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41.
《Fluid Dynamics Research》2007,39(7):526-551
A review is made of a two-point closure approximation called Lagrangian renormalized approximation (LRA), which is derived by a simple truncation of systematic Lagrangian renormalized expansions and is free from any ad hoc adjusting parameters or quantities. Emphasis is given to three key ideas: (i) representative, (ii) mapping and (iii) renormalized expansion underlying the LRA. The nature of the method of the expansion is explained by simple models, and general properties of the expansion as well as the truncated approximation are discussed in a general framework. A brief survey of the consequences of the LRA applied to three- and two-dimensional turbulences and passive scalar fields convected by turbulence is also presented. 相似文献
42.
The series solutions of unsteady flows of a viscous incompressible electrically conducting fluid caused by an impulsively
rotating infinite disk are given by means of an analytic technique, namely the homotopy analysis method. Using a set of new
similarity transformations, we transfer the Navier–Stokes equations into a pair of nonlinear partial differential equations.
The convergent series solutions are obtained, which are uniformly valid for all dimensionless time 0 ≤ τ < ∞ in the whole
spatial region 0 ≤ η < ∞. To the best of our knowledge, such kind of series solutions have never been reported. The effect
of magnetic number on the velocity is investigated. 相似文献
43.
44.
This paper reports the results of an investigation into the characteristics of wave propagation in carbon nanotubes embedded
in an elastic matrix, based on an exact shell model. Each of the concentric tubes of multi-walled carbon nanotubes is considered
as an individual elastic shell and coupled together through the van der Waals forces between two adjacent tubes. The matrix
surrounding carbon nanotubes is described as a spring element defined by the Winkler model. The effects of rotatory inertia
and elastic matrix on the wave velocity, the critical frequency, and the amplitude ratio between two adjacent tubes are described
and discussed through numerical examples. The results obtained show that wave propagation in carbon nanotubes may appear in
a critical frequency at which the wave velocity changes suddenly; the elastic matrix surrounding carbon nanotubes debases
the critical frequency and the wave velocity, and changes the vibration modes between two adjacent tubes; the rotatory inertia
based on an exact shell model obviously influences the wave velocity at some wave modes. Finally, a comparison of dispersion
solutions from different shell models is given. The present work may serve as a useful reference for the application and the
design of nano-electronic and nano-drive devices, nano-oscillators, and nano-sensors, in which carbon nanotubes act as basic
elements. 相似文献
45.
This paper presents a method for determining the nonlinear dynamic responses of structures under moving loads. The load is considered as a four degrees-of-freedom system with linear suspensions and tires flexibility, and the structure is modeled as an Euler–Bernoulli beam with simply supported at both ends. The nonlinear dynamic interaction of the load–structure system is discussed, and Kelvin−Voigt material model is employed for the beam. The nonlinear partial differential equations of the dynamic interaction are derived by using the von Kármán nonlinear theory and D'Alembert's principle. Based on the Galerkin method, the partial differential equations of the system are transformed into nonlinear ordinary equations, which can be solved by using the Newmark method and Newton−Raphson iteration method. To validate the approach proposed in this paper, the comparison are performed using a moving mass and a moving oscillator as the excitation sources, and the investigations demonstrate good reliability. 相似文献
46.
Most parallel efficient global optimization (EGO) algorithms focus only on the parallel architectures for producing multiple updating points, but give few attention to the balance between the global search (i.e., sampling in different areas of the search space) and local search (i.e., sampling more intensely in one promising area of the search space) of the updating points. In this study, a novel approach is proposed to apply this idea to further accelerate the search of parallel EGO algorithms. In each cycle of the proposed algorithm, all local maxima of expected improvement (EI) function are identified by a multi-modal optimization algorithm. Then the local EI maxima with value greater than a threshold are selected and candidates are sampled around these selected EI maxima. The results of numerical experiments show that, although the proposed parallel EGO algorithm needs more evaluations to find the optimum compared to the standard EGO algorithm, it is able to reduce the optimization cycles. Moreover, the proposed parallel EGO algorithm gains better results in terms of both number of cycles and evaluations compared to a state-of-the-art parallel EGO algorithm over six test problems. 相似文献
47.
48.
《Journal of Fluids and Structures》2006,22(4):493-504
The purpose of the paper is to demonstrate the feasibility of the direct coupling of the finite element method for the structural part with a Wagner representation of the hydrodynamic loads during the impact of an elastic body onto the water surface. An efficient and very general method is developed and validated in two dimensions. Advantages of the present method are outlined for the elastic wedge impact problem; however, the method is applicable to any elastic body with small deadrise angle entering water vertically at moderate velocity. Strategy for coupling of this method with commercial finite element codes is discussed. 相似文献
49.
《European Journal of Mechanics - A/Solids》2007,26(1):1-19
Interfacial fibrilation is a typical mechanism that frequently occurs during delamination of a polymer coating from a steel substrate. It involves large displacements at the interface as well as large deformations in the bulk material. Classical small displacement cohesive zone formulations fail to describe such large deformations correctly. Therefore, a generic cohesive zone model is introduced that is suitable to describe both uniform and non-uniform fracture at an interface with large deformations in the delaminating bulk and large displacements at the crack tip. 相似文献
50.
The paper is concerned with a formulation of anisotropic finite strain inelasticity based on the multiplicative decomposition of the deformation gradient F=FeFp. A major feature of the theory is its invariance with respect to rotations superimposed on the inelastic part of the deformation gradient. The paper motivates and shows how such an invariance can be achieved. At the heart of the formulation is the mixed-variant transformation of the structural tensor, defined as the tensor product of the privileged directions of the material as given in a reference configuration, under the action of Fp. Issues related to the plastic material spin are discussed in detail. It is shown that, in contrast to the isotropic case, any flow function formulated purely in terms of stress quantities, necessarily exhibits a non-vanishing plastic material spin. The possible construction of spin-free rates is discussed as well, where it is shown that the flow rule must then depend not only on the stress but on the strain as well. 相似文献