• Composites Research
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• v.35 no.3
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• pp.196-200
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• 2022

Split Hopkinson Pressure Bar (SHPB) is a general test equipment for measuring the mechanical properties of high modulus metal and composite materials at high strain rate. However, for the soft plastic material, it is difficult to hold the specimen and achieve dynamic stress equilibrium due to the weak transmitted signals. In this study, SHPB test apparatus were designed to measure accurately the high strain rate stress-strain curve of the soft plastic materials by changing the incident bar materials and the shape of the specimen holder parts. In addition, to verify the high strain-rate tensile strain data obtained from SHPB, the strain distribution of the specimen was measured and analyzed with a high-speed camera and the digital image correlation (DIC), which was compared with the strain history measured from SHPB.

• Structural Engineering and Mechanics
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• v.81 no.6
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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.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.518-518
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• 2023

자연하천에서 오염물질의 혼합 거동은 비균일한 지형학적 요인으로 인해 매우 복잡한 특성을 나타낸다. 일반적으로 오염물질 거동 모델링에서는 수체에서의 혼합을 Fick의 법칙에 따라 유속에 의한 이송과 난류에 의한 확산으로 계산하고, 국부적인 정체현상 등에 의한 non-Fickian 혼합을 야기하는 하천의 특성을 기하학적 지형 형상으로 구현하여 실제 현상에 근접한 혼합 거동을 재현한다. 하지만 계산의 효율성을 위하여 모델링의 차원을 낮추는 경우, 하천의 지형을 경계조건으로 고려할 수 없게 된다. 특히, 1차원 모델링의 경우 하천의 비균일성을 무시하고 1개의 유선으로 간주하며, 이 경우 non-Fickian 물질이동 해석을 위한 추가적인 현상학적 해석이 필요하다. 지난 50년간, non-Fickian 물질이동 해석을 위한 다양한 현상학적 모형이 제시되어 왔다. 하천을 흐름영역과 정체영역으로 구분하고 두 개의 영역 사이의 물질교환 속도를 모델링하거나, Random walk 개념으로 물질이 이동하는 경우와 이동하지 않는 경우를 확률론적으로 모델링하거나, 물질이 정체되었을 때 다시 빠져나오는 시간을 모델링하는 경우가 그 예이다. 본 연구에서는 선행연구에서 제시한 음함수 형태의 현상학적 모형을 기반으로, 수치적 반복계산 없이 상류 경계에서 임의의 형태의 농도곡선(shape-free breakthrough curve)을 갖는 오염물질운(cloud)이 일정 거리를 유하하며 발생하는 변화를 예측할 수 있는 해를 제시한다. 본 연구의 방법론은 추적법(routing procedure)을 활용한 Fickian 혼합 해석, 전달함수(transfer function) 형태의 정체시간분포 해석, 그리고 라플라스 도메인에서의 해석해 유도를 포함한다. 본 연구에서 제시된 해는 2020년 경상북도 김천시에 위치한 감천의 4.5 km 구간에서 수행한 추적자 실험의 현장 자료를 통해 정확도를 검증하여 타당성을 입증하였다.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.5
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• pp.84-94
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• 1996

In order to prevent shell sticking by providing sufficient lubrication between the strand and the mold, the mold oscillation has been used. Now it is well known that the shape of the oscillation curve has a decisive effect on the surface quality of the cast product. Besides, oscillation parameters such as stroke and frequency are also very important. In order to guarantee that parameters which have been found to be optimal for a certain grade of steel do not change with time, periodical checks of the physical condition of the whole equipment are necessary. The portable mold oscillation analyzer with integrated computer, developed by POSCO, records the movement of the mold in every spatial direction. The system uses the gap sensors to measure the mold movement (displacement ) in the two horizontal directions according to the mold narrow and broad faces and the vertical strokes in the four corners of mold. The gap sensor is a non-contacting minute displacement measuring device using the principle of high frequency eddy current loss. The mold oscillation diagnosis system integrates the gap sensors, their converters and the industrial portable computer with plug-in data acquisition boards. The all programs, such as the fast Fourier transformation module (amplitude and phase spectrums) and harmonic analysis module, was coded by LabVIEW$^{TM}$ software as the graphical language. In an own 'expert module' which is included in the diagnosis program, one can obtain much information about the mold oscillation equipment.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4244-4252
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• 2022

The accuracy of Monte Carlo (MC) simulations in estimating the computed tomography radiation dose is highly dependent on the accuracy of CT scanner model. A system was developed to observe the 3D model intuitively and to calculate the X-ray energy spectrum and the bowtie (BT) filter model more accurately in Monte Carlo N-particle (MCNP). Labview's built-in Open Graphics Library (OpenGL) was used to display basic surfaces, and constructive solid geometry (CSG) method was used to realize Boolean operations. The energy spectrum was calculated by simulating the process of electronic shooting and the BT filter model was accurately modeled based on the calculated shape curve. Physical data from a study was used as an example to illustrate the accuracy of the constructed model. RMSE between the simulation and the measurement results were 0.97% and 0.74% for two filters of different shapes. It can be seen from the comparison results that to obtain an accurate CT scanner model, physical measurements should be taken as the standard. The energy spectrum library should be established based on Monte Carlo simulations with modifiable input files. It is necessary to use the three-segment splicing modeling method to construct the bowtie filter model.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.101-106
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• 2009

In this study we analyzed the seepage characteristics of meandering section of rivers commonly seen in domestic terrain. The seepage analysis is designed to be more realistic by considering a tangent and meandering section of levee. The levee was idealized to reflect the relevant characteristics by considering the curved angle of 90 degrees and 130 degrees in the spatial frequencies, water elevation conditions, and hydraulic conductivities. Seepage analysis becomes more detailed and precise with the seepage curve shape which is interpreted to indicate the flow of three-dimensional numerical analysis program using VisualFEA. As a result of the analysis, it is shown that the water level in the straight levee was constant, regardless of hydraulic conductivities, and the total head in the meandering section was increased by the overlapping of seepage. Consequently, it is found that the total head was increased more significantly in the case of 90 degrees curved levees than 130 degrees, and the total head showed similar characteristics In the straight levee.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.3
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• pp.121-127
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• 2023

When high carbon steel is heated in an appropriate austenizing temperature range and subjected to austempering, the size and shape of lamellar structure can be controlled. The high carbon steel sheet having the pearlite structure has excellent elastic characteristics because it has strong restoring force when properly rolled, and is applied in a process known as patenting-process using lead bath. In the case of isothermal treatment using lead-medium, it is possible to quickly reach a uniform temperature due to high heat transfer characteristics, but it is difficult to replace it with process technology that requires treatment to remove harmfulness lead. In this study, we intend to develop fluidization technology using garnet powder to replace the lead medium. After heating the high-carbon steel, the cooling rate was changed by compressed air to the vicinity of the nose of the continuous cooling curve, and then maintained for 90 s and then exposed to room temperature. The microstructure of the treated specimens were analyzed and compared with the existing products treated with lead bath. The higher the flow rate of compressed air, the faster the cooling rate to the pearlite transformation temperature, so lamellar spacing decreases and the hardness tends to increase.

• The Korean Journal of Pain
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• v.36 no.2
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• pp.208-215
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• 2023

Background: To evaluate the feasibility, inter-reader reliability, and intra-reader reliability for various morphological features reported to be related to iliotibial band friction syndrome (ITBFS) on knee magnetic resonance imaging (MRI). Methods: A total of 145 patients with a clinical diagnosis and knee MRI findings consistent with ITBFS were included in the "study group" and 232 patients without knee pathology on both physical examination and MRI were included in the "control group". Various morphologic features on knee MRI were assessed including the patella shape, patella height, lateral epicondyle anterior-posterior (AP) width, lateral epicondyle height, ITB diameter (ITB-d), and ITB area (ITB-a). Results: Patients in the study group had significantly higher lateral epicondyle height (13.9 mm vs. 12.92 mm, P = 0.003), ITB-d (2.9 mm vs. 2.0 mm, P = 0.022), and ITB-a (38.5 mm² vs. 23.8 mm², P < 0.001) than the control group. ITB-a showed higher area under the curve index (0.849 with 74.1% sensitivity and 72.4% specificity at a 30.3 mm² cutoff) than ITB-d (0.710 with 70.8% sensitivity and 61.2% specificity at 2.4 mm cutoff) and lateral epicondyle height (0.776 with 72.4% sensitivity and 67.8% specificity at 13.4 mm cutoff). However, only the inter-reader agreement for ITB-a (intraclass correlation coefficient = 0.65) was moderate, while the agreements for other morphologic features were good or excellent. Conclusions: Lateral epicondyle height seems to be a reliable and feasible morphologic feature for diagnosis of ITBFS.

• Journal of the Korea Convergence Society
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• v.13 no.1
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• pp.189-199
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• 2022

While modern illustration designs require originality, the shape and color of marine life provide rich materials for illustration creation. Illustration has a very high artistic creation value. Based on the knowledge of color science and visual form design, this study takes illustration design and marine biology as the main research object. The purpose of this study is: ① The typical features of Marine life are sorted by color and form. ② Lead out graphic symbols representing Marine life. ③ Combine Marine life with illustration design to make design cases. Through research, it is highlighted that the curve feature is a typical feature for distinguishing marine organisms from terrestrial organisms. The classification and comparative analysis of the color phenomena of tropical fish help to extract and process the color of marine tropical fish on the basis of understanding the color characteristics of tropical fish, and apply it to the illustration design.

• Steel and Composite Structures
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• v.42 no.5
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• pp.617-631
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• 2022

To study the eccentric compressive performance of the basalt-fiber reinforced recycled aggregate concrete (BFRRAC)-filled circular steel tubular stub column, 8 specimens with different replacement ratios of recycled coarse aggregate (RCA), basalt fiber (BF) dosage, strength grade of recycled aggregate concrete (RAC) and eccentricity were tested under eccentric static loading. The failure mode of the specimens was observed, and the relationship curves during the entire loading process were obtained. Further, the load-lateral displacement curve was simulated and verified. The influence of the different parameters on the peak bearing capacity of the specimens was analyzed, and the finite element analysis model was established under eccentric compression. Further, the design-calculation method of the eccentric bearing capacity for the specimens was suggested. It was observed that the strength failure is the ultimate point during the eccentric compression of the BFRRAC-filled circular steel tubular stub column. The shape of the load-lateral deflection curves of all specimens was similar. After the peak load was reached, the lateral deflection in the column was rapidly increased. The peak bearing capacity decreased on enhancing the replacement ratio or eccentric distance, while the core RAC strength exhibited the opposite behavior. The ultimate bearing capacity of the BFRRAC-filled circular steel tubular stub column under eccentric compression calculated based on the limit analysis theory was in good agreement with the experimental values. Further, the finite element model of the eccentric compression of the BFRRAC-filled circular steel tubular stub column could effectively analyze the eccentric mechanical properties.