• Structural Engineering and Mechanics
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• 제59권6호
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• pp.1037-1054
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• 2016

Structural parameter evaluation and external force estimation are two important parts of structural health monitoring. But the structural parameter identification with limited input information is still a challenging problem. A new simultaneous identification method in time domain is proposed in this study to identify the structural parameters and evaluate the external force. Each sampling point in the time history of external force is taken as the unknowns in force evaluation. To reduce the number of unknowns for force evaluation the time domain measurements are divided into several windows. In each time window the structural excitation is decomposed by orthogonal polynomials. The time-variant excitation can be represented approximately by the linear combination of these orthogonal bases. Structural parameters and the coefficients of decomposition are added to the state variable to be identified. The extended Kalman filter (EKF) is augmented and selected as the mathematical tool for the implementation of state variable evaluation. The proposed method is validated numerically with simulation studies of a time-invariant linear structure, a hysteretic nonlinear structure and a time-variant linear shear frame, respectively. Results from the simulation studies indicate that the proposed method is capable of identifying the dynamic load and structural parameters fairly accurately. This method could also identify the time-variant and nonlinear structural parameter even with contaminated incomplete measurement.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.543-550
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• 2000

Rock slopes along the road or railroad are affected by temperature and therefore experienced iterative freezing-thawing process between winter and early spring. The purpose of this study is to analyze the stability of rock slopes which are influenced by the deterioration due to the freezing-thawing. The analysis is the homogenization method which evaluates the strength property of discontinuous rock mass, and as a strength failure criterion, Drucker-Prager failure criterion is used. The deterioration property of real rock is obtained by a freezing-thawing laboratory test of tuff and this property of deterioration is quantitated and used as a basic data of stability analysis for rock mass. To evaluate the deterioration depth due to the freezing-thawing in situ rock slope, one dimensional heat conductivity equation is used and as the result I can find that the depth of which is affected by a temperature. After the freezing-thawing depth of model slope is determined, we analyze the pattern of rock mass stength value of rock slope model which excesses the limit of self-load.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.140-147
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• 2007

Whenever the hinge axis of aircraft wing rotates, its stiffness varies. Also, there are nonlinearities in the connection of the actuator and the hinge axis, and it is necessary to inspect the coupled effects between the actuator dynamics and the hinge nonlinearity. Nonlinear aeroelastic characteristics are investigated by using the iterative V-g method. Time domain analyses are also performed by using Karpel's minimum state approximation technique. The doublet hybrid method(DHM) is used to calculate the unsteady aerodynamic forces in subsonic regions. Structural nonlinearity located in the load links of the actuator is assumed to be friction. The friction nonlinearity of an actuator is identified by using the describing function technique. The nonlinear flutter analyses have shown that the flutter characteristics significantly depends on the structural nonlinearity as well as the dynamic stiffness of an actuator. Therefore, the dynamic stiffness of an actuator as well as the nonlinear effect of hinge axis are important factors to determine the flutter stability.

• Advances in Computational Design
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• 제5권3호
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• pp.305-321
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• 2020

In this paper is presented the solution method for three-dimensional problem of transversely isotropic body's elastoplastic deformation by the finite element method (FEM). The process of problem solution consists of: determining the effective parameters of a transversely isotropic medium; construction of the finite element mesh of the body configuration, including the determination of the local minimum value of the tape width of non-zero coefficients of equation systems by using of front method; constructing of the stiffness matrix coefficients and load vector node components of the equation for an individual finite element's state according to the theory of small elastoplastic deformations for a transversely isotropic medium; the formation of a resolving symmetric-tape system of equations by summing of all state equations coefficients summing of all finite elements; solution of the system of symmetric-tape equations systems by means of the square root method; calculation of the body's elastoplastic stress-strain state by performing the iterative process of the initial stress method. For each problem solution stage, effective computational algorithms have been developed that reduce computational operations number by modifying existing solution methods and taking into account the matrix coefficients structure. As an example it is given, the problem solution of fibrous composite straining in the form of a rectangle with a system of circular holes.

• 한국지반공학회지:지반
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• 제14권5호
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• pp.173-180
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• 1998

본 논문은 연약한 기초지반위의 토목섬유 보강제방의 2차원 안정해석을 위한 설계도표를 제시한다. 반복계산을 수행하기 위하여 보강제방의 요구되어지는 안전율에 필요한 보강재의 인장력을 산정하는 프로그램이 개발되었으며, 이 프로그램은 여러개의 토층과 토질로 이루어진 상황에도 사용될 수 있다. 도식화된 단면에 대하여 많은 계산결과들이 만들어 졌으며, 그 결과들로서 설계도 I를 만들었으며, 정적인 경우와 지진하중을 고려할 경우에도 적용시킬 수 있다. 예비설계단계에서 이러한 도표들을 이용하여 보강제방에 대한 비교적 정확한 보강재의 인장력을 근사적으로 구할 수 있으며, 실시설계단계에서는 개발된 프로그램에 의하여 정확한 결과를 산정할 수 있다.

• 한국정밀공학회지
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• 제32권2호
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• pp.117-125
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• 2015

This paper presents a dynamic modeling method for the indeterminate spindle-bearing system supported by multiple bearings of different types. A spindle-bearing system supported by ball and cylindrical roller bearings is considered. The de Mul's bearing model is extended for calculating ball and cylindrical roller bearing stiffness matrices with inclusion of centrifugal force and gyroscopic moment. The dependence between spindle shaft reaction forces and bearing stiffness is effectively resolved using an iterative approach. The spindle rotor dynamics is established with the Timoshenko beam theory based finite elements. The spindle reaction forces, bearings stiffness and spindle natural frequencies are obtained with taking into account spindle radial load, ball bearing axial preload and rotational speed effects. The developed method is verified by comparing the simulation results with those from a commercial program.

• Journal of Theoretical and Applied Mechanics
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• 제2권1호
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• pp.31-50
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• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

• 한국통신학회논문지
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• 제35권6C호
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• pp.562-571
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• 2010

차세대 대부분의 무선 통신 시스템에서는 심각한 페이딩을 극복하기 위하여 터보부호와 같은 연판정 입출력을 반복적으로 사용하는 오류정정부호화 방식을 사용하는 동시에, 시공간부호를 활용하여 다이버시티 이득을 얻고자 한다. 그러므로 수신단에서 시공간부호에서 검출된 신호는 연판정 출력 형태로 오류정정 복호기에 전달되어야 한다. 본 논문에서는 QAM과 같은 고차원 변조방식을 사용하여 시공간부호화와 반복 복호를 사용하는 오류정정부호화 방식이 결합된 경우에 성능의 극대화를 위하여 최적의 연판정 검출 방법을 제시한다. 터보부호를 사용하는 시스템에서 여러 가지 시공간부호화 방식과 고차원 변조 방식이 결합될 경우 여러 가지 연판정 검출 방법에 대한 시뮬레이션 결과를 제시하여, 제안된 방식이 적은 복잡도로 우수한 성능을 얻을 수 있음을 보인다.

• ETRI Journal
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• 제28권5호
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• pp.593-606
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• 2006

Thanks to the great possibilities of providing different types of telecommunication traffic to a large geographical area, satellite networks are expected to be an essential component of the next-generation internet. As a result, issues concerning the designing and testing of efficient connection-admission-control (CAC) strategies in order to increase the quality of service (QoS) for multimedia traffic sources, are attractive and at the cutting edge of research. This paper investigates the potential strengths of a generic digital-video-broadcasting return-channel-via-satellite (DVB-RCS) system architecture, proposing a new CAC algorithm with the aim of efficiently managing real-time multimedia video sources, both with constant and high variable data rate transmission; moreover, the proposed admission strategy is compared with a well-known iterative CAC mainly designed for the managing of real-time bursty traffic sources in order to demonstrate that the new algorithm is also well suited for those traffic sources. Performance analysis shows that, both algorithms guarantee the agreed QoS to real-time bursty connections that are more sensitive to delay jitter; however, our proposed algorithm can also manage interactive real-time multimedia traffic sources in high load and mixed traffic conditions.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.669-676
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• 2018

Transmission system has been well studied since long time and power system techniques of distribution system are more or less derived from transmission system. However, unlike transmission systems, many practical issues are encountered in the distribution system. Considerable amount of error is observed in voltage obtained from the Feeder Remote Terminal Units (FRTUs) measured by the pole mounted PTs along the distribution feeder. Load uncertainty is also an issue in distribution system. Further, penetration of Distributed Generators (DGs) creates voltage variations in the system. Hybrid radial/ loop distribution system also make it complicated to handle distribution system. How these constraints to be handled under Distribution Automation (DAS) environment in order to obtain error free voltage is described in this paper and therefore, a new approach of voltage error correction technique has been proposed. The proposed technique utilizes reliable data from substation and the FRTUs installed in DAS. The proposed technique adopts an iterative process for voltage error correction. It has been tested and proved accurate not only for conventional radial systems but also for loop distribution systems.