• Spatial Information Research
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• 제21권4호
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• pp.1-6
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• 2013

본 연구는 2002년부터 2009년까지 국내에서 발생한 돌풍에 대한 시계열 및 공간분포를 분석하였다. 태풍 기간 동안에 발생한 돌풍에 대해서는 제외하였으며, 지형에 의한 풍속 할증 효과는 KBC 2005 기준을 적용하여 보정하였다. 분석 결과, 돌풍 발생 빈도는 해안지역을 따라 높은 빈도가 나타났으며, 대상 기간 중 최대 286회의 발생 빈도를 보였다. 본 연구에서는 뇌우에 의한 돌풍과 종관 기상에 의해 발생한 돌풍의 시계열 분포의 비교를 통해 뇌우에 의한 돌풍의 불확실성이 높음을 확인하였다. 또한 누적운량과 뇌우 돌풍의 공간적 상관분석을 통해 두 인자간 높은 상관관계가 있음을 근거로 하여 돌풍에 대한 공간적 위험도를 평가하는데 활용할 수 있음을 제시하였다.

• 한국공간구조학회논문집
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• 제20권2호
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• pp.77-85
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• 2020

This paper examined the dynamic instability of a shallow arch according to the response characteristics when nearing critical loads. The frequency changing feathers of the time-domain increasing the loads are analyzed using Fast Fourier Transformation (FFT), while the response signal around the critical loads are analyzed using Hilbert-Huang Transformation (HHT). This study reveals that the models with an arch shape of h = 3 or higher exhibit buckling, which is very sensitive to the asymmetric initial conditions. Also, the critical buckling load increases as the shape increases, with its feather varying depending on the asymmetric initial conditions. Decomposition results show the decrease in predominant frequency before the threshold as the load increases, and the predominant period doubles at the critical level. In the vicinity of the critical level, sections rapidly manifest the displacement increase, with the changes in Instantaneous Frequency (IF) and Instant Energy (IE) becoming apparent.

• 한국공간구조학회논문집
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• 제15권2호
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• pp.113-120
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• 2015

This study investigate the dynamic response changes of rib dome structure according to property changes of Substructure. Eigenvalue analysis is conducted in first natural frequency of rib dome versus substructure and searched in the dominant mode of horizontal and vertical direction. Resonance frequency by each first natural frequency of the rib dome structure, substructure and total structure is applied for a seismic wave. That is analyzed about maximum displacement response ratio and maximum acceleration response ratio.

• 한국공간구조학회논문집
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• 제15권4호
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• pp.99-105
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• 2015

The serviceability design of the high-rise building is affected by the wind response vibration such as the acceleration, at this time it is important to calculate the natural frequency correctly. Since the suggestion equation of the natural frequency being used in the design phase is not the regression equation obtained from the vibration measurement of the high-rise building, the verification to use for the serviceability design of the high-rise building is necessary. This thesis conducted an ambient vibration measuring on the high-rise building through the mobile-phone application to calculate the natural frequency and suggested a natural frequency approximate expression following the building's height, and compared with the domestic/foreign standard and the result of the eigen-value analysis.

• International Journal of Automotive Technology
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• 제3권3호
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• pp.101-109
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• 2002

A time domain method for solving nonstationary random vibration caused by vehicle acceleration is first proposed in which a time changing model is established for representing nonstationary excitation of a rough road. Furthermore a novel frequency domain method called the transient power spectral density with spatial frequency (TPSD) is presented to obtain a response of vehicle system in frequency domain. This method has been proved to be valid by comparing numerical results with the exact solution.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 공동학술대회 논문집
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• pp.1-6
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• 2007

Two impedance imaging systems of multi-frequency electrical impedance tomography (MFEIT) and magnetic resonance electrical impedance tomography (MREIT) are described. MFEIT utilizes boundary measurements of current-voltage data at multiple frequencies to reconstruct cross-sectional images of a complex conductivity distribution (${\sigma}+i{\omega}{\varepsilon}$) inside the human body. The inverse problem in MFEIT is ill-posed due to the nonlinearity and low sensitivity between the boundary measurement and the complex conductivity. In MFEIT, we therefore focus on time- and frequency-difference imaging with a low spatial resolution and high temporal resolution. Multi-frequency time- and frequency-difference images in the frequency range of 10 Hz to 500 kHz are presented. In MREIT, we use an MRI scanner to measure an internal distribution of induced magnetic flux density subject to an injection current. This internal information enables us to reconstruct cross-sectional images of an internal conductivity distribution with a high spatial resolution. Conductivity image of a postmortem canine brain is presented and it shows a clear contrast between gray and white matters. Clinical applications for imaging the brain, breast, thorax, abdomen, and others are briefly discussed.

• 한국공간구조학회논문집
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• 제16권2호
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• pp.47-54
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• 2016

It is very important to calculate natural frequency of the observatory tower correctly because it is keenly affected by wind response vibration due to its large slenderness ratio, weight and small damping ratio. Additionally, suggestion equation of natural frequency being used in the design phase has considerable difference between actual measured value thereby making it inappropriate to be used in the serviceability design of the observatory tower. Therefore, this paper conducted an ambient vibration measuring on 10 observatory towers through mobile-phone application thereby calculating the natural frequency and comparing the result with the domestic and foreign standards and that of the eigen-value analysis. This paper suggested approximate equation of the natural frequency of the observatory tower; T=0.0266H. The square of the corelation coefficient is 0.940, which is high.

• Spatial Information Research
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• 제18권2호
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• pp.25-34
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• 2010

본 연구에서는 무주남대천 일부구간을 대상으로 GIS 공간정보와 FLUMEN 모형을 이용하여 빈도별 홍수범람을 모의하였다. 홍수범람해석을 위한 지형을 생성을 위해 수치지형도와 하천구간의 실제지형을 표현하는 종횡단측량 자료를 기반으로 GIS 공간보간법을 이용하여 불규칙삼각망을 구축하였으며, 극한의 홍수피해 시나리오를 고려하기 위해 제방 붕괴에 따른 홍수범람을 실시하였다. 분석결과, 좌안은 넓은 농경지의 영향으로 우안에 비해 50년, 100년, 200년 빈도에서의 침수면적이 각각 3.13배, 3.69배, 4.17배 높게 나타났으며, 인명피해가 발생할 수 있는 1.0m 이상의 침수지역에서는 각각 1.00배, 2.15배, 3.34배로 나타났다. 좌안의 제방 붕괴시 인명피해가 발생할 수 있는 1.0m 이상의 침수면적을 분석한 결과, 홍수량이 50년 빈도에서 100년과 200년 빈도로 증가시 침수면적이 각각 263%와 473%로 크게 증가하였다. 또한 우안 파제시에는 1.0m 이상의 침수심면적이 홍수량이 50년 빈도에서 100년과 200년 빈도로 증가시 침수면적이 각각 123%와 142% 증가한 것으로 분석되었으며, 특히 3.0~3.5m의 침수면적은 각각 263%와 489%로 크게 증가한 것으로 분석되었다. 본 연구에서 제시된 홍수범람도는 토지이용계획 및 치수대책 수립을 위한 중요한 의사결정 자료가 될 것으로 기대된다.

• 한국측량학회지
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• 제29권2호
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• pp.175-181
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• 2011

원격탐사 분야에서 고해상도의 멀티스펙트럴 영상은 위성센서의 기술적인 제약 때문에 직접적으로 취득하기 어렵다. 이러한 문제를 극복하기 위하여 다양한 위성영상 융합 기법이 제안되어졌다. 그러나, 대부분의 영상융합기법들은 원 멀티스펙트럴 영상의 분광정보를 왜곡시키거나 고해상도 흑백영상의 공간해상도에 비하여 융합영상의 공간해상도가 저하되는 문제점을 지닌다. 최근 들어 융합영상의 분광왜곡을 최소화시키면 서 공간해상도를 효율적으로 증가시킬 수 있는 공간상관도 기반의 하이브리드 융합 기법이 제안되었다. 본 연구에서는 하이브리드 융합기법에 다양한 공간상관도 추출 식을 적용하여 보고 이에 따른 분광/공간정보 왜곡의 양을 비교 평가하였다. 실험 결과 라플라시안 필터를 이용한 하이브리드 융합 기법이 다른 고주파 정보 추출 기법에 비하여 하이브리드 융합 기법에 효과적으로 적용할 수 있다는 것을 확인할 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.892-911
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• 2019

Biometric recognition systems have been widely used for information security. Among the most popular biometric traits, there are fingerprint and face due to their high recognition accuracies. However, the security system that uses face recognition as the login method are vulnerable to face-spoofing attacks, from using printed photo or video of the valid user. In this study, we propose a fast and robust method to detect face-spoofing attacks based on the analysis of spatial frequency differences between the real and fake videos. We found that the effect of a spoofing attack stands out more prominently in certain regions of the 2D Fourier spectra and, therefore, it is adequate to use the information about those regions to classify the input video or image as real or fake. We adopt a divide-conquer-aggregate approach, where we first divide the frequency domain image into local blocks, classify each local block independently, and then aggregate all the classification results by the weighted-sum approach. The effectiveness of the methodology is demonstrated using two different publicly available databases, namely: 1) Replay Attack Database and 2) CASIA-Face Anti-Spoofing Database. Experimental results show that the proposed method provides state-of-the-art performance by processing fewer frames of each video.