Abstract
Mooring systems exhibit high failure rates. This is especially problematic for offshore renewable energy systems, like wave and floating wind, where the mooring system can be an active component and the redundancy in the design must be kept low. Here we investigate how uncertainty in input parameters propagates through the mooring system and affects the design and dynamic response of mooring and floaters. The method used is a nonintrusive surrogate based uncertainty quantification (UQ) approach based on generalized Polynomial Chaos (gPC). We investigate the importance of the added mass, tangential drag, and normal drag coefficient of a catenary mooring cable on the peak tension in the cable. It is found that the normal drag coefficient has the greatest influence. However, the uncertainty in the coefficients plays a minor role for snap loads. Using the same methodology we analyze how deviations in anchor placement impact the dynamics of a floating axi-symmetric point-absorber. It is shown that heave and pitch are largely unaffected but surge and cable tension can be significantly altered. Our results are important towards streamlining the analysis and design of floating structures. Improving the analysis to take into account uncertainties is especially relevant for offshore renewable energy systems where the mooring system is a considerable portion of the investment.
Highlights
Mooring systems play an important role in assuring the safe operation of floating structures like oil and gas (O&G) platforms
Brindley and Comley [1] analyzed the times to failure of mooring cables for semisubmersible mobile offshore drilling units (MODUs) operating in the North Sea during the years 1996–2005, concluding that there is an average time of 24 operational years per failure of single lines and 112 years for multiple lines
In coastal engineering generalized Polynomial Chaos (gPC) has been used to study the sensitivity of coastal inundation to parameters like Manning’s number [16,17], while in ocean engineering the method has been applied to phase-averaging spectral wave modeling [18], water wave propagation and transformation [19], wave scattering from an ice floe [20], and the motions of a heaving cylinder [21] in irregular waves
Summary
Mooring systems play an important role in assuring the safe operation (to life and to the environment) of floating structures like oil and gas (O&G) platforms. In coastal engineering gPC has been used to study the sensitivity of coastal inundation to parameters like Manning’s number [16,17], while in ocean engineering the method has been applied to phase-averaging spectral wave modeling [18], water wave propagation and transformation [19], wave scattering from an ice floe [20], and the motions of a heaving cylinder [21] in irregular waves It is seeing applications in the field of marine renewable energy and moored structures, in the prediction of extreme loads on wave energy converters [22], and long-term extreme responses of moored floating structures [23].
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