{HEAD ~ Several such helicoid structures} are combined with {TAIL ~ their radii overlapping}, for the most effective interception of a certain cross sectional area of the fluid flow 
are combined with
{ HEAD ~ Several such helicoid structures } are combined with { TAIL ~ their radii overlapping } , for the most effective interception of a certain cross sectional area of the fluid flow
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH