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This paper presents an iterated local search for the fixed-charge uncapacitated network design problem with user-optimal flow (FCNDP-UOF), which concerns routing multiple commodities from its origin to its destination by designing a network through selecting arcs, with an objective of minimizing the sum of the fixed costs of the selected arcs plus the sum of variable costs associated to the flows on each arc. Besides that, since the FCNDP-UOF is a bilevel problem, each commodity has to be transported through a shortest path, concerning the edges length, in the built network. The proposed algorithm generate a initial solution using a variable fixing heuristic. Then a local branching strategy is applied to improve the quality of the solution. At last, an efficient perturbation strategy is presented to perform cycle-based moves to explore different parts of the solution space. Computational experiments shows that the proposed solution method consistently produces high-quality solutions in reasonable computational times.

This paper is concerned with the unit commitment of hydro generating units on an hourly basis throughout a single day. The performance criterion to be optimized includes the efficiency of hydro conversion, which depends on variations in tailrace elevation, penstock head losses and turbine-generator efficiency, as well as the cost of startup/shutdown of the hydro generating units. The paper presents a comparison of two heuristic approaches for solving the optimization problem. One heuristic is based on decomposing the problem into Generation Scheduling (GS) and Unit Scheduling (US) sub-problems, and solving the sub-problems by Lagrangian Relaxation and Dynamic Programming, respectively. The other heuristic makes use of a Genetic Algorithm combined with Lagrangian Relaxation to solve the original problem. The two heuristics were tested on a system composed of sixteen hydro plants, one hundred generating units, and an installed capacity of 21,933 MW in the Brazilian power system. The actual scheduling of generation actual for a typical day was used for comparison with the solutions proposed by the two heuristics. The results of both heuristics show significant savings in terms of hydro conversion efficiency and startup/shutdown costs.

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