Alberto Doria

The Effect of Tyre and Rider Properties on the Stability of a Bicycle

To work towards an advanced model of the bicycle-rider-environment system, an open-loop bicycle-rider model was developed in the commercial multibody dynamics software ADAMS. The main contribution of this article to bicycle dynamics is the analysis of tyre and rider properties that influence bicycle stability. A system identification method is used to extract linear stability properties from time domain analysis. The weave and capsize eigenmodes of the bicycle-rider system are analysed. The effect of tyre properties is studied using the tyre’s forces and torques that have been measured in several operating conditions. The main result is that extending simplified models with a realistic tyre model leads to a notable decrease in the weave stability and a stabilization of the capsize mode. This effect is mainly caused by the twisting torque. Different tyres and tyre inflation pressures have little effect on the bicycle’s stability, in the case of riding straight at a constant forward speed. On the other hand, the tyre load does have a large effect on bicycle stability. The sensitivity study of rider properties shows that body stiffness and damping have a small effect on the weave and capsize mode, whereas arm stiffness destabilizes the capsize mode and arm damping destabilizes the weave mode.

The plasma system of RFX

Abstract The “plasma system” of RFX includes the first wall, the vacuum vessel, the stabilizing shell, the vacuum and gas injection system, the remote handling system and the relevant auxiliary plants (cooling, baking, glow discharge cleaning, etc.). Since no limiters are provided, the full energy and particle flux from the plasma must be absorbed by the first wall. Taking into account the significant power losses from the plasma in nominal conditions, the high peaking factors due to “dynamo” effects, field errors and plasma shift, and possible sudden losses of configuration, the first wall was designed to be able to withstand high thermal loads. Also the need to use a low Z plasma-facing material led to the choice of pure, microcrystalline graphite. The wall is subdivided into 2016 tiles, individually clamped to the vacuum vessel by means of a special bayonet system suitable for remote handling. The remote handling system, which was designed to facilitate the replacement and inspection of all 2016 graphite tiles, comprises an arm with five degrees of freedom, two grippers for different tasks, two television cameras, and a control system for automatic or teleoperated motions. The vacuum vessel is a stiff sandwich structure with 72 solid poloidal rings bearing the first wall tile supports. It is cooled by CO 2 flowing through the interspace; baking up to 350°C is also provided by means of heating cables attached to the outer surface. The vessel is closely surrounded by a shell, giving passive stabilization against magnetohydrodynamic modes; the shell is made of aluminium alloy, 65 mm thick, and, to allow fast field penetration, it is electrically subdivided into four sections, by means of epoxy-glass layers. The RFX vacuum system is a combination of 12 cryopumps and 12 turbomolecular pumps, giving a total pumping speed at the vessel of 4500 1 s −1 for nitrogen. Because of the short plasma pulse duration, the gas injection system must produce high gas throughputs (up to 700 Pa m 3 s −1 ) with very short response times (some milliseconds). The glow discharge cleaning system utilizes four anodes toroidally equispaced and located at the centre of the vessel minor cross-section, is r.f. assisted and allows wall conditioning in hydrogen, helium or methane. In this paper we present the basic concepts underlying the main design choices and then, for the main components and plants, we describe the significant design features, as well as the methods and results of the structural, thermal and electromagnetic calculations. We also deal with preliminary tests on prototypes and with the most important manufacturing technologies, production cycles, and assembly procedures. Finally, the preliminary design of the control system for the plasma main electromagnetic parameters is presented.

DYNAMIC PROPERTIES OF MOTORCYCLE AND SCOOTER TIRES: MEASUREMENT AND COMPARISON

Summary Results of an experimental research program dealing with motorcycle and scooter tires are presented. Experimental tests were carried out by means of a rotating disk test machine, which is particularly suited to test tires in the presence of large camber angles. First, the capabilities of the rotating disk machine are discussed and results are compared with the ones obtained by means of other test machines. Then the properties of several motorcycle and scooter tires are presented and compared. The advantage of presenting results in terms of camber and sideslip stiffness is highlighted. The effect of tire working conditions (inflation pressure, load and temperature) is analyzed. Finally the measurement of tire torques is discussed and some results dealing with self-aligning, twisting and rolling resistance torques are presented.

A simple numerical approach for optimum synthesis of a class of planar mechanisms

Abstract In this study a numerical method for optimum synthesis of planar mechanisms, generators of functions, paths and rigid motions, is presented. Design parameters have wide variability ranges, inside which first guesses, demanded by the iterative minimization procedure, can be chosen at random. Kinematic analysis is carried out by decomposition of the mechanism into Assur groups; mechanism assembly is managed by the construction of a proper penalty function. Optimization is carried out by using a non-derivative and a quasi-Newton method in series. Some optimum design examples are presented to illustrate the power of the method.

Design of synchronous reluctance motor for hybrid electric vehicles

The paper deals with the design of a synchronous reluctance motor suited for hybrid electric vehicles. At first, the focus is on rotor design. In particular an useful approach is proposed to choose the proper angles of the flux-barrier ends with the aim of reducing the torque ripple due to the slot harmonics. In the second part a comparison among different rotor arrangements (one, two and three flux-barriers per pole) is presented. Furthermore an improvement in terms of low ripple and high average torque is given thanks to the ”Machaon” configuration. The third part of the paper deals with the analysis of the improved layout. The current vector control method used to maximize the torque according to the voltage and current constraints is shown. Saturation effects are taken into account. The impact of electrical design on the mechanical characteristics of the rotor (and natural frequencies) is discussed as well. At last the predicted mechanical characteristics of the reluctance motor are presented: torque versus speed behavior, power losses and power factor. The efficiency map of the machine based on Finite Elements analysis is also reported.

Frequency-domain method for evaluating the ride comfort of a motorcycle

In many European towns, the demand for fast and efficient mobility is frequently satisfied by means of two-wheeled vehicles. The improvement of comfort of two-wheeled vehicles used by tired and busy workers can increase safety in ground transport. Nowadays, multibody codes make it possible to predict the ride comfort of two-wheeled vehicles by means of time-domain or frequency-domain simulations. Comfort indices can be developed by post-processing the results of numerical simulations. This task is difficult, because the indices should depend on vehicle characteristics and should be independent of road quality and vehicle speed. Poor quality roads may generate nonlinear effects. Speed influences the trim of the vehicle and the wheelbase filtering, which takes place because the same road unevenness excites the front and rear wheel with a time delay which depends on the vehicle’s speed. In this paper, the comfort of two-wheeled vehicles is studied by means of a frequency-domain approach. The wheelbase filtering is averaged considering typical missions of the vehicle. The missions are journeys with a forward speed that assumes different values according to a probability density function. Indices of comfort are calculated taking into account the human sensitivity. The examples show that the proposed comfort indices depend on suspensions’ characteristics and, hence, are useful design tools. Finally, some time-domain calculations are carried out to give emphasis to nonlinear effects and to show the limits of the frequency-domain analysis.

A Spatial Mechanism for the Measurement of the Inertia Tensor: Theory and Experimental Results

This paper deals with the problem of measuring the inertia tensor of rigid bodies. An original approach is adopted, different from classical modal analysis techniques. The rigid body is forced by a spatial mechanism to rotate around different axes. Once the mechanism is calibrated, i.e., its inertia and stiffness matrices are known, the inertia tensor of the rigid body may be determined by measuring the frequencies of the small oscillations around the selected axes and then solving a least-squares identification problem. Two prototypes of the spatial mechanism were built. The first was used to perform tests and to measure the inertia tensor of some compressors for domestic refrigeration. The second was constructed to measure the inertia tensor of large mechanical systems.

Design of Synchronous Reluctance Motor for Hybrid Electric Vehicles

This paper deals with the design of a synchronous reluctance motor suited for hybrid electric vehicles. The focus is mainly on rotor design: the angles of the flux barrier ends are chosen with the aim of reducing the torque ripple due to the slot harmonics. A comparison among different rotor arrangements (one, two, and three flux barriers per pole) is presented. Furthermore, an improvement in terms of low ripple and high average torque is given owing to the “Machaon” configuration. The current vector control method is used to maximize the torque according to the voltage and current constraints, taking into account the saturation effects. The impact of the electrical design on the mechanical characteristics of the rotor (natural frequencies) is discussed as well. At last, the predicted mechanical characteristics of the reluctance motor are presented: torque versus speed behavior, power losses, and power factor. The efficiency map of the machine is also reported in the whole operating region.

Identification of the mechanical properties of bicycle tyres for modelling of bicycle dynamics

Advanced simulation of the stability and handling properties of bicycles requires detailed road–tyre contact models. In order to develop these models, in this study, four bicycle tyres are tested by means of a rotating disc machine with the aim of measuring the components of tyre forces and torques that influence the safety and handling of bicycles. The effect of inflation pressure and tyre load is analysed. The measured properties of bicycle tyres are compared with those of motorcycle tyres.

Experimental and numerical analysis of the influence of tyres’ properties on the straight running stability of a sport-touring motorcycle

The behaviour of a motorcycle on the road is largely governed by tyre properties. This paper presents experimental and numerical analyses dealing with the influence of tyre properties on the stability of weave and wobble in straight running. The final goal is to find optimal sets of tyre properties that improve the stability of a motorcycle. The investigation is based on road tests carried out on a sport-touring motorcycle equipped with sensors. Three sets of tyres are tested at different speeds in the presence of weave and wobble. The analysis of telemetry data highlights significant differences in the trends of frequency and damping of weave and wobble against speed. The experimental analysis is integrated by a parametric numerical analysis. Tyre properties are varied according to the design of experiments method, in order to highlight the single effects on stability of lateral and cornering coefficient of front and rear tyres.