Mantle convection: A review

The solid-state convection in the Earth mantle is characterized by plate tectonics, which shapes the tectonic activities of the Earth, and superplumes as broad hot regions chemically distinct from the surrounding regions in deep lower mantle. Recent numerical studies of mantle convection suggest that the rigidly moving plates occur on the Earth because the rupture strength of plate margins is sufficiently low, while that of plate interiors is high enough to inhibit spontaneous formation of new plate boundaries by the weight of the plates themselves. This implies that the activity of plate tectonics has fluctuated much in the Earth history. Recent numerical studies also suggest that the superplumes develop owing to the chemical differentiation of the mantle by ridge magmatism. Superplumes have probably induced frequent and vigorous hot spot volcanism in the early Earth. It is now within reach to construct an integrated model for tectonic and structural evolution of the mantle in the Earth and other terrestrial planets.     

On trailing vortices: A short review

This paper reviews some mechanisms involved in the dynamics of vortices in fluid flows. The topic is first introduced by pointing out its importance in aerodynamics. Several basic notions useful to appraise experimental observations are then surveyed, namely: centrifugal instabilities, inertial waves, cooperative instabilities, vortex merger, vortex breakdown and turbulence in vortices. Each topic is illustrated with experimental or numerical results.     

Effective electromechanical properties of cellular piezoelectret: A review

Due to the large quasi-piezoelectric d 33 coefficient in the film thickness direction,cellular piezoelectret has emerged as a new kind of compliant electromechanical transducer materials.The macroscopic piezoelectric effect of cellular piezoelectret is closely related to the void microstructures as well as the material constants of host polymer.Complex void microstructures are usually encountered in the optimum design of cellular piezoelectret polymer film with advanced piezoelectric properties.Analysis of the effective electromechanical properties is generally needed.This article presents an overview of the recent progress on theoretical models and numerical simulation for the effective electromechanical properties of cellular piezoelectret.Emphasis is placed on our own works of cellular piezoelectret published in past several years.     

A first assessment of the NEPTUNE_CFD code: Instabilities in a stratified flow comparison between the VOF method and a two-field approach

This paper presents some results concerning a first benchmark for the new European research code for thermal hydraulics computations: NEPTUNE_CFD. This benchmark relies on the Thorpe experiment to model the occurrence of instabilities in a stratified two-phase flow. The first part of this work is to create a numerical trial case with the VOF approach. The results, in terms of time of onset of the instability, critical wave-number or wave phase speed, are rather good compared to linear inviscid theory and experimental data. Additional numerical tests showed the effect of the surface tension and density ratio on the growing dynamics of the instability and the structure of the waves. In the second part, a code to code (VOF/multi-field) comparison is performed for a case with zero surface tension. The results showed some discrepancies in terms of wave amplitudes, growing rates and a time shifting in the global dynamics. Afterward, two surface tension formulations are proposed in the multi-field approach. Both formulations provided similar results. The time for onset of the instability, the most amplified wave-number and its amplitude were in rather good agreement with the linear analysis and VOF results. However, the time-shifted dynamics was still observed.     

On Symmetries and Anisotropies of Classical and Micropolar Linear Elasticities: A New Method Based upon a Complex Vector Basis and Some Systematic Results

A complete and unified study of symmetries and anisotropies of classical and micropolar elasticity tensors is presented by virtue of a novel method based on a well-chosen complex vector basis and algebra of complex tensors. It is proved that every elasticity tensor has nothing but 1-fold, 2-fold, 3-fold, 4-fold and ∞-fold symmetry axes. From this fact it follows that the crystallographic symmetries plus the isotropic symmetry are complete in describing the symmetries of any kind of classical elasticity tensors and micropolar elasticity tensors. Further, it is proved that for each given integer m>>2 every classical Green elasticity tensor with an m-fold symmetry axis must have at least m elastic symmetry planes intersecting each other at this symmetry axis. From this fact and the aforementioned fact it follows that for all possible material symmetry groups, there exist only eight distinct symmetry classes for classical Green elasticity tensors, which correspond to the isotropy group and the seven crystal classes S ₂, C _2h , D _2h , D _3d , D _4h , D _6h and O _h , while it is shown that there exist twelve distinct symmetry classes for any other kind of elasticity tensors, including the classical Cauchy elasticity tensor and the micropolar elasticity tensors, which correspond to the eight subgroup classes just mentioned and the four crystal classes S ₆, C _4h , C_6h and T _h . From these results, it turns out that all possible elasticity symmetry groups are nothing but the full orthogonal group, the transverse isotropy groups C _{∞ h} and D _{∞ h} , and the nine centrosymmetric crystallographic point groups except C _6h and D _6h . This revised version was published online in August 2006 with corrections to the Cover Date.