| Smart materials working as sensors and actuators can be directly applied to the shell structures.A structronic shell system is composed of smart materials,electronic control modules and the shell structures.Structronic shell system takes the advantage of high integration,precision control and high reliability.Thin shell structures are commonly used in aerospace and mechanical structures and systems.With the characteristics of light weight and high flexibility,the vibration of thin shell structures is hard to be damped quickly.Thus active vibration control of thin shell structures is important.Light-activated shape memory polymer(LaSMP)exhibits low density,large deformation,non-contact actuation and little temperature change during transformation.It is a novel smart material with great application potentials.LaSMP actuators are able to act on the thin shell structures through the light-elastic coupling effect.The stiffness of thin shells can be adjusted by LaSMP actuators and the dynamic response of forced vibration can be controlled.The thesis is focused on the study the light-elastic coupling relationship of LaSMP.As the actuating mechanisms of LaSMP synthesized by different formulations are different,a general constitutive equation is established based on the chemical kinetics.The models of LaSMP under two different conditions are introduced:without initial strain and with initial strain.The LaSMP based on spiropyran is synthesized.The characteristics and parameters of LaSMP are measured.The one-dimensional and two-dimensional LaSMP actuators are fabricated.Young’s modulus variation and the stress variation of LaSMP actuators are measured.The stress and strain of LaSMP laminated shells are analyzed.Based on Hamilton’s principle,the dynamic equations of thin shells coupled with LaSMP actuators are established.The general dynamic equations are simplified to the laminated cylindrical shell panel,conical shell and toroidal shell.These simplifications are the base of vibration and frequency control.Though the modal expansion method,the independent modal control of LaSMP laminated shells and the modal control force of LaSMP actuators are derived.With the dynamic stiffness feature of LaSMP,the natural frequencies of thin shells are adjusted.Accordingly,the frequencies of a one-dimensional cantilever beam and a two-dimensional cylindrical shell with LaSMP actuators are analyzed.Through the governing equations of the laminated cylindrical shell,the frequency variation process is studied.The natural frequency of the cantilever beam is analyzed through the stepped and laminated composite beam theory.To broaden the frequency control range of LaSMP,variable-length LaSMP actuators are designed and applied to the cantilever beam.A laminated cantilever beam is made with elastic beam and the LaSMP composed of spiropyran.The experiment is carried out to measure the frequency variation of the beam under UV exposures.The independent modal control is applied to the one-dimensional ring structure and the two-dimensional parabolic cylindrical shell.The LaSMP actuators are applied to suppress the force harmonic response of ring.As the LaSMP actuators exhibit nonlinear feature,the phase shift and neural network control methods are used.Through adjusting the light intensity,the vibration control effect of LaSMP actuators is enhanced.Besides,LaSMP as a kind of thin film material is easy to be formed and imposed with prestrain,thus the LaSMP actuators are designed able to generate shear strain.The distributions of LaSMP’s modal control force on the surface of parabolic cylindrical shell are analyzed.The snap-back vibration of the parabolic cylindrical shell is controlled by the LaSMP actuators.In the thesis the governing equations of LaSMP laminated thin shell are established,and the natural frequencies and vibration of thin shell are controlled with LaSMP actuators.Thus,the research provides a new method for the distributed control of intelligent structures. |
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