• 한국산학기술학회논문지
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• 제17권12호
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• pp.17-25
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• 2016

호안은 하천제방의 비탈면이 침식되지 않도록 보호하는 기능을 갖는다. 호안의 설계가 적정하지 않을 경우 강한 유속과 소류력에 의해 제방이 세굴되어 붕괴에 이를 수도 있다. 따라서 호안의 설계시 필요한 대표유속을 산정하는 것은 매우 중요하나 대부분 1차원 부등류해석에서 얻어진 수위와 평균유속자료를 적용한다. 이 경우 만곡 수로에서 발생하는 자유소용돌이와 강제소용돌이에 의한 유속증가는 반영되지 않으므로 만곡부 호안의 안정성을 확보하기 위해서는 대표유속에 대한 보정이 필요하다. 본 연구에서는 수치모의를 통해 단면의 최대유속과 평균유속을 산정하여 만곡 및 세굴영향을 고려한 대표유속 산정방법의 적용성에 대해 검토하였다. 그 결과 단면평균유속에 만곡의 영향과 세굴의 영향을 고려하여 적용한 대표유속과 수치모의결과에 추출된 최대유속을 비교한 결과가 거의 일치하는 것으로 나타났다. 또한, 호안재로로써 돌망태를 사용하는 경우에 대해서 만곡하도와 직선하도 일때의 사석크기를 기존 설계식에 적용하여 비교하였다. 향후, 우리나라의 특성에 맞는 호안설계방법을 제시하기 위하여 하천특성이 다른 대표적인 하천에 대한 추가적인 수치모의 및 분석이 필요하며, 이때 본 연구결과가 기초자료로 활용될 수 있을 것으로 기대된다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.69-70
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• 2013

By using differential force between left and right wheel, lateral motion can be controlled known as Direct Yaw-moment Control (DYC). In previous researches, DYC control is proposed to increase the stability of the vehicle, but maneuverability has not been discussed sufficiently. The car handling condition which is called the index parameter of maneuverability is dependent on the vehicle velocity and steering angle. To achieve the desired vehicle's cornering path, the car handling condition must be considered sufficiently. In this paper, the novel DYC method is proposed which gives the car handling condition regardless of the longitudinal speed. The proposed controller is based on the PI controller to feedback the curvature parameter. The controlled system shows the advantages of DYC regarding to the reference trajectory by the dual motor system. With respect to the uncontrolled model, the effectiveness of the proposed method is validated by numerical examples.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.787-792
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• 1991

This paper proposes a steering control algorithm for non-holonomic mobile robots. The steering control algorithm is essential to navigate autonomous vehicles which employ comination of the dead reckoning and absolute sensor system such as a machine vison for detecting landmarks in order to estimate the current location of the mobile robot. The proposed algorithm is based on the minimum time BANG-BANG controller and curvature-continuity curve design method. In the BANG-BANG control scheme we introduce velocity/acceleration limiter to avoid any slippage of driving wheels. The proposed scheme is robot-independent and hence can be applied to various kinds of mobile robot or vehicles. To show the effectness of the proposed control algorithm, a series of computer simulations were conducted for two-wheel driven mobile robot.

• 설비공학논문집
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• 제3권1호
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• pp.11-25
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• 1991

The steady, incompressible developing 3-dimensional turblent flow in a square sectioned curved duct has been investigated by using partially-parabolic equation and Finite Analytic Method. The calculation of turbulent flow field is performed using 2-equation K-$\epsilon$ turbulence model, modified wall function, simpler algorithm and numerically generated body fitted coordinates. Iso-mean velocity contours at the various sections are compared with the existing experimental data and elliptic solutions by other authors. In the region of $0^{\circ}<{\theta}<71^{\circ}$, present results agree with the experimental data much better than the elliptic solution for the similar number of grid points. Furthermore, for the same tolerance, the present solution converges four times faster than the elliptic solution.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제12권3호
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• pp.256-262
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• 2012

Direct teaching of the industrial robot is a novel technique to easily teach manipulators. However, teaching data by human hand cannot help having large noise errors ranging from low to high frequency. To use teaching data, post-processing to correct the teaching trajectory is required. Here, a novel shape-based trajectory correction method to rebuild teaching data with the feature information of curvature and velocity is proposed. The proposed method is tested on square and circular objects.

• 로봇학회논문지
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• 제16권3호
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• pp.250-259
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• 2021

Path planning is one of the important technologies for automated parking. It requires to plan a collision-free path considering the vehicle's kinematic constraints such as minimum turning radius or steering velocity. In a complex parking lot, Rapidly-exploring Random Tree^* (RRT^*) can be used for planning a parking path, and Reeds-Shepp or Hybrid Curvature can be applied as a tree-extension method to consider the vehicle's constraints. In this case, each of these methods may affect the computation time of planning the parking path, path-tracking error, and parking success rate. Therefore, in this study, we conduct comparative analysis of two tree-extension functions: Reeds-Shepp (RS) and Hybrid Curvature (HC), and show that HC is a more appropriate tree-extension function for parking path planning. The differences between the two functions are introduced, and their performances are compared by applying them with RRT^*. They are tested at various parking scenarios in simulation, and their advantages and disadvantages are discussed by computation time, cross-track error while tracking the path, parking success rate, and alignment error at the target parking spot. These results show that HC generates the parking path that an autonomous vehicle can track without collisions and HC allows the vehicle to park with lower alignment error than those of RS.

• Korea-Australia Rheology Journal
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• 제14권3호
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• pp.107-114
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• 2002

Residual stress distribution in injection molded short fiber composites is determined by using the layer-removal method. Polystyrene is mixed with carbon fibers of 3% volume fraction (4.5% weight fraction) in an extruder and the tensile specimen is injection-molded. The layer-removal process, in which removing successive thin uniform layers of the material from the surface of the specimen by a milling machine, is employed and the resulting curvature is acquired by means of an image processing. The isotropic elastic analysis proposed by Treuting and Read which assumes a constant Yaung’s modulus in the thickness direction is one of the most frequently used methods to determine residual stresses. However, injection molded short fiber composites experience complex fiber orientation during molding and variation of Yaung’s modulus distribution occurs in the specimen. In this study, variation of Yaung’s modulus with respect to the thickness direction is considered for calculation of the residual stresses as proposed by White and the result is compared with that by assuming constant modulus. Residual stress distribution obtained from this study shows a typical stress profile of injection-molded products as reported in many literatures. Young’s modulus distribution is predicted by using numerical methods instead of experimental results. For the numerical analysis of injection molding process, a hybrid FEM/FDM method is used in order to predict velocity, temperature field, fiber orientation, and resulting mechanical properties of the specimen at the end of molding.

• 한국추진공학회지
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• 제26권5호
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• pp.11-23
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• 2022

길이를 단축한 ED(Expansion Deflection) 노즐의 설계를 위해 길이 단축 방안에 따른 ED 노즐의 수치적 연구를 수행하였다. 첫 번째 방안은 80% 벨 노즐 길이를 갖는 ED 노즐의 확장부 길이를 10%, 20%와 30%씩 단축하는 것이다. 두 번째 방안은 노즐 목 각도를 증가시켜 확장부 길이를 단축하는 것이다. 길이 단축에 따른 윤곽선의 곡률 증가로 인해 80% 벨 노즐 길이인 ED 노즐과 첫 번째 방안의 ED 노즐의 출구 유동 속도의 감소폭이 줄어들어 추력이 유사해졌다. 두 번째 방안의 ED 노즐은 80% 벨 노즐 길이인 ED 노즐보다 출구 유동 속도가 증가하여 추력이 증가하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.391-396
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• 2008

A level set based topological shape optimization using extended B-spline basis functions is developed for steady state heat conduction problems. The only inside of complicated domain is identified by the level set functions and taken into account in computation. The solution of Hamilton-Jacobi equation leads to an optimal shape according to the normal velocity field determined from the sensitivity analysis, minimizing a thermal compliance while satisfying a volume constraint. To obtain exact shape sensitivity, the precise normal and curvature of geometry need to be determined using the level set and B-spline basis functions. The nucleation of holes is possible whenever and wherever necessary during the optimization using a topological derivative concept.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.464-467
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• 1999

Usually, more reference signatures result in better performance in signature verification. However, registering .many signatures may be a tedious work for users, so algorithms that use less signatures for the registration without increasing error rate is needed. In this paper, we find the features such as pen-down duration, the number of locally minimum velocity points, and the number of locally maximum curvature points. Then we find the relationship between these features and the optimal decision boundary. We apply this relationship in deciding threshold for signature verification. Experimental results show that the method using three reference signatures has almost same error rate as algorithms with many references.