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Hello,


 


I'm to optimize an CFRP drive shaft for an formula student race car. The shaft itself is produced in a winding process. The tulips of the homokinetic joints are glued into the ends of the shaft.


For that I created a model with a PCOMPP property and a laminate with 4 plies. The tulips are simplified as rod elements with HyperBeam tubesections and PROD properties with characteristical values of aluminium. The measurements are:


 


length of the shaft: ca. 300 mm


inner diameter: 65 mm


laminate thickness: 8 mm


length of the rods: 80 mm


inner diameter of the tulips: 45 mm


 


If I run an analysis of the model and check the out.file, the mass is calculated as about 1350g. If I run the free-size optimization afterwards, the mass before the first iteration is calculated as 1270g. I don't understand why the two values aren't the same. Is the calculated mass in the analysis the mass of the tulips and the shaft an the mass before the free-size optimization only the mass of the shaft because of the objective function? I don't really get, why there is a difference. Because the mass of the tulips should be about 600g and not 100g.


 


The objective funktion ist minmass and the contraints are set by the displacement of the nodes of one end of the shaft. 


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