Connecting your numerical modelling to the real world
Computer modeling is becoming more popular with improved computer power and cheaper software. However, in order to gain confidence that the model is a true representation of the real world, it is necessary to calibrate the model against real world conditions.
Colourful computer models look convincing, but can often be inaccurate.
Small changes in loading, boundary conditions and model parameters can result in large variation in results. It is therefore necessary to gain confidence in the predicted result in order to quantify how accurate the model really is. This sort of sensitivity analysis is seldom performed and hence computer model results should be viewed with caution.
As a minimum, the following should be conducted on any computer model:
• Run a simple model and compare the results to those of more complex models and compare the results - if there are marked differences you need to understand why.
• Run the model with multiple, but well considered, boundary conditions and compare the results.
• Run the model with well considered material conditions. Quoted material properties are often minimums and, particularly where partial strain is considered, can lead to large variations in results.
• Conduct a manual stress analysis on a simple section of the model and compare results.
• Strain gauge the manufactured component and compare the measured results for specific load condition to those predicted by the model. This latter test is the definitive test of the accuracy of the computer model but can only be conducted after the component (or prototypes) have been manufactured. But this is still well worth doing in critical applications or where fatigue loading and life prediction is important. Digital Image Correlation (DIC) can also be used similarly.
Computer modelling is without doubt an extremely valuable tool when done by experts and is well validated. Beware of accepting computer results at face value especially where the source of the model is unknown or the modelling process is poorly documented!
Published in Technical Tips by Origen Engineering Solutions on 1 January 2015