The sinking of the El Faro: predicting real world rogue waves during Hurricane Joaquin

We present a study on the prediction of rogue waves during the 1-hour sea state of Hurricane Joaquin when the Merchant Vessel El Faro sank east of the Bahamas on October 1, 2015. High-resolution hindcast of hurricane-generated sea states and wave simulations are combined with novel probabilistic models to quantify the likelihood of rogue wave conditions. The data suggests that the El Faro vessel was drifting at an average speed of approximately~$2.5$~m/s prior to its sinking. As a result, we estimated that the probability that El Faro encounters a rogue wave whose crest height exceeds 14 meters while drifting over a time interval of 10~(50) minutes is $\sim1/400$~$(1/130)$. The largest simulated rogue wave has similar generating mechanism and characteristics of the Andrea, Draupner and Killard rogue waves as the constructive interference of elementary waves enhanced by bound nonlinearities

Comparison of nonlinear wave-loading models on rigid cylinders in regular waves

© 2019 by the authors. Monopiles able to support very large offshore wind turbines are slender structures susceptible to nonlinear resonant phenomena. With the aim to better understand and model the wave-loading on these structures in very steep waves where ringing occurs and the numerical wave-loading models tend to lose validity, this study investigates the distinct influences of nonlinearities in the wave kinematics and in the hydrodynamic loading models. Six wave kinematics from linear to fully nonlinear are modelled in combination with four hydrodynamic loading models from three theories, assessing the effects of both types of nonlinearities and the wave conditions where each type has stronger influence. The main findings include that the nonlinearities in the wave kinematics have stronger influence in the intermediate water depth, while the choice of the hydrodynamic loading model has larger influence in deep water. Moreover, finite-depth FNV theory captures the loading in the widest range of wave and cylinder conditions. The areas of worst prediction by the numerical models were found to be the largest steepness and wave numbers for second harmonic, as well as the vicinity of the wave-breaking limit, especially for the third harmonic. The main cause is the non-monotonic growth of the experimental loading with increasing steepness due to flow separation, which leads to increasing numerical overpredictions since the numerical wave-loading models increase monotonically

comparison of hydrodynamic loading models for vertical cylinders in nonlinear waves

Abstract This paper introduces a comparison study between various hydrodynamic loading models in highly nonlinear waves and discusses its first phase - comparing Morison equation and Rainey corrections on a fixed cylinder in regular steep waves. In this study both of these two models showed similar results when compared against experimental data. Morison equation is found to capture the amplitude of the loading sufficiently well. However, neither model was able to capture higher-order loading components which are apparent in very steep waves and are associated with ringing. The main conclusion of this work is the identification of the need of a more appropriate loading model

Development of a 3D Domain-Decomposition strategy for violent head-sea wave-vessel interactions: Challenges

This research activity represents an additional step toward a three-dimensional Domain-Decomposition strategy for violent wave-ship interaction involving water-on-deck and slamming phenomena. The focus is on FPSO ships and on head-sea waves and vessel without forward speed. The compound solver under development aims to couple a global 3D linear seakeeping solver with an inner 3D single-phase (water) Navier-Stokes (NS) method in a region containing the forward portion of the vessel. The NS solver is characterized by a Projection method with a finite-difference scheme on an Eulerian grid. The Level-Set (LS) technique is applied to step in time the free surface and combined with point markers to enforce adequately the body-boundary condition within a hybrid Eulerian-Lagrangian approach. This requires a much finer discretization than the computational grid around the body to preserve its geometrical details in time. As time goes on, the markers move in a Lagrangian fashion and then the LS function is estimated on the Eulerian grid by interpolation from the markers locations. Previous efforts have been documented for instance in Greco et al. (2009)) and Colicchio et al. (2010). Here some of the challenges and the possible solutions for the development of the inner 3D NS solver are discussed. The stress is on the boundary conditions

Assessment study of a domain-decomposition strategy for marine applications

Greco et al. (2011) tried to identify the proper numerical choices for the development of a three-dimensional Domain- Decomposition (DD) strategy. It aims to study the violent interaction of FPSO ships with head-sea regular waves. The present work represents a contribution in this direction

The relevance of recoil and free swimming in aquatic locomotion

The study of the free swimming of undulating bodies in an otherwise quiescent fluid has always encountered serious difficulties for several reasons. When considering the full system, given by the body and the unbounded surrounding fluid, the absence of external forces leads to a subtle interaction problem dominated, at least at steady state conditions, by the equilibrium of strictly related internal forces, e.g. thrust and drag, under the forcing of a prescribed deformation. A major complication has been dictated by the recoil motion induced by the non linear interactions, which may find a quite natural solution when considering as unknowns the velocity components of the body center of mass. A simplified two-dimensional model in terms of impulse equations has been used and a fruitful separation of the main contributions due to added mass and to vorticity release is easily obtained. As main results we obtain either the mean locomotion speed and the oscillating recoil velocity components which have a large effect on the overall performance of free swimming. Several constrained gaits are considered to highlight the relevance of recoil for realizing graceful and efficient trajectories and to analyze its potential means for active control

Experimental and Numerical Investigation of 2D Sloshing with Slamming

Partially filled tanks can experience sloshing in several practical circumstances. This is a resonance phenomenon where the free-surface can highly deform. The liquid will move back and forth rising along the side walls, possibly impacting against the roof. Impact on a side tank wall may also occur,e. g. in shallow water conditions. Resulting slamming loads are of main concern. A synergic experimental-numerical investigation of the sloshing flows is currently performed. Here the main focus is on the occurrence of slamming events and on the prediction of the related loads. Numerically, our approach is based on the SPH method. This method is able to follow the whole flow evolution in the tank and handle the many relevant and complicated phenomena generally involved. Among those we can list: water run-up and run-down along the side walls, roof impacts, freesurface overturning and breaking onto the underlying water, air cushioning. Often these features characterize the flow for intermediate and shallow water depths which can establish in real tanks and are of interest in the present research activity

Sloshing in a rotating liquid inside a closed sea cage for fish farming

Sloshing in a sea cage with a slowly rotating liquid is investigated. The cage is axisymmetric, and the liquid is subjected to a nearly uniform angular velocity about the vertical axis of the cage. Both experimental and theoretical investigations are presented. It is shown that rotation modifies the sloshing regimes of a non-rotating liquid by splitting the natural frequencies. Therefore, resonant sloshing regimes can be manipulated by varying the rotation rate of the liquid.acceptedVersio

Bathymetry Determination via X-Band Radar Data: A New Strategy and Numerical Results

This work deals with the question of sea state monitoring using marine X-band radar images and focuses its attention on the problem of sea depth estimation. We present and discuss a technique to estimate bathymetry by exploiting the dispersion relation for surface gravity waves. This estimation technique is based on the correlation between the measured and the theoretical sea wave spectra and a simple analysis of the approach is performed through test cases with synthetic data. More in detail, the reliability of the estimate technique is verified through simulated data sets that are concerned with different values of bathymetry and surface currents for two types of sea spectrum: JONSWAP and Pierson-Moskowitz. The results show how the estimated bathymetry is fairly accurate for low depth values, while the estimate is less accurate as the bathymetry increases, due to a less significant role of the bathymetry on the sea surface waves as the water depth increases