Reserch On Three-Dimensional Vibration Characteristics And Control Of Multi-Gyro-Coupled Fluid-Conveying Pipe

As a fundamental structure,fluid-conveying pipe is widely used in various engineering fields such as nuclear engineering,aerospace science and agriculture.As a typical fluid-structure interaction(FSI)system,when the flow velocity exceeds a certain threshold,it can cause strong vibration,induce noise and even lead to pipe rupture,resulting in enormous losses.To ensure the safe and stable operation of pipe in various fields,it is necessary to conduct in-depth research on their dynamic characteristics and vibration control issues.Due to the axial motion characteristics,the pipe belongs to a type of gyroscopic system,and circular motions such as rotating and spinning motions can also cause gyroscopic effects.The coupling of these gyroscopic motions makes the dynamic behavior of the pipe system more complex and interesting.In this paper,a novel triple-gyroscopic system is proposed in Chapter 2,where the fluid-conveying pipe undergoes both spinning and rotating motions simultaneously.Based on the Rayleigh beam model,the coupled differential equations for the in-plane,out-of-plane transverse and axial vibration are derived,and gyroscopic forces of spinning speed,rotating speed and flow velocity are fully consideration.Theoretical methods are used to obtain the three-dimensional vibration frequencies and stability evolution of the pipe,revealing the effects of triple-gyroscopic and centrifugal effects.The influence of geometric and physical parameters of the pipe is also discussed,and the three-dimensional backward whirling and forward whirling precession modes of the pipe are simulated.Chapter 2 will help deepen the understanding of multiple gyroscopic coupling dynamics,provide theoretical and design references for engineering gyroscopic structures,and lay the foundation for subsequent research.Phononic Crystals(PCs)are a class of novel periodic composite materials,which offer new avenues for vibration control of pipe through band gap(BG)properties.Chapters 3 and 4 of this paper explore the vibration control mechanisms of gyroscopic PC pipe,and delve into an in-depth study of vibration suppression in non-spinning,spinning and rotating pipes.Chapter 3 establishes the bending wave equation of gyroscopic pipe based on the classical Euler-Bernoulli(E-B)beam model.Band structure,BG distribution,and frequency response function(FRF)of system are obtained by the Spectral Element Method(SEM)and Transfer Matrix Method(TMM),and the influence of key parameters is discussed.When the pipe has spinning motion,the periodic pipe becomes a two-dimensional PC structure,producing two bending waves in orthogonal transverse directions to form a planar PC structure.The BG structure,combined with the FRF and vibration waveform,reveals an important mechanism:for gyroscopic PC pipe,there exist two pseudo BGs in the two transverse directions,which is not present in non-spinning PC pipes.The effective BG region where the two transverse waves truly attenuate is actually located in the overlap region of the pseudo BGs.Furthermore,compared to traditional TMM,SEM can more effectively analyze the BG problem of PC structures.Chapter 3 on the dynamics of gyroscopic PC pipes provides a deep theoretical basis for the vibration control of engineering gyroscopic pipe.In Chapter 4,the rotating motion of pipe is considered.Based on the Rayleigh beam model,a system of coupled differential equations for the in-plane,out-of-plane transverse and axial vibration of pipe are established,where the axial and in-plane equations are coupled.SEM and TMM are employed to perform a comprehensive analysis of the band structure,BG distribution,FRF and vibration attenuation of the rotating PC pipe.The effects of several key parameters are also discussed in detail.Some important conclusions are drawn:the periodic pipe possesses two types of BGs,namely the transverse and axial vibration BGs.The width of the axial vibration BG is much wider than that of the transverse vibration BGs.The BG distribution of in-plane and out-of-plane transverse vibration hardly changes at low rotating speeds,while the difference in the BG distribution becomes more pronounced as the rotating speed increases.Chapter 4 provides useful guidance for parameter design and vibration suppression analysis of rotating pipe.In summary,this paper analyzes the frequencies and modes of multi-gyro coupled fluid-conveying pipe and systematically explores the vibration suppression characteristics of dual-gyro PC pipes,including their band structure,BG distribution,FRF and attenuation pattern.These findings are expected to provide theoretical references for the dynamic design of complex motion fluid-conveying pipes in engineering and offer technical approaches for vibration suppression of pipe.