EBSILON®Professional Online Documentation
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Line connections |
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1 |
Reference line |
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General User Input Values Physics Used Displays Example
This component does not actually contain a component physics and, in particular, does not generate any equations but enables several tuning measures for the iteration behaviour:
The parameters set here have a direct impact on the solution procedure of the equation system. It should be taken into account that an incorrect application of this component may also prevent finding the right solution.
The main application of this component is to define a lower and/or upper limit for the pressure, the enthalpy or the mass flow on an individual line. Here the limits set model-wide can both be expanded or constricted. For instance (see sample model), in spite of a model-wide upper limit for the enthalpy of 10,000 kJ/kg it is possible to admit a higher enthalpy on an individual hydrogen line, or to enable a negative output on an electric line although the global lower limit for the output is 0 kW for electric lines.
However, the limits should be dimensioned so generously that at least at the end of the iteration they no longer delimit the solution. As these limit values do not interfere with the equation system but with the solution procedure, an interference of the limiter may lead to the situation that equations are no longer adhered to and balancing errors occur. An exception is the application in constructions with several controllers where another controller ensures the adherence.
You can specify for each limit value whether
As a rule, limit values are only considered on the line on which the Component 147 is positioned. There is no propagation to other lines.
Initialization values only affect the first iteration step. This serves to define which values the components see on the lines at the beginning of the calculation, before the equation system has been solved for the first time. Subsequently, the initialization values are overwritten by the solution of the equation system.
By default, the values entered in the Model Options are used for the initialization. Component 147, however, allows to overwrite these values for individual lines.
Please note: These initialization values are not suitable as start values for controllers because for the control, an equation has to be generated that allocates the desired value to the line. This is either done by the controller components themselves (internal start value specification) or by one of the Components 1, 33, 46 or 132 on the line (external start value specification).
The iteration precision in EBSILON is a model-wide setting. It is an upper bound for the admissible relative change of a variable (mass flow, pressure, enthalpy) from one iteration step to the next. Only if the relative change is smaller than this bound in terms of the amount in the case of all variables will the iteration procedure be successfully terminated.
Normally this relative change is related to the value of the variable. Thus if e.g. a mass flow changes from 50 to 51 kg/s, the relative change is 1%. With a convergence precision of 10-7 (this is the default value), the mass flow may then only change by another 0.000005 kg/s (i.e. 5 mg/s) for the value to be considered as convergent. With a mass flow of 0.01 kg/s, the admissible change would then only be 10-9 kg/s. Such small changes, however, are not significant in practice and would unnecessarily prolong the iteration. In many cases, no convergence would be achieved anyway due to the “numerical noise“.
For this reason, a minimum reference quantity for calculating the relative change has been defined in EBSILON. If the value of the variable is smaller than the reference quantity, the relative change is calculated not in relation to the variable but in relation to the reference quantity. By default, this reference quantity is
Thus (at a convergence precision of 10-7)
are no longer considered a convergence obstacle.
Now Component 147 allows to define certain areas of the model where the calculation is to be more or less precise. This is done by entering reference quantities for the respective line for MINREFITP, MINREFITH and/or MINREFITM. These reference quantities are then valid for the respective line, but then they are also handed down along the main flow. In a mixer, the reference quantities are ignored by the auxiliary connection (Pin 3). This makes it easier to calculate with a lower precision in the sub stream while downstream of the mixer, with the main flow, the higher precision applies again.
This is particularly helpful if the overall model does not converge because there are still major fluctuations in a less interesting area. With Component 147, you can then allow greater imprecision in this area.
Usually in the case of convergence difficulties, a relaxation is carried out for the entire model. Here the solution of the equation system in the current iteration step is combined with a smaller or greater portion of the solution of the previous iteration step. With Component 147, this relaxation can also be carried out for an individual line.
The relaxation levels correspond to the levels available in the Model Options; here, too, different relaxation levels can be defined at the beginning of the iteration (up to iteration step ITRX) and at the end of the iteration (from iteration step ITRX on). ITRX, however, is always taken from the Model Options.
The line-specific specification of a relaxation allows to make certain areas of a model converge faster or more slowly. This enables a fine-tuning of the convergence behaviour for time-critical applications.
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MINP |
Minimum value for pressure |
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FERRMINP |
Flag for notification, when P< MINP Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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MINH |
Minimum value for enthalpy |
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FERRMINH |
Flag for notification, when H< MINH Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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MINM |
Minimum value for mass flow |
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FERRMINM |
Flag for notification, when M< MINM Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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MAXP |
Maximum value for pressure |
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FERRMAXP |
Flag for notification, when P> MAXP Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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MAXH |
Maximum value for enthalpy |
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FERRMAXH |
Flag for notification, when H> MAXH Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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MAXM |
Maximum value for mass flow |
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FERRMAXM |
Flag for notification, when M> MAXM Like in Parent Profile (Sub profile option only) Expression =-1: Defined from superior model |
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INIP |
Initial value for pressure |
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INIH |
Initial value for enthalpy |
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INIM |
Initial value for mass flow |
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MINREFITP |
Minimum reference value for DITP |
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MINREFITH |
Minimum reference value for DITH |
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MINREFITM |
Minimum reference value for DITM |
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FRELAXUP |
Flag for relaxation of pressure up to ITRX Like in Parent Profile (Sub profile option only) Expression |
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FRELAXFP |
Flag for relaxation of pressure from ITRX Like in Parent Profile (Sub profile option only) Expression |
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FRELAXUH |
Flag for relaxation of enthalpy up to ITRX Like in Parent Profile (Sub profile option only) Expression |
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FRELAXFH |
Flag for relaxation of enthalpy from ITRX Like in Parent Profile (Sub profile option only) Expression |
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FRELAXUM |
Flag for relaxation of mass flow unto ITRX Like in Parent Profile (Sub profile option only) Expression |
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FRELAXFH |
Flag for relaxation of mass flow from ITRX Like in Parent Profile (Sub profile option only) Expression |
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Display Option 1 |
Click here >> Component 147 Demo << to load an example.
