The application of pulsation ratio preprocessing method in researching density wave instability

2018 ◽  
Vol 10 (3) ◽  
pp. 140-145
Author(s):  
Yefei Liu ◽  
Yang Liu ◽  
Xingtuan Yang ◽  
Haijun Jia
Keyword(s):  
Frequency Domain ◽  
Density Wave ◽  
Annular Channel ◽  
Frequency Domain Analysis ◽  
Wave Instability ◽  
Two Phase ◽  
Transform Method ◽  
Modified Method ◽  
Fast Fourier Transform Method ◽  
Dc Component

A modified Fast Fourier Transform method based on the pulsation ratio preprocessing is carried out in this study. When the density wave instability occurs, the method is applied to capture the characteristic signals in the frequency domain. Thus, the stable boundary in two-phase flow can be recognized accurately. In this paper, experiments are conducted in a system based on a narrow annular channel. The method is verified through two groups of experimental data collected in different conditions. The results indicate that the modified method can avoid the problem of DC component spectrum leakage in traditional frequency-domain analysis with the false value interference eliminated. Accordingly, it can improve the accuracy of boundary identification effectively when the instability occurs.

Analysis of Electrocardio Signal Based on Approximate Entropy

2012 ◽  
Vol 429 ◽  
pp. 195-199
Author(s):  
Xiao Lei Zhao ◽  
Ming Rong Ren ◽  
Ya Ting Zhang ◽  
Pu Wang
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Approximate Entropy ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Spectrum Estimation ◽  
Transform Method ◽  
Time Frequency ◽  
Relationship Of

The research and detection of heart disease depends on the analysis of the characteristic of electrocardio signal. Current analysis methods mainly include: (1) time domain analysis is a common used approach. With experience learned by observation and calculation, researchers examine errors and interferences to calculate means and variances directly within time domain. Analysis quality of this method demands higher request for researchers’ experience and skill although it’s a direct and significant result. (2) Frequency domain analysis, such as spectrum estimation, is largely applied to electrocardio signal researches and clinical applications. The analysis reflects abundant electrocardio activities, but failed to show details of the characteristics due to lack of time information. (3) time-frequency domain analysis describes energy density under different time and frequency of electrocardio signal at one time. It clarifies the relationship of signal frequency’s changing along with time such as wavelet transform method. (4) Nonlinear analysis is generally applied to biomedicine signal research in recent years. Correlation dimension, kolmogorov entropy, lyapunov component are major research methods to estimate some nonlinear dynamic parameters to represent the characteristic of electrocardio signal.

Research of two‐phase density wave instability in reactor core channels with rolling motion

2020 ◽  
Vol 44 (9) ◽  
pp. 7323-7341
Author(s):  
Wenxi Tian ◽  
Qiang Lian ◽  
Suizheng Qiu ◽  
G.H. Su
Keyword(s):  
Density Wave ◽  
Reactor Core ◽  
Rolling Motion ◽  
Wave Instability ◽  
Two Phase ◽  
Phase Density

scholarly journals Diving behaviour of whale sharks in relation to a predictable food pulse

2005 ◽  
Vol 3 (6) ◽  
pp. 109-116 ◽  
Author(s):  
Rachel T Graham ◽  
Callum M Roberts ◽  
James C.R Smart
Keyword(s):  
Frequency Domain Analysis ◽  
Diving Behaviour ◽  
Whale Shark ◽  
Transform Method ◽  
Fast Fourier Transform Method ◽  
Fish Spawning ◽  
Whale Sharks ◽  
Spawning Periods ◽  
Fine Resolution ◽  
Free Ranging

We present diving data for four whale sharks in relation to a predictable food pulse (reef fish spawn) and an analysis of the longest continuous fine-resolution diving record for a planktivorous shark. Fine-resolution pressure data from a recovered pop-up archival satellite tag deployed for 206 days on a whale shark were analysed using the fast Fourier Transform method for frequency domain analysis of time-series. The results demonstrated that a free-ranging whale shark displays ultradian, diel and circa-lunar rhythmicity of diving behaviour. Whale sharks dive to over 979.5 m and can tolerate a temperature range of 26.4 °C. The whale sharks made primarily diurnal deep dives and remained in relatively shallow waters at night. Whale shark diving patterns are influenced by a seasonally predictable food source, with shallower dives made during fish spawning periods.

Instability Analysis of Once-Through Steam Generator

2013 ◽  
Vol 756-759 ◽  
pp. 4596-4599
Author(s):  
Su Xia Hou ◽  
Ji Jun Luo ◽  
Jun Xu ◽  
Qing Hua Zhang
Keyword(s):  
Frequency Domain ◽  
Steam Generator ◽  
Moving Boundary ◽  
Stability Boundary ◽  
Feedback System ◽  
Frequency Domain Analysis ◽  
Frequency Domain Method ◽  
Two Phase ◽  
Instability Analysis ◽  
Major Factors

Considering the characteristic of Once-Through steam generator, the simplified dynamic model with lumped parameters moving boundary is used to describe two-phase flow feedback system in this paper. The feedback system and transfer-function for instability analysis are derived from the model. The instability analysis of the system is based on the frequency-domain analysis method. The Matlab software and its simulink tools are used to analyze the instability of the system. Then the stability boundary under the effect of some major factors is obtained. The results of stability boundary are compared to the concerned experiments by frequency-domain method.

Experimental Study on Density Wave Instability of Sodium Boiling Two-Phase Flow in an Annulus

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Dounan Jia
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Density Wave ◽  
Inlet Temperature ◽  
Phase Flow ◽  
Wave Instability ◽  
Two Phase ◽  
System Pressure

Experiments of density wave instability in a liquid sodium boiling two-phase flow experiments in an annulus were carried out in the following parameters range: heat flux from 80kW/m2 to 976kW/m2, inlet subcooling from 25.6°C to 226.8°C, mass flow rate from 7.92kg/h to 68.9kg/h, system pressure from 2600Pa to 0.12Mpa. Not only the mechanism of the instability, critical conditions and oscillation period, but also the effects of pressure, mass flow rate and inlet subcooling on the density wave instability were explored experimentally and theoretically. From the experimental data, it was found that the lower the inlet temperature was, the higher the system pressure and the mass flow rate that could result in a more stable boiling two-phase flow were. A correlation for the density wave instability was obtained on from the dimensional analysis for the conservation equations of mass, momentum and energy.

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