The finite element model is established according to the experimental results, and then the experimental results are verified by simulation calculation. In terms of the combination of finite element analysis and experiment, the effect of particle size of CuO and SnO2 on the stress, strain and microstructure of AgCuOSnO2 composite during hot extrusion was studied. The results illustrate that with the decrease of particle size, the dispersion of the second phase increases gradually, while the possibility of “tail shrinkage” of the billet decreases continuously; cubic CuO will evolve to fibrosis, and the degree of fibrosis will increase with the decrease of the particle size and ring clusters. Specifically, the degree of fibrosis at the middle end of the billet is higher than that at the front end, the degree of fibrosis at the front end is higher than that at the back end, and the degree of fibrosis on the surface is higher than that in the core; part of CuO fibers will bend, and the degree of buckling strength is positively correlated with the size of particles and their annular clusters. Additionally, there is fiber CuO in the front and back end of the billet that are inconsistent with the extrusion direction, and the degree of difference was negatively correlated with the particle size.
To study the influence of B4C particle size on the microstructure and damping capacities of (B4C+Ti)/Mg composites, in situ reactive infiltration technique was utilized to prepare Mg-matrix composites. The microstructure, produced phases and damping capacities of the composites prepared with different particle size of B4C were characterized and analyzed. The results show that the reaction between B4C and Ti tends to be more complete when finer B4C particle was used to prepare the composites. But the microstructure of the as-prepared composites is more homogenous when B4C and Ti have similar particle size. The strain-dependent damping capacities of (B4C+Ti)/Mg composites improve gradually with the increase of strain amplitude, and composites prepared with coarser B4C particles tend to have higher damping capacities. The temperature-dependent damping capacities improve with increasing the measuring temperatures, and the kind of damping capacities of the composites prepared with 5 B4C are inferior to those of coarser particles. The dominant damping mechanism for the strain-damping capacity is dislocation damping and plastic zone damping, while that for the temperature-damping capacity is interface damping or grain boundary damping.
Fiber metal laminates (FMLs), a kind of lightweight material with excellent comprehensive performance, have been successfully applied in aerospace. FMLs reinforced with carbon fiber have better mechanical properties than those with glass or aramid fiber. However, carbon fiber binding metal may lead to galvanic corrosion which limits its application. In this paper, electrochemical methods, optical microscope and scanning electron microscope were used to analyze the corrosion evolution of carbon fiber reinforced aluminum laminate (CARALL) in corrosive environment and explore anti-corrosion ways to protect CARALL. The results show that the connection between carbon fiber and aluminum alloy changes electric potential, causing galvanic corrosion. The galvanic corrosion will obviously accelerate CARALL corroded in solution, leading to a 72.1% decrease in interlaminar shear strength, and the crevice corrosion has a greater impact on CARALL resulting in delamination. The reduction of interlaminar shear strength has a similar linear relationship with the corrosion time. In addition, the adhesive layers between carbon fiber and aluminum alloy cannot protect CARALL, while side edge protection can effectively slow down corrosion rate. Therefore, the exposed edges should be coated with anti-corrosion painting. CARALL has the potential to be used for aerospace components.
The highly-dispersed iron element decorated Ni foam was prepared by simple immersion in a ferric nitrate solution at room temperature without using acid etching, and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), EDAX spectrum (EDAX mapping) and Raman spectroscopy. The EDAX spectrum illustrated that iron element was highly-dispersed over the entire surface of nickel foam, and the Raman spectroscopy revealed that both Ni-O and Fe-O bonds were formed on the surface of the as-prepared electrode. Moreover, the iron element decorated Ni foam electrode can be used as non-enzymatic glucose sensor and it exhibits not only an ultra-wide linear concentration range of 1–18 mmol/L with an outstanding sensitivity of 1.0388 mA·mmol/(L·cm2), but also an excellent ability of stability and selectivity. Therefore, this work presents a simple yet effective approach to successfully modify Ni foam as non-enzymatic glucose sensor.
An excellent extraction selectivity towards Sc over other REEs in 4 mol/L HCl solution was achieved with the separation factor βSc/REEs over 8000 by 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester (HEHEHP) and the extraction equilibrium can be obtained within 20 min. The extracted Sc can be stripped using 5 mol/L NaOH solution as eluent at 363 K with the stripping rate of 92.1% obtained. The extraction mechanism was clearly elucidated by slope analysis, saturation extraction, IR, and NMR analysis. It was revealed that the extraction of Sc in 4 mol/L HCl solution is still dominated by cation exchange process between P—O—H and Sc, and coordination process between P=O and Sc, with 6 molecules of extractant as dimer participating in the process. Finally, a flowsheet for the recovery of Sc from ion-adsorption rare earth elements (REEs) concentrate was proposed and proved in lab-scale experiment.
In order to reduce the materials cost of COREX ironmaking process, sinter has been introduced into the composite burden in China. This work explored the reducing process of sinter in COREX shaft furnace to clarify its reduction properties change and then the effect of sinter proportion on metallurgical performance of composite burden was investigated. The results show that the reducing process of sinter in COREX shaft furnace was basically same with that in blast furnace but sinter seems like breaking faster. Under reducing condition simulated COREX shaft furnace, sinter possessed the worst reduction degradation index (RDI) and undifferentiated reduction index (RI) compared with pellet and iron ore lumps. Macroscopic and microscopic mineralogy changes indicated that sinter presents integral cracking while pellet and lump ore present surface cracking, and no simple congruent relationship exists between cracks of the burden and its ultimate reduction degradation performance. The existence of partial metallurgical performance superposition between composite and single ferrous burden was confirmed. RDI+6.3≥70% and RDI+3.15≥80% were speculated as essential requirements for the composite burden containing sinter in COREX shaft furnace.
The qualitative relationship between hydrogen concentration and notch tensile strength has been investigated for 5Ni-16Cr-Mo steel with different strength. The notch tensile strength was determined by means of slow strain rate test (SSRT) on circumferentially notched round bar specimens with the notch root radius of 0.15 mm after hydrogen charging. Meanwhile, the hydrogen diffusion behaviors of various strength steel were studied by thermal desorption spectroscopy (TDS) analysis. The SSRT results show that the T460 steel has higher susceptibility of hydrogen embrittlement in contrast with T520 steel. The activation energies and microstructure indicate that the dislocations and interfaces of martensitic laths are hydrogen traps in 5Ni-16Cr-Mo steel. By SSRT, the elastic limit of charged specimen loaded in air is higher than the flow stress without hydrogen charging before unloading, while the difference is defined as hydrogen-induced stress. The value of hydrogen-induced stress σ* increases linearly with hydrogen concentration: σ*=−0.622+2.015C0. The finite element analysis results of stress distributions near the notch tip have shown that the maximum principal stress increases with the notch root radius decreasing.
The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism. Therefore, we established the dynamic model of a 3RSR (R is the revolute joint and S is the spherical joint) parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method. The standard quaternion was introduced in the constraint equation, and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model. The simulation results were compared and analyzed with the numerical results. The geometrical parameters of the worn ball socket were solved based on the Archard wear model, and the geometrical reconstruction of the worn surface was carried out. The geometric reconstruction parameters were substituted into the dynamic model, which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance. The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force. The long-term wear will increase the fluctuation of the contact force, thereby decreasing the movement stability of the mechanism.
With the warming up and continuous development of machine learning, especially deep learning, the research on visual question answering field has made significant progress, with important theoretical research significance and practical application value. Therefore, it is necessary to summarize the current research and provide some reference for researchers in this field. This article conducted a detailed and in-depth analysis and summarized of relevant research and typical methods of visual question answering field. First, relevant background knowledge about VQA(Visual Question Answering) was introduced. Secondly, the issues and challenges of visual question answering were discussed, and at the same time, some promising discussion on the particular methodologies was given. Thirdly, the key sub-problems affecting visual question answering were summarized and analyzed. Then, the current commonly used data sets and evaluation indicators were summarized. Next, in view of the popular algorithms and models in VQA research, comparison of the algorithms and models was summarized and listed. Finally, the future development trend and conclusion of visual question answering were prospected.
Visual background extraction algorithm (ViBe) uses the first frame image to initialize the background model, which can easily introduce the “ghost”. Because ViBe uses the fixed segmentation threshold to achieve the foreground and background segmentation, the detection results in many false detections for the highly dynamic background. To solve these problems, an improved ghost suppression and adaptive Visual Background Extraction algorithm is proposed in this paper. Firstly, with the pixel’s temporal and spatial information, the historical pixels of a certain combination are used to initialize the background model in the odd frames of the video sequence. Secondly, the background sample set combined with the neighborhood pixels are used to determine a complex degree of the background, to acquire the adaptive segmentation threshold. Thirdly, the update rate is adjusted based on the complexity of the background. Finally, the detected result goes through a post-processing to achieve better detection results. The experimental results show that the improved algorithm will not only quickly suppress the “ghost”, but also have a better detection in a complex dynamic background.
In the age of online workload explosion, cloud users are increasing exponentialy. Therefore, large scale data centers are required in cloud environment that leads to high energy consumption. Hence, optimal resource utilization is essential to improve energy efficiency of cloud data center. Although, most of the existing literature focuses on virtual machine (VM) consolidation for increasing energy efficiency at the cost of service level agreement degradation. In order to improve the existing approaches, load aware three-gear THReshold (LATHR) as well as modified best fit decreasing (MBFD) algorithm is proposed for minimizing total energy consumption while improving the quality of service in terms of SLA. It offers promising results under dynamic workload and variable number of VMs (1–290) allocated on individual host. The outcomes of the proposed work are measured in terms of SLA, energy consumption, instruction energy ratio (IER) and the number of migrations against the varied numbers of VMs. From experimental results it has been concluded that the proposed technique reduced the SLA violations (55%, 26% and 39%) and energy consumption (17%, 12% and 6%) as compared to median absolute deviation (MAD), inter quartile range (IQR) and double threshold (THR) overload detection policies, respectively.
In this paper, an active fault-tolerant control (FTC) strategy of aerial manipulators based on non-singular terminal sliding mode (NTSM) and extended state observer (ESO) is proposed. Firstly, back-stepping technology is adopted as the control framework to ensure the global asymptotic stability of the closed-loop system. Next, the NTSM with estimated parameters of actuator faults is used as main robustness controller to deal with actuator faults. Then, the ESO is utilized to estimate and compensate the complex coupling effects and external disturbances. The Lyapunov stability theory can guarantee the asymptotic stability of aerial manipulators system with actuator faults and external disturbances. The proposed FTC scheme considers both actuator fault and modelling errors, combined with the adaptive law of actuator fault, which has better performance than traditional FTC scheme, such as NTSM. Finally, several comparative simulations are conducted to illustrate the effectiveness of the proposed FTC scheme.
The formation maintenance of multiple unmanned aerial vehicles (UAVs) based on proximity behavior is explored in this study. Individual decision-making is conducted according to the expected UAV formation structure and the position, velocity, and attitude information of other UAVs in the azimuth area. This resolves problems wherein nodes are necessarily strongly connected and communication is strictly consistent under the traditional distributed formation control method. An adaptive distributed formation flight strategy is established for multiple UAVs by exploiting proximity behavior observations, which remedies the poor flexibility in distributed formation. This technique ensures consistent position and attitude among UAVs. In the proposed method, the azimuth area relative to the UAV itself is established to capture the state information of proximal UAVs. The dependency degree factor is introduced to state update equation based on proximity behavior. Finally, the formation position, speed, and attitude errors are used to form an adaptive dynamic adjustment strategy. Simulations are conducted to demonstrate the effectiveness and robustness of the theoretical results, thus validating the effectiveness of the proposed method.
Ventilation system is significant in underground metal mine of alpine region. Reasonable evaluation of ventilation effectiveness will lead to a practical improvement for the maintenance and management of ventilation system. However, it is difficult to make an effective evaluation of ventilation system due to the lack of classification criteria with respect to underground metal mine in alpine region. This paper proposes a novel evaluation method called the cloud model-clustering analysis (CMCA). Cloud model (CM) is utilized to process collected data of ventilation system, and they are converted into cloud descriptors by CM. Cloud similarity (CS) based Euclidean distance (ED) is proposed to make clustering analysis of assessed samples. Then the classification of assessed samples will be identified by clustering analysis results. A case study is developed based on CMCA. Evaluation results show that ventilation effectiveness can be well classified. Moreover, CM is used alone to make comparison of evaluation results obtained by CMCA. Then the availability and validity of CMCA is verified. Meanwhile, difference of CS based ED and classical ED is analyzed. Two new clustering analysis methods are introduced to make comparison with CMCA. Then the ability of proposed CMCA to meet evaluation requirements of ventilation system is verified.
On the eve of the occurrence of geological hazards, part of the rock and soil body begins to burst, rub, and fracture, generating infrasound signals propagating outward. 3D advanced positioning of the landslide has remained unsolved, which is important for disaster prevention. Through the Fourier transform and Hankel transform of the wave equation in cylindrical coordinates, this work established a three-dimensional axisymmetric sound field model based on normal waves, and designed a 4-element helix triangular pyramid array with vertical and horizontal sampling capabilities. Based on this, the three-dimensional matching localization algorithm of infrasound for geological hazards is proposed. Applying the algorithm to the infrasound signal localization of rock and soil layers, it was found that the helix triangular pyramid array can achieve accurate estimation of depth and distance with a smaller number of array elements than the traditional array, and may overcome the azimuth symmetry ambiguity. This study shows the application prospects of this method for predicting geohazards position several hours in advance.
Sandstone oil reservoirs with huge bottom water and high permeability are generally developed with high flow rate. After long-term water flooding (LTWF), the water flooding characteristics are quite different from that of original reservoir. In this paper, the effects of the PV number, viscosity, and displacement rate during LTWF are studied through experiments. The mechanism is analyzed based on analysis of changes in oil composition, rock mineral composition and wettability. The oil-water relative permeability curves, oil recovery and wettability were obtained with new experiments methods, which avoids the oil metering error by measuring oil and water separately. The research indicates that when the viscosity increases, the water phase permeability decreases, the residual oil saturation increases, and the water content rate increases earlier. A higher water flooding rate results in a higher ultimate recovery. A higher asphaltene content results in a higher viscosity and more oil-wet reservoir conditions. After LTWF, the wettability tends to water-wet, which is more favorable for heavy oil recovery. Moreover, LTWF reduces the clay content, which creates a more water-wet surface and a larger reservoir pore throat environment. This research provides insightful characteristics of offshore sandstone oil reservoirs, which can be used to enhance oil recovery.
To study the energy storage and dissipation characteristics of deep rock under two-dimensional compression with constant confining pressure, the single cyclic loading-unloading two-dimensional compression tests were performed on granite specimens with two height-to-width (H/W) ratios under five confining pressures. Three energy density parameters (input energy density, elastic energy density and dissipated energy density) in the axial and lateral directions of granite specimens under different confining pressures were calculated using the area integral method. The experimental results show that, for the specimens with a specific H/W ratio, these three energy density parameters in the axial and lateral directions increase nonlinearly with the confining pressure as quadratic polynomial functions. Under constant confining pressure compression, the linear energy storage law of granite specimens in the axial and lateral directions was founded. Using the linear energy storage law in different directions, the elastic energy density in various directions (axial elastic energy density, lateral elastic energy density and total elastic energy density) of granite under any specific confining pressures can be calculated. When the H/W ratio varies from 1:1 to 2:1, the lateral compression energy storage coefficient increases and the corresponding axial compression energy storage coefficient decreases, while the total compression energy storage coefficient is almost independent of the H/W ratio.
A novel horizontal trap-door test system was devised in this study to analyze the face stability of shield tunnels in sands. The test system can be used to investigate both the longitudinal and cross sections of the face failure simultaneously at one single apparatus and was employed to perform face stability tests on small-scaled tunnel models at single gravity. The lateral support pressures and failure zones were studied with varying sand materials and earth covers. The results demonstrate that the tunnel face moves back, the lateral active earth pressure on the tunnel face decreases rapidly to a residual value, and the lateral pressure distribution can be categorized into three stages during the failure process: 1) initial state; 2) pressure dissipation stage; and 3) pressure zone diminution stage. Furthermore, face failure firstly develops from a stable condition to the local failure state, and then continues to develop to the global failure state that can be divided into two sub-zones with different failure mechanisms: rotational failure zone (lower zone) and gravitational failure zone (upper zone). Further discussion shows that under the effects of soil arching, the shape of the gravitational failure zone can adopt arch shaped (most frequent) and column shaped (in shallow tunnels). Limit support pressure for face stability usually appears at δ/D=0.2%–0.5% (ratio of face displacement to tunnel diameter).
A case of Qinghuayuan tunnel excavation below the existing Beijing Subway Line 10 is presented. The new Qinghuayuan tunnel, part of the Beijing-Zhangjiakou High-speed Railway, was excavated by a shield machine with an outer diameter of 12.2 m. The existing subway was excavated by shallow tunnelling method. The project layout, geological conditions, reinforcement measures, operational parameters of shield machine and monitoring results of the project are introduced. During the Qinghuayuan tunnel excavation below the existing subway, total thrust, shield driving speed, cutterhead rotation speed and torque were manually controlled below the average values obtained from the previous monitoring of this project, which could effectively reduce the disturbance of the surrounding soil induced by shield excavation. The Gaussian fitting function can appropriately fit both the ground and the existing subway settlements. The trough width is influenced not only by the excavation overburden depth, but also by the forepoling reinforcement and tail void grouting measures.
The resilient modulus (MR) of subgrade soils is usually used to characterize the stiffness of subgrade and is a crucial parameter in pavement design. In order to determine the resilient modulus of compacted subgrade soils quickly and accurately, an optimized artificial neural network (ANN) approach based on the multi-population genetic algorithm (MPGA) was proposed in this study. The MPGA overcomes the problems of the traditional ANN such as low efficiency, local optimum and over-fitting. The developed optimized ANN method consists of ten input variables, twenty-one hidden neurons, and one output variable. The physical properties (liquid limit, plastic limit, plasticity index, 0.075 mm passing percentage, maximum dry density, optimum moisture content), state variables (degree of compaction, moisture content) and stress variables (confining pressure, deviatoric stress) of subgrade soils were selected as input variables. The MR was directly used as the output variable. Then, adopting a large amount of experimental data from existing literature, the developed optimized ANN method was compared with the existing representative estimation methods. The results show that the developed optimized ANN method has the advantages of fast speed, strong generalization ability and good accuracy in MR estimation.
It is important to calibrate micro-parameters for applying partied flow code (PFC) to study mechanical characteristics and failure mechanism of rock materials. Uniform design method is firstly adopted to determine the microscopic parameters of parallel-bonded particle model for three-dimensional discrete element particle flow code (PFC3D). Variation ranges of microscopic of the microscopic parameters are created by analyzing the effects of microscopic parameters on macroscopic parameters (elastic modulus E, Poisson ratio v, uniaxial compressive strength σc, and ratio of crack initial stress to uniaxial compressive strength σci/σc) in order to obtain the actual uniform design talbe. The calculation equations of the microscopic and macroscopic parameters of rock materials can be established by the actual uniform design table and the regression analysis and thus the PFC3D microscopic parameters can be quantitatively determined. The PFC3D simulated results of the intact and pre-cracked rock specimens under uniaxial and triaxial compressions (including the macroscopic mechanical parameters, stress–strain curves and failure process) are in good agreement with experimental results, which can prove the validity of the calculation equations of microscopic and macroscopic parameters.
As it is commonly known, the estimation of physical and mechanical characteristics of rocks is very important issue in various geotechnical projects. The characteristics are mainly influenced by the microfabric-texture features of rocks. In this research, dry unit weight, effective porosity, point load index, Schmidt rebound hardness, uniaxial compressive strength, and texture coefficient were measured with the aim of correlating the physical and mechanical properties to the texture coefficient. For this purpose, a comprehensive laboratory testing program was conducted after collecting twenty sedimentary block samples including nine limestones and eleven mudstones, taken from Kalidromo (central Greece) in accordance with ASTM and ISRM standards. Also, mineralogical and petrographic properties, textural characteristics as well as X-ray diffractions were studied and the obtained results were statistically described and analysed. The maximum and minimum values of the texture coefficient were 0.13 and 0.50, respectively. The highest value was obtained for the rocks with a large amount of grains. Regression analyses were used to investigate the relationships between the texture coefficient and the engineering properties. Thus, empirical equations were developed and because of the good determination coefficients, they showed that all of the engineering properties were well correlated to the texture coefficient.
Foundation settlement is of great significance for high-fill engineering in collapsible loess areas. To predict the construction settlement of Lüliang Airport located in Shanxi Province, China, a plane strain finite element method considering the linear variation in the modulus, was carried out in this paper based on the results of geotechnical tests. The stress and deformation of four typical sections caused by layered fill are simulated, and then the settlement of the high-fill airport is calculated and analyzed by inputting three sets of parameters. The relative soft parameters of loess geomaterials produce more settlement than the relatively hard parameters. The thicker the filling body is, the greater the settlement is. The filling body constrained by mountains on both sides produces less settlement than the filling body constrained by a mountain on only one side even the filling thickness is almost the same. The settlement caused by the original subbase accounts for 56%–77% of the total settlement, while the fill soils themselves accounts for 23%–44% of the total settlement, which is approximately consistent with the field monitoring results. It provides a good reference for predicting the settlement of similar high-fill engineering.
To study rock damage characteristics under long-term freeze-thaw cycles and loads, rock freeze-thaw and creep damage factors were defined based on nuclear magnetic resonance porosity and volume strain, respectively. The damage factor is introduced into the basic rheological element, and the non-linear creep damage constitutive model and freeze-thaw rock equation are established to describe non-linear creep characteristics under a constant load. Simultaneously, the creep test of freeze-thaw rock under step loading is performed. Based on the test data, the applicability and accuracy of the creep damage freeze-thaw rock model are analyzed and verified. The results show that freeze-thaw cycles result in continuous rock pore structure damage and deterioration, and nuclear magnetic resonance porosity enhancement. The constant load induces increasing rock plastic deformation, volume, and creep aging damage. As the loading stress increases, the instantaneous rock elastic parameters increase, and the rheological elastic and viscosity parameters decrease. Furthermore, the damage degradation of freeze-thaw cycles weakens the rock viscoplasticity, resulting in a rapid decrease in the viscosity parameter with an increase in freeze-thaw cycles. Generally, the continuous damage of the rock is degraded, and the long-term strength decreases continuously.
Due to the wide railway network and different characteristics of many earthquake zones in China, considering the running safety performance of trains (RSPT) in the design of high-speed railway bridge structures is very necessary. In this study, in order to provide the seismic design and evaluation measure of the bridge structure based on the RSPT, a calculation model of RSPT on bridge under earthquake was established, and the track surface response measure when the derailment coefficient reaches the limit value was calculated by referring to 15 commonly used ground motion (GM) intensity measures. Based on the coefficient of variation of the limit value obtained from multiple GM samples, the optimal measures were selected. Finally, the limit value of bridge seismic response based on RSPT with different train speeds and structural periods was determined.
Because of an unfortunate mistake during the production of this article, the initial printed versions and the online PDF had incorrect DOI numbers. The DOI has now been corrected and synchronized with the correct DOIs of the HTML versions.
Because of an unfortunate mistake during the production of this article, the initial printed versions and the online PDF had incorrect DOI numbers. The DOI has now been corrected and synchronized with the correct DOIs of the HTML versions.