• Computers and Concrete
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• 제24권6호
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• pp.561-570
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• 2019

Understanding the realistic behavior of concrete up to failure under different loading conditions within the framework of damage mechanics and plasticity would lead to an enhanced design of concrete structures. In the present investigation, QR (Quick Response) code based random speckle pattern is used as a non-contact sensor, which is an innovative approach in the field of digital image correlation (DIC). A four-point bending test was performed on RC beams of size 1800 mm × 150 mm × 200 mm. Image processing was done using an open source Ncorr algorithm for the results obtained using random speckle pattern and QR code based random speckle pattern. Load-deflection curves of RC beams were plotted for the results obtained using both contact and non-contact (DIC) sensors, and further, Moment (M)-Curvature (κ) relationship of RC beams was developed. The loading curves obtained were used as input data for material model parameters in finite element analysis. In finite element method (FEM) based software, concrete damage plasticity (CDP) constitutive model is used to predict the realistic nonlinear quasi-static flexural behavior of RC beams for monotonic loading condition. The results obtained using QR code based DIC are observed to be on par with conventional results and FEM results.

• 한국지진공학회논문집
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• 제19권1호
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• pp.29-36
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• 2015

Base isolation is considered as a seismic protective system in the design of next generation Nuclear Power Plants (NPPs). If seismic isolation devices are installed in nuclear power plants then the safety under a seismic load of the power plant may be improved. However, with respect to some equipment, seismic risk may increase because displacement may become greater than before the installation of a seismic isolation device. Therefore, it is estimated to be necessary to select equipment in which the seismic risk increases due to an increase in the displacement by the installation of a seismic isolation device, and to perform research on the seismic performance of each piece of equipment. In this study, modified NRC-BNL benchmark models were used for seismic analysis. The numerical models include representations of isolation devices. In order to validate the numerical piping system model and to define the failure mode, a quasi-static loading test was conducted on the piping components before the analysis procedures. The fragility analysis was performed by using the results of the inelastic seismic response analysis. Inelastic seismic response analysis was carried out by using the shell finite element model of a piping system considering internal pressure. The implicit method was used for the direct integration time history analysis. In addition, the collapse load point was used for the failure mode for the fragility analysis.

• 한국지반공학회논문집
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• 제38권12호
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• pp.91-101
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• 2022

1995년 일본에서 발생한 고베지진으로 인하여 고베항에 대규모 피해가 발생하면서, 기존 내진설계 기준의 문제점이 제기됨에 따라 기존의 유사정적해석 및 허용응력 설계법으로는 Level II(규모 6.5) 수준의 지진에 대하여 항만 구조물 설계가 불가능한 사실이 지적되어 내진설계에 있어서 성능기반 설계법의 필요성이 대두되었다. 지진이 빈번한 일본 및 미국의 경우 항만시설에 대한 가장 선진화된 설계기준을 도입하여 적용하고 있으며, 기존 내진설계기준을 성능기반설계로 전환하였다. 1999년 이후 현재까지 국내 항만내진설계법은 내진설계가 필요한 시설과 이들의 내진등급에 대한 정의가 불명확한 점에 대해 연구를 통해 필요한 시설과 내진등급에 대한 정의를 확립하고 실험적 검증을 바탕으로 국내 실정에 부합한 성능기반 내진설계법을 확립하고 있는 단계이다. 본 연구에서 개발한 방파제의 성능기반 내진설계법은 원지반의 지표면에서의 가속도 시간이력을 고속 푸리에 변환(FFT) 후 방파제의 해당성능수준별 최대허용변위에 대응한 주파수 특성을 보정해주는 필터처리를 하였고, 필터 처리된 스펙트럼을 다시 가속도 시간이력으로 역변환(IFFT) 하여 가속도 최대값을 산정함으로써 변위를 고려한 등가정적해석을 위한 수평지진계수를 산정하였다. 또한 국내 지진 수준에 맞는 방파제의 성능기반 내진설계법의 검증을 위해서 실험과 수치해석을 수행하였다.

• 열처리공학회지
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• 제36권5호
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• pp.311-317
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• 2023

An autofilter is a device that removes impurities contained in heavy fuel oil used in diesel engines of ships or power plants, and also automatically removes impurities accumulated in the filter through a reverse washing function. The reducer-integrated motor serves to rotate the filter at low speed to enable reverse automatic cleaning in the autofilter device. To achieve a low speed of 0.65 to 0.75 rpm in a reducer-integrated motor, a small motor that can operate at 97rpm at a rated voltage of 110 V and 112.5 rpm at 220 V is required. Additionally, a large gear ratio of 1/150 is required. To ensure the durability and reliability of these reducers, the strength of the gear must be evaluated at the design stage. In general, there is a limit to evaluating the stress and strain state according to the vibration characteristics acting on each gear in the driving state of the reducer through quasi-static analysis. Therefore, in this study, the operation characteristics of the auto filter's reducer-integrated motor were first analyzed using the rigid body dynamics analysis method. Then, this rigid body dynamics analysis model was extended to a flexible multibody dynamics analysis model to analyze the stress and strain states acting on each gear and evaluate the design feasibility of the gear.

• 한국기계가공학회지
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• 제13권5호
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• pp.50-56
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• 2014

A technique based on the finite element method (FEM) is used in the simulation of metal cutting process. This offers the advantages of the prediction of the cutting force, the stresses, the temperature, the tool wear, and optimization of the cutting condition, the tool shape and the residual stress of the surface. However, the accuracy and reliability of prediction depend on the flow stress of the workpiece. There are various models which describe the relationship between the flow stress and the strain. The Johnson-Cook model is a well-known material model capable of doing this. Low-alloy steel is developed for a dry storage container for used nuclear fuel. Related to this, a process analysis of the plastic machining capability is necessary. For a plastic processing analysis of machining or forging, there are five parameters that must be input into the Johnson-Cook model in this paper. These are (1) the determination of the strain-hardening modulus and the strain hardening exponent through a room-temperature tensile test, (2) the determination of the thermal softening exponent through a high-temperature tensile test, (3) the determination of the cutting forces through an orthogonal cutting test at various cutting speeds, (4) the determination of the strain-rate hardening modulus comparing the orthogonal cutting test results with FEM results. (5) Finally, to validate the Johnson-Cook material parameters, a comparison of the room-temperature tensile test result with a quasi-static simulation using LS-Dyna is necessary.

• 한국농공학회지
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• 제40권5호
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• pp.91-99
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• 1998

The widespread use of thin shell structures has created a need for a systematic method of analysis which can adequately account for arbitrary geometric form and boundary conditions as well as arbitrary general type of loading. Therefore, the stress and analysis of thin shell has been one of the more challenging areas of structural mechanics. A wide variety of numerical methods have been applied to the governing differential equations for spherical and cylindrical structures with a few results applicable to practice. The analysis of axisymmetric spherical shell is almost an every day occurrence in many industrial applications. A reliable and accurate finite element analysis procedure for such structures was needed. Dynamic loading of structures often causes excursions of stresses well into the inelastic range and the influence of geometry changes on the response is also significant in many cases. Therefore both material and geometric nonlinear effects should be considered. In general, the shell structures designed according to quasi-static analysis may fail under conditions of dynamic loading. For a more realistic prediction on the load carrying capacity of these shell, in addition to the dynamic effect, consideration should also include other factors such as nonlinearities in both material and geometry since these factors, in different manner, may also affect the magnitude of this capacity. The objective of this paper is to demonstrate the dynamic characteristics of spherical shell. For these purposes, the spherical shell subjected to uniformly distributed step load was analyzed for its large displacements elasto-viscoplastic static and dynamic response. Geometrically nonlinear behaviour is taken into account using a Total Lagrangian formulation and the material behaviour is assumed to elasto-viscoplastic model highly corresponding to the real behaviour of the material. The results for the dynamic characteristics of spherical shell in the cases under various conditions of base-radius/central height(a/H) and thickness/shell radius(t/R) were summarized as follows : The dynamic characteristics with a/H. 1) AS the a/H increases, the amplitude of displacement in creased. 2) The values of displacement dynamic magnification factor (DMF) were ranges from 2.9 to 6.3 in the crown of shell and the values of factor in the mid-point of shell were ranged from 1.8 to 2.6. 3) As the a/H increases, the values of DMF in the crown of shell is decreased rapidly but the values of DMF in mid-point shell is increased gradually. 4) The values of DMF of hoop-stresses were range from 3.6 to 6.8 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.3 to 2.6, and the values of DMF of stress were larger than that of displacement. The dynamic characteristics with t/R. 5) With the thickness of shell decreases, the amplitude of the displacement and the period increased. 6) The values of DMF of the displacement were ranged from 2.8 to 3.6 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.1 to 2.2.

• 한국산학기술학회논문지
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• 제13권12호
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• pp.5689-5695
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• 2012

본 연구에서는 차량에 적용되는 시트 재질인 폴리우레탄 폼의 점탄성 특성을 고려하여 시트와 인체의 진동특성을 시험 및 수치해석 방법을 이용하여 분석하였다. 압축 시험을 통해 폴리우레탄 폼의 점탄성 특성인 비선형성과 준-정역학적 특성을 구하였다. 또한 컨벌루션 적분법 및 비선형 강성 모델을 이용하여 폴리우레탄 폼의 점탄성 특성을 수학적으로 모델링하였다. 시트의 승차감 기여도를 분석하기 위하여 시트의 동역학 모델과 ISO5982의 표준 인체 수직진동 모델을 이용하여 수직 진동모델을 구성하고 관련 운동방정식을 유도하였다. 비선형 운동방정식은 Runge-Kutta 적분법을 이용하여 수치해석 시뮬레이션을 수행하였다. 철도차량의 차체 바닥에서 측정한 진동가속도 입력에 대한 시트와 인체의 응답 특성을 분석하고 시트 설계 파라미터에 대한 승차감 지수 값들의 변화를 분석하여 시트 설계에 대한 방법론을 제시하고자 한다.

• 복합신소재구조학회 논문집
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• 제6권2호
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• pp.52-62
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• 2015

This study aims at developing a new seismic resistant method by using precast concrete wall panels for existing low-rise, reinforced concrete beam-column buildings such as school buildings. Three quasi-static hysteresis loading tests were performed on one unreinforced beam-column specimen and two reinforced specimens with U-type precast wall panels. Top shear connection of the PC panel was required to show the composite strength of RC column and PC wall panel. However, the strength of the connection did not influence directly on the ultimate loading capacities of the specimens in the positive loading because the loaded RC column push the side of PC wall panel and it moved horizontally before the shear connector receive the concentrated shear force in the positive loading process. Under the positive loading sequence(push loading), the reinforced concrete column and PC panel showed flexural strength which is larger than 97% of the composite section because of the rigid binding at the top of precast panel. Similar load-deformation relationship and ultimated horizontal load capacities were shown in the test of PR1-LA and PR1-LP specimens because they have same section dimension and detail at the flexural critical section. An average of 4.7 times increase in the positive maximum loading(average 967kN) and 2.7 times increase in the negative maximum loading(average 592.5kN) had resulted from the test of seismic resistant specimens with anchored and welded steel plate connections than that of unreinforced beam-column specimen. The maximum drift ratios were also shown between 1.0% and 1.4%.

• 한국전자파학회논문지
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• 제14권10호
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• pp.1004-1010
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• 2003

본 논문에서는 유한한 도체 두께를 갖는 결합선로를 이용하여 1/4파장 역방향 방향성 결합기를 설계하였다. 방향성 결합기를 구성하는 유한 도체 두께를 갖는 결합선로를 해석하기 위한 방법으로 간단하고 빠른 수치해석 방법인 모드정합법을 사용하였다. 본 논문의 해석 결과는 도체 두께를 고려한 역방향 방향성 결합기의 설계가, 도체 두께를 고려하지 않고 설계한 경우 기존에 알려졌던 단점들인 약한 결합특성, 낮은 지향성, 그리고 비현실적인 결합선로의 폭을 극복할 수 있음을 보여준다. 또한, 수치해석 결과로부터 l/4파장 역방향 방향성 결합기에서는 도체 두께의 고려로 강한 결합특성을 만드는 것이 가능하지만, 결합길이가 약간 길어진다는 사실을 확인하였다. 본 논문에서 해석한 유한한 도체 두께는 역방향 방향성 결합기의 새로운 설계 변수로서 사용이 가능하며, 아울러 다양한 마이크로파 집적회로의 설계에도 응용이 가능함을 보여준다.

• 전자공학회논문지D
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• 제35D권10호
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• pp.22-28
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• 1998

플라스틱 패키지 재료가 본딩와이어의 혼신에 미치는 영향을 모멘트법 (Method of Moments)을 이용하여 주파수 영역에서 해석하고, fast Fourier transform을 적용하여 시간 영역에서의 전송 및 혼신 펄스 응답을 구하였다. 해석결과, 본딩와이어가 플라스틱 패키지 내부에 있을 때, 전송 특성은 유전효과로 인하여 개선되나 혼신은 증대된 방사효과로 인하여 크게 증가하며, 이러한 혼신 증가는 시간영역에서의 혼신 펄스 왜곡 현상을 현저하게 함을 관찰하였다. 한편, 정적 해석 방법을 이용한 플라스틱 패키지에 묻힌 본딩와이어의 해석 결과로부터, 모멘트법 결과와는 달리 방사효과에 의하여 증대되는 혼신현상을 계산하지 못하므로 본딩와이어 초고속 펄스 혼신 예측에는 적합하지 않음을 확인하였다. 또한, 본딩와이어 구조를 변화시키면서 혼신 펄스 응답을 살펴 본 결과, 방사효과에 의한 혼신의 우세함으로 인하여 본딩와이어간의 단순한 사이 간격 증가는 혼신감소에 효과적이지 않음을 관찰하였다. 본 해석 결과는 고속 디지털 IC 및 초고주파 소자의 플라스틱 패키지 설계시 유용하게 사용될 수 있으리라 기대된다.