A practical approach to parameter identification for a lightly damped, weakly nonlinear system

Abstract

Fluidelastic systems are often lightly damped and exhibit weak non-linear damping. The weak linear and non-linear damping forces have a significant effect on the long term behaviour of the system. However, parameter identification methods tend to concentrate on identifying the strongest forces. In this paper the applicability of two identification methods to a single degree of freedom fluidelastic system is investigated using experimental data. The system is weakly non-linear under the flow conditions and is prone to the fluidelastic instability (i.e. self excited limit cycle behaviour). The crucial effect of the weak damping forces on the system stability and post-stable behaviour has been demonstrated. The non-linearity detection and identification has been done using an analytic representation of the displacement signal (FREEVIB method) and subsequently a non-linear decrement method was used for comparison. The identified models were used to predict the global behaviour of the system in the form of limit cycle amplitudes and this has been used as an indication of accuracy. It was found that the non-linear decrement method yields superior predictions, but it suffers from the limitation that the functional form of the system must be known a priori. Therefore it is concluded that employing both methods together provides a more powerful approach for parameter estimation in a lightly damped system where weak non-linear damping plays an important role.

A Critical Review of Nonlinear Damping Identification in Structural Dynamics: Methods, Applications, and Challenges

“…The matrix pencil method was demonstrated to be the most effective approach in estimating damping over a set of input signals. In another study of heat exchanger tube arrays, Eret and Meskell [ 86 ] investigated the validity of two identification methods applied in a SDOF fluid elastic system by using experimental data. The free vibration analysis (FREEVIB) method was used to identify nonlinearity and was then compared with the nonlinear decrement method.…”

Effect of noise reducing components on nose landing gear stability for a mid-size aircraft coupled with vortex shedding and freeplay

“…The presence of fairings also requires an investigation into their influence on the aerodynamic load of the system. As nose landing gear assembly has reasonably high values of mechanical parameters (stiffness, damping), motion dependent fluid forces, which have usually crucial effect on the stability of weakly damped, light systems such as tube array in heat exchanger (see example in [10]), are not considered. An effect of motion independent fluid forces in a form of vortex shedding oscillator acting on the strut in the lateral mode is modelled.…”

Jump-based estimation for nonlinear stiffness and damping parameters

“…(2016) proposed a quasi-modal parameter estimation method for nonproportional hysteretic damping. Eret and Meskell (2008) integrated an analytical expression of displacements into a nonlinear decrement method to estimate parameters of a nonlinear single-degree-of-freedom system with light damping. Liu et al.…”