• 한국항공우주학회지
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• 제35권6호
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• pp.503-508
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• 2007

본 연구에서는 대변형 보이론을 이용하여 무베어링 로터 시스템의 공력탄성학적 안정성 해석을 수행하였다. 무베어링 로터 시스템의 유연보, 토오크 튜브, 그리고 메인 블레이드를 각각 탄성 운동을 하는 보로 가정하고, 1차원 보 요소로 모델링을 하였다. 외력으로는 2차원 준-정상 공기력 모델을 적용하였으며, 보의 유한 요소 지배방정식은 헤밀턴 원리(Hamilton's Principle)를 이용하여 얻었다. 공력탄성학적 안정성 해석을 수행하기 위하여 정지 비행시는 모달 접근법을, 전진 비행시는 주기적인 특성을 갖는 비선형 정적 트림해를 얻기 위해 동체 평형을 고려한 연계 평형 해석을 통한 완전 유한요소 방정식을 이용하였다. 본 연구에서 구한 결과를 기존의 적정변형 보이론에 모달 접근법을 이용한 무베어링 로터 시스템의 결과와 비교하였다.

• 한국터널지하공간학회 논문집
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• 제16권1호
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• pp.13-24
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• 2014

본 논문에서는 TBM 터널의 세그먼트 라이닝 설계 자동화 기술 개발의 일환으로 인공신경망기법을 이용한 세그먼트 라이닝 부재력 산정기법 개발에 관한 내용을 다루었다. 부재력 평가가 가능한 인공신경망을 개발하기 위해 먼저 다양한 설계조건을 도출하고 이에 대해 2-Ring Beam 모델을 이용한 유한요소해석을 수행하여 인공신경망 학습에 필요한 설계조건별 부재력에 관한 DB를 구축하였다. 구축된 DB를 활용하여 인공신경망의 최적화 과정을 통해 최대 부재력 및 분포도를 예측할 수 있는 인공신경망을 구축하였다. 검토 결과 구축된 인공신경망은 유한요소해석과 동일한 정밀도의 부재력 산정 기능을 확보하는 것으로 검토되었으며 따라서 TBM 세그먼트 라이닝 설계시 필요한 부재력 평가를 위한 효율적인 수단으로 활용될 수 있는 것으로 판단된다.

• 한국인터넷방송통신학회논문지
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• 제14권5호
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• pp.81-86
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• 2014

이동통신망 사용자는 인터넷 서비스를 위해 빠른 데이터 전송 및 넓은 대역폭을 필요로 한다. 기존의 MIMO 시스템은 주어진 환경에서 광대역서비스를 위한 방법으로 안테나의 개수를 수요 대역 만큼 계속 추가하는 것인데, 이 방법은 이동통신 단말기의 제한된 공간으로 계속적인 추가가 어렵다. 이는 추가되는 안테나간 간격을 사용주파수의 파장만큼 거리를 두어야 하는 공간적 제한 때문이다. 컴팩트 MIMO 기술은 이를 해결하는 방법으로 등장하고 있으며, 액티브 안테나 주변에 가변 리액턴스 값을 갖는 PE(parasitic element)를 두어 하나의 안테나 구성으로 다수 안테나의 효과를 얻는 방법이다. 이때 가변 리액턴스를 제어하기 위해 사용되는 회로의 구성 및 간섭에 강인한 스위칭 속도를 갖는 제어회로가 요구된다. 본 논문에서는 리액턴스 제어를 위한 스위칭 블록을 제안하고, 이 방법에 의한 빔의 영향을 분석하였다.

• KCI Concrete Journal
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• 제13권1호
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• pp.19-25
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• 2001

Based on the orthotropic hypoelasticity formulation, a constitutive material model of concrete taking account of triaxial stress state is presented. In this model, the ultimate strength surface of concrete in triaxial stress space is described by the Hsieh's four-parameter surface. On the other hand, the different ultimate strength surface of concrete in strain space is proposed in order to account for increasing ductility in high confinement pressure. Compressive ascending and descending behavior of concrete is considered. Concrete cracking behavior is considered as a smeared crack model, and after cracking, the tensile strain-softening behavior and the shear mechanism of cracked concrete are considered. The proposed constitutive model of concrete is compared with some results obtained from tests under the states of uniaxial, biaxial, and triaxial stresses. In triaxial compressive tests, the peak compressive stress from the predicted results agrees well with the experimental results, and ductility response under high confining pressure matches well the experimental result. The reinforcing bars embedded in concrete are considered as an isoparametric line element which could be easily incorporated into the isoparametric solid element of concrete, and the average stress - average strain relationship of the bar embedded in concrete is considered. From numerical examples for a reinforced concrete simple beam and a structural beam type member, the stress state of concrete in the vicinity of talc critical region is investigated.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
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• pp.465-470
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• 2002

A novel phased array antenna system for space-borne polarimetric SAR is proposed and completed in this paper.The antenna system assures polarimetric and multi-mode capability of SAR. It has broadband, high polarization isolation and high port to port isolation. The antenna system is composed of broadband polarimetric microstrip antenna, T/R modules and multifunction beam controller nit. The polarimetric microstrip antenna has more than 100MHz bandwidth at L-band with -30dB polarization isolation and high port to port isolation. The microstrip element and T/R module's structure and characteristics, the subarray's performances measuring results are presented in detail in this paper. A design scheme on beam controller of the phased array antenna is also proposed and completed, which is based on Digital Signal Processing (DSP) chip -TMS320F206. This beam controller unit has small size and high reliability compared with general beam controller. In addition, the multifunction beam controller unit can acquire and then send the T/R module's working states to detection system in real time.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
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• pp.37-44
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• 1996

When a load such as the mechanical load, the wind load, and the seismic load causing a vibration, acts on the body of the 3-D frameworks with slab, it is required to consider the dynamic behavior of elastic soil as well as that of 3-D structure in the structural analysis. Thus, this study presents the analysis of dynamic behavior using finite element method that is formulated by using a model of the 3-D structure. For the idealization of the actual structure closely into a geometric shape, plate is subdivided into 4-node plate element with the flexibility, beam-column is subdivided into 2-node beam element, and elastic soil is subdivided into 8-node brick element.

• Earthquakes and Structures
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• 제27권4호
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• pp.263-283
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• 2024

This research introduces a new composite system that utilizes multiple moving masses to identify cracks in structures resembling beams. The process starts by recording displacement time data from a set of these moving masses and converting this information into a relative time history through weighted aggregation. This relative time history then undergoes wavelet transform analysis to precisely locate cracks. Following wavelet examinations, specific points along the beam are determined as potential crack sites. These points, along with locations on the beam susceptible to cracked point due to support conditions, are marked as crack locations within the optimization algorithm's search domain. The model uses equations of motion based on the finite element method for the moving masses on the beam and employs the Runge-Kutta numerical solution within the state space. The proposed system consists of three successive moving masses positioned at even intervals along the beam. To assess its effectiveness, the method is tested on two examples: a simply supported beam and a continuous beam, each having three scenarios to simulate the presence of one or multiple cracks. Additionally, another example investigates the influence of mass speed, spacing between masses, and noise effect. The outcomes showcase the method's effectiveness and efficiency in localizing crack, even in the presence of noise effect in 1%, 5% and 20%.

• 자연, 터널 그리고 지하공간
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• 제21권2호
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• pp.117-129
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• 2019

Tunnelling in urban environments is very common nowadays as large cities are expanding and transportation demands require the use of the underground space for creating extra capacity. Inevitably, any such new construction may have significant effects on existing nearby infrastructure and therefore relevant assessment of structural integrity and soil-structure interaction is required. Foundation piles can be rather sensitive to nearby tunnel construction and therefore their response needs to be evaluated carefully. Although detailed three-dimensional continuum finite element analysis can provide a wealth of information about this behaviour of piles, such analyses are generally very computationally demanding and may require a number of material and other model parameters to be properly calibrated. Therefore, relevant simplified approaches are used to provide a practical way for such an assessment. This paper presents a simple method where the pile is modelled with beam finite elements, pile-soil interaction is modelled with soil springs and tunnelling-induced displacements are introduced as an input boundary condition at the end of the soil springs. The performance of this approach is assessed through some examples of applications.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.904-921
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• 2014

The main objective of this paper is to propose a new Finite Element (FE) model updating technique for damped beam structures. The present method consists of a FE model updating, a Degree of Freedom (DOF) reduction method and a damping matrix identification method. In order to accomplish the goal of this study, first, a sensitivity-based FE model updating method using the natural frequencies and the zero frequencies is introduced. Second, an Iterated Improved Reduced System (IIRS) technique is employed to reduce the number of DOF of FE model. Third, a damping matrix is estimated using modal damping ratios identified by a curve-fitting method and modified matrices which are obtained through the model updating and the DOF reduction. The proposed FE model updating method is verified using a real cantilever beam attached damping material on one side. The updated result shows that the proposed method can lead to accurate model updating of damped structures.

• Smart Structures and Systems
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• 제18권2호
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• pp.355-374
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• 2016

This paper presents and compares a one-dimensional (1D) bending theory for piezoelectric thin beam-type structures with resistive-inductive electrodes to ANSYS$^{(R)}$ three-dimensional (3D) finite element (FE) analysis. In particular, the lateral deflections and vibrations of slender piezoelectric beams are considered. The peculiarity of the piezoelectric beam model is the modeling of electrodes in such a manner that is does not fulfill the equipotential area condition. The case of ideal, perfectly conductive electrodes is a special case of our 1D model. Two-coupled partial differential equations are obtained for the lateral deflection and for the voltage distribution along the electrodes: the first one is an extended Bernoulli-Euler beam equation (second-order in time, forth order in space) and the second one the so-called Telegrapher's equation (second-order in time and space). Analytical results of our theory are validated by 3D electromechanically coupled FE simulations with ANSYS$^{(R)}$. A clamped-hinged beam is considered with various types of electrodes for the piezoelectric layers, which can be either resistive and/or inductive. A natural frequency analysis as well as quasi-static and dynamic simulations are performed. A good agreement between the extended beam theory and the FE results is found. Finally, the practical relevance of this type of electrodes is shown. It is found that the damping capability of properly tuned resistive or resistive-inductive electrodes exceeds the damping performance of beams, where the electrodes are simply linked to an optimized impedance.