• Journal of Korea Society of Industrial Information Systems
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• v.24 no.2
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• pp.15-23
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• 2019

High temperature superconducting (HTS) generators for wind power systems are attractively researched with the advantages of high efficiency and smaller size compared with conventional generator. However, the HTS generators have high Lorentz force problem, which acts on HTS field coils due to their high current density and magnetic field. This paper deals with characteristic analysis of the modularized HTS field coil for a 750 kW superconducting wind power generator according to field coil structure. The modularized HTS field coil structure was designed based on the electromagnetic and mechanical analysis results obtained using a 3D finite element method. The electromagnetic force of the module coil was also analyzed. As a result, the perpendicular and maximum magnetic fields of the HTS coils were 2.5 T and 3.9 T, respectively. The maximum stress of the supports was less than the allowable stress of the glass-fiber reinforced plastic material, and displacement was within the acceptable range. The design specifications and the results of the HTS module coil structure can be effectively utilized to develop large-scale superconducting wind power generators.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.21-32
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• 2020

As the global large-scale infrastructure construction market expands, the construction of civil engineering structures in extreme environments such as cold or hot regions is being planned or constructed. Accordingly, the construction of the pile foundation is essential to secure the bearing capacity of the upper structure, but there is a concern about loss of stability and function of the pile foundation due to the possibility of ground deformation in extreme cold and hot regions. Therefore, in this study, a new type of pile foundation is developed to respond with the deformation of the ground, and the ground deformation that can occur in extreme cold and hot region is largely divided into heaving and settlement. The new type of pile foundation is a form in which a cylinder capable of shrinkage and expansion is inserted inside the steel pipe pile, and the effect of the cylinder during the heaving and settlement process was analyzed numerically. As a result of the numerical analysis, the ground heaving caused excessive tensile stress of the pile, and the expansion condition of the cylinder shared the tensile stress acting on the pile and reduced the axial stress acting on the pile. Ground settlement increased the compressive stress of the pile due to the occurrence of negative skin friction. The cylinder must be positioned below the neutral point and behave in shrinkage for optimum efficiency. However, the amount and location of shrinkage and expansion of cylinder must comply with the allowable displacement range of the upper structure. It is judged that the design needs to be considered.

• Journal of the Korean Geotechnical Society
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• v.23 no.9
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• pp.5-16
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• 2007

The simple linear elastic-perfectly plastic model with soil parameters $s_u,\;E_u$ and n of undrained condition is usually applied to predict the displacement of a constructed diaphragm wall(DW) on soft soils during excavation. However, the application of this soil model for finite element analysis could not interpret the continued increment of the lateral displacement of the DW for the large and deep excavation area both during the elapsed time without activity of excavation and after finishing excavation. To study the characteristic behaviors of soil behind the DW during the periods without excavation, a series of tests on soft Bangkok clay samples are simulated in the same manner as stress condition of soil elements happening behind diaphragm wall by triaxial tests. Three kinds of triaxial tests are carried out in this research: $K_0$ consolidated undrained compression($CK_0U_C$) and $K_0$ consolidated drained/undrained unloading compression with periodic decrement of horizontal pressure($CK_0DUC$ and $CK_0UUC$). The study shows that the shear strength of series $CK_0DUC$ tests is equal to the residual strength of $CK_0UC$ tests. The Young's modulus determined at each decrement step of the horizontal pressure of soil specimen on $CK_0DUC$ tests decreases with increase in the deviator stress. In addition, the slope of Critical State Line of both $CK_0UC$ and $CK_0DUC$ tests is equal. Moreover, the axial and radial strain rates of each decrement of horizontal pressure step of $CK_0DUC$ tests are established with the function of time, a slope of critical state line and a ratio of deviator and mean effective stress. This study shows that the results of the unloading compression triaxial tests can be used to predict the diaphragm wall deflection during excavation.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.85-93
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• 2021

The seventy percentage of Korean Peninsular is covered by the mountainous area, and the depth of west sea and south sea is relatively shallow. Therefore, a large scale land reclamation from the sea has been implemented for the construction of industrial complex, residental area, and port and airport facilities. The common problem of reclaimed land is consisted of soft ground, and hence it has low load bearing capacity as well as excessive settlement upon loading on the ground surface. The hollow concrete block has been used to reinforce the loose and soft foundation soil where the medium-high apartment or one-story industrial building is being planned to be built. Recently the earthquakes with the magnitude of 4.0~5.0 have been occurred in the west coastal and southeast coastal areas. Lee (2019) reported the advantages of hollow concrete block reinforced shallow foundation through the static laboratory bearing capacity tests. In this study, the dynamic behavior of hollow concrete block reinforced sandy ground with filling the crushed stone in the hollow space has been investigated by the means of shaking table test with the size of shaking table 1000 mm × 1000 mm. Three types of seismic wave, that is, Ofunato, Hachinohe, Artificial, and two different accelerations (0.154 g, 0.22 g) were applied in the shaking table tests. The horizontal displacement of structure which is situated right above the hollow concrete block reinforced ground was measured by using the LVDT. The relative density of soil ground are varied with 45%, 65%, and 85%, respectively, to investigate the effectiveness of reinforcement by hollow block and measured the magnitude of lateral movement, and compared with the limit value of 0.015h (Building Earthquake Code, 2019). Based on the results of shaking table test for hollow concrete block reinforced sandy ground, honeycell type hollow block gives a large interlocking force due to the filling of crushed stone in the hollow space as well as a great interface friction force by the confining pressure and punching resistance along the inside and outside of hollow concrete block. All these factors are contributed to reduce the great amount of horizontal displacement during the shaking table test. Finally, hollow concrete block reinforced sandy ground for shallow foundation is provided an outstanding reinforced method for medium-high building irrespective of seismic wave and moderate accelerations.

• Archives of Plastic Surgery
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• v.38 no.6
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• pp.783-790
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• 2011

Purpose: The zygoma (Zygomaticomaxillary) complexes make up a large portion of the orbital floor and lateral orbital walls. Zygoma fracture frequently causes the posteromedial displacement of bone fragments, and the collapse or overlapping of internal orbital walls. This process consequently can lead to the orbital volume change. The reduction of zygoma in an anterolateral direction may influence on the potential bone defect area of the internal orbital walls. Thus we performed the quantitative analysis of orbital volume change in zygoma fracture before and after operation. Methods: We conducted a retrospective study of preoperative and postoperative three-dimensional computed tomography scans in 39 patients with zygoma fractures who had not carried out orbital wall reconstruction. Orbital volume measurement was obtained through Aquarius Ver. 4.3.6 program and we compared the orbital volume change of injured orbit with that of the normal contralateral orbit. Results: The average orbital volume of normal orbit was 19.68 $cm^3$. Before the operation, the average orbital volume of injured orbit was 18.42 $cm^3$. The difference of the orbital volume between the injured orbit and the normal orbit was 1.18 $cm^3$ (6.01%) on average. After operation, the average orbital volume of injured orbit was 20.81 $cm^3$. The difference of the orbital volume between the injured orbit and the normal orbit was 1.17 $cm^3$ (5.92%) on average. Conclusion: There are considerable volume changes in zygoma fracture which did not accompany internal orbital wall fracture before and after operation. Our study reflects the change of bony frame, also that of all parts of the orbital wall, in addition to the bony defect area of orbital floor, in an isolated zygoma fracture so that it evaluates orbital volume change more accurately. Thus, the measurement of orbital volume in isolated zygoma fractures helps predict the degree of enophthalmos and decide a surgical plan.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.614-627
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• 2018

Urban railway lines have been constructed adjacent to residential buildings and urban areas. The expansion of transportation networks and reconstruction of residential buildings in highly populated urban areas require deep excavations in areas adjacent to urban railways. Mobilized soil stresses and changes in the groundwater level induced by deep excavations results in track irregularities in urban railways. In this study, a three-dimensional finite difference model using the commercial program FLAC3D was adopted to estimate the horizontal displacements of earth retaining structures, settlements of backfill, the stability of track irregularity and underground box structure based on the criteria of each railway organization and its relationships. In deep excavations, a change in groundwater level induces relatively very small differences for track gauge irregularities, whereas relatively large differences for longitudinal irregularities of 72.5%, twist irregularities of 83.3%, cross level irregularities of 61.9%, and alignments of 43.3% were found to be the maximum differences when the horizontal displacement of earth retaining wall and settlement of backfill were 65.1% and 21.4%, respectively, because the groundwater level (GWL) on the ground surface-mobilized tensile strength of the underground box structure exceeds the allowable value. Therefore, three-dimensional numerical analysis was performed in this study. Overall, real-time monitoring should be carried out to prevent railway accidents in advance when a deep excavation adjacent to urban railway structures is constructed.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.203-212
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• 2008

The cyclic behavior and energy dissipation mechanism of short coupling beams with various reinforcement layouts were studied. For numerical analysis of coupling beams, nonlinear truss model was used. The results of numerical analysis showed that the coupling beams with conventional reinforcement layout showed pinched cyclic behavior without significant energy dissipation, whereas the coupling beams with diagonal reinforcement exhibited stable cyclic behavior without pinching. The energy dissipation of the coupling beams was developed mainly by diagonal reinforcing bars developing large plastic strains rather than concrete which is a brittle material Based on this result, simplified equations for evaluating the energy dissipation of coupling beams were developed. For verification, the predicted energy dissipation was compared with the test results. The results showed that the simplified equations can predict the energy dissipation of short coupling beams with shear span-to-depth ratio less than 1.25 with reasonable precision, addressing various design parameters such as reinforcement layout, shear span-to-depth ratio, and the magnitude of inelastic displacement. The proposed energy equations can be easily applied to performance-based seismic evaluation and design of reinforced concrete structures and members.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.128-135
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• 2021

Thin-walled tubes have been widely used as energy absorbing devices because they are light and have high energy-absorption efficiency. However, the downside is that conventional thin-walled tubes usually exhibit an excessive initial peak crushing force (IPCF) and a large fluctuation in the load-displacement curve, and thus lack stability as energy absorbing devices. Corrugated tubes were introduced to reduce IPCF and to increase the stability of collision energy-absorbing devices. Since the performance of corrugated tubes is highly influence by geometry, design optimization methods can be utilized to optimize the performance of corrugated tubes. In this paper, we utilize shape design optimization based on an adaptive surrogate model for crashworthiness analysis. The amplitude and wavelength of the corrugation, as well as curvature changes in the features, are the design variables. A morphing methodology is adopted to perform shape design parameterization. Through numerical examples, we compare optimal design results based on the adaptive surrogate model, with optimal results based on conventional surrogate models, and we show that direct optimal design methods produce more efficient results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.175-181
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• 2019

In the case of a conventional single stage decompression regulator used for large depressurization in the hydrogen fuel cell system of a fuel cell electric vehicle (FCEV), problems can arise, such as pulsation, slow response, hydrogen brittleness, leakage, high weight, and high cost due to high decompression. Most of these problems can be overcome easily using two decompression mechanisms (two-stage structures). In addition, a wide outlet-pressure control range can be secured if an electronic solenoid is applied to the second decompression. Accordingly, it is necessary to improve the precision of the outlet pressure of a two-stage pressure-reducing regulator and develop techniques, such as leakage prevention, durability, light weight, and price reduction. Therefore, to improve the outlet pressure accuracy and prevent leakage, the structural part before and after decompression to improve the air tightness were divided and the analysis was carried out assuming that the valve part was closed (open ratio: 0%) after each initial internal pressure application.

• 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.