Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape not...Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape notch on the spool, such as mass flow rates, flow coefficients, effiux angles and steady state flow forces under different operating conditions. At last, the reliability of the mathematical model of the flow area for the sloping U-shape notch orifice on the spool was demonstrated by the comparison between the orifice area curve derived and the corresponding experimental data provided by the test. It is presented that the bottom arc of sloping U-shape notch （ABU） should not be omitted when it is required to accurately calculate the orifice area of ABU. Although the theoretical flow area of plain bottom sloping U-shape notch （PBU） is larger than that of ABU at the same opening, the simulated mass flow and experimental flow area of ABU are both larger than these of PBU at the same opening, while the simulated flow force of PBU is larger than that of ABU at the same opening. Therefore, it should be prior to adapt the ABU when designing the spool with proportional character.展开更多
Batch extractive distillation(BED)is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separati...Batch extractive distillation(BED)is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separation. A comprehensive design and simulation method is required due to the complexity of BED.In this study,a quasi-steady-state model for BED is proposed,the derivation and solution of the model are presented.This shortcut model can be used to simulate the composition and temperature of the reboiler,the top and other plates of the column in a batch extractive distillation operation.The calculated values are in good agreement with the experimental data.The results show that the quasi-steady-state model is a practical method because of some advantages such as high precision and fast calculation.展开更多
In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifug...In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.展开更多
We present a newly developed global magnetohydrodynamic(MHD) model to study the responses of the Earth's magnetosphere to the solar wind. The model is established by using the space-time conservation element and s...We present a newly developed global magnetohydrodynamic(MHD) model to study the responses of the Earth's magnetosphere to the solar wind. The model is established by using the space-time conservation element and solution element(CESE) method in general curvilinear coordinates on a six-component grid system. As a preliminary study, this paper is to present the model's numerical results of the quasi-steady state and the dynamics of the Earth's magnetosphere under steady solar wind flow with due northward interplanetary magnetic field(IMF). The model results are found to be in good agreement with those published by other numerical magnetospheric models.展开更多
Weak signal detection based on stochastic resonance （SR） can hardly succeed when noise intensity exceeds the optimal value of SR. This paper explores a novel parallel bistable SR array mechanism by decomposed multi-...Weak signal detection based on stochastic resonance （SR） can hardly succeed when noise intensity exceeds the optimal value of SR. This paper explores a novel parallel bistable SR array mechanism by decomposed multi-scale noises from input signal. A smoother output with lower noise is obtained from the combination of colored noise SR ellect and parallel bistable SR array. The influence of noise intensity and array size on the SR effect and output noise intensity is analyzed through numerical simu- lation. A signal detection method based on the new SR mechanism and normalized scale transform is proposed for the case of heavy background noise. Simulation is conducted to confirm the effectiveness of parameter tuning and amplitude tuning of normalized scale transform on the proposed SR model. The proposed method has three advantages： the input noise intensity of each unit is reduced by wavelet decomposition; the output noise level decreases due to array ensemble average; the SR effect of each unit is optimized by normalized scale transform for high frequency signal. Experiment on bearing inner and outer race fault diagnosis has verified the effectiveness and advantages of the proposed SR model in comparison with traditional SR method and kurlogram.展开更多
基金Project(51004085)supported by the National Natural Science Foundation of China
文摘Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape notch on the spool, such as mass flow rates, flow coefficients, effiux angles and steady state flow forces under different operating conditions. At last, the reliability of the mathematical model of the flow area for the sloping U-shape notch orifice on the spool was demonstrated by the comparison between the orifice area curve derived and the corresponding experimental data provided by the test. It is presented that the bottom arc of sloping U-shape notch （ABU） should not be omitted when it is required to accurately calculate the orifice area of ABU. Although the theoretical flow area of plain bottom sloping U-shape notch （PBU） is larger than that of ABU at the same opening, the simulated mass flow and experimental flow area of ABU are both larger than these of PBU at the same opening, while the simulated flow force of PBU is larger than that of ABU at the same opening. Therefore, it should be prior to adapt the ABU when designing the spool with proportional character.
基金Supported by the Natural Science Foundation of Hebei Province（B2006000018）
文摘Batch extractive distillation(BED)is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separation. A comprehensive design and simulation method is required due to the complexity of BED.In this study,a quasi-steady-state model for BED is proposed,the derivation and solution of the model are presented.This shortcut model can be used to simulate the composition and temperature of the reboiler,the top and other plates of the column in a batch extractive distillation operation.The calculated values are in good agreement with the experimental data.The results show that the quasi-steady-state model is a practical method because of some advantages such as high precision and fast calculation.
基金supported by the State Key Program of National Natural Science Foundation of China (Grant No. 51239005)the National Science & Technology Pillar Program (Grant No. 2011BAF14B04)the Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No. CXZZ11_0564)
文摘In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB825601,2014CB845903,2012CB825604)the National Natural Science Foundation of China(Grant Nos.41031066,41231068,41274192,41074121,41204127,41174122)+1 种基金the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZZD-EW-01-4)the Specialized Research Fund for State Key Laboratories
文摘We present a newly developed global magnetohydrodynamic(MHD) model to study the responses of the Earth's magnetosphere to the solar wind. The model is established by using the space-time conservation element and solution element(CESE) method in general curvilinear coordinates on a six-component grid system. As a preliminary study, this paper is to present the model's numerical results of the quasi-steady state and the dynamics of the Earth's magnetosphere under steady solar wind flow with due northward interplanetary magnetic field(IMF). The model results are found to be in good agreement with those published by other numerical magnetospheric models.
基金supported by the National Natural Science Foundation of China (Grant Nos. 5107539, 51105366 and 51205401)the Research Project of National University of Defense Technology (Grant No. JC12-03-02)
文摘Weak signal detection based on stochastic resonance （SR） can hardly succeed when noise intensity exceeds the optimal value of SR. This paper explores a novel parallel bistable SR array mechanism by decomposed multi-scale noises from input signal. A smoother output with lower noise is obtained from the combination of colored noise SR ellect and parallel bistable SR array. The influence of noise intensity and array size on the SR effect and output noise intensity is analyzed through numerical simu- lation. A signal detection method based on the new SR mechanism and normalized scale transform is proposed for the case of heavy background noise. Simulation is conducted to confirm the effectiveness of parameter tuning and amplitude tuning of normalized scale transform on the proposed SR model. The proposed method has three advantages： the input noise intensity of each unit is reduced by wavelet decomposition; the output noise level decreases due to array ensemble average; the SR effect of each unit is optimized by normalized scale transform for high frequency signal. Experiment on bearing inner and outer race fault diagnosis has verified the effectiveness and advantages of the proposed SR model in comparison with traditional SR method and kurlogram.
