Assessment of Experimental Uncertainty for a Floating Wind Semisubmersible Under Hydrodynamic Loading

Abstract

The objective of this paper is to assess the sources of experimental uncertainty in an offshore wind validation campaign focused on better understanding the nonlinear hydrodynamic response behavior of a floating semisubmersible. The test specimen and conditions were simplified compared to other floating wind test campaigns to reduce potential sources of uncertainties and better focus on the hydrodynamic load attributes. Repeat tests were used to understand the repeatability of the test conditions and to assess the level of random uncertainty in the measurements. Attention was also given to understanding bias in all components of the test. The end goal of this work is to set uncertainty bounds on the response metrics of interest, which will be used in future work to evaluate the success of modeling tools in accurately calculating hydrodynamic loads and the associated motion responses of the system.

Recent Advances in Integrated Response Analysis of Floating Wind Turbines in a Reliability Perspective

“…The variation in the results is significant and may be due to both intentional and unintentional actions. Recent work focused on quantifying the uncertainty in the experimental results, to try to better understand the discrepancies, suggests that the differences between simulations and experiments are larger than the experimental uncertainties [148][149][150]. Comparisons against full-scale data have also shown large discrepancies; however, the reasons for these discrepancies are more difficult to discern: difficulties in obtaining information about the exact wind and wave conditions, yaw misalignment, or details of the control system, contribute in addition to limitations in the software or user error [151].…”

Uncertainty in the Physical Testing of Floating Wind Energy Platforms’ Accuracy versus Precision

“…The shaded region in Figure 9 indicates the error range which can be attributed to sensor noise, the values in Table 2. The orange data points indicate the error range observed across the 5 repetitions for the 10 top peaks, the precision metric used in [18]. As can be seen in Figures 8 and 9, the magnitude of the error range is not well correlated to the magnitude of the value being measured with 8 of the top 10 peak error range values being exceeded for at least 85% of the 10-min time concurrent time series for Group B in pitch.…”

“…There are exceptions to this trend of omitting an assessment of experimental uncertainty in FOWT test campaigns. Most notably, in a recent paper [18], the subject of which is a test campaign on the OC5-DeepCwind semisubmersible platform at a scale of 1:50. The authors followed the uncertainty assessment guidelines provided by ASME [5], identified all potential sources of experimental uncertainty, and quantified some examples, such as wave elevation, model centre of gravity determination, platform motions, and mooring line loads.…”

“…The authors followed the uncertainty assessment guidelines provided by ASME [5], identified all potential sources of experimental uncertainty, and quantified some examples, such as wave elevation, model centre of gravity determination, platform motions, and mooring line loads. The ultimate aim of the work presented in [18] was to quantify all sources of both experimental precision and accuracy for a particular test campaign and to propagate using statistical techniques to determine an overall threshold for experimental uncertainty. The motivation for this rigorous assessment were the requirements of the OC5 community to allow a meaningful inter-comparison of their increasingly advanced FOWT numerical simulations with a robust physical validation dataset.…”

“…Three test groups were conducted, with each being repeated 5 times to provide an assessment of experimental precision as per [18]. These three test groups are described in Table 1.…”