Mixed mode simulation - Adding equation oriented convergence to a sequential modular simulation tool

Publisher Summary This chapter provides an introduction to the methods of solution for flowsheet simulations—sequential modular (SM) or equation oriented (EO). EO methods are gaining popularity and availability because of increased performance of computing equipment and improved high-level computer languages. EO techniques (also called “equation-based techniques”) involve expressing all the governing relationships as residuals that have a value of zero at solution. If sequential modular and equation-oriented techniques could be combined into a single framework, users have the potential to gain the strengths of both techniques while minimizing their weaknesses. An advantage of the tearing or SM methods is that the number of equations being solved at any given time is reduced. These techniques can be tailored so that they are very good at solving specific types of problems. SM simulation packages are generally very user friendly and easy for a novice to use. Adding EO solution techniques to an existing sequential modular flowsheet simulation tool requires the addition of many tools and features to guide users through specifying, solving, and interpreting results of EO simulation. Some of the key elements discussed are the EO variable grid, specification management, connection management, and objective functions.