| This study addresses several aspects of dynamic simulation in an equation-solving based flowsheeting environment. The ASCEND-II Dynamic Simulation System, the product of this study, eliminates the boundary between the integrator and the flowsheeting system, thus making it possible to utilize all the features of the underlying flowsheeting system. Differential equations, integral equations and retarded equations are treated by universal mathematical units which can be used to form the unit modules. With this structure, essentially the same unit modules are used both in steady-state analysis and dynamic simulation. The equation solving method employed permits the degrees of freedom in a flowsheet to be changed almost arbitrarily, allowing simulation and design to be done simultaneously. Decision variables specified as trajectories are handled cleanly and neatly. The tear variable concept is introduced in order to reduce computation time in the numerical integration of differential-algebraic systems.; With the equation-solving approach, natural strategies can be developed to handle dynamic simulation related problems such as latency, point constraints, numerical singularities, discontinuities in the right-hand sides of differential equations, as well as the free boundary problem, for both discrete-variable and global approximation methods.; A method is developed to treat the integration step-size as a variable to be calculated such that the integration error criteria is automatically satisfied at each step of numerical integration.; The spline collocation method is studied within the context of flowsheeting and is found to be a suitable global approximation method, not only in handling the above mentioned problems but also in extending the scope of flowsheeting to include optimal control. |
