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Has files: YesSubject: search.filters.subject.Multi-objective optimization

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Now showing 1 - 5 of 5
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    PublicationEmbargo
    Review of binary tournament constraint handling technique in NSGA II for optimal control of combined sewer systems
    (Taylor & Francis, 2016-01) Rathnayake, U. S
    Binary tournament constraint handling technique in Non Sorted Genetic Algorithm II (NSGA II) has both advantages and disadvantages. This constraint handling technique is fairly simple; however, it solves the issues in identifying the penalty functions for multi- objective optimization problems. This paper reviews the constraint handling approach in NSGA II and compares it with an alternative constraint handling approach for optimal control of combined sewer systems. Interesting results are presented and it can be concluded that the alternative constraint handling approach produces better results; however, this alternative constraint handling approach has to be used with adequate care.
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    PublicationOpen Access
    Integrated Optimal Control of Urban wastewater Systems
    (2012) Rathnayake, U. S; Tanyimboh, T. T
    Sewer networks are designed to collect and transport wastewater to treatment plants. However, during wet weather periods stormwater runoff flows into these sewers and combined sewer overflows (CSOs) occur. Damage to the nearby natural waters from these CSOs is noticeable. This is because of the high pollution concentrations in CSOs. Controlling urban wastewater systems is one possible way of addressing the environmental issues from CSOs. Therefore, this research explores the development of a holistic framework that is intended to be used for the multi-objective optimization of urban wastewater systems, considering water quality in both sewers and receiving waters and the economics of wastewater treatment. Dry weather flows (DWFs) and stormwater runoff water quality compositions were considered. Temporal and spatial variations of the stormwater runoff were incorporated using pollutographs for different land-uses.
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    PublicationEmbargo
    Dynamic control of urban sewer systems to reduce combined sewer overflows and their adverse impacts
    (10.1016/j.jhydrol.2019.124150, 2019-09-15) Rathnayake, U; Anwar, A. H. M. F
    Sewer network planners use control algorithms, based on optimization techniques, to control urban wastewater systems. These control algorithms have been used to ease the stress on the sewer networks and then, to reduce or to minimize the combined sewer overflows (CSOs). CSOs are not only risking human health but also adversely affecting the aquatic lives. Therefore, many cities try to avoid CSOs. However, this cannot be done to the perfect level due to the capacity limitations of the existing combined sewer networks. In addition, climate variabilities have caused unpredictable precipitation increments and therefore, the control is extremely difficult. Therefore, considering the spatial and temporal variations of runoffs and qualities of stormwater generated from the pre- cipitation, an enhanced optimal control algorithm is illustrated in this paper to control the existing combined sewer networks. Minimizing the pollution load to the receiving water and minimizing the cost of wastewater treatment and pump operation are the two objective functions in the developed optimization algorithm. The algorithm was then successfully applied to a real-world combined sewer network in Liverpool, United Kingdom. Results reveal that the developed optimal control model is capable of handling the dynamic control settings of combined sewer system to minimize the two objective functions simultaneously. With a little computational appreciation, the developed optimal control model can be well-used in the real-time control of combined sewer networks
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    PublicationOpen Access
    Designing standalone hybrid energy systems minimizing initial investment, life cycle cost and pollutant emission
    (Pergamon, 2013-06-01) Perera, A. T. D; Attalage, R. A; Perera, K. K. C. K; Dassanayake, V. P. C
    HES (hybrid energy system)s are becoming energy systems of choice for standalone applications due to ever increasing fuel costs and global concern on GHG (Green House Gas) emissions. However, it is difficult to justify the higher ICC (Initial Capital Cost) of renewable energy components, especially for rural electrification projects in developing countries. This paper illustrates the modeling and simulation of HESs, and multi-objective optimization carried out in order to support decision-making in such instances. LEC (Levelized Energy Cost), ICC and GHG emission were taken as objective functions in the optimization and the sensitivity of market prices and power supply reliability was further evaluated. Results depict that Pareto front of LEC, ICC and GHG emission can be simplified as a combination of ICC–LEC and LEC–GHG emission Pareto fronts making the decision-making process simpler. Gradual integration of renewable energy sources in a number of design stages is proposed for instances where it is difficult to bear the higher ICC. Finally, importance of planning integration of renewable energy sources at early design stages of the project is highlighted in order to overcome the difficulties that need to be faced when coming up with the optimum design.
  • Thumbnail Image
    PublicationEmbargo
    Designing standalone hybrid energy systems minimizing initial investment, life cycle cost and pollutant emission
    (Pergamon, 2013-06-01) Perera, A. T. D; Attalage, R. A; Perera, K. K. C. K; Dassanayake, V. P. C
    HES (hybrid energy system)s are becoming energy systems of choice for standalone applications due to ever increasing fuel costs and global concern on GHG (Green House Gas) emissions. However, it is difficult to justify the higher ICC (Initial Capital Cost) of renewable energy components, especially for rural electrification projects in developing countries. This paper illustrates the modeling and simulation of HESs, and multi-objective optimization carried out in order to support decision-making in such instances. LEC (Levelized Energy Cost), ICC and GHG emission were taken as objective functions in the optimization and the sensitivity of market prices and power supply reliability was further evaluated. Results depict that Pareto front of LEC, ICC and GHG emission can be simplified as a combination of ICC–LEC and LEC–GHG emission Pareto fronts making the decision-making process simpler. Gradual integration of renewable energy sources in a number of design stages is proposed for instances where it is difficult to bear the higher ICC. Finally, importance of planning integration of renewable energy sources at early design stages of the project is highlighted in order to overcome the difficulties that need to be faced when coming up with the optimum design.