Abstract: A drill string (2) for a floating drill rig, the drill string (2) comprising: a bore (4) running the length of the drill string (2) and configured to receive a drilling fluid; and a controllable dynamic flow restriction (14) in the bore, wherein the controllable dynamic flow restriction (14) is operable to restrict flow of the drilling fluid through the bore (4) and thereby generate excess pressure in the drill string when the drill string (2) moves down, and to allow additional drilling fluid to be pushed through the bore (4) and out of the fluid connection under the excess pressure generated when the drill string (2) moves upward.