To simulate the bending behavior of wheat straw,a flexible straw model was developed based on the Hertz-Mindlin with bonding model using discrete element method.The proposed model was constructed by bonding straw unit...To simulate the bending behavior of wheat straw,a flexible straw model was developed based on the Hertz-Mindlin with bonding model using discrete element method.The proposed model was constructed by bonding straw units(filled by multi-spherical method)through parallel bonding keys.By means of a three-point bending test,single-factor sensitivity analysis and calibration of bonding parameters were performed.Results showed that elastic modulus of the flexible straw enhanced with the increase of bonded disk radius,normal stiffness per unit area and shear stiffness per unit area.The three bonding parameters were respectively calibrated to be 2.11 mm,9.48×10^(9)N/m^(3)and 4.67×10^(9)N/m^(3) by solving the regression equation developed from Box-Behnken design.The simulated elastic modulus(in terms of those three calibrated parameters)exhibited 4.20%difference with the measured one.It proved that the flexible straw could accurately demonstrate bending property of the wheat straw.This would not only help to improve accuracy in simulating wheat straw,but also provide references for flexible straw modeling and parameters calibration of other crops.展开更多
The wind pressure measurement,especially on curved surfaces is imperative in revealing flow characteristics.The flexible sensor with high linear sensitivity over large pressure range is still a significant challenge,e...The wind pressure measurement,especially on curved surfaces is imperative in revealing flow characteristics.The flexible sensor with high linear sensitivity over large pressure range is still a significant challenge,especially for commutatively positive and negative pressure measurement.Here,we propose a conformable,range-programmable capacitive sensor that can extremely extend the measuring range but with high linear sensitivity.The key point is to precisely control the reference pressure of the flexible capacitive sensor array through microchannel network.The proposed sensor with reference pressure 0 kPa keeps stable at a highly-linear sensitivity of 0.28 kPa-1 in an initial measurement regime from 0 to 3 kPa,beyond which the linearity changes significantly.Via the tunable reference pressure,the linear ranges can be customized arbitrarily according to different flight conditions and measured positions,but without any deterioration of sensitivity.The theoretical model is built for the flexible capacitive sensor with tunable reference pressure,agreeing well with the experimental and finite element method results.Additionally,the bending effect is discovered when the flexible sensor is conformed on curved surfaces.This surface-mounted sensor skin is tested on a plate and is integrated with acquisition circuits on a standard airfoil NACA0012 in a wind tunnel and compares with the standard destructive method of pressure taps.It shows great potential applications in measuring wind pressure on curved surfaces,such as for"Fly-by-Feel"of unmanned aerial vehicles and wind tunnel test.展开更多
基金This research was financially supported by Research Fund for the Doctoral Program of Higher Education of China(Grant No.20130204110020).
文摘To simulate the bending behavior of wheat straw,a flexible straw model was developed based on the Hertz-Mindlin with bonding model using discrete element method.The proposed model was constructed by bonding straw units(filled by multi-spherical method)through parallel bonding keys.By means of a three-point bending test,single-factor sensitivity analysis and calibration of bonding parameters were performed.Results showed that elastic modulus of the flexible straw enhanced with the increase of bonded disk radius,normal stiffness per unit area and shear stiffness per unit area.The three bonding parameters were respectively calibrated to be 2.11 mm,9.48×10^(9)N/m^(3)and 4.67×10^(9)N/m^(3) by solving the regression equation developed from Box-Behnken design.The simulated elastic modulus(in terms of those three calibrated parameters)exhibited 4.20%difference with the measured one.It proved that the flexible straw could accurately demonstrate bending property of the wheat straw.This would not only help to improve accuracy in simulating wheat straw,but also provide references for flexible straw modeling and parameters calibration of other crops.
基金the National Natural Science Foundation of China(Grant Nos.51635007 and 51925503)the Fundamental Research Funds for the Central Universities(Grant No.2016YXZD068)。
文摘The wind pressure measurement,especially on curved surfaces is imperative in revealing flow characteristics.The flexible sensor with high linear sensitivity over large pressure range is still a significant challenge,especially for commutatively positive and negative pressure measurement.Here,we propose a conformable,range-programmable capacitive sensor that can extremely extend the measuring range but with high linear sensitivity.The key point is to precisely control the reference pressure of the flexible capacitive sensor array through microchannel network.The proposed sensor with reference pressure 0 kPa keeps stable at a highly-linear sensitivity of 0.28 kPa-1 in an initial measurement regime from 0 to 3 kPa,beyond which the linearity changes significantly.Via the tunable reference pressure,the linear ranges can be customized arbitrarily according to different flight conditions and measured positions,but without any deterioration of sensitivity.The theoretical model is built for the flexible capacitive sensor with tunable reference pressure,agreeing well with the experimental and finite element method results.Additionally,the bending effect is discovered when the flexible sensor is conformed on curved surfaces.This surface-mounted sensor skin is tested on a plate and is integrated with acquisition circuits on a standard airfoil NACA0012 in a wind tunnel and compares with the standard destructive method of pressure taps.It shows great potential applications in measuring wind pressure on curved surfaces,such as for"Fly-by-Feel"of unmanned aerial vehicles and wind tunnel test.
