• Smart Structures and Systems
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• 제25권3호
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• pp.301-310
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• 2020

The laser ultrasonic technique is gaining popularity for nondestructive evaluation (NDE) applications because it is a noncontact and couplant-free method and can inspect a target from a remote distance. For the conventional laser ultrasonic techniques, a pulsed laser is often used to generate broadband ultrasonic waves in a target structure. However, for crack detection using nonlinear ultrasonic modulation, it is necessary to generate narrowband ultrasonic waves. In this study, a pulsed laser is shaped into dual-line arrays using a spatial mask and used to simultaneously excite narrowband ultrasonic waves in the target structure at two distinct frequencies. Nonlinear ultrasonic modulation will occur between the two input frequencies when they encounter a fatigue crack existing in the target structure. Then, a nonlinear damage index (DI) is defined as a function of the magnitude of the modulation components and computed over the target structure by taking advantage of laser scanning. Finally, the fatigue crack is detected and localized by visualizing the nonlinear DI over the target structure. Numerical simulations and experimental tests are performed to examine the possibility of generating narrowband ultrasonic waves using the spatial mask. The performance of the proposed fatigue crack localization technique is validated by conducting an experiment with aluminum plates containing real fatigue cracks.

• 한국해양공학회지
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• 제32권6호
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• pp.511-517
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• 2018

This paper proposes a vision-based underwater laser scanner with separate structures for an underwater camera and a line laser projector. Because the two devices can be adaptively placed regardless of the features of the unmanned underwater vehicle (UUV), the scanner has significant advantages in relation to its availability and flexibility. Position calibration between the underwater camera and laser projector guarantees a 3D measuring performance with high accuracy. To verify the proposed underwater laser scanner, a test-bed system was manufactured, which consisted of the laser projector, camera, Pan&Tilt, and Attitude and Heading Reference System (AHRS). A camera-laser calibration test and simple 3D reconstruction test were performed in a water tank and the experimental results are reported.

• 한국기계가공학회지
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• 제21권1호
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• pp.8-14
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• 2022

A computer simulation was performed to investigate the heat source distribution and temperature distribution of a laser having multiple characteristics. To simulate the actual size of a welding specimen, the temperature distributions at 0 s, 1 s, and 2 s were analyzed by increasing the domain size to 50 mm in length and 25 mm in width in a material of the same thickness. As indicated by the results, because of the characteristics of metals with high thermal conductivity, the temperature at the welding center line and the temperature distribution at the offset position were not significant. When the core part was cooled by irradiating with a laser, it cooled at a rate of up to 500 ℃/s. In contrast, when the laser was irradiated to the ring part, the cooling proceeded at a rate of over 1800 ℃/s. Comparing the relative numerical values rather than the absolute values, it was found that the cooling rate was approximately 3.6 times faster when the laser was irradiated through the ring than when the laser was irradiated through the core. As a result of irradiating with the same heat source (at 100 W) into the core, ring, and ring + core, it was confirmed that the highest temperature was irradiated to the ring part and the lowest temperature was irradiated to the core part.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 추계학술발표대회 개요집
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• pp.49-52
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• 2001

• 한국생산제조학회지
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• 제9권4호
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• pp.48-55
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• 2000

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimens was joined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm) .As a base test, mechanical properties around weld zone were examined . The results indicated that there were no significant decreases in mechanical properties , but hardness around weld bead was 2.3 times greater than base material . The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimens and base metal was different, and it was increased by 25% when pres-strain was applied. The crack propagation rate was noticeably decreased around weld line and rapidly increased as it passed through weld line. Reviewing the shape of the crack propagation , crack width around weld line was around the weld zone due to retardation of crack growth , but is became narrow passing weld line due to decreased toughness.

• 제어로봇시스템학회논문지
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• 제20권11호
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• pp.1153-1163
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• 2014

An efficient 3D SLAM (Simultaneous Localization and Map Building) method is developed for urban building environments using a tilted 2D LRF (Laser Range Finder), in which a 3D map is composed of perpendicular/horizontal planar polygons. While the mobile robot is moving, from the LRF scan distance data in each scan period, line segments on the scan plane are successively extracted. We propose an "expected line segment" concept for matching: to add each of these scan line segments to the most suitable line segment group for each perpendicular/horizontal planar polygon in the 3D map. After performing 2D localization to determine the pose of the mobile robot, we construct updated perpendicular/horizontal infinite planes and then determine their boundaries to obtain the perpendicular/horizontal planar polygons which constitute our 3D map. Finally, the proposed SLAM algorithm is validated via extensive simulations and experiments.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.339-344
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• 1999

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimen and base material was different, and it is increased by 25% when pre-strain was applied. The crack propagation rate was noticeable decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1020-1026
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• 2011

전차선은 철도 전기차량에 전기를 안정적으로 공급하기 위한 시설물로서, 차량이나 외부요인에 의한 전차선의 변형 및 파손을 검지하여 전기철도 시설물 규정에 따라 최적의 상태로 유지해야 할 필요성이 있다. 본 논문에서는 전차선 마킹을 위한 라인레이저와 고속카메라 간에 기하학적 구성을 이용하여 3차선 거리측정방식으로 전차선 높이와 편위를 측정하기 위한 시스템 개발에 관하여 기술하였다. 전차선 거리 측정방법은 이미지 상에 마킹된 전차선 프로파일의 픽셀위치를 삼각함수 기법을 적용하여 카메라와의 전차선간에 각도를 계산하였으며, 카메라는 랜즈 왜곡 및 심도, 원금감 등에 따라 측정대상에 대한 픽셀 해상도가 다르므로 전차선 위치변화에 따른 픽셀당 각도 분해능을 적용하였다. 또한 전차선은 조가선과 급전선등과 같은 다른 전기배선보다 가장 아래에 설비되어 있는 특징을 이용하여 FPGA 상에서 전차선에 마킹된 레이저 프로파일 데이터를 고속으로 추출하여 처리하였다. 개발시스템은 전차선 시설물 평가기준에 따라 전차선 높이, 편위 측정데이터를 실시간 분석하여 이상구간에 대한 실시간 자동화 진단기능을 수행토록 하였다.

• 한국터널지하공간학회 논문집
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• 제12권3호
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• pp.239-245
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• 2010

본 논문에서는 방대한 크기의 지상 레이저 스캔 자료로부터 터널의 내공 단면을 효율적으로 추출하기 위하여, 헤시(hash) 기반 구조체를 이용한 터널 중심선 자동 추정 및 터널 내공 단면 구성 포인트 클라우드 추출 방식을 제안하였다. 즉, 헤시 기반 구조체에 입력한 레이저 스캔 자료로부터 일정한 방향의 단면들을 추출한 후 각 단면의 중심점을 연결하여 터널의 중심선을 추정하였으며, 추정된 중심선을 따라 일정 간격 및 두께로 터널 내공 단면 구성 포인트 클라우드를 추출하였다. 결과적으로 약 750만개의 포인트로 구성된 레이저 스캔 자료로부터 1 m 간격으로 0.1 m 두께의 단면 구성 포인트 클라우드를 추출하는데 3초미만의 시간이 소요되었으며 메모리는 124 MB가 소요되었다. 그러나 터널 중심선 추정 후 오류 포인트 제거, 시점 및 종점 추가 작업을 수동으로 수행해야 히는 한계도 드러내었다.

• Journal of Oral Medicine and Pain
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• 제20권1호
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• pp.53-65
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• 1995

The growth and synthetic activities of fibroblasts are regulated by cytokines and growth factors derived from activated inflammatory cells. Stimulatory effect of low level laser (LLL) radiation on wound healing seems to be in part due to direct stimulatory action on cell proliferation and synthetic activities of fibroblasts. Also indirect stimulatory effect on the fibroblast function through inflammatory or immune cells is another possible mechanism of biostimulatory action of LLL. This study was performed to determine the growth rate of human gingival fibroblasts obtained biopsy and culture, fibroblast cell line, and immune cell line by using $[^3H]-$ thymidine incorporation test. And gene expression pattern was also analyzed by using the DNA probe such as Hsp70, IL-1$\beta$, MIP-1$\alpha$ and actin cDNA. Proliferation rate of gingival fibroblast was increased by LLL irradiation, but no more effect was added by LPS or IL-1$\beta$ pretreatment Enhanced Hsp70 gene expression was found from gingival fibroblasts and fibroblast cell line COS by LLL irradiation., which was not more increased by LPS or IL-1$\beta$ pretreatment. LLL-irradiated promyelcytic cell line HL-60 and macrophage cell line RAW264.7 showed significant stimulatory effect of proliferation rate when compared with respective control. However there were no changes in growth rate of other immune cell tested in this study, such as B cell line WR19n.l and 230, helper T cell line Jurkat and Hut78, cytolytic T cell line CTLL-r8. By LLL-irradiation Hsp70 gene expression was increased in RAW246.7 and HL-60, not in CTLL-R8. And IL-1$\beta$ and MIP-1$\alpha$ gene expression were induced only from LLL-irradiated RAW264.7. These results led us to presume that LLL radiation may affect to the immune cells, especially to macrophage, through which it might promote wound healing process.