The petroleum exploration in deep water induces many challenges. Several problems are due to the extremely long structure that links the platform to the wellhead (risers). The depth increase makes the structure more slender, and consequently much more flexible. Its dynamical behavior can be described by an infinite dimensional system. Two associated problems are studied in this report: the positioning of the bottom end of structure, to connect it to the wellhead (reentry operation), and the vortex induced vibrations (VIV) of these slender structures.