Gas-liquid flow in simple systems consisting of capillaries is analyzed by theory of irreversible thermodynamics so as to shed light on induction of nonuniformity of multiphase flow. By the Prigogine’s theorem of min...Gas-liquid flow in simple systems consisting of capillaries is analyzed by theory of irreversible thermodynamics so as to shed light on induction of nonuniformity of multiphase flow. By the Prigogine’s theorem of minimum entropy production, stability of uniform two-phase flow and possible transition to nonuniform distribution are discussed. The analysis of model systems suggests potential application of irreversible thermodynamics to research of multiphase hydrodynamics in chemical reactors.展开更多
For infrared focal plane graded during signal acquisition array sensors, imagery is departicularly nonuniformity. In this paper, an adaptive nonuniformity correction technique is proposed which simultaneously estimate...For infrared focal plane graded during signal acquisition array sensors, imagery is departicularly nonuniformity. In this paper, an adaptive nonuniformity correction technique is proposed which simultaneously estimates detector-level and readout- channel-level correction parameters using neural network approaches. Firstly, an improved neural network framework is designed to compute the desired output. Secondly, an adaptive learning rate rule is used in the gain and offset parameter estimation process. Experimental results show the proposed algorithm can achieve a faster convergence speed and better stability, remove nonuniformity and track parameters drift effectively, and present a good adaptability to scene changes and nonuniformity conditions.展开更多
The spatially and time resolved 2D images of x-ray emission of line-shaped Ti laser plasmas have been obtained with a pinhole transmission grating spectrometer coupled with a x-ray streak camera.The x-ray emission non...The spatially and time resolved 2D images of x-ray emission of line-shaped Ti laser plasmas have been obtained with a pinhole transmission grating spectrometer coupled with a x-ray streak camera.The x-ray emission nonuniformity of the plasma is quantitatively analyzed using a perturbation spectrum analysis method.The results show that the nonuniformity has a minimum value at a time corresponding to the peak time of the pumping laser pulse,and increases after that.A brief discussion on the nonuniformity mechanism has also been presented.展开更多
In the feed injection zone of a multiphase fluidized bed reactor, nonuniform distribution exists due to the introduction of feed nozzle jets and circulating catalyst, which ultimately have an impact on the performance...In the feed injection zone of a multiphase fluidized bed reactor, nonuniform distribution exists due to the introduction of feed nozzle jets and circulating catalyst, which ultimately have an impact on the performance of the reactor. The transient sectional nonuniformity index (TSNI) is proposed as a new index to quantify the nonuniformity of solid distribution in both radial and circumferential dimensions at the same time, based on the transient solids holdup data in the feed zone. The temporal and spatial distributions of TSNI can more accurately reflect the changes in the real-time gas-solid distribution uniformity of the cross-sections and the efficiency of gas-solid contact in the feed injection zone. The feed injection zone can be divided into three regions according to the characteristics of TSNI: the bubble-influenced zone, the jet-influenced zone, and the acceleration zone. According to the numerical simulation results, it was analyzed that TSNI is highly correlated with operating conditions, such as nozzle gas velocity and catalyst circulation rate.展开更多
The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave...The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.展开更多
The striping pattern nonuniformity of the infrared line scanner （IRLS） severely limits the system performance. An adaptive nonuniformity correction （NUC） algorithm for IRLS using neural network is proposed. It use...The striping pattern nonuniformity of the infrared line scanner （IRLS） severely limits the system performance. An adaptive nonuniformity correction （NUC） algorithm for IRLS using neural network is proposed. It uses a one-dimensional median filter to generate ideal output of network and can complete NUC by a single frame with a high correction level. Applications to both simulated and real infrared images show that the algorithm can obtain a satisfactory result with low complexity, no need of scene diversity or global motion between consecutive frames. It has the potential to realize real-time hardware-based applications.展开更多
The assembling error may lead to variation in stagger angles,which would affect the aerodynamic performance of the turbine.To investigate this underlying effect,two parallel numerical experiments on two turbines with ...The assembling error may lead to variation in stagger angles,which would affect the aerodynamic performance of the turbine.To investigate this underlying effect,two parallel numerical experiments on two turbines with the same profile,but uniform and nonuniform vane stagger angle respectively,were conducted in both steady and unsteady methods.The results indicate that certain changes in the detailed flow field of the turbine occur when the stagger angles are nonuniform,further,the blade loading distribution of the vane and rotor become markedly different from that in uniform vane stagger angle situation.Then these consequences caused by nonuniformity mentioned above enhance the unsteadiness of the flow,finally,the aerodynamic performance changes dramatically.It also shows that,compared with steady simulation,the unsteady numerical simulation is necessary in this investigation.展开更多
Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-...Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.展开更多
Physics-informed neural networks(PINNs)have shown remarkable prospects in solving the forward and inverse problems involving partial differential equations(PDEs).The method embeds PDEs into the neural network by calcu...Physics-informed neural networks(PINNs)have shown remarkable prospects in solving the forward and inverse problems involving partial differential equations(PDEs).The method embeds PDEs into the neural network by calculating the PDE loss at a set of collocation points,providing advantages such as meshfree and more convenient adaptive sampling.However,when solving PDEs using nonuniform collocation points,PINNs still face challenge regarding inefficient convergence of PDE residuals or even failure.In this work,we first analyze the ill-conditioning of the PDE loss in PINNs under nonuniform collocation points.To address the issue,we define volume weighting residual and propose volume weighting physics-informed neural networks(VW-PINNs).Through weighting the PDE residuals by the volume that the collocation points occupy within the computational domain,we embed explicitly the distribution characteristics of collocation points in the loss evaluation.The fast and sufficient convergence of the PDE residuals for the problems involving nonuniform collocation points is guaranteed.Considering the meshfree characteristics of VW-PINNs,we also develop a volume approximation algorithm based on kernel density estimation to calculate the volume of the collocation points.We validate the universality of VW-PINNs by solving the forward problems involving flow over a circular cylinder and flow over the NACA0012 airfoil under different inflow conditions,where conventional PINNs fail.By solving the Burgers’equation,we verify that VW-PINNs can enhance the efficiency of existing the adaptive sampling method in solving the forward problem by three times,and can reduce the relative L 2 error of conventional PINNs in solving the inverse problem by more than one order of magnitude.展开更多
To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.U...To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.Using the transmission reconstruction equation and the Monte Carlo program Geant4,an innovative virtual trajectory length model was constructed.This model integrated the solving process for the trajectory length and detection efficiency within the same model.To mitigate the influence of the angular distribution ofγ-rays emitted by the transmitted source at the detector,the transport processes of numerous particles traversing a virtual nuclear waste barrel with a density of zero were simulated.Consequently,a certain amount of information was captured at each step of particle transport.Simultaneously,the model addressed the nonuniform detection efficiency of the detector end face by considering whether the energy deposition of particles in the detector equaled their initial energy.Two models were established to validate the accuracy and reliability of the virtual trajectory length model.Model 1 was a simplified nuclear waste barrel,whereas Model 2 closely resembled the actual structure of a nuclear waste barrel.The results indicated that the proposed virtual trajectory length model significantly enhanced the precision of the trajectory length determination,substantially increasing the quality of the reconstructed images.For example,the reconstructed images of Model 2 using the“point-to-point”and average trajectory models revealed a signalto-noise ratio increase of 375.0%and 112.7%,respectively.Thus,the virtual trajectory length model proposed in this study holds paramount significance for the precise reconstruction of transmission images.Moreover,it can provide support for the accurate detection of radioactive activity in nuclear waste barrels.展开更多
This paper presents a method for obtaining the displacement of sand particles in a sand–bentonite mixture(SBM)when saturated with water,based on particle tracking velocimetry(PTV).The raw photographs were first conve...This paper presents a method for obtaining the displacement of sand particles in a sand–bentonite mixture(SBM)when saturated with water,based on particle tracking velocimetry(PTV).The raw photographs were first converted into binary images.The sand particles were then detected,and the displacement of the sand particles was obtained by comparing their positions in adjacent images.The swelling strain induced by saturation was also obtained using the proposed PTV method.This method was validated by comparing the result with those obtained using a displacement transducer.Subsequently,a comparative analysis of sand particle displacements was conducted for specimens with varying bentonite content(BC),initial thickness,and water infiltration directions.The experimental results obtained were as follows:(1)For specimens with different BCs,local swelling displacement of sand particles at the top part of the specimen increased with higher BCs;(2)For specimens with various heights(hsp),larger local swelling displacement was generated at lower hsp at the initial state;(3)Local swelling characteristics differed in different water infiltration directions.Top-side infiltration showed a significant downward movement of particles during the first several hours of swelling.An estimation method for the dry density distribution of the specimen was proposed based on PTV data and then verified by slicing dry density and water content measurement results.展开更多
Water dissolution ultraprecision continuous polishing is a nontraditional machining method specifically designed for water-soluble crystals.The aim of this study is primarily to reduce the surface roughness for small ...Water dissolution ultraprecision continuous polishing is a nontraditional machining method specifically designed for water-soluble crystals.The aim of this study is primarily to reduce the surface roughness for small sizes from an experimental standpoint.A trajectory uniformity simulation analysis is carried out for a consistent material removal.A material removal model is developed based on the water dissolution principle and kinematic analysis.Numerical simulations of single-and multiple-water-core polishing trajectories are performed to explore the influences of the processing parameters such as movement form,number of water cores,speed ratio,polishing time,and period ratio on the material removal uniformity.The material removal rate is calculated according to the Preston equation.The trajectory density nonuniformity is utilized to evaluate the global uniformity of the trajectory distributions and optimize the processing parameters for a better material removal uniformity.Verification experiments are conducted on a large-size ultraprecision continuous polisher using a typical potassium dihydrogen phosphate(KDP)crystal with a water-soluble structure.The edge collapse is improved from 51.499μm to 1.477μm by trajectory uniformity optimization.The changing trends of line profile variations in the validation experiment and simulation are similar.An ultrasmooth surface of a 180 mm×180 mm KDP crystal with a surface roughness root mean square of 1.718 nm is obtained after water dissolution ultraprecision continuous polishing.This study provides a comprehensive method for evaluation of material removal uniformity,which is valuable for the realization of high-quality machining for water-soluble crystals.展开更多
After cooling in the hot rolling process,the metallographic structure of microalloyed dual-phase steel is nonuniform along the rolling direction,while the thickness fluctuation of microalloyed dual-phase steel with a ...After cooling in the hot rolling process,the metallographic structure of microalloyed dual-phase steel is nonuniform along the rolling direction,while the thickness fluctuation of microalloyed dual-phase steel with a nonuniform metallographic structure will occur during cold rolling.The mechanism of nonuniform phase transformation of microalloyed dual-phase steels was studied during the cooling process after hot rolling,and the nonuniform phase transformation of microalloyed dual-phase steel was regulated during the cooling process after hot rolling through process optimization.First,the empirical equation of phase transformation temperature was measured by a dilatometer considering thermal expansion.Then,the phase field and temperature field of laminar cooling process were calculated to provide initial boundary conditions for the finite element model.After that,the coupling finite element model of the temperature phase transformation of the strip steel in coiling transportation process was established.The simulation results show that the different thermal contact conditions of the microalloyed dual-phase steel during coil transportation lead to uneven cooling of the coil,which leads to nonuniform transformation of the coil along the rolling direction.In addition,by prolonging the time interval from coiling to unloading,the phenomenon of nonuniform phase transformation of microalloyed dual-phase steel can be effectively controlled.The simulation results are applied to industrial production.The application results show that prolonging the time interval from coiling to unloading can effectively improve the nonuniform phase transformation of microalloyed dual-phase steel in the cooling process after hot rolling.展开更多
Reinforcement corrosion is the main cause of performance deterioration of reinforced concrete(RC)structures.Limited research has been performed to investigate the life-cycle cost(LCC)of coastal bridge piers with nonun...Reinforcement corrosion is the main cause of performance deterioration of reinforced concrete(RC)structures.Limited research has been performed to investigate the life-cycle cost(LCC)of coastal bridge piers with nonuniform corrosion using different materials.In this study,a reliability-based design optimization(RBDO)procedure is improved for the design of coastal bridge piers using six groups of commonly used materials,i.e.,normal performance concrete(NPC)with black steel(BS)rebar,high strength steel(HSS)rebar,epoxy coated(EC)rebar,and stainless steel(SS)rebar(named NPC-BS,NPC-HSS,NPC-EC,and NPC-SS,respectively),NPC with BS with silane soakage on the pier surface(named NPC-Silane),and high-performance concrete(HPC)with BS rebar(named HPC-BS).First,the RBDO procedure is improved for the design optimization of coastal bridge piers,and a bridge is selected to illustrate the procedure.Then,reliability analysis of the pier designed with each group of materials is carried out to obtain the time-dependent reliability in terms of the ultimate and serviceability performances.Next,the repair time of the pier is predicted based on the time-dependent reliability indices.Finally,the time-dependent LCCs for the pier are obtained for the selection of the optimal design.展开更多
Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can pred...Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can predict the region of occurrence of mth-order SRSS and estimate its threshold.The rescattering process is identified by the 2D PIC simulations under typical conditions of a direct-drive inertial confinement fusion scheme.Hot electrons produced by second-order SRSS propagate nearly perpendicular to the density gradient and gain nearly the same energy as in first-order SRSS,but there is no cascade acceleration to produce superhot electrons.Parametric studies for a wide range of ignition conditions show that SRSS and associated rescatterings are robust and important processes in inertial confinement fusion.展开更多
Convection driven by a spatially non-uniform internal heat source between two horizontal isothermal walls is studied by theoretical analysis and numerical simulation,in order to explore the bounds of the temperature a...Convection driven by a spatially non-uniform internal heat source between two horizontal isothermal walls is studied by theoretical analysis and numerical simulation,in order to explore the bounds of the temperature and the vertical heat flux.Specifically,the rigorous lower bound of the weighted average temperature<QT>is derived analytically,by decomposing the temperature field into a background profile and a fluctuation part.This bound obtained for the first time to consider non-uniform heat sources is found to be compatible with the existing bound obtained in uniform internal heat convection.Of physical importance,an analytical relationship is derived as an inequality connecting<QT>and the average vertical heat flux<wT>,by employing the average heat flux on the bottom wall(qb)as an intermediary variable.It clarifies the intrinsic relation between the lower bound of<QT>and the upper bound of<wT>,namely,these two bounds are essentially equivalent providing an easy way to obtain one from another.Furthermore,the analytical bounds are extensively demonstrated through a comprehensive series of direct numerical simulations.展开更多
The tunnel subjected to strike-slip fault dislocation exhibits severe and catastrophic damage.The existing analysis models frequently assume uniform fault displacement and fixed fault plane position.In contrast,post-e...The tunnel subjected to strike-slip fault dislocation exhibits severe and catastrophic damage.The existing analysis models frequently assume uniform fault displacement and fixed fault plane position.In contrast,post-earthquake observations indicate that the displacement near the fault zone is typically nonuniform,and the fault plane position is uncertain.In this study,we first established a series of improved governing equations to analyze the mechanical response of tunnels under strike-slip fault dislocation.The proposed methodology incorporated key factors such as nonuniform fault displacement and uncertain fault plane position into the governing equations,thereby significantly enhancing the applicability range and accuracy of the model.In contrast to previous analytical models,the maximum computational error has decreased from 57.1%to 1.1%.Subsequently,we conducted a rigorous validation of the proposed methodology by undertaking a comparative analysis with a 3D finite element numerical model,and the results from both approaches exhibited a high degree of qualitative and quantitative agreement with a maximum error of 9.9%.Finally,the proposed methodology was utilized to perform a parametric analysis to explore the effects of various parameters,such as fault displacement,fault zone width,fault zone strength,the ratio of maximum fault displacement of the hanging wall to the footwall,and fault plane position,on the response of tunnels subjected to strike-slip fault dislocation.The findings indicate a progressive increase in the peak internal forces of the tunnel with the rise in fault displacement and fault zone strength.Conversely,an augmentation in fault zone width is found to contribute to a decrease in the peak internal forces.For example,for a fault zone width of 10 m,the peak values of bending moment,shear force,and axial force are approximately 46.9%,102.4%,and 28.7% higher,respectively,compared to those observed for a fault zone width of 50 m.Furthermore,the position of the peak internal forces is influenced by variations in the ratio of maximum fault displacement of the hanging wall to footwall and the fault plane location,while the peak values of shear force and axial force always align with the fault plane.The maximum peak internal forces are observed when the footwall exclusively bears the entirety of the fault displacement,corresponding to a ratio of 0:1.The peak values of bending moment,shear force,and axial force for the ratio of 0:1 amount to approximately 123.8%,148.6%,and 111.1% of those for the ratio of 0.5:0.5,respectively.展开更多
In this paper,we study systems of conservation laws in one space dimension.We prove that for classical solutions in Sobolev spaces H^(s),with s>3/2,the data-to-solution map is not uniformly continuous.Our results a...In this paper,we study systems of conservation laws in one space dimension.We prove that for classical solutions in Sobolev spaces H^(s),with s>3/2,the data-to-solution map is not uniformly continuous.Our results apply to all nonlinear scalar conservation laws and to nonlinear hyperbolic systems of two equations.展开更多
Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suf...Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.展开更多
Clearance-fit(side-fit)spline joints are a key component in a permanent magnet synchronous motor(PMSM)in electric submersible pumping wells.The nonuniform spline clearance affects the output performance of a PMSM.A co...Clearance-fit(side-fit)spline joints are a key component in a permanent magnet synchronous motor(PMSM)in electric submersible pumping wells.The nonuniform spline clearance affects the output performance of a PMSM.A concept for energy conservation is optimized in this study to improve the modeling accuracy of electromagnetic torque.However,most existing computation models are one-way model with a magneto-mechanical simulation.In this study,a more accurate two-way coupling method is presented for simulating the electromagnetic and mechanical characteristics of PMSM.Additionally,importance should be attached to this two-way magneto-mechanical coupling methodology in an actual simulation.The coupled power,electrical and magnetic energy,and electromagnetic torque equations are solved iteratively until convergence for PMSMs with a segmented rotor and a non-segmented rotor.The optimal electromagnetic torque is obtained for different rotor configurations with the change of temperatures and rotational speeds.The results show that the output performance and electromagnetic torque of the PMSM are seriously affected by the effects of two-way magneto-mechanical coupling and nonuniform spline clearance.The proposed two-way coupling model gives more reasonable predictions than other one-way models do,because the power transfer between the electrical and magnetic energy can be modeled more accurately.The self-centralizing performance of clearance-fit splines and the sensitivity to the radial clearance magnitude lead to the reduction of the electromagnetic torque for the PMSM.Additionally,the electromagnetic torques decrease with the enhanced rotor temperatures and rotational speeds.The best rotor temperature and rotational speed are chosen through a comparison of the experimental results,and then the optimal electromagnetic torque is provided to ensure the output performance of the PMSM in electric submersible pumping wells.展开更多
基金the National Natural Science Foundation of China
文摘Gas-liquid flow in simple systems consisting of capillaries is analyzed by theory of irreversible thermodynamics so as to shed light on induction of nonuniformity of multiphase flow. By the Prigogine’s theorem of minimum entropy production, stability of uniform two-phase flow and possible transition to nonuniform distribution are discussed. The analysis of model systems suggests potential application of irreversible thermodynamics to research of multiphase hydrodynamics in chemical reactors.
基金supported by the National Natural Science Foundation of China (61101199)the Natural Science Foundation of Jiangsu Province (K2011699)the Colleges and Universities Innovation Projects (CX08B 045Z)
文摘For infrared focal plane graded during signal acquisition array sensors, imagery is departicularly nonuniformity. In this paper, an adaptive nonuniformity correction technique is proposed which simultaneously estimates detector-level and readout- channel-level correction parameters using neural network approaches. Firstly, an improved neural network framework is designed to compute the desired output. Secondly, an adaptive learning rate rule is used in the gain and offset parameter estimation process. Experimental results show the proposed algorithm can achieve a faster convergence speed and better stability, remove nonuniformity and track parameters drift effectively, and present a good adaptability to scene changes and nonuniformity conditions.
基金Supported by the National Natural High Technology Program.
文摘The spatially and time resolved 2D images of x-ray emission of line-shaped Ti laser plasmas have been obtained with a pinhole transmission grating spectrometer coupled with a x-ray streak camera.The x-ray emission nonuniformity of the plasma is quantitatively analyzed using a perturbation spectrum analysis method.The results show that the nonuniformity has a minimum value at a time corresponding to the peak time of the pumping laser pulse,and increases after that.A brief discussion on the nonuniformity mechanism has also been presented.
基金support from the Technology Development Program of China National Petroleum Corporation(grant No.2023ZZ36).
文摘In the feed injection zone of a multiphase fluidized bed reactor, nonuniform distribution exists due to the introduction of feed nozzle jets and circulating catalyst, which ultimately have an impact on the performance of the reactor. The transient sectional nonuniformity index (TSNI) is proposed as a new index to quantify the nonuniformity of solid distribution in both radial and circumferential dimensions at the same time, based on the transient solids holdup data in the feed zone. The temporal and spatial distributions of TSNI can more accurately reflect the changes in the real-time gas-solid distribution uniformity of the cross-sections and the efficiency of gas-solid contact in the feed injection zone. The feed injection zone can be divided into three regions according to the characteristics of TSNI: the bubble-influenced zone, the jet-influenced zone, and the acceleration zone. According to the numerical simulation results, it was analyzed that TSNI is highly correlated with operating conditions, such as nozzle gas velocity and catalyst circulation rate.
基金Supported by the Short-wave Infrared Camera Systems(B025F40622024)。
文摘The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.
基金This work was supported by the Pre-Research Foundation of National Defense under Grant No. 30404.
文摘The striping pattern nonuniformity of the infrared line scanner （IRLS） severely limits the system performance. An adaptive nonuniformity correction （NUC） algorithm for IRLS using neural network is proposed. It uses a one-dimensional median filter to generate ideal output of network and can complete NUC by a single frame with a high correction level. Applications to both simulated and real infrared images show that the algorithm can obtain a satisfactory result with low complexity, no need of scene diversity or global motion between consecutive frames. It has the potential to realize real-time hardware-based applications.
基金supported by National Nature Science Foundation of China under Grant Number 50776003the Innovation Foundation of BUAA for PhD Graduates
文摘The assembling error may lead to variation in stagger angles,which would affect the aerodynamic performance of the turbine.To investigate this underlying effect,two parallel numerical experiments on two turbines with the same profile,but uniform and nonuniform vane stagger angle respectively,were conducted in both steady and unsteady methods.The results indicate that certain changes in the detailed flow field of the turbine occur when the stagger angles are nonuniform,further,the blade loading distribution of the vane and rotor become markedly different from that in uniform vane stagger angle situation.Then these consequences caused by nonuniformity mentioned above enhance the unsteadiness of the flow,finally,the aerodynamic performance changes dramatically.It also shows that,compared with steady simulation,the unsteady numerical simulation is necessary in this investigation.
文摘Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.
基金supported by the National Natural Science Foundation of China(Grant No.92152301)the National Key Research and Development Program of China(Grant No.2022YFB4300200)the Shaanxi Provincial Key Research and Development Program(Grant No.2023-ZDLGY-27).
文摘Physics-informed neural networks(PINNs)have shown remarkable prospects in solving the forward and inverse problems involving partial differential equations(PDEs).The method embeds PDEs into the neural network by calculating the PDE loss at a set of collocation points,providing advantages such as meshfree and more convenient adaptive sampling.However,when solving PDEs using nonuniform collocation points,PINNs still face challenge regarding inefficient convergence of PDE residuals or even failure.In this work,we first analyze the ill-conditioning of the PDE loss in PINNs under nonuniform collocation points.To address the issue,we define volume weighting residual and propose volume weighting physics-informed neural networks(VW-PINNs).Through weighting the PDE residuals by the volume that the collocation points occupy within the computational domain,we embed explicitly the distribution characteristics of collocation points in the loss evaluation.The fast and sufficient convergence of the PDE residuals for the problems involving nonuniform collocation points is guaranteed.Considering the meshfree characteristics of VW-PINNs,we also develop a volume approximation algorithm based on kernel density estimation to calculate the volume of the collocation points.We validate the universality of VW-PINNs by solving the forward problems involving flow over a circular cylinder and flow over the NACA0012 airfoil under different inflow conditions,where conventional PINNs fail.By solving the Burgers’equation,we verify that VW-PINNs can enhance the efficiency of existing the adaptive sampling method in solving the forward problem by three times,and can reduce the relative L 2 error of conventional PINNs in solving the inverse problem by more than one order of magnitude.
基金supported by The Youth Science Foundation of Sichuan Province(Nos.2022NSFSC1230,2022NSFSC1231,and 23NSFSC5321)the Science and Technology Innovation Seedling Project of Sichuan Province(No.MZGC20230080)+2 种基金the General project of national Natural Science Foundation of China(No.12075039)the Youth Science Foundation of China(No.12105030)the Key project of the National Natural Science Foundation of China(No.U19A2086)。
文摘To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.Using the transmission reconstruction equation and the Monte Carlo program Geant4,an innovative virtual trajectory length model was constructed.This model integrated the solving process for the trajectory length and detection efficiency within the same model.To mitigate the influence of the angular distribution ofγ-rays emitted by the transmitted source at the detector,the transport processes of numerous particles traversing a virtual nuclear waste barrel with a density of zero were simulated.Consequently,a certain amount of information was captured at each step of particle transport.Simultaneously,the model addressed the nonuniform detection efficiency of the detector end face by considering whether the energy deposition of particles in the detector equaled their initial energy.Two models were established to validate the accuracy and reliability of the virtual trajectory length model.Model 1 was a simplified nuclear waste barrel,whereas Model 2 closely resembled the actual structure of a nuclear waste barrel.The results indicated that the proposed virtual trajectory length model significantly enhanced the precision of the trajectory length determination,substantially increasing the quality of the reconstructed images.For example,the reconstructed images of Model 2 using the“point-to-point”and average trajectory models revealed a signalto-noise ratio increase of 375.0%and 112.7%,respectively.Thus,the virtual trajectory length model proposed in this study holds paramount significance for the precise reconstruction of transmission images.Moreover,it can provide support for the accurate detection of radioactive activity in nuclear waste barrels.
基金support from a Grant-in-Aid for Scientific Research(KAKENHI B),Japan(Project/Area code:23H01505)the Institute for Sustainable Future Society,Waseda Research Institute for Science and Engineering,Research Initiatives in Japansupport from the Chinese Scholar Council for PhD scholarships(Grant No.202206220061)was acknowledged。
文摘This paper presents a method for obtaining the displacement of sand particles in a sand–bentonite mixture(SBM)when saturated with water,based on particle tracking velocimetry(PTV).The raw photographs were first converted into binary images.The sand particles were then detected,and the displacement of the sand particles was obtained by comparing their positions in adjacent images.The swelling strain induced by saturation was also obtained using the proposed PTV method.This method was validated by comparing the result with those obtained using a displacement transducer.Subsequently,a comparative analysis of sand particle displacements was conducted for specimens with varying bentonite content(BC),initial thickness,and water infiltration directions.The experimental results obtained were as follows:(1)For specimens with different BCs,local swelling displacement of sand particles at the top part of the specimen increased with higher BCs;(2)For specimens with various heights(hsp),larger local swelling displacement was generated at lower hsp at the initial state;(3)Local swelling characteristics differed in different water infiltration directions.Top-side infiltration showed a significant downward movement of particles during the first several hours of swelling.An estimation method for the dry density distribution of the specimen was proposed based on PTV data and then verified by slicing dry density and water content measurement results.
基金Supported by National Key Research and Development Program of China(Grant No.2023YFB4603602)High-Quality Development Project(Grant No.TC220H05S-007)。
文摘Water dissolution ultraprecision continuous polishing is a nontraditional machining method specifically designed for water-soluble crystals.The aim of this study is primarily to reduce the surface roughness for small sizes from an experimental standpoint.A trajectory uniformity simulation analysis is carried out for a consistent material removal.A material removal model is developed based on the water dissolution principle and kinematic analysis.Numerical simulations of single-and multiple-water-core polishing trajectories are performed to explore the influences of the processing parameters such as movement form,number of water cores,speed ratio,polishing time,and period ratio on the material removal uniformity.The material removal rate is calculated according to the Preston equation.The trajectory density nonuniformity is utilized to evaluate the global uniformity of the trajectory distributions and optimize the processing parameters for a better material removal uniformity.Verification experiments are conducted on a large-size ultraprecision continuous polisher using a typical potassium dihydrogen phosphate(KDP)crystal with a water-soluble structure.The edge collapse is improved from 51.499μm to 1.477μm by trajectory uniformity optimization.The changing trends of line profile variations in the validation experiment and simulation are similar.An ultrasmooth surface of a 180 mm×180 mm KDP crystal with a surface roughness root mean square of 1.718 nm is obtained after water dissolution ultraprecision continuous polishing.This study provides a comprehensive method for evaluation of material removal uniformity,which is valuable for the realization of high-quality machining for water-soluble crystals.
基金financially supported by the National Natural Science Foundation of China(Grant No.52004029).
文摘After cooling in the hot rolling process,the metallographic structure of microalloyed dual-phase steel is nonuniform along the rolling direction,while the thickness fluctuation of microalloyed dual-phase steel with a nonuniform metallographic structure will occur during cold rolling.The mechanism of nonuniform phase transformation of microalloyed dual-phase steels was studied during the cooling process after hot rolling,and the nonuniform phase transformation of microalloyed dual-phase steel was regulated during the cooling process after hot rolling through process optimization.First,the empirical equation of phase transformation temperature was measured by a dilatometer considering thermal expansion.Then,the phase field and temperature field of laminar cooling process were calculated to provide initial boundary conditions for the finite element model.After that,the coupling finite element model of the temperature phase transformation of the strip steel in coiling transportation process was established.The simulation results show that the different thermal contact conditions of the microalloyed dual-phase steel during coil transportation lead to uneven cooling of the coil,which leads to nonuniform transformation of the coil along the rolling direction.In addition,by prolonging the time interval from coiling to unloading,the phenomenon of nonuniform phase transformation of microalloyed dual-phase steel can be effectively controlled.The simulation results are applied to industrial production.The application results show that prolonging the time interval from coiling to unloading can effectively improve the nonuniform phase transformation of microalloyed dual-phase steel in the cooling process after hot rolling.
基金National Natural Science Foundation of China under Grant Nos.51921006 and 51725801Fundamental Research Funds for the Central Universities under Grant No.FRFCU5710093320Heilongjiang Touyan Innovation Team Program。
文摘Reinforcement corrosion is the main cause of performance deterioration of reinforced concrete(RC)structures.Limited research has been performed to investigate the life-cycle cost(LCC)of coastal bridge piers with nonuniform corrosion using different materials.In this study,a reliability-based design optimization(RBDO)procedure is improved for the design of coastal bridge piers using six groups of commonly used materials,i.e.,normal performance concrete(NPC)with black steel(BS)rebar,high strength steel(HSS)rebar,epoxy coated(EC)rebar,and stainless steel(SS)rebar(named NPC-BS,NPC-HSS,NPC-EC,and NPC-SS,respectively),NPC with BS with silane soakage on the pier surface(named NPC-Silane),and high-performance concrete(HPC)with BS rebar(named HPC-BS).First,the RBDO procedure is improved for the design optimization of coastal bridge piers,and a bridge is selected to illustrate the procedure.Then,reliability analysis of the pier designed with each group of materials is carried out to obtain the time-dependent reliability in terms of the ultimate and serviceability performances.Next,the repair time of the pier is predicted based on the time-dependent reliability indices.Finally,the time-dependent LCCs for the pier are obtained for the selection of the optimal design.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25050700)the Fund of the National Key Laboratory of Plasma Physics(Grant No.6142A04230103)+2 种基金the National Natural Science Foundation of China(Grant No.11805062)the China Postdoctoral Science Foundation(Grant No.2022M720513)the Anhui Provincial Natural Science Foundation(Grant No.2308085QA25).
文摘Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can predict the region of occurrence of mth-order SRSS and estimate its threshold.The rescattering process is identified by the 2D PIC simulations under typical conditions of a direct-drive inertial confinement fusion scheme.Hot electrons produced by second-order SRSS propagate nearly perpendicular to the density gradient and gain nearly the same energy as in first-order SRSS,but there is no cascade acceleration to produce superhot electrons.Parametric studies for a wide range of ignition conditions show that SRSS and associated rescatterings are robust and important processes in inertial confinement fusion.
基金supported by the National Natural Science Foundation of China(Grant Nos.92252202,92152301,12293000,12293002,12302320,and 12388101)the Fundamental Research Funds for the Central Universities.
文摘Convection driven by a spatially non-uniform internal heat source between two horizontal isothermal walls is studied by theoretical analysis and numerical simulation,in order to explore the bounds of the temperature and the vertical heat flux.Specifically,the rigorous lower bound of the weighted average temperature<QT>is derived analytically,by decomposing the temperature field into a background profile and a fluctuation part.This bound obtained for the first time to consider non-uniform heat sources is found to be compatible with the existing bound obtained in uniform internal heat convection.Of physical importance,an analytical relationship is derived as an inequality connecting<QT>and the average vertical heat flux<wT>,by employing the average heat flux on the bottom wall(qb)as an intermediary variable.It clarifies the intrinsic relation between the lower bound of<QT>and the upper bound of<wT>,namely,these two bounds are essentially equivalent providing an easy way to obtain one from another.Furthermore,the analytical bounds are extensively demonstrated through a comprehensive series of direct numerical simulations.
基金Projects(52378411,52208404)supported by the National Natural Science Foundation of China。
文摘The tunnel subjected to strike-slip fault dislocation exhibits severe and catastrophic damage.The existing analysis models frequently assume uniform fault displacement and fixed fault plane position.In contrast,post-earthquake observations indicate that the displacement near the fault zone is typically nonuniform,and the fault plane position is uncertain.In this study,we first established a series of improved governing equations to analyze the mechanical response of tunnels under strike-slip fault dislocation.The proposed methodology incorporated key factors such as nonuniform fault displacement and uncertain fault plane position into the governing equations,thereby significantly enhancing the applicability range and accuracy of the model.In contrast to previous analytical models,the maximum computational error has decreased from 57.1%to 1.1%.Subsequently,we conducted a rigorous validation of the proposed methodology by undertaking a comparative analysis with a 3D finite element numerical model,and the results from both approaches exhibited a high degree of qualitative and quantitative agreement with a maximum error of 9.9%.Finally,the proposed methodology was utilized to perform a parametric analysis to explore the effects of various parameters,such as fault displacement,fault zone width,fault zone strength,the ratio of maximum fault displacement of the hanging wall to the footwall,and fault plane position,on the response of tunnels subjected to strike-slip fault dislocation.The findings indicate a progressive increase in the peak internal forces of the tunnel with the rise in fault displacement and fault zone strength.Conversely,an augmentation in fault zone width is found to contribute to a decrease in the peak internal forces.For example,for a fault zone width of 10 m,the peak values of bending moment,shear force,and axial force are approximately 46.9%,102.4%,and 28.7% higher,respectively,compared to those observed for a fault zone width of 50 m.Furthermore,the position of the peak internal forces is influenced by variations in the ratio of maximum fault displacement of the hanging wall to footwall and the fault plane location,while the peak values of shear force and axial force always align with the fault plane.The maximum peak internal forces are observed when the footwall exclusively bears the entirety of the fault displacement,corresponding to a ratio of 0:1.The peak values of bending moment,shear force,and axial force for the ratio of 0:1 amount to approximately 123.8%,148.6%,and 111.1% of those for the ratio of 0.5:0.5,respectively.
文摘In this paper,we study systems of conservation laws in one space dimension.We prove that for classical solutions in Sobolev spaces H^(s),with s>3/2,the data-to-solution map is not uniformly continuous.Our results apply to all nonlinear scalar conservation laws and to nonlinear hyperbolic systems of two equations.
基金National Natural Science Foundation of China(61973037)National 173 Program Project(2019-JCJQ-ZD-324)。
文摘Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.
基金financially supported by National Natural Science Foundation of China(Grant Nos.52074161 and 52005281)Taishan Scholar Project of Shandong Province(Grant No.tsqn202211177)+2 种基金Shandong Provincial Plan for Introduction and Cultivation of Young Pioneers in Colleges and Universities(Grant No.2021-Qing Chuang-30613019)Natural Science Foundation of Shandong Province(Grant Nos.ZR2022ME173 and ZR2023QE011)Projects of CNOOC Research Institute Ltd.(Grant Nos.CCL2023RCPS0237RSN and CCL2023RCPS0319RSN)。
文摘Clearance-fit(side-fit)spline joints are a key component in a permanent magnet synchronous motor(PMSM)in electric submersible pumping wells.The nonuniform spline clearance affects the output performance of a PMSM.A concept for energy conservation is optimized in this study to improve the modeling accuracy of electromagnetic torque.However,most existing computation models are one-way model with a magneto-mechanical simulation.In this study,a more accurate two-way coupling method is presented for simulating the electromagnetic and mechanical characteristics of PMSM.Additionally,importance should be attached to this two-way magneto-mechanical coupling methodology in an actual simulation.The coupled power,electrical and magnetic energy,and electromagnetic torque equations are solved iteratively until convergence for PMSMs with a segmented rotor and a non-segmented rotor.The optimal electromagnetic torque is obtained for different rotor configurations with the change of temperatures and rotational speeds.The results show that the output performance and electromagnetic torque of the PMSM are seriously affected by the effects of two-way magneto-mechanical coupling and nonuniform spline clearance.The proposed two-way coupling model gives more reasonable predictions than other one-way models do,because the power transfer between the electrical and magnetic energy can be modeled more accurately.The self-centralizing performance of clearance-fit splines and the sensitivity to the radial clearance magnitude lead to the reduction of the electromagnetic torque for the PMSM.Additionally,the electromagnetic torques decrease with the enhanced rotor temperatures and rotational speeds.The best rotor temperature and rotational speed are chosen through a comparison of the experimental results,and then the optimal electromagnetic torque is provided to ensure the output performance of the PMSM in electric submersible pumping wells.
