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1.
Rheological analysis of highly concentrated w/o emulsions 总被引:2,自引:0,他引:2
Nathalie Jager-Lézer Jean-Francois Tranchant Valérie Alard Can Vu Pierre Cyrill Tchoreloff J.-L. Grossiord 《Rheologica Acta》1998,37(2):129-138
A series of highly concentrated lipophilic cosmetic emulsions were analysed, in order to determine their rheological and
textural properties, as a function of their microstructure. The originality of this study lies in the methodology used, especially
the shear-stress scanning analysis. The results of a very powerful and comprehensive dynamic rheological analysis suggest
the existence of two critical volume fraction values: besides the “close-packed” value φ
c
, a “slack-packed” value φ0, close to 0.60 could be demonstrated. It has been shown that the close-packed structure is stable under shear; in constrast,
the slack-packed configuration, defined as φ0<φ<φ
c
is unstable under shear. A comparison with theoretical models, especially that of Princen, showed good agreement and allowed
the close-packed value φ
c
to be defined more precisely as 0.67. The gap between 0.67 and 0.74 is probably indicative of a highly polydisperse distribution,
as confirmed by microscopic analysis. Flow experiments confirmed the validity of Princen‘s model.
Received: 20 February 1997 Accepted: 20 January 1998 相似文献
2.
The aim of this work is to propose design criteria, based on rheological characterisation for improving drill-in fluids performance.
In particular, it reports an example in which rheological approaches helped improve drill-in fluids resistance to temperature.
As a starting system a commercial drill-in fluid containing xanthan gum and calcium carbonate was chosen and evaluated. Different
samples were then prepared by changing the initial formulation in order to increase the system's stability to temperature.
Drill-in fluids' performance have been compared by considering their “damaging potential”, filtration properties and, “cakes”.
All drill-in fluids have been tested before and after aging at a given temperature with “hot rolling tests”. The systems'
gel structure was characterized by measuring dynamic moduli (G′ and G′′) in the linear viscoelastic range and all samples
were compared by evaluating their “melting” temperature and gel network strength during time cure tests. The results obtained
from this work suggest that the rheological tests carried out on the whole drill-in fluid can provide insights into fluids'
damaging potential and “cake” structure. In particular, rheology proved to be able to provide quantitative information about
gel strength and temperature stability that permitted one to improve drill-in fluids' formulation in order to preclude formation
damage and to meet industrial requirements.
Received: 6 February 2000 Accepted: 15 November 2000 相似文献
3.
S.A. Thorpe 《Theoretical and Computational Fluid Dynamics》1998,11(3-4):171-181
This is an overview of knowledge, derived mainly from observations, of turbulence in the stratified and rotating World Ocean
from the 1960s, when mesoscale motions with scales of 30–150 km and 100 days were discovered by neutrally buoyant floats,
to the present decade and the use of SF6“purposeful tracer” release study in the North Atlantic.
Most of the ocean is stably stratified, but it contains a rotational turbulent “continua” and isolated rotating eddies, as
well as Rossby waves, and many features similar to those of, say, planetary atmospheres. It differs however because (a) the
presence of lateral boundaries, the continental land masses, islands, and seamounts, provides constraints to the circulation and to the propagation
of eddies, and possibly substantial sources and sinks of eddy motion; (b) channels connecting the oceans to land-locked seas
(e.g., the Mediterranean; the formation of water with anomalous properties, “natural tracers”, e.g., temperature or salinity,
allows “interthermocline eddies” to be readily detected); and (c) convection and differential seasonal latitudinal forcing
introduce upper-ocean variability and intrathermocline eddies. The focus of research interest has moved from “turbulence”per se towards study of its consequences, for example towards dispersion of material particles and dissolved solutes, and the meridional
and inter-basin transfers of heat.
Received 2 December 1996 and accepted 18 September 1997 相似文献
4.
Bernadette Miara 《Archive for Rational Mechanics and Analysis》1998,142(4):331-353
We consider a family of three‐dimensional shells with the same middle surface, all composed of the same nonlinearly elastic
Saint Venant‐Kirchhoff material. Using the method of asymptotic expansions with the thickness as the “small” parameter, and
making specific assumptions on the applied forces, the geometry of the middle surface, and the kinematic boundary conditions,
we show how a “limiting”, “large‐deformation” two‐dimensional model can be identified in this fashion. By linearization, this
nonlinear membrane model reduces to the linear membrane model.
(Accepted January 13, 1997) 相似文献
5.
This investigation explores the mass/heat transfer from a wall-mounted block in a rectangular fully developed channel flow.
The naphthalene sublimation scheme was used to measure the level of local mass transfer from the block’s surfaces. The heat
transfer coefficient can be obtained by analogy between heat and mass transfer. The effects of the Reynolds number on the
local mass transfer from the block’s surfaces have been widely discussed. Results showed that, owing to the flow complexity
induced by vortices around the block, the block’s surfaces appeared four different spatial Sherwood number distributions,
termed “Wave type”, “U type”, “Slant type”, and “Pit type”. A change in the Reynolds number significantly altered the spatial Sherwood number distributions on the block’s surfaces.
Besides, four correlations between the Reynolds number and the surface-averaged Sherwood number were presented for the front,
top, side, and rear surfaces of the block at a given block’s height, for the purpose of practical applications. 相似文献
6.
The development of Micro Air Vehicles with flapping wings is inspired from the observation and study of natural flyers such
as insects and birds. This article explores the rotational power consumption of a flapping wing using a mechanical flapper
at Re ≃ 4,500. This mechanical flapper is simplified to a 2D translation and a rotation in a water tank. Moreover, the wing kinematics
are reduced to a linear translation and a rotation for the purpose of our study. We introduce the notion of non-ideal flapper
and associated non-ideal rotational power. Such non-ideal devices are defined as consuming power for adding and removing mechanical
power to and from the flow, respectively. First, we use a traditional symmetrical wing kinematic which is a simplified kinematic
inspired from natural flyers. The lift coefficient of this flapping is about C
L ≃ 1.5. This symmetrical wing kinematic is chosen as a reference. Further, wing kinematics with asymmetric rotations are then
compared with this one. These new kinematics are built using a differential velocity defined according to the translational
kinematics, a time lag and a distance, r
kp. The analogy of this distance is discussed as a key point to follow along the chord. First, the wing kinematics are varied
keeping a similar shape for the profiles of the angular velocity. It is shown that when compared to the reference wing kinematic,
a 10% reduction in the rotational power is obtained whilst the lift is reduced by 9%. Second, we release the limitation to
a similar shape for the profiles of the angular velocity leading to a novel shape for the angular velocity profile named here
as “double bump” profile. With these new wing kinematics, we show that a 60% reduction in the non-ideal rotational power can
be achieved whilst the lift coefficient is only reduced by 1.7%. Such “double bump kinematics” could then be of interest to
increase the endurance of Micro Air Vehicles. 相似文献
7.
Summary Reflected and transmitted pressure waves take place when an incident pressure wave reaches a screen placed in a duct and crossed
by a previous steady flow.
The thickness of the screen is assumed to be negligible and essure losses through it in the quasi steady flow, which takes
place after the passage of the incident pressure wave, are assumed be steady flow ones.
The strength of reflected and transmitted pressure waves is related to the strength of the incident wave, to the porosity
of the screen and to the previous flow through it. Subsonic and just supersonic quasi steady flow inside the screen are considered.
Five commercial screens have been tested with incident shock waves and the experimental results have been compared with the
theoretical ones: the agreement is quite satisfactory.
The present work has been supported by the “Consiglio Nazionale delle Ricerche” (C.N.R.) under Contract no. 115.4075.69.01220.
The suffixes “u” and “d” pertain to the conditions upstream and downstream of the screen with reference to the flow through it. The suffix “j” refers to the region “j” of the wave diagrams in Fig. 1. 相似文献
Sommario L'interazione di un'onda di pressione con una rete intubata attraversata da un flusso preesistente produce un'onda riflessa ed una trasmessa. Si presenta un modello teorico basato essenzialmente sulle potesi che lo spessore della rete sia trascurabile e che le perdite carico attraverso di essa, nel flusso quasi stazionario indotto dalla suddetta interazione, coincidano con quelle proprie di un oto permanente. Si analizza il caso di flusso indotto nella rete ia subsonico che sonico. Si eseguono prove sperimentali su cinque reti di diverse porosità differenti condizioni di flusso, e si verifica l'attendibilità del odello teorico proposto.
The present work has been supported by the “Consiglio Nazionale delle Ricerche” (C.N.R.) under Contract no. 115.4075.69.01220.
The suffixes “u” and “d” pertain to the conditions upstream and downstream of the screen with reference to the flow through it. The suffix “j” refers to the region “j” of the wave diagrams in Fig. 1. 相似文献
8.
According to constructal theory, the “generation of flow configuration” is a universal phenomenon in physics. This phenomenon is covered by the constructal law: “For a finite-size flow system to persist in time (to live)
it must evolve such that it provides greater and greater access to the currents that flow through it.” This paper shows how
the constructal law can be used to (1) predict and explain features of “design” in nature, and (2) design effective strategies
and configurations for engineering. Many natural flow designs rely on two flow mechanisms: channels with relatively low resistivity,
interwoven with diffusion across the interstices. The “design” is the balance between the two mechanisms. The flow from line
to line (or plane to plane) through a sufficiently fine porous medium encounters less resistance than the flow through parallel
channels when it is configured as trees that alternate with upside down trees: from this follows the prediction that natural
porous media (e.g., hill slope) should be multiscale (bidisperse) and non-uniformly distributed. A porous medium contaminated
with ionic species is decontaminated the fastest when the ionic flow is configured as two flow mechanisms in balance: “channeling”
driven by potential differences between optimally positioned electrodes, and diffusion driven by concentration differences
across the interstices between the channels. 相似文献
9.
M. Sugawara E. Tamura Y. Satoh Y. Komatsu M. Tago H. Beer 《Heat and Mass Transfer》2007,43(10):1009-1018
Visual observations reveal a complicated flow in the liquid melt and a melting front configuration resulting from horizontal
ice plate melting from above into a 20 wt% calcium chloride aqueous solution. The initial temperature of the ice plate and
the mixture are both −5°C. Small scale “mountain and valley” structures (∼1 mm) appear on the flat melting front just after
melting begins, which have been called “sharkskin”. Innumerable upward and downward flows appear near the sharkskin and are controlled by its “mountain and valley” structure. These typical flows will considerably promote the melting of the
ice plate to be 30% larger as compared to the numerically predicted results assuming a flat melting front (i.e., without the
sharkskin), and also by three times larger compared with the results for melting from below. 相似文献
10.
11.
The variable-interval time-averaging (“VITA”) algorithm has been tested in a variety of turbulent boundary layers for its
ability to detect shear-stress-producing motions from hot-wire signals. A “VITA + LEVEL” scheme (which uses criteria for both
short-time variance and short-time average, i.e.“level”) has been devised, and used in several different boundary layers.
This scheme yields length-scale statistics that are acceptably independent of the conditioning criteria, which the VITA scheme
does not. 相似文献
12.
An equivalent circuit model of a novel fence structure vibratory micromachined gyroscope‘s oscillating properties is modeled by electrical equivalent circuits according to its dynamics equation. Equivalent circuit model of oscillating and differential detection capacitance model are implemented in the circuit simulation tool PSPICE, which is available in oscillating properties analysis such as oscillating‘s transient response, steady response and frequency response to angular rate to optimize working mode of the gyroscope. The model also enables sensor simulation with the interfacing electronics to analyse the performances of the whole system. Behavioral simulation of the system is performed to prove the function of detection circuits. The simulation results and measurement results show that the design of circuits is feasible. 相似文献
13.
R. Fosdick 《Continuum Mechanics and Thermodynamics》2011,23(6):483-489
Recently, a “principle of virtual power” has been adopted to model the behavior of materials that involve multiple length
scales. In these works, the “principle” is stated for arbitrary parts of a body and this arbitrariness is used, but not to its fullest extent, to draw conclusions concerning the structure of
the theory that results. Here, a theorem and an example application are given to illustrate the restrictive nature of the
requirement that it hold for arbitrary parts of a body and to draw attention to the full consequences that result from this
requirement. Several key results that have been reported in the recent literature are incomplete, and this incompleteness
has lead to superficial conclusions. 相似文献
14.
Frédéric Pignon Albert Magnin Jean-Michel Piau Gàbor Belina Pierre Panine 《Rheologica Acta》2009,48(5):563-578
The structure and orientation dynamics of sepiolite clay fibers about 1,000 nm long and 10 nm thick, suspended in an aqueous
poly(ehtylene oxide) matrix of 105 g/mol molecular mass, have been studied under control extensional and shear flow. A new extensional flow cell developed at
the “Laboratoire de Rhéologie” and the combined rheology and small angle X-ray scattering (Rheo-SAXS) setup available at the
European Synchrotron Radiation Facility have allowed access to in situ and time-resolved fiber orientations and structure
properties in the volume of suspensions under flow. In the volume fractions and shear rate domains for which the suspensions
exhibit shear-thinning properties, two regimes of orientation separated by a critical strain rate have been identified under
extensional flow. 相似文献
15.
B. M. Zhirnov 《International Applied Mechanics》2000,36(7):969-977
A technique is proposed to study and design a mechanical self-oscillating system in the quasiharmonic-oscillation regime.
The technique is based on the polynomial approximation of the force due to dry sliding friction by a finite number of terms
in the Taylor-series expansion with allowance for energy dissipation in accordance with Pisarenko's hypothesis and the first
“improved” asymptotic approximation.
Transport University, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 36, No. 7, pp. 137–144, July, 2000. 相似文献
16.
Klaus Zimmermann Igor Zeidis Michail Pivovarov Carsten Behn 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(11):1317-1328
This paper deals with the analysis of a one-dimensional motion of two mass points in a resistive medium. The force of resistance
is described by small non-symmetric viscous friction acting on each mass point. The magnitude of this force depends on the
direction of motion. The mass points are interconnected with a kinematic constraint or with an elastic element. Using the
averaging method the expressions for the stationary “on the average” velocity of the systems’s motion as a single whole is
found. In case of a small degree of non-symmetry an explicit expression for the stationary “on the average” velocity of the
system is derived. For the other case we obtained algebraic equations for the corresponding stationary velocity. 相似文献
17.
The mechanical model was established for the anti-plane fracture problem of a functionally graded coating–substrate system
with a coating crack inclined to the weak/micro-discontinuous interface. The Cauchy singular integral equation for the crack
was derived using Fourier integral transform, and the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta was
used to get its numerical solution. Finally, the effects of the weak/micro-discontinuity of the interface on SIFs were analyzed,
the “affected regions” corresponding to the two crack tips have been obtained and their engineering significance was discussed.
It was indicated that, for the crack tip in the corresponding “affected region”, to reduce the weak-discontinuity of the interface
and to make the interface micro-discontinuous are the two effective ways to reduce the SIF, and the latter way always has
more remarkable SIF-reduction effect. For the crack tip outside the “affected region”, its SIF is mainly influenced by material
stiffness, and to prevent such a tip from growing toward the interface “softer coating and stiffer substrate” is a more advantageous
combination than “stiffer coating and softer substrate”. 相似文献
18.
The interior transmission problem (ITP), which plays a fundamental role in inverse scattering theories involving penetrable
defects, is investigated within the framework of mechanical waves scattered by piecewise-homogeneous, elastic or viscoelastic
obstacles in a likewise heterogeneous background solid. For generality, the obstacle is allowed to be multiply connected,
having both penetrable components (inclusions) and impenetrable parts (cavities). A variational formulation is employed to
establish sufficient conditions for the existence and uniqueness of a solution to the ITP, provided that the excitation frequency does not belong
to (at most) countable spectrum of transmission eigenvalues. The featured sufficient conditions, expressed in terms of the
mass density and elasticity parameters of the problem, represent an advancement over earlier works on the subject in that
(i) they pose a precise, previously unavailable provision for the well-posedness of the ITP in situations when both the obstacle
and the background solid are heterogeneous, and (ii) they are dimensionally consistent, i.e., invariant under the choice of
physical units. For the case of a viscoelastic scatterer in an elastic solid it is further shown, consistent with earlier
studies in acoustics, electromagnetism, and elasticity that the uniqueness of a solution to the ITP is maintained irrespective
of the vibration frequency. When applied to the situation where both the scatterer and the background medium are viscoelastic, i.e., dissipative, on the other hand, the same type of analysis
shows that the analogous claim of uniqueness does not hold. Physically, such anomalous behavior of the “viscoelastic-viscoelastic”
case (that has eluded previous studies) has its origins in a lesser known fact that the homogeneous ITP is not mechanically
insulated from its surroundings—a feature that is particularly cloaked in situations when either the background medium or
the scatterer are dissipative. A set of numerical results, computed for ITP configurations that meet the sufficient conditions
for the existence of a solution, is included to illustrate the problem. Consistent with the preceding analysis, the results
indicate that the set of transmission values is indeed empty in the “elastic-viscoelastic” case, and countable for “elastic-elastic”
and “viscoelastic-viscoelastic” configurations. 相似文献
19.
A new microtensile tester for the study of MEMS materials with the aid of atomic force microscopy 总被引:4,自引:0,他引:4
An apparatus has been designed and implemented to measure the elastic tensile properties (Young's modulus and tensile strength)
of surface micromachined polysilicon specimens. The tensile specimens are “dog-bone” shaped ending in a large “paddle” for
convenient electrostatic or, in the improved apparatus, ultraviolet (UV) light curable adhesive gripping deposited with electrostatically
controlled manipulation. The typical test section of the specimens is 400 μm long with 2 μm×50 μm cross section. The new device
supports a nanomechanics method developed in our laboratory to acquire surface topologies of deforming specimens by means
of Atomic Force Microscopy (AFM) to determine (fields of) strains via Digital Image Correlation (DIC). With this tool, high
strength or non-linearly behaving materials can be tested under different environmental conditions by measuring the strains
directly on the surface of the film with nanometer resolution. 相似文献
20.
Vortex Shedding from a Hemisphere in a Turbulent Boundary Layer 总被引:1,自引:0,他引:1
Michael Manhart 《Theoretical and Computational Fluid Dynamics》1998,12(1):1-28
Supercritical turbulent boundary layer flow over a hemisphere with a rough surface (Re= 150000) has been simulated using Large Eddy Simulation (LES) and analyzed using the Karhunen--Loève expansion (“Proper Orthogonal
Decomposition,” POD). The time-dependent inflow condition is provided from a separate LES of a boundary layer developing behind
a barrier fence and a set of vorticity generators. LES results using significantly different grid resolutions are compared
with a corresponding wind tunnel experiment to demonstrate the reliability of the simulation. The separation processes are
analyzed by inspecting second-order moments, time spectra, and instantaneous velocity distributions. Applying POD, a detailed
study of the spatiotemporal structure of the separation processes has been carried out. From this analysis it can be concluded
that the major event in the separated flow behind the obstacle is the shedding of “von Kármán”-type vortices, which can be
represented by the first three energetically dominant modes.
Received 23 January 1997 and accepted 19 February 1998 相似文献