## 8 Conclusions  
There are many factors that may affect the accuracy of riser response reconstruction and the selection of a method for assessing fatigue damage; these include characteristics of the motion (standing or traveling waves), the arrangement of sensors (their number and spacing), non-stationary characteristics of the riser response, complex configurations of the riser (e.g., the distribution of mass and buoyancy), unknown or uncertain boundary conditions, etc. It was impossible to examine all these factors in the current work. Based on the studies using the available NDP data sets and the simulated data (all the results involving the use of these simulated data were not included for the sake of brevity), some conclusions may be summarized as follows:  
* For the case where traveling waves are not dominant in the riser's response, the WWA method is preferred over the modified WWA method for response reconstruction over the entire riser span. For the case where strong traveling waves exist and when a sufficient number of sensors is available, the modified WWA procedure may be a better choice than the WWA procedure. * If very limited or no physical information about the riser is available, the POD or MPR methods may be employed to estimate the response over the region where sensors are closely spaced, no matter whether traveling waves are indicated or not. * The hybrid method appears to be the most accurate among the five methods tested, no matter how dominant the influence of traveling waves is and no matter how many sensors are available. Due to the limited number of data sets analyzed in this study, it is appropriate to state that this conclusion is tentative and the method should be applied with caution. Note that all of these empirical methods are neither perfect nor suggested for use in all situations. Riser response reconstructed by these methods should always be checked against expected physical behavior of the riser, based on engineering judgement. Furthermore, uncertainties and errors in estimates of fatigue damage rates must be quantified through a cross-validation analysis that is easily incorporated into such empirical procedures as has been demonstrated. After \"short-term\" fatigue damage distributions conditional on specific current profiles are obtained using such empirical methods, it is possible next to estimate the \"long-term\" fatigue life of risers by integrating the short-termfatigue damage distributions (appropriately corrected using variability factors) with the likelihood of different current profiles. In this way, long-term fatigue damage and fatigue failure probabilities may be directly estimated using the empirical methods presented here that make use of available riser response measurements [36]. [PERSON] was responsible for all the computations, validation, and original draft preparation, [PERSON] was responsible for overall direction and review of the work and manuscript drafts; [PERSON] assisted with problem definition and oversight. Financial support is provided by the National Key R&D Program \"Research, development and project demonstration of a multipurpose flexible pipe for ultra-deepwaters (Grant No. 2016 YFC0303800)\", Fundamental Research Funds for Central University (Grant No. 16 CX02024A), and BP America Production Co. are greatly appreciated. The authors acknowledge with gratitude the permission granted by the Norwegian Deepwater Programme (NDP) Riser and Mooring Project to use the Riser High Mode VIV test data. The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.