The pressure pulsation of axial piston pump is not only an important cause of rotation speed fluctuation,vibration noise and output stability of the hydraulic system,but also the main information source for obtaining ...The pressure pulsation of axial piston pump is not only an important cause of rotation speed fluctuation,vibration noise and output stability of the hydraulic system,but also the main information source for obtaining fault information.Hydraulic system is characterized by strong noise interference,which leads to low signal-to-noise ratio(SNR)of detection signals.Therefore,it is necessary to dig deep into the system operating state information carried by pressure signals.Firstly,based on flow loss mechanism of the plunger pump,the mapping relationship between flow pulsation and pressure pulsation is analyzed.After that,the pressure signal is filtered and reconstructed based on standard Gabor transform.Finally,according to the time-domain waveform morphology of pressure signal,four characteristic indicators are proposed to analyze the characteristics of pressure fluctuations under different working conditions.The experimental results show that the standard Gabor transform can accurately extract high-order harmonics and phase frequencies of the signal.The reconstructed time-domain waveform of pressure pulsation of the axial piston pump contains a wealth of operating status information,and the characteristics of pulsation changes under various working conditions can provide a new theoretical basis and a method support for fault diagnosis and health assessment of hydraulic pumps,motors and key components.展开更多
This paper proposes an advanced substation integrated protection communication system based on the latest development in power system.The integrated protection communication system within a substation comprises a numb...This paper proposes an advanced substation integrated protection communication system based on the latest development in power system.The integrated protection communication system within a substation comprises a number of major components such as the merging unit, communication network and integrated protection unit.The design and capability evaluation of the communication network based on IEC61850 are focused on.Results show that huge information from 4 merging units can be transmitted real-time via adopting 100 Mbit/s optical fiber in a substation,and the proposed communication network is able to achieve required performance.展开更多
Considering the central and eastern tropical Pacific （CETP） has important climate impacts, and its seasonal variability is also thought to be important, the authors used the monsoon investigation method named ＇dyna...Considering the central and eastern tropical Pacific （CETP） has important climate impacts, and its seasonal variability is also thought to be important, the authors used the monsoon investigation method named ＇dynamical normalized seasonality＇, which can precisely describe the wind vector direction over time, to analyze the upper-tropospheric circulation over the region. The authors discovered that there is a clear reversal of seasonal changes between winter and summer wind, just like the classic monsoon. Accordingly, the authors propose the new concept of the upper- troposphere monsoon over the CETP. The results extend the classical lower-troposphere monsoon region into the upper troposphere.展开更多
Define the incremental fractional Brownian field with parameter H ∈ （0, 1） by ZH（τ, s） = BH（s-＋τ） - BH（S）, where BH（s） is a fractional Brownian motion with Hurst parameter H ∈ （0, 1）. We firstly deriv...Define the incremental fractional Brownian field with parameter H ∈ （0, 1） by ZH（τ, s） = BH（s-＋τ） - BH（S）, where BH（s） is a fractional Brownian motion with Hurst parameter H ∈ （0, 1）. We firstly derive the exact tail asymptoties for the maximum MH＊（T） = max（τ,s）∈[a,b]×[0,T] ZH（τ, s）/τH of the standardised fractional Brownian motion field, with any fixed 0 〈 a 〈 b 〈 ∞ and T 〉 0; and we, furthermore, extend the obtained result to the ease that T is a positive random variable independent of {BH（s）, s ≥ 0}. As a by-product, we obtain the Gumbel limit law for MH＊r（T） as T →∞.展开更多
基金National Natural Science Foundation of China(No.51675399)。
文摘The pressure pulsation of axial piston pump is not only an important cause of rotation speed fluctuation,vibration noise and output stability of the hydraulic system,but also the main information source for obtaining fault information.Hydraulic system is characterized by strong noise interference,which leads to low signal-to-noise ratio(SNR)of detection signals.Therefore,it is necessary to dig deep into the system operating state information carried by pressure signals.Firstly,based on flow loss mechanism of the plunger pump,the mapping relationship between flow pulsation and pressure pulsation is analyzed.After that,the pressure signal is filtered and reconstructed based on standard Gabor transform.Finally,according to the time-domain waveform morphology of pressure signal,four characteristic indicators are proposed to analyze the characteristics of pressure fluctuations under different working conditions.The experimental results show that the standard Gabor transform can accurately extract high-order harmonics and phase frequencies of the signal.The reconstructed time-domain waveform of pressure pulsation of the axial piston pump contains a wealth of operating status information,and the characteristics of pulsation changes under various working conditions can provide a new theoretical basis and a method support for fault diagnosis and health assessment of hydraulic pumps,motors and key components.
基金National Natural Science Foundation of China(No.50677003).
文摘This paper proposes an advanced substation integrated protection communication system based on the latest development in power system.The integrated protection communication system within a substation comprises a number of major components such as the merging unit, communication network and integrated protection unit.The design and capability evaluation of the communication network based on IEC61850 are focused on.Results show that huge information from 4 merging units can be transmitted real-time via adopting 100 Mbit/s optical fiber in a substation,and the proposed communication network is able to achieve required performance.
基金supported by the National Natural Science Foundation of China Projects(41530424)SOA Program on Global Change and Air-Sea Interactions(GASI-IPOVAI-03)
文摘Considering the central and eastern tropical Pacific （CETP） has important climate impacts, and its seasonal variability is also thought to be important, the authors used the monsoon investigation method named ＇dynamical normalized seasonality＇, which can precisely describe the wind vector direction over time, to analyze the upper-tropospheric circulation over the region. The authors discovered that there is a clear reversal of seasonal changes between winter and summer wind, just like the classic monsoon. Accordingly, the authors propose the new concept of the upper- troposphere monsoon over the CETP. The results extend the classical lower-troposphere monsoon region into the upper troposphere.
基金supported by National Natural Science Foundation of China(Grant Nos.11326175 and 71471090)Natural Science Foundation of Zhejiang Province of China(Grant No.LQ14A010012)+2 种基金Research Start-up Foundation of Jiaxing University(Grant No.70512021)China Postdoctoral Science Foundation(Grant No.2014T70449)Natural Science Foundation of Jiangsu Province of China(Grant No.BK20131339)
文摘Define the incremental fractional Brownian field with parameter H ∈ （0, 1） by ZH（τ, s） = BH（s-＋τ） - BH（S）, where BH（s） is a fractional Brownian motion with Hurst parameter H ∈ （0, 1）. We firstly derive the exact tail asymptoties for the maximum MH＊（T） = max（τ,s）∈[a,b]×[0,T] ZH（τ, s）/τH of the standardised fractional Brownian motion field, with any fixed 0 〈 a 〈 b 〈 ∞ and T 〉 0; and we, furthermore, extend the obtained result to the ease that T is a positive random variable independent of {BH（s）, s ≥ 0}. As a by-product, we obtain the Gumbel limit law for MH＊r（T） as T →∞.
