OC5 Project Phase II: Validation of Global Loads of the DeepCwind Floating Semisubmersible Wind Turbine

This paper summarizes the findings from Phase II of the Offshore Code Comparison, Collaboration, Continued, with Correlation project. The project is run under the International Energy Agency Wind Research Task 30, and is focused on validating the tools used for modeling offshore wind systems through the comparison of simulated responses of select system designs to physical test data. Validation activities such as these lead to improvement of offshore wind modeling tools, which will enable the development of more innovative and cost-effective offshore wind designs. For Phase II of the project, numerical models of the DeepCwind floating semisubmersible wind system were validated using measurement data from a 1/50th-scale validation campaign performed at the Maritime Research Institute Netherlands offshore wave basin. Validation of the models was performed by comparing the calculated ultimate and fatigue loads for eight different wave-only and combined wind/wave test cases against the measured data, after calibration was performed using free-decay, wind-only, and wave-only tests. The results show a decent estimation of both the ultimate and fatigue loads for the simulated results, but with a fairly consistent underestimation in the tower and upwind mooring line loads that can be attributed to an underestimation of waveexcitation forces outside the linear wave-excitation region, and the presence of broadband frequency excitation in the experimental measurements from wind. Participant results showed varied agreement with the experimental measurements based on the modeling approach used. Modeling attributes that enabled better agreement included: the use of a dynamic mooring model; wave stretching, or some other hydrodynamic modeling approach that excites frequencies outside the linear wave region; nonlinear wave kinematics models; and unsteady aerodynamics models. Also, it was observed that a Morison-only hydrodynamic modeling approach could create excessive pitch excitation and resulting tower loads in some frequency bands.This work was supported by the U.S. Department of Energy under Contract No. DEAC36- 08GO28308 with the National Renewable Energy Laboratory. Some of the funding for the work was provided by the DOE Office of Energy Efficiency and Renewable Energy, Wind and Water Power Technologies Office

Verification of a Numerical Model of the Offshore Wind Turbine From the Alpha Ventus Wind Farm Within OC5 Phase III

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

Loads Analysis of Several Offshore Floating Wind Turbine

ABSTRACT This work presents a comprehensive dynamic-response analysis of six offshore floating wind turbine concepts. Each of the six models contained the same 5-megawatt (MW) turbine. The platforms modeled included: a barge, a semisubmersible, two tension-leg platforms (TLP), and a spar buoy at two different depths. The performance of these models was compared to that of a base model with a turbine supported by a fixed land-based tower. Performance was evaluated via a comprehensive loads and stability analysis adhering to the procedures of the International Electrotechnical Commission (IEC) 61400-3 offshore wind turbine design standard. The loads in the turbine supported by the barge are the highest found for the floating concepts. The differences in the loads between the TLP, the semisubmersible, and the spar buoy are not significant, except for the loads in the tower, which are greater in the spar and semisubmersible systems. The results of this analysis will help resolve the fundamental design trade-offs between the floating-system concepts

2013, “Implementation of a Multisegmented, Quasi-Static Cable Model

ABSTRACT The Mooring Analysis Program (MAP) is a library designed to be used in parallel with other computer-aided engineering (CAE) tools to model the static and dynamic forces of mooring systems. In this paper, the implementation of a multisegmented, quasi-static (MSQS) mooring model in MAP is investigated. The MSQS model was developed based on an extension of conventional single-line static solutions. Conceptually, the MSQS program simultaneously solves the algebraic equations for all elements with the condition that the total force at connection points sum to zero. Seabed contact, seabed friction, and externally applied forces can be modeled with this tool, and it allows multielement mooring systems with arbitrary connection configurations to be analyzed. This paper provides an introduction to MAP's MSQS model, its underlying theory, and a demonstration of its abilities

Importance of Second-Order Difference-Frequency Wave-Diffraction Forces in the Validation of a FAST Semi-Submersible Floating Wind Turbine Model

To better access the abundant offshore wind resource, efforts are being made across the world to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools. The National Renewable Energy Laboratory (NREL) has created FAST, a comprehensive, coupled analysis CAE tool for floating wind turbines, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are underway to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. The research employs the 1/50th-scale DeepCwind wind/wave basin model test dataset, which wa