• Wind and Structures
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• 제25권3호
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• pp.301-328
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• 2017

Multivariate fluctuating pressures acting on a 2:1 rectangular section (2-D) with dimensions of 9 cm by 4.5 cm has been studied using wind tunnel experiments under uniform and smooth flow condition for various angles of wind incidence. Based on the variation of mean pressure coefficient distributions along the circumference of the rectangular section with angle of wind incidence, and with the aid of skin friction coefficients, three distinct flow regimes with two transition regimes have been identified. Further, variations of mean drag and lift coefficients, Strouhal number with angles of wind incidence have been studied. The applicability of Universal Strouhal number based on vortex street similarity of wakes in bluff bodies to the 2:1 rectangular section has been studied for different angles of wind incidence. The spatio-temporal correlation features of the measured pressure data have been studied using Proper Orthogonal Decomposition (POD) technique. The contribution of individual POD modes to the aerodynamic force components, viz, drag and lift, have been studied. It has been demonstrated that individual POD modes can be associated to different physical phenomena, which contribute to the overall aerodynamic forces.

• 한국터널공학회:학술대회논문집
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• 한국터널공학회 2005년도 학술발표회 논문집
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• pp.270-281
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• 2005

An especial attention for old tunnel safety is required on increasing of The various tunnel recently. Specially, the lining investigation method of the old tunnel will be able to presume condition of concrete lining indirectly. Because it is many restriction thought of environment and ground condition investigation method of tunnel lining rear. This study carried out section & convergence measurement of part which was deformed in tunnel lining. It had been observed for the change of tunnel behavior with a continuous measurement. It has been analyzed for a cause of tunnel deformation and inspected for the effect after a repair-reinforcement to tunnel compared with the effect before those by structure analysis. By establishing automatic measurement system after repair-reinforcement to tunnel, it would be accomplished to convergence measurement continually. As a result, it was observed that deflection and deformation of tunnel was convergent. but it should be followed to a continuous maintenance because of unstable ground condition, cause of inner tunnel, environment. The railroad tunnel which was executed a reinforcement of the tunnel lining must investigate the close condition of reinforcement lining and concrete lining.

• Geomechanics and Engineering
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• 제15권5호
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• pp.1039-1046
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• 2018

This paper presents a limit analysis of the series of construction stages of shallow tunneling method by investigating their respective safety factors and failure mechanisms. A case study for one particular cross-section of Beijing Subway Line 7 is undertaken, with a focus on the effects of multiple soil layers and construction sequencing of dual tunnels. Results show that using the step-excavation technique can render a higher safety factor for the excavation of a tunnel compared to the entire cross-section being excavated all at once. The failure mechanisms for each different construction stage are discussed and corresponding key locations are suggested to monitor the safety during tunneling. Simultaneous excavation of dual tunnels in the same cross-section should be expressly avoided considering their potential negative interactions. The normal and shear forces as well as bending moment of the primary lining and locking anchor pipe are found to reach their maximum value at Stage 6, before closure of the primary lining. Designing these struts should consider the effects of different construction stages of shallow tunneling method.

• 한국전산유체공학회지
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• 제1권1호
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• pp.134-141
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• 1996

Wall interference is one of the major obstacles to increase the model size and data accuracy. There have been many treatments for wall interference including interference correction and adaptive wall test section. Recently, two-flexible-walled adaptive wall test section is concluded adequate for three-dimensional test. But proper location of target line and pressure holes are critical to its success. In this study, a new adaptive algorithm which dispenses target line and dependency of pressure hole distribution is suggested. The wind tunnel and free air tests are simulated by the numerical computation of Euler equations. The optimum wall shape is achieved by two variable optimization which is composed of two base streamlines. The wall interference is reduced well in the optimized result which is not sensitive to the base streamlines.

• 한국지반신소재학회논문집
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• 제15권2호
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• pp.45-54
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• 2016

본 연구에서는 증가하는 도심지 정체와 신설터널 건설에 따른 여러 제약의 문제를 해소하는 방안으로 향후 국내에서 수요가 증가할 것으로 전망되는 대심도 지하도로를 복층터널로 건설시 본선 복층터널에서 단층터널로 분기가 되는 구간의 터널 거동과 본선과 분기터널간의 필라 안정성을 수치해석을 통하여 검토하였다. 이를 위해 본선터널과 분기터널의 이격거리를 본선터널의 직경(D)을 기준으로 0.1D부터 2.0D까지 변화하는 조건과 지반조건을 암반등급에 따라 1~5등급으로 변화하는 조건들에 대하여 유한요소해석을 수행하였으며, 터널의 전체적인 거동과 함께 그 결과를 기반으로 기존의 경험식 등을 이용한 안전율, 강도-응력비, 그리고 간섭체적비를 산정하여 굴착에 따른 안정성 영향을 검토하였다. 검토 결과 수치해석결과를 이용해 산정된 강도-응력비와 간섭체적비는 경험식을 이용한 방법에 비해 암반강도보다는 이격거리가 안정성에 더욱 크게 영향을 미침을 나타내었고, 그에 따라 본선과 분기터널의 이격거리가 0.7D 이하인 경우는 본선과 분기터널을 모자 형태의 하나의 대단면으로 시공하는 것이 안정성 측면에서 유리한 것으로 판단되었다.

• Archives of Plastic Surgery
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• 제45권5호
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• pp.474-478
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• 2018

While the success or failure of carpal tunnel release ultimately depends on the interplay of a wide array of factors, a broad understanding of the normal anatomy of the carpal tunnel accompanied by awareness of the possible variations of the individual structures that make up its contents is crucial to optimizing surgical outcomes. While anatomic variants such as extension of the flexor digitorum muscle bellies have been described as a cause of primary carpal tunnel syndrome (CTS), there have been no reports depicting its association with recurrent CTS following initially successful carpal tunnel release, a finding with potentially significant prognostic implications that can aid in operative planning. In such cases where muscle extension is identified preoperatively, careful debulking of the muscle belly may be beneficial in improving long-term surgical outcomes.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.33-37
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• 2003

This paper presents the characteristics of large-scale fading in a tunnel environment. The Ray-Launching Method has been used to analyze the characteristics of the tunnel. For a curved tunnel, The concept of RDN (Ray Density Normalization) is introduced in order to obtain more accurate results. For our purposes, the structure of tunnel is assumed to be either a straight or curved tunnel having rectangular cross-section. A large scale fading has been presented shown in several tunnel cases.

• International Journal of Aeronautical and Space Sciences
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• 제2권1호
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• pp.103-109
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• 2001

Productivity enhancement program of wind tunnel testing has begun at Korea Aerospace Research Institute Low Speed Wind Tunnel (KARI LSWT). A previous test record of a canard airplane model was adopted to examine the current status of wind tunnel testing efficiency. The time consumed to perform testing activities from the model preparation to data collection was broken down and the results were compared with those of the recent Boeing low speed test result. The efforts to improve the wind tunnel productivity consisted of the installation of mini crane underneath of test section, fabricating lift device for image fairings, model configuration changing rigs and the modifications of external balance system. Time reductions for changing strut interface platform and installation of image fairings. These effects showed more than 70% improvement over the previous test time. Integration of the new and modified systems will improve productivity of wind tunnel testing in KARI LSWT.

• Wind and Structures
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• 제12권5호
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• pp.413-424
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• 2009

A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.

• Earthquakes and Structures
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• 제17권4호
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• pp.411-424
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• 2019

In this study, a numerical model of a shield tunnel with an assembled segmental lining was built. The seismic response of the segmental lining of the section of the shield tunnel in Line 1 of the Chengdu Metro is analyzed as it passes through the interface of sand-cobble and mudstone layers. To do so, the node-stress seismic-motion input method was used to input the seismic motion measured during the 2008 Wenchuan earthquake, and the joint openings and dislocations associated with the earthquake action were obtained. With reference to the Ethylene-Propylene-Diene Monomer (EPDM) sealing gaskets used in the shield tunnels in the Chengdu Metro, numerical simulation was applied to analyze the contact pressure along the seepage paths and the waterproof property under different joint openings and dislocations. A laboratory test on the elastic sealing gasket was also conducted to study its waterproof property. The test results accord well with the numerical results and the occurrence of water seepage in the section of the shield tunnel in Line 1 of the Chengdu Metro during the 2008 Wenchuan earthquake was verified. These research results demonstrate the deformation of segmental joint under earthquake, also demonstrate the relationship between segmental joint deformation and waterproof property.