• Wind and Structures
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• 제35권5호
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• pp.309-322
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• 2022

Due to the complex terrain around high-speed railways, the windbreaks were established along different landforms, resulting in irregular windbreak transition regions between different subgrade infrastructures (flat ground, cutting, embankment, etc). In this paper, the effect of a windbreak transition on the wind flow around railways subjected to crosswinds was studied. Wind tunnel testing was conducted to study the wind speed change around a windbreak transition on flat ground with a uniform wind speed inflow, and the collected data were used to validate a numerical simulation based on a detached eddy simulation method. The validated numerical method was then used to investigate the effect of the windbreak transition from the flat ground to cutting (the "cutting" is a railway subgrade type formed by digging down from the original ground) for three different wind incidence angles of 90°, 75°, and 105°. The deterioration mechanism of the flow fields and the reasons behind the occurrence of the peak wind velocities were explained in detail. The results showed that for the windbreak transition on flat ground, the impact was small. For the transition from the flat ground to the cutting, the influence was relatively large. The significant increase in the wind speeds was due to the right-angle structure of the windbreak transition, which resulted in sudden changes of the wind velocity as well as the direction. In addition, the height mismatch in the transition region worsened the protective effect of a typical windbreak.

• Geomechanics and Engineering
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• 제30권6호
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• pp.539-549
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• 2022

Accidental anchor drop can cause disturbances to seabed materials and pose significant threats to the safety and serviceability of submarine structures such as pipelines. In this study, a series of anchor drop tests was carried out to investigate the penetration mechanism of a Hall anchor in sand and clay. A special anchor drop apparatus was designed to model the inflight drop of a Hall anchor. Results indicate that Coriolis acceleration was the primary cause of large horizontal offsets in sand, and earth gravity had negligible impact on the lateral movement of dropped anchors. The indued final horizontal offset was shown to increase with the elevated drop height of an anchor, and the existence of water can slow down the landing velocity of an anchor. It is also observed that water conditions had a significant effect on the influence zone caused by anchors. The vertical influence depth was over 5 m, and the influence radius was more than 3 m if the anchor had a drop height of 25 m in dry sand. In comparison, the vertical influence depth and radius reduced to less than 3 m and 2 m, respectively, when the anchor was released from 10 m height and fell into the seabed with a water depth of 15 m. It is also found that the dynamically penetrating anchors could significantly influence the earth pressure in clay. There is a non-linear increase in the measured penetration depth with kinematic energy, and the resulted maximum earth pressure increased dramatically with an increase in kinematic energy. Results from centrifuge model tests in this study provide useful insights into the penetration mechanism of a dropped anchor, which provides valuable data for design and planning of future submarine structures.

• 한국철도학회논문집
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• 제16권1호
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• pp.7-13
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• 2013

철도차량의 실차 규모 동특성시험은 설비 구축, 대차의 제작 및 시험 조건의 설정등과 관련하여 비용, 시간 등의 증대로 많은 어려움이 따른다. 본 연구에서는 실험실 환경에서 차량 진동문제와 안전성을 평가하기 위한 목적으로 축소모델을 제작하고, 개발된 축소모델이 해당 철도차량의 동특성을 정밀하게 모사하는지를 검증하는 평가방법에 대한 연구를 수행하였다. 축소이론은 Jaschinski 상사기법의 이론을 적용하였으며, 1/10 축소모델을 구축하였다. 본 연구에서는 축소 대차의 상하 진동에 초점을 맞혀 시스템을 제작하였다. 시스템은 구동부, 보기, 대차 등 3개의 하부구조로 구성되었으며, 실제 차량으로 환산 시 400km/hr까지 실험가능 하도록 목표로 하였다. 축소 대차의 설계 및 제작과 함께, 동역학해석 프로그램인 ADAMS/View를 이용하여 고유치 해석을 수행하였다. 전산해석으로 도출된 고유진동수는 실험결과와 비교 분석되었다. 시스템이 가지고 있는 초기 5개의 자유도에 상응한 고유진동수를 비교한 결과, 개발된 상사 이론에 따른 축소모형은 충분한 신뢰성을 확보한 것으로 검증되었다. 본 연구에서 개발된 축소모델은 대학실험실에서 차량진동모드를 모사하는 용도로 기획되었으나, 추후 자유도의 추가보완을 통해 고속철도 차량의 대차와 보기구조 동특성 해석에 활용될 수 있을 것으로 판단된다.

• The Korean Journal of Physiology
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• 제7권1호
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• pp.23-31
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• 1973

Numerous factors concern with the absorption of substances through the membrane of the gastrointestinal tract. To simplify the experimental condition, present work has been restricted to observe the disappearance rate of substance from the intestinal loop which was made in the jejunum, 70 cm apart from the pylorus of the adult rabbit. The purpose of the study is to clarify the absorption of urea through the jejunal wall is solely attributable to the concentration difference between the luminal fluid and plasma, and to observe the effect of adding red pepper upon the rate of absorption. The rabbits were anesthetized with nembutal, 35mg/kg I.V. Jejunal loop was made by ligating at 2 spots, 70 cm and 80cm apart from the pylorus. After rinsing with normal saline solution through the polyethylene tubing inserted from the end of the loop, 8 ml of test solution was placed through the same tubing. The test solution contained 200 mg% of urea and 150mg% of polyethylene glycol(M.W. 4,000) in normal saline solution. Right after placing the test solution the first specimen was taken through the tubing, and successive samplings were performed at 5, 10, 20, and 30 minutes. Logarithm of the difference of urea concentration between the luminal fluid and plasma was plotted against time elapsed after the onset of the experiment. If straight line is revealed, it would verify the nature of transport mechanism as diffusion, obeying the Fick's principle. The concentration of polyethylene glycol (PEG) was also measured in order to examine the change in the volume. PEG was used as the marker substance because it is not absorbable in the intestinal tract. Consequently the concentration of PEG relates inversely to the volume of the loop. Instantaneous concentration of urea in the loop times the volume will give the amount of urea remaining in the luminal fluid. The change in the amount of any substance is directly relate to the volume of the compartment and differs from the change in the concentration which is independent of the volume. After completion of the experiment without red pepper, it was added in the test solution and was centrifuged after thorough mixing. Supernatant of the mixture was placed in the loop and similar sampling were performed with the same time intervals that of previous run in order to observe the effects of the red pepper on the passive transport of the water soluble small substance, urea. The results obtained were as follows: 1. Logarithm of the concentration difference of urea between the luminal fluid and plasma was diminished exponentially as time elapsed. The decay constant in the experiment without red pepper was 0.0563/min. By adding red pepper in the test solution as much as the concentration rose to 4,000 mg% and 8,000 mg%, the decay constants were lowered to 0.0493/min and to 0.0506/min, respectively. The time interval by which the concentration difference dropped to one half of the initial value was prolonged. Without red pepper the half concentration time was 13.30 minutes, and by adding extract of red pepper, 15.31 minutes and 15.71 minutes were revealed. 2. The profile of the diminishing rate of tile amount of urea was quite different from that of the concentration because of the change in the volume of the loop during the observed period. 3. By adding the extract of red pepper, it slowed down the rate of absorption of urea in the intestinal loop, suggesting an increase in the diffusional barrier. 4. Larger dosage of red pepper brought an increase in the secretion of intestinal fluid with concomitant expansion of the luminal volume, and the retardation of the absorption of urea was noticed. This effect was largely dependent on the sensitivity of the individual animal to the red pepper, extract. The amount of urea remained after 10 minutes interval was 55.5% of the initial amount in the experiment without red pepper. On the other hand it was not consistent after administration of red pepper, showing 50.6% and 66.5% of the initial figures by adding 400 mg and 800 mg of red pepper in the test solution, respectively. It was postulated that symptom of diarrhea often encountered by taking a hot (red pepper) food might be attributable to the increase of secretion and the retardation of absorption in the intestinal tract.

• Asia Marketing Journal
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• 제14권1호
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• pp.83-98
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• 2012

신차와 중고차가 함께 경쟁하는 시장에서 신차의 경쟁만을 모형화한다면 가격이나 기타 프로모션 탄력성의 추정이 왜곡될 수 있다. 그러나 자동차 시장을 연구대상으로 한 선행연구의 대부분이 신차 시장의 경쟁에만 관심을 기울였던 바, 합리적인 가격결정이나 프로모션 기획에 도움을 주기에 미흡한 점이 있었다. 본 연구는 신차의 가격결정 및 프로모션 기획이 향후 중고차 시장을 통해 리바운드되어 신차 매출에 다시 영향을 미친다는 점을 반영하여 모형을 설정하였다. 즉, 서로 다른 신차간의 (혹은 서로 다른 중고차간의) 교차탄력성보다, 동일 모델의 신차와 중고차간의 교차탄력성이 높다는 가정하에 모형을 설정하였다. 방법론적으로는 네스티드 로짓(Nested Logit) 모형을 설정하여 소비자의 자동차 선택은 단계적으로 이루어진다고 가정하였다. 즉, 1단계에서 자동차 모델을 선택하고, 모델이 정해지면 2단계에서 신차와 중고차 중 선택하는 구조를 가정하였다 실증분석은 미국 전역에서 2009년 1월부터 2009년 6월까지 판매된 모든 컴팩트 카 모델 중에서 시장점유율 상위 9개 모델의 신차와 중고차를 대상으로 하였다. 실증분석을 통하여 비교 대상 모형보다 제안된 모형이 모형 적합도 측면에서 우월하고 예측타당성도 높다는 것을 보여주었다. 제안된 모형으로 부터 추정된 모수를 사용하여 몇 가지 시나리오를 상정하여 시뮬레이션을 실시한 결과, 신차(중고차)가 점유율을 높이고자 리베이트를 실시할 경우 중고차(신차)는 현재의 시장점유율을 유지하기 위해 대응 가격할인을 실시하게 되는데 할인 폭은 반대의 경우에 비해 높다는(낮다는)점을 확인하였다. 또한 시뮬레이션 결과가 시사하는 바는 신차와 중고차가 함께 경쟁하는 시장에서 IIA(Independence of Irrelevant Alternatives)모형을 적용할 경우 동일모델의 신차와 중고차간의 교차 탄력성을 과소평가하게 되어 현상유지를 위한 가격할인을 실시할 경우 적정한 수준이하로 하게 된다는 것이다.