Understanding friction induced damping in bolted assemblies through explicit transient simulation

The design of joints is seeing increased interest as one of the ways of controlling damping levels in lighter and more flexible aeronautic structures. Damping induced by joint dissipation has been studied for more than a decade, mostly experimentally due to the difficulty of simulating large structures with non-linearities. Experimentally fitted meta-models were thus used for damping estimation at design stage without a possible optimization. The aim of this paper is to demonstrate that damping estimation using local friction models is feasible and that it can be usable for design. The simulation methodology is based on an explicit Newmark time scheme with model reduction and numerical damping that can be compensated for the modes of interest. Practical simulation times counted in minutes are achieved for detailed models. The illustration on a lap-joint shows how simulations can be used to predict the amplitude dependence of modal damping, answer long standing questions such as “does the modeshape change?” or analyze the evolution of pressure fields during a cycle

Probing cilia-driven flow in living embryos using femtosecond laser ablation and fast imaging

Embryonic development strictly depends on fluid dynamics. As a consequence, understanding biological fluid dynamic is essential since it is unclear how flow affects development. For example, the specification of the left-right axis in vertebrates depends on fluid flow where beating cilia generate a directional flow necessary for breaking the embryonic symmetry in the so-called left-right organizer. To investigate flow dynamics in vivo proper labeling methods necessitate approaches that are compatible with both normal biology and in vivo imaging. In this study, we describe a strategy for labeling and analyzing microscopic fluid flows in vivo that meets this challenge. We developed an all-optical approach based on three steps. First we used sub-cellular femtosecond laser ablation to generate fluorescent micro-debris to label the flow. The non-linear effect used in this technique allows a high spatial confinement and a low invasiveness, thus permitting the targeting of sub-cellular regions deep inside the embryo. Then, we used fast confocal imaging and 3Dparticle tracking were used to image and quantify the seeded flow. This approach was used to investigate the flow generated within zebrafish left-right organizer, a micrometer scale ciliated vesicle located deep inside the embryo and involved in breaking left-right embryonic symmetry. We mapped the velocity field within the vesicle and surrounding a single beating cilium, and showed that this method can address the dynamics of cilia-driven flows at multiple length scales. We could validate the flow features as predicted from previous simulations. Such detailed descriptions of fluid movements will be valuable in unraveling the relationships between cilia-driven flow and signal transduction. More generally, this all-optical approach opens new opportunities for investigating microscopic flow in living tissues

An all-optical approach for probing microscopic flows in living embryos

Living systems rely on fluid dynamics from embryonic development to adulthood. To visualize biological fluid flow, devising the proper labeling method compatible with both normal biology and in vivo imaging remains a major experimental challenge. Here, we describe a simple strategy for probing microscopic fluid flows in vivo that meets this challenge. An all-optical procedure combining femtosecond laser ablation, fast confocal microscopy and 3D-particle tracking was devised to label, image and quantify the flow. This approach is illustrated by studying the flow generated within a micrometer scale ciliated vesicle located deep inside the zebrafish embryo and involved in breaking left-right embryonic symmetry. By mapping the velocity field within the vesicle and surrounding a single beating cilium, we show this method can address the dynamics of cilia-driven flows at multiple length scales, and can validate the flow features as predicted from previous simulations. This approach provides new experimental access to questions of microscopic fluid dynamics in vivo

Interactions humaines et théorie des catastrophes : une application au comportement du vacancier

Examination of recent information about tourist journeys outside Quebec Province has given rise to the idea that such trips do not take place in accordance with conventional laws such as those based on the universal gravitation model, but rather are governed by criteria of decision in which distance is not a continuous variable. After emphasizing certain weaknesses of conventional models of spatial interaction, this article shows that the theory of catastrophes, developed from R. Thom's studies of morphogenesis, makes possible a new approach, based on utilitarian concepts, to the role played by distance in tourist journeys

Benchmarking Signorini and exponential contact laws for an industrial train brake squeal application

Contact representation of structure interactions for finite element models is nowadays of great interest in the industry. Two contact modellig strategies exist in the literature, either based on a perfect contact with no interpenetration of structures at contact points, or based on functional laws releasing the contact constraint through pressure-penetration relationships. Both strategies require very different and rarely documented numerical implementations, making difficult any objective comparison. This paper presents a benchmark between ideal contact and a functional law of the exponential type applied to squeal simulations by complex mode analysis of an industrial railway brake

Design oriented simulation of contact-friction instabilities in application to realistic brake assemblies

This paper presents advances in non-linear simulations for systems with contact-friction, with an application to brake squeal. A method is proposed to orient component structural modifications from brake assembly simulations in the frequency and time domains. A reduction method implementing explicitly component-wise degrees of freedom at the system level allows quick parametric analyses giving modification clues. The effect of the modification is then validated in the time domain where non-linearities can be fully considered. A reduction method adapted for models showing local non-linearities is purposely presented along with an optimization of a modified non linear Newmark scheme to make such computation possible for industrial models. The paper then illustrates the importance of structural effects in brake squeal, and suggests solutions