Periodic Fluctuation
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2021 ◽  
Author(s):  
Jingzhou Gao ◽  
Jingxiang Li ◽  
Shengdun Zhao ◽  
Wei Du ◽  
Fei Jiang ◽  
...  

Abstract In this paper, a novel type of low frequency vibration plastic forming equipment is proposed, in which the slotted tubular permanent magnet synchronous liner motor (slotted – TPMLM) is the core component and plays the roles of power source and vibration source. So, this paper focuses on the research about the design of the slotted - TPMLM. The suppression and optimization of motor thrust fluctuation has always been a hot research issue. But that is not the purpose of this article. Here, the effect of the length of stator core on end force and the influence of the number of poles and slots on the cogging force are discussed in detail. The purpose is to design the thrust fluctuation of slotted – TPMLM reasonably so that the thrust fluctuation can be used in the low frequency plastic forming. The slotted – TPMLM is designed, manufactured, and tested. The experimental results show that the motor can output thrust with periodic fluctuation (low frequency, about 4.8 Hz), and the thrust fluctuation accounts for about 16.5% of the average thrust, which meets the metal low frequency vibration plastic forming requirements. Consequently, the low frequency vibration plastic forming equipment can be realized, which contributes to the field of the plastic forming.


2021 ◽  
Vol 263 (2) ◽  
pp. 4634-4640
Author(s):  
Nozomiko Yasui ◽  
Masanobu Miura ◽  
Tetsuya Shimamura

The motor sound on electric powered vehicle is quiet at low speeds. Thus, pedestrians have difficulty detecting the vehicles approaching them under urban noise. Although the vehicles were designed to play an alert sound to solve this problem, it has not been solved yet. Our previous studies found that characteristics of amplitude fluctuation, fluctuation frequency, non-periodic fluctuation and amplitude envelope, are effective to make them detect approaching vehicles. However, those studies were investigated under only a specific actual environment, weren't examined validity of detectability in those studies. Here, this paper investigates under another actual environment, examine the validity. Investigations were carried out by using synthesized complex sounds which were designed to have periodic and non-periodic amplitude fluctuations. Those complex sounds have characteristics of amplitude fluctuations in gasoline powered vehicle. Amplitude envelopes such as modulation wave in amplitude-modulated sound were set for deviations for time and amplitude, and amplitude-modulated complex sounds were synthesized using sine wave, sawtooth wave, and rectangle wave. Then, their effects on detectability by pedestrians were assessed in another actual environment. The results found that amplitude fluctuation enhances the ability with which people detect approaching electric powered vehicles in case of some complex sound.


Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 4996
Author(s):  
Ye Xi ◽  
Zhejun Guo ◽  
Longchun Wang ◽  
Qingda Xu ◽  
Tao Ruan ◽  
...  

pH value plays an important role in many fields such as chemistry and biology; therefore, rapid and accurate pH measurement is very important. Because of its advantages in preparation, wide test range, rapid response, and good biocompatibility, iridium oxide material has received more and more attention. In this paper, we present a method for preparing iridium oxide pH microelectrodes based on the sputter deposition method. The sputtering parameters of iridium oxide are also studied and optimized. Open-circuit potential tests show that microelectrodes exhibit near-Nernstian pH response with good linearity (about 60 mV/pH), fast response, high stability (a slight periodic fluctuation of potential change <2.5 mV in 24 h), and good reversibility in the pH range of 1.00–13.00.


Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 843
Author(s):  
Jiaqi Tian ◽  
Chunsheng Fang ◽  
Jiaxin Qiu ◽  
Ju Wang

The increase in tropospheric ozone (O3) concentration has become one of the factors restricting urban development. This paper selected the important economic cooperation areas in Northeast China as the research object and collected the hourly monitoring data of pollutants and meteorological data in 11 cities from 1 January 2015 to 31 December 2019. The temporal and spatial variation trend of O3 concentration and the effects of meteorological factors and other pollutants, including CO (carbon monoxide), SO2 (sulfur dioxide), NO2 (nitrogen dioxide), and PM2.5 and PM10 (PM particles with aerodynamic diameters less than 2.5 μm and 10 μm) on ozone concentration were analyzed. At the same time, the variation period of O3 concentration was further analyzed by Morlet wavelet analysis. The results showed that the O3 pollution in the study area had a significant spatial correlation. The spatial distribution showed that the O3 concentration was relatively high in the south and low in the northeast. Seasonally, the O3 concentration was the highest in spring, followed by summer, and the lowest in winter. The diurnal variation of O3 concentration presented a “single peak” pattern. O3 concentration had a significant positive correlation with temperature, sunshine duration, and wind speed and a significant anticorrelation with CO, NO2, SO2, and PM2.5 concentration. Under the time scale of a = 9, 23, O3 had significant periodic fluctuation, which was similar to those of wind speed and temperature.


2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Ping Xie ◽  
Linqian Wu ◽  
Yan-Fang Sang ◽  
Faith Ka Shun Chan ◽  
Jie Chen ◽  
...  

AbstractIdentification of periodicities in hydrological time series and evaluation of their statistical significance are not only important for water-related studies, but also challenging issues due to the complex variability of hydrological processes. In this article, we develop a “Moving Correlation Coefficient Analysis” (MCCA) method for identifying periodicities of a time series. In the method, the correlation between the original time series and the periodic fluctuation is used as a criterion, aiming to seek out the periodic fluctuation that fits the original time series best, and to evaluate its statistical significance. Consequently, we take periodic components consisting of simple sinusoidal variation as an example, and do statistical experiments to verify the applicability and reliability of the developed method by considering various parameters changing. Three other methods commonly used, harmonic analysis method (HAM), power spectrum method (PSM) and maximum entropy method (MEM) are also applied for comparison. The results indicate that the efficiency of each method is positively connected to the length and amplitude of samples, but negatively correlated with the mean value, variation coefficient and length of periodicity, without relationship with the initial phase of periodicity. For those time series with higher noise component, the developed MCCA method performs best among the four methods. Results from the hydrological case studies in the Yangtze River basin further verify the better performances of the MCCA method compared to other three methods for the identification of periodicities in hydrologic time series.


2020 ◽  
Vol 1634 ◽  
pp. 012132
Author(s):  
Zhaonan Li ◽  
Daliang Gong ◽  
Fengfeng Shi ◽  
Jiangting Wang

Entropy ◽  
2020 ◽  
Vol 22 (6) ◽  
pp. 614
Author(s):  
Yong Shi ◽  
Yuanchun Zheng ◽  
Kun Guo ◽  
Zhenni Jin ◽  
Zili Huang

The stock market is a complex system with unpredictable stock price fluctuations. When the positive feedback in the market amplifies, the systemic risk will increase rapidly. During the last 30 years of development, the mechanism and governance system of China’s stock market have been constantly improving, but irrational shocks have still appeared suddenly in the last decade, making investment decisions risky. Therefore, based on the daily return of all a-shares in China, this paper constructs a dynamic complex network of individual stocks, and represents the systemic risk of the market using the average weighting degree, as well as the adjusted structural entropy, of the network. In order to eliminate the influence of disturbance factors, empirical mode decomposition (EMD) and grey relational analysis (GRA) are used to decompose and reconstruct the sequences to obtain the evolution trend and periodic fluctuation of systemic risk. The results show that the systemic risk of China’s stock market as a whole shows a downward trend, and the periodic fluctuation of systemic risk has a long-term equilibrium relationship with the abnormal fluctuation of the stock market. Further, each rise of systemic risk corresponds to external factor shocks and internal structural problems.


2020 ◽  
Vol 30 (10) ◽  
pp. 4425-4452
Author(s):  
Adrián Vazquez Gonzalez ◽  
Andrés Meana-Fernández ◽  
Jesús Manuel Fernández

Purpose The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan. Design/methodology/approach A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region. Findings It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes. Research limitations/implications Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy. Originality/value The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.


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