• 연구논문집
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• 통권27호
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• pp.183-200
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• 1997

We have calculated the energy of three distinct grain configurations, namely completely connected, partially connected and unconnected configurations, evolving during a spheroidization of polycrystalline thin film by extending a geometrical model due to Miller et al. to the case of spheroidization at both the surface and film-substrate interface. "Stabilitl" diagram defining a stable region of each grain configuration has been established in terms of the ratio of grain size to film thickness vs. equilibrium wetting or dihedral angles at various interface energy conditions. The occurrence of spheroidization at the film-substrate interface significantly enlarges the stable region of unconnected grain configuration thereby greatly facilitating the occurrence of agglomeration. Complete separation of grain boundary is increasingly difficult with a reduction of equilibrium wetting angle. The condition for the occurrence of agglomeration differs depending on the equilibrium wetting or dihedral angles. The agglomeration occurs, at low equilibrium angles, via partially connected configuration containing stable holes centered at grain boundary vertices, whereas it occurs directly via completely connected configuration at large equilibrium angles except for the case having small surface and/or film-substrate interface energy. The initiation condition of agglomeration is defined by the equilibrium boundary condition between the partially connected and unconnected configurations for the former case, whereas it can, for the latter case, largely deviate from the equilibrium boundary condition between the completely connected and unconnected configurations because of the presence of a finite energy barrier to overcome to reach the unconnected grain configuration.

• 한국항공운항학회지
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• 제25권2호
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• pp.63-68
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• 2017

In the present study, a wind tunnel test for a rotor-blade configuration was conducted to investigate a basic aerodynamic performance and a effect of the cross wind. The diameter of the configuration was 1.46 m and the test was carried out for both a clean and a tripped configurations. The boundary layer for the trip configuration was simulated by zig-zag tape and the test performed on constant-velocity and constant-rotational modes. It was shown that the test result for the tripped configuration reduces the maximum power coefficient by 9.4% ~ 12.1% compared to the clean one. Within $5^{\circ}$ of the flow angle, there is no significant loss of power, however, the coefficient is reduced by 5.3% ~ 36.7% in the range of $10^{\circ}{\sim}30^{\circ}$.

• 한국공간구조학회논문집
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• 제2권3호
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• pp.71-79
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• 2002

The purpose of this paper is to study the buckling characteristics of elliptical latticed domes under conservative loading conditions. The latticed domes are usually designed in geometrically spherical shape. For this type of latticed domes, many researchers have researched and even the simplified estimation codes for the buckling load level have been available. However, geometrically elliptical latticed domes have been often constructed, and show different buckling characteristics following with geometrical parameters as rise-to-span ratio and so on. Therefore, it is necessary to investigate the general tendency of buckling characteristics of the elliptical latticed domes. In this paper, to find out some buckling characteristics of elliptical latticed domes, height, boundary configuration and gap are used as the shape coefficients. For each model with different parameters, the eigen values and the buckling loads are evaluated.

• 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.

• International Journal of Aeronautical and Space Sciences
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• 제6권2호
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• pp.33-45
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• 2005

The 1/9-scale model of a fighter-type configuration was tested in the Micro-Craft 8ft ${\times}$ 12ft wind tunnel facility. An abrupt lift dump was found at a certain range of angle of attack under the pre-scheduled approach configuration. To avoid a probable unsatisfactory flight behavior due to the lift dump, various aerodynamic devices were suggested. Extensive tests applying the cutoff leading edge flaps, boundary layer fences, saw tooth and vortex generators were performed with flow visualization as well as force and moment measurements. Test results showed that the origin of the lift dump was caused by the secondary boundary layer flow separation generated from the strong interaction between wing and flap. Various solutions for avoiding the unfavorable feature were suggested with the merits and demerits.

• Journal of Information Processing Systems
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• 제16권6호
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• pp.1324-1342
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• 2020

Various modified algorithms of rapidly-exploring random tree (RRT) have been previously proposed. However, compared to the RRT algorithm for collision avoidance with global and static obstacles, it is not easy to find a collision avoidance and local path re-planning algorithm for dynamic obstacles based on the RRT algorithm. In this study, we propose boundary-RRT*, a novel-algorithm that can be applied to aerial vehicles for collision avoidance and path re-planning in a three-dimensional environment. The algorithm not only bounds the configuration space, but it also includes an implicit bias for the bounded configuration space. Therefore, it can create a path with a natural curvature without defining a bias function. Furthermore, the exploring space is reduced to a half-torus by combining it with simple right-of-way rules. When defining the distance as a cost, the proposed algorithm through numerical analysis shows that the standard deviation (σ) approaches 0 as the number of samples per unit time increases and the length of epsilon ε (maximum length of an edge in the tree) decreases. This means that a stable waypoint list can be generated using the proposed algorithm. Therefore, by increasing real-time performance through simple calculation and the boundary of the configuration space, the algorithm proved to be suitable for collision avoidance of aerial vehicles and replanning of local paths.

• 대한토목학회논문집
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• 제29권4A호
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• pp.337-346
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• 2009

타정식 현수교의 보강형 가설중의 경계조건과 하중조건의 변화를 고려하여 초기형상을 결정하기 위한 구조해석 모델링 방법 및 해석 알고리즘을 제안하였다. 타정식 현수교의 가설단계를 보강형의 가설시점을 기준으로 보강형 가설단계인 1단계와 완공단계의 2단계로 구분하였으며 이러한 가설단계를 고려하여 초기형상해석 단계를 1차 형상해석과 2차 형상보정해석의 2단계로 구분하였다. 각 해석단계에 대한 보강형의 경계조건과 작용하중의 모델링 방법 및 반복해석 알고리즘을 제안하였으며 실 교량에 대해 수치해석을 수행하여 기존 해석방법에 의한 초기형상해석결과와 비교, 분석하였다. 실 교량에 대한 수치해석 결과 기존 초기형상해석방법의 문제점을 파악할 수 있었으며 본 연구에서 제안된 방법을 적용할 경우 기존 방법의 문제점을 해결할 수 있음을 확인하였다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제13권2호
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• pp.100-105
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• 2013

In this study, we analyze the balance of quadruped walking robots. For this purpose, a simplified polygonal model of a quadruped walking configuration is considered. A boundary-range-based balance margin is used for determining the system stability of the polygonal walking configuration considered herein. The balance margin enables the estimation of the walking configuration's balance for effective walking. The usefulness of the balance margin is demonstrated through exemplary simulations. Furthermore, balance compensation by means of foot stepping is addressed.

• 오토저널
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• 제10권2호
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• pp.61-69
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• 1988

The finite-difference three-dimensional boundary layer procedure of Chang and Patel is modified and applied to solve the boundary layer development on the automobile surface. The inviscid pressure distribution needed to solve the boundary layer equations is obtained by using a low order panel method. The plane of symmetry boundary layer exhibits the strong streamline divergence up to the midbody and convergence thereafter. The streamline divergence in front of the windshield helps the boundary layer to overcome the sever adverse pressure gradient and avoid the separation. The relaxation of the pressure right after the top of the wind-shield, on the other hand, makes the overly thinned boundary layer to readjust and prompts the streamlines to converge into the symmetry plane before the external streamlines do. The three-dimensional characteristics are less apparent after the midbody and the boundary layer is similar to that of the two-dimensional flow. The results of the off-plane-of-symmetry boundary layer are also presented.

• 한국연소학회지
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• 제21권4호
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• pp.48-60
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• 2016

Experimental and numerical studies were conducted to investigate flame behaviors near flammable limits for downstream-interacting SNG-air premixed flames in a counter-flow configuration. The SNG fuel consisted of a methane, a propane, and a hydrogen with volumetric ratios of 91, 6, and 3%, respectively. The most appropriate priority for some reliable reaction mechanisms examined was given to the mechanism of UC San diego via comparison of lean extinction limits attained numerically with experimental ones. Flame stability map was presented with a functional dependencies of lower and upper methane concentrations in terms of global strain rate. The results show that, at the global strain rate of $30s^{-1}$, lean extinction boundary is slanted while rich extinction one is relatively less inclined because of the dependency of such extinction boundary shapes on deficient reactant Lewis number governed by methane mainly. Further increase of global strain rate forces both extinction boundaries to be more slanted and to be shrunk, resulting in an island of extinction boundary and subsequently one flame extinction limit. Extinction mechanisms for lean and rich, symmetric and asymmetric extinction boundary were identified and discussed via heat losses and chemical interaction.