I've been able to import the STEP file of the CAD geometry into Design Modeler and successfully created mid surface of the tube and coupler/clamp. However, the difficulty I am now having is trying to apply the force and fixed support at designated positions on the tube/pipe as shown on the original solid model screenshots. During the mid surface operation the tube/pipe has now lost all it's 'reference' edges that were once visible in the solid model. 

Sorry for the many issues - I'm still trying to get to grips with the basics.