| Pipe conveying fluid have been widely used in aviation industry,nuclear engineering,chemical coolers,oil exploitation,micro-/nano-sensors and other fields.Their stability and vibration are key issues in academic research and practical engineering.It is observed that when the flow velocity of fluid at a higher velocity or with some certain disturbance,the pipe may have strong buckling or vibration,which will produce large noise and then threaten the safety of environmental equipment.Therefore,it is of great significance to explore the vibration suppression of fluid-conveying pipe.As typical artificial structural composites,phononic crystals(PCs)and acoustic metamaterials(AMs)have excellent functions in controlling the propagation of elastic waves.Inspired by the theory of PCs and AMs,the pipe is designed as a periodic structure,and the spinning motion is considered.The natural properties and vibration self-suppression characteristics are investigated by employing the spectral element method.The research contents are as follows:(1)Based on the Timoshenko beam model,the dispersion equation of the periodic pipe is established.Combining the spectral element method with the finite element method,the natural frequencies,vibration modes,band gap(BG)regions and vibration attenuation shapes are further derived.It is found that the number,physical and geometric properties of the substructure as well as the fluid-structure interaction have significant impact on the natural frequency,mode shape and BG performance of the PC pipe.(2)A model of spinning fluid-conveying pipe composed of different materials is established.The transverse free vibration and BG characteristics of the spinning periodic structure are discussed by using the two-dimensional spectral element method.It is seen that there are different pseudo-BGs in the two transverse directions,and the effective BG is actually located in their overlapping region,in which the vibration is truly self-suppressed.The spinning motion will impair the vibration reduction of the PC pipe.Furthermore,the effects of element number,flow velocity and other geometric parameters on the natural frequency and coupled BG are studied.(3)According to Hamilton’s principle,the differential equation of the orthogonal transverse vibration of the spinning Timoshenko pipe conveying fluid is derived.Based on the two resulting of transverse waves,a dynamic two-dimensional local resonance(LR)pipe structure is established.The additional centrifugal force due to spin and the traditional inertial force are introduced into the local resonators.The research results show that the current LR pipe has a great contribution to the formation of low-frequency BGs below 500 Hz,which is conducive to the vibration suppression of large structures in engineering.The numerical results also show that various physical,geometric and motional parameters have significant effects on the low-frequency BG of the pipe.(4)A motional two-dimensional hybrid Bragg-LR meta-pipe model is developed.The pipe is composed of alternating axial materials,and a double-layer ring is used to periodically surround the pipe,which generate Bragg scattering and local resonance at the same time.The research results reveal the formation of hybrid BGs in this motional meta-structure,and further prove their complex evolutions with the location,number and geometry of local resonators and the pipe material.The influence of motion characteristics on the hybrid BG is discussed and compared with the behavior of Euler-Bernoulli model.This study provides a more in-depth explanation for the interaction between Bragg and LR BGs,especially for the vibration and noise reduction of rotor and pipe conveying fluid structure.(5)Based on the Timoshenko and Euler-Bernoulli beam models,the dimensionless partial differential equations of the spinning functional gradient(FG)nanotube conveying fluid are derived respectively.The natural properties of the spinning FG Timoshenko nanotube are studied,and the effects of motion parameters,nonlocal parameters,temperature difference and power gradient index of different models on the natural frequency are further discussed.The BG of the Euler-Bernoulli model is analyzed by spectral element method.It is observed that the influence of spinning motion and fluid-structure interaction(FSI)weakens the vibration suppression of nanotube in the dimensionless BG analysis.The numerical results also show that various physical and geometric parameters have a significant impact on the effective BGs of the nanotubes,which has developed new technical approaches for the vibration reduction of meta-structures in practical engineering. |
