Modeling Stiffness and Damping in Rotational Degrees of Freedom Using Multibond Graphs

A contribution is proposed for the modeling of mechanical systems using multibond graphs. When modeling a physical system, it may be needed to catch the dynamic behavior contribution of the joints between bodies of the system and therefore to characterize the stiffness and damping of the links between them. The visibility of where dissipative or capacitive elements need to be implemented to represent stiffness and damping in multibond graphs is not obvious and will be explained. A multibond graph architecture is then proposed to add stiffness and damping in hree rotational degrees of freedom. The resulting joint combines the spherical joint multibond graph relaxed causal constraints while physically representing three concatenated revolute joints. The mathematical foundations are presented, and then illustrated through the modeling and simulation of an inertial navigation system; in which stiffness and damping between the gimbals are taken into account. This method is particularly useful when modeling and simulating multibody systems using Newton-Euler formalism in multibond graphs. Future work will show how this method can be extended to more complex systems such as rotorcraft blades' connections with its rotor hub.Fondation Airbus Grou

Analytical modeling of rotor-structure coupling using modal decomposition for the structure and the blades.

This paper presents a linear semi-analytical model that is able to predict complex rotor-structure coupling phenomena and their stability. It was primarily designed so as to gain a better physical understanding of this kind of aeroelastic instabilities, triggering at higher frequencies than air and ground resonance, and involving several blade and structure modes. The analytical approach has a two-fold advantage since fast parametric studies can be carried out and a term-by-term analysis of the helicopter stability equations can be performed. In order to represent the elasticity of the structure and the blades, a modal decomposition method is introduced. The modal basis for the structure can either be obtained by a Finite Element Method or rigid degrees of freedom can be inputted. For the blades, a preliminary finite element routine is run, allowing for varying characteristics along the span. Blade offsets are introduced, and an unsteady aerodynamic model is implemented. The modal basis of the coupled system is then computed and a partial validation is done with HOST (Helicopter Overall Simulation Tool), a comprehensive aeroelastic code. Except for the built-in twist and the non-circulatory terms which are taken in a different manner in HOST and the presented model, the linearization results are similar. Future work using this model includes investigation of the helicopter stability thanks to parametric studies

Designing redundant metering valves for hydraulic actuators under mixability and low cost-constraints

This article deals with the design of redundant metering valves for mechanically signalled hydraulic actuators. The final aim of the work is to manufacture a new low-cost valve in replacement of the existing expensive valve with an additional leakage requirement in case of seizure. The new valve must ensure the same closed-loop behaviour of the actuator. The article presents the design of the valve according to the actuator specifications and to a criterion of mixability (capacity to replace the existing valve by a new one). The valve pre-design is based on the common sharp edges and rectangular orifice slots combined with a serial restrictor inserted on the supply line. After partial experimental validation, the proposed design process points out the interest of using a trapezoidal slot in order to get the required speed gain over the whole valve opening range. The proposal is validated through the experimental measurement of the actuator no-load speed as a function of the valve opening

Multi-physic system simplification method applied to a helicopter flight axis active control

A helicopter flight axis control, which is a complex multi-physic system, is modelled using an energetic based graphical tool: the Energetic Macroscopic Representation. Elements of the system are mainly composed of passive technologies and their number tends to increase year after year to improve the pilots comfort by adding new functions. A new methodology is proposed to transform the system into a new active one by replacing some hydro-mechanical elements by a new controllable active mechanical source. The challenge is to simplify the flight control architecture while preserving the global behaviour of the system

Minimisation des oscillations d'un système mécanique excité à l'aide d'une commande semi active. Application à un atterrissage d'hélicoptère

Cet article présente une étude portant sur la minimisation de la réponse dynamique d'un système mécanique soumis à une excitation extérieure en pilotant son comportement. Dans un premier temps, on expose de manière générale comment on peut envisager de minimiser les amplitudes de la réponse d'un système excité. Ensuite on étudie le cas concret d'un atterrissage d'hélicoptère pour lequel on analyse comment la régulation de la dissipation de l'énergie due à l'impact de l'atterrissage, permet de minimiser la réponse de la poutre de queue. Puis on analyse les différentes méthodes de commande qui peuvent être adaptées à ce problème et on présente une mise en oeuvre expérimentale. De récentes études expérimentales sur des situations d'atterrissages d'hélicoptères à grande vitesse, révèlent que de part la courte durée de l'atterrissage et le couplage existant entre le fuselage et les trains d'atterrissage, la poutre de queue d'un appareil dont le premier mode de flexion se situe dans les basses fréquences pouvait être excitée. Afin d'assurer la pérennité de l'appareil, une solution passive consiste à rigidifier la liaison entre la cabine et la poutre de queue. Coûteuse en poids, celle-ci peut être évitée en pilotant le comportement des trains d'atterrissage

Lightweight design: mass in transit

This paper is part of an effort to reduce a vehicle’s CO2 emissions through lightweight design. The originality of the approach consists in harnessing the optimal vehicle architecture with regard to CO2 emissions. Reducing a vehicle’s weight provides an opportunity to reassess performance features like shock, noise, vibrations and road holding, thereby generating additional savings through a virtuous cycle of weight reduction. The paper sheds light on some methodological aspects used by PSA Peugeot-Citroen for designing lightweight vehicles

Study and Analysis of Anti Vibratory Passive and Active Methods Applied to Complex Mechanical System

This paper studies problematic of a mechanical system composed of different coupled parts submitted to a high speed shock and proposes analysis of anti vibratory passive and active methods based on an experimental and theoretical coupled approach. After a shock, different parts of the system oscillate. If one of them is excited at a particular frequency, such as its proper frequency, important oscillations appear and can lead to the deterioration of the system by introducing important stresses. In this paper, we propose an analysis in order to understand this kind of problem and what we can do to avoid it. Firstly, we discuss problematic and we expose the studied system. In a second time, we develop two approaches of modeling that allow us to understand the phenomenon by carrying out numerical simulations. Then cross checking of model is completed via experimental study on drop test bench. Passive minimization method of vibrations based on experimental and theoretical coupled approach is exposed. Finally, a comparative analysis of different methods of control and experimental results of controlled system are presented

Experimental analysis and simulation of the dynamix response of a propeller pitch change actuator

This paper focuses specifically on the control of the propeller pitch change mechanisms and their associated dynamics. The subject of this article is restricted to the mechanisms using a hydraulic single acting actuator. They function asymmetrically and are subject to important varying external loads under the full flight envelope. This phenomenon has an impact on their dynamic response. The question of the dynamics of these systems is rarely dealt with because, usually for aircraft applications, there is no real requirement for propeller pitch dynamic control. But, in the case of some applications, such as the Eurocopter X3, this dynamic control aspect and the safety aspect of the propeller pitch change mechanism are particularly important, because this mechanism is fully involved in aircraft safety, control and handling qualities. Firstly, this paper gives an explanation of the phenomena applied to the propeller pitch change mechanism and their contributions to its dynamic response. Then, a model of the dynamic response is proposed. Finally, an experimental identification of the pitch change mechanism dynamics concludes this article.ACKNOWLEDGMENTS This work has been supported by Eurocopter’s Innovation department, Marignane, FRANC

Nouvelle approche pour l’optimisation de systèmes mécaniques en vue de la récupération d'énergie vibratoire

La récupération d’énergie à partir des vibrations mécaniques est une préoccupation importante à l’heure actuelle car elle permet de rendre autonome les systèmes de surveillance vibratoire ou de contrôle de vibration (semi-actif). Cet article se positionne sur le thème de la récupération d’énergie vibratoire et plus particulièrement, dans la phase de conception d’un tel système, lors de l’étape de la « transformation et l’optimisation mécanique ». Dans ce sens, l’article propose une méthode d’aide à la conception des résonateurs équipant les systèmes de récupération. Cette méthode utilise les fonctions habituelles des interfaces (débattement, isolation) plus une fonction récupération d’énergie. La démarche intègre une étape supplémentaire aux démarches classiques de mise sous forme adimensionnelle de ces fonctions afin de minimiser le nombre de paramètres de plus haut niveau à utiliser lors d’une optimisation globale

Procédé de commande et de régulation de l’angle braquage d’un empennage d’hélicoptére hybride

La présente invention concerne un procédé de commande et de régulation d'un giravion à vitesse d'avancement élevée et stabilisée, comportant au moins un rotor principal (10) de sustentation, au moins une hélice (6) propulsive à pas variable et au moins une source motrice pour entraîner le(s) rotor(s) principal(aux) (10) et au moins une hélice (6), ledit procédé consistant à utiliser une première boucle de régulation en tangage ou assiette et une seconde boucle de régulation en vitesse par l'intermédiaire d'une commande du pas moyen de la ou des hélices (6) propulsives, caractérisé en ce qu'il consiste à commander l'angle de braquage d'un empennage (30,25,35) horizontal en utilisant une troisième boucle de commande et de régulation dudit angle de braquage de l'empennage (30,25,35) horizontal, pour minimiser la puissance totale consommée par le rotor principal (10) et la ou les hélices (6) propulsives, pour une assiette et une vitesse donnée