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1.
The segregation of bismuth atoms on the [101] tilt copper grain boundaries Σ3 (
) 70.53°, Σ33 (
) 58.99°, Σ11 (
) 50.48° and Σ9 (
) 38.94° has been studied by pseudo-molecular dynamics using the empiricalN-body potentials. The relationship between bismuth segregation and grain boundary structure has been discussed in detail.
The subject supported by the Chinese Academy of Sciences and National Natural Science Foundation of China 相似文献
2.
The characteristics of low-speed fluid streaks occurring under sheared air-water interfaces were examined by means of hydrogen
bubble visualization technique. A critical shear condition under which the streaky structure first appears was determined
to beu
τ≈0.19 cm/s. The mean spanwise streak spacing increases with distance from the water surface owing to merging and bursting
processes, and a linear relationship describing variation of non-dimensional spacing
versusy
+ was found essentially independent of shear stress on the interface. Values of
, however, are remarkably smaller than their counterparts in the near-wall region of turbulent boundary layers. Though low-speed
streaks occur randomly in time and space, the streak spacing exhibits a lognormal probability distribution behavior. A tentative
explanation concerning the formation of streaky structure is suggested, and the fact that
takes rather smaller values than that in wall turbulence is briefly discussed.
The project supported by the National Natural Science Foundation of China (19672070) 相似文献
3.
Inrecentyears,applicationsofquaternionmatricesarebecomingmoreandmoreimportantandextensiveinrigidmechanics,quantummechanics,controltheoryandhelicaltechnology[1~3].Withtherapiddevelopmentoftheabovedisciplines,itisgettingmoreandmorenecessaryforustofurth… 相似文献
4.
The microprocesses of deformation and fracture of Bi-segregated copper bicrystals Σ33 (
) 58.99°, Σ11 (
) 50.48° and Σ9 (
) 38.94° have been simulated by molecular dynamics in order to study the relationship between the grain boundary embrittlement
(GBE) and grain boundary (GB) structure. It is shown that GBE is related to the segregated concentration and distribution
of Bi atoms, while Bi segregation is related to the GB structure. Due to their different structures, the bicrystals Σ33, Σ11
and Σ9 show an increasing propensity for Bi segregated concentration. So under the action of external force, Σ33, Σ11 and
Σ9 show transgranular ductile, intergranular tearing and intergranular brittle fracture modes, respectively.
The subject supported by the Chinese Academy of Sciences and National Natural Science Foundation of China 相似文献
5.
Fu Song 《Acta Mechanica Sinica》1992,8(3):208-214
Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect
of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect
of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation
between
and
, established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect.
Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show
that the spreading rate of these flows can be satisfactorily captured. 相似文献
6.
Dr. M. Dow Dr. H. Nakamura Prof. Dr. G. I. N. Rozvany 《Archive of Applied Mechanics (Ingenieur Archiv)》1982,52(5):335-353
Summary The first part of this paper is concerned with the optimal design of spherical cupolas obeying the von Mises yield condition. Five different load combinations, which all include selfweight, are investigated. The second part of the paper deals with the optimal quadratic meridional shape of cupolas obeying the Tresca yield condition, considering selfweight plus the weight of a non-carrying uniform cover. It is established that at long spans some non-spherical Tresca cupolas are much more economical than spherical ones.
List of Symbols ak, bk, ck, Ak, Bk, Ck coefficients used in series solutions - A, B constants in the nondimensional equation of the meridional curve - normal component of the load per unit area of the middle surface - meridional and circumferential forces per unit width - radial pressure per unit area of the middle surface, - skin weight per unit area of the middle surface, - vertical external load per unit horizontal area, - base radius, - R radius of convergence - s - cupola thickness, - u, w subsidiary functions for quadratic cupolas - vertical component of the load per unit area of middle surface - resultant vertical force on a cupola segment - structural weight of cupola, - combined weight of cupola and skin, - distance from the axis of rotation, - vertical distance from the shell apex, - z auxiliary variable in series solutions - specific weight of structural material of cupola - radius of the middle surface, - uniaxial yield stress - meridional stress, - circumferential stress, - a, b, c, d, e subsidiary variables used in evaluating the meridional stress - auxiliary function used in series solutions This paper constitutes the third part of a study of shell optimization which was initiated and planned by the late Prof. W. Prager 相似文献
Optimale Kuppeln gleicher Festigkeit: Kugelschalen und axialsymmetrische Schalen
Übersicht Im ersten Teil dieser Arbeit wird der optimale Entwurf sphärischer Kuppeln behandelt, wobei die von Misessche Fließbewegung zugrunde gelegt wird. Fünf verschiedene Lastkombinationen werden untersucht. Der zweite Teil befaßt sich mit der optimalen quadratischen Form des Meridians von Kuppeln, die der Fließbedingung von Tresca folgen.
List of Symbols ak, bk, ck, Ak, Bk, Ck coefficients used in series solutions - A, B constants in the nondimensional equation of the meridional curve - normal component of the load per unit area of the middle surface - meridional and circumferential forces per unit width - radial pressure per unit area of the middle surface, - skin weight per unit area of the middle surface, - vertical external load per unit horizontal area, - base radius, - R radius of convergence - s - cupola thickness, - u, w subsidiary functions for quadratic cupolas - vertical component of the load per unit area of middle surface - resultant vertical force on a cupola segment - structural weight of cupola, - combined weight of cupola and skin, - distance from the axis of rotation, - vertical distance from the shell apex, - z auxiliary variable in series solutions - specific weight of structural material of cupola - radius of the middle surface, - uniaxial yield stress - meridional stress, - circumferential stress, - a, b, c, d, e subsidiary variables used in evaluating the meridional stress - auxiliary function used in series solutions This paper constitutes the third part of a study of shell optimization which was initiated and planned by the late Prof. W. Prager 相似文献
7.
The in-plane deformation fields near a stationary crack tip for thin, single edge-notched (SEN) specimens, made from Plexiglas, 3003 aluminum alloy and 304 stainless steel, have been successfully obtained by using computer vision. Results from the study indicate that (a) in-plane deformations ranging from elastic to fully plastic can be obtained accurately by the method, (b) for U,
and
, the size of the HRR dominant zone is much smaller than forV and
, respectively. Since these results are in agreement with recent analytical work, suggesting that higher order terms will be needed to accurately predict trends in the data, it is clear that the region where the first term in the asymptotic solution is dominant is dependent on the component of the deformation field being studied, (c) the HRR solution can be used to quantity
only in regions where theplastic strains strongly dominate the elastic strain components (i.e., when
); forV, the HRR zone appears to extend somewhat beyond this region, (d) the displacement componentU does not have the HRR singularity anywhere within the measurement region for either 3003 aluminum or 304 SS. However, the displacement componentV agrees with the HRR slope up to the plastic-zone boundary in 3003 aluminum (
) and over most of the region where measurements were obtained (
) in 304 SS and (e) the effects of end conditions must be included in any finite-element model of typical SEN specimen geometries to accurately calculate theJ integral and the crack-tip fields.Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 8–11. 相似文献
8.
The work presented is a wind tunnel study of the near wake region behind a hemisphere immersed in three different turbulent boundary layers. In particular, the effect of different boundary layer profiles on the generation and distribution of near wake vorticity and on the mean recirculation region is examined. Visualization of the flow around a hemisphere has been undertaken, using models in a water channel, in order to obtain qualitative information concerning the wake structure.List of symbols
C
p
pressure coefficient,
-
D
diameter of hemisphere
-
n
vortex shedding frequency
-
p
pressure on model surface
-
p
0
static pressure
-
Re
Reynolds number,
-
St
Strouhal number,
-
U, V, W
local mean velocity components
-
mean freestream velocity inX direction
-
U
*
shear velocity,
-
u, v, w
velocity fluctuations inX, Y andZ directions
-
X
Cartesian coordinate in longitudinal direction
-
Y
Cartesian coordinate in lateral direction
-
Z
Cartesian coordinate in direction perpendicular to the wall
- it*
boundary layer displacement thickness,
-
diameter of model surface roughness
-
elevation angleI
-
O
boundary layer momentum thickness,
-
w
wall shearing stress
-
dynamic viscosity of fluid
-
density of fluid
-
streamfunction
- x
longitudinal component of vorticity,
- y
lateral component of vorticity,
-
z
vertical component of vorticity,
This paper was presented at the Ninth symposium on turbulence, University of Missouri-Rolla, October 1–3, 1984 相似文献
9.
A new concept of pseudo mean wave resistance is introduced to find theoretical mean wave resistances of the precursor soliton
generation in two-layer flow over a localized topography at near-resonance in this paper. The pseudo mean wave resistance
of the precursor soliton generation of two-layer flow is determined in terms of the AfKdV equation. From the theoretical results
it is shown that the theoretical mean wave resistance is equal to the pseudo mean wave resistance times 1/m
1, wherem
1 is the coefficient of the fKdV equation. From the regional distribution of the energy of the precursor soliton generation
at the resonant points, it is shown that ratios of the theoretical mean wave resistance and regional mean energy to the total
mean energy are invariant constants, i.e.
: (−1/2):1:1, in which
and
are the mean energy of the generating regions of the precursor solitons, of the depression and of the trailing, wavetrain
at the resonant points respectively,
and <D> are the total energy of the system and the theoretical mean wave resistance at the resonant points. A prediction of the
theoretical mean wave resistance flow over the semicircular topography is carried out in terms of the theoretical results
of the present paper. The comparison shows that the theoretical mean wave resistance is in good agreement with the numerical
calculation.
The project supported by the Foundation of The State Education Commission “The Dynamics of Upper Ocean” and the Grants of
The Physical Oceanography Laboratory of Ocean University of Qingdao 相似文献
10.
ConsidertheCauchyproblemforthewaveequationinRN×R+(N≥2):2u(x,t)t2-xiaij(x)xju=|u|p-1·u ((x,t)∈RN×(0,T)),u(x,0)=g(x) (x∈RN),ut(x,0)=h(x) (x∈RN),(1)whereu(x,t)isnontrivialsolutionwithfinitespeedofpropagationandissupportedonaforwardcone(x,t)·t≥0,|… 相似文献
11.
Based on the plastic-dynamic equations, the asymptotic behaviour of the near-tip fields for a plane stress tensile crack propagating
in a power-law material has been studied in this paper. It is shown that the stress and strain singularities are, respectively,
of the order
and
, whereA is a constant which is related to the size of plastic region,r is the distance to the crack tip,n is the power-law exponent.
Projects sponsored by the National Science Foundation. 相似文献
12.
W. L. Esmeijer 《Applied Scientific Research》1949,1(1):151-168
Summary An elastically supported beam of infinite length, initially at rest, carries a variable concentrated force
at a prescribed point A. General expressions are given for the deflection and the bending moment at A (6.3 and 6.4). Three special cases are considered; the first one is defined by
=0 for
and
=K=const. for
; the second one by
=0 for 0 >
>
,
given function of
for 0
; the third one applies to problems in which, during the period of impact,
itself is an unknown. The results given here may be of use in those railway-engineering problems in which a rail can be considered as a beam of infinite length, and in which the supporting ground has the required properties. 相似文献
13.
In [1], a class of multiderivative block methods (MDBM) was studied for the numerical solutions of stiff ordinary differential
equations. This paper is aimed at solving the problem proposed in [1] that what conditions should be fulfilled for MDBMs in
order to guarantee the A-stabilities. The explicit expressions of the polynomials
and
in the stability functions
are given. Furthermore, we prove
. With the aid of symbolic computations and the expressions of diagonal Pade' approximations, we obtained the biggest block
size k of the A-stable MDBM for any given l (the order of the highest derivatives used in MDBM, l≥1) 相似文献
14.
A basic re-examination of the traditional dimensional analysis of microscopic and macroscopic multiphase flow equations in porous media is presented. We introduce a macroscopic capillary number
which differs from the usual microscopic capillary number Ca in that it depends on length scale, type of porous medium and saturation history. The macroscopic capillary number
is defined as the ratio between the macroscopic viscous pressure drop and the macroscopic capillary pressure.
can be related to the microscopic capillary number Ca and the LeverettJ-function. Previous dimensional analyses contain a tacit assumption which amounts to setting
= 1. This fact has impeded quantitative upscaling in the past. Our definition for
, however, allows for the first time a consistent comparison between macroscopic flow experiments on different length scales. Illustrative sample calculations are presented which show that the breakpoint in capillary desaturation curves for different porous media appears to occur at
1. The length scale related difference between the macroscopic capillary number
for core floods and reservoir floods provides a possible explanation for the systematic difference between residual oil saturations measured in field floods as compared to laboratory experiment. 相似文献
15.
THECOMPRESSIONLSESTIMATEOFREGRESSIONCOEFFICIENTINMULTIVARIATELINEARMODELChenShi-ji(陈世基)(Dept.ofMathematics,FUjianNormalUniver... 相似文献
16.
Phil Diamond Peter Kloeden Aleksej Pokrovskii 《Journal of Dynamics and Differential Equations》1995,7(2):341-364
The concept of an interval stochastic matrix
is introduced. We prove a combinatorial theorem which describes the network flow associated with an interval matrix. The semi-invariant vectors of
are characterized in terms of eigenvectors with unit eigenvalue of stochastic matrices
. These results are then applied to the approximation and machine computation of invariant measures of dynamical systems.Funded under Australian Research Council Grant A 8913 2609. 相似文献
17.
R. B. Dingle 《Applied Scientific Research》1955,4(1):401-410
Summary A number of methods for obtaining expansions and approximations to an integral containing a parameter are expounded, and each
illustrated by evaluating the function
相似文献
18.
An analysis is presented for the unsteady laminar flow of an incompressible Newtonian fluid in an annulus between two concentric spheres rotating about a common axis of symmetry. A solution of the Navier-Stokes equations is obtained by employing an iterative technique. The solution is valid for small values of Reynolds numbers and acceleration parameters of the spheres. In applying the results of this analysis to a rotationally accelerating sphere, a virtual moment of intertia is introduced to account for the local inertia of the fluid.Nomenclature
R
i
radius of the inner sphere
-
R
o
radius of the outer sphere
-
radial coordinate
-
r
dimensionless radial coordinate,
-
meridional coordinate
-
azimuthal coordinate
-
time
-
t
dimensionless time,
- Re
i
instantaneous Reynolds number of the inner sphere,
i
R
k
2
/
- Re
o
instantaneous Reynolds number of the outer sphere,
o
R
o
2
/
-
radial velocity component
-
V
r
dimensionless radial velocity component,
-
meridional velocity component
- V
dimensionless meridional velocity component,
-
azimuthal velocity component
-
V
dimensionless azimuthal velocity component,
-
viscous torque
-
T
dimensionless viscous torque,
-
viscous torque at surface of inner sphere
-
T
i
dimensionless viscous torque at surface of inner sphere,
-
viscous torque at surface of outer sphere
-
T
o
dimensionless viscous torque at surface of outer sphere,
-
externally applied torque on inner sphere
-
T
p,i
dimensionless applied torque on inner sphere,
-
moment of inertia of inner sphere
-
Z
i
dimensionless moment of inertia of inner sphere,
-
virtual moment of inertia of inner sphere
-
Z
i,v
dimensionless virtual moment of inertia of inner sphere,
-
virtual moment of inertia of outer sphere
-
i
instantaneous angular velocity of the inner sphere
-
o
instantaneous angular velocity of the outer sphere
-
density of fluid
-
viscosity of fluid
-
kinematic viscosity of fluid,/
-
radius ratio,R
i/R
o
-
swirl function,
-
dimensionless swirl function,
-
stream function
-
dimensionless stream function,
-
i
acceleration parameter for the inner sphere,
-
o
acceleration parameter for the outer sphere,
-
shear stress
-
r
dimensionless shear stress,
相似文献
19.
D. Quemada 《Rheologica Acta》1978,17(6):643-653
Summary A non-newtonian viscosity equation
where is the volume concentration and
is an intrinsic viscosity, function of a relative shear rate
and
being structural parameters, has been proposed in a previous paper (1). From empirical grounds, the valuep = 1/2 holds for a large class of systems, like suspensions of rodand disc-shaped particles. In the high shear rate limit, aCasson law-type is recovered and discussed, especially the concentration dependence of the yield stress. However, the latter disappears in the low shear limit, and must be considered as a pseudo-yield stress. Good agreement is found in this low shear limit with some theoretical results ofBueche for polymers. More generally, the viscosity equation displays pseudo-plastic behaviour and fitting it on experimental data allows the determination of the structural parameters. Some examples (especially Red Blood Cell suspensions and Blood) are studied and support the model. Nevertheless, for spherical particle suspensions, the best fitting is reached forp = 1. Accurate values of particle diameters can be deduced from the structural parameter
, in this case.
With 5 figures and 3 tables 相似文献
Zusammenfassung In einer vorangegangenen Arbeit (1) wurde eine Viskositätsgleichung für eine nicht-newtonsche Flüssigkeit von der Form vorgeschlagen, worin die Volumenkonzentration und eine Grenzviskosität bedeutet; die letztere stellt eine Funktion der relativen Schergeschwindigkeit dar, die Konstantenk 0,k und bezeichnen Strukturparameter. Empirisch wird gefunden, daß für eine große Klasse von Systemen, wie z. B. stäbchen- und scheibchenförmigen Teilchen,p = 1/2 gilt. In der Grenze hoher Schergeschwindigkeiten wird ein Verlauf gemäß einer Casson-Gleichung gefunden und diskutiert, insbesondere bezüglich der Konzentrationsabhängigkeit der Fließspannung. Allerdings verschwindet diese in der Grenze niedriger Schergeschwindigkeiten und muß daher als Pseudo-Fließspannung betrachtet werden. In diesem Grenzfall wird eine gute Übereinstimmung mit theoretischen Voraussagen vonBueche an Polymeren gefunden. Ganz allgemein beschreibt die obige Viskositätsgleichung ein pseudoplastisches Verhalten, und ihre Anpassung an experimentelle Werte erlaubt die Bestimmung der Strukturparameter. Einige Beispiele, insbesondere Suspensionen von roten Blutkörperchen und Blut, werden untersucht und bestätigen das Modell. Allerdings erhält man bei Suspensionen kugelförmiger Teilchen die beste Anpassung fürp = 1. In diesem Fall kann man mit Hilfe des Strukturparameters genaue Werte der Teilchendurchmesser bestimmen.
With 5 figures and 3 tables 相似文献
20.
Part I of this work addressed quasi-static loading of the shear compression specimen (SCS), which has been especially developed
to investigate the shear dominant response of materials at various strain rates. The stress and strain states were characterized
numerically. Approximations were presented to reduce the measured load,P, and displacement,d, into equivalent stress
and strain
. This paper addresses dynamic loading of the SCS. Several simulations were made for representative materials, whose stress-strain
behavior is assumed to be rate-independent. The results show that stress wave loading induces strong oscillations in theP-d curve. However, the
curve remains smooth in the gage section. The oscillations are about the quasistatic load values, so that with suitable filtering
of the dynamicP-d curves, the quasi-static ones are readily recovered. Consequently, the approach that was developed for quasi-static loading
of the SCS is now extended to dynamic loading situations. The average strain rate is rather constant and scales linearly with
the prescribed velocity. As the plastic modulus becomes smaller, the strain rate reaches higher values. Friction at the end
pieces of the specimen is also investigated, and shown to have a small overall influence on the determined mechanical characteristics.
This paper thereby confirms the potential of the SCS for large strain testing of materials, using a unified approach, over
a large range of strain rates in a seamless fashion. 相似文献