• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.784-787
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• 2002

The NURBS surfaces are widely employed for exchanging geometric models between different CAD/CAE systems. However if the input NURBS surfaces are poorly parameterized, most surface meshing algorithms may fail or the constructed meshes can be ill-conditioned. In this paper presents a new method is presented that can generate well conditioned meshes even on poorly parameterized NURBS surfaces by regenerating NURBS surfaces. To begin with, adequate Points are sample on original poorly parameterized surfaces and new surfaces are created by interpolating these points. And then. mesh generation is performed on new surfaces. With this method, models with poorly parameterized NURBS surfaces can be meshed successfully.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.192-198
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• 1997

In the concurrent engineering, the CAD-based design model is necessary for multidisciplinary analysis and for computer-aided manufacturing (CAM). A shape and configuration design velocity field computation of structure has been developed using a computer-aided design (CAD) tool, Pro/ENGINEER. The design Parameterization with CAD tool is to characterize the change in dimensions and movements of geometric control points that govern the shape/orientation of the structural boundary. The boundary velocity is obtained by using a CAD-based finite difference method and the domain velocity field is obtained from finite element analysis (FEA) using the boundary displacement method. In this paper, the continuum configuration DSA for NVH problem, which requires the shape velocity field and the orientation velocity field at the same time, is developed using linear shape functions. For validation of continuum design sensitivity coefficients, design sensitivity coefficients are compared with the coefficients computed using by the finite difference method.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.577-582
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• 2007

A variational formulation for plane elasticity problems is derived based on an isogeometric approach. The isogeometric analysis is an emerging methodology such that the basis functions in analysis domain arc generated directly from NURBS (Non-Uniform Rational B-Splines) geometry. Thus. the solution space can be represented in terms of the same functions to represent the geometry. The coefficients of basis functions or the control variables play the role of degrees-of-freedom. Furthermore, due to h-. p-, and k-refinement schemes, the high order geometric features can be described exactly and easily without tedious re-meshing process. The isogeometric sensitivity analysis method enables us to analyze arbitrarily shaped structures without re-meshing. Also, it provides a precise construction method of finite element model to exactly represent geometry using B-spline base functions in CAD geometric modeling. To obtain precise shape sensitivity, the normal and curvature of boundary should be taken into account in the shape sensitivity expressions. However, in conventional finite element methods, the normal information is inaccurate and the curvature is generally missing due to the use of linear interpolation functions. A continuum-based adjoint sensitivity analysis method using the isogeometric approach is derived for the plane elasticity problems. The conventional shape optimization using the finite element method has some difficulties in the parameterization of boundary. In isogeometric analysis, however, the geometric properties arc already embedded in the B-spline shape functions and control points. The perturbation of control points in isogeometric analysis automatically results in shape changes. Using the conventional finite clement method, the inter-element continuity of the design space is not guaranteed so that the normal vector and curvature arc not accurate enough. On tile other hand, in isogeometric analysis, these values arc continuous over the whole design space so that accurate shape sensitivity can be obtained. Through numerical examples, the developed isogeometric sensitivity analysis method is verified to show excellent agreement with finite difference sensitivity.

• 대한전자공학회논문지SP
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• 제46권6호
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• pp.43-57
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• 2009

여러 시점에서 계측한 3차원 데이터를 통합하는 기술은 3차원 모델링에 매우 중요한 기술이다. 기존의 표면(Surface)통합 방법들은 정합오차와 잡음에 민감하다. 본 논문에서는 표면의 지역적 지형을 이용하는 표면통합 알고리즘을 제안한다. 제안하는 알고리즘은 먼저 인접한 표면 사이에서 일정 지형적 조건을 만족하는 외곽정점의 쌍, 즉 대응정점을 찾아 표면 사이의 지역을 여러 지역으로 구분한다. 다음으로 주성분 분석(PCA)을 통해 각 지역에 대한 최접합 평면(Best Pitting Plane)을 계산하여 표면 사이에 삽입될 삼각형의 생성에 이용한다. 제안하는 알고리즘은 지역적 단위로 지형을 이용하여 인접한 표면을 통합하기 때문에 정합오차와 잡음에 강건하다. 본 논문에서는 또한 변수화(Parameterization)기술을 이용하는 질감(Texture)통합 방법을 제안한다. 제안하는 방법은 통합된 표면을 각 표면의 초기시점으로 변환하고 해당 시점의 질감영상을 투영한다. 투영된 질감영상들을 통합된 표면의 2차원 변수화 표면에 할당하여 표면들이 통합된 이음새를 따라 통합한다. 실험을 통해 제안하는 방법이 얼굴모델링에 효율적임을 보인다.

• 한국전산구조공학회논문집
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• 제20권3호
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• pp.339-345
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• 2007

본 논문에서는 등기하 해석법을 이용하여 평면 탄성문제의 변분식을 유도하였다. 등기하 해석법은 새로이 부각되고 있는 해석법으로서 기저 함수가 NURBS(Non-Uniform Rational B-Splines) 로부터 직접 생성되므로 해 공간은 CAD 모델을 구성하는 함수로써 표현된다. 또한 CAD 모델의 B-Spline 기저 함수를 직접 사용하므로 기하학적으로 엄밀한 형상을 표현할 수 있고 요소망의 재구성 없이 해석모델을 정밀화(Refinement)할 수 있는 강점이 있다. 본 논문에서는 이를 확장하여 연속체 기반의 애드조인트 설계 민감도 해석법을 사용하는 등기하 설계민감도 해석법을 유도하였다. 기존의 유한요소 기반형상 최적설계는 형상의 매개화에 어려움을 겪었으나 등기하 기반 최적설계에서는 기하학적 정보가 이미 B-spline 기저함수와 조정점에 포함되어 있으므로 이러한 어려움을 피할 수 있는 잠재력을 가지고 있다. 몇몇 수치 예제를 통해서 등기하 해석법을 사용한 설계 민감도 해석을 수행하였으며 유한차분 민감도와 비교하여 정확성을 확인하였다.

• Steel and Composite Structures
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• 제37권6호
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• pp.663-678
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• 2020

This paper proposes a novel topology optimization method generating multiple materials for external linear plane crack structures based on the combination of IsoGeometric Analysis (IGA) and eXtended Finite Element Method (X-FEM). A so-called eXtended IsoGeometric Analysis (X-IGA) is derived for a mechanical description of a strong discontinuity state's continuous boundaries through the inherited special properties of X-FEM. In X-IGA, control points and patches play the same role with nodes and sub-domains in the finite element method. While being similar to X-FEM, enrichment functions are added to finite element approximation without any mesh generation. The geometry of structures based on basic functions of Non-Uniform Rational B-Splines (NURBS) provides accurate and reliable results. Moreover, the basis function to define the geometry becomes a systematic p-refinement to control the field approximation order without altering the geometry or its parameterization. The accuracy of analytical solutions of X-IGA for the crack problem, which is superior to a conventional X-FEM, guarantees the reliability of the optimal multi-material retrofitting against external cracks through using topology optimization. Topology optimization is applied to the minimal compliance design of two-dimensional plane linear cracked structures retrofitted by multiple distinct materials to prevent the propagation of the present crack pattern. The alternating active-phase algorithm with optimality criteria-based algorithms is employed to update design variables of element densities. Numerical results under different lengths, positions, and angles of given cracks verify the proposed method's efficiency and feasibility in using X-IGA compared to a conventional X-FEM.

• 대한공간정보학회지
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• 제17권3호
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• pp.115-120
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• 2009

기존의 도화사 수작업에 의한 기준점기반 항공삼각측량 기법은 전통적인 사진측량에서 유용하게 이용되어 왔으나, 자동화된 수치사진측량 기법이 확산되면서 기존방법의 문제점이 대두되었다. 따라서 본 논문은 보다 발전된 자동화 기술 개발을 위하여 상위 레벨인 선형객체들을 이용한 항공삼각측량 가능성을 제시하고 검증하고자 하였다. 최근에 발달된 선형 객체 추출기법 알고리즘은 보다 정확한 선형 객체 추출기법을 제공하였지만, 포인트 추출기법에 비하여 추출하기 어려운 단점이 존재한다. 따라서 본 논문은 이를 극복하기 위하여 수동 디지타이징이나 에지 연산자를 통하여 쉽게 획득되는 포인트를 이용하여 상위레벨 선형객체를 생성하고, 이를 통해 지형공간정보 이용 가능성을 높이고자 하였다. 본 연구 결과를 통해 진화하고 있는 컴퓨터 환경에 적합한 선형객체를 이용한 항공삼각측량 기법을 발전시킬 것으로 기대된다.

• 한국측량학회지
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• 제37권2호
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• pp.55-62
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• 2019

The stereo geometry establishment based on the precise sensor modeling is prerequisite for accurate stereo data processing. Ground control points are generally required for the accurate sensor modeling though it is not possible over the area where the accessibility is limited or reference data is not available. For the areas, the relative orientation should be carried out to improve the geometric consistency between the stereo data though it does not improve the absolute positional accuracy. The relative orientation requires conjugate points that are well distributed over the entire image region. Therefore the automatic conjugate point extraction is required because the manual operation is labor-intensive. In this study, we applied the method consisting of the key point extraction, the search space minimization based on the epipolar line, and the rigorous outlier detection based on the RPCs (Rational Polynomial Coefficients) bias compensation modeling. We tested different parameters of window sizes for Kompsat-2 across track stereo data and analyzed the RPCs precision after the bias compensation for the cases whether the epipolar line information is used or not. The experimental results showed that matching outliers were inevitable for the different matching parameterization but they were successfully detected and removed with the rigorous method for sub-pixel level of stereo RPCs precision.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2471-2478
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• 2020

Pumps are essential machinery in the various industries. With the development of high-speed and large-scale pumps, especially high energy density, high requirements have been imposed on the vibration and noise performance of pumps, and cavitation is an important source of vibration and noise excitation in pumps, so it is necessary to improve pumps cavitation performance. The modern pump optimization design method mainly adopts parameterization and artificial intelligence coupling optimization, which requires direct correlation between geometric parameters and pump performance. The existing cavitation performance calculation method is difficult to be integrated into multi-objective automatic coupling optimization. Therefore, a fast prediction method for pump cavitation performance is urgently needed. This paper proposes a novel cavitation prediction method based on impeller pressure isosurface at single-phase media. When the cavitation occurs, the area of pressure isosurface S_iso increases linearly with the NPSH_a decrease. This demonstrates that with the development of cavitation, the variation law of the head with the NPSH_a and the variation law of the head with the area of pressure isosurface are consistent. Therefore, the area of pressure isosurface S_iso can be used to predict cavitation performance. For a certain impeller blade, since the area ratio R_s is proportional to the area of pressure isosurface S_iso, the cavitation performance can be predicted by the R_s. In this paper, a new cavitation performance prediction method is proposed, and the feasibility of this method is demonstrated in combination with experiments, which will greatly accelerate the pump hydraulic optimization design.

• 한국전산구조공학회논문집
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• 제25권6호
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• pp.497-504
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• 2012

유한요소 해석법에서는 CAD 모델을 유한요소 모델로 이산화하기 때문에 CAD와 해석 모델의 차이로 인해 형상 설계민감도 및 최적설계에서 설계영역 매개 변수화에 어려움이 있다. 반면에 아이소-지오메트릭 해석법은 CAD 모델과 동일한 NURBS 기저함수와 조정점을 해석에 이용함으로써 설계의 기하학적 변화를 해석모델에 직접적으로 표현할 수 있기 때문에 전술된 여러 어려움들을 개선할 수 있다. 본 연구에서는 일반 곡면 좌표계에서 아이소-지오메트릭 해석 모델을 정식화하여 곡면 부재에 대한 구조해석과 형상 설계민감도 해석을 수행하였다. 아이소-지오메트릭 해석에서는 법선, 접선, 곡률 등과 같은 고차의 기하학적 정보들이 엄밀하게 표현될 수 있기 때문에 주어진 CAD 모델에 적합한 일반 곡면 좌표계를 생성해 낼 수 있다. 기존의 아이소-지오메트릭 구조해석 및 설계민감도 해석 결과와 비교하여 제안된 해석방법론이 더 정확한 해와 더 빠른 수렴성을 보이는 것을 확인하였다.