No abstract

Resource assessment as well as characterisation of site climatologies for the design of Marine Energy Converters requires data bases allowing an accurate description of the environmental forcing, especially waves and sea-states, on a high resolution grid. As a support to its research activities related to the development of marine renewable energies, Ifremer is building a specific hindcast data set for the assessment of sea-states climatologies. The main features of this database, built running an up-to-date configuration of the WaveWatch III ® wave model on an unstructured grid extending from the South of the North Sea to the Bay of Biscay are presented here. Attention is given to the parameterization and forcing as well as the specific output data sets and validation processes.

A topical collection on "Advances in Search and Rescue at Sea" has appeared in recent issues of Ocean Dynamics following the latest in a series of workshops on "Technologies for Search and Rescue and other Emergency Marine Operations" (2004, 2006, 2008 and 2011), hosted by IFREMER in Brest, France.Here we give a brief overview of the history of search and rescue at sea before we summarize the main results of the papers that have appeared in the topical collection.

Velocity measurements collected by an upward-looking acoustic Doppler current profiler were used to provide the first study of ambient turbulence in Alderney Race. Turbulence metrics were estimated at middepth during peak flooding and ebbing tidal conditions. The dissipation rate ε and the integral lengthscale (L) were estimated using two independent methods: the spectral method and the structure function method. The spectral method provided ε and (L) estimates with standard deviations twice lower than that obtained from the structure function method. Removal of wave and Doppler noise-induced bias when estimating the dissipation rate was shown to be a crucial step in turbulence characterization. It allowed for a significant refining in (L) estimates derived from the spectral and structure function methods of 35 and 20 respectively. The integral lengthscale was found to be 2-3 times the local water depth. It is considered that these findings could be valuable for current turbine designers, helping them optimizing their designs as well as improving loading prediction through the lifetime of the machines. Highlights ► The first study of ambient turbulence in Alderney Race is provided. ► Two independent methods are used to quantify turbulence metrics. ► Removal of wave and Doppler noise-induced bias is a crucial step. ► The integral lengthscale was found to be 2-3 times the local water depth. ► Unique dataset of turbulence metrics computed at mid-depth are provided.

The leeway of 20-ft containers in typical distress conditions is established through field experiments in a Norwegian fjord and in open-ocean conditions off the coast of France with a wind speed ranging from calm to 14 ms −1 . The experimental setup is described in detail, and certain recommendations were given for experiments on objects of this size. The results are compared with the leeway of a scaled-down container before the full set of measured leeway characteristics are compared with a semianalytical model of immersed containers. Our results are broadly consistent with the semianalytical model, but the model is found to be sensitive to choice of drag coefficient and makes no estimate of the crosswind leeway of containers. We extend the results from the semianalytical immersion model by extrapolating the observed leeway divergence and estimates of the experimental uncertainty to various realistic immersion levels. The sensitivity of these leeway estimates at different immersion levels are tested using a stochastic trajectory model. Search areas are found to be sensitive to the exact immersion levels, the choice of drag coefficient, and somewhat less sensitive to the inclusion of leeway divergence. We further compare the search areas, thus, found with a range of trajectories estimated using the semianalytical model with only perturbations to the immersion level. We find that the search areas calculated without estimates of crosswind leeway and its uncertainty will grossly underestimate the rate of expansion of the search areas. We recommend that stochastic trajectory models of container drift should account for these uncertainties by generating search areas for different immersion levels and with the uncertainties in crosswind and downwind leeway reported from our field experiments.