The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conduc...The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conducted by manually disconnecting the generator from the grid.In this study,reactor transients were analyzed using the THERMIX model.Some of the important thermal–fluid phenomena that occurred after the test initiation are discussed here,including the natural convection of helium in the core and the temperature redistribution in the reactor.Temperatures reproduced for the measuring points arranged in the internals were in agreement with the test data.This demonstrated that the code and calculation model are suitable for posttest analysis applications.Regarding the safety features of the reactor,there was a large margin between the predicted maximum fuel temperature of 997℃and the safety limit of 1620℃.展开更多
Calculated results of inertia moment of turbo-generator rotor can be quite different by methods used in load rejection tests. In view of fluctuation features of rotor speed rise curve during load rejection tests, the ...Calculated results of inertia moment of turbo-generator rotor can be quite different by methods used in load rejection tests. In view of fluctuation features of rotor speed rise curve during load rejection tests, the measurement principle of rotor inertia moment was expounded. Based on the measured data in load rejection tests for an imported type of domestic 300-MW generating unit, the rotor speed rise curve was fitted with three kinds of functions to get initial runup rate, but the obtained results differed a lot from each other. According to analysis on the mechanism of rotor speed rise, m=2 consecutive points averaging or FFT (Fast Fourier Transform) smoothing technology was introduced to process test data, and then the initial runup rate was determined by the method of linear fitting of rotor speed in the range of governing valve closing time. Although the obtained curves had a fluctuating shape, the results of rotor inertia moment for 50% and 100% load rejection tests were of good consistency.展开更多
This paper presents a new Ultra-WideBand (UWB) BandPass Filter (BPF) using half-wavelength Stepped-Impedance Stub-Loaded Resonator (SISLR). Analytical equations derived by the even-odd mode analysis show the new filte...This paper presents a new Ultra-WideBand (UWB) BandPass Filter (BPF) using half-wavelength Stepped-Impedance Stub-Loaded Resonator (SISLR). Analytical equations derived by the even-odd mode analysis show the new filter has two tunable transmission zeros at both sides of the passband to provide a sharp rejection and seven transmission poles inside the passband to achieve U.S. UWB performance. For verification, a UWB BPF is designed, fabricated and measured. The measured results show that the fabricated filter has a -3 dB fractional bandwidth from 3.0 GHz to 10.9 GHz and its insertion loss less than 0.9 dB over the whole passband. Furthermore, the new filter exhibits a simple topology, sharp rejection, and deep stopband suppression.展开更多
To evaluate the safety of the bulb tubular turbine,the dynamic hydraulic characteristics of a hydropower station system during the load rejection process are studied through numerical simulations and a prototype test....To evaluate the safety of the bulb tubular turbine,the dynamic hydraulic characteristics of a hydropower station system during the load rejection process are studied through numerical simulations and a prototype test.In the developed model,a dynamic grid technology(DGT)controls the closure of the guide vane and the blade,whilst the moment balance equation and the user-defined function(UDF)provide the runner’s rotation speed.The 3-D transient simulation method can well predict the rotation speed and mass flow curves in the state of load rejection.The simulation outcomes of the system performance are basically consistent with the measurement data of the prototype.As observed,the runner is subjected to the reversely increased torque and axial force,the system is in a braking phase,and the maximum speed peaks at 144.6%of the rated speed.Moreover,the internal flow of the runner is greatly affected by the closure of the guide vane,and the draft tube forms an eccentric spiral vortex rope.It breaks downstream,aggravating the instability of the draft tube.Overall,the transient characteristics span for the first five seconds,demonstrating the importance of establishing an efficient governing controller.The obtained results are useful for designing the turbine’s flow channel with a double regulating function and comprehending the turbine’s transient characteristics.展开更多
In this paper, the attitude tracking and load relief control problems against wind disturbances and uncertain aerodynamics as well as the engine thrust of launch vehicles are studied.Firstly, a framework of Compensate...In this paper, the attitude tracking and load relief control problems against wind disturbances and uncertain aerodynamics as well as the engine thrust of launch vehicles are studied.Firstly, a framework of Compensated Acceleration Feedback based Active Disturbance Rejection Control(CAF-ADRC) is established to achieve both desired attitude tracking and load relief performances. In particular, the total disturbance that includes the effects caused by both aerocoefficient perturbations and disturbances is estimated by constructing an Extended State Observer(ESO) to achieve attitude tracking. Furthermore, combined with the normal acceleration due to the engine thrust, the accelerometer measurement is also compensated to enhance the load relief effect.Secondly, the quantitative analysis of ESO and the entire closed-loop system are studied. It can be concluded that the desired attitude tracking and load relief performances can be achieved simultaneously under the proposed approach. Besides, tuning laws of the proposed approach are systematically given, which are divided into ESO, Proportional Derivative(PD) and Compensated Acceleration Feedback(CAF) modules. Moreover, the performances under CAF-ADRC approach can be better than those under CAF based PD(CAF-PD) approach by tuning load relief gain.Finally, the approach presented is applied to a typical control problem of launch vehicles with wind disturbances and parameter uncertainties.展开更多
Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this...Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this study, firstly, the load rejection process in a pump-turbine was simulated with a three-dimensional unsteady turbulent numerical method using the technology of dynamic mesh and the user-defined functions in the FLUENT software. The rotational speed predicted through numerical simulation agrees well with experimental data. Secondly, based on numerical simulations, a dynamic instability in the load rejection process was found and presented that the pressure and performance characteristics, including hydraulic torque on the runner and the discharge, fluctuate in the overall trend. Meanwhile, all the performance characteristics and the pressure fluctuate sharply near the operating condition points, where hydraulic torque on the runner is equal to zero or reverse flow is maximum at reverse pump conditions. Finally, the time-frequency features and formation mechanism of the dynamic instability were analyzed emphatically. The analysis of the internal flow in the pump-turbine reveals that dynamic instability in the load rejection process are mainly caused by the vortex flow in the tandem cascades regions. Furthermore, the possible methods to improve the dynamic instability in the load rejection process were recommended.展开更多
The load rejection imposes a danger in the pumped storage hydropower plants(PSPs),especially when two or more pump turbines reject their loads simultaneously.In this paper,the simultaneous load rejection scenarios in ...The load rejection imposes a danger in the pumped storage hydropower plants(PSPs),especially when two or more pump turbines reject their loads simultaneously.In this paper,the simultaneous load rejection scenarios in the PSPs are simulated and analyzed by using a 1-D,3-D coupling method.The PSP pipe system is modeled by using the 1-D method of characteristics(MOC)and one pump turbine is modeled by using the 3-D computational fluid dynamics(CFD).The simulated flow and head are transmitted between the 1-D,3-D regions through the interfaces between these two regions.By assuming that the installed pump turbines are of the same type and the corresponding branch pipes have the same properties,the variations of the transient pressures and the flowrates in different pump turbines will be identical.Therefore,only one pump turbine is modeled by the CFD in this study.A new branching junction boundary is proposed to assign the simulated dynamic pressures and flowrates obtained by the 3-D model to other pump turbines.The 1-D-3-D coupling method is validated by experiments with only one pump turbine rejecting its load.The simultaneous load rejection of two pump turbines is then simulated and validated by comparing the results with those of the 1-D simulation.By building only one pump turbine 3-D model,a large amount of computational resources can be saved.The simultaneous load rejection scenario is then analyzed and compared with the single load rejection scenario.Higher water hammer pressures and a larger rotational speed occur in the simultaneous load rejection scenario,which leads to larger pressure pulsations in the pump turbine.The larger pressure pulsations can be further explained by the flow patterns in the runner channels,in which heavier flow separations and vortexes can be observed in the simultaneous load rejection scenario.展开更多
基金supported by the Chinese National S&T Major Project(No.ZX069)
文摘The HTR-10 is a small modular high-temperature reactor located in Tsinghua University,in China.After the reactor ran continuously for 72 h at full power in the commissioning stage,a full load rejection test was conducted by manually disconnecting the generator from the grid.In this study,reactor transients were analyzed using the THERMIX model.Some of the important thermal–fluid phenomena that occurred after the test initiation are discussed here,including the natural convection of helium in the core and the temperature redistribution in the reactor.Temperatures reproduced for the measuring points arranged in the internals were in agreement with the test data.This demonstrated that the code and calculation model are suitable for posttest analysis applications.Regarding the safety features of the reactor,there was a large margin between the predicted maximum fuel temperature of 997℃and the safety limit of 1620℃.
文摘Calculated results of inertia moment of turbo-generator rotor can be quite different by methods used in load rejection tests. In view of fluctuation features of rotor speed rise curve during load rejection tests, the measurement principle of rotor inertia moment was expounded. Based on the measured data in load rejection tests for an imported type of domestic 300-MW generating unit, the rotor speed rise curve was fitted with three kinds of functions to get initial runup rate, but the obtained results differed a lot from each other. According to analysis on the mechanism of rotor speed rise, m=2 consecutive points averaging or FFT (Fast Fourier Transform) smoothing technology was introduced to process test data, and then the initial runup rate was determined by the method of linear fitting of rotor speed in the range of governing valve closing time. Although the obtained curves had a fluctuating shape, the results of rotor inertia moment for 50% and 100% load rejection tests were of good consistency.
文摘This paper presents a new Ultra-WideBand (UWB) BandPass Filter (BPF) using half-wavelength Stepped-Impedance Stub-Loaded Resonator (SISLR). Analytical equations derived by the even-odd mode analysis show the new filter has two tunable transmission zeros at both sides of the passband to provide a sharp rejection and seven transmission poles inside the passband to achieve U.S. UWB performance. For verification, a UWB BPF is designed, fabricated and measured. The measured results show that the fabricated filter has a -3 dB fractional bandwidth from 3.0 GHz to 10.9 GHz and its insertion loss less than 0.9 dB over the whole passband. Furthermore, the new filter exhibits a simple topology, sharp rejection, and deep stopband suppression.
基金supported by the National Natural Science Foundation of China(Grant No.52271275).
文摘To evaluate the safety of the bulb tubular turbine,the dynamic hydraulic characteristics of a hydropower station system during the load rejection process are studied through numerical simulations and a prototype test.In the developed model,a dynamic grid technology(DGT)controls the closure of the guide vane and the blade,whilst the moment balance equation and the user-defined function(UDF)provide the runner’s rotation speed.The 3-D transient simulation method can well predict the rotation speed and mass flow curves in the state of load rejection.The simulation outcomes of the system performance are basically consistent with the measurement data of the prototype.As observed,the runner is subjected to the reversely increased torque and axial force,the system is in a braking phase,and the maximum speed peaks at 144.6%of the rated speed.Moreover,the internal flow of the runner is greatly affected by the closure of the guide vane,and the draft tube forms an eccentric spiral vortex rope.It breaks downstream,aggravating the instability of the draft tube.Overall,the transient characteristics span for the first five seconds,demonstrating the importance of establishing an efficient governing controller.The obtained results are useful for designing the turbine’s flow channel with a double regulating function and comprehending the turbine’s transient characteristics.
基金supported by the National Key R&D Program of China (No. 2022YFA1004703)the National Natural Science Foundation of China (Nos. 62122083 and 62103014)Chinese Academy of Sciences Youth Innovation Promotion Association (No. 2021003)。
文摘In this paper, the attitude tracking and load relief control problems against wind disturbances and uncertain aerodynamics as well as the engine thrust of launch vehicles are studied.Firstly, a framework of Compensated Acceleration Feedback based Active Disturbance Rejection Control(CAF-ADRC) is established to achieve both desired attitude tracking and load relief performances. In particular, the total disturbance that includes the effects caused by both aerocoefficient perturbations and disturbances is estimated by constructing an Extended State Observer(ESO) to achieve attitude tracking. Furthermore, combined with the normal acceleration due to the engine thrust, the accelerometer measurement is also compensated to enhance the load relief effect.Secondly, the quantitative analysis of ESO and the entire closed-loop system are studied. It can be concluded that the desired attitude tracking and load relief performances can be achieved simultaneously under the proposed approach. Besides, tuning laws of the proposed approach are systematically given, which are divided into ESO, Proportional Derivative(PD) and Compensated Acceleration Feedback(CAF) modules. Moreover, the performances under CAF-ADRC approach can be better than those under CAF based PD(CAF-PD) approach by tuning load relief gain.Finally, the approach presented is applied to a typical control problem of launch vehicles with wind disturbances and parameter uncertainties.
基金supported by Open Fund of Key Laboratory of Fluid and Power Machinery(Xihua Uninversity)Ministry of Education Sichuan(Grant Nos.SZJJ-2017-089 and SZJJ-2017-100-1-001)Open Research Fund Program of State Key Laboratory of Hydroscience and Engineering(Grant No.sklhse-2018-E-02)
文摘Load rejection is one of the most crucial transient processes in pump-turbines. However, only a few achievements on the internal flow mechanism of pump-turbines in load rejection processes have been presented. In this study, firstly, the load rejection process in a pump-turbine was simulated with a three-dimensional unsteady turbulent numerical method using the technology of dynamic mesh and the user-defined functions in the FLUENT software. The rotational speed predicted through numerical simulation agrees well with experimental data. Secondly, based on numerical simulations, a dynamic instability in the load rejection process was found and presented that the pressure and performance characteristics, including hydraulic torque on the runner and the discharge, fluctuate in the overall trend. Meanwhile, all the performance characteristics and the pressure fluctuate sharply near the operating condition points, where hydraulic torque on the runner is equal to zero or reverse flow is maximum at reverse pump conditions. Finally, the time-frequency features and formation mechanism of the dynamic instability were analyzed emphatically. The analysis of the internal flow in the pump-turbine reveals that dynamic instability in the load rejection process are mainly caused by the vortex flow in the tandem cascades regions. Furthermore, the possible methods to improve the dynamic instability in the load rejection process were recommended.
基金supported by the Open Research Fund Program of the State Key Laboratory of Water Resources and Hydropower Engineering Science,Whan University(Grant No.2017SDG01).
文摘The load rejection imposes a danger in the pumped storage hydropower plants(PSPs),especially when two or more pump turbines reject their loads simultaneously.In this paper,the simultaneous load rejection scenarios in the PSPs are simulated and analyzed by using a 1-D,3-D coupling method.The PSP pipe system is modeled by using the 1-D method of characteristics(MOC)and one pump turbine is modeled by using the 3-D computational fluid dynamics(CFD).The simulated flow and head are transmitted between the 1-D,3-D regions through the interfaces between these two regions.By assuming that the installed pump turbines are of the same type and the corresponding branch pipes have the same properties,the variations of the transient pressures and the flowrates in different pump turbines will be identical.Therefore,only one pump turbine is modeled by the CFD in this study.A new branching junction boundary is proposed to assign the simulated dynamic pressures and flowrates obtained by the 3-D model to other pump turbines.The 1-D-3-D coupling method is validated by experiments with only one pump turbine rejecting its load.The simultaneous load rejection of two pump turbines is then simulated and validated by comparing the results with those of the 1-D simulation.By building only one pump turbine 3-D model,a large amount of computational resources can be saved.The simultaneous load rejection scenario is then analyzed and compared with the single load rejection scenario.Higher water hammer pressures and a larger rotational speed occur in the simultaneous load rejection scenario,which leads to larger pressure pulsations in the pump turbine.The larger pressure pulsations can be further explained by the flow patterns in the runner channels,in which heavier flow separations and vortexes can be observed in the simultaneous load rejection scenario.
