The study employs slope, aspect, relief degree of land surface, land use, vegetation index, hydrology and climate, as evaluation indexes to set up the Human Settlements Environmental Index （HEI） model to evaluate th...The study employs slope, aspect, relief degree of land surface, land use, vegetation index, hydrology and climate, as evaluation indexes to set up the Human Settlements Environmental Index （HEI） model to evaluate the environmental suitability for human settlements in the Shiyang River Basin. By using GIS spatial analysis technology, such as spatial overlay analysis, buffer analysis and density analysis, the environmental suitability of the human set- tlement spatial situation and spatial pattern are established to analyze their spatial distribution The results show that the index of suitability for human settlements in the Shiyang River Basin is between 17.13 and 84.32. In general, suitability for human settlements decreases from the southwest to the northeast. Seen from an area pattern, the suitable region is mainly distributed in the Minqin oasis, Wuwei oasis and Changning basin, which are about 1080.01 km2 and account for 2.59% of the total area. Rather and comparatively suitable region is mainly distributed around the counties of Gulang, Yongchang and north of Tianzhu, which is about 1100.30 km2. The common suitable region is mainly distributed outside the counties of Yongchang, Jinchuan and most parts of Minqin County, which are about 23328.04 km2, accounting for 56.08% of the total area. The unsuitable region is mainly distributed upstream and to the north of the river, which is about 9937.60 km2, accounting for 23.89% of the total area. Meanwhile, the least suitable region is distributed around the Qilian Mountains, which are covered by snow and cold desert and lie in the intersecting area between the Tengger Desert and Badain Jaran Desert. The total area is about 6154.05 km2, accounting for 14.79% of the total area. Suitable regions for human habitation are mainly distributed around rivers in the form of ribbons and batches, while others are scattered. The distribution pattern is iden- tical to the residential spatial pattern. In addition, the relationships between HEI and other factors have been analyzed. There is a clear logarithmic correlation between the residential environment and population, that is, the correlation coefficient between the evaluation valueand population density reaches 0.851. There is also a positive correlation between the residential environment and economy, which reaches an evaluation value of 0.845 between the residential environment and GDP. Results also show that the environment is out of bearing with the existing population in Shiyang River Basin. Spatial distribution of population is pro- foundly affected by severe environmental problems, such as the expanded deserts, the hilly terrain and the changing climate. Surface water shortage and slow economic growth are bot- tlenecks for suitable human settlement in the Shiyang River Basin. Combining these prob- lems with planning for construction of new country and the exploitation of local land, some residential areas should be relocated to improve the residential environment.展开更多
In the data processing of the precise point positioning (PPP), the un-difference method is commonly used. However, GPS measurements can be differenced with satellites or different observation epochs. In theory,these d...In the data processing of the precise point positioning (PPP), the un-difference method is commonly used. However, GPS measurements can be differenced with satellites or different observation epochs. In theory,these differencing approaches should be mathematically equivalent. The positioning performance of different PPP data models, including un-difference (UD), satellite difference (SD), time difference (TD) and time-satellite difference (TSD), is examined using the 24 h GPS observation. The positioning accuracy, convergence of ambiguity, and tropspheric delay estimation with these four models are compared with each other.展开更多
Nonlinear dynamic equations can be solved accurately using a precise integration method. Some algorithms exist, but the inversion of a matrix must be calculated for these al- gorithms. If the inversion of the matrix d...Nonlinear dynamic equations can be solved accurately using a precise integration method. Some algorithms exist, but the inversion of a matrix must be calculated for these al- gorithms. If the inversion of the matrix doesn’t exist or isn’t stable, the precision and stability of the algorithms will be afected. An explicit series solution of the state equation has been pre- sented. The solution avoids calculating the inversion of a matrix and its precision can be easily controlled. In this paper, an implicit series solution of nonlinear dynamic equations is presented. The algorithm is more precise and stable than the explicit series solution and isn’t sensitive to the time-step. Finally, a numerical example is presented to demonstrate the efectiveness of the algorithm.展开更多
Based on the analysis of existing relevant research result, a theoretical basis for the defining freeze- thaw erosion zones of Qinghai-Tibet Plateau was been put forward, and a equation for calculating the altitude of...Based on the analysis of existing relevant research result, a theoretical basis for the defining freeze- thaw erosion zones of Qinghai-Tibet Plateau was been put forward, and a equation for calculating the altitude of the lower bound of the freeze-thaw erosion zones of Qinghai-Tibet Plateau was been established in this paper. Moreover, the freeze-thaw erosion zones in Tibet was been identified by using Geographical Information System (GIS) software. Next, based on the comprehensive analysis of impact factors of freeze-thaw erosion, this paper chooses annul temperature range, slop and vegetation as three indexes, works out the criteria for relative classification of freeze-thaw erosion, and realizes the relative classification of the freeze-thaw erosion in Tibet under the support of GIS software. Then, a synthetic assessment of freeze-thaw erosion in Tibet was been done according to the relative classification result.展开更多
It is analyzed that the impacts of vegetation type and soil moisture contenton shear strength of unsaturated soil through direct shearing tests for various vegetation types,different soil moisture contents and differe...It is analyzed that the impacts of vegetation type and soil moisture contenton shear strength of unsaturated soil through direct shearing tests for various vegetation types,different soil moisture contents and different-depth unsaturated soil. The results show that thecohesion of unsaturated soil changes greatly, and the friction angle changes a little with soilmoisture content. It is also shown that vegetation can improve shear strength of unsaturated soil,which therefore provides a basis thatvegetation can reinforce soil and protect slopes.展开更多
Haloacetic acids(HAAs) are formed during the chlorination of drinking water,which are harmful to people′s health due to their carcinogenic and mutagenic effects. In the present study,a detection method combining meth...Haloacetic acids(HAAs) are formed during the chlorination of drinking water,which are harmful to people′s health due to their carcinogenic and mutagenic effects. In the present study,a detection method combining methyl tert -butyl ether(MtBE) extraction with acid catalysis and gas chromatography coupled with an electron capture detector(GC/ECD) was developed for determining HAAs. The detection limit of this method(MDL) and relative standard deviation(RSD) were below 0.37 μg/L and 6.2%,respectively. The laboratory chlorination experiments were conducted with the purpose of investigating the influences of reaction time,temperature,UV_ 254 ,bromide and ammonia-nitrogen on the formation of HAAs. The results show that the formation amount of HAAs increases with increasing reaction time and temperature,respectively;and there exists a linear relationship between the formation of HAAs and UV_ 254 . The formation amount of HAAs decreases first and then increases as the bromide ion concentration increases,and adding NH +_4 is a possible way to control the formation of HAAs.展开更多
The thinking of co evolution is applied to the optimization of retaining and protecting structure for deep foundation excavation, and the system of optimization of anchored row piles for deep foundation pit has been a...The thinking of co evolution is applied to the optimization of retaining and protecting structure for deep foundation excavation, and the system of optimization of anchored row piles for deep foundation pit has been already developed successfully. For the co evolution algorithm providing an evolutionary mechanism to simulate ever changing problem space, it is an optimization algorithm that has high performance, especially applying to the optimization of complicated system of retaining and protecting for deep foundation pit. It is shown by many engineering practices that the co evolution algorithm has obvious optimization effect, so it can be an important method of optimization of retaining and protecting for deep foundation pit. Here the authors discuss the co evolution model, object function, all kinds of constraint conditions and their disposal methods, and several key techniques of system realization.展开更多
The liquefaction of loess under dynamic loading is studied experimentally with a dynamic triaxial test system. The effects of over-consolidation ratio (OCR), saturation degree and the frequency of dynamic loading upon...The liquefaction of loess under dynamic loading is studied experimentally with a dynamic triaxial test system. The effects of over-consolidation ratio (OCR), saturation degree and the frequency of dynamic loading upon loess liquefaction are investigated. The development of pore pressure within loess samples is also discussed. Based on the experimental results, the empirical relationship between pore pressure ratio and loading cycle number ratio is established for normal consolidated saturated loess.展开更多
This paper demonstrates an experiment on the generation of 3D virtual geographic environment on the basis of experimental flight laser scanning data by a set of algorithms and methods that were developed to automatica...This paper demonstrates an experiment on the generation of 3D virtual geographic environment on the basis of experimental flight laser scanning data by a set of algorithms and methods that were developed to automatically interpret range images for extracting geo-spatial features and then to reconstruct geo-objects. The algorithms and methods for the interpretation and modeling of laser scanner data include triangulated-irregular-network (TIN)-based range image interpolation; mathematical-morphology (MM)-based range image filtering, feature extraction and range image segmentation, feature generalization and optimization, 3D objects reconstruction and modeling; computer-graphics (CG)-based visualization and animation of geographic virtual reality environment.展开更多
A procedure for identifying the dynamic parameter of offshore platform is presented. The present procedure consists of two key features. First uses random decrement (RD) technology to extract free vibration signal in ...A procedure for identifying the dynamic parameter of offshore platform is presented. The present procedure consists of two key features. First uses random decrement (RD) technology to extract free vibration signal in strong noise environment in which it may not white noise. Second technology which called autoregressive moving average (ARMA) was used to model the data treated by the random decrement method. In order to get rid of the color noise in the output signal response from the offshore platform an imaginary system is added in RD system and make the course of extracting performed under the state of color input by choosing the breakover condition and lead time. For eliminating multi_values of parameters identified, an updating moving average method is used. The dynamic parameters of structure under arbitrary input are identified. Example of the method as applied to a scale_model offshore platform was used to evaluate the technology of efficiency and the value of on_line.展开更多
A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and...A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (oε) ∝ r- 1/( n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain.展开更多
A method is presented that coordinates the calculation of the displacement, velocity and acceleration of structures within the time-steps of different types of step-by-step integration. The dynamic equation is solved ...A method is presented that coordinates the calculation of the displacement, velocity and acceleration of structures within the time-steps of different types of step-by-step integration. The dynamic equation is solved using an energy equation and the calculating data of the original method. The method presented is better than the original method in terms of calculating postulations and is in better conformity with the system's movement. Take the Wilson-θ method as an example. By using the coordination process, the calculation precision has been greatly im proved (reducing the errors by approximately 90% ), and the greater part of overshooting of the calculation result has been eliminated. The study suggests that the mal-coordination of the motion parameters within the time-step is the major factor that contributes to the result errors of step-by-step integration for the dynamic equation.展开更多
A superfine slag powder (SP) made from granulated blast furnace slag incorporating activators by using special millingtechnique, was used as supplementary cementitious material in high performance concrete (HPC), repl...A superfine slag powder (SP) made from granulated blast furnace slag incorporating activators by using special millingtechnique, was used as supplementary cementitious material in high performance concrete (HPC), replacing part ofthe mass of normal Portland cement. The effects of the SP on the workability, mechanical and crack self-healingproperties of HPC were studied. The hydration process and microstructure characteristics were investigated by X-raydiffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The crack self-healing capacitywas evaluated by Brazilian test. The test results indicate that the SP has especially supplementary effect on waterreducing and excellent property of better control of slump loss. The concrete flowability increases remarkably withthe increase of SP replacement level in the range of 20% to 50%. The compressive and splitting tensile strengthsof HPC containing SP are higher than the corresponding strength of the control concrete at all ages. The crackself-healing ability is highly dependent on SP content of HPC.展开更多
Presents the components and flow diagram of a heat pump water heater with heat reclaim applied In household bathing room, analyzes its characteristics from thermodynamical principle, calculates its theoretical heating...Presents the components and flow diagram of a heat pump water heater with heat reclaim applied In household bathing room, analyzes its characteristics from thermodynamical principle, calculates its theoretical heating coefficient under different operating conditions. The result shows that the maximum value of its heating coefficient is 12.9 under a typical operating condition.展开更多
Based on the characteristics of the ripping of rock, the simulated conditions that would be satisfied by the prototype ripping and the model ripping have been derived in this paper. In order to .nanufacture the satisf...Based on the characteristics of the ripping of rock, the simulated conditions that would be satisfied by the prototype ripping and the model ripping have been derived in this paper. In order to .nanufacture the satisfying equivalent materials for the model ripping, a new method has been set up, and the materials, which can simulate the prototype rock "Hawkesbury sandstone", have been made by using the methed.展开更多
According to the experimental results of model beams, the curvature of a partially prestressed concrete beam is defined, then the influence of PPR(partial prestressing ratio), net reinforcement index, concrete streng...According to the experimental results of model beams, the curvature of a partially prestressed concrete beam is defined, then the influence of PPR(partial prestressing ratio), net reinforcement index, concrete strength and fatigue on ductility of partially prestressed concrete beam are discussed respectively.展开更多
In order to make trend analysis and prediction to acquisition data in amechanical equipment condition monitoring system, a new method of trend feature extraction andprediction of acquisition data is proposed which con...In order to make trend analysis and prediction to acquisition data in amechanical equipment condition monitoring system, a new method of trend feature extraction andprediction of acquisition data is proposed which constructs an adaptive wavelet on the acquisitiondata by means of second generation wavelet transform ( SGWT), Firstly, taking the vanishing momentnumber of the predictor as a constraint, the linear predictor and updater are designed according tothe acquisition data by using symmetrical interpolating scheme. Then the trend of the data isobtained through doing SGWT decomposition , threshold processing and SGWT reconstruction. Secondly,under the constraint of the vanishing moment number of the predictor, another predictor based on theacquisition data is devised to predict the future trend of the data using a non-symmetricalinterpolating scheme, A one-step prediction algorithm is presented to predict the future evolutiontrend with historical data. The proposed method obtained a desirable effect in peak-to-peak valuetrend analysis for a machine set in an oil refinery.展开更多
In this paper, a mathematical model for the urban rainstorm water logging wasestablished on the basis of one- and two-dimensional unsteady flow theory and the technique ofnon-structural irregular grid division. The co...In this paper, a mathematical model for the urban rainstorm water logging wasestablished on the basis of one- and two-dimensional unsteady flow theory and the technique ofnon-structural irregular grid division. The continuity equation was discretized with the finitevolume method. And the momentum equations were differently simplified and discretized for differentcases. A method of ''special passage'' was proposed to deal with small-scale rivers and open channels.The urban drainage system was simplified and simulated in the model. The method of ''open slot'' wasapplied to coordinate the alternate calculation of open channel flow and pressure flow in drainagepipes. The model has been applied in Tianjin City and the verification is quite satisfactory.展开更多
In a Maxwell’s demon experiment on a dilute granular gas made up of two species of particles placed in two closely connected containers, a cyclic oscillation similar to the chemical oscillations is recognized that th...In a Maxwell’s demon experiment on a dilute granular gas made up of two species of particles placed in two closely connected containers, a cyclic oscillation similar to the chemical oscillations is recognized that the two species of particles cluster alternately in the two containers. Then the nonlinear behavior is qualitatively explained based on a flux model.展开更多
A two-layer model, with the upper layer being the perfect fluid and the lowerlayer being the pseudo-plastic fluid describing water wave attenuation over mud bed, wasestablished. A simplified method based on the princi...A two-layer model, with the upper layer being the perfect fluid and the lowerlayer being the pseudo-plastic fluid describing water wave attenuation over mud bed, wasestablished. A simplified method based on the principle of e-quivalcnt work was applied to solve theboundary value problems. The computational results of the model show that the two-layer perfectfluid model and the perfect-viscous fluid model are all special cases of the present model. Thecomplex nonlinear properties of wave attenuation over mud bed, can be explained by the presentmodel, e. g., the wave dissipation rale decreases wilh the wave height in certain cases, while thesmall wave propagates over mud bed with less energy dissipation and large wave attenuates rapidly inother cases. Other factors influencing the wave attenuation were also discussed.展开更多
基金National Natural Science Foundation of China, No.41261104 No.40971078+1 种基金 National Social Science Foundation Youth Project of China, No.12CTJ001 Youth Fund Projects of Science and Technology from Gansu Province, No.1107RJYA077
文摘The study employs slope, aspect, relief degree of land surface, land use, vegetation index, hydrology and climate, as evaluation indexes to set up the Human Settlements Environmental Index （HEI） model to evaluate the environmental suitability for human settlements in the Shiyang River Basin. By using GIS spatial analysis technology, such as spatial overlay analysis, buffer analysis and density analysis, the environmental suitability of the human set- tlement spatial situation and spatial pattern are established to analyze their spatial distribution The results show that the index of suitability for human settlements in the Shiyang River Basin is between 17.13 and 84.32. In general, suitability for human settlements decreases from the southwest to the northeast. Seen from an area pattern, the suitable region is mainly distributed in the Minqin oasis, Wuwei oasis and Changning basin, which are about 1080.01 km2 and account for 2.59% of the total area. Rather and comparatively suitable region is mainly distributed around the counties of Gulang, Yongchang and north of Tianzhu, which is about 1100.30 km2. The common suitable region is mainly distributed outside the counties of Yongchang, Jinchuan and most parts of Minqin County, which are about 23328.04 km2, accounting for 56.08% of the total area. The unsuitable region is mainly distributed upstream and to the north of the river, which is about 9937.60 km2, accounting for 23.89% of the total area. Meanwhile, the least suitable region is distributed around the Qilian Mountains, which are covered by snow and cold desert and lie in the intersecting area between the Tengger Desert and Badain Jaran Desert. The total area is about 6154.05 km2, accounting for 14.79% of the total area. Suitable regions for human habitation are mainly distributed around rivers in the form of ribbons and batches, while others are scattered. The distribution pattern is iden- tical to the residential spatial pattern. In addition, the relationships between HEI and other factors have been analyzed. There is a clear logarithmic correlation between the residential environment and population, that is, the correlation coefficient between the evaluation valueand population density reaches 0.851. There is also a positive correlation between the residential environment and economy, which reaches an evaluation value of 0.845 between the residential environment and GDP. Results also show that the environment is out of bearing with the existing population in Shiyang River Basin. Spatial distribution of population is pro- foundly affected by severe environmental problems, such as the expanded deserts, the hilly terrain and the changing climate. Surface water shortage and slow economic growth are bot- tlenecks for suitable human settlement in the Shiyang River Basin. Combining these prob- lems with planning for construction of new country and the exploitation of local land, some residential areas should be relocated to improve the residential environment.
文摘In the data processing of the precise point positioning (PPP), the un-difference method is commonly used. However, GPS measurements can be differenced with satellites or different observation epochs. In theory,these differencing approaches should be mathematically equivalent. The positioning performance of different PPP data models, including un-difference (UD), satellite difference (SD), time difference (TD) and time-satellite difference (TSD), is examined using the 24 h GPS observation. The positioning accuracy, convergence of ambiguity, and tropspheric delay estimation with these four models are compared with each other.
基金Project supported by the National Natural Science Foundation of China(Nos.60273048and60174023).
文摘Nonlinear dynamic equations can be solved accurately using a precise integration method. Some algorithms exist, but the inversion of a matrix must be calculated for these al- gorithms. If the inversion of the matrix doesn’t exist or isn’t stable, the precision and stability of the algorithms will be afected. An explicit series solution of the state equation has been pre- sented. The solution avoids calculating the inversion of a matrix and its precision can be easily controlled. In this paper, an implicit series solution of nonlinear dynamic equations is presented. The algorithm is more precise and stable than the explicit series solution and isn’t sensitive to the time-step. Finally, a numerical example is presented to demonstrate the efectiveness of the algorithm.
文摘Based on the analysis of existing relevant research result, a theoretical basis for the defining freeze- thaw erosion zones of Qinghai-Tibet Plateau was been put forward, and a equation for calculating the altitude of the lower bound of the freeze-thaw erosion zones of Qinghai-Tibet Plateau was been established in this paper. Moreover, the freeze-thaw erosion zones in Tibet was been identified by using Geographical Information System (GIS) software. Next, based on the comprehensive analysis of impact factors of freeze-thaw erosion, this paper chooses annul temperature range, slop and vegetation as three indexes, works out the criteria for relative classification of freeze-thaw erosion, and realizes the relative classification of the freeze-thaw erosion in Tibet under the support of GIS software. Then, a synthetic assessment of freeze-thaw erosion in Tibet was been done according to the relative classification result.
文摘It is analyzed that the impacts of vegetation type and soil moisture contenton shear strength of unsaturated soil through direct shearing tests for various vegetation types,different soil moisture contents and different-depth unsaturated soil. The results show that thecohesion of unsaturated soil changes greatly, and the friction angle changes a little with soilmoisture content. It is also shown that vegetation can improve shear strength of unsaturated soil,which therefore provides a basis thatvegetation can reinforce soil and protect slopes.
文摘Haloacetic acids(HAAs) are formed during the chlorination of drinking water,which are harmful to people′s health due to their carcinogenic and mutagenic effects. In the present study,a detection method combining methyl tert -butyl ether(MtBE) extraction with acid catalysis and gas chromatography coupled with an electron capture detector(GC/ECD) was developed for determining HAAs. The detection limit of this method(MDL) and relative standard deviation(RSD) were below 0.37 μg/L and 6.2%,respectively. The laboratory chlorination experiments were conducted with the purpose of investigating the influences of reaction time,temperature,UV_ 254 ,bromide and ammonia-nitrogen on the formation of HAAs. The results show that the formation amount of HAAs increases with increasing reaction time and temperature,respectively;and there exists a linear relationship between the formation of HAAs and UV_ 254 . The formation amount of HAAs decreases first and then increases as the bromide ion concentration increases,and adding NH +_4 is a possible way to control the formation of HAAs.
基金National Natural Science Foundation of China( 5 986 80 0 1)
文摘The thinking of co evolution is applied to the optimization of retaining and protecting structure for deep foundation excavation, and the system of optimization of anchored row piles for deep foundation pit has been already developed successfully. For the co evolution algorithm providing an evolutionary mechanism to simulate ever changing problem space, it is an optimization algorithm that has high performance, especially applying to the optimization of complicated system of retaining and protecting for deep foundation pit. It is shown by many engineering practices that the co evolution algorithm has obvious optimization effect, so it can be an important method of optimization of retaining and protecting for deep foundation pit. Here the authors discuss the co evolution model, object function, all kinds of constraint conditions and their disposal methods, and several key techniques of system realization.
基金The project supported by the National Natural Science Foundation of China(50178005)
文摘The liquefaction of loess under dynamic loading is studied experimentally with a dynamic triaxial test system. The effects of over-consolidation ratio (OCR), saturation degree and the frequency of dynamic loading upon loess liquefaction are investigated. The development of pore pressure within loess samples is also discussed. Based on the experimental results, the empirical relationship between pore pressure ratio and loading cycle number ratio is established for normal consolidated saturated loess.
文摘This paper demonstrates an experiment on the generation of 3D virtual geographic environment on the basis of experimental flight laser scanning data by a set of algorithms and methods that were developed to automatically interpret range images for extracting geo-spatial features and then to reconstruct geo-objects. The algorithms and methods for the interpretation and modeling of laser scanner data include triangulated-irregular-network (TIN)-based range image interpolation; mathematical-morphology (MM)-based range image filtering, feature extraction and range image segmentation, feature generalization and optimization, 3D objects reconstruction and modeling; computer-graphics (CG)-based visualization and animation of geographic virtual reality environment.
文摘A procedure for identifying the dynamic parameter of offshore platform is presented. The present procedure consists of two key features. First uses random decrement (RD) technology to extract free vibration signal in strong noise environment in which it may not white noise. Second technology which called autoregressive moving average (ARMA) was used to model the data treated by the random decrement method. In order to get rid of the color noise in the output signal response from the offshore platform an imaginary system is added in RD system and make the course of extracting performed under the state of color input by choosing the breakover condition and lead time. For eliminating multi_values of parameters identified, an updating moving average method is used. The dynamic parameters of structure under arbitrary input are identified. Example of the method as applied to a scale_model offshore platform was used to evaluate the technology of efficiency and the value of on_line.
文摘A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (oε) ∝ r- 1/( n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain.
文摘A method is presented that coordinates the calculation of the displacement, velocity and acceleration of structures within the time-steps of different types of step-by-step integration. The dynamic equation is solved using an energy equation and the calculating data of the original method. The method presented is better than the original method in terms of calculating postulations and is in better conformity with the system's movement. Take the Wilson-θ method as an example. By using the coordination process, the calculation precision has been greatly im proved (reducing the errors by approximately 90% ), and the greater part of overshooting of the calculation result has been eliminated. The study suggests that the mal-coordination of the motion parameters within the time-step is the major factor that contributes to the result errors of step-by-step integration for the dynamic equation.
基金The research work presented in this paper was conducted with partial support from the Foundation for University Key Teacher by the Ministry of EducationThe first author also gratefully acknowledges the financial support from NSFC (No. 59908007) t
文摘A superfine slag powder (SP) made from granulated blast furnace slag incorporating activators by using special millingtechnique, was used as supplementary cementitious material in high performance concrete (HPC), replacing part ofthe mass of normal Portland cement. The effects of the SP on the workability, mechanical and crack self-healingproperties of HPC were studied. The hydration process and microstructure characteristics were investigated by X-raydiffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The crack self-healing capacitywas evaluated by Brazilian test. The test results indicate that the SP has especially supplementary effect on waterreducing and excellent property of better control of slump loss. The concrete flowability increases remarkably withthe increase of SP replacement level in the range of 20% to 50%. The compressive and splitting tensile strengthsof HPC containing SP are higher than the corresponding strength of the control concrete at all ages. The crackself-healing ability is highly dependent on SP content of HPC.
文摘Presents the components and flow diagram of a heat pump water heater with heat reclaim applied In household bathing room, analyzes its characteristics from thermodynamical principle, calculates its theoretical heating coefficient under different operating conditions. The result shows that the maximum value of its heating coefficient is 12.9 under a typical operating condition.
文摘Based on the characteristics of the ripping of rock, the simulated conditions that would be satisfied by the prototype ripping and the model ripping have been derived in this paper. In order to .nanufacture the satisfying equivalent materials for the model ripping, a new method has been set up, and the materials, which can simulate the prototype rock "Hawkesbury sandstone", have been made by using the methed.
文摘According to the experimental results of model beams, the curvature of a partially prestressed concrete beam is defined, then the influence of PPR(partial prestressing ratio), net reinforcement index, concrete strength and fatigue on ductility of partially prestressed concrete beam are discussed respectively.
文摘In order to make trend analysis and prediction to acquisition data in amechanical equipment condition monitoring system, a new method of trend feature extraction andprediction of acquisition data is proposed which constructs an adaptive wavelet on the acquisitiondata by means of second generation wavelet transform ( SGWT), Firstly, taking the vanishing momentnumber of the predictor as a constraint, the linear predictor and updater are designed according tothe acquisition data by using symmetrical interpolating scheme. Then the trend of the data isobtained through doing SGWT decomposition , threshold processing and SGWT reconstruction. Secondly,under the constraint of the vanishing moment number of the predictor, another predictor based on theacquisition data is devised to predict the future trend of the data using a non-symmetricalinterpolating scheme, A one-step prediction algorithm is presented to predict the future evolutiontrend with historical data. The proposed method obtained a desirable effect in peak-to-peak valuetrend analysis for a machine set in an oil refinery.
文摘In this paper, a mathematical model for the urban rainstorm water logging wasestablished on the basis of one- and two-dimensional unsteady flow theory and the technique ofnon-structural irregular grid division. The continuity equation was discretized with the finitevolume method. And the momentum equations were differently simplified and discretized for differentcases. A method of ''special passage'' was proposed to deal with small-scale rivers and open channels.The urban drainage system was simplified and simulated in the model. The method of ''open slot'' wasapplied to coordinate the alternate calculation of open channel flow and pressure flow in drainagepipes. The model has been applied in Tianjin City and the verification is quite satisfactory.
基金supported by the National Natural Science Foundation of China(Grant Nos.10172041 and 10402012).
文摘In a Maxwell’s demon experiment on a dilute granular gas made up of two species of particles placed in two closely connected containers, a cyclic oscillation similar to the chemical oscillations is recognized that the two species of particles cluster alternately in the two containers. Then the nonlinear behavior is qualitatively explained based on a flux model.
基金This work was supported by the National Natural Science Foundation of China (Grant No: 50279029)the Central Funding of Hong Kong Polytechnic University (Grant No: GT219)Hong Kong RGC/NSFC Funding. (Grant No: NSFC/HKU 26)
文摘A two-layer model, with the upper layer being the perfect fluid and the lowerlayer being the pseudo-plastic fluid describing water wave attenuation over mud bed, wasestablished. A simplified method based on the principle of e-quivalcnt work was applied to solve theboundary value problems. The computational results of the model show that the two-layer perfectfluid model and the perfect-viscous fluid model are all special cases of the present model. Thecomplex nonlinear properties of wave attenuation over mud bed, can be explained by the presentmodel, e. g., the wave dissipation rale decreases wilh the wave height in certain cases, while thesmall wave propagates over mud bed with less energy dissipation and large wave attenuates rapidly inother cases. Other factors influencing the wave attenuation were also discussed.
