Novel method for identifying the stages of discharge underwater based on impedance change characteristic

It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter(STF) and impedance change characteristics. The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process. The STF is used to reduce the randomness of the impedance of repeated discharges underwater, and then the universal identification resistance data is obtained. Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown, main, and oscillatory discharge stages, the threshold values for determining the discharge stage are obtained. These include the threshold values for the resistance variation rate(K) and the moment(t).Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination, with a maximum mean square deviation of Scrless than 1.761.

Predicting dynamic compressive strength of frozen-thawed rocks by characteristic impedance and data-driven methods

In cold regions,the dynamic compressive strength(DCS)of rock damaged by freeze-thaw weathering significantly influences the stability of rock engineering.Nevertheless,testing the dynamic strength under freeze-thaw weathering conditions is often both time-consuming and expensive.Therefore,this study considers the effect of characteristic impedance on DCS and aims to quickly determine the DCS of frozen-thawed rocks through the application of machine-learning techniques.Initially,a database of DCS for frozen-thawed rocks,comprising 216 rock specimens,was compiled.Three external load parameters(freeze-thaw cycle number,confining pressure,and impact pressure)and two rock parameters(characteristic impedance and porosity)were selected as input variables,with DCS as the predicted target.This research optimized the kernel scale,penalty factor,and insensitive loss coefficient of the support vector regression(SVR)model using five swarm intelligent optimization algorithms,leading to the development of five hybrid models.In addition,a statistical DCS prediction equation using multiple linear regression techniques was developed.The performance of the prediction models was comprehensively evaluated using two error indexes and two trend indexes.A sensitivity analysis based on the cosine amplitude method has also been conducted.The results demonstrate that the proposed hybrid SVR-based models consistently provided accurate DCS predictions.Among these models,the SVR model optimized with the chameleon swarm algorithm exhibited the best performance,with metrics indicating its effectiveness,including root mean square error(RMSE)﹦3.9675,mean absolute error(MAE)﹦2.9673,coefficient of determination(R^(2))﹦0.98631,and variance accounted for(VAF)﹦98.634.This suggests that the chameleon swarm algorithm yielded the most optimal results for enhancing SVR models.Notably,impact pressure and characteristic impedance emerged as the two most influential parameters in DCS prediction.This research is anticipated to serve as a reliable reference for estimating the DCS of rocks subjected to freeze-thaw weathering.

Empirical equations between characteristic impedance and mechanical properties of rocks

Based on a great number of experimental data on various mechanical properties of rock in the literature,six empirical equations between the characteristic impedance(product of density and P-wave velocity)and mechanical properties of rock are proposed.These properties include uniaxial compressive strength,tensile strength,shear strength,mode I fracture toughness,Young’s modulus,and Poisson’s ratio.These empirical equations show that the values of the aforementioned properties increase with increase in characteristic impedance.It also implies that the characteristic impedance of rock may be considered as an index to represent the main properties of rock.In this sense,it is possible to consider using characteristic impedance to classify rock masses for studies in the future.

Measured Impedance and Threshold Value of Electrode Line Impedance Supervision Based Protection in HVDC Transmission System

At present,electrode line impedance supervision(ELIS)based protection is widely used to detect faults on grounding electrode lines,which are indispensable elements of high-voltage direct current(HVDC)systems.The existing theoretical analysis of measured impedance is based on lumped line model and the threshold value is generally set according to engineering experience,which have caused the dead zone problem and even accidents.Therefore,a study on measured impedance of ELIS-based protection and its threshold value selection method is carried out to solve this problem.In this study,the expressions of measured impedance under normal operation and fault conditions are deduced based on rigorous and accurate line model.Based on the expressions,the characteristics of the measured impedance are calculated and analyzed.With the characteristics of the measured impedance,the applicability of the protection with the traditional threshold value is further discussed and the distribution of the dead zone can be located.Then,the method to calculate the threshold value of ELIS-based protection is proposed.With a proper threshold value selected by the proposed method,the dead zone of ELIS-based protection is effectively eliminated,and the protection can identify all types of faults even with large transition resistances.Case studies on PSCAD/EMTDC have been conducted to verify the conclusion.

Two Independent Numerical Studies Demonstrating How to Efficiently Eliminate Electrolysis Side Reactions in Magneto-Hydro-Dynamic Pumping System

In this work, a numerical study for designing a new kind of MHD （Magneto-Hydrn-Dynamic） pumps is presented. This technique makes a compromise between electrolysis prevention and high flow rate performance. This technique should eliminate electrolytic bubble generation, electrodes wear and fluid propriety modification. All these side phenomena are prevented by considering isolated electrodes. The numerical presented results in this paper demonstrate that continuous MHD pumping is possible with isolated electrodes. The MHD excitation combines a high frequency altering current with a low frequency altering magnetic field. In order to validate our results, two independent theoretical methods for computing flow rate are followed. The two presented independent approaches show that high flow rate is possible even with isolated electrodes. To overcome the problem of dimensioning this kind of pumps, a generic numerical analysis is proposed. Hence, the pump performances as functions of the external parameter are studied and tools to calculate for a given fluid and the optimal high frequency regime are provided.

A fractional-order multifunctional n-step honeycomb RLC circuit network

We investigate a multifunctional n-step honeycomb network which has not been studied before. By adjusting the circuit parameters, such a network can be transformed into several different networks with a variety of functions, such as a regular ladder network and a triangular network. We derive two new formulae for equivalent resistance in the resistor network and equivalent impedance in the LC network, which are in the fractional-order domain. First, we simplify the complex network into a simple equivalent model. Second, using Kirchhoff＇s laws, we establish a fractional difference equation. Third, we construct an equivalent transformation method to obtain a general solution for the nonlinear differential equation. In practical applications, several interesting special results are obtained. In particular, an n-step impedance LC network is discussed and many new char- acteristics of complex impedance have been found.

System Adaptive AC Filter for a Line Commutated Converter High Voltage DC Transmission System

This paper proposes a novel AC filter system for a line commutated converter high voltage DC(LCC-HVDC)transmission system.Through the coordination of the hybrid active power filters(APF)and the existing reactive compensation devices,the proposed filter system can not only enhance the suppression performance for LCC-HVDC harmonics,but also optimize the AC yard layout with reduced reactive power subbanks,reducing the cost of HVDC projects.The novel filter system adopts a serial passive resonance topology obtained by careful comparison of different APFs.A proper control scheme is then designed integrating the control strategy of the APF and impedance characteristics of the HVDC system,which is able to realize harmonic suppression and dynamic reactive power support simultaneously.In addition,a novel self-adaption digital low-pass filter algorithm is presented,which is used in the APF harmonic detecting step,enhancing both high precision and fast dynamic response.On the basis of a real HVDC project,the advantages of proposed filter system in harmonic suppression,reactive power regulation,and sub-banks reduction are simulated and demonstrated.

Heterogeneous ZnO@CF structures and their excellent microwave absorbing properties with thin thickness and low filling

With the aim to obtain enhanced absorbing performance at small thickness and low filling,a robust strat-egy to fabricate zinc oxide(ZnO)modified carbon fiber(CF)structures have been successfully prepared by using low temperature hydrothermal method.Due to the multi-interface polarization caused by the high specific surface area of the complex heterostructures and the improvement of impedance matching,the composites show excellent electromagnetic wave absorption properties.Under the condition of low filling content(20 wt%)and ultra-thin thickness(1.5 mm),the excellent absorption performance of minimal reflection loss of−34.4 dB and an effective absorption bandwidth(RL≤−10 dB)of 4.94 GHz is achieved.In addition,the effective absorption bandwidth covers the whole 2-18 GHz band with the increase of thickness from 0.5 to 10 mm.This work provides an innovative method for designing the matching layer of carbon-based absorbing materials,and ZnO@CF heterostructure is expected to become a potential absorbing material.

Electrical analysis of single-walled carbon nanotube as gigahertz on-chip interconnects

The single-walled carbon nanotube （SWCNT） is a promising nanostructure in the design of future high- frequency system-on-chip, especially in network-on-chip, where the quality of communication between intellectual property （IP） modules is a major concern. Shrinking dimensions of circuits and systems have restricted the use of high-frequency signal characteristics for frequencies up to 1000 GHz. Four key electrical parameters, impedance, propagation constant, current density, and signal delay time, which are crucial in the design of a high-quality interconnect, are derived for different structural configurations of SWCNT. Each of these parameters exhibits strong dependence on the frequency range over which the interconnect is designed to operate, as well as on the configuration of SWCNT. The novelty of the proposed model for solving next-generation high-speed integrated circuit （IC） interconnect challenges is illustrated, compared with existing theoretical and experimental results in the literature.

Design and simulation of a beam position monitor for the high current proton linac

In this paper, the 2-D electrostatic field software, POISSON, is used to calculate the characteristic impedance of a BPM （beam position monitor） for a high current proton linac. Furthermore, the time-domain 3-D module of MAFIA with a beam microbunch at a varying offset from the axis is used to compute the induced voltage on the electrodes as a function of time. Finally, the effect of low β beams on the induced voltage, the sensitivity and the signal dynamic range of the BPM are discussed.