166 research outputs found
Multimodal electromechanical model of piezoelectric transformers by Hamilton's principle
This work deals with a general energetic approach
to establish an accurate electromechanical model of a
piezoelectric transformer (PT). Hamiltonâs principle is used to obtain the equations of motion for free vibrations. The modal characteristics (mass, stiffness, primary and secondary electromechanical conversion factors) are also deduced. Then, to illustrate this general electromechanical method, the variational principle is applied to both homogeneous and nonhomogeneous Rosen-type PT models. A comparison of modal parameters, mechanical displacements, and electrical potentials are presented for both models.
Finally, the validity of the electrodynamical
model of nonhomogeneous Rosen-type PT is confirmed
by a numerical comparison based on a finite elements
method and an experimental identification
First Approach for the Modelling of the Electric Field Surrounding a Piezoelectric Transformer in View of Plasma Generation
This paper is about an open multi-physics modelling problem resulting from recent investigations into plasma generation by piezoelectric transformers. In this first approach, the electric field distribution surrounding the transformer is studied according to a weak coupling formulation. Electric potential distribution views obtained numerically are compared to real views of plasma generation observed experimentally
Identification Methodology of Electrical Equivalent Circuit of the Piezoelectric Transformers by FEM
Methodology using Ansys analyses for the identification of Electrical Equivalent Circuit of piezoelectric transformer. The demonstration is done with typical multilayered Rosen transformer but the method is relevant for any kind of transformer structures
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Small acoustically forced symmetric bodies in viscous fluids.
The total force exerted on a small rigid body by an acoustic field in a viscous fluid is addressed analytically in the limit where the typical size of the particle is smaller than both the viscous diffusion length scale and the acoustic wavelength. In this low-frequency limit, such a force can be calculated provided the effect of the acoustic steady streaming is negligible. Using the Eulerian linear expansion of Lagrangian hydrodynamic quantities (velocity and pressure), the force on a small solid sphere free to move in an acoustic field is first calculated in the case of progressive and standing waves, and it is compared to past results. The proposed method is then extended to the case of more complex shapes with three planes of symmetry. For a symmetric body oriented with one of its axis along the wave direction, the acoustic force exerted by a progressive wave is affected by the particle shape at leading order. In contrast, for a standing wave (with the same orientation), the force experienced by the particle at leading order is the same as the one experienced by a sphere of same volume and density.This work was funded in part by the European Union through a Marie-Curie CIG grant to E.L. and by the Direction Générale de l'Armement (project ERE 12C0020, contract 2012600091) to F.N.This is the author accepted manuscript. The final version is available from the American Institue of Physics via http://dx.doi.org/10.1121/1.494259
Modeling of a Ring Rosen-Type Piezoelectric Transformer by Hamiltonâs Principle
This paper deals with the analytical modeling of a ring Rosen-type piezoelectric transformer. The developed model is based on a Hamiltonian approach, enabling to obtain main parameters and performance evaluation for the first radial vibratory modes. Methodology is detailed, and final results, both the input admittance and the electric potential distribution on the surface of the secondary part, are compared with numerical and experimental ones for discussion and validation
Convective dissolution of CO in 2D and 3D porous media: the impact of hydrodynamic dispersion
Convective dissolution is the process by which CO injected in deep
geological formations dissolves into the aqueous phase, which allows storing it
perennially by gravity. The process results from buoyancy-coupled Darcy flow
and solute transport. Proper theoretical modeling of the process should
consider in the transport equation a diffusive term accounting for
hydrodynamics (or, mechanical) dispersion, with an effective diffusion
coefficient that is proportional to the local interstitial velocity. A few
two-dimensional (2D) numerical studies, and three-dimensional (3D) experimental
investigations, have investigated the impact of hydrodynamic dispersion on
convection dynamics, with contradictory conclusions. Here, we investigate
systematically the impact of the dispersion strength (relative to molecular
diffusion), and of the anisotropy of its tensor, on convective
dissolution in 2D and 3D geometries. We use a new numerical model and analyze
the solute fingers' number density (FND), penetration depth and maximum
velocity; the onset time of convection; the dissolution flux in the
quasi-constant flux regime; the mean concentration of the dissolved CO2; and
the scalar dissipation rate. The efficiency of convective dissolution over long
times is observed to be mostly controlled by the onset time of convection. For
most natural porous media (), the onset time is found to increase
as a function of , in agreement with previous experimental findings and in
stark contrast to previous numerical findings. However, if is
sufficiently large this behavior is reversed. Furthermore, results in 3D are
fully consistent with the 2D results on all accounts, except that in 3D the
onset time is slightly smaller, the dissolution flux in the quasi-constant flux
regime is slightly larger, and the dependence of the FND on the dispersion
parameters is impacted by .Comment: 30 pages, 18 figure
Learning Energy-Efficient Hardware Configurations for Massive MIMO Beamforming
Hybrid beamforming (HBF) and antenna selection are promising techniques for
improving the energy efficiency~(EE) of massive multiple-input
multiple-output~(mMIMO) systems. However, the transmitter architecture may
contain several parameters that need to be optimized, such as the power
allocated to the antennas and the connections between the antennas and the
radio frequency chains. Therefore, finding the optimal transmitter architecture
requires solving a non-convex mixed integer problem in a large search space. In
this paper, we consider the problem of maximizing the EE of fully digital
precoder~(FDP) and hybrid beamforming~(HBF) transmitters. First, we propose an
energy model for different beamforming structures. Then, based on the proposed
energy model, we develop an unsupervised deep learning method to maximize the
EE by designing the transmitter configuration for FDP and HBF. The proposed
deep neural networks can provide different trade-offs between spectral
efficiency and energy consumption while adapting to different numbers of active
users. Finally, to ensure that the proposed method can be implemented in
practice, we investigate the ability of the model to be trained exclusively
using imperfect channel state information~(CSI), both for the input to the deep
learning model and for the calculation of the loss function. Simulation results
show that the proposed solutions can outperform conventional methods in terms
of EE while being trained with imperfect CSI. Furthermore, we show that the
proposed solutions are less complex and more robust to noise than conventional
methods.Comment: This preprint comprises 15 pages and features 15 figures. Copyright
may be transferred without notic
RSSI-Based Hybrid Beamforming Design with Deep Learning
Hybrid beamforming is a promising technology for 5G millimetre-wave
communications. However, its implementation is challenging in practical
multiple-input multiple-output (MIMO) systems because non-convex optimization
problems have to be solved, introducing additional latency and energy
consumption. In addition, the channel-state information (CSI) must be either
estimated from pilot signals or fed back through dedicated channels,
introducing a large signaling overhead. In this paper, a hybrid precoder is
designed based only on received signal strength indicator (RSSI) feedback from
each user. A deep learning method is proposed to perform the associated
optimization with reasonable complexity. Results demonstrate that the obtained
sum-rates are very close to the ones obtained with full-CSI optimal but complex
solutions. Finally, the proposed solution allows to greatly increase the
spectral efficiency of the system when compared to existing techniques, as
minimal CSI feedback is required.Comment: Published in IEEE-ICC202
High-Cycle Fatigue Behaviour of Pure Tantalum under Multiaxial and Variable Amplitude Loadings
Due to its specific mechanical properties, tantalum is often used in strength-demandingmilitary applications. High-cycle fatigue (HCF) behaviour of pure tantalum, however, has been rarely reported and the mechanisms at stake to account for deformation under cyclic loadings are still badly understood. This paper aims at better understanding the fatigue behaviour of tantalum and at clarifying the mechanisms of damage formation encountered under such loadings. HCF experiments performed at room temperature on commercially-pure tantalum are presented. Mean stress effects were investigated in the aim of clarifying the interaction between fatigue and creep. Fracture mechanisms were observed to vary from intergranular to transgranular depending on applied stress amplitude and mean stress. Damage mechanisms were investigated under tension and torsion. Results are analyzed in the light of existing fatigue criteria, the limitations of which are discussed. Finally, complex sequential loadings, representative of in-service loadings, were applied to tantalum smooth specimens. The contribution of each loading sequence to the overall damage was quantified and analyzed in terms of linear or non-linear cumulative damage ruleInternational audienceDue to its specific mechanical properties, tantalum is often used in strength-demandingmilitary applications. High-cycle fatigue (HCF) behaviour of pure tantalum, however, has been rarely reported and the mechanisms at stake to account for deformation under cyclic loadings are still badly understood. This paper aims at better understanding the fatigue behaviour of tantalum and at clarifying the mechanisms of damage formation encountered under such loadings. HCF experiments performed at room temperature on commercially-pure tantalum are presented. Mean stress effects were investigated in the aim of clarifying the interaction between fatigue and creep. Fracture mechanisms were observed to vary from intergranular to transgranular depending on applied stress amplitude and mean stress. Damage mechanisms were investigated under tension and torsion. Results are analyzed in the light of existing fatigue criteria, the limitations of which are discussed. Finally, complex sequential loadings, representative of in-service loadings, were applied to tantalum smooth specimens. The contribution of each loading sequence to the overall damage was quantified and analyzed in terms of linear or non-linear cumulative damage rul
Reversible Trapping of Colloids in Microgrooved Channels via Diffusiophoresis under Steady-State Solute Gradients
The controlled transport of colloids in dead-end structures is a key
capability that can enable a wide range of applications, such as bio-chemical
analysis, drug delivery and underground oil recovery. This letter presents a
new trapping mechanism that allows the fast (i.e., within a few minutes) and
reversible accumulation of sub-micron particles within dead-end micro-grooves
by means of parallel streams with different salinity level. For the first time,
particle focusing in dead-end structures is achieved under steady-state
gradients. Confocal microscopy analysis and numerical investigations show that
the particles are trapped at a flow recirculation region within the grooves due
to a combination of diffusiophoresis transport and hydrodynamic effects.
Counterintuitively, the particle velocity at the focusing point is not
vanishing and, hence, the particles are continuously transported in and out of
the focusing point. The accumulation process is also reversible and one can
cyclically trap and release the colloids by controlling the salt concentration
of the streams via a flow switching valve.Comment: Manuscript under review. 6 pages, 5 figures + Supplementary
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