In order to review storage performance of the electric double layer capacitor （EDLC） in microgrid applications, charging time and storage efficiency issues are mainly studied aiming at three different charging modes...In order to review storage performance of the electric double layer capacitor （EDLC） in microgrid applications, charging time and storage efficiency issues are mainly studied aiming at three different charging modes, including the constant voltage charging mode （CVCM）, the constant current charging mode （CCCM） and the constant power charging mode （CPCM）, based on the practical EDLC product. Numerical calculation methods are presented for different charging modes, and the charging efficiency is also reviewed with strict mathematical deductions, which is validated to be accurate enough and applicable through a simple case with the PV/EDLC system illustration. Finally, trade-off problems between charging time and energy loss are also studied. Research results show that the CPCM is more suitable for microgrid networks compared with the traditional constant-voltage and constant-current charging modes. The hybrid charging method is recommended to save energy and keep high efficiency relatively at the same time. However, how to manage the combination percentage of different charging modes in a reasonable way should be dealt with according to the practical requirements.展开更多
Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the ...Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the impeller inlet.Four variations of lean angles,that is,8°,10°,15° and 20°,were made at first stage impeller.Reynolds Average Navier Stokes equation was used in simulation together with a shear?stress transport(SST) k-w turbulence model and mixing-plane approach,respectively.Three dimensional fluid flows were simplified using periodic model to reduce the computational cost and time required.A good performance was expected that the secondary flow can be effectively reduced in the flow passage of the impeller without excessive increase in manufacturing cost caused by the secondary flow.The results show that secondary flow affects the main flow intricately to form vortices or having non-uniform velocity in the flow passage,which in turn results in substantial fluid energy loss not only in the impeller but also in the guide vane downstream of impeller.The numerical solutions were performed and allowed the optimum design and operating conditions to be obtained.展开更多
The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of ...The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of the riser under VIVs are calculated and the mean stresses,the number of stress cycles and amplitudes are determined by the rainflow counting method.The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser.The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled.Finally the influences of the riser's parameters such as flexural rigidity,top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.展开更多
The high-accuracy, wide-range frequency estimation algorithm for multi-component signals presented in this paper, is based on a numerical differentiation and central Lagrange interpolation. With the sample sequences, ...The high-accuracy, wide-range frequency estimation algorithm for multi-component signals presented in this paper, is based on a numerical differentiation and central Lagrange interpolation. With the sample sequences, which need at most 7 points and are sampled at a sample frequency of 25600 Hz, and computation sequences, using employed a formulation proposed in this paper, the frequencies of each component of the signal are all estimated at an accuracy of 0.001% over 1 Hz to 800 kHz with the amplitudes of each component of the signal varying from 1 V to 200 V and the phase angle of each component of the signal varying from 0° to 360°. The proposed algorithm needs at most a half cycle for the frequencies of each component of the signal under noisy or non-noisy conditions. A testing example is given to illustrate the proposed algorithm in Matlab environment.展开更多
基金The National Natural Science Foundation of China (No.50907010)Ph.D.Programs Foundation of Ministry of Education of China(No.20070286047)Scientific Innovation Foundation for Youngsters of CSEE
文摘In order to review storage performance of the electric double layer capacitor （EDLC） in microgrid applications, charging time and storage efficiency issues are mainly studied aiming at three different charging modes, including the constant voltage charging mode （CVCM）, the constant current charging mode （CCCM） and the constant power charging mode （CPCM）, based on the practical EDLC product. Numerical calculation methods are presented for different charging modes, and the charging efficiency is also reviewed with strict mathematical deductions, which is validated to be accurate enough and applicable through a simple case with the PV/EDLC system illustration. Finally, trade-off problems between charging time and energy loss are also studied. Research results show that the CPCM is more suitable for microgrid networks compared with the traditional constant-voltage and constant-current charging modes. The hybrid charging method is recommended to save energy and keep high efficiency relatively at the same time. However, how to manage the combination percentage of different charging modes in a reasonable way should be dealt with according to the practical requirements.
基金Project(NRF-2010-013-D00007) supported by the National Research Foundation of KoreaWork finacially supported by the 2010 Research Professor Fund of Gyeongsang National University,Korea
文摘Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the impeller inlet.Four variations of lean angles,that is,8°,10°,15° and 20°,were made at first stage impeller.Reynolds Average Navier Stokes equation was used in simulation together with a shear?stress transport(SST) k-w turbulence model and mixing-plane approach,respectively.Three dimensional fluid flows were simplified using periodic model to reduce the computational cost and time required.A good performance was expected that the secondary flow can be effectively reduced in the flow passage of the impeller without excessive increase in manufacturing cost caused by the secondary flow.The results show that secondary flow affects the main flow intricately to form vortices or having non-uniform velocity in the flow passage,which in turn results in substantial fluid energy loss not only in the impeller but also in the guide vane downstream of impeller.The numerical solutions were performed and allowed the optimum design and operating conditions to be obtained.
基金supported by the High Technology Research and Development Program of China (863 Program,Grant Nos.2006AA09Z356 and 2007AA09Z313)
文摘The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of the riser under VIVs are calculated and the mean stresses,the number of stress cycles and amplitudes are determined by the rainflow counting method.The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser.The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled.Finally the influences of the riser's parameters such as flexural rigidity,top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.
文摘The high-accuracy, wide-range frequency estimation algorithm for multi-component signals presented in this paper, is based on a numerical differentiation and central Lagrange interpolation. With the sample sequences, which need at most 7 points and are sampled at a sample frequency of 25600 Hz, and computation sequences, using employed a formulation proposed in this paper, the frequencies of each component of the signal are all estimated at an accuracy of 0.001% over 1 Hz to 800 kHz with the amplitudes of each component of the signal varying from 1 V to 200 V and the phase angle of each component of the signal varying from 0° to 360°. The proposed algorithm needs at most a half cycle for the frequencies of each component of the signal under noisy or non-noisy conditions. A testing example is given to illustrate the proposed algorithm in Matlab environment.
