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排序方式: 共有98条查询结果,搜索用时 15 毫秒
71.
首先引入Nataf变换的基本原理,并基于可靠指标标准正态空间计算的数学模型,将Nataf变换与拉格朗日乘数法相结合,提出了基于Nataf变换和拉格朗日乘数法的一次可靠度的计算方法。然后针对相关非正态变量分布函数的反函数表达式不易给出的情况,引入有理多项式法求解其偏导数。通过算例进行分析,结果表明:该方法简单、可靠和有效,值得在工程实践中推广。 相似文献
72.
73.
Extreme value predictions using Monte Carlo simulations with artificially increased load spectrum 总被引:1,自引:0,他引:1
Jørgen Juncher Jensen 《Probabilistic Engineering Mechanics》2011,26(2):399-404
In the analysis of structures subjected to stationary stochastic load processes the mean out-crossing rate plays an important role as it can be used to determine the extreme value distribution of any response, usually assuming that the sequence of mean out-crossings can be modelled as a Poisson process. The mean out-crossing rate of a response level r can be expressed in terms of the reliability index, which for linear systems is r divided by the standard deviation of the response in question. For non-linear processes the reliability index depends non-linearly on r and a good estimate can be found using the First Order Reliability Method (FORM). The FORM analysis also shows that the reliability index is strictly inversely proportional to the square root of the magnitude of the load spectrum, irrespectively of the non-linearity in the system. However, the FORM analysis only gives an approximation to the mean out-crossing rate. Better accuracy can be obtained by Monte Carlo simulations, but the necessary length of the time domain simulations for very low out-crossing rates might be prohibitively long. In such cases the property mentioned above for the FORM reliability index might be assumed to be valid in the Monte Carlo simulations, making it possible to increase the out-crossing rates and thus reduce the necessary length of the time domain simulations by applying a larger load spectrum than relevant from a design point of view. The mean out-crossing rate thus obtained can then afterwards be scaled down to its actual value.In the present paper the usefulness of this approach is investigated, considering problems related to wave loads on marine structures. Here the load scale parameter is conveniently taken as the square of the significant wave height. 相似文献
74.
The PHI2 method: a way to compute time-variant reliability 总被引:2,自引:0,他引:2
Time-variant reliability problems appear in the engineering practice when (a) the material properties of the structure deteriorate in time or (b) random loading modelled as random processes is involved. This paper presents a method called PHI2 which is based on the outcrossing approach and allows to solve such problems using classical time-invariant reliability tools such as FORM/SORM methods. The PHI2 method is first presented. Then it is benchmarked with the well-established ‘asymptotic methods’ [Stochast. Process. Appl. 13 (1988) 195; J. Offshore Mech. Arctic Engng 113 (1991) 241; Probab. Engng Mech. 10 (1995) 53; J. Struct. Engng 25 (1998) 1] on three examples dealing with scalar or vector processes and linear or non-linear limit state functions. The PHI2 method appears more accurate in all cases. As an application example, the method is finally applied on a case representing a mechanical system (a beam) placed in an environment that can have exceptional configuration. 相似文献
75.
Afeefa Shaker Wael Abdelrahman Mohammad Tawfik Edward Sadek 《Computational Mechanics》2008,41(5):707-714
The superior properties of functionally graded materials (FGM) are usually accompanied by randomness in their properties due
to difficulties in tailoring the gradients during manufacturing processes. Using the stochastic finite element method (SFEM)
proved to be a powerful tool in studying the sensitivity of the static response of FGM plates to uncertainties in their material
properties. This tool is yet to be used in studying free vibration of FGM plates. The aim of this work is to use both a First
Order Reliability Method (FORM) and the Second Order Reliability Method (SORM), combined with a nine-noded isoparametric Lagrangian
element based on the third order shear deformation theory to investigate sensitivity of the fundamental frequency of FGM plates
to material uncertainties. These include the effect of uncertainties on both the metal and ceramic constituents. The basic
random variables include ceramic and metal Young’s modulus and Poisson’s ratio, their densities and ceramic volume fraction.
The developed code utilizes MATLAB capabilities to derive the derivatives of the stiffness and mass matrices symbolically
with a considerable reduction in calculation time. Calculating the eigenvectors at the mean values of the variables proves
to be a reasonable simplification which significantly increases solution speed. The stochastic finite element code is validated
using available data in the literature, in addition to comparisons with results of the well-established Monte Carlo simulation
technique with importance sampling. Results show that SORM is an excellent rapid tool in the stochastic analysis of free vibration
of FGM plates, when compared to the slower Monte Carlo simulation techniques. 相似文献
76.
Yibing XiangYongming Liu 《Probabilistic Engineering Mechanics》2011,26(2):148-156
A general probabilistic life prediction methodology for accurate and efficient fatigue prognosis is proposed in this paper. The proposed methodology is based-on an inverse first-order reliability method (IFORM) to evaluate the fatigue life at an arbitrary reliability level. This formulation is different from the forward reliability problem, which aims to calculate the failure probability at a fixed time instant. The variables in the fatigue prognosis problem are separated into two categories, i.e., random variables and index variables. An efficient searching algorithm for fatigue life prediction is developed to find the corresponding index variable at a certain confidence level. Numerical examples using direct Monte Carlo simulation and the proposed IFORM method are compared for algorithm verification. Following this, various experimental data for metallic materials are used for model prediction validation. 相似文献
77.
Jongmin Lim Byungchai Lee Ikjin Lee 《International journal for numerical methods in engineering》2014,100(10):773-792
First‐order reliability method (FORM) has been mostly utilized for solving reliability‐based design optimization (RBDO) problems efficiently. However, second‐order reliability method (SORM) is required in order to estimate a probability of failure accurately in highly nonlinear performance functions. Despite accuracy of SORM, its application to RBDO is quite challenging due to unaffordable numerical burden incurred by a Hessian calculation. For reducing the numerical efforts, a quasi‐Newton approach to approximate the Hessian is introduced in this study instead of calculating the true Hessian. The proposed SORM with the approximated Hessian requires computations only used in FORM, leading to very efficient and accurate reliability analysis. The proposed SORM also utilizes a generalized chi‐squared distribution in order to achieve better accuracy. Furthermore, SORM‐based inverse reliability method is proposed in this study. An accurate reliability index corresponding to a target probability of failure is updated using the proposed SORM. Two approaches in terms of finding an accurate most probable point using the updated reliability index are proposed. The proposed SORM‐based inverse analysis is then extended to RBDO in order to obtain a reliability‐based optimum design satisfying probabilistic constraints more accurately even for a highly nonlinear system. The numerical study results show that the proposed reliability analysis and RBDO achieve efficiency of FORM and accuracy of SORM at the same time. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
78.
Jaejin Lee Samuel P. Midkiff David A. Padua 《International journal of parallel programming》1998,26(5):563-589
In this paper, we present a constant propagation algorithm for explicitly parallel programs, which we call the Concurrent Sparse Conditional Constant propagation algorithm. This algorithm is an extension of the Sparse Conditional Constant propagation algorithm. Without considering the interaction between threads, classical optimizations lead to an incorrect program transformation for parallel programs. To make analyzing parallel programs possible, a new intermediate representation is needed. We introduce the Concurrent Static Single Assignment (CSSA) form to represent explicitly parallel programs with interleaving semantics and synchronization. The only parallel construct considered in this paper is cobegin/coend. A new confluence function, the -assignment, which summarizes the information of interleaving statements between threads, is introduced. The Concurrent Control Flow Graph, which contains information about conflicting statements, control flow, and synchronization, is used as an underlying representation for the CSSA from. 相似文献
79.
Joseph Rosa 《Architectural Design》2007,77(1):90-94
For Joseph Rosa, John H Bryan Curator of Architecture at the Institute of Chicago, elegance with its ‘refined aesthetic ability’ represents a concurrent maturing of design culture and technologies. It builds on the pioneering fabrication techniques of the late 1990s, spearheaded in seminal projects such as the Korean Presbyterian Church in New York by Greg Lynn, Douglas Garofalo and Michael McInturf, and the Yokohama Port Terminal by Foreign Office Architects. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
80.
图片越来越多的出现在Web应用程序中,传统的文件存储方式已经不能满足要求。文中列举了数据库存储的好处,介绍了数据库对大容量字段的支持,并以JSP和MySql为例,介绍了Web服务器上图片的数据库存储和显示技术。 相似文献