• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.187-194
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• 2010

As the design of the pillar width (PW) of the parallel tunnels in downtown area, in which are located in plains zone with deep alluvium compared with mountain tunnels, is directly related with pre-compensation payment and costs of the underground area, it has to be planned as to keep minimum distance while securing the stability of the parallel tunnels. Although PW of downtown road tunnel in Korea is standardized as 1.5D(D: diameter of the tunnels), PW sometimes has to be reduced within 1.5D to adjust the tunnel lines to the city plan in the cases of the inlet and outlet of the tunnels. In this paper, the design and the analyses of optimum PW of the NATM type road tunnel in the downtown area are introduced. The relationship among the tunnel line planning and underground compensation fee, and ground characteristics are evaluated. In the determination of PW distance, the numerical analyses of underground road tunnels were performed, including the use of the strength decrease method and strength/stress ratio method. In the cases of inlet and outlet part of the tunnels where the stability of the pillars is poor due to contiguous construction of the parallel tunnels, the reinforcement methods are recommended for securing the stability. Numerical verification was performed for the reinforcement proposed.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.131-149
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• 2008

A transmission tower was designed according to general and special load cases based on KEPCO Design Specifications. The special load case such as unbalanced load a cording to some broken wires has not been considered significantly. Therefore, this paper presents investigations on the stability and safety of main post members subjected to unbalanced load and design wind load. In this study, all cases totally considered. From the finite element analyses using LUSAS program, the stresses on the tower subjected to unbalanced load and design wind load were very high in comparison to the allowable stresses of the steel post member that was used. Some of the post member had higher stresses than the yield stress of the steel member. This paper also shows an example to improve the capacity of the post members using increased cross-section members. Based on the analyses results, when investigating the safety of the transmission tower, one must consider thenew design philosophy including ultimate strength of the member and reliability of the special loading cases.

• Journal of Biomedical Engineering Research
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• v.24 no.6 s.81
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• pp.515-522
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• 2003

Pharynx is a system transporting foods by peristaltic motion(contraction and expansion movement! into the esophagus and functioning as airway passages. In this study, structural changes of pharyngeal dysfunction are analyzed by biomechanical model using CT and FEM(finite clement method). Loading condition was assumed that equal pressure was loaded sequentially to inside of pharyngeal tissue. In order to analyze the pharyngeal muscular dysfunction by biomechanical model. the pharyngeal dysfunctions was classified into 3 cases. Taking into account the clinical complication by neuromuscular symptoms such as pharyngeal dysfunction after stroke. we assumed that a change of material property is caused by muscular tissue stiffness. A deformation of cross sectional area of the pharynx is analyzed increasing the stiffness $25\%,\;50\%,\;75\%$ in each case on the basis of stress-strain relationship. Based on three-dimensional reconstruction of pharyngeal structure using limited factor - techniques and the optimization procedure by means of inverse dynamic approach. the biomechanical model of the human pharynx is implemented. The results may be used as clinical index illustrating the degree of pharyngeal muscular dysfunction. This study may be used as useful diagnostic model in discovering early deglutitory impediment caused by physiological or pathological pharyngeal dysfunction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.302-307
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• 2016

The technology of multistage deep drawing has been widely applied in the metal forming industry, in order to reduce both the manufacturing cost and time. A battery can used for mobile phone production is a well-known example of multistage deep drawing. It is very difficult to manufacture a battery can, however, because of its large thickness to height aspect ratio. Furthermore, the production of the final parts may result in assembly failure due to springback after multistage deep drawing. In industry, empirical methods such as over bending, corner setting and ironing have been used to reduce springback. In this study, a bottoming approach using the finite element method is proposed as a practical and scientific method of reducing springback. Bottoming induces compression stress in the deformed blank at the final stroke of the punch and, thus, has the effect of reducing springback. Different cases of the bottoming process are studied using the finite element program, DYNAFORM, to determine the optimal die design. The results of the springback simulation after bottoming were found to be in good agreement with the experimental results. In conclusion, the proposed bottoming method is expected to be widely used as a practical method of reducing springback in industry.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.475-481
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• 2018

In this study, the safety and effectiveness of ope cutter, developed to prevent frequent accident propeller windingness at sea. First, we calculated the bolt strength of the three types of rope cutting devices used in the experiment and the torsional stresses on the shafting system theoretical equation and the finite element method. As a result, the bolts used in the rope cutter confirmed from the viewpoint of safety life design and fail safe design. Also, safety satisfactory because of the small effect on the shaft system when locking up. Experiments were carried out to cut ropes and fishing nets from the sea using the ships equipped with three types of rope cutters verified to be safe. As a result, ropes of 20 to 50 mm in thickness were generally cut. It was found that the cutting efficiency of a rope cutter attached to shafting decreased when cutting thick ropes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.230-236
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• 2018

Earthquakes over 5.0 on the Richter scale have recently occurred in Korea, which has led to interest in the seismic safety of structures. If a water storage facility is damaged by an earthquake, the water could leak, and the insufficient water would make fire suppression difficult. Therefore, a water storage facility should satisfy safety requirements for earthquakes. In this study, the seismic performance of a water tank was improved by installing a lead rubber bearing between the foundation and the tank. It designed the lead rubber bearing available to the existed concrete foundation. ANSYS was used for modeling to consider the interaction between the fluid and structure of the tank and the hydrostatic and hydrodynamic pressure using four seismic waves. In the case of hydrostatic pressure at 2.5 water level, full level, the same stress appeared irrespective of whether the seismic isolation was installed. When hydrostatic pressure and hydrodynamic pressures are applied at the same time, the seismic-isolated water tank showed less seismic force, and the damping ratio was lower than that of general seismic isolation. This occurred because the weight of the water tank is much smaller than the stiffness of the seismic isolation. The result is expected to be used for further research on seismic capacity evaluation for water tanks.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.41-46
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• 2018

The wireless sensor network system has the advantage of confirming the behavior of the entire facility by improving the disadvantages of conventional monitoring system. As a result, it is widely proposed as safety diagnosis and measurement of structures, water management systems, and management systems for dam structures. However, there is a lack of research that can evaluate the condition of facilities such as safety at the same time as monitoring. In this study, it is proposed a wireless sensor network system which can evaluate the behavior characteristics of facilities and evaluate the safety status for improving the technical disadvantages on conventional monitoring system. The geotechnical risk factors for the reservoir dam facility were evaluated and the limit values for the risk factors causing the failure of the facility were set. In other words, the system was set up so that the risk factors can be measured and the limit status can be evaluated immediately for each factor. In this study, numerical analysis is carried out for seepage and slope stability analysis using the typical cross section for reservoir dams. The stress-porewater coupling finite difference numerical analysis is performed for establishing the limit displacement for reservoir dam structures. It is developed a system that can estimate the time to reach the critical value by regression analysis using the measured datas.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.20-26
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• 2019

Where hydraulic structures are to be installed over the entire width of a river or stream, usually a bed protection structure is to be installed. However, a local scour occurs in which the river bed downstream of the river protection system is eroded due to the influence of the upstream flow characteristics. This local scour is dominant in the flow and turbulence characteristics at the boundary of the flow direction and in the material of the bed materials, and may gradually become dangerous over time. Therefore, in this study, we compared the turbulence patterns in the local scour hole at the downstream of the river bed protection with the results of the analysis of the mobile bed experiment, and compared with the application of OpenFoam, a three dimensional numerical analysis model. The distribution of depth-averaged relative turbulence intensities along the flow direction was analyzed. In addition to this result, the stabilization of scour hole was compared with the bed shear stress and Shields parameter, and the results were compared by changing the initial turbulent flow conditions. From the results, it was confirmed that the maximum depth of generation of the three-stage was dominantly developed by the magnitude of depth-averaged relative turbulence intensity rather than the mean flow velocity. This result also suggests that design, construction or gate control are needed to control the depth-averaged relative turbulence intensities in order to reduce or prevent the local scour faults that may occur in the downstream part of the bed protection.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.593-601
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• 2021

The axial fan is an element of a blower used for ventilation in various industrial fields. Many studies on aerodynamic performance have been conducted to assess axial fans using fluid dynamics. The subject was a large axial fan size, 1800 mm in diameter with 100 horsepower. The blower's axial fan consisted of blades, hubs, hub caps, and bosses are important components. The blade design has a great influence on the aerodynamic performance. 3D point data is extracted using an aerodynamic performance prediction program, and a 3D modeling shape is generated. The blades and hubs, which are important components, can be easily modified if processed by cutting owing to the environment in which blades and hubs are manufactured through die casting or gravity casting. In this study, the structural safety of components and the analysis results of weak areas at the rated operating speed of the axial fan were verified using the maximum stress and safety factor. The tip clearance reflected in the design was the rotation of the blade. To check whether there is interference with other components, the displacement result was derived to verify the structural safety of the axial fan.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.77-84
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• 2021

In this study, flexural tests of prestressed high strength spun concrete (PHC) piles reinforced with infilled concrete and longitudinal rebars were conducted, where the longitudinal rebar ratio and the presence of sludge formed on the inner surface of PHC pile were set as key test variables. A total of six PHC pile specimens were manufactured, and their flexural behaviors including failure mode, crack pattern, longitudinal strain distribution in a section and end slip between external PHC pile and infilled concrete were measured and discussed in detail. The test results revealed that the flexural stiffness and strength increased as the longitudinal rebar ratio became larger, and that the sludge formed on the inner surface of PHC pile did not show any detrimental effect on the flexural performance. In addition to the experimental approach, this study presents a nonlinear flexural analysis model considering compatibility conditions and strain and stress distributions of the PHC piles and infilled concrete. The rationality of the nonlinear flexural analysis model was verified by comparing it with test results, and it appeared that the proposed model well evaluated the flexural behavior of PHC piles reinforced with infilled concrete and longitudinal rebars with a good accuracy.