氯离子侵蚀环境下混凝土结构耐久性寿命评估方法研究

根据氯离子侵蚀环境下混凝土结构中钢筋锈蚀的发生和发展,分析了结构性能的衰退过程,得到了氯离子侵蚀环境下结构耐久性寿命评估模型.考虑到寿命评估模型中主要参数的不确定性影响,基于Monte Carlo原理,采用CrvstalBall软件对混凝土构件进行了随机模拟.随机模拟结果显示,保护层厚度及氯离子浓度是影响氯离子侵蚀环境下混凝土结构耐久性寿命的重要参数.     

A strategy for the development of optimised lubricants

The design of lubricants has traditionally relied on the use of single dimension constitution / performance or structure / property relationships. In this paper a strategy is described whereby consideration is given to the inherent property / property (physical and chemical) correlations that exist for fluid lubricants. Progress towards the development of optimised lubricants is then achieved by identifying the molecular structural or compositional traits associated with ‘extensions’ to or ‘deviations’ from the mainstream correlations. Some examples of the success of this novel strategy will be provided, and the directions of its further refinement briefly outlined.     

Cash farming in building and construction: a stochastic analysis

Cash flow management is a significant issue in the management of a building or construction firm. This paper steps back from the well researched area of poor cash management and its relationship with failure, to focus on the funds which are generated through operations, and the positive benefits which can follow in a well managed organization. A stochastic model is developed which illustrates how an average of 16% of turnover can be available for reinvestment. This is sufficient to allow investment in non-liquid assets, provided that this is managed carefully and precautions are taken against a severe reduction in turnover. This level of funds is sufficient to encourage firms to enter the industry with the motivation of generating funds, rather than a desire to build. This has implications for large clients and for government when dealing with the industry.     

基于灰色预测理论的实物期权波动率计算——以房地产项目为例

实物期权理论已广泛应用于投资开发领域,但期权中各参数的确定,尤其是波动率估算的不精确,导致期权价值计算不准确,在一定程度上制约了实物期权的应用。为提高波动率的准确性,采用预测模型预测项目价值未来的波动情况,进而计算其波动率。以房地产项目为例,采用灰色预测模型,计算房价波动率,并与传统方法进行比较讨论,结果验证了该方法的有效性。弥补了传统波动率计算中现金流假设不充分或主观因素影响等不足,为波动率的计算提供了一种新的有效理论方法。     

Service quality,technical efficiency and total factor productivity growth in Pakistan's post-reform electricity distribution companies

Pakistan's energy sector has undergone substantial reforms during the last three decades with the aim to improve its operational performance and to cater to the growing energy needs of the economy. In the wake of these reforms, the WAPDA Act was passed in 1998 to achieve operational and financial efficiencies. Pakistan's electricity market is still hampered by issues like extended blackouts, electricity thefts, high circular debt and poor service quality. The electricity distribution sector is thus an interesting case to investigate its efficiency in the post-reform period by examining the impact of service-quality parameters (SQPs), which have generally been neglected in the literature. Stochastic frontier analysis has been used to estimate technical efficiency, while the Malmquist Productivity Index is implemented to decompose total factor productivity (TFP) into scale change, technical change and efficiency change from 2006 to 2016. We conclude that the technical efficiency score declines from 98 percent to 36 percent with the inclusion of SQPs in the models. The results also indicate a negative trend in scale change, implying that distribution companies are not operating at the technically optimal scale. We propose that the regulatory body should change its governance regime and focus on incentive-based regulation instead of rate-of-return regulation.     

Urine separation as part of a real-time control strategy

Considering wastewater from household sources, urine accounts for approximately 80% of the ammonia loads but for only 1% of the hydraulic load. Where classical urine separation deals with the separation and subsequent removal of urine from the wastewater stream, the method promoted here (urine separation for waste design) aims to (1) separate urine from the wastewater stream, (2) store it at the household and (3) release it in a controlled manner into the drainage system. The ultimate goal is on the one hand to average the daily dynamics in the ammonia load to the wastewater treatment plant (WWTP) and on the other hand to reduce ammonia emissions towards receiving waters. All process steps from urine production, separation, harvesting and controlled release of urine have been modelled on a micro-level where all toilets in the system are balanced separately. As a case study the integrated urban drainage system of Vils/Reutte in Tyrol was used where a total of 11 different control strategies – ranging from simple to highly complex real-time control (RTC) applications – have been developed and tested. The evaluation (taking into account both aims as expressed above) showed that the simplest RTC applications are the most effective. The optimal performance achieved in the case study resulted in an ammonia reduction of 62% (load based) compared to the status quo. As such a method would require considerable systems changes, an incremental implementation of associated improvements were also tested in this work. An important outcome was that a large proportion of the final improvement is gained already with the first 25% of installed separation toilets.     

Adapting rain data for hygrothermal models

Design for moisture control has now become an established part of building envelope design. Hygrothermal modeling tools, capable of simulating moisture transfer in materials, are a key element of the design process. There are three principle methods of moisture transfer in envelopes. They are, in order of magnitude, capillary action, vapour convection, and vapour diffusion. Wind-driven rain has the potential to deposit large amounts of liquid water on the exterior surface, as well inside walls through rain penetration, providing a significant source for moisture transport. Most hygrothermal models are capable of handling wind-driven rain impinging on or penetrating the surface of the envelope. Correct results presuppose the availability of reliable rain intensity data. Many data sets, however, do not record hourly rain intensities but qualitative intensities such as light, moderate, or heavy. This paper examines several methods for assigning quantitative values to weather observations available in Canada. Real data, such as data from rain gauges, is preferable although the latter have shortcomings. Differences in catch can be up to 50% depending on gauge type, size, and exposure. When only rain codes are available the values recommended by the local meteorological service can provide adequate estimates. In case where there is observer bias a better estimate can be obtained by adjusting the value for light rainfall. If very little information is available stochastic modeling of rainfall is possible though the accuracy, especially for individual months is low.     

Optimum design of tuned liquid column dampers under stochastic earthquake load considering uncertain bounded system parameters

The Tuned Liquid Column Damper (TLCD) is an effective alternative to the Tuned Mass Damper (TMD) to reduce the response of structures due to dynamic loads. The optimum TLCD parameters are normally obtained based on the implicit assumption that the system parameters involved are deterministic. But, the efficiency of dampers may reduce if the TLCD parameters are not tuned to the vibrating mode it is designed to suppress due to the unavoidable presence of system parameter uncertainty. The study of TMD parameters’ optimization considering random system parameters is noteworthy. But, the same is not the case for liquid dampers. Moreover, though the damper parameters optimization under uncertain parameters in probabilistic framework is powerful; the approach cannot be applied in many real situations when the required detailed information to describe the parameters in probabilistic format is limited. In present work, the TLCD parameters optimization to control vibration of structures subjected to stochastic earthquake load under uncertain system parameters modeled as uncertain but bounded (UBB) type is studied. With the aid of matrix perturbation theory using first-order Taylor series expansion and interval extension of the dynamic response function, the vibration control problem is transformed to appropriate deterministic optimization problems yielding the lower and upper bound solution. Numerical study is performed to elucidate the effect of parameters’ uncertainties on the optimization of damper parameters and the performance of TLCD.     

结构疲劳寿命稳健性优化设计

由于材料特性、构件的几何特性、载荷历程和环境条件等随机因素的影响,造成结构的疲劳寿命往往偏离结构的设计寿命.为了减少疲劳寿命的分散性,建立一种结构疲劳寿命稳健性优化模型.该模型将结构优化设计理论和随机有限元法相结合,在考虑设计变量和其他随机变量的变异性对结构疲劳寿命影响情况下,将结构疲劳寿命稳健性优化问题构造成包含结构疲劳寿命均值和标准差的双目标优化问题,并通过权因子来平衡结构疲劳寿命的均值和标准差关系,在约束函数中将结构疲劳寿命控制在最低寿命和最高寿命之间.经疲劳稳健性优化设计后的结构疲劳寿命在其均值处波动较小,而且分布曲线远离疲劳寿命底限.最后通过承受脉冲载荷的平面10杆桁架结构疲劳寿命稳健性优化算例显示了此方法的有效性.     

相平衡计算中全局优化算法的研究及发展现状

综述了相平衡计算中常用的全局优化算法,并对其现状做了比较。全局优化算法可分为随机性算法和确定性算法。确定性算法通常不能保证得到吉布斯自由能最小值;而随机性算法发展迅速,在化工领域得到了广泛应用。最后,对相平衡算法可能发展方向做了预测。