| The overall objective of this work has been to apply high-performance, parallel computers to equation-based chemical process flowsheeting. The primary focus was on investigating parallel techniques for improving the reliability of equation-based flowsheeting, and the secondary goal was to examine the effects of parallel function evaluation on the performance of traditional, Newton-like solvers.; To accomplish the principal goal, an interval Newton/generalized bisection technique was studied. This approach to solving systems of nonlinear equations often involves high computational cost and therefore has been considered impractical for solving the large, sparse systems associated with equation-based flowsheeting. However, advances in parallel computer architectures and increases in computational power indicate that efficient implementations will become practical for solving flowsheeting problems. In the first stage of this study, SQUIB, a serial code using an interval Newton/generalized bisection algorithm for solving large, sparse flowsheeting systems, was developed. Then two large grained parallel algorithms, one synchronous and the other asynchronous, based on the serial algorithm were developed and implemented with the Uniform System programming model on a BBN TC2000 high-performance computer. All of the programs were used to solve several small flowsheeting problems. The serial code usually successfully located solutions in well under the number of computations predicted by the worst-case scenario, and it also isolated multiple roots. The asynchronous parallel code outperformed the synchronous code, and the results from running the asynchronous code on increasing numbers of processors indicate that maximum speedups are limited to about four or five. However, if additional levels of parallelism are exploited in future research, the resulting speedups should improve as the number of processors increases. These methods thus hold promise for solving flowsheeting problems when other, less computationally expensive, approaches have failed.; To achieve the secondary goal, the function evaluations required for the Newton-like solvers in a prototype equation-based flowsheeting package were computed in parallel on a Cray-2. The results indicate that this strategy could improve performance for very large problems or for problems involving several computationally intensive functions. |
