Gas foil bearing faces severe and complex thermal-fluid–solid coupling issues when in ultra-high speed and miniaturized impeller machineries.In this study,a Thermo-Elasto-Hydrodynamic(TEHD)analysis of a specific mult...Gas foil bearing faces severe and complex thermal-fluid–solid coupling issues when in ultra-high speed and miniaturized impeller machineries.In this study,a Thermo-Elasto-Hydrodynamic(TEHD)analysis of a specific multi-layer gas foil thrust bearing on the continuous loading process within a steady rotational speed is numerically investigated by a three-dimensional thermal-fluid–solid coupling method.Results indicate that the multi-layer foil exhibits nonlinear overall stiffness,with the thrust bottom foil serving as the primary elastic deformation structure,while the thrust top foil maintains a well-defined aerodynamic shape during a loading process,which helps reduce frictional damage and achieve an adequate loading capacity.For low loads,the fluctuation of the gas film is extremely sensitive,and it weakens dramatically as the load increases.The viscous heating and friction torque exhibit a linear relationship with an increasing bearing load after a rapid growth.Depending on the exact stacking sequence and contact position of the multi-layer gas foil,the overlapping configuration allows for efficient transfer of viscous-shearing heat accumulated at the smallest air film through thermal conduction while providing elastic support.Due to the strong inhomogeneity of the viscous heat under varying loads,the temperature distribution on the top foil surface shows pronounced variations,while the difference between the peak and average temperatures of the thrust plate and top foil surfaces widens substantially with an increasing load.展开更多
Magneto-mechanical coupling vibration arises in the in-vessel components of Tokamak devices especially during the plasma disruption. Strong electromagnetic forces cause the structures to vibrate while the motion in tu...Magneto-mechanical coupling vibration arises in the in-vessel components of Tokamak devices especially during the plasma disruption. Strong electromagnetic forces cause the structures to vibrate while the motion in turn changes the distribution of the electromagnetic field. To ensure the Tokamak devices operating in a designed state, numerical analysis on the coupling vibration is of great importance. This paper introduces two numerical methods for the magneto-mechanical coupling problems. The coupling term of velocity and magnetic flux density is manipulated in both Eulerian and Lagrangian description, which brings much simplification in numerical implementation. Corresponding numerical codes have been developed and applied to the dynamic simulation of a test module in J-TEXT and the vacuum vessel of HL-2M during plasma disruptions. The results reveal the evident influence of the magnetic stiffness and magnetic damping effects on the vibration behavior of the in-vessel structures. Finally, to deal with the halo current injection problem, a numerical scheme is described and validated which can simulate the distribution of the halo current without complicated manipulations.展开更多
The coupling behavior of the imbedded weapon store occurring between the local unsteady flow field round the store and the structure response on the processing of opening its bay-door is simulated by using numerical m...The coupling behavior of the imbedded weapon store occurring between the local unsteady flow field round the store and the structure response on the processing of opening its bay-door is simulated by using numerical method based on computational fluid mechanics(CFD).The transient aerodynamic behaviors when opening door under various flight altitudes and the corresponding structure deformation evolution in the unsteady flow fields are analyzed respectively and presented.The rules of aircraft attitude parameters′impacting to the responses of structure and the bay-door′s opening process are obtained by comparing with the analysis results.These rules can be applied to the structure design of bay-door and route specification of missile when disengaged and launched from within store.展开更多
Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the...Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.展开更多
Finite element simulations were conducted to study the mechanism of spark plasma sintering. The spark plasma sintering of SiC ceramics was simulated by the Marc software based on the load current curve and temperature...Finite element simulations were conducted to study the mechanism of spark plasma sintering. The spark plasma sintering of SiC ceramics was simulated by the Marc software based on the load current curve and temperature-time curve deserved by SPS experiment. The concept of equivalent radiation coefficient was presented and applied during the simulation. The temperature distribution regularity of SiC ceramics sintered by SPS technology was got by thermal-electrical coupled finite element simulation. The experimental results show that by thermal-electrical coupled finite element analysis, the temperature rising and distribution regularity of nonconductive material can be preferable forecasted in the sintering process of SPS. In the initial stage of the heat preservation, the temperature of the central part of the sample has achieved sintering temperature, but now, the temperature of the sample is not uniform. The temperature for each part of the die is also quite different and the sample temperature in the center is higher than that in the edge. In the end of heat preservation, the central temperature of the sample is 50 ℃higher than the required sintering temperature, and the temperature gap for each part of the die decreases gradually.展开更多
The similitude theory helps to understand the physical behaviors of large structures through scaled models. Several papers have studied the similitude of shock issues. However, the dynamic similitude for shock respons...The similitude theory helps to understand the physical behaviors of large structures through scaled models. Several papers have studied the similitude of shock issues. However, the dynamic similitude for shock responses of coupled structures is rarely incorporated in open studies. In this paper, scaling laws are derived for the shock responses and spectra of coupled structures. In the presented scaling laws, the geometric distortion and energy loss are considered. The ability of the proposed scaling laws is demonstrated in the simulation and experimental cases. In both cases, the similitude prediction for the prototype's time-domain waveform and spectrum is conducted with the scaled model and scaling laws. The simulation and experimental cases indicate that the predicted shock responses and spectra agree well with those of the prototype, which verifies the proposed scaling laws for predicting shock responses.展开更多
Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation ...Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation to microscopic mechanisms,remains relatively sparse.This study utilizes microscopic visualization experiments to investigate the mechanisms of residual oil mobilization under various IPC scenarios,complemented by mechanical analysis at different stages.The research quantitatively assesses the degree of microscopic oil recovery and the distribution of residual oil across different injection-production methods.Findings reveal that during the initial phase of continuous gas injection(CGI),the process closely mimics miscible displacement,gradually transitioning to immiscible displacement as CO_(2)extraction progresses.Compared to CGI,the asynchronous injection-production(AIP) method improved the microscopic oil recovery rate by 6.58%.This enhancement is mainly attributed to significant variations in the pressure field in the AIP method,which facilitate the mobilization of columnar and porous re sidual oil.Furthermo re,the synchronous cycle injection(SCI) method increased microscopic oil recovery by 13.77% and 7.19% compared to CGI and AIP,respectively.In the SCI method,membrane oil displays filame ntary and Karman vo rtex street flow patterns.The dissolved and expanded crude oil te nds to accumulate and grow at the oil-solid interface due to adhesive forces,thereby reducing migration resistance.The study findings provide a theoretical foundation for improving oil recovery in lowpermeability reservoirs.展开更多
In order to meet the urgent need for diversified and multi-functional deployable antennas in many major national aerospace projects,such as interstellar exploration,the fourth phase of lunar exploration project,and th...In order to meet the urgent need for diversified and multi-functional deployable antennas in many major national aerospace projects,such as interstellar exploration,the fourth phase of lunar exploration project,and the industrial application of Bei Dou,a deployable antenna structure composed of hexagonal prism and pentagonal prism modules is proposed.Firstly,the arrangement and combination rules of pentagonal prism and hexagonal prism modules on the plane were analyzed.Secondly,the spatial geometric model of the deployable antenna composed of pentagonal prism and hexagonal prism modules was established.The influence of module size on the antenna shape was then analyzed,and the kinematic model of the deployable antenna established by coordinate transformation.Finally,the above model was verified using MATLAB software.The simulation results showed that the proposed modular deployable antenna structure can realize accurate connection between modules,complete the expected deployment and folding functional requirements.It is hoped that this research can provide reference for the basic research and engineering application of deployable antennas in China.展开更多
The properties of the magnetic mold in magnetic mold casting directly determine the quality of the final cast parts.In this study,the magnetic mold properties in magnetic mold casting,were studied utilizing a coupled ...The properties of the magnetic mold in magnetic mold casting directly determine the quality of the final cast parts.In this study,the magnetic mold properties in magnetic mold casting,were studied utilizing a coupled electromagnetic-structural method through numerical simulation.This study investigated key factors including equivalent stress,the distribution of tensile and compressive stresses,and the area ratio of tensile stress.It compared molds made entirely of magnetic materials with those made partially of magnetic materials.Simulation results indicate that as current increases from 4 A to 8 A,both the initial magnetic mold and the material-replaced magnetic mold initially show an increasing trend in equivalent stress,tensile-compressive stress,and the area ratio of tensile stress,peaking at 6 A before declining.After material replacement,the area ratio of tensile stress at 6 A decreases to 19.84%,representing a reduction of 29.72%.Magnetic molds comprising a combination of magnetic and non-magnetic materials exhibit sufficient strength and a reduced area ratio of tensile stress compared to those made entirely from magnetic materials.This study provides valuable insights for optimizing magnetic mold casting processes and offers practical guidance for advancing the application of magnetic molds.展开更多
Based on test data from the hot forge experiments on Gleeble 1500, a Kumar type constitutive equation for 33Mn2V steel is established. Applying this constitutive equation in commercial FEM software of MSC/SuperForm 20...Based on test data from the hot forge experiments on Gleeble 1500, a Kumar type constitutive equation for 33Mn2V steel is established. Applying this constitutive equation in commercial FEM software of MSC/SuperForm 2005, the piercing process of 33Mn2V steel in Mannesmann mill is then simulated. The modeling results visualized the dynamic evolution of equivalent stress, especially inside the workpieee. It is shown that the non-uniform distribu- tion of stress on the internal and external surface of the workpiece is a distinct characteristic of processing tube pierc- ing. The numerical model was verified by comparing the values of calculated force parameters of the piercing process with those measured in laboratory eonditions. And it shows that the Kumar-type constitutive relationship meets the practical needs.展开更多
Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafros...Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer （i.e., mass equation） and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety （FOS）, which is definitely useful for embankment design in frozen ground regions.展开更多
Simulation models of heat and water transport have not been rigorously tested for the red soils of southern China. Based on the theory of nonisothermal water-heat coupled transfer, a simulation model, programmed in Vi...Simulation models of heat and water transport have not been rigorously tested for the red soils of southern China. Based on the theory of nonisothermal water-heat coupled transfer, a simulation model, programmed in Visual Basic 6.0, was developed to predict the coupled transfer of water and heat in hilly red soil. A series of soil column experiments for soil water and heat transfer, including soil columns with closed and evaporating top ends, were used to test the simulation model. Results showed that in the closed columns, the temporal and spatial distribution of moisture and heat could be very well predicted by the model, while in the evaporating columns, the simulated soil water contents were somewhat different from the observed ones. In the heat flow equation by Taylor and Lary (1964), the effect of soil water evaporation on the heat flow is not involved, which may be the main reason for the differences between simulated and observed results. The predicted temperatures were not in agreement with the observed one with thermal conductivities calculated by de Vries and Wierenga equations, so that it is suggested that Kh, soil heat conductivity, be multiplied by 8.0 for the first 6.5 h and by 1.2 later on. Sensitivity analysis of soil water and heat coefficients showed that the saturated hydraulic conductivity, KS, and the water diffusivity, D(θ), had great effects on soil water transport; the variation of soil porosity led to the difference of soil thermal properties, and accordingly changed temperature redistribution, which would affect water redistribution.展开更多
An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper,and technical issues related to turbine structure modeling and stress combination are also addressed.Th...An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper,and technical issues related to turbine structure modeling and stress combination are also addressed.The NREL-5MW ＂Hywind＂ Spar type wind turbine is adopted as study object.Time-domain dynamic coupled simulations are performed by a fully-coupled aero-hydro-servo-elastic tool,FAST,on the purpose of obtaining the dynamic characteristics of the floating wind turbine,and determining parameters for design load cases of finite element calculation.Then design load cases are identified,and finite element analyses are performed for these design load cases.The structural stresses due to wave-induced loads and wind-induced loads are calculated,and then combined to assess the structural strength of the floating wind turbine.The feasibility of the proposed structural strength analysis method for floating wind turbines is then validated.展开更多
The heated test pieces of diamond segments were treated by alternating magnetic field,the influences of magnetic treatment on microstructure densification of diamond segments were studied through metallurgical structu...The heated test pieces of diamond segments were treated by alternating magnetic field,the influences of magnetic treatment on microstructure densification of diamond segments were studied through metallurgical structure analysis.The experiment results indicated that,the densification of diamond segments was further improved after magnetized.The alternating magnetic force distributions in the diamond segments were calculated by numerical simulation according to the coupled field theory.In alternating magnetic field,a prodigious swirl current field appeared in the component.The magnetic vibrating due to alternating magnetic force was obvious,which was in favor of microcosmic structure compacter.The numerical analysis results provided direct evidences for that the alternating magnetic treatment can act as an effective technique to improve the microstructure densification of diamond segments.展开更多
A trunk-vibrating screen is widely used in olive harvesting machinery.Because of the irregularity of fruit recovery efficiency,the recovery efficiency fluctuates greatly.Vibration harvesting parameters are important f...A trunk-vibrating screen is widely used in olive harvesting machinery.Because of the irregularity of fruit recovery efficiency,the recovery efficiency fluctuates greatly.Vibration harvesting parameters are important factors affecting the percentage of olive harvest.Therefore,the study of vibration picking parameters is of great significance for olive harvest.Vibration parameters,governed by tree morphological parameters,strongly influence the efficiency of vibration harvesting.In this study,a combination of response surface simulation and harvesting experiments was used to investigate the relationship between morphological and vibration harvesting parameters in“three open-center shape”olive trees.First,force analysis and experimental measurements were performed on the olive fruit,and the Box-Behnken design was used to obtain the vibration parameters through finite element simulation and to establish the response surface model of the parameters(main trunk diameter,main trunk height,main branch angles A and B)and the vibration parameters(vibration frequency and vibration force)of the“three open-center-shape”olive trees.In addition,the mapping relationship between tree shape parameters and vibration parameters was obtained.The results show that the 90%quantile of the acceleration of abscission of olives is 1113.35 m/s2;the average correlation coefficient between the simulation and the experiment results was 0.73,and the simulation was a good representation of the experimental results.When the tree shape was“three open-center”,the trunk diameter and height were related to the vibration harvesting parameters;the average harvesting efficiency of olives was 91.22%,and the resonance frequency of the monitoring points was similar to that of the simulation results.This study provides a reference for the design of vibration harvesting equipment and fruit tree shaping.展开更多
为准确描述下降管反应器内生物质颗粒与高温陶瓷球之间的瞬态传热与热解行为,该研究提出了一种基于分布活化能模型(distributed activation energy model,DAEM)的多物理场耦合数值模型。该模型在颗粒能量平衡框架下,引入接触导热、气膜...为准确描述下降管反应器内生物质颗粒与高温陶瓷球之间的瞬态传热与热解行为,该研究提出了一种基于分布活化能模型(distributed activation energy model,DAEM)的多物理场耦合数值模型。该模型在颗粒能量平衡框架下,引入接触导热、气膜导热、对流与辐射多种传热机制,并与质量转化过程和活化能分布特征相耦合,建立了用于描述生物质快速热解过程的常微分方程模型。基于热重分析试验数据,对高斯、洛伦兹及逻辑斯谛3种活化能分布函数进行了参数反演与对比分析。结果表明,洛伦兹分布能够更准确地再现试验热重曲线,其平均绝对误差(mean absolute error,MAE)和均方根误差(root mean square error,RMSE)分别为0.0116和0.0138。数值模拟结果显示,生物质颗粒在初始阶段经历了极高的升温速率(峰值达到2.14×10^(3)℃/s),但热解反应相对于温度演化存在明显的动力学滞后特征。传热机制分析表明,对流与导热在整个热解过程中占主导地位,而在高温阶段辐射传热的贡献不可忽略。参数敏感性分析进一步揭示,陶瓷球温度和生物质颗粒粒径对热解效率具有显著影响,反应焓和颗粒碰撞概率次之,而辐射视角因子的影响相对有限。研究结果表明,在传热条件充分的快速热解工况下,过程控制机理由传热受限逐渐转变为化学反应动力学受限。研究为深入理解下降管反应器内多物理场耦合热解行为特征及反应器结构与工艺参数优化提供了理论依据和数据支持。展开更多
基金the financial supports provided by the Natural Science Fund of Jiangsu Province,China(No.BK20200448)the Postdoctoral Science Foundation of China(No.2020TQ0143)。
文摘Gas foil bearing faces severe and complex thermal-fluid–solid coupling issues when in ultra-high speed and miniaturized impeller machineries.In this study,a Thermo-Elasto-Hydrodynamic(TEHD)analysis of a specific multi-layer gas foil thrust bearing on the continuous loading process within a steady rotational speed is numerically investigated by a three-dimensional thermal-fluid–solid coupling method.Results indicate that the multi-layer foil exhibits nonlinear overall stiffness,with the thrust bottom foil serving as the primary elastic deformation structure,while the thrust top foil maintains a well-defined aerodynamic shape during a loading process,which helps reduce frictional damage and achieve an adequate loading capacity.For low loads,the fluctuation of the gas film is extremely sensitive,and it weakens dramatically as the load increases.The viscous heating and friction torque exhibit a linear relationship with an increasing bearing load after a rapid growth.Depending on the exact stacking sequence and contact position of the multi-layer gas foil,the overlapping configuration allows for efficient transfer of viscous-shearing heat accumulated at the smallest air film through thermal conduction while providing elastic support.Due to the strong inhomogeneity of the viscous heat under varying loads,the temperature distribution on the top foil surface shows pronounced variations,while the difference between the peak and average temperatures of the thrust plate and top foil surfaces widens substantially with an increasing load.
基金the National Magnetic Confinement Fusion Program of China(Grant 2013GB113005)the National Natural Science Foundation of China(Grants51577139 and 51407132)for funding in part
文摘Magneto-mechanical coupling vibration arises in the in-vessel components of Tokamak devices especially during the plasma disruption. Strong electromagnetic forces cause the structures to vibrate while the motion in turn changes the distribution of the electromagnetic field. To ensure the Tokamak devices operating in a designed state, numerical analysis on the coupling vibration is of great importance. This paper introduces two numerical methods for the magneto-mechanical coupling problems. The coupling term of velocity and magnetic flux density is manipulated in both Eulerian and Lagrangian description, which brings much simplification in numerical implementation. Corresponding numerical codes have been developed and applied to the dynamic simulation of a test module in J-TEXT and the vacuum vessel of HL-2M during plasma disruptions. The results reveal the evident influence of the magnetic stiffness and magnetic damping effects on the vibration behavior of the in-vessel structures. Finally, to deal with the halo current injection problem, a numerical scheme is described and validated which can simulate the distribution of the halo current without complicated manipulations.
文摘The coupling behavior of the imbedded weapon store occurring between the local unsteady flow field round the store and the structure response on the processing of opening its bay-door is simulated by using numerical method based on computational fluid mechanics(CFD).The transient aerodynamic behaviors when opening door under various flight altitudes and the corresponding structure deformation evolution in the unsteady flow fields are analyzed respectively and presented.The rules of aircraft attitude parameters′impacting to the responses of structure and the bay-door′s opening process are obtained by comparing with the analysis results.These rules can be applied to the structure design of bay-door and route specification of missile when disengaged and launched from within store.
基金the National High Technical Reasearch and Development Programme of China （No. 2003AA327140） the National Natural Science Foundation of China （No. 50374081）.
文摘Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.
基金Funded by the Natural Science Foundation of Hebei Province, China (No.E2012203086)
文摘Finite element simulations were conducted to study the mechanism of spark plasma sintering. The spark plasma sintering of SiC ceramics was simulated by the Marc software based on the load current curve and temperature-time curve deserved by SPS experiment. The concept of equivalent radiation coefficient was presented and applied during the simulation. The temperature distribution regularity of SiC ceramics sintered by SPS technology was got by thermal-electrical coupled finite element simulation. The experimental results show that by thermal-electrical coupled finite element analysis, the temperature rising and distribution regularity of nonconductive material can be preferable forecasted in the sintering process of SPS. In the initial stage of the heat preservation, the temperature of the central part of the sample has achieved sintering temperature, but now, the temperature of the sample is not uniform. The temperature for each part of the die is also quite different and the sample temperature in the center is higher than that in the edge. In the end of heat preservation, the central temperature of the sample is 50 ℃higher than the required sintering temperature, and the temperature gap for each part of the die decreases gradually.
基金Project supported by the National Natural Science Foundation of China (Nos. 12272089 and U1908217)the Fundamental Research Funds for the Central Universities of China (Nos. N2224001-4 and N2003013)the Basic and Applied Basic Research Foundation of Guangdong Province of China (No. 2020B1515120015)。
文摘The similitude theory helps to understand the physical behaviors of large structures through scaled models. Several papers have studied the similitude of shock issues. However, the dynamic similitude for shock responses of coupled structures is rarely incorporated in open studies. In this paper, scaling laws are derived for the shock responses and spectra of coupled structures. In the presented scaling laws, the geometric distortion and energy loss are considered. The ability of the proposed scaling laws is demonstrated in the simulation and experimental cases. In both cases, the similitude prediction for the prototype's time-domain waveform and spectrum is conducted with the scaled model and scaling laws. The simulation and experimental cases indicate that the predicted shock responses and spectra agree well with those of the prototype, which verifies the proposed scaling laws for predicting shock responses.
基金supported by the National Natural Science Foundation of China (Nos.52374064,51974347,52474072)the Shandong Provincial Universities Youth Innovation and Technology Support Program (2022KJ065)。
文摘Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation to microscopic mechanisms,remains relatively sparse.This study utilizes microscopic visualization experiments to investigate the mechanisms of residual oil mobilization under various IPC scenarios,complemented by mechanical analysis at different stages.The research quantitatively assesses the degree of microscopic oil recovery and the distribution of residual oil across different injection-production methods.Findings reveal that during the initial phase of continuous gas injection(CGI),the process closely mimics miscible displacement,gradually transitioning to immiscible displacement as CO_(2)extraction progresses.Compared to CGI,the asynchronous injection-production(AIP) method improved the microscopic oil recovery rate by 6.58%.This enhancement is mainly attributed to significant variations in the pressure field in the AIP method,which facilitate the mobilization of columnar and porous re sidual oil.Furthermo re,the synchronous cycle injection(SCI) method increased microscopic oil recovery by 13.77% and 7.19% compared to CGI and AIP,respectively.In the SCI method,membrane oil displays filame ntary and Karman vo rtex street flow patterns.The dissolved and expanded crude oil te nds to accumulate and grow at the oil-solid interface due to adhesive forces,thereby reducing migration resistance.The study findings provide a theoretical foundation for improving oil recovery in lowpermeability reservoirs.
文摘In order to meet the urgent need for diversified and multi-functional deployable antennas in many major national aerospace projects,such as interstellar exploration,the fourth phase of lunar exploration project,and the industrial application of Bei Dou,a deployable antenna structure composed of hexagonal prism and pentagonal prism modules is proposed.Firstly,the arrangement and combination rules of pentagonal prism and hexagonal prism modules on the plane were analyzed.Secondly,the spatial geometric model of the deployable antenna composed of pentagonal prism and hexagonal prism modules was established.The influence of module size on the antenna shape was then analyzed,and the kinematic model of the deployable antenna established by coordinate transformation.Finally,the above model was verified using MATLAB software.The simulation results showed that the proposed modular deployable antenna structure can realize accurate connection between modules,complete the expected deployment and folding functional requirements.It is hoped that this research can provide reference for the basic research and engineering application of deployable antennas in China.
基金the National Natural Science Foundation of China(No.51875062,No.52205336)the China Postdoctoral Science Foundation(No.2021M700567).
文摘The properties of the magnetic mold in magnetic mold casting directly determine the quality of the final cast parts.In this study,the magnetic mold properties in magnetic mold casting,were studied utilizing a coupled electromagnetic-structural method through numerical simulation.This study investigated key factors including equivalent stress,the distribution of tensile and compressive stresses,and the area ratio of tensile stress.It compared molds made entirely of magnetic materials with those made partially of magnetic materials.Simulation results indicate that as current increases from 4 A to 8 A,both the initial magnetic mold and the material-replaced magnetic mold initially show an increasing trend in equivalent stress,tensile-compressive stress,and the area ratio of tensile stress,peaking at 6 A before declining.After material replacement,the area ratio of tensile stress at 6 A decreases to 19.84%,representing a reduction of 29.72%.Magnetic molds comprising a combination of magnetic and non-magnetic materials exhibit sufficient strength and a reduced area ratio of tensile stress compared to those made entirely from magnetic materials.This study provides valuable insights for optimizing magnetic mold casting processes and offers practical guidance for advancing the application of magnetic molds.
基金Item Sponsored by Tianjin Natural Science Foundation of China(06YFJ MJC02200,11JCZDJC22600)
文摘Based on test data from the hot forge experiments on Gleeble 1500, a Kumar type constitutive equation for 33Mn2V steel is established. Applying this constitutive equation in commercial FEM software of MSC/SuperForm 2005, the piercing process of 33Mn2V steel in Mannesmann mill is then simulated. The modeling results visualized the dynamic evolution of equivalent stress, especially inside the workpieee. It is shown that the non-uniform distribu- tion of stress on the internal and external surface of the workpiece is a distinct characteristic of processing tube pierc- ing. The numerical model was verified by comparing the values of calculated force parameters of the piercing process with those measured in laboratory eonditions. And it shows that the Kumar-type constitutive relationship meets the practical needs.
基金supported by the National 973 Project of China (No. 2012CB026104)the National Natural Science Foundation of China (No. 51378057)
文摘Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer （i.e., mass equation） and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety （FOS）, which is definitely useful for embankment design in frozen ground regions.
基金Project supported by the National Natural Science Foundation ofChina (No. 40171047) and the Doctoral Foundation of NationalEducation Ministry China
文摘Simulation models of heat and water transport have not been rigorously tested for the red soils of southern China. Based on the theory of nonisothermal water-heat coupled transfer, a simulation model, programmed in Visual Basic 6.0, was developed to predict the coupled transfer of water and heat in hilly red soil. A series of soil column experiments for soil water and heat transfer, including soil columns with closed and evaporating top ends, were used to test the simulation model. Results showed that in the closed columns, the temporal and spatial distribution of moisture and heat could be very well predicted by the model, while in the evaporating columns, the simulated soil water contents were somewhat different from the observed ones. In the heat flow equation by Taylor and Lary (1964), the effect of soil water evaporation on the heat flow is not involved, which may be the main reason for the differences between simulated and observed results. The predicted temperatures were not in agreement with the observed one with thermal conductivities calculated by de Vries and Wierenga equations, so that it is suggested that Kh, soil heat conductivity, be multiplied by 8.0 for the first 6.5 h and by 1.2 later on. Sensitivity analysis of soil water and heat coefficients showed that the saturated hydraulic conductivity, KS, and the water diffusivity, D(θ), had great effects on soil water transport; the variation of soil porosity led to the difference of soil thermal properties, and accordingly changed temperature redistribution, which would affect water redistribution.
基金financially supported by the National Natural Science Foundation of China(Grant No.51239007)
文摘An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper,and technical issues related to turbine structure modeling and stress combination are also addressed.The NREL-5MW ＂Hywind＂ Spar type wind turbine is adopted as study object.Time-domain dynamic coupled simulations are performed by a fully-coupled aero-hydro-servo-elastic tool,FAST,on the purpose of obtaining the dynamic characteristics of the floating wind turbine,and determining parameters for design load cases of finite element calculation.Then design load cases are identified,and finite element analyses are performed for these design load cases.The structural stresses due to wave-induced loads and wind-induced loads are calculated,and then combined to assess the structural strength of the floating wind turbine.The feasibility of the proposed structural strength analysis method for floating wind turbines is then validated.
基金supported by National Natural Science Foundation of China(50675190)
文摘The heated test pieces of diamond segments were treated by alternating magnetic field,the influences of magnetic treatment on microstructure densification of diamond segments were studied through metallurgical structure analysis.The experiment results indicated that,the densification of diamond segments was further improved after magnetized.The alternating magnetic force distributions in the diamond segments were calculated by numerical simulation according to the coupled field theory.In alternating magnetic field,a prodigious swirl current field appeared in the component.The magnetic vibrating due to alternating magnetic force was obvious,which was in favor of microcosmic structure compacter.The numerical analysis results provided direct evidences for that the alternating magnetic treatment can act as an effective technique to improve the microstructure densification of diamond segments.
基金supported by the Key Research and Development Plan of Shaanxi Province(Grant No.2024NCZDCYL-05-03)the Key Programs of the Joint Fund of the National Natural Science Foundation of China(Grant No.U2243235)the Introduction of High-level Talents in Hohhot(Grant No.2023RC-High Level-7).
文摘A trunk-vibrating screen is widely used in olive harvesting machinery.Because of the irregularity of fruit recovery efficiency,the recovery efficiency fluctuates greatly.Vibration harvesting parameters are important factors affecting the percentage of olive harvest.Therefore,the study of vibration picking parameters is of great significance for olive harvest.Vibration parameters,governed by tree morphological parameters,strongly influence the efficiency of vibration harvesting.In this study,a combination of response surface simulation and harvesting experiments was used to investigate the relationship between morphological and vibration harvesting parameters in“three open-center shape”olive trees.First,force analysis and experimental measurements were performed on the olive fruit,and the Box-Behnken design was used to obtain the vibration parameters through finite element simulation and to establish the response surface model of the parameters(main trunk diameter,main trunk height,main branch angles A and B)and the vibration parameters(vibration frequency and vibration force)of the“three open-center-shape”olive trees.In addition,the mapping relationship between tree shape parameters and vibration parameters was obtained.The results show that the 90%quantile of the acceleration of abscission of olives is 1113.35 m/s2;the average correlation coefficient between the simulation and the experiment results was 0.73,and the simulation was a good representation of the experimental results.When the tree shape was“three open-center”,the trunk diameter and height were related to the vibration harvesting parameters;the average harvesting efficiency of olives was 91.22%,and the resonance frequency of the monitoring points was similar to that of the simulation results.This study provides a reference for the design of vibration harvesting equipment and fruit tree shaping.
文摘为准确描述下降管反应器内生物质颗粒与高温陶瓷球之间的瞬态传热与热解行为,该研究提出了一种基于分布活化能模型(distributed activation energy model,DAEM)的多物理场耦合数值模型。该模型在颗粒能量平衡框架下,引入接触导热、气膜导热、对流与辐射多种传热机制,并与质量转化过程和活化能分布特征相耦合,建立了用于描述生物质快速热解过程的常微分方程模型。基于热重分析试验数据,对高斯、洛伦兹及逻辑斯谛3种活化能分布函数进行了参数反演与对比分析。结果表明,洛伦兹分布能够更准确地再现试验热重曲线,其平均绝对误差(mean absolute error,MAE)和均方根误差(root mean square error,RMSE)分别为0.0116和0.0138。数值模拟结果显示,生物质颗粒在初始阶段经历了极高的升温速率(峰值达到2.14×10^(3)℃/s),但热解反应相对于温度演化存在明显的动力学滞后特征。传热机制分析表明,对流与导热在整个热解过程中占主导地位,而在高温阶段辐射传热的贡献不可忽略。参数敏感性分析进一步揭示,陶瓷球温度和生物质颗粒粒径对热解效率具有显著影响,反应焓和颗粒碰撞概率次之,而辐射视角因子的影响相对有限。研究结果表明,在传热条件充分的快速热解工况下,过程控制机理由传热受限逐渐转变为化学反应动力学受限。研究为深入理解下降管反应器内多物理场耦合热解行为特征及反应器结构与工艺参数优化提供了理论依据和数据支持。
