An investigation was carried out by numerical simulation on a wind turbine airfoil and a blunt trailing-edge airfoil with and without vortex generators (VGs), and the performance of the airfoils was analyzed. By the s...An investigation was carried out by numerical simulation on a wind turbine airfoil and a blunt trailing-edge airfoil with and without vortex generators (VGs), and the performance of the airfoils was analyzed. By the simulation of airfoil DU 91-W2-250 it was verified that the numerical method and model were credible. Based on this airfoil, a new one with a blunt trailing edge of 6% chord was blended by symmetrically adding thickness, and its characteristics curves were obtained through computing at key angles of attack. Additionally, the pressure distribution on blended airfoil was analyzed by comparing to the airfoil without blend. The interaction of streamwise vortices induced by VGs with trailing vortex or separation vortex was considered, followed by the uncovery of how VGs can suppress the boundary layer separation.展开更多
In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex ge...In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.展开更多
In this paper,we give a relationship between projective generators（resp.,injective cogenerators） in the category of R-modules and the counterparts in the category of complexes of R-modules.As a consequence,we get th...In this paper,we give a relationship between projective generators（resp.,injective cogenerators） in the category of R-modules and the counterparts in the category of complexes of R-modules.As a consequence,we get that complexes of W^--Gorenstein modules are actually W-Gorenstein complexes whenever W is a subcategory of R-modules satisfying W⊥W,where W^- is the subcategory of exact complexes with all cycles in W.We also study when all cycles of a W-Gorenstein complexes are W^--Gorenstein modules.展开更多
To verify the performance of NR-PSS (Nonlinear Robust Power System Stabilizer) for large synchronous generators, field experiments were carried out on a 300 MW generator in Baishan Hydro Plant of Northeast China Power...To verify the performance of NR-PSS (Nonlinear Robust Power System Stabilizer) for large synchronous generators, field experiments were carried out on a 300 MW generator in Baishan Hydro Plant of Northeast China Power Grid. The experiment results show that NR-PSS can improve the generator damping and enhance system stability remarkably.展开更多
Monitoring various medical information distributed throughout the body is of great importance in early clinic diagnosis and treatment of disease.To discover abnormal medical signals and find their causes in good time,...Monitoring various medical information distributed throughout the body is of great importance in early clinic diagnosis and treatment of disease.To discover abnormal medical signals and find their causes in good time,the human body should be monitored continuously and accurately.To meet the requirements,various battery-less and self-powered information acquisition techniques are invented.In this review,the recent advances in self-powered medical information sensors(SMIS)with different functions,structure design,and electric performance are summarized and discussed.The SMIS mainly involves triboelectric nanogenerator(TENG),piezoelectric nanogenerator(PENG),pyroelectric nanogenerator(PyNG)/thermoelectric generator(TEG)and solar cell.Additionally,this review also analyzed the remaining challenges and prospected the development direction of SMIS in future.展开更多
Recently microgrids have drawn a potential attraction by fulfilling the environmental demands and the increasing energy demands of the end-users. It is necessary to focus on various protection and control aspects of a...Recently microgrids have drawn a potential attraction by fulfilling the environmental demands and the increasing energy demands of the end-users. It is necessary to focus on various protection and control aspects of a microgrid. During the transition between the grid-following and grid-forming modes, the voltage and the frequency instability due to the power mismatch condition becomes the major point of concern. Therefore, the paper executes a frequency-active power and voltage-reactive power drooping control strategy for the precise power-sharing among the distributed power generators. Furthermore, to handle the power deficit scenarios and to maintain the system stability, a system independent and priority-based adaptive three-stage load shedding strategy is proposed. The sensitivity of the strategy depends on the system inertia and is computed according to the varying absolute rate-of-change-of-frequency. The strategy incorporates the operation of battery storage system and distributed static compensator (D-STATCOM) in the microgrid, to provide a reliable power supply to the customers for a considerable time instead of a sudden load shedding. The effectiveness of the proposed strategies is investigated on a scaled-down modified IEEE 13-bus microgrid system on the podium of MATLAB 2015b through the time-domain simulation.展开更多
A novel scheme was proposed to generate a millimeter-wave （MMW） optical pulse by combining pulse repetition rate multiplication （PRRM） technology and temporal Talbot effect （TTE）. A cascaded Mach- Zehnder interf...A novel scheme was proposed to generate a millimeter-wave （MMW） optical pulse by combining pulse repetition rate multiplication （PRRM） technology and temporal Talbot effect （TTE）. A cascaded Mach- Zehnder interferometer （MZI） lattice was used for PRRM, and a linearly chirped fiber grating （LCFG） was used as TTE. The basic principle was analyzed by using a Gaussian input short pulse and its characteristics were discussed by numerical simulation. It is shown that the proposed scheme is feasible for MMW signal generation and has potential merits for practical application of radio over fiber （ROF） technology.展开更多
All modes of operation of a two-capacitor generator based on overflow of the charge accumulated in capacitors through the load resistance between two capacitors with antiphase modulated capacitances by means of in-pla...All modes of operation of a two-capacitor generator based on overflow of the charge accumulated in capacitors through the load resistance between two capacitors with antiphase modulated capacitances by means of in-plane or out-of-plane shift of the electrode plates under action of a mechanical force are analyzed paying the especial attention to fabrication of the generators with small sizes. Numerical solutions for all the modes are obtained, and they are found to be universal. Analytical estimates of the maximum power of the generator as a function of the capacitances modulation factor are derived. Experimental investigations of a two-capacitor rotational electric generator show that its characteristics are consistent with the analysis performed and that this analysis can be used to describe all specific features of operation of particular generators. Applications of the devices in micro-design for feeding the remote sensors are discussed.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.50836006)
文摘An investigation was carried out by numerical simulation on a wind turbine airfoil and a blunt trailing-edge airfoil with and without vortex generators (VGs), and the performance of the airfoils was analyzed. By the simulation of airfoil DU 91-W2-250 it was verified that the numerical method and model were credible. Based on this airfoil, a new one with a blunt trailing edge of 6% chord was blended by symmetrically adding thickness, and its characteristics curves were obtained through computing at key angles of attack. Additionally, the pressure distribution on blended airfoil was analyzed by comparing to the airfoil without blend. The interaction of streamwise vortices induced by VGs with trailing vortex or separation vortex was considered, followed by the uncovery of how VGs can suppress the boundary layer separation.
基金supported by National Natural Science Foundation of China(61533013,61273144)Scientific Technology Research and Development Plan Project of Tangshan(13130298B)Scientific Technology Research and Development Plan Project of Hebei(z2014070)
基金co-supported by the National Natural Science Foundation of China(Grants Nos.51576162 and 51536006)
文摘In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.
基金Supported by National Natural Science Foundation of China(Grant Nos.11301240,11371187 and 11101197)the Young Scholars Science Foundation of Lanzhou Jiaotong University(Grant No.2012020)
文摘In this paper,we give a relationship between projective generators（resp.,injective cogenerators） in the category of R-modules and the counterparts in the category of complexes of R-modules.As a consequence,we get that complexes of W^--Gorenstein modules are actually W-Gorenstein complexes whenever W is a subcategory of R-modules satisfying W⊥W,where W^- is the subcategory of exact complexes with all cycles in W.We also study when all cycles of a W-Gorenstein complexes are W^--Gorenstein modules.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50525721, 59837270)
文摘To verify the performance of NR-PSS (Nonlinear Robust Power System Stabilizer) for large synchronous generators, field experiments were carried out on a 300 MW generator in Baishan Hydro Plant of Northeast China Power Grid. The experiment results show that NR-PSS can improve the generator damping and enhance system stability remarkably.
基金National Key R&D Project from Minister of Science and Technology,Grant/Award Number:2016YFA0202703National Natural Science Foundation of China,Grant/Award Numbers:21801019,31571006,61875015,81601629。
文摘Monitoring various medical information distributed throughout the body is of great importance in early clinic diagnosis and treatment of disease.To discover abnormal medical signals and find their causes in good time,the human body should be monitored continuously and accurately.To meet the requirements,various battery-less and self-powered information acquisition techniques are invented.In this review,the recent advances in self-powered medical information sensors(SMIS)with different functions,structure design,and electric performance are summarized and discussed.The SMIS mainly involves triboelectric nanogenerator(TENG),piezoelectric nanogenerator(PENG),pyroelectric nanogenerator(PyNG)/thermoelectric generator(TEG)and solar cell.Additionally,this review also analyzed the remaining challenges and prospected the development direction of SMIS in future.
文摘Recently microgrids have drawn a potential attraction by fulfilling the environmental demands and the increasing energy demands of the end-users. It is necessary to focus on various protection and control aspects of a microgrid. During the transition between the grid-following and grid-forming modes, the voltage and the frequency instability due to the power mismatch condition becomes the major point of concern. Therefore, the paper executes a frequency-active power and voltage-reactive power drooping control strategy for the precise power-sharing among the distributed power generators. Furthermore, to handle the power deficit scenarios and to maintain the system stability, a system independent and priority-based adaptive three-stage load shedding strategy is proposed. The sensitivity of the strategy depends on the system inertia and is computed according to the varying absolute rate-of-change-of-frequency. The strategy incorporates the operation of battery storage system and distributed static compensator (D-STATCOM) in the microgrid, to provide a reliable power supply to the customers for a considerable time instead of a sudden load shedding. The effectiveness of the proposed strategies is investigated on a scaled-down modified IEEE 13-bus microgrid system on the podium of MATLAB 2015b through the time-domain simulation.
文摘A novel scheme was proposed to generate a millimeter-wave （MMW） optical pulse by combining pulse repetition rate multiplication （PRRM） technology and temporal Talbot effect （TTE）. A cascaded Mach- Zehnder interferometer （MZI） lattice was used for PRRM, and a linearly chirped fiber grating （LCFG） was used as TTE. The basic principle was analyzed by using a Gaussian input short pulse and its characteristics were discussed by numerical simulation. It is shown that the proposed scheme is feasible for MMW signal generation and has potential merits for practical application of radio over fiber （ROF） technology.
文摘All modes of operation of a two-capacitor generator based on overflow of the charge accumulated in capacitors through the load resistance between two capacitors with antiphase modulated capacitances by means of in-plane or out-of-plane shift of the electrode plates under action of a mechanical force are analyzed paying the especial attention to fabrication of the generators with small sizes. Numerical solutions for all the modes are obtained, and they are found to be universal. Analytical estimates of the maximum power of the generator as a function of the capacitances modulation factor are derived. Experimental investigations of a two-capacitor rotational electric generator show that its characteristics are consistent with the analysis performed and that this analysis can be used to describe all specific features of operation of particular generators. Applications of the devices in micro-design for feeding the remote sensors are discussed.
