Merging the nodes is equivalent of a continuous body (see welded).
Using a contact definition, means that there are two separate surfaces which are connected through a layer/thin film (although this is a simplification). Using the contact definition means that usually there is a surface and adjacent nodes and/or elements are checked against that surface (to ...
Compute the wave velocity in a 3.05-m-diameter steel penstock having a
wall thickness of 25 mm if it:
i. is embedded in a concrete dam;
ii. is anchored at the upstream end; and
iii. has expansion joints throughout its length.