• 한국분무공학회지
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• 제16권2호
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• pp.82-89
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• 2011

When pipe components made of carbon steel in nuclear, fossil, and industry plants are exposed to flowing fluid, wall thinning caused by FAC(flow accelerated corrosion) can be generated and eventually ruptured at the position of pressure boundary. The aim of this study is to identify the locations at which local wall thinning occurs and to determine the turbulence coefficient related to local wall thinning. Experiment and numerical analyses for the tee sections of down scaled piping components were performed and the results were compared. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning inside tee components. In order to determine the relationship between turbulence coefficients and local wall thinning, numerical analyses were performed for tee components in the main feedwater systems. The turbulence coefficients based on the numerical analyses were compared with the local wall thinning based on the measured data. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.83-90
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• 2002

There are few earthquake records in Korea and the Japanese or American representative earthquake records have been generally used in the seismic design. In this study, some earthquake records which the range of earthquake magnitudes varies from 5.3 to 7.9 were collected and analyzed to assess which record can rationally reflect Korean seismic characteristics. In this assessment, each seismic energy and acceleration spectrum were analyzed with the unified maximum ground acceleration. Several numerical analyses on Korean representative caisson structures were also carried out to compare each dynamic displacement. In these numerical analyses, soil conditions and the dimension of structure such as height and width were changed. Through this assessment, it is found that the compatible earthquake magnitude in Korea is lower than 7. From the result of numerical analyses, it is shown that horizontal dynamic displacements corresponding to earthquake magnitudes over than 7 are quite larger than those below earthquake magnitude 7. Based on this study, it is necessary that Korean seismic design guideline will refer earthquake magnitude criteria for the construction of the economical aseismic structure.

• 산업기술연구
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• 제23권A호
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• pp.109-118
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• 2003

This paper is results of numerical works of investigating effects of horizontal drain arrangements on vacuum consolidation. Extensive numerical analyses were carried out to find the appropriate arrangements of horizontal drain of vacuum consolidation. Commercially available program of CRISP, well known to be good to modelling the behavior of clay material, was used Cam-clay model, based on the Critical State of Soil Mechanics(CSSM), was used to simulate the geotechnical engineering behavior of clay. Model test results carried out previously in the laboratory were compared with numerically estimated results and it was found that results about consolidational settlement with times were in good agreements. Based on this confirmation, parametric numerical study was performed to investigate effects of horizontal drain arrangements on vacuum consolidation with changing the vertical and horizontal spacings between drains for the given soil properties and vacuum. The effect of distance of drain located in top layer from the surface of the ground on the settlement due to vacuum was also investigated. As a results of numerical analyses, appropriate arrangements of horizontal drain to maximize the consolidation settlement due to vacuum were found. The mechanism of vacuum consolidation about the vacuum pressures being transferred to the effective stresses around drains was also evaluated.

• International Journal of Fluid Machinery and Systems
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• 제5권4호
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• pp.168-173
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• 2012

This paper presents a numerical investigation on the aerodynamic performance according to the application of splitter blades in an impeller of a centrifugal fan used for a refuse collection system. Numerical analysis of a centrifugal fan was carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. A validation of numerical results was conducted by comparison with experimental data for the pressure and efficiency. From analyses of the internal flow field of the reference fan, the losses by the reverse-flows were observed in the region of the blade passage. In order to reduce these losses and enhance fan performance, two splitter blades were applied evenly between the main blades, and centrifugal impellers having the different numbers of the main blades were tested with their application. Throughout the numerical analyses of the centrifugal fan with splitter blades, it was found that the reverse-flow regions in the blade passage can be reduced by controlling the main blade numbers with splitter blades. The application of splitter blades in a centrifugal fan leads to significant improvement in the overall fan performance.

• Geomechanics and Engineering
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• 제18권1호
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• pp.29-39
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• 2019

In this paper, it was presented an investigation on the load-settlement and vertical stress analysis of the ring footings on the loose sand bed by conducting both laboratory model tests and numerical analyses. A total of twenty tests were conducted in geotechnical laboratory and numerical analyses of the test models were carried out using the finite element package Plaxis 3D to find the ultimate capacities of the ring footings. Moreover, the results obtained from both foregoing methods were compared with theoretical results given in the literature. The effects of the ring width on bearing capacity of the footings and vertical stresses along the depth were investigated. Consequently, the experimental observations are in a very good agreement with the numerical and theoretical results. The variation in the bearing capacity is little when $r_i/R_o$ <0.3. That means, when the ring width ratio, $r_i/R_o$, is equal to 0.3, this option can provide more economic solutions in the applications of the ring footings. Since, this corresponds to less concrete consumption in the ring footing design.

• Earthquakes and Structures
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• 제23권1호
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• pp.13-21
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• 2022

Masonry constructions exhibit uncertain behaviors under dynamic effects such as seismic action. Complex issues arise in the idealization of structural systems of buildings having different material types and mechanical properties. In this study, the structural behavior of a vaulted masonry building constructed using full clay brick and lime-based mortar and sitting on consecutive arches was investigated by experimental and numerical approaches. The dimensions of the structure built in the laboratory were 391 × 196 cm, and its height was 234 cm. An incremental repetitive loading was applied to the prototype construction model. Along the gradually increasing loading pattern, the load-displacement curves of the masonry structure were obtained with the assistance of eight linear displacement transducers. In addition, crack formation areas, and relevant causes of its formation were determined. The experimental model was idealized using the finite element method, and numerical analyses were performed for the area considered as linear being under similar loading effect. From the linear analyses, the displacement values and stress distribution of the numerical model were obtained. In addition, the effects of tie members, frequently being used in the supports of curved load-bearing elements, on the structural behavior were examined. Consequently, the experimental and numerical analysis results were comparatively evaluated.

• Computers and Concrete
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• 제31권1호
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• pp.71-84
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• 2023

In this paper, the effects of the thickness of cubic samples on the tensile strength of concrete blocks were studied using experimental tests in the laboratory and numerical simulation by the particle flow code in three dimensions (PFC3D). Firstly, the physical concrete blocks with dimensions of 150 mm×190 mm (width×height) were prepared. Then, three specimens for each of seven different samples with various thicknesses were built in the laboratory. Simultaneously with the experimental tests, their numerical simulations were performed with PFC3D models. The widths, heights, and thicknesses of the numerical models were the same as those of the experimental samples. These samples were tested with a new tensile testing apparatus. The loading rate was kept at 1 kg/sec during the testing operation. Based on these analyses, it is concluded that when the thickness was less than 5 cm, the tensile strength decreased by increasing the sample thickness. On the other hand, the tensile strength was nearly constant when the sample thickness was raised to more than 5 cm (which can be regarded as a threshold limit for the specimens' thickness). The numerical outputs were similar to the experimental results, demonstrating the validity of the present analyses.

• 대한조선학회논문집
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• 제61권2호
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• pp.77-87
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• 2024

In the present study, seakeeping performance for an amphibious vehicle in regular head waves was analyzed and evaluated experimentally and numerically. First, seakeeping tests were performed to confirm the vehicle's motion response of heave, pitch motion and vertical acceleration in restricted wavelength ratio conditions for a simplified vehicle shape. Numerical analyses were also conducted for a simplified vehicle shape to validate the numerical solver. To simulate the vehicle's motions, multi-degrees of freedom were calculated by a dynamic fluid-body interaction solver in STAR-CCM+. Comparison between numerical and experimental results was carried out for a simplified vehicle shape. Numerical results are in good agreement with experimental results. Second, numerical analyses were performed for a detailed vehicle shape considering seaway wavelength conditions. The seakeeping performance for an amphibious vehicle was evaluated by comparing with the existing ship's seakeeping performance standards.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.800-807
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• 2010

In this study, a series of numerical analyses has been performed in order to evaluate the performance of a full-scale closed-loop vertical ground heat exchanger constructed in Wonju. The circulation pipe HDPE, borehole and surrounding ground were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the system. Two user-defined functions (UDFs) accounting for the difference in the temperatures of the circulating inflow and outflow water and the change of the surrounding ground temperature with depth were adopted in the FLUENT model. The thermal properties of materials estimated in laboratory were used in the numerical analyses to compare the thermal efficiency of the cement grout with that of the bentonite grout used in the construction. The results of the simulation provide a verification of the in situ thermal response test data. The numerical model with the ground thermal conductivity of 4W/mK yielded the simulation result closer to the in-situ thermal response test than with the ground thermal conductivity of 3W/mK. From the results of the numerical analyses, the effective thermal conductivities of the cement and bentonite grouts were obtained to be 3.32W/mK and 2.99 W/mK, respectively.

• 한국산학기술학회논문지
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• 제15권6호
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• pp.3916-3922
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• 2014

일반적으로 옹벽은 높이가 높아질수록 안정성이 작아진다. 하지만 선반식 옹벽은 선반 설치로 인하여 옹벽에 작용하는 수평토압의 크기가 감소하기 때문에 다른 옹벽과 비교하면 안정성 및 경제성에서 우수하다고 할 수 있다. 이 연구에서는 기존에 연구된 선반식 옹벽의 수치해석 연구에서와는 다르게 옹벽의 종류, 선반의 길이, 선반의 위치 등의 조건을 변화시켜 총 15가지의 해석 조건으로 수치해석을 실시하였다. 수치해석을 통해 얻은 결과를 비교하여 선반식 옹벽의 수평토압 감소효과를 확인하였고, 또한 모형시험의 결과와 이론해를 동시에 비교하여 수평토압의 감소효과를 확인하고자 하였다. 연구결과 선반식 옹벽은 캔틸레버식 옹벽에 비해 수평토압 감소효과가 뚜렷한 것으로 나타났고, 선반의 위치, 선반의 길이 등에 따라 수평토압의 크기가 영향을 받는 것으로 나타났다.