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초음파 tomography를 응용한 콘크리트 구조물의 비파괴 시험에 관한 연구
김영기,윤영득,윤종열,김정수,김운경,송문호,Kim, Young-Ki,Yoon, Young-Deuk,Yoon, Chong-Yul,Kim, Jung-Soo,Kim, Woon-Kyung,Song, Moon-Ho 대한전자공학회 2000 電子工學會論文誌-SP (Signal processing) Vol.37 No.1
As a potential approach for non-destructive testing of concrete structures, we evaluate the time-of-flight (TOF) ultrasound tomography technique In conventional X ray tomography, the reconstructed Image corresponds to the internal attenuation coefficient However, in TOF ultrasound tomography, the reconstructed Image is proportional to the retractive index of the medium Because refractive effects are minimal for X-rays, conventional reconstruction techniques are applied to reconstruct the Image in X-ray tomography However, since ultrasound travels in curved path, due to the spatial variations in the refractive index of the medium, the path must be known to correctly reconstruct the Image. Algorithm for determining the ultrasound path is developed from a Geometrical Optics point view and the image reconstruction algorithm, since the paths are curved It requires the algebraic approach, namely the ART or the SIRT Here, the difference between the computed and the measured TOP data is used as a basis, for the iteration process First the initial image is reconstructed assuming straight paths. It then updates the path based on the recently reconstructed image This process of reconstruction and path determination repeats until convergence The proposed algorithm is evaluated by computer simulations, and in addition is applied to a real concrete structure. 본 연구에서는 초음파와 tomography 기법을 기반으로 콘크리트 구조물의 비파괴 시험에 대한 방법론을 정립하고 검증하였다 일반적인 X-ray tomography에서는 물체를 통과하는 파동의 감쇠(attenuation) 데이터에 기초를 두고있는 반면에, 본 연구에서는 time-of-flight(TOF) 데이터를 사용하여 매질의 굴절률(refractive index)을 포괄적으로 표현하는 단층영상을 복원한다 X-ray tomography에서는 측정된 감쇠 데이터를 영상복원(Image reconstruction) 알고리즘에 의해서 처리하며, 파동의 굴절은 고려할 필요가 없다 그러나 초음파는 매질(medium)의 굴절률(refractive index)에 따라 초음파의 경보가 변경되므로 초음파 tomography에서는 초음파 경로의 연산이 선행되어야만 단층영상을 복원할 수 있게 된다 초음파 정보의 연산은 가하광학(Geometrical Optic)에서 사용되는 굴절률과 경로의 관계에 기초를 둔다 영상 복원은 대수학적 접근 방법인 ART (algebraic reconstruction technique) 또는 SIRT(simultaneous iterative reconstruction technique)를 기초로 연산된 초음파의 경로를 따라 선적분한 TOF 값과 측정된 TOF 값의 차이를 기반으로 수행된다 실제 구현에서는 초음파가 직진한다는 가정하에 영상을 복원하고, 이를 기반으로 초음파의 경로를 연산하였다 본 논문에서는 이들 두 과정(경로연산 및 영상복원)의 반복연산을 통하여 영상을 복원하였다. 세안하는 알고리즘을 모의실험으로 평가하였고, 실제 콘크리트 구조물에 적용하여 본 방법론의 무한한 가능성을 입증하였다.
김동홍(Dong Hong Kim),채수하(Soo Ha Chae),윤순종(Soon Jong Yoon),윤종열(Chong Yul Yoon),이원복(Won Bok Lee) 한국강구조학회 1996 韓國鋼構造學會誌 Vol.8 No.2
Elastic buckling behavior of an orthotropic plate with an intermediate stiffener, placed parallel to the longitudinal axis, is investigated. Non-dimensional closed-form solution that predicts the buckling strength and the effect of ratio of plate and stiffener widths on the buckling coefficients is developed. When the orthotropic material property in this solution is replaced by an isotropic material property, the result agrees with that obtained by Bulson. Parameter study shows the buckling coefficient of the plate is linearly proportional to the ratio of plate and stiffener widths in the range between 0.2 to 0.4.
정경희(Kyung Hee Chung),김진성(Jin Sung Kim),윤순종(Soon Jong Yoon),윤종열(Chong Yul Yoon),이원복(Won Bok Lee) 한국강구조학회 1996 韓國鋼構造學會誌 Vol.8 No.2
In this paper 3-span continuous composite plate girder bridges were analyzed by the unified autostress design method. In order to determine the autostress in the interior support section, modified moment-inelastic rotation curve and moment-inelastic rotation curve for the positive moment region developed by Frank and Vasseghi were used. In the analysis, the compression flange of I-girder was assumed to be ultracompact while the web was considered to be a noncompact section. From the trial design it was realized that the autostresses were about 20-30% of stresses due to elastic moments at the negative and positive moment region.
횡형과 주형의 접합부에서 횡형단부의 경계조건에 관한 연구
이채성(Chae Sung Lee),김우기(Woo Gi Kim),이기범(Ki Bum Lee),윤순종(Soon Jong Yoon),윤종열(Chong Yul Yoon),이원복(Won Bok Lee) 한국강구조학회 1996 韓國鋼構造學會誌 Vol.8 No.2
In a beam-to-girder connection system, the boundary condition of the cross beam is assumed as a fixed support and the cross beam is welded to the web of a girder in practice. But, in general, the torsional rigidity of I-shape girder arid the out-of-plane bending rigidity of slender-web plate are small. Hence the interaction behavior between the cross beam and the girder must be considered in the connection design. In this paper, cross beam ends are assumed as a fixed support and the moment reduction effects, caused by the torsion of a main girder and the out-of-plane deformation of the web, are evaluated, respectively. Based on this practical example, it was found that the moment reduction is significant and therefore it is recommended to design the cross beam as a simply supported beam.
Adaptive Scheme에 의한 평면응력 유한요소망의 자동형성화에 관한 연구
朴昶勳,尹鍾烈 弘益大學校 科學技術硏究所 1999 科學技術硏究論文集 Vol.10 No.1
The finite element method(FEM) has been widely accepted as one of the most powerful analytical techniques in solving complex engineering problems. In using a FEM program, the results of analysis depend on the finite element mesh. Expertise and experience are required in forming an efficient mesh. Adaptive mesh generation is the process automatically forming an efficient mesh by moving existing nodes, subdividing elements, or increasing the order of polynomials used in the shape functions. As the scheme depends on the error estimates used to evaluate the meshes, the definition of error estimator affects the quality of the final mesh. In this study, a simple error estimator is developed and a new approach for combining different errors is proposed. Plane stress problems are considered. The r method, which is the scheme where nodes are moved, the h method, which is the scheme where elements are subdivided and the rh method, which is the scheme that combines r and h method, are investigated in this study with the proposed error estimator. The proposed error estimator is constituted from the domain and the boundary errors. The difference of stresses in the domain of an element and the difference of strains on the boundaries between the element and its neighboring elements are used as error estimators. Each error is normalized and the final error estimator is the weighted sum of each error. The analysis results using the adaptive mesh obtained with the proposed error estimator are compared to the exact solution. The comparisons show that the proposed error estimators are good error indicators for generating efficient final meshes in the applied examples. The generated final meshes use less number of elements than fine mesh and obtained same result of analysis.
평면응력 문제의 동적해석을 위한 적응적 요소망 형성 전략
尹鍾烈,洪承杓 弘益大學校 科學技術硏究所 2005 科學技術硏究論文集 Vol.16 No.-
Finite Element Method(FEM) is the representative approximate analysis method which is the most widely used in various fields of engineering. In order to use the FEM for structural analysis, element type and mesh should be chosen. The effective mesh is essential to get more accurate results in short time using FEM, and the expert knowledge and experience are necessary. Adaptive mesh generation is a technique that improves the accuracy of FEM results through a refinement of mesh using the results of the previous analysis step. In this study, the concept of representative strain value is introduced to analyze structures subjected to dynamic loadings using the adaptive mesh generation. Representative strain value based on the standard deviation of strain can be used as a sign of error in an element. The study presents a criteria for regeneration of mesh that applies for both r-method and h-method. This study examines the validity of the suggested strategy to obtain effective mesh through a culvert examples under fixed varying load. The proposed strategy reduces the calculation and a good accuracy is obtained.
국부불연속 단면을 갖는 직교이방성 박판요소의 좌굴에 관한 연구
李菜城,尹順鍾,尹鍾烈 弘益大學校 科學技術硏究所 1997 科學技術硏究論文集 Vol.8 No.-
As a modern material, fibers are embedded in surrounding matrix materials and unidirectionally reinforced to form orthotropic fiber-reinforced plastic materials. Desirable material characteristics such as corrosion resistance, light weight, high specific strength and stiffness make this material an alternative construction materials. For effective use of such materials, the stability of various orthotropic structural shapes composed of thin plates need to be analyzed. Generally, the buckling behavior of thin plates with a cutout at the center has been limited to empirical studies and finite element analyses. A general formulation for the buckling behavior for this case is studied. Theoretical buckling analyses of plates with a hole at the center is investigated. The geometric complexity of the problem prohibits derivation of closed-form solutions from the equilibrium equations. Thus energy principles and the assumed displacement shapes are used to consider the effects of the cutout on buckling. On all edges, the boundary conditions are assumed to be simply supported with uniformly distributed stress. Experiments are based on rectangular box specimens. The results from finite element analyses and experiments are used to evaluate the validity of the theoretical results where theoretical results are concluded to be sound.