Version 1 (modified by Rafael de Pelegrini Soares, 16 years ago) (diff)

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# Convergence Problems

Most interesting engineering problems are highly nonlinear. This kind of problems are very difficult to solve using Newton's like solvers without a good approximation of the solution. EMSO assembles the initial guess for a problem from the Default attribute of the variables. For several cases this approximation is enough, but for more difficult to converge it is not.

## Initial Guess From Saved Results

In some cases the user can obtain a solution for a specific configuration or simplified model. Examples are:

• To choose simplified thermodynamic models (ideal gas and ideal liquid)
• To supply a specifications or parameter settings which have better convergence characteristics

With a solution at hand, even for unrelated cases, it is much easier for a Newton's like method to obtain the final solution. This can be achieved using the guessFile option:

1. Obtain a solution using simplified models or at conditions with better convergence characteristics
2. Once you got convergence, using the EMSO graphical interface save the result to a file (eg. result.rlt)
3. Use the option guessFile="result.rlt" on the difficult to converge case, as follows:
```FlowSheet MyFlowSheet
...

OPTIONS
guessFile = "result";
end
```

Note: This option can be used in both, dynamic and static simulation.

## Initial Condition From Saved Results

Dynamic simulations requires the specification of a initial condition. In several dynamic simulation experiments the user wants to start the simulation from a previous simulated or steady state point. In several cases it is very hard to give a steady-state initial condition manually.

For these cases the initalFile option can be used. This option is analogous to the guessFile option but it instructs the simulator to ignore the manually specified initial conditions and to use a previously saved result instead:

```FlowSheet MyFlowSheet
...

OPTIONS
initialFile = "result";
end
```

Note: This option makes sense only for dynamic simulations.