• Wind and Structures
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• 제22권1호
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• pp.89-106
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• 2016

With an aim to assess the wind damage to urban trees in more realistic conditions, the nonlinear dynamics of structured trees subjected to strong winds with different levels is investigated in the present paper. For the logical treatment of dynamical behavior of trees, material nonlinearities of green wood associated with tree biomechanics and geometric nonlinearity of tree configuration are included. Applying simulated fluctuating wind velocity to the numerical model, the dynamical behavior of the structured tree is explored. A comparative study against the linear dynamics analysis usually involved in the previous researches is carried out. The failure wind velocity of urban trees is then defined, whereby the failure percentages of the tree components are exposed. Numerical investigations reveal that the nonlinear dynamics analysis of urban trees results in a more accurate solution of wind-induced response than the classical linear dynamics analysis, where the nonlinear effect of the tree behavior gives rise to be strengthened as increasing of the levels of wind velocity, i.e., the amplitude of 10-min mean wind velocity. The study of relationship between the failure percentage and the failure wind velocity provides a new perspective towards the vulnerability assessment of urban trees likely to fail due to wind actions, which is potential to link with the practical engineering.

• 로봇학회논문지
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• 제11권3호
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• pp.163-171
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• 2016

A modular manipulator in serial-chain structure usually consists of a series of modularized revolute joint and link modules. The geometric shapes of these modules affect the number of possible configurations of modular manipulator after assembly. Therefore, it is important to design the geometry of the joint and link modules that allow various configurations of the manipulators with minimal set of modules. In this paper, a new 1-DoF(degree of freedom) joint module and simple link modules are designed based on a methodology of joint configurations using a series of Rotational(type-R) and Twist(type-T) joints. Two of the joint modules can be directly connected so that two types of 2-DoFs joints could be assembled without a link module between them. The proposed geometries of joint and link modules expand the possible configurations of assembled modular manipulators compared to existing ones. Modular manipulator system of this research can be a cornerstone of user-centered markets with various solution but low-cost, compared to conventional manipulators of fixed-configurations determined by the provider.

• Korean Journal of Geomatics
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• 제1권1호
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• pp.69-74
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• 2001

In conventional photogrammetry, three-dimensional coordinates are obtained from two consecutive images of a stationary object photographed from two exposure stations, separated by a certain distance. However, it is impossible to photograph moving objects from two stations with one camera at the same time. Various methods to overcome this obstacle were devised e. g. taking the left and right scenes simultaneously with one camera using a beam splitter attached to the front, thus creating a stereo scene in one image. A beam splitter consists of two outer mirrors and two inner mirrors. This paper deals with research where the optical principles of the beam splitter were evaluated based on light path phenomena between the outer mirrors and the inner mirrors. A mathematical model of the geometric configuration was derived for the beam splitter. This allows us to design and control a beam splitter to obtain maximum scale and maximum base-height ratio by stepwise application of the mathematical model. The results show that the beam splitter is a very useful tool for stereophotography with one camera. The optimum geometric configurations ensuring maximum scale and base-height ratio are closely related to inner and outer reflector sizes, their inclination angles and the offsets between the outer mirrors.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권6호
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• pp.995-1006
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• 2015

Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB), is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line, and the section is defined with symmetrical airfoil NACA 0012. Computational investigations are carried out to study the hydrodynamic performance of the glider using the commercial Computational Fluid Dynamics (CFD) code Fluent. The Kriging-based genetic algorithm, called Efficient Global Optimization (EGO), is applied to hydrodynamic design optimization. The result demonstrates that the BWB underwater glider has excellent hydrodynamic performance, and the lift to drag ratio of initial design is increased by 7% in the EGO process.

• 한국전산구조공학회논문집
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• 제25권6호
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• pp.477-485
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• 2012

내압구조물의 구조적 성능에 영향을 주는 주요 요소로 형상, 쉘 두께, 보강재 배치 안 그리고 제작 재료 등을 나열할 수 있다. 전통적인 이론적 방법론에 근거한 내압구조물의 설계는 신속하며 만족할 만한 결과를 제공하지만 이는 일부 특정한 형상, 쉘 두께 및 제작 재료 등에 제한되어 있다. 본 논문에서는 최적화된 형상, 쉘 두께, 보강재 배치 안 그리고 복합재료 적층 정보 등을 얻을 수 있는 최적설계 기법에 근거한 진보된 대체 방법론을 다루고 있다. CAE 기반의 최적설계 기법을 활용하여 내압구조물 설계에 요구되는 구조적 성능과 최적화된 설계 인자들을 얻었다. 상용화된 유한요소 프로그램임 ANSYS의 CAE 플랫폼으로부터 메타모델 기반 최적화 기법을 수행하여 원통형 내압구조물의 설계를 위한 최적의 타원형 형상을 결정하였다. 또한 최적설계 프로그램인 OptiStruct의 기울기 기반 최적설계 방법을 이용하여 복합재료 기반 내압구조물의 설계시 최적의 적층순서와 쉘 두께가 얇은 내압구조물에 대한 최적의 보강재 배치 안을 각각 도출하였다. 최적설계 예제를 통해 본 논문에서 제시하고 있는 최적설계 기법에 근거한 방법론이 내압구조물의 설계에 효과적임을 확인할 수 있었다.

• 한국철도학회논문집
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• 제17권3호
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• pp.186-192
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• 2014

본 연구에서는 콘크리트 진공튜브 구조의 설계에 있어서 주어진 재료 및 시스템 구성에서 존재하는 불확실성을 정량화하여 내부기압의 변화를 확률적으로 예측할 수 있는 신뢰성 평가를 수행하였다. 시스템 등가투기계수의 산정 및 외부기압에 영향을 주는 인자들 중 불확실성을 내재하고 있는 인자들을 확률변수로 모델링한 후 수식 유도 및 시뮬레이션을 통해 시간에 따른 내부기압의 변화를 확률적으로 예측하였으며 확정적 해석과 그 결과를 비교 분석한 결과 적정 수준의 신뢰성을 얻기 위해서는 단면의 변화가 반드시 필요한 것으로 나타났다. 이와 같은 튜브구조의 기밀성능에 대한 확률적 해석 결과는 튜브 내부를 주행하는 열차 또는 다른 운송수단의 추진력과 공기저항, 그리고 펌프의 용량을 복합적으로 고려하여 목표 압력을 정하고 튜브 단면을 결정하는데 필요한 기술적 자료로써 활용될 수 있을 것이다.

• 한국주거학회논문집
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• 제27권6호
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• pp.85-93
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• 2016

The spaces have a variety of sizes dependent upon their function and significance as well as their geometric shape. An architect Adolf Loos (1870-1933) had incorporated a correlation between the unconstrained formation of space into design. He had noticeably revealed the features of space that are unconstrained and mutually related with each other, for the space compositions among modern architects. This study is about to analyze the feature of space structure for houses of Adolf Loos through Space syntax which is the quantitative space analyzing method for the subject of his detached houses. These houses were emphasized for functional aspects of space without unnecessary decorations. Le Corbusier's Villa Savoye was analysed along with it to review a comparative point of view of his house's characteristic. Based on this, the features of the spatial structure of Loos' house were examined in conjunction with his views space as essence. A J-Graph and VGA for Adolf Loos' detached house revealed the structure's spatial characteristics in which the interior space is located deeply removed from exterior yet it is integrated as a whole. Also, it revealed that the experiments of the various spatial structures shown in Adolf Loos' detached house and European rationalist architects like Le Corbusier affected each other at the same time.

• 한국자동차공학회논문집
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• 제21권3호
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• pp.30-42
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• 2013

This study investigates the effects of OSRVM mounting location and its configurations such as stalk height and housing height on the aerodynamic performance of the passenger car. In order to validate the flow solver, FLUENT which is very well known commercial code, the flow field around an Ahmed Body was analyzed numerically and compared with the experimental data. The predicted aerodynamic performance and flow patterns around a car show good agreements with the experimental data. Mounting location and stalk height should be designed while OSRVM is mounted on the car to evaluate the aerodynamic performance precisely. Housing height, however, may be designed independent of the car because the aerodynamic interference between housing height and car configuration is negligible.

• Structural Engineering and Mechanics
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• 제61권2호
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• pp.193-207
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• 2017

In this study, the vibration of an electrostatically actuated micro cantilever beam is analyzed in which a viscoelastic layer covers a portion of the micro beam length. This proposed model is considered as the main element of mass and pollutant micro sensors. The nonlinear motion equation is extracted by means of Hamilton principle, considering nonlinear shortening effect for Euler-Bernoulli beam. The non-linear effects of electrostatic excitation, geometry and inertia have been taken into account. The viscoelastic model is assumed as Kelvin-Voigt model. The motion equation is discretized by Galerkin approach. The linear free vibration mode shapes of non-uniform micro beam i.e. the linear mode shape of the system by considering the geometric and inertia effects of viscoelastic layer, have been employed as comparison function in the process of the motion equation discretization. The discretized equation of motion is solved by the use of multiple scale method of perturbation theory and the results are compared with the results of numerical Runge-Kutta approach. The frequency response variations for different lengths and thicknesses of the viscoelastic layer have been founded. The results indicate that if a constant volume of viscoelastic layer is to be deposited on the micro beam for mass or gas sensor applications, then a modified configuration may be found by using the analysis of this paper.

• Structural Engineering and Mechanics
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• 제59권6호
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• pp.1095-1120
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• 2016

This paper investigates the change of structural characteristics of steel cable-stayed bridges after cable failure. Cables, considered as the intermediate supports of cable-stayed bridges, can break or fail for several reasons, such as fire, direct vehicle clash accident, extreme weather conditions, and fatigue of cable or anchorage. Also, the replacement of cables can cause temporary disconnection. Because of the structural characteristics with various geometric nonlinearities of cable-stayed bridges, cable failure may cause significant change to the structural state and ultimate behavior. Until now, the characteristics of structural behavior after cable failure have rarely been studied. In this study, rational cable failure analysis is suggested to trace the new equilibrium with structural configuration after the cable failure. Also, the sequence of ultimate analysis for the structure that suffers cable failure is suggested, to study the change of ultimate behavior and load carrying capacity under specific live load conditions. Using these analysis methods, the statical behavior after individual cable failure is studied based on the change of structural configuration, and distribution of internal forces. Also, the change of the ultimate behavior and load carrying capacity under specific live load conditions is investigated, using the proposed analysis method. According to the study, significant change of the statical behavior and ultimate capacity occurs although just one cable fails.