Biaxial tensile behavior and strength of architectural fabric membranes

The utilization of composite fabric membrane materials for large-span membrane structures has attracted considerable attention in recent decades due to enhanced material properties. Biaxial mechanical properties with respect to real engineering applications are essential and indispensable in comparison with uniaxial ones. This study focuses on true biaxial characteristics of a typical polyvinylidene fluoride (PVDF)-coated polyester membrane material in terms of stress-strain characteristics and breaking criteria.The true stress-strain curves obtained from an experimental study, i.e. seven loading ratios on the basis of symmetry and typical conditions, are investigated with digital image correlation method. The interpolation of these curves in combination of least square method achieves a three-dimensional strain surface as a function of warp and weft strains, which is useful to assess reasonable structural behavior. A new breaking criteria intended for architectural fabric membrane is proposed in analogy to Tsai-Hill, Yeh-Stratton and Norris failure criteria. The basic constants in the criteria are determined using experimental results. A comparative analysis between available uniaxial and biaxial criteria shows that the new criteria can cover all criteria due to the fact that biaxial mechanical properties are larger than uniaxial ones. Furthermore, a similar but glued specimen is employed to compare welded specimens. It is obtained that observations, values and curve tendency are similar, demonstrating the suitability of using new specimens to identify true biaxial properties.     

Remarks on the regularity criteria for generalized MHD equations

We study the Cauchy problem for the generalized MHD equations, and prove some regularity criteria involving the integrability of ∇u in the Morrey, multiplier spaces.     

模糊综合评判法在创业机会评估中的应用研究

创业是极具风险的活动.在我国,创业企业的失败率是非常高的.创业机会稍纵即失,正确评价和把握创业机会,这对创业者和创业资本的提供者都十分重要.在Timmons的创业机会评价框架下,提出了创业机会综合评价的指标体系,建立了创业机会模糊综合评价模型,并给出算法,最后进行了实证分析.     

OSCILLATION OF SOLUTIONS TO SECOND ORDER NEUTRAL PARTIAL FUNCTIONAL DIFFERENTIAL EQUATIONS

Some new oscillation criteria are established for a second order neutral partial functional differential equation.Assumptions in our theorems are less restrictive,also the proofs are simpler than those in Li and Cui [11].We remove some assumptions that are required for the related results in the previous papers,thus our results generalize and improve many known conclusions.     

ELECTRE: Robust ordinal regression for outranking methods

We present a new method, called ELECTRE^GKMS, which employs robust ordinal regression to construct a set of outranking models compatible with preference information. The preference information supplied by the decision maker (DM) is composed of pairwise comparisons stating the truth or falsity of the outranking relation for some real or fictitious reference alternatives. Moreover, the DM specifies some ranges of variation of comparison thresholds on considered pseudo-criteria. Using robust ordinal regression, the method builds a set of values of concordance indices, concordance thresholds, indifference, preference, and veto thresholds, for which all specified pairwise comparisons can be restored. Such sets are called compatible outranking models. Using these models, two outranking relations are defined, necessary and possible. Whether for an ordered pair of alternatives there is necessary or possible outranking depends on the truth of outranking relation for all or at least one compatible model, respectively. Distinguishing the most certain recommendation worked out by the necessary outranking, and a possible recommendation worked out by the possible outranking, ELECTRE^GKMS answers questions of robustness concern. The method is intended to be used interactively with incremental specification of pairwise comparisons, possibly with decreasing confidence levels. In this way, the necessary and possible outranking relations can be, respectively, enriched or impoverished with the growth of the number of pairwise comparisons. Furthermore, the method is able to identify troublesome pieces of preference information which are responsible for incompatibility. The necessary and possible outranking relations are to be exploited as usual outranking relations to work out recommendation in choice or ranking problems. The introduced approach is illustrated by a didactic example showing how ELECTRE^GKMS can support real-world decision problems.     

An effective Markov based approach for calculating the Limit Matrix in the analytic network process

Analytic network process is a multiple criteria decision analysis (MCDA) method that aids decision makers to choose among a number of possible alternatives or prioritize the criteria for making a decision in terms of importance. It handles both qualitative and quantitative criteria, that are compared in pairs, in order to forge a best compromise answer according to the different criteria and influences involved. The method has been widely applied and the literature review reveals a rising trend of ANP-related articles. The ‘power’ matrix method, a procedure necessary for the stability of the decision system, is one of the critical calculations in the mathematical part of the method. The present study proposes an alternative mathematical approach that is based on Markov chain processes and the well-known Gauss-Jordan elimination. The new approach obtains practically the same results as the power matrix method, requires slightly less time and number of calculations and handles effectively cyclic supermatrices, optimizing thus the whole procedure.     

基于动态规划原理的平方套期保值策略研究

在自融资约束下研究了标的资产价格服从跳扩散过程时欧式未定权益的平方套期保值问题。假定套期保值者用与未定权益相关的风险资产和另一种无风险资产来进行套期保值,利用动态规划原理,得到了离散时间集上均方最优套期保值策略的显式解。文章最后通过对比分析不同期限、不同策略调整频率的欧式看涨期权的套期保值结果表明:(1)对冲头寸与期限具有相依关系,期限越长,头寸比例通常也高;(2)对冲头寸与标的资产价格呈同向变化,标的资产价格越高,可以持有的头寸比例也高;(3)对冲头寸与交割价格呈反向变化,交割价格越高,可以适当降低头寸比例。     

Validation of a complex urban noise model close to a road

The adequacy of a model for the sound level close to a road is investigated by comparing resulting predictions for the sound level over a building façade with measurements. The road model involves the road geometry (the number and positions of traffic lanes), the traffic structure (vehicle flow rates and their average speeds in each lane) and equivalent omnidirectional point sources representing the vehicles. It is found that the assumed road traffic noise source model is adequate only for predicting levels over the higher part of the façade. However the investigation has allowed definition of what improvements are needed in the road source modelling to enable adequate predictions over the whole of the building façade.     

单模激光Lorenz系统与Duffing系统缩阶反同步

 对于2阶Duffing系统与3阶单模激光Lorenz系统,用主动控制方法设计了一种同步控制器,实现二者之间的缩阶反同步。依据罗斯 霍维兹判据,给出误差系统在原点处渐进稳定的条件。数值试验证实：在控制器作用下,2阶Duffing系统的状态变量与3阶单模激光Lorenz投影子系统的状态变量振动的幅值相同但方向相反,且在随机噪声干扰下反同步仍能很好地实现。这表明所设计的控制器对于不同阶的Duffing系统与Lorenz系统的缩阶反同步的实现是可行的、有效的,而且具有很好的鲁棒性。     

Ductile fracture criteria for simulating shear by node separation method

This study is concerned with the mechanics of ductile fracture in bulk metal forming processes by a finite-element analysis and experiments. Developed is a computer program using conventional finite-element method such that the behavior of crack propagation after ductile fracture can be analyzed. The phenomenon of a material separating into two pieces upon shearing and tensile tests has been simulated using the developed computer program. Special attention is focused on the effect of various ductile fracture criteria on crack initiation and propagation during shearing and tensile tests.