Abstract This paper provides a summary of the work done within the OC6 Phase II project, which was focused on the implementation and verification of an advanced soil–structure interaction model for offshore wind system design and analysis. The soil–structure interaction model comes from the REDWIN project and uses an elastoplastic, macroelement model with kinematic hardening, which captures the stiffness and damping characteristics of offshore wind foundations more accurately than more traditional and simplified soil–structure interaction modeling approaches. Participants in the OC6 project integrated this macroelement capability to coupled aero‐hydro‐servo‐elastic offshore wind turbine modeling tools and verified the implementation by comparing simulation results across the modeling tools for an example monopile design. The simulation results were also compared to more traditional soil–structure interaction modeling approaches like apparent fixity, coupled springs, and distributed springs models. The macroelement approach resulted in smaller overall loading in the system due to both shifts in the system frequencies and increased energy dissipation. No validation work was performed, but the macroelement approach has shown increased accuracy within the REDWIN project, resulting in decreased uncertainty in the design. For the monopile design investigated here, that implies a less conservative and thus more cost‐effective offshore wind design.

In order to tap the world wide offshore wind resources above deep waters, cost efficient floating platforms are inevitable. Tension-Leg Platforms (TLPs) could enable that crucial cost reduction in floating wind due to their smaller size and lighter weight compared to spars and semi-submersibles. The continuous development of the GICON®-TLP is driven by computer-aided engineering. So-called aero-hydro-servo-elastic coupled simulations are state-of-the-art for predicting loads and simulating the global system behavior for floating offshore wind turbines. Considering the complexity of such simulations, it is good scientific praxis to validate these numerical calculations by use of scaled model testing. This paper addresses the setup of the scaled model testing as carried out at the offshore basin of the École Centrale de Nantes, as well as the numerical model for the GICON®-TLP. The results of dedicated decay tests of the scaled model are used to validate the computational model at the first stage and to determine the natural frequencies of the system. Besides different challenges to the scaled model during the survey, it was possible to take these difficulties into account when updating the numerical model. The results show good agreements for the tank tests and the numerical model.

Floating substructures for wind turbines are commonly credited for enabling the offshore wind industry, so far focused on fixed substructures, to expand into deeper waters. As per Arent et al. (Improved offshore wind resource assessment in global climate stabilization scenarios, [4]), 77% of global offshore wind potential is located in water depths deeper than 60 m. However, floating substructures do not yet meet the market expectations with regard to LCOE. By integrating new materials as well as modularity into the design, the costs of the tension leg platform (TLP) development presented in this pater have been significantly reduced. Pre-stressed Ultra-High-Performance-Concrete (UHPC) pipes will be used for this sub-structure. The buoyancy bodies will be fabricated using concrete shell elements known from tunnel engineering. The use of casted iron for the nodes and the Transition Piece (TP) leads to further advantages regarding design and costs. All components are designed for transportability (e.g. via railway) in order to ensure a high level of flexibility within the supply chain. The structural design has been calculated to support turbines of up to 6 MW rated power and more. In October 2017, a scaled model (1:50) of the new substructure design for use with a 6 MW turbine was successfully exposed to wind and wave loads at the Ocean Engineering Tank of the École Centrale de Nantes (ECN). In June 2018, a second measurement campaign was started, and in September 2018 a third campaign will be run to verify the transport & installation process. Th presentation and paper will focus on the TLP design as well as on the model fabrication and scaling. Furthermore, measurement results from the ECN test will be presented. Therefore, the presentation will introduce the measurement setup as well as the measurement types to verify the simulation model. Finally, the verification of the simulation model with the measurements will be highlighted.

Quantifying the uncertainty in experimental results is a critical step in properly validating numerical simulation tools for designing floating wind turbines; without a good understanding of the experimental uncertainties, it is impossible to determine if numerical simulation tools can capture the physics with acceptable accuracy. Recent validation studies suggest that the wave-induced, low-frequency surge and pitch motions of semisubmersible-type floating wind turbines are consistently underpredicted by numerical simulations, but it has not been possible to state whether or not this underprediction is within the level of experimental error. In the present work, previously assessed systematic uncertainty components in hydrodynamic tests of the OC5-DeepCwind semisubmersible are propagated to response metrics of interest using numerical simulation tools, and combined with the system's random uncertainty to obtain the total experimental uncertainty. The uncertainty in the low-frequency response metrics is found to be most sensitive to the system properties (e.g., mooring stiffness and center of gravity), and also the wave elevation. The results of the present study suggest that the underprediction of the low-frequency response behavior observed in previous validation studies is larger than the experimental uncertainty.

Floating wind turbine systems will play an important role for a sustainable energy supply in the future. The dynamic behavior of such systems is governed by strong couplings of aerodynamic, structural mechanic and hydrodynamic effects. To examine these effects scaled tank tests are an inevitable part of the design process of floating wind turbine systems. Normally Froude scaling is used in tank tests. However, using Froude scaling also for the wind turbine rotor will lead to wrong aerodynamic loads compared to the full-scale turbine. Therefore the paper provides a detailed description of designing a modified scaled rotor blade mitigating this problem. Thereby a focus is set on preserving the tip speed ratio of the full scale turbine, keeping the thrust force behavior of the full scale rotor also in model scale and additionally maintaining the power coefficient between full scale and model scale. This is achieved by completely redesigning the original blade using a different airfoil. All steps of this redesign process are explained using the example of the generic DOWEC 6MW wind turbine. Calculations of aerodynamic coefficients are done with the software tools XFoil and AirfoilPrep and the resulting thrust and power coefficients are obtained by running several simulations with the software AeroDyn.

The objective of this paper is to assess the sources of experimental uncertainty in an offshore wind validation campaign focused on better understanding the nonlinear hydrodynamic response behavior of a floating semisubmersible. The test specimen and conditions were simplified compared to other floating wind test campaigns to reduce potential sources of uncertainties and better focus on the hydrodynamic load attributes. Repeat tests were used to understand the repeatability of the test conditions and to assess the level of random uncertainty in the measurements. Attention was also given to understanding bias in all components of the test. The end goal of this work is to set uncertainty bounds on the response metrics of interest, which will be used in future work to evaluate the success of modeling tools in accurately calculating hydrodynamic loads and the associated motion responses of the system.

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project, is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project analyzes the Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. This paper shows results of the verification of the OWT models (code-to-code comparison). A subsequent publication will focus on their validation (comparison of simulated results to measured physical system response data). Based on the available data, the participants of Phase III set up numerical models of the OWT in their simulation tools. It was necessary to verify and to tune these models. The verification and tuning were performed against an OWT model available at the University of Stuttgart – Stuttgart Wind Energy (SWE) and documentation provided by Senvion and OWEC Tower. A very good match was achieved between the results from the reference SWE model and models set up by OC5 Phase III participants. INTRODUCTION The Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project [1], which operates under the International Energy Agency (IEA) Wind Task 30 is the follow-up project of OC3 and OC4, which ran from 2005 to 2009 1 Copyright c © 2018 by ASME and from 2010 to 2014, respectively. The focus of OC3 and OC4 was to verify and benchmark simulation tools for offshore wind turbines (OWTs) with an emphasis on support structures through code-to-code comparison. This verification work led to dramatic improvements in model accuracy, which is a crucial achievement as the advancement of the offshore wind industry is closely tied to the development and accuracy of aero-servo-hydro-elastic OWT models [2, 3]. Participants of OC3 and OC4 expressed great interest in creating an extension to IEA Task 30 to focus on validating offshore wind modeling tools against experimental and/or in-situ data. The OC5 project is focused on validation of aero-hydroservo-elastic simulation tools for OWTs through comparison of simulated results to the response data of physical systems. OC5 is organized in three phases jointly coordinated by the National Renewable Energy Laboratory (NREL) from the USA and the Fraunhofer Institute for Wind Energy Systems IWES (IWES) from Germany. While the first two phases dealt with physical response data from tank tests [4, 5], Phase III aims to use openocean data for the validation work. Such data are obtained from alpha ventus—the first German offshore wind farm. Alpha ventus is located in the North Sea at the site of the average water depth of 28 m, around 45 km north of the Borkum island, as shown in Fig. 1.

This paper presents a model-based tracking control design for a mechanism dedicated to accurately reproduce the breathing-induced motion of a human lung tumour. A lung tumour mimic model should perform the same smooth motion as a real one in a human body during inhalation and exhalation. For this purpose, a 3-dimensional mechanism with three pneumatically driven axes has been developed and built up. The proposed control structure represents a cascaded flatness-based tracking control structure: In the fast inner loops, the chambers pressures of the pneumatic cylinders are controlled, whereas the outer loops are related to the position control of the cylinders. Furthermore, sliding mode observers are employed for each cylinder to estimate the corresponding states and a lumped disturbance force. The proposed overall control structure has been implemented and successfully validated on an innovative test rig.