The accurate characterization of thermoelectric properties at low temperatures is crucial for the development of high-performance thermoelectric cooling devices. While measurement errors of thermoelectric properties a...The accurate characterization of thermoelectric properties at low temperatures is crucial for the development of high-performance thermoelectric cooling devices. While measurement errors of thermoelectric properties at temperatures above room temperature have been extensively discussed, there is a lack of standard measurement protocols and error analyses for low-temperature transport properties. In this study, we present a measurement system capable of characterizing all three key thermoelectric parameters, i.e., Seebeck coefficient, electrical conductivity, and thermal conductivity, for a single sample across a temperature range of 10 K to 300 K. We investigated six representative commercial Bi_(2)Te_(3)-based samples(three N-type and three P-type). Using an error propagation model, we systematically analyzed the measurement uncertainties of the three intrinsic parameters and the resulting thermoelectric figure of merit. Our findings reveal that measurement uncertainties for both N-type and P-type Bi_(2)Te_(3)-based materials can be effectively maintained below 5% in the temperature range of 40 K to 300 K. However, the uncertainties increase to over 10% at lower temperatures, primarily due to the relatively smaller values of electrical resistivity and Seebeck coefficients in this regime. This work establishes foundational data for Bi_(2)Te_(3)-based thermoelectric materials and provides a framework for broader investigations of advanced low-temperature thermoelectrics.展开更多
In this letter, the attached turbulent cavitating flow around the Clark-Y hydrofoil is investigated by the numerical simulation with special emphasis on error analysis of large eddy simulation（LES） for the unsteady ...In this letter, the attached turbulent cavitating flow around the Clark-Y hydrofoil is investigated by the numerical simulation with special emphasis on error analysis of large eddy simulation（LES） for the unsteady cavitation simulation. The numerical results indicate that the present simulation can capture the periodic cavity shedding behavior and show a fairly good agreement with the available experimental data. Further analysis demonstrates that the cavitation has a great influence on LES numerical error and modeling error. The modeling error and numerical error are almost on the same order of magnitude, while the modeling error often shows a little bit larger magnitude than numerical error. The numerical error and modeling error sometimes can partially offset each other if they have the opposite sign. Besides, our results show that cavitation can extend the magnitudes and oscillation levels of numerical error and modeling error.展开更多
Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an...Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an asymptotic range.Hence,a new V&V approach for large eddy simulation(LES)is proposed.This approach offers a viable solution for the error estimation of simulation data that are unable to satisfy the asymptotic range.The simulation errors of cavitating flow around a projectile near the free surface are assessed using the new V&V method.The evident error values are primarily dispersed around the cavity region and free surface.The increasingly intense cavitating flow increases the error magnitudes.In addition,the modeling error magnitudes of the Dynamic Smagorinsky-Lilly model are substantially smaller than that of the Smagorinsky-Lilly model.The present V&V method can capture the decrease in the modeling errors due to model enhancements,further exhibiting its applicability in cavitating flow simulations.Moreover,the monitoring points where the simulation data are beyond the asymptotic range are primarily dispersed near the cavity region,and the number of such points grows as the cavitating flow intensifies.The simulation outcomes also suggest that the re-entrant jet and shedding cavity collapse are the chief sources of vorticity motions,which remarkably affect the simulation accuracy.The results of this study provide a valuable reference for V&V research.展开更多
In order to reduce the cost,3-PRS mechanism is introduced into the application of supporting theactive reflector unit of large radio telescope.The kinematic model of 3-PRS mechanism with rotationaljoint errors is deri...In order to reduce the cost,3-PRS mechanism is introduced into the application of supporting theactive reflector unit of large radio telescope.The kinematic model of 3-PRS mechanism with rotationaljoint errors is derived to solve the error problem in actual engineering application.Then based on the errormodel,inverse and forward kinematics are analyzed.Because the solutions can not be analytically ex-pressed,a numerical method is applied.Afterwards,the parasitic motion errors are analyzed using searchmethod and empirical formulas of the maximum parasitic motion error are put forward.Finally,the toler-ance is distributed using empirical formulas to avoid interference between adjacent reflector units.Theanalyses provide a theoretical basis for the design and installation of large radio telescope active reflector.展开更多
The supersonic multi-hole probe is an essential test tool for wind tunnel experiments, which is necessary to develop the basic research of improving the measurement accuracy and expanding the application of the probes.
基金supported by the National Natural Science Foundation of China (Grant No. 52172259)the National Key Research and Development Program of China (Grant Nos. 2021YFA0718700 and 2022YFB3803900)the Fundamental Research Funds for the Inner Mongolia Normal University (Grant No. 2022JBTD008)。
文摘The accurate characterization of thermoelectric properties at low temperatures is crucial for the development of high-performance thermoelectric cooling devices. While measurement errors of thermoelectric properties at temperatures above room temperature have been extensively discussed, there is a lack of standard measurement protocols and error analyses for low-temperature transport properties. In this study, we present a measurement system capable of characterizing all three key thermoelectric parameters, i.e., Seebeck coefficient, electrical conductivity, and thermal conductivity, for a single sample across a temperature range of 10 K to 300 K. We investigated six representative commercial Bi_(2)Te_(3)-based samples(three N-type and three P-type). Using an error propagation model, we systematically analyzed the measurement uncertainties of the three intrinsic parameters and the resulting thermoelectric figure of merit. Our findings reveal that measurement uncertainties for both N-type and P-type Bi_(2)Te_(3)-based materials can be effectively maintained below 5% in the temperature range of 40 K to 300 K. However, the uncertainties increase to over 10% at lower temperatures, primarily due to the relatively smaller values of electrical resistivity and Seebeck coefficients in this regime. This work establishes foundational data for Bi_(2)Te_(3)-based thermoelectric materials and provides a framework for broader investigations of advanced low-temperature thermoelectrics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11772239,51576143 and 91752105)the Outstanding Youth Foundation of Natural Science Foundation of Hubei Province(Grant No.2017CFA048)
文摘In this letter, the attached turbulent cavitating flow around the Clark-Y hydrofoil is investigated by the numerical simulation with special emphasis on error analysis of large eddy simulation（LES） for the unsteady cavitation simulation. The numerical results indicate that the present simulation can capture the periodic cavity shedding behavior and show a fairly good agreement with the available experimental data. Further analysis demonstrates that the cavitation has a great influence on LES numerical error and modeling error. The modeling error and numerical error are almost on the same order of magnitude, while the modeling error often shows a little bit larger magnitude than numerical error. The numerical error and modeling error sometimes can partially offset each other if they have the opposite sign. Besides, our results show that cavitation can extend the magnitudes and oscillation levels of numerical error and modeling error.
基金Supported by the National Key R&D Program of China(2022YFB3303501)the National Natural Science Foundation of China(Project Nos.52176041 and 12102308)the Fundamental Research Funds for the Central Universities(Project Nos.2042023kf0208 and 2042023kf0159).
文摘Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an asymptotic range.Hence,a new V&V approach for large eddy simulation(LES)is proposed.This approach offers a viable solution for the error estimation of simulation data that are unable to satisfy the asymptotic range.The simulation errors of cavitating flow around a projectile near the free surface are assessed using the new V&V method.The evident error values are primarily dispersed around the cavity region and free surface.The increasingly intense cavitating flow increases the error magnitudes.In addition,the modeling error magnitudes of the Dynamic Smagorinsky-Lilly model are substantially smaller than that of the Smagorinsky-Lilly model.The present V&V method can capture the decrease in the modeling errors due to model enhancements,further exhibiting its applicability in cavitating flow simulations.Moreover,the monitoring points where the simulation data are beyond the asymptotic range are primarily dispersed near the cavity region,and the number of such points grows as the cavitating flow intensifies.The simulation outcomes also suggest that the re-entrant jet and shedding cavity collapse are the chief sources of vorticity motions,which remarkably affect the simulation accuracy.The results of this study provide a valuable reference for V&V research.
基金the National High Technology Research and Development Programme of China(No.2006AA04Z133)the National Natural Science Foundation of China(No.50605035,10778625)
文摘In order to reduce the cost,3-PRS mechanism is introduced into the application of supporting theactive reflector unit of large radio telescope.The kinematic model of 3-PRS mechanism with rotationaljoint errors is derived to solve the error problem in actual engineering application.Then based on the errormodel,inverse and forward kinematics are analyzed.Because the solutions can not be analytically ex-pressed,a numerical method is applied.Afterwards,the parasitic motion errors are analyzed using searchmethod and empirical formulas of the maximum parasitic motion error are put forward.Finally,the toler-ance is distributed using empirical formulas to avoid interference between adjacent reflector units.Theanalyses provide a theoretical basis for the design and installation of large radio telescope active reflector.
基金This study was co-supported by the National Natural Science Foundation of China(No.51906134 and 51436002).
文摘The supersonic multi-hole probe is an essential test tool for wind tunnel experiments, which is necessary to develop the basic research of improving the measurement accuracy and expanding the application of the probes.
