An advanced Actuator Surface Method(ASM)coupled with Computational Fluid Dynamics(CFD)is developed and applied to the complex unsteady aerodynamic simulation of helicopter.By introducing an improved three-dimensional ...An advanced Actuator Surface Method(ASM)coupled with Computational Fluid Dynamics(CFD)is developed and applied to the complex unsteady aerodynamic simulation of helicopter.By introducing an improved three-dimensional anisotropic Gaussian kernel,this method effectively addresses the severe aerodynamic load fluctuations commonly associated with traditional Virtual Blade Method(VBM)due to turbulent flow around blade elements.To manage the issues of regional shape and grid cell quantity variations caused by virtual blade sweeping,a universal hybrid grid generation strategy is established without body-fitted and disk interpolation grids,which enhances the computational stability at both blade elements and blade edges.Aerodynamic numerical simulations of helicopter are performed using this method,focusing on rotor/fuselage interaction dominated by rotor wake motion and fuselage blockage effects,Blade-Vortex Interaction(BVI)induced by tip vortices,and maneuvering flights involving collective pitch ramp increases.The results indicate that the advanced ASM demonstrates reliability and robustness in the simulation of complex unsteady flow fields around helicopter.Under similar computational accuracy,the advanced ASM improves computational efficiency by nearly 40 times compared to the oversetgrid-based full Blade-Resolved(B-R)method,and by 6 times compared to the VBM.It shows significant advantages when applied to complex full-aircraft interaction and maneuvering flight conditions that require substantial computational resources.展开更多
In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake d...In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence,this work proposes some improvements to the actuator line-large-eddy simulation(AL-LES)method.Based on the dynamic k-equation large-eddy simulation(LES),this method uses a precursor method to generate atmospheric inflow turbulence,models the tower and nacelle wakes,and improves the body force projection method based on an anisotropic Gaussian distribution function.For these three improvements,three wind tunnel experiments are used to validate the numerical accuracy of this method.The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results.After modeling the tower and nacelle wakes,the wake velocity distribution is consistent with the experimental result.The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s,which is about 6%different from the experimental value and improves the prediction accuracy of the tip vortex radial movement.The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.展开更多
In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a ...In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test setup.The energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the actuator.Based on the experimental results of concrete cube and cylinder specimens,the effect of excitation frequencies,excitation amplitude,wave propagation paths and the curing age on the output signals of sensors are evaluated.The results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.展开更多
Plasma synthetic jet actuator（PSJA） has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrod...Plasma synthetic jet actuator（PSJA） has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrode PSJA is investigated by the schlieren method in a large range from 7 k Pa to 100 k Pa.The energy consumed by the PSJA is roughly the same for all the pressure levels.Traces of the precursor shock wave velocity and the jet front velocity vary a lot for different pressures.The precursor shock wave velocity first decreases gradually and then remains at 345 m/s as the air pressure increases.The peak jet front velocity always appears at the first appearance of a jet,and it decreases gradually with the increase of the air pressure.A maximum precursor shock wave velocity of 520 m/s and a maximum jet front velocity of 440 m/s are observed at the pressure of 7 k Pa.The averaged jet velocity in one period ranges from 44 m/s to 54 m/s for all air pressures,and it drops with the rising of the air pressure.High velocities of the precursor shock wave and the jet front indicate that this type of PSJA can still be used to influence the high-speed flow field at 7 k Pa.展开更多
In this paper, the effect of van der Waals （vdW） force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated. First, the minimum po- tential energy principle is utilized to find the...In this paper, the effect of van der Waals （vdW） force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated. First, the minimum po- tential energy principle is utilized to find the equation gov- erning the static behavior of nano/micromirror under electro- static and vdW forces. Then, the stability of static equilib- rium points is analyzed using the energy method. It is found that when there exist two equilibrium points, the smaller one is stable and the larger one is unstable. The effects of dif- ferent design parameters on the mirror＇s pull-in angle and pull-in voltage are studied and it is found that vdW force can considerably reduce the stability limit of the mirror. At the end, the nonlinear equilibrium equation is solved numer- ically and analytically using homotopy perturbation method （HPM）. It is observed that a sixth order perturbation approx- imation can precisely model the mirror＇s behavior. The re- suits of this paper can be used for stable operation design and safe fabrication of torsional nano/micro actuators.展开更多
The coupling iteration (CI) of the finite element method(FEM) is used to simulate the magnetic and mechanical characteristics for a GMM actuator. The convergent ability under different prestress and different load typ...The coupling iteration (CI) of the finite element method(FEM) is used to simulate the magnetic and mechanical characteristics for a GMM actuator. The convergent ability under different prestress and different load types is investigated. Then the calculated deformations are compared with the experimental values. The results convince that the CI of FEM is suitable for the simulation of energy coupling and transformation mechanism of the GMM. At last, the output deformation properties are studied under different input currents, showing that there is a good compromise between good linearity and large strain under the prestress 6 MPa.展开更多
This paper presents a robust adaptive state feedback control scheme for a class of parametric-strict-feedback nonlinear systems in the presence of time varying actuator failures. The designed adaptive controller compe...This paper presents a robust adaptive state feedback control scheme for a class of parametric-strict-feedback nonlinear systems in the presence of time varying actuator failures. The designed adaptive controller compensates a general class of actuator failures without any need for explicit fault detection. The parameters, times, and patterns of the considered failures are completely unknown. The proposed controller is constructed based on a backstepping design method. The global boundedness of all the closed-loop signals is guaranteed and the tracking error is proved to converge to a small neighborhood of the origin. The proposed approach is employed for a two-axis positioning stage system as well as an aircraft wing system. The simulation results show the correctness and effectiveness of the proposed robust adaptive actuator failure compensation approach.展开更多
The environmental effects of hydrokinetic turbines are still under investigation,reflecting the emerging status of this technology.This study investigates the interaction between hydrokinetic rotor wakes and fish swim...The environmental effects of hydrokinetic turbines are still under investigation,reflecting the emerging status of this technology.This study investigates the interaction between hydrokinetic rotor wakes and fish swimming,revealing insights into fish biomechanics in complex flows and assessing the environ-mental implications of marine energy solutions.We conducted numerical simulations with the URANS approach and k−ω−SST turbulence closuremodeltopredictthree-dimensionalturbulent flowinthe OpenFOAM software.The hydrokinetic rotor wake was simulated employing the actuator line method,providing a computationally efficient alternative to full geometry simulations.For accurate replication of the motion of a fish-like tuna(Thunnus atlanticus),dynamic adaptive mesh discretization was employed.The results offer a comparative analysis of fish swimming performance within the wake rotor,particularly when immersed in the tip blade vortex,contrasted with scenarios where fish swim in undisturbed flow conditions.The analysis encompasses three-dimensional wake structures,force generation,efficiency,and equilibrium states(balancing drag and thrust)across varying Swimming numbers(Sw).Key findings in-clude the enhanced attachment of the leading-edge vortex due to the caudal fin’s interaction with the tip blade vortex,resulting in improved auto-propulsive force production;a reduced tail stride frequency observed in fish swimming downstream of the rotor to achieve longitudinal force balance compared to unperturbed flow;and transverse hydrodynamic forces pushing fish radially away from the wake’s influ-ence zone,potentially mitigating the risk of collision with turbine blades.展开更多
基金co-supported by the Foundation of the State Key Laboratory of Aerodynamics(No.RAL202203)the National Key Laboratory Foundation(No.6142202202)the China Postdoctoral Science Foundation(No.2024M754133)。
文摘An advanced Actuator Surface Method(ASM)coupled with Computational Fluid Dynamics(CFD)is developed and applied to the complex unsteady aerodynamic simulation of helicopter.By introducing an improved three-dimensional anisotropic Gaussian kernel,this method effectively addresses the severe aerodynamic load fluctuations commonly associated with traditional Virtual Blade Method(VBM)due to turbulent flow around blade elements.To manage the issues of regional shape and grid cell quantity variations caused by virtual blade sweeping,a universal hybrid grid generation strategy is established without body-fitted and disk interpolation grids,which enhances the computational stability at both blade elements and blade edges.Aerodynamic numerical simulations of helicopter are performed using this method,focusing on rotor/fuselage interaction dominated by rotor wake motion and fuselage blockage effects,Blade-Vortex Interaction(BVI)induced by tip vortices,and maneuvering flights involving collective pitch ramp increases.The results indicate that the advanced ASM demonstrates reliability and robustness in the simulation of complex unsteady flow fields around helicopter.Under similar computational accuracy,the advanced ASM improves computational efficiency by nearly 40 times compared to the oversetgrid-based full Blade-Resolved(B-R)method,and by 6 times compared to the VBM.It shows significant advantages when applied to complex full-aircraft interaction and maneuvering flight conditions that require substantial computational resources.
基金Project supported by the National Key Research and Development Program of China(Nos.2019YFE0192600,2017YFE0132000,and 2019YFB1503700)the National Natural Science Foundation of China(Nos.51761135012 and 11872248)。
文摘In a large wind farm,the wakes of upstream and downstream wind turbines can interfere with each other,affecting the overall power output of the wind farm.To further improve the numerical accuracy of the turbine wake dynamics under atmosphere turbulence,this work proposes some improvements to the actuator line-large-eddy simulation(AL-LES)method.Based on the dynamic k-equation large-eddy simulation(LES),this method uses a precursor method to generate atmospheric inflow turbulence,models the tower and nacelle wakes,and improves the body force projection method based on an anisotropic Gaussian distribution function.For these three improvements,three wind tunnel experiments are used to validate the numerical accuracy of this method.The results show that the numerical results calculated in the far-wake region can reflect the characteristics of typical onshore and offshore wind conditions compared with the experimental results.After modeling the tower and nacelle wakes,the wake velocity distribution is consistent with the experimental result.The radial migration velocity of the tip vortex calculated by the improved blade body force distribution model is 0.32 m/s,which is about 6%different from the experimental value and improves the prediction accuracy of the tip vortex radial movement.The method proposed in this paper is very helpful for wind turbine wake dynamic analysis and wind farm power prediction.
基金Funded by the National Natural Science Foundation of China (No.50708065)the National High-tech R&D Program(863 Program )(No.2007-AA-11-Z-113)the Key Projects in the Science and Technology Pillar Program of Tianjin(No.11ZCKFSF00300)
文摘In order to monitor the basic mechanical properties and interior damage of concrete structures,the piezoelectric actuator/sensor based wave propagation method was investigated experimentally in the laboratory using a specifically designed test setup.The energy attenuation of stress waves was measured by the relative index between the output voltage of sensors and the excitation voltage at the actuator.Based on the experimental results of concrete cube and cylinder specimens,the effect of excitation frequencies,excitation amplitude,wave propagation paths and the curing age on the output signals of sensors are evaluated.The results show that the relative voltage attenuation coefficient RVAC is an effective indicator for measuring the attenuation of stress waves through the interior of concrete.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51407197,51522606,51336011,91541120,and 11472306)
文摘Plasma synthetic jet actuator（PSJA） has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrode PSJA is investigated by the schlieren method in a large range from 7 k Pa to 100 k Pa.The energy consumed by the PSJA is roughly the same for all the pressure levels.Traces of the precursor shock wave velocity and the jet front velocity vary a lot for different pressures.The precursor shock wave velocity first decreases gradually and then remains at 345 m/s as the air pressure increases.The peak jet front velocity always appears at the first appearance of a jet,and it decreases gradually with the increase of the air pressure.A maximum precursor shock wave velocity of 520 m/s and a maximum jet front velocity of 440 m/s are observed at the pressure of 7 k Pa.The averaged jet velocity in one period ranges from 44 m/s to 54 m/s for all air pressures,and it drops with the rising of the air pressure.High velocities of the precursor shock wave and the jet front indicate that this type of PSJA can still be used to influence the high-speed flow field at 7 k Pa.
文摘In this paper, the effect of van der Waals （vdW） force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated. First, the minimum po- tential energy principle is utilized to find the equation gov- erning the static behavior of nano/micromirror under electro- static and vdW forces. Then, the stability of static equilib- rium points is analyzed using the energy method. It is found that when there exist two equilibrium points, the smaller one is stable and the larger one is unstable. The effects of dif- ferent design parameters on the mirror＇s pull-in angle and pull-in voltage are studied and it is found that vdW force can considerably reduce the stability limit of the mirror. At the end, the nonlinear equilibrium equation is solved numer- ically and analytically using homotopy perturbation method （HPM）. It is observed that a sixth order perturbation approx- imation can precisely model the mirror＇s behavior. The re- suits of this paper can be used for stable operation design and safe fabrication of torsional nano/micro actuators.
基金This project is supported by National Natural Science Foundation of China (No.50077019).
文摘The coupling iteration (CI) of the finite element method(FEM) is used to simulate the magnetic and mechanical characteristics for a GMM actuator. The convergent ability under different prestress and different load types is investigated. Then the calculated deformations are compared with the experimental values. The results convince that the CI of FEM is suitable for the simulation of energy coupling and transformation mechanism of the GMM. At last, the output deformation properties are studied under different input currents, showing that there is a good compromise between good linearity and large strain under the prestress 6 MPa.
基金supported by Esfahan Regional Electric Company(EREC)
文摘This paper presents a robust adaptive state feedback control scheme for a class of parametric-strict-feedback nonlinear systems in the presence of time varying actuator failures. The designed adaptive controller compensates a general class of actuator failures without any need for explicit fault detection. The parameters, times, and patterns of the considered failures are completely unknown. The proposed controller is constructed based on a backstepping design method. The global boundedness of all the closed-loop signals is guaranteed and the tracking error is proved to converge to a small neighborhood of the origin. The proposed approach is employed for a two-axis positioning stage system as well as an aircraft wing system. The simulation results show the correctness and effectiveness of the proposed robust adaptive actuator failure compensation approach.
文摘The environmental effects of hydrokinetic turbines are still under investigation,reflecting the emerging status of this technology.This study investigates the interaction between hydrokinetic rotor wakes and fish swimming,revealing insights into fish biomechanics in complex flows and assessing the environ-mental implications of marine energy solutions.We conducted numerical simulations with the URANS approach and k−ω−SST turbulence closuremodeltopredictthree-dimensionalturbulent flowinthe OpenFOAM software.The hydrokinetic rotor wake was simulated employing the actuator line method,providing a computationally efficient alternative to full geometry simulations.For accurate replication of the motion of a fish-like tuna(Thunnus atlanticus),dynamic adaptive mesh discretization was employed.The results offer a comparative analysis of fish swimming performance within the wake rotor,particularly when immersed in the tip blade vortex,contrasted with scenarios where fish swim in undisturbed flow conditions.The analysis encompasses three-dimensional wake structures,force generation,efficiency,and equilibrium states(balancing drag and thrust)across varying Swimming numbers(Sw).Key findings in-clude the enhanced attachment of the leading-edge vortex due to the caudal fin’s interaction with the tip blade vortex,resulting in improved auto-propulsive force production;a reduced tail stride frequency observed in fish swimming downstream of the rotor to achieve longitudinal force balance compared to unperturbed flow;and transverse hydrodynamic forces pushing fish radially away from the wake’s influ-ence zone,potentially mitigating the risk of collision with turbine blades.
