Shimmy Phenomenon Research Articles

State Feedback Fuzzy Adaptive Control for Active Shimmy Damping

In the context of aircraft, shimmy is an oscillatory phenomenon of the landing gear mainly due to the tire and the landing gear structural dynamics. This phenomenon which can result in severe damage to the landing gear must be damped. This paper presents a new nose landing gear model including an actuator model and a simple tire/road interface description approximating the Pacejka model to allow the active damping of the shimmy phenomenon. Two state feedback control solutions, based on indirect and direct fuzzy adaptive theories, are also presented and compared with a more classic Proportional Integral Derivative (PID) solution. Results corresponding to different test scenarios and robustness analysis show that the proposed controllers are able to efficiently damp the shimmy phenomenon, unlike the PID controller.

유격을 고려한 노즈 랜딩기어의 비선형 쉬미 해석

In this paper, we studied the shimmy phenomena of an aircraft nose landing gear considering free-play. Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. This phenomena is caused by a couple of conditions such as low torsional stiffness of the strut, friction and free-play in the gear, wheel imbalance, or worn parts, and it may make an aircraft unstable. Free-play non-linearity is linearized by the described function for a stability analysis in a frequency domain, and time marching is performed using the fourth-order Runge-Kutta method. We performed the numerical simulation of the nose landing gear shimmy and investigated its linear and nonlinear characteristics. From the numerical results, we found limit-cycle-oscillations at the speed under linear shimmy speed for the case considering free-play and it can be concluded that the shimmy stability can be decreased by free-play.

Theory of the shimmy phenomenon

The shimmy phenomenon is the appearance of angular self-excited vibrations of the carriage wheels. Such self-excited vibrations provide a serious safety hazard for motion, which explains the great interest of scientists in this phenomenon [1–6]. This problem is most serious for the aircraft fore wheels.

The causes of the shimmy phenomenon

The causes of the shimmy phenomenon

Non-linear analysis of a typical nose landing gear model with torsional free play

One of the problems faced by the aircraft community is the landing gear dynamics, especially the shimmy. Non-linear behaviour of landing gear makes the evaluation of the shimmy phenomenon more complex and its prediction more difficult. Notably the non-linearities in landing gear torsional free play tend to destabilize the landing gear, whereas the frictional non-linearity dissipates energy and thus increases the landing gear stability. This article presents the study of the shimmy instability of a typical nose landing gear model developed based on the Li formulations with torsional free play. Finally, the study has been performed to postpone the dynamic instability by introducing magneto rheological fluid-based damper.

Analysis of Shimmy Phenomenon of Two-Wheeled Vehicles with a Three-Degree-of-Freedom Model

Analysis of Shimmy Phenomenon of Two-Wheeled Vehicles with a Three-Degree-of-Freedom Model

Active Shimmy Damping Using Direct Adaptive Fuzzy Control

The shimmy phenomenon is a self-excited limit cycle oscillation occurring in many physical rolling systems, particularly in aircraft nose landing gears (NLG). This paper presents a new active damping controller developed in the context of the European DRESS (“Distributed and Redundant Electro-mechanical nose gear Steering System”) project for avoiding the shimmy oscillation. The controller based on the direct adaptive control approach, consists of two terms: the fuzzy adaptive term approximates the feedback linearization control law, and the stabilizing control term compensates the structural modelling error. The closed-loop system stability is proven by using Lyapunov theory. Simulation results corresponding to different test scenarios show that the proposed controller is able to effectively damp the shimmy phenomenon.

Lateral Response of Nonlinear Nose Wheel Landing Gear Models with Torsional Free-play

Nose-wheel landing gears can, under certain conditions, exhibit instability in lateral dynamics, causing divergent coupled lateral flexural and torsional oscillations called shimmy. The stability of the system depends on the dynamic characteristics of the gear and tires, nonlinearities in the system, and vibratory modes of the vehicle as a whole, as well as the degree of coupling that exists between them. Shimmy may be caused by a number of conditions such as low torsional stiffness of the strut, free play in the gear, wheel imbalance, or worn parts. Free play in the steering degree of freedom has the potential to significantly reduce the divergent shimmy velocity. Nonlinear behavior of landing gear makes the evaluation of the shimmy phenomenon more complex and its prediction more difficult. This work presents a study of the shimmy instability of a three-degree-of-freedom simplified nose-wheel landing gear model with linear flexible tire model and nonlinearities arising out of torsional free play. Response results are presented for a typical range of values of various problem parameters. Numerical studies bring out several interesting features of the shimmy and its dependence on free play.

History of Stability of Railway and Road Vehicles

Stability of running of vehicles is one of the important design criteria of railway and road vehicles. Railway vehicle stability is based on kinematics as well as contact mechanics. It reaches back to the 19th century and had its first hey-day with the work of Carter and Rocard on stability of locomotives. A rediscovery of their knowledge, which seemed to have been forgotten, was inevitable due to increased vehicle speeds since the early Fifties. — Though investigations on road vehicle stability only began approximately in 1930 with the treatment of the shimmy phenomenon, realistic solutions were available at the same time as for railway vehicles. Besides considering historical aspects we discuss in the paper links which exist between both approaches; open questions are described.

Modeling of shimmy phenomenon on steering system of large size vehicle Toshiki Ezoe, Ichiro Kageyama (Nihon University), Fujio Momiyama, Kiyoaki Miyazaki (Hino Motors, Ltd.)

Modeling of shimmy phenomenon on steering system of large size vehicle Toshiki Ezoe, Ichiro Kageyama (Nihon University), Fujio Momiyama, Kiyoaki Miyazaki (Hino Motors, Ltd.)

Analysis of steering shimmy accompanied by sprung mass vibration on light duty truck — Fundamental mechanism

Steering shimmy phenomena are classified into two groups according to vehicle speeds. One is self-excited vibration at low vehicle speeds, and the other is forced vibration at high speeds. Shimmy on a light duty truck has been considered as that of self-excited vibration. However, it causes vibration not only on the steering system but also on the cabin, with a large amplitude at relatively high speeds. The phenomenon was analyzed by performing vehicle tests and numerical simulations using simplified models. As a result, the phenomenon was found to be self-excited vibration basically caused by two closed-loop vibration mechanisms.

Shimmy Phenomenon on Steering System of Two-Wheeled Vehicles.

The shimmy that appears in two-wheeled vehicles has been regarded as a self-exited vibration, but this has yet to be clearly proven. Here, we provide experimental and theoretical analyses based on three experiments. It is found that the shimmy phenomenon can be clearly defined by the experimental analyses. It is impossible for previous theoretical models to describe the shimmy phenomenon. Therefore, we propose a new tire model which includes the dynamics of side force and self-aligning torque. From the results of the theoretical analyses, it is found that the model describes the shimmy phenomena not only qualitatively but also quantitatively. Furthermore we analyze the influence of the design parameters of the tire and their main influences on shimmy. Consequently, it is clarified that cornering stiffness, tire lateral and torsional rigidity, relaxation length of lateral displacement of contact patch, tire lateral damping and moment of inertia around the steering axis all have strong influences on shimmy.

Non-linearities in Road Vehicle Dynamics

SUMMARY In the study of lateral vehicle dynamics with the objective to enhance stability and handling qualities, non-linear aspects may have to be included to cover also larger lateral accelerations and amplitudes. The paper treats whole vehicle motions and relative motions of vehicle subsystems. In particular, single car stability, also in the large, is discussed as well as the shimmy phenomenon and the car-trailer instability.

A Comparison of Tyre Representations in a Simple Wheel Shimmy Problem

SUMMARY A simple system capable of wheel shimmy is analysed in three different ways and the results are compared. The tyre in each case is taken to be representable by a “taut string”, and the three ways involve (a) developing a digital tyre simulation which operates sequentially with a digital simulation of the mechanical system, (b) representing the tyre responses by linear constant coefficient differential equations derived empirically to match the string responses, and (c) as in (b) but employing fundamentally derived equations which approximate the exact string responses. The approximations are shown to give good results at reduced frequencies typical of the wheel shimmy phenomenon.

Synthesis of tire equations for use in shimmy and other dynamic studies

.4 system of transfer functions relating the cornering force and aligning torque of a rolling pneumatic tire to its yaw angle and lateral displacement are developed from experimental and theoretical frequency response curves. These transfer functions consist of ratios of polynomials in the Laplaciari variable s, which lead to a system of linear constant coefficient differential equations. The resulting equations have the advantage of both simplicity and accuracy and are ideally suited for use in dynamical analysis such as the study of wheel shimmy phenomena. These differential equations, along with the corresponding experimental frequency response curves, are compared with those derived from the widely used Moreland tire theory. This comparison reveals a number of inadequacies in the Moreland theory.

Analysis of the Shimmy Phenomenon

The shimmy phenomenon has been treated as a non-linear problem which is solved using the method of equivalent linearization and also with the aid of an analogue computer. Three non-linear elements are considered: the tyre characteristics, the Coulomb friction in the king-pin bearings, and clearance in the wheel bearings. The theory is substantiated by experiments with a test vehicle and a mechanical model. Two different kinds of shimmy appear to exist, one originating from the tyre elasticity and the other from the gyroscopic coupling. Results showing the effect of changing a number of important parameters on the shimmy phenomenon are presented.