Question: I have a question regarding to the marine growth thickness. In Sacs, the format input included marine growth thickness and surface roughness Do the thickness of a tubular will account for 03 thick (tubular + marine growth thickness + surface roughness) for wave force calculation? Answer: Yes, the thickness of tubular added with marine growth is used for the wave+current load calculations. The surface roughness factor [k] is used to adjust the Cd and Cm values accordingly [as per water depths indicated in the card], unless a constant value specified in the same card. For a normal offshore structure diameter range, the drag coefficient [Cd] values are adjusted on the higher side nearing high tide zone [MWL], hence, a higher ‘k’ value is adopted. Generally, as Cd increases with surface roughness, Cm decreases for these type of structures [drag dominated]. Both Reynolds Number and Keulegan-Carpenter Number [flow parameters] plays a vital role in determining so. SACS uses the marine growth override card [MGROV] to define marine growth and indicates that the marine growth are not the part of structural analysis [no stiffness effect].
