A model of the Dutch Tri-floater semi-submersible platform equipped with the NREL 5MW wind turbine has been tested in the hydrodynamic and ocean engineering tank of École Centrale Nantes under wind and wave loads. This paper aims at comparing the results obtained with numerical simulations with these experimental results. The numerical model is based on the FAST design code from NREL and a user defined platform load model for calculating hydrodynamic and mooring loads. This hydrodynamic model includes non linear hydrostatic and Froude-Krylov forces, diffraction/radiation forces obtained from linear potential theory and Morison forces to take into account viscous effects on the braces and heave plates. First the hydrodynamic model is calibrated against the results of free decay tests without wind. A good agreement is achieved by calibrating mooring properties and heave plates properties of the numerical model. Then a comparison of regular wave cases without wind is realised, and a fair agreement is observed for surge, heave and pitch motions of the floating system. Finally comparisons are realised for regular wave cases with a constant wind speed. A good agreement is observed for the steady state surge and pitch offset. Surge and heave motions also shown a good agreement, these degrees of freedom are not being strongly influenced by wind loading. For pitch motion, numerical simulations show differences around 0.4 rad/s wave frequency, for which model tests have shown a significant influence of wind loading on system motion.
Roll-on/roll-off vessels appear to be sensitive to rapid capsizing due to an abrupt ingress of water caused by maritime accidents. As a result of the damage creation, the flooded ship can experience intermediate stages, which might be more devastating than the final condition, as the sudden loading could significantly alter the ship stability characteristics. Far from a probabilistic analysis, the paper under study presents the state-of-the-art in regards to flooding physics by treating some relevant important topics. It sheds light on the transient and progressive flooding stages, focuses on relevant factors, and suggests combinations between factors that strongly affect the flooding before the steady state is reached. Furthermore, the authors comment on some points, which remain difficult to take into consideration either numerically or experimentally, and propose, where found necessary, recommendations for a more reliable assessment of the flooding process. This review shows that the intermediate flooding phase depends upon many factors, and its assessment could be adequate in calm water condition. The effects and interdependency between these factors still require further investigation. Therefore, we recommend carrying out a wide range parametric investigation into these factors, which consider their interdependency and encourage the application of the design of experiments methodology.
Wall Shear Stress (WSS) has been demonstrated to be a biomarker of the development of atherosclerosis. In vivo assessment of WSS is still challenging, but 4D Flow MRI represents a promising tool to provide 3D velocity data from which WSS can be calculated. In this study, a system based on Laser Doppler Velocimetry (LDV) was developed to validate new improvements of 4D Flow MRI acquisitions and derived WSS computing. A hydraulic circuit was manufactured to allow both 4D Flow MRI and LDV velocity measurements. WSS profiles were calculated with one 2D and one 3D method. Results indicated an excellent agreement between MRI and LDV velocity data, and thus the set-up enabled the evaluation of the improved performances of 3D with respect to the 2D-WSS computation method. To provide a concrete example of the efficacy of this method, the influence of the spatial resolution of MRI data on derived 3D-WSS profiles was investigated. This investigation showed that, with acquisition times compatible with standard clinical conditions, a refined MRI resolution does not improve WSS assessment, if the impact of noise is unreduced. This study represents a reliable basis to validate with LDV WSS calculation methods based on 4D Flow MRI.
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