• Structural Engineering and Mechanics
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• 제9권2호
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• pp.141-152
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• 2000

Based on the discussion about some empirical coherency models resulted from earthquake-induced ground motion recordings at the SMART-1 array in Taiwan, and a heuristic model of the coherency function from elementary notions of stationary random process theory and a few simplifying assumptions regarding the propagation of seismic waves, a practical coherency model for spatially varying ground motions, which can be applied in aseismic analysis and design, is proposed, and the regressive coefficients are obtained using least-square fitting technique from the above recordings.

• Communications for Statistical Applications and Methods
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• 제26권1호
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• pp.27-34
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• 2019

We study the effect of detrending on the coherency between two time series processes. Many economic and financial time series variables include nonstationary components; however, we analyze the two most popular cases of stochastic and deterministic trends. We analyze the asymptotic behavior of coherency under incorrect detrending, which includes the cases of first-differencing the deterministic trend process and, conversely, the time trend removal of the unit root process. A simulation study is performed to investigate the finite sample performance of the sample coherency due to incorrect detrending. Our work is expected to draw attention to the possible distortion of coherency when the series are incorrectly detrended. Further, our results can extend to various specification of trends in aggregate time series variables.

• Computational Structural Engineering : An International Journal
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• 제1권2호
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• pp.139-150
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• 2001

An initial approach for the identification of physical causes underlying the spatial coherency of seismic ground motions it presented. The approach relies on the observation that amplitude and phase variability of seismic data recorded over extended areas around the amplitude and phase of a common, coherent component are correlated. It suffices then to examine the physical causes for the amplitude variability in the seismic motions, in order to recognize the causes for the phase variability and, consequently, the spatial coherency. In this study, the effect of randomness in the shear wave velocity at a site on the amplitude variability of the surface motions mi investigated by means of simulations. The amplitude variability of the simulated motions around the amplitude of the common component is contained within envelope functions, the shape of which suggests, on a preliminary basis, the trend of the decay of coherency with frequency.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.265-268
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• 2008

The safety of a tunnel under seismic motion is most often evaluated by ovalling deformation of tunnel. This paper research about tunnel's longitudinal deformation. Because of spatial variation of seismic ground motion, the longitudinal structures like tunnel are likely to experience relative displacements along longitudinal direction. The spatially variable ground motion can be estimated by coherency function obtained empirically, and can be considered from different arrival times of ground motion. As a result of estimating tunnel's relative displacements at maximum curvature of tunnel, the displacements and curvatures estimated by coherency function affect the tunnel's safety more than different arrival times. However, if tunnel's displacements by coherency function superpose on displacements by different arrival times, the relative displacements and curvatures of tunnel will be more severe. Therefore, to estimate accurately tunnel's deformation in longitudinal direction has to consider both coherency and wave passage effects.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.651-666
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• 2020

In this study, the spatial variation mechanisms of large far-field earthquakes at engineering scales are first investigated with data from the 2008 Ms 8.0 Wenchuan earthquake. And a novel 'coherency cut-off frequency' is proposed to distinguish the spatial variations in ground motions in the low-frequency and high-frequency ranges. Then, a practical piecewise coherency model is developed to estimate and characterize the spatial variation in earthquake ground motions, including the effects of source-to-site distances, site conditions and neighboring topography on these variations. Four particular earthquake records from dense seismograph arrays are used to investigate values of the coherency cut-off frequency for different source-to-site distances. On the basis of this analysis, the model is established to simulate the spatial variations, whose parameters are suitable for both near- and far-field earthquake conditions. Simulations are conducted to validate the proposed model and method. The results show that compared to the existing models, the proposed model provides an effective method for simulating the spatial correlations of ground motions at local sites with known source-to-site distances.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.316-318
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• 2003

An eigen-analysis of the coherency matrix provides the polarimetric scattering mechanisms with the matrix characterizing parameters. In this paper, the coherency matrices of deciduous and coniferous vegetation are calculated using the analytical method. The Generalized Rayleigh-Gans approximation is used to model backscattering from distributed coniferous and deciduous leaves. The characteristics of eigen-parameters of simulated coherency matrix for deciduous and coniferous leaves with respect to the leaf shapes and orientations are illustrated.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.625-633
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• 2006

Spatial variability of ground motions has significant influence on dynamic response of longitudinal structures such as bridges and tunnels. The coherency function, which quantifies the degree of positive or negative correlation between two ground motions, is often used to describe the spatially variable ground motions. This paper compares two available procedures for developing spatially variable ground time histories from a given coherency function. Hao's method shows serious limitation, resulting in unrealistic decrease in coherency with increase in distance Abrahamason's method, on the other hand, preserves important characteristics of the reference ground motion. Therefore, the Abrahamason's method is recommended to be used in developing spatially varying ground motions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.162-166
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• 1990

This paper proposes a new method of the state reduction in dynamic equations of generators in large electric power system stability analysis. This method assumes study groups whose state trajectories we are interested in, coherency groups whose state trajectories are similar to the other state trajectories of generators in the same coherency group by a certain disturbance. By the weighted sum or the other method, the states of generators in one coherency group can be reduced to the equivalent states of an equivalent generator. This method is shown to be highly efficient in reducing the number of states with small error by the result of case study presented latter part of this paper.

• 전기학회논문지
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• 제56권8호
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• pp.1367-1372
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• 2007

The modem large electric power system has made power system analysis much more complex and difficult. For effective analysis of the power system, model reduction and aggregation is required. In this paper, a new relation index to identify the coherency among the generators is presented and also a new aggregation method is presented to aggregate the coherent generators in the large scale power system while matching the power flow. In order to demonstrate the effects of this aggregation method, it is applied to the IEEE 39 bus test power system and to the 2006 summer power system of Korea Electric Power Corporation, and the simulation results are compared with those of the original system.

• 한국정보과학회논문지:데이타베이스
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• 제36권5호
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• pp.399-404
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• 2009

공유디스크 모델을 사용하는 다중 서버 DBMS에서는 서버 프로세스들이 서로 독립된 메모리를 가지므로, 특정 서버 프로세스가 데이터베이스를 수정하더라도 다른 서버 프로세스들의 버퍼에는 수정된 내용이 반영되지 않는다. 따라서, 다른 서버 프로세스들이 수정되기 전 내용에 대하여 데이터 처리 요청을 수행하면 문제가 발생한다. 본 논문에서는 큰 단위의 로크(여기서는 볼륨 로크)를 사용하는 DBMS에서 이러한 문제를 해결하기 위한 새로운 방법을 제안한다. 이 방법에서는 서버 프로세스가 트랜잭션을 커밋할 때 수정한 페이지의 식별자와 타임스탬프를 일관성 볼륨에 저장하고, 이 정보를 통하여 다른 서버 프로세스가 로크를 획득하는 시점에 일관성 볼륨에서 다른 프로세스가 먼저 수정하였는지 여부를 확인하여 해당 페이지를 버퍼에서 무효화시켜 디스크에서 최신의 버전을 새로 읽어 들인다. 이 방법은 매우 작은 크기의 일관성 볼륨만을 사용하고, 액세스하는 데이터의 양이 적어서 성능이 매우 빠르다.