CAREER: Irregular Environmental Loading and Response of Offshore Structures, CMS proposal 0448730
PI: Sweetman, Texas A&M - Galveston
Recent computer and sensor hardware developments have dramatically increased field data collection capabilities, outpacing development of new methodologies to make optimal use of these data. Hydrodynamic loading and fluid-structure interaction on offshore structures have long been targeted with computer-intensive deterministic calculations, but these processes are inherently stochastic, for which no adequate methodologies exist to quantify structural loads and response. Here, random process theory, structural dynamics, hydrodynamics, and measured data interpretation will be combined to improve design methods for offshore structures and enable verification of deterministic hydrodynamic theories with full-scale measured data. New methodologies and associated numerical tools for prediction of fluid-structure interaction in both shallow and very deep waters are proposed. Example applications will be worked in detail relevant to load and response predictions for offshore wind turbines and marine risers. Marine risers are the vertical pipes carrying fluids between the sea-floor and sea-surface. The PI's doctoral research at Stanford integrated fluid-structure interaction, random vibrations and extreme value theory and included extensive comparison with measured data. He also has ten years of industry experience in advanced methods for design and construction of offshore structures where he saw the need for new ways to quantify environmental load and response of offshore structures. Intellectual Merit: This research increases the fundamental understanding of fluid-structure interaction in both shallow and very deep waters, develops new engineering methods, and applies these new methods to develop new numerical tools for use in design and test of hydrodynamic theories. The wind turbine work combines statistical methods and stream function wave theory with a new dynamic numerical model to better predict wave loading on the structure and to better understand the complicated interaction between winds, waves, and the structure. The marine riser work addresses vortex-induced vibration (VIV), a fluid-structure interaction problem dominating design of long marine risers in high currents. A new random vibration methodology will be developed where statistical distributions built from measured data are used to quantitatively assess the effectiveness of hydrodynamic theories. The new methodology may find use in various structural vibration applications. Specific research goals include: (1) develop a new irregular wave simulation methodology to predict ocean wave profiles and kinematics based on stream function theory; (2) develop a new random process model to combine the new irregular wave methodology with irregular wind characterizations to predict extreme loading on offshore wind turbines; (3) critically compare the results from (1) and (2) with full-scale measured data to verify the new methods; (4) develop a deterministic dynamic model of a marine riser in very deep water; (5) develop statistical distributions of riser accelerations from measured data; (6) use results of (4) and (5) to quantitatively assess the likelihood that hypothesized hydrodynamic theories explain observed acceleration data; and (7) other applications of the new methodology. Broader Impact: The proposed work will have direct impact on future design of offshore wind turbines and marine risers by providing a better understanding of complex interactions between a structure and its environment. Both of these areas are relevant to present and future world energy supplies. The project will also enhance cross-pollination of ideas between two different technical cultures: European-dominated offshore wind energy and the US-dominated deep-water offshore oil production. Specific educational and broader impact goals include: (1) development of a new course in off- shore and near-shore structural dynamics and fluid-structure interaction including some results from this research; (2) outreach to science and technology students from historically underrepresented and financially challenged situations through the NSF-funded "GATES" program; (3) outreach to K-12 students and educators through the existing Sea Camp Program, which has hosted over 10,000 K-12 students and 1,000 K-12 teachers at TAMUG to date, and (4) education of promising graduate students in important emerging technical areas.
