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Phase I of the OC6 project is focused on examining why offshore wind design tools underpredict the response (loads/motion) of the OC5-DeepCwind semisubmersible at its surge and pitch natural frequencies. Previous investigations showed that the underprediction was primarily related to nonlinear hydrodynamic loading, so two new validation campaigns were performed to separately examine the different hydrodynamic load components. In this paper, we validate a variety of tools against this new test data, focusing on the ability to accurately model the low-frequency loads on a semisubmersible floater when held fixed under wave excitation and when forced to oscillate in the surge direction. However, it is observed that models providing better load predictions in these two scenarios do not necessarily produce a more accurate motion response in a moored configuration.

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This paper deals with the problem of multi-objective fault-tolerant output tracking control for the longitudinal model of a flexible air-breathing hypersonic vehicle (FAHV). There exist some challenges for control design for the vehicles due to the inherent couplings between the propulsion system, the airframe dynamics, and the presence of strong flexibility effects. This paper addresses the problem of guaranteed cost fault-tolerant output tracking control with regional pole constraints against actuator faults for the FAHV system. A non-linear longitudinal model is adopted for control design because of the complexity of the FAHV systems. First, a linearized model is established around the trim point including the state of altitude, velocity, angle of attack, pitch angle, and pitch rate, etc. for a non-linear, dynamically coupled simulation model of a FAHV with the aim to address the multi-objective fault-tolerant output tracking control problem. Second, the control objective and models of actuator faults are presented. Third, by utilizing the Lyapunov functional approach, a multi-objective analysis condition is proposed in terms of convex optimization problems, that can be easily solved via standard numerical software. Then, a multi-objective fault-tolerant controller is designed such that the resulting closed-loop system is asymptotically stable and satisfies a prescribed performance cost with the simultaneous consideration of poles assignment in spite of possible actuator failure. Finally, the simulation results are given to show the effectiveness of the proposed method, which is verified by an excellent altitude reference and velocity tracking performance.

This article investigates the problem of guaranteed cost control for a flexible air-breathing hypersonic vehicle (FAHV). The FAHV includes intricate coupling between the engine and flight dynamics as well as complex interplay between flexible and rigid modes, which results in an intractable system for the control design. A longitudinal model is adopted for control design due to the complexity of the vehicle. First, for a highly nonlinear and coupled FAHV, a linearised model is established around the trim condition, which includes the state of altitude, velocity, angle of attack, pitch angle and pitch rate, etc. Secondly, by using the Lyapunov approach, performance analysis is carried out for the resulting closed-loop FAHV system, whose criterion with respect to guaranteed performance cost and poles assignment is expressed in the framework of linear matrix inequalities (LMIs). The established criterion exhibits a kind of decoupling between the Lyapunov positivedefinite matrices to be determined and the FAHV system matrices, which is enabled by the introduction of additional slack matrix variables. Thirdly, a convex optimisation problem with LMI constraints is formulated for designing an admissible controller, which guarantees a prescribed performance cost with the simultaneous consideration of poles assignment for the resulting closed-loop system. Finally, some simulation results are provided to show that the guaranteed cost controller could assign the poles into the desired regional and achieve excellent reference altitude and velocity tracking performance. Nomenclature

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