Generating Power From Ocean Waves Using a Float With Excessive Buoyancy: Theory and Dynamic Model Results

2003 ◽  
Author(s):  
T. MacCready ◽  
T. Zambrano ◽  
B. D. Hibbs
Keyword(s):  
Numerical Model ◽  
Natural Frequency ◽  
Power Output ◽  
Ocean Surface ◽  
Ocean Waves ◽  
The Body ◽  
Energy Extraction ◽  
Ocean Energy ◽  
Wave Conditions ◽  
Rich Data

We are exploring a new approach to ocean energy extraction through a device that we refer to as the NAF (an acronym for Non-Archimedean Float). The NAF is a fully submerged body with excess buoyancy; i.e., the mass of the body is far less than the mass of the water it displaces. When such a float is tethered beneath the ocean surface the buoyancy yields a large force vector in the direction perpendicular to the isobaric surfaces that parallel the water/air interface. The constant shifting of the wave troughs provides the opportunity for energy extraction using turbines affixed to the float. We are exploring the NAF concept because its simplicity results in many inherent benefits. The device has few moving parts, gathers energy from waves coming in any direction, and exists as a non-obtrusive, completely submerged installation. A numerical model of the NAF has been created to determine the dynamic behavior and power output for various configurations and under various wave conditions. The numerical model is set up to calculate the various forces experienced by the NAF float, and from these it calculates the velocity and position of the float through time series steps. The model effectively demonstrates which variables are important and how power output relates to NAF dimensions. One early finding from the model result relates to tuning the natural frequency of the NAF to match the natural frequency of the waves. The NAF moves like an inverted pendulum, and its natural frequency is primarily dependent on the length of the pendulum. Regardless of the actual float buoyancy, the 6 to 12 second periods that typify average wave conditions dictate that the NAF tether should be between 30-m and 60-m long. Also, a scale version of this novel energy device consisting of a float tethered beneath the ocean surface was deployed off the coast of southern California. The deployment yielded rich data sequences that are sufficient for comparison with a dynamic numerical model.

Multi-Objective Optimal Design of a Passenger Car’s Body

2010 ◽  
Author(s):  
Amir Hosein Adl ◽  
Masoud Shariat Panahi
Keyword(s):  
Fatigue Life ◽  
Numerical Model ◽  
Natural Frequency ◽  
Optimization Algorithm ◽  
Optimization Problem ◽  
Early Stage ◽  
Computational Cost ◽  
The Body ◽  
Fe Model ◽  
Multi Objective

The body of a passenger car roughly constitutes 25–30% of its overall weight. Any reduction in the weight of the car’s body would not only mean less materials and fuel to be consumed, but also less exhaust emissions to be released and less non-biodegradable materials to be dumped or recycled. However, the automotive industry’s desire for an increasing weight reduction of passenger cars is inevitably limited by other design considerations such as mechanical strength, overall stiffness of the body, durability, safety and corrosion resistance. The problem of weight minimization can be expressed in the form of a constrained, multi-objective optimization problem in which the weight of the body and its fatigue life constitute the conflicting cost functions and values of such critical performance parameters as body’s natural frequency forms the constraint set. The above optimization problem poses a challenge to the designer, as the weight, fatigue life and natural frequency of the geometrically complex body cannot be readily evaluated and a comprehensive numerical model, such as a Finite-Elements (FE) one, has to be employed. This numerical model would nonetheless be highly time-consuming, especially considering the need for re-assessing the model dozens, and sometimes hundreds, of times per iteration of the optimization algorithm. To avoid this, we use a neural approximation of the FE model to reduce the time and computational cost. Results of a finite number of FE simulations are used to train the Multi-Layer Perceptron (MLP) neural network which will then be used as the evaluation engine of the optimization algorithm. An efficient computer code based on the improved Non-dominated Sorting Genetic Algorithms (NSGA II) is used to find the Pareto set of distinct solutions. The designer would then be able to choose from a set of non-dominated, feasible solutions based on economical and/or logistics requirements at an early stage of the design process.

Influence of the Guide Vanes Solidity on the Performance of a Radial Impulse Turbine With Pitch-Controlled Guide Vanes

2011 ◽  
Author(s):  
Bruno Pereiras ◽  
Manabu Takao ◽  
Fernando Garcia ◽  
Francisco Castro
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Essential Role ◽  
Experimental Tests ◽  
Energy Extraction ◽  
Ocean Energy ◽  
Impulse Turbine ◽  
Guide Vanes ◽  
Turbine Efficiency ◽  
Turbine Design

One of the most developed technologies in ocean energy is the OWC concept. In this kind of device there is a turbine which plays an essential role, it is one of the factors which determine the efficiency of the system because of its own efficiency and its coupling with the chamber. One of the main characteristics in a turbine for OWC purposes, especially impulse turbines, is to use Guide vanes to optimize the energy extraction. However, they also are the largest source of losses. Improving the Guide vanes performance could reduce the pressure drop and, thus, the efficiency increases and the damping becomes smaller. In this paper the solidity of the guide vanes is analyzed to determine the optimum one. The study has been conducted on a radial impulse turbine with pitch-controlled guide vanes to minimize the incidence losses and, therefore, analyze the effect of the solidity. Experimental tests were carried out to validate a numerical model created in FLUENT®. The numerical model has been used to analyze the same turbine design but with different solidities of the guide vanes. The results have been conclusive: there is an optimal solidity for the guide vanes, which maximize the turbine efficiency by means of improving the guide vanes performance. Moreover, it has been seen that the optimum solidity is different for the inner and outer guide vanes.

A Developed Numerical Method for Turbulent Unsteady Fluid Flow in Two-Phase Systems with Moving Interface

2017 ◽  
Vol 14 (06) ◽  
pp. 1750063 ◽  
Author(s):  
A. M. Hegab ◽  
S. A. Gutub ◽  
A. Balabel
Keyword(s):  
Numerical Model ◽  
Gas Phase ◽  
Level Set ◽  
The Body ◽  
Phase System ◽  
Computational Domain ◽  
Two Phase ◽  
Moving Interface ◽  
Level Set Function ◽  
Gas System

This paper presents the development of an accurate and robust numerical modeling of instability of an interface separating two-phase system, such as liquid–gas and/or solid–gas systems. The instability of the interface can be refereed to the buoyancy and capillary effects in liquid–gas system. The governing unsteady Navier–Stokes along with the stress balance and kinematic conditions at the interface are solved separately in each fluid using the finite-volume approach for the liquid–gas system and the Hamilton–Jacobi equation for the solid–gas phase. The developed numerical model represents the surface and the body forces as boundary value conditions on the interface. The adapted approaches enable accurate modeling of fluid flows driven by either body or surface forces. The moving interface is tracked and captured using the level set function that initially defined for both fluids in the computational domain. To asses the developed numerical model and its versatility, a selection of different unsteady test cases including oscillation of a capillary wave, sloshing in a rectangular tank, the broken-dam problem involving different density fluids, simulation of air/water flow, and finally the moving interface between the solid and gas phases of solid rocket propellant combustion were examined. The latter case model allowed for the complete coupling between the gas-phase physics, the condensed-phase physics, and the unsteady nonuniform regression of either liquid or the propellant solid surfaces. The propagation of the unsteady nonplanar regression surface is described, using the Essentially-Non-Oscillatory (ENO) scheme with the aid of the level set strategy. The computational results demonstrate a remarkable capability of the developed numerical model to predict the dynamical characteristics of the liquid–gas and solid–gas flows, which is of great importance in many civilian and military industrial and engineering applications.

scholarly journals POWER OUTPUT AND PROPULSIVE EFFICIENCY OF SWIMMING BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS)

1993 ◽  
Vol 185 (1) ◽  
pp. 179-193 ◽  
Author(s):  
F. E. Fish
Keyword(s):  
Power Output ◽  
Tursiops Truncatus ◽  
High Performance ◽  
Bottlenose Dolphins ◽  
The Body ◽  
Hydrodynamic Performance ◽  
Propulsive Efficiency ◽  
Velocity Amplitude ◽  
Swimming Depth ◽  
Maximum Angle

The power output and propulsive efficiency of swimming bottlenose dolphins (Tursiops truncatus) were determined from a hydromechanical model. The propulsive movements were filmed as dolphins swam in large pools. Dolphins swam at velocities of 1.2-6.0 m s-1. Propulsion was provided by dorsoventral oscillations of the posterior body and flukes. The maximum angle of attack of the flukes showed a linear decrease with velocity, whereas the frequency of the propulsive cycle increased linearly with increasing velocity. Amplitude was 20 % of body length and remained constant with velocity. Propulsive efficiency was 0.81. The thrust power computed was within physiological limits. After correction for effects due to swimming depth, the coefficient of drag was found to be 3.2 times higher than the theoretical minimum assuming turbulent boundary conditions. The motions of the body and flukes are primarily responsible for the increased drag. This analysis supports other studies that indicate that bottlenose dolphins, although well adapted for efficient high- performance swimming, show no unusual hydrodynamic performance.

Simulation of Hurricane Seas in a Multidirectional Wave Basin

1991 ◽  
Vol 113 (3) ◽  
pp. 219-227 ◽  
Author(s):  
A. Cornett ◽  
M. D. Miles
Keyword(s):  
Ocean Waves ◽  
Entropy Method ◽  
Wave Spectra ◽  
Single Wave ◽  
Wave Condition ◽  
Wave Basin ◽  
Wide Range ◽  
Directional Wave ◽  
Wave Conditions ◽  
Multidirectional Wave

This paper describes the generation and verification of four realistic sea states in a multidirectional wave basin, each representing a different storm wave condition in the Gulf of Mexico. In all cases, the degree of wave spreading and the mean direction of wave propagation are strongly dependent on frequency. Two of these sea states represent generic design wave conditions typical of hurricanes and winter storms and are defined by JONSWAP wave spectra and parametric spreading functions. Two additional sea states, representing the specific wave activity during hurricanes Betsy and Carmen, are defined by tabulated hindcast estimates of the directional wave energy spectrum. The Maximum Entropy Method (MEM) of directional wave analysis paired with a single-wave probe/ bi-directional current meter sensor is found to be the most satisfactory method to measure multidirectional seas in a wave basin over a wide range of wave conditions. The accuracy of the wave generation and analysis process is verified using residual directional spectra and numerically synthesized signals to supplement those measured in the basin. Reasons for discrepancy between the measured and target directional wave spectra are explored. By attempting to reproduce such challenging sea states, much has been learned about the limitations of simulating real ocean waves in a multidirectional wave basin, and about techniques which can be used to minimize the associated distortions to the directional spectrum.

Climbing Performance of Harris' Hawks (Parabuteo Unicinctus) with Added Load: Implications for Muscle Mechanics and for Radiotracking

1989 ◽  
Vol 142 (1) ◽  
pp. 17-29 ◽  
Author(s):  
C. J. PENNYCUICK ◽  
M. R. FULLER ◽  
LYNNE McALLISTER
Keyword(s):  
Body Mass ◽  
Power Output ◽  
Muscle Power ◽  
Muscle Mechanics ◽  
The Body ◽  
Power Product ◽  
Horizontal Flight ◽  
Flight Muscles ◽  
Food Load ◽  
Parabuteo Unicinctus

Two Harris' hawks were trained to fly along horizontal and climbing flight paths, while carrying loads of various masses, to provide data for estimating available muscle power during short flights. The body mass of both hawks was about 920 g, and they were able to carry loads up to 630 g in horizontal flight. The rate of climb decreased with increasing all-up mass, as also did the climbing power (product of weight and rate of climb). Various assumptions about the aerodynamic power in low-speed climbs led to estimates of the maximum power output of the flight muscles ranging from 41 to 46 W. This, in turn, would imply a stress during shortening of around 210 kPa. The effects of a radio package on a bird that is raising young should be considered in relation to the food load that the forager can normally carry, rather than in relation to its body mass.

Scalable Coupled Ocean and Water Turbine Modeling for Assessing Ocean Energy Extraction

2018 ◽  
Author(s):  
Stefano Deluca ◽  
Stefania Zanforlin ◽  
Benedetto Rocchio ◽  
Patrick J. Haley ◽  
Corbin Foucart ◽  
...  
Keyword(s):  
Energy Extraction ◽  
Ocean Energy ◽  
Water Turbine

scholarly journals Performance assessment of a small-size ocean wave energy harvester

2019 ◽  
Vol 283 ◽  
pp. 05006
Author(s):  
Yongjie Sang ◽  
Bertrand Dubus
Keyword(s):  
Electrical Power ◽  
Vertical Motion ◽  
Electrical Energy ◽  
Ocean Waves ◽  
Electrical Circuit ◽  
Optimal Choice ◽  
Ocean Wave ◽  
Unit Weight ◽  
Ocean Energy ◽  
Ocean Wave Energy

A lightweight electromechanical device is studied to harvest energy of ocean waves and supply electrical power to small-size ocean observation equipment such as sonobuoys. It is composed of a magnet fixed to the floating housing which follows the motion of the ocean surface and a moving coil connected to the case via a flexible spring. As the floating housing follows the vertical motion of water surface, a voltage is induced in the coil due to relative velocity between the coil and the magnet, and kinetic energy of the ocean wave is converted into electrical energy. Full bridge rectifying circuit and smoothing capacitor are used to convert AC voltage to constant voltage. Single degree of freedom electromechanical model of the prototype transducer (LGT-4.5 geophone) is developed and simulated with an electrical circuit software to predict energy harvesting performance. Vibration experiments are also performed with a shaker to validate transducer model and quantify output voltage. Parametric analysis is conducted to identify optimal choice of capacitance in terms of maximum stored energy and minimum charging time. This device is simple and small size relative to ocean wavelength compared to classical linear permanent magnetic generator used in offshore power plant. Its power generation per unit weight is compared to larger scale ocean energy converters.

scholarly journals Wave interaction with Floating platform of different shapes and supports using BEM approach

2017 ◽  
Vol 14 (2) ◽  
pp. 115-133
Author(s):  
Anoop I. Shirkol ◽  
Nasar Thuvanismail
Keyword(s):  
Numerical Model ◽  
Elastic Plate ◽  
Wave Interaction ◽  
Wave Force ◽  
Ocean Waves ◽  
Wave Forces ◽  
Thin Elastic Plate ◽  
Floating Platform ◽  
Floating Elastic Plate ◽  
Different Shapes

Wave interaction with a floating thin elastic plate which can be used as floating platform is analyzed using Boundary Element Method (BEM) for different shapes such as rectangular, circular and triangular. Different support conditions are considered and the performance of the floating platform under the action of ocean waves is explored. The study is performed under the assumption of linearized water wave theory and the floating elastic plate is modelled based on the Euler-Bernoulli beam theory. Using Galerkin’s approach, a numerical model has been developed and the hydrodynamic loading on the floating elastic plate of shallow draft (thickness) is investigated. The wave forces are generated by the numerical model for the analysis of the floating plate. The resulting bending moment and optimal deflection due to encountering wave force is analysed. The present study will be helpful in design and analysis of the large floating platform in ocean waves.

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