When ultrasonically cutting honeycomb core curved parts,the tool face of the straight blade must be along the curved surface’s tangent direction at all times to ensure high-quality machining of the curved surface.How...When ultrasonically cutting honeycomb core curved parts,the tool face of the straight blade must be along the curved surface’s tangent direction at all times to ensure high-quality machining of the curved surface.However,given that the straight blade is a nonstandard tool,the existing computer-aided manufacturing technology cannot directly realize the above action requirement.To solve this problem,this paper proposed an algorithm for extracting a straight blade real-time tool face vector from a 5-axis milling automatically programmed tool location file,which can realize the tool location point and tool axis vector conversion from the flat end mill to the straight blade.At the same time,for the multi-solution problem of the rotation axis,the dependent axis rotation minimization algorithm was introduced,and the spindle rotation algorithm was proposed for the tool edge orientation problem when the straight blade is used to machine the curved part.Finally,on the basis of the MATLAB platform,the dependent axis rotation minimization algorithm and spindle rotation algorithm were integrated and compiled,and the straight blade ultrasonic cutting honeycomb core postprocessor was then developed.The model of the machine tool and the definition of the straight blade were conducted in the VERICUT simulation software,and the simulation machining of the equivalent entity of the honeycomb core can then be realized.The correctness of the numerical control program generated by the postprocessor was verified by machining and accuracy testing of the two designed features.Observation and analysis of the simulation and experiment indicate that the tool pose is the same under each working condition,and the workpieces obtained by machining also meet the corresponding accuracy requirements.Therefore,the postprocessor developed in this paper can be well adapted to the honeycomb core ultrasonic cutting machine tool and realize high-quality and high-efficient machining of honeycomb core composites.展开更多
Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct...Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.展开更多
Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis ...Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT) with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD) prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.展开更多
Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especia...Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.展开更多
In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.Th...In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.The effect of the azimuthal angle of blade position relative to wind direction on the self-starting capability was discussed based on the results of flow visualization.The torque and centripetal force of the rotor when the self-starting behavior starts were roughly calculated with the flow visualization results of the rotor.It is suggested that there exists the condition of wind speed and configuration of the blade position of the rotor at the rest of rotor to the reach to situational rotation number.展开更多
To invest the condition of ice accretion on the blade used for straight-bladed vertical axis wind turbine (SB-VAWT), wind tunnel tests were carried out on a blade with NACA0015 airfoil by using a small simple icing wi...To invest the condition of ice accretion on the blade used for straight-bladed vertical axis wind turbine (SB-VAWT), wind tunnel tests were carried out on a blade with NACA0015 airfoil by using a small simple icing wind tunnel. Tests were carried out at some typical attack angles under different wind speeds and flow discharges of a water spray with wind. The icing shape and area on blade surface were recorded and measured. Then the numerical computation was carried out to calculate the lift and drag coefficients of the blade before and after ice accretion according to the experiment result, the effect of icing on the aerodynamic characteristics of blade were discussed.展开更多
基金support from the National Natural Science Foundation of China (Grant No.U20A20291).
文摘When ultrasonically cutting honeycomb core curved parts,the tool face of the straight blade must be along the curved surface’s tangent direction at all times to ensure high-quality machining of the curved surface.However,given that the straight blade is a nonstandard tool,the existing computer-aided manufacturing technology cannot directly realize the above action requirement.To solve this problem,this paper proposed an algorithm for extracting a straight blade real-time tool face vector from a 5-axis milling automatically programmed tool location file,which can realize the tool location point and tool axis vector conversion from the flat end mill to the straight blade.At the same time,for the multi-solution problem of the rotation axis,the dependent axis rotation minimization algorithm was introduced,and the spindle rotation algorithm was proposed for the tool edge orientation problem when the straight blade is used to machine the curved part.Finally,on the basis of the MATLAB platform,the dependent axis rotation minimization algorithm and spindle rotation algorithm were integrated and compiled,and the straight blade ultrasonic cutting honeycomb core postprocessor was then developed.The model of the machine tool and the definition of the straight blade were conducted in the VERICUT simulation software,and the simulation machining of the equivalent entity of the honeycomb core can then be realized.The correctness of the numerical control program generated by the postprocessor was verified by machining and accuracy testing of the two designed features.Observation and analysis of the simulation and experiment indicate that the tool pose is the same under each working condition,and the workpieces obtained by machining also meet the corresponding accuracy requirements.Therefore,the postprocessor developed in this paper can be well adapted to the honeycomb core ultrasonic cutting machine tool and realize high-quality and high-efficient machining of honeycomb core composites.
基金Project(HEUCF110707)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(E201216)supported by Heilongjiang Natural Science Fund,China
文摘Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.
基金Project (E201216) supported by Heilongjiang Provincial Natural Science Foundation,China
文摘Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT) with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD) prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.
文摘Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and easy installation and maintenance. But its aerodynamic performance is very complicated,especially for the existence of dynamic stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus wind turbine. In this paper,mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical investigation,an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient. As to the numerical method,the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate the eligibility of the turbine.
基金supported in part by International Platform for Dryland Research and Education (IPDRE),Tottori University
文摘In this study,wind tunnel experiment was carried out to investigate the self-staring capability for straight-bladed vertical axis wind turbine.The flow visualization also was been performed at the rest of the rotor.The effect of the azimuthal angle of blade position relative to wind direction on the self-starting capability was discussed based on the results of flow visualization.The torque and centripetal force of the rotor when the self-starting behavior starts were roughly calculated with the flow visualization results of the rotor.It is suggested that there exists the condition of wind speed and configuration of the blade position of the rotor at the rest of rotor to the reach to situational rotation number.
基金Supported by National Natural Science Foundation of China (10702015)
文摘To invest the condition of ice accretion on the blade used for straight-bladed vertical axis wind turbine (SB-VAWT), wind tunnel tests were carried out on a blade with NACA0015 airfoil by using a small simple icing wind tunnel. Tests were carried out at some typical attack angles under different wind speeds and flow discharges of a water spray with wind. The icing shape and area on blade surface were recorded and measured. Then the numerical computation was carried out to calculate the lift and drag coefficients of the blade before and after ice accretion according to the experiment result, the effect of icing on the aerodynamic characteristics of blade were discussed.