James H. VanZwieten

Numerical Simulation of an Experimental Ocean Current Turbine

The development of a numeric simulation for predicting ocean current turbine performance is presented in this paper along with performance predictions. This numeric model uses an unsteady blade element momentum (BEM) rotor model to calculate the rotor forces and seven degree-of-freedom (DOF) equations of motion to calculate the coupled effects between the rotor and the main body. For the results presented in this paper, this simulation is set to model a 20-kW experimental ocean current turbine, and performance predictions are made for environmental condition that it will likely operate when deployed in the Gulf Stream off Southeast Florida. This model predicts that this turbine will have a maximum rotor power coefficient of 0.45 and that the vertical current gradient will only minimally affect the system performance. This simulation is also used to quantify the cyclic loadings that will be induced for misalignments between the rotor axis and the incoming flow, and it predicts the system motions and the forces on the rotor when the system is operating in a wave field.

In-stream hydrokinetic power: Review and appraisal

AbstractThe objective of this paper is to provide a review of in-stream hydrokinetic power, which is defined as electric power generated by devices capturing the energy of naturally flowing water—stream, tidal, or open ocean flows—without impounding the water. North America has significant in-stream energy resources, and hydrokinetic electric power technologies to harness those resources have the potential to make a significant contribution to U.S. electricity needs by adding as much as 120  TWh/year from rivers alone to the present hydroelectric power generation capacity. Additionally, tidal and ocean current resources in the U.S. respectively contain 438  TWh/year and 163  TWh/year of extractable power. Among their attractive features, in-stream hydrokinetic operations do not contribute to greenhouse gas emissions or other air pollution and have less visual impact than wind turbines. Since these systems do no utilize dams the way traditional hydropower systems typically do, their impact on the environme...

Design and Analysis of a Rotor Blade Optimized for Extracting Energy From the Florida Current

The Florida Current flowing past Southeast Florida represents an untapped renewable energy resource with a mean kinetic energy flux near its core of 2.32 kW/m2 . The research presented in this paper details the hydrodynamic optimization of a three meter diameter, three-bladed rotor for an experimental research turbine. The proposed deployment site for this turbine is located 24 km off the coast of Southeast Florida in 300 m of water. At this location, thirteen months of continuous ocean current profile measurements have been collected. A genetic algorithm rotor optimization code was used to vary the geometry of the proposed rotor to maximize the average power output using the oceanographic measurements. The optimized rotor, operating in the observed flow field, is predicted to produce a mean shaft power of 7.153 kW when operating at 40 RPM. A sensitivity analysis shows that by increasing the RPM by 25% and 50%, the average power output can be increased by 3.56% and 4.99% respectively. Additionally, using a four-bladed rotor can increase the average power output by 4.22% when operating at 40 RPM.Copyright

Adaptive Disturbance Rejection for the Rapidly Deployable Stable Platform when Transferring Cargo in Seas

In this paper, we will consider an adaptive output feedback control law with direct adaptive disturbance rejection for the Rapidly Deployable Stable Platform (RDSP). The RDSP is a combined spar and catamaran where the spar lifts the catamaran completely out of the water when transferring cargo, creating a much more stable platform than traditional craneships. This vessel is under development for potential sea cargo transfer applications. The controller, developed to minimize the pitch of the platform when transferring cargo at sea, requires only pitch measurements in near real time. The results in this paper show that the adaptive control and disturbance rejection technique can effectively reduce roll in seas when cargo is being lifted or when waves are producing the primary external forces on the vessel.

Response characteristics and maneuverability of a small twin screw displacement hull vessel in seas

Abstract This paper presents the response characteristics and maneuverability of a small twin screw displacement hull vessel quantified through a series of full-scale trials conducted in different environmental conditions. The 20-m test vessel is instrumented with actuator, environmental, and motion sensors. Several different maneuvers are performed at different speeds, including steady maneuvers with constant control input and transient maneuvers with varied control input to quantify and characterize the response of small vessels to aid in automatic controller and simulation development. Straight-line runs are performed in both forward and reverse over the entire operating range of the test vessel to investigate the relationship between throttle position, RPM, and surge velocity. Turning maneuvers are conducted over the achievable rudder deflection range to quantify the vessels turning radius and the relationships with surge, sway, and rotational speed. Other maneuvers include stationary rotation with the engines operating in opposite gears, and transient tests when the vessel is rapidly accelerated and decelerated. These actuator tests not only quantify the response of the actuators, but also set guidelines for the minimum dwell times that should be observed when shifting gears. These data found using a comprehensive sensor suite provide valuable benchmarks for several maneuvers that can be used for simulation validation and the actuator response information provides valuable set points and performance characteristics/limitations that should be considered in control development. The data from these tests were repeatable from run to run and thus, with sufficient instruments, at sea maneuvers can be used to collect a comprehensive set of data that can expand on data collected in tow tests.

Mitigation of vortex-induced disturbances for the rapidly deployable stable platform

The rapidly deployable stable platform (RDSP) is a concept vessel that is being developed for missions, such as at-sea cargo transfer, that will benefit from a stable spar-like platform that can transit under its own power at medium speeds (∼5–10 m/s). The stability and transit qualities of the RDSP extend from its two distinct modes of operation. These operating modes are the horizontal transit mode (HTM), where the RDSP is configured like a trimaran and the vertical operating mode (VOM), where the RDSP is configured like a spar buoy. In VOM, the RDSP will use the thrusters that are located on its spar section to manoeuvre at slow speeds, mitigate disturbances and dynamically position itself. When the RDSP is moving through the water in VOM, vortices will oscillate off of its spar section and produce forces that are primarily perpendicular to the direction of oncoming flow. Mitigating these disturbances is the focus of this work and is done using an adaptive control algorithm. This algorithm includes a disturbance rejection component that is capable of compensating for any unknown disturbance and phase information, as well as a phase locked loop (PLL) that improves the disturbance frequency estimate on-line. Using this technique, the vortex-induced motions are reduced to 18% of their open loop values using control inputs that are obtainable for the proposed RDSP thrusting system.

Efficiency assessment of an experimental ocean current turbine generator

This document presents the experimentally determined power generation efficiency for the drive-train and motor of a 20 kW experimental ocean current turbine. This efficiency assessment was performed using a custom designed dynamometer and covered much of the generators expected operating range. These measurements are used with numerically modeled rotor performance to predict the overall efficiency of the ocean current turbine when converting kinetic energy flux to electric power.

Power Take-Off Control of In-Stream Hydrokinetic Turbines

In-stream hydrokinetic electricity production, electricity generation from moving currents without the use of dams, has significant potential for increasing electric power production. This project evaluates a control system designed to regulate rotor rate (rpm) to improve power production from in-stream hydrokinetic turbines. The control algorithm is evaluated using both a numerical model of a rigidly mounted tidal turbine and a numerical model of a moored ocean current turbine system. These two system models are each coupled to an induction electric machine model. Based on the turbine torque-speed characteristic, as well as the asynchronous machine features, a Look-Up-Table (LUT) is used to generate the frequency of the sinusoidal voltages of the three phases to be supplied to the machine. However, to compensate for disturbances and perturbations of the power-plant a PI controller is generating a correction term for electrical frequency superimposed to the output of the LUT. A first round of simulations using the numerical models was performed in order to evaluate the developed algorithms.Copyright

Global numeric analysis of a moored ocean current turbine testing platform

In response to Floridas growing energy needs and drive to develop renewable power, Florida Atlantic Universitys Center for Ocean Energy Technology (COET) plans to deploy a mooring near the core of the Gulf Stream off southeast Floridas coast. This mooring system testing platform will be used to evaluate the performance of prototype ocean current turbines including COETs 20 kW turbine that is currently under development. No mooring systems for deepwater hydrokinetic turbines have been constructed, tested and installed; therefore little is known about the performance of these moorings. To investigate this, a numeric model is used to predict the static and dynamic behavior of the mooring system and attachments, quantifying sensitivity of the systems response to parametric variations. This numeric model of COETs proposed mooring system has been created in OrcaFlex to model static and dynamic effects of the system. It includes numerical models of its two surface buoys, a rotating ocean current turbine, and the lines associated with the system. Wind, wave, and current profiles represent the environmental conditions the system is expected to experience.

Direct Adaptive Rejection of Vortex-Induced Disturbances for a Powered Spar Platform

The Rapidly Deployable Stable Platform (RDSP) is a novel vessel designed to be a reconfigurable, stable at-sea platform. It consists of a detachable catamaran and spar, performing missions with the spar extending vertically below the catamaran and hoisting it completely out of the water. Multiple thrusters located along the spar allow it to be actively controlled in this configuration. A controller is presented in this work that uses an adaptive feedback algorithm in conjunction with Direct Adaptive Disturbance Rejection (DADR) to mitigate persistent, vortex-induced disturbances. Given the frequency of a disturbance, the nominal DADR scheme adaptively compensates for its unknown amplitude and phase. This algorithm is extended to adapt to a disturbance frequency that is only coarsely known by including a Phase Locked Loop (PLL). The PLL improves the frequency estimate on-line, allowing the modified controller to reduce vortex-induced motions by more than 95% using achievable thrust inputs.© 2009 ASME