《Calculation of turbulent dissipation rate with acoustic Doppler velocimeter》

  • 来源专题:物理海洋学知识资源中心
  • 编译者: cancan
  • 发布时间:2018-12-05
  • 摘要:Turbulent dissipation rates are calculated from an acoustic Doppler velocimeter by fitting the measured wavenumber spectrum to a universal turbulence spectrum. A combination of the Butterworth filter and empirical model decomposition is employed to reduce Doppler noise and high‐frequency fluctuations. Different from the classical inertial subrange dissipation method fitting to the Kolmogorov − 5/3 slope, we propose the method here which can make longer available spectrum bands. We analyzed 408 bursts with turbulent dissipation rates ranging from 10−8 to 10−5 W kg−1 as measured in the coastal ocean of the South China Sea and found for all of these bursts, features of the clean spectrum can be resolved to the dissipation range of turbulence, in which about 15% bursts can be resolved to the Kolmogorov wavenumber, and 51% to 1/2 Kolmogorov wavenumber. Comparisons of this method with the inertial subrange method indicated that its estimated turbulent dissipation rates were somewhat smaller than those from the inertial subrange method in most of the bursts. Their ratios had a mean value of 0.77, which is typical for oceanic turbulence measurements.

    全文链接:https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lom3.10243

  • 原文来源:https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lom3.10243
相关报告
  • 《On estimating turbulent Reynolds stress in wavyaquatic environment》

    • 来源专题:物理海洋学知识资源中心
    • 编译者:cancan
    • 发布时间:2018-12-05
    • 摘要:Several methods have been developed for the estimation of the turbulent Reynolds stress inwavy aquatic environment. They are based on different physical assumptions and often give discrepantresults. It is practically difficult to quantify the uncertainties in these estimations. Using high-resolutionvelocity measurements of acoustic Doppler velocimeter (ADV) from a coastal benthic layer subject to mod-erate wave influence (the ratio of rms wave orbital velocity to current magnitude was 0.23–0.92), this studytests a Synchrosqueezed Wavelet Transform (SWT)-based method and three existing methods (i.e., theCoherence, Cospectra, and Ensemble Empirical Mode Decomposition [EEMD] methods) for wave-turbulencedecomposition. In particular, we evaluate the performance of different methods for objective estimation ofthe turbulent Reynolds stress. Power spectra and cospectra analysis is conducted to quantify the uncertain-ties in the estimations. The results suggest that the Coherence method tends to overestimate the Reynoldsstress due to incomplete removal of wave motions from the observed velocity records; the Cospectramethod performs poorly because the empirical model does not fit the observed cospectra well; both theEEMD and SWT methods underestimate the Reynolds stress, as they tend to attribute turbulent fluctuationsat frequencies in the vicinity of the wave frequencies to wave motions. In general, the SWT method per-forms best inducing lowest uncertainty in the Reynolds stress estimation. For the data set analyzed in thisstudy, the estimations with the Coherence, Cospectra, EEMD, and SWT methods account for 70%, 50%, 51%,and 60% of the total covariance of horizontal and vertical velocities, respectively 全文链接:https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017JC013230
  • 《Decision fractional fast Fourier transform Doppler compensation in underwater acoustic orthogonal frequency division multiplexing》

    • 来源专题:水声领域信息监测
    • 发布时间:2016-11-21
    • A method of compensating for Doppler distortions of underwater acoustic channels for orthogonal frequency division multiplexing (OFDM) signals is proposed. This method is based on symbol rebuilding. OFDM symbol rebuilding is performed after fractional fast Fourier transform (F-FFT) processing. A stochastic gradient-type adaptive algorithm is designed to learn the combiner weights for detection. Synthetic data and experimental data from a recent mobile acoustic communication experiment are used to demonstrate the performance of the proposed method, which represents a significant improvement over the F-FFT detection technique.