Y. G. Wang  D. R. Li  Z. C. Lu  S. X. Zhou 《Journal of Materials Science》2004,39(11):3833-3837

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Y. X. Zhang  K. S. Kim 《International journal for numerical methods in engineering》2004,61(11):1771-1796

Two simple 4‐node 20‐DOF and 4‐node 24‐DOF displacement‐based quadrilateral elements named RDKQ‐L20 and RDKQ‐L24 are developed in this paper based on the first‐order shear deformation theory (FSDT) for linear analysis of thin to moderately thick laminates. The deflection and rotation functions of the element sides are obtained from Timoshenko's laminated composite beam functions. Linear displacement interpolation functions of the standard 4‐node quadrilateral isoparametric plane element and displacement functions of a quadrilateral plane element with drilling degrees of freedom are taken as in‐plane displacements of the proposed elements RDKQ‐L20 and RDKQ‐L24, respectively. Due to the application of Timoshenko's laminated composite beam functions, convergence can be ensured theoretically for very thin laminates. The elements are simple in formulation, and shear‐locking free for extremely thin laminates even with full integration. A hybrid‐enhanced procedure is employed to improve the accuracy of stress analysis, especially for transverse shear stresses. Numerical tests show that the new elements are convergent, not sensitive to mesh distortion, accurate and efficient for analysis of thin to moderately thick laminates. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

    

X. Zhou  K. K. Tamma 《International journal for numerical methods in engineering》2004,60(10):1699-1740

A new unified theory underlying the theoretical design of linear computational algorithms in the context of time dependent first‐order systems is presented. Providing for the first time new perspectives and fresh ideas, and unlike various formulations existing in the literature, the present unified theory involves the following considerations: (i) it leads to new avenues for designing new computational algorithms to foster the notion of algorithms by design and recovering existing algorithms in the literature, (ii) describes a theory for the evolution of time operators via a unified mathematical framework, and (iii) places into context and explains/contrasts future new developments including existing designs and the various relationships among the different classes of algorithms in the literature such as linear multi‐step methods, sub‐stepping methods, Runge–Kutta type methods, higher‐order time accurate methods, etc. Subsequently, it provides design criteria and guidelines for contrasting and evaluating time dependent computational algorithms. The linear computational algorithms in the context of first‐order systems are classified as distinctly pertaining to Type 1, Type 2, and Type 3 classifications of time discretized operators. Such a distinct classification, provides for the first time, new avenues for designing new computational algorithms not existing in the literature and recovering existing algorithms of arbitrary order of time accuracy including an overall assessment of their stability and other algorithmic attributes. Consequently, it enables the evaluation and provides the relationships of computational algorithms for time dependent problems via a standardized measure based on computational effort and memory usage in terms of the resulting number of equation systems and the corresponding number of system solves. A generalized stability and accuracy limitation barrier theorem underlies the generic designs of computational algorithms with arbitrary order of accuracy and establishes guidelines which cannot be circumvented. In summary, unlike the traditional approaches and classical school of thought customarily employed in the theoretical development of computational algorithms, the unified theory underlying time dependent first‐order systems serves as a viable avenue to foster the notion of algorithms by design. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

    

A. C. Edrington  A. M. Urbas  P. DeRege  C. X. Chen  T. M. Swager  N. Hadjichristidis  M. Xenidou  L. J. Fetters  J. D. Joannopoulos  Y. Fink  E. L. Thomas 《Advanced materials (Deerfield Beach, Fla.)》2001,13(6):421-425

In this report, we highlight the development of polymers as 1D photonic crystals and subsequently place special emphasis on the activities in self‐assembled block copolymers as a promising platform material for new photonic crystals. We review recent progress, including the use of plasticizer and homopolymer blends of diblock copolymers to increase periodicity and the role of self‐assembly in producing 2D and 3D photonic crystals. The employment of inorganic nanoparticles to increase the dielectric contrast and the application of a biasing field during self‐assembly to control the long‐range domain order and orientation are examined, as well as in‐situ tunable materials via a mechanochromic materials system. Finally, the inherent optical anisotropy of extruded polymer films and side‐chain liquid‐crystalline polymers is shown to provide greater degrees of freedom for further novel optical designs.  相似文献   

    

L. Gu  Z. Xiong  G. Chen  Z. Xiao  D. Gong  X. Hou  X. Wang 《Advanced materials (Deerfield Beach, Fla.)》2001,13(18):1402-1405

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Y.L. Hua  T.X. Yu  S.R. Reid 《International Journal of Impact Engineering》1988,7(4):401-413

In this paper, double-hinge modes are introduced to analyse the response of a stepped or bent cantilever beam subjected to step loading at its free end. The material of the beams is assumed to be rigid-perfectly plastic, and complete solutions are constructed for four cases, which are summarized in tables. An analogy is found between the responses of stepped and bent cantilevers. For the bent cantilevers, the results herein provide a replacement for the ‘unstable hinge’ solutions previously derived, which violate the yield criterion. The results obtained are also useful for estimating the effects of imperfections in beams during dynamic loading.  相似文献   

    

X. Dong  C. D. Tuffile  T. Ando 《Advanced Engineering Materials》2000,2(5):284-289

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Zhang X  Koropchak JA 《Analytical chemistry》1999,71(15):3046-3053

A sensitive technique for speciation and quantification of Cr(III) and Cr(VI) has been developed using thermospray (TSP) sample introduction with inductively coupled plasma atomic emission spectrometry (ICPAES). For unacidified solutions, the sensitivity for Cr(III) was found to be lower than that for Cr(VI). The sensitivity for Cr(III) was further depressed to a negligible level by adjusting sample and thermospray operating parameters. The low sensitivity for Cr(III) was thought to result from the precipitation of that species to form Cr(OH)(3), which deposited within the vaporizer. For acidic solutions (1% v/v HNO(3)), the sensitivities for both species were essentially identical. On the basis of these results, methods for speciation of Cr(III) and Cr(VI) were developed. With samples buffered to pH 4.4, Cr(VI) could be selectively determined. With acidic sample aliquots (1% v/v HNO(3)), the total chromium concentration could also be determined, and the Cr(III) concentration could be calculated by difference. Parameters affecting Cr(III) sensitivity, such as control temperature, pH, and pump flow rate, were studied in addition to optimal TSP-ICPAES parameters. The limits of detection (LODs) for Cr(VI) and for total Cr were 0.47 and 0.61 μg/L with standard deviations of 1.5% and 2.0%, respectively. Good accuracy and precision of the method were demonstrated for analysis of spiked tap water and lake water samples. Mobile phase ion-pairing chromatography with ICPAES detection provided comparable results for moderately high concentration samples. Accuracy of measurements for Cr(VI) was within 1% of the certified value for NIST standard reference material 2109.  相似文献   

    

K. K. Tamma  X. Zhou  D. Sha 《International journal for numerical methods in engineering》1999,44(10):1545-1572

New theoretical ideas and developments describing the fundamental underlying basis for formulating a general family of time discretization operators for first‐order parabolic systems emanating from the framework of a generalized time weighted philosophy are first presented which can be broadly classified as pertaining to Type 1, Type 2 and Type 3 family of time discretization operators. As a consequence, the evolution including the clear distinction and the bridging of the relationships between time operators termed as integral operators to the so‐called integration operators in time are theoretically developed and demonstrated. The present developments seem to not only provide avenues leading to new algorithms for transient analysis but also provide generalizations and framework to recover a wide variety of existing algorithms. Consequently, under the umbrella of the present framework, a variety of plausible new approaches for generating Nth‐order accurate time discretization operators from approximations introduced to Type 1 integral operators in time are first described followed by the developments systematically leading to Type 2 time discretization operators, and subsequently to a wide class of Type 3 time integration operators including the recovery of a variety of known existing time integration operators which can be uniquely identified by Discrete Numerically Assigned (DNA) algorithmic markers. Of the various developments, of noteworthy mention and emphasis here are a new family of L‐stable Nth‐order Integration Operators (LNInO) of Type 2 for transient computations. Subsequently, some practically useful second‐order forms are specifically illustrated and highlighted. The stability and accuracy characteristics are also described for a variety of generated algorithms applicable for transient heat transfer computations. Although the primary focus is on the theoretical developments encompassing linear operators, some simple numerical examples are finally demonstrated to merely illustrate the salient features of the proposed developments. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

    

Chen XW  Karim MA 《Applied optics》1997,36(15):3547-3550

We used a real-time joint transform correlation technique for sizing opaque particles. The scheme can be used to estimate the size of both nonspherical and spherical particles. Computer simulation results are presented to illustrate the performance of this technique.  相似文献