Flowshop Scheduling Using a Network Approach

In this paper, a network based formulation of a permutation flow shop problem is presented. Two nuances of flow shop problems with different levels of complexity are solved using different approaches to the linear programming formulation. Key flow shop parameters inclosing makespan of the flow shop problems were obtained without recourse to the traditional approach of using Gantt charts. The linear programming models of the flow shop problems considered were solved using LINGO 7.0. The present technique has been shown to be very effective and efficient.http://dx.doi.org/10.4314/njt.v34i2.1

Robust Stabilization of Jet Engine Compressor In The Presence of Noise and Unmeasured States

Compressors for jet engines in operation experience disturbances such asvariations in the states of the system, mass flow, and pressure. These disturbances sometimes result in instabilities due to surge and stall, which adversely affect performance. In this work, first we modify the Moore and Grietzer three-state model for compressors to include disturbance (noise signals) and then use the method of integrator backstepping, coupled with saturation functions to develop robust controllers for the stabilization of the compressor. Also, we develop robust observers for estimating the states of the system in situation where there exist some states that cannot be measured. Implementing the developed controllers on the system, simulation results showed that stability was achieved. Also, the observer designed for the jet compressor was able to provide accurate state estimates.Keywords: Integrator backstepping, observer, robust control, stall and surge, unmeasured state