• 한국소음진동공학회논문집
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• 제20권7호
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• pp.677-684
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• 2010

Backlashes of gears provide gears for good lubrication and for removal of the interference between teeth by the wear and manufacturing errors. The backlash is the strong nonlinear factor to gears. This study deals with nonlinear modeling of helical gears with backlash. Excitation of helical gears comes from torque variation, the tooth surface error, and the periodical change of mesh stiffness. To study the effect of torque fluctuation, equation of motion for the single degree of freedom torsional model of helical gears with the periodical change of mesh stiffness and the backlash was derived. The Newmark beta method and the Newton-Raphson method were used to obtain the nonlinear behaviors of mesh forces of helical gears. All excitation frequencies initially caused the tooth separation and single-sided impacts of the gear pair and eventually led to the normal tooth contact. However, some special excitation frequencies caused the single-sided impacts in the entire time as well as the initial time. Damping increase reduced the duration of single-sided impacts, and the backlash increase caused those in the entire time domain.

• 한국CDE학회논문집
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• 제18권4호
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• pp.283-289
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• 2013

Presented in this paper is an adaptive measuring procedure of dental impression using the Structured Light System. While measuring a complex object, such as dental impression, in the reverse engineering, it is not possible to acquire all parts of the scanned surface. Missing scanned data is resulted in holes in a created triangular mesh. The focus of this paper is to introduce an algorithm for automatic identification of additional scanning orientations to fill holes that are created by a default scan. The proposed algorithm was developed by the three major technological requirements: camera visibility, projector visibility, data reliability. In order to satisfy the requirements, the proposed algorithm determines additional scanning orientation from the orientation of a projection plane derived from the average normal vector of boundary triangles.

• Journal of applied mathematics & informatics
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• 제38권3_4호
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• pp.311-334
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• 2020

The solution of the elliptic partial differential equation has interface singularity at the points which are either the intersections of interfaces or the intersections of interfaces with the boundary of the domain. The singularities that arises in the elliptic interface problems are very complex. In this article we propose an exponentially accurate nonconforming spectral element method for these problems based on [7, 18]. A geometric mesh is used in the neighbourhood of the singularities and the auxiliary map of the form z = ln ξ is introduced to remove the singularities. The method is essentially a least-squares method and the solution can be obtained by solving the normal equations using the preconditioned conjugate gradient method (PCGM) without computing the mass and stiffness matrices. Numerical examples are presented to show the exponential accuracy of the method.

• Progress in Superconductivity
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• 제1권2호
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• pp.125-134
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• 2000

A quench phenomenon is caused by an external disturbance in a superconducting magnet, where the magnet is operating in a cryogenic environment. The heat coupling between the layers and pancakes of the magnet can induce the normal zone propagation with fast speed. In order to analyze quench behavior in a pancake-shaped superconducting magnet, a quasi-three-dimensional model is proposed. A moving mesh finite volume method is employed in solving the heat conduction equation. The quench process of the superconducting magnet is studied under the various operating conditions and cooling conditions.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.39-42
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• 2000

In our study, by observing and analyzing normal liver in abdominal CT image, we estimated gray value range and generated binary image. In the binary image, we achieved the number of hole which is located between pixels. Depending on the ratio, we processed the input image to 4 kinds of mesh images to remove the noise part that has the different ratio. With the Union image of 4 kinds of mesh images, we generated the template representing general outline of liver and subtracted from the binary image so the we can represent the organ boundary to be minute. With results of proposed method, processing time is reduced compared with existing method and we compared the result image to manual image of medical specialists.

• 한국정밀공학회지
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• 제13권10호
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• pp.46-55
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• 1996

As industrial standard data, the STL format which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system in recent days. Because most RP system take the only form of two dimensional line segments as an input stream inspite of its imperfectness while converting into STL format, a CAD model is converted into a standard industrial format which is composed of many triangular facets. The error verifying process is composed of four main steps, and these are 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to anedge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Correct the wrong direction and normal vectors. This paper is concerned with serching the mentioned errors in advance and modifying them.

• Journal of Korean Neurosurgical Society
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• 제29권1호
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• pp.58-65
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• 2000

Objective : Thoracolumbar junction is second most common level of injury next to cervical spine. The object of this study is to study the usefulness of surgical titanium mesh instead of bone graft, as well as to evaluate the correction of spinal deformity and safety of early ambulation in patients with injury at thoracolumbar junction. Patients and Methods : This review included 51 patients who were operated from July 1994 to December 1997. The injured spine is considered to be unstable, if it shows involvement of two or more columns, translatory displacement more than 3.5mm, decrease more than 35% in height of vertebral body and progression of malalignment in serial X-ray. The decision to operate was determined by (1) compression of spinal cord or cauda eguina, (2) unstable fracture, (3) malalignment and (4) fracture dislocation. The procedure consisted of anterior decompression through corpectomy and internal fixation with anterior instrument and surgical titanium mesh which was impacted with gathered bone chip from corpectomy. Results : Fifty-one patients were followed up for at least 12 months. The main causes of injury were fall and vehicle accident. The twelfth thoracic and the first and the second lumbar vertebrae were frequently involved. Complete neural decompression was possible under direct vision in all cases. Kyphotic angulation occurred in a patient. Radiologic evaluation showed correction of deformity and no distortion or loosening of surgical titanium mesh with satisfactory fixation postoperatively. Conclusions : We could obtain neurological improvement, relief of pain, immediate stabilization and early return to normal activities postoperatively. Based on these results, authors recommend anterior decompression and internal fixation with surgical titanium mesh in thoracolumbar unstable spine injuries.

• 한국통신학회논문지
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• 제24권10B호
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• pp.1937-1945
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• 1999

본 논문에서는 정점 군집화(vertex clustering) 방법에 기반한 3차원 물체의 단순한 기법을 제안한다. 제안한 방법은 3차원 물체의 국부 영역의 특성에 따라 군집화하는 격자의 크기를 다르게 한다. 격자의 크기는 삼각형의 법선 벡터와 정점 분포를 이용하여 결정한다. 인접한 삼각형의 법선 벡터가 이루는 각이 크고 정점들이 흩어져 있으면 작은 격자로 분할하여 자세한 표현을 한다. 격자의 분할 과정은 8진 나무(octree)로 나타낸다. 단순화 오차를 추정하기 위해 하우스도르프 거리(Hausdorff distance)를 이용한다. 제안한 방법은 정점 군집화의 적은 계산량과 효과적인 단순화의 장점을 그대로 유지할 수 있다. 그리고 3차원 물체의 특성에 따라 격자의 크기를 다르게 하므로 기존의 방법에 비해 단순화 오차가 적고 작은 영역의 변화까지 세밀히 나타낼 수 있다. 또한, 다양한 단순화 단계를 가지는 다해상도 모델로의 표현이 가능하고 격자 크기의 조절이 가능하므로 선택된 영역에 대해서 세밀한 표현도 가능하다.

• 한국정보통신학회논문지
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• 제12권12호
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• pp.2307-2314
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• 2008

유비쿼터스 센서 네트워크는 현재 다양한 분야로 활용되고 있는 추세이다. 이러한 유비쿼터스 센서 네트워크를 그린 하우스에 적용하여 작물생장정보 및 환경데이터 수집 등 유용한 정보를 모니터링 할 수 있다. 하지만 센서노드의 한정된 에너지 자원으로 네트워크 확장을 통한 대규모 네트워크를 구성하여 운영하기에는 부적절하다. 본 논문에서는 상기 문제점을 해결하기 위해 유비쿼터스 센서 네트워크에 무선 메쉬 네트워크 기술을 적용하여 시뮬레이션을 구현하였다. 도출된 결론을 통해 유비쿼터스 센서 네트워크에 무선 메쉬 네트워크 기술을 적용했을 때 에너지 측면에서 효율성이 높아진 것을 확인할 수 있었다.

• International Journal of CAD/CAM
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• 제9권1호
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• pp.79-83
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• 2010

Tidal bore is a peculiar nature phenomenon which is caused by the lunar and solar gravitation. Based on the physical characters of tidal bores, in this paper we propose a novel method to model and render this phenomenon, especially the tidal waves in Qiantang estuary. According to Boltzmann equation for tidal waves, we solve it with the novel triangle mesh of Kinectic Flux Vector Splitting (KFVS) mode. Then a method combining a curve forecasting wave and particles model is proposed to render the dynamic scenes of overturning tidal waves. Finally, with some rendering technologies, various realistic tidal waves under diversified conditions is rendered in real time.