• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.111-117
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• 2018

In this study, an MEMS thrust measurement system was designed and a study on the performance prediction of system was performed to evaluate the performance of micro thruster. Thrust measurement system consists of beam, membrane, and piezoresistive sensor. An FEM analysis was carried out to verify the stability of the system, confirm the stress variation at the beam, and position the piezoresistive sensor. The stability of the designed system was verified by comparing the yield strength of the material with the maximum stress. The piezoresistive sensor was designed to be 20% of the length of the beam to obtain a high gauge factor. The size of the membrane and the beam of the reference model were designed to be $15mm{\times}15mm$, and $500{\mu}m{\times}500{\mu}m$, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1D
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• pp.11-15
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• 2010

It is necessary to improve transfer impedance of Urban Rail Station station users in order to increase the usage of public transportation. This study constructed a model for calculating transfer impedance based on bodily sensational transfer time in Urban Rail Station stations and calculated transfer impedance on major Urban Rail Station stations in Korea. The study results show that the addition of 100 meter exterior walking distance increases 2 minute travel time, 100 meter interior walking distance increases 3 minute travel time, 100 stairways increase 4 minute travel time, and escalators decreases 1 minute travel time. The calculated transfer impedance based on bodily sensational transfer time in this study can be utilized as objective criteria to compare transfer conditions of different Urban Rail Station stations and to prioritize them for facility improvement. The calculated transfer impedance also can be used as facility guidelines for designing a new transit center.

• The Journal of Engineering Geology
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• v.7 no.2
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• pp.139-149
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• 1997

Electrical resistivity monitoring methods were adopted to detect groundwater table change in alluvium. Numerical modelling test using finite element method(FEM) and field resisfivity monitoring were conducted in the study. The field monitoring data were acquired in the alluvium deposit site in Jeong-Dong Ri, Geum River where pumping test had been conducted continuously for 20 days to make artificial changes of groundwater table. The unit distance of the electrode array was 4m and 21 fixed electrodes were applied in numerical calculation and field data acquisition. "Modified Wenner" and dipole-dipole array configurations were used in the study. The models used in two-dimensional numerical test were designed on the basis of the simplifving geological model of the alluvium in Jeong Dong Ri, Geum River. Numerical test results show that the apparent resistivity pseudosections were changed in the vicinity of the pootion where groundwater table was changed. Furthermore, there are some apparent resistivity changes in the boundary between aquifer and crystalline basement rock which overlays the aquifer. The field monitoring data also give similar results which were observed in numerical tests. From the numerical test using FEM and field resistivity monitoring observations in alluvium site of Geum River, the electrical monitoring method is proved to be a useful tool for detecting groundwater behavior including groundwater table change. There are some limitations, however, in the application of the resistivity method only because the change of groundwater table does not give enough variations in the apparent resistivity pseudosections to estimate the amount of groundwater table change. For the improved detection of groundwater table changes, it is desirable to combine the resistivity method with other geophysical methods that reveal the underground image such as high-resolution seismic and/or ground penetrating radar surveys.

• Geophysics and Geophysical Exploration
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• v.5 no.4
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• pp.236-249
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• 2002

We have extended the three-dimensional (3-D) resistivity imaging algorithm to cover the 3-D resistivity tomography problem, where resistivity data are acquired using electrodes installed in several boreholes as well as at the earth surface. The imaging algorithm consists of the 3-D finite element forward modeling and least-squares inversion scheme, where the ACB (Active Constraint Balancing) is adopted to enhance the resolving power of the inversion. Sensitivity analysis with numerical verifications shows that 3-D resistivity tomography is a very appealing method and can be used to get 3-D attitude of subsurface structures with very high-resolution. Moreover, we could accurately handle the topography effect, which could cause artifacts in the resistivity tomography. In the application of 3-D resistivity tomography to the real field data set acquired at the quarry mine, we could derive a very reasonable and accurate image of the subsurface.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.353-362
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• 2004

Prediction of fragmentation in bench blasting is one of the most important factors to establish the production plan. It is widely accepted that fragmentation could be accurately predicted using the Kuz-Ram model in bench blasting. Nevertheless, the model has an ambiguous or subjective aspect in evaluating the model parameters such as joint condition, rock strength, density, burden, explosive strength and spacing. This study proposes a new method to evaluate the parameters of Kuz-Ram model, and the predicted mean fragment sizes using the proposed method are examined by comparing the measured sizes in the field. The results show that the predictions using Kuz-Ram model with the proposed method coincide with field measurements, but Kuz-Ram model does not reflect the in-situ rock condition and hence needs to be improved.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.367-374
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• 2012

A dynamic simulation and test of frame with thin walled closed section beams considering warping conditions have been performed. When a beam is subjected under torsional moment, the cross section will deform an warping as well as twist. For some thin-walled sections warping will be large, and accompanying warping restraint will induce axial and shear stresses and reduce the twist of beam which stiffens the beam in torsion. This paper presents that an warping restraint factor in finite element model effects the behavior of beam deformation and dynamic mode shape. The computer modelling of frame is discussed in linear beam element model and linear thin shell element model, also presents a correlation between computer predicted and actual experimental results for static deflection, natural frequencies and mode shapes of frame.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.377-388
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• 2010

The flexural behavior of composite HSB600 and HSB800 I-girders under a positive moment was investigated using the material non-linear moment-curvature analysis method. Three representative composite sections with different ductility properties were selected as the baseline sections in this study. Using these baseline sections, the moment-curvature program was verified by comparing the flexural strength and the moment-curvature curve obtained from the program with those obtained using the non-linear FE analysis of ABAQUS. In the FE analysis, the composite girders were modeled three-dimensionally with flanges, the web, and the concrete slab as thin shell elements, and initial imperfections and residual stresses were imposed on the FE model. In the moment-curvature and FE analyses, the 28-day compressive strength of the concrete slab was assumed to be 30-50 MPa, and the HSB600 and HSB800 steels were modeled as elasto-plastic strain-hardening materials, with the concrete as the CEB-FIP model. The effects of the ductility ratio of the composite girder, the type of steel, the compressive strength of the concrete deck, and the location of the plastic neutral axis on the flexural characteristics were analyzed.

• Journal of Korean Society of Transportation
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• v.20 no.6
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• pp.69-80
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• 2002

차로변경이 발생하는 두 가지 상황 즉, 강제 차로 변경과 선택적 차로 변경 중, 선택적 차로변경 상황에서 운전자가 수락 가능한 간격을 발견했을 때, 차로별 속도 차가 차로 변경 의사결정에 미치는 영향을 모사할 수 있는 모형식을 추정하였다. 즉, 선택적 차로 변경은 운전자의 차로 변경 여부에 대한 상황판단과 함께 목적 차로의 간격 수락여부에 대한 의사결정으로 이루어지는데, 본 논문에서는 목적 차로에 수락 가능한 간격이 존재할 경우 차로별 속도차가 운전자의 의사결정에 어떤 영향을 미치는지에 대해 분석하였다. 이를 위해, 운전자 의 의사결정에 영향을 미칠 수 있는 다른 요소 즉, 중차량, 기하구조, 및 합·분류의 영향을 최소화하는 지점을 선택하여 표본조사를 실시하였으며, 보다 설명력 있는 모형식을 얻기 위해 상관분석 등을 수행하여 불필요하다고 생각되는 변수는 제외시켰다. 또한, 운전자의 희망속도와 주행 속도 차에 의한 영향을 반영하기 위해 현 차로 속도를 부가적인 변수로 추가하였으며, 계수추정은 통계패키지인 SAS를 이용하였는데, 자료분석에 있어, 속도차 구간에 따라 다른 간격수락 특성을 보여 차로별 속도차를 0∼2.0m/s구간과 2∼11.52m/s구간으로 나누어 분석을 수행하였다. 분석결과 속도차 0∼2.0m/s구간에서는 속도차가 증가할수록 차로 변경률이 높아졌으나, 2∼11.52m/s구간에서는 오히려 차로 변경률이 낮아지는 것으로 나타났는데, 이는 속도 차의 증감에 대해 운전자로 하여금 차로 변경을 유도하는 요소와 함께 저항하게 하는 요소가 있다는 것을 알 수 있었다. 분석결과. 2.0m/s 이상의 속도차에서 차로변경에 대한 저항이 상대적으로 크게 작용한다는 것을 알 수 있었으며, 도로 설계시 이를 반영하여 도로기하구조 및 안전성 등을 향상시킬 수 있을 것으로 보인다.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.255-263
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• 2006

In an electrical tomographic survey using an inclined borehole with a pole-dipole array, we must consider several factors: a singular point associated with zero potential difference, a spatial discrepancy between electrode and nodal point in a model due to a inclined borehole, and a variation of geometric factors in connection with a irregular topography. Singular points which are represented by the normal distance from current source to the ground surface can be represented by serveral regions due to a irregular topography of ground surface. The method of element division can be applied to the region in which the borehole is curved, inclined or the distance between the electrodes is shorter than that of nodal points, because the coordinate of each electrode cannot be assigned directly to the nodal point if several electrodes are in an element. Test on a three-dimensional (3-D) synthetic model produces good images of conductive target and shoves stable convergence.

• Journal of The Korean Society For Urban Railway
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• v.6 no.4
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• pp.417-426
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• 2018

Piezoelectric shunt is an electric type damper capable of reducing the vibration of the structure. Vibration generated at the natural frequency of the structure are converted into electrical energy through the piezoelectric material attached to the structure. Electric energy can be dissipated by thermal energy using piezoelectric shunt composed of inductor and resistance to reduce vibration. In this paper, the equation for the optimum inductance required to reduce the vibration of the cantilever beam was examined and the vibration of the aluminum cantilever was reduced by using finite element analysis and experiments. In the finite element analysis, the mode shape and the strain energy distribution were calculated to examine the mounting position, and the vibration reduction of the cantilever was calculated by adjusting the inductance and resistance circuit values. In addition, in the experiment, a variable inductor module was used to reduce the vibration occurring at a specific frequency of the cantilever. Finally, based on the results of the finite element analysis and the experiment, it was verified that the piezoelectric shunt can effectively reduce the vibration of the cantilever.