Great Engineering Value Research Articles

Study on Nonlinear Dielectric Properties of Micro Silica

Inorganic insulating powder can potentially be used in nuclear power plant cables, fire-resistant cables, and so on due to its high heat resistance and radiation resistance. It is of great academic and engineering value to study the dielectric properties of inorganic insulating powder. In this paper, we aim to study the nonlinear dielectric properties via the measurement of the time-domain polarization current spectrum under the application of a DC electric field. Three kinds of silica powders are measured by a measurement system with adjustable pressure. The effects of powder shape, particle size, and packing pressure and temperature on the dependence of relaxation polarization and electrical conductivity on the applied electric field are studied. The experimental results show that the relationship between electrical conductivity and the electric field of inorganic insulating powder presents two different characteristics, i.e., field-induced enhancement and field-induced weakening. The relationship between conductance and temperature shows an increase with temperature. That is, the electrical conductivity increases or decreases with the increase in temperature. The inorganic powder insulation can be regarded as a composite, which is composed of inorganic powder particles and air gaps. The interface between the powder particles and air gaps contributes a lot to the polarization of inorganic insulating powder. The phenomena (including the field-induced weakening characteristic between relaxation polarization and electric field and the decrease characteristic of polarization with increasing temperature) can be explained by a simplified interface polarization mechanism.

Self-Calibration Method of Noncontact AC Voltage Measurement

Realizing stable and reliable monitoring of a distribution network voltage environment can obtain real-time power parameter information and ensure the normal and safe operation of transmission lines, which is of great research significance and engineering value. Based on the distributed capacitance relationship between sensor and transmission line, an equivalent circuit capacitance voltage dividing model is proposed, and the relevant factors affecting the stability of the voltage dividing ratio are analyzed. The self-calibration principle of noncontact AC voltage measurement is proposed based on the system identification theory. The noncontact sensing structure is designed, a sensor probe prototype is fabricated, and a back-end conditioning circuit is designed to realize the overall measurement system. Finally, the validity of the measurement model is verified by simulation and experiment, and a measurement platform is built which proves the feasibility of the self-calibration method for noncontact voltage measurement. The experimental results show that the error is less than ±2%. This method can correctly restore the measured voltage waveform, has good linearity, and can realize wireless data transmission, which provides a new idea for the voltage measurement method of a distribution network.

Analysis and Optimization Based on Factors Affecting the Spiral Climbing Locomotion of Snake-like Robot

The snake-like robot is a limbless bionic robot widely used in unstructured environments to perform tasks with substantial functional flexibility and environmental adaptability in complex environments. In this paper, the spiral climbing motion of a snake-like robot on the outer surface of a cylindrical object was studied based on the three-dimensional motion of a biological snake, and we carried out the analysis and optimization of the motion-influencing factors. First, the spiral climbing motion of the snake-like robot was implemented by the angle control method, and the target motion was studied and analyzed by combining numerical and environmental simulations. We integrated the influence of kinematics and dynamics factors on the spiral climbing motion. Based on this, we established a multi-objective optimization function that utilized the influence factors to optimize the joint module. In addition, through dynamics simulation analysis, the change of the general clamping force of the snake-like robot’s spiral climbing motion was transformed into the analysis of the contact force between the joint module and the cylinder. On the basis of the results, the effect of the control strategy adopted in this paper on the motion and change rule of the spiral climbing motion was analyzed. This paper presents the analysis of the spiral climbing motion, which is of great theoretical significance and engineering value for the realization of the three-dimensional motion of the snake-like robot.

A model test on an open-cut tunnel structure under the effect of a stick-slip normal fault

PurposeLarge displacement misalignment under the action of active faults can cause complex three-dimensional deformation in subway tunnels, resulting in severe damage, distortion and misalignment. There is no developed system of fortification and related codes to follow. There are scientific problems and technical challenges in this field that have never been encountered in past research and practices.Design/methodology/approachThis paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation based on the open-cut tunnel project of the Urumqi Rail Transit Line 2, which passes through the Jiujiawan normal fault. The test simulated the subway tunnel passing through the normal fault, which is inclined at 60°. This research compared and analyzed the differences in mechanical behavior between two types of lining section: the open-cut double-line box tunnel and the modified double-line box arch tunnel. The structural response and failure characteristics of the open-cut segmented lining of the tunnel under the stick-slip part of the normal fault were studied.FindingsThe results indicated that the double-line box arch tunnel improved the shear and longitudinal bending performance. Longitudinal cracks were mainly distributed in the baseplate, wall foot and arch foot, and the crack position was basically consistent with the longitudinal distribution of surrounding rock pressure. This indicated that the longitudinal cracks were due to the large local load of the cross-section of the structure, leading to an excessive local bending moment of the structure, which resulted in large eccentric failure of the lining and formation of longitudinal cracks. Compared with the ordinary box section tunnel, the improved double-line box arch tunnel significantly reduced the destroyed and damage areas of the hanging wall and footwall. The damage area and crack length were reduced by 39 and 59.3%, respectively. This indicates that the improved double-line box arch tunnel had good anti-sliding performance.Originality/valueThis paper adopted a self-designed large-scale active fault dislocation simulation loading system to conduct a similar model test of the tunnel under active fault dislocation. This system increased the similarity ratio of the test model, improved the dislocation loading rate and optimized the simulation scheme of the segmented flexible lining and other key factors affecting the test. It is of great scientific significance and engineering value to investigate the structure of subway tunnels under active fault misalignment, to study its force characteristics and damage modes, and to provide a technical reserve for the design and construction of subway tunnels through active faults.

Prediction of Rainfall Using Hybrid SVM-HHO Model

Rainfall modeling is considered a need of the hour in order to understand, control, and monitor the quality and quantity of water resources. Modeling rainfall is one of the key components of the meteorological engineering process. Hydrological and climatological studies require accurate rainfall estimation in order to effectively manage water resources. Thus, adopting an advanced, reliable, and intelligent model for forecasting will be of great value in water resources engineering. The present study tried to establish a hybrid model with the combination of Support Vector Machine (SVM) and Harris Hawks Optimization (SVM-HHO) for predicting the rainfall time series of Cachar district located in Assam, India. The predictive performance of models is examined based on statistical analysis. Statistical measures like root mean squared error (RMSE) and coefficient of correlation (CC) is used to evaluate the considered hybrid model. It is observed from obtained results that proposed hybrid model exhibited least RMSE value of 20.29, and highest CC value of 0.9714, during testing period. Findings of this study confirm that proposed hybrid optimisation strategy can be regarded as a powerful forecasting tool for achieving better generalisation capability and higher forecasting accurateness.

Construction parameters of graded sand-gravel foundation on seismic response law of nuclear safety grade underground corridor

The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect. It is of great engineering value to explore the influence of construction parameters of graded sand and gravel foundation on the seismic response of gallery structures. Taking the safety grade underground corridor of a nuclear power plant as the engineering background, the equivalent linear method is used to consider the nonlinear dynamic characteristics of graded sand and gravel. The energy transfer boundary is applied at the truncation boundary to simulate the dissipation effect of scattered wave fluctuation energy and the ground motion input. The thicknessless contact element is introduced to consider the contact effect between the corridor structure and the graded sand and gravel foundation, so as to establish the calculation model of the dynamic interaction between the graded sand and gravel foundation and the corridor structure. Furthermore, the influence of the relative compactness and the foundation treatment depth on the seismic response of the corridor structure is studied, and the calculation results of the acceleration response spectrum and relative displacement of the corridor structure are analyzed. The calculation results show that the two construction parameters have different degrees of influence on the seismic response of corridor structure. The research results can provide reference for the engineering design and construction of underground corridors, and provide technical support for the application of graded gravel materials in soft soil foundation treatment.

Experimental Study on Nanomechanical Properties of Yunnan Red-Bed Mudstone

As a natural building material and building environment, red-bed mudstone has special engineering properties due to its special formation conditions. The engineering disaster caused by these special properties is becoming increasingly prominent. Therefore, it is of great theoretical significance and practical engineering value to study the macro- and micromechanical properties of red-bed mudstone. Nanoindentation mechanical tests are carried out on the red-bed mudstone from Chuxiong, Jingdong, and Nanhua in Yunnan. The microstructure, residual indentation morphology, and nanomechanical parameters of red-bed mudstone in different areas are compared and analyzed. The results show that the load-displacement curves can be divided into four stages, which are the compaction stage, linear elastic stage, holding stage, and unloading stage. Under the same loading and holding time conditions, sample 3 (Nanhua) has the deepest residual indentation, and SEM tests show that the damage to indentation is obvious. Sample 2 (Jingdong) has the shallowest residual indentation. The indentation morphology is complete and the size is small by SEM tests. The residual indentation depth of sample 1 (Chuxiong) is between sample 2 and sample 3. The average elastic modulus of sample 1 (Chuxiong) is 38.0 ± 2.29 GPa. The average hardness is 1.36 ± 0.42 GPa, and the fracture toughness is 0.966 ± 0.048 MPa·m0.5. The average elastic modulus of sample 2 (Jingdong) is 40.1 ± 2.03 GPa. The average hardness is 1.71 ± 0.35 GPa, and the fracture toughness is 1.142 ± 0.053 MPa·m0.5. However, the average elastic modulus of sample 3 (Nanhua) is 25.1 ± 2.53 GPa. The average hardness is 0.61 ± 0.21 GPa, and the fracture toughness is 0.507 ± 0.043 MPa·m0.5. Overall, the elastic modulus and the hardness of sample 2 (Jingdong) are the greatest because of its high quartz crystal content. It shows that the nanomechanical properties of red-bed mudstone in Jingdong are better than those in Chuxiong and Nanhua. The results can provide a basis for revealing the regional differences in macroscopic mechanical properties of Yunnan red-bed mudstone.

Rolling bearing fault diagnosis based on quantum LS-SVM

Rolling bearing is an indispensable part of the contemporary industrial system, and its working conditions affect the state of the entire industrial system. Therefore, there is great engineering value to researching and improving the fault diagnosis technology of rolling bearings. However, with the involvement of the whole mechanical equipment, we need to have a large quantity of data to support the accuracy of fault diagnosis, while the efficiency of classical machine learning algorithms is poor in processing big data, and huge amount of computing resources is required. To solve this problem, this paper combines the HHL algorithm in quantum computing with the LS-SVM algorithm in machine learning and proposes a fault diagnosis model based on a quantum least square support vector machine (QSVM). Based on experiments simulated on analog quantum computers, we demonstrate that our fault diagnosis based on QSVM is feasible, and it can play a far superior advantage over the classical algorithm in the context of big data.

Nonlinear Modeling Study of Aerodynamic Characteristics of an X38-like Vehicle at Strong Viscous Interaction Regions.

Strong viscous interaction and multiple flow regimes exist when vehicles fly at high altitude and high Mach number conditions. The Navier–Stokes(NS) solver is no longer applicable in the above situation. Instead, the direct simulation Monte Carlo (DSMC) method or Boltzmann model equation solvers are usually needed. However, they are computationally more expensive than the NS solver. Therefore, it is of great engineering value to establish the aerodynamic prediction model of vehicles at high altitude and high Mach number conditions. In this paper, the hypersonic aerodynamic characteristics of an X38-like vehicle in typical conditions from 70 km to 110 km are simulated using the unified gas kinetic scheme (UGKS), which is applicable for all flow regimes. The contributions of pressure and viscous stress on the force coefficients are analyzed. The viscous interaction parameters, Mach number, and angle of attack are used as independent variables, and the difference between the force coefficients calculated by UGKS and the Euler solver is used as a dependent variable to establish a nonlinear viscous interaction model between them in the range of 70–110 km. The evaluation of the model is completed using the correlation coefficient and the relative orthogonal distance. The conventional viscous interaction effect and rarefied effect are both taken into account in the model. The model can be used to quickly obtain the hypersonic aerodynamic characteristics of X38-like vehicle in a wide range, which is meaningful for engineering design.

A Novel Condenser Vacuum Degree Prediction Model Based on LSTM and MemN2N

Condenser vacuum degree prediction of power plants is a challenge task in power system security field. Most existing studies are based on shallow machine learning algorithms, which fail to leverage historical data comprehensively, resulting inaccuracy and unreliable predictions. Therefore, using a serialization model like Recurrent Neural Network to capture time-series information from historical data is necessary. However, these serialization model alone has inherent defects in dealing with long-distance dependence, which may cause historical information forgetting problem. This paper proposes a new prediction model combining LSTM and End-To-End Memory Network (MemN2N). We use LSTM to mine the long-distance dependency information in historical data, and introduce the encoding historical information into the memory pool of MemN2N. MemN2N allows better preservation of historical information for serialization model LSTM, and can make accurate and reliable predictions through soft attention mechanism. Through the experiments on real data from the power plant show that, compared with other prediction models, the model proposed in this paper achieves higher prediction accuracy and has great engineering value.

Analysis of Traction Reflux Characteristics of EMU and Improvement of Its Protective Grounding System

The traction reflux characteristics of an electric multiple unit (EMU) are directly related to its safe operation. It is of great engineering value to improve the reflux characteristics by improving the protective grounding system. The typical Chinese EMU with the eight-car power distribution marshaling and decentralized grounding model is taken as the research object of this study, and the circuit model of the traction reflux system is established by Multisim software, the effectiveness of which is verified by field tests. Combining the simulation and measured data, the distribution law of the traction current is analyzed. Based on the advantages of different grounding modes, three improvement schemes of the protective grounding system are proposed. The results show the following: 1) the circuit model of the traction reflux system is effective; 2) the traction current is mainly discharged from the end cars to the railway track; 3) the improvement schemes of the protective grounding system under the normal operation can also improve the traction reflux characteristics under the power loss condition; and 4) based on the proposed protective grounding improvement schemes, on the condition that the car body potential meets the standard requirements, the maximum grounding current amplitude is reduced to 48.4% of the original value, the circulating current is eliminated, the maximum current difference between the two axles of the same coach is reduced to 5.2% of the original value, and the effectiveness of the improvement schemes is verified by field tests.

Study on Influencing Factors of Temperature Variation Displacement Compensation Behavior of Gas Insulated Switchgear Shell Bellows

Bellows are the key structures that compensate for and absorb the temperature-dependent displacement of a gas insulated switchgear (GIS) shell. It is of great engineering value to master the relationship between the temperature-dependent displacement behavior and various influencing factors. Based on the analysis of the influencing factors of the temperature variation displacement compensation ability of the GIS bellows, a bellows model was established. By coupling it with a shell having different degrees of bending through two layout methods, finite element simulation was carried out based on ABAQUS software to obtain the regular relationship between the temperature variation displacement compensation behavior of the bellows and various influencing factors. The results of the case study show that the temperature change displacement compensation ability of the bellows is most significantly affected by their own structural size. Reducing the wall thickness and increasing the wave height of the bellows can effectively improve the temperature change displacement compensation ability of the bellows and reduce the stress concentration in the compensation process. The change in the GIS shell shape is the second-most important influence; when the sliding support base of the bus barrel is lower than the fixed support base, the amount of temperature change displacement compensation of the bellows increases and the compensation capacity decreases, and, on the contrary, the temperature compensation capacity increases. Within the operating temperature range, the compensation ability of bellows with a distributed arrangement is better than that of a centralized arrangement, and can alleviate the initial deformation caused by gravity and gas pressure in GIS equipment.

Rolling Bearing Fault Diagnosis Based on SVM Optimized with Adaptive Quantum DE Algorithm

In order to optimize traditional fault diagnosis models for practical applications, a fault diagnosis model based on support vector machines optimized with the adaptive quantum differential evolution of (AQDE-SVM) is proposed in this study. First, the traditional differential evolution is rewritten based on real number encoded into a qubit encoding. Second, this study proposes an adaptive quantum rotation gate and uses this gate to update the probability amplitude of the qubits. Finally, compared with quantum genetic algorithm support vector machines (QGA-SVM) and differential evolution-support vector machines (DE-SVM), etc., the results show that the algorithm proposed in this study has a higher diagnosis accuracy and shorter running time, providing great practical engineering value in the application of rolling bearing fault diagnosis.

A Comprehensive Performance Evaluation Method Targeting Efficiency and Noise for Muzzle Brakes Based on Numerical Simulation

The installation of muzzle brake changes the flow direction of propellant gas, which leads to a decline in the recoil force but an increase in the muzzle flow noise of the side rear. Therefore, the coordination between high efficiency and low harm of muzzle brake is one of the factors limiting its optimization. To address this problem, a numerical method for evaluating the comprehensive performance of muzzle brake targeting muzzle brake efficiency and impulse noise is proposed in the present study. The two performance indexes are calculated using a computational fluid dynamics (CFD)-computational aeroacoustics (CAA) coupled method. Afterwards, a corresponding experiment is conducted to verify its feasibility. Furthermore, the comprehensive performance of muzzle brakes with three different structures are analysed based on the two indexes obtained by the proposed numerical method. The results reveal that both indexes can be influenced by the structure of muzzle brakes. The increased braking efficiency is almost accompanied by increased impulse noise, but the functional relation is not linear dependence. Thus, the comprehensive performance can be improved by optimization of the structure. The evaluation method proposed in this paper has theoretical significance for optimizing muzzle brakes, which is of great engineering value.

Prediction of Hardenability Curves for Non-Boron Steels via a Combined Machine Learning Model.

Hardenability is one of the most basic criteria influencing the formulation of the heat treatment process and steel selection. Therefore, it is of great engineering value to calculate the hardenability curves rapidly and accurately without resorting to any laborious and costly experiments. However, generating a high-precision computational model for steels with different hardenability remains a challenge. In this study, a combined machine learning (CML) model including k-nearest neighbor and random forest is established to predict the hardenability curves of non-boron steels solely on the basis of chemical compositions: (i) random forest is first applied to classify steel into low- and high-hardenability steel; (ii) k-nearest neighbor and random forest models are then developed to predict the hardenability of low- and high-hardenability steel. Model validation is carried out by calculating and comparing the hardenability curves of five steels using different models. The results reveal that the CML model works well for its distinguished prediction performance with precise classification accuracy (100%), high correlation coefficient (≥0.981), and low mean absolute errors (≤3.6 HRC) and root-mean-square errors (≤3.9 HRC); it performs better than JMatPro and empirical formulas including the ideal critical diameter method and modified nonlinear equation. Therefore, this study demonstrates that the CML model combining material informatics and data-driven machine learning can rapidly and efficiently predict the hardenability curves of non-boron steel, with high prediction accuracy and a wide application range. It can guide process design and machine part selection, reducing the cost of trial and error and accelerating the development of new materials.

Experimental and Numerical Analysis on the Damage and Failure Characteristics of Bituminous Coal under Multilevel Cyclic Loads

The coal mining process is often accompanied by periodic disturbance of the surrounding rock mass around the coal mining face. Therefore, it is of great theoretical and engineering value to investigate the damage pattern of bituminous coal under cyclic loading and unloading conditions and analyze its damage precursors. The experiments of uniaxial multistage cyclic loading and unloading of bituminous coal were carried out, and the loading and unloading response ratios were extracted using the elastic modulus variation to describe the damage characteristics and damage precursors of bituminous coal. Based on the accumulated acoustic emission ringing counts, the response ratios were defined, and the internal damage evolution characteristics and damage laws during the damage of bituminous coal were analyzed. The CT scan images of the internal structure of the coal sample before and after the experiment were used to analyze the damage characteristics of the coal sample and the influence of the number of simulation units on the results using the inverse modeling simulation analysis method. The research shows that the response ratio of bituminous coal under uniaxial cyclic loading has three stages of variation, and it is characterized by periodic “W”-type variation at each level of stress. In addition, the inverse modeling and simulation can better characterize the damage evolution of the coal specimen.

An ultra-thin ventilated metasurface with extreme asymmetric absorption

Recent progress in minimizing sound absorbers is driven by their great scientific significance and engineering value; however, compact devices for low-frequency sound are still challenging. Here, we construct an ultra-thin metasurface by parallel connecting resonators with high dissipation loss to a non-resonant reactance-dominated boundary (RDB) with high radiation loss, which realizes extreme absorption asymmetry at the exceptional point of scattering eigenvalue. We develop a parallel transfer matrix method to design the system, and a deep-subwavelength absorber (the operating wavelength is 120 times of its thickness) with 99.2% and 0.5% absorption for sound incident from opposite ports is achieved. The extreme absorption asymmetry is ascribed to the distinct coupling between the RDB and resonant meta-atom in an unbalanced dissipating state with excellent robustness against geometrical reconfigurations originated from the broadband near-unity reflection characteristics of the RDB. In particular, the proposed strategy brings the design of a degree of freedom rather than typical multiple resonant modes, and an extensible prototype showing >90% (<1%) absorptance for left- (right-) incidence within a wavelength from 23.3 to 18 times its thickness is demonstrated.

Current Understanding of the Applications of Photocrosslinked Hydrogels in Biomedical Engineering.

Hydrogel materials have great application value in biomedical engineering. Among them, photocrosslinked hydrogels have attracted much attention due to their variety and simple convenient preparation methods. Here, we provide a systematic review of the biomedical-engineering applications of photocrosslinked hydrogels. First, we introduce the types of photocrosslinked hydrogel monomers, and the methods for preparation of photocrosslinked hydrogels with different morphologies are summarized. Subsequently, various biomedical applications of photocrosslinked hydrogels are reviewed. Finally, some shortcomings and development directions for photocrosslinked hydrogels are considered and proposed. This paper is designed to give researchers in related fields a systematic understanding of photocrosslinked hydrogels and provide inspiration to seek new development directions for studies of photocrosslinked hydrogels or related materials.

Strength Characteristics and Failure Mechanism of Granite with Cross Cracks at Different Angles Based on DIC Method

The engineering rock mass is generally composed of the rock matrix and structural plane and is an anisotropic inhomogeneous geological body. Accidents such as roof collapse and well caving caused by joint and fissure expansion occur frequently during tunnel excavation and service, resulting in serious casualties and economic losses. It is of great theoretical significance and engineering value to study the fracture mechanism of the jointed rock mass to ensure the stability of the surrounding rock and the safe and efficient utilization of the urban underground space. To investigate the effects of crossed cracks on mechanical properties and failure characteristics of rock, wire cutting equipment is employed to make rock samples with different crossed cracks, and then acoustic emission system and digital image correlation technique are used to study the fracture process of rock samples under uniaxial compression. It has been found that the strength of rock samples with a single crack is generally larger than that of samples with cross cracks, and the strength changed with the angle of the crack in a “V” shape. When the angle of preexisting crack is 60°, the rock strength reaches the lowest. The primary crack has a more obvious influence on rock strength and is the main controlling factor of rock fracture. The initiation stress of rock samples with a single crack changes more significantly with angle. When the angle of the primary crack is 45°, the rock sample is most prone to crack initiation failure, and the crack initiation stress is only 1/4 to 1/2 of the strength. There are two types of cracks: wing and anti-wing, and the tensile cracks are the main ones. It is revealed that the fracture of cracked rock has significant directional characteristics. For the samples with cross cracks, the primary crack is the main control factor of crack initiation, and the secondary crack has a certain guiding effect on the crack.

A Fast Screening and Recombinant Method Based on Short-Time Pulse Discharge and Electrochemical Impedance Spectroscopy for Decommissioned Power Batteries

Abstract Aiming at the problems of low screening efficiency, high energy consumption and low grouping rate of decommissioned power batteries at this stage, a fast screening and recombinant method based on short-time pulse discharge and electrochemical impedance spectroscopy (EIS) for decommissioned power batteries is proposed. More than 200 decommissioned lithium iron phosphate power batteries of the same type and different batches were tested and analyzed by short-time pulse discharge and EIS. Then, the obtained pulse voltage difference, DC internal resistance, EIS curve shape characteristics and EIS equivalent circuit model parameters are used as screening indexes, and a mathematical model is established to realize the rapid and effective sorting and reorganization of decommissioned power batteries. The experimental results show that this method has low energy consumption, the average test time of single cell is less than 20 min, and the consistency index is good after grouping, so it has great practical value in engineering.