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101.
轻质夹层材料的制备和振动声学性能 总被引：2，自引：0，他引：2
轻质夹层材料被广泛地用来制备动车组车体和飞机的机身,其结构设计面临着一系列挑战:即同时要求质量轻、力学强度高、散热性能好、动力学性能和隔声性能可调等多功能特性.针对动车组高速运行和飞机飞行过程中经常面临的振动及噪声问题,以及如何在现有的材料和结构基础上进一步减轻重量并获得更优良的综合性能是材料制备、固体力学、流体力学、声学、智能材料和结构、优化设计等诸多领域工作者面临的共同挑战.结合近年来围绕\"超轻多孔结构创新构型的多功能化基础研究\"国家基础研究计划项目所开展的一系列工作,综述了有关轻质三明治材料及结构振动和声学特性的国内外研究进展及现状,以及相应的主被动控制技术;针对目前存在的问题,讨论并展望了有关轻质材料和结构动力学性能及隔声性能的研究发展趋势. 相似文献
102.
103.
A. Evgrafov 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2006,86(1):46-62
We consider the problem of optimal design of flow domains for Navier–Stokes flows in order to minimize a given performance functional. We attack the problem using topology optimization techniques, or control in coefficients, which are widely known in structural optimization of solid structures for their flexibility, generality, and yet ease of use and integration with existing FEM software. Topology optimization rapidly finds its way into other areas of optimal design, yet until recently it has not been applied to problems in fluid mechanics. The success of topology optimization methods for the minimal drag design of domains for Stokes fluids (see the study of Borrvall and Petersson [12]) has lead to attempts to use the same optimization model for designing domains for incompressible Navier–Stokes flows. We show that the optimal control problem obtained as a result of such a straightforward generalization is ill‐posed, at least if attacked by the direct method of calculus of variations. We illustrate the two key difficulties with simple numerical examples and propose changes in the optimization model that allow us to overcome these difficulties. Namely, to deal with impenetrable inner walls that may appear in the flow domain we slightly relax the incompressibility constraint as typically done in penalty methods for solving the incompressible Navier–Stokes equations. In addition, to prevent discontinuous changes in the flow due to very small impenetrable parts of the domain that may disappear, we consider so‐called filtered designs, that has become a “classic” tool in the topology optimization toolbox. Technically, however, our use of filters differs significantly from their use in the structural optimization problems in solid mechanics, owing to the very unlike design parametrizations in the two models. We rigorously establish the well‐posedness of the proposed model and then discuss related computational issues. 相似文献
104.
G. Rauchs 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2006,86(7):539-562
The calculation of the derivatives of the state variables with respect to material parameters using the direct differentiation method is developed for the case of a finite strain finite element analysis in corotational formulation for material behaviour including hypo‐elasticity and non‐linear isotropic and kinematic hardening plasticity. The sensitivity analysis for the case of flexible‐to‐flexible contact, required in indentation testing, has been included. The derivatives obtained in a rotating‐stretching bar problem are compared to results obtained by the finite difference method in order to verify the suitability of the corotational formulation in sensitivity analysis for dealing with rigid body rotations. Material parameter identification using a gradient‐based numerical optimization procedure is assessed with respect to stability by using pseudo‐experimental indentation curves, obtained from modelling with known material parameters, and superposed with artificial noise. The effect of the load history on parameter identification is investigated. 相似文献
105.
M. Stelzer O. von Stryk 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2006,86(10):828-840
The modeling of the time dependent, dynamic behavior of the human musculoskeletal system results in a large scale mechanical multibody system. This consists of submodels for the skeleton, wobbling masses, muscles and tendons as redundant actuators. Optimization models are required for the simulation of the muscle groups involved in a motion. In contrast to the inverse dynamics simulation the forward dynamics simulation enables to consider very general problem statements in principle. The paper presents a new approach to the forward dynamics simulation and optimization of human body dynamics which overcomes the enormous computational cost of current approaches for solving the resulting optimal control problems. The presented approach is based on a suitable modeling of the dynamics of the musculoskeletal system in combination with a tailored direct collocation method for optimal control. First numerical results for a human kick demonstrate an improvement in computational time of two orders of magnitude when compared to standard methods. 相似文献
106.
A drill-string is a slender structure with nonlinear dynamics; it is an equipment used in the oil industry to drill the rock in the search of oil and gas. The aim of this paper is to investigate the efficiency of the drilling process in terms of input/output power. The continuum system is linearized about a prestressed configuration, the finite element method is applied to discretize the linear system, then a reduced-order model is constructed using the normal modes of the linear system; only torsional and axial vibrations are considered in the analysis. Uncertainties related to the speed imposed at the top are also included in the analysis. The rotational top speed is modeled using two different stochastic processes and the Monte Carlo Method is employed to approximate the statistics of the response of the resulting stochastic differential equations. 相似文献
107.
A computational fluid dynamics‐based optimization methodology is developed, appropriate for the geometric optimization of enhanced heat transfer devices based upon the principle of entropy generation minimization, in which the objective function is evaluated from a flow field obtained by computational simulation. A quasi‐Newton optimization procedure is employed, with computation of the objective function gradients based upon a finite difference approach. The optimization procedure is developed to be general with regard to the choice of objective function, the details of the problem under consideration, and the computational methodology employed in solving the fluid flow and heat transfer problems. A novel implementation of a Taylor series‐based procedure for the fast solution of nearby problems is presented, which is found to greatly benefit the efficiency of the present methodology. Finally, a numerical experiment is presented, illustrating the use of the present method in the geometric optimization of a practical enhanced heat transfer device on the basis of the criterion of entropy generation minimization. The optimization of the fin spacing of a simple plate fin heat sink is considered, and a comparison of the computational results with results obtained by analytical optimization based upon empirical friction factor and Nusselt number correlations is given. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
108.
Robust design problems in aerodynamics are associated with the design variables, which control the shape of an aerodynamic body, and also with the so‐called environmental variables, which account for uncertainties. In this kind of problems, the set of design variables, which leads to optimal performance, taking into account possible variations in the environmental variables, is sought. One of the possible ways to solve this problem is by means of the second‐order second‐moment approach, which requires first‐order and second‐order derivatives of the objective function with respect to the environmental variables. Should the minimization problem be solved using a gradient‐based method, algorithms for the computation of up to third‐order sensitivity derivatives (twice with respect to the environmental variables and once with respect to the shape controlling design variables) must be devised. In this paper, a combination of the continuous adjoint variable method and direct differentiation to compute the third‐order sensitivities is proposed. This is shown to be the most efficient among all alternative methods provided that the environmental variables are much less than the design ones. Apart from presenting the method formulation, this paper focuses on the assessment of the so‐computed up‐to third‐order mixed derivatives through comparison with costly finite‐difference schemes. To this end, the robust design of a two‐dimensional duct is performed. Then, using the validated method, the robust design of a two‐dimensional cascade airfoil is demonstrated. Although both cases are handled as inverse design problems, the method can be extended to other objective functions or three‐dimensional problems in a straightforward manner. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
109.
The automatic optimization of flow control devices is a delicate issue because of the drastic computational time related to unsteady high‐fidelity flow analyses and the possible multimodality of the objective function. Thus, we experiment in this article the use of kriging‐based algorithms to optimize flow control parameters because these methods have shown their efficiency for global optimization at moderate cost. Navier–Stokes simulations, carried out for different control parameters, are used to build iteratively a kriging model. At each step, a statistical analysis is performed to enrich the model with new simulation results by exploring the most promising areas, until optimal flow control parameters are found. This approach is validated and demonstrated on two problems, including comparisons with similar studies: the control of the flow around an oscillatory rotating cylinder and the reduction of the intensity of a shock wave for a transonic airfoil by adding a bump to the airfoil profile. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
110.
C. Barbarosie A.‐M. Toader 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2008,88(1):23-32
A version of Saint‐Venant's principle is stated and proven for a scalar elliptic equation in a domain of arbitrary shape, loaded only in a small ball. Some links are pointed out to the bubble method in topology optimization: when a small hole is introduced in a given shape, the difference between the perturbed solution and the unperturbed one satisfies the hypotheses of Saint‐Venant's principle. An important tool is the Poincaré‐Wirtinger inequality for functions defined on a sphere; results from spectral geometry are used to determine the constant therein. 相似文献