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3D printing (3DP) technology is a groundbreaking technology that can offer valuable insight into rock characterization and theoretical model verification due to its specimen reproducibility and unprecedented flexibility in manufacturing various structural shapes. Previous studies have explored the effect of printing direction on the mechanical properties of 3D-printed rocks, but the underlying cause of macroscopic mechanical anisotropy in 3D-printed gypsum rocks remains unclear. In this study, the effect of the movement direction of the printer head and bedding plane on macroscopic mechanical behavior and failure modes of 3D printed gypsum rocks were investigated. Uniaxial compression tests were conducted to investigate the mechanical properties of 3D-printed gypsum rocks. Along with the mechanical studies, the composition change of the raw powder before and after printing was studied based on particle size diameter (PSD), x-ray diffraction (XRD), and thermogravimetric differential thermal analysis (TG–DTA) experiments. Furthermore, Micro-CT imaging was conducted to investigate the microstructural characteristics of 3D-printed rocks (e.g. pore size, pore shape, and pore anisotropy). The results indicated that 3DP gypsum specimens printed on the yoz plane, which were only affected by the bedding direction, exhibited the lowest strength and mechanical anisotropy. In contrast, specimens printed on the xoy plane, influenced solely by the movement direction of printer head, showed the highest strength. Specimens printed on the xoz plane displayed the greatest mechanical anisotropy due to the joint effect of the bedding direction and the movement direction of the printer head. In terms of strength and mechanical anisotropic properties of 3D-printed specimens, the movement of the printer head was found to be more significant than the bedding direction, whereas the bedding direction was more crucial for peak strain. As for the failure mode, most of the 3D-printed specimens failed by shear failure of which the bedding planes played an important role in the specimens with small inclined angles. Highlights: This study investigated the effect of the movement direction of the printer head and bedding planes on mechanical anisotropy and the failure mode of 3DP gypsum rocks. Three types of experiments were conducted to enhance the understanding of how material composition and microstructure impact the macroscopic mechanical response of 3DP gypsum rocks. Micro-CT scanning tests were performed to reveal the failure mode and microstructural characteristics of 3D printed gypsum rocks. [ABSTRACT FROM AUTHOR]

The forming of Li-Bi alloy can build a lithiophilic protective layer on the lithium anode, however, it is found that the lithium dendrites trend to grow on the surface of bismuth-rich solid electrolyte interphase (SEI) and there is an exfoliation of SEI from substrate caused by de-alloying process at a large current density. The failure cause of the bismuth-rich SEI is considered as the inadequate Li-ionic conductivity of the passivation layer, which cannot facilitate the lithium deposition on the substrate. Then the components with high Li-ionic conductivities such as Li 3 N, LiF and Li 2 S are introduced into the SEI to adjust the characteristic of the bismuth-rich layer by the addition of LiNO 3 , Bi 2 S 3 and FEC. All of them enhance the SEI's performances effectively and LiNO 3 presents the best. With the addition of LiNO 3 , the SEI thickness is decreased and Li-ionic conductivity is enhanced while Li 3 N became one of the major components of the layer. Utilizing the improved bismuth-rich protective layer the Li/Li symmetric cell presents an overpotential at ∼10 mV in a long cycle over ∼1700 h at 4 mA cm−2, and the LiFePO 4 /Li cell with the cathode loading of ∼10 mg cm−2 exhibits a capacity retention rate 72.1% in 400 cycles. This work provides a new SEI design strategy for lithium metal anode operating at high current density and an inspiration for improving other functional interfacial layers in lithium batteries. • Lithium bismuth alloy and dendrites trend to dealloy and grow on the SEI at high current density. • Additives enhancing Li-ionic conductivities are introduced to adjust the bismuth-rich layer's components. • Lithium nitrate addition make Li 3 N a major component of the layer and significantly enhances SEI electrochemical properties. [ABSTRACT FROM AUTHOR]

Three-dimensional printing (3DP) technology has shown great potential in rock mechanics and mining engineering due to its ability to create complex and customized objects with high precision and accuracy. At present, an emerging research focus is improving the mechanical properties of 3D-printed samples, which originally has low strength and stiffness, to match those of natural rocks. The objective of this study was to investigate the effectiveness of different post-treatments on the strength enhancement of 3D-printed gypsum samples. To achieve this goal, 3D-printed gypsum samples were subjected to different post-treatments including dipped infiltration treatment and vacuum infiltration treatment using different infiltrants: water, saltwater, ColorBond, and StrengthMax. Subsequently, each sample was subjected to ultrasonic wave velocity testing and uniaxial compression experiments to characterize their mechanical properties, CT scans to investigate their microstructural characteristics. Additionally, X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) tests were conducted to explore the underlying reasons for changes in macroscopic strength. Finally, the physical characteristics and mechanical properties of untreated and post-processed 3D-printed gypsum samples were compared with natural rocks. The results showed that the strength of samples treated with water and saltwater was much lower than that of those treated with ColorBond and StrengthMax, while the porosity was the opposite. In water-treated and saltwater-treated samples, water or saltwater treatment can alter particle characteristics, but weak adhesive bonding and numerous pores result in low mechanical strength. Samples treated with Colorbond or StrengthMax exhibit improved strength due to effective gap filling and cohesive structure formation, with StrengthMax-treated samples showing higher strength despite having more pores than Colorbond-treated ones. Moreover, the physical and mechanical properties of these treated samples matched a wider range of natural rock types compared to the untreated samples. [ABSTRACT FROM AUTHOR]

3D printing technology allows for precise control of preparing complex geometries and internal defects in printed rock analogs, while in-situ Micro-CT imaging enables real-time observation of crack behavior. The combination of these technologies offers a new research approach for studying rock crack behavior. In this study, 3D-printed rock-like specimens containing a pre-existing flaw were prepared using a gypsum powder-based 3D printer. An advanced in-situ Micro-CT system equipped with a loading device was used to quantitatively and visually investigate the crack behavior in 3D-printed specimens under uniaxial compression testing. 2D CT images obtained from in-situ compression testing at different deformations could be used to reconstruct a 3D model and visually identify the crack patterns of the extracted cracks in 3D-printed specimens. The initiation angle of cracks, volume of the pre-existing flaw, volume of newly formed cracks, and damage value with respect to strains were analyzed to quantitatively investigate crack behavior. The results indicated that within the 3D-printed specimens, tensile cracks were first initiated near the internal flaw, followed by the occurrence of shear cracks or tensile-shear mixed cracks at the flaw tips. Additionally, there was a negative linear correlation between the initiation angle of newly formed cracks and the initial flaw angle. For flaw angles in the range of 0° ≤ α ≤ 45°, a higher number of newly formed cracks were observed in the 3D-printed specimens, and the rates of increase in crack volume and damage values with strain were faster. However, for flaw angles in the range of 45° < α ≤ 90°, the results showed the opposite trend. Furthermore, through comparison with the crack behavior of natural rocks containing a single flaw, it was found that the failure modes and crack behavior of the 3D-printed specimens exhibit certain similarities with natural rocks. [ABSTRACT FROM AUTHOR]

In this paper, three typical permanent magnet machines for All-Electric aircraft propulsion are designed, optimized and compared. Firstly, the necessary performances are determined based on the requirements of high power/torque density and an aircraft with a maximum takeoff weight of 1500 kg. The initial structures of interior permanent magnet (IPM) synchronous machine, vernier permanent magnet (VPM) machine and flux-switching permanent magnet (FSPM) machine are designed with identical stator outer radius and rotor shaft length. Then, parametric sensitivity analysis and multi-objective particle swarm are combined as an optimization methodology to optimize these machines. Based on the finite element analysis, the electromagnetic performances such as no-load airgap flux density harmonic spectrum, cogging torque, average output torque, losses, efficiency and power factor, etc., are generally compared and analyzed. Subsequently, the discussions are carried out, where the strength and weakness of these three machines are concluded and the future prospects are suggested. Finally, it is concluded that if effective measures are implemented to reduce the permanent magnet eddy current loss and improve the power factor, the VPM machine would be the most suitable choice among these machines for All-Electric aircraft propulsion. [ABSTRACT FROM AUTHOR]

• An adaptive consistent element-free Galerkin method (CEFG) for four-order phase-field model is proposed. • Two different consistent integration schemes, namely quadratically consistent one-point integration scheme and three-point integration scheme, are employed to evaluate the fourth-order phase-field model. • The adaptive criterion of local mesh refinement for four-order phase-field model is proposed. An adaptive fourth-order phase-field model is proposed using consistent element-free Galerkin method (EFG). Convenient construction of high-order interpolation functions in EFG method is fully utilized. Requirement of C 1 continuity of shape functions is satisfied in fourth-order phase-field model. Two different consistent integration schemes with high efficiency and high accuracy, namely quadratically consistent one-point integration scheme and three-point integration scheme, are employed to evaluate the fourth-order phase-field equation and displacement equation, respectively. To reduce computational cost, the adaptive strategy of local background mesh refinement is established on basis of strain energy history and phase field. Background mesh is refined via the insertion of nodes at the midpoints of each side of the integration element. Comparing with EFG method, computational accuracy and efficiency are enhanced by the proposed method. Load-displacement response, the smoothness of the resulting stress and crack paths are predicted well. [ABSTRACT FROM AUTHOR]

Efficient implementation of the element-free Galerkin (EFG) method for a phase-field model of linear elastic fracture mechanics is presented, in which the convenience of the meshfree method to construct high order approximation functions and to implement h-adaptivity is fully exploited. A second-order moving-least squares approximation for both displacement and phase field is employed. Domain integration of the weak forms is evaluated by the quadratically consistent 3-point integration scheme. The refinement criterion using maximum residual strain energy history is proposed and the insertion of nodes is based on the background mesh. Numerical results show that the developed method is more efficient than the standard finite element method (3-node triangle element) due to the proposed h-adaptivity. In comparison with the standard EFG method, the proposed consistent EFG method significantly improves the computational efficiency and accuracy. The advantage of the quadratic approximation is also demonstrated. In addition, the feasibility of extending the proposed method to 3D is validated by the modeling of a twisting crack. [ABSTRACT FROM AUTHOR]

[Display omitted] The demand of microwave absorption materials (MAMs) with unique morphologies and electromagnetic (EM) balance has become necessary in recent years. Due to the ease of synthesis and tunable structure, metal–organic frameworks (MOFs) are widely used for this special MAMs. In this study, a new three-dimensional hybrid MOF is proposed that is co-doped with six equally branched star morphologies. The Co-C composite has the same six-branched morphology as that of the precursor. When the EM wave is incident, this special structure makes it easier for the EM wave to enter the material vertically due to the expansion of the incident surface, which is effective in adjusting the transmission path of the electron and the reflection and distribution of the EM wave. Because of the special morphology and magneto-dielectric synergy, the Co-C composite shows a minimum reflection loss (R Lmin) of −48.5 dB at 11.0 GHz at an absorption thickness of 3.0 mm, with a microwave absorption bandwidth (EAB) of 6.1 GHz. This research provides a practical guidance for preparing the MAMs of special star structure. [ABSTRACT FROM AUTHOR]

• An efficiently adaptive EFG for phase-field of brittle fracture of FGMs is developed. • The adaptive criterion for phase-field model of brittle fracture of FGMs is proposed. • Fracture mechanism of FGMs is revealed using phase-field model. Gradient distributions of material properties are taken into account in phase-field model of fracture and the adaptive consistent element-free Galerkin method (EFG) for the fracture analysis of functionally graded materials (FGMs) is presented. Considering the fact that both the moving least-square approximation and the consistent integration scheme contribute to producing the accurate stress fields, the phase-field model of fracture for FGMs is numerically solved by the consistent EFG method in this paper. The corresponding adaptive criterion is established and 2D and 3D crack propagation of FGMs is simulated. Numerical results indicate that the proposed method can accurately reflect the influence of different distributions of material parameters on the crack propagation and has high efficiency compared with the standard EFG method and linear FEM. At some level, the fracture mechanism that crack propagation is driven by both the strain energy history and the critical energy release rate is revealed using phase-field model. [ABSTRACT FROM AUTHOR]

This study employs 3D printing and Digital Image Correlation technology to investigate rock-like specimens with nonpenetrating and nonpersistent rough joints under uniaxial compression. It analyzes crack propagation and elucidates the mechanical mechanisms by summarizing surface displacement features. Findings reveal the influence of nonpenetrating joint number, penetration depth, and arrangement on mechanical performance. The displacement X field exhibits high sensitivity to both the arrangement type and penetration depth of nonpenetrating joints, while the displacement Z field is particularly sensitive to the arrangement type. Nonpenetrating joints locally inhibit discontinuity of displacement X, globally inhibit attenuation of displacement Y, and overall promote displacement Z. Pre-existing joints are categorized into main and subordinate joints. The distribution of displacement X is influenced by the relative penetration depth of horizontally adjacent joints, both main and subordinate. Consequently, under the control of subordinate joints, this leads to the development of wing extension cracks characterized by a pure tensile mechanism and obliquely parallel cracks exhibiting a tensile-shear mechanism. As a result, four distinct failure modes are manifest on the frontal face. Nonpenetrating joints, which form the significant spalling surface, induce noncoplanar extension cracks on the lateral face, exacerbating surface spalling on the back face. The presence of nonpenetrating joints in symmetric specimens effectively enhances the strength, while weakening the strength in asymmetric specimens. The defined joint parameter, including penetration rate and type, exhibits a monotonic decreasing relationship with the peak strength. The study provides compelling evidence that specimens with nonpenetrating joints reproduce layered step path failure surfaces. [ABSTRACT FROM AUTHOR]

• This paper presents a model to reveal the heat transfer mechanism and simulate the heat-flow coupling process in fractured rock masses. • The effects of fracture density and diameter on percolation probability are studied based on Monte-Carlo tests with each group for 10,000 times. • The effects of fracture density, roughness, and percolation of fracture network on heat-flow coupling in hot rock masses with embedded three-dimensional fracture network are studied. This paper presents a model to reveal the heat transfer mechanism and simulate the heat-flow coupling process in fractured rock masses. Specifically, effects of fracture density, roughness, and percolation on heat-flow coupling are investigated systematically. The fractured rock masses are composed of a discrete fracture network and a rock matrix. Regarding the mesh discretisation for finite element analysis, the rock matrix is discretised into three-dimensional (3D) solid elements, whereas the discrete fractures are modelled by zero-thickness elements. Fracture and matrix elements share the same nodes. Considering the effect of temperature on fluid density and dynamic viscosity, a heat-flow coupled model of fractured rock masses is established with an embedded 3D fracture network. The reliability of the model is verified by comparing it with the analytical solution of a two-dimensional single-fracture heat-flow coupling problem. The effects of fracture density and diameter on percolation probability are studied based on Monte-Carlo tests with each group for 10,000 times. Finally, numerical samples of the 3D discrete fracture network with different geometric parameters are generated to characterise fractured rock masses, and heat-flow coupling numerical simulation is conducted simultaneously. Results show that the percolation of the fracture network is the decisive factor affecting heat-flow coupling. The average outlet flow rate of the percolation network under the same fracture density is much larger than that of the nonpercolation fracture network, which results in a more rapid decrease in the outlet temperature. Other factors such as fracture roughness are also investigated. It is discovered that the effect of fracture roughness on heat-flow coupling is almost negligible for the nonpercolation fracture network model. [ABSTRACT FROM AUTHOR]

Consistent element-free Galerkin (CEFG) method for phase-field model of 3D cracks with adaptive nodal refinement. Element-free Galerkin (EFG) method for three-dimensional phase-field model of cracks is described. Quadratic moving least-squares (MLS) approximation is constructed for both the phase field and the displacement. The quadratically consistent 4-point (QC4) integration scheme using background tetrahedral elements (cells) is employed to efficiently compute the domain integrals in weak forms. As cracks propagate, adaptive refinement of the approximation nodes around crack fronts is implemented with the use of background integration cells. The refinement is triggered by the maximum residual strain energy history. New approximation nodes are inserted at the midpoints of the element edges. Several benchmark examples are investigated. Numerical results show that three-dimensional crack propagation is successfully modeled by the proposed method and correct crack paths and load-displacement responses are obtained. Due to the implemented h-adaptivity, lots of approximation nodes are saved and the computational scale is significantly reduced. Improved accuracy of the proposed method in stress distribution and crack width is also demonstrated. [ABSTRACT FROM AUTHOR]

Porous carbon materials typically exhibit excellent microwave absorption performance and lightweight characteristics, providing a positive significance for controlling the composites weight. This work employed a one-step method, and in situ growth techniques to fabricate a foam-structure Fe 3 C/Fe/C with a density of only 0.142 g/cm3. The carbon skeleton encapsulates Fe 3 C/Fe nanoparticles to slow down its oxidation in the natural environment. Remarkably, the Fe 3 C/Fe/C composite achieves an impressive effective bandwidth of 5.73 GHz with a 2.2 mm thickness and only 10 wt% filling ratio. The outstanding performance can be ascribed to the enhanced interfacial polarization caused by high porosity. Additional nitrogen doping provides active sites to enhance dipole polarization. Additionally, after in-depth analysis of the various magnetic loss mechanisms present in Fe 3 C/Fe/C, we have revealed the promotion of introducing magnetic nanoparticles on the microwave absorption performance of foam-like carbon. This work provides an effective reference for reducing the weight of microwave absorbers, simplifying preparation methods, and understanding the mechanisms of magnetic nanoparticles in foam-like carbon. [Display omitted] [ABSTRACT FROM AUTHOR]

The research on the factors of heat recovery performance of Enhanced Geothermal Systems (EGS) is an important issue, especially in the well position optimization in EGS, because it can maximize the economic benefits of EGS. Based on the three-dimensional thermo and hydro (TH) single-fracture model, a flow field in the EGS is added to the model, the thermal energy mining of the EGS thermal reservoir is realized through the double well and better study of the impact of regional flow on EGS well placement. To verify the reliability of the three-dimensional numerical model, the comparison between the two-dimensional single fracture model and the single fracture analytical model is performed under the same conditions, and it is found that there is a good agreement between the numerical and the analytical solutions. The influence of the direction of regional flow on the thermal recovery performance of EGS is studied, and the operating lifetime, power generation and heat production rate of the system are used as the evaluation indicators. It is found that there are two stagnation points in the flow field under regional flow conditions, and the stagnation point position changes regularly with regional flow direction. The direction of regional flow has a great influence on the heat extraction ratio and service lifetime of the geothermal system, the layout of the double well must take into account the regional flow. When only considered the influence of regional flow on EGS, after 50 years of EGS operation, the production well temperature and system operating lifetime increase with the increase of β (the angle between the direction of the regional flow and the line connecting the centers of the two wells). When it has regional flow, the greater the well spacing, the greater the temperature of the production well, but when the well spacing increases to a certain value, the well spacing will not affect the temperature of the production well. [ABSTRACT FROM AUTHOR]

Magnetic metal modified carbon-based composites synthesized through chemical methods have shown great potential in the field of electromagnetic wave (EMW) absorption. Biomass-derived carbon, as an alternative to traditional carbon sources, has better economic and environmental benefits. In this work，we embedded magnetic iron ions in dried agaric through multi-effect adsorption and obtained ripple-like Fe/C composites after high-temperature annealing. The effective absorption bandwidth (EAB) of Fe/C composites can reach 6.3 GHz (11.5–17.8 GHz) at 2.5 mm, achieving broadband electromagnetic response. The excellent performance can be attributed to the ripple-like carbon, which enhances the transmission path of EMW in the absorber. On the other hand, the uniform loading of Fe nanoparticles on biomass-derived carbon promotes the interface polarization and dipole polarization and coordinates the impedance matching of the composites. This study provides a reference for the design and construction of efficient biomass-derived magnetic carbon-based absorbers. [Display omitted] • Fe/C composites have been synthesized using biomass-derived method. • Fe/C composites exhibit an effective bandwidth (R L min ≤ −10 dB) of 6.3 GHz with the thickness of 2.5 mm. • The great absorption performance of Fe/C composites stems from proper impedance match and boosted dielectric-magnetic loss. [ABSTRACT FROM AUTHOR]

• Adaptive finite element method for hybrid phase-field model of 3D cracks is present. • Efficient and robust modelling of complex crack propagation in 3D is achieved. • Industrial application is demonstrated by modelling fracture of a turbine blade. Phase-field modeling of cracks in three dimensions (3D) is challenging due to expensive computational efforts caused by inefficient solution of non-linear governing equations as well as the requirement of extremely fine mesh for crack resolution. In this paper, a combination technique aiming at these two issues is presented. Firstly, a hybrid phase-field model is implemented in 3D with a simple and robust one-pass staggered solution scheme, yielding a linear system of governing equations which can be solved efficiently. Secondly, adaptive mesh refinement using the predictor-corrector algorithm is developed such that this hybrid model can be solved with minimal number of nodes. Numerical results show that computational cost of 3D phase-field modeling is dramatically reduced and complex crack events including initiation, mixed mode propagation, non-planar extension and twisting can be efficiently modeled with preferable robustness. Perfect agreement between numerical and experimental results on crack paths and application of the proposed method to the fracture of complicated engineering structures are demonstrated. [ABSTRACT FROM AUTHOR]

A stable and efficient integration scheme which evaluates the Galerkin weak form only at the centers of background tetrahedral elements (cells) for three-dimensional element-free Galerkin method with quadratic approximation is proposed. The derivation of the method is based on the Hu–Washizu three-field variational principle and the orthogonality condition between stress and strain difference is satisfied by correcting the nodal derivatives at quadrature points with Taylor series expansion technique. The consistency of such corrected derivatives is theoretically proved. Numerical experiments validate that the proposed method can exactly pass linear and quadratic patch tests. Therefore, it is named as quadratically consistent one-point (QC1) integration. The superiority of the proposed QC1 than other integration schemes for three-dimensional element-free Galerkin methods in accuracy, convergence, efficiency and stability is sufficiently demonstrated by several 3D examples. [ABSTRACT FROM AUTHOR]

Discrete fracture network (DFN) is an effective means of describing the coupling of heat flow in an underground fractured rock mass. In this paper, an improved DFN is proposed by introducing the correlation function of fracture trace length and aperture, which is more consistent with the real fracture data. Next, based on the improved model, the influence of fracture roughness on the fluid flow and heat transmission was evaluated, and the relationship between the fracture aperture and the joint roughness coefficient (JRC) is established. Finally, based on the exponential function between confining pressure and aperture, the influence of confining pressure on the heat‐flow coupling process is considered in the improved model. Besides, the reliability of the model was verified by comparing with the analytical solution of the two‐dimensional single‐fracture heat‐flow coupling problem. The results show that under the same conditions, considering the correlation between the geometric parameters of the fracture, the seepage and heat transfer rates of the model increased, the outlet boundary flow reached the maximum value, and the average outlet temperature dropped rapidly. However, the fracture roughness reduces the outlet flow rate and the decline rate of average temperature. The confining pressure will lead to a decrease of about 3.5% in the outlet flow of the model, which is consistent with the seepage law in practical engineering. The model presented in this paper is an effective supplement to the two‐dimensional fracture network heat‐flow coupling model and can provide a theoretical basis and a numerical calculation tool for related underground rock mass engineering. [ABSTRACT FROM AUTHOR]

An accurate state of charge (SOC) can provide effective judgment for the BMS, which is conducive for prolonging battery life and protecting the working state of the entire battery pack. In this study, the first-order RC battery model is used as the research object and two parameter identification methods based on the least square method (RLS) are analyzed and discussed in detail. The simulation results show that the model parameters identified under the Federal Urban Driving Schedule (HPPC) condition are not suitable for the Federal Urban Driving Schedule (FUDS) condition. The parameters of the model are not universal through the HPPC condition. A multitimescale prediction model is also proposed to estimate the SOC of the battery. That is, the extended Kalman filter (EKF) is adopted to update the model parameters and the adaptive unscented Kalman filter (AUKF) is used to predict the battery SOC. The experimental results at different temperatures show that the EKF-AUKF method is superior to other methods. The algorithm is simulated and verified under different initial SOC errors. In the whole FUDS operating condition, the RSME of the SOC is within 1%, and that of the voltage is within 0.01 V. It indicates that the proposed algorithm can obtain accurate estimation results and has strong robustness. Moreover, the simulation results after adding noise errors to the current and voltage values reveal that the algorithm can eliminate the sensor accuracy effect to a certain extent. [ABSTRACT FROM AUTHOR]

• Nonhomogeneous poisson distribution and annealing arithmetic was used to realize the clustering phenomenon of fractures. • The support-based connection was used to reduce the uncertainty errors caused by the lack of data. • Optimization of connectivity evaluation by considering the correlation between fracture parameters. • The potential seepage path can be predicted by this extended method, which is important for engineering applications. Connectivity evaluation of fracture networks is important in the design, assessment, and development of reservoirs in various engineering applications involving geothermal exploitation and the petroleum industry. By employing nonhomogeneous Poisson distribution and annealing arithmetic, this study generates fracture networks that fit well with actual outcrop fracture data. Based on Allard's definition of the connectivity index, a weighted factor is introduced, and an extended connectivity evaluation method is proposed to consider the effects of the aperture and its correlation with trace length. The results of the analysis show that the extended method improves the accuracy and reliability of connectivity evaluation compared with the traditional method. Moreover, the extended method is effective and accurate at predicting potential preferential flow paths in a practical example of the Dragon and Tiger Mountain (Jiangxi, China), and can better show the anisotropy with a change in the aperture. Hence, the proposed method extends the function of connectivity analysis and can benefit well location optimization in geothermal or petroleum exploration. [ABSTRACT FROM AUTHOR]

Connectivity is an effective indicator to describe the flow paths and mechanical behavior of reservoir fractured rock masses. The connectivity evaluation of fracture networks plays an important role in the design, assessment, and development of reservoirs in several important engineering applications, such as geothermal recovery and petroleum industry. Based on Allard's definition of a connectivity index, a 3D connectivity evaluation method is proposed in this study by building the connectivity functions of the supports. Meanwhile, different connectivity functions are built for different situations. In addition, a convex polygon is used to simulate the fracture to make the fracture network as real as possible. The accuracy of the generated fracture network was verified by comparing three parameters of fracture, and the results showed that the relative error was less than 5%. Some examples in the Ordos Basin, China, are given to verify the correctness of the program and method. Analysis results show that the 3D method is more realistic than the 2D connectivity evaluation, and the connectivity field of the fracture network is more reliable in the 3D method. Moreover, the proposed method can show the potential preferential flow path in a stereoscopic manner and thus greatly extends the function of connectivity analysis. This method provides important information for the prediction of paths and the evaluation of the connectivity of the fracture network and is important in evaluating the optimal location of geothermal recovery and petroleum industry. [ABSTRACT FROM AUTHOR]

To address the problems of low efficiency and high fuel consumption during the cold start and warm-up processes of internal combustion engines, a series hybrid electric vehicle was selected as the research object and two optimal control strategies were designed. A bench test was performed to determine the following: (a) the influence of engine coolant temperature on effective thermal efficiency; and (b) the relationship between engine operating conditions and coolant temperature increase rate. On the basis of the test results, two sets of warm-up process optimization control strategies were designed using a dynamic programming method and a fuzzy control method based on equivalent consumption minimization strategy (ECMS). The test results show that the fuzzy control method for the coolant temperature can effectively shorten the time required to warm up the engine, and the energy consumption of warm-up process can be reduced by nearly 10% through the dynamic programming method. [ABSTRACT FROM AUTHOR]

An accurate state-of-charge (SOC) can not only provide a safe and reliable guarantee for the entirety of equipment but also extend the service life of the battery pack. Given that the chemical reaction inside the lithium-ion battery is a highly nonlinear dynamic system, obtaining an accurate SOC for the battery management system is very challenging. This paper proposed a gated recurrent unit recurrent neural network model with activation function layers (GRU-ATL) to estimate battery SOC. The model used deep learning technology to establish the nonlinear relationship between current, voltage, and temperature measurement signals and battery SOC. Then the online SOC estimation was carried out on different testing sets using the trained model. The experiments in this paper showed that the GRU-ATL network model could realize online SOC estimation under different working conditions without relying on an accurate battery model. Compared with the gated recurrent unit recurrent neural (GRU) network model and long short-term memory (LSTM) network model, the GRU-ATL network model had more stable and accurate SOC prediction performance. When the measurement data contained noise, the experimental results showed that the SOC prediction accuracy of GRU-ATL model was 0.1–0.4% higher than the GRU model and 0.3–0.7% higher than the LSTM model. The mean absolute error (MAE) of SOC predicted by the GRU-ATL model was stable in the range of 0.7–1.4%, and root mean square error (RMSE) was stable between 1.2–1.9%. The model still had high prediction accuracy and robustness, which could meet the SOC estimation in complex vehicle working conditions. [ABSTRACT FROM AUTHOR]

Vehicle detection is an indispensable part of environmental perception technology for smart cars. Aiming at the issues that conventional vehicle detection can be easily restricted by environmental conditions and cannot have accuracy and real-time performance, this article proposes a front vehicle detection algorithm for smart car based on improved SSD model. Single shot multibox detector (SSD) is one of the current mainstream object detection frameworks based on deep learning. This work first briefly introduces the SSD network model and analyzes and summarizes its problems and shortcomings in vehicle detection. Then, targeted improvements are performed to the SSD network model, including major advancements to the basic structure of the SSD model, the use of weighted mask in network training, and enhancement to the loss function. Finally, vehicle detection experiments are carried out on the basis of the KITTI vision benchmark suite and self-made vehicle dataset to observe the algorithm performance in different complicated environments and weather conditions. The test results based on the KITTI dataset show that the mAP value reaches 92.18%, and the average processing time per frame is 15 ms. Compared with the existing deep learning-based detection methods, the proposed algorithm can obtain accuracy and real-time performance simultaneously. Meanwhile, the algorithm has excellent robustness and environmental adaptability for complicated traffic environments and anti-jamming capabilities for bad weather conditions. These factors are of great significance to ensure the accurate and efficient operation of smart cars in real traffic scenarios and are beneficial to vastly reduce the incidence of traffic accidents and fully protect people's lives and property. [ABSTRACT FROM AUTHOR]

Pedestrian detection is an important aspect of the development of intelligent vehicles. To address problems in which traditional pedestrian detection is susceptible to environmental factors and are unable to meet the requirements of accuracy in real time, this study proposes a pedestrian detection algorithm for intelligent vehicles in complex scenarios. YOLOv3 is one of the deep learning-based object detection algorithms with good performance at present. In this article, the basic principle of YOLOv3 is elaborated and analyzed firstly to determine its limitations in pedestrian detection. Then, on the basis of the original YOLOv3 network model, many improvements are made, including modifying grid cell size, adopting improved k-means clustering algorithm, improving multi-scale bounding box prediction based on receptive field, and using Soft-NMS algorithm. Finally, based on INRIA person and PASCAL VOC 2012 datasets, pedestrian detection experiments are conducted to test the performance of the algorithm in various complex scenarios. The experimental results show that the mean Average Precision (mAP) value reaches 90.42%, and the average processing time of each frame is 9.6 ms. Compared with other detection algorithms, the proposed algorithm exhibits accuracy and real-time performance together, good robustness and anti-interference ability in complex scenarios, strong generalization ability, high network stability, and detection accuracy and detection speed have been markedly improved. Such improvements are significant in protecting the road safety of pedestrians and reducing traffic accidents, and are conducive to ensuring the steady development of the technological level of intelligent vehicle driving assistance. [ABSTRACT FROM AUTHOR]

This study designs an active equilibrium control strategy based on model predictive control (MPC) for series battery packs. To shorten equalisation time and reduce unnecessary energy consumption, bidirectional active equalisation is modelled and analysed, and the model predictive control algorithm is then applied to the established state space equation. The optimisation problem that minimises the equilibrium time is transformed to a linear programming form in each cycle. By solving the linear programming problem online, a group of control optimal solutions is found and the series equalisation problem is decoupled. The equalisation time is shortened by dynamically adjusting the equalisation current. Simulation results show that the MPC algorithm can avoid unnecessary energy transfer and shorten equalisation time. The bench experimental result shows that the equilibrium time is reduced by 31%, verifying the rationality of the MPC strategy. [ABSTRACT FROM AUTHOR]