黏性流体环境中压电宏纤维致动柔性结构的流固耦合振动特性及试验

Analysis and Experiment of Fluid-structure Coupled Vibration of MFC-actuated Flexible Structure Immersed in Viscous Fluids

柔性结构与周围流体的耦合作用机制广泛应用于仿生机器人、水下航行器、精密仪器及生命医疗等领域。具有驱动变形大、防水性好且柔韧性好的压电宏纤维(Macro fiber composite,MFC)致动器是水下柔性结构变形控制的首选。建立MFC内部致动弯矩和水动力载荷共同作用下柔性结构的流固耦合动力学模型。对粘贴MFC致动器的柔性结构特征截面进行计算流体动力学(Computational fluid dynamics,CFD)分析,得到不同振动特征频率下柔性结构周围流场、压力分布及所受水动力载荷,分别拟合得到MFC致动柔性结构水动力函数的实部和虚部表达式。结果表明柔性结构水动力载荷的附加质量和阻尼效应都随着振动频率的增加而减小。在等振动特征频率下,MFC致动梁结构水动力函数的实部大于匀质等截面梁的实部;在高振动频率下其水动力函数虚部同样大于匀质等截面梁。试验测试了MFC致动柔性结构的水下振动特性,试验所得MFC激励下柔性结构末端稳定振动的幅频特性和相频特性与建立的耦合动力模型相吻合,证实了所建立MFC致动柔性结构的水动力函数及流固耦合振动模型的有效性。

The fluid-structure coupled vibration behavior of flexible structure has been widely applicated in bionic robot,underwater autonomous vehicle,precision instrument,medical Engineering,and so on.Macro fiber composite(MFC)possesses the advantages of being highly flexible and waterproof,with large actuation ability.Thus,MFC actuator is a perfect option for active deformation control of underwater flexible structure.The fluid-structure coupled dynamic model of an MFC-actuated flexible structure is established,both the internally actuation moment provided by the MFC actuators and the hydrodynamic load caused by the surrounding fluid are considered.CFD simulations on the cross section of the flexible structure bonded with MFC actuators are conducted.The flow and pressure distributions around the oscillating structure are visualized,and the hydrodynamic forces applied to the flexible structure are also extracted at different non-dimensional oscillating frequencies.Then,expressions of the real and imaginary parts of the hydrodynamic function for the MFC-actuated flexible structure are obtained,respectively.It is demonstrated that the added mass and damping effects of the surrounding fluid weaken with an increase in the non-dimensional oscillating frequency.Moreover,the real part of the hydrodynamic function for the MFC-actuated beam is larger than that of the uniform beam at the same non-dimensional frequency,so is the imaginary part of the hydrodynamic function at a high oscillating frequency.The vibration responses of the proposed underwater structure are obtained experimentally.Experimental results show that the magnitude-frequency and phase-frequency spectrums of the MFC-actuated flexible structure in experiments match well with those of the established model.Accordingly,the effectiveness of the proposed hydrodynamic function and fluid-structure coupled dynamic model for the MFC-actuated flexible structure is validated.