最新刊期
卷 56 ， 期 2 ， 2024
- 摘要：The role of software is crucial for the stable operation of safety-critical systems such as nuclear equipment. In the face of the advancement and complexity of safety-critical software, new challenges are encountered in the design and development of highly reliable software, and new methods and paradigms for software development and verification are urgently needed. Both formal methods and model-driven techniques have gained increasing attention in this field. In response to this demand, combined with the latest technological trends, this paper focuses on three key scientific problems and explores one basic theory and seven key technologies. Additionally, a prototype software platform is developed. Aiming to overcome the technical bottleneck faced by automatic code-generation software for nuclear equipment in modelling, code generation, testing, and verification, we perform the following tasks: overall design and evaluation of automatic code-generation software for nuclear safety control systems, software modelling technology for nuclear safety control and human-machine interactive systems, model analysis and verification technology for safety control systems, and automatic code-generation technology for verified software for safety control systems. Based on this research, we establish a new safety-critical software development and verification method and paradigm. Moreover, we construct a prototype automatic code-generation system for safety control in nuclear equipment, applying verified software and safety-certification technology. With regard to the overall design and evaluation of the software platform, we perform requirements analysis considering specific application scenarios in various fields and construct domain models. We design the architecture of the software platform and examine the key platform technologies and methods to support module development, functional safety, and compliance with standards. It is necessary to solve the scientific problem of the formal method and model-driven fusion theory and develop a novel technology for safety control software code based on the architecture design of a model-based development environment. In software modelling, it is essential to accurately describe the requirements of the target system in the nuclear domain, characterize the control, interaction, and coordination of the target system, realize accurate modelling of the nuclear domain model, and provide a basis for the analysis and verification of the relevant safety properties of the subsequent model, simulation, and code generation. These can be achieved by solving the scientific problems of the formal semantic theory of nuclear control and the human-interaction model and developing two key technologies: enhanced synchronous data flow modelling technology with safety embedded state machines and graphical human-computer interaction configuration technology for nuclear control systems. In terms of model analysis and test verification, the correctness verification of the safety control system model based on formal and simulation methods should be completed. To achieve this, following key technologies should be developed: model correctness checking technology for safety control systems, intelligent generation and accurate testing technology for high coverage test cases, a general high-reliability virtual simulation driver, and automatic execution technology. In terms of code generation, a highly verified code generator should be developed based on formal verification of transformation from the nuclear power control and interaction system modelling language to a domain-specific safe subset of the C language. It is necessary to solve the scientific problem of the reliable construction theory and synchronous data flow model code generator of control systems extended by safety state machines and develop the key technology for formal verification of synchronous data flow language verified code generators based on theorem proof. The main innovations introduced in this study are as follows: First, we present a new method for developing nuclear safety control software based on the integration of formal methods with model-driven development. This approach guarantees both the reliability of the software and the efficiency of its development. We provide a theoretical basis for the abstract transformation from software code to theorems, and also study, deploy, and schedule the construction of the tool chain around formal verification. Second, we extend the state-machine schema to construct a new language (based on the Lustre language) conforming to the synchronous data-flow theory. A complete and accurate description of complex control logic in safety-critical domains such as nuclear power equipment is provided. Third, we propose a verified code generator based on interactive theorem proving and use it to explore and solve the problem of generating high-reliability safety control code. Fourth, we propose a data-driven and intelligent test-case generation method based on machine learning for exploring the correlation between abstract models and software codes. Finally, we describe an integrated development platform for nuclear safety control software that meets high-level quality and safety requirements. It includes model-based design, simulation, verification, code generation, and other functions, providing one-stop solutions for software development in safety-critical areas. The goal of our research is to offer a new and highly reliable method for developing and verifying safety-critical software. Our results have considerable theoretical and practical implications for scientific research and development of industrial software in domains such as nuclear equipment.关键词：nuclear equipment;code generation;formal;model-driven394|474|0更新时间：2024-03-19
FOCUS ON STATE KEY RESEARCH DEVELOPMENT PROGRAM OF CHINA
- 摘要：Materials science and engineering play a pivotal role in supporting our country’s Four Orientations. Advanced materials and manufacturing is the national strategic and basic industry, is the core field involving national security. This article addresses the urgent national demand for high-quality materials science professionals and the limitations found in traditional undergraduate materials science programs, such as overly narrow specialization, weak practical skills, and insufficient innovation capabilities. Approaching from the perspective of undergraduate education at top-tier universities, and building on the substantial foundation and comprehensive strengths of Sichuan University, it integrates two decades of reform practices in the College of Materials Science and Engineering to systematically explicate the characteristics and new model of undergraduate talent development in materials science, which emphasizes a solid foundation, strong practical skills, and a focus on innovation. The primary objective of this paper is to explore how Materials Science and Engineering, recognized as a world-class construction discipline and a top-tier national key discipline, can be leveraged to meet the significiant demands of the country and play a pivotal role in the national economy’s main arena. It aims to provide a thorough summary of systematic and multi-tiered exploration in education and teaching reforms within this field. Further, the current research analyzes the specific connotation, implementation path and education effect of cultivating outstanding material undergraduate talents with firm ideals, solid foundation and courage to innovate, and forecasts the further continuous reform work.关键词：materials science and engineering;undergraduate major;talent cultivation;educational reform370|419|0更新时间：2024-03-19
PROJECT OF THE NATIONAL TEACHING ACHIEVEMENT AWARD FOR HIGHER EDUCATION
- 摘要：The widespread development and integration of distributed photovoltaic power sources across the county, alongside the the large-scale grid connection of these distributed energy sources, play a crucial role in supporting two national strategies: achieving “carbon peaking and neutrality” and “revitalizing rural areas”. However, The misalignment between the peak and trough phases of distributed power generation and those of the load demand often leads to voltage fluctuations within the distribution system. Such fluctuations not only degrade the quality of power but also pose significant risks to system stability. To mitigate these issues, this study introduces a hierarchical voltage cooperative control strategy for distribution networks based on “reactive power first–active power later” power compensation. Initially, a hierarchical voltage cooperative control framework based on “reactive power first–active power later” power compensation was established. Subsequently, combining the equation of injected current and voltage at the nodes of multi-microgrid with power-voltage sensitivity analysis, a multi-intelligent cooperative regulation strategy based on “reactive power first–active power later” power compensation was proposed according to the voltage crossing degree of multiple nodes. In this strategy, reactive power regulation was first performed via reactive power compensator, and then multi-microgrid was used for active power regulation when the voltage had not been effectively governed. Furthermore, in order to further satisfy the active power regulation requirements of each node, and to consider the internal source–load–storage operation cost and pollution emission of the grid, a multi-objective optimization-based distributed internal source–load–storage optimal coordinated power control strategy of the microgrid was proposed. Finally, three simulation scenarios were designed in MATLAB platform and IEEE test system model to validate the proposed control strategy. The results indicated that the proposed voltage cooperative control method facilitates comprehensive and efficient voltage regulation at each node, achieving this under economically optimal conditions. Additionally, the proposed microgrid’s optimal coordinated power control strategy effectively ensures that source–load–storage meets the microgrid’s active power regulation requirements. This is accomplished in a timely and precise manner, adhering to both green and economic power supply principles. The effectiveness of the proposed control strategy is verified by the simulation results.关键词：distribution network;“reactive power first–active power later” power compensation;voltage cooperative control;source–load–storage coordination control859|476|0更新时间：2024-03-19
- 摘要：The power system serves as a crucial infrastructure for daily human activities and represents one of the most intricate artificial systems. To ensure the stable and reliable operation of the power system, precise and dependable state monitoring becomes imperative. Varied state monitoring scenarios necessitate distinct measurement methods to obtain more accurate results. Currently, online monitoring of current within the power system primarily focuses on wire current measurement in indoor locations, leaving a gap in measurement methods for the working current of copper bars in the power system. In addressing the need for monitoring the current of the power system busbar, the utilization of the magnetic field as the coupling method demands attention to resolving two key problems: 1) Developing a magnetic field model for rectangular cross-section copper busbars with current flow; 2) Creating a magnetic field measurement and current inversion method based on the magnetic field of the copper busbar with current flow. This paper, based on Biot Savart’s law, establishes an ideal magnetic field model for copper busbars with current flow. The study delves into the magnetic fields of rectangular cross-section copper bars in both near and far fields. Through magnetic field calculations, the impact of the number of measurement units within the current sensor array on current measurement is explored, and the array structure is optimized. Employing Ampere’s loop law and a mean algorithm, the error between the array current back-calculation result and the given current is determined. Building upon this, a design is proposed, encompassing a rectangular array, a measurement information processing module, a data path, and associated hardware circuits for measuring current in a rectangular copper busbar. A unique double-layer circuit board structure is employed to secure and position multiple tunnel junction magnetoresistive effect sensing units. Ultimately, an experimental platform, utilizing electrified copper bars, is established to measure the current of a copper busbar under laboratory conditions using the array measurement system. Experimental results demonstrate that the current measurement array outlined in this paper achieves an accuracy of less than 1%.关键词：current measurement;tunnel junction magnetoresistive sensor;array;measurement system899|344|0更新时间：2024-03-19
- 摘要：Under the prerequisite that the privacy protection requirements of each involved agent are satisfied, ensuring a dependable power supply and flexible power allocation stands as the cornerstone for the privacy-preserving operation of a power system, taking into account the interaction of multiple agents. In this paper, we present a distributed economic dispatch scheme utilizing the modified consensus alternating direction method of multipliers (C–ADMM). Global optima are attained by solely exchanging coupling line information among interconnected areas, thereby achieving simultaneous privacy protection and dispatch goals. Firstly, based on the privacy requirements of agents participating in the day-ahead dispatch, we construct a multi-agent collaborative scheduling model. Each adjacent subject achieves decoupling by solely sharing the boundary coupling branch impedance information. The optimal scheduling problem of each subject is independently solved in each area, and the coupled multipliers are continuously updated in the iterative process to achieve global optimization. Considering the impact of distributed adjustable loads on the convergence of C–ADMM, we employ the cutting-plane method to relax and approximate the integer variables. This facilitates the transformation of the problem by removing integer restrictions and introducing new constraints, thereby obtaining the optimal coordinated dispatch results for discrete adjustable loads and other resources. Finally, we conduct simulation calculations using the IEEE 30-bus system. Specifically, we partition the IEEE 30-bus system into different subjects and perform case tests to validate the effectiveness of the proposed distributed collaborative optimization scheduling strategy. The results indicate that, under different division methods, the improved C–ADMM algorithm can yield relatively stable convergent solutions compared to the centralized method. Under different calculation parameters, the proposed and centralized methods, considering various parameters, are approximately the same, with a maximal error of 0.42%. Additionally, the convergence criterion is reduced to one hundredth compared to the conventional C–ADMM.关键词：discrete adjustable loads;source-storage-load coordinated scheduling;privacy and security;distributed optimization996|508|0更新时间：2024-03-19
- 摘要：With the continuous increase in photovoltaic (PV) access capacity, voltage sag in the grid when the PV is off-grid can adversely impact the stable operation of the system. Therefore, it is imperative for the PV system to possess low-voltage ride-through (LVRT) capability. However, the existing PV LVRT strategy, which is based on a fixed DC bus voltage, indirectly adjusts PV output power according to changes in the DC bus voltage, resulting in a slow dynamic response. A two-stage PV LVRT control strategy based on the PV power–voltage (P–U) characteristic curve directly controls PV output power based on the inverter’s output active power during a fault. However, a drawback is that the PV voltage and current reference values must be obtained through model solving, and the model accuracy is susceptible to the completeness of the PV nameplate and irradiance. Moreover, the LVRT effect under partial shadow shading scenarios has not been considered. To address these challenges, a dynamic current reference value-based LVRT control strategy for two-stage grid-connected PV systems is introduced, specifically designed for partial shading scenarios. Initially, a mathematical model is established based on the characteristics of the two-stage grid-connected PV system and PV cells. The strengths and weaknesses of existing LVRT control strategies are analyzed. Subsequently, a dynamic current reference value with adaptive convergence characteristics is constructed, and its convergence under scenarios of uniform illumination and local shadow shading is examined. The pre-stage boost circuit is employed to control PV output current using the set dynamic current reference value. This adjustment of the PV operating point accelerates the dynamic response of the PV system and mitigates errors caused by model solutions. Additionally, a fault decoupling module is incorporated into the maximum power tracking algorithm, enabling the system to lock the maximum power point tracking output voltage reference value by switching input quantities during a fault. This facilitates a quick system recovery to the maximum power point after the fault concludes. Finally, the proposed strategy is compared with fixed DC bus voltage control and PV P–U curve-based LVRT control strategies under various environmental conditions through simulation. The results indicate that the proposed strategy exhibits a faster dynamic response compared to the fixed DC bus voltage control strategy. Moreover, in comparison to the control strategy based on the P–U characteristic curve of PV, the proposed strategy effectively achieves LVRT under different irradiance levels, particularly in partial shadow shading conditions, making it more adaptable to varying environmental conditions.关键词：two-stage PV grid-connected system;low-voltage ride-through;partial shadow;dynamic current reference value827|387|0更新时间：2024-03-19
- 摘要：Objective The accurate assessment of sensitive equipment fault probability caused by voltages sags is an important reference to precisely mitigate voltage sags. Currently, the fault probability assessment of sensitive equipment due to voltage sags faces two major problems: small samples and insufficient a priori knowledge. A stochastic modeling method for fault probability assessment with small samples of sensitive equipment due to voltage sag was proposed by using autoencoder technology and maximum entropy principle.Methods Firstly, the fault samples of sensitive equipment would be constrained into the same uncertainty area in voltage tolerance curve (VTC). Meanwhile, considering the fact that the sensitive equipment is mainly sensitive to the voltage sag magnitude and duration, and has the uncertainty of VTC, the adaptive Kmeans clustering algorithm was utilized to cluster the magnitudes and durations of voltage sag samples respectively to find out the center vector not only representing VTC uncertainty constraints but also neglecting the influence of samples of outlier, and then added it to the loss function of the sparse autoencoder (SAE) for better sample feature learning. The modified SAE was used to produce new samples with the input of the processed fault samples, so that a fault sample augmentation method based on SAE–Adaptive Kmeans was proposed. Secondly, in view of the problem of insufficient a priori knowledge, a maximum entropy modeling method for the fault probability assessment of sensitive equipment based on the augmented samples was proposed. Finally, taking personal computers (PCs) as examples, simulation verifications were carried out in the cases that the VTC probability density function obeys uniform distribution, normal distribution, different exponential distribution and the sample number was only 5, and the proposed method was compared with the traditional maximum entropy method and the method with SAE sample augmentation that introduced the constraints of the uncertain region of the VTC but didn’t introduce adaptive Kmeans clustering. In the same time, the proposed method was compared with the assessment methods based on subjective assumption under insufficient a priori knowledge.Results and Discussions From the distribution of the 5 augmented PC’s fault samples of Case 1 to 4 produced by the proposed SAE-Adaptive Kmeans augmentation method, the augmented fault samples were always distributed into the uncertainty area of VTC, which meant the SAE-Adaptive Kmeans augmentation method assured the constraint of VTC uncertainty. Meanwhile, on the basis of conforming to the characteristics of the original sample distribution and neglecting the outlier samples, it realized the effective supplementation of the original sample space. The methods to be compared under small sample circumstances included the proposed assessment method (Method 1), the assessment method based on the maximum entropy principle (Method 2) and the proposed assessment method only constraining the VTC uncertainty boundaries without using adaptive Kmeans clustering algorithm (Method 3). The assessment results of PC’s voltage sag fault probability from Cases 1 to 4 under small sample circumstances showed that: The single largest errors for Methods 1 to 3 in Case 1 were 52.76%, 41.87%, and 20.36%; The single largest errors for Methods 1 to 3 in Case 2 were 20.72%, 32.99%, and 41.98%; The single largest errors for Methods 1 to 3 in Case 3 were 7.54%, 32.15%, and 13.37%; The single largest errors for Methods 1 to 3 in Case 4 were 102.67%, 918.67%, and 197.90%. At the same time, the mean errors for Methods 1 to 3 in Case 1 were 33.89%, 21.00%, and 12.86%; and the mean errors for Methods 1 to 3 in Case 2 were 8.60%, 15.60%, and 21.56%; and the mean errors for Methods 1 to 3 in Case 3 were 3.72%, 14.04%, and 5.58%; and the mean errors for Methods 1 to 3 in Case 4 were 30.05%, 203.60%, and 92.81%. It can be seen that Method 1 minimizes both single and average errors, except for Case 1 which is not obvious enough. The fault frequency assessment results of PC showed that the assessment errors for Method 1 from the four cases were 0.63%, 6.03%, 2.28%, and 3.11%, which were all lower than those for Method 2. The methods to be compared under insufficient a priori knowledge circumstances included Method 1, the method assuming VTC obeys a uniform distribution in the uncertain area (Method 4), the method assuming VTC obeys a normal distribution in the uncertain area (Method 5), the method assuming VTC obeys an exponential distribution in the uncertain area (Method 6), and the method assuming VTC obeys an inverse exponential distribution in the uncertain area (Method 7). The assessment errors of PC’s voltage sag fault probability from the four cases under insufficient a priori knowledge circumstances showed that: Methods 1, 5 to 7 had single maximum errors of 52.78%, 43.50%, 222.04%, and 97.00% in Case 1, with the mean errors of 33.89%, 23.12%, 92.76%, and 82.83%; Methods 1, 4, 6, and 7 had single maximum errors of 20.72%, 30.31%, 267.70%, and 96.57% in Case 2, with the average errors of 8.60%, 19.41%, 88.19%, and 85.55%; Methods 1, 4, 5, and 7 in Case 3 had single maximum errors of 7.54%, 68.95%, 72.80%, and 99.07%, and the average errors of 3.72%, 44.17%, 34.43%, and 89.04%; and Methods 1, 4 to 6 had single maximum errors in Case 4 of 102.67%, 3228.00%, 2814.70%,10617.00%, and the average error of 30.05%, 864.24%, 863.69%, 2199.80%. It can be seen that Method 1 still minimizes both single and average errors except for Case 1 which is not obvious enough. The fault frequency assessment results of PC showed that: Method 1 has the lowest error in evaluating the frequency of failures in each case after removing the most desirable method in every case, while the average of the total errors for the four cases of Method 1, Methods 4 to 7 are 3.01%, 114.01%, 135.25%, 225.30%, and 62.88%, respectively, which further proves the validity and accuracy of the methodology of this paper.Conclusions The results show that the proposed method is applicable to the small samples and different distributions, and the errors of assessment results are lower than those of the traditional maximum entropy method and those of the methods based on subjective assumption, which verifies the effectiveness, rationality and feasibility of the SAE sample augmentation and the maximum entropy modeling for the probability assessment due to voltage sags of small-sample equipment failures, and insures the accurate further analysis of voltage sag corresponding problems.关键词：voltage sag;sensitive equipment;fault probability;small sample;sparse autoencoder;maximum entropy modeling505|317|0更新时间：2024-03-19
- 摘要：The cascaded hybrid DC transmission system offers advantages in restraining commutation failure and transmitting large capacity power. However, when the downside MMC inverter of the cascaded hybrid HVDC employs master-slave control, AC/DC faults or sudden load increases can lead to a current imbalance problem. This results in large-scale power reverse transmission on the AC side and a decrease in voltage support ability. To enhance the stability of the receiving end power grid, this paper introduces a flexible power flow coordination control strategy based on UPFC for cascaded hybrid DC transmission systems. The article investigates the power flow control characteristics of a cascaded hybrid DC system with UPFC connected nearby. To address issues such as inverse power transmission and voltage support stability during faults and large disturbances, the paper proposes a frequency support strategy based on UPFC and a voltage support strategy based on dynamic limiting. This strategy redirects the power disturbance caused by the sending side fault to the UPFC line of the receiving AC system, leveraging UPFC’s power compensation ability for coordination. Additionally, the dynamic limiting control strategy enlarges reactive power output capacity. Subsequently, the paper establishes a model of the cascaded hybrid DC transmission system with the receiving AC system using PSCAD–EMTDC software. Firstly, the simulation demonstrates the decrease in LCC DC current command value, showing that the coordinated control strategy based on UPFC effectively reduces frequency fluctuations in AC systems and suppresses power backflow phenomena. Secondly, the simulation of a sudden increase in system load verifies that the dynamic limiting control strategy enhances the voltage support capability of MMC for the AC system. Finally, the paper simulates the cascading fault process, revealing that the proposed coordinated control strategy effectively supports system frequency and voltage. It suppresses power fluctuations, thereby improving the stability of the cascaded hybrid DC system and the receiving power grid. In conclusion, the results demonstrate the effectiveness and feasibility of the flexible power flow coordination control strategy proposed in this paper for cascaded hybrid DC and UPFC.关键词：hybrid DC system;UPFC;dynamic limit;coordinated control strategy;voltage support545|495|0更新时间：2024-03-19
- 摘要：With the continuous growth of energy consumption and the increasingly severe global climate problem, the installed capacity of clean energy represented by wind power is steadily increasing under the strategic background of the “carbon peak” and “carbon neutral.” Due to the fluctuating and intermittent nature of wind power generation, accurate power forecasts for wind farms are needed to provide an effective basis for the construction of supporting facilities and future planning to better utilize wind power. Therefore, improving the accuracy of wind power farm generation forecasting in the planning stage is crucial to promoting the rapid development of wind energy. To address the problem of low forecasting accuracy in the absence of wind power historical operation data, a CNN–LSTM hybrid neural network-based wind farm power generation forecasting model in the planning stage is proposed. Firstly, the wind speed-wind power measured data points in each wind speed interval are extracted based on the historical data of the reference power station, and the wind power curve is modeled using cubic spline interpolation. Then, the K–means clustering algorithm is used to classify the regional categories of reference wind power farms based on the characteristic relationship of wind speed-wind power. Wind power is affected by multidimensional meteorological factors, and the CNN–LSTM forecasting model is constructed by considering the characteristic relationship between wind power-meteorological factors and the time-series characteristics of wind power. Finally, a case study is performed based on the actual data of a local wind farm, and the forecasting results are compared with those using the standard power curve and without correction. The results show that the proposed model is better than the traditional standard power curve forecasting method and can effectively improve the prediction accuracy of wind farm power generation in the planning stage.关键词：wind power forecasting;long and short term memory neural network;convolutional neural network;power curve;wind farm planning1419|550|0更新时间：2024-03-19
NEW TYPE POWER SYSTEM
- 摘要：Microwave heating of chemical reactions offers the advantages of rapid heating, high efficiency, and selective heating, contributing to energy conservation and emission reduction. However, challenges such as significant microwave reflection, non-uniform heating, and thermal runaway hinder its broader applications. Addressing these issues and designing high-performance microwave reactors requires an in-depth study of the macro-level dynamics of microwave chemistry, encompassing Maxwell’s equations, the heat transfer equation, and the chemical kinetic equation. Unfortunately, existing research lacks the necessary coupling among these equations. This paper aims to establish a dynamic model of microwave heating in chemical reactions at the macro level, incorporating polarization and power loss of microwaves during chemical reactions. The initial focus involves reviewing the coupling model for the dynamics of microwave heating, acknowledging the challenge of neglecting polarization and power loss in chemical reactions. To overcome this, a new dielectric characterization is introduced, revealing that the dielectric properties of chemical reactions are determined by the coefficients of the first-order Legendre polynomial expansion. To address the issue of microwave power loss in chemical reactions, a dissipation power formula is proposed based on the law of energy conservation. Results demonstrate that microwave power loss in chemical reactions comprises three components: power loss in reactants, power loss in products, and power loss generated by the coupling between products and reactants. Finally, an illustrative example is provided to demonstrate the application of the proposed dynamic model in practical scenarios.关键词：microwave chemistry;dynamics;multi-physics;polarization;power loss961|363|0更新时间：2024-03-19
- 摘要：The Full Face Rock Tunnel Boring Machine (TBM) is increasingly prevalent in China's tunnel construction. However, the significant wear of the disk cutter in extremely hard rock layers has resulted in low efficiency in rock-breaking, leading to project cost escalation and other contradictions. These challenges are increasingly prominent and hinder the TBM's normal usage. Microwave-assisted TBM disk cutter rock-breaking, a novel technology, is gaining attention from engineering researchers due to its advanced technology, safe and controllable nature, rapid heating, and environmental friendliness. In light of this, this study explores the damage mechanism of microwaves on rocks under various factors. Basalt from Chifeng, Inner Mongolia, was chosen as the study object. X-ray diffraction results revealed that the rock primarily consists of 65% plagioclase, 23.9% pyroxene, and 11.1% olivine. The Particle Discrete Element PFC2D simulation software was employed to model the three-phase mineral rocks by randomly distributing them based on mineral content ratios. To eliminate boundary effects and enhance simulation model efficiency, a mineral particle size of 1.7 mm to 2.0 mm and a rock model size of 400 mm × 160 mm were selected. The rock model’s left and right sides act as confining pressure boundaries, the bottom is a fixed boundary, and the top (Tunnel face) is a free boundary, with the initial rock temperature set at 25 ℃. Simplifying the heating effect of microwave radiation on the rock, the heating area of microwave radiation on the rock, and the attenuation of microwave with depth, enables a more efficient and intuitive study of the microwave radiation’s influence mechanism. To validate the numerical model calculation’s rationality, a 90 mm × 180 mm three-phase mineral rock model is established to analyze the microwave radiation rock cracks’ change rule and expansion characteristics. The study utilizes a dual waveguide with a microwave power density of 1 × 1010 W/m3 to radiate the rock. The effects of waveguide spacing (60 mm, 70 mm, 80 mm, 90 mm, 100 mm), radiation time (0 s, 0.04 s, 0.06 s, 0.08 s, 0.1 s), and confining pressure (5 MPa, 10 MPa, 15 MPa, 20 MPa) on rock damage, crack sprouting, and expansion are investigated. The results show that the change characteristics of rock cracks follow a consistent pattern during microwave irradiation. Cracks begin to appear when the microwave radiation time is 0.04 s, with no cracks sprouting before that time. Subsequently, as the microwave radiation time increases, the thermal expansion and thermal stress inside the rock gradually intensify, resulting in more bonding fractures between mineral particles. The number of cracks rises, leading to crack penetration between the dual waveguide radiation regions. Upon analyzing the location of damage cracks in relation to the distribution of three-phase minerals within the microwave radiation area, it becomes evident that these cracks predominantly occur between plagioclase feldspar and pyroxene. Additionally, a majority of the cracks terminate at olivine minerals. The impact of different waveguide spacings on rock cracks follows a consistent pattern: the variation in waveguide spacings exhibits a similar influence on the expansion of rock cracks. As radiation time increases, there is a growing occurrence of cementation breaks at the pyroxene-plagioclase junction, leading to the formation of extension cracks. For instance, considering the rock model with a confining pressure of 5 MPa, when the waveguide spacing is 60 mm, 70 mm, 80 mm, 90 mm, and 100 mm, the radiation time required for crack penetration between microwave radiation areas is 0.08 s, 0.10 s, 0.12 s, 0.145 s, and 0.15 s, respectively. The corresponding number of cracks generated inside the rock is 91, 163, 280, 495, and 462. The effects of different confining pressures on rock cracking exhibit consistency within the 20 MPa range. Comparative analysis, using confining pressures of 5 MPa and 10 MPa as representatives, indicates that, when exposed to microwave radiation for 0.08 s, the rock sample with a confining pressure of 10 MPa produces five fewer cracks than the sample with a confining pressure of 5 MPa. However, the remaining cracks are identical. Continuous radiation of rock samples at a confining pressure of 10 MPa for 0.10 s reveals the regeneration of the same cracks at the locations where the initial five cracks were absent. In summary, when utilizing microwave power density of 1 × 1010 W/m3 for basalt heating, a radiation time of no less than 0.04 s is necessary to achieve effective rock-breaking assistance. Microwave radiation induces large temperature gradients and thermal stresses between strong wave-absorbing minerals (pyroxene) and weak wave-absorbing minerals (plagioclase), resulting in damage cracks. The location of these cracks is closely related to the distribution of rock minerals. As waveguide spacing increases, the radiation time needed for crack penetration between microwave radiation regions gradually extends. Confining pressure exerts inhibiting and restraining effects on crack generation and expansion. Changes in confining pressure do not significantly impact the location and expansion path of damage cracks in rock samples. Compensating for the reduction of cracks due to increased confining pressure can be achieved by prolonging the microwave radiation time.关键词：microwave assistance;PFC2D;crack;irradiation time;waveguide spacing;confining pressure910|254|0更新时间：2024-03-19
- 摘要：The thermal wave propagation characteristics within refractory structures significantly affect the efficiency and method of microwave heating. Therefore, understanding the dynamic thermal wave propagation within these structures during microwave heating is crucial. This study focuses on boron nitride ceramic (BN) to explore its behavior under microwave heating. The dielectric properties of BN in a wide temperature range (25~1000 °C) at frequencies of 915 MHz and 2450 MHz are tested experimentally. The power transmission coefficient of BN is calculated by transmission line theory. The temperature characteristics of dielectric constant, dielectric loss factor and other parameters of BN are analyzed. The results show that the dielectric constant changes little at two frequencies from 25 to 1000 °C, and the dielectric constant only changes by about 1.8%. However, the dielectric loss factor fluctuates with temperature, exhibiting an exponential increase beyond 900 °C. Concurrently, both the wavelength and penetration depth of microwaves within BN diminish as temperature rises. Additionally, an increase in frequency leads to a reduction in penetration depth. Notably, the study reveals significant disparities in BN’s wave transmission performance between two polarization modes, with horizontal polarization markedly outperforming vertical polarization. At the frequency of 915 MHz, a material thickness of approximately 0.08 meters is identified as the optimal, yielding a a transmission performance (PTC ≥ 0.7) in the range of
$ {\theta _{\rm i}} $ $ {\theta _{\rm i}} $ $ {\theta _{\rm i}} $ 关键词：microwave heating;boron nitride;wave-transparent properties;dielectric constant;refractory structure585|554|0更新时间：2024-03-19 - 摘要：The innovative application of microwaves in the chemical industry is a focal point of research in the trend of chemical electrification. This encompasses various areas such as heating, industrial wastewater treatment, mineral impurity removal, organic catalysis, material synthesis, and medical sterilization. Microwave technology is gaining considerable attention as an external field–strengthening method applied to membrane separation. This is because this technology decreases the preparation time and production cost of membranes materials as well as enhances permeability and improves the separation process of membrane processes. Firstly, this paper provides a comprehensive overview of the typical applications of microwaves for preparing various membrane types, including molecular sieve membranes (such as MOF, MFI, and NaA type), polymer films, mixed matrix films, etc. The utilization of microwave technology is shown to result in membranes with higher flux and selectivity, as molecular sieve membranes preparation of microwave assistance exhibit more uniform crystal size and consistent crystal orientation, thinner membrane layers, and reduced defects. Polymer membranes synthesized using microwave routes demonstrate an improved polymerization rate, smoother surface, and a more regular internal structure. Additionally, mixed matrix membranes prepared using microwaves exhibit enhanced mechanical properties. This review summarizes the strengthening mechanisms of microwave technology in the preparation of diverse membrane materials. In the case of inorganic membranes, such as molecular sieve films, microwave irradiation is utilized to reduce the effective activation energy of crystalline nucleation, adjust crystal size, and induce crystal orientation. For polymer membranes, microwave technology is employed to modify membrane structure, alter the direction of heat transfer, increase polymerization grafting rates, and reduce reaction activation energy. Furthermore, the research explores microwave enhancement of membrane material performance in gas and liquid separation. Recognizing the dearth of basic research in this field, the paper proposes five potential mechanisms of microwave enhancement for membrane separation. These mechanisms leverage the unique heating advantages of microwaves and include selective vaporization, induced hydrogen bond weakening, local overheating, induced nanobubble formation, and molecular perturbation. The review suggests that these microwave effects hold promise in improving both selectivity and permeate flux by compensating for temperature gradients, reducing membrane pollution, and mitigating concentration polarization in microwave-assisted membrane separation processes.关键词：microwave;membrane separation;membrane preparation;external field intensification610|406|0更新时间：2024-03-19
- 摘要：In contemporary cancer therapy, traditional chemotherapy drugs often lack specificity and are frequently accompanied by severe side effects, restricting their clinical utility. In recent years, advancements in nanotechnology have yielded targeted chemotherapy using nanomaterials as a promising, new treatment strategy. Specifically, the drug release capabilities of composite nanomaterials under microwave stimulation have shown remarkable potential. This paper provides an overview of the latest developments in this field, focusing on how composite nanomaterials can achieve precise drug release under microwave stimulation and their potential impact on cancer treatment. Composite nanomaterials find widespread application in cancer treatment due to their unique physicochemical properties, such as high stability and excellent biocompatibility. When exposed to microwave stimulation, these materials can precisely control drug release, enhancing therapeutic efficacy while minimizing harm to healthy tissues. Nevertheless, composite nanocarriers face certain challenges, including issues related to their distribution within the body, targeting precision, and overall biocompatibility. For instance, further optimization is necessary to improve in vivo stability and targeting capabilities of nanoparticles to maximize treatment effectiveness while minimizing side effects. Regarding microwave-induced controlled drug release, despite considerable progress, achieving precise control over microwave energy delivery and local tissue heating continues to pose a major challenge. Additionally, ensuring that microwave energy is concentrated on tumor tissues without adversely affecting surrounding healthy tissues is an ongoing research concern. In the future, as nanotechnology continues to advance and microwave control techniques improve, it is anticipated that more efficient and safer composite nanocarriers will be developed. These advanced carriers have the potential not only to enhance drug targeting and treatment effectiveness but also to achieve even more precise control over drug release under microwave stimulation. In summary, the drug release capabilities of composite nanomaterials under microwave stimulation represent a critical research direction in the field of cancer treatment, holding the promise of providing more effective therapeutic options for cancer patients.关键词：composite nanomaterials;nanocarriers;targeted drug delivery;microwave controlled release drug729|351|0更新时间：2024-03-19
MICROWAVE ENERGY APPLICATIONS
- 摘要：China is one of the countries in the world that have suffered more severely from earthquake disasters. In recent years, catastrophic earthquakes have greatly harmed people's lives and properties. The seismic isolation design of major engineering structures to carry out seismic isolation design has become an indispensable part of the structural design. The Fast Multipole Indirect Boundary Element Method (FMIBEM) was applied to the simulation of seismic wave scattering by 2D seismic metamaterials, and the seismic Isolation effect of a kind of periodic seismic isolation material, i.e., the geotechnical composite seismic metamaterial (RSCSM), was solved. Based on the accuracy verification, the bandgap structure of RSCSM and the seismic isolation effect and bandgap range under different single-cell structures were numerically analyzed in detail. The results show that the broadband scattering of seismic waves by large seismic metamaterials can be effectively dealt with by using FMIBEM; RSCSM can isolate the ultra-low-frequency bandgap of seismic waves, and the width of the bandgap generated by the square-cell structure (0.5~17.0 Hz and 54.0~72.0 Hz) covers the main frequency bands of seismic wave hazards (0.5~2.0 Hz), with an isolation effect of up to 35% or more; and the effect of changing the single-cell structure of RSCSM can be analyzed. Single-cell structure of RSCSM has an important effect on the seismic metamaterial bandgap structure. The bandgap generated by the square cell structure is approximately 0.5~17.0 Hz and 54.0~72.0 Hz; the bandgap generated by the rhombic cell structure is approximately 0.5~20.0 Hz; the bandgap generated by the rhombic single-dot cell structure is approximately 0.5~16.0 Hz and 40.0~57.0 Hz; and the bandgap generated by the rhombic double-dot cell structure is approximately 0.5~14.0 Hz. The filling rate of the hard scatterer also has an important impact on the bandgap, which can be significantly influenced by the same filling rate. The tetragonal cell produces a wider bandgap at the same filling rate, and the tetragonal cell produces a better bandgap effect at lower filling rates. The rhombic single-dot and rhombic double-dot cell structures can only produce better bandgap effects at very high filling rates. This study provides an efficient method for the simulation of seismic wave scattering by the seismic metamaterials, and the conclusions of the study can provide a partial scientific basis for the design of foundation seismic isolation.关键词：seismic isolation;metamaterials;boundary element method (BEM);bandgap205|333|0更新时间：2024-03-19
- 摘要：In response to the limitations of traditional strengthening solutions, such as the lack of aesthetics and significant spatial occupancy, this study proposes a new rotational-based metallic damper (RMD) designed for beam-column joints. The RMD features an arc-shaped appearance, and its placement is strategically set at the corners of beam-column frames, meeting functional building requirements while ensuring effective energy dissipation. The fundamental principle of energy dissipation relies on inducing displacement in a shear plate inside the damper when there is a change in the beam-column angle. Subsequently, hyperbolic-shaped steel bars (HSBs), connected to the shear plate, undergo flexural deformation with the motion of shear plates to dissipate seismic energy. Through finite element (FE) numerical analysis and mechanical performance testing, the RMD demonstrates excellent energy dissipation and plastic deformation capabilities, with minimal risk of failure even under large deformations. By adjusting the number of HSBs, various engineering requirements and objectives can be satisfied. However, existing commonly used engineering design software lacks a rotational link element to simulate the RMD. To address this, we propose an equivalent model to facilitate engineering design. The approach for determining physical properties of the equivalent model is derived and validated using the FE analysis method. To evaluate the energy dissipation and seismic mitigation performance of the damper, comparisons are made with ordinary knee braces and viscous-elastic dampers in a design analysis of a specific power plant structure based on the same quantity and arrangement form. Our calculations demonstrate that the newly proposed damper effectively reduces the seismic response of the structure and exhibits a better damping effect compared to conventional techniques.关键词：rotational–based metallic damper;seismic mitigation;equivalent mechanical model;power plant structure;seismic response188|348|0更新时间：2024-03-19
- 摘要：On September 5, 2022, a seismic event with a magnitude of 6.8 occurred in Luding, Sichuan, resulting in varying degrees of damage to non-structural components inside a seismic isolation-designed building located near the epicenter fault. Non-structural components constitute a substantial portion of the overall structural economic value, and their seismic damage is crucial for post-earthquake functional recovery. Consequently, this study presents the primary seismic damage to non-structural components within the building, employing a two-stage cascading analysis approach. In the first stage, nonlinear response history analyses of an 8-story frame-shear wall building's Etabs model were conducted, utilizing a set of ground motion records from nearby monitoring stations to simulate floor seismic response. In the second stage, employing common freestanding non-structural components, such as document cabinets inside the building as prototypes, nonlinear response history analyses of a zero-length rotation spring OpenSees model were performed. This analysis considered a suite of floor acceleration responses obtained from the previous stage to simulate rocking and overturning responses of non-structural components with varying sizes and slenderness throughout the building. Rocking and overturning responses of non-structural components subjected to both bidirectional and unidirectional inputs were examined, with a specific emphasis on the impact of the strong vertical component of the near-fault ground motion. The results indicate that the isolation system effectively reduces the horizontal floor acceleration response of the upper structure. However, the vertical peak floor acceleration is significantly amplified compared to the vertical peak ground acceleration. Furthermore, under bidirectional horizontal and vertical excitations, the rocking angles and the probability of overturning for freestanding non-structural components exceed those observed under horizontal unidirectional excitation. The influence of vertical excitation significantly increases the risk of damage to freestanding equipment. Therefore, in the seismic design of structures located near-fault sites, the substantial impact of intense vertical ground motion on internal non-structural components cannot be overlooked.关键词：Luding earthquake;isolation building;near-fault earthquake;bidirectional seismic input;non-structural component;rocking response;overturning response178|393|0更新时间：2024-03-19
SEISMIC ISOLATION AND ENERGY DISSIPATION FOR ENGINEERING STRUCTURES
- 摘要：Rocks in the deep underground are commonly situated in a hydrostatic stress state, and it is susceptible to complex dynamic compressive-shear disturbances due to the existence of a multi-scale structural surface. Thus, it is of great significance to investigate the dynamic responses and the constitutive model of hydrostatically pressurized rocks subjected to combined compressive-shear impacting for rock stability assessment and disaster prevention in the deep underground. Using the modified split Hopkinson pressure bar (SHPB), the dynamic compression-shear impacting tests were conducted on the oblique sandstone specimens with hydrostatic confinement. The effects of hydrostatic confining pressure, the shear component in the dynamic loading and the loading rate on the rock mechanical properties have been revealed. Based on the Drucker–Prager criterion and Weibull distribution, the damage constitutive model of hydrostatically pressurized rocks under combined compressive-shear impacting was established. Results showed that as loading rate and hydrostatic confining pressure increased, dynamic strength and deformation modulus of rock showed an increasing trend. It indicated that both the hydrostatic confining pressure and loading rate had an enhancement effect on the rock dynamic strength. The shear component in dynamic load weakened the stiffness of rocks and improved its deformation ability. As the tilting angle and hydrostatic confining pressure increased, the impact failure pattern of rocks under coupled hydrostatic confining pressure and compressive-shear impacting changed from the tensile-dominated failure with a truncated conical surface to the shear-dominated failure with a single shear plane along the short diagonal of the specimen. The shear component in dynamic load had obvious limitations on the fragmentation of rock with hydrostatic confinement. Furthermore, the analytical expression of distribution parameters F0, m, and q were deduced, and the influence of such distribution parameters on the constitutive model was explored for a better understanding of their physical significance. Experimental and theoretical stress–strain curves were compared, and the consistency between these two category curves indicated that the established damage constitutive model could characterize the mechanical properties of hydrostatically pressurized rocks under combined compressive-shear impacting. This study could provide some theoretical support for safety construction and disaster protection of deep rock engineering under complex dynamic disturbance.关键词：deep underground rocks;hydrostatic confinement;SHPB;compressive-shear impacting;dynamic responses;damage constitutive model201|396|0更新时间：2024-03-19
- 摘要：Lightning is a form of extreme weather in nature, often causing serious damage to foundations, ground, towering buildings, etc. Engineering lightning protection measures depend on the lightning impact characteristics of soil. At this stage, the hazards caused by lightning impact on soil are mostly explored from the perspective of electrical engineering, but the cross-fertilization research between geotechnical engineering and electrical engineering under lightning action is very lacking due to the differences and limitations between disciplines. This paper constructs a lightning shock model for soil, calculates the shock wave pressure generated by lightning discharge based on the arc channel energy balance equation, applies the shock wave pressure as an applied load to the soil, and considers soil strain hardening under dynamic load by modifying the Mohr−Coulomb yielding criterion. The ILEOS (Idealized Locked Equation of State) and dynamic reaming methods are used to consider the unsteady loading of shock waves and to investigate the elastic−plastic interface and stress time course change law of soil under lightning impact. The study shows that under the lightning shock, the soil stress changes steeply with time and then decays rapidly, and the sudden change point of stress indicates that the soil is at the elasto-plastic interface, before the sudden change point, the additional stress of the soil tends to zero and is in an elastic state. At any moment, the soil stresses show a rapid decay as one moves away from the lightning impact point, and when the stress suddenly decreases, it indicates that the soil is at the elasto−plastic interface, and after the sudden change point, the additional stress of the soil tends to zero and is in an elastic state. Soil compression coefficient has a significant effect on the elastic-plastic interface change of the soil, with the increase of compression index, the radius of the plastic zone of the soil gradually decreases. As the cohesive force of the soil gradually increases, the radius of the the plastic zone of the soil gradually decreases. Increasing the modulus of soil elasticity can increase the radius of soil plastic zone, but the change is relatively small.关键词：lightning impact;shock wave pressure;strain hardening;soil stress;elasto-plastic interface;time course change156|399|0更新时间：2024-03-19
- 摘要：By adding lignin into silty soil, a new lignin-modified silty soil was proposed to overcome the disadvantages of silty soil such as low strength and poor dry–wet cycle performance, and to solve the problem of resource utilization of solid waste lignin. In order to study the shear strength and dry–wet cycle performance of lignin-modified silty soil, direct shear tests and X-ray diffraction tests were conducted on the modified soil samples with different lignin content after dry–wet cycles. The effects of lignin content 0, 2%, 5%, 8%, 12%, 15% and dry–wet cycles 0, 1, 2, 3, 4 times on the shear strength of lignin-modified silty soil were studied. The experimental results showed that lignin incorporation could significantly improve the shear strength and dry–wet cycle resistance of the modified soil. Under a certain number of dry–wet cycles, the shear strength and cohesion of the modified soil increased first and then decreased with the increase of lignin content, and the internal friction angle increased linearly at first and then remained unchanged. The highest shear strength, cohesion and internal friction angle were found when the lignin content was 8%. The shear strength, cohesion and internal friction angle of the modified soil decreased with the increase of the number of dry–wet cycles. When lignin content was 8%, the strength loss rate of the modified soil after dry–wet cycles was the lowest. When the lignin content was 8%, the content of quartz, calcite and dolomite was the highest, the content of clay minerals was higher, and the content of albite was the lowest, which was the direct cause for improving the strength of modified soil and its dry–wet cycle performance. The results showed that when lignin content was 8%, the modified soil had obvious advantages in improving shear strength and dry–wet cycle performance.关键词：lignin;silty soil;dry–wet cycle;shear strength156|437|1更新时间：2024-03-19
- 摘要：Near-fault ground motion represents an exceptionally hazardous seismic activity characterized by high-energy velocity pulses. These pulses rapidly input a substantial amount of seismic energy into structures, causing significant damage in a very short time. With the expanding urban and transportation infrastructures, an increasing number of large-scale structures find themselves within the proximity of near-fault zones, subjecting them to the impact of near-fault ground motions. This phenomenon significantly compromises the safety of crucial structures. Identifying near-fault ground motions is challenging due to the intricate waveforms of ground motion. Currently, Baker’s wavelet-based method is widely used for recognition. This method leverages the local focusing characteristics of wavelets to extract high-energy velocity pulses in near-fault ground motions. The velocity amplitude and energy extracted are then employed to determine whether the ground motion is near-fault. Baker’s method offers advantages such as rapid recognition and high accuracy. However, it relies on wavelet technology, leading to identification errors due to the significant difference between the mother wavelet and potential pulses. To address this limitation, an improved approach incorporates the use of Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN). This enhancement introduces white noise to assist in the signal decomposition process, enhancing the method's responsiveness to complex signals like ground motions. The enhanced method eliminates the reliance on the basis function in wavelet technology, allowing for a more efficient extraction of velocity pulses with diverse waveforms in complex ground motions. Consequently, the extracted velocity pulse is more comprehensive, enhancing the overall recognition efficiency of the near-fault ground motion recognition method. To enhance the efficiency and quality of this improved method, 3655 ground motions from the Pacific Engineering Earthquake Resistance Center’s database were identified. The improved ground motion recognition method identified a total of 192 near-fault ground motions, while the classical Baker method identified only 163. The incorporation of ICEEMDAN technology resulted in the identification of 17.79% additional near-fault ground motions. To further investigate the near-fault characteristics of the identified ground motion, seismic response spectra and seismic damage were analyzed. Two methods were employed to obtain near-fault ground motion response spectra characterized by strong long-period response, high peak period, and distinct near-fault features. Concerning seismic damage, a typical concrete-filled steel tubular arch bridge was considered as an example. The seismic response of near-fault ground motions identified by both methods was compared with non-near-fault ground motions. Results indicated minimal differences between the near-fault ground motions obtained by the two methods in terms of the damage to the concrete-filled steel tubular arch bridge, with a maximum difference of only 1.83%. However, both methods showed a significant increase in damage for near-fault ground motions compared to non-near-fault ground motions. The near-fault characteristics of ground motions identified by both methods were notably strong, leading to a substantial increase in damage compared to non-near-fault ground motions. On average, the damage probability for each failure state of near-fault ground motions increased by 10.06% compared to non-near-fault ground motions. Despite the similarities in seismic damage laws between the two methods, both demonstrated a significant increase in damage compared to non-near-fault ground motions. In summary, the introduction of ICEEMDAN technology leverages its robustness, enabling the recognition of velocity pulses with complex waveforms. This, in turn, improves the efficiency and accuracy of the Baker recognition method for near-fault ground motions.关键词：near fault ground motion;identification method;empirical mode decomposition;wavelet decomposition;earthquake damage154|280|0更新时间：2024-03-19
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μ–CT Tests and Seepage Simulations of Residual Soil Under the Influence of Wetting–Drying Cycles AI导读
摘要：Granite residual soil is widely distributed in southeast coastal areas of China, and its pore structure is often damaged by the wetting–drying cycles caused by hot and rainy environments, changing the permeability of the soil and inducing numerous engineering accidents. In order to reveal the evolution law of fine microstructure and permeability characteristics of granite residual soil under the action of wetting–drying cycles, the undisturbed samples were subjected to dehumidification and moisture absorption treatment for 0 to 8 times, and then a micro-computed tomography (μ–CT) scanning test was carried out to obtain three-dimensional digital model of the soil. Finally, the multi-channel seepage simulations were carried out by combining the scanning results and AVIZO software. Based on the test results, the evolution law of soil pore volume distribution and permeability coefficient was investigated from qualitative and quantitative perspectives. The results show that the internal structure of granite residual soil can be divided into hematite, quartz, clay, and pore according to the image results of μ–CT scan. The 3D reconstruction model reflected the expansion and connectivity pattern of the pore structure. The number and size of pores increased significantly during the wetting–drying cycles, and both the porosity and pore connectivity were positively correlated with the number of cycles. According to the pore volume distribution curve, the pores in the soil can be divided into four categories: micropores, mesopores, macropores, and fissures. Small-volume micropores were gradually transformed into large-volume interconnected fissures during the wetting-drying cycles. The number and distribution density of streamlines in the 3D seepage model increased significantly with the increase of the number of wetting–drying cycles, and the absolute permeability and permeability coefficient calculated by seepage simulations also increased continuously. The calculation results of seepage simulations can generally reflect the evolution law of the measured value of permeability coefficient, indicating that the seepage simulations based on μ–CT scanning results can be used as an auxiliary means to evaluate soil permeability characteristics. The research results provide an important reference value for in-depth understanding of the environmental damage effect of the macro-mesoscopic characteristics of granite residual soil.关键词：granite residual soil;wetting–drying cycles;μ–CT scan;three-dimensional digital model;seepage simulation166|404|0更新时间：2024-03-19 - 摘要：Due to the heterogeneity of carbonate rocks, the pore-structure is typically characterized by low connectivity and high tortuosity. However, the previous studies on fractal permeability model assume that pore-structure is composed of impermeable capillary tubes. The effects of cementation on the reduction of capillary connectivity and the increase of tortuosity are neglected. This assumption makes it difficult to accurately evaluate the permeability characteristics of low-permeability carbonate rocks. For the overestimation of permeability, the capillary connectivity is used to characterize the area loss of inlet and outlet capillary flow. At the same time based on the relationship between geometrical tortuosity and porosity of fluid permeation path, the tortuosity index is introduced to reflect the actual cementation tortuosity. Finally, a new fractal permeability model of carbonate rocks considering capillary connectivity and cementation tortuosity is established, which adopts fractal geometry Apollonian packing models of a compact pile of equal diameter particles. Comparing with the experimental results, the calculated value of cementation tortuosity is more consistent with the experimental value of mercury intrusion method and the proposed model considering capillary connectivity and cementation tortuosity has a good agreement with the value of microscopic measurement and permeability test. It shows that the new fractal model can better predict the permeability of carbonate rocks. Through sensitivity analyses, it is found that the permeability of rocks with the same porosity and different particle sizes increases with the increase of diameter; on the other hand, the permeability of rocks with the same particle size increases with the increase of porosity. However, because both the minimum/maximum pore area and the pore area fractal dimension are related to porosity, the relationship between permeability and porosity is not a simple linear relationship, i.e., as the porosity becomes higher, the permeability increases but with a gradually reducing rate, while the sensitivity of permeability to porosity decreases.关键词：Apollonian packing;cementation tortuosity;capillary cross-flow coefficient;permeability;fractal173|333|0更新时间：2024-03-19
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Equivalent Energy-based Design Method of Bridge Bents with Multistage Buckling–Restrained Brace AI导读
摘要：Traditional buckling-restrained brace (BRB) is widely used for damage control of bridge bents. However, it is difficult to effectively control peak displacement and residual displacement of the system under strong earthquakes due to its low post-yield stiffness and small deformation capacity. Therefore, two kinds of material with different yield points were used to replace the single material in the core deformation section of the traditional BRB, so that its overall mechanical properties are multi-linear with staged yield, forming a multistage buckling-restrained brace (MSBRB). MSBRB was used as a fuse to improve the seismic performance of bridge bents. With an equivalent energy-based design procedure, taking the capacity curve of the bridge bent with MSBRB as the design objective, considering the plastic deformation mechanism and capacity curve of the system under gradually increasing seismic dynamic load, a three-stage seismic design process has been developed based on code for seismic design of highway bridges in China. Finally, based on a design example, the feasibility and accuracy of the design procedure were validated with nonlinear time history analyses. The results showed that the design procedure could well predict the performance state of a bridge bent with MSBRB under different seismic levels. The maximum error between the design value and the simulation value was less than 6%, which could achieve the design objectives of different seismic levels. It was also found that after adding MSBRB, the displacement of the bridge bents was significantly reduced. Under earthquake action E2, the bridge bents can maintain an elastic state, and under more severe earthquake levels, the damage of the bent pier can also be effectively controlled. It shows that MSBRB can effectively improve the seismic performance of bridge bents and control the damage of bridge bents.关键词：bridge bents;equivalent energy-based design procedure;structural fuse;multistage buckling-restrained brace;energy modify factor162|308|0更新时间：2024-03-19 - 摘要：Understanding the shear failure characteristics of shale is of great significance to the drilling stability control of shale gas reservoirs and reservoir reconstruction designs. However, due to the anisotropic properties of shale itself, the shear failure behavior of shale is complex, and the isotropic shear strength model is no longer applicable. Therefore, a systematic direct shear failure test was carried out on six kinds of cubic shale with different bedding dip angles (0°, 30°, 60°, 90°, 120° and 150°). The anisotropic behavior of shear stress-shear displacement, shear strength, shear modulus, and failure mode of shale under the influence of a weak bedding plane was analyzed in detail. The results show that the shear failure of shale is a typical nonlinear progressive failure. The average shear strength and shear modulus of shale show an ‘M’ trend with the increase of bedding dip angle. The extreme value difference of average shear strength in 90°~180° bedding angle range is significantly greater than that in 0°~90°, but the shear modulus changes approximately symmetrically. This indicates that when the bedding angle changes from 0° to 180°, the shear anisotropy behavior of shale shows asymmetric evolution. Under the action of bedding dip angle and direct shear load, the failure mode of shale is complex, and the shear failure along the bedding plane is 0°. When the bedding dip angle is 30°, 60° and 90°, the shear slip failure through the bedding and the matrix; at other dip angles, the composite failure of penetrating bedding and matrix shear slip combined with tensile splitting along bedding is presented. Based on the experimental results and the fabric tensor, a new direct shear failure criterion considering the effects of intrinsic anisotropy and shear stress-induced anisotropy of shale is proposed. The average deviation between the theoretical prediction and the experimental results is less than 3%. In addition, the new criterion can quantitatively characterize the degree of anisotropy of cohesion and friction coefficient, and reasonably evaluate the sensitivity of shale direct shear strength to applied normal stress, which can be applied to the theoretical characterization of direct shear strength of all layered geotechnical materials.关键词：anisotropy;direct shear;shear strength;asymmetric failure mode;shear failure criterion215|470|2更新时间：2024-03-19
CIVIL ENGINEERING
- 摘要：To assess the leakage control capability of a newly developed grooved cylindrical air film seal on the sleeve side, a numerical model was established using the finite difference method. The model encompassed various positional features and spiral directions. By comparing the air film pressure distribution and sealing performance parameters across different groove types, the impact mechanisms of positional features and spiral directions on various groove types were elucidated. Subsequently, a parametric analysis was conducted for the reverse dovetail groove type, exploring the influence of parameters such as spiral groove angle, groove length-to-ridge length ratio, groove width-to-ridge width ratio, and groove depth ratio on leakage, buoyancy force, friction force, and other sealing performance parameters. Simultaneously, an assessment was made regarding the ability of the reverse dovetail groove with specific structural parameter combinations to control leakage through reverse flow pumping. The research findings indicate that the stepped change in air film thickness and the eccentric converging wedge effect create a high-pressure air film region on the sealing surface, effectively preventing axial leakage and sealing the main leakage channel of the grooved cylindrical air film seal on the sleeve side. Moreover, with an increase in rotational speed, the leakage along the axial gap of the new cylindrical air film seal shows a decreasing trend, a crucial characteristic for effective leakage control, especially in high-speed operating conditions. Furthermore, it was observed that a rational structural design for the reverse dovetail groove type can achieve zero or even negative gas leakage for the cylindrical air film seal. Adjusting groove parameters appropriately compensates for the leakage of sealing gas along the axial gap caused by pressure differential flow, precisely counteracted by the reverse dovetail groove’s reverse flow pumping effect. This enables the reverse dovetail groove type of cylindrical air film seal to achieve zero or even negative gas leakage, providing valuable theoretical guidance for the design of grooved cylindrical air film seal structures.关键词：new cylindrical air film seal;different groove;pumping characteristics;performance analysis502|332|0更新时间：2024-03-19
- 摘要：In the utilization of CNC machine tools, thermal deformation occurs in the spindle due to the generated processing heat, leading to a reduction in processing accuracy. In the field of high-precision machining, the spindle error of CNC machine tools considerably affects machining accuracy. In particular, thermal error, a primary source of error directly affecting machine tool accuracy, constitutes 40%~70% of the total error. To enhance thermal error prediction accuracy and subsequently improve CNC machine tool processing precision, a novel modeling approach is proposed. This method utilizes the Seahorse Optimization (SHO) algorithm, incorporating seahorse population movement, predation, reproduction, and other behaviors to optimize the hyperparameters of the long short-term memory (LSTM) time-series prediction network. Accurate prediction of spindle thermal error aids in better control of machine parameters by operators, leading to improved machining accuracy and product quality. To achieve more precise thermal error prediction, the Gazelle Optimization Algorithm (GOA) is employed in the selection of temperature measurement points. GOA optimizes the fuzzy matrix constant, maximum number of iterations, and iteration termination condition of fuzzy C-means clustering (FCM), enhancing the accuracy and convergence speed of the clustering algorithm. FCM, a commonly used clustering algorithm, determines the geometric proximity of data points through Euclidean space, clustering temperature measurement points. The optimal temperature measurement point grouping is determined by dividing the nearest temperature points into clusters. The optimal number of groups is identified using the elbow method, calculating the sum of squares of distance between data points under different groupings. Furthermore, a combination of Person, Spearman, and Kendall correlation analysis methods optimizes temperature measuring points in each group. The temperature measurement points with the highest correlation with the five thermal errors are selected, and their data is input into the prediction model. These steps reduce collinearity between temperature measurement points, improve the prediction model’s accuracy, and reduce computational complexity in the prediction process. Subsequently, thermal error data from the lathe spindle, obtained using the five-point method, and optimized temperature data are used as inputs to construct an LSTM model. The LSTM model is optimized using the SHO algorithm, which enhances fitting and generalization abilities, preventing underfitting and overfitting. The SHO algorithm, with its hippocampal optimization, avoids local optimal problems, resulting in higher optimization efficiency. To determine the optimal group size, the S-fold cross-validation method is employed to establish a spindle thermal error prediction model with optimized performance, known as SHO–LSTM. The thermal error model constructed is evaluated at various spindle speeds, assessing prediction performance through metrics such as Mean Absolute Error, Root Mean Square Error (RMSE), and Mean Absolute Percentage Error. These metrics serve to gauge the effectiveness of predictions. In the final step, verification is conducted on the CKA6163A lathe as an example. Measurement identification was performed using the five-point method to ensure precise data collection. Simultaneously, temperature near the spindle was measured to provide comprehensive thermal information. Based on experimental results, the temperature measuring point optimization algorithm in this study significantly improve compared to the unoptimized fuzzy C-means clustering (FCM). Specifically, the algorithm reduced the DB index by 89%, the Between-Cluster Within-Cluster Proportion metric showed a remarkable 59% improvement, and the Silhouette coefficient experienced an 8.17% increase. These findings indicate that the optimized clustering algorithm significantly reduces collinearity among temperature measuring points, yielding improved prediction performance of the model. When comparing the proposed prediction network with the LSTM, the use of SHO notably improved accuracy. The RMSE of the proposed prediction network was reduced by an impressive 42%, indicating a substantial enhancement in predictive performance. A comparison with the AO convolutional neural network (CNN) showed a 3% reduction in RMSE, highlighting the effectiveness of the proposed model in enhancing prediction accuracy. Compared with the backpropagation neural network (BP), the proposed prediction network achieved a significant 57% reduction in RMSE, emphasizing its substantial impact on accuracy improvement. The comparison results clearly indicate that the SHO–LSTM prediction model for spindle thermal error surpasses others in terms of robustness and accuracy. This underscores the superiority of the SHO–LSTM model in predicting spindle thermal error with improved robustness and accuracy. In conclusion, introducing the SHO algorithm to optimize the LSTM time-series prediction network remarkably enhances both the robustness and accuracy of the spindle thermal error prediction model. This model not only efficiently mitigates the deleterious impact of spindle thermal errors on machining precision but also serves as a pivotal cornerstone in providing indispensable support for precision machining within the realm of CNC machine tools. This pioneering research endeavor exhibits tremendous practical value by further optimizing the performance attributes of CNC machine tools, augmenting the quality standards of machining processes, and facilitating the realization of high-accuracy machining endeavors.关键词：CNC machine tools;spindle thermal error;GOA–FCM algorithm;thermal error prediction;SHO–LSTM network646|494|0更新时间：2024-03-19
- 摘要：In order to precisely diagnose the operational status and fault categories of rolling bearings, this paper employs a long short-term memory (LSTM) neural network as a classifier to categorize and diagnose the rolling bearing dataset. Initially, time-domain and frequency-domain characteristic parameters are derived from the raw vibration signals of rolling bearings, creating a dataset with high-dimensional characteristic parameters. The Kernel Principal Component Analysis method is utilized to reduce the dimensionality of the high-dimensional characteristic set. The features with a high degree of significance are then selected to compose the input characteristic vector. Addressing the challenge of determining hyperparameters for the LSTM neural network in rolling bearing fault diagnosis research, a fault diagnosis model (tSSA–LSTM) is proposed based on the adaptive t-distribution sparrow search algorithm (tSSA) to optimize the LSTM neural network. Finally, several simulation experiments, including fault diagnosis accuracy tests, generalization performance tests, and fault diagnosis performance tests in noisy environments, are conducted using data from the Rolling Bearings Data Center at Case Western Reserve University. The proposed diagnostic model is experimentally compared with SSA–LSTM, GA–LSTM, PSO–LSTM, and traditional LSTM diagnostic models. The experimental results demonstrate that tSSA can more effectively optimize the hyperparameters of LSTM, such as the number of neurons in the hidden layer, the number of cycles, and the learning rate. The proposed method achieves an average diagnostic accuracy of 98.86% and a cross-validation result of 98.57%. Furthermore, the fault diagnosis accuracy of the proposed method under noisy interference surpasses that of the compared methods. Consequently, the tSSA–LSTM model not only accurately diagnoses the state of rolling bearing faults but also exhibits stronger generalization and anti-interference capabilities, effectively enhancing the performance of rolling bearing fault diagnosis.关键词：sparrow search algorithm;fault diagnosis;long short-term memory neural network;feature extraction;rolling bearing842|412|0更新时间：2024-03-19
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