Assignment-10 a

This is a review of the paper "GA-QP Model to Optimize Sewer Systems Design" by T.C.Pan et.al. published in the Journal of Environmental Engineering (ASCE), January 2009.

In this paper the authors have discussed using a hybrid optimization scheme to come up with the best cost sewer systems design. A genetic algorithm approach is proposed to find low cost schemes for sewer systems where the costs are calculated through a quadratic programming approach which takes care of pipe geometry, topological and other deterministic factors to come up with the cost of a candidate scheme. The candidate schemes thus obtained are represented as chromosomes and the fitness function being the reciprocal of the total cost of the scheme represented. The genetic algorithm uses three operations of selection, crossover, and mutation with the selection probability being proportional to the fitness of the individual chromosome.

The authors propose that the QP-GA approach could yield better results than a LP-GA approach used previously by Berry et.al. and others to simplify non-linear problems as QP conserves some non-linearty while exihibiting a uni-modal behavior facilitating a global optimal solution. Though with the use of the GA its still not guaranteed.

The authors also raise concerns over the factors like human intervention etc which aren't easily modelled and not included in this approach. They in turn use the idea of Modeling to generate alternatives(MGAs) as an approach to come up with new and different solutions to get near-optimal solutions. Finally, they do some comparative studies of the new QP-GA solutions and other classical methods like the DDDP (Discrete Dynamic Programming) etc.

Thoughts:

I like the idea of the hybrid optimization and alternative solutions but I would really like to see a way to establish hydraulic feasibility of such schemes. Like coupling this system to a hydraulic modeling s/w like sewerCAD and see for hydraulic instabilites and feasibilites in terms of O&M.