Anaerobic digestion of Chinese cabbage waste was investigated through a pilot-scale two-stage digester at a mesophilic temperature of 37 °C. In the acidification digester, the main product was acetic acid, with t...Anaerobic digestion of Chinese cabbage waste was investigated through a pilot-scale two-stage digester at a mesophilic temperature of 37 °C. In the acidification digester, the main product was acetic acid, with the maximum concentration of 4289 mg·L-1on the fourth day, accounting for 50.32% of total volatile fatty acids. The oxidation reduction potential(ORP) and NH+4-N level decreased gradually with hydraulic retention time(HRT)of acidification. In the second digestion phase, the maximum methanogenic bacterial concentration reached9.6 × 1010ml-1at the organic loading rate(OLR) of 3.5–4 kg VS·m-3, with corresponding HRT of 12–16 days.Accordingly, the optimal biogas production was 0.62 m3·(kg VS)-1, with methane content of 65%–68%. ORP and NH+4-N levels in the methanizer remained between- 500 and- 560 m V and 2000–4500 mg·L-1, respectively. Methanococcus and Methanosarcina served as the main methanogens in the anaerobic digester.展开更多
Aiming at the problem of low accuracy of traditional target detection methods for target detection in endoscopes in substation environments, a CNN-based real-time detection method for masked targets is proposed. The m...Aiming at the problem of low accuracy of traditional target detection methods for target detection in endoscopes in substation environments, a CNN-based real-time detection method for masked targets is proposed. The method adopts the overall design of backbone network, detection network and algorithmic parameter optimisation method, completes the model training on the self-constructed occlusion target dataset, and adopts the multi-scale perception method for target detection. The HNM algorithm is used to screen positive and negative samples during the training process, and the NMS algorithm is used to post-process the prediction results during the detection process to improve the detection efficiency. After experimental validation, the obtained model has the multi-class average predicted value (mAP) of the dataset. It has general advantages over traditional target detection methods. The detection time of a single target on FDDB dataset is 39 ms, which can meet the need of real-time target detection. In addition, the project team has successfully deployed the method into substations and put it into use in many places in Beijing, which is important for achieving the anomaly of occlusion target detection.展开更多
The effects of different concentrations of oxytetracycline (OTC) on the dynamics of bacterial and archaeal communities during the mesophilic anaerobic digestion (37°C) of cow manure were investigated. Before...The effects of different concentrations of oxytetracycline (OTC) on the dynamics of bacterial and archaeal communities during the mesophilic anaerobic digestion (37°C) of cow manure were investigated. Before anaerobic digestion, OTC was added to digesters at concentrations of 20, 50, and 80 mg L-1, respectively. Compared with no-antibiotic control, all methane productions underwent different levels of inhibition at different concentrations of OTC. Changes in the bacterial and archaeal communities were discussed by using PCR-denaturing gradient gel electrophoresis (DGGE). Results showed that OTC affected the richness and diversity of bacterial and archaeal communities. The bacterial genus Flavobacterium and an uncultured bacterium (JN256083.1) were detected throughout the entire process of anaerobic digestion and seemed to be the functional bacteria. Methanobrevibacter boviskoreani and an uncultured archaeon (FJ230982.1) dominated the archaeal communities during anaerobic digestion. These microorganisms may have high resistance to OTC and may play vital roles in methane production.展开更多
A mathematical mechanism model was proposed for the description and analysis of the heat-stirring-acid leaching process.The model is proved to be effective by experiment.Afterwards,the leaching problem was formulated ...A mathematical mechanism model was proposed for the description and analysis of the heat-stirring-acid leaching process.The model is proved to be effective by experiment.Afterwards,the leaching problem was formulated as a constrained multi-objective optimization problem based on the mechanism model.A two-stage guide multi-objective particle swarm optimization(TSG-MOPSO) algorithm was proposed to solve this optimization problem,which can accelerate the convergence and guarantee the diversity of pareto-optimal front set as well.Computational experiment was conducted to compare the solution by the proposed algorithm with SIGMA-MOPSO by solving the model and with the manual solution in practice.The results indicate that the proposed algorithm shows better performance than SIGMA-MOPSO,and can improve the current manual solutions significantly.The improvements of production time and economic benefit compared with manual solutions are 10.5% and 7.3%,respectively.展开更多
The performance of the Dongying multi-stage ponds-wetlands ecosystem was investigated in this work. Study of the removal of different pollutants (BOD5, COD, SS, TP, TN, NH3-N, etc.) in different temperature seasons an...The performance of the Dongying multi-stage ponds-wetlands ecosystem was investigated in this work. Study of the removal of different pollutants (BOD5, COD, SS, TP, TN, NH3-N, etc.) in different temperature seasons and different units in this system indicated that effluent BOD5 and SS were constant to less than 11 mg/L and 14 mg/L throughout the experimental proc- esses; but that the removal efficiencies of pollutants such as TP, TN, NH3-N, COD varied greatly with season. The higher the temperature was, the higher was the observed removal in this system. Additionally, each unit of the system functioned differently in removing pollutants. BOD5 and SS were mainly removed in the first three units (hybrid facultative ponds, aeration ponds and aerated fish ponds), whereas nitrogen and phosphates were mainly removed in hydrophyte ponds and constructed reed wetlands. The multi-stage ponds-wetlands ecosystem exhibits good potential of removing different pollutants, and the effluent quality meet several standards for wastewater reuse.展开更多
A process design approach for multi-stage stretch forming was proposed by combining the strain distribution method and finite element method(FEM)to determine the minimum stage number and deformation amount of each sta...A process design approach for multi-stage stretch forming was proposed by combining the strain distribution method and finite element method(FEM)to determine the minimum stage number and deformation amount of each stage.The strain distribution method was used to calculate the deformation amount of each stage and evaluate the formability through a safety criterion.FE simulation was taken as an analysis tool to reveal the deformation behaviour,to predict the strain contour and to determine the process parameters at each stage.To evaluate the effect of heat treatment after pre-strain on occurrence of deformation defects during the subsequent deformation,a multi-stage uniaxial tension test for 2B06 aluminium alloy sheet was carried out.A case study demonstrates that the approach has high reliability and good practicability.展开更多
Springback of a SUS321 complex geometry part formed by the multi-stage rigid-flexible compound process was studied through numerical simulations and laboratory experiments in this work.The sensitivity analysis was pro...Springback of a SUS321 complex geometry part formed by the multi-stage rigid-flexible compound process was studied through numerical simulations and laboratory experiments in this work.The sensitivity analysis was provided to have an insight in the effect of the evaluated process parameters.Furthermore,in order to minimize the springback problem,an accurate springback simulation model of the part was established and validated.The effects of the element size and timesteps on springback model were further investigated.Results indicate that the custom mesh size is beneficial for the springback simulation,and the four timesteps are found suited for the springback analysis for the complex geometry part.Finally,a strategy for reducing the springback by changing the geometry of the blank is proposed.The optimal blank geometry is obtained and used for manufacturing the part.展开更多
A multi-stage influence diagram is used to model the pilot's sequential decision making in one on one air combat. The model based on the multi-stage influence diagram graphically describes the elements of decision pr...A multi-stage influence diagram is used to model the pilot's sequential decision making in one on one air combat. The model based on the multi-stage influence diagram graphically describes the elements of decision process, and contains a point-mass model for the dynamics of an aircraft and takes into account the decision maker's preferences under uncertain conditions. Considering an active opponent, the opponent's maneuvers can be modeled stochastically. The solution of multistage influence diagram can be obtained by converting the multistage influence diagram into a two-level optimization problem. The simulation results show the model is effective.展开更多
Multi-stage hydraulic fracturing of horizontal wells is the main stimulation method in recovering gas from tight shale gas reservoirs, and stage spacing deter- mination is one of the key issues in fracturing design. T...Multi-stage hydraulic fracturing of horizontal wells is the main stimulation method in recovering gas from tight shale gas reservoirs, and stage spacing deter- mination is one of the key issues in fracturing design. The initiation and propagation of hydraulic fractures will cause stress redistribution and may activate natural fractures in the reservoir. Due to the limitation of the analytical method in calculation of induced stresses, we propose a numerical method, which incorporates the interaction of hydraulic fractures and the wellbore, and analyzes the stress distri- bution in the reservoir under different stage spacing. Simulation results indicate the following: (1) The induced stress was overestimated from the analytical method because it did not take into account the interaction between hydraulic fractures and the horizontal wellbore. (2) The hydraulic fracture had a considerable effect on the redis- tribution of stresses in the direction of the horizontal wellbore in the reservoir. The stress in the direction per- pendicular to the horizontal wellbore after hydraulic frac- turing had a minor change compared with the original in situ stress. (3) Stress interferences among fractures were greatly connected with the stage spacing and the distance from the wellbore. When the fracture length was 200 m, and the stage spacing was 50 m, the stress redistribution due to stage fracturing may divert the original stress pat- tern, which might activate natural fractures so as to generate a complex fracture network.展开更多
Multi-stage triaxial compression tests for cylindrical red sandstone specimens(diameter of 50 mm,height of 100 mm) were carried out with a rock mechanics testing system and spatial acoustic emission(AE) locations were...Multi-stage triaxial compression tests for cylindrical red sandstone specimens(diameter of 50 mm,height of 100 mm) were carried out with a rock mechanics testing system and spatial acoustic emission(AE) locations were obtained by adopting an AE monitoring system.Based on spatial AE distribution evolution of red sandstone during multi-stage triaxial deformation,the relation between spatial AE events and triaxial deformation of red sandstone was analyzed.The results show that before peak strength,the spatial AE events are not active and distribute stochastically in the specimen,while after peak strength,the spatial AE events are very active and focus on a local region beyond final microscopic failure plane.During multi-stage triaxial deformation with five different confining pressures,the spatial AE distribution evolution in the red sandstone was obtained.The obtained spatial AE locations of red sandstone at the final confining pressure agree very well with the ultimate failure experimental mode.Finally,the influence of confining pressure on the spatial AE evolution characteristics of red sandstone during triaxial deformation was discussed.The AE behavior of red sandstone during multi-stage triaxial deformation is interpreted in the light of the Kaiser effect,which has a significant meaning for predicting the unstable failure of engineering rock mass.展开更多
A novel rule-based model for multi-stage multi-product scheduling problem(MMSP)in batch plants with parallel units is proposed.The scheduling problem is decomposed into two sub-problems of order assignment and order s...A novel rule-based model for multi-stage multi-product scheduling problem(MMSP)in batch plants with parallel units is proposed.The scheduling problem is decomposed into two sub-problems of order assignment and order sequencing.Firstly,hierarchical scheduling strategy is presented for solving the former sub-problem,where the multi-stage multi-product batch process is divided into multiple sequentially connected single process stages,and then the production of orders are arranged in each single stage by using forward order assignment strategy and backward order assignment strategy respectively according to the feature of scheduling objective.Line-up competition algorithm(LCA)is presented to find out optimal order sequence and order assignment rule,which can minimize total flow time or maximize total weighted process time.Computational results show that the proposed approach can obtain better solutions than those of the literature for all scheduling problems with more than 10 orders.Moreover,with the problem size increasing,the solutions obtained by the proposed approach are improved remarkably.The proposed approach has the potential to solve large size MMSP.展开更多
Nowadays, security defence of network uses the game theory, which mostly applies complete information game model or even the static game model. To get closer to the actual network and defend actively, we propose a net...Nowadays, security defence of network uses the game theory, which mostly applies complete information game model or even the static game model. To get closer to the actual network and defend actively, we propose a network attack-defence game model by using signalling game, which is modelled in the way of dynamic and incomplete information. We improve the traditional attack-defence strategies quantization method to meet the needs of the network signalling game model. Moreover, we give the calculation of the game equilibrium and analyse the optimal defence scheme. Finally, we analyse and verify effectiveness of the model and method through a simulation experiment.展开更多
A 22-stage 4 MV laser-triggered multistage multi-channel switch (LTS) was designed according to the hypothesis that the well-proportioned electrical field distribution is helpful in reducing the jitter of delay. Fie...A 22-stage 4 MV laser-triggered multistage multi-channel switch (LTS) was designed according to the hypothesis that the well-proportioned electrical field distribution is helpful in reducing the jitter of delay. Field distribution in the switch section is regulated by a metal field regulation ring and several gradient rings. In order to reduce the jitter further, a SFB/N2 mixture is chosen as the switching medium. The generalized standard deviation of the self-breakdown voltage and the deviation of the average value from the prediction is less than 4.4% and 13% respectively. Linearity of the self-breakdown voltage is better than 0.95. Triggered by a laser pulse of 35 mJ/3 ns, the delay is about 26 ns at a working voltage of 85±3% USB (Self-breakdown Voltage). Maximum deviation of delay is less than =t=2.5 ns. Jitter is less than 1.5 ns. The delay and jitter decrease with the increase in the working ratio (the ratio of working voltage to USB), pressure or voltage.展开更多
Although multi-stage incremental sheet forming has always been adopted instead of single-stage forming to form parts with a steep wall angle or to achieve a high forming performance, it is largely dependent on empiric...Although multi-stage incremental sheet forming has always been adopted instead of single-stage forming to form parts with a steep wall angle or to achieve a high forming performance, it is largely dependent on empirical designs. In order to research multi-stage forming further, the effect of forming stages(n) and angle interval between the two adjacent stages(Δα) on thickness distribution was investigated. Firstly, a finite element method(FEM) model of multi-stage incremental forming was established and experimentally verified. Then, based on the proposed simulation model, different strategies were adopted to form a frustum of cone with wall angle of 30° to research the thickness distribution of multi-pass forming. It is proved that the minimum thickness increases largely and the variance of sheet thickness decreases significantly as the value of n grows. Further, with the increase of Δα, the minimum thickness increases initially and then decreases, and the optimal thickness distribution is achieved with Δα of 10°.Additionally, a formula is deduced to estimate the sheet thickness after multi-stage forming and proved to be effective. And the simulation results fit well with the experimental results.展开更多
The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscop...The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscopy. The true stress vs true strain curves and the microstructure evolution of two hot deformation procedures were gained. The flow stress of the alloy studied decreases with increasing the deforming passes and declining the temperature, and the larger the temperature decline between adjacent stages, the larger the peak stress fall is. The stress-strain behavior mainly result from the dynamic recovery during deformation, the static recovery and recrystallization in the delay time, and the second phases precipitated from the matrix at high temperature.展开更多
The final product quality is determined by cumulation, coupling and propagation of product quality variations from all stations in multi-stage manufacturing systems (MMSs). Modeling and control of variation propagat...The final product quality is determined by cumulation, coupling and propagation of product quality variations from all stations in multi-stage manufacturing systems (MMSs). Modeling and control of variation propagation is essential to improve product quality. However, the current stream of variations (SOV) theory can only solve the problem that a single SOV affects the product quality. Due to the existence of multiple variation streams, limited research has been done on the quality control in serial-parallel hybrid multi-stage manufacturing systems (SPH-MMSs). A state space model and its modeling strategies are developed to describe the multiple variation streams stack-up in an SPH-MMS. The SOV theory is extended to SPH-MMS. The dimensions of system model are reduced to the production-reality level, and the effect and feasibility of the model is validated by a machining case.展开更多
Fatigue properties of Reactive Powder Concrete (RPC) under axial compression of single-stage and multi-level amplitude in cycles were studied. The tests reveal the fatigue life, the strain and residual life of the R...Fatigue properties of Reactive Powder Concrete (RPC) under axial compression of single-stage and multi-level amplitude in cycles were studied. The tests reveal the fatigue life, the strain and residual life of the RPC samples. Through the analysis of the test results under cyclic loads of single amplitude, the S-N curve of RPC and the evolution rule of macro-damage of RPC were presented, which can be divided into latency stage, stable development stage and instability development stage according to the evolution pattern of the fatigue crack. Accordingly, the development of longitudinal deformation presents the similar three-stage-model, and the proportion of each stage is 15%, 75%, and 10%. According to test results, the fatigue strength reduction factor is 0.564. We brought forward an empirical formula to predict the life of RPC via total longitudinal strain and got the evolving rule for the residual strength of the RPC. The analysis of the test results under cyclic loads of multi-level amplitude shows that the strain under this loading pattern experiences three stages. The characteristic value for the residual strain was obtained. The irreversible damage and non-linear evolution of RPC was described by the development of the residual plastic strain.展开更多
In this paper, wind-induced vibration control of a single column tower of a cable-stayed bridge with a multi- stage pendulum mass damper (MSPMD) is investigated. Special attention is given to overcoming space limita...In this paper, wind-induced vibration control of a single column tower of a cable-stayed bridge with a multi- stage pendulum mass damper (MSPMD) is investigated. Special attention is given to overcoming space limitations for installing the control device in the tower and the effect of varying natural frequency of the towers during construction. First, the finite element model of the bridge during its construction and the basic equation of motion of the MSPMD are introduced. The equation of motion of the bridge with the MSPMD under along-wind excitation is then established. Finally, a numerical simulation and parametric study are conducted to assess the effectiveness of the control system for reducing the wind-induced vibration of the bridge towers during construction. The numerical simulation results show that the MSPMD is practical and effective for reducing the along-wind response of the single column tower, can be installed in a small area of the tower, and complies with the time-variant characteristics of the bridge during its entire construction stage.展开更多
基金the National Science-Technology Support Plan of China(2014BAD02B04)
文摘Anaerobic digestion of Chinese cabbage waste was investigated through a pilot-scale two-stage digester at a mesophilic temperature of 37 °C. In the acidification digester, the main product was acetic acid, with the maximum concentration of 4289 mg·L-1on the fourth day, accounting for 50.32% of total volatile fatty acids. The oxidation reduction potential(ORP) and NH+4-N level decreased gradually with hydraulic retention time(HRT)of acidification. In the second digestion phase, the maximum methanogenic bacterial concentration reached9.6 × 1010ml-1at the organic loading rate(OLR) of 3.5–4 kg VS·m-3, with corresponding HRT of 12–16 days.Accordingly, the optimal biogas production was 0.62 m3·(kg VS)-1, with methane content of 65%–68%. ORP and NH+4-N levels in the methanizer remained between- 500 and- 560 m V and 2000–4500 mg·L-1, respectively. Methanococcus and Methanosarcina served as the main methanogens in the anaerobic digester.
文摘Aiming at the problem of low accuracy of traditional target detection methods for target detection in endoscopes in substation environments, a CNN-based real-time detection method for masked targets is proposed. The method adopts the overall design of backbone network, detection network and algorithmic parameter optimisation method, completes the model training on the self-constructed occlusion target dataset, and adopts the multi-scale perception method for target detection. The HNM algorithm is used to screen positive and negative samples during the training process, and the NMS algorithm is used to post-process the prediction results during the detection process to improve the detection efficiency. After experimental validation, the obtained model has the multi-class average predicted value (mAP) of the dataset. It has general advantages over traditional target detection methods. The detection time of a single target on FDDB dataset is 39 ms, which can meet the need of real-time target detection. In addition, the project team has successfully deployed the method into substations and put it into use in many places in Beijing, which is important for achieving the anomaly of occlusion target detection.
基金supported by the Major Science and Technology Program for Water Pollution Control and Treatment,China (2012ZX07202-004-02)
文摘The effects of different concentrations of oxytetracycline (OTC) on the dynamics of bacterial and archaeal communities during the mesophilic anaerobic digestion (37°C) of cow manure were investigated. Before anaerobic digestion, OTC was added to digesters at concentrations of 20, 50, and 80 mg L-1, respectively. Compared with no-antibiotic control, all methane productions underwent different levels of inhibition at different concentrations of OTC. Changes in the bacterial and archaeal communities were discussed by using PCR-denaturing gradient gel electrophoresis (DGGE). Results showed that OTC affected the richness and diversity of bacterial and archaeal communities. The bacterial genus Flavobacterium and an uncultured bacterium (JN256083.1) were detected throughout the entire process of anaerobic digestion and seemed to be the functional bacteria. Methanobrevibacter boviskoreani and an uncultured archaeon (FJ230982.1) dominated the archaeal communities during anaerobic digestion. These microorganisms may have high resistance to OTC and may play vital roles in methane production.
基金Project(2006AA060201) supported by the National High Technology Research and Development Program of China
文摘A mathematical mechanism model was proposed for the description and analysis of the heat-stirring-acid leaching process.The model is proved to be effective by experiment.Afterwards,the leaching problem was formulated as a constrained multi-objective optimization problem based on the mechanism model.A two-stage guide multi-objective particle swarm optimization(TSG-MOPSO) algorithm was proposed to solve this optimization problem,which can accelerate the convergence and guarantee the diversity of pareto-optimal front set as well.Computational experiment was conducted to compare the solution by the proposed algorithm with SIGMA-MOPSO by solving the model and with the manual solution in practice.The results indicate that the proposed algorithm shows better performance than SIGMA-MOPSO,and can improve the current manual solutions significantly.The improvements of production time and economic benefit compared with manual solutions are 10.5% and 7.3%,respectively.
基金Project (No. GA02C201) supported by the Key Project of Scienceand Technology Commission of Heilongjiang Province China
文摘The performance of the Dongying multi-stage ponds-wetlands ecosystem was investigated in this work. Study of the removal of different pollutants (BOD5, COD, SS, TP, TN, NH3-N, etc.) in different temperature seasons and different units in this system indicated that effluent BOD5 and SS were constant to less than 11 mg/L and 14 mg/L throughout the experimental proc- esses; but that the removal efficiencies of pollutants such as TP, TN, NH3-N, COD varied greatly with season. The higher the temperature was, the higher was the observed removal in this system. Additionally, each unit of the system functioned differently in removing pollutants. BOD5 and SS were mainly removed in the first three units (hybrid facultative ponds, aeration ponds and aerated fish ponds), whereas nitrogen and phosphates were mainly removed in hydrophyte ponds and constructed reed wetlands. The multi-stage ponds-wetlands ecosystem exhibits good potential of removing different pollutants, and the effluent quality meet several standards for wastewater reuse.
基金Project(2006AA04Z143) supported by the National High-tech Research and Development Program of ChinaProject(2006BAF04B00) supported by the National Key Technologies R&D Program of ChinaProject(2007ZE51055) supported by the Aviation Science Foundation of China
文摘A process design approach for multi-stage stretch forming was proposed by combining the strain distribution method and finite element method(FEM)to determine the minimum stage number and deformation amount of each stage.The strain distribution method was used to calculate the deformation amount of each stage and evaluate the formability through a safety criterion.FE simulation was taken as an analysis tool to reveal the deformation behaviour,to predict the strain contour and to determine the process parameters at each stage.To evaluate the effect of heat treatment after pre-strain on occurrence of deformation defects during the subsequent deformation,a multi-stage uniaxial tension test for 2B06 aluminium alloy sheet was carried out.A case study demonstrates that the approach has high reliability and good practicability.
基金Project(2014ZX04002041)supported by the National Science and Technology Major Project,ChinaProject(51175024)supported by the National Natural Science Foundation of China
文摘Springback of a SUS321 complex geometry part formed by the multi-stage rigid-flexible compound process was studied through numerical simulations and laboratory experiments in this work.The sensitivity analysis was provided to have an insight in the effect of the evaluated process parameters.Furthermore,in order to minimize the springback problem,an accurate springback simulation model of the part was established and validated.The effects of the element size and timesteps on springback model were further investigated.Results indicate that the custom mesh size is beneficial for the springback simulation,and the four timesteps are found suited for the springback analysis for the complex geometry part.Finally,a strategy for reducing the springback by changing the geometry of the blank is proposed.The optimal blank geometry is obtained and used for manufacturing the part.
文摘A multi-stage influence diagram is used to model the pilot's sequential decision making in one on one air combat. The model based on the multi-stage influence diagram graphically describes the elements of decision process, and contains a point-mass model for the dynamics of an aircraft and takes into account the decision maker's preferences under uncertain conditions. Considering an active opponent, the opponent's maneuvers can be modeled stochastically. The solution of multistage influence diagram can be obtained by converting the multistage influence diagram into a two-level optimization problem. The simulation results show the model is effective.
基金supported by the Natural Science Foundation of China (Grant No. 51490653, Basic Theoretical Research of Shale Oil and Gas Effective Development)
文摘Multi-stage hydraulic fracturing of horizontal wells is the main stimulation method in recovering gas from tight shale gas reservoirs, and stage spacing deter- mination is one of the key issues in fracturing design. The initiation and propagation of hydraulic fractures will cause stress redistribution and may activate natural fractures in the reservoir. Due to the limitation of the analytical method in calculation of induced stresses, we propose a numerical method, which incorporates the interaction of hydraulic fractures and the wellbore, and analyzes the stress distri- bution in the reservoir under different stage spacing. Simulation results indicate the following: (1) The induced stress was overestimated from the analytical method because it did not take into account the interaction between hydraulic fractures and the horizontal wellbore. (2) The hydraulic fracture had a considerable effect on the redis- tribution of stresses in the direction of the horizontal wellbore in the reservoir. The stress in the direction per- pendicular to the horizontal wellbore after hydraulic frac- turing had a minor change compared with the original in situ stress. (3) Stress interferences among fractures were greatly connected with the stage spacing and the distance from the wellbore. When the fracture length was 200 m, and the stage spacing was 50 m, the stress redistribution due to stage fracturing may divert the original stress pat- tern, which might activate natural fractures so as to generate a complex fracture network.
基金Project(2014CB046905)supported by the National Basic Research Program of ChinaProject(2014YC10)supported by the Fundamental Research Funds for the Central Universities,China
文摘Multi-stage triaxial compression tests for cylindrical red sandstone specimens(diameter of 50 mm,height of 100 mm) were carried out with a rock mechanics testing system and spatial acoustic emission(AE) locations were obtained by adopting an AE monitoring system.Based on spatial AE distribution evolution of red sandstone during multi-stage triaxial deformation,the relation between spatial AE events and triaxial deformation of red sandstone was analyzed.The results show that before peak strength,the spatial AE events are not active and distribute stochastically in the specimen,while after peak strength,the spatial AE events are very active and focus on a local region beyond final microscopic failure plane.During multi-stage triaxial deformation with five different confining pressures,the spatial AE distribution evolution in the red sandstone was obtained.The obtained spatial AE locations of red sandstone at the final confining pressure agree very well with the ultimate failure experimental mode.Finally,the influence of confining pressure on the spatial AE evolution characteristics of red sandstone during triaxial deformation was discussed.The AE behavior of red sandstone during multi-stage triaxial deformation is interpreted in the light of the Kaiser effect,which has a significant meaning for predicting the unstable failure of engineering rock mass.
基金Supported by the National Natural Science Foundation of China(21376185)
文摘A novel rule-based model for multi-stage multi-product scheduling problem(MMSP)in batch plants with parallel units is proposed.The scheduling problem is decomposed into two sub-problems of order assignment and order sequencing.Firstly,hierarchical scheduling strategy is presented for solving the former sub-problem,where the multi-stage multi-product batch process is divided into multiple sequentially connected single process stages,and then the production of orders are arranged in each single stage by using forward order assignment strategy and backward order assignment strategy respectively according to the feature of scheduling objective.Line-up competition algorithm(LCA)is presented to find out optimal order sequence and order assignment rule,which can minimize total flow time or maximize total weighted process time.Computational results show that the proposed approach can obtain better solutions than those of the literature for all scheduling problems with more than 10 orders.Moreover,with the problem size increasing,the solutions obtained by the proposed approach are improved remarkably.The proposed approach has the potential to solve large size MMSP.
基金supported by the National Natural Science Foundation of China under Grant No. 61303074 and No. 61309013the Henan Province Science and Technology Project Funds under Grant No. 12210231002
文摘Nowadays, security defence of network uses the game theory, which mostly applies complete information game model or even the static game model. To get closer to the actual network and defend actively, we propose a network attack-defence game model by using signalling game, which is modelled in the way of dynamic and incomplete information. We improve the traditional attack-defence strategies quantization method to meet the needs of the network signalling game model. Moreover, we give the calculation of the game equilibrium and analyse the optimal defence scheme. Finally, we analyse and verify effectiveness of the model and method through a simulation experiment.
文摘A 22-stage 4 MV laser-triggered multistage multi-channel switch (LTS) was designed according to the hypothesis that the well-proportioned electrical field distribution is helpful in reducing the jitter of delay. Field distribution in the switch section is regulated by a metal field regulation ring and several gradient rings. In order to reduce the jitter further, a SFB/N2 mixture is chosen as the switching medium. The generalized standard deviation of the self-breakdown voltage and the deviation of the average value from the prediction is less than 4.4% and 13% respectively. Linearity of the self-breakdown voltage is better than 0.95. Triggered by a laser pulse of 35 mJ/3 ns, the delay is about 26 ns at a working voltage of 85±3% USB (Self-breakdown Voltage). Maximum deviation of delay is less than =t=2.5 ns. Jitter is less than 1.5 ns. The delay and jitter decrease with the increase in the working ratio (the ratio of working voltage to USB), pressure or voltage.
基金Project(51005258) supported by the National Natural Science Foundation of ChinaProject(CDJZR12130065) supported by the Fundamental Research Funds for the Central Universities,China
文摘Although multi-stage incremental sheet forming has always been adopted instead of single-stage forming to form parts with a steep wall angle or to achieve a high forming performance, it is largely dependent on empirical designs. In order to research multi-stage forming further, the effect of forming stages(n) and angle interval between the two adjacent stages(Δα) on thickness distribution was investigated. Firstly, a finite element method(FEM) model of multi-stage incremental forming was established and experimentally verified. Then, based on the proposed simulation model, different strategies were adopted to form a frustum of cone with wall angle of 30° to research the thickness distribution of multi-pass forming. It is proved that the minimum thickness increases largely and the variance of sheet thickness decreases significantly as the value of n grows. Further, with the increase of Δα, the minimum thickness increases initially and then decreases, and the optimal thickness distribution is achieved with Δα of 10°.Additionally, a formula is deduced to estimate the sheet thickness after multi-stage forming and proved to be effective. And the simulation results fit well with the experimental results.
基金supported by the National Key Basic Research and Development Program of China(No.G1999064908)
文摘The mechanical behavior and microstructures of an Al-Zn-Mg-Cu-Cr aluminum alloy during multi-stage hot deformation were investigated by thermal stimulation test, optical microscopy, and transmission electron microscopy. The true stress vs true strain curves and the microstructure evolution of two hot deformation procedures were gained. The flow stress of the alloy studied decreases with increasing the deforming passes and declining the temperature, and the larger the temperature decline between adjacent stages, the larger the peak stress fall is. The stress-strain behavior mainly result from the dynamic recovery during deformation, the static recovery and recrystallization in the delay time, and the second phases precipitated from the matrix at high temperature.
基金This project is supported by National Natural Science Foundation of China(No.50675137).
文摘The final product quality is determined by cumulation, coupling and propagation of product quality variations from all stations in multi-stage manufacturing systems (MMSs). Modeling and control of variation propagation is essential to improve product quality. However, the current stream of variations (SOV) theory can only solve the problem that a single SOV affects the product quality. Due to the existence of multiple variation streams, limited research has been done on the quality control in serial-parallel hybrid multi-stage manufacturing systems (SPH-MMSs). A state space model and its modeling strategies are developed to describe the multiple variation streams stack-up in an SPH-MMS. The SOV theory is extended to SPH-MMS. The dimensions of system model are reduced to the production-reality level, and the effect and feasibility of the model is validated by a machining case.
基金Funded by the National 863 Plan Foundation of China (No.2006AA03Z536)the National Natural Science Foundation of China (No.50778021)
文摘Fatigue properties of Reactive Powder Concrete (RPC) under axial compression of single-stage and multi-level amplitude in cycles were studied. The tests reveal the fatigue life, the strain and residual life of the RPC samples. Through the analysis of the test results under cyclic loads of single amplitude, the S-N curve of RPC and the evolution rule of macro-damage of RPC were presented, which can be divided into latency stage, stable development stage and instability development stage according to the evolution pattern of the fatigue crack. Accordingly, the development of longitudinal deformation presents the similar three-stage-model, and the proportion of each stage is 15%, 75%, and 10%. According to test results, the fatigue strength reduction factor is 0.564. We brought forward an empirical formula to predict the life of RPC via total longitudinal strain and got the evolving rule for the residual strength of the RPC. The analysis of the test results under cyclic loads of multi-level amplitude shows that the strain under this loading pattern experiences three stages. The characteristic value for the residual strain was obtained. The irreversible damage and non-linear evolution of RPC was described by the development of the residual plastic strain.
基金Area Strategic Development Program inStructural Control and Intelligent Building from The HongKong Polytechnic University, and National Natural SciencFoundation of China Under Grant No. 50408011
文摘In this paper, wind-induced vibration control of a single column tower of a cable-stayed bridge with a multi- stage pendulum mass damper (MSPMD) is investigated. Special attention is given to overcoming space limitations for installing the control device in the tower and the effect of varying natural frequency of the towers during construction. First, the finite element model of the bridge during its construction and the basic equation of motion of the MSPMD are introduced. The equation of motion of the bridge with the MSPMD under along-wind excitation is then established. Finally, a numerical simulation and parametric study are conducted to assess the effectiveness of the control system for reducing the wind-induced vibration of the bridge towers during construction. The numerical simulation results show that the MSPMD is practical and effective for reducing the along-wind response of the single column tower, can be installed in a small area of the tower, and complies with the time-variant characteristics of the bridge during its entire construction stage.