Dynamic Analysis Of Fluid-Structure Interaction Of Pipe Systems Conveying Fluid

Pipe vibrations induced by fluid-structure interaction(FSI)have been with us since time immemorial.A simultaneous treatment of fluid fluctuations and pipe vibrations is necessary for accurately analyzing the structural vibrations,fluid transients and anchor and support forces of a flexible pipe system,which are important for the optimized design of pipe systems.Therefore,during the early design phase,it is crucial to accurately analyze and mitigate the FSI behaviors of conveying-fluid pipes in the fields of marine engineering,nuclear and electric power industries,petroleum and chemical process industries.And the importance of FSI in pipe systems conveying fluid has led to an extensive and constantly expanding literature.This thesis summarizes the state of the models and methods.And the pipe layouts and the influences of fluidic and structural parameters on the dynamic characteristics of pipes are also summarized.Based on the development of dynamic analysis of pipes and the problems actually occurred in practical pipe system,the research is primarily focused on the following contents.Firstly,several improved 14-equation FSI models for liquid filled pipes are established.In the perfect model,the effects of pipe wall radial stress and displacement,fluid velocity and pressure are taken into account.Using the proposed models,it is easy to calculate the nature frequencies and frequency responses of both the normal water-filled pipe and high pressure and velocity steam pipe.Therefore the application of FSI models is extended.Secondly,based on the balance of displacement and force of branch point,the universal model for solving free and forced vibration response of branch pipeline with one branch point(tee,cross pipe and arbitrary-way pipe included)and multi-branch point(the branch pipes are distributed along the main pipeline)are also obtained.Here,using the absorbing transfer matrix method,the point transfer matrix,representing the influence of branched pipes at the junction on the dominant pipeline,can be “absorbed” by the dominant chain.Based on this method,the branches and dominant pipe can be modeled separately.And the dimensions of global transmission matrix are independent of the number and shapes of the branched pipes.This gives transfer matrix method(TMM)greater flexibility and higher efficiency in solving more branched pipe systems.Thirdly,in order to explore the precision of calculation,the dimensionless FSI equations are presented.A provisional guideline is formulated which helps to judge when the calculation results are precarious.Then a method is proposed to avoid the disadvantages as data over flow and the distortion of higher frequencies.Fourthly,a vibration-to-sound conversion method(VSCM)used for predicting valve noise is proposed.To facilitate the difficulties for conversion the pipe wall vibration,the conversion loss(CL)is employed to quantify relationship between the pipe internal sound pressure level and pipe wall acceleration level.The experiment is carried out in a pipe system with a high pressure air tank and a low pressure air tank.Comparison of experimental data with calculation results proved that the present approach should give reliable estimates of valve noise in practical situations,especially at 1/3-octave band.VSCM is very convenient and is a non-invasive method because it avoids drilling through the pipe wall in contrast to most existing methods.Fifthly,the models of pipe accessories such as tapering pipes,valves,flexible hoses,flanges and clamps are established.In addition,the arbitrary constraints are simplified to various fluidic boundary impedance conditions,translational and rotational damping springs.Therefore,it is possible to predict the dynamic characteristics of the common fluid-filled pipe section such as straight pipe,bend,branches with arbitrary supports and the complex pipe systems consisted by these sections.And results from the present approach are validated against experimental and numerical data and other available analytical solutions.Sixthly,the last,based on the improved models and algorithms,the influence laws of supports,structural properties and fluid parameters on the dynamic response and natural frequencies of pipeline are comprehensively summarized and critically evaluated utilizing the dimensionless method,representing some fresh results which may be useful for both researchers and practitioners.