• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.5
• /
• pp.439-446
• /
• 2012

This paper presents an implicit moving least squares(MLS) difference method for improving the solution accuracy of 1-D free boundary problems, which implicitly updates the topology change of moving interface. The conventional MLS difference method explicitly updates the moving interface; it requires no iterative solution procedure but results in the loss of accuracy. However, the newly developed implicit scheme makes the total system nonlinear involving iterative solution procedure, but numerical verification show that it dramatically elevates the solution accuracy with moderate computation increase. Through numerical experiments for melting problems having moving singularity, it is verified that the proposed method can achieve the second order accuracy.

• Proceedings of the Optical Society of Korea Conference
• /
• 2002.07a
• /
• pp.26-27
• /
• 2002

광학식 3차원 형상측정 기술은 산업현장과 의료분야에서 광범위하게 사용되어지고 있으며, 이에 대한 연구도 활발히 진행되고 있다. 본 연구에서는 비접촉식 3차원 형상측정 방법인 위상측정법(Phase Measuring Profilometry; PMP)을 실험적으로 구현하였으며 위상추출 알고리즘으로는 위상이동방법(Phase shifting method)과 푸리에 변환법(Fourier Transform)을 사용하여 그 결과를 비교 및 고찰하였다. (중략)

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.1
• /
• pp.39-48
• /
• 2013

This paper develops a 2-D moving least squares(MLS) difference method for Stefan problem by extending the 1-D version of the conventional method. Unlike to 1-D interfacial modeling, the complex topology change in 2-D domain due to arbitrarily moving boundary is successfully modelled. The MLS derivative approximation that drives the kinetics of moving boundary is derived while the strong merit of MLS Difference Method that utilizes only nodal computation is effectively conserved. The governing equations are differentiated by an implicit scheme for achieving numerical stability and the moving boundary is updated by an explicit scheme for maximizing numerical efficiency. Numerical experiments prove that the MLS Difference Method shows very good accuracy and efficiency in solving complex 2-D Stefan problems.

• Korean Journal of Optics and Photonics
• /
• v.5 no.2
• /
• pp.191-197
• /
• 1994

We investigated the properties of various methods of 3 dimensional profilometry to choose the phase shifting technique for the reconstruction of the shape of a given specimen. The pattern was generated by a Twyman-Green interferometer and a PZT was used to shift the fringes on the target surface. The shape was calculated with Hariharan algorithm within the uncertainty of a scaling factor. The optical noise inherent in the laser source was observed to influence the final outcome to a great extent and the need for an exact calibration was noted. noted.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2004.05a
• /
• pp.178-178
• /
• 2004

본 연구에서는 폴리카보나이트의 재료로 만들어진 인장시편과 원형시편을 다목적 광탄성 측정기를 사용하여 프린지 차수를 측정한 후 프린지 상수를 도출하였다. 특히, 새로 개발된 다목적 광탄성기를 이용하여 지랫대 형식으로 프린지 차수를 측정하였고, 시편에 직접 응력을 가하는 방식의 직접(DIRECT) 실험법으로 프린지 차수를 측정하였다. 위와 같은 방식은 나타난 결과를 가지고 프린지 상수를 서로 비교할 수 있다는 장점이 있어 다목적 광탄성기에 대한 신뢰도를 얻을 수 있다 아울러 광탄성 4단계 위상 이동법에서는 주응력 방향, 즉 등경선이 일정한 선상에서는 연속적인 응력분포를 얻을 수 있다.(중략)

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.1
• /
• pp.15-22
• /
• 2007

A hybrid experimental-numerical method is presented for determining the stresses around a circular hole in a finite-width, tensile loaded plate. Measured fringe orders along straight lines provided the input information on the external boundary of the hybrid element. In order to see the effects of varying stress field, different numbers of terms in a power-series representation of the complex type conformal mapping stress function were tested. For qualitative comparison, actual isochromatic fringes were compared with reconstructed theoretical fringes using stress-optic law. For quantitative comparison, relative errors and standard deviations with respective to relative errors were analyzed for all measured points by changing the number of terms of stress function. The hybrid results are highly comparable with those predicted by FEA. The results show that this approach is effective and promising because isochromatic data along the straight lines in photoelasticity can be conveniently measured by use of phase shifting photoelasticity.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.421-424
• /
• 2002

The 3-D measurement using a sinusoidal grating pattern projection is very attractive because of its high measuring speed and high sensitivity. When a sinusoidal amplitude grating was projected on an object, the surface-height distribution of the object is translated into a phase distribution of the deformed grating image. The phase-acquisition algorithms are so sufficiently simple that high-resolution phase maps using a CCD camera can be generated in a short time. The PMP technique is discussed, and the analysis of the systematic errors, the calibration procedure designed to determined the optimal setting of the measurement parameters is illustrated. Results of measurements and calibrations on the measurement plane objects are described.

• Proceedings of the KIEE Conference
• /
• 2003.07c
• /
• pp.1987-1989
• /
• 2003

3차원 형상을 측정하는 측정법으로는 접촉식과 비접촉식이 있는데 최근에는 물체의 표면을 손상 시키지 않으면서 물체의 변형 상태 등을 정밀하게 측정할 수 있는 비접촉식 측정법이 주로 사용되어 지면서 변형, 진동, 결함 등의 다양한 측정 분야에 찰용되고 있다. 이는 광학 간섭의 하나인 Twyman-Green 간섭계를 이용하여 간섭 무의 패턴을 PZT Controller로 위상 이동하여 CCD 카메라로 물체의 영상을 얻어 위상 지도를 추출, 이미지를 분석하여 3차원 물체를 해석하고자 한다. 하지만 이미지 측정시 미세 진동 및 조명 등에 의한 노이즈가 발생하게 되어 물체의 정확한 정보를 얻기가 어려워 노이즈 제거를 위한 이미지 처리 알고리즘 개발과 Unwrapping 처리, 위상이동 알고리즘 개발 등을 통하여 좀더 정확한 정보를 얻고자 한다.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2004.05a
• /
• pp.181-181
• /
• 2004

3 차원 형상측정기술(3-D Profile Measurement Method)은 가공품의 치수검사 및 형상측정 등의 공학분야뿐만 아니라 최근에는 의류산업 및 의학산업은 물론 오락산업의 가상현실 구현 등 여러 분야로 점차 사용이 확대되고 있다. 이러한 요구를 만족시킬 수 있는 광학을 바탕으로 한 비접촉 3 차원 형상측정방법(Non-contacting 3-D Profile Measuring Method)은 고속, 고정밀도 측정이 가능하기 때문에 활발히 연구되고 있다. 광학을 이용한 대표적인 3 차원 비접촉 측정방법의 하나인 영사식 무아레는 그림자식 무아레의 단점인 격자의 크기가 측정물체보다 커야 한다는 점과 측정물체와 격자사이의 거리 제한 문제를 해결하였으며, 위상이동법을 사용함으로서, 무아레 무늬 형태의 영향을 받지 않고 측정이 가능해졌다.(중략)

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2001.04a
• /
• pp.226-230
• /
• 2001

Electronic Speckle Pattern Interferometry (ESPI) has been recently developed and widely used because it has advantage to be able to measure surface deformations of engineering components and materials in industrial areas with non-contact. The spekle patterns to be formed with interference phenomena of scattering phenomena measure the out-of-plane deformations, together with the use of digital image equipment to process the informations included in the speckle patterns and the display consequent interferogram on a computer monitor. In this study, the experimental results of a canti-levered plate using ESPI were compared with those obtained from the simple beam theory. The ESPI results of the canti-levered plate analyzed by 4-step phase shifting method are close to the theoretical expectation. Also, out-0of-plane displacements of a spot welded canti-levered plate were measured by ESPI with 4-step phase shifting technique. The phase map of the spot welded canti-levered plate is quite different from that of the canti-levered plate without spot welding.