Overview of Numerical Methods for Predicting Flow-Induced Vibration

Abstract

A predictive analysis of an heat-exchanger design against severe vibration and wear has to cope with experimental data on flow-induced vibration and fretting wear, together with the use of analytical and numerical methods for predicting linear and nonlinear tube response. This paper describes a general approach of the problem currently under development at C.E.A. Attention is especially paid to some key aspects of the numerical techniques, namely, the modelization of flow-induced forcing functions and the modelization of impact and sliding at tube-support gaps. These topics are exemplified by numerical results related to some typical situations including the case of random vibration induced by flow turbulence and fluidelastic vibration.

Methodological advances in predicting flow-induced dynamics of plants using mechanical-engineering theory

“…A proper modeling, as described above, requires going from the modeling of the flow pattern in the SG or PC to the modeling of the dynamic response of individual plants or tubes, taking into account local effects at even smaller scales. These slender individual components have several, and quite different, scales of length: their length-to-diameter ratio can be of the order of 100:1 or even 1000:1, and even smaller length scales are also involved, such as gaps at the supports of SG tubes, of the order of 0.1mm (Axisa et al, 1988), or the thickness of leaves, which play a role in the stiffness of interplant contact (Doaré et al, 2004). In both systems, the ratio of large-to-small scales can exceed 10,000.…”

“…For PCs, this requires the use of plate models for leaves, spring models for contacts and beam models for stems (Niklas, 1992). In SGs, beam models and nonlinear spring models are necessary (Axisa et al, 1988). These can also be used for nonlinear contacts between plants (Doaré et al, 2004).…”

Contact Force Model for a Beam With Discretely Spaced Gap Supports and Its Approximated Solution

“…To consider the contacting force acting on the beam as an external force, the equation of motion can be written as follows [1,3,8,10,12]: where gi and ki c denote the i th gap distance and i th support spring constant, respectively. Note that Eq.…”

“…Significant model reductions can be made using a finite number of normal modes [1,10], and computation times can be drastically reduced for a system with a large degree of freedom. However, when stiff springs are prescribed, it is recommended that the high modes are not truncated since the high frequency impact cannot be described with insufficient modes [3].…”

“…Structures subjected to dynamic contact exist in many industrial and engineering fields [1][2][3][4][5][6][7][8][9][10][11][12]. In the nuclear industry, there are several regularly occurring examples of dynamic contacts, such as U tubes in the heat exchanger and fuel rods in the reactor of nuclear power plants.…”