多目标遗传算法用于给水管网优化设计的研究

建立了一个基于经济性和可靠性的多目标数学模型用于给水管网优化设计。利用惩罚函数法对遗传算法进行改进后,应用其对多目标数学模型进行求解,并将该优化方法运用于实际工程。结果表明,采用多目标遗传算法得出的结果优于常规优化方法。     

基于遗传算法的建设工程风险决策多目标优化研究

在建设工程风险决策过程中,只考虑单个目标因素的决策并不能满足实际工程的要求。为了使决策更加科学、合理,在风险识别和风险评价的基础上,综合考虑包括风险管理成本在内的多个目标因素对决策结果的影响,建立了工程风险多目标决策优化模型,通过多目标遗传算法NSGA-Ⅱ,实现了工程风险决策方案的优化。最后,对优化结果的分析和评价,证明了所建立的模型在解决工程风险决策问题上的有效性和实用性。     

A multi-objective optimisation approach for sustainable pavement management

Addressing the multidimensional challenges involved in advancing the sustainability of pavement systems requires the development of optimisation-based decision support system (DSS) for pavement management with the capability to identify optimally sustainable pavement maintenance and rehabilitations (M&R) strategies. The main objective of this research work is to develop a multi-objective optimisation framework that hosts a comprehensive and integrated pavement life cycle costs–life cycle assessment model that covers the pavement’s whole life cycle, from the extraction and production of materials to construction and maintenance, transportation of materials, work-zone traffic management, usage and end-of-life. The capability of the proposed DSS is analysed in a case study aiming at investigating, from a full life cycle perspective, the extent to which a number of pavement engineering solutions are efficient in improving the environmental and economic aspects of pavement sustainability, when applied in the management of a road pavement section. Multiple bi-objective optimisation analyses considering accordingly agency costs, user costs and greenhouse gas emissions were conducted based on a multi-objective genetic algorithm. Pareto fronts were obtained for each analysis, originating a set of non-dominated maintenance and rehabilitation solutions. Posteriorly, a multi-criteria decision analysis method was used to find the best compromise solution for pavement management.     

浅谈施工企业项目管理中人才素质要求

经过对建设项目管理进行了解,提出了施工企业项目经营管理者的长、宽、高三方面的素质要求,将高素质的复合型人才运用在项目施工生产实践中,取得了良好的效果。     

A simple, conceptual mathematical model for the activated sludge process and its variants

A simple structured kinetic model is applied to the activated sludge process. The objective is less to predict exact process performance than to illustrate some of the possibilities and difficulties in producing a comprehensive model for all the process variants. The rate equations are chosen so as to reduce to the Monod equation during balanced growth. Because these rate equations are linear, the cell growth and substrate uptake in a stirred tank can be defined exactly in terms of the average composition of the biomass. It is shown that this is not valid for other forms of rate equations. The stored substrate to protoplasm ratio in the flocs is found to decrease with increasing mean cell residence time. If extracellular biopolymers are included in the stored substrate this corresponds qualitatively to observations of poor flocculation in extended aeration. The model is also applied to the contact stabilization process and is found to be in agreement with the essential process variables.     

Optimal strategy for inspection and repair of structural systems

A new strategy for inspection and repair of structural elements and systems is presented. The total cost of inspection and repair is minimized with the constraints that the reliability of elements and/or of the structural system are acceptable. The design variables are the time intervals between inspections and the quality of the inspections. Numerical examples are presented to illustrate the performance of the strategy. The strategy can be used for any engineering system where inspection and repair are required.     

Programming model for multiprojects

In developing countries, managers of multiprojects using single-project programming techniques are frustrated by the inadequacy of these techniques to solve their problems. Multiproject programmes should have their own tools and techniques, because, although they stem from a common principle, they are unique. A model to satisfy this need is discussed.     

Development of a customer satisfaction evaluation model for construction project management

Construction project management (CPM) is a technical-oriented service for construction project clients. Evaluating the performance of service providers is beneficial both to purchasers, enabling them to appraise the services received, and to providers, helping them to improve their services. However, no appraisal system for such services exists. This study developed a novel customer satisfaction evaluation model for CPM services that was developed using a questionnaire-based survey and statistical analysis. Test results show that the developed model is a feasible system. Research using this model reveals that CPM services in Taiwan are satisfactory with acceptable performance for clients. The developed model is a good reference for evaluating and assessing CPM performance.     

Decision model for allocating human resources in information system projects

Human resource allocation (HRA) can be viewed as core processes of the project management of information systems. Both in organizations, the business of which is to provide solutions for Information Systems, as in units of companies that work with Information Systems (IS), there are frequent demands for human resources to be allocated to IS projects. However, this is not a simple task and becomes more complex as the numbers of projects and professionals, including the range of expertise required, increase. This paper presents a methodology, based on dynamic programming, to assign human resources to software development projects. The methodology takes into account the complexity of each project and the existing capabilities of staff and the skills required for the project. A simulation is used to demonstrate the decision model.     

A multi-objective approach for detecting and responding to accidental and intentional contamination events in water distribution systems

The protection against contamination events in water distribution systems involves two distinct phases: detection of the presence of a contaminant and implementation of actions to isolate and/or expel it rapidly. The problem of detection is confronted by installing a series of monitoring stations, strategically placed across the distribution system and consisting of sensors to detect the presence of contaminants. The actions to be implemented may include operations on distribution system devices (valves and hydrants) or injection of reagents to eliminate the contaminant, or simply alert users. The procedure proposed here attempts to address the problems related to the two phases by means of two consecutive optimisation processes, both of them performed off-line and assuming a specific 24-hour water demand sequence in each network node, whereas the accidental/intentional injection of contaminant can occur in any node and at any hour of the day. With reference to this vast range of possible injection scenarios, the first multi-objective optimisation process defines the position of a pre-selected number n_s of sensors across the distribution system in order to minimise the expected percentage of undetected contamination events and the expected volume of contaminated water consumed up to the beginning of the response operations following detection. A single configuration of stations is then selected from the Pareto front produced by this optimisation process (‘knee point’ of the Pareto front). At the end of this first optimisation process and with reference to the selected set of sensors, a potentially contaminated area in the network is associated to each sensor for each sub-period of the day. The second multi-objective optimisation process is then aimed to identify, with reference to each station and sub-period, and thus inside the corresponding potentially contaminated area, the hydrant-opening and valve-closing operations to be carried out in order to minimise both the number of operations and the expected volume of contaminated water consumed between the beginning of the response operations and the disappearance of the contaminant, assuming the availability of an unlimited number of response teams. Once these devices have been identified (‘knee point’ of the Pareto front relevant to the second optimisation process), an a posteriori analysis is performed to determine the sequence in which they should be activated based on the number of response teams actually available. In these optimisation processes, a hydraulic and quality simulator (EPANET) is linked to a multi-objective genetic algorithm (NSGA-II) in order to compute the value of the objective functions of the problem across different contamination scenarios. The results obtained applying the procedure to a real and complex water distribution system have shown it to be a robust and effective method for reducing the impact on the population.     

A high-resolution domestic building occupancy model for energy demand simulations

Energy use in the home is a major source of carbon emissions and is highly dependent on the activities of the residents. More specifically, the timing of energy use, particularly electricity, is highly dependent on the timing of the occupants’ activities. Thus, in order to model domestic demand profiles with high temporal resolution, for example, in the context of designing and assessing demand side management systems (including the time-shifting of demand), it is of great benefit to take account of residents’ behaviour in terms of when they are likely to be using household appliances, lighting and heating. This paper presents a thorough and detailed method for generating realistic occupancy data for UK households, based upon surveyed time-use data describing what people do and when. The approach presented generates statistical occupancy time-series data at a ten-minute resolution and takes account of differences between weekdays and weekends. The model also indicates the number of occupants that are active within a house at a given time, which is important for example in order to model the sharing of energy use (shared use of appliances, etc.) The data from the model can be used as input to any domestic energy model that uses occupancy time-series as a base variable, or any other application that requires detailed occupancy data. The model has been implemented in Excel and is available for free download.     

Water industry asset management: a proposed service-performance model for investment

The water industry in England and Wales has developed over the last century, from small organisations serving local communities to large integrated companies in private ownership, overseen by a government regulator. Asset management practice has developed greatly in the 17 years since privatisation, with companies able to plan their operations and investment as they believe appropriate for the provision of customer services, subject to justifying their plans to the economic, quality and environmental regulators. Investment has flowed into the industry to replace deteriorated assets and to improve the quality of drinking water and rivers. The asset base is complex and, with a replacement value of approximately £231 billion at the 2002–2003 price base index suitable approaches are required to ensure that both the water service and the sewerage service are delivered at the most appropriate long‐term cost. The 2004 UK water industry price review was supported by the introduction of a Capital Maintenance Planning Common Framework to help companies understand and explain their maintenance investment requirement. In this paper, a service‐performance model is proposed to improve managers' understanding of the way in which businesses and the environment change over time, taking account of maintenance and other strategic requirements. Although developed with the water industry in mind, the model is equally applicable to other asset‐intensive industries.     

A nonlinear projection method for constrained optimization

An algorithm is presented for the solution of nonlinear optimization problems involving locally differentiable functions with known analytical expressions. The algorithm is based on perturbation methods of system analysis and develops from a set of easy to implement procedures designed to detect and solve the activation and deactivation of constraints while selecting the steepest feasible trajectory and the largest step length. Numerical applications are presented to illustrate the performance of the algorithm.     

A linearly constrained algorithm not requiring derivative continuity

Many problems of mathematical programming, particularly the structural design optimization problem with discrete variables, pose the task of minimizing, under constraints, a non-differentiable function of several variables. In some cases that task is inherent in the problem. In other cases setting such a task is just one of several ways of formulating the problem. This paper describes a new feasible descent method for finding epsilon-solutions of non-differentiable convex optimization problems under general linear constraints.     

自由曲面结构形态创构方法——高度调整法的建立与其在工程设计中的应用

曲面结构(如壳体)的受力性能主要取决于结构的曲面形状。在实际工程中,常规的简单曲面一般较难有效满足结构的受力合理性。利用曲面高度参数与结构应变能之间的关系,提出了一种自由曲面创构方法来保证结构达到“薄”而“刚”的统一。该方法基于有限元法,通过计算应变能对曲面高度的微分,并根据应变能变化的敏感程度对曲面高度进行调整,最终得到一个结构应变能最小的合理结构形态。利用该方法,可以通过调整设计参数(约束条件,空间条件)得到多种合理曲面形态,供设计人员参考。同时,也可以对建筑意图所设定的初始形状进行修改,求得近似合理的结构几何形状。工程设计实例表明,该方法所得到的曲面结构基本以薄膜应力为主,而且能保证足够的刚度。     

A biofiltration model for tertiary nitrification of municipal wastewaters

The main objective of this work concerns the evaluation of the biological aerated filtration model found in GPS-X^®, which had never been evaluated with adequate data. This model is interesting since it integrates the physical and biological phenomena involved during filtration with a low complexity of use. The validation of the model parameters combines experimental and theoretical approaches. Experimental data were recorded at a semi-industrial pilot scale submerged biofilter operated at a tertiary nitrification stage, receiving the effluent of a medium loaded activated sludge process for municipal wastewater. Also, several protocols were regularly applied to characterize the biofilm and the nitrogen removal performances: dry density and thickness of biofilm, nitrification rates and corresponding quantity of autotrophic biomass accumulated inside the filtering media, quantity of extracted autotrophic bacteria in the backwash water, nitrification capacity along the biofilter, as well as nitrogen compounds in the effluent. For short-term dynamic conditions, a set of reliable parameter values has been used to predict nitrogen removal for different data sets. For long-term dynamic periods, the need to adapt some of the parameters from one set of data to another is demonstrated. It is shown that the hydraulic loading rate and the backwashing frequency are the main parameters responsible for these modifications.     

A contact model for rough crushable sand

Sand roughness is now accessible to measurement. Incorporating this parameter into sand models using the discrete element method (DEM) is known to improve bulk small strain response. In this work we explore the effect on problems where particle crushing takes place. A well-established DEM particle crushing model and a rough Hertzian contact model are here combined to incorporate both effects in a single contact model. Including contact roughness results in stronger particles whilst all other material parameters being equal. The model is then used to simulate high pressure oedometric compression tests on a strong silica sand. It is shown that including realistic values of surface roughness enables to correctly capture both load-unload behaviour and particle size distribution evolution while using realistic values of elastic bulk properties for the sand grains. Roughness is then a model refinement that may result in simpler, more objective DEM calibrations.     

An analytical model for solute mixing in surcharged manholes

A mathematical model has been developed to describe solute mixing in surcharged manholes using the submerged jet theory. The model has been applied for straight-through flow manholes and for manholes with a difference in the level of the inlet and outlet pipes. The model is applicable to dissolved substances, i.e. the model has not been validated for high sediment concentrations (above 1 g/l) and care should be taken in such cases. Simulation results from the new model are compared with laboratory measurements and are further compared to conventional modelling techniques currently available in commercial software specially developed for modelling the water quality in sewers. The results prove that the new model produces considerably better results compared to the traditional assumption of full mixing in a manhole. The new model compares well to the laboratory measurements and hence improves the accuracy of modelling soluble pollutant transport in sewers. The applicability of the new modelling approach is discussed and further studies are recommended.     

A simplified model for lateral load analysis of asymmetrical buildings

An analytical model is proposed for an approximate three-dimensional lateral load analysis of asymmetrical tall buildings, taking advantage of inherent features of typical buildings. The framing elements of the buildings are grouped into two sets of orthogonally intersecting bents modelled as shear-flexure beams. Both pure torsion and warping of thin members are included. The accuracy of the model is tested through three examples of different nature. The model can be used to analyse buildings with varying properties along the height of the building. Furthermore non-uniform lateral and torsional loads are permitted. Solution by the use of the finite-difference technique makes the model fast, economical and suitable for preliminary analysis on a small computer.