• Wind and Structures
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• 제19권1호
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• pp.35-58
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• 2014

A numerical simultaneous solution involving a linear elastic model was applied to study the fluid-structure interaction (FSI) of membrane structures under wind actions, i.e., formulating the fluid-structure system with a single equation system and solving it simultaneously. The linear elastic model was applied to managing the data transfer at the fluid and structure interface. The monolithic equation of the FSI system was formulated by means of variational forms of equations for the fluid, structure and linear elastic model, and was solved by the Newton-Raphson method. Computation procedures of the proposed simultaneous solution are presented. It was applied to computation of flow around an elastic cylinder and a typical FSI problem to verify the validity and accuracy of the method. Then fluid-structure interaction analyses of a saddle membrane structure under wind actions for three typical cases were performed with the method. Wind pressure, wind-induced responses, displacement power spectra, aerodynamic damping and added mass of the membrane structure were computed and analyzed.

• 한국표면공학회지
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• 제47권4호
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• pp.186-191
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• 2014

Double layer films which consisted of aluminum(Al) and magnesium(Mg) have been prepared by e-beam deposition. The structure, alloy phase, and corrosion resistance of the prepared films were investigated before and after heat treatment. The first (bottom) layer fixed with Al, and the thickness ratio between Al and Mg layers has been changed from 1 : 1 to 5 : 1, respectively. Total thickness of Al-Mg film was fixed at $3{\mu}m$. The cold-rolled steel sheet was used as a substrate. Heat treatment was fulfilled in an nitrogen atmosphere at the temperature of $400^{\circ}C$ for 2, 3 and 10 min. Surface morphology of as-deposited Al-Mg film having Mg top layer showed plate-like structure. The morphology was not changed even after heat treatment. However, cross-sectional morphology of Al-Mg films was drastically changed after heat treatment, especially for the samples heat treated for 10 min. The morphology of as-deposited films showed columnar structure, while featureless structure of the films appeared after heat treatment. The x-ray diffraction data for as-deposited Al-Mg films showed only pure Al and Mg peaks. However, Al-Mg alloy peaks such as $Al_3Mg_2$ and $Al_{12}Mg_{17}$ appeared after heat treatment of the films. It is believed that the formation of Al-Mg alloy phase affected the structure change of Al-Mg film. It was found that the corrosion resistance of Al-Mg film was increased after heat treatment.

• Coupled systems mechanics
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• 제2권2호
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• pp.127-146
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• 2013

A closed-form solution for a fluid-structure system is presented in this article. The closed-form is used to evaluate the finite element method results through a numeric example with consideration of high frequencies of excitation. In the example, the structure is modeled as a cantilever beam with rectangular cross-section including only shear deformation and the reservoir is assumed semi-infinite rectangular filled with compressible fluid. It is observed that finite element results deviate from the closed-form in relatively higher frequencies which is the case for the near field earthquakes.

• 로봇학회논문지
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• 제17권3호
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• pp.288-295
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• 2022

This study shows a system identification method of a balancing loading device for a stair climbing delivery robot. The balancing loading device is designed as a 2-axes gimbal structure and is interpreted as two independent pendulum structures for simplifying. The loading device's properties such as mass, moment of inertia, and position of the center of gravity are changeable for luggage. The system identification process of the loading device is required, and the controller should be optimized for the system in real-time. In this study, the system identification method is based on least squares method to estimate the unknown parameters of the loading device's dynamic equation. It estimates the unknown parameters by calculating them that minimize the error function between the real system's motion and the estimated system's motion. This study improves the accuracy of parameter estimation using a null space solution. The null space solution can produce the correct parameters by adjusting the parameter's relative sizes. The proposed system identification method is verified by the simulation to determine how close the estimated unknown parameters are to the real parameters.

• 한국안전학회지
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• 제18권1호
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• pp.101-107
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• 2003

Dynamic behavior of flexible rectangular liquid storage structures is analysed by the developed method. The rectangular liquid storage structures are assumed to be fixed to the ground and a moving coordinate system is used. The irrotational motion of invicid and incompressible ideal fluid is represented by two analytic solutions. One is the solution of the fluid motion in the rigid rectangular liquid storage structure due to ground motions and the other is the solution of the fluid motion by the motion of the wall in the flexible rectangular liquid storage structure. The motion of structure is modeled by finite elements. The fluid-structure interaction effect is reflected into the coupled equation of motion as added fluid mass matrix. The free surface sloshing motion and hydrodynamic pressure acting on the wall in the flexible rectangular liquid storage structure due to the horizontal ground motion are obtained by the developed method and verified.

• 한국콘텐츠학회논문지
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• 제5권6호
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• pp.360-367
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• 2005

인터넷의 보급으로 인해 기업의 전산화가 발전함에 따라, 바이러스, 전산망 침해 등 정보화의 역기능도 크게 증가하고 있다. 따라서 오늘날, 기업 보안의 중요성이 매우 강조되고 있다. 이렇게 보안의 중요도가 높아짐으로 인하여 보안 솔루션도 함께 발전하고 있다. 보안 솔루션은 기존 단일 체제에서 통합 보안 관리 시스템으로 발전하고 있으며 통합보안관리 시스템에서 중요한 것은 각 보안 솔루션의 기능과 정책 의 적합한 설계이다. 기존의 보안 정책은 외부의 침입으로 부터의 보안을 중요시 해왔으나 현재는 내부의 보안도 그 중요도가 높아지고 있다 이를 위하여 새로운 구조의 통합 보안관리 시스템을 구축해야 한다. 본 논문에서는 침입탐지차단 시스템을 활용하여 내부보안을 강화한 통합 보안 관리 시스템을 제안, 구현하였으며. 내 외부의 IP와 ID접근을 실험하여 그 결과를 분석하였다.

• 시스템엔지니어링학술지
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• 제8권1호
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• pp.21-28
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• 2012

Development of the system that has required performance is the most important figure and that is the key of project succeed. In order to perform that, systems engineering has come to the fore as a solution. In each step of system engineering process, particularly, requirement analysis and derivation, logical solution, architecture design step are known to affect many of the function and efficiency. Of these, this paper focus on architecture design. We introduce methodology for physical architecture design by applying DSM(Design Structure Matrix) methodology which is based on result of logical solution from MBSE methodology.

• Smart Structures and Systems
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• 제29권4호
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• pp.641-652
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• 2022

High-rise structures prone to large vibrations under the action of strong winds, resulting in fatigue damage of the structural components and the foundation. A novel compound damping cable system (CDCS) is proposed to suppress the excessive vibrations. CDCS uses tailored double cable system with increased tensile stiffness as the connecting device, and makes use of the relative motion between the high-rise structure and the ground to drive the damper to move back-and-forth, dissipating the vibration mechanical energy of the high-rise structure so as to decaying the excessive vibration. Firstly, a third-order differential equation for the free vibration of high-rise structure with CDCS is established, and its closed form solution is obtained by the root formulas of cubic equation (Shengjin's formulas). Secondly, the analytical solution is validated by a laboratory model experiment. Thirdly, parametric analysis is conducted to investigate how the parameters affect the vibration control performance. Finally, the dynamic responses of the high-rise structure with CDCS under harmonic and stochastic excitations are calculated and its vibration mitigation performance is further evaluated. The results show that the CDCS can provide a large equivalent additional damping ratio for the vibrating structures, thus suppressing the excessive vibration effectively. It is anticipated that the CDCS can be used as a good alternative energy dissipation system for vibration control of high-rise structures.

• Structural Engineering and Mechanics
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• 제65권1호
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• pp.111-120
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• 2018

This paper presents a new and simple solution for determining the natural frequencies of framed tube combined with shear-walls and tube-in-tube systems. The novelty of the presented approach is based on the bending moment function approximation instead of the mode shape function approximation. This novelty makes the presented solution very simpler and very shorter in the mathematical calculations process. The shear stiffness, flexural stiffness and mass per unit length of the structure are variable along the height. The effect of the structure weight on its natural frequencies is considered using a variable axial force. The effects of shear lag phenomena has been investigated on the natural frequencies of the structure. The whole structure is modeled by an equivalent non-prismatic shear-flexural cantilever beam under variable axial forces. The governing differential equation of motion is converted into a system of linear algebraic equations and the natural frequencies are calculated by determining a non-trivial solution for the system of equations. The accuracy of the proposed method is verified through several numerical examples and the results are compared with the literature.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2002년도 제18회 학술발표대회 논문초록집
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• pp.10-13
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• 2002

Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. The constitutive equation of propulsion system is a homogeneous second-order equation form in the Laplace domain. Rocket structure is modeled using FEM. From the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed of all propulsion system equations and vehicle motion equations reacting on the vehicle by each component of propulsion system. The stability is obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability is carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.