Perform calculation

Use case objective

Performing the provided example computation

Computations in openCDT are defined as Calculation objects. One or more calculations are organized in a Calculation Set. When executing a computation, a CalculationSet is executed.

This use case demonstrates how a computation in the provided Demo aircraft model (see [Create aircraft model]) is executed.

1. Install and configure Scilab

This use case depends on a local Scilab installation on your computer. If Scilab is not installed on your computer, please download it from http://www.scilab.org/products/scilab/download. OpenCDT has been developed and tested with Scilab-5.3.0.

Once Scilab is installed on your computer, you need to tell openCDT where to find your Scilab installation. Open the Preferences dialog in openCDT, and select the Scilab Preferences. Please enter the path to the Scilab Console Executable on your computer, or use the Browse button. Please leave the Options field empty.

2. Locate CalculationSet MassPerformanceLoop

If not yet done, please generate the example data model (see [Create aircraft model]). Please open the Configuration Demo aircraft model in the openCDT Navigotor. The CalculationSet CS_Mass Performance Loop is the fourth element contained in this configuration. The calculation set element gives you acces to all commands that can be performed on it. By expanding the calculation set element you can also see the different elements contained in a calculation set: calculations, (sub-) calculation sets and a calculation graph.

3. Verify CalculationSet

A calculation set needs to adhere to a set of rules for calculation sets. As the current release does not provide any GUI for modeling calculation sets and as the provided example calculation set is conform with these rules, this step can be skipped.

4. Determine initial parameters

Before a calculation set can be executed, it must be ensured that all parameters that are required to execute it are provided by the user. openCDT provides the Determine initial parameters command to achieve this. Please right-click the calculation set CS_Mass Performance Loop and select the Determine initial parameters command.

As a result of this command, openCDT identifies all parameters that have to be user defined and creates empty values that can be edited by the user (see next step).

5. Enter values for initial parameters

Please expand all components in the example configuration, and locate all parameters that have values attached to them (these are the parameters that can be expanded; they can also be identified by the litle star in the lower left corner of the parameter symbol).

For all initial parameters: expand Parameter, Value and Measured Value. A single click on Measured Value shows its properties in the lower part of openCDT. The following values are entered into Value property of the respective Measured Value element:

• s_wet_fus (in component fuselage): 200
• s_ref (in compenent wing): 50
• aspect_ratio (in component wing): 9.0
• Oswald efficieny (in component wing): 0.85
• ff_ref (in component Fuel system): 0.9
• m_to (in component aircraft): 23000
• m_Payload (in component aircraft): 6250
• R (in component aircraft): 2000000
• Altitude (in component Mission): 10668
• Mach Number (in component Mission): 0.75

6. Execute CalculationSet MassPerformanceLoop

Now that the calculation set CS_Mass Performance Loop is prepared, it can be executed by right_clicking the calculation set symbol and chosing Execute calculation. openCDT calculates all missing parameters and stores them in values that are inserted into the parameters.

Note: The example calculation set does overdetermine the resulting m_to parameter, and does perform a feedback loop until the value for m_to is stabilized (the criterion used is a deviation smaller than 0.001%). For each iteration loop, some parameters are re-calculated, and the results are inserted into new values. When expanding a parameter, the final result is in the latest value.

Note: In some situations there is a delay when starting Scilab the first time that causes an error with a corresponding rollback (i.e. all values that have been inserted into the corresponding parameters are removed again). Should this be the case, execute the calculation set a second time.