Instead of establishing mathematical hydraulic system models from physical laws usually done with the problems of complex modelling processes, low reliability and practicality caused by large uncertainties, a novel mo...Instead of establishing mathematical hydraulic system models from physical laws usually done with the problems of complex modelling processes, low reliability and practicality caused by large uncertainties, a novel modelling method for a highly nonlinear system of a hydraulic excavator is presented. Based on the data collected in the excavator＇s arms driving experiments, a data-based excavator dynamic model using Simplified Refined Instrumental Variable （SRIV） identification and estimation algorithms is established. The validity of the proposed data-based model is indirectly demonstrated by the performance of computer simulation and the.real machine motion control exoeriments.展开更多
In the model developed in this paper, taking the characters and requirements of meteorological services into account, some conventional meteorological observations which are easy to be obtained have been ch.osen, and ...In the model developed in this paper, taking the characters and requirements of meteorological services into account, some conventional meteorological observations which are easy to be obtained have been ch.osen, and mathematical equations describing micro-growth processes of crops have been established on the basis of the field experiments, laboratorial analysis and computer's modelling tests with time interval of ten-days for several years (1987-1989), in accordance with the known biological and physical rules and corresponding reference literatures. It is a preliminary simplified simulation model of spring wheat growth in optimal water and nutrient conditions. The field experiments show that simulation results of this simplified model are satisfactory. The potential operational application and theoretical sense are significant in the meteorological forecast of yield and in the assessment of influences of climatic change on agriculture.展开更多
A series of simulations of air flow through three kinds of2 D vegetation canopies along with different canopy morphology have been conducted by computational fluid dynamics( CFD). Two different turbulent closure model...A series of simulations of air flow through three kinds of2 D vegetation canopies along with different canopy morphology have been conducted by computational fluid dynamics( CFD). Two different turbulent closure models have been used, including standard k-ε turbulent model and RNG k-ε turbulent model with or without source / sink terms,respectively,for the purpose of wind energy applications. In this study,the complicated morphology of3 D vegetation canopy is simplified to three types of 2D simplified canopy model analyzed by the main parameter leaf area index( LAI). Effects of branches and leaves on airflow are also modelled by introducing circles into the 2D simplified canopy model with or without source / sink terms by adding drag force terms in the momentum and turbulent energy equations in porous sub-domains.The main model parameters of source / sink terms are identified thanks to experimental data obtained by direct wind tunnel measurements of the air flow speeds through a branch of Osmanthus fragrans. Moreover,three different canopy shapes of the vegetation canopy are introduced into the simulation. The predictive skills of single-and two-equation( k-ε) models with or without source / sink to compute profiles of mean velocity( u),turbulent kinetic energy( TKE),TKE dissipation rate( ε) and turbulent intensity( I) are compared against datasets collected from other works and field measurements. In conclusion, it is demonstrated that vegetation canopy model 1 using RNG or standard k-ε turbulent model with source / sink terms proves to be a physically accurate and numerically robust method. The method which is better than other two vegetation canopy models is recommended for future use in simulating turbulent flows within and above the canopy in 3D in more details.展开更多
For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine tra...For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.展开更多
A simplified dynamic model of a dish antenna in satellite is established in this article.The modelcan be easily used to analyze the dynamic behaviour of the antenna structure.In terms of the simplifiedmodel,effects on...A simplified dynamic model of a dish antenna in satellite is established in this article.The modelcan be easily used to analyze the dynamic behaviour of the antenna structure.In terms of the simplifiedmodel,effects on dynamic characters due to the disorder of parameters are investigated in details.Thefrequencies calculated by the simplified model accord with those computed by ANSYS.Based on the modeshapes of disordered and perfect structure,the influence law and varying trend of dynamic characters ofantenna structures in satellites produced by stiffness and mass of antenna ribs,stiffness of antenna mem-branes and angles between adjacent ribs,are obtained.The analyses in the paper indicate that the effectsby disordered parameters can not be ignored in the dynamic analysis of such structures.展开更多
Quickly and accurately obtaining the internal temperature distribution of a transformer plays a key role in predicting its operating conditions and simplifying the maintenance process.A reasonable equivalent thermal c...Quickly and accurately obtaining the internal temperature distribution of a transformer plays a key role in predicting its operating conditions and simplifying the maintenance process.A reasonable equivalent thermal circuit model is a relatively reliable method of obtaining the internal temperature distribution.However,thermal circuit models without targeted consideration of operating conditions and parameter corrections usually limit the accuracy of the results.This paper proposed a five-node transient thermal circuit model with the introduction of nonlinear thermal resistance,which considered the internal structure and winding layout of the core-type high-frequency transformer.The Nusselt number,a crucial variable in heat convection calculations and directly related to the accuracy of thermal resistance parameters,was calibrated on the basis of the distribution of external cooling air.After parameter calibration,the maximum computational error of the hotspot temperature is reduced by 5.48%compared with that of the uncalibrated model.Finally,an experimental platform for temperature monitoring was established to validate the five-node model and its ability to track the temperature change at each reference point after calibrating the Nusselt number.展开更多
With the expansion of tunnel construction scale,accurate modeling of 3D unsteady flow fields in ultra-long tunnels requires high computational resources.In this study,a resistance compensation method based on the St a...With the expansion of tunnel construction scale,accurate modeling of 3D unsteady flow fields in ultra-long tunnels requires high computational resources.In this study,a resistance compensation method based on the St and Eu similarity criterion is proposed to construct the simplified model to rapidly and precisely replicate the train-driven unstable airflow.A 6000 m ultra-long tunnel is utilized as a reference model and simplified models with the scale ratio varying from 80%to 10%are developed to assess the method performance.The multi-region dynamic mesh model is employed to simulate train tracking motion.After weighing the computational accuracy and efficiency,the results show that 20%is the optimal scale ratio.The unsteady wind speed of the simplified model deviates 6.96%from the reference model,while the simulation computation time is reduced by 85.01%.On this basis,the simplified model is applied to analyze the impacts of tunnel friction coefficients,blockage rates,train lengths and speeds,and departure intervals.The mean bias error(MBE)and Pearson correlation coefficient(PCC)are within 10%and over 0.8 respectively,confirming the reliability of the simplified model.The resistance compensation method is a crucial technique to improve the accuracy and efficiency of the unsteady flow field in ultra-long tunnels.展开更多
A temperature-based method is usually applied in displacement ventilation (DV) design when overheating is the primary indoor climate concern. Different steady-state models have been developed and implemented to calcul...A temperature-based method is usually applied in displacement ventilation (DV) design when overheating is the primary indoor climate concern. Different steady-state models have been developed and implemented to calculate airflow rate in rooms with DV. However, in practical applications, the performance of DV depends on potentially dynamic parameters, such as strength, type and location of heat gains and changing heat gain schedule. In addition, thermal mass affects dynamically changing room air temperature. The selected steady-state and dynamic models were validated with the experimental results of a lecture room and an orchestra rehearsal room. Among the presented models, dynamic DV model demonstrated a capability to take into account the combination of dynamic parameters in typical applications of DV. The design airflow rate is calculated for the case studies of dynamic DV design in the modelled lecture room in both dynamic and steady-state conditions. In dynamic conditions of heavy construction in 2–4 hours occupancy periods, the actual airflow rate required could be 50% lower than the airflow rate calculated with the steady-state models. The difference between steady-state and dynamic multi-nodal model is most significant with heavyweight construction and short occupancy period (17%–28%). In cases with light construction, the dynamic DV model provides roughly the same airflow rates for four-hour occupancy period than the Mund’s model calculates. The dynamic model can significantly decrease the design airflow rate of DV, which can result in a reduction of investment costs and electrical consumption of fans.展开更多
文摘Instead of establishing mathematical hydraulic system models from physical laws usually done with the problems of complex modelling processes, low reliability and practicality caused by large uncertainties, a novel modelling method for a highly nonlinear system of a hydraulic excavator is presented. Based on the data collected in the excavator＇s arms driving experiments, a data-based excavator dynamic model using Simplified Refined Instrumental Variable （SRIV） identification and estimation algorithms is established. The validity of the proposed data-based model is indirectly demonstrated by the performance of computer simulation and the.real machine motion control exoeriments.
文摘In the model developed in this paper, taking the characters and requirements of meteorological services into account, some conventional meteorological observations which are easy to be obtained have been ch.osen, and mathematical equations describing micro-growth processes of crops have been established on the basis of the field experiments, laboratorial analysis and computer's modelling tests with time interval of ten-days for several years (1987-1989), in accordance with the known biological and physical rules and corresponding reference literatures. It is a preliminary simplified simulation model of spring wheat growth in optimal water and nutrient conditions. The field experiments show that simulation results of this simplified model are satisfactory. The potential operational application and theoretical sense are significant in the meteorological forecast of yield and in the assessment of influences of climatic change on agriculture.
基金National Natural Science Foundations of China(Nos.51178094,41371445)
文摘A series of simulations of air flow through three kinds of2 D vegetation canopies along with different canopy morphology have been conducted by computational fluid dynamics( CFD). Two different turbulent closure models have been used, including standard k-ε turbulent model and RNG k-ε turbulent model with or without source / sink terms,respectively,for the purpose of wind energy applications. In this study,the complicated morphology of3 D vegetation canopy is simplified to three types of 2D simplified canopy model analyzed by the main parameter leaf area index( LAI). Effects of branches and leaves on airflow are also modelled by introducing circles into the 2D simplified canopy model with or without source / sink terms by adding drag force terms in the momentum and turbulent energy equations in porous sub-domains.The main model parameters of source / sink terms are identified thanks to experimental data obtained by direct wind tunnel measurements of the air flow speeds through a branch of Osmanthus fragrans. Moreover,three different canopy shapes of the vegetation canopy are introduced into the simulation. The predictive skills of single-and two-equation( k-ε) models with or without source / sink to compute profiles of mean velocity( u),turbulent kinetic energy( TKE),TKE dissipation rate( ε) and turbulent intensity( I) are compared against datasets collected from other works and field measurements. In conclusion, it is demonstrated that vegetation canopy model 1 using RNG or standard k-ε turbulent model with source / sink terms proves to be a physically accurate and numerically robust method. The method which is better than other two vegetation canopy models is recommended for future use in simulating turbulent flows within and above the canopy in 3D in more details.
基金supported by the National Key R&D Program of China (No.2018YFB1105100)the National Natural Science Foundation of China (No.51975246)+2 种基金the Advanced Manufacturing Project of Provincial School Construction of Jilin Province (No. SXGJSF2017-2)the Program for JLU Science and Technology Innovative Research Team (2019TD-34)the China Postdoctoral Science Foundation Funded Project (No. 2016M590256)
文摘For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.
基金Supported by the Innovative Fund of China Aerospace Science and Technology Corporation (CASC0113)
文摘A simplified dynamic model of a dish antenna in satellite is established in this article.The modelcan be easily used to analyze the dynamic behaviour of the antenna structure.In terms of the simplifiedmodel,effects on dynamic characters due to the disorder of parameters are investigated in details.Thefrequencies calculated by the simplified model accord with those computed by ANSYS.Based on the modeshapes of disordered and perfect structure,the influence law and varying trend of dynamic characters ofantenna structures in satellites produced by stiffness and mass of antenna ribs,stiffness of antenna mem-branes and angles between adjacent ribs,are obtained.The analyses in the paper indicate that the effectsby disordered parameters can not be ignored in the dynamic analysis of such structures.
基金supported by the National Natural Science Foundation of China(Grant 52207180)Xi'an High Voltage Apparatus Research Institute Co.Ltd.(Grant K222301-01)the Anhui Provincial Natural Science Foundation(Grant 2208085UD18).
文摘Quickly and accurately obtaining the internal temperature distribution of a transformer plays a key role in predicting its operating conditions and simplifying the maintenance process.A reasonable equivalent thermal circuit model is a relatively reliable method of obtaining the internal temperature distribution.However,thermal circuit models without targeted consideration of operating conditions and parameter corrections usually limit the accuracy of the results.This paper proposed a five-node transient thermal circuit model with the introduction of nonlinear thermal resistance,which considered the internal structure and winding layout of the core-type high-frequency transformer.The Nusselt number,a crucial variable in heat convection calculations and directly related to the accuracy of thermal resistance parameters,was calibrated on the basis of the distribution of external cooling air.After parameter calibration,the maximum computational error of the hotspot temperature is reduced by 5.48%compared with that of the uncalibrated model.Finally,an experimental platform for temperature monitoring was established to validate the five-node model and its ability to track the temperature change at each reference point after calibrating the Nusselt number.
基金supported by the Laboratory Basic Research Program of China State Railway Group Co.,Ltd.(L2021G011).
文摘With the expansion of tunnel construction scale,accurate modeling of 3D unsteady flow fields in ultra-long tunnels requires high computational resources.In this study,a resistance compensation method based on the St and Eu similarity criterion is proposed to construct the simplified model to rapidly and precisely replicate the train-driven unstable airflow.A 6000 m ultra-long tunnel is utilized as a reference model and simplified models with the scale ratio varying from 80%to 10%are developed to assess the method performance.The multi-region dynamic mesh model is employed to simulate train tracking motion.After weighing the computational accuracy and efficiency,the results show that 20%is the optimal scale ratio.The unsteady wind speed of the simplified model deviates 6.96%from the reference model,while the simulation computation time is reduced by 85.01%.On this basis,the simplified model is applied to analyze the impacts of tunnel friction coefficients,blockage rates,train lengths and speeds,and departure intervals.The mean bias error(MBE)and Pearson correlation coefficient(PCC)are within 10%and over 0.8 respectively,confirming the reliability of the simplified model.The resistance compensation method is a crucial technique to improve the accuracy and efficiency of the unsteady flow field in ultra-long tunnels.
文摘A temperature-based method is usually applied in displacement ventilation (DV) design when overheating is the primary indoor climate concern. Different steady-state models have been developed and implemented to calculate airflow rate in rooms with DV. However, in practical applications, the performance of DV depends on potentially dynamic parameters, such as strength, type and location of heat gains and changing heat gain schedule. In addition, thermal mass affects dynamically changing room air temperature. The selected steady-state and dynamic models were validated with the experimental results of a lecture room and an orchestra rehearsal room. Among the presented models, dynamic DV model demonstrated a capability to take into account the combination of dynamic parameters in typical applications of DV. The design airflow rate is calculated for the case studies of dynamic DV design in the modelled lecture room in both dynamic and steady-state conditions. In dynamic conditions of heavy construction in 2–4 hours occupancy periods, the actual airflow rate required could be 50% lower than the airflow rate calculated with the steady-state models. The difference between steady-state and dynamic multi-nodal model is most significant with heavyweight construction and short occupancy period (17%–28%). In cases with light construction, the dynamic DV model provides roughly the same airflow rates for four-hour occupancy period than the Mund’s model calculates. The dynamic model can significantly decrease the design airflow rate of DV, which can result in a reduction of investment costs and electrical consumption of fans.
