• 전기전자학회논문지
• /
• 제23권3호
• /
• pp.893-898
• /
• 2019

시주파수 표현법은 시간과 주파수의 2차원 평면에 대하여 신호의 크기 혹은 에너지 밀도의 분포를 표현하는 방법이다. 이러한 기술은 시변 신호(Time-varying signal)의 특성 분석에 유용하다. 연주음은 대표적인 시변신호이며 특성 분석을 위하여 시주파수 표현법을 사용할 수 있다. 최근 악기에 사운더를 부착하여 음질을 변화시키는 작업이 주목 받고 있다. 비교적 저렴한 비용을 지불하고 음질을 변화시켜 주관적인 평가를 개선하려는 시도로 시행되고 있다. 이러한 연주신호는 시간영역에서는 사운더가 없는 악기 원형으로 연주한 경우와 차이점을 찾기가 어렵지만 주파수 영역, 그리고 시간-주파수 영역에서 분석하면 차이점을 쉽게 볼 수 있다. 본 논문에서는 사운더를 부착한 악기의 연주신호를 주파수 영역에서 분석하여 사운더의 효과를 확인하고 더 나아가 시주파수 표현법을 활용하여 사운더의 영향을 분석한다. 악기에 따라 사운더의 효과는 다르지만 대체로 인간의 주관적인 평가에 영향을 주는 중간주파수대에서 강화된 효과를 확인할 수 있다.

• Earthquakes and Structures
• /
• 제3권2호
• /
• pp.97-115
• /
• 2012

The energy-transmitting boundary, which is used in the well-known finite element method (FEM) program FLUSH, is quite efficient for the earthquake response analysis of buildings considering soil-structure interaction. However, it is applicable only in the frequency domain. The author proposed methods for transforming frequency dependent impedance into the time domain, and studied the time domain transform of the boundary. In this paper, first, the estimation methods for both the halfspace condition under the bottom of the soil model and the pseudo three-dimensional effect were studied with the time domain transmitting boundary. Next, response behavior when using the boundary was studied in detail using a practical soil and building model. The response accuracy was compared with those using viscous boundary, and the boundary that considers the excavation force. Through these studies, the accuracy and efficiency of the proposed time domain transmitting boundary were confirmed.

• 한국항공우주학회지
• /
• 제45권8호
• /
• pp.627-638
• /
• 2017

항공기에 탑재된 레이더 장비는 무작위진동 환경에 장기간 노출되어, 설계 시 피로수명 예측이 중요한 요소로 고려된다. 피로수명을 예측하는 방법 중 주파수영역 피로해석 방법이 지속적으로 제안되고 있다. 본 논문은 많이 사용되는 4가지의 주파수영역 피로해석 방법을 선정하여, 시편 피로시험 결과와 비교하였다. Strain gage를 이용한 시편 피로시험을 통해 시간영역 피로해석과 주파수영역 피로해석 방법을 비교한 결과, Dirlik과 Benasciutti-Tovo방법이 주파수영역 피로해석법 중 시간영역 피로해석법과 잘 일치하였다. 시편 피로시험 결과를 토대로 Dirlik과 Benasciutti-Tovo방법과 유한요소모델을 이용하여 항공기 탑재 장비의 피로해석을 수행하였으며, 요구수명이 만족함을 확인하였다.

• 한국수산과학회지
• /
• 제30권1호
• /
• pp.16-30
• /
• 1997

Application of digital filter to the wave analysis is studied using the observed data by wave gauge. Sea wave data obtained from wave gauge always include long wave frequency components. In order to estimate the sea wave parameters, we must re-analyzed wave data by using a digital filter and the concept of mean sea level correction method. By the wave by wave analysis and spectral methods, sea wave parameters on the basis of wave data obtained by the conventional method and digital filter are compared. The best-fitted design filter determined by the necessary conditions of frequency responses, can be obtained by calculating various transfer functions. Thus, to get the best the digital filter design, both Butterworth filter and Savitzky-Golay filter of digital filter are used in the frequency and time domain, respectively. Three cases of observation wave data are calculated by applying digital filter. The components of different frequency bands in the surf zone are coexisted in three cases. The wave data for wind wave components is computed using the digital filter the surf zone and off-surf zone, and based on the filtered data, wave parameters are calculated by the spectral analysis and wave by wave analysis methods, respectively. As a results, when sea wave data observed by wave gauge are analyzed, the Savitzky-Golay method is recommended which can well appear cut-off frequency by experimental choosing filter length in the time domain. The better mean sea level correction method is the Butterworth filter in the frequency domain.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계학술대회논문집
• /
• pp.812-817
• /
• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2000년도 추계학술대회 논문집
• /
• pp.118-122
• /
• 2000

In this study, Ringing is investigated by continuous wavelet transform. Ringing is considered to be one of the typical transient phenomena in the field of ocean engineering. The wavelet analysis is adopted to analyze ringing from the point that wavelet analysis is capable of frequency analysis as well as time domain analysis. The use mother wavelet is the Morlet wavelet. The relation between the frequency of the time series and that of wavelet can be clearly defined with Mor1et wavelet. Experimental data obtained by other researchers was used. The wave height time series and acceleration times series of the surface piercing cylinder were analyzed. The results show that the proposed scheme can detect typical frequency region by the time domain analysis which could hardly be detected if one relied on the frequency analysis.

• 전자공학회논문지B
• /
• 제31B권3호
• /
• pp.24-38
• /
• 1994

In this paper we develop the software simulator written in a C language for a frequency modulation synthesis and the approximate range of parameters, for a musically satisfactory timbre, obtained by using the software simulator will be applied to develop an algorithm for parameter extraction. For a frequency modulation synthesis, we also develop an algorithm for parameter extraction through waveform analysis in the time domain as well as spectrum analysis using a FFT in the frequency domain. To verify the validity of the developed algorithm as well as software simulator experimentally, we extract parameters for the several music instruments using the suggested algorithm and analyze the synthesized sound by applying the parameters to the software simulator. The evaluation of the synthesized sound is first done by listening the sound directly as a subjective testing. Secondly, to evaluate the synthesized sound objectively with an engineering sense, we compare the synthesized sound with an original one in a time domain and a frequency domain.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
• /
• pp.125-129
• /
• 1987

The stability margin of the LQ regulator is investigated in the time domain. it is shown that the same guaranteed gain margin as that of the frequency domain analysis can be obtained with simple assumptions for the continuous time systems. It is also shown that the allowable modelling error bound can be expressed in terms of system matrices and Riccati equation solution. Guaranteed qain. margin and the allowable modelling error bound for the discrete time systems are also obtained by the similar procedures. In this case, through the some examples, the gain margin is shown to be less conservative than the frequency domain analysis result.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 춘계학술대회논문집
• /
• pp.732-737
• /
• 2005

This paper performed pseudo static analysis and dynamic analysis for CFRD and evaluated reliability with the results of Shaking Table Test. The Seismic coefficient method, modified seismic coefficient method, Newmark method of Pseudo static analysis and frequency domain response analysis, time domain history analysis of dynamic analysis were used. The analysis results were differ between analysis method, but the trends of acceleration and displacement were good agreement with the results of shaking table test.

• 소음진동
• /
• 제6권3호
• /
• pp.341-347
• /
• 1996

진동해석을 이용한 기계계통의 진단에는 시간영역(time domain)에서의 해석 과 FFT(Fast Fourier Transform)를 이용한 주파수영역(frequency domain)에서의 해석 을 생각할 수 있다. 이중 FFT 방법은 고속연산기의 출현과 물리적인 이해의 편이성 등오로 인하여 널리 사용되고 있으나, 시간 함수인 비정상 상태신호(nonstationary signal)의 경우는 주파수영역 해석만으로는 물리적 이해를 구하는데는 한계가 있다. 그래서, 최근 신호처리기법 분야에서는 주파수영역 해석과 시간영역 해석을 보완적 으로 표현할 수 있는 기간-주파수영역 해석기법에 많은 연구가 진행되고 있다. 그중 대표적인 신호처리 기법은 Wigner-Ville Distribution이며, 특히 본 Wigner-Ville Distribution은 많은 물리적 의미를 갖고 있어 주요 연구 대상이며, 많은 응용분야 를 갖고 있다. 그러나, 기계계통중 회전체의 진동신호을 분석하여 고장 진단 및 감시를 용이하기 위해서는 새로운 형태의 시간.주파수영역 해석기법이 필요하다. 본 논문에서는 회전체의 진동신호 분석이 용이하도록 물리적인 의미와 응용상에 중점을 둔 방향서 Wigner-Ville 분포라는 시간-주파수 분석기법을 제안하였고, 회전체를 이용한 실험을 실시하였다. 그 결과 제안된 방향성 Wigner-Ville Distribution은 회전체 진동신호를 시간-주파수 영역에서 잘 표현하고 있으며, 특히 회전체의 수직 및 수평방향 진동신호로 부터 얻어지는 방향성 Wigner-Ville Distribution은 각 주파수 성분의 방향성 정보를 갖고 있어 이를 회전체의 고장 진단 및 감시에 이용 하였다.