• Earthquakes and Structures
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• 제17권5호
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• pp.477-487
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• 2019

Understanding the behavior of skew bridges under the action of earthquakes is quite challenging due to the combined transverse and longitudinal responses even under unidirectional hit. The main goal of this research is to assess the response of skew bridges when subjected to longitudinal and transversal earthquake loading. The effect of skew on the response considering two- and three- span bridges with skew angles varying from 0 to 60 degrees is illustrated. Various pier fixities (and hence stiffness) and cross-section shapes, as well as different abutment's bearing articulations, are also studied. Finite-element models are established for modal and seismic analyses. Around 900 models are analyzed under the action of the code design response spectrum. $Vis-{\grave{a}}-vis$ modal properties, the higher the skew angle, the less the fundamental period. In addition, it is found that bridges with skew angles less than 30 degrees can be treated as straight bridges for the purpose of calculating modal mass participation factors. Other monitored results are bearings' reactions at abutments, shear and torsion demand in piers, as well as deck longitudinal displacement. Unlike straight bridges, it has been typically noted that skew bridges experience non-negligible torsion and bi-directional pier base shears. In a complementary effort to assess the accuracy of the conducted response spectrum analysis, a series of time-history analyses are applied under seven actual earthquake records scaled to match the code design response spectrum and critical comparisons are performed.

• Journal of Astronomy and Space Sciences
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• 제35권4호
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• pp.211-218
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• 2018

Solar microwave bursts carry information about the magnetic field in the emitting region as well as about electrons accelerated during solar flares. While this sensitivity to the coronal magnetic field must be a unique advantage of solar microwave burst observations, it also adds a complexity to spectral analysis targeted to electron diagnostics. This paper introduces a new spectral analysis procedure in which the cross-section and thickness of a microwave source are expressed as power-law functions of the magnetic field so that the degree of magnetic inhomogeneity can systematically be derived. We applied this spectral analysis tool to two contrasting events observed by the Owens Valley Solar Array: the SOL2003-04-04T20:55 flare with a steep microwave spectrum and the SOL2003-10-19T16:50 flare with a broader spectrum. Our analysis shows that the strong flare with the broader microwave spectrum occurred in a region of highly inhomogeneous magnetic field and vice versa. We further demonstrate that such source properties are consistent with the magnetic field observations from the Michelson Doppler Imager instrument onboard the Solar and Heliospheric Observatory (SOHO) spacecraft and the extreme ultraviolet imaging observations from the SOHO extreme ultraviolet imaging telescope. This spectral inversion tool is particularly useful for analyzing microwave flux spectra of strong flares from magnetically complex systems.

• 한국소음진동공학회논문집
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• 제19권7호
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• pp.710-718
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• 2009

The time difference of arrival(TDOA) algorithm is being used widely for identifying the location of a source emanating either electrical or acoustic signal. It's application areas will not be limited to identifying the source at a fixed location, for example the origin of an earthquake, but will also include the trajectory monitoring for a moving source equipped with a GPS sensor. Most of the TDOA algorithm uses time correlation technique to find the time delay between received signals, and therefore difficult to be used for identifying the location of multiple sources. In this paper a TDOA algorithm based on cross-spectrum is developed to find the trajectory of two sound sources with different frequencies. Although its application is limited to for the sources on a disk plane, it can be applied for identifying the locations of more than two sources simultaneously.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.483-489
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• 2009

The Time Difference of Arrival (TDOA) algorithm is being used widely for identifying the location of a source emanating either electrical or acoustic signal. It's application areas will not be limited to identifying the source at a fixed location, for example the origin of an earthquake, but will also include the trajectory monitoring for a moving source equipped with a GPS sensor. Most of the TDOA algorithm uses time correlation technique to find the time delay between received signals, and therefore difficult to be used for identifying the location of multiple sources. In this paper a TDOA algorithm based on cross-spectrum is developed to find the trajectory of two sound sources with different frequencies. Although its application is limited to for the sources on a disk plane, but it can be applied for identifying the locations of more than two sources simultaneously.

• 한국음향학회지
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• 제19권3호
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• pp.3-10
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• 2000

본 논문에서는 등간격으로 직선배열된 마이크로폰 어레이군으로 각 측정지점마다 빔패턴을 형성하고 이를 기준신호로 이용하여 각 마이크로폰들간의 신호와 크로스스펙트럼 알고리즘에 의하여 음원의 절대위치를 추정할 수 있는 빔포밍 음향홀로그래픽 시스템을 제안한다. 실음장 측정을 통하여 기준 마이크로폰을 사용하는 음향홀로그래픽법과 본 연구에서 제안한 방법을 동일 알고리즘으로 비교·검토한 결과, 약 20% 이상의 분해능 향상을 가져왔으며 제작한 시스템의 음장측정에 대한 유용성을 확인하였다.

• 물과 미래
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• 제14권4호
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• pp.19-26
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• 1981

자연하천에서의 수질은 유량의 변화에 많은 영향을 받을 것으로 기대되는 바, 유량과 각 수질인자의 통계적 특성 및 유량변화와 수질인자간의 상관관계를 조사하기 위하여 자기 및 상호상관함수 power spectrum, coherence 함수 및 Markov 모형을 적용하였다. 일부 자료만이 입수 가능한 한강 하류부 인도교 지점에서의 유량, 용존산소, 전기전도도는 명백한 1년 주기와 6, 4, 3개월의 약한 주기를 가지며, 유량과 용존산소, 유량과 전도도 사이의 상관은 약하게 나타났고 상호상관함수에서 첨두가 지체 1일에서 발생하여 미약하지만 유량의 변화에 의한 영향이 1일 정도 차이로 수질인자에게 미치는 것으로 해석된다. 계열 발생 및 예측수단인 선형회귀모형의 검토에서 유량은 1차 및 2차 Markov 모형과, 용존산소와 전도도는 1차 Markov 모형과 흡사하게 나타났다.

• Journal of Communications and Networks
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• 제6권2호
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• pp.93-105
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• 2004

This paper discusses cyclostationary interference suppression for multiuser wired communication systems. Crosstalk interference from digital signals in multipair cables has been shown to be cyclostationary. Many crosstalk equalization or suppression techniques have been proposed which make implicit use of the cyclostationarity of the crosstalk interferer. In this paper, the convergence and steady-state behaviors of a fractionally spaced equalizer (FSE) in the presence of multiple cyclostationary crosstalk interference are thoroughly analyzed by using the equalizer's eigenstructure. The eigenvalues with multiple cyclostationary interference depend upon the folded signal and interferer power spectra, the cross power spectrum between the signal and the interferer, and tile cross power spectrum between the interferers, which results in significantly different initial convergence and steady-state behaviors as compared to the stationary noise case. The performance of the equalizer varies depending on the relative clock phase of the symbol clocks used by the signal and multiple interferers. Measued characteristics as well as analytical model of NEXT/FEXT channel are used to compute the optimum and worst relative clock phases among the signal and multiple interferers.

• Asia Pacific Journal of Business Review
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• 제1권2호
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• pp.63-88
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• 2017

With the advent of new frontiers in robotics, the spectrum of robot research area has widened in many fields and applications. Other than conventional robot research, many technologies such as smart devices, drones, healthcare robots, and soft robots are emerging as promising applications. Due to the research complexity of this topic, this research requires international collaboration and should be fertilized by R&D policies. This paper aims to propose a method to perform a cross-national analysis of robot research with unstructured data such as papers in the proceedings of an international conference. Text analytics are applied to extract research issues and applications in an automatic manner.

• 한국항공운항학회지
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• 제17권2호
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• pp.1-7
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• 2009

This paper illustrates how simulation modeling can be of substantial help in designing constructions in the vicinity of airport runway and presents results about the influence of aircraft wake vortices through computer simulation. The cross-wind energy dissipation rate is estimated from the Y-directional velocity spectrum for a sample in a real meteorological observation data. The eddy region about cross wind in the vicinity of airport runway is highly dependent on the height and shape of the buildings and the AOA of aircraft is greatly influenced by Y-directional velocity occurred by dint of separation region in runway.

• 국제초고층학회논문집
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• 제8권4호
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• pp.313-324
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• 2019

This paper presents the analysis of wind speeds data measured on top of three neighboring high-rise buildings close to a beach in Xiamen city, China, during Typhoon "Usagi" 2013. Wind tunnel simulation was carried out to validate the field measurement results. Turbulence intensity, turbulence integral scale, power spectrum and cross correlation of recorded wind speed were studied in details. The low frequency trend component of the typhoon speed was also discussed. The field measurement results show turbulence intensity has strong dependence to the wind speed, upwind terrain and even the relative location to the Typhoon center. The low frequency fluctuation could severely affect the characteristics of wind. Cross correlation of the measured wind speeds on different buildings also showed some dependence on the upwind terrain roughness. After typhoon made landfall, the spatial correlation of wind speeds became weak with the coherence attenuating quickly in frequency domain.