摘要:

A design-point method, or advanced first-order second-moment technique, is used for reliability-based analyses of activated sludge processes in meeting specified effluent standards. Three non-normal random variables, namely flow, influent biochemical oxygen demand (BOD), and influent suspended solids (SS) concentrations, are utilized in evaluating the performance of the activated sludge system. Two types of failure to attain specified effluent standards are considered, namely BOD failure and SS failure. The reliability of activated sludge system is studied with respect to the volume of the aeration tank using design-point method.Key words: reliability analyses, BOD, activated sludge.

ISSN:0315-1468    

DOI:10.1139/l93-022

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A new heuristic-based resource-scheduling algorithm called the least impact model is developed. Unlike available heuristic models, the least impact model allocates resources to a set or a group of activities simultaneously rather than sequentially to individual activities, so as to minimize the negative impact on the remaining total float calculated from a project CPM-type network. A new parameter called future float is introduced as an indicator for assigning scheduling priorities to the sets of activities being considered. Activity sets are generated by first considering all possible combinations of current activities experiencing resource conflict and then narrowing them down to those feasible, which in turn are assigned priorities for allocation of resources based on the least negative impact on the duration of the project. Two examples are worked out to illustrate the use and capabilities of the present model. The results indicate that the least impact model is capable of producing better solutions than those generated from the commonly used total float and the recently proposed current float techniques.Key words: planning and scheduling, resource allocation, resource-constraints scheduling, heuristic scheduling.

ISSN:0315-1468    

DOI:10.1139/l93-023

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The present paper describes a study carried out to verify a new net pen system which has been developed for aquaculture farming at exposed coastal sites. The structure is based on the use of spar buoys rather than rigid floats to support the net. A prototype structure has been deployed in Juan de Fuca Strait, and a verification of the system is described. This has involved an assessment of the environmental conditions and hydrodynamic loading for the structure, strength and fatigue analyses, and a calibration of wave conditions and mooring line forces with respect to prototype measurements. Overall, the system has been found to perform very well. Recommendations are made for monitoring the prototype system and for carrying out a refined verification of the system based on additional data.Key words: aquaculture, fish farms, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

ISSN:0315-1468    

DOI:10.1139/l93-024

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A simple method is proposed as a substitute for the usual process of factoring loads, performing a linear elastic analysis, and determining an envelope of the results. The method is based on statistical principles, but only a minimum knowledge of statistics is required for its use. It involves conventional structural analysis followed by some processing of the results which could readily be incorporated into existing computer programs.The practice of performing two-dimensional analyses on parts of three-dimensional structures is possible with the proposed approach. The implications are clarified and the necessary statistical parameters are derived.Deterministically derived design envelopes represent all the extremes of loading that can reasonably be considered. The envelopes found by the new method not only reflect loading variations but also consider their relative probabilities of occurrence so that excursions beyond the envelope are expected to be equally infrequent along the entire length of the structure. Inconsistencies inherent in the conventional approach are highlighted by comparison with the proposed method for a number of examples.Key words: probabilistic, safety, load, imposed load, load effect envelope, building.

ISSN:0315-1468    

DOI:10.1139/l93-025

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

This paper is a state-of-the-art review of the formulations for the different processes responsible for the transport and mixing of petroleum oil spilled in natural waters. Processes accounting for the transfer and loss of the surface oil, such as initial spreading, evaporation, dissolution, emulsification, dispersion, photo-oxidation, and sedimentation, are included. Based on the findings, a dynamic mathematical model describing the fate of spilled oil was developed. To reflect field observations, the surface oil composition in the model is allowed to vary with time as a result of weathering. Initial results for model testing are presented.Key words: oil spill, mathematical model, fate model, weathering processes.

ISSN:0315-1468    

DOI:10.1139/l93-026

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Solid waste receiving facilities such as recycling centres, transfer stations, incinerators, and landfills may experience significant traffic congestion and waste storage buildup problems due to the random arrival patterns of waste delivery vehicles. The provision of an increased number of service channels and increased waste storage area will reduce the congestion and buildup problems and the associated costs, but will also incur increased capital and operating costs. A simulation modelling approach for evaluating system performance is described in this paper, and the modelling approach is applied to representative Canadian waste receiving facilities. A minimum cost approach is implemented to determine the preferred number of service channels for one application example. The sizing methodology developed should be useful to waste management engineers and planners for both the design of planned solid waste receiving facilities and the operational analysis of existing facilities for a range of projected conditions.Key words: waste management, facility sizing, simulation modelling.

ISSN:0315-1468    

DOI:10.1139/l93-027

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Image analysis for traffic data collection has been studied throughout the world for more than a decade. A survey of existing systems shows that research was focused mainly on the monochrome image analysis and that the field of color image analysis was rarely studied. With the application of color image analysis in mind, this paper proposes a new algorithm for vehicle speed measurement in daytime. The new algorithm consists of four steps: (i) image input, (ii) pixel analysis, (iii) single image analysis, and (iv) image sequence analysis. It has three significant advantages. First, the algorithm can distinguish the shadows caused by moving vehicles outside the detection area from the actual vehicles passing through the area, which is a difficult problem for the monochrome image analysis technique to handle. Second, the algorithm significantly reduces the image data to be processed; thus only a personal computer is required without the addition of any special hardware. The third advantage is the flexible placement of detection spots at any position in the camera's field of view. The accuracy of the algorithm is also discussed.Key words: speed measurement, vehicle detection, image analysis, image processing, traffic control, traffic measurement and road traffic.

ISSN:0315-1468    

DOI:10.1139/l93-028

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

This paper describes the ingredients of a knowledge-based framework for selection of construction methods. They include an operational definition of construction method, a conceptual model of the decision-making process, an explanation of how project context and construction methods may be represented for methods selection and analysis purposes, the range of criteria that need to be considered, and a representation of construction expertise. These ingredients are illustrated using a prototype expert system, called CMSA (Construction Methods Selection Assistant), to select a shoring system for cut-and-cover tunnelling.Key words: construction methods, decision-making, expert system, prototype.

ISSN:0315-1468    

DOI:10.1139/l93-029

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Frost damage in the exterior, loadbearing, clay brick walls of two 5-storey apartment buildings could have seriously affected their loadbearing capacity if left unchecked. A coating applied to the exterior had not stopped further damage from occurring. This paper describes the work to determine the cause of the damage. The work included a condition survey, tests on the brick, and monitoring temperature and moisture levels in a section of the wall. Bricks on an easterly exposure suffered the most damage. The cause was traced to poor quality bricks combined with water infiltration mainly from rain. Remedial measures included cladding the exterior of the brickwork with an insulated siding and replacing severely damaged bricks.Key words: building, masonry, loadbearing, frost resistance, clay brick, moisture, exterior insulation.

ISSN:0315-1468    

DOI:10.1139/l93-030

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Recently, consideration has been given to replacing conventional steel rebars with glass-fiber-reinforced plastic rods in specific applications such as structures subjected to corrosive or marine environment or where electrical or electro magnetic insulation is required. The paper presents the results of a laboratory investigation including physical and mechanical behaviour of a glass-fiber-reinforced plastic rod. The following tests were conducted: thermal expansion, tension at ambient and high temperatures, compression, flexure, shear, fatigue on bare rods, and pullout of rods embedded in concrete. It was found that the glass-fiber-reinforced plastic rod possessed a higher ultimate tensile stress but much lower modulus of elasticity than steel rebars. The plastic rods withstood fewer cycles than steel bars, particularly at higher levels of stress. The loss of strength at temperatures above 200 °C was found to be considerably higher than steel. The coefficient of longitudinal thermal expansion was similar to that of concrete and steel. In light of the results, examples for concrete structural elements have been illustrated in the paper.Key words: glass-fiber rod, plastic, reinforced concrete, thermal expansion, tension, compression, flexure, shear, high temperature, fatigue, pullout, bond strength, development length, beams, slabs, median barriers.

ISSN:0315-1468    

DOI:10.1139/l93-031

出版商:NRC Research Press    

年代:1993

数据来源: NRC