Anthony M. Viselli

Model Test of a 1:8-Scale Floating Wind Turbine Offshore in the Gulf of Maine

A new floating wind turbine platform design called VolturnUS developed by the University of Maine uses innovations in materials, construction, and deployment technologies such as a concrete semisubmersible hull and a composite tower to reduce the costs of offshore wind. These novel characteristics require research and development prior to full-scale construction. This paper presents a unique offshore model testing effort aimed at derisking full-scale commercial projects by providing scaled global motion data, allowing for testing of materials representative of the full-scale system, and demonstrating full-scale construction and deployment methods. A 1:8-scale model of a 6 MW semisubmersible floating wind turbine was deployed offshore Castine, ME, in June 2013. The model includes a fully operational commercial 20 kW wind turbine and was the first gridconnected offshore wind turbine in the U.S. The testing effort includes careful selection of the offshore test site, the commercial wind turbine that produces the correct aerodynamic thrust given the wind conditions at the test site, scaling methods, model design, and construction. A suitable test site was identified that produced scaled design load cases (DLCs) prescribed by the American Bureau of Shipping (ABS) Guide for Building and Classing Floating Offshore Wind Turbines. A turbine with a small rotor diameter was selected because it produces the correct thrust load given the wind conditions at the test site. Some representative data from the test are provided in this paper. Model test data are compared directly to full-scale design predictions made using coupled aeroelastic/ hydrodynamic software. Scaled VolturnUS performance data during DLCs show excellent agreement with full-scale predictive models. Model test data are also compared directly without scaling against a numerical representation of the 1:8-scale physical model for the purposes of numerical code validation. The numerical model results compare favorably with data collected from the physical model. [DOI: 10.1115/1.4030381]

Methodology for optimizing composite towers for use on floating wind turbines

A methodology for the design and optimization of a composite wind turbine tower for use on a floating offshore platform is presented. A composite turbine tower on a floating offshore platform not only has the potential to reduce maintenance and upkeep costs associated with the use of steel offshore but also has potential to reduce the tower mass and subsequently the support platform mass. The optimization problem is formulated to obtain a turbine tower that meets all strength and serviceability criteria and minimizes the tower mass. The optimization and design process link a number of dynamic analyses and finite element routines using a genetic algorithm. This work documents the optimization and design software and illustrates its use in various case studies for a 6 MW floating wind turbine system. Case studies include the optimization of a steel tower as a comparison to a composite material tower and the use of a cored, sandwich panel composite tower versus a solid composite tower. The results demonstrat...

VolturnUS 1:8: Conclusion of 18-Months of Operation of the First Grid-Connected Floating Wind Turbine Prototype in the Americas

This paper presents an overview of the successful conclusion of 18 months of testing the first grid-connected floating offshore wind turbine prototype in the Americas. The prototype, called VolturnUS 1:8, was installed off Castine, Maine, USA. The prototype is a 1:8 scale prototype and serves to de-risk the deployment of a full-scale 6MW turbine. VolturnUS utilizes innovations in materials, construction, and deployment technologies such as a concrete semi-submersible hull and an advanced composite tower to reduce the costs of offshore wind. The prototype unit was designed following the American Bureau of Shipping (ABS) “Guide for Building and Classing Floating Offshore Wind Turbine Installations”. Froude scaling was used in designing the 1:8-scale VolturnUS prototype so that the motions of the prototype in the relatively protected site represent those of the full-scale unit in an open site farther offshore. During the past year, a comprehensive instrumentation package monitored key performance characteristics of the platform during operational, extreme, and survival storm conditions. Data collected include: wind speed, turbine power, rotor angular frequency, blade pitch, torque, acceleration; tower bending moment, 6 DOF accelerations at tower top and base, mooring line tensions, and wave elevation at the platform. During the past year the prototype has experienced many environments representative of scaled ABS design conditions including operational wind and sea-states, 50-year sea states and 500-year survival sea states.This large data set provides a unique view of a near full-scale floating wind turbine subjected to its prescribed environmental conditions. Inspections of the concrete hull following removal provided confirmation of material durability. Marine growth measurements provide data for future design efforts.Copyright

Validation of Global Performance Numerical Design Tools Used for Design of Floating Offshore Wind Turbines

In an effort to harness the abundant offshore wind resource over deepwater, the development of numerical design tools for floating offshore wind turbines (FOWTs) has progressed steadily in recent years. However, at present, a validated model capable of completely coupling the full elastodynamic response between the mooring system, floating support structure, turbine tower and the wind turbine is not commercially available.The University of Maine has developed a new FOWT design, VolturnUS, which utilizes a concrete semi-submersible hull. For the VolturnUS design effort a number of numerical models were developed to analyze the system’s global performance. This paper presents the results of a validation study conducted to quantify the accuracy and suitability of a subset of these models for use in the design of the VolturnUS FOWT. Validation was conducted via comparisons of numerical model results to test data obtained from a 1:50 scale model testing campaign conducted by the University of Maine at the Maritime Research Institute, Netherlands offshore basin.The validation study evaluated the performance and capabilities of the numerical models over a range of design conditions. Emphasis was placed on design load cases (DLCs), which were found to govern the design of the FOWT. The DLCs follow the American Bureau of Shipping’s (ABS) Guide for Building and Classing Floating Offshore Wind Turbines.Through this method of model validation this work sought to quantify the numerical models’ accuracy, highlight their limitations, justify design assumptions, and identify areas requiring further development in the field of FOWT numerical modeling.Copyright

VolturnUS 1:8-Scale FRP Floating Wind Turbine Tower: Analysis, Design, Testing and Performance

In May of 2013 the VolturnUS 1:8 floating semi-submersible wind turbine was successfully deployed off the coast of Castine, Maine, making the unit the first grid connected offshore turbine in the United States. The VolturnUS 1:8 structure features a 20 kW turbine, a post-tensioned and reinforced concrete semi-submersible base and a fiber reinforced plastic (FRP) tower (E-glass and polyester resin). The VolturnUS 1:8 structure is a geometrically 1:8-scale of a 6 MW floating turbine design and is used to demonstrate the feasibility of both the concrete base and FRP tower and validate the performance of the structure in a scaled environment. Data collected from the deployed 1:8-scale structure will be used for modeling and simulating the behavior of the system at full-scale. The effort was led by the University of Maine’s Advanced Structures and Composites Center (UMaine) and a consortium of industry partners, including FRP manufacturer Ershigs, Inc.An overview of the process and methodology used in the analysis, design and testing of the 1:8 scale FRP floating wind turbine tower is presented. The use of an FRP tower on a floating wind turbine platform offers the benefits of reduced tower mass and maintenance requirements and has the potential to further reduce hull mass by lowering the global center of gravity of the structure. An FRP tower for use on the UMaine semi-submersible concrete VolturnUS 1:8 platform was developed that meets all strength and serviceability criteria and is robust enough to withstand the loading from both wind and waves. An overview of the tower loads analysis and FAST modeling, tower structural design, structural proof testing and preliminary analysis of performance are presented.The VolturnUS 1:8 wind turbine tower is the first time FRP materials have been used in an offshore wind tower application. Further, the methodologies and procedures that were developed in the design of the pilot-scale tower are directly applicable to the design and analysis of composite wind turbine towers at the full-scale level. These “lessons learned” are already in use as Ershigs and UMaine work to design a full-scale composite tower over 80 meters tall for use on the VolturnUS platform with a 6MW wind turbine. The results of the 1:8-scale program demonstrate the successful use of an FRP wind turbine tower on a floating platform and highlights the potential for the use of an FRP tower at the full-scale (6 MW) level.Copyright

Model Test of a 1:8 Scale Floating Wind Turbine Offshore in the Gulf of Maine

A new floating wind turbine platform design called VolturnUS developed by the University of Maine uses innovations in materials, construction, and deployment technologies such as a concrete semi-submersible hull and a composite tower to reduce the costs of offshore wind. These novel characteristics require research and development prior to full-scale construction. This paper presents a unique offshore model testing effort aimed at de-risking full-scale commercial projects by providing properly scaled global motion data, allowing for implementation of full-scale structural materials, and demonstrating full-scale construction and deployment methods. The model is a 1:8-scale model of a 6MW semi-submersible floating wind turbine and was deployed offshore Castine, Maine, USA in June, 2013. The model uses a fully operational turbine and was the first grid connected offshore wind turbine in the Americas.The testing effort includes careful treatment of the offshore test site, scaling methods, model design, and construction. A suitable test site was identified that provides the correct proportions of wind and wave loading in order to simulate design load cases prescribed by the American Bureau of Shipping Standard for Building and Classing Floating Offshore Wind Turbines.Sample model test data is provided. Model test data is directly compared to full-scale design predictions made using coupled aeroelastic/ hydrodynamic software. VolturnUS performance data from scaled extreme sea states show excellent agreement with predictive models. Model test data are also compared to a numerical representation of the physical model for the purposes of numerical code validation. The numerical model results compare very favorably with data collected from the physical model.Copyright