In this paper, based on the idea of profit and loss modification, we presentthe iterative non-uniform B-spline curve and surface to settle a key problem in computeraided geometric design and reverse engineering, that ...In this paper, based on the idea of profit and loss modification, we presentthe iterative non-uniform B-spline curve and surface to settle a key problem in computeraided geometric design and reverse engineering, that is, constructing the curve (surface)fitting (interpolating) a given ordered point set without solving a linear system. We startwith a piece of initial non-uniform B-spline curve (surface) which takes the given point setas its control point set. Then by adjusting its control points gradually with iterative formula,we can get a group of non-uniform B-spline curves (surfaces) with gradually higherprecision. In this paper, using modern matrix theory, we strictly prove that the limit curve(surface) of the iteration interpolates the given point set. The non-uniform B-spline curves(surfaces) generated with the iteration have many advantages, such as satisfying theNURBS standard, having explicit expression, gaining locality, and convexity preserving,etc展开更多
A new method for direct numerical simulation of incompressible Navier-Stokes equations is studied in the paper. The compact finite difference and the non-linear terms upwind compact finite difference schemes on non-un...A new method for direct numerical simulation of incompressible Navier-Stokes equations is studied in the paper. The compact finite difference and the non-linear terms upwind compact finite difference schemes on non-uniform meshes in x and y directions are developed respectively. With the Fourier spectral expansion in the spanwise direction, three-dimensional N-S equation are converted to a system of two-dimensional explicit-implicit The treatment of equations. The third-order mixed scheme is employed the three-dimensional for time integration. non-reflecting outflow boundary conditions is presented, which is important for the numerical simulations of the problem of transition in boundary layers, jets, and mixing layer. The numerical results indicate that high accuracy, stabilization and efficiency are achieved by the proposed numerical method. In addition, a theory model for the coherent structure in a laminar boundary layer is also proposed, based on which the numerical method is implemented to the non-linear evolution of coherent structure. It is found that the numerical results of the distribution of Reynolds stress, the formation of high shear layer, and the event of ejection and sweeping, match well with the observed characteristics of the coherent structures in a turbulence boundary layer.展开更多
This paper discusses the problem of direction of departure （DOD） and direction of arrival （DOA） estimation for a bistatic multiple input multiple output （MIMO） radar, and proposes an improved reduced-dimension C...This paper discusses the problem of direction of departure （DOD） and direction of arrival （DOA） estimation for a bistatic multiple input multiple output （MIMO） radar, and proposes an improved reduced-dimension Capon algorithm therein. Compared with the reduced-dimension Capon algorithm which requires pair matching between the two-dimensional angle estimation, the pro- posed algorithm can obtain automatically paired DOD and DOA estimation without debasing the performance of angle estimation in bistatic MIMO radar. Furthermore, the proposed algorithm has a lower complexity than the reduced-dimension Capon algorithm, and it is suitable for non-uniform linear arrays. The complexity of the proposed algorithm is analyzed and the Cramer-Rao bound （CRB） is also derived. Simulation results verify the usefulness of the proposed algorithm.展开更多
In this work, hot isostatic pressing （HIPing） technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters （temperature and rates of heating and pressurizing） on m...In this work, hot isostatic pressing （HIPing） technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters （temperature and rates of heating and pressurizing） on microstructure and properties of PM Ti2AINb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties （especially high temper- ature rupture lifetime） of PM Ti2AINb alloys in the present work. A finite element method （FEM） model for predicting the final densification was developed and was used to optimize the HIPing procedure.展开更多
In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems...In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems of nonuniform backgrounds of wood defect images.The proposed algorithm calculates the threshold by the mean,standard deviation and the extreme value of the window.The results indicate that this modified algorithm enhances the image segmentation for wood defect images on a complex background,which is much superior to the global threshold algorithm and the Bernsen algorithm,and slightly better than the Niblack algorithm and Sauvola algorithm.Compared with similar models,the algorithm proposed in this paper has higher segmentation accuracy,as high as 92.6%for wood defect images with a complex background.展开更多
A 2-D non-uniform sediment mat hmatical model in the boundary-fitting orthogonal coordinate system was develop ed in this paper. The governing equations, the numerical scheme, the boundary con ditions, the movable bou...A 2-D non-uniform sediment mat hmatical model in the boundary-fitting orthogonal coordinate system was develop ed in this paper. The governing equations, the numerical scheme, the boundary con ditions, the movable boundary technique and the numerical solutions were present ed. The model was verified by the data of the reach 25km upstream the Jialingjia ng estuary and the 44km long main stream of the Chongqing reach of the Yangtze r iver. The calculated results show that, the water elevation, the velocity distri bution and the river bed deformation are in agreement with the measured data.展开更多
Maximum power output of a class of irreversible non-regeneration heat engines with non-uniform working fluid,in which heat transfers between the working fluid and the heat reservoirs obey the linear phenomenological h...Maximum power output of a class of irreversible non-regeneration heat engines with non-uniform working fluid,in which heat transfers between the working fluid and the heat reservoirs obey the linear phenomenological heat transfer law [q ∝Δ(T-1)],are studied in this paper. Optimal control theory is used to determine the upper bounds of power of the heat engine for the lumped-parameter model and the distributed-parameter model,respectively. The results show that the maximum power output of the heat engine in the distributed-parameter model is less than or equal to that in the lumped-parameter model,which could provide more realistic guidelines for real heat engines. Analytical solutions of the maximum power output are obtained for the irreversible heat engines working between constant temperature reservoirs. For the irreversible heat engine operating between variable temperature reservoirs,a numerical example for the lumped-parameter model is provided by numerical calculation. The effects of changes of reservoir's temperature on the maximum power of the heat engine are analyzed. The obtained results are,in addition,compared with those obtained with Newtonian heat transfer law [q ∝Δ(T)].展开更多
A three-dimensional disc model with non-uniform heat generating is built.A series of cooling channels are inserted to cool this disc which is strewn in a hierarchical pattern.To reveal thermal and flow characteristics...A three-dimensional disc model with non-uniform heat generating is built.A series of cooling channels are inserted to cool this disc which is strewn in a hierarchical pattern.To reveal thermal and flow characteristics,a composite objective function comprised of the maximum temperature difference(MTD)and pumping power is constructed.The deployment pattern of cooling channels contains two cases,i.e.,the radial-pattern and dendritic-pattern.By capitalizing on constructal design method together with finite element method,the diameter of radial-pattern cooling channels is optimized in the first place.Next,the diameter,angle coefficient and length coefficient of dendritic-pattern cooling channels are three degrees-of-freedom to be stepwise optimized at different heat generating conditions.Furthermore,NSGA-II algorithm is introduced into the multiobjective problem.Upon obtaining its Pareto optimal solution set,Topsis method is invoked to yield the optimal solutions under given weighted coefficients.The heat generation over the entire body and the volume ratio of cooling channels operate as the primary constraints.Based on these premises,constructal design will be stepwise performed by varying three degrees-offreedom.The obtained results state that more heating components or devices should be installed as close to the cooling water inlet as possible.This can further reduce MTD at the same cost of pumping power,thereby improve thermal and flow performance and prolong the lifespan of devices.As optimized with two degrees-of-freedom,the MTD is reduced by 18.6%compared with the counterpart obtained from single degree-of-freedom optimization,while the pumping power is increased by 59.8%.As optimized with three degrees-of-freedom,the MTD is decreased by 6.2%compared with the counterpart from two degrees-of-freedom optimization,while the pumping power is increased by 3.0%.It is manifest that when two sub-objectives form a composite objective,the performance improvement of one sub-objective will inevitably elicit the vitiation o展开更多
The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deteriorati...The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction.The governing equations of mass,momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method.The re-normalization group(RNG)k-εturbulence model with an enhanced wall treatment was selected.Considering the heat conduction in the solid wall,the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed.The evolution of secondary flow was analyzed.Effects of the outer-wall heat flux,mass flux,pressure and tube thermal conductivity on heat transfer were investigated.Moreover,the buoyancy criterion and the heat transfer correlation were obtained.Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling,further leads to the heat transfer deterioration.The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube,and weakening the heat transfer at the top of tube,which results in the non-uniform inner-wall temperature and heat flux distributions.Decreasing the ratio of outer-wall heat flux and mass flux,increasing the pressure could weaken the heat transfer difference along the circumferential direction,while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated.When the buoyancy criterion of(Grq/Grth)max≤0.8 is satisfied,the effect of buoyancy could be ignored.The new correlations work well for non-uniform heat transfer predictions.展开更多
Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on...Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom (PTPB) or for pervious top and impervious bottom (PTIB). For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper.展开更多
Currently, transplanting mechanisms for dryland plug seedlings in China are mainly semiautomatic and have low efficiency. The rotary seedling pick-up mechanism with a planetary gear train for non-uniform intermittent ...Currently, transplanting mechanisms for dryland plug seedlings in China are mainly semiautomatic and have low efficiency. The rotary seedling pick-up mechanism with a planetary gear train for non-uniform intermittent transmission, and a concave and convex locking arc device, has a large rigid impact. To solve these problems, according to the design requirements for a dryland plug seedling transplanting mechanism, a rotary seedling pick-up mechanism of a planetary gear train with combined non-circular gear transmission of incomplete eccentric circular and noncircular gears was proposed. This has the characteristics of two-times greater fluctuation of the transmission ratio in a cycle, and can achieve a non-uniform continuous drive. Through analysis of the working principle of the seedling pick-up mechanism, its kinematics model was established. The human–computer interaction optimization method and self-developed computer-aided analysis and optimization software were used to obtain a set of parameters that satisfy the operation requirements of the seedling pick-up mechanism. According to the optimized parameters, the structure of the seedling pick-up mechanism was designed, a virtual prototype of the mechanism was created, and a physical prototype was manufactured. A virtual motion simulation of the mechanism was performed, high-speed photographic kinematics tests were conducted, and the kinematic properties of the physical prototype were investigated, whereby the correctness of the theoretical model and the optimized design of the mechanism were verified. Further, laboratory seedling pick-up tests were conducted. The success ratio of seedling pick-up was 93.8% when the seedling pick-up efficiency of the mechanism was 60 plants per minute per row, indicating that the mechanism has a high efficiency and success ratio for seedling pick-up and can be applied to a dryland plug seedling transplanter.展开更多
This article presents a new well test model for two-zone linear composite reservoirs, where the rock and fluid properties as well as the formation thicknesses on both sides of the discontinuity are distinctly differen...This article presents a new well test model for two-zone linear composite reservoirs, where the rock and fluid properties as well as the formation thicknesses on both sides of the discontinuity are distinctly different. An analytical solution of pressure-transient behavior for a line-source, constant-rate well in this type of reservoir configuration is obtained with Fourier space transformation and Laplace transformation. By applying Duhamel principle, the wellbore storage and skins effects can easily be included. A set of type curves are generated and the sensitivities of the relevant parameters are discussed. A new correlating parameter MhDl√ηD is proposed to identify the pressure response in the pressure derivative curve. The model as well as the corresponding type curves are quite general that they are useful in predicting the production performance or analyzing the production data from this type of well-reservoir systems.展开更多
A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the Wenzhou Bay. This model accomodates complicated features including multiple islands, existence of turbidity, an...A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the Wenzhou Bay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport are presented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with their initial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of the critical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested. The model verification computation shows that, the tidal levels computed from the model are in good agreement with the field data at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measured along the totally 52 synchronously observed verticals distributed over 8 cross sections. The coraputed tidal water throughputs through the Huangda'ao cross section are close to the measured data. And the computed values of bed deformation from Yangfushan to the estuary outfall and in the outer-sea area are in good agreement with the data observed from 1986 to 1992. The changes of tidal volumes through the estuary, velocities in different channels and the bed form due to the influence of the reclamation project on the Wenzhou shoal are predicted by means of this model.展开更多
The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. Ho...The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.展开更多
经典DBSCAN(density based spatial clustering of applications with noise)算法需要人工指定邻域半径(Eps)和点数阈值(Minpts),且均为全局参数,导致聚类准确率低。针对此问题,为了提高经典DBSCAN聚类算法的聚类准确率,基于网格划分思...经典DBSCAN(density based spatial clustering of applications with noise)算法需要人工指定邻域半径(Eps)和点数阈值(Minpts),且均为全局参数,导致聚类准确率低。针对此问题,为了提高经典DBSCAN聚类算法的聚类准确率,基于网格划分思想,提出了一种局部自适应DBSCAN聚类算法。根据数据集自身特征生成网格空间,将特征数据映射至相应的网格空间;利用高斯核函数估计每个网格区间的局部密度;联合多维度网格密度分布信息,寻找无连接或弱连接高密度网格之间的区域,同时统计同区域的波峰数量,从而自适应确定各区域的Eps及Minpts参数;使用每个区域独有的参数作为DBSCAN算法输入,并进行聚类。实验结果表明,该算法能够在聚类过程中自适应确定每个局部区域的Eps和Minpts参数,聚类准确率高且耗时较低。展开更多
文摘In this paper, based on the idea of profit and loss modification, we presentthe iterative non-uniform B-spline curve and surface to settle a key problem in computeraided geometric design and reverse engineering, that is, constructing the curve (surface)fitting (interpolating) a given ordered point set without solving a linear system. We startwith a piece of initial non-uniform B-spline curve (surface) which takes the given point setas its control point set. Then by adjusting its control points gradually with iterative formula,we can get a group of non-uniform B-spline curves (surfaces) with gradually higherprecision. In this paper, using modern matrix theory, we strictly prove that the limit curve(surface) of the iteration interpolates the given point set. The non-uniform B-spline curves(surfaces) generated with the iteration have many advantages, such as satisfying theNURBS standard, having explicit expression, gaining locality, and convexity preserving,etc
基金Project supported by the National Natural Science Foundation of China (Grant No:10272040) and Doctor Foundation of Education Ministry (Grant No:20050294003)
文摘A new method for direct numerical simulation of incompressible Navier-Stokes equations is studied in the paper. The compact finite difference and the non-linear terms upwind compact finite difference schemes on non-uniform meshes in x and y directions are developed respectively. With the Fourier spectral expansion in the spanwise direction, three-dimensional N-S equation are converted to a system of two-dimensional explicit-implicit The treatment of equations. The third-order mixed scheme is employed the three-dimensional for time integration. non-reflecting outflow boundary conditions is presented, which is important for the numerical simulations of the problem of transition in boundary layers, jets, and mixing layer. The numerical results indicate that high accuracy, stabilization and efficiency are achieved by the proposed numerical method. In addition, a theory model for the coherent structure in a laminar boundary layer is also proposed, based on which the numerical method is implemented to the non-linear evolution of coherent structure. It is found that the numerical results of the distribution of Reynolds stress, the formation of high shear layer, and the event of ejection and sweeping, match well with the observed characteristics of the coherent structures in a turbulence boundary layer.
基金supported by the National Natural Science Foundation of China(6080105261271327)+2 种基金Jiangsu Planned Projects for Postdoctoral Research Funds(1201039C)the China Postdoctoral Science Foundation (2012M521099)Hubei Key Laboratory of Intelligent Wireless Communications(IWC2012002)
文摘This paper discusses the problem of direction of departure （DOD） and direction of arrival （DOA） estimation for a bistatic multiple input multiple output （MIMO） radar, and proposes an improved reduced-dimension Capon algorithm therein. Compared with the reduced-dimension Capon algorithm which requires pair matching between the two-dimensional angle estimation, the pro- posed algorithm can obtain automatically paired DOD and DOA estimation without debasing the performance of angle estimation in bistatic MIMO radar. Furthermore, the proposed algorithm has a lower complexity than the reduced-dimension Capon algorithm, and it is suitable for non-uniform linear arrays. The complexity of the proposed algorithm is analyzed and the Cramer-Rao bound （CRB） is also derived. Simulation results verify the usefulness of the proposed algorithm.
文摘In this work, hot isostatic pressing （HIPing） technique was used to densify the Ti2AINb pre-alloyed powder. The influence of HIPing loading route parameters （temperature and rates of heating and pressurizing） on microstructure and properties of PM Ti2AINb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties （especially high temper- ature rupture lifetime） of PM Ti2AINb alloys in the present work. A finite element method （FEM） model for predicting the final densification was developed and was used to optimize the HIPing procedure.
基金supported by National Forestry Public Welfare Industry Scientific Research Special Subsidy Project(201304502)
文摘In this study,an image binarization optimization algorithm,based on local threshold algorithms,is proposed because global and traditional local threshold segmentation algorithms cannot effectively address the problems of nonuniform backgrounds of wood defect images.The proposed algorithm calculates the threshold by the mean,standard deviation and the extreme value of the window.The results indicate that this modified algorithm enhances the image segmentation for wood defect images on a complex background,which is much superior to the global threshold algorithm and the Bernsen algorithm,and slightly better than the Niblack algorithm and Sauvola algorithm.Compared with similar models,the algorithm proposed in this paper has higher segmentation accuracy,as high as 92.6%for wood defect images with a complex background.
文摘A 2-D non-uniform sediment mat hmatical model in the boundary-fitting orthogonal coordinate system was develop ed in this paper. The governing equations, the numerical scheme, the boundary con ditions, the movable boundary technique and the numerical solutions were present ed. The model was verified by the data of the reach 25km upstream the Jialingjia ng estuary and the 44km long main stream of the Chongqing reach of the Yangtze r iver. The calculated results show that, the water elevation, the velocity distri bution and the river bed deformation are in agreement with the measured data.
基金Supported by the Program for New Century Excellent Talents in University of China (Grant No. 20041006)the Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 200136)
文摘Maximum power output of a class of irreversible non-regeneration heat engines with non-uniform working fluid,in which heat transfers between the working fluid and the heat reservoirs obey the linear phenomenological heat transfer law [q ∝Δ(T-1)],are studied in this paper. Optimal control theory is used to determine the upper bounds of power of the heat engine for the lumped-parameter model and the distributed-parameter model,respectively. The results show that the maximum power output of the heat engine in the distributed-parameter model is less than or equal to that in the lumped-parameter model,which could provide more realistic guidelines for real heat engines. Analytical solutions of the maximum power output are obtained for the irreversible heat engines working between constant temperature reservoirs. For the irreversible heat engine operating between variable temperature reservoirs,a numerical example for the lumped-parameter model is provided by numerical calculation. The effects of changes of reservoir's temperature on the maximum power of the heat engine are analyzed. The obtained results are,in addition,compared with those obtained with Newtonian heat transfer law [q ∝Δ(T)].
基金supported by the National Natural Science Foundation of China(Grant Nos.51779262 and 51579244)the Independent Project of Naval University of Engineering(Grant No.425317Q017)。
文摘A three-dimensional disc model with non-uniform heat generating is built.A series of cooling channels are inserted to cool this disc which is strewn in a hierarchical pattern.To reveal thermal and flow characteristics,a composite objective function comprised of the maximum temperature difference(MTD)and pumping power is constructed.The deployment pattern of cooling channels contains two cases,i.e.,the radial-pattern and dendritic-pattern.By capitalizing on constructal design method together with finite element method,the diameter of radial-pattern cooling channels is optimized in the first place.Next,the diameter,angle coefficient and length coefficient of dendritic-pattern cooling channels are three degrees-of-freedom to be stepwise optimized at different heat generating conditions.Furthermore,NSGA-II algorithm is introduced into the multiobjective problem.Upon obtaining its Pareto optimal solution set,Topsis method is invoked to yield the optimal solutions under given weighted coefficients.The heat generation over the entire body and the volume ratio of cooling channels operate as the primary constraints.Based on these premises,constructal design will be stepwise performed by varying three degrees-offreedom.The obtained results state that more heating components or devices should be installed as close to the cooling water inlet as possible.This can further reduce MTD at the same cost of pumping power,thereby improve thermal and flow performance and prolong the lifespan of devices.As optimized with two degrees-of-freedom,the MTD is reduced by 18.6%compared with the counterpart obtained from single degree-of-freedom optimization,while the pumping power is increased by 59.8%.As optimized with three degrees-of-freedom,the MTD is decreased by 6.2%compared with the counterpart from two degrees-of-freedom optimization,while the pumping power is increased by 3.0%.It is manifest that when two sub-objectives form a composite objective,the performance improvement of one sub-objective will inevitably elicit the vitiation o
基金support from the National Natural Science Foundation of China(No.51576027)。
文摘The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3)aviation kerosene in a horizontal circular tube has been numerically studied,focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction.The governing equations of mass,momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method.The re-normalization group(RNG)k-εturbulence model with an enhanced wall treatment was selected.Considering the heat conduction in the solid wall,the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed.The evolution of secondary flow was analyzed.Effects of the outer-wall heat flux,mass flux,pressure and tube thermal conductivity on heat transfer were investigated.Moreover,the buoyancy criterion and the heat transfer correlation were obtained.Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling,further leads to the heat transfer deterioration.The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube,and weakening the heat transfer at the top of tube,which results in the non-uniform inner-wall temperature and heat flux distributions.Decreasing the ratio of outer-wall heat flux and mass flux,increasing the pressure could weaken the heat transfer difference along the circumferential direction,while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated.When the buoyancy criterion of(Grq/Grth)max≤0.8 is satisfied,the effect of buoyancy could be ignored.The new correlations work well for non-uniform heat transfer predictions.
基金Project (No. 50878191) supported by the National Natural Science Foundation of China
文摘Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom (PTPB) or for pervious top and impervious bottom (PTIB). For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper.
基金Supported by National Key Research and Development Program of China(Project No.2017YFD0700800)Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ16E050003)+1 种基金Natural Science Foundation of China(Grant No.51505429)Science Foundation of Zhejiang Sci-Tech University(Grant No.15022011-Y)
文摘Currently, transplanting mechanisms for dryland plug seedlings in China are mainly semiautomatic and have low efficiency. The rotary seedling pick-up mechanism with a planetary gear train for non-uniform intermittent transmission, and a concave and convex locking arc device, has a large rigid impact. To solve these problems, according to the design requirements for a dryland plug seedling transplanting mechanism, a rotary seedling pick-up mechanism of a planetary gear train with combined non-circular gear transmission of incomplete eccentric circular and noncircular gears was proposed. This has the characteristics of two-times greater fluctuation of the transmission ratio in a cycle, and can achieve a non-uniform continuous drive. Through analysis of the working principle of the seedling pick-up mechanism, its kinematics model was established. The human–computer interaction optimization method and self-developed computer-aided analysis and optimization software were used to obtain a set of parameters that satisfy the operation requirements of the seedling pick-up mechanism. According to the optimized parameters, the structure of the seedling pick-up mechanism was designed, a virtual prototype of the mechanism was created, and a physical prototype was manufactured. A virtual motion simulation of the mechanism was performed, high-speed photographic kinematics tests were conducted, and the kinematic properties of the physical prototype were investigated, whereby the correctness of the theoretical model and the optimized design of the mechanism were verified. Further, laboratory seedling pick-up tests were conducted. The success ratio of seedling pick-up was 93.8% when the seedling pick-up efficiency of the mechanism was 60 plants per minute per row, indicating that the mechanism has a high efficiency and success ratio for seedling pick-up and can be applied to a dryland plug seedling transplanter.
基金Project supported by the National Key Basic Research Program of China (973 Program,Grant No.2006CB705808)the State Major Science and Technology Special Project during the 11th Five-year Plan (Grant No.2008ZX05054)
文摘This article presents a new well test model for two-zone linear composite reservoirs, where the rock and fluid properties as well as the formation thicknesses on both sides of the discontinuity are distinctly different. An analytical solution of pressure-transient behavior for a line-source, constant-rate well in this type of reservoir configuration is obtained with Fourier space transformation and Laplace transformation. By applying Duhamel principle, the wellbore storage and skins effects can easily be included. A set of type curves are generated and the sensitivities of the relevant parameters are discussed. A new correlating parameter MhDl√ηD is proposed to identify the pressure response in the pressure derivative curve. The model as well as the corresponding type curves are quite general that they are useful in predicting the production performance or analyzing the production data from this type of well-reservoir systems.
文摘A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the Wenzhou Bay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport are presented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with their initial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of the critical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested. The model verification computation shows that, the tidal levels computed from the model are in good agreement with the field data at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measured along the totally 52 synchronously observed verticals distributed over 8 cross sections. The coraputed tidal water throughputs through the Huangda'ao cross section are close to the measured data. And the computed values of bed deformation from Yangfushan to the estuary outfall and in the outer-sea area are in good agreement with the data observed from 1986 to 1992. The changes of tidal volumes through the estuary, velocities in different channels and the bed form due to the influence of the reclamation project on the Wenzhou shoal are predicted by means of this model.
基金supported by the National Natural Science Foundation of China (No’s. 51575448 and 51135007)
文摘The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.
文摘经典DBSCAN(density based spatial clustering of applications with noise)算法需要人工指定邻域半径(Eps)和点数阈值(Minpts),且均为全局参数,导致聚类准确率低。针对此问题,为了提高经典DBSCAN聚类算法的聚类准确率,基于网格划分思想,提出了一种局部自适应DBSCAN聚类算法。根据数据集自身特征生成网格空间,将特征数据映射至相应的网格空间;利用高斯核函数估计每个网格区间的局部密度;联合多维度网格密度分布信息,寻找无连接或弱连接高密度网格之间的区域,同时统计同区域的波峰数量,从而自适应确定各区域的Eps及Minpts参数;使用每个区域独有的参数作为DBSCAN算法输入,并进行聚类。实验结果表明,该算法能够在聚类过程中自适应确定每个局部区域的Eps和Minpts参数,聚类准确率高且耗时较低。
