Characteristic Analysis Of Fluid Structure Interaction In Liquid-filled Pipe

Very often when mechanical operation applied to piped flowing fluid, a state transform will occur as a result inducing a hydraulic transient, or even waterhammer when situation is severe. As most industrial piping systems are weakly restricted, waterhammer will bring self-excited vibration of the piping system, which further engenders new hydraulic transients, therefore to produce a sophisticated coupling of different influences caused by fluid flow, pressure wave and pipe vibration. We name it fluid structure interaction, or simply FSI.Piping system has already seen a wide use in many fields of industry, and has acted an important role. However, FSI deteriorates the performance of the system, worsens the reliability of operation, affects on the precision of the instruments, and even blows out the pipe. Thus the research on this phenomenon is very important to understand the systems mechanical characteristics so that some effective methodologies can be adapted to avoid those bad effects, which could also be important in the industrial fields of aeronautics and space, petroleum chemistry, electric power, civil drainage, and so on.In this thesis we studied FSI in liquid-filled pipe and analyzed the straight and L-shaped pipes. The research work involves several aspects as follows:1. summarize and develop the linear differential equations of axial and transverse vibrations of piping systems filled with liquid. Herein we show that the axial and transverse movements are separable, and the effect of FSI is achieved by the interaction of the fluid and the structure of the piping.2.based on the axial and transverse vibration differential equations, considering Poisson coupling, the transfer matrixes of the axial and transverse movements are developed. According to the inextensible axes discrete model, L-shaped pipe is viewed as a series of end to end short straight pipe elements jointed together, therefore to establish the force balance equations and continuity equations, and the transfer matrix of L-shaped pipe in-plane vibration.3.After a detailed discussion on some practical numerical methods on the problem of boundary conditions, an effective way using transfer matrix to calculatethe modal frequency, modal vibration mode shape, and response in frequency domain is established. The numerical results are compared with these from concerned literature and from ANSYS, which proves the validity of our method. A further discussion on the influence of FSI on the system characteristics is followed. Our results show that FSI affects the system modal frequencies seriously, but mode shapes slightly.