Capillary pinching in a pinched microchannel

We report a study of the capillary pinching of a gas bubble by a wetting liquid inside a pinched channel. The capillary pinching induces very reproducible bubbling, at a very well-defined frequency. There are two regimes associated with drip and jet bubbling. In the latter, we show that highly monodispersed bubbles are formed by our pinched channel. The dynamics of the bubble formation also shows two distinct regimes: a long-duration elongation of the air bubble and a rapid relaxation of the interface after interface breakup. The slow regime depends on the flux imposed and the channel geometry. The rapid deformation dynamic regime depends very weakly on the boundary conditions. Scaling arguments are proposed in the context of the lubrication approximation to describe the two regimes

Capillary jumps of fluid-fluid fronts across an elementary constriction in a model open fracture

We study experimentally the quasistatic displacement of an oil-air front across a localized constriction in a model open fracture. The front experiences capillary jumps at one end of the constriction in both imbibition and drainage, leading to a microscale pressure-saturation hysteresis cycle. At the other end the front is reversibly pinned. A condition of local mechanical equilibrium between the restoring elasticity of the front and the distortion produced by the local change in aperture captures all we measure quantitatively, in terms of material and geometrical properties only

Development and experimental validation of self-centering buckling-restrained braces with shape memory alloy

Although conventional earthquake-resisting structural systems provide adequate life safety when properly designed, they often rely on significant structural damage to dissipate the seismic energy. The structural damage and the residual drift that may result from the inelastic response can make a building difficult, if not financially unreasonable, to repair after an earthquake. As a result, development of systems that return to their initial position (i.e., ???self-center???) following an earthquake and minimize structural damage is a crucial need. The research presented in this thesis aims to address this need by creating an innovative self-centering brace for advanced seismic performance. In the present study, the seismic behavior and performance of self-centering buckling-restrained braces (SC-BRBs) using shape memory alloys (SMAs) is investigated. The SC-BRBs consist of a typical BRB component, which provides energy dissipation, and pre-tensioned superelastic NiTi shape memory alloy rods, which provide self-centering. The SMA rods are attached to the BRB portion of the brace using a set of concentric tubes and free-floating anchorage plates that cause the SMA rods to elongate when the brace is both in tension and compression. Using a five-story building as context, half-scale SC-BRBs are designed and fabricated for experimental validation. To characterize hysteretic response, the braces are subjected to a cyclic loading protocol adapted from the AISC Seismic Provisions for Structural Steel Buildings. The results of the experiments are used to validate an SC-BRB model in OpenSEES, which is used to conduct further parametric studies of SC-BRB behavior

Calculus of Variations

[no abstract available

Zero-phase propagation in realistic plate-type acoustic metamaterials

[EN] We theoretically, numerically, and experimentally analyze the Density-Near-Zero (DNZ) regime of a one-dimensional acoustic metamaterial. This acoustic metamaterial is composed of thin elastic plates periodically clamped in an air-filled waveguide, and the effective dynamic zero mass density is obtained from the strong dispersion around the bandgaps associated with the resonances of the plates. We emphasize the importance of the impedance mismatch between the acoustic metamaterial and the surrounding waveguide at the frequency of the zero effective density in addition to the consequences of the inherent losses. As a result, the frequency of the zero phase propagation, i.e., the acoustic propagation with zero phase delay, is not exactly the frequency of the zero density and lies in the frequency bandgap where the effective density is negative. Considering these limitations, the zero phase propagation is still experimentally observed and a subwavelength acoustic dipole is numerically designed, thus demonstrating the possible realistic implementations of DNZ acoustic metamaterials.This article is based upon work from COST Action DENORMS CA15125, supported by COST (European Cooperation in Science and Technology). This work was funded by the Metaroom Project No. ANR-18-CE08-0021 and co-funded by ANR and RCG. J. Christensen acknowledges the support from the MINECO through a Ramon y Cajal grant (Grant No. RYC-2015-17156). J. Sanchez-Dehesa acknowledges the support from the Ministerio de Economia y Competitividad of the Spanish government and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-R.Malléjac, M.; Merkel, A.; Sánchez-Dehesa Moreno-Cid, J.; Christensen, J.; Tournat, V.; Groby, J.; Romero García, V. (2019). Zero-phase propagation in realistic plate-type acoustic metamaterials. Applied Physics Letters. 115(13):134101-1-134101-5. https://doi.org/10.1063/1.5121295S134101-1134101-511513Graciá-Salgado, R., García-Chocano, V. M., Torrent, D., & Sánchez-Dehesa, J. (2013). Negative mass density andρ-near-zero quasi-two-dimensional metamaterials: Design and applications. Physical Review B, 88(22). doi:10.1103/physrevb.88.224305Huang, T.-Y., Shen, C., & Jing, Y. (2016). Membrane- and plate-type acoustic metamaterials. The Journal of the Acoustical Society of America, 139(6), 3240-3250. doi:10.1121/1.4950751Ma, G., Yang, M., Xiao, S., Yang, Z., & Sheng, P. (2014). Acoustic metasurface with hybrid resonances. Nature Materials, 13(9), 873-878. doi:10.1038/nmat3994Romero-García, V., Theocharis, G., Richoux, O., Merkel, A., Tournat, V., & Pagneux, V. (2016). Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators. Scientific Reports, 6(1). doi:10.1038/srep19519Stinson, M. R. (1991). The propagation of plane sound waves in narrow and wide circular tubes, and generalization to uniform tubes of arbitrary cross‐sectional shape. The Journal of the Acoustical Society of America, 89(2), 550-558. doi:10.1121/1.400379Niskanen, M., Groby, J.-P., Duclos, A., Dazel, O., Le Roux, J. C., Poulain, N., … Lähivaara, T. (2017). Deterministic and statistical characterization of rigid frame porous materials from impedance tube measurements. The Journal of the Acoustical Society of America, 142(4), 2407-2418. doi:10.1121/1.5008742Groby, J.-P., Lauriks, W., & Vigran, T. E. (2010). Total absorption peak by use of a rigid frame porous layer backed by a rigid multi-irregularities grating. The Journal of the Acoustical Society of America, 127(5), 2865-2874. doi:10.1121/1.3337235Allard, J. F., & Atalla, N. (2009). Propagation of Sound in Porous Media. doi:10.1002/9780470747339De Ryck, L., Groby, J.-P., Leclaire, P., Lauriks, W., Wirgin, A., Fellah, Z. E. A., & Depollier, C. (2007). Acoustic wave propagation in a macroscopically inhomogeneous porous medium saturated by a fluid. Applied Physics Letters, 90(18), 181901. doi:10.1063/1.243157

In silico study on in vitro experiments to determine the electric membrane properties of a realistic cochlear model for electric field simulations on cochlear implants

To further develop and optimise the design of cochlear implants, a numerical model with precise material properties and authentic geometry is required. Since simulation results strongly depend on the accuracy of the estimates of the electrical properties of cochlear membranes, it is important to have a reliable in vivo method for measuring electrical impedance changes in the cochlear compartments. This work is a preliminary attempt to model, simulate and analyse the behaviour of a novel in-vitro experimental system for conducting plausible in-vivo measurements on mammalian cochlea membranes.Zur Weiterentwicklung und Optimierung des Designs von Cochlea-Implantaten ist ein detailliertes numerisches Modell der Cochlea erforderlich. Da die Simulationsergebnisse stark von den elektrischen Eigenschaften der Cochlea-Membranen abhängen, ist es wichtig, ein zuverlässiges In-vivo-Verfahren zur Messung des elektrischen Impedanzverlaufs zu haben. Diese Arbeit ist eine vorbereitende Studie, das Verhalten eines neuartigen In-vitro-Versuchssystems zur Durchführung plausibler In-vivo-Messungen an Cochlea-Membranen von Säugetieren zu modellieren, zu simulieren und zu analysieren

The Total In-Flight Simulator (TIFS) aerodynamics and systems: Description and analysis

The aerodynamics, control system, instrumentation complement and recording system of the USAF Total In/Flight Simulator (TIFS) airplane are described. A control system that would allow the ailerons to be operated collectively, as well as, differentially to entrance the ability of the vehicle to perform the dual function of maneuver load control and gust alleviation is emphasized. Mathematical prediction of the rigid body and the flexible equations of longitudinal motion using the level 2.01 FLEXSTAB program are included along with a definition of the vehicle geometry, the mass and stiffness distribution, the calculated mode frequencies and mode shapes, and the resulting aerodynamic equations of motion of the flexible vehicle. A complete description of the control and instrumentation system of the aircraft is presented, including analysis, ground test and flight data comparisons of the performance and bandwidth of the aerodynamic surface servos. Proposed modification for improved performance of the servos are also presented