Time-Domain Modeling of the Random Vibrations of Tubes Subjected to Turbulence-Conveying Flows

Abstract

The vibrations of multi-supported tubes subjected to flow excitation have been the subject of active research for many years, in particular connected with the critical design of heat exchangers and fuel bundles of nuclear power facilities. Because tubes are often loosely supported, their nonlinear dynamics are conveniently addressed through time-domain numerical simulations, for the predictive analysis with respect to wear and fatigue. Turbulence is one of the main excitation mechanisms which drive tube vibrations. We recently revisited the problem of random excitation generation in the time domain, for transverse flows. A new simplified an efficient technique was developed, which properly emulates the spectral and spatial features of the turbulence force field. Results were successfully compared with those from another generation method based on the classical work by Shinozuka and co-workers. In the present paper, we extend our previous work by modeling the time-domain random excitation from flows which display a significant axial velocity component, leading to the convection of turbulence fluctuations. This problem has been addressed by many authors in the past, mainly focusing on linear analysis in the frequency domain, for flow-excited plates, pipes and tubes. Here, for the purpose of nonlinear analysis, we focus on two techniques for generating time-domain turbulence excitations which properly account for the effects of the axial transport term in convective flows. We start by extending our original random force generation method, in order to emulate axial turbulent flows. For the purpose of physical discussion and computational efficiency evaluation, we also implemented an updated version of Shinozuka’s excitation generation technique. We discuss the use of random forces applied at fixed locations, but also investigate the use of axially convected travelling forces. The practical significance of the cross-spectral convection term is evaluated for pure axial and mixed flows. Finally, because time-domain dynamical simulations of practical interest are usually two-dimensional, we discuss the correlation of the orthogonal random forces generated along the motion directions, when simulating two-dimensional turbulence fields.