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Multibody modeling of mechanical systems can be applied to various applications. Human-in-the-loop interfaces is a growing research field, for which more and more devices include a dynamic multibody model to emulate the system physics in real-time. In this scope, reliable and highly dynamic sensors, to both validate those models and to measure in real-time the physical system behavior have become crucial. In this paper, a multibody modeling approach in relative coordinates is proposed, based on symbolic equations of the dynamic system. The model is running in a ROS environment, which interacts with sensors and actuators. Two real time applications with haptic feedback are presented: a piano key and a car simulator. In the present work, several sensors are used to characterize and validate the multibody model, but also to measure the system kinematics and dynamics within the human-in-the-loop process, and to ultimately validate the haptic device behavior. Experimental results for both developed devices confirm the interest of an embedded multibody model to enhance the haptic feedback performances. Besides, model parameters variations during the experiments illustrate the infinite possibilities that such model-based configurable haptic devices can offer.

Many engineering applications involve a mechanical articulated system interacting with granular media: an everyday application is the passenger train which is a mechanical articulated system guided by rails that transmit the load to the ground via the ballast. The ballast, composed of crushed stones, is a granular media. To study the global dynamic behavior of a railway system, a lumped mass model of the track (i.e.: rail and ballast) may be sufficient. Contrarily, the study of maintenance operations requires methods that consider the dynamics of each grain of the ballast. Indeed, during these operations, strong dynamic interactions occur between the grains and the maintenance tools. Approaches that take each grain of the media into account are called Discrete Element Methods (DEM). In case of the ballast, the high stiffness of the stones requires the use of the so-called Non-Smooth Contact Dynamics (NSCD) method to properly model the contact phenomena. One of the maintenance operations is the tamping process of the ballast. This operation restores the railway track geometry to improve the safety of the traffic and the passenger’s comfort. During this operation, the rail is firstly moved to its correct position, then the tamping machine vibrates the ballast in such a way that it behaves more like a fluid. This allows to squeeze the ballast with less load, reducing the stones degradation rate. To study this operation, one may use co-simulation approaches between granular media using DEM and the machine using MultiBody System dynamics (MBS). This solution faces stability problems due to the stiffness of the media. Another approach models the dynamics of the granular media using DEM, while imposing the kinematics of the machine whose dynamics is then neglected. In this thesis, we have firstly developed a monolithic approach in which the dynamics of the DEM and of the MBS are solved simultaneously. This formalism has shown a good stability and versatility. Secondly, we, Énormément d’applications industrielles mettent en interaction des systèmes multicorps avec des milieux granulaires. L’industrie ferroviaire en fait partie, et impacte quotidiennement des millions de voyageurs à travers le monde. Une maintenance continue des voies de chemin de fer est nécessaire afin de conserver la sécurité du transport. L’opération de bourrage des voies de chemin de fer est une opération de maintenance qui consiste à restaurer les caractéristiques géométriques de la voie. Pour y arriver, une vibration est introduite dans le milieu granulaire afin de le fluidifier. Cela permet de réduire les forces nécessaires à la restauration de la géométrie, ce qui entraine une diminution de l’usure du ballast. L’objectif de cette thèse est de permettre d’étudier numériquement de telles applications. La première partie de ce travail est dédiée au développement d’une méthodologie de résolution innovante qui permet de résoudre simultanément la dynamique multicorps et la dynamique granulaire. Cette méthodologie est capable de résoudre des systèmes composés d’un nombre important de grains extrêmement rigides, tout en respectant les contraintes des systèmes multicorps. La seconde partie de cette thèse est dédiée à la création d’une expérience afin de comparer les résultats expérimentaux avec ceux obtenus par la méthodologie proposée. L’opération de bourrage est ensuite utilisée pour illustrer l’importance de considérer la dynamique du système dans sa globalité afin d’obtenir des résultats fiables., (FSA - Sciences de l'ingénieur) -- UCL, 2019

In a context of technical, ideological, social and political upheavals, the mobility is, today more than ever, deeply questioned. The automotive industry must constantly reinvent itself and, to do so, develops both innovative technologies and the design methods able to optimize them and to integrate them into new solutions. Thus, considering ever more numerous and diversified aspects, the design of vehicles responding to current and future challenges is an ever more ambitious task. This thesis aims at proposing a multidisciplinary and integrated design approach, specifically addressed to the conception of road vehicles. Precisely, the strategy consists of the synthesis of automobile suspensions, the optimization of their kinematics in order to obtain the best road performances, while taking the mechanical constraints of design and manufacturing into account. An algorithm combining several numerical processes based on the multibody formalism allows, first, to satisfy the constraints to which the vehicle is subjected, then to test this vehicle through a hybrid simulator in which transient simulation and steady-state analysis are juxtaposed, and finally, to evaluate it according to the whole of selected criteria. The method enables obtaining judicious trade-off between the exhaustiveness of the tests and the criteria and the computational time and, thus, handling the design process in its wholeness, in a consistent and efficient way. This strategy has been successfully applied to the design of a new concept of electric unipersonal three-wheeler dedicated to urban mobility: the Wemoov, characterized by its narrowness imposing its tilting in curve. This particular dynamics has been made possible by the development of an innovative front axle., Optimisation conjointe de la dynamique et de la conception mécanique de véhicules routiers au travers d’une stratégie basée sur l’approche multi-corps Dans un contexte de bouleversements techniques, idéologiques, sociaux et politiques, la mobilité est, aujourd’hui plus que jamais, profondément remise en question. L’industrie automobile doit sans cesse se réinventer et, pour se faire, développe autant les technologies innovantes que les méthodes de conception capables de les optimiser et de les intégrer au sein de nouvelles solutions. Ainsi, considérant des facteurs toujours plus nombreux et diversifiés, la conception de véhicules répondant aux défis actuels et futurs est une tâche toujours plus ardue. L’objectif de la thèse est de proposer une démarche de conception multidisciplinaire et intégrée, spécifiquement dédié à la création de véhicules routiers. Précisément, la stratégie consiste en la synthèse de suspensions automobiles, l’optimisation de leur cinématique en vue d’obtenir les meilleures performances routières, tout en tenant compte des contraintes mécaniques de conception et de fabrication. Un algorithme combinant plusieurs méthodes numériques sur la base du formalisme multi-corps permet, d’une part, de satisfaire les contraintes auxquelles le véhicule est soumis, d’ensuite tester ce véhicule au travers d’un simulateur hybride dans lequel analyse transitoire et calcul des états stationnaires se juxtaposent, et finalement d’évaluer celui-ci selon l’ensemble des critères retenus. La méthode permet d’obtenir de judicieux compromis entre l’exhaustivité des tests et des critères et le temps de calcul et, ainsi, d’appréhender de façon cohérente et efficace la démarche de conception dans sa globalité. Cette stratégie a été appliquée avec succès à la conception d’un nouveau concept de tricycle électrique, unipersonnel et dédié la mobilité urbaine: le Wemoov, caractérisé par son étroitesse imposant son inclinaison en courbe. Cette dynamique particulière a été rendu, (FSA - Sciences de l'ingénieur) -- UCL, 2019

A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a century, whether in the service of art, education, or scientific research. In this review article in honor of Robert Behringer, we highlight both his pioneering use of the method in physics research, and its reach into the public sphere through museum exhibits and outreach programs. We aim to provide clear protocols for artists, exhibit-designers, educators, and scientists to use in their own endeavors. It is our hope that this will build awareness about the ubiquitous presence of granular matter in our lives, enlighten its puzzling behavior, and promote conversations about its importance in environmental and industrial contexts. To aid in this endeavor, this paper also serves as a front door to a detailed wiki containing open, community-curated guidance on putting these methods into practice (Abed-Zadeh et al. in Photoelastic methods wiki https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/home, 2019).

Multibody systems can interact with other systems or with the environment via contacts.Such interactions can be solved by different techniques such as the co-simulation process, or a mono-lithic solver. In some fields of application specific treatments are needed for example when the contactsare stiff and numerous, and when vibrations dramatically impact the behavior of one system. For theseapplications, dedicated solving strategies have to be applied. To check the coherence of such strategywith the real process, we developed an experimental setup involving a multibody system blending agranular media. The proposed planar experiment consists of a modified four-bar linkage blending aset of disks contained in a vibrating box shaked at different frequencies. The experiment measures theinteractions between both systems at different frequencies via a telescopic bar included in the four-barlinkage.

We present a benchmark to experimentally validate the method we have developed to simulate mechanical devices interacting with granular media. Consequently the method we develop is able to solve problems involving bilateral and unilateral constraints. The mechanical device is modelled with the multibody system approach and is described by the use of relative coordinates. With these coordinates, the bilateral constraints are mainly due to loop-closure conditions (or specific bilateral constraints such as imposed screw-joint motion). The bilateral constraints are solved thanks to the coordinate partitioning method. The problem of contact dynamics, which introduces the unilateral constraints, is solved by a non-linear Gauss-Seidel procedure applied in the contacts coordinates. The procedure accounts for the constrained motion of the mechanism because the coordinate partitioning is also applied to the mapping between the contacts coordinates and the generalized coordinates. Consequently the solution of the unilateral constraints problem is locally compatible with the set of bilateral constraints coming from the mechanical system. The proposed planar benchmark consists of a modified four-bar mechanism blending a set of disks contained in a vibrating box. The numerical results reveals the influence of the vibration frequency on the granular compactness and thus the mechanism motion.

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Today, multibody dynamics simulation packages are more and more in use in industries. Most of these software are distributed by commercial companies and have been developed by various research teams having previously published scientific papers describing the details of their methods. However, software implementation packages without a detailed theoretical manual are unfortunately not rare and the training courses organized by those companies focus on the working features of their own codes and less on the theoretical bases. As a consequence, there is a real danger of practical engineers misusing a multibody code because they are not aware of the underlying hypotheses and/or limitations included in the code. In facing that situation, and since the number of engineers who are potential users of such software is growing, there is a real need for including the field of Multibody Dynamics (MBD) in a standard engineering education curriculum. Teaching multibody dynamics responds to a specific industrial demand. But in addition to doing that, and thanks to the very large class of practical applications covered by the field, MBD can also be very useful in the global engineering education context. In particular, three basic domains are immediately concerned: classical mechanics, mathematics and numerical methods. We claim that there is a real educational challenge in organizing an activity in which these three domains strongly interact, which helps student appreciate the interest of the underlying theories and which deals with realistic applications and problems to be solved.

This paper reports on development of an open source dynamic simulator for the Compliant huMANoid robot, COMAN. The key advantages of this simulator are: it generates efficient symbolic dynamical equations of the robot with high degrees of freedom, it includes a user-defined model of the actuator dynamics (the passive elasticity and the DC motor equations), user defined ground models and fall detection. Users have the freedom to choose the proposed features or include their own models. The models are generated in Matlab and C languages, where the user can leverage the power of Matlab and Simulink to carry out analysis to parameter variations or optimization and also have the flexibility of C language for realtime experiments on a DSP or FPGA chip. The simulation and experimental results of the robot as well as an optimization example to tune the ground model coefficients are presented. This simulator can be downloaded from the IIT website [1].

The present project has been achieved in close collaboration with the MIM, the Musical Instruments Museum of Brussels. Thanks to our multibody modeling and analysis capabilities, we have carried out a virtual demonstrator of a grand piano action in order to understand, explain and demystify the functioning of the “from key-to-string” transmission, and especially the single and double escapement principle. The developed demonstrator takes advantage of multibody dynamics as well as of an experimental set up to analyze this highly dynamic system. Our work is based on previous mathematical models available in the literature but also on the large expertise of our collaborators at the MIM, for piano action tuning and for the historical aspects relating to this instrument. In this paper, we highlight the main issues and outcomes of the project – namely the multibody modeling of a grand piano action together with the experimental validation – and some key results related to the tuning of the aftertouch and the double escapement principle.

Medical robotics is shifting from merely customized industrial manipulators to tailormade devices. In the late eighties, pioneer researchers adapted existing robots to fit the operating room environment, as the first robotized gestures in orthopedic, urologic and neurosurgery were similar to common positioning and machining tasks in automated factories. Nowadays, the range of applications expands continuously (e.g. radiotherapy, rehabilitation, beating heart surgery). Demands become more and more specific in terms of ergonomics, compactness, and interactivity, and push researchers and engineers to design new robots with kinematics and dynamics perfectly suited to a particular task or gesture. In this context, CAE and especially multibody modeling software can provide a most valuable help. This paper illustrates the use of such tools throughout the design and performance assessment processes of an active endoscope holder for minimally invasive surgery. The control algorithm is based on its kinematic model, computed analytically. A dexterity analysis of the Jacobian matrix is also presented to identify singular configurations. The dynamical model is computed with the Robotran software so as to size the required actuators and transmission precisely. A back-drivability analysis is finally performed to assess the force required to move the laparoscope manually with robot actuators switched off.

It is a well-known fact that railway dynamics is far from being trivial, mostly because of the wheel/rail contact phenomenon. Except for specialists in this field who are obviously familiar with notions like wheelset equivalent conicity, hunting motion, limit cycles, etc., most of people, including engineers, have no or few idea about the guidance principle of railway vehicles equipped with standard bogies with rigid wheelsets. The present project has been initiated at the Center for Research in Mechatronics of the Université catholique de Louvain within the framework of a master thesis under our supervision. The main objective is essentially educational and led us to build an experimental bench to highlight the wheel/rail guidance phenomenon of railway vehicles.

For several decades, pneumatic suspensions have been used on most of passenger trains. This technology has many advantages such as the possibility of controlling the carbody height, the adaptive stiffness with payload, etc. It relies on the use of air springs but also implies a complete pneumatic circuit composed of auxiliary tanks, pipes and various valves. Consequently, such a complex system requires the development of specific modelling techniques for understanding its dynamic behaviour. Furthermore, as recommended by the UIC~518 standard, the various failure modes that may arise on a train, not only for the pneumatic suspension, have to be identified. Regarding this question, the various components of the pneumatic suspension can increase the possibility of breakdowns. The goal of this paper is thus to show how we can quantify the consequences of a failure of one element thanks to the developed models, as needed by the rail industry.\\ In the first part of this paper, we describe the analysed vehicle and some potential failure mode that could arise on its pneumatic suspension. Then, we briefly present the modelling approach based on mass and energy balances. Finally, we focus on a specific failure mode and we show how we can analyse its consequences on the vehicle behaviour in a specific situation.

For several decades, Computer Aided Engineering has been widely used in many fields such as fluid mechanics, structural dynamics, control, etc. Within this context, multibody dynamics deals with systems composed of several rigid or flexible bodies connected by joints and submitted to internal and external forces. Multibody dynamics is especially suitable for the analysis of road and rail vehicles. Concerning the latter, a noticeable evolution has followed the use of pneumatic suspensions which replace conventional helical springs. Such a system allows to adapt the suspension height and stiffness to a varying payload and provides better comfort and sound insulation. However it involves a complete pneumatic circuit composed of auxiliary tanks, pipes, orifices and valves. From an industrial point of view, resorting to a simulation tool could be very beneficial in addressing the increasing complexity due to these various components. The present thesis deals with the modelling of coupled multibody and pneumatic systems with application to railway pneumatic suspensions. We first focus on the modelling of the pneumatic circuit itself and we emphasize how the model refinement must be adapted to the circuit configuration. Then, experiments carried out on a real air spring are presented. In particular, dynamic tests are analysed, showing a good match between experimental and simulation results. Finally, we implemented a model of a metro car and its pneumatic suspension and analysed its performances for tests such as curve passing or rail twist in which components like pneumatic valves play an important role. Novel suspension morphologies inspired from automotive suspensions are also explored and compared to well-established suspension designs., Depuis plusieurs décennies, l'Ingénierie Assistée par Ordinateur se développe dans de nombreux domaines comme la mécanique des fluides, la dynamique des structures, le contrôle, etc. Dans ce contexte, la dynamique multicorps s'intéresse aux systèmes polyarticulés constitués de plusieurs corps rigides ou flexibles interconnectés par des articulations et soumis à des forces internes ou externes. Ses applications sont très variées, allant de la quantification des efforts musculaires dans le corps humain à l’analyse dynamique des véhicules. Concernant les véhicules ferroviaires, la suspension secondaire (située entre la traverse et le châssis du bogie) est souvent constituée d'un coussin pneumatique (cfr figure). Ce système permet d’améliorer le confort des passagers ou l’isolation acoustique et de contrôler la hauteur et la raideur de la suspension en fonction de la charge embarquée. Cependant, il implique un circuit pneumatique relativement complexe composé de réservoirs additionnels, d'orifices, de tuyaux plus ou moins longs et de différentes sortes de vannes. D'un point de vue industriel, disposer d'un outil de simulation présente un intérêt certain en vue d’analyser la complexité croissante d’un tel système. Cette thèse s'intéresse à la modélisation de systèmes impliquant le couplage entre la dynamique multicorps et la pneumatique dans le contexte des suspensions pneumatiques de véhicules ferroviaires. Dans un premier temps, nous expliquons comment modéliser l'ensemble du circuit pneumatique et montrons comment le choix du modèle le plus approprié dépend de la topologie de ce circuit. Ensuite, nous présentons des résultats expérimentaux menés sur un coussin pneumatique de métro. Ces essais ont notamment mis en évidence une bonne adéquation entre les modèles proposés et les mesures d’essais dynamiques. Finalement, le modèle hybride d’un métro et de sa suspension pneumatique a été mis au point. Nous avons ainsi analysé, à l’aide de simulations numériques, les interac, (FSA 3) -- UCL, 2010

The goal of the present research is rst to work out the dynamic behavior of an independent wheeled articulated bogie, by means of a 3D detailed multibody model. Previous research works have pointed out the poor dynamic behavior of the bogie on a straight track, whereas in curve it correctly deforms, leading to a noticeable reduction of the wheel/rail angle of attack and thus of wear. Then, to improve the above-mentioned straight track behavior, we have carried out a model-based study and proposed a technically reasonable solution in order to re-stabilize the vehicle by means of slight geometrical modications of the articulated structure. The modied vehicle behavior is compared with the original one and also with equivalent wheelset bogies in terms of mean dissipated power along a representative tramway trajectory.

Multibody dynamics underlies modeling projects for undergraduate students at the Université catholique de Louvain (UCL, Belgium) since 1995. Being still very active in this field – about hundred students/year dealing with a MBS-based project – we are now focusing on an important aspect of this modeling activity: the statement and formulation of ”reasonable modeling hypotheses”, which represents a crucial step in any modeling process. At the beginning of the project, their rigorous formulation is indispensable to build a model according to the problem specification. At the end of the process, students are encouraged to check – a posteriori - for the validity and/or limitation of their hypotheses on the basis of their simulation results. This educational topic will be illustrated via the modeling of mountain bikes equipped with modern suspensions and for which bounce performances are analyzed. This was the project theme of the 2008-2009 academic year at UCL for undergraduate students in Mechanical engineering (3rd year).

This paper deals with the modelling of railway pneumatic suspension which is commonly used as the secondary suspension on passenger trains and involves a set of various pneumatic components such as tanks, pipes and valves. It focuses on the analysis of the heat transfer between the suspension system and the atmosphere and investigates its influence on the vehicle behaviour. First, pneumatic component models are presented and it is explained how the heat exchanges are taken into account. Then, the system composed of an airspring connected to an auxiliary tank is analysed and it is shown how the dynamic stiffness is affected by the heat transfer. Finally, a metro car is analysed for a stationary twist test called Q=Q and a curve entry which show discrepancies between adiabatic and isotherm cases in term of safety, dynamics and air consumption.

During the last decades, the railway industry has focused its attention on new bogie designs and secondary suspension technologies, as well in the field of high speed trains as in the field of urban tramways. The goal mainly consists in improving the vehicle rolling behaviour in terms of stability and longevity, but also to enhance the passenger comfort and to reduce the inconvenience of the railway track neighborhood (noise, vibration, etc.). The use of independent wheels certainly represents one of the most ”revolutionary” innovation of the last decades. Indeed, it aims at replacing the traditional wheelset which exists for more than one century and is at the root of the bogie guidance thanks to its well-established self-steering capability. Various contributions have pointed out the advantages of bogies equipped with independent (or ”freely-rotating”) wheels such as the absence of the hunting critical speed (high speed train dynamics) or the possibility of low-floor vehicles (tramway design). On the other hand, freely rotating wheels lack the steering performances of the traditional rigid wheelsets and must rely, to steer the vehicle back into a centered position, on the wheel/track gravitational stiffness phenomenon and/or on any additional”mechanism” to ensure a good bogie guidance (active/passive steering mechanism, left/right actuation control, steerable wheels, etc.). The goal of the present paper is to show that, thanks to the multibody approach, it is possible to analyze the dynamic behavior of a complex articulated bogie with independent wheels, to reveal its stable and unstable motions and to propose, via ”numerical experimentations” a technical solution in order to re-stabilize the vehicle.

On classical passenger trains, the secondary Suspension is commonly ensured by airsprings which are integrated in a pneumatic circuit. In addition to the pneumatic bellows. the circuit contains various pneumatic components such as tanks, pipes, orifices, levelling valves. etc., the purpose of the latter being, to maintain a costant height between the carbody and the bogie. These elements can be connected in several ways leading, to many existing suspension topologies. This paper deals with multidisciplinary modelling of a vehicle equipped with such a suspension taking into account both multibody and pneumatic aspects. First, it depicts in more detail the various elements of a pneumatic; suspension. Then, many criteria that influence the suspension morphology are presented: the kind of bogie, the use of an auxiliary tank, the position of this tank relative to the bellows, the kind of levelling system, the use of all additional anti-roll bar, the use of an additional hydraulic damper, etc. The description of the complete pneumatic Circuit implies the use of thermodynamic models which take into account the airflow through the pipes and the valves, the pressure in the bellows, etc, Several pipe models are presented, the choice depending on the length of the pipe: an algebraic model is sufficient for short pipes, while a differential model is needed to take into account the dynamics of longer pipes. The pneumatic model is then coupled with a SIMPACK multibody model in order to analyse the behaviour of the complete vehicle. Two-point and four-point configurations are compared for Delta Q/Q and curve entry tests.

This article presents a multidisciplinary approach of railway pneumatic suspension modelling: both multibody and pneumatic aspects are taken into account. The work aims at obtaining a realistic model of the secondary suspension and coupling it with a multibody model of a train. Various components of the pneumatic circuit such as bellows, tanks, pipes and valves are taken into account. The article focuses on the bellow - pipe - tank subsystem for which several modelling approaches are presented and compared. Differences between differential and algebraic models are highlighted, and an application-dependent choice between them is suggested. A complete model of the pneumatic circuit is then obtained and coupled with a multibody model of the train. As a result, the behaviour of a suburban train equipped with a pneumatic secondary suspension is analysed, in particular undesired oscillating motions which affect the comfort. Topological modifications and improvements of the suspension are also investigated and discussed.