MOBILE OFFSHORE BASE RESEARCH CHALLENGES Dr. Paul Palo U. S. Naval Facilities Engineering Service Center Centre for Ships and Ocean Structures Norwegian University of Science and Technology 29 October 2004

Outline l Summary: ONR MOB S&T Program l Research Challenges

MOB Hydromechanics S&T Summary l Broad, balanced program addressing a range of S&T topics corresponding to MOB design l Driven by: USER! –operational, survival and transit aspects –wide range of MOB platform characteristics –ALL accompanying support information l Deliverables include: –preliminary and final analysis tools –pioneering hydroelastic models and data –wave excitation - structural loads interface –pioneering wave coherence information

MOB Hydromechanics S&T Technology Transfer l MOB Hydromechanics S&T is applicable to all large offshore vessels and structures l Commercial airports (cargo) l Remote military training airfields

MOB Hydromechanics S&T Summary l Key S&T Opportunities: –Analyze hydroelastic data! –Continue wave coherence studies –Complete Classification Guide –develop a technique that will apply viscous damping to VLFS structures with “small” modules

Crest Only; “This is not a wave.” “Paired Crest + Trough; “This is a wave.” “Disjointed Crest; “This is unknown!” “What is a [3D] ‘wave’?”

MOB Hydromechanics 4.1 Automatic Control: Multibody Dynamic Positioning UC Berkeley Algorithms and Demonstration

MOB Hydromechanics Time Domain Limitations, LAMP Pitch Exper, freq f forcing f forcing + f nat a nat ~ 4 * a forcing Semis have low pitch radiation damping. LAMP model generated resonance during the ramp, no decay mechanism.  (t)

MOB Hydromechanics Other “VLFS” Structures Amphibious Lighterage Waterside Security Barriers

MOB Hydromechanics Navy Amphibious Lighterage l Platform dimensions –Module: 100 by 24 by 2 ft, 100 tons (30 by 7 by.6 m) –Causeway: 1,200 ft (366 m) –Water depths: 0 to 9 m

MOB Hydromechanics Navy Amphibious Lighterage l Problem: damping! Front MiddleBack + Sway

MOB Hydromechanics Navy Waterside Barriers l “VLFS?” Note aspect ratio! l Problem: damping again.