• 한국기계가공학회지
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• 제19권1호
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• pp.29-35
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• 2020

Car inspection systems are regularly carried out by the state to ensure the safety and emission status of cars, thereby improving the safety and quality of life by reducing fine dust and greenhouse gases that are the main culprits of vehicle defects and air pollution. These automobile inspections are largely divided into either regular or comprehensive inspections. This study analyzed the smoke measuring probes used in the lug - down 3 mode. In the previously issued paper "Improvement of Soot Probe Efficiency for Automotive Emission Measurement," an improved smoke measurement probe(B) improved on the problems that arise from the current smoke measurement probe (A). In this study, a technique that can improve the probe's inhalation efficiency over the improved (B) probes was applied to probes (C). Probe (C) involves a structure designed close to the center of the circumference of the exhaust pipe, and the suction efficiency was improved by adding a variable center unit.

• 대한기계학회논문집A
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• 제21권8호
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• pp.1270-1275
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• 1997

This paper concerns with the finite element analysis of reactor internals with structural faults. For investigating the influence of hold-down spring faults on dynamic characteristics of CSB (core support barrel), reactor internals of Ulchin-1 nuclear power plant are modeled using finite element method and simulated with artificial defects on the hold-down springs. To prove the validity of the finite element models, the calculated natural frequencies of CSB in normal state are compared with those from the measurement results, which shows good agreement. According to results of finite element analysis, CSB beam mode natural frequency decreases by 4.5% in the case of 10% partial relaxation of hold-down springs, and decreases by 18.4% in the case of 20%. The range of shell mode natural frequency change is within 5.3%.

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.371-379
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• 2017

Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, two crack growth criteria and the respective crack paths prediction in functionally graded materials (FGM) are compared. The maximum tangential stress criterion (${\sigma}_{\theta}-criterion$) and the minimum strain energy density criterion (S-criterion) are investigated using advanced finite element technique. Using Ansys Parametric Design Language (APDL), the variation continues in the material properties are incorporated into the model by specifying the material parameters at the centroid of each finite element. In this paper, the displacement extrapolation technique (DET) proposed for homogeneous materials is modified and investigated, to obtain the stress intensity factors (SIFs) at crack-tip in FGMs. Several examples are modeled to evaluate the accuracy and effectiveness of the combined procedure. The effect of the defects on the crack propagation in FGMs was highlighted.

• Computers and Concrete
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• 제33권5호
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• pp.481-496
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• 2024

Internal erosion around pipes can lead to the failure of earth dams through various mechanisms. This study investigates the displacement patterns in earth dam models under three different failure modes due to internal erosion, using digital image correlation (DIC) methods. Three failure modes—erosion along a pipe (FM1), pipe leakage leading to soil erosion (FM2), and erosion in a pipe due to defects (FM3)—are analyzed using two- and three-dimensional image- processing techniques. The internal displacement of the cross-sectional area and the surface displacement of the downstream slope in the dam models are monitored using an image acquisition system. Physical model tests reveal that FM1 exhibits significant displacement on the upper surface of the downstream slope, FM2 shows focused displacement around the pipe defect, and FM3 demonstrates increased displacement on the upstream slope. The variations in internal and surface displacements with time depend on the segmented area and failure mode. Analyzing the relationships between internal and surface displacements using Pearson correlation coefficients reveals various displacement patterns for the segmented areas and failure modes. Therefore, the image-based characterization methods presented in this study may be useful for analyzing the displacement distribution and behavior of earth dams around pipes, and further, for understanding and predicting their failure mechanisms.

• Smart Structures and Systems
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• 제22권4호
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• pp.481-493
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• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.

• 대한기계학회논문집A
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• 제40권11호
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• pp.919-925
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• 2016

본 연구에서는 비선형 체적파 혼합 기법의 선행연구를 토대로 램파 기법에 적용하여 램파 혼합 기법에 대한 연구를 수행하였다. 램파 혼합 기법의 타당성을 증명하기 위해 결함이 없는 시편과 부식에 의해 발생된 표면 결함이 있는 시편에 대해 실험을 진행하였다. 실험 대조군으로는 램파의 지배적인 면내변위와 면외변위를 가지는 모드 및 주파수로 선정하였다. 그 결과 램파 혼합 기법으로도 결함 검출이 가능하였고, 기존의 램파 기법의 경향성과 유사하게 나타났다. 그리고 이론과 동일한 지배적인 변위와 모드가 발생된 것을 확인 할 수 있었다. 그러나 결함 검출 성능은 측정 방법 및 단순 모드 선정에 따라 결정되는 것이 아니라 변위 비율에 따라 결정된다.

• 비파괴검사학회지
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• 제24권2호
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• pp.136-141
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• 2004

배관에서의 균열 탐지를 위해서 비틀림 모드 유도초음파 검사법을 적용하였다. 배관에서 비틀림 모드의 생성 및 수신을 위하여 배열형 전자기음향 탐촉자 (EMAT, electromagnetic acoustic transducer)를 설계, 제작하였다. 직경 2.5 인치의 배관에 대해 주파수 2000kHz의 비틀림 모드 유도초음파를 적용하였으며 가진용으로 4개의 배열형 EMAT를 제작하였으며, 별도의 수신용 EMAT를 설계 제작하였다. 실제 중수로 피더관 mock-up에 대해 곡관부에 다양한 깊이의 인공 결함을 가공한 뒤 약 2 hi 거리에서 각각의 탐지능을 실험하였다. 결함 깊이가 관 두께 대비 5% 인 경우에도 결함 신호를 탐지할 수 있었으나 결함의 깊이와 신호 진폭과의 관계성은 나타나지 않았다.

• 한국컴퓨터산업학회논문지
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• 제3권1호
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• pp.57-66
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• 2002

본 논문에서는 전류모드 CMOS의 기본회로를 이용해 다치 논리(Multiple-Valued Logic) 연산기를 설계하고자 한다. 우선, 2진(Binary)FFT(Fast Fourier Transform)를 확장해 다치 논리회로를 이용해서 고속 다치 FFT 연산기를 구현하였다. 다치 논리회로를 이용해서 구현한 FFT연산은 기존의 2치 FFT과 비교를 해 본 결과 상당히 트랜지스터의 수를 줄일 수 있으며 회로의 간단함을 알 수가 있었다. 또한, 캐리 전파 없는 가산기를 구현하기 위해서 ｛0,1,2,3｝의 불필요한(Redundant) 숫자 집합을 이용한 양의 수 표현을 FFT회로에 내부적으로 이용하여 결선의 감소와 VLSI 설계시 정규성과 규칙성으로 효과적이다. FFT승산을 위해서는 승산기의 연산시간과 면적을 다치 LUT(Look Up Table)로 이용해 승산의 역할을 하였다. 마지막으로 이진시스템(Bin system)과의 호환을 위해 다치 하이브리드형 FFT 프로세서를 제시하여 2진4치 부호기와 4치 2진 복호기 및 전류모드 CMOS회로를 사용하여 상호 호환성을 갖도록 설계를 하였다.

• 한국정밀공학회지
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• 제16권9호
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• pp.179-190
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• 1999

To automate the polishing process, a polishing robot with two axes which is attached to a machining center with three axes has been developed by our previous research. This automatic polishing robot is able to keep the polishing tool normal to the curved surface of die and is able to maintain a constant pneumatic pressure. Therefore, in the case of a curved surface die, the surface roughness to be polished by the system with five axes is improved superior than the surface by a three-axis machining center. However, because the polishing robot was big and heavy, a polishing workspace was limited and then it was difficult to attach the robot to machining center. In this study, the smaller and lighter polishing robot than the previous has been designed to improve defects due to the magnitude and weight of the robot. And the sliding mode control ins applied to polishing robot to improve the tracking performance. To obtain switching parameters of sliding mode control, the signal compression method is used. Code separation program to separate the date for a three-axis machining center and a two-axis polishing robot from a five-axis NC data is improved for users to check conveniently the separated trajectory and to handle many data by using the graphic user interface. To evaluate the polishing performance of the developed robot, the polishing experiment for shadow mask was carried out. The result shows the automatic polishing robot has a good trajectory tracking performance and obtains a good polished workpiece efficiently under recommended polishing conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.268-273
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• 2004

This study is conducted to clarify the effect of internal pressure on the deformation and collapse behaviors of wall thinned elbow under in-plane bending moment. Thus the nonlinear three-dmensional finite element analyses were performed to obtain the moment-rotation curve of elbow contatining various wall thinning defects located at intrados and extrados under in-plane bending (closing and opening modes) with internal pressure of $0{\sim}15MPa.$ From the results of analysis, the effect of internal of collapse moment of elbow on the global deformation behavior of wall thinned elbow was discussed, and the dependence of collapse moment of elbow on the magnitude of internal pressure was investigated under different loading mode, defect location, and defect shape.