The effects of different Zn contents in Al−Mg alloy on the microstructure characterizations were observed by advanced electron microscopy and the corrosion properties were investigated by the inter-granular corrosion tests, the exfoliation corrosion tests, and the Potentiodynamic polarizaion tests. The τ phase (Mg32 (Al, Zn)49) forms on the pre-existing Mn-rich particles and at the grain boundaries. According to the theory of binding energy, the formation of τ phase is much easier than that of β phase (Al3Mg2), somehow replacing β phase and reducing the possibility of β phase precipitation. This change dramatically decreases the susceptibility of corrosion. The Zn addition increases the corrosion resistance of Al−Mg alloy with an optimal value of 0.31%. When the Zn addition is increased to 0.78%, however, the corrosion resistance of alloy decreases once again but it is still better than that of the alloy without Zn addition.
Molybdenum disilicide (MoSi2) based composites with various contents of carbon nanotubes (CNTs) were fabricated by spark plasma sintering (SPS) in vacuum under a pressure of 25 MPa. The composites obtained under a sintering temperature of 1500 °C and time of 10 min exhibited optimum mechanical properties at room temperature in terms of fracture toughness and transverse rupture strength. MoSi2 based composite with 6.0% CNTs (volume fraction) had the highest fracture toughness, transverse rupture strength and hardness, which were improved by about 25.7%, 51.5% and 24.4% respectively, as compared with pure MoSi2. A Mo4.8Si3C0.6 phase was detected in CNTs/MoSi2 composites by both X-ray diffraction (XRD) method and microstructure analysis with scanning electron microscopy (SEM). It is believed that the fine grains and well dispersed small Mo4.8Si3C0.6 particles had led to a higher hardness and strength of CNTs/MoSi2 composites because of their particle pullout, crack deflection and micro-bridging effects.
The hot deformation behaviors of Cr5 steel were investigated. The hot compression tests were conducted in the temperature range of 900−1150 °C under strain rates of 0.01, 0.1 and 1 s−1. The constitutive equation and material constants (Q, n, α lnA) are obtained according to the hyperbolic sine function and Zener-Hollomon parameter. Besides, dynamic recrystallization (DRX) grain size model and critical strain model are acquired. The processing maps with the strain of 0.1, 0.3 and 0.5 are obtained on the basis of dynamic materials model. It has been observed that DRX occurs at high temperature and low strain rate. According to the processing map, the safety region exists in the temperature range of 920−1150 °C with strain rate of 0.01−0.20 s−1.
Nucleation mechanism and technological process for Ni-Fe co-deposition with a relatively high Fe2+ concentration surrounded were described, and the effects of Fe2+ concentration, solution pH, temperature, and sodium dodecyl sulfonate concentration were investigated. Electrochemical experiments demonstrate that iron’s electrodeposition plays a leading role in the Ni-Fe co-deposition process, and the co-deposition nucleation mechanism accords with a progressive nucleation. Temperature increase does favor in increasing nickel content in the ferronickel (Ni-Fe co-deposition products), while Fe2+ concentration increase does not. When solution pH is higher than 3.5, nickel content in the ferronickel decreases with pH because of the hydrolysis of Fe2+. With the current density of 180 A/m2, Na2SO4 concentration of 100 g/L and Ni2+ concentration of 60 g/L, a smooth ferronickel deposit containing 96.21% Ni can be obtained under the conditions of temperature of 60 °C, Fe2+ concentration of 0.3 g/L, solution pH of 3 and sodium dodecyl sulfonate concentration of 40 mg/L.
Surface tension of calcium aluminate refining slag was measured by the Slide method at 1823 K. Based on different levels of the MgO content and the mass ratio of CaO to Al2O3, the effects of MgO content and the mass ratio of CaO to Al2O3 on surface tension were investigated. The results indicate that surface tension decreased with increasing MgO content (from 0 to 4.86%), followed by an increase with further increasing MgO content up to 11.33%. The trend that surface tension changed with the mass ratio of CaO to Al2O3 was the same as the trend that surface tension changed with the MgO content. The surface tension was varied from 0.617 N/m to 0.710 N/m, for the mass ratio of CaO to Al2O3 varying between 0.60 and 1.28. An attempt was made to estimate surface tension of CaO−Al2O3−MgO slag and its sub-system, and the application showed that the model worked well.
Tributyl phosphate (TBP) was employed for the Bi(III) extraction from hydrochloric acid medium. The effects of extraction time and material concentration were examined. The replacement mechanism between the anion (Cl−) and TBP was proposed for extraction. The results show the species extracted into the organic phase were found to be mainly BiCl3·xTBP (x=2 or 3). Thermodynamic parameters of the extraction reaction were obtained from the thermodynamics analysis, which illustrates that higher temperatures show a negative effect on the extraction. Extraction isotherm was obtained with 2.16 mol/L TBP for a typical solution containing 0.1 mol/L of bismuth and 1.0 mol/L of hydrochloric acid. About 98.5 % of bismuth has been extracted from the leaching solution under the optimum condition. Moreover, oxalate was explored as a precipitation stripping agent for BiCl3·xTBP (x=2 or 3) complexes, by which Bi(III) was stripped in the form of Bi2(C2O4)3·7H2O. A stripping efficiency of 99.3% was obtained in only one stage at the phase ratio of 1 and TBP also could be recycled. Therefore, the method is an efficient, effective and highly selective approach to extract Bi(III) and to recover metal bismuth.
ZnO/ZnGa2O4 composite microspheres with heterojunction were successfully synthesized by one-pot hydrothermal method. These samples were characterized by TG/DTA, XRD, TEM, HRTEM, UV-vis DRS, FL and BET techniques. The results indicated the as-prepared samples showed better degree of crystalline and large specific surface area. The photocatalytic activity was evaluated by degradation of methyl orange with the concentration of 50 mg/L under the irradiation of simulated sunlight. The effects of molar ratio of Zn to Ga and calcination temperature on the photocatalytic activity were investigated in detail. The results showed that the highest photocatalytic degradation efficiency was observed at the molar ratio of Zn to Ga of 1:0.5 in the starting materials and the calcination temperature of 400 °C. The maximum photocatalytic degradation rate of MO was 97.1% within 60 min under the simulated sunlight irradiation, which is greatly higher than that of ZnO and ZnGa2O4.
B3LYP/6-31G(d, p) method was used to investigate the catalytic cracking mechanism of biomass tar model compound. Phenol, toluene and benzene were selected as the tar model compounds and CaO was selected as the catalyst. The pathways of tar compound radical absorbed by CaO were determined firstly through comparing enthalpy changes of the absorption, and then Mulliken population changes were analyzed. The results show that the absorption of tar model compound radical and CaO is an exothermic reaction. Formation of C—O—Ca is more easily than that of C—Ca—O and formation of Caromatic—Caromatic—Ca—O is more easily than that of Caromatic—C(O)—Ca—O. The C—C bond Mulliken populations in tar model compound radicals are reduced by 11.9%, 10.5% and 15.5% in the case of a hydrogen atom removed, and those are 15.7%, 14.3% and 16.3% in the case of two hydrogen atoms removed through the absorption of CaO. Catalytic ability of CaO acting on the tar model compound is in an order of phenol>benzene>toluene.
The pulsed power is a potential means for energy saving and presents an alternative to the conventional mechanical communication for minerals. The effect of magnetic pulse treatment on grindability of a magnetite ore was investigated by grindability tests. The results of the investigation show that the pulsed treatment has little effect on the particle size distribution of the magnetite ore. Significant micro-cracks or fractures are not found by SEM analysis in magnetic pulse treated sample. Magnetic separation of magnetic pulse treated and untreated magnetite ore indicates that iron recovery increases from 81.3% in the untreated sample to 87.7% in the magnetic pulse treated sample, and the corresponding iron grade increases from 42.1% to 44.4%. The results demonstrate that the magnetic pulse treatment does not significantly weaken the mineral grain boundaries or facilitate the liberation of minerals, but is beneficial to magnetic separation.
The disinfected bacteria will be a photoreactivation under the irradiation of the sunlight, and the light intensity plays an important role in the bacteria resurrection. The effect of light intensity on photoreactivation of Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) in secondary effluents which were disinfected respectively by pure UV and UV-TiO2 was investigated. The results show that the disinfection efficiency of UV-TiO2 is much higher than that of the pure UV disinfection. The photoreactivation rate of E. coli is much higher in pure UV disinfection than in UV-TiO2 photocatalytic disinfection. Under high light intensity in UV-TiO2 disinfection, high resurrection rate can be induced. However, a higher resurrection rate can be introduced even under low light intensity in pure UV disinfection alone. Meanwhile, UV-TiO2 disinfection has a strong inhibition effect on E. faecalis photoreactivation. When the light intensity is lower than 21 μW/cm2, nearly no resurrection of E. faecalis occurs after 72 h resurrection irradiation, and a little resurrection rate is observed only under a strong photoreactivating light intensity.
Bentonite has been proven to be effective in enhancing the membrane property of clay, by which landfill liners can have better barrier performance with regard to the migration of contaminants. In this work, 5% sodium bentonite amended with locally available Fukakusa clay was utilized to evaluate the membrane behavior toward different kinds of ions: K, Na and Ca. The chemico-osmotic efficiency coefficient, ω, was obtained in electrolyte solution with different concentrations of 0.5, 1, 5, 10, and 50 mmol/L. According to the results, solute type and ion valence have a significant effect on membrane behaviors. Additionally, ω continually decreased as the Na and Ca concentrations increased, which is consistent with the Gouy-Chapman theory. The membrane behavior toward Na was similar to that toward K, according to the chemico-osmotic efficiency coefficient ω. In the case of the divalent ion Ca, the membrane behavior was lower compared to monovalent ions Na and K at the same concentration. The mechanisms of the membrane performance change were discussed with the assistance of XRD patterns, free-swelling results and SEM images.
Volumetric efficiency and air charge estimation is one of the most demanding tasks in control of today’s internal combustion engines. Specifically, using three-way catalytic converter involves strict control of the air/fuel ratio around the stoichiometric point and hence requires an accurate model for air charge estimation. However, high degrees of complexity and nonlinearity of the gas flow in the internal combustion engine make air charge estimation a challenging task. This is more obvious in engines with variable valve timing systems in which gas flow is more complex and depends on more functional variables. This results in models that are either quite empirical (such as look-up tables), not having interpretability and extrapolation capability, or physically based models which are not appropriate for onboard applications. Solving these problems, a novel semi-empirical model was proposed in this work which only needed engine speed, load, and valves timings for volumetric efficiency prediction. The accuracy and generalizability of the model is shown by its test on numerical and experimental data from three distinct engines. Normalized test errors are 0.0316, 0.0152 and 0.24 for the three engines, respectively. Also the performance and complexity of the model were compared with neural networks as typical black box models. While the complexity of the model is less than half of the complexity of neural networks, and its computational cost is approximately 0.12 of that of neural networks and its prediction capability in the considered case studies is usually more. These results show the superiority of the proposed model over conventional black box models such as neural networks in terms of accuracy, generalizability and computational cost.
Since the complex impeller structure and the difficult remanufacturing process may easily cause advance remanufacturing or excessive use, an optimized design method of impeller and service mapping model was presented for its proactive remanufacturing with setting up to explore the best remanufacturing time point in this work. Considering a certain model of long distance pipeline compressor impeller with the Basquin equation and the design method of impeller, the mathematical relationship between the changes of structure and life of the impeller was established. And the service mapping model between the structure and life was set up and simulated by ANSYS software. Thus, the service mapping model was applied to feedback the original design for proactive remanufacturing. In this work, the best proactive remanufacturing time point of impeller was analyzed with the service mapping model, and the structural parameter values could be optimized at this time point. Meanwhile, in the results of this simulation, it proves that the impeller under this optimization performance could satisfy the impeller operating demands. Therefore, comparing with the traditional optimization design method, the remanufacturing optimized design based on the service mapping model is feasible in proactive remanufacturing for sustainable development.
A theoretical model for mixed lubrication with more accurate contact length has been developed based on the average volume flow model and asperity flattening model, and the lubricant volume flow rate and outlet speed ratio are determined by integrating differential equations based on rolling parameters. The lubrication characteristics at the roll−strip interface with different surface roughness, rolling speed, reduction and lubricant viscosity are analyzed respectively. Additionally, the average volume flow rates of lubricant under different rolling conditions are calculated and used to explain the change rule of lubrication characteristics. The developed scheme is able to determine the total pressure, lubricant pressure, film thickness and real contact area at any point within the work zone. The prediction and analysis of mixed lubrication characteristics at the interface is meaningful to better control the surface quality and optimize the rolling process.
Numerous innovative heat recovery-to-power technologies have been resourcefully and technologically exploited to bridge the growing gap between energy needs and its sustainable and affordable supply. Among them, the proposed trilateral-cycle (TLC) power system exhibits high thermodynamic efficiency during heat recovery-to-power from low-to-medium temperature heat sources. The TLCs are proposed and analysed using n-pentane as working fluid for waste heat recovery-to-power generation from low-grade heat source to evaluate the thermodynamic efficiency of the cycles. Four different single stage TLC configurations with distinct working principles are modelled thermodynamically using engineering equation solver. Based on the thermodynamic framework, thermodynamic performance simulation and efficiency analysis of the cycles as well as the exergy efficiencies of the heating and condensing processes are carried out and compared in their efficiency. The results show that the simple TLC, recuperated TLC, reheat TLC and regenerative TLC operating at subcritical conditions with cycle high temperature of 473 K can attain thermal efficiencies of 21.97%, 23.91%, 22.07% and 22.9%, respectively. The recuperated TLC attains the highest thermodynamic efficiency at the cycle high temperature because of its lowest exergy destruction rates in the heat exchanger and condenser. The efficiency analysis carried out would assist in guiding thermodynamic process development and thermal integration of the proposed cycles.
The present research relies on a cascade control approach through the Monte-Carlo based method in the presence of uncertainties to evaluate the performance of the real overactuated space systems. A number of potential investigations in this area are first considered to prepare an idea with respect to state-of-the-art. The insight proposed here is organized to present attitude cascade control approach including the low thrust in connection with the high thrust to be implemented, while the aforementioned Monte-Carlo based method is carried out to guarantee the approach performance. It is noted that the investigated outcomes are efficient to handle a class of space systems presented via the center of mass and the moments of inertial. And also a number of profiles for the thrust vector and the misalignments as the disturbances all vary in its span of nominal variations. The acquired results are finally analyzed in line with some well-known benchmarks to verify the approach efficiency. The key core of finding in the research is to propose a novel 3-axis control approach to deal with all the mentioned uncertainties of space systems under control, in a synchronous manner, as long as the appropriate models in the low-high thrusts are realized.
Role based access control is one of the widely used access control models. There are investigations in the literature that use knowledge representation mechanisms such as formal concept analysis (FCA), description logics, and Ontology for representing access control mechanism. However, while using FCA, investigations reported in the literature so far work on the logic that transforms the three dimensional access control matrix into dyadic formal contexts. This transformation is mainly to derive the formal concepts, lattice structure and implications to represent role hierarchy and constraints of RBAC. In this work, we propose a methodology that models RBAC using triadic FCA without transforming the triadic access control matrix into dyadic formal contexts. Our discussion is on two lines of inquiry. We present how triadic FCA can provide a suitable representation of RBAC policy and we demonstrate how this representation follows role hierarchy and constraints of RBAC on sample healthcare network available in the literature.
The exothermic efficiency of microwave heating an electrolyte/water solution is remarkably high due to the dielectric heating by orientation polarization of water and resistance heating by the Joule process occurred simultaneously compared with pure water. A three-dimensional finite element numerical model of multi-feed microwave heating industrial liquids continuously flowing in a meter-scale circular tube is presented. The temperature field inside the applicator tube in the cavity is solved by COMSOL Multiphysics and professional programming to describe the momentum, energy and Maxwell’s equations. The evaluations of the electromagnetic field, the temperature distribution and the velocity field are simulated for the fluids dynamically heated by single- and multi-feed microwave system, respectively. Both the pilot experimental investigations and numerical results of microwave with single-feed heating for fluids with different effective permittivity and flow rates show that the presented numerical modeling makes it possible to analyze dynamic process of multi-feed microwave heating the industrial liquid. The study aids in enhancing the understanding and optimizing of dynamic process in the use of multi-feed microwave heating industrial continuous flow for a variety of material properties and technical parameters.
Water eutrophication has become a worldwide environmental problem in recent years. Once a water body is eutrophicated, it will lose its primary functions and subsequently influence sustainable development of society and economy. Therefore, analysis of eutrophication becomes one of the most essential issues at present. With the ability to deal with vague and uncertain information, and express knowledge in a rule form, the rough set theory (RST) has been widely applied in diverse domains. The advantage of RST is that it can compress the rule and remove needless features by reduction inference rule. By this way, the rule gets effectively simplified and inference efficiency gets improved. However, if data amount is relatively big, it could be a process with large calculated amount to search rules by looking up tables. Petri nets (PNs) possesses so powerful parallel reasoning ability that inference result could be obtained rapidly merely by simple matrix manipulation with no need for searching rules by looking up tables. In this work, an integrated RPN model combining RST with PN was used to analyze relations between degrees of water eutrophication level and influence factors in the Pengxi River of Three Gorges Reservoir. It was shown that the RPN model could analyze water eutrophicaion accurately and quickly, and yield decision rules for the decision-makers at water purification plants of the water quality and assist them in making more cost-effective decisions.
Cloud computing has emerged as a leading computing paradigm, with an increasing number of geographic information (geo-information) processing tasks now running on clouds. For this reason, geographic information system/remote sensing (GIS/RS) researchers rent more public clouds or establish more private clouds. However, a large proportion of these clouds are found to be underutilized, since users do not deal with big data every day. The low usage of cloud resources violates the original intention of cloud computing, which is to save resources by improving usage. In this work, a low-cost cloud computing solution was proposed for geo-information processing, especially for temporary processing tasks. The proposed solution adopted a hosted architecture and can be realized based on ordinary computers in a common GIS/RS laboratory. The usefulness and effectiveness of the proposed solution was demonstrated by using big data simplification as a case study. Compared to commercial public clouds and dedicated private clouds, the proposed solution is more low-cost and resource-saving, and is more suitable for GIS/RS applications.
A new strategy is presented to solve robust multi-physics multi-objective optimization problem known as improved multi-objective collaborative optimization (IMOCO) and its extension improved multi-objective robust collaborative (IMORCO). In this work, the proposed IMORCO approach combined the IMOCO method, the worst possible point (WPP) constraint cuts and the Genetic algorithm NSGA-II type as an optimizer in order to solve the robust optimization problem of multi-physics of microstructures with uncertainties. The optimization problem is hierarchically decomposed into two levels: a microstructure level, and a disciplines levels. For validation purposes, two examples were selected: a numerical example, and an engineering example of capacitive micro machined ultrasonic transducers (CMUT) type. The obtained results are compared with those obtained from robust non-distributed and distributed optimization approach, non-distributed multi-objective robust optimization (NDMORO) and multi-objective collaborative robust optimization (McRO), respectively. Results obtained from the application of the IMOCO approach to an optimization problem of a CMUT cell have reduced the CPU time by 44% ensuring a Pareto front close to the reference non-distributed multi-objective optimization (NDMO) approach (mahalanobis distance, DM2 =0.9503 and overall spread, So=0.2309). In addition, the consideration of robustness in IMORCO approach applied to a CMUT cell of optimization problem under interval uncertainty has reduced the CPU time by 23% keeping a robust Pareto front overlaps with that obtained by the robust NDMORO approach (DM2 =10.3869 and So=0.0537).
When detecting deletions in complex human genomes, split-read approaches using short reads generated with next-generation sequencing still face the challenge that either false discovery rate is high, or sensitivity is low. To address the problem, an integrated strategy is proposed. It organically combines the fundamental theories of the three mainstream methods (read-pair approaches, split-read technologies and read-depth analysis) with modern machine learning algorithms, using the recipe of feature extraction as a bridge. Compared with the state-of-art split-read methods for deletion detection in both low and high sequence coverage, the machine-learning-aided strategy shows great ability in intelligently balancing sensitivity and false discovery rate and getting a both more sensitive and more precise call set at single-base-pair resolution. Thus, users do not need to rely on former experience to make an unnecessary trade-off beforehand and adjust parameters over and over again any more. It should be noted that modern machine learning models can play an important role in the field of structural variation prediction.
Homing trajectory planning is a core task of autonomous homing of parafoil system. This work analyzes and establishes a simplified kinematic mathematical model, and regards the homing trajectory planning problem as a kind of multi-objective optimization problem. Being different from traditional ways of transforming the multi-objective optimization into a single objective optimization by weighting factors, this work applies an improved non-dominated sorting genetic algorithm II (NSGA II) to solve it directly by means of optimizing multi-objective functions simultaneously. In the improved NSGA II, the chaos initialization and a crowding distance based population trimming method were introduced to overcome the prematurity of population, the penalty function was used in handling constraints, and the optimal solution was selected according to the method of fuzzy set theory. Simulation results of three different schemes designed according to various practical engineering requirements show that the improved NSGA II can effectively obtain the Pareto optimal solution set under different weighting with outstanding convergence and stability, and provide a new train of thoughts to design homing trajectory of parafoil system.
During well drilling process, original stress state of hard brittle shale will be changed due to stress redistribution and concentration, which leads to stress damage phenomenon around the borehole. Consequently, drilling fluid will invade into formation along the tiny cracks induced by stress damage, and then weaken the strength of hard brittle shale. Based on this problem, a theoretical model was set up to discuss damage level of shale under uniaxial compression tests using acoustic velocity data. And specifically, considering the coupled effect of stress damage and drilling fluid, the relationship between hard brittle shale strength and elapsed time was analyzed.
The mining space of large mining height coal face is large, the range of movement and caving of rock strata is large and the stability of supports at coal face is low and damage rate of supports is high, which significantly affects the safe and efficient production of coal mines. By similar simulation experiment and theoretical analysis, the mode of fractured roofing structure of large mining height coal face and the method of determination of reasonable support resistance of the support was evaluated. Analysis shows that the structural mode of “combined cantilever beam–non-hinged roofing–hinged roofing” of the large mining height coal face appears at the roofing of large mining height coal face. The supporting factor of caved gangue at the gob is introduced, the calculating equations of the fractured step distance of roofing were derived and conventional calculating method of caved height of roofing was corrected and the method of determination of the length and height of each structural area of the roofing was provided. With reference to the excavating conditions at Jinhuagong coal mine in Datong minefield, the dimensions of structural areas of the roofing of the coal face were determined and analyzed, and reasonable support resistance of the height coal face was acquired. By selecting Model ZZ13000/28/60 support and with procedures of advanced pre-cracking blasting, the safe production of large mining height coal face was assured.
This study aims to predict ground surface settlement due to shallow tunneling and introduce the most affecting parameters on this phenomenon. Based on data collected from Shanghai LRT Line 2 project undertaken by TBM-EPB method, this research has considered the tunnel’s geometric, strength, and operational factors as the dependent variables. At first, multiple regression (MR) method was used to propose equations based on various parameters. The results indicated the dependency of surface settlement on many parameters so that the interactions among different parameters make it impossible to use MR method as it leads to equations of poor accuracy. As such, adaptive neuro-fuzzy inference system (ANFIS), was used to evaluate its capabilities in terms of predicting surface settlement. Among generated ANFIS models, the model with all input parameters considered produced the best prediction, so as its associated R2 in the test phase was obtained to be 0.957. The equations and models in which operational factors were taken into consideration gave better prediction results indicating larger relative effect of such factors. For sensitivity analysis of ANFIS model, cosine amplitude method (CAM) was employed; among other dependent variables, fill factor of grouting (n) and grouting pressure (P) were identified as the most affecting parameters.
To investigate the relationship between nonlinear parameters and spontaneous combustion tendency of sulfide ores, nine different sulfide ore samples were taken from a pyrite mine in China, and induced spontaneous combustion experiment was carried out in the laboratory. Different stages of the induced spontaneous combustion process were studied by integrating wavelet technology and nonlinear dynamics theory. The results show that ignition points of all the ore samples are above 330 °C, indicating that sulfide ores of the pyrite mine are difficult to combust spontaneously under normal mining conditions. Spontaneous combustion process includes three stages: incubation stage, development stage and approaching stage. The average temperature rising rate of the three stages are 1.0 °C/min, 2.0 °C/min and 4.2 °C/min, respectively. During the spontaneous combustion process, mean values of approximate entropy and correlation dimension increase at first, and then decrease in the following stage. The mean value of the maximum Lyapunov exponent increases with the passage of reaction time. In a whole, correlation among the three nonlinear parameters firstly weakens, then enhances, and the best correlation period is at approaching stage. As ignition point increases, the maximum Lyapunov exponent of approaching stage decreases. Therefore, combustible tendency of sulfide ores could be qualitatively evaluated based on the maximum Lyapunov exponent of this stage.
The possible collapse of different circumstances is derived with the help of the limit analysis theory. Analytical equations related to collapsing mechanisms in deep tunnel with smooth three-centered arc cross sections are derived on the basis of Hoek-Brown failure criterion and upper bound limit analysis. The pore water pressure is considered in the analysis, as a work rate of external force. Numerical results about the shape of detaching curve and the weight of collapsing block per unit length corresponding to different parameters are obtained with the help of mathematical software. The shapes of collapsing block are drawn with respected to different parameters. Furthermore, the effects of different parameters on the shape of detaching curve and the weight of the collapsing block are discussed.
A nonlinear pressure controller was presented to track desired feeding pressure for the cutter feeding system (CFS) of trench cutter (TC) in the presence of unknown external disturbances. The feeding pressure control of CFS is subjected to unknown load characteristics of rock or soil; in addition, the geological condition is time-varying. Due to the complex load characteristics of rock or soil, the feeding velocity of TC is related to geological conditions. What is worse, its dynamic model is subjected to uncertainties and its function is unknown. To deal with the particular characteristics of CFS, a novel adaptive fuzzy integral sliding mode control (AFISMC) was designed for feeding pressure control of CFS, which combines the robust characteristics of an integral sliding mode controller and the adaptive adjusting characteristics of an adaptive fuzzy controller. The AFISMC feeding pressure controller is synthesized using the backstepping technique. The stability of the overall closed-loop system consisting of the adaptive fuzzy inference system, integral sliding mode controller and the cutter feeding system is proved using Lyapunov theory. Experiments are conducted on a TC test bench with the AFISMC under different operating conditions. The experimental results demonstrate that the proposed AFISMC feeding pressure controller for CFS gives a superior and robust pressure tracking performance with maximum pressure tracking error within ±0.3 MPa.
Based on the similarity theory, a tunnel excavation simulation testing system under typical unsymmetrical loading conditions was established. Using this system, the failure mechanism of surrounding rock of shallow-bias tunnels with small clear distance was analyzed along with the load characteristics. The results show that: 1) The failure process of surrounding rock of shallow-bias tunnels with small clear distance consists of structural and stratum deformation induced by tunnel excavation; Micro-fracture surfaces are formed in the tunnel surrounding rock and extend deep into the rock mass in a larger density; Tensile cracking occurs in shallow position on the deep-buried side, with shear slip in deep rock mass. In the meantime, rapid deformation and slip take place on the shallow-buried side until the surrounding rocks totally collapse. The production and development of micro-fracture surfaces in the tunnel surrounding rock and tensile cracking in the shallow position on the deep-buried side represent the key stages of failure. 2) The final failure mode is featured by an inverted conical fracture with tunnel arch as its top and the slope at tunnel entrance slope as its bottom. The range of failure on the deep-buried side is significantly larger than that on the shallow-buried side. Such difference becomes more prominent with the increasing bias angle. What distinguishes it from the "linear fracture surface" model is that the model proposed has a larger fracture angle on the two sides. Moreover, the bottom of the fracture is located at the springing line of tunnel arch. 3) The total vertical load increases with bias angle. Compared with the existing methods, the unsymmetrical loading effect in measurement is more prominent. At last, countermeasures are proposed according to the analysis results: during engineering process, 1) The surrounding rock mass on the deep-buried side should be reinforced apart from the tunnel surrounding rock for shallow-buried tunnels with small clear distance; moreover, the scope of consolidation should go beyond the midline of tunnel (along the direction of the top of slope) by 4 excavation spans of single tunnel. 2) It is necessary to modify the load value of shallow-bias tunnels with small clear distance.
Coalbed gas non-Darcy flow has been observed in high permeable fracture systems, and some mathematical and numerical models have been proposed to study the effects of non-Darcy flow using Forchheimer non-Darcy model. However, experimental results show that the assumption of a constant Forchheimer factor may cause some limitations in using Forchheimer model to describe non-Darcy flow in porous media. In order to investigate the effects of non-Darcy flow on coalbed methane production, this work presents a more general coalbed gas non-Darcy flow model according to Barree-Conway equation, which could describe the entire range of relationships between flow velocity and pressure gradient from low to high flow velocity. An expanded mixed finite element method is introduced to solve the coalbed gas non-Darcy flow model, in which the gas pressure and velocity can be approximated simultaneously. Error estimate results indicate that pressure and velocity could achieve first-order convergence rate. Non-Darcy simulation results indicate that the non-Darcy effect is significant in the zone near the wellbore, and with the distance from the wellbore increasing, the non-Darcy effect becomes weak gradually. From simulation results, we have also found that the non-Darcy effect is more significant at a lower bottom-hole pressure, and the gas production from non-Darcy flow is lower than the production from Darcy flow under the same permeable condition.
A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow. The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated. The numerical results indicate that heat transfer effective enhances near the stagnation region for the intermittent pulsed flow with jet chamber compared to that without jet chamber. Simulations of the flow through a jet chamber show that the heat transfer rate on the impingement surface is highly dependent on the velocity at the position which is really close to target surface. Examination of the velocity field suggests that the velocity exists a maximum value as the axis distance increases. In addition, the velocity at the jet hole is enlarged by the jet chamber due to the entrainment effect, and the velocity is amplified even greater as the size of the jet chamber becomes bigger. Nevertheless, the velocity declines quickly while the flow axis distance is more than a certain range, leading to poor heat transfer. Thus, intermittent pulsed flow with jet chamber is suggested as a method of improving heat transfer by employing larger dimensions of jet chamber for appropriate jet-to-surface spacing.
This study investigated the temperature field and thawing depth of wide embankment for expressway in permafrost regions based on numerical analysis by using finite element method (FEM). According to specific embankment section of Qinghai−Tibet highway, computational region for numerical analysis was defined. And numerical model was developed through FEM software named as ABAQUS and was verified by field observed data. The effects by width and height of embankment on the thermal regime of computational region were analyzed based on FEM modeling. Numerical analysis showed that embankment construction has serious disturbance on the thermal stability of ground permafrost showing as annual average ground temperature and the maximum thawing depth keeps increasing with service time increasing. And larger embankment width leads to poorer thermal stability and more serious uneven temperature field of embankment. Raising embankment height can improve the thermal stability; however, the improvement is restricted for wide embankment and it cannot change the degradation trend of thermal stability with service life increasing. Thus, to construct expressway with wide embankment in permafrost regions of Qinghai−Tibet Plateau, effective measures need to be considered to improve the thermal stability of underlying permafrost.
A nonlinear robust control strategy is proposed to force an underactuated surface ship to follow a predefined path with uncertain environmental disturbance and parameters. In the controller design, a high-gain observer is used to estimate velocities, thus only position and yaw angle measurements are required. The control problem of underactuated system is transformed into a control of fully actuated system through adopting an improved line-of-sight (LOS) guidance law. A sliding-mode controller is designed to eliminate the yaw angle error, and provide the control system robustness. The control law is proved semi-globally exponentially stable (SGES) by applying Lyapunov stability theory, and numerical simulation using real data of a monohull ship illustrates the effectiveness and robustness of the proposed methodology.