• 한국터널지하공간학회 논문집
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• 제10권1호
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• pp.49-57
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• 2008

라이닝 작용수압과 유입량은 지하수 수위 아래 혹은 하 해저터널 설계시 중요하게 고려되어야할 수리요소이다. 이 요소들은 수심, 심도, 수리경계조건의 영향을 받는다. 본 논문에서는 각 설계요소가 라이닝하중과 유입량에 미치는 영향을 수치해석적 도구를 이용하여 살펴보았다. 수심영향해석은 심도 30 m에 건설된 마제형 터널에 대하여 수심과 라이닝/지반 상대투수계수 비를 다양하게 변화시켜 조사하였고, 심도영향 해석은 수심 60 m의 터널에 대하여 심도 및 라이닝/지반 상대투수계수 비를 변화시켜 해석하였다. 해석결과 수리경계조건과 상관없이 수심 및 심도가 증가함에 따라 지반하중이 증가하였다. 이는 배수터널은 침투력의 영향으로, 비배수 터널은 정수압의 영향으로 수두가 증가함에 따라 지반하중이 증가함을 보여준 것이다. 수심, 심도의 증가에 따라 유입량은 선형적으로 증가하였으며, 라이닝/지반 상대투수계수비와 유입량관계는 펼쳐진 S자 곡선(stretched S-curve)형태로 나타남을 확인하였다.

• Geomechanics and Engineering
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• 제5권4호
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• pp.363-377
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• 2013

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size $900mm{\times}1200mm{\times}1000mm$ is used for conducting model tests. Bearing capacity factor $N_{\gamma}$ is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's $N_{\gamma}$ values. From the experimental investigations it is found that, as the depth of sand cushion below the footing ($D_{sc}$) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

• 한국기계가공학회지
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• 제17권5호
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• pp.30-36
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• 2018

Automotive fuel efficiency regulations and air pollution control are hot issues of recent years in the automotive industry. To solve these regulation problems, many studies are continuing to improve the transmission efficiency of transmissions. Tapered roller bearings are useful to improve the transmission efficiency in the recent automobile parts. The frictional losses in the tapered roller bearings are mainly composed of the rolling friction and the sliding friction, and are dependent upon the load, the lubrication, the rotation speed of bearings, and etc. In this paper, the operating conditions of the transmission are defined and then the power losses of each bearing are calculated. In addition, improvement options are suggested after identifying the design factors influenced much by the improvement effect of power loss under the operating conditions of each bearing. We compare the power losses of the entire transmission system due to bearing improvements by comparing the friction losses between the original design and the improved design. Lastly, it is shown that the calculated power losses are valid by comparing the test values and the theoretical values for the frictional torque characteristics of the original and improved bearings.

• International Journal of Control, Automation, and Systems
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• 제6권6호
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• pp.915-927
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• 2008

Networked control systems(NCSs) have gained increasing attention in recent years due to their advantages and potential applications. The network Quality-of-Service(QoS) in NCSs always fluctuates due to changes of the traffic load and available network resources. To handle the network QoS variations problem, this paper presents an intelligent scheduling control method for NCSs, where the sampling period and the control parameters are simultaneously scheduled to compensate the effect of QoS variation on NCSs performance. For NCSs with network-induced delays and packet dropouts, a discrete-time switch model is proposed. By defining a sampling-period-dependent Lyapunov function and a common quadratic Lyapunov function, the stability conditions are derived for NCSs in terms of linear matrix inequalities(LMIs). Based on the obtained stability conditions, the corresponding controller design problem is solved and the performance optimization problem is also investigated. Simulation results are given to demonstrate the effectiveness of the proposed approaches.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 C
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• pp.1344-1346
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• 1995

The interrupting capability of gas circuit breakers(GCB) are critically dependent on the pressure rise of the puffer cylinder or the thermal expansion chamber at current zero. Therefore it's very useful for the designers to know the pressure rise there at the design stage. Much effort has been done to predict the pressure rise in the puffer cylinder or the thermal expansion chamber in no-load condition. Thus, we now calculate it with reasonable accuracy with the simple programs coded by ourselves or with the commercial CFD packages. However, it has been still difficult problem to calculate it under the existence of arc. In this paper, we propose a method which can be used to predict the pressure rise in the thermal expansion chamber of thermal expansion type GCB. The method has been applied to the 25.8kV 25kA thermal expansion type model GCB and the calculated results have been compared with those from experiment.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1533-1538
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• 2011

The dynamic characteristics such as resonant frequencies and dampings have been utilized as important parameters in dynamic behavior and inverse analyses. In general, the dynamic parameters have been determined based on design and experimental data, but experimental studies on the time-dependent changes of the dynamic parameters during service have rarely been conducted. Especially, unlike highway bridges, it is much easier for railroad bridges to estimate accumulated amount of fatigue because of the controlled train operation, and the study of dynamic characteristic change due to fatigue is useful, since it can enhance the accuracy of dynamic analysis. In this paper, the dynamic characteristic change due to fatigue is measured via the modal test on the PSC girder during a fatigue test. The test specimen utilized in the test is the IT girder which enhances the sectional capacity of the conventional PSC girders. The test specimen is designed 10m long and the modal tests are conducted during the application of fatigue load two million times. The test result shows that considerable changes in the measured dynamic parameters are observed as the fatigue accumulates, and these changes during the service life should be considered in designing railroad bridges.

• Structural Engineering and Mechanics
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• 제24권4호
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• pp.463-478
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• 2006

The design of structural frameworks for buildings is constantly evolving and is dependent on regional issues such as loading and constructability. One of the most promising recent developments for low to medium rise construction in terms of efficiency of construction, robustness and aesthetic appearance utilises concrete-filled steel tubular sections as the columns in a moment-resisting frame. These are coupled to rigid or semi-rigid connections to composite steel-concrete beams. This paper includes the results of a pilot experimental programme leading towards the development of economical, reliable connections that are easily constructed for this type of frame. The connections must provide the requisite strength, stiffness and ductility to suit gravity loading conditions as well as gravity combined with the governing lateral wind or earthquake loading. The aim is to develop connections that are stiffer, less expensive and easier to construct than those in current use. A proposed fabricated T-stub connection is to be used to connect the beam flanges and the column. These T-stubs are connected to the column using "blind bolts" with extensions, allowing installation from the outside of the tube. In general, the use of the extensions results in a dramatic increase in the strength and stiffness of the T-stub to column connection in tension, since the load is shared between membrane action in the tube wall and the anchorage of the bolts through the extensions into the concrete.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.122-127
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• 2001

As pipelines are often used to transport gas, oil, water and oil products, there are more than one pipeline installed in the offshore field. The size and space of pipelines are various depending on the design specifications. The pipelines are to be designed and installed to secure the stability to external loads during the installation and operation period. The flow patterns are very complex around the pipelines being dependent on incoming flow velocity, pipelines size and space. To investigate the flow patterns, number of experiment are conducted with visualization equipment in a circulating water channel. The flow motion and trajectory were recorded from the laser reflected particles by camera. From the experiment the flow patterns around spaced pipelines were obtained. Also pressure gradient was measured by mano-meter to estimate the hydrodynamic forces on the behind pipeline. The results show that the various sizes and spaces can be affected in the estimation of external load. The complex flow patterns and pressure gradients can be effectively used in the understanding of flow motion and pressure gradient.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.179-181
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• 2003

Conventional P/PI speed controller of today's servo drives should be manually tuned the controller switching set-point by trial-and-errors, which may translate the drive system down-time and loss of productivity. The adjustable drive performance is heavily dependent on the qualify of the expert knowledge and becomes inadequate in applications where the operating conditions change in a wide range, i.e., tracking command, cceleration/deceleration time, and load disturbances. In this paper, the demands on simple controls/setup are discussed for industry servo drives. Analyzing the frequency content of motor torque command, P/PI control mode switching is automatically peformed with some prior knowledge of the mechanical dynamics. The dynamic performance of the proposed scheme assures a desired tracking response curve with minimal oscillation and settling time over the whole operating conditions. For comprehensive comparison of traditional P/PI control scheme, extensive test is carried out on actual servo system.

• Wind and Structures
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• 제7권3호
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• pp.145-158
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• 2004

The evaluation of the accumulation of permanent set for inelastic structures due to wind action is important in establishing a criterion to select a reduced design wind load and in incorporating the beneficial ductile behaviour in wind engineering. A parametric study of the accumulation of the permanent set as well as the ductility demand for bilinear single-degree-of-freedom (SDOF) systems is presented in the present study. The dynamic analysis of the inelastic SDOF system is carried out using the method of Newmark for artificially generated time history of wind speed. Simulation results indicate that the mean of the normalized damage rate is highly dependent on the natural frequency of vibration. This mean value is relatively insensitive to the damping ratio if the damping ratio is larger than 5%. The scatter associated with the accumulation of the permanent set is very significant. The consideration of the postyield stiffness can significantly reduce the accumulation of the permanent set if the ratio of the yield strength to the expected peak response is small. The results also show that the ductility demand due to the wind action over a period of one hour for flexible structures can be much less than that for rigid structures or structures with larger damping ratio if the SDOF systems are designed with a reduced peak response caused by the fluctuating wind.