Assessment of CFD for KCS added resistance and for ONRT course keeping/speed loss in regular head and oblique waves

Abstract

CFD is assessed for added resistance for KCS (captive test cases 2.10 and 2.11) and course keeping/speed loss for ONRT (free running test cases 3.9/3.12/3.13) in head and oblique waves. The number of submissions were 10, 2, and 8 for test cases 2.10, 2.11, and 3.9/3.12/3.13, respectively. The assessment approach uses both solution and N-version validation. The former considers whether the absolute error |Ei| = |D- Si| is less, equal or greater than the validation uncertainty, which is the root sum square of the numerical and experimental uncertainties, i.e., |Ei|≤UVi=USNi2+UD2. The latter considers whether the absolute error is less, equal or greater than the state-of-the-art SoAi uncertainty, i.e., |Ei|≤USoAi=UVi2+P|Ei|2 where P|Ei|=kσ|E| is the uncertainty due to the scatter in the solution absolute error. Errors and uncertainties are normalized using both the data value D and its dynamic range DR. The captive resistance CT and free running self-propulsion propeller revolutions RPS | E| ？ < 2 % D with UD less than but comparable P|Ei|<3%D such that 3/1 solutions were validated but 8/4 codes/solutions were N-version validated for CT/RPS. The head waves captive and free running heave and pitch | E| ？ is less than 8%DR with UD less than 5%DR and P|Ei| less than 13%DR such that about 5 for captive and 2 for free running solutions were validated and about 7 for captive and 5 for free running codes/solutions were N-version validated. The errors for added resistance and speed loss were less than 13%DR with UD less than 7%DR and P|Ei|=25 and 13%DR such that about 4 for captive and 1 for free running solutions were validated and 7 for captive 4 for free running codes/solutions were N-version validated. For captive head waves, the errors and scatter are smaller than those for potential flow. The oblique waves captive and free running motion errors | E| ？ are less than 10%DR except for roll with UD large 23%DR for captive pitch and other wise small <2%DR. The errors for added resistance and speed loss were <8%DR with UD？<？9%DR. The largest errors were for roll, which had errors for captive of 12%DR and for free running of 20%DR. None of the KCS and ONRT test cases were able to achieve a programmatic requirement of 5%D and 5%DR for calm water and waves, respectively. Note that not all the experimental uncertainties are able to meet this requirement either such that both experiments and CFD need to reduce their uncertainties and in addition CFD its errors. Nonetheless, in view the comparable CFD capability for ONRT free running vs. KCS captive conditions, the prognosis for CFD capability is excellent. Future CFD assessment should extend the current test cases for consideration of added power in regular and irregular waves. Verification should be required, and more limited/most important validation variables should be confirmed and used for the V&V and SoA assessment. ？ The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021.