共查询到20条相似文献,搜索用时 62 毫秒
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 transient response of a central crack in an orthotropic strip under the in-plane shear impact loading is studied by using
the dual integral equation method proposed by Copson and Sih. The general formula for the shear stress intensity factor
near the crack tip is derived. Numerical results of
with
in various cases are obtained by solving the second kind Fredholm integral equation and by performing the inverse Laplace
transform. 相似文献
3.
The convection in atmosphere discussed in ref. [1] is rigorously treated by considering the variation of environmental temperature
with the height. This represents an example of applications of the elementary catastrophe theory in Hamiltonian systems. 相似文献
4.
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
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.
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
7.
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
8.
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
9.
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
10.
THECOMPRESSIONLSESTIMATEOFREGRESSIONCOEFFICIENTINMULTIVARIATELINEARMODELChenShi-ji(陈世基)(Dept.ofMathematics,FUjianNormalUniver... 相似文献
11.
Summary An analysis of the effects of couple-stresses on the effective Taylor diffusion coefficient has been carried out with the help of two non-dimensional parameters
based on the concentration of suspensions and
, a constant associated with the couple-stresses. It is observed that the concentration distribution increases with increasing
or
The effective Taylor diffusion coefficient falls rapidly with increasing
when
is negative.
a Tube radius - C Concentration - C i Body moment vector - C 0 Concentration at the axis of the tube - C m Mean concentration - D Molecular diffusion coefficient - d ij Symmetric part of velocity gradient - F Function of and characterising effective Taylor diffusion coefficient - f i Body force vector - H A function of and - K 2 Integration constant - K * Effective Taylor diffusion coefficient - k Radius of gyration of a unit cuboid with its sides normal to the spatial axes - I n Modified Bessel's function ofnth order - L Length of the tube over which the concentration is spread - M Function ofH and - M ij Couple stress tensor - P Function of - p Fluid pressure - Q Volume rate of the transport of the solute across a section of the tube - r Radial distance from the axis of the tube - T ij Stress tensor - t Time coordinate - T ij A Antisymmetric part of the stress tensor - u Relative fluid velocity - Average velocity - v i Velocity vector - Fluid velocity at any point of the tube - v 0 n Velocity of Newtonian fluid at the axis of the tube - i Vorticity vector - x Axial coordinate - x 1 Relative axial coordinate - z Non-Dimensional radial coordinate - Density - ij Symmetric part of the stress tensor - µ Viscosity of the fluid - µ ij Deviatoric part ofM ij - , Constants associated with couple-stress With 3 figures 相似文献
Zusammenfassung Der Einfluß der Momentenspannungen auf den effektiven Taylorschen Diffusionskoeffizienten wird untersucht. Dabei treten zwei dimensionslose Parameter and auf: Der erste bezieht sich auf die Suspensionskonzentration, der zweite kennzeichnet die Momentenspannungen. Man findet, daß die Verteilungsgeschwindigkeit mit wachsendem oder zunimmt. Dagegen fällt der Taylorsche Diffusionskoeffizient bei wachsendem stark ab, wenn negativ ist.
a Tube radius - C Concentration - C i Body moment vector - C 0 Concentration at the axis of the tube - C m Mean concentration - D Molecular diffusion coefficient - d ij Symmetric part of velocity gradient - F Function of and characterising effective Taylor diffusion coefficient - f i Body force vector - H A function of and - K 2 Integration constant - K * Effective Taylor diffusion coefficient - k Radius of gyration of a unit cuboid with its sides normal to the spatial axes - I n Modified Bessel's function ofnth order - L Length of the tube over which the concentration is spread - M Function ofH and - M ij Couple stress tensor - P Function of - p Fluid pressure - Q Volume rate of the transport of the solute across a section of the tube - r Radial distance from the axis of the tube - T ij Stress tensor - t Time coordinate - T ij A Antisymmetric part of the stress tensor - u Relative fluid velocity - Average velocity - v i Velocity vector - Fluid velocity at any point of the tube - v 0 n Velocity of Newtonian fluid at the axis of the tube - i Vorticity vector - x Axial coordinate - x 1 Relative axial coordinate - z Non-Dimensional radial coordinate - Density - ij Symmetric part of the stress tensor - µ Viscosity of the fluid - µ ij Deviatoric part ofM ij - , Constants associated with couple-stress With 3 figures 相似文献
12.
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
13.
Inrecentyears,applicationsofquaternionmatricesarebecomingmoreandmoreimportantandextensiveinrigidmechanics,quantummechanics,controltheoryandhelicaltechnology[1~3].Withtherapiddevelopmentoftheabovedisciplines,itisgettingmoreandmorenecessaryforustofurth… 相似文献
14.
A novel method for measuring and characterizing dynamic fracture-initiation toughness of elastic-plastic materials 总被引:5,自引:0,他引:5
The characterization and testing methods of the dynamic fracture initiation toughness of elastic-plastic materials under tensile
impact are studied. By using the self-designed bar-bar tensile impact apparatus, a novel test method for studying dynamic
fracture-initiation has been proposed based on the one-dimensional test principle. The curve of average loadv. s. displacement
is smooth until unstable crack propagation, and the kinetic energy which does not contribute to the crack growth can be removed
from total work done by external-force to the specimen. The fracture-initiation point is determined by compliance-changing
rate method. The results show that these methods are feasible and effective. Through the analysis of the conversion between
work and energy of a fracture specimen, the dynamicJ-integral is adopted as a characteristic parameter for elastic-plastic materials under impact loading. TheJ-integral is calculated from
and
curves by using the formula proposed, by Rice. TheJ-integral at fracture initiation is employed to describe the dynamic fracture-initiation toughness of elastic-plastic materials
and the experimental results indicate thatJ
ID can be regarded as a material constant. 相似文献
15.
A parameter t is introduced to boundary slip line of rigid regions for plane strain and indirect extrusions with a fractional
reduction R=0.5. Integration by substitution has been used along the boundary slip line in order to obtain the extrusion pressure.
By the integration depending on a parameter, the following results are obtained,
and die pressure is 5.14k for backward extrusion;
and pad average pressure is 2.57k for forward extrusion. All the results from this method are the same as those of the conventional
solution. 相似文献
16.
Xu Lanxi 《Acta Mechanica Sinica》2000,16(2):113-120
Nonlinear stability of the motionless state of a heterogeneous fluid with constant temperature-gradient and concentration-gradient
is studied for both cases of stress-free and rigid boundary conditions. By introducing new energy functionals we have shown
that for τ=P
C
/P
T
≤1,
the motionless state is always stable and for τ≤1,
the sufficient and necessary conditions for stability coincide, whereP
C
,P
T
,C andR are the Schmidt number, Prandtl number, Rayleigh number for solute and heat respectively. Moreover, the criteria guarantees
the exponential stability.
The Project supported by SRF for ROCS, China Postdoctoral Science Foundation and the National Basic Research Project “Nonlinear
Science” 相似文献
17.
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
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.
Shear flow properties of concentrated solutions of linear and star branched polystyrenes 总被引:2,自引:0,他引:2
Summary The linear viscoelastic and viscometric functions have been determined for solutions of wellcharacterized monodisperse linear and star-branched polystyrenes and for commercial, polydisperse polystyrene. The value of the product c
for these solutions was large and was obtained by using both high and low
The effect of structure on the rheological properties was determined by examining how parameters in a modified Carreau viscosity equation (used to fit the data) varied with c,
, and branching. No enhancement effects on the rheological properties were observed because of branching.The Cox-Merz rule was observed to describe the similarities between the viscosity and complex viscosity for most of the monodisperse samples studied. The broad molecular weight distribution polystyrene solutions did not follow this empiricism.With 17 figures and 4 tables 相似文献
20.
V. N. Churakov 《International Applied Mechanics》1975,11(6):659-662
Conclusions Similariry conditions have been established on the basis of which the viscosity can be simulated in testing viscoelastic materials for tension (compression) under hydrostatic pressure. It has been shown that criteria
and
account for the effect of viscosity, while the II number accounts for the effect of pressure. The criterion
is, in form, identical to the analogous parameter in the theory of non-Newtonian fluid flow. It has been shown, furthermore, that criterion
is the monodromic version of criterion
(the similarity number). When P=0 or P is very small and the II number degenerates, then only criterion
or criterion
should be used.Institute of Problems in Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Prikladnaya Mekhanika, Vol. 11, No. 6, pp. 109–114, June, 1975. 相似文献