Antoine Peiffer

Design, Analysis, and Evaluation of the UC-Berkeley Wave-Energy Extractor

This paper evaluates the technical feasibility and performance characteristics of an ocean-wave energy to electrical energy conversion device that is based on a moving linear generator. The UC-Berkeley design consists of a cylindrical floater, acting as a rotor, which drives a stator consisting of two banks of wound coils. The performance of such a device in waves depends on the hydrodynamics of the floater, the motion of which is strongly coupled to the electromagnetic properties of the generator. Mathematical models are developed to reveal the critical hurdles that can affect the efficiency of the design. A working physical unit is also constructed. The linear generator is first tested in a dry environment to quantify its performance. The complete physical floater and generator system is then tested in a wave tank with a computer-controlled wavemaker. Measurements are compared with theoretical predictions to allow an assessment of the viability of the design and future directions for improvements.

Modeling of an Oscillating Water Column on the Floating Foundation WindFloat

This paper summarizes the theory behind the modeling that was performed to incorporate an oscillating- water-column type Wave energy Converter (WEC) into the WindFloat hull. The WindFloat is a floating structure supporting a very large (>5MW) wind turbine. By adding a WEC to the structure, the overall economic cost of the project can be improved by sharing both mooring and power infrastructure. A numerical model was developed using the diffraction-radiation code WAMIT and assuming as PTO equipment, a generic wells turbine. It is important to model the turbine accurately, to understand the power capacity of the device. Details on the modeling of the system are discussed and numerical results and compared against experiments as a validation of the model. The effect of coupling between the floating foundation of the WindFloat and the OWC is investigated thoroughly.

Design of a Point Absorber Inside the WindFloat Structure

This paper summarizes the modeling and testing that was performed to integrate a point-absorber type Wave-Energy Converter (WEC) within the WindFloat hull. The WindFloat is a floating structure supporting a very large (>5MW) wind turbine. By adding a wave-energy device to the structure, one can improve the overall economic cost of the project, since both the mooring system and power infrastructure are shared. For the device analyzed here, the modeling is first described and then the Motion Response Amplitude Operators (RAOs) are computed. From these motion responses, the theoretical mechanical power available is calculated. The power values depend on empirical coefficients that need to be confirmed through model testing in the lab. The hydrodynamic forces on each device are often dependent on the interference between the device and the hull, the mooring, and the non-linear effects which are challenging to model. Therefore, these forces are approximated using a Morrison-type formulation in the numerical models. The empirical values for drag coefficients, damping coefficients, and stiffness coefficients in this report are validated against model tests, which are also described.Copyright

VIM Testing of a Paired Column Semi Submersible

This paper summarizes VIM towing test results of Houston Offshore Engineering’s Paired-Column Semisubmersible (PC Semi) platform that was performed at the UC Berkeley towing tank. The PC semi configuration is different from a conventional Deep Draft Semi (DD Semi) in three aspects, 1) 8 columns vs. 4 columns; 2) rectangle column vs. square column; 3) larger column slenderness ratio. Typically, a larger column slenderness ratio may result in more pronounced VIM. Since VIM significantly affects mooring and riser strength and fatigue, it is crucial to explore the VIM response characteristics of the PC Semi configuration.VIM has been characterized as a difficult subject with a complicated structural-hydrodynamic interaction. The physical mechanics is generally less well understood and numerical prediction is generally less reliable. Model testing has become an important and widely accepted design tool to derive reliable A/D envelops and drag coefficients.This project builds on the VIM testing experiences obtained in Finnigan and Roddier (2007), which showed that VIM testing at small scale is only slightly conservative. A scale factor of 1:160 was used in the present tests. The Reynolds Number for the tests varied from 15,000 to 30,000 depending on the towing speeds. This manuscript provides some details on the test setup and overall program, and highlights the key results of the tests.Copyright

WindFloat Contraption: From Conception to Reproduction

This paper will discuss the very serious topic of the design of the WindFloat, a full-scale floating wind turbine. The importance of the fundamentals of hydrodynamics in achieving the desired performance cannot be overstressed. These will be discussed in this paper, together with some of the key considerations that entered into the design process. At the time of writing of this manuscript, a full-scale WindFloat prototype has been spinning for a few months, and the electricity it generated powered all the Christmas lights of Povoa de Varzim, a small town in the north of Portugal — whose inhabitants are not seeing a reduction in their electricity bill.The authors have chosen to disassociate the presentation — a progress report — from this manuscript, which should discuss a topic more appropriate to the permanent literature.© 2012 ASME

Validation of Floating Behavior of a Robinson R66 Helicopter After a Water Landing

This paper summarizes the hydrodynamic work that was performed on the Robinson R66 helicopter’s water emergency landings as part of the roadmap to obtain FAA approval. The emergency system consists of two floats that are rapidly inflated as soon as the helicopter touches the water using gas from a high pressure cylinder. This type of design is common in the helicopter industry and is known as a “pop out” float system. The floats have already been shown to provide enough buoyancy to keep the helicopter afloat in calm water.Recognizing that once the helicopter is in the water, it is subjected to wave forces and behaves as a small water craft, a numerical study was performed using OrcaFlex. Over 500 numerical simulations, each lasting 10 minutes, of the helicopter floating in different wave environments were performed. The helicopter’s 6 degree-of-freedom (DOF) motions were monitored throughout. At the end of the run, if the helicopter had not capsized, the run would report: “no capsizing”. Sensitivity studies were performed by varying parameters individually. This led to an understanding of each parameter’s effects on the overall helicopter floating performance. These parameters included: wind, wave period, initial helicopter relative heading against the waves, wave height, and simulation seed (different random wave sets with the same spectral characteristics). The FAA expects floatation characteristics to be evaluated in “reasonably probable” water conditions and has issued guidance that World Meteorological Organization (WMO) sea state 4 is one acceptable definition of reasonably probable. A wind speed of up to 21 knots is also associated with sea state 4.Copyright

Estimation of Onsite Wave Parameters From the WindFloat Platform

The WindFloat is a semi-submersible floating foundation supporting multi-megawatt wind turbines. A full-scale 2MW WindFloat demonstration unit was installed off the coast of Portugal in October 2011. Many instruments are installed on this prototype to measure the environmental conditions and the response of the platform at the site. The first section of the paper focuses on the validation of the wave measurements obtained from two radar-based wave probes onboard the platform. The wave elevation at the site is reconstructed and typical wave statistics are computed. The results are compared and validated with independent buoy measurements close to site. The second section of the paper presents estimates of prevailing wave direction and directional wave spectra based on platform motions. These results are also benchmarked with onsite buoy measurements.Copyright

Analysis, Design, and Evaluation of the UC-Berkeley Wave-Energy Extractor

This paper evaluates the technical feasibility and performance characteristics of an ocean-wave energy to electrical energy conversion device that is based on a moving linear generator. The UC-Berkeley design consists of a cylindrical floater, acting as a rotor, which drives a stator consisting of two banks of wound coils. The performance of such a device in waves depends on the hydrodynamics of the floater, the motion of which is strongly coupled to the electromagnetic properties of the generator. Mathematical models are developed to reveal the critical hurdles that can affect the efficiency of the design. A working physical unit is also constructed. The linear generator is first tested in a dry environment to quantify its performance. The complete physical floater and generator system is then tested in a wave tank with a computer-controlled wavemaker. Measurements are compared with theoretical predictions to allow an assessment of the viability of the design and future directions for improvements.Copyright