• Title, Summary, Keyword: modified stability number

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The application of simplified risk assessment for tunnel (터널 리스크 평가 기법의 적용성에 대한 연구)

  • Kim, Sang-Hwan;Lee, Chung-Hwan
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.9 no.1
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    • pp.63-74
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    • 2007
  • Unexpected ground conditions have always been a major problem for the construction of tunnel. Therefore, it is necessary to evaluate the risk capacity before and/or during construction of new tunnel. This paper presents the simplified risk assessment system using modified stability number (N), namely Underground Risk Index (URI) system, to evaluate the tunnel risk possibility in the design stage. URI is a scoring system for risk possibility by rating the each appraisal elements. The modified stability number (N) which is one of risk factor in the Interaction Matrix parameters such as RQD, UCS, weathering, overburden, stability number, ground water-table, RMR, permeability and so on, is used in the system. In addition, the case study is performed in order to verify the applicability of URI-system in practice.

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독립모달공간 제어기법에서 작동기 수의 절감에 대한 연구

  • 황재혁;김준수;박명호
    • Journal of KSNVE
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    • v.7 no.2
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    • pp.273-279
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    • 1997
  • Reduction of number of actuators for independent modal space control In this paper, a new modified independent modal space control (IMSC), which relaxes the fundamental hardware limitation of IMSC, is suggested to handle the vibration and attitude control problem for flexible large structures. This method has adapted a new switching algorithm between controlled modes and a novel design technique for modal control force. The main advantage of this method is to minimize the discontinuity of the modal control forces and to assure the asymptotic stability of the closed-loop systems. This process is shown to be simple and efficient in a realistic example of vibration control of a cantiloever beam. It has been found that the modified IMSC suggested in this paper, which can reduce the number of actuators, is highly excellent compared to other previous methods in terms of the performance and stability of the vibration control systems.

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Effect of coarse aggregates and sand contents on workability and static stability of self-compacting concrete

  • Mohamed, Sahraoui;Taye, Bouziani
    • Advances in concrete construction
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    • v.7 no.2
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    • pp.97-105
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    • 2019
  • In this paper, the workability and static stability were evaluated using a proposed test method. Workability and static stability represent a key property of self-compacting concrete (SCC) in fresh state. A number of standardized test methods were developed to assess these properties. However, no accelerated test method reliably predicts both workability and static stability of SCC. In the present work, a modified K-slump test method was developed to evaluate workability and static stability of SCC. In order to take implicit mixture variations of SCC constituents that can affect fresh SCC properties, a central composite design was adopted to highlight the effect of gravel to sand ratio (G/S), gravel 3/8 to gravel 8/15 ratio (G1/G2), water to cement ratio (W/C), marble powder to cement ratio (MP/C) and superplasticizer content (SP) on workability measured with slump and flow time (T50) tests and static stability measured with sieve stability test (Pi), segregation test index (SSI), Penetration test (Pd) and the proposed K-slump test (Km). The obtained results show that G/S ratio close to 1 and G1/G2 ratio close to 60% can be considered as optimal values to achieve a good workability while ensuring a sufficient static stability of SCC. Acceptable relationships were obtained between Slump flow, Pi, Pd and Km. Results show that the proposed K-slump test allow to assess both workability and static stability of fresh SCC mixtures.

Reduction of Number of Actuators for Independent Modal Space Control (독립모달공간 제어기법에서 작동기 수의 절감에 대한 연구)

  • 황재혁;김준수;박명호
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.166-174
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    • 1996
  • In this paper, a new modified independent modal space control(IMSC), which relaxes the fundamental hardware limitation of IMSC, is suggested to handle the vibration and attitude control problem for flexible large structures. This method has adapted a new switching algorithm between controlled modes and a novel design technique for modal control force. The main advantage of this method is to minimize the discontinuity of the modal control forces and to assure the asymptotic stability of the closed-loop systems. This process is shown to be simple and efficient in a realistic example of vibration control of a cantilever beam. It has been found that the modified IMSC suggested in this paper, which can reduce the number of actuators, is highly excellent compared to other previous methods in terms of the performance and stability of the vibration control systems.

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The Surgical Treatment of Acute Rupture of the Lateral Ligaments of the Ankle (급성 족관절 외측 인대 파열의 수술적 치료)

  • Lee, Keun-Il;Roh, Su-In;Choi, Ik-Su
    • Journal of Korean Foot and Ankle Society
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    • v.5 no.1
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    • pp.5-12
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    • 2001
  • Purpose: To find out the priority of which procedure has had a better outcome both clinically and radiographically between the two groups, one is treated by primary repair and the other by modified Brostr$\ddot{o}$m's procedure, by comparing the postoperative ankle joint stability and the patient's degree of satisfaction. Material and methods: 16 cases were taken into consideration whose number of severed ligaments were at least two or more of the lateral collateral ligaments of the ankle, and also were confirmed intraoperatively. Among them, 8 cases were treated with primary repair and the other 8 cases were treated with primary repair and the other 8 cases by modified Brostr$\ddot{o}$m's procedure. Results: There was no distinguishable difference for the patient's degree of satisfaction between the two procedures above mentioned. In 3 cases treated with primary repair, functional instability was observed. In case of postoperative ankle joint stability, 7 of 8 cases treated by modified Brostr$\ddot{o}$m's procedure has revealed increased joint stability. And 3 of 8 cases which were treated by primary repair have showed postoperative residual instability. Conclusion: Actually, the severed ligament can not maintain its normal strength though several months has elapsed, and possible residual instability could be remained. Therefore, it can be expected that modified Brostr$\ddot{o}$m's procedure also would be a .good method in obtaining suitable ankle joint stability as well as subtalar joint stability because of its reinforcement using extensor retinaculum.

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The wave stability of the nonparallel natural convection flows adjacent to an inclined isothermal surface submerged in water at $4degC$ ($4degC$ 물에 잠겨있는 경사진 등온 벽주위 비평행 자연대류의 파형 안정성)

  • 황영규;장명륜
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.644-653
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    • 1991
  • A wave instability problem is formulated for natural convection flows adjacent to a inclined isothermal surface in pure water near the density extremum. It accounts for the nonparallelism of the basic flow and temperature fields. Numerical solutions of the hydrodynamic stability equations constitute a two-point boundary value problem which are accurately solved using a computer code COLSYS. Neutral stability results for Prandtl number of 11.6 are obtained for various angles of inclination of a surface in the range from-10 to 30 deg. The neutral stability curves are systematically shifted toward modified Grashof number G=0 as one proceeds from downward-facing inclined plate(.gamma.<0.deg.) to upward-facing inclined plate (.gamma.>0.deg.). Namely, an increase in the positive angle of inclination always cause the flows to be significantly more unstable. The present results are compared with the results for the parallel flow model. The nonparallel flow model has, in general, a higher critical Grashof number than does the parallel flow model. But the neutral stability curves retain their characteristic shapes.

A Modified Method for the Boundary Fitted Coordinate Systems to Analysis of Gas Bearings Considering Upstream In Extremely High Compressibility Number Region

  • Khan, Polina;Hwang, Pyung;Park, Sang-Shin
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.105-106
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    • 2002
  • An expanded scheme of direct numerical solution method for solving the Reynolds' equation in the boundary fitted coordinate systems for the gas lubrication with ultra low clearance is presented. Skewed slider is calculated by this scheme and results are compared to the original direct numerical solution. The modified scheme has advantages in stability in high compressibility number region. At the lower A region the difference in results of original and modified method is several percents.

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Evaluation of Atmospheric Stability Classification Methods for Practical Use (대기안정도 분류방법의 평가 및 실용화에 관한 연구)

  • 김정수;최덕일;최기덕;박일수
    • Journal of Korean Society for Atmospheric Environment
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    • v.12 no.4
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    • pp.369-376
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    • 1996
  • Major atmospheric stability classification methods were evaluated with meteorological data obtained by scoustic sounding profiler (SODAR/RASS) in Seoul. The Psequill classificatio method, the method most widely used because of its good agreement in respect of synoptic scope under the steady state, fails to describe the time lag, the response time on stability by heating or cooling caused by daily insolation or noctrunal surface radiation. Horizontal and vertical standard deviation of wind fluctuation $(\sigma_A and \sigma_E)$ method tend to classify night-time stable condition (E, F class) into unstable condition (A, B class). The classification matrix tables for Vogt's vertical temperature difference and wind speed using method ($\Delta$T $\cdot$ U) and bulk Richardson number (Rb) were amended for practical use over Seoul. The modified tables for $\Delta$T $\cdot$ U and Rb method were made by using comprehensive frequency distribution from Pasquill's method and other existing results, and the correlation coefficient(r) was equal to 0.829. It was confirmed that atmospheric stability could be changed with monitoring site characteristics, height and vertical difference between sensors of monitoring station, and classification method itself.

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Effects of pH and Gamma Irradiation on the Physicochemical Properties of Corn Starch

  • Kang, Il-Jun;Chung, Cha-Kwon;Sohn, Jeong-In
    • Preventive Nutrition and Food Science
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    • v.4 no.3
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    • pp.175-179
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    • 1999
  • To develop a production method for modified starches with less pollution, pH adjustment and gamma irradiation were applied to commerical corn starch. Blue values were significantly decreased , while alkali number, optical transmittance and solubility markedly increased when gamma irradiation was applied to pH 2 adjusted corn starch. Water binding capacity and swelling power at pH 5 were the highest among the samples. Gelatinization viscosity was considerably affected by gamma irradiation and pH of the starch. Gamma irradiation of pH 2 adjusted starch showed the lowest peak viscosity and the best cooling stability among the tested samples . Therefore, the production of modified starch with low viscosity as well as with sufficient viscosity stability seems feasible by controlling the pH of the starch and gamma irrdiation.

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Numerical stability and parameters study of an improved bi-directional evolutionary structural optimization method

  • Huang, X.;Xie, Y.M.
    • Structural Engineering and Mechanics
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    • v.27 no.1
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    • pp.49-61
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    • 2007
  • This paper presents a modified and improved bi-directional evolutionary structural optimization (BESO) method for topology optimization. A sensitivity filter which has been used in other optimization methods is introduced into BESO so that the design solutions become mesh-independent. To improve the convergence of the optimization process, the sensitivity number considers its historical information. Numerical examples show the effectiveness of the modified BESO method in obtaining convergent and mesh-independent solutions. A study of the effects of various BESO parameters on the solution is then conducted to determine the appropriate values for these parameters.