In order to solve the problem of large error of delay estimation in low SNR environment, a new delay estimation method based on cross power spectral frequency domain weighting and spectrum subtraction is proposed. Through theoretical analysis and MATLAB simulation, among the four common weighting functions, it is proved that the cross-power spectral phase weighting method has a good sharpening effect on the peak value of the cross-correlation function, and it is verified that the improved spectral subtraction method generally has a good noise reduction effect under different SNR environments. Finally, the joint simulation results of the whole algorithm show that the combination of spectrum subtraction and crosspower spectrum phase method can effectively sharpen the peak value of cross-correlation function and improve the accuracy of time delay estimation in the low SNR environment. The results of this paper can provide useful help for sound source localization in complex environments.
The fracture and fragmentation of concrete under static and dynamic loads are studied. The uniaxial compressive strength test is employed to study the concrete behavior under static loads while the split Hopkinson pressure bar is used to study the dynamic behavior of the concrete under static loads. The theories for acquiring the stress, strain and strain rate of the concrete in the dynamic test by Hopkinson pressure bar has been introduced. The fracture patterns of the concrete in the uniaxial compressive test have been obtained and the static concrete compressive strengths have been calculated. The fracture patterns of the concrete in the uniaxial compressive test have been obtained and the static concrete compressive strengths have been calculated. The fracture and fragmentation of the specimen under dynamic loads have been acquired and the stress-strain curves of concrete under various impact loads are obtained. The stress-strain curve indicates a typical brittle material failure process which includes existing micro-fracture closure stage, linear-elastic stage, nonlinear-elastic stage, and post-failure stages. The influence of the loading rate for the compressive strength of the concrete has compared. Compared with the concrete under static loads, the dynamic loads can produce more fractures and fragments. The concrete strength is influenced by the strain rate and the strength increases almost linearly with the increase of the strain rate.
The study of the subdivision driving technology of a stepper motor and two types of typical acceleration and deceleration curves aims at optimizing the open-loop control performance of the stepper motor. The simulation model of a two-phase hybrid stepper motor open-loop control system is set up based on the mathematical model of the stepper motor, in order to let the stepper motor have the smaller stepper angle, two types of typical acceleration and a deceleration curve algorithm are designed for the real- time online calculation based on the subdivision driving technology. It respectively carries out the simulation analysis for their control effects. The simulation results show that the parabolic acceleration and deceleration curves have a larger maximum in-step rotation angle and the faster dynamic response ability in the same control period, and at the same time, the position tracking error of an intermediate process is smaller.
Dynamic angle measurement (DAM) plays an important role in precision machining, aerospace, military and artificial intelligence. Because of its advantages including high sensitivity, solid state and miniaturization, fibre-optic gyroscope (FOG) has great application prospects in the field of DAM. In this paper, we propose a dynamic angle metrology method based on FOG and a rotary table to evaluate the DAMaccuracy with FOG. The system synchronously collects data from the FOG and rotary table, and analyses the DAM accuracy of the FOG for different sway conditions compared with that of the angle obtained from the rotary table. An angle encoder in the rotary table provides absolute or incremental angular displacement output with angular displacement measurement accuracy of 10′′ (0:0028◦) and angular displacement repeat positioning accuracy of 3′′ (0:00083◦), and can be used as an angle reference. The experimental results show that the DAM accuracy of the FOG is better than 0:0028◦ obtained with the angular encoder, and the absolute DAM accuracy of the FOG is better than 0:0048◦ for given conditions. At the same time, for the multi-path signal synchronization problem in the metrology field, this paper proposes a signal delay measurement method combining test and algorithm procedures, which can control a delay within 25 μs.
The cohesion and internal friction angle were characterized as quadratic functions of strain and were assumed to follow the Mohr-Coulomb criterion after the yield of peak strength. These mechanical parameters and their variations in post-peak softening stage can be exactly ascertained through the simultaneous solution based on the data points of stress-strain curves of triaxial compression tests. Taking the influence of the fault into account, the variation of strata pressure and roadway convergence with coal advancement, the temporal and spatial distribution of axial bolt load were numerically simulated by FLAC3D (Fast Lagrangian Analysis of Continua) using the ascertained post-peak mechanical parameters according to the cohesion weakening and friction strengthening model. The change mechanism of axial load of single rock bolt as abutment pressure changes was analyzed, through the comparison analysis with the results of axial bolt load by field measurements at a coal mine face. The research results show that the simulated results such as the period of main roof weighting, temporal and spatial distribution of axial bolt load are in accordance with field measurement results, so the validity of the numerical model is testified. In front of the working face, the front abutment pressure increases first and then decreases, finally tends to be stable. A corresponding correlation exists between the variation of axial bolt load and rock deformation along the bolt body. When encountered by a fault, the maximum abutment pressure, the influential range of mining disturbance and the roadway convergence between roof and floor before the working face are all increased. In the roadways along the gob, axial bolt loads on the side of the working face decrease, while the other side one increases after the collapse of the roof. As superficial surrounding rock mass is damaged, the anchoring force of rock bolts will transfer to inner rock mass for balancing the tensile load of the bolts.
[1] Liang X.D., Gao Y.F., Wang J.F. et al., Rapid development of silicone rubber composite insulators in China, High Voltage Engineering, vol. 42, no. 9, pp. 2888–2896 (2016), DOI: 10.13336/j.1003- 6520.hve.20160907025.
[2] Yuan Z.K., Degradation characteristics and mechanism of materials in composite insulator under high humidity, PhD Thesis, North China Electric Power University, Beijing (2019).
[3] Xoa Y.F., Song X.M., He J.Z. et al., Evaluation method of aging for silicone rubber of compos- ite insulator, Transactions of China Electrotechnical Society, vol. 34, no. S1, pp. 440–448 (2019), DOI: 10.19595/j.cnki.10006753.tces.L80647.
[4] Tang J., Liu Q.S., Liu J.W. et al., Evaluation of composite insulators based on fuzzy comprehen- sive evaluation, Engineering Journal of Wuhan University, vol. 52, no. 5, pp. 451–456 (2019), DOI: 10.14188/j.1671-8844.2019-05-012.
[5] Huang X., Wang L.Y., Wang Q. et al., Grey fuzzy comprehensive evaluation model of contamina- tion state for insulators based on IFAHP with bayesian modified method, Science Technology and Engineering, vol. 20, no. 13, pp. 5135–5141 (2020), DOI: CNKI:SUN:KXJS.0.2020-13-018.
[6] Liu Y.P., Xu Z.Q., Fu H.C. et al., Insulation Condition Assessment Method of Power Transformer Based on Improved Extension Cloud Theory With Optimal Cloud Entropy, High Voltage Engineering, vol. 46, no. 2, pp. 397–405 (2020), DOI: 10.13336/j.1003-6520.hve.20190215004.
[7] Fan L., Xia F., Su H.Y. et al., Risk assessment of high voltage insulator contamination condition by cloud theory, Power System Protection and Control, vol. 40, no. 15, pp. 57–62 (2012), DOI: CNKI: SUN:JDQW.0.2012-15-014.
[8] Wang S.H., Jing H., Study on method for predicting pollution Flashover insulators in contact network, Journal of the China Railway Society, vol. 40, no. 3, pp. 58–67 (2018), DOI: CNKI:SUN:TDXB.0.2018- 03-011.
[9] Huai M.Q., Research on prediction of contamination state of insulator on catenary based on fuzzy neural network, Master Thesis, Lanzhou Jiaotong University, Gansu (2018).
[10] Yang Z.C., Zhang C.L., Ge L. et al., Comprehensive fuzzy evaluation based on entropy weight method for insulator flashover pollution, Electric Power Automation Equipment, vol. 34, no. 4, pp. 90–94 (2014), DOI: CNKI:SUN:DLZS.0.2014-04-016.
[11] Zhou Y.M., Studies on the degradation depth of silicon composite insulator in service, Master Thesis, Wuhan University, Wuhan (2018).
[12] Chen X.C., Li L.Q., Wu Z.G. et al., Research on shed properties of network operating composite insulators, Guangdong Electric Power, vol. 29, no. 6, pp. 104–108 (2016), DOI: 10.3969/j.issn.1007- 290X.2016.06.019.
[13] Yang L.G., Florian Pauli, Kay Hameyer, Influence of thermal-mechanical stress on the insulation system of a low voltage electrical machine, Archives of Electrical Engineering, vol. 70, no. 1, pp. 233–244 (2021), DOI: 10.24425/aee.2021.136064.
[14] Liu Y., Wang J.G., Han F. et al., Electrical and mechanical properties of composite insulators af- ter different operation periods, High Voltage Engineering, vol. 34, no. 5, pp. 1017–1021 (2008), DOI: 10.13336/j.1003-6520.hve.2008.05.027.
[15] Yao L.N., Wu Y.H., Wang S.H. et al., Electrical and mechanical properties of on-line compos- ite insulators, Insulating Materials, vol. 48, no. 8, pp. 23–27 (2015), DOI: 10.16790/j.cnki.1009- 9239.im.2015.08.005.
[16] Jia Z.D., Yang C.X., Wang X.L. et al., Aging characteristics of composite insulators based on hydropho- bicity transfer test, High Voltage Engineering, vol. 41, no. 6, pp. 1907–1914 (2015), DOI: 10.13336/ j.1003-6520.hve.2015.06.019.
[17] Zhang M.M., Research on evaluation Method of Insulator pollution Status Assessment Based on UV Pulse Parameters, Master Thesis, Southwest Jiaotong University, Sichuan (2019).
[18] Mao Y.K., Guan Z.C., Wang L.M. et al., Evaluation of contamination levels of outdoor insulators based on the principal components analysis of leakage current Pulse, Transactions of China Electrotechnical Society, vol. 24, no. 8, pp. 39–45 (2009), DOI: 10.19595/j.cnki.10006753.tces.2009.08.007.
[19] Ning G.T., Fang B., Qin D. et al., Design and application of comprehensive evaluation index system of smart grid based on coordinated planning of major network and power distribution network, Archives of Electrical Engineering, vol. 70, no. 1, pp. 103–113 (2021), DOI: 10.24425/aee.2021.136055.
[20] Zhou L.L., Research of methods and their application of determining the weights of attributes in fuzzy comprehensive evaluation, Master Thesis, Northeastern University, Liaoning (2014).
[21] Li G., Li J.P., Sun X.L. et al., Research on a combined methods of subjective-objective weighting and its rationality, Management Review, vol. 29, no. 12, pp. 17–26+61 (2017), DOI: 10.14120/j.cnki. cn115057/f.2017.12.002.
[22] Chen Y.C., Dai J.Y., Xie D., Comprehensive evaluation of mine ventilation system based on combi- nation weighting cloud model, Systems Engineering, vol. 38, no. 6, pp. 35–42 (2020), DOI: 1001- 4098(2020)06-0035-08.
[23] Wang L.L., Research on cleaner production evaluation index system and grade comprehensive evalua- tion methodologies of wastewater treatment plants in cities and towns, PhD Thesis, Dalian University of Technology, Dalian (2015).
Room temperature vulcanized (RTV) silicone rubber is widely used to prevent pollution flashover with its excellent hydrophobicity and hydrophobicity transfer. However, RTV coatings are at the risk of deterioration and failure in heavily polluted operating environment. In this paper, RTV coated insulators with different suspension heights operating in coal ash polluted areaswere sampled. Pollution degree, pollution composition and aging degree of coatings were tested. The result shows that the insoluble pollution contains Al(OH)3 filler precipitated from RTV coating, which indicates the aging of the RTV coating. The top surface coating is more affected by ultraviolet and rainwater than the bottom surface resulting in more serious degradation. As the pollution degree of the lower phase insulator is heavier than that of the upper phase insulator, the erosion effect of pollution on the RTV coating is more intense. The fillers and rubber molecules of RTV continuously precipitate into the pollution layer, leading to further aging. Therefore, the overall aging degree of the lower insulator coating is more serious than that of the upper insulator coating.
en
pl
