간이 지난 후 동일한 유량의 배수실험에서 표면유출이 관찰되었다. 이는 간극 내부의 물이 투수성을 저감시키는 역할로 작용한 것으로, 투수성 보도블록의 투수성과 배수 성능은 간극비나 간극연결도 만으로 결정되는 것이 아니고 시간에 따른 증발, 선행우수조건에 의해 좌우됨을 나타낸다. 또한 초기 포화도보다는 이중선형 형태의 시간당 증발 양상과 유입량과 증발로 인한 내부 포화도 변화가 표면유출에 미치는 영향이 큰 것으로 나타났다.

석탄하역기 붐 호이스팅 실린더의 구조 안전성에 관한 연구 (A Study on Structural Safety of the Boom Hoisting Cylinder of a Coal Handling Machine)

  • 최용훈;곽효서;김철
    • 대한기계학회논문집A
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    • 제39권12호
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    • pp.1265-1273
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    • 2015
  • 석탄하역기는 화력발전소의 주 원료인 석탄을 체인 버킷을 구동하여 선박으로부터 컨베이어 벨트로 하역하는 장비이다. 그러나 국내에서는 석탄하역기의 하역위치에 따라 붐 각도를 제어하는 유압시스템인 붐 호이스팅 실린더에 대한 연구가 이루어지지 않아, 전량 수입하고 있는 실정이다. 이에 본 연구에서는 두꺼운 실린더에서 접촉면압의 이론 값을 FEM 을 수행하여 얻은 결과 값과 비교하여 접촉면압 해석기법의 타당성을 확립하였고, 이를 통하여 브이 실을 갖는 붐 호이스팅 실린더에서 작동유의 누설 여부 판단과 접촉면압을 최대로 갖는 브이 실 형상을 설계하였다. 또한, 실린더의 스트로크에 따른 구동시뮬레이션을 수행하였고, 최대 출력 상태에서의 붐 호이스팅 실런더의 구조 안전성을 검증하였다.

Effects of load variation on a Kaplan turbine runner

  • Amiri, K.;Mulu, B.;Cervantes, M.J.;Raisee, M.
    • International Journal of Fluid Machinery and Systems
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    • 제9권2호
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    • pp.182-193
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    • 2016
  • Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations since they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating directions called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

THM analysis for an in situ experiment using FLAC3D-TOUGH2 and an artificial neural network

  • Kwon, Sangki;Lee, Changsoo
    • Geomechanics and Engineering
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    • 제16권4호
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    • pp.363-373
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    • 2018
  • The evaluation of Thermo-Hydro-Mechanical (THM) coupling behavior is important for the development of underground space for various purposes. For a high-level radioactive waste repository excavated in a deep underground rock mass, the accurate prediction of the complex THM behavior is essential for the long-term safety and stability assessment. In order to develop reliable THM analysis techniques effectively, an international cooperation project, Development of Coupled models and their Validation against Experiments (DECOVALEX), was carried out. In DECOVALEX-2015 Task B2, the in situ THM experiment that was conducted at Horonobe Underground Research Laboratory(URL) by Japan Atomic Energy Agency (JAEA), was modeled by the research teams from the participating countries. In this study, a THM coupling technique that combined TOUGH2 and FLAC3D was developed and applied to the THM analysis for the in situ experiment, in which rock, buffer, backfill, sand, and heater were installed. With the assistance of an artificial neural network, the boundary conditions for the experiment could be adequately implemented in the modeling. The thermal, hydraulic, and mechanical results from the modeling were compared with the measurements from the in situ THM experiment. The predicted buffer temperature from the THM modelling was about $10^{\circ}C$ higher than measurement near by the overpack. At the other locations far from the overpack, modelling predicted slightly lower temperature than measurement. Even though the magnitude of pressure from the modeling was different from the measurements, the general trends of the variation with time were found to be similar.

서해안 저소성 준설매립 지반의 역학적 특성 (Mechanical Characteristics of Dredged and Reclaimed Ground with Low Plasticity from Western Coastal Site)

  • 정상국
    • 한국지반신소재학회논문집
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    • 제14권4호
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    • pp.97-104
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    • 2015
  • 실제 현장에서 준설매립공사를 수행하기 전의 설계 단계에서, 연약지반 개량설계를 수행할 때, 압축지수와 비배수 전단강도와 같은 설계정수를 합리적으로 평가하는 것은 최적공사비 산정측면에서 매우 중요한 사항이라고 할 수 있다. 본 연구에서는 유사 준설매립 현장에서 실시된 원위치 전단강도시험 및 불교란 시료 채취를 통해서 압밀 및 강도정수를 평가하였다. 이때, 배사관을 이용한 준설매립방법으로 투기된 준설매립층의 함수비 및 압축지수는 원지반 조건보다 오히려 감소하는 경향을 나타냈다. 압밀시험에 의해 준설매립지반의 압축지수와 함수비의 관계, 원위치 베인전단 시험으로 비배수 전단강도와 함수비의 관계를 각각 평가하였으며, 저소성 실트지반에 대한 Schmertmann의 압축지수 보정방법의 적용성을 판단하기 위해서 실제 침하량과 설계 예측침하량의 비교 분석을 실시하였다.

잠제의 전달율과 안정성에 관한 실험적 연구 (Experimental study on transmission and stability of submerged breakwater)

  • 김용우;윤한삼;김홍진;류청로;손병규
    • 한국해양공학회:학술대회논문집
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    • 한국해양공학회 2003년도 추계학술대회 논문집
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    • pp.213-219
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    • 2003
  • As the 2-D hydraulic experimental results for the submerged rubble-mound structure, we have concerned with their stability/function characteristics of structures by the effects of wave force, scour/deposition at the toe and wave transmission ratio at the lee-side sea. And as to investigate the variation characteristics of wave transmission ratio which depended to a geometrical structure of the submerged breakwater profiles, the critical conditions for the depth of submergence and crest width obviously presented. In summary, there results lead us to the conclusions that the wave control capabilities of submerged breakwaters by the variation of the submergence depth is high about 4 time degrees at the efficiency than the that of crest width. The destruction of covering block at the crest generated at the region which located between maximum damage curve, it maximum damage/failure station from the toe of the structure were 0.2L. As the wave transmission coefficient and the slope of the structure increase, the damage/failure ratio and the maximum scour depth at the toe was extended, respectively. When maximum scour depth happened. The destruction of covering block which located at the toe generated at the front slope destruction. Finally, it was found from the results that the optimization of structure may be obtained by the efficiently decision of the submergence depth and crest width in the permissible range of wave transmission ratio.

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Restoration Modeling Analysis for Abandoned Channels of the Mangyeong River

  • Kim, Jae-Hoon;Julien, Pierre Y.;Ji, Un;Kang, Joon-Gu
    • 한국환경과학회지
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    • 제20권5호
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    • pp.555-564
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    • 2011
  • This study examines the potential restoration of abandoned channels of the Mangyeong River in South Korea. To analyze the morphological changes and equilibrium conditions, a flow duration analysis was performed to obtain the discharge of 255 m3/s with a recurrence interval of 1.5 year. It is a gravel-bed stream with a median bed diameter of 36 mm. The reach-averaged results using HEC-RAS showed that the top width is 244 m, the mean flow depth is 1.11 m, the width/depth ratio is very high at 277, the channel velocity is 1.18 m/s, and the Froude number is also high at 0.42. The hydraulic parameters vary in the vicinity of the three sills which control the bed elevation. The total sediment load is 6,500 tons per day and the equivalent sediment concentration is 240 mg/l. The Engelund-Hansen method was closer to the field measurements than any other method. The bed material coarser than 33 mm will not move. The methods of Julien-Wargadalam and Lacey gave an equilibrium channel width of 83 m and 77 m respectively, which demonstrates that the Mangyeong River is currently very wide and shallow. The planform geometry for the Mangyeong River is definitely straight with a sinuosity as low as 1.03. The thalweg and mean bed elevation profiles were analyzed using field measurements in 1976, 1993 and 2009. The measured profiles indicated that the channel has degraded about 2 m since 1976. The coarse gravel material and large width-depth ratio increase the stability of the bed material in this reach.

셰일가스 플랜트 용수 처리를 위한 직접 접촉 막 증발법 적용 가능성 연구 (A Feasibility Study on Shale Gas Plant Water Treatment by Direct Contact Membrane Distillation)

  • 구재욱;한지희;이상호;홍승관
    • 한국유체기계학회 논문집
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    • 제16권1호
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    • pp.56-60
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    • 2013
  • Non-conventional oil resources such as shale gas are becoming increasingly important and have drawn the attention of several major oil companies all over the world. Nevertheless, the market-changing growth of shale gas production in recent years has resulted in the emergence of environmental and water management challenges. This is because the water used in the hydraulic fracturing process contains large amount of pollutants including ions, organics, and particles. Accordingly, the treatment of this flowback water from shale gas plant is regarded as one of the key technologies. In this study, we examined the feasibility of membrane distillation as a treatment technology for the water from shale gas plants. Direct contact membrane distillation (DCMD) is a thermally-driven process based on a vaper pressure gradient across a hydrophobic membrane, allowing the treatment of feed waters containing high concentration of ions. Experiments were carried out put in the lab-scale under various conditions such as membrane types, temperature difference, flow rate and so on. Synthetic feed water was prepared and used based on the data from literature. The results indicated that DCMD is suitable for treating not only low-range flowback water but also high-range flowback water. Based on the theoretical calculation, DCMD could have over 80% of recovery. Nevertheless, organic pollutants such as oil and surfactant were identified as serious barriers for the application of MD. Further works will be required to develop the optimum pretreatment for this MD process.