Nonlocal continuum mechanics is a popular growing theory for investigating the dynamic behavior of Carbon nanotubes (CNTs). Estimating the nonlocal constant is a crucial step in mathematical modeling of CNTs vibration behavior based on this theory. Accordingly, in this study a vibration-based nonlocal parameter estimation technique, which can be competitive because of its lower instrumentation and data analysis costs, is proposed. To this end, the nonlocal models of the CNT by using the linear and nonlinear theories are established. Then, time response of the CNT to impulsive force is derived by solving the governing equations numerically. By using these time responses the parametric model of the CNT is constructed via the autoregressive moving average (ARMA) method. The appropriate ARMA parameters, which are chosen by an introduced feature reduction technique, are considered features to identify the value of the nonlocal constant. In this regard, a multi-layer perceptron (MLP) network has been trained to construct the complex relation between the ARMA parameters and the nonlocal constant. After training the MLP, based on the assumed linear and nonlinear models, the ability of the proposed method is evaluated and it is shown that the nonlocal parameter can be estimated with high accuracy in the presence/absence of nonlinearity.
The Fe-based coatings in powder form were deposited on a steel type E335 by flame spraying technique. The effects of the post heat treatment on the microstructure and the mechanical properties of sprayed coatings were studied. Post heat treatment was conducted in a furnace in air at 623 K, 823 K and 1023 K for 1 h and then cooled in air. The results showed that with the increase of annealing temperature, the microstructure of coating treated at 823 K and 1023 K had several changes as follows: the reduction of porosity, formation of carbides and oxides. It was found that the solid solution FCC (Fe, Ni), intermetallic compound AlFe3 and carbides [Fe, C] were the main phases for coatings as-sprayed and treated at 623 K and while iron carbide, molybdenum carbide and oxide as Fe3O4 became the main phases and reinforced the solid solution FCC (Fe, Ni) phase for annealed coatings at 823 K. However, it was observed the disappearance of molybdenum carbide and oxide Fe3O4 at 1023 K. The coating annealed at 823 K exhibited an excellent wear resistance than the as-sprayed and annealed coatings at 623 K and 1023 K and shows the lower wear rate than another coating treated or as sprayed.
The bubble behavior is one of the key factors for the design and the process of aluminum reduction cell using inert anode. A see-through cell is constructed to investigate the bubble flow behavior and the electrolyte flow pattern induced by bubbles. The test results show that the electrolyte is driven by the bubble to move around the cathode, and also some vortices occur in local areas. The bubble generated at the anode bottom undergoes the processes of formation, growth, sliding, detachment and coalescence. However, the bubble generated at the middle of anode detaches rapidly from the anode surface and moves upward and collides with other bubbles, which results in coalescence or break-up. Most bubbles are released into the atmosphere at the liquid surface, while some other bubbles taken by the electrolyte flush to the height higher than the mean horizontal level of the liquid and then drop down and move horizontally and they are released finally. Some bubbles are kept unbroken and are sliding on the electrolyte surface. The diameter of bubble generated at inert anode is smaller than that of bubble generated at graphite anode. Moreover, the bubbles on inert anode are spherical, which was different from those in tubular or disk form on graphite anode.
The microstructural evolution of 2026 aluminum alloy during homogenization treatment was investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results show that severe dendritic segregation exists in the as-cast 2026 alloy and the main secondary phases at grain boundary are S (Al2CuMg) and θ (Al2Cu) phases. Elements Cu, Mg and Mn distribute unevenly from grain boundary to the inside of as-cast alloy. With the increase of homogenization temperature or the prolongation of holding time, the residual phases gradually dissolve into the matrix α(Al) and all the elements become more homogenized. According to the results of microstructural evolution, differential scanning calorimetry and X-ray diffraction, the optimum homogenization parameter is at 490 °C for 24 h, which is consistent with the result of homogenization kinetic analysis.
In this study, conductive polymer polyaniline (PANI) is employed to modify the anodes of benthic microbial fuel cells (BMFC). Four electrochemical methods are used to synthesize the polyaniline anodes; the results show that the PANI modification, especially the pulse potential method for PANI synthesis could obviously improve the cell energy output and reduce the anode internal resistance. The anode is modified by PANI doped with Fe or Mn to further improve the BMFC performance. A maximum power density of 17.51 mW/m2 is obtained by PANI-Fe anode BMFC, which is 8.1 times higher than that of control. The PANI-Mn anode BMFC also gives a favorable maximum power density (16.78 mW/m2). Fe or Mn modification has better effect in improving the conductivity of polyaniline, thus improving the energy output of BMFCs. This work applying PANI composite anode into BMFC brings new development prospect and could promote the practical application of BMFC.
AlTiN, AlTiN-Cu and AlTiN/AlTiN-Cu coatings were prepared on WC-6%Co substrates by cathode arc evaporation deposition technology. Two kinds of nitrogen pressures were used to deposit both AlTiN-Cu and AlTiN/AlTiN-Cu coatings. Surface and cross-sectional morphologies of films were observed by scanning electron microscopy (SEM). Crystal structure of films was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Hardness and adhesion of films were measured by nano-indentation and nano-scratch tester. Cutting tests were performed under milling conditions during wet machining of TC4 alloy. The results show that with addition of Cu, more droplets occur on AlTiN coating surface, but the grain size of it is refined, and the hardness decreases but the toughness is improved. Under higher N2 pressure, the defects on the surface of AlTiN-Cu and AlTiN/AlTiN-Cu coatings diminish, and the hardness of them is enhanced, while the adhesion is reduced. Compared to AlTiN coated cemented carbide tool, the lifetimes of AlTiN-Cu and AlTiN/AlTiN-Cu coated tools under the same N2 pressure are improved by 11% and 24%, respectively.
Because co-occurring native and invasive plants are subjected to similar environmental selection pressures, the differences in functional traits and reproductive allocation strategies between native and invasive plants may be closely related to the success of the latter. Accordingly, this study examines differences in functional traits and reproductive allocation strategies between native and invasive plants in Eastern China. Plant height, branch number, reproductive branch number, the belowground-to-aboveground biomass ratio, and the reproductive allocation coefficient of invasive plants were all notably higher than those of native species. Additionally, the specific leaf area (SLA) values of invasive plants were remarkably lower than those of native species. Plasticity indexes of SLA, maximum branch angle, and branch number of invasive plants were each notably lower than those of native species. The reproductive allocation coefficient was positively correlated with reproductive branch number and the belowground-to-aboveground biomass ratio but exhibited negative correlations with SLA and aboveground biomass. Plant height, branch number, reproductive branch number, the belowground-to-aboveground biomass ratio, and the reproductive allocation coefficient of invasive plants may strongly influence the success of their invasions.
In order to produce α-calcium sulfate hemihydrate (α-CaSO4·0.5H2O) whiskers with high aspect ratios, a minor amount of CuCl2·2H2O was used as the modifying agent in the process of hydrothermal treatment of calcium sulfate dihydrate (CaSO4·2H2O) precursor. The presence of 2.60×10-3 mol/L CuCl2·2H2O resulted in the increase of the aspect ratios of α-CaSO4·0.5H2O whiskers from 81 to 253. The preferential adsorption of Cu2+ on the negative {110} and {100} facets of α-CaSO4·0.5H2O crystal structures was confirmed by EDS and XPS. And ATR-FTIR demonstrated the ligand adsorption of Cu2+ on the surface of α-CaSO4·0.5H2O whiskers. The experimental results reveal that the whiskers with high aspect ratios are attributed to the adsorption of Cu2+, which promotes the 1-D growth of α-CaSO4·0.5H2O whiskers along the c axis.
The effect of pre-recovery on the recrystallization kinetics of a supersaturated Al-Mn alloy annealed at 530 °C was investigated. The results show that the pre-recovery treatment can lead to faster recrystallization kinetics at the initial stage but cause sluggish recrystallization at the later stage. This different recrystallization behavior is explained by the formation of precipitates-free zones and the consumption of driving force during the pre-recovery treatment. The promoted recrystallization at the early stage can be interpreted by the promotion of recrystallization nucleation through sub-grain growth to a critical size inside precipitates-free zones. A simple model is presented to describe the nucleation of recrystallization with pre-recovery treatment in the supersaturated Al-Mn alloys.
In this work, a novel alcohol alkali hydrolysis method was explored for the preparation of terephthalic acid (TPA) from waste polyethylene terephthalate (PET). First, a series of single factor experiments on the depolymerization rate of waste PET bottles and the yield of TPA were conducted to determine the optimized experimental conditions, in terms of reaction time, reaction temperature, dosage of ethylene glycol and sodium bicarbonate, amount of distilled water and stirring rate. Then IR spectra and elemental analysis were carried out for the characterization of obtained product. Under optimal experimental conditions, over 98% PET can be depolymerized into the target product (TPA) and the purity and yield of TPA are over 97% and 94%, respectively. Both the experimental and analytical results support a feasible process for the preparation of TPA from waste PET. It is expected that this alcohol alkali hydrolysis method can promise an effective way for the sustainable recycling of waste PET.
A new two-step synthetic method was successfully developed to simplify the recrystallization process of lithium difluoro(oxalate)borate (LiODFB). Meanwhile, the purity of LiODFB as-prepared was determined by NMR, ICP-AES and Karl Fisher measurements, respectively. The as-prepared LiODFB presents a high purity up to 99.95%. Its metal ions and water contents are under good control as well. Besides, its structure information and thermal properties were confirmed by FTIR, Raman and DSC-TGA analyses, respectively. LiODFB exerts fine thermostability and hypo-water-sensitivity and its structure information agrees well with previous literature. Furthermore, a combination of phase diagram and Raman spectroscopy were utilized to study the thermal phase behavior and ions coordination of LiODFB-DMC binary system to optimize the synthesis and recrystallization process. Although there are three types of molecular interaction forms (CIPs, AGG-IIa, AGG-IIIb) in LiODFB-DMC binary system, LiODFB can only be isolated as large single crystal solvate as LiODFB·(DMC)3/2 by slowly cooling subjected to the nucleation kinetics. Therefore, the fundamental information of our work is helpful in accelerating the application of LiODFB in Li-ion secondary batteries.
In current research, the interactive effects of different parameters such as melt overheating temperature, the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechanical and structural characteristics of commercially pure aluminium are examined. Results show that increasing the melt temperature as well as employing a gating system with higher heat transfer rate increases the ultimate tensile strength (UTS) of the pure aluminium by 7%. Also, the introduction of 2wt% Al–5Ti–1B grain refiner in bar form into the overheated melt enhances the UTS values by two times, while incorporating 2wt% Al–5Ti–1B grain refiner in micro-powder form leads to achieving 32% higher UTS compared to the samples with grain refiner in the bar form due to the elimination of Al3Ti brittle phase, as confirmed by XRD patterns and SEM fracture surface images.
Proper solid waste disposal is an important socioeconomic concern for all developing countries. Municipalities have their own policies, individual approaches and methods to manage the solid wastes. They consider wastelands outside the urban area as the best suitable for the solid waste disposal. Such improper site selection will create morphological changes that lead to environmental hazards in the urban and its surrounding areas. In this research, the site selection for urban solid waste disposal in the Coimbatore district used geographical information system (GIS) and multi-criteria decision analysis (MCDA). Thematic layers of lineament density, landuse/landcover, population density, groundwater depth, drainage density, slope, soil texture, geology and geomorphology were considered as primary criteria and weights for criteria, and sub-criteria were assigned by MCDA analysis. The resultant weight score was validated by consistency ratio so that the efficiency of the selected criteria was justified. The overlay analysis in GIS environment provides 17 potential zones in Coimbatore district, among which, four suitable sites were screened and refined with the help of field investigation and visual interpretation of satellite image. The result of landfill suitability map shows the effectiveness of the proposed method.
In recent years, unmanned aerial vehicles (UAVs) have acquired an increasing interest due to their wide range of applications in military, scientific, and civilian fields. One of the quadcopter limitations is its lack of full actuation property which limits its mobility and trajectory tracking capabilities. In this work, an overactuated quadcopter design and control, which allows independent tilting of the rotors around their arm axis, is presented. Quadcopter with this added tilting mechanism makes it possible to overcome the aforementioned mobility limitation by achieving full authority on torque and force vectoring. The tilting property increases the control inputs to 8 (the 4 propeller rotation speed plus the 4 rotor tilting angles) which gives a full control on the quadcopter states. Extensive mathematical model for the tilt rotor quadcopter is derived based on the Newton-Euler method. Furthermore, the feedback linearization method is used to linearize the model and a mixed sensitivity H∞ optimal controller is then designed and synthesized to achieve the required performance and stability. The controlled system is simulated to assure the validity of the proposed controller and the quadcopter design. The controller is tested for its effectiveness in rejecting disturbances, attenuating sensor noise, and coping with the model uncertainties. Moreover, a complicated trajectory is examined in which the tilt rotor quadcopter has been successfully followed. The test results show the supremacy of the overactuated quadcopter over the traditional one.
With the development of automation in smart grids, network reconfiguration is becoming a feasible approach for improving the operation of distribution systems. A novel reconfiguration strategy was presented to get the optimal configuration of improving economy of the system, and then identifying the important nodes. In this strategy, the objectives increase the node importance degree and decrease the active power loss subjected to operational constraints. A compound objective function with weight coefficients is formulated to balance the conflict of the objectives. Then a novel quantum particle swarm optimization based on loop switches hierarchical encoded was employed to address the compound objective reconfiguration problem. Its main contribution is the presentation of the hierarchical encoded scheme which is used to generate the population swarm particles of representing only radial connected solutions. Because the candidate solutions are feasible, the search efficiency would improve dramatically during the optimization process without tedious topology verification. To validate the proposed strategy, simulations are carried out on the test systems. The results are compared with other techniques in order to evaluate the performance of the proposed method.
To overcome nonlinear and 6-DOF (degrees of freedom) under-actuated problems for the attitude and position of quadrotor UAVs, an adaptive backstepping sliding mode method for flight attitude of quadrotor UAVs is proposed, in which an adaptive law is designed to online estimate the parameter variations and the upper bound of external disturbances and the assessments is utilized to compensate the backstepping sliding mode control. In addition, the tracking error of the design method is shown to asymptotically converge to zero by using Lyapunov theory. Finally, based on the numerical simulation of quadrotor UAVs using the setting parameters, the results show that the proposed control approach can stabilize the attitude and has hover flight capabilities under the parameter perturbations and external disturbances.
Thin-walled tubes are increasingly used in automobile industries to improve structural safety. The present work deals with the collapse behavior of double-cell conical tubes subjected to dynamic axial and oblique loads. Crashworthiness of these tubes having different sections (e.g., circular, square, hexagonal, octagonal, decagonal) was numerically investigated by using an experimentally validated finite element model generated in LS-DYNA. Geometry of these tubes was then optimized by decreasing the cross section dimensions at the distal end while the weight remained unchanged. Octagonal conical tube was finally found to be more preferable to the others as a collision energy absorber. In addition, square and circular tubes showed diamond deformation mode, while the other tubes collapsed in concertina mode. A decision making method called TOPSIS was finally implemented on the numerical results to select the most efficient energy absorber.
A 500 N model engine filled with LO2/GCH4 was designed and manufactured. A series of ignition attempts were performed in it by both head spark plug and body spark plug. Results show that the engine can be ignited but the combustion cannot be sustained when head spark plug applied as the plug tip was set in the gaseous low-velocity zone with thin spray. This is mainly because flame from this zone cannot supply enough ignition energy for the whole chamber. However, reliable ignition and stable combustion can be achieved by body spark plug. As the O/F ratio increases from 2.61 to 3.49, chamber pressure increases from 0.474 to 0.925 MPa and combustion efficiency increases from 57.8% to 95.1%. This is determined by the injector configuration, which cannot produce the sufficiently breakup of the liquid oxygen on the low flow rate case.
In order to investigate the failure mechanism of rock joint, a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL) conditions were conducted. Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine. All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions. Degradation of rock joint surface during cyclic shear tests was also analyzed. The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation. During cyclic shear tests, joints surfaces evolve from rough state to smooth state but keep an overall undulation. Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads. The closure deformation of joint is larger than that of the intact rock, and the normal stiffness increases with the increase of shearing times.
Due to the fact that the turbine outlet temperature of aeroderivative three-shaft gas turbine is low, the conventional combined cycle is not suitable for three-shaft gas turbines. However, the humid air turbine (HAT) cycle provides a new choice for aeroderivative gas turbine because the humidification process does not require high temperature. Existing HAT cycle plants are all based on single-shaft gas turbines due to their simple structures, therefore converting aeroderivative three-shaft gas turbine into HAT cycle still lacks sufficient research. This paper proposes a HAT cycle model on a basis of an aeroderivative three-shaft gas turbine. Detailed HAT cycle modelling of saturator, gas turbine and heat exchanger are carried out based on the modular modeling method. The models are verified by simulations on the aeroderivative three-shaft gas turbine. Simulation results show that the studied gas turbine with original size and characteristics could not reach the original turbine inlet temperature because of the introduction of water. However, the efficiency still increases by 0.16% when the HAT cycle runs at the designed power of the simple cycle. Furthermore, simulations considering turbine modifications show that the efficiency could be significantly improved. The results obtained in the paper can provide reference for design and analysis of HAT cycle based on multi-shaft gas turbine especially the aeroderivative gas turbine.
In the present research, by using a numerical model, some analyses were performed on flows around a T-shape spur dike and a support structure located at its upstream under different wing to length ratios of T-shape spur dike in the order of 0.25, 0.50, 0.75 and 1.00. In order to verify numerical model, physical model data were used in presence of a single T shape spur dike. Results from numerical model are desirably in agreement with those of physical one because the regression between both data is 0.86 up to 0.92. In this research, all hydraulic parameters of flows, streamlines and dimensions of flow separation zones were studied in order to select the most practical model. Increased W/L results in 7%–12% increase in the length of flow separation zone and in 2% increase in the width of this zone compared to W/L=0.25.
Health state of shield tunnels is one of the most important parameters for structure maintenance. Usually, the shield tunnel is extremely long in longitude direction and composed by many segments. It is difficult to quantify the relationship between the structure damage state and shield tunnel structure deformation by the model test because of unpredictable effects of different scales between model test and prototype tunnel structure. Here, an in-situ monitoring project was conducted to study the excavation induced shield tunnel structure damage, which could be considered a prototype test on the tunnel deformation. The disaster performance of tunnel leakage, segment crack, segment dislocation and segment block drop-off during longitude deformation and cross-section ovality developments was analyzed. The results indicate that instead of the longitude deformation, the ovality value has the strongest correlation to the rest disease performance, which could be used as the assessment index of the tunnel health. For this tunnel, it is in health state when the ovality is less than 0.5%, and the serious damage could be found when the ovality value is higher than 0.77%. The research results provide valuable reference to shield tunnel health assessment and help complete the standard of shield tunnel construction.
The first author’s affiliation was no longer in use in the original version of the article and it should be replaced as follows: School of Mechano-Electronic Engineering, Xidian University, Xi’an 710071, China.