Validation of uncertainty quantification methods for high-fidelity CFD of ship response in irregular waves

Simulation based design methodologies are replacing the costly and time-consuming build-and-test paradigm for the design of naval vehicles. On the one hand, accurate high-fidelity simulations are required to guarantee the accuracy of the solution and ensure adequate design decisions. On the other hand, high-quality experiments are needed to validate high-fidelity simulations, ensuring the reliability of the computational tools. In real-world applications, all the relevant parameters are affected by uncertainty and its assessment is necessary to provide the required confidence intervals of all relevant variables used for validation. Here a high-fidelity uncertainty quantification (UQ) of a high-speed catamaran is presented, with focus on (a) the validation methods for ship response in irregular waves and (b) the validation of a stochastic regular wave UQ method. The approach includes a priori CFD simulations by URANS, followed by the ex post facto EFD campaign. The validation variables are the wave elevation, x-force, heave and pitch motions, vertical acceleration of the bridge and vertical velocity of the flight deck. Time series value is addressed as primary variable, whereas the mean-crossing wave height is indicated as secondary variable. Bootstrap methods are applied to estimate validation values and 95% confidence intervals for expected value (EV), standard deviation (SD), mode, and quantiles. Additionally, validation values and confidence intervals for time series EV and SD are evaluated by classical time series theory, based on the sample variance, size, and autocovariance function. The regular wave UQ method evaluates EV of force and SD of pitch, acceleration, and velocity, as relevant merit factors for design optimization. The present work extends the EFD and CFD studies presented in earlier work with the aim of achieving high-quality rigorous statistical validation. Both EFD and CFD data are provided with a larger run length and a larger number of encounter waves. New EFD data address the dynamic part of the force, which was one of the limitations of earlier work. The CFD simulations include a larger number of runs without significant self-repetition, which was also a limitation of earlier studies.