• Title/Summary/Keyword: 파워 스펙트럼 밀도함수

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Identification of Two-Phase Flow Patterns Based on Statistical Characteristics of Differential Pressure Fluctuations (차압교란치의 통계적 특성에 의한 2상유동양식의 판별)

  • 이상천;이정표;김중엽
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1290-1299
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    • 1990
  • Characteristics of flow patterns in horizontal gas-liquid two-phase flow for two different sizes of pipe were investigated based upon a statistical analysis of differential pressure fluctuations at an orifice. The probability density function and the power spectral density function of the traces indicate peculiar shapes depending upon the two-phase flow regime. Mixed and separated flows also could be identified by the autocorrelation function. The transition region from separated flow to mixed flow also could be identified by these statistical properties. The experimental data determined by this method were compared with the flow pattern maps suggested by other investigators. The result indicates that the statistical characteristics of differential pressure fluctuations at orifices may be a useful tool for identifying flow patterns of horizontal gas-liquid two-phase flow.

Turbulent Wake Flow around Tubes in Single Row Tube Banks (일렬관군에서의 난류 후류특성에 관한 연구)

  • 조석호;부정숙
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.5
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    • pp.1023-1031
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    • 1989
  • An experimental study is conducted to investigate the turbulent wake flow around tubes in vertical single row tube banks. All measurements are performed at Reynolds number(Re$_{max}$) 4.2*10$_{3}$ - 2.5*10$_{4}$ with varying tube spacings from the wide pitch ratio(H/D=3.07) to the very narrow one(H/D=1.23). Flow patterns are visualized using the smoke-wire method. Mean static pressures, velocity components, and various statistical quantities of turbulence are obtained by the computer on-line technique. In the case of wide tube spacings, the near wakes of tube show similar trends to those of a single tube, and their flow indicats an anisotropic turbulence. However, as the pitch ratio decreases, wide and narrow wakes appear alternately behind adjacent tubes due to the deflected flow. Also, in the case of H/D .leq. 1.54, Karman vortex is not formed at the side of relatively wide wake.e.

Estimation on the Power Spectral Densities of Daily Instantaneous Maximum Fluctuation Wind Velocity (변동풍속의 파워 스펙트럴 밀도에 관한 평가)

  • Oh, Jong Seop
    • Journal of Korean Society of Disaster and Security
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    • v.10 no.2
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    • pp.21-28
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    • 2017
  • Wind turbulence data is required for engineering calculations of gust speeds, mean and fluctuating loading. Spectral densities are required as input data for methods used in assessing dynamic response. This study is concerned with the estimation of daily instantaneous maximum wind velocity in the meteorological major cities (selected each 6 points) during the yearly 1987-2016.12.1. The purpose of this paper is to present the power spectral densities of the daily instantaneous maximum wind velocity. In the processes of analysis, used observations data obtained at Korea Meteorological Adminstration(KMA), it is assumed as a random processes. From the analysis results, in the paper estimated power spectral densities function(Blunt model) shows a very closed with von Karman and Solari's spectrum models.

Multi frequency band noise suppression system using signal-to-noise ratio estimation (신호 대 잡음비 추정 방법을 이용한 다중 주파수 밴드 잡음 억제 시스템)

  • Oh, In Kyu;Lee, In Sung
    • The Journal of the Acoustical Society of Korea
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    • v.35 no.2
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    • pp.102-109
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    • 2016
  • This paper proposes a noise suppression method through SNR (Singal-to Noise Ratio) estimation in the two microphone array environment of close spacing. The conventional method uses a noise suppression method for a gain function obtained through the SNR estimation based on coherence function from full band. However, this method cause performance decreased by the noise damage that affects all the feature vector component. So, we propose a noise suppression method that allocates a frequency domain signal into N constant multi frequency band and each frequency band gets a gain function through SNR estimation based on coherence function. Performance evaluation of the proposed method is shown by comparison with PESQ (Perceptual Evaluation of Speech Quality) value which is an objective quality evaluation method provided by the ITU-T (International Telecommunications Union Telecommunication).

Development of Simulation Method of Doppler Power Spectrum and Raw Time Series Signal Using Average Moments of Radar Wind Profiler (윈드프로파일러의 평균모멘트 값을 이용한 도플러 파워 스펙트럼 및 시계열 원시신호 시뮬레이션기법 개발)

  • Lee, Sang-Yun;Lee, Gyu-Won
    • The Journal of the Korea institute of electronic communication sciences
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    • v.15 no.6
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    • pp.1037-1044
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    • 2020
  • Since radar wind profiler (RWP) provides wind field data with high time and space resolution in all weather conditions, their verification of the accuracy and quality is essential. The simultaneous wind measurement from rawinsonde is commonly used to evaluate wind vectors from RWP. In this study, the simulation algorithm which produces the spectrum and raw time series (I/Q) data from the average values of moments is presented as a step-by-step verification method for the signal processing algorithm. The possibility of the simulation algorithm was also confirmed through comparison with the raw data of LAP-3000. The Doppler power spectrum was generated by assuming the density function of the skew-normal distribution and by using the moment values as the parameter. The simulated spectrum was generated through random numbers. In addition, the coherent averaged I/Q data was generated by random phase and inverse discrete Fourier transform, and raw I/Q data was generated through the Dirichlet distribution.

Identification of Two-phase Flow Patterns in a Horizontal Tubular Condenser (수평 응축관내 2상유동양식의 판별에 관한 연구)

  • Lee, S.C.;Han, Y.O.;Shin, H.S.;Lee, H.D.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.1
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    • pp.65-72
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    • 1993
  • An experiment has been carried out to identify flow patterns in a horizontal condensing flow with R-113. Characteristics of flow patterns were determined based upon a statistical analysis of differential pressure fluctuations at an orifice. The probability density function and power spectral density function of instantaneous pressure drop curves for various flow conditions were obtained. In comparison to the results of air-water flows, the flow patterns in a condensing flow such as annular, wavy, slug and plug could be identified. The experimental data determined by this technique were compared with the flow pattern maps suggested by other investigators. The result indicates that the statistical characteristics of differential pressure fluctuations at an orifice may be a useful tool for identifying flow patterns both in condensing flows and in adiabatic two-phase flows.

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Fatigue Strength Analysis of Propulsion Shafting System with Two Stroke Low Speed Diesel Engine by Torsional Vibration in Frequency Domain (주파수 영역에서 비틀림진동에 의한 저속 2행정 디젤엔진을 갖는 추진축계의 피로강도 해석)

  • Kim, S.H.;Lee, D.C.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.416-422
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    • 2007
  • Prime movers in most large merchant ships adapt two stroke low speed diesel engine which has higher efficiency, mobility and durability. However, severe torsional vibration in these diesel engines may be induced by higher fluctuation of combustion pressures. Consequently, it may lead sometimes to propulsion shafting failure due to the accumulated fatigue stresses. Shaft fatigue strength analysis had been done traditionally in time domain but this method is complicated and difficult in analysing bi-modal vibration system such as the case of cylinder misfiring condition. In this paper authors introduce an assessment method of fatigue strength estimation for propulsion shafting system with two stroke low speed diesel engine in the frequency domain.

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Characteristics of Low-frequency Ambient Seismic Noise in South Korea (국내 저주파수 무작위 지진잡음의 특성 연구)

  • Park, Iseul;Kim, Ki Young;Byu, Joongmoo
    • Geophysics and Geophysical Exploration
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    • v.19 no.2
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    • pp.67-75
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    • 2016
  • To investigate spatial and temporal variations of low-frequency (${\leq}5Hz$) ambient seismic noise, we analyzed the noise data recorded for one whole year of 2014 at surface accelerometer stations in South Korea. After decomposed into low-frequency (LF; < 1 Hz) and high-frequency (HF; ${\geq}1Hz$) components, the root-mean-squared (RMS) amplitudes and power spectral densities (PSD) of the noise data were computed. The RMS amplitudes were larger on islands and near-shore stations, but also large RMS amplitudes were observed at inland stations in large cities only for HF components. The RMS amplitudes of HF components were larger in the daytime than at nighttime and during weekdays than on Sunday and holidays. This indicates the HF components are closely related to human activities. On the contrary, daily and weekly variations were not clear in the LF components while they showed seasonal variations with its maximum during the winter and a good correlation with significant wave height. Therefore, we interpret the mechanism of LF components is closely related to natural phenomena such as sea. The amplitude of LF components decreased as an exponential function of the distance to the center of typhoons. The exponential index of -0.76 suggested that ambient seismic noise included both surface and body waves. Peak frequencies of the PSD curves were near 0.34 Hz indicating the double frequency. No temporal variation in the peak frequency was clearly noticed.

Development of a 9as-liquid two-phase flowmeter using double orifice plates (2중판 오리피스를 이용한 기액 2상유량계의 개발)

  • 이상천;이상무;남상철
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.5
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    • pp.619-629
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    • 1998
  • An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.

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Development of Programs to Analyze Mechanical Load Data of Wind Turbine Generator Systems and Case Studies on Simulation Data (풍력발전시스템의 기계적 하중 데이터 분석 프로그램 개발과 시뮬레이션 데이터 적용 사례)

  • Bang, Je-Sung;Han, Jeong-Woo;Gil, Kyehwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.8
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    • pp.789-798
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    • 2013
  • The procedures and relevant programs developed for analyzing mechanical load data of wind turbine generator systems, which are obtained through type certification tests, are verified. The following issues according to IEC 61400-13 are covered in the developed programs: data validation, time series analysis, summary load statistics, generation of fatigue load spectra, and estimation of equivalent loads. A capture matrix for normal power production is generated to determine whether the collected data sets are sufficient to carry out fatigue analysis. Fatigue load spectra are obtained through the rainflow counting method using 50 load ranges; finally, equivalent loads are calculated using different S-N curve slopes, m, according to the relevant materials. Case studies are performed using aero-elastic simulation data of the NREL 5 MW baseline wind turbine with a monopile foundation.