• Steel and Composite Structures
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• 제38권1호
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• pp.79-86
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• 2021

Due to the complex geological conditions, a large number of high quality coal seams was buried in the western of China which cannot be mining in open-pit methods. The dynamic properties of that coal cannot be studied easily in real site for the complex working condition. The compound coal blocks made on the basis of the real situation were studied in the laboratory. The physical and mechanical properties of the compound coal blocks and the raw coal were contrasted by using the UCS tests. The results show that the compound coal blocks made by mixing coal powder, cement and water in proportion of 2.5:2:1 are the closest to that of standard raw coal. Then the propagation of strain waves and crushing effects on the coal were studied in the compound coal blocks by using the super dynamic strain test system and the numerical calculated method of ANSYS/LS-DYNA. The results show that the diameter of the crushing zone in the compound coal blocks was similar to that in the numerical results. The fractures distribution in laboratory tests also has a similar trend to the calculation results. The measured strain waves at the distance of 50 cm, 100 cm, and 150 cm from the center of the charge are mainly concerned at -1.0×104 με and have a similar trend as that in the numerical simulation.

• 한국전산유체공학회지
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• 제21권2호
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• pp.70-80
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• 2016

The comparison of two commercial codes(FLUENT and STAR-CCM+) and an open-source code(OpenFOAM) are carried out for the aerodynamic analysis of flight vehicles at low speeds. Tailless blended-wing-body UCAV, main wing and propeller of HALE UAV(EAV-3) are chosen as geometries for the investigation. Using the same mesh, incompressible flow simulations are carried out and the results from three different codes are compared. In the linear region, the maximum difference of lift and drag coefficients of UCAV are found to be less than 2% and 5 counts, respectively and shows good agreement with wind tunnel test data. In a stall region, however, the reliability of RANS simulation is found to become poor and the uncertainty according to code also increases. The effect of turbulence models and meshes generated from different tools are also examined. The transition model yields better results in terms of drag which are much closer to the test data. The pitching moment is confirmed to be sensitive to the existence and the location of transition. For the case of EAV-3 wing, the difference of results with ${\kappa}-{\omega}$ SST model is increased when Reynolds number becomes low. The results for the propeller show good agreement within 1% difference of thrust. The reliability and uncertainty of three codes is found to be reasonable for the purpose of engineering use. However, the physical validity and reliability of results seem to be carefully examined when ${\kappa}-{\omega}$ SST model is used for aerodynamic simulation at low speeds or low Reynolds number conditions.

• 한국안전학회지
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• 제36권3호
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• pp.74-80
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• 2021

Korea Atomic Energy Research Institute (KAERI) has been operating an integral effects test facility, the Advanced Thermal-Hydraulic Test Loop for Accident Simulation (ATLAS), according to APR1400 for transient experimental and design basis accident simulation. Moreover, based on the experimental data, the domestic standard problem (DSP) program has been conducted in Korea to validate system codes. Recently, through DSP-05, the performance of the passive auxiliary feedwater system (PAFS) in the event of multiple steam generator tube rupture (MSGTR) has been analyzed. However, some errors exist in the reference input model distributed for DSP-05. Furthermore, the calculation results of the heat loss correlation for the secondary system presented in the technical report of the reference indicate that a large difference is present in heat loss from the target value. Thus, in this study, the reference model is corrected using the geometric information from the design report and drawings of ATLAS. Additionally, a new heat loss correlation is suggested by fitting the results of the heat loss tests. Herein, MSGTR-PAFS accident analysis is performed using MARS-KS 1.5 with the improved model. The steady-state calculation results do not significantly differ from the experimental values, and the overall physical behavior of the transient state is properly predicted. Particularly, the predicted operating time of PAFS is similar to the experimental results obtained by the modified model. Furthermore, the operating time of PAFS varies according to the heat loss of the secondary system, and the sensitivity analysis results for the heat loss of the secondary system are presented.

• Computers and Concrete
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• 제27권2호
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• pp.99-109
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• 2021

Experimental and discrete element methods were used to investigate the effects of echelon non-persistent joint on the failure behaviour of joint's bridge area under uniaxial compressive test. Concrete samples with dimension of 150 mm×100 mm×50 mm were prepared. Uniaxial compressive strength and tensile strength of concrete were 14 MPa and 1MPa, respectivly. Within the specimen, three echelon non-persistent notches were provided. These joints were distributed on the three diagonal plane. the angle of diagonal plane related to horizontal axis were 15°, 30° and 45°. The angle of joints related to diagonal plane were 30°, 45°, 60°. Totally, 9 different configuration systems were prepared for non-persistent joint. In these configurations, the length of joints were taken as 2 cm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increase by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.665-675
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• 2022

The safety problems of giant hydraulic structures such as dams caused by terrorist attacks, earthquakes, and wars often have an important impact on a country's economy and people's livelihood. For the national defense department, timely and effective assessment of damage to or impending damage to dams and other structures is an important issue related to the safety of people's lives and property. In the field of damage assessment and vulnerability analysis, it is usually necessary to give the damage assessment results within a few minutes to determine the physical damage (crack length, crater size, etc.) and functional damage (decreased power generation capacity, dam stability descent, etc.), so that other defense and security departments can take corresponding measures to control potential other hazards. Although traditional numerical calculation methods can accurately calculate the crack length and crater size under certain combat conditions, it usually takes a long time and is not suitable for rapid damage assessment. In order to solve similar problems, this article combines simulation calculation methods with machine learning technology interdisciplinary. First, the common concrete gravity dam shape was selected as the simulation calculation object, and XFEM (Extended Finite Element Method) was used to simulate and calculate 19 cracks with different initial positions. Then, an LSTM (Long-Short Term Memory) machine learning model was established. 15 crack paths were selected as the training set and others were set for test. At last, the LSTM model was trained by the training set, and the prediction results on the crack path were compared with the test set. The results show that this method can be used to predict the crack propagation path rapidly and accurately. In general, this article explores the application of machine learning related technologies in the field of mechanics. It has broad application prospects in the fields of damage assessment and vulnerability analysis.

• 한국지하수토양환경학회지:지하수토양환경
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• 제27권spc호
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• pp.99-112
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• 2022

From early 2000, many researchers in the groundwater and soil environment remediation project tried to calculate the pollution level and pollution remediation cost and reflect it in the design. In addition, by identifying the movement characteristics of oil pollutants in the underground environment, many researchers tried to derive design factors necessary for pollution purification. However, although the test should be conducted in an area contaminated with oil, the toxicity and risk are too great for testing by deliberately leaking pollutants that are harmful to the human body. And as oil-contaminated areas are promoted by military units such as returned US military bases, there is a limit to access by the general public. In addition, since the indoor simulation test and the field application test have been carried out separately from each other, it was difficult to compare and review various simulation tests Therefore, in this study, PITT (Partitioning Interwell Tracer Test) and analysis methods were specifically presented through actual tests so that field workers could easily use them with the help of the military base and the Korea Rural Community Corporation Soil Environment Restoration Team. However, in order to directly reflect the distribution tracer test results in the pollution remediation design, it is necessary to reduce the analysis errors by comparing the analysis results of the existing soil pollution survey, physical exploration, and numerical modeling. In addition, it is judged to be cautious in the analysis because errors can easily occur due to various factors such as the type of oil at the polluted site, the hydraulic conductivity of the aquifer, and the skill of the researcher.

• Journal of Radiation Protection and Research
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• 제48권4호
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• pp.167-174
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• 2023

Background: A nondestructive test is commonly used to inspect the surface defects and internal structure of an object without any physical damage. X-rays generated from an electron accelerator or a tube are one of the methods used for nondestructive testing. The high penetration of X-rays through materials with low atomic numbers makes it difficult to discriminate between these materials using X-ray imaging. The interaction characteristics of neutrons with materials can supplement the limitations of X-ray imaging in material discrimination. Materials and Methods: The radiation image acquisition process for air-cargo security inspection equipment using X-rays and neutrons was simulated using a GEometry ANd Tracking (Geant4) simulation toolkit. Radiation images of phantoms composed of 13 materials were obtained, and the R-value, representing the attenuation ratio of neutrons and gamma rays in a material, was calculated from these images. Results and Discussion: The R-values were calculated from the simulated X-ray and neutron images for each phantom and compared with those obtained in the experiments. The R-values obtained from the experiments were higher than those obtained from the simulations. The difference can be due to the following two causes. The first reason is that there are various facilities or equipment in the experimental environment that scatter neutrons, unlike the simulation. The other is the difference in the neutron signal processing. In the simulation, the neutron signal is the sum of the number of neutrons entering the detector. However, in the experiment, the neutron signal was obtained by superimposing the intensities of the neutron signals. Neutron detectors also detect gamma rays, and the neutron signal cannot be clearly distinguished in the process of separating the two types of radiation. Despite these differences, the two results showed similar trends and the viability of using simulation-based radiation images, particularly in the field of security screening. With further research, the simulation-based radiation images can replace ones from experiments and be used in the related fields. Conclusion: The Korea Atomic Energy Research Institute has developed air-cargo security inspection equipment using neutrons and X-rays. Using this equipment, radiation images and R-values for various materials were obtained. The equipment was reconstructed, and the R-values were obtained for 13 materials using the Geant4 simulation toolkit. The R-values calculated by experiment and simulation show similar trends. Therefore, we confirmed the feasibility of using the simulation-based radiation image.

• 한국전자파학회논문지
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• 제24권2호
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• pp.214-217
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• 2013

본 논문에서는 박막 필름의 유전율 측정이 가능한 슬랏을 갖는 도파관형 공진기를 제안하였으며, 시료에 의한 공진 주파수 천이 현상으로부터 유전율을 측정한다. 이를 위하여 공진기 한 쪽에 얇은 슬랏을 두고, 그 위에 부착된 시료에 의해 공진기 내부 전자기장 분포가 섭동되어 공진 주파수 천이 현상이 발생될 수 있도록 하였다. 유전율에 따른 공진 주파수 천이량은 수치 해석을 통하여 계산하였으며, 이를 기반으로 2~3 GHz 대역에서 $65{\mu}m$ 두께의 박막 필름 유전율을 측정하였다. 측정 결과, 유전율은 평균 $3.3492{\pm}0.0605$(표준오차)를 보였으며, 유전체 공진기나 도파관 프로브 방법과 같은 다른 측정법들과 상호 비교를 통해 제안 방법의 유효성을 검증하였다.

• 지구물리와물리탐사
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• 제19권4호
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• pp.187-199
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• 2016

연약지반의 층서 파악을 위해 대상 지역 전체에서 취득되는 다중채널 표면파 탐사(Multichannel Analysis of Surface Wave; MASW)와 지반에 대한 직접적인 정보를 제공하는 피에조콘 관입시험(Piezo Cone Penetration Test; CPTu) 자료를 지구통계학적으로 복합 분석하였다. MASW 자료는 지반 강성도와 밀접한 관계를 갖는 것으로 알려져 있는데, 2개의 측선에 대해 자료를 취득하고 연구 지역 시료의 실내시험을 통해 이를 확인하였다. CPTu는 대상지역 내 6개 지점에서 취득하였고 선단저항($q_c$) 및 간극수압(u) 자료에 지구통계학적 복합 분석을 적용하여 3차원 물성 분포를 확보하였다. 복합 분석은 MASW 자료와 선단저항 및 간극수압의 공간적 상관성에 따라 시뮬레이션 할 수 있는 순차 가우시안 공동 위치 시뮬레이션(Sequential Gaussian Co-Simulation; COSGSIM) 기술을 적용하였다. 분석 결과의 검증을 위해 CPTu 자료 취득 위치와 다른 2개 지점에서 시추가 이루어졌으며, 이 지점에서 SPT N 값과 시추 주상도를 확보할 수 있었고 이 자료를 복합 분석 결과의 지반 공학적 정확도 분석을 위해 사용하였다. 복합 분석을 통해 확보한 3차원 선단저항 및 간극수압 분포도의 신뢰성 검증을 위해 2개의 시추 지역에서 획득한 지반 조사 자료와 비교한 결과, 매우 상관성이 좋은 결과를 확인할 수 있었다.

• 한국콘텐츠학회논문지
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• 제15권9호
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• pp.21-28
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• 2015

반도체 공정에서는 소자 내부의 물리량 계산을 통해 불순물의 움직임을 해석하여 결점을 검출하는 시뮬레이션을 수행하게 된다. 이를 위해 유한 차분 시간 영역 알고리즘(Finite-Difference Time-Domain, 이하 FDTD)과 같은 수치해석 기법이 사용된다. 반도체 칩의 집적도 향상으로 인하여 소자의 크기는 나노스케일 시대로 접어들었으며, 시뮬레이션 사이즈 또한 커지고 있는 추세이다. 이에 따라 CPU와 GPU 같은 하나의 연산 장치에서 수행할 수 없는 문제와 다중의 연산 장치로 구성된 한 대의 컴퓨터에서 수행할 수 없는 문제가 발생하기도 한다. 이러한 문제로 인해 분산 병렬처리를 통한 FDTD 알고리즘 연구가 진행되고 있다. 하지만 기존의 연구들은 단일 연산장치만을 이용하기 때문에 GPU를 사용하는 경우 연산 속도는 빠르나 메모리의 제한이 있으며 CPU의 경우 GPU에 비해 연산 속도가 느린 단점이 존재한다. 이를 해결하기 위해 본 논문에서는 CPU, GPU의 이기종 연산 장치를 포함하는 컴퓨터로 구축된 클러스터 상에서 작업 사이즈에 제한되지 않고 시뮬레이션 수행이 가능한 컴퓨팅 모델을 구현하였다. 점대점 통신 기반의 MPI 라이브러리를 이용하여 연산 장치 간 통신을 통한 시뮬레이션을 테스트 하였고 사용하는 연산 장치의 종류와 수에 상관없이 시뮬레이션이 정상 동작함을 확인하였다.