最新刊期
卷 51 ， 期 6 ， 2019
- 摘要：With the increasingly stringent wastewater discharge standard and increasing demand for efficient wastewater treatment technology around the world, the inverse fluidized bed bioreactor as a newly developed biofilm reactor for wastewater treatment has gained extensive attention from researchers in recent years. However, the start-up stage of inverse fluidized bed bioreactor used in aerobic wastewater treatment process is still under-explored. This work aimed to explore the effects of operational parameters on the biofilm formation and the reactor performance in the start-up stage of aerobic inverse fluidized bed bioreactors (AIFB) and establish an optimal short-term start-up strategy. Activated carbon coated polyethylene particles (PEC) were prepared in house and used as bio-carrier. The volatile suspended solids (VSS), attached volatile solids (AVS), chemical oxygen demand (COD) of the influent and the effluent, and the organic loading rate (OLR) in the reactor were recorded to evaluate the biofilm accumulation activity and reactor performance. Three start-up strategies were studied sequentially and the start-up strategy which successfully established a bioreactor was further optimized. It was found that the 32-day intermittent cultivation strategy and the 15-day continuous inflow strategy with fixed HRT of 72 h both achieved low biofilm concentrations (AVS<50 mg/L) and limited COD reduction abilities. However, the 6-day continuous inflow start-up strategy with gradually shortened HRT established a high biofilm concentration (AVS=514 mg/L) and a satisfied COD removal efficiency of 95% under a high OLR of 6 gCOD/(L·d). The performance of the reactors using PE and PEC were compared and found that the biofilm concentration of PEC (514 mg/L) was twice bigger than that of PE (AVS=269 mg/L). In the start-up of AIFB, short hydraulic retention time (HRT<3 h) was the key factor to wash out suspended microorganisms and facilitate the biofilm growth and the carrier coated with activated carbon could promote the biofilm formation.关键词：inverse fluidized bed bioreactor;start-up strategy;aerobic wastewater treatment
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发布时间：2024-01-05 - 摘要：In the parallel acetalization of EG and 1,2–BDO towards aldehyde, the existence of trans-acetalization has significant effect on the design and optimization of reversible reaction intensified separation method for EG recovery in syngas-based EG production process. Thus, aimed at exploring the reaction of 1,2–butanediol (1,2–BDO) with 2–ethyl–1,3-dioxolane (2ED) under acidic ion exchange resin catalyst, the impacts of main variables, such as the string speed, catalyst particle size and loading, reaction temperature and reactants feed molar ratio, on trans-acetalization reaction conversion were studied. High reaction temperature and 2ED to 1,2–BDO molar ratio facilitated the conversion of 2ED to 2–ethyl–4–ethyl–1,3–dioxolane (24DED). The activation energies (Ea) of the forward and backward reaction were 70.48 kJ/mol and 80.14 kJ/mol, respectively, and the corresponding pre-exponential factors were 3.79×1010 L/(mol·min·g) and 1.95×1012 L/(mol·min·g), respectively. The results also showed that the trans-acetalization reaction was exothermic with a reaction heat of –7.83 kJ/mol. The study of trans-acetalization reaction can provide guidance on properly altering the reaction conditions to promote the 1,2–BDO conversion and decrease the EG conversion and provide reliable basic data for process design as well as industrial application.关键词：acetal exchange;1, 2–butanediol;2–ethyl–1,3–dioxolane;kinetics
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发布时间：2024-01-05 - 摘要：In various process industries such as chemical production and petrochemical industry, the interphase heat (mass) transfer in many systems is involved. The exploration of enhanced transfer process has become the focus and hot spot of research. As a new technology to effectively enhance the heat and mass transfer between phases and promote micro-mixing, impinging stream has shown good application prospects in the fields of absorption, crystallization and ultra-fine powder preparation and so on. Based on the author’s years of experience in the field of impinging stream and research results, the research progress of impinging stream technology and the development of new reactors were reviewed. Using LDA, PDA, PLIF and other advanced visual testing techniques, the rich information such as pressure fluctuation, instantaneous and time-average velocity and concentration signal in the impinging stream field under different structural arrangements were extracted, and the macroscopic pressure, velocity and concentration distribution of the flow field were obtained. At the same time, the role of each physical parameter in the fluid mechanics equations was accurately grasped. The chaotic analysis, fractal analysis, wavelet transform and Hilbert-Huang transform were used to identify the chaotic and random components of the signal, calculate the quantitative description of nonlinear characteristic parameters, such as correlation dimension, Kolmogorov entropy, Lyapunov exponent and Hurst exponent and clarify the macroscopic motion characteristics, heat transfer, mass transfer and reaction effects of flow field. In addition, the indicators such as separation degree IOSand plane mixing uniformity U were introduced to quantitatively characterize the mixing and oscillation characteristics of impinging stream mix-reactor under different structural characteristic parameters (nozzle diameter d, nozzle spacing L, etc.), and determine the best working conditions for mixing.Through the above research, the theory of complex turbulence system was constantly improved. Combined with FLUENT numerical simulation software, experiments and theories confirm each other, providing guiding parameters for the optimization of the structure of the impinging stream reactor and the development of new equipment. Based on this, the author has independently developed multiple sets of coaxial impinging mix-reactor and horizontal three-way impinging stream mix-reactor with intellectual property and establishing a two-component layer impinging stream reactor as the core to establish an industrial scale demonstration device for preparation of ultrafine powder, which provides a new idea for the development and application of impinging stream technology in industry. Finally, it was pointed out that the complex impinging stream mix-reactor that explores synergy with other advanced technologies (ultra-high pressure, supercritical, etc.) has become a major direction for future research and development.关键词：impinging stream;flow field characteristics;mixing;nonlinear analysis
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发布时间：2024-01-05 - 摘要：The modified mechanism of iron-based OC doped by Co were studied. Three microscopic Co-doped models of iron-based OC were established based on density functional theory (DFT) to research the changes of electronic structure and reaction characteristics of doping model surfaces. Firstly, the periodic slab models of Fe2O3(104) were built using CASTEP, one of the module of Material Studio software; Secondly, the Co-doped models (Co–Fe2O3(104)) were built via replacing different coordinate Fe atoms (Fe5f, Fe6f and Fe7f) with Co atoms; Finally, the surface energy, binding energy and density of state (DOS) of all models were calculated. Moreover, the bond length, angle and distance of doping sites atoms with other atoms were calculated. Besides the isothermal adsorption features of CO on Fe2O3(104) and Co–Fe2O3(104) were detected. CO molecules were selected as a probe to test the oxidation reaction properties of Co-doped and pure Fe2O3(104) models and get the information of the reaction path, transition state and reaction activation energy. The stability order of Co-doped models obtained after geometric optimization as follows: Co5f–Fe2O3(104) > Co 6f–Fe2O3(104) > Co 7f–Fe2O3(104), corresponding to the binding energy is –0.399 eV, –0.215 eV and 0.487 eV (1 eV=96.485 3 kJ/mol), respectively. The doping of Co at Fe5f and Fe6f sites were exothermic process, and released much more energy at Fe5f atom site. However, the doping of Fe7f atoms was an endothermic reaction. Co doping changed the average bond length (LO-M) of adjacent O atoms at doping site, where the M represents Fe or Co atoms. Especially, the LO3 f-M increased 0.004 4 nm after Co atom replacing Fe7f atom. The total state density (DOS) of the models all moved towards Fermi level (0 eV), and the delocalization was enhanced in the range of –8 eV～0 eV energy, and the filling state energy of the Co5f–Fe2O3(104) model system near Fermi level was higher than that of other models. The isothermal adsorption of CO indicated that Co doping improved the adsorption amount of CO on the surface of the model. It shown two ways of adsorption: the peak near –2.0 eV was the adsorption peak of CO formed at the alkaline site on the surface of the model, and the peak near –0.75 eV was formed at the non-alkaline site. The adsorption energy of CO on the surface of Co5f–Fe2O3(104) was largest (–0.851 eV), while the adsorption on the surface of Co7f–Fe2O3(104) required additional energy (0.386 eV). The bond length (LCO) of Co6f and Co7f doped sites were increased by 0.000 4 nm and 0.001 1 nm compared with the pure surface model, indicating that Co-doped surfaces had a greater activation effect on CO molecules. The transition state analysis illustrated that the reaction activation energy of CO oxidized to CO2 at Co-doped surfaces decreased significantly. It also shown that the activation energy of CO on the surface of Co5f–Fe2O3(104) was the lowest, decreased 0.518 eV (49.974 kJ/mol) less than that on the surface of Fe2O3(104), and the corresponding reaction energy increased by 0.445 eV. It is indicated that the different bonding structures in their oxides of Co and Fe lead to an increase in suspended bonds and surface energy on the doped model surface, and a shift in state density toward Fermi level, which improved the surface activity of Fe2O3(104). In addition, Co doping at the low coordination of Fe atom sites was more conducive to reducing the reaction activation energy of oxidized CO. Therefore, it was feasible to improve the reactivity of iron-base OC by doping metal Co, and its modification effect was closely related to the characteristics of the components and the doping mode.关键词：chemical looping combustion;density functional theory;Co-doped;iron-based oxygen carrier
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发布时间：2024-01-05 -
Microfluidical-synthesis and Quantum Chemistry Insight into Ionic Imprinted Chitosan Adsorbents AI导读
摘要：In order to selectively remove targeted metal ions from complex metal ions contained wastewater, ionic imprinted chitosan microspheres were synthesized by combining with microfluidics and ion imprinting technologies. Its adsorption performance of as-prepared microspheres were systematically investigated by batch adsorption experiments and DFT molecular simulation to reveal the interaction mechanism and selective binding principle between as-prepared microspheres and targeted Cu ions. The results showed that under the optimized adsorption condition (initial Cu concentration: 400 mg/L, pH = 6) in a thermostatic shock state (35 °C and 160 r/min), the adsorption equilibrium can be achieved within 48 h with the maximum adsorbance of 117.76 mg/g for Cu ions. Besides, the adsorption kinetics and isotherms results were well fitted with pseudo-second order model and Langmuir model, respectively, which demonstrated that the adsorption process was a monolayer chemisorption process accompanied by electron transfer. Moreover, as-prepared microspheres exhibited rapid recognition and selective adsorption property towards targeted Cu ions in binary and/or ternary coexistence systems, which could be attributed to the ionic scale effect and higher electronegativity of Cu ion, as well as the stronger adsorption energy between the targeted Cu ion and the molecular monomers of as-prepared chitosan microspheres. It was concluded that the obtained research achievements could provide theoretical guidance for the development and optimization of new generation biosorbents with high efficiency performance.关键词：chitosan adsorption microspheres;selective removal;microfluidic technique;ion imprinting technology;DFT molecular simulation- 2882
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发布时间：2024-01-05 - 摘要：Due to the limitations of powdered catalysts in continuous catalytic system, such as high pressure drop, easy blocking and the loss of active components, monolithic carbonaceous composite catalyst with high voidage was employed for phenol degradation in fixed bed reactor. Firstly, monolithic NCNTs/PSSF microfibrous composite catalyst was synthesized by chemical vapor deposition (CVD) method using melamine as the sole carbon and nitrogen source, and effects of temperature, flow rate of carrier gas and the amount of melamine on the morphology and structure of catalyst were investigated. Then catalyst synthesized under optimized conditions was applied for catalytic wet peroxide oxidation of phenol in a fixed bed reactor. Characterization results indicated that the catalyst exhibited a three-dimensional network structure and stainless steel fibers were wrapped with NCNTs. The quality and yield of NCNTs increased with the increase of temperature, while morphology transition could be observed at 1 000 ℃. With the increase of carrier gas flow rate, the yield and quality of NCNTs decreased while the specific surface areas and total pore volume increased.With the increase of the amount of melamine, the yield of NCNTs increased and the quality remained nearly unchanged. The specific surface areas of catalyst synthesized under optimized conditions was 14.50 m2/g, about 45 times larger than that of the bare PSSF support, and TEM images showed that NCNTs with a nitrogen-doping level about 4% exhibited distinct inter-linked corrugated morphology and highly wrinkled nanotube walls. CWPO of phenol under conditions of 2 cm of catalyst bed height (contained only about 0.5 g NCNTs), 2 mL/min of feed flow rate and temperature of 80 ℃ showed that 99% of H2O2 conversion could be achieved, and phenol and TOC conversions could reach 80% and 45%, respectively, after 9 h continuous reaction. Moreover, only few Fe3+ leaching concentration (1.5 mg/L) was detected. Long term catalytic tests further indicated that high phenol conversion over 80% could still be achieved by using the catalyst over 100 h, and Fe3+ leaching concentration was detected lower than 5 mg/L.关键词：nitrogen-doped carbon nanotubes;catalytic wet peroxide oxidation;phenol;fixed bed reactor
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发布时间：2024-01-05 - 摘要：Middle and low temperature geothermal power generation by thermoelectric materials receives increasingly attention, while the key difficulty involved is how to increase the thermoelectric conversion efficiency. This paper presents a conceptual design of heat exchanger on the basis of a Self-Similarity microchannel Heat Sink (SSHS) which can reduce the volume and weight of the system to a great extent and increase the thermo-electric conversion efficiency. With a heat exchanger of the hot side as an example, its heat transfer and flow resistance characteristics were numerically evaluated and compared with two traditional heat exchange structures. The calculation results indicate that the current design of SSHS has a better performance and uniformity in heat transfer. Under conditions of flow rates of 0.0103～0.0186 kg/s, heat flux of 2 W/cm2 and entrance water temperature of 100 ℃, its heat transfer ability is over twice of that of a conventional heat exchanger, and average temperature of the heat release surface is raised by 5～10 K, and uniformity in temperature distribution is increased over 50%. As a consequence, an improved thermoelectric conversion efficiency is obtained, although a larger flow resistance is hard to avoid. For the current design the total pressure drop is no more than 450 Pa, it is still very suitable for a direct thermo-electric conversion system.关键词：geothermal heat;thermo-electric conversion;self-similarity microchannel sink;heat exchanger structure
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发布时间：2024-01-05 - 摘要：To investigate the anti-seismic resilience of inter-story substructure of PEC column-steel beam frame with partial self-centering friction damped connection, a specimen with 1∶2 scale was designed and fabricated, then two tests before and after renovation were conducted under cyclic lateral loading. Based on the test observations and measurements, the specimens’ anti-seismic behaviors such as the hysteretic characteristics, lateral stiffness, self-centering function and energy-dissipation capacity were studied. The results indicated that rational dimension of bolt slotted hole was designed to achieve the force-transfer mechanism of partial self-centering friction damped connection at design-earthquake level and bearing-type connection was formed at maximum considered earthquake level; the force-transfer mode of concrete equivalent strut was formed in the panel zone due to pre-tension penetrating bolts and pre-tensioned bars, and reinforced gusset plate was designed to confine concrete in the panel zone, correspondingly the anti-seismic requirements of strong joint were met; when the inter-story drift arrived at the inter-story drift limit of frame structure at design-based earthquake level, self-centering functions were sound for residual drifts of inter-story were 0.11% and 0.13%, respectively, while the inter-story drift surpassed the inter-story drift limit of frame structure at maximum considered earthquake level, self-centering functions were still good for residual drifts of inter-story were 0.42% and 0.44%, respectively; with simple repairmen, the force-transfer developing process, lateral stiffness, self-centering function and evolution mechanism of energy dissipation were restored, hence the specimen owned superior anti-seismic resilience.关键词：partial self-centering connection;inter-story substructure of PEC column frame;self-centering function;seismic resilience;test research
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发布时间：2024-01-05 - 摘要：The Hong Kong–Zhuhai–Macao Bridge submarine tunnel was constructed by the immersed pipe. Before the final joint is installed, a closure gap will be formed in the middle of the immersed pipe. The water flow is often concentrated in the closure cap with a fast increasing velocity, which adds difficulty to the installation of the final joint. In this article, a three-dimensional mathematical model of water flow in the local waters of the closure gap was established, and the flow structure in the closure gap area was simulated. The relationship between the closure gap water flow and the Pearl River runoff including the tidal range was analyzed. The simulation results showed that the surface velocity in the closure gap was greater than the bottom one, and the velocity of ebb tide was greater than that of flood tide. The closure gap water flow increased with the increase of the tidal range under the same runoff, and the closure gap water flow increased with the increase of the upstream runoff under the same tidal range. The crane ship used in the final joint installation were only 30 m away from the closure gap. The bowing action of the bow made the flow rate of the local waters on the west side of closure gap increase sharply, but it had less influence on closure gap water flow conditions. According to the numerical simulation results of the hydrodynamic conditions in the closure gap, the external water conditions and the appropriate time for the final joint installation and construction were determined, which provided technical support for the final completion of the Hong Kong–Zhuhai–Macao Bridge immersed tunnel.关键词：Hong Kong–Zhuhai–Macao Bridge;immersed tube tunnel;3D current model;closure gap;tidal current
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发布时间：2024-01-05 - 摘要：The damage evolution of concrete is a process during which internal cracks emerge and propagate, and correspondingly the electromagnetic properties of concrete is changed according to the degree of damage development. In order to figure out the relationship between mechanical properties and electric behaviors as well as the propagation properties of electromagnetic waves during the damaging or failure of reinforced concrete members, a reinforced cement paste coaxial component (reinforced cement paste coaxial component, RCPCC) was designed based on the principle of coaxial cable, in which cement paste was regarded as the dielectric for its homogeneousness. The inner bar and outer reinforcement cage were used as conductors. According to the basic principles of electromagnetism, the finite element analysis on RCPCC was carried out. Following that, the simplified equivalent circuit model of the components with different damage levels and the corresponding electrical parameter expressions that can characterize the structural properties of RCPCC were established. Based on this model, the effect of the damage degree on alternating current circuit parameters (series impedance value, series capacitance and phase angle value) of component was analyzed. Furthermore, the bending and shearing failure experiments on RCPCC were carried out. The alternating current circuit parameters of the component during the bending and shearing failure process were measured by LCR instrument. Meanwhile, the spectrum analyzer was used to record the variation of the fundamental peak during the testing. The results show that the bending and shearing failure process of RCPCC could be divided into three phases, and the change of electromagnetic property value of each phase was different. The changing rate of the measured electrical parameters was consistent with the damage evolution rate. Consequently, there was an intrinsic connection between mechanical properties and electrical behaviors during the failure process. With the propagation of cracks, series impedance value increased, while series capacitance and phase angle value decreased. With the internal crack development of the component, the obstruction of the electromagnetic wave propagation reduced, resulting in the increase of fundamental peak. The damage degree of the component could be characterized by fundamental peak. The laws conducted by the results of testing were in good agreement with the analysis results of theoretical model, which verified the reliability of the model.关键词：cement paste coaxial component;equivalent circuits;electromagnetic properties;damage evolution;bending tests
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发布时间：2024-01-05 - 摘要：In the rectangular open channel, the free overfall can be used as the discharge measure device. In the channel project, the channel usually has the features as a rough and steep one. Few study is conducted on the hydraulic characteristics of free overfall in a rough and steep rectangular channel. An experimental study of the free overfall from a rectangular channel with differing slopes and wall roughness were investigated in this paper. In the tests, the bed slope S ranged from 0.002 6 to 0.097 3, the wall Manning roughness coefficient n ranged from 0.009 3 to 0.019 3, and the flow Froude number Fr0 ranged from 1.0 to 6.62, which were much wider than previous studies. The results showed that, when the flow of upstream at the end was supercritical, the ratio of the end-depth he and critical-depth hc (he/hc) was linearly related to
$\sqrt S /n $ $\sqrt S /n $ $\sqrt S /n $ 关键词：open flow;free overfall;supercritical flow;rough and steep channel;hydraulic characteristics- 2208
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发布时间：2024-01-05 - 摘要：With the characteristics of loose structure, low cohesion and poor stability, the aeolian sand is of poor stability against wind erosion under the arid and windy environment, which affects the stability of transmission line tower foundation. Sand consolidation technology developed in recent years can effectively improve the physical and mechanical properties of aeolian sand and improve the bearing capacity of foundation. To study the influence of cement solidification technology on the bearing capacity and failure mode of tower foundation, aeolian sand in the Taklimakan Desert in the south of Xinjiang Province is taken as the research object. The aeolian sands with water contents
$\omega$ $\omega$ $\omega$ $\omega$ $\omega$ 关键词：aeolian sand;consolidating with cement;pull-out test;the ultimate uplift bearing capacity;tensile failure;microstructure- 2121
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发布时间：2024-01-05 - 摘要：The impact effects of the vehicle dynamic loads should be considered in designing bridge structures. To calculate the vibration response of long-span curved bending beam bridge caused by vehicle, form function matrix was created by introducing high order displacement interpolation function in the nodes. Based on virtual work principle and dynamic finite element theory, spatial element stiffness matrix and density matrix of curved box girder bridge with 9 freedom degrees in each node were deduced, the restricted torsion and shear lag effect were considered in deducing stiffness matrix, the influence that mass center didn’t coincides with torsion center was also considered in deducing density matrix. The vibration equations of vehicle-bridge coupling were established by introducing vehicle mode with 7 freedom degrees. Newmark–β method was used on MATLAB to solve vibration response of system under vehicle dynamic loads, and influences of vehicle speed, vehicle weight and primary beam stiffness on impact coefficient were analyzed. The results show that when displacement impact coefficient was used to replace moment and shear impact coefficient for section internal force design, moment design value would maximally increase by 2.89%, shear force design value would maximally decrease by 34.9%; vehicle weight had a little influence on impact coefficient; displacement and moment impact coefficients decreased with the increasing of primary beam stiffness, while shear force impact coefficient increased with the increasing of primary beam stiffness; the theoretical calculation values agreed well with the finite element results of ANSYS.关键词：dynamic impact coefficient;element matrix;Newmark–β method;finite element;curved box girder bridge;vehicle–bridge coupling
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发布时间：2024-01-05 - 摘要：As a kind of absolute stress measurement method, hydraulic fracturing technology is widely used in the field of in-situ stress measurement. The hydrodynamic influence factors which affect the rock fracture value during the measurement process are mainly the injection rate, viscosity and density of the fracturing fluid. Because the number of influencing factors is large and the experiment is a destructive experiment for the testing core, the experimental design is under a complex condition, and the comprehensive or orthogonal experimental method will seriously affect the experimental results. Based on the theoretical analysis of fluid mechanics influence on crack propagation and fracturing pressure, An optimization scheme for hydraulic fracturing simulation based on the mixed-level uniform design method was proposed in the paper. According to the influencing factors such as loading rate, viscosity and density of the fracturing fluid and its parameter values (number of levels), a uniform experimental design scheme was constructed. The DPS data processing software was used to obtain the table of optimal mixed-level uniform design, and then according to this table the typical points of different hydrodynamic parameters could be selected. Finally, the experimental results were compared to comprehensive experimental results. It was proved that the rock fracturing pressure value of the optimization experiment was within the comprehensive experimental measurement interval, which confirmed the influence of different fluid mechanics factors on the rock fracturing pressure value. The number of experiments in this optimization scheme is only one quarter of the orthogonal experimental scheme, therefore, the efficiency of simulation experiments of multiple factors affecting hydraulic fracturing is significantly improved. It provides a fast and effective experimental method for the subsequent establishment of the fracture pressure correction formula and compensation model for different fluid mechanics influencing factors, and it also has positive significance for accurating measurement of in-situ stress.关键词：hydraulic fracturing;fluid mechanics;simulation experiment;uniform design method;optimization research
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发布时间：2024-01-05 - 摘要：With the increasing depth of underground engineering, the accurate evaluation of the depth and the degree of excavation damage zone (EDZ) in deep rock engineering is gradually influenced by the high geostress field and it is important to assess the impact reasonably. Relying on the excavation of a deep diversion tunnel, the drilling plan of distressing the in-situ stress step by step was adopted. At the outer zone of sampling area, conventional sampling holes were drilled in the form of a circular closed boundary. And boreholes and low stress coring were also carried out at the centre of the sampling area. The acoustic detection results of the depth and the degree of the damage area under different in-situ stress levels were obtained at the same location by acoustic detection device, and laboratory tests were carried out based on the core samples from the holes above. The uniaxial compressive strength of rock mass under different in-situ stress levels were given from acoustic wave velocity results by Hoek-Brown strength empirical formula to represent rock mechanics properties. These above contributed to judge the influence of the different in-situ stress levels on acoustic detection and damage degree evaluation in blasting EDZ. Researches showed that the conventional acoustic detection of excavation damage zone in high stress area would underestimate the depth of surrounding rock and the damage degree, which would be underestimated about 10% to 30% when the initial stress was 45 MPa. When the local stress level was reduced from 45 MPa to 30 MPa, the uniaxial compressive strength of rock mass would be seriously overestimated about 30% to 100%. Therefore, the high in-situ stress level had a significant impact on the results of acoustic detection and damage zone evaluation of surrounding rock. The effect of in-situ stress level on acoustic detection must be taken into account and corrected properly by reducing and increasing in evaluating rock mass quality by using wave velocity index in engineering.关键词：in-situ stress;surrounding rock damage;acoustic detection;rock mass quality
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发布时间：2024-01-05 - 摘要：There are few in-situ creep test data of tunnel anchor for suspension bridge. To obtain the creep deformation law of tunnel anchor of Xingkang Bridge on Yakang Expressway and enrich creep test data of tunnel anchor of super-large suspension bridge, creep tests of 1∶10 in-situ shrinkage model of the Ya’an side slope tunnel anchor of Xingkang Bridge were carried out, based on the specific geological conditions in the Ya’an side slope tunnel anchorage area of Xingkang Bridge and the similar theory of elastic mechanics. According to the creep characteristics of the model anchor and surrounding rock mass under 1.0P, 3.5P and 7.0P loads, the whole creep process of the model anchor, surrounding rock and interfacial dislocation were analyzed. The results show that under 1.0P, 3.5P and 7.0P loads, the maximum creep deformation of anchor body was 0.62 mm, 0.97 mm and 1.58 mm, the maximum creep deformation of surrounding rock was 0.49 mm, 0.85 mm and 1.38 mm, and the maximum creep deformation of anchor body and surrounding rock was 0.15 mm, 0.64 mm and 1.43 mm, respectively. On the basis of in-situ scale tests, the three-dimensional viscoelastic-plastic numerical analysis of the interaction between anchorage and surrounding rock mass was carried out by using FLAC3D finite element software. The comparison between the field measured values and numerical analysis results shows that the measured creep deformation and calculation results of the anchorage and surrounding rock of the Ya’an side bank slope tunnel of Xingkang Bridge have the similar evolution trends and range of amounts. The creep of tunnel anchorage and surrounding rock mass of Xingkang Bridge on Yakang Expressway belong to stable creep stage under various loads. The long-term stability of suspension bridge was not affected by the creep of anchorage and surrounding rock mass. The test results provide a basis for the reliability evaluation of the tunnel anchorage system of Xingkang Bridge, and also provide a reference for similar engineering designs.关键词：Xingkang Bridge;unnel-type anchorage;scaling model;creep test;long-time stability
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发布时间：2024-01-05 -
Experimental Study on the Effect of Siltation Height on Water Level Change in Steep Slope Channel AI导读
摘要：In a steep slope river, the local siltation may be caused by the change of sediment transport rate, and then the water level will change with the siltation height. In this paper, a generalized model for simulating the height of silt body was established in four kinds of specific slopes, and the effect of silt height on water level was explored. The results showed that under different inflow conditions, the water level will suddenly increased or fall in the process of increasing and decreasing the siltation height, and there were differences between the siltation height corresponding to the sudden increase and the sudden fall. In the course of increasing the silt height, the maximum increase of the upstream water level of the silt body could be up to 6 times, while in the course of decreasing the silt body, the recovery of the water level was delayed. Through linear regression analysis, the relationship between critical siltation height and hydraulic index of inflow was obtained. Based on the criterion of critical siltation height, the judgement methods of safe area, possible disaster area and disaster area are established. The research results can provide reference for river dike design and river regulation in flood for sediment disaster prevention.关键词：steep rivers;model test;siltation;adverse jump;water level- 2296
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发布时间：2024-01-05 - 摘要：Alluvial channels tend to adjust their themselves and finally develop a stable hydraulic geometry in response to the change of water and sediment from upstream. The design of alluvial channels to conduct a specified flow is one of the major problems in the field of hydraulic engineering, as well as a good channel section can effectively transfer water and sediment and avoid the equilibrium damage of erosion and depositon. In the paper, the Darcy friction factor gradient was analysed, and it was found that the adjustment of friction factor gradient was composed of three parts, namely, the depth adjustment, the width adjustment and the slope adjustment. With the hypothesis that a linear relationship between the probabilities of adjustments of widths and depths exists, an analytical regime method was proposed to determine the stable open channel dimensions. Because of the transportation of sediment, the hydraulic radius in an open channel could be divided into two parts, i.e. the hydraulic radius without sediment transportation and with sediment transportation. The hydraulic radius without sediment transportation could be computed with traditional log or exponential law of Darcy friction factor, also, empirical expression for the hydraulic radius with sediment transportation was proposed based on the measured data. Furthermore, the analytical regime equation showed that a linear relationship exists between the unknown function of the hydraulic radius and the 0.3th power of the slope. The exponential parameter decreases with increasing parameter. Then, the unknown variable and exponential parameter in the new analytical regime equation were also determined using collected field data and the formula was suitable for sandy, gravel and pebble rivers. Finally, the validity of the presented model was tested with field data, and the computed water depth and width were all in good agreement with measured data. The comparison between measured data and computed data with previous modes showed that present equation gets the lowest errors.关键词：stable alluvial channel;Darcy friction factor;friction factor gradient;water and sediment transport;additional slope
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发布时间：2024-01-05 -
Distribution Characteristics Calculation of Temperature and Shrinkage Cracks in Large Concrete Floor AI导读
摘要：It is difficult to solve the leakage problem of large underground structures,in which the width and quantity of cracks on concrete floor directly determine the leakage severity of the whole underground structure, but there are few studies on the distribution characteristics of cracks after cracking. In this paper, the expressions of crack location, width, and spacing of concrete floor under increasing temperature and shrinkage effect were obtained by analytic method, and the distribution characteristics of cracks were described. Under the condition that the surface of the slipping steel bar was subjected to approximately uniform friction (concrete tensile strength) and the concrete at the slipping critical point was the ultimate 100×10–6 tensile strain, the relationship among the parameters of the steel bar tension, the slipping length and the deformation of the steel bar was obtained, and then the width of the first crack and the displacement and stress distribution in the new floor plate were calculated. When the location of cracks and the stiffness of slipping reinforcement were constant, the new combination stiffness and free displacement value of the floor body were obtained from the calculation of the coordinate origin and the end block to a crack, and then the crack width after stress redistribution was solved. Under the continuous increase of temperature or shrinkage strain, the assembly block stiffness and maximum tensile stress after the emergence of new cracks were calculated, and the position of existing cracks and the stiffness of slipping bar for the next step were stored. Up to the strain maximum, the final crack width and spacing of the whole block were obtained. The method of describing cracks character of concrete floor was established. Finally, 0 ~ 350×10–6 temperature or shrinkage strain was continuously applied to a concrete floor with a size of 80 m×20 m×0.4 m, and the cracks distribution characteristics calculation was finished in five time cracking process.关键词：concrete floor;temperature and shrinkage;slippage reinforcement;cracks- 2453
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发布时间：2024-01-05 - 摘要：When the standard binary particle swarm is used for the feature selection optimization of Mahalanobis–Taguchi system, the computational speed is slow and the selected features combination of Mahalanobis–Taguchi system is prone to falling into the local optimal solution. To address these problems, a feature selection optimization method of Mahalanobis–Taguchi system based on an improved binary quantum behavior particle swarm was proposed. Firstly, in order to avoid the influence of complex collinearity for the distance metric, the Gram–Schmidt orthogonalization method was used to calculate the Mahalanobis distance value. Through the ROC curve, the optimal threshold point for the system classification was determined. The misclassification rate and the selected variables rate were defined and a multi-objective optimization model was built. Then, an improved quantum behavior particle swarm optimization algorithm was presented to solve the optimization model, which performs binary coding on the particle based on probability. Through the optimized features combination, a new Mahalanobis–Taguchi prediction system was established. Finally, the fetal health diagnosis was carried out. The experimental results showed that the improved quantum behavior particle swarm optimization algorithm could effectively enhance the iterative speed, and the optimized Mahalanobis–Taguchi system had the better prediction accuracy.关键词：Mahalanobis–Taguchi system;variable selection;binary quantum behavior particle swarm;optimization
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发布时间：2024-01-05 - 摘要：In order to address the problems that the original teaching–learning-based optimization (TLBO) cannot balance the global exploration and the local exploitation well, and the current opposition-based learning (OBL) strategies are too simple, a multi-opposition teaching–learning-based optimization (MOTLBO) was proposed by combining various opposition-based strategies with TLBO. Firstly, learning from the idea of OBL, a nonlinear mixed opposition-based learning model with a Sigmoid function and gradual evolution change was designed, in which the boundary search information and the population historical search information systematically were taken into account. Secondly, a self-learning stage guided by search boundary was added based on the existing teaching and learning stages, which can enhance the population diversity greatly. Finally, combining the mixed model with each stage of the algorithm, the calculation methods of opposition-based solutions according to mean individual, randomly selected individual, and optimal individual, respectively, were presented, which fully utilized the historical search experience of the population and hence improved the convergence precision and speed. The Benchmark test functions with different characteristics were used to test the nonlinear mixed opposition-based learning model and convergence performance of the proposed algorithm. The experimental results showed that the nonlinear mixed opposition-based learning model has stronger capability of global exploration and local exploitation than the one that only uses the boundary search information or population historical search information. By compared with the TLBO and some of its current outstanding variants, the proposed algorithm obtained high optimization accuracy and stability while guaranteeing the convergence speed, achieving great improvements on comprehensive performances. Moreover, the experimental results of the spread spectrum radar Polly phase code design demonstrated that the proposed algorithm can escape from local optimum effectively. Hence, the proposed algorithm can also be used to handle the real-word engineering optimization problems.关键词：teaching–learning-based optimization;opposition-based learning;search boundary;population information;nonlinear mixed model
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发布时间：2024-01-05 - 摘要：In order to solve the problems that servers and users may collect and query user’s attribute information, malicious attackers may launch man-in-the-middle attack, replay attack and forgery identity attack when attributes were matched by users in mobile social networks, a privacy protection scheme for social discovery based on key agreement and identity anonymity technology was proposed. In the scheme, the respective attribute hash sets of the query user and the response user whose identity were authenticated by the system were generated by irreversible hash functions and random numbers randomly selected by the query user. The server was responsible for calculating attribute matching values between all responding users and querying users, and recommending friends to querying users according to the size of the values. The Private keys used in the secure communication in the process of query matching and subsequent establishment of friendship by legal users of the system, were generated by secretly transferring public parameters through the server based on Diffie–Hellman key agreement technology, and confidential to the server. The security analysis demonstrated that the scheme could prevent the leakage of user’s privacy information and ensure the anonymity of user’s identity. At the same time, a simulation experiment was designed on MyEclipse platform based on the jPBC cryptographic algorithm library. Experimental results showed that compared with the similar schemes, the proposed scheme is more effective in reducing user’s computation and communication burden.关键词：social discovery;key agreement;identity anonymity;bilinear pairing
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发布时间：2024-01-05 - 摘要：To meet the application requirements of large-scale secret sharing for electronic voting and improve the efficiency of secret sharing among a large number of devices, a secret sharing scheme based on random linear block code was proposed and applied to electronic voting. First, a parity-check matrix of random linear block code was constructed, which gives the coefficient matrix of the decoding equation set an extremely high probability of full rank, and ensures correct decoding of the secret. The encoding matrix was then generated from the parity-check matrix, and the voting information was encoded. Part of code word elements of the voting information were distributed to other equipment as shares without revealing the original information. Finally, the received shares were sentback by equipment to the source and the voting information with the shares received from others for restoration was decoded. The secret sharing based on random linear block code can discover the restored secret and shares error while restoring the secret. In this paper, the secret sharing speed, recovery speed and data redundancy volume under different data sizes of secret and the number of sharing participants were tested. Experiments showed that the proposed scheme has higher sharing and restoration efficiency, and lower data redundancy than traditional schemes. The proposed secret sharing based on random linear block code provides an efficient secret sharing scheme, which can effectively solve the key security problems such as privacy protection, voting record tamper-proof and storage security of large-scale electronic voting.关键词：random linear block code;secret sharing;electronic voting;random matrix
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发布时间：2024-01-05 - 摘要：As a candidate non-orthogonal multiple access technology for 5G, the sparse code multiple access (SCMA) can effectively improve spectrum efficiency. In this paper, the layered multicast scheme in SCMA network was first studied, of which the system capacity is not limited by the worst channel quality user in the multicast group. Specifically, a network energy efficiency (EE) maximization problem subject to quality of service (QoS) requirements, codebook assignment, and power allocation was formulated. In order to reduce the computational complexity, a fast sub-optimization algorithm (FSA) by separating codebook assignment and power allocation was then proposed. Finally, the simulation results verified the network EE of the proposed algorithm significantly outperforms conventional multicast (CM) scheme in SCMA systems and orthogonal frequency division multiple access (OFDMA) systems. Moreover, the performance of SCMA systems with FSA is better than the performance of OFDMA systems with FSA.关键词：SCMA;layered multicast;codebook assignment;power allocation;network energy efficiency
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发布时间：2024-01-05 - 摘要：Volumetric error (VE) is determined by machine tool geometric error elements (GEE). Most of VE models in recent studies have a common issue that some GEE are missing in models explicit mathematical expressions, which directly affects machine tool VE prediction accuracy. Therefore, a methodology for complete modeling machine tool VE was proposed. Multi-body system theorem and homogeneous coordinate transformations were borrowed as analysis approaches. On the basis that initial positions and original errors eigen matrix were fully considered, VE model was guaranteed to have total machine tool GEE. Furthermore, aiming at the residual error limitation in traditional NC code VE compensation technique, NC code coordinates optimization design problem was described to replace the former reversal accumulation process. Genetic algorithm (GA) was then utilized to solve the proposed optimization problem so that VE compensation residual error was eliminated. A horizontal machining center was selected as study object, on which both numerical and experimental analyses were performed to verify the proposed modeling methodology and compensation technique. The results indicated that complete VE model comprises total 21 GEE of machining center and that VE prediction was fairly accurate. It was also showed that NC code optimized compensation technique presented in this paper may promote machining center volumetric position precision (VPP). The maximum growth of VPP, compared to uncompensated value, was 90.92%. Research results can be regarded as theorem and engineering supports for investigations on numerical manufacturing equipment precision problems.关键词：geometric error element;machine tool volumetric error;complete modeling;NC codes;optimized compensation
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发布时间：2024-01-05 - 摘要：In order to analyze the effect of coupling relationship between joint stiffness parameters on the dynamic performance of machine tool bolt joints surface, a response surface method which is based on the theory of response surface statistics was proposed to fit the natural frequency of generalized modal states and the dynamic stiffness of the joints. In this method, the natural frequency was taken as the critical index to describe the object dynamic characteristics, with which the mathematic relationship between dynamic characteristics and the stiffness parameters between the joints were analyzed. The response surface model of predicating the varying dynamic characteristics with the finite element models of single and two nodes was established by central composite experiment design and response surface method theory. The least square method with the response function and the experimental test value were taken as the optimization objective, the nonlinear programming and genetic algorithm were combined to realize the stiffness parameter identification of the joint part. The type of response surface function expression was selected to display the stiffness coupling relationship between multiple pairs of nodes, and the influence with the coupling of stiffness on the dynamics of components was revealed. In order to verify the feasibility of the method, one bolt assembly was taken as the research object. The central composite experiment was designed to determine the different combination values of the stiffness between the joints, and the natural frequencies related to the first 11 orders were acquired by conducting the modal analyses with the ANSYS software. Utilizing the acquired dynamic data, a second-order polynomial response surface model was established to describe the connections between the stiffness and the natural frequencies. The accuracy of the established model was validated after calculating the valuating indexes, the influence of the coupling of stiffness on the dynamic characteristics of the components was analyzed, and the effects of multiple rigidness coupling, uncoupling and single stiffness on the dynamic performance of structures were compared and analyzed. The results showed that the dynamic modeling simulation with multi-stiffness coupling is in good agreement with the modal frequency and mode of vibration measured in the test. The first 11 mean modal frequency error is only 1.6%, which proves the necessity of considering the coupling relation between equivalent stiffness.关键词：dynamic stiffness of the joint;response surface function identification method;algorithm of genetic algorithm;nonlinear programming
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发布时间：2024-01-05
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