This work presents the results of a benchmark study on aero-servo-hydro-elastic codes for offshore wind turbine dynamic simulation. The codes verified herein account for the coupled dynamic systems including the wind inflow, aerodynamics, elasticity and controls of the turbine, along with the incident waves, sea current, hydrodynamics and foundation dynamics of the support structure. A large set of time series simulation results such as turbine operational characteristics, external conditions, and load and displacement outputs was compared and interpreted. Load cases were defined and run with increasing complexity to trace back differences in simulation results to the underlying error sources. This led to a deeper understanding of the underlying physical systems. In four subsequent phases-dealing with a 5-MW turbine on a monopile with a fixed foundation, a monopile with a flexible foundation, a tripod and a floating spar buoy-the latest support structure developments in the offshore wind energy industry are covered, and an adaptation of the codes to those developments was initiated. The comparisons, in general, agreed quite well. Differences existed among the predictions were traced back to differences in the model fidelity, aerodynamic implementation, hydrodynamic load discretization and numerical difficulties within the codes. The comparisons resulted in a more thorough understanding of the modeling techniques and better knowledge of when various approximations are not valid. More importantly, the lessons learned from this exercise have been used to further develop and improve the codes of the participants and increase the confidence in the codes' accuracy and the correctness of the results, hence improving the standard of offshore wind turbine modeling and simulation. One purpose of this paper is to summarize the lessons learned and present results that code developers can compare to. The set of benchmark load cases defined and simulated during the course of this project-the raw data for this paper-is available to the offshore wind turbine simulation community and is already being used for testing newly developed software tools. Despite that no measurements are included, the large number of participants and the-in general-very fine level of agreement indicate high trustworthy results within the physical assumptions of the codes and the simulation cases chosen. Other cases, such as large prebend flexible blades, large wind shear, large yaw error or transient maneuvers, may not show the same level of agreement. These cases were deliberately left out because the focus is on the specific offshore application. Further on, this benchmark study includes participating codes and organizations by name (contrary to several previous benchmark studies) that gives the reader a chance to find results from one particular code of interest

At Fraunhofer IWES a Modelica Library including all major components needed for load calculations of current offshore wind turbines is developed. The library additionally includes models for external conditions, like wind, soil and waves, and their respective influence on the structures. The library constitutes a large effort in the creation of a highly coupled multiphysics model with Modelica for an industrial project. The results obtained with this library are compared to the results from the IEA Wind Task 23 project OC3 1 (Offshore code comparison collaboration). The OC3 project is an international effort to define a set of loadcases and a reference wind turbine that are used to verify simulation systems on a code-to-code basis. In this paper the status and the implemented theories of the individual models at IWES are explained and verification results are presented and discussed.

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This paper summarizes the statistics of observations of wind and surface gravity waves in Long Island Sound, a large estuarine embayment in southern New England. We examine the relationship between significant wave height and wind speed and direction and show that the significant wave height and dominant period in western Long Island Sound have an asymmetric response to the wind direction. Waves are larger and have longer periods when the wind is from the east than when the same stress is directed from the west. The data are consistent with the predictions of empirical parameterizations of fetch limited wave growth when the wind is from the west. However, for easterly winds, the westward narrowing of the Sound limits wave growth and requires that an effective fetch of approximately 30 km be used in the empirical formulae. An examination of the extreme values in the time series shows that previous estimates based on simulations significantly underestimates the occurrence of large waves with the important consequence that design guidance for shore protection structures may underestimate wave heights during severe storms. We speculate that earlier work has not adequately represented the consequences of fetch asymmetry on wave growth. Plain Language Summary Measurements of wind and waves from a long-term deployment of a buoy show that wave height and period in the western end of Long Island Sound vary with season, and we describe how the wind speed and direction influence them. The shape and size of the Sound limits how big waves can be. We demonstrate that the significant wave height in the western Sound is larger when the wind is from the east, along the long axis of the basin, and smaller when from the west. To guide shore protection project designers, we also examine how often we should expect very large waves and show that previous analyses underestimate the probability of big waves. SHIN ET AL.

Low level helicopter operations in Degraded Visual Environment (DVE) still are a major challenge and bear the risk of potentially fatal accidents. DVE generally encompasses all degradations to the visual perception of the pilot ranging from night conditions via rain and snowfall to fog and maybe even blinding sunlight or unstructured outside scenery. Each of these conditions reduce the pilots' ability to perceive visual cues in the outside world reducing his performance and finally increasing risk of mission failure and accidents, like for example Controlled Flight Into Terrain (CFIT). The basis for the presented solution is a fusion of processed and classified high resolution ladar data with database information having a potential to also include other sensor data like forward looking or 360° radar data. This paper reports on a pilot assistance system aiming at giving back the essential visual cues to the pilot by means of displaying 3D conformal cues and symbols in a head-tracked Helmet Mounted Display (HMD) and a combination with synthetic view on a head-down Multi-Function Display (MFD). Each flight phase and each flight envelope requires different symbology sets and different possibilities for the pilots to select specific support functions. Several functionalities have been implemented and tested in a simulator as well as in flight. The symbology ranges from obstacle warning symbology via terrain enhancements through grids or ridge lines to different waypoint symbols supporting navigation. While some adaptations can be automated it emerged as essential that symbology characteristics and completeness can be selected by the pilot to match the relevant flight envelope and outside visual conditions.