FRP管约束混凝土的轴压应力-应变关系研究

目前FRP约束混凝土轴压应力-应变关系大都只考虑FRP管环向受拉。针对FRP管约束混凝土的轴心受压性能进行分析,考虑其承受压力造成约束模量降低的影响,在现有约束混凝土模型的基础上,提出一种考虑FRP管在双向受力情况下的应力-应变关系分析模型,并与试验结果进行了分析对比,分析结果与试验结果吻合较好。还依据这一模型进行了参数研究。

钢筋对混凝土收缩应力的影响

研究了钢筋对收缩应力的影响,提出了描述约束关系的新的力学模型。基于增量分析,严格推导了钢筋内约束系数(配筋构件相比素混凝土构件的收缩应力增幅)的表达式。研究表明,钢筋内约束系数随配筋率增大而线性增大,但增长速度(直线斜率)受外约束大小影响,外约束越大,增长速度越小。现有的以钢筋混凝土体为计算对象的收缩应力计算方法,一方面由于忽略了钢筋的内约束效应,另一方面错误地将钢筋内约束与骨料约束类同,因此将导致计算结果低估常规配筋构件的实际收缩应力约10%～40%。

钢筋对混凝土收缩应力的影响

研究了钢筋对收缩应力的影响。提出了描述约束关系的新的力学模型。基于增量分析 ,推导了钢筋内约束系数 (配筋构件相比素混凝土构件的收缩应力增幅 )的表达式。研究表明 ,钢筋内约束系数随配筋率增大而线性增大 ,但增长速度 (直线斜率 )受外约束大小影响 ,外约束越大 ,增长速度越小。现有的以钢筋混凝土为计算对象的收缩应力计算方法 ,一方面由于忽略了钢筋的内约束效应 ,另一方面错误地将钢筋内约束与骨料约束类同 ,因此将导致其低估通常配筋构件的实际收缩应力 ,计算结果约低10%～40%。

基于IRS辅助多用户通信系统的信道容量优化

智能反射表面(intelligent reflecting surface,IRS)通过对无线传播环境的智能配置进而获得极好的信道容量增益。在IRS辅助多用户下行链路通信中,本文通过共同优化基站处受功率限制的预编码器和IRS处受单位模量约束的相移器来最大化信道容量。针对由此产生的非确定性多项式难问题,首先将其转换成等效问题,再利用交替优化算法来求解预编码矩阵和相移向量。当固定相移向量时,优化问题可转换为二阶锥规划问题后直接使用标准优化包获得最优预编码矩阵。当固定预编码矩阵时,单位模量约束是解决问题的难点,本文将其嵌入搜索空间之后提出黎曼信赖域(Riemannian trust-region,RTR)算法来求解。仿真结果表明,与现有方法相比,RTR算法不仅具有性能的提升,还有更快的收敛速度。

Reducing semantic bias of annotations for semantic web service discovery

In order to improve the effectiveness of semantic web service discovery, the semantic bias between an interface parameter and an annotation is reduced by extracting semantic restrictions for the annotation from the description context and generating refined semantic annotations, and then the semantics of the web service is refined. These restrictions are dynamically extracted from the parsing tree of the description text, with the guide of the restriction template extracted from the ontology definition. New semantic annotations are then generated by combining the original concept with the restrictions and represented via refined concept expressions. In addition, a novel semantic similarity measure for refined concept expressions is proposed for semantic web service discovery. Experimental results show that the matchmaker based on this method can improve the average precision of discovery and exhibit low computational complexity. Reducing the semantic bias by utilizing restriction information of annotations can refine the semantics of the web service and improve the discovery effectiveness.

Fracture of thermal barrier coating with multiple surface cracks and delaminations:Interlayer effect

Multiple surface cracks and interfacial delamination are the major failure mechanisms in film/substrate systems.The effect of interlayer upon the failure mechanisms of interfacial delamination concomitant to surface crack was explored.Finite element model was developed to obtain the stress and energy release rate(ERR),which governs the propagation of interface cracks.The dependences of delamination upon the geometry and constitutive properties of interlayer were examined.The results indicate that the effect of elastic modulus of interlayer on the steady state ERR is insignificant.In cases of different geometrical parameters,however,the steady ERR decreases with the increase of the interlayer thickness.These findings lead to the conclusion that the interlayer constraint has significant effect on the ERR and thus coating life,which can be adopted to modify the ceramic top coat.

Regression model for daily passenger volume of high-speed railway line under capacity constraint

A non-linear regression model is proposed to forecast the aggregated passenger volume of Beijing-Shanghai high-speed railway(HSR) line in China. Train services and temporal features of passenger volume are studied to have a prior knowledge about this high-speed railway line. Then, based on a theoretical curve that depicts the relationship among passenger demand, transportation capacity and passenger volume, a non-linear regression model is established with consideration of the effect of capacity constraint. Through experiments, it is found that the proposed model can perform better in both forecasting accuracy and stability compared with linear regression models and back-propagation neural networks. In addition to the forecasting ability, with a definite formation, the proposed model can be further used to forecast the effects of train planning policies.

Modeling and Parametric Study of the Heat Transfer Inside a Lithium Bromide Flow Confined by Wire Screen

The present study deals with the numerical analysis of heat transfer inside a lithium bromide-water solution flowing down between finely meshed plastic wire screens. These screens confine the flow through capillary action while allowing the water vapour transfer inside an innovative absorber technology. The complex menisci shape formed on the confinement grid level, where the surface tension forces are of first importance, are reconstructed by a volume-of-fluid model. A continuum surface force model is used to account for the surface tension force. A static contact angle is used to define the wall adhesion. A new algorithm, consisting to set an unique constant temperature at the liquid/vapour interface and to determine the evolution of heat transfer characteristics over the simulation domain, has been implemented and validated by analytical solution. A parametric study has been conducted to determine the effect of the geometry, the contact angle and the shape of the wire on the heat transfer.

Institutional Constraints to the Competitiveness of the South African Citrus Exports

This paper examined the dual institutional constraints arising from the market liberalisation of the South African citrus industry and the stringent food safety health and private standards associated with the globalisation of the agri-business industry. The aim of this paper was to explore the institutional challenges influencing the competitiveness of the South African citrus industry in the export markets. It also explored the implications of the institutional environment on market access. The logistic regression model was used to analyse the statistical data while simple ranking was used to indicate the new and emerging forces affecting the profitability of the industry in recent years. The results show that access to market information, economies of scale, compliance with strict food safety and quality standards, lack of proper infrastructure including transport and challenges of managing a business within the international business environment exerted significant effects on the competitiveness of the industry as well as the ability of domestic producers to enter the export markets. There is need for government intervention especially aligned to investing in infrastructure. Coupled with the support of private institutions, the government needs to support the exporters and producers in complying with private standards.

Planning for space station long-duration orbital mission under multi-constraints

An integrated nonlinear planning(NLP) model is built for space station long-duration orbital missions considering both the vehicle visiting schedules and the interaction effects between target phasing,vehicle return adjusting and Earth observation aiming.A two-level optimization approach is proposed to solve this complicated problem.The up-level problem employs the launch times of visiting vehicles as design variables,considers the constraints of crew rotations,resource resupplies and rendezvous launch windows,and is solved by a genetic algorithm.The low-level problems employ the maneuver impulses and burn times within each orbital mission as design variables,and a high-efficient shooting iteration method is proposed based on an analytical equation for the phase angle correction considering the J 2 perturbation.The results indicate that the integrated NLP model for space station long-duration orbital missions is effective,and the proposed optimization approach can obtain the optimal solutions that satisfy the multiple constraints and reduce the total propellant consumption.

Properties of strangelets in a new quark mass confinement model with one-gluon-exchange interaction

The properties of strangelets at zero temperature with a new quark model that includes both the confinement and one-gluonexchange interactions is studied in a fully self-consistent method.The charge and parameter dependence of the stability of strangelets are discussed.It is found that the one-gluon-exchange interaction lowers the energy of a strangelet,and consequently allows the strangelet to be absolutely stable.The stable strangelet radius in the present model is smaller in comparison with the absence of one-gluon-exchange interaction,and can thus be much less than that of a normal nucleus with the same baryon number,according to the strength of the confinement and one-gluon-exchange interactions.

Feature of thermohaline circulation in two-layer conceptual model based on energy constraint

The assertion that the thermohaline circulation(THC)is driven and sustained by mechanical energy has been increasingly accepted.The simplest conceptual model describing the THC is the Stommel two-box model.Given the vertical stratification in the real ocean,layered models were designed and used.In this research,using a two-layer conceptual model based on energy constraint,we studied basic features of thermal-mode and saline-mode circulations.We focused on the effects of freshwater flux and mixing energy on the intensity and multiple equilibrium states of the THC.The results show that more important than affecting the THC intensity,both the decrease of freshwater flux and increase of mixing energy can lead to an"abrupt transition"in the THC from a stable saline to a stable thermal mode,which further develops the THC energy theory.

Probabilistic steady-state and dynamic security assessment of power transmission system

Two-level system model based probabilistic steady-state and dynamic security assessment model is introduced in this paper.Uncertainties of nodal power injection caused by wind power and load demand,steady-state and dynamic security constraints and transitions between system configurations in terms of failure rate and repair rate are considered in the model.Time to insecurity is used as security index.The probability distribution of time to insecurity can be obtained by solving a linear vector differential equation.The coefficients of the differential equation are expressed in terms of configuration transition rates and security transition probabilities.The model is implemented in complex system successfully for the first time by using the following effective measures:firstly,calculating configuration transition rates effectively based on component state transition rate matrix and system configuration array;secondly,calculating the probability of random nodal power injection belonging to security region effectively according to practical parts of critical boundaries of security region represented by hyper-planes;thirdly,locating non-zero elements of coefficient matrix and then implementing sparse storage of coefficient matrix effectively;finally,calculating security region off-line for on-line use.Results of probabilistic security assessment can be used to conduct operators to analyze system security effectively and take preventive control.Test results on New England 10-generators and 39-buses power system verify the reasonableness and effectiveness of the method.