Passive suppression of internal axial-flow-induced vibrations of a cantilevered pipe discharging fluid using non-linear vibration absorber: a numerical, analytical and experimental study

Abstract

The phenomenon of internal axial-flow-induced vibrations is one among many different types of fluid-structure interactions and is present in many engineering applications such as systems of pipes conveying fluid in heat exchangers, water supply networks and in the oil & gas industry. Since, in their myriad of applications, these systems are susceptible to flow-induced vibrations which can lead to excessive noise, leaks and fatigue failure, the need to suppress these vibrations becomes imperative. In this context, the use of a recently conceived class of suppressors called Non-linear Vibration Absorbers (NVAs) emerges as a promising alternative. The research herein described will numerically, analytically and experimentally address the problem of passive suppression of vibrations induced by internal axial flow in a vertical cantilevered pipe discharging fluid. The device to be utilized, named rotative NVA, is composed of a mass connected to the extremity of a rigid bar which is, in turn, hinged to the main structure by means of a rotational damper. It is defined by its mass, radius and damping coefficient. For the numerical and analytical studies, a non-linear mathematical model for a vertical cantilevered pipe discharging fluid coupled to a rotative NVA will be developed using the extended Hamilton's principle. Aiming at reducing the number of degrees of freedom of the Reduced-Order Model (ROM), the resultant equations of motions will be discretized using non-linear normal modes of vibration. It is worth noting that this modeling approach has not been found in the literature, to the best of the author's and of the advisor's knowledge. With the ROM, a sensitivity analysis of the suppression effectiveness with respect to the rotative NVA's parameters and to its attachment position will be carried out. To that end, objective criteria for both the suppression and associated robustness will be conceived. For the experimental studies, physical models for both the pipe discharging fluid and for the rotative NVA will be designed and constructed. The design of the rotative NVA's physical model will allow for the free varying of its mass, radius and damping coefficient, as well as of its placement position. At the end of this research, tables, maps and plots showing the device's suppression effectiveness as a function of the aforementioned parameters will be obtained and the numerical results will be compared with experimental data. It is important to mention that, to the best of the author's and of the advisor's knowledge, this particular problem of passive suppression has not been found in the literature, which provides novelty to the work herein proposed. (AU)