The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels.Its outlet velocity uniformity directly determines the heating uniformity of textiles,significantly af...The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels.Its outlet velocity uniformity directly determines the heating uniformity of textiles,significantly affecting the heat setting performance.In a traditional heat setting machine,the outlet airflow maldistribution of the plenum chamber still exists.In this study,a novel plenum chamber with an airfoil baffle was established to improve the uniformity of the velocity distribution at the outlet in a heat setting machine.The structural influence of the plenum chamber on the velocity distribution was investigated using a computational fluid dynamics program.It was found that a chamber with a smaller outlet partition thickness had a better outlet velocity uniformity.The structural optimization of the plenum chamber was conducted using the particle swarm optimization algorithm.The outlet partition thickness,the transverse distance and the longitudinal distance of the optimized plenum chamber were 20,686.2 and 274.6 mm,respectively.Experiments were carried out.The experimental and simulated results showed that the optimized plenum chamber with an airfoil baffle could improve the outlet velocity uniformity.The air outlet velocity uniformity index of the optimized plenum chamber with an airfoil baffle was 4.75%higher than that of the plenum chamber without an airfoil baffle and 5.98%higher than that of the conventional chamber with a square baffle in a commercial heat setting machine.展开更多
Based on one type of practical Biot's equation and the dynamic-stiffness matrices ofa poroelastic soil layer and half-space, Green's functions were derived for unitformly distributed loads acting on an inclined line...Based on one type of practical Biot's equation and the dynamic-stiffness matrices ofa poroelastic soil layer and half-space, Green's functions were derived for unitformly distributed loads acting on an inclined line in a poroelastie layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems.展开更多
In the manufacture of SiC_p/Al completes via powder metallurgy, the method of assessing the distri-bution uniformity of SiC particles is very important. The SiC_p distribution uniformity on each processingprocedure a...In the manufacture of SiC_p/Al completes via powder metallurgy, the method of assessing the distri-bution uniformity of SiC particles is very important. The SiC_p distribution uniformity on each processingprocedure at the macro- and micro-mixed stages was investigated and the methods for determining mix-ture quality were put forward.展开更多
In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition und...In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition.The criticality conditions for a slab,an infinite cylinder,and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system.Exact solution for a Semenov model with convection heat loss was also presented.The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared.The critical parameterδis calculated and compared with those of Frank-Kamenetskii solution values.The validation of the calculated ignition temperatures with other exact solution and experimental results were offered.The relation between critical parameters form Semenov and F.K.models solution was introduced.展开更多
After expanding the capacity by widening the trolley of the No. 3 sintering machine, severe uneven sintering occurred in the trolley' s lateral distribution, which affected the output and quality of sinter. In this s...After expanding the capacity by widening the trolley of the No. 3 sintering machine, severe uneven sintering occurred in the trolley' s lateral distribution, which affected the output and quality of sinter. In this study, the quantitative evaluation indices of the burden uniform distribution in the width direction of the sintering machine is introduced for the first time. By measuring the temperature of discharged gas, a plane temperature field is constructed. Through analyzing the temperature field and the burden layer' s differential thermal equilibrium, a mathematical model for evaluating the indices, which is an online reflection of the degree of uniform distribution, is built. Following the improvements in burden distribution equipment ,the optimization of the ignition system and the dynamic adjustment of the process ,the problem of uneven sintering in lateral distribution has been solved, and the quality and the yield of sinter have been improved.展开更多
The present study proposes a novel method based on the geometric theory for measuring the distribution of bubble swarms in the circular region of a direct-contact heat exchanger.It was determined that the mixing is un...The present study proposes a novel method based on the geometric theory for measuring the distribution of bubble swarms in the circular region of a direct-contact heat exchanger.It was determined that the mixing is uniform when the average distance between the bubble swarms in the unit circular region is approximately 0.9054,which is the standard reference value.The effect of sample size(i.e.,the number of bubbles)on mixing uniformity was investigated to determine the optimal sample size.It was verified that the metric's accuracy and stability were higher with a sample size of 155.Accordingly,it was proposed to increase the sample size by filling irregular bubbles using a segmentation method,which enabled a further accurate assessment of the mixing uniformity.The mixing uniformity of bubble swarms in the circular region and its maximum internal connection with the square region was accurately quantified.It was revealed that the relative average error increased by approximately 3.47% due to information loss.The proposed method was demonstrated to be rotationally invariant.The present study provided novel insights into evaluating mixing uniformity,which would guide enhanced heat transfer and the effective evaluation of the spatiotemporal characteristics of transient mixing in circular regions or the cross-sections of chemical transport pipelines.展开更多
The generation of good pseudo-random numbers is the base of many important fields in scientific computing, such as randomized algorithms and numerical solution of stochastic differential equations. In this paper, a cl...The generation of good pseudo-random numbers is the base of many important fields in scientific computing, such as randomized algorithms and numerical solution of stochastic differential equations. In this paper, a class of random number generators (RNGs) based on Weyl sequence is proposed. The uniformity of those RNGs is proved theoretically. Statistical and numerical computations show the efficiency of the methods.展开更多
A level-value estimation method was illustrated for solving the constrained global optimization problem. The equivalence between the root of a modified variance equation and the optimal value of the original optimizat...A level-value estimation method was illustrated for solving the constrained global optimization problem. The equivalence between the root of a modified variance equation and the optimal value of the original optimization problem is shown. An alternate algorithm based on the Newton's method is presented and the convergence of its implementable approach is proved. Preliminary numerical results indicate that the method is effective.展开更多
High-speed, high-accuracy data converters are attractive for use in most RF applications. Such converters allow direct conversion to occur between the digital baseband and the antenna. However, high speed and high acc...High-speed, high-accuracy data converters are attractive for use in most RF applications. Such converters allow direct conversion to occur between the digital baseband and the antenna. However, high speed and high accuracy make the analog components in a converter more complex, and this complexity causes more power to be dissipated than if a traditional approach were taken. A static calibration technique for flash analog-to-digital converters (ADCs) is discussed in this paper. The calibration is based onhistogram test methods, and equivalent errors in the flash ADC comparators are estimated in the digital domain without any significant changes being made to the ADC comparators. In the trimming process, reference voltages are adjusted to compensate for static errors. Behavioral-level simulations of a moderate-resolution 8-bit flash ADC show that, for typical errors, ADC performance is considerably improved by the proposed technique. As a result of calibration, the differential no.nlinearities (DNLs) are reduced on average from 4 LSB to 0.5 LSB, and the integral nonlinearities (INLs) are reduced on average from 4.2 LSB to 0.35 LSB. Implementation issues for this proposed technique are discussed in our subsequent paper, “A Histogram-Based Static-Error Correction Technique for Flash ADCs: Implementation Aspects. ”展开更多
The random step maneuver with uniformly distributed starting times has the disadvantage that it cannot focus the starting time on the more efficiency time. It decreases the penetration probability. To resolve this pro...The random step maneuver with uniformly distributed starting times has the disadvantage that it cannot focus the starting time on the more efficiency time. It decreases the penetration probability. To resolve this problem, a random step penetration algorithm with normal distribution starting time is proposed. Using the shaping filters and adjoint system method, the miss distance with different starting times can be acquired. According to the penetration standard, the time window ensuring successful penetration can be calculated and it is used as the 3σ bound of the normally distributed random maneuver. Simulation results indicate that the normally distributed random maneuver has higher penetration probability than the uniformly distributed random maneuver.展开更多
In some old industrial plants,in order to meet the increasingly strict requirements of pollutant emission limits,it is necessary to install the compact filtration and/or purification devices in a given narrow machine ...In some old industrial plants,in order to meet the increasingly strict requirements of pollutant emission limits,it is necessary to install the compact filtration and/or purification devices in a given narrow machine room.Different types of structural configuration might influence air distribution inside these devices.The unreasonable air distribution might lead each part of filtration or purification media to operating at largely different air flow rates.Based on a computational fluid dynamics(CFD)model,this study explores the influence of different outlet positions and different upper heights on the flow field inside chamber.The porous medium model is employed to simulate the air flow in porous media.The changing structural configurations include three positioning cases of the outlet opening and eight height cases of the upper chamber.The root mean square is defined as the non-uniformity coefficient to evaluate the uniformity of air flow distribution.The results show that the farther distance between inlet and outlet openings will bring more uniform air distribution,and the increasing height of upper chamber totally trends to exhibit more uniform air distribution.展开更多
With the development of modern electronic countermeasure technology,the fight between radar jamming and anti-jamming in aviation military has become increasingly fierce.There are some special requirements for radar co...With the development of modern electronic countermeasure technology,the fight between radar jamming and anti-jamming in aviation military has become increasingly fierce.There are some special requirements for radar countermeasure experiments.For example,such experiments are often divided into several stages,and responses of the previous stages will become factors of the next stages.Moreover,the experiment design can only consider some typical level values of the factors.However,the experiment factors are mostly continuous variables.Thus when there are some jumps in the response,and the value granularity of the factor level is large,the responses fail to reflect the distortion process,which makes it difficult to explore the radar performance boundary.Therefore,it is necessary to study the sequential experiment design method with the optimization goals of response uniformization and response distortion process characterization.In this paper,a sequential experiment design strategy based on Kriging model is established.Firstly,Kriging model is used to fit the initial experimental data to obtain the response surface.In order to enhance the uniformity of response distribution,Shannon entropy is applied to the objective function as the measure of uniformity.While for the situation of response distortion,we consider replacing the existing experiment points with those whose corresponding responses have a larger gradient norm.It means that the response value near these points will change rapidly,so they are more valuable for research.Then we use the peak surface in the three-dimensional space to intuitively verify the effect of the above algorithms on response uniformization and response distortion process characterization,and use the simulated annealing algorithm to solve them.The simulation results show that our sequential experiment strategy has a good effect.Finally,we apply the strategy to the practical problem of radar countermeasure experiment,and the obtained results also perform well.展开更多
A horizontal distributor for biogas slurry application was proposed to explore the distribution performance through CFD analysis and verified by field test.The rheological properties of biogas slurry were analyzed at ...A horizontal distributor for biogas slurry application was proposed to explore the distribution performance through CFD analysis and verified by field test.The rheological properties of biogas slurry were analyzed at first,and key parameters were obtained for the next simulation.The effects of distribution modes,inlet direction,and outlets number on the velocity distribution of flow field and mass flow rate of the horizonal distributor were investigated by CFD simulations.Results of rheological properties indicated that biogas slurry was a non-Newtonian fluid and exhibited shear-thinning behavior.It can be well described by power-law model.The simulation results showed that the geometry of rotor,especially the block numbers was the main factor that determining the fluid movement and trajectory of distribution and output.The mode rotor 1 with two blocks reached the lowest variable coefficient of mass flow rate(4.49%),indicating a higher degree of uniformity.The upward inlet direction would obtain less dead zone,and the distributor with an even outlets number would possess more uniform distribution and less dead zone.The field test of the distributor with rotor 1,upward inlet direction,and 24 outlets has been carried on to verify the simulation results,the variable coefficient of mass flow was 13.06%,which was slightly higher than the simulation(9.23%),but it still within the range of requirement(<15%).The proposed model and the findings of this work are of guiding significance for the study of the utilization technology and equipment of liquid biogas residue.展开更多
Let Vk=u1u2……uk, ui's be i.i.d - U(0, 1), the p.d.f of 1 - Vk+l be the GF of the unsigned Stirling numbers of the first kind s(n, k). This paper discusses the applications of uniform distribution to combinator...Let Vk=u1u2……uk, ui's be i.i.d - U(0, 1), the p.d.f of 1 - Vk+l be the GF of the unsigned Stirling numbers of the first kind s(n, k). This paper discusses the applications of uniform distribution to combinatorial analysis and Riemann zeta function; several identities of Stifling series are established, and the Euler's result for ∑ Hn/n^k-l, k ≥ 3 is given a new probabilistic proof.展开更多
The tilt-blade mechanical stirring of A356-2.5vol.%SiCp liquid was conducted in a cylindrical crucible to solve the problem of nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechani...The tilt-blade mechanical stirring of A356-2.5vol.%SiCp liquid was conducted in a cylindrical crucible to solve the problem of nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring. The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25° for horizontal tilt angle α of the blade, 200 r/min for rotating speed of stirrer and 10 mm/s for speed of moving up and down of stirrer. The results show that there exists a nonlinear relationship between circumferential tilt angle β of the blade and radial relative deviation d of SiCp content in A356 liquid. When β is smaller than 20°, the d of SiCp content in A356 liquid between the center and the periphery of crucible decreases with increasing β. Conversely, when β is bigger than 26°, d increases with increasing β. Only when β is about 20°, d can be equal to nought i.e. uniform radial distribution of SiC particles can be realized. It can be seen that the nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring can be eliminated in this tilt-blade mechanical stirring of A356-SiCp liquid.展开更多
The evaluation of the performance of distribution uniformity by linearly moved irrigation system(LMIS)should consider the impacts of non uniformity of the water on crop yield.With increasing pressures to improve water...The evaluation of the performance of distribution uniformity by linearly moved irrigation system(LMIS)should consider the impacts of non uniformity of the water on crop yield.With increasing pressures to improve water use efficiency,plant productivity and farm profitability,questions continue to be raised concerning the future direction of irrigated agriculture.This study therefore aimed at evaluating water distribution under LMIS newly designed by the National Research Centre of Fluid Machinery Engineering and Technology,Jiangsu University,China.This article reports the real distribution of irrigation water under the LMIS with respect to sprinkler height above the ground surface as well as the consequence of different operating pressures.Water distribution coefficients used in the performance assessment were Christiansen’s coefficient of uniformity(CU),distribution uniformity(DU),scheduling coefficients(Sc)and the coefficient of variation(CV).The results showed that the mean CU ranged from 82.30%to 93.17%,and mean DU ranged from 70.39%to 88.44%.Also Sc values ranged from 1.13 to 1.42 with CV values ranging from 10.3%to 22.5%.The optimum method and results in this study can provide a reference to the operations for saving water and cost in the application of LMIS.展开更多
In this note we construct certain sequences of finite point sets in [0, 1) s (s ≥ 1) and give the upper bounds of their discrepancy. Furthermore we prove that these sequences are uniformly distrbuted in [0, 1) s .
Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large ...Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large number of obvious EMI peaks in the frequency spectrum of the carrier phase-shifted constant-switching-frequency pulse-width modulation(CSFPWM).Spreading the EMI across a wider frequency range can help to reduce the EMI peaks.In this study,we designed a uniform distribution(UD)spread-spectrum modulation technology using the principle of uniform switching frequency distribution and minimum switching loss for MMC.Its feasibility is verified by theoretical derivation and simulation.Then,the effectiveness of UDPWM in reducing the EMI is verified in experiments with a prototype MMC testbed in the lab.Compared with traditional CSFPWM,UDPWM can reduce conducted EMI by 10-20 dB.Also,compared with random PWM(RPWM),UDPWM can improve efficiency and reduce total harmonic distortion(THD)of output voltage and current in MMC.展开更多
It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost ...It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost uniform transverse distributed(UTD) beam within undulators are required. This study shows that a UTD electron beam can be generated within evenly distributed drift sections where undulators can be placed, by means of octupoles and particular optics. A specific design is presented, and numerical simulations are performed to verify the proposed method.展开更多
The uniform distribution of radial velocities of flow is of great importance for a cylindrical vessel with annular packed-bed (CVAPB). In this paper, a theoretical analysis for producing a uniform radial velocity dist...The uniform distribution of radial velocities of flow is of great importance for a cylindrical vessel with annular packed-bed (CVAPB). In this paper, a theoretical analysis for producing a uniform radial velocity distribution within a vessel is presented and a design method is established for a specially designed conical chock (SDCC). A differential equation for determining the contour size of SDCC is derived. Experimental verification is performed in a test model of CVAPB. The results show that the axial distribution of differential pressures across the packed-bed become uniform for CVAPB with SDCC and the uniformity of radial velocity is improved.展开更多
基金National Natural Science Foundation of China(No.62173307)the Key R&D Projects of Science and Technology Department of Zhejiang Province,China(Nos.2023C01158,2022C01065 and 2022C01188)the Fundamental Research Funds of Zhejiang Sci-Tech University,China(No.22242298-Y)。
文摘The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels.Its outlet velocity uniformity directly determines the heating uniformity of textiles,significantly affecting the heat setting performance.In a traditional heat setting machine,the outlet airflow maldistribution of the plenum chamber still exists.In this study,a novel plenum chamber with an airfoil baffle was established to improve the uniformity of the velocity distribution at the outlet in a heat setting machine.The structural influence of the plenum chamber on the velocity distribution was investigated using a computational fluid dynamics program.It was found that a chamber with a smaller outlet partition thickness had a better outlet velocity uniformity.The structural optimization of the plenum chamber was conducted using the particle swarm optimization algorithm.The outlet partition thickness,the transverse distance and the longitudinal distance of the optimized plenum chamber were 20,686.2 and 274.6 mm,respectively.Experiments were carried out.The experimental and simulated results showed that the optimized plenum chamber with an airfoil baffle could improve the outlet velocity uniformity.The air outlet velocity uniformity index of the optimized plenum chamber with an airfoil baffle was 4.75%higher than that of the plenum chamber without an airfoil baffle and 5.98%higher than that of the conventional chamber with a square baffle in a commercial heat setting machine.
基金National Natural Science Foundation of China Under Grant No.50378063
文摘Based on one type of practical Biot's equation and the dynamic-stiffness matrices ofa poroelastic soil layer and half-space, Green's functions were derived for unitformly distributed loads acting on an inclined line in a poroelastie layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems.
文摘In the manufacture of SiC_p/Al completes via powder metallurgy, the method of assessing the distri-bution uniformity of SiC particles is very important. The SiC_p distribution uniformity on each processingprocedure at the macro- and micro-mixed stages was investigated and the methods for determining mix-ture quality were put forward.
文摘In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition.The criticality conditions for a slab,an infinite cylinder,and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system.Exact solution for a Semenov model with convection heat loss was also presented.The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared.The critical parameterδis calculated and compared with those of Frank-Kamenetskii solution values.The validation of the calculated ignition temperatures with other exact solution and experimental results were offered.The relation between critical parameters form Semenov and F.K.models solution was introduced.
文摘After expanding the capacity by widening the trolley of the No. 3 sintering machine, severe uneven sintering occurred in the trolley' s lateral distribution, which affected the output and quality of sinter. In this study, the quantitative evaluation indices of the burden uniform distribution in the width direction of the sintering machine is introduced for the first time. By measuring the temperature of discharged gas, a plane temperature field is constructed. Through analyzing the temperature field and the burden layer' s differential thermal equilibrium, a mathematical model for evaluating the indices, which is an online reflection of the degree of uniform distribution, is built. Following the improvements in burden distribution equipment ,the optimization of the ignition system and the dynamic adjustment of the process ,the problem of uneven sintering in lateral distribution has been solved, and the quality and the yield of sinter have been improved.
基金the National Natural Science Foundation of China(project No.52166004)Yunnan Major Scientific and Technological Projects(grant No.202202AG050002)+2 种基金Scientific Research Fund Project of Yunnan Education Department,China(grant No.2021j0063)Natural Science FoundationofYunnan Province,China(grant No.202101AU070031)the teaching projects A Quality Course for Graduate Students in Yunnan Province"Numerical Analysis","Advanced Mathematics Teaching Team of Engineering Subjects of Kunming University of Science and Technology".
文摘The present study proposes a novel method based on the geometric theory for measuring the distribution of bubble swarms in the circular region of a direct-contact heat exchanger.It was determined that the mixing is uniform when the average distance between the bubble swarms in the unit circular region is approximately 0.9054,which is the standard reference value.The effect of sample size(i.e.,the number of bubbles)on mixing uniformity was investigated to determine the optimal sample size.It was verified that the metric's accuracy and stability were higher with a sample size of 155.Accordingly,it was proposed to increase the sample size by filling irregular bubbles using a segmentation method,which enabled a further accurate assessment of the mixing uniformity.The mixing uniformity of bubble swarms in the circular region and its maximum internal connection with the square region was accurately quantified.It was revealed that the relative average error increased by approximately 3.47% due to information loss.The proposed method was demonstrated to be rotationally invariant.The present study provided novel insights into evaluating mixing uniformity,which would guide enhanced heat transfer and the effective evaluation of the spatiotemporal characteristics of transient mixing in circular regions or the cross-sections of chemical transport pipelines.
基金Supported by National Natural Science Foundation of China (19871047)and National Key Basic Research Special Fund(1998020306).
文摘The generation of good pseudo-random numbers is the base of many important fields in scientific computing, such as randomized algorithms and numerical solution of stochastic differential equations. In this paper, a class of random number generators (RNGs) based on Weyl sequence is proposed. The uniformity of those RNGs is proved theoretically. Statistical and numerical computations show the efficiency of the methods.
基金Project supported by the National Natural Science Foundation of China (No.19871053)
文摘A level-value estimation method was illustrated for solving the constrained global optimization problem. The equivalence between the root of a modified variance equation and the optimal value of the original optimization problem is shown. An alternate algorithm based on the Newton's method is presented and the convergence of its implementable approach is proved. Preliminary numerical results indicate that the method is effective.
文摘High-speed, high-accuracy data converters are attractive for use in most RF applications. Such converters allow direct conversion to occur between the digital baseband and the antenna. However, high speed and high accuracy make the analog components in a converter more complex, and this complexity causes more power to be dissipated than if a traditional approach were taken. A static calibration technique for flash analog-to-digital converters (ADCs) is discussed in this paper. The calibration is based onhistogram test methods, and equivalent errors in the flash ADC comparators are estimated in the digital domain without any significant changes being made to the ADC comparators. In the trimming process, reference voltages are adjusted to compensate for static errors. Behavioral-level simulations of a moderate-resolution 8-bit flash ADC show that, for typical errors, ADC performance is considerably improved by the proposed technique. As a result of calibration, the differential no.nlinearities (DNLs) are reduced on average from 4 LSB to 0.5 LSB, and the integral nonlinearities (INLs) are reduced on average from 4.2 LSB to 0.35 LSB. Implementation issues for this proposed technique are discussed in our subsequent paper, “A Histogram-Based Static-Error Correction Technique for Flash ADCs: Implementation Aspects. ”
文摘The random step maneuver with uniformly distributed starting times has the disadvantage that it cannot focus the starting time on the more efficiency time. It decreases the penetration probability. To resolve this problem, a random step penetration algorithm with normal distribution starting time is proposed. Using the shaping filters and adjoint system method, the miss distance with different starting times can be acquired. According to the penetration standard, the time window ensuring successful penetration can be calculated and it is used as the 3σ bound of the normally distributed random maneuver. Simulation results indicate that the normally distributed random maneuver has higher penetration probability than the uniformly distributed random maneuver.
基金National Key Research and Development Program of China(No.2018YFC0705305)。
文摘In some old industrial plants,in order to meet the increasingly strict requirements of pollutant emission limits,it is necessary to install the compact filtration and/or purification devices in a given narrow machine room.Different types of structural configuration might influence air distribution inside these devices.The unreasonable air distribution might lead each part of filtration or purification media to operating at largely different air flow rates.Based on a computational fluid dynamics(CFD)model,this study explores the influence of different outlet positions and different upper heights on the flow field inside chamber.The porous medium model is employed to simulate the air flow in porous media.The changing structural configurations include three positioning cases of the outlet opening and eight height cases of the upper chamber.The root mean square is defined as the non-uniformity coefficient to evaluate the uniformity of air flow distribution.The results show that the farther distance between inlet and outlet openings will bring more uniform air distribution,and the increasing height of upper chamber totally trends to exhibit more uniform air distribution.
基金the National Natural Science Foundation of China(No.12071329)the State Key Laboratory of Complex Electromagnetic Environment Effects on Electronics and Information System(No.2021G0301)。
文摘With the development of modern electronic countermeasure technology,the fight between radar jamming and anti-jamming in aviation military has become increasingly fierce.There are some special requirements for radar countermeasure experiments.For example,such experiments are often divided into several stages,and responses of the previous stages will become factors of the next stages.Moreover,the experiment design can only consider some typical level values of the factors.However,the experiment factors are mostly continuous variables.Thus when there are some jumps in the response,and the value granularity of the factor level is large,the responses fail to reflect the distortion process,which makes it difficult to explore the radar performance boundary.Therefore,it is necessary to study the sequential experiment design method with the optimization goals of response uniformization and response distortion process characterization.In this paper,a sequential experiment design strategy based on Kriging model is established.Firstly,Kriging model is used to fit the initial experimental data to obtain the response surface.In order to enhance the uniformity of response distribution,Shannon entropy is applied to the objective function as the measure of uniformity.While for the situation of response distortion,we consider replacing the existing experiment points with those whose corresponding responses have a larger gradient norm.It means that the response value near these points will change rapidly,so they are more valuable for research.Then we use the peak surface in the three-dimensional space to intuitively verify the effect of the above algorithms on response uniformization and response distortion process characterization,and use the simulated annealing algorithm to solve them.The simulation results show that our sequential experiment strategy has a good effect.Finally,we apply the strategy to the practical problem of radar countermeasure experiment,and the obtained results also perform well.
基金supported by the Jiangsu Modern Agricultural Machinery Equipment and Technology Demonstration and Promotion Project(Grant No.NJ2021-23)Jiangsu Province Agricultural Science and Technology Independent Innovation Fund Project(Grant No.CX(22)3093)+1 种基金the Fundamental Research Fund of the Chinese Academy of Agricultural Sciences at the Institute Level(Grant No.S202106-02)the Key Research and Development Program of Hebei Province(Grant No.20327313D).
文摘A horizontal distributor for biogas slurry application was proposed to explore the distribution performance through CFD analysis and verified by field test.The rheological properties of biogas slurry were analyzed at first,and key parameters were obtained for the next simulation.The effects of distribution modes,inlet direction,and outlets number on the velocity distribution of flow field and mass flow rate of the horizonal distributor were investigated by CFD simulations.Results of rheological properties indicated that biogas slurry was a non-Newtonian fluid and exhibited shear-thinning behavior.It can be well described by power-law model.The simulation results showed that the geometry of rotor,especially the block numbers was the main factor that determining the fluid movement and trajectory of distribution and output.The mode rotor 1 with two blocks reached the lowest variable coefficient of mass flow rate(4.49%),indicating a higher degree of uniformity.The upward inlet direction would obtain less dead zone,and the distributor with an even outlets number would possess more uniform distribution and less dead zone.The field test of the distributor with rotor 1,upward inlet direction,and 24 outlets has been carried on to verify the simulation results,the variable coefficient of mass flow was 13.06%,which was slightly higher than the simulation(9.23%),but it still within the range of requirement(<15%).The proposed model and the findings of this work are of guiding significance for the study of the utilization technology and equipment of liquid biogas residue.
基金the Mathematical Tianyuan Foundation (Grant No.A0324645) of China
文摘Let Vk=u1u2……uk, ui's be i.i.d - U(0, 1), the p.d.f of 1 - Vk+l be the GF of the unsigned Stirling numbers of the first kind s(n, k). This paper discusses the applications of uniform distribution to combinatorial analysis and Riemann zeta function; several identities of Stifling series are established, and the Euler's result for ∑ Hn/n^k-l, k ≥ 3 is given a new probabilistic proof.
基金supported by the National Natural Science Foundation of China (No. 50974010)the Natural Science Foundation of Beijing (No. 2102039)
文摘The tilt-blade mechanical stirring of A356-2.5vol.%SiCp liquid was conducted in a cylindrical crucible to solve the problem of nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring. The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25° for horizontal tilt angle α of the blade, 200 r/min for rotating speed of stirrer and 10 mm/s for speed of moving up and down of stirrer. The results show that there exists a nonlinear relationship between circumferential tilt angle β of the blade and radial relative deviation d of SiCp content in A356 liquid. When β is smaller than 20°, the d of SiCp content in A356 liquid between the center and the periphery of crucible decreases with increasing β. Conversely, when β is bigger than 26°, d increases with increasing β. Only when β is about 20°, d can be equal to nought i.e. uniform radial distribution of SiC particles can be realized. It can be seen that the nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring can be eliminated in this tilt-blade mechanical stirring of A356-SiCp liquid.
基金the National Key Research and Development Program of China(No.2016YFC0400202)the Project of New Agricultural Machinery in Jiangsu Province(No.NJ2016-11)+1 种基金the Postdoctoral Science Foundation Special Support of China(No.2016T90428)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘The evaluation of the performance of distribution uniformity by linearly moved irrigation system(LMIS)should consider the impacts of non uniformity of the water on crop yield.With increasing pressures to improve water use efficiency,plant productivity and farm profitability,questions continue to be raised concerning the future direction of irrigated agriculture.This study therefore aimed at evaluating water distribution under LMIS newly designed by the National Research Centre of Fluid Machinery Engineering and Technology,Jiangsu University,China.This article reports the real distribution of irrigation water under the LMIS with respect to sprinkler height above the ground surface as well as the consequence of different operating pressures.Water distribution coefficients used in the performance assessment were Christiansen’s coefficient of uniformity(CU),distribution uniformity(DU),scheduling coefficients(Sc)and the coefficient of variation(CV).The results showed that the mean CU ranged from 82.30%to 93.17%,and mean DU ranged from 70.39%to 88.44%.Also Sc values ranged from 1.13 to 1.42 with CV values ranging from 10.3%to 22.5%.The optimum method and results in this study can provide a reference to the operations for saving water and cost in the application of LMIS.
基金Supported by the National Natural Science Foundation of Chinathe "333 Project" Foundation of Jiangsu Province of China
文摘In this note we construct certain sequences of finite point sets in [0, 1) s (s ≥ 1) and give the upper bounds of their discrepancy. Furthermore we prove that these sequences are uniformly distrbuted in [0, 1) s .
基金Supported by the National Natural Science Fundation of China(U1866211)。
文摘Modular multilevel converters(MMCs)have been widely used owing to their superior performance.However,the rapid switching of power electronics devices causes serious electromagnetic interference(EMI).There are a large number of obvious EMI peaks in the frequency spectrum of the carrier phase-shifted constant-switching-frequency pulse-width modulation(CSFPWM).Spreading the EMI across a wider frequency range can help to reduce the EMI peaks.In this study,we designed a uniform distribution(UD)spread-spectrum modulation technology using the principle of uniform switching frequency distribution and minimum switching loss for MMC.Its feasibility is verified by theoretical derivation and simulation.Then,the effectiveness of UDPWM in reducing the EMI is verified in experiments with a prototype MMC testbed in the lab.Compared with traditional CSFPWM,UDPWM can reduce conducted EMI by 10-20 dB.Also,compared with random PWM(RPWM),UDPWM can improve efficiency and reduce total harmonic distortion(THD)of output voltage and current in MMC.
基金Supported by National Natural Science Foundation of China(11475202,11405187)Youth Innovation Promotion Association of Chinese Academy of Sciences(2015009)
文摘It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost uniform transverse distributed(UTD) beam within undulators are required. This study shows that a UTD electron beam can be generated within evenly distributed drift sections where undulators can be placed, by means of octupoles and particular optics. A specific design is presented, and numerical simulations are performed to verify the proposed method.
基金the National Natural science Foundation of China.
文摘The uniform distribution of radial velocities of flow is of great importance for a cylindrical vessel with annular packed-bed (CVAPB). In this paper, a theoretical analysis for producing a uniform radial velocity distribution within a vessel is presented and a design method is established for a specially designed conical chock (SDCC). A differential equation for determining the contour size of SDCC is derived. Experimental verification is performed in a test model of CVAPB. The results show that the axial distribution of differential pressures across the packed-bed become uniform for CVAPB with SDCC and the uniformity of radial velocity is improved.