• Computers and Concrete
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• 제5권2호
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• pp.117-134
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• 2008

An experimental and numerical research was conducted to gain a deeper insight on the structural behaviour of deep-beams with indirect supports and to assess the size effects in the ultimate state behaviour. The experimental campaign focused on the influence of the reinforcement tie distribution height on the compression check of the support region and on the benefits of using unbonded prestressing steel. Three reduced scale specimens were tested and used to validate the results obtained with a nonlinear finite element model. As a good agreement could be found between the numerical and the experimental results, the numerical model was then further used to perform simulations in large scale deep-beams, with dimensions similar to the ones to be adopted in a practical case. Two sources of size effects were identified from the simulation results. Both sources are related to the concrete quasi-brittle behaviour and are responsible for increasing failure brittleness with increasing structural size. While in the laboratory models failure occurred both in the experimental tests as well as in the numerical simulations after reinforcement yielding, the numerically analysed large scale models exhibited shear failures with reinforcement still operating in the elastic range.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2346-2351
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• 2008

This study deals with heat pipes inserted into the metal hydride(MH) reactor to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. A numerical analysis was conducted to predict the effect of inserted heat pipes on the heat transfer characteristics of MH, which inherently has extremely low thermal conductivity. The numerical model was a cylindrical container of O.D. 76.3 mm and length 1 m, which is partially filled with about 60% of MH material. The heat pipe was made of copper-water combination, which is suitable for operation temperature range between $10^{\circ}C$ and $80^{\circ}C$. Both inner -and outer- heat pipes were considered in the model. Less than two hours of transient time is of concern when decreasing or increasing the temperature for absorption and discharge of hydrogen gas. FLUENT, a commercial software, was employed to predict the transient as well as steady-state temperature distribution of the MH reactor system. The numerical results were compared and analyzed from the view point of temperature uniformity and transient time up to the specified maximum or minimum temperatures.

• 아동학회지
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• 제36권4호
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• pp.229-242
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• 2015

The purpose of this study was to investigate young children's nonsymbolic arithmetic ability according to task difficulty. The participants in this study comprised 43 2-year-old children and 48 4-year-old children recruited from 5 childcare centers located in Seoul, Korea. All tasks were composed of comparison, addition, subtraction, multiplication and division tasks. In addition, each arithmetic task varied with the ratio of the two quantities; low level(1:2), middle level(2:3), high level(4:5). The results revealed that 2 & 4-year-old children could perform a large numerical range of nonsymbolic arithmetic tasks without influences from previously learned mathematics. This finding suggests that children have a degree of numerical capacity prior to symbolic mathematics instruction. Furthermore, children's performance on nonsymbolic arithmetic tasks indicated the ratio signature of large approximate numerical representation. This result implies that large approximate numerical representation can be used in arithmetical manipulations.

• 대기
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• 제31권3호
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• pp.251-265
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• 2021

This study examined the impact of assimilating the bending angle (BA) obtained via the global navigation satellite system radio occultation (GNSS RO) of the three new satellites (KOMPSAT-5, FY-3C, and FY-3D) on analyses and forecasts of a numerical weather prediction model. Numerical data assimilation experiments were performed using a three-dimensional variational data assimilation system in the Korean Integrated Model (KIM) at a 25-km horizontal resolution for August 2019. Three experiments were designed to select the height and quality control thresholds using the data. A comparison of the data with an analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) integrated forecast system showed a clear positive impact of BA assimilation in the Southern Hemisphere tropospheric temperature and stratospheric wind compared with that without the assimilation of the three new satellites. The impact of new data in the upper atmosphere was compared with observations using the infrared atmospheric sounding interferometer (IASI). Overall, high volume GNSS RO data helps reduce the RMSE quantitatively in analytical and predictive fields. The analysis and forecasting performance of the upper temperature and wind were improved in the Southern and Northern Hemispheres.

• Geomechanics and Engineering
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• 제24권4호
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• pp.323-335
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• 2021

This paper aims to estimate the range of the excavation damaged zone (EDZ) formation caused by the tunnel boring machine (TBM) advancement through dynamic three-dimensional large deformation finite element analysis. Large deformation analysis based on Coupled Eulerian-Lagrangian (CEL) analysis is used to accurately simulate the behavior during TBM excavation. The analysis model is verified based on numerous test results reported in the literature. The range of the formed EDZ will be suggested as a boundary under various conditions - different tunnel diameter, tunnel depth, and rock type. Moreover, evaluation of the integrity of the tunnel structure during excavation has been carried out. Based on the numerical results, the apparent boundary of the EDZ is shown to within the range of 0.7D (D: tunnel diameter) around the excavation surface. Through series of numerical computation, it is clear that for the rock of with higher rock mass rating (RMR) grade (close to 1st grade), the EDZ around the tunnel tends to increase. The size of the EDZ is found to be direct proportional to the tunnel diameter, whereas the depth of the tunnel is inversely proportional to the magnitude of the EDZ. However, the relationship between the formation of the EDZ and the stability of the tunnel was not found to be consistent. In case where the TBM excavation is carried out in hard rock or rock under high confinement (excavation under greater depth), large range of the EDZ may be formed, but less strain occurs along the excavation surface during excavation and is found to be more stable.

• 한국군사과학기술학회지
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• 제20권1호
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• pp.55-62
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• 2017

For evaluating a large caliber ammunition tests, indoor ballistic test range is required to reduce the noise and fragments occurring during the test. To ensure the reliability of the indoor ballistics test range design, we carried out the analysis of the indoor test range using the AUTODYNE hydrodynamic code before its construction. The 120 mm tank ammunition is adopted as a reference model and we analysed the characteristics of the pressure distribution at fire area, the structure design at impact area, the over-pressure applied to the tunnel, and the sabot stopper design. The results of the analysis were applied to the design of the indoor ballistic test range.

• 전기전자학회논문지
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• 제22권2호
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• pp.309-315
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• 2018

계단 주파수 레이더(Stepped Frequency Radar: SFR)는 송신 펄스의 주파수를 점진적으로 증가시켜 넓은 합성 대역폭을 만듦으로써 높은 거리 해상도를 얻는 방식이다. 그런데 이동표적의 경우 거리-도플러 결합(range-Doppler coupling) 현상으로 정확한 거리 추정을 할 수 없게 되므로 정확한 속도 추정을 통한 보상이 필요하다. 본 논문에서는 코히어런트 펄스열(Coherent Pulse Train: CPT)을 갖는 계단 주파수 레이더 파형을 제안하고, 이를 이용한 속도 추정 및 파라미터에 따른 결과를 기존의 VMD(Velocity Measurement Data) 방식과 시뮬레이션을 통해 비교하고 분석하였다.

• 시스템엔지니어링학술지
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• 제19권1호
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• pp.107-113
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• 2023

For one-shot systems such as 81mm high-explosive ammunition, research on performance prediction is insignificant due to research manpower infrastructure and lack of interest and difficulties in securing field data, which can only be done by special task workers. In order to evaluate the actual range of ammunition, the storage ammunition reliability evaluation checks the range by firing actual ammunition through a functional test. Test evaluation is a method of extracting a sample from the population, launching it, and recording the results accordingly. As a result of these tests, the range, which is an indicator of ammunition performance, can be measured differently according to meteorological factors such as temperature, atmospheric pressure, and humidity according to the location of the test site. In this study, various environmental factors generated at the test site and storage period analyze the correlation with the range, which is the performance of ammunition, and analyze the priority of importance for each factor and the numerical standards that environmental factors affect range. Through this, a new approach to one-shot system performance prediction was presented.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.375-378
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• 1998

Scattering of TE waves by a periodic conducting surface with dielectric cover is considered. A method for the aalysis of scattering from periodic structures based on the numerical solution of the integral equations is further developed. Using periodicity (Floquet's theorem), the range of the integral equations is reduced to a single period where the kernels are the Green's functions for periodic arrays. The numerical solution of the intergral equations is obtained using the method of moments. From numerical results for the reflected power the effects of surface profile shape, period-to-depth ratio, and cover permittivity on the scattering behaviors are examined.

• 한국안전학회지
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• 제9권1호
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• pp.146-154
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• 1994

A series of numerical calculations are performed in order to investigate the dispersion mechanism of toxic gaseous and solid pollutants in extremely short-term and short range. The calculations are carried out in an open space characterized by turbulent boundary layer. The simulation is made by the use of numerical model, in which a control-volume based finite difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling problem. The Reynolds stresses are solved by two-equation, k-$\varepsilon$ model modified for buoyancy. The major parameters consider-ed in this study are temperature, velocity and Injection height of toxic gases, environmental conditions such as temperature and velocity of free stream air, and topographic factor. The results are presented and discussed in detail. The flow field is commonly characterized by the formation of a strong recirculation zone due to the upward motion of the hot toxic gas and ground shear stress. The driving force of the upward motion is explained by the effect of thermal buoyancy of hot gas and the difference of inlet velocity between toxic gas and free stream.