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941.
To model mathematically the problem of a rigid body moving below the free surface, a control surface surrounding the body is introduced. The linear free surface condition of the steady waves created by the moving body is satisfied. To describe the fluid flow outside this surface a potential integral equation is constructed using the Kelvin wave Green function whereas inside the surface, a source integral equation is developed adopting a simple Green function. Source strengths are determined by matching the two integral equations through continuity conditions applied to velocity potential and its normal derivatives along the control surface. After solving for the induced fluid velocity on the body surface and the control surface, an integral equation is derived involving a mixed distribution of sources and dipoles using a simple Green function and one component of the fluid velocity. The normal derivatives of the fluid velocity on the body surface, namely the m‐terms, are then solved by this matching integral equation method (MIEM). Numerical results are presented for two elliptical sections moving at a prescribed Froude number and submerged depth and a sensitivity analysis undertaken to assess the influence of these parameters. Furthermore, comparisons are performed to analyse the impact of different assumptions adopted in the derivation of the m‐terms. It is found that the present method is easy to use in a panel method with satisfactory numerical precision. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
942.
Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The
results show that excessive arsenic atoms of about 1020 cm−3 exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs.
The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing
above 300°C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing.
The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity,
and the effects of backgating or sidegating are effectively restrained. 相似文献
943.
We investigated site specific reactivity of the α-Cu-Al(17 at.%)(1 0 0) alloy surface versus that of Al and Cu by measuring neutralisation of Li+ ions. Experiments show that Li+ neutralisation on the α-CuAl(1 0 0) alloy surface does not occur efficiently on Al and is somewhat more efficient on Cu as compared to a pure Cu sample, indicating depletion of electron density on Al and transfer to neighboring Cu. It can thus be concluded that Cu sites in presence of Al are more reactive in the sense that processes involving electron capture from the surface would proceed more efficiently on these. 相似文献
944.
探讨了推广EZ模型的可能性,并给出了相应的模型中人群大小分布函数的形式解.研究表明金融市场中不同大小的人群数目的交易人的数目在重新标度后将具有最广泛的普适性行为
关键词:
金融物理
人群效应
主方程 相似文献
945.
The method of wave function expansion is adopted to study the scattering of a plane harmonic acoustic wave incident at an arbitrary angle upon an arbitrarily thick cylindrically orthotropic homogeneous cylindrical shell submerged in and filled with compressible ideal fluids. A laminate approximate model and the so-called state space formulation in conjunction with the classical transfer matrix (T-matrix) approach are employed to present an analytical solution based on the three-dimensional exact equations of anisotropic elasticity. The solution is used to correlate the perturbation in the material elastic constants of an air-filled and water-submerged aluminium cylindrical shell to the sensitivity of resonances associated with various modes of wave propagation appearing in the backscattered amplitude spectrum (i.e., axially guided, Lamb, Rayleigh and Whispering Gallery waves). The effects of shell wall thickness as well as inner fluid loading on the frequency response of the shell are also examined. A limiting case is considered and good agreement with the solution available in the literature is obtained. 相似文献
946.
An original set-up is used to study the adhesive properties of two hemispherical soap bubbles put into contact. The contact
angle at the line connecting the three films is extracted by image analysis of the bubbles profiles. After the initial contact,
the angle rapidly reaches a static value slightly larger than the standard 120° angle expected from Plateau rule. This deviation is consistent with previous experimental and theoretical studies: it can
be quantitatively predicted by taking into account the finite size of the Plateau border (the liquid volume trapped at the
vertex) in the free energy minimization. The visco-elastic adhesion properties of the bubbles are further explored by measuring
the deviation Δθd(t) of the contact angle from the static value as the distance between the two bubbles supports is sinusoidally modulated. It
is found to linearly increase with Δr
c/r
c , where rc is the radius of the central film and Δr
c the amplitude of modulation of this length induced by the displacement of the supports. The in-phase and out-of-phase components
of Δθd(t) with the imposed modulation frequency are systematically probed, which reveals a transition from a viscous to an elastic
response of the system with a crossover pulsation of the order 1rad · s^-1. Independent interfacial rheological measurements,
obtained from an oscillating bubble experiment, allow us to develop a model of dynamic adhesion which is confronted to our
experimental results. The relevance of such adhesive dynamic properties to the rheology of foams is briefly discussed using
a perturbative approach to the Princen 2D model of foams. 相似文献
947.
Ultrasound has been proven to enhance the mass transfer process and impact the fabrication of anodic aluminum oxide (AAO). However, the different effects of ultrasound propagating in different media make the specific target and process of ultrasound in AAO remain unclear, and the effects of ultrasound on AAO reported in previous studies are contradictory. These uncertainties have greatly limited the application of ultrasonic-assisted anodization (UAA) in practice. In this study, the bubble desorption and mass transfer enhancement effects were decoupled based on an anodizing system with focused ultrasound, such that the dual effects of ultrasound on different targets were distinguished. The results showed that ultrasound has the dual effects on AAO fabrication. Specifically, ultrasound focused on the anode has a nanopore-expansion effect on AAO, leading to a 12.24 % improvement in fabrication efficiency. This was attributed to the promotion of interfacial ion migration through ultrasonic-induced high-frequency vibrational bubble desorption. However, AAO nanopores were observed to shrink when ultrasound was focused on the electrolyte, accompanied by a 25.85 % reduction in fabrication efficiency. The effects of ultrasound on mass transfer through jet cavitation appeared to be the reason for this phenomenon. This study resolved the paradoxical phenomena of UAA in previous studies and is expected to guide AAO application in electrochemistry and surface treatments. 相似文献
948.
When an elastomeric material is deformed and subjected to temperatures above some chemorheological value T
cr (near 100°C for natural rubber), its macromolecular structure undergoes time and temperature dependent chemical changes.
The process continues until the temperature decreases below T
cr. Compared to the virgin material, the new material system has modified properties (often a reduced stiffness) and permanent
set on removal of the applied load. A recently proposed constitutive theory is used to study the influence of chemorheological
changes on the inflation of an initially isotropic spherical rubber membrane. The membrane is inflated while at a temperature
below T
cr. We then look at the pressure response assuming the sphere's radius is held fixed while the temperature is increased above
T
cr for a period of time and then returned to its original value. The inflation pressure during this process is expressed in
terms of the temperature, representing entropic stiffening of the elastomer, and a time dependent property that represents
the kinetics of the chemorheological change in the elastomer. When the membrane has been returned to its original temperature,
it is shown to have a permanent set and a modified pressure-inflated radius relation. Their dependence on the initial inflated
radius, material properties and kinetics of chemorheological change is studied when the underlying elastomeric networks are
neo-Hookean or Mooney–Rivlin. 相似文献
949.
Experimental observations show that quasi-isotropic materials, such as N-axial fibre-reinforced composites and woven materials, exhibit various degrees of anisotropy in elasticity and strength, and the anisotropy in strength is normally stronger than that in elasticity. In view of some available experimental data and based on the general formulation of the constitutive equations and failure criteria of quasi-isotropic materials established by using the theory of representations for tensor functions, we postulate several applicable models of the constitutive equations and strength for 3-and 4-axial quasi-isotropic materials to reveal the anisotropic effects. In a continued work (Part II), the anisotropic effect in strength of an infinitely large plate with a single elliptical hole or crack is studied, and the proposed stiffness and strength models are verified in terms of micro-mechanical analyses.Project supported by the National Natural Science Foundation of China and the State Education Commission Foundation of China 相似文献
950.
The linear stability theory is used to investigate analytically the Coriolis effect on centrifugally driven convection in a rotating porous layer. The problem corresponding to a layer placed far away from the axis of rotation was identified as a distinct case and therefore justifying special attention. The stability of the basic centrifugally driven convection is analysed. The marginal stability criterion is established as a characteristic centrifugal Rayleigh number in terms of the wavenumber and the Taylor number. 相似文献