A comparative study on the corrosion resistance of NiFe2O4 ceramic inert anode for aluminum electrolysis prepared in the different sintering atmosphere was carried out in Na3AlF6–Al2O3 melt. The results show that the corrosion rates of NiFe2O4 ceramic inert anodes prepared in the vacuum and the atmosphere with oxygen content of 1×10–2 are 6.08 cm/a and 2.59 cm/a, respectively. A densification layer is formed at the surface of anode due to some reactions which produce aluminates. For the anode prepared in the atmosphere with oxygen content of 1×10–2, the thickness of the densification layer (about 50 μm) is thicker than that (about 20 μm) formed at the surface of anode prepared in the vacuum. The content of NiO and Fe(II) in Ni(II)xFe(II)1–xFe(III)2O4 increases with the decrease of the oxygen content of sintering atmosphere, which reduces the corrosion resistance of the material.
SiC foam ceramic reinforced aluminum matrix composites (SFCAMCs) were prepared by squeeze casting aluminum alloy (Al–23Si) into the SiC foam ceramic with different pore sizes, and the corrosion behavior of the SFCAMCs was studied in NaCl solutions. Static immersion corrosion tests were conducted at 20 °C, 50 °C and 80 °C, respectively. Corrosion morphology and products were analyzed by scanning electron microscope, energy dispersive system and X-ray diffraction. It was found that the corrosion rate of SFCAMCs increases as the temperature rising, and the bigger pore size of SiC foam ceramic reinforcement, the better corrosion resistance of SFCAMCs.
The desorption test was conducted to evaluate the desorption behavior of Pb(II) and Cd(II) using citric acid. The influential factors that were considered included initial Pb(II), Cd(II) contamination levels in soil, concentration of citric acid, reaction time, soil pH value and ionic strength. The test results indicated that the desorption was a rapid reaction (less than 6 h), and the removal percentages of Cd(II) and Pb(II) increased with the increasing contamination levels, concentration of citric acid and the addition of Na+, Ca2+, Cl–. However, the desorption of Pb(II) and Cd(II) decreased with the addition of SO42– because of the precipitation in the form of MSO4(s). The high pH condition indicated a negative effect on Pb(II) desorption. The removal percentage decreased from 71.39% to 10.9% as pH increased from 2 to 10.8. The desorption behavior predicted by Visual MINTEQ was in good agreement with the experimental testing result. The results of X-ray diffraction (XRD), X-ray fluorescence (XRF) and N2-BET adsorption test demonstrated that the desorption behavior of heavy metals (i.e., Pb(II) and Cd(II)) was controlled by the affinity of sorption sites for heavy metals, the competition of H+, Ca2+, Na+, Cl– and the chelating of organic ligands.
Penicillium simplicissimum was cultured and preserved on the potato dextrose agar (PDA) medium. PDA-RBBR (Remazal Brilliant Blue R) medium was used for the screening of the strains, which is able to produce enzymes. After the mutation process in Penicillium simplicissimum induced by chemical reagent and ultraviolet radiation, a high laccase-producing strains Penicillium simplicissimum was obtained. When 5 mL diethyl sulfate (2%) was mixed along with 5 mL spore suspension for 30 min, chemical mutagenesis reached its best condition. And the optimum conditions of UV mutagenesis were that spore suspension was irradiated for 4 min under 15 W UV lamp at a distance of 30 cm. The highest activity of C5E4 strains was 4.80 U/g over 18% higher than the maximum laccase activity of original microorganism. Five generations of the mutant strains were cultured, and the laccase activity of the strains was measured. The result showed that C5E4 strains can product laccase of the five subcultures stably.
The chemical compositions, mineralogical characteristics, as well as dissemination of iron- and phosphorus-based minerals were studied for the E’xi oolitic hematite from western Hubei Province in China by using chemical analysis, optical microscope, electron probe micro-analyzer (EPMA) and energy dispersive spectroscopy (EDS). It is found that this kind of oolitic hematite ore contains 47.71% TFe, 10.96% SiO2, as well as 0.874% P, with hematite as the dominant Fe-bearing minerals, and quartz, chamosite, illite and cellophane as main gangue minerals. The microscope examination showed that the ore has an oolitic structure, with some ooids principally formed by a series of concentric layers of hematite collophanite around nucleus that is hematite in the association with collophanite. Based on the EPMA and EDS analysis, it can be known that some ooids are primarily composed of hematite and collophanite. The separation can be achieved through fine grinding for those collophanite laminae with a higher P content. However, the dissemination of two minerals at the interface will result in the difficulty in effective separation. Besides, some ooids are made of chamosite with some nucleus formed of quartz, which is principally finely disseminated with hematite. In view of the close association and dissemination of iron- and phosphorus-based minerals in the ooids, it is found that the process of stage-grindings and stage-separations can be adopted to effectively increase the iron recovery and decrease the P content in the concentrate to some extent.
This paper focuses on the distributed parameter modeling of the zinc electrowinning process (ZEWP) to reveal the spatiotemporal distribution of concentration of zinc ions (CZI) and sulfuric acid (CSA) in the electrolyte. Considering the inverse diffusion of such ions in the electrolyte, the dynamic distribution of ions is described by the axial dispersion model. A parameter estimation strategy based on orthogonal approximation has been proposed to estimate the unknown parameters in the process model. Different industrial data sets are used to test the effectiveness of the spatiotemporal distribution model and the proposed parameter estimation approach. The results demonstrate that the analytical model can effectively capture the trends of the electrolysis reaction in time and thus has the potential to implement further optimization and control in the ZEWP.
Surface strain fields of the designed compact tension (CT) specimens were investigated by digital image correlation (DIC) method. An integrative computer program was developed based on DIC algorithms to characterize the strain fields accurately and graphically. Strain distribution of the CT specimen was predicted by finite element method (FEM). Good agreement is observed between the surface strain fields measured by DIC and predicted by FEM, which reveals that the proposed method is practical and effective to determine the strain fields of CT specimens. Moreover, strain fields of the CT specimens with various compressive loads and notch diameters were studied by DIC. The experimental results can provide effective reference to usage of CT specimens in triaxial creep test by appropriately selecting specimen and experiment parameters.
Deformation characteristics and constitutive model of seafloor massive sulfide (SMS) were selected as the research object. Uniaxial/triaxial compression test were carried out on the mineral samples, and the deformation characteristics of specimens under various conditions were studied. According to characteristics of the mineral, a new three stages constitutive equation was proposed. The conclusions are as follows: The axial strain, peak strain and maximum strength of seafloor massive sulfide increase with the confining pressure. The elastic modulus of the metal sulfide samples is decreased sharply with the increase of confining pressure. According to characteristics of seafloor massive sulfide, the constitutive equation is divided into three parts, the comparison between theoretical curves and experimental data shows that both of them are in good agreement, which also proves the correctness of the constitutive equation for uniaxial compression.
The design of servo controllers for flexible ball screw drives with matched and mismatched disturbances and uncertainties is focused to improve the tracking performance and bandwidth of ball screw drives. A two degrees of freedom mass model is established based on the axial vibration characteristics of the transport ball screw, and the controller of an adaptive integral sliding mode is proposed combining the optimal design of state feedback gain matrix K to restrain the vibration and the matched disturbances and uncertainties. Then for the counteraction of the mismatched disturbances and uncertainties, a nonlinear disturbance observer is also developed. The trajectory tracking performance experiments and bandwidth analysis were conducted on experimental setup with the proposed control method. It is proved that the adaptive integral sliding mode controller has a high tracking performance and bandwidth especially for the axial vibration characteristics model of ball screw drives. And the ball screw tracking accuracy also has a considerable improvement with the application of the proposed nonlinear disturbance observer.
Nanoparticles are increasingly being used to improve the friction and wear performance of polymers. In this study, we investigated the tribological behavior and energy dissipation characteristics of nano-Al2O3-reinforced polytetrafluoroethylene-polyphenylene sulfide (PTFE-PPS) composites in a sliding system. The tribological behaviors of the composites were evaluated under different normal loads (100–300 N) at a high linear velocity (2 m/s) using a block-on-ring tester. Addition of the nano-Al2O3 filler improved the antiwear performance of the PTFE-PPS composites, and the friction coefficient increased slightly. The lowest wear rate was obtained when the nano-Al2O3 content was 3% (volume fraction). Further, the results indicated a linear correlation between wear and the amount of energy dissipated, even though the wear mechanism changed with the nano-Al2O3 content, independent of the normal load applied.
This work deals with analysis of dynamic behaviour of hydraulic excavator on the basis of developed dynamic-mathematical model. The mathematical model with maximum five degrees of freedom is extended by new generalized coordinate which represents rotation around transversal main central axis of inertia of undercarriage. The excavator is described by a system of six nonlinear, nonhomogenous differential equations of the second kind. Numerical analysis of the differential equations has been done for BTH-600 hydraulic excavator with moving mechanism with pneumatic wheels.
In the Raymond mill grinding processes, high-accuracy control for the current of Raymond mill is vital to enhance the product quality and production efficiency as well as cut down the consumption of spare parts. However, strong external disturbances, such as variations of ore hardness and ore size, always exist. It is not easy to make the current of Raymond mill constant due to these strong disturbances. Several control strategies have been proposed to control the grinding processes. However, most of them (such as PID and MPC) reject disturbances merely through feedback regulation and do not deal with the disturbances directly, which may lead to poor control performance when strong disturbances occur. To improve disturbance rejection performance, a control scheme based on PI and disturbance observer is proposed in this work. The scheme combines a feedforward compensation part based on disturbance observer and a feedback regulation part using PI. The test results illustrate that the proposed method can obtain remarkable superiority in disturbance rejection compared with PI method in the Raymond mill grinding processes.
An improved model predictive control algorithm is proposed for Hammerstein-Wiener nonlinear systems. The proposed synthesis algorithm contains two parts: offline design the polytopic invariant sets, and online solve the min-max optimization problem. The polytopic invariant set is adopted to replace the traditional ellipsoid invariant set. And the parameter-correlation nonlinear control law is designed to replace the traditional linear control law. Consequently, the terminal region is enlarged and the control effect is improved. Simulation and experiment are used to verify the validity of the wind tunnel flow field control algorithm.
Due to development of distribution systems and increase in electricity demand, the use of capacitor banks increases. From the other point of view, nonlinear loads generate and inject considerable harmonic currents into power system. Under this condition if capacitor banks are not properly selected and placed in the power system, they could amplify and propagate these harmonics and deteriorate power quality to unacceptable levels. With attention of disadvantages of passive filters, such as occurring resonance, nowadays the usage of this type of harmonic compensator is restricted. On the other side, one of parallel multi-function compensating devices which are recently used in distribution system to mitigate voltage sag and harmonic distortion, performs power factor correction, and improves the overall power quality as active power conditioner (APC). Therefore, the utilization of APC in harmonic distorted system can affect and change the optimal location and size of shunt capacitor bank under harmonic distortion condition. This paper presents an optimization algorithm for improvement of power quality using simultaneous optimal placement and sizing of APC and shunt capacitor banks in radial distribution networks in the presence of voltage and current harmonics. The algorithm is based on particle swarm optimization (PSO). The objective function includes the cost of power losses, energy losses and those of the capacitor banks and APCs.
A new chaotic image encryption scheme based on permutation and substitution in the Fourier domain is presented. Fractional Fourier Transform (FRFT) is used before the encryption scheme to get a large degree of randomization. The permutation is achieved by Baker map and the substitution by a key-related-to-plain-image algorithm based on the modified Logistic map. Modification of the Logistic map is developed to increase the space of the encryption key, and hence increase the security. The key of the encryption algorithm dependents on the plain image, and thus, the cipher image is sensitive to both the initial key and the plain image to resist known-plaintext and chosen plaintext attacks. The key space is large and hence the algorithm can effectively resist brute-force attacks. The proposed scheme is examined using different performance evaluation metrics and the results prove that the proposed scheme is highly secure, and it can effectively resist different attacks.
Since the amplitude and frequency of irregular waves change with time, great difficulties are brought for solving ship load responses in random waves. To take the effect of various frequencies of irregular waves into consideration in load responses of hull, the wave memory effect is necessary. A semi-analytical method is introduced for the time-domain retardation functions, and then a nonlinear hydroelastic method considering memory effect for ships in irregular waves is proposed. Segmented self-propelling model experiments of a container ship were carried out in a towing tank, a ship motion measuring device for self-propelling model test was designed. Whipping responses of the ship in regular and irregular waves are analyzed. Finally, the calculation results are compared with those measured by segmented model experiments, and the result indicates that the memory effect has little effect on load responses of ship in regular waves, but pronounced effect on results in irregular waves. Moreover, the presented method is reasonable for the prediction of ship load responses in irregular waves.
Crowd behaviors analysis is the ‘state of art’ research topic in the field of computer vision which provides applications in video surveillance to crowd safety, event detection, security, etc. Literature presents some of the works related to crowd behavior detection and analysis. In crowd behavior detection, varying density of crowds and motion patterns appears to be complex occlusions for the researchers. This work presents a novel crowd behavior detection system to improve these restrictions. The proposed crowd behavior detection system is developed using hybrid tracking model and integrated features enabled neural network. The object movement and activity in the proposed crowded behavior detection system is assessed using proposed GSLM-based neural network. GSLM based neural network is developed by integrating the gravitational search algorithm with LM algorithm of the neural network to increase the learning process of the network. The performance of the proposed crowd behavior detection system is validated over five different videos and analyzed using accuracy. The experimentation results in the crowd behavior detection with a maximum accuracy of 93% which proves the efficacy of the proposed system in video surveillance with security concerns.
The investigation of supporting pressure is of great significance to the design of underground structures. Based on the kinematical approach of limit analysis, an improved failure mechanism is proposed, and the supporting pressure is investigated for deep buried cavity. Three failure mechanisms are first introduced according to the existing failure mechanisms of geotechnical structures of limit analysis. A comparison with respect to the optimal failure mechanisms and the upper bound solutions provided among these three mechanisms are then conducted in an attempt to obtain the improved failure mechanism. The results provided by the improved failure mechanism are in good agreement with those by the existing method, the numerical solution and field monitoring, which demonstrates that the proposed failure mechanism is effective for the upper bound analysis of supporting pressure.
When mining metal mines with steep structure planes by the caving method, there is a mechanical model in which the horizontal stress on the rock mass is simplified as a column before surface subsidence. The model is used to deduce critical support load and limiting column length for a given horizontal stress and support pressure. Considering the impact of the column effect, a method is proposed to determine the movement of the ground and caving area in a mine. After surface subsidence, the horizontal stress on a surrounding rock mass can be simplified to a cantilever beam mechanical model. Expressions for its bending fracture length are deduced, and a method is given to determine its stability. On this basis, an explanation for the large ground movement and subsidence scope was given. A case study shows that the damage effect of column and cantilever beam is significant for ground movement in metal-ore mine, and an appropriate correction value should be applied when designing for its angle of ground movements.
Rock burst is a kind of geological disaster in rock excavation of high stress areas. To evaluate intensity of rock burst, the maximum shear stress, uniaxial compressive strength, uniaxial tensile strength and rock elastic energy index were selected as input factors, and burst pit depth as output factor. The rock burst prediction model was proposed according to the genetic algorithms and extreme learning machine. The effect of structural surface was taken into consideration. Based on the engineering examples of tunnels, the observed and collected data were divided into the training set, validation set and prediction set. The training set and validation set were used to train and optimize the model. Parameter optimization results are presented. The hidden layer node was 450, and the fitness of the predictions was 0.0197 under the optimal combination of the input weight and offset vector. Then, the optimized model is tested with the prediction set. Results show that the proposed model is effective. The maximum relative error is 4.71%, and the average relative error is 3.20%, which proves that the model has practical value in the relative engineering.
In order to investigate the characteristics of particle-induced pressure loss in the solid–liquid lifting pipe, a series of experiments were conducted in 200 mm diameter lifting pipe. Simulation manganese nodules with five different mean diameters of 10 mm, 20 mm, 30 mm, 40 mm and 50 mm were used, both in isolation and a combination in equal fraction by mass. The flow velocities in the lifting pipe ranged from 0.12 m/s to 1.61 m/s, and the mass of particles employed was 10 kg for each particle diameter. Three regimes, wavy bed, partly fluidization, and fully fluidization, were observed over the flow velocity. The solid–liquid pressure drop data were measured by differential pressure transmitter, and pressure drop caused by the solid particles was calculated and analyzed. The results show that the evolutions of the pressure loss due to solid particles are relevant to the solid–liquid flow regimes, and they are distinctly influenced by fluid velocity and particle size.
Geogrid has been extensively used in geotechnical engineering practice due to its effectiveness and economy. Deep insight into the interaction between the backfill soil and the geogrid is of great importance for proper design and construction of geogrid reinforced earth structures. Based on the calibrated model of sand and geogrid, a series of numerical pullout tests are conducted using PFC3D under special considerations of particle angularity and aperture geometry of the geogrid. In this work, interface characteristics regarding the displacement and contact force developed among particles and the deformation and force distribution along the geogrid are all visualized with PFC3D simulations so that new understanding on how geogrid-soil interaction develops under pullout loads can be obtained. Meanwhile, a new variable named fabric anisotropy coefficient is introduced to evaluate the inherent relationship between macroscopic strength and microscopic fabric anisotropy. A correlation analysis is adopted to compare the accuracy between the newly-proposed coefficient and the most commonly used one. Furthermore, additional pullout tests on geogrid with four different joint protrusion heights have been conducted to investigate what extent and how vertical reinforcement elements may result in reinforcement effects from perspectives of bearing resistance contribution, energy dissipation, as well as volumetric response. Numerical results show that both the magnitude and the directional variation of normal contact forces govern the development of macroscopic strength and the reinforcing effects of joint protrusion height can be attributed to the accelerated energy dissipation across the particle assembly and the intensive mobilization of the geogrid.
Actual sandstone micromodel was used in this work to conduct the microscopic waterflooding experiment of ultra-low sandstone reservoir, since the inside seepage characteristics of microscopic waterflooding process of Chang 8 ultra-low permeability sandstone reservoir of Upper Triassic Yanchang formation in Huaqing region of the Ordos Basin, China is difficult to observe directly. Combined with physical property, casting thin sections, constant-rate mercury injection capillary pressure and nuclear magnetic resonance, the influence of reservoir property on the waterflooding characteristics in pores were analyzed and evaluated. Seepage paths of waterflooding characteristics were divided into four types: homogeneous seepage, reticular-homogeneous seepage, finger-reticular seepage and finger-like seepage, the waterflooding efficiency of which decreases in turn. More than 70% of residual oil occurs as flowing-around seepage and oil film. Physical property, pore structure and movable fluid characteristics are all controlled by digenesis and their impacts on waterflooding efficiency are in accordance. Generally, the pore throat radius size and distribution and movable fluid percentage are closely related to waterflooding law.
In order to study the bearing capacity and stability behavior of cold-formed steel flexural members with complicated sections, a total of 12 specimens divided into 6 groups were tested, including 3 groups of pure bending tests and non-pure bending tests each. There were three types of sections considered in this investigation, including channels with complex edge stiffeners (called B1-section), Σ section with complex edge stiffeners (called B2-section), and channels with complex edge stiffeners and V-type web stiffeners (called B3-section). Local buckling, distortional buckling and interaction buckling between them were observed in tests. The experimental results indicate that the bending strengths of B2-section specimens were the largest of these three types of specimens under the same conditions. It is found that the bending strength of B2-section specimens was increased by 6.47% for pure bending state and 8.12% for non-pure bending state, compared with that of B1-section specimens. Bending strength of B3-section specimens was almost the same with that of B1-section specimens under pure bending, but a little smaller than that of B1-section under non-pure bending state. It is also shown that B2-section specimens have better plastic deformation behavior than the other two sections. In addition, a non-linear finite element model was presented and verified against tests. The finite element analysis results agree well with experimental bending strength and failure modes.
Hoek–Brown (HB) strength criterion can reflect rock’s inherent failure nature, so it is more suitable for analyzing the stability of rock slopes. However, the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb (EMC) strength parameters instead of the nonlinear HB strength criterion. Therefore, a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework. The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stress σ0 obtained without considering the effect of inter-slice forces, and it can satisfy all static equilibrium conditions of the sliding body, so the current method can obtain the reasonable and strict factor of safety (FOS) solutions. Compared with the results of other methods in some examples, the feasibility of the current method was verified. Meanwhile, the parametric analysis shows that the slope angle β has an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters. For β≤45°, both of the results are similar, showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability, but for β>60°, the differences of both the results are obvious, showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods, and then the current method should be used.
A new analytical solution for ground surface settlement induced by deep excavation is proposed based on the elastic half space Melan’s solution, and the analytical model is related to the physical and mechanical properties of soil with the loading and unloading action during excavation process. The change law of earth pressure of the normal consolidation soil after the foundation pit excavation was analyzed, and elastic displacement calculation methods of analytic solution were further established given the influence of excavation and unloading. According to the change of stress state in the excavation process of foundation pit, the planar mechanical analysis model of the foundation excavation problem was established. By combining this model with the physical equations and geometric equations of plane strain problem with consideration of the loading and unloading modulus of soil, constitutive equation of the plane strain problem was also established. The loading and unloading modulus formula was obtained by using the parameter calculation method in Duncan-Chang curve model. The constitutive equation obtained from the model was used to calculate the soil stress state of each point to determine its loading and unloading modulus. Finally, the foundation pit displacement change after excavation was calculated, and thus the soil pressure distribution after retaining structure deformation. The theoretical results calculated by making corresponding programs were applied to engineering practice. By comparing the conventional calculation results with monitoring results, the practicability and feasibility of the calculation model were verified, which should provide a theoretical basis for similar projects.
The coupled effect of viscosity enhancing admixtures (VEA) and superplasticizer (SP) on the rheological behavior of cement paste was investigated in this work. Two types of VEAs, including hydroxypropyl methylcellulose (HPMC) and Welan gum, and two types of SPs, i.e. polycarboxylate (PCA) and polynaphthalenesulfonate (PNS) were used as admixtures for cement paste. Rheological curves of cement paste and simulated pore solution containing VEA and SP were tested. Simulated pore solution test results show that molecules of different SPs may generate different effects on the viscosity of VEA solutions. Hershel-Bulkley (H-B) model was used to fit rheological curve of cement paste. Strong interaction between PNS and HPMC was observed in this work.
The performance-based passive control analysis of the Maxwell dampers between one 10-story and one 6-story adjacent RC frames is conducted in this work. Not only the optimal parameters but also the optimal arrangements of the Maxwell dampers are proposed based on the optimal target of making the total exceeding probability of the adjacent structures to be minimal. The applicability of the analytical expressions of the Maxwell damper damping parameters under different seismic performance targets are firstly examined and then the preferable damping parameters of the Maxwell dampers are proposed through the extensive parametric studies. Furthermore, the optimal arranging positions and optimal arranging numbers of the Maxwell dampers between the adjacent buildings are derived based on a large number of seismic fragility analyses, as well. The general arranging laws of the Maxwell dampers between the adjacent buildings are generated based on the discussion of the theoretical method through the simplified plane model. The optimal parameters and optimal arrangement of the Maxwell dampers presented make both the adjacent structures have preferable controlled effects under each seismic performance target which can satisfy the requirements of multi-performance seismic resistance of the modern seismic codes.
In order to investigate the energy absorption characteristics of multi-cell polygonal tubes with different cross-sectional configurations, firstly, the theoretical formulae of the mean crushing force under axial load for four multi-cell polygonal tubes were derived by combining the Super Folding Element theory with Zhang’s research results. These formulae can be used to validate the numerical model and quickly evaluate the energy absorption ability of multi-cell polygonal tubes. Furthermore, a comparative study on the energy absorption performance of eight multi-cell polygonal tubes under axial and oblique loads was conducted. The results show that all tubes have a stable mixed deformation mode under axial load. The multi-cell decagon tube has better energy-absorption ability compared with other tubes. When θ is less than 10°, all the tubes maintain a stable deformation mode, and the multi-cell decagon tube also has the biggest crushing force efficiency and specific energy absorption among these eight tubes; meanwhile compared with the results at θ=0°, the specific energy absorption of all tubes decreases by about 8%–21%, while the crushing force efficiency increases by 20%–56%. However, at large angles 20° and 30°, all of the tubes collapse in bending modes and lose their effectiveness at energy absorption.