Error Analysis

General

After you have done a calculation, you will be interested to know whether it was successful or not. There are three sources that tell you about the last calculation:

• the message box after the calculation
• the error analysis window
• the calculation information sheet

After finishing a calculation, Ebsilon shows by default whether the calculation has been successful, how long it took, and how many errors or

warnings exist.

It contains detailed information about the success of your calculation. It is possible that

• the calculation could not be done at all e.g. because the input data were missing. In this case, the error analysis tells you what is missing and you have to specify the missing values,
• the calculation could be started, but did not converge within the specified limit of iteration steps. In this case, take a look at the convergence diagram to check whether it is reasonable to increase the limit or eliminate the origin of the convergence problems, e.g. controllers that work against each other. The error analysis can be used to figure out the regions with the lowest convergence.
• the calculation was done, but certain errors appeared
• the calculation was successful. In this case, there may be warnings or comments.

If the message box has closed, you can also look up this information in the calculation information sheet.

Under “General Options“ à “Calculation“ it is possible to set if this message is to occur

• always
• never
• only in the case of errors
• only in the case of errors and warnings
     

The error analysis window opens automatically, if the calculation fails. You can also open it manually with the menu command "CalculationàError Analysis". It contains all the messages of the calculation kernel: errors, warnings and comments.

You can open the calculation information sheet from the menu command "ExtrasàModel Options", page "Results". it contains summary information, such as the type and the state of the calculation, number of iteration steps and the run time. For more information, see "Model Options-Results"

The error analysis window

This window can be opened by the menu command "CalculationàError Analysis". If a calculation ends with at least one message of the class "error", this window pops up automatically.

The error dialog has been completely revised. All errors are displayed in table form.

When it is displayed, the colour of the model turns from coloured to gray.

In the top line, the number of 

• "Errors",
• "Warnings", and
• "Comments"

is displayed.

By clicking, the messages of the corresponding category are shown in the table.

For each class, there are certain types.

Errors can be

• P/T/H definition errors
• Missing start value
• Missing mass flow
• Missing pressure
• Missing mass flow
• Negative mass flow
• Negative pressure
• Negative enthalpy
• Component error
• Over-determination in mass flow (error)
• Over-determination in pressure (error)
• Over-determination in enthalpy (error)
  

Warnings can be

• Over-determination in mass flow (warning)
• Over-determination in pressure (warning)
• Over-determination in enthalpy (warning)
• Component warnings
  

Comments are

• Component comments

You can read about the meaning of the error classes in the description of the simulation.

Note that over-determination can be an error as well as a warning:

• It is an error if there is a contradiction between two or more redundant equations in the matrix solution. In this case, one of these equations is discarded, and the result is arbitrary, depending on the order of equations. This cannot result in a correct solution.
• It is a warning if there are redundant equations in the matrix solution, but the redundant equations are equivalent. The calculation is correct in this case, but an error may arise if some input values are changed, e.g. in a part load case, and the redundant equations are no longer equivalent.

Intentional over-determinations that arise due to redundant measured values in case of a validation are neither an error nor a warning and will not be reported here.

The fourth button “Pipe Residuals“ allows to display lines for which there were changes between the second last and the last iteration step

that transgressed a definable threshold. This button serves as a combo box for selecting whether residuals in the mass flows, in the

pressures, or in the enthalpies are to be displayed, or also if all residuals are to be displayed. The convergence limit set in the model can

be used as a threshold, or the limits for each quantity can be entered by selecting “Edit thresholds”.

Moreover there are buttons in the top line that allow to

• reset the display of the model to total view
• activate the convergence diagram
• activate and deactivate the error display (gray representation of all components and lines not affected by the error)
• close the dialog
• activate and deactivate an automatic closing of the dialog when carrying out a calculation

When clicking on the column headlines in the following line, the table is sorted according the respective size, first in ascending order, and

when clicking again in descending order.

By selecting one or more lines of the table, the corresponding objects in the model are displayed in colour.

In the error list, equation list, and measured value list you can select the corresponding component in the model.

The right mouse key allows defining which action is to be triggered by double-clicking:

• Opening the properties window of the respective component
• Selecting the respective component
• Enlarging the respective component
• Selecting and enlarging the respective component 

Treatment of Topology Errors

The check of the topology for the connection of logic lines, set point value lines, and actual value lines has been tightened. This may result in error messages in the case of some models that previously calculated without an error message.

The following problem cases are detected:

• Ambiguous structures (when there is more than one possibility in which direction a value is passed on)
  
• Ring-shaped structures (this will also result when an actual value line and a logic line are connected at their ends as in this case it is not clear whether the actual value line is supposed to take over the value from the logic line or the other way round)

In most cases, these errors will have been caused by unintentionally snapping a free end of a line with activated snap radius. Users who often work with logic constructions are therefore recommended to deactivate the snap radius (under General Options --> Edit).

Evaluation of the convergence

When you click on "OK", warning messages appear for each pipe where the relative deviation for the considered quantity between the two last iteration steps exceeds this limit. For these message, three additional error types are provided:

• Lower precision in mass flow
• Lower precision in pressure
• Lower precision in enthalpy

You can view these messages, like all other messages, by going through the warnings. The message includes the actual value of the deviation for the corresponding quantity. 

Note: If you want to figure out the convergence situation of a specific iteration step, set the limit of iteration steps temporary to that number and do a calculation. The calculation will stop at this iteration step, and you can evaluate it.