Year 2003
Mika Friman

Modularisation Issues in Dynamic Equation-Based Process Simulation Solvers – Comparison of Two Different Approaches

Modularisation from the software point of view regarding dynamic equation-based process simulation solvers is studied in this work. The aim is to evaluate various modularisation alternatives and to discuss the resulting influence on the overall simulation environment.

At first, dynamic process simulation and its strengths and weaknesses are introduced. The equation-based solving technique is selected as the basis for this study and its characteristics are discussed. CAPE-Open Consortium has produced a specification defining the interfaces of the software components of a process simulator. This specification is also evaluated. In order to discuss the modularisation issues, two different solving approaches were chosen. The first one was based on solving implicitely flow network problems that were assembled in a specific matrix form. The second approach followed the newly found guidelines described by CAPE-Open Consortium, in which the flow network was defined as an ODE-set and solved as an initial value problem. In order to test these two solving approaches, a simple flow network test case was constructed.

A modularised simulation environment enables the reuse and extensibility of separate components. Compatibility between the modules is guaranteed by conforming to well-defined interfaces, even if the modules originate from different vendors. Moreover, the components do not need to know about the functionality and the inner structure of other components. The results produced with both approaches are equal and they are verified using commercial simulation software. Mass flow responses and pressures tend to oscillate under unrealistic process conditions and smaller time steps have to be used in the ODE-set solving approach. The modularisation task in the other approach is more laborious and requires special observations.

Although a modularised simulation environment is not implemented in this work, it is observed that the simulator executive, the solver, unit operations and the supplementary thermodynamic and physical property libraries should be separated, as also suggested by others. In order to assess the overall performance and scalability, a generic modularised simulation environment should be implemented for both approaches.

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