Search results for "Compres"
showing 10 items of 1107 documents
Frequency-dependent hydrodynamic interaction between two solid spheres
2017
Hydrodynamic interactions play an important role in many areas of soft matter science. In simulations with implicit solvent, various techniques such as Brownian or Stokesian dynamics explicitly include hydrodynamic interactions a posteriori by using hydrodynamic diffusion tensors derived from the Stokes equation. However, this equation assumes the interaction to be instantaneous which is an idealized approximation and only valid on long time scales. In the present paper, we go one step further and analyze the time-dependence of hydrodynamic interactions in a compressible fluid on the basis of the linearized Navier-Stokes equation. The theoretical results show that the compressibility of the…
CFD prediction of shell-side flow and mass transfer in regular fiber arrays
2021
Numerical simulations were conducted for fully developed, steady-state flow with mass transfer in fiber bundles arranged in regular lattices. The porosity was 0.5 and the Schmidt number 500. Several combinations of axial flow, transverse flow and flow attack angles in the cross-section plane were considered. The axial and transverse Reynolds numbers Rez , ReT were made to vary from 10(^−4) to 10(^2). Concentration boundary conditions, and the definition of an average Sherwood number, were addressed. Results for the hydraulic permeability were compared with the literature. Both hexagonal and square lattices were found to be hydraulically almost isotropic up to transverse flow Reynolds number…
A simple procedure to improve the pressure evaluation in hydrodynamic context using the SPH
2009
In literature, it is well know that the Smoothed Particle Hydrodynamics method can be affected by numerical noise on the pressure field when dealing with liquids. This can be highly dangerous when an SPH code is dynamically coupled with a structural solver. In this work a simple procedure is proposed to improve the computation of the pressure distribution in the dynamics of liquids. Such a procedure is based on the use of a density diffusion term in the equation for the mass conservation. This diffusion is a pure numerical effect, similar to the well known artificial viscosity originally proposed in SPH method to smooth out the shock discontinuities. As the artificial viscosity, the density…
Tissue Sparing Posterior Cervical Indirect Decompression and Fusion in Foraminal Stenosis
2016
Treatment for patients with cervical foraminal stenosis that present with cervical radiculopathy has experienced rapid progress. Cervical spine surgical options have improved through advances in imaging, instrumentation, implant innovations and novel surgical techniques. While historical treatments are largely safe, comorbidities associated with procedures such as ACDF, TDR, and posterior foraminotomy beg the question if these procedures are too much surgery for select patients that could benefit from a tissue sparing approach. This chapter will introduce a novel, less disruptive surgical technique for achieving indirect decompression and fusion utilizing an intervertebral cervical implant.…
Study of interface formation during diffusion bonding : compact heat exchangers application
2014
Compact diffusion bonded heat exchangers are an attractive option in many fields (nuclear, (petro-)chemistry, solar…) due to their performance. This type of concept is especially intended for manufacturing the energy conversion system of the ASTRID reactor. During diffusion bonding by HIP, the problem is twofold: the channel deformation and microstructure evolution must be controlled, while at the same time, highly resistant interfaces are desired. This thesis is focused on the understanding and the control of the bonded components microstructure prepared by HIP in order to define « process » criteria to achieve welds in agreement with specifications of components containing fluidic channel…
Refined Sellmeier equations from phase-matching measurements over the complete transparency range of KTiOAsO4, RbTiOAsO4 and CsTiOAsO4
2000
Sum- and difference- frequency generation phasematching properties are measured in spheres of KTiOAsO4, RbTiOAsO4 and CsTiOAsO4 for Sellmeier equations refinement over their complete transparency range.
Subjective image fidelity metric based on bit allocation of the human visual system in the DCT domain
1997
Until now, subjective image distortion measures have partially used diverse empirical facts concerning human perception: non-linear perception of luminance, masking of the impairments by a highly textured surround, linear filtering by the threshold contrast frequency response of the visual system, and non-linear post-filtering amplitude corrections in the frequency domain. In this work, we develop a frequency and contrast dependent metric in the DCT domain using a fully non-linear and suprathreshold contrast perception model: the Information Allocation Function (IAF) of the visual system. It is derived from experimental data about frequency and contrast incremental thresholds and it is cons…
Friction stir consolidation of aluminum machining chips
2017
Friction stir consolidation (FSC) is a solid-phase manufacturing process that consolidates metal powder, chips, or scraps into solid blocks via severe plastic deformation and solid state welding. It has the potential to be a more economical and âgreenâ process to recycle metal waste. In this study, solid discs were made from AA6061 aluminum alloy machining chips by FSC. The progression of the process was revealed by analyzing the motion of the tool, consolidating force, power history, and macro/microstructure of discs produced from a series of partial consolidation experiments. A bowl-shaped recrystallized zone in the vertical cross-sections of the disc products was observed and conside…
Impact of cyclic mechanical stress on the electrical contact resistance between gas diffusion layer and bipolar plates in Polymer Electrolyte Membran…
2018
WHEC 2018, 22nd edition of the WORLD HYDROGEN ENERGY CONFERENCE, Rio de Janeiro, BRESIL, 17-/06/2018 - 22/06/2018; and collisions) and the mechanical clamping stress applied during the stack assembly. The internal stresses come from the shrinking and the swelling of the membrane caused by water content and the difference between the thermal expansion coefficients of the cell components. These mechanical stresses have an impact on the global fuel cell's performance and one of the most sensitive cell's components to this pressure is the Gas Diffusion Layer (GDL). This layer, assembled with the membrane electrode assembly, provides the reactant gases, evacuates the produced heat and …
Adaptive Control of a Gas Turbine Engine for Axial Compressor Faults
1996
An adaptive control system for a gas turbine engine which diagnoses conditions of axial compressor faults is proposed and analyzed. Nonlinear models of the gas turbine, neural networks and genetic algorithms are used in this research. The adaptive control system minimizes the reduction in gas turbine performance deriving from non-destructive faults. In the absence of faults, the system automatically performs the optimization of the engine between overhauls. Improvements concern the definition of adaptive control with faults in progress, and the real-time optimization of the engine during its operative life between overhauls. Simulation results of the suggested control system are also discus…