• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.8
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• pp.741-746
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• 2007

In this study, transfer path identification and output estimation are simulated by multi-dimension spectral analysis method (MDSA). Multi -input/single-output system give expression the vehicle suspension which each inputs are correlated reciprocally. In case of correlating with inputs, the system needs separating the each input signal by MDSA. Main simulations are about finding effective input by coherent output spectrum and selecting optimal input's number by multiple coherence function. Also, by shielding transfer path of each input, transfer path characteristic is identified in terms of overall integrated contribution level.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.442-449
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• 1986

본 연구에서는 소음원 및 진동원을 규명하기 위하여 사용되어 온 종래의 주파 수응답함수(Frequency Response Function`FRF)법과 소음원 및 진동원 간에 강한 상관 관계가 존재한 경우에 사용되는 기여도함수(coherence function)법을 이용한 다차원 스텍트럼해석(Multi-Dimensional Spectral Analysis`MDSA)법에 의하여 가속도응답 및 방사음과의 기여관계를 규명하였다.

• Journal of Biosystems Engineering
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• v.26 no.6
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• pp.503-508
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• 2001

In this paper, time-fiequency analysis and multi-dimensional spectral analysis methods are applied for source identification and diagnosis of non-stationary sound/vibration signals. Sound or vibration problems of general vehicle and agricultural machinary are under 500 Hz. So We used linearly increased chirp signals under 500 Hz. By checking the coherences on concerned time, fur time-variant non-stationary signals, this simulation it very well coincident to expected results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.260-265
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• 2001

본 연구에서는 연속 웨이블렛 변환을 이용하여 Ringing 현상을 연구하였다. 사용되어진 웨이블렛은 Morlet 웨이블렛이었고, 실험은 파수조에서 수행되었다. 또한 Ringing 현상을 다루고자 쇄파를 발생시켰다. 실험에 쓰인 모델은 수면을 통과하여 수직으로 고정된 원주 실린더였고, 이 실린더에 작용된 힘과 파고가 측정되어졌다. 이들은 연속 웨이블렛 변환으로 분석되어졌고, 이러한 분석으로 얻어진 scalogram 들은 고주파 성분이 쇄파 충격시 만들어진다는 사실을 시간영역상에서 보여주었다. 이는 기존의 스펙트럼 분석에서는 찾기 힘든 것이다. Coherence 분석도 위의 결론을 뒷받침해 주었다.

• Proceedings of KOSOMES biannual meeting
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• 2017.11a
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• pp.75-75
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• 2017

• Research in Mathematical Education
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• v.17 no.1
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• pp.1-14
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• 2013

Stochastic phenomena induce us to construct a probability model and structure our thinking; corresponding models help us to understand and interpret the reality. They in turn equip us with tools to recognize, reconstruct and solve problems. Therefore, various implications in terms of methodology as well as epistemology naturally flow from different adoptions of models for probability. Right from the basic scenarios of different perspectives to explore reality, students are occasionally exposed to misunderstanding and misinterpretations. With realistic examples a multi-faceted image of probability and different interpretation will be considered in mathematical modelling activities. As an exploratory investigation, mathematical modelling activity for probability learning was elaborated through semiotic analysis. Especially, the coherence structure in mathematical modelling discourse was reviewed form a semiotic perspective. The discourses sampled from group activities were analyzed on the basis of semiotic perspectives taxonomical coherence relations.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.1-8
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• 2019

This paper estimated communication parameters according to underwater channel environment of lake for underwater acoustic communication. This paper calculated coherence time and coherence bandwidth through two experiments in actual lake environments. In both experiments, the chirp signal for channel estimation and the BPSK (Binary Phase Shift Keying) signal for calculating the bit error rate were transmitted. In each experiment, the distance between transmitter and receiver was 300 m to 400 m, and 500 m to 600 m. The coherence times calculated in experiment 1 and experiment 2 are 175 msec and 340 msec, and the coherence bandwidths are 10 Hz and 5.71 Hz, respectively. It is confirmed that the experimental results are more appropriate because the synchronization and the bit error rate performance are better only when the length of the synchronization signal and the interval of the pilot signal in the frame are shorter than the coherence time.

• Wind and Structures
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• v.16 no.5
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• pp.433-455
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• 2013

A phase delay spectrum model towards the representation of spatial coherence of stochastic wind fields is proposed. Different from the classical coherence functions used in the spectral representation methods, the model is derived from the comprehensive description of coherence of fluctuating wind speeds and from the thorough analysis of physical accounts of random factors affecting phase delay, building up a consistent mapping between the simulated fluctuating wind speeds and the basic random variables. It thus includes complete probabilistic information of spatial stochastic wind fields. This treatment prompts a ready and succinct scheme for the simulation of fluctuating wind speeds, and provides a new perspective to the accurate assessment of dynamic reliability of wind-induced structures. Numerical investigations and comparative studies indicate that the developed model is of rationality and of applicability which matches well with the measured data at spatial points of wind fields, whereby the phase spectra at defined datum mark and objective point are feasibly obtained using the numerical scheme associated with the starting-time of phase evolution. In conjunction with the stochastic Fourier amplitude spectrum that we developed previously, the time history of fluctuating wind speeds at any spatial points of wind fields can be readily simulated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.12
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• pp.2603-2608
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• 2009

Document clustering is an important method for document analysis and is used in many different information retrieval applications. This paper proposes a new document clustering model using the clustering method based NMF(non-negative matrix factorization) and refinement of documents in cluster by using coherence of cluster. The proposed method can improve the quality of document clustering because the re-assigned documents in cluster by using coherence of cluster based similarity between documents, the semantic feature matrix and the semantic variable matrix, which is used in document clustering, can represent an inherent structure of document set more well. The experimental results demonstrate appling the proposed method to document clustering methods achieves better performance than documents clustering methods.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.3
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• pp.221-229
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• 2004

The Continuous Wavelets Transform project signal f(t) to "Time-scale"plan utilizing the time varied function which called "wavelets". This Transformation permit to analyze scale time dependence of signal f(t) thus the local or global scale properties can be extracted. Moreover, the signal f(t) can be reconstructed stably by utilizing the Inverse Continuous Wavelets Transform. In this paper, the EEG signal is analyzed by wavelets coherence method and the De-noising procedure is represented.