• 한국컴퓨터그래픽스학회논문지
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• 제25권3호
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• pp.123-131
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• 2019

본 연구에서는 CT 영상의 대퇴골 부위를 해부학적으로 의미 있게 변형하여 CT 영상의 대퇴골 영역을 분할하기 위한 컨벌루션 신경망(CNN)의 훈련 데이터를 증강하는 방법을 제안한다. 먼저 CT 영상으로부터 삼차원 삼각형 대퇴골 메쉬를 얻는다. 그 후 메쉬의 국소부위에 대한 기하학적 특성을 계산하고, 군집화하여 메쉬를 의미 있는 부분들로 분할한다. 마지막으로, 분할한 부분들을 적절한 알고리즘으로 변형한 뒤, 이를 바탕으로 CT 영상을 와핑하여 새로운 CT영상을 생성하였다. 본 연구의 데이터 증강 방법을 이용하여 학습시킨 딥러닝 모델은 기하학적 변환이나 색상 변환 같이 일반적으로 사용되는 데이터 증강법과 비교하여 더 나은 영상분할 성능을 보인다.

• 대한두개안면성형외과학회지
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• 제19권4호
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• pp.264-269
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• 2018

Background: Orbital resorbable mesh plates are adequate to use for isolated floor and medial wall fractures with an intact bony buttress, but are not recommended to use for large orbital wall fractures that need load bearing support. The author previously reported an orbital wall restoring surgery that restored the orbital floor to its prior position through the transnasal approach and maintained temporary extraorbital support with a balloon in the maxillary sinus. Extraorbital support could reduce the load applied on the orbital implants in orbital wall restoring surgery and the use of resorbable implants was considered appropriate for the author's orbital wall restoring technique. Methods: A retrospective review was conducted of 31 patients with pure unilateral orbital floor fractures between May 2014 and May 2018. The patients underwent transnasal restoration of the orbital floor through insertion of a resorbable mesh plate and maintenance of temporary balloon support. The surgical results were evaluated by the Hertel scale and a comparison of preoperative and postoperative orbital volume ratio (OVR) values. Results: The OVR decreased significantly, by an average of 6.01% (p<0.05) and the preoperative and postoperative Hertel scale measurements decreased by an average of 0.34 mm with statistical significance (p<0.05). No complications such as buckling or sagging of the implant occurred among the 31 patients. Conclusion: The use of resorbable mesh plate in orbital floor restoration surgery is an effective and safe technique that can reduce implant deformation or complications deriving from the residual permanent implant.

• 항공우주시스템공학회지
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• 제16권5호
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• pp.86-93
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• 2022

우주용 전개형 메쉬 안테나는 궤도 운용 시 RF 성능을 보장하기 위해 극한의 궤도 열 환경 하에서 극심한 온도변화에 의한 열변형을 최소화할 수 있는 열설계가 필수적이다. 일반적으로 궤도 상에서 전력 생성을 위해 전개형 태양전지판이 주로 적용되고 있으나, 태양전지판으로 인한 그림자로 인해 안테나 표면에 극심한 온도구배가 발생할 수 있다. 본 논문에서는 전개형 메쉬 안테나 후면부에 멤브레인 시트를 적용하고, 시트 후면부에 유연 태양전지셀을 부착하여 전개형 태양전지판으로 인한 온도구배를 최소화할 수 있는 이중막 구조의 설계 방식을 제안하였다. 제안된 안테나 열설계의 유효성을 검증하기 위해 궤도 열해석을 통해 안테나 표면에서 발생하는 온도구배 분석을 수행하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.247-250
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• 2007

Flexible media such as the paper, the film, etc. are thin, light and very flexible. They behave in geometrically nonlinear. Any of small force makes large deformation. So we must including aerodynamic effect when its behavior is predicted. Thus, it becomes fully coupled fluid-structure interaction(FSI) problem. In FSI problems, where the fluid mesh near the structure undergoes large deformations and becomes unacceptably distorted, which drive the time step to a very small value for explicit calculations, the arbitrary Lagrangian-Eulerian(ALE) methods or rezoning are used to create a new undistorted mesh for the fluid domain, which allows the calculations to continue. In this paper, FE sheet model considering geometric nonlinearity is formulated to simulate the behavior of the flexible media. Aerodynamic force to the media by surrounding air is calculated by solving the incompressible Navier-Stokes equations. Q2Q1(Taylor-Hood) element which means biquadratic for velocity and bilinear for pressure is used for fluid domain. Q2Q1 element satisfies LBB condition and any stabilization technique is not needed. In this paper, cantilevered sheet in the viscous incompressible Navier-Stokes flow is simulated to check the mesh motion and numerical integration scheme, and then falling paper in the air is simulated and the effects of some representative parameters are investigated.

• 한국게임학회 논문지
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• 제8권2호
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• pp.47-55
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• 2008

본 논문에서는 스켈레톤(skeleton)의 리깅(rigging)방식을 사용하여 해부학을 기초로 한 14개의 표정근과 동일한 기능을 수행하게 얼굴의 표정을 표현하는 SSFE(Skeleton System for Facial Expression)를 제안한다. SSFE는 3차원애니메이션저작도구(MAYA 8.5)에서 제공하는 스켈레톤을 Deformer로 이용하여 메시모델(mesh model)의 눈, 코, 입 주변의 얼굴표정을 단위 동작별로 구분하여 조합하여 얼굴표정을 만들어 내는 방식이다. 이 결과, SSFE식 스켈레톤은 다른 모델에 무한대로 변형하여 재활용 할 수 있게 해준다. 이러한 재활용성은 애니메이션의 제작방식의 OSMU(One Source Multi Use)로 이해 될 수 있으며 애니메이션의 제작비용을 줄일 수 있는 대체방식이다. 또한 3차원 애니메이션 관련업체 즉 가상현실이나 게임, 제작에 활용될 수 있다.

• Design & Manufacturing
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• 제15권3호
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• pp.39-44
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• 2021

In molding of continuous fiber-reinforced thermoplastic composites, it is very difficult to impregnate between the reinforcements and the matrix since the matrix has a high melting temperature and high viscosity. Therefore, most of composite molding processes are divided in the manufacturing processes of intermediate materials called prepreg and the forming of products from intermediate materials. The divided process requires additional facilities and thermoforming, and they increase the cycle time and cost of composite products. These problems can be resolved by combining the continuous fiber-reinforced composite molding process with injection molding. However, when a composite material is manufactured by inserting woven fabric into the injection mold, poor impregnation occurs on the surface of the molded product. It affects the properties of the composites. In this paper, through an impregnation experiment using cores with different heat transfer rates and pore densities, the reason for the poor impregnation was confirmed, and molding experiments were conducted to produce composite with improved surface impregnation by inserting the mesh. And also, the surface impregnation and deformation of composites molded using different types of mesh were compared with each other.

• Computers and Concrete
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• 제31권2호
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• pp.151-161
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• 2023

This paper presents an investigation of variables that cause spurious cracking in numerical modeling of concrete fracture. Spurious cracks appear due to the approximate nature of numerical modeling. They overestimate the dissipated energy, leading to divergent results with mesh refinement. This paper is limited to quasi-static loading regime, homogeneous models, cracking as the only nonlinear mode of deformation and cracking only due to tensile loading. Under these conditions, some variables that can be related to spurious cracking are: mesh alignment, ductility, crack band width, structure size, mesh refinement and load increment size. Case studies illustrate the effect of each variable and convergence analyses demonstrate that, after all, load-increment size is the most important variable. Theoretically, a sufficiently small load increment is able to eliminate or at least alleviate the detrimental influence of the other variables. Such load-increment size might be prohibitively small, rendering the simulation unfeasible. Hence, this paper proposes two alternatives. First, it is proposed an algorithm that automatically find such small load increment size automatically, which not necessarily avoid large computations. Then, it is proposed a double simulation technique, in which the crack is forced to propagate through the localization zone.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.128-131
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• 2009

In this paper, three-dimensional finite element analysis of screw rolling process of a long shaft bolt is conducted by using a rigid-plastic finite element method based metal forming simulator AFDEX 3D. A whole sequence of cold forming processes of a long shaft bolt composed of forging and screw rolling processes is simulated to reveal the mechanism of screw formation. A mesh density control function is applied near the major plastic deformation region to achieve computational efficiency.

• Structural Engineering and Mechanics
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• 제55권3호
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• pp.473-494
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• 2015

A graded harmonic finite element formulation based on three-dimensional elasticity theory is developed for the structural analysis of 2D functionally graded axisymmetric structures. The mechanical properties of the axisymmetric solid structures composed of two different metals and ceramics are assumed to vary in radial and axial directions according to power law variations as a function of the volume fractions of the constituents. The material properties of the graded element are calculated at the integration points. Effects of material distribution profile on the static deformation, natural frequency and dynamic response analyses of particular axisymmetric solid structures are investigated by changing the power law exponents. It is observed that the displacements, stresses and natural frequencies are severely affected by the variation of axial and radial power law exponents. Good accuracy is obtained with fewer elements in the present study since Fourier series expansion eliminates the need of finite element mesh in circumferential direction and continuous material property distribution within the elements improves accuracy without refining the mesh size in axial and radial directions.

• Journal of Advanced Marine Engineering and Technology
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• 제35권8호
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• pp.994-1000
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• 2011

본 논문은 압전소자의 주기적인 발진운동을 탄성 변환하여 유체유동을 유발하는 압전소자 팬의 수치해석 모델에 대한 연구이다. LED 모듈 등의 고밀도 열이 발생하는 소형 전자장치의 냉각에 적용이 가능한 압전소자 냉각팬의 성능 향상을 위해 CFD 도구를 이용하였다. 본 논문의 결과는 압전소자의 길이 5cm와 방열판의 길이 3cm라는 비율이 효과적이었다. 이는 기하학적으로 비슷한 형태를 가지고 다른치수를 가지는 모델에서 기초적인 설계를 하는데 도움이 될 것이다.