The nonlinear static characteristic of a piezoelectric unimorph cantilever micro actuator driven by a strong applied electric field is studied based on the couple stress theory.The cantilever actuator consists of a pi...The nonlinear static characteristic of a piezoelectric unimorph cantilever micro actuator driven by a strong applied electric field is studied based on the couple stress theory.The cantilever actuator consists of a piezoelectric layer,a passive（elastic）layer and two electrode layers.First,the nonlinear static characteristic of the actuator caused by the electrostriction of the piezoelectric layer under a strong applied electric field is analyzed using the Rayleigh-Ritz method.Secondly,since the thickness of the cantilever beam is in micro scale and there exists a size effect,the size dependence of the deformation behavior is evaluated using the couple stress theory.The results show that the nonlinearities of the beam deflection increase along with the increase of the applied electric field which means that softening of the micro beam rigidity exists when a strong external electric field is applied.Meanwhile,the optimal value of the thickness ratio for the passive layer and the piezoelectric layer is not around 1.0 which is usually adopted by some previous researchers.Since there exists a size effect of the micro beam deflection,the optimal value of this thickness ratio should be greater than 1.0 in micro scale.展开更多
One promising joining method for NiTi-SMA （shape memory alloy）-components is laser welding. This joining technology bears huge potential regarding process automation and mechanical properties as well as durability, ...One promising joining method for NiTi-SMA （shape memory alloy）-components is laser welding. This joining technology bears huge potential regarding process automation and mechanical properties as well as durability, especially within the field of small- and medium-sized actuators. However, there is still need for research due to unsolved issues influencing the microstructure and thus effecting mechanical properties as well as SMA-characteristics of these joints. Therefore, the purpose of this paper is the evaluation of quality parameters of NiTi-NiTi-wire-joints. For this purpose, design of experiments with a fractional factorial design is used for the investigation, because of its high potential to decrease experimental effort. This paper provides a basis for future research in the field of SMA-actuators and joining.展开更多
Experimental investigation was conducted to investigate the impingement heat transfer performance of a synthetic jet driven by piston actuator on a constant heat flux surface. Effects of jet formation frequency, nozzl...Experimental investigation was conducted to investigate the impingement heat transfer performance of a synthetic jet driven by piston actuator on a constant heat flux surface. Effects of jet formation frequency, nozzle-to-surface spacing ratio and con- jugation of cross flow were considered. The synthetic jet is of stronger penetration and heat transfer capacity when the piston reciprocates at relatively high frequency. Similar to the continuous jet impingement, nozzle-to-surface spacing ratio plays an important role in the heat transfer enhancement of synthetic jet. The optimum nozzle-to-surface spacing ratio corresponding to maximum heat transfer enhancement is considerably high in the synthetic jet, as compared to that in a continuous jet, which indicates that the synthetic jet introduces a stronger entrainment and more vigorous penetration in the surrounding fluid. The convective heat transfer capacity is enhanced significantly under the conjugate action of a synthetic jet and cross flow in com- narison with their individual action.展开更多
A novel circulation control technique is proposed to overcome the shortcomings of blowing jet circulation control, which uses the synthetic jet as the actuator and avoids the limitation about air supply requirement. T...A novel circulation control technique is proposed to overcome the shortcomings of blowing jet circulation control, which uses the synthetic jet as the actuator and avoids the limitation about air supply requirement. The effectiveness of synthetic jet circulation control to enhance lift of NCCR1510-7067N airfoil is confirmed by solving the 2-D unsteady Reynolds-averaged Na- vier-Stokes equations. The aerodynamic characteristics and the flow structure （especially close to the trailing edge） of NCCR 1510-7067N airfoil at zero angle of attack are also presented to discuss the mechanism of lift enhancement of the airfoil with synthetic jet circulation control. The results indicate that the synthetic jet can effectively delay the separation point on the airfoil trailing edge and increase the circulation and lift of the airfoil by Coanda effect. The numerical simulation results demonstrate that the lift augmentation efficiency with synthetic jet circulation control reaches △C1/Cμ,=114 in the present study, which is much higher than the value 12.1 in the case with steady blowing jet circulation control.展开更多
基金The National Natural Science Foundation of China(No.10772086,10772085)
文摘The nonlinear static characteristic of a piezoelectric unimorph cantilever micro actuator driven by a strong applied electric field is studied based on the couple stress theory.The cantilever actuator consists of a piezoelectric layer,a passive（elastic）layer and two electrode layers.First,the nonlinear static characteristic of the actuator caused by the electrostriction of the piezoelectric layer under a strong applied electric field is analyzed using the Rayleigh-Ritz method.Secondly,since the thickness of the cantilever beam is in micro scale and there exists a size effect,the size dependence of the deformation behavior is evaluated using the couple stress theory.The results show that the nonlinearities of the beam deflection increase along with the increase of the applied electric field which means that softening of the micro beam rigidity exists when a strong external electric field is applied.Meanwhile,the optimal value of the thickness ratio for the passive layer and the piezoelectric layer is not around 1.0 which is usually adopted by some previous researchers.Since there exists a size effect of the micro beam deflection,the optimal value of this thickness ratio should be greater than 1.0 in micro scale.
文摘One promising joining method for NiTi-SMA （shape memory alloy）-components is laser welding. This joining technology bears huge potential regarding process automation and mechanical properties as well as durability, especially within the field of small- and medium-sized actuators. However, there is still need for research due to unsolved issues influencing the microstructure and thus effecting mechanical properties as well as SMA-characteristics of these joints. Therefore, the purpose of this paper is the evaluation of quality parameters of NiTi-NiTi-wire-joints. For this purpose, design of experiments with a fractional factorial design is used for the investigation, because of its high potential to decrease experimental effort. This paper provides a basis for future research in the field of SMA-actuators and joining.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50276028,51106073)
文摘Experimental investigation was conducted to investigate the impingement heat transfer performance of a synthetic jet driven by piston actuator on a constant heat flux surface. Effects of jet formation frequency, nozzle-to-surface spacing ratio and con- jugation of cross flow were considered. The synthetic jet is of stronger penetration and heat transfer capacity when the piston reciprocates at relatively high frequency. Similar to the continuous jet impingement, nozzle-to-surface spacing ratio plays an important role in the heat transfer enhancement of synthetic jet. The optimum nozzle-to-surface spacing ratio corresponding to maximum heat transfer enhancement is considerably high in the synthetic jet, as compared to that in a continuous jet, which indicates that the synthetic jet introduces a stronger entrainment and more vigorous penetration in the surrounding fluid. The convective heat transfer capacity is enhanced significantly under the conjugate action of a synthetic jet and cross flow in com- narison with their individual action.
基金supported by the National Natural Science Foundation of China (Grant No. 10872021)the Open Research Project of the State Key Laboratory of Mechanical System and Vibration (Grant No. MSV-2012-09)
文摘A novel circulation control technique is proposed to overcome the shortcomings of blowing jet circulation control, which uses the synthetic jet as the actuator and avoids the limitation about air supply requirement. The effectiveness of synthetic jet circulation control to enhance lift of NCCR1510-7067N airfoil is confirmed by solving the 2-D unsteady Reynolds-averaged Na- vier-Stokes equations. The aerodynamic characteristics and the flow structure （especially close to the trailing edge） of NCCR 1510-7067N airfoil at zero angle of attack are also presented to discuss the mechanism of lift enhancement of the airfoil with synthetic jet circulation control. The results indicate that the synthetic jet can effectively delay the separation point on the airfoil trailing edge and increase the circulation and lift of the airfoil by Coanda effect. The numerical simulation results demonstrate that the lift augmentation efficiency with synthetic jet circulation control reaches △C1/Cμ,=114 in the present study, which is much higher than the value 12.1 in the case with steady blowing jet circulation control.
