MultiLevel Simulation Problems
Oil Refinery Example Problem
Site Simulation: Combine all processor optimizations under one roof. These are called nested optimizations. Each will solve its control valve settings for a suboptimum result in order to achieve an overall objective set for this total site optimization problem. But at first one must insure that all nested optimizations work okay under all simulation testing (ie. no solver trying for an optimum here). When all nested optimizations seem working okay together then move on to building an overall objective (function) for this site.
Site Constraints: include things like minimum inventory, maximum inventory, allowable temperature & pressure ranges, etc. Add such equation constraints to your Total site math model. These will insure that any optimal solution found is within these ranges and boundaries.
Site Goal / Objective: Determine Total site objective function. For example,
 Minimize Pollution;
 Maximize Profit while Minimizing Pollution; or,
 Optimize ???.
Site Optimization: Given some input and initial parameter value settings, constraints, and objective(s) one is ready to start finding process control settings in order to arrive at desired objective for a site. As site processes are added or removed and other changes occur this total site optimization problem will need to be rerun.
Multiple Sites?: Yes one can make each site optimization a suboptimization under a Corporate optimization problem. There is no limit on number of optimization levels in FortranCalculus compiler software. As long as ones hardware has room for the largest array you are in good shape.
Transportation MultiLevel Example Problem
Arterial Roads Simulation: (Inner most level) Key roads where traffic monitoring with stoplights on a timer is desired. Need to find the optimal stoplight timing settings to insure objective is met. Objective concidered might be
 Maximize Traffic Flow;
 Minimize Pollution; or,
 Optimize ???.

This is normal Operations Research material at this level of simulation.

City Level Simulation: Group of Artial Road Simulations / Optimizations with their models and objectives all under one umbrella. This City level Simulation has an objective such as
 Minimize Pollution while Maximizing Traffic Flow;
 Minimize Repair Costs while Minimizing Pollution; or,
 Optimize ???.
State Level Simulation: Group of City Simulations / Optimizations with their models and objectives all under one umbrella. This State level Simulation has an objective such as
 Minimize Pollution while Maximizing Traffic Flow;
 Minimize Repair Costs while Minimizing Pollution; or,
 Optimize ???.