Extraction Of Kinetic Energy Research Articles

Field-testing of model helical-bladed hydrokinetic turbines for small-scale power generation

Abstract The vertical-axis helical-bladed hydrokinetic turbine serves as a viable source of renewable power that can extract kinetic energy of the free flowing water to generate electricity. Such helical-bladed turbines are characterized by lesser pulsation of torque and marginally favorable starting capability as compared to straight-bladed turbines. The present study aims at evaluating the performance of NACA 0020 bladed helical turbines of different solidity ratios. In-situ experiments of the developed turbines have been carried out in an open channel where the turbine with solidity ratio (σ) of 0.38 achieves a maximum power coefficient of 0.20 at a tip-speed ratio (TSR) of 1.02 and an inlet water velocity of 0.87 m/s. The effect of σ on the performance of different turbines is investigated at various immersion levels. For all the tested turbines, it has been observed that with the decrease of immersion levels, the power coefficient values decrease along with the optimum TSRs and this change is found to be predominant for the turbine having lowest σ = 0.31. Higher starting ability has been noticed for the helical-bladed turbine with σ = 0.38 in comparison to lower solidity ratio variants.

Insights on the Provision of Frequency Support by Wind Power and the Impact on Energy Systems

This paper implements and compares between the key concepts to enable wind power short-term frequency support from electrical and mechanical loads perspectives. Pitch de-loading, kinetic energy extraction, and wind turbine (WTG) over-speeding are investigated, where each concept is integrated as a supplementary controller to the conventional controls of WTG. Different patterns of wind speed are examined, step-change and real intermittent of high resolution. The examined aggregated synchronous area has a relatively high wind penetration with frequency support. The overall dynamic inertia of the system is assessed to analyze the impact of the integrated support methods and their key parameters. The coordination between synchronous areas and wind farms, which are interconnected through a multiterminal high-voltage direct-current network (MT-HVDC) is examined. A novel definition of the virtual inertia of MT-HVDC grid is proposed. Results show that pitch de-loading secures support reserve most of the time, and kinetic energy extraction provides sustainable support for a short interval, while accelerative de-loading could reach a compromise. The three methods are adaptable with the MT-HVDC holistic frequency support controller, with a slight advantage of kinetic energy extraction over the virtual inertia of the MT-HVDC. MATLAB/Simulink is the simulation environment.

Geophysical potential for wind energy over the open oceans

Wind turbines continuously remove kinetic energy from the lower troposphere, thereby reducing the wind speed near hub height. The rate of electricity generation in large wind farms containing multiple wind arrays is, therefore, constrained by the rate of kinetic energy replenishment from the atmosphere above. In recent years, a growing body of research argues that the rate of generated power is limited to around 1.5 W m-2 within large wind farms. However, in this study, we show that considerably higher power generation rates may be sustainable over some open ocean areas. In particular, the North Atlantic is identified as a region where the downward transport of kinetic energy may sustain extraction rates of 6 W m-2 and above over large areas in the annual mean. Furthermore, our results indicate that the surface heat flux from the oceans to the atmosphere may play an important role in creating regions where sustained high rates of downward transport of kinetic energy and thus, high rates of kinetic energy extraction may be geophysical possible. While no commercial-scale deep water wind farms yet exist, our results suggest that such technologies, if they became technically and economically feasible, could potentially provide civilization-scale power.

Experimental study of wake structure behind a horizontal axis tidal stream turbine

A detailed experimental investigation of the wake propagation behind a horizontal axis turbine with three blades was conducted in a recirculating water flume. An Acoustic Doppler Velocimeter was employed to measure the time varying velocities at fifteen depths across the width of the open flume to obtain the three-dimensional velocity and turbulence fields within the length of 20 Rotor Diameters downstream. The experimental results indicated that velocity reduction in the wake was caused by both the kinetic energy extraction and blockage effects of the tidal stream turbine rotor and stanchion. The maximum velocity deficit occurred at the wake core due to a lower tip speed ratio and blockage of the hub. The wake strip gradually enlarged with the distance downstream, with less mixing in the transverse direction. The wake zone shifted towards the water surface in the vertical direction, which mainly resulted from the merging of two wakes induced by turbine rotor and stanchion. The wake rotation was also observed, and the maximum circumfluence velocity was approximately 20% of the stream-wise velocity; thus, it had a significant influence on the process of near wake mixing. Furthermore, the wake turbulence of the turbine was strong and anisotropic, which would have an impact on the behaviour of other turbines located downstream if they were in a turbine array. In addition, the turbine stanchion had a visible influence on the wake structure, especially near the wake, which should not be neglected when studying the wake characteristics.

Influence of the material used to build the blades of a wind turbine on their starting conditions

Wind energy has been shown to be one of the most viable sources of renewable energy. Hydraulic machines that convert the energy of a fluid into mechanical energy are called turbines. A wind turbine is a device which extracts kinetic energy from the wind. With increasing energy demands is necessary to increase the size of wind turbines. Under these conditions the turbine will start only at high wind speeds. On the other hand, the control of high speed is more difficult and the reduction of the inertial forces becomes mandatory. This study presents an analysis of the material influence on the wind turbine starting conditions.

Conceptual duct shape design for horizontal-axis hydrokinetic turbines

In the present paper, conceptual duct shape design for kinetic energy extraction with hydrokinetic turbines is discussed. The goal is to nd a single-passage axisymmetric geometry that holds stable flow with maximum kinetic energy ux at duct throat. For nding the optimum duct shape, the fluid flow was numerically simulated in a wedge shaped space with Flow-Simulation Software. In a multi-stage conceptual design, tabulated con gurations were employed to study each geometrical characteristic separately. These include curvature of pro le camber, trailing edge shape, pro le tip shape, and duct exit cross sectional area. The revolved pro le of each duct consists of a well constrained composite curve with few degrees of freedom. The Sketcher environment of SolidWorks Software provides a feasible method of rebuilding constrained curves. Duct shape optimization was performed based on successive flow simulation and approximation of optimum geometric dimension at optimum flow condition. The drag coecients were compared with available experiments. Based on the numerical simulations with needle shaped leading edge, the duct throat velocity can be increased. Inversely, the flow blockage can reduce the kinetic energy flux at duct throat. The optimum duct shape has shown the greatest frictional drag coecient and the minimum flow separation.

Marine Hydrokinetic Energy from Western Boundary Currents.

The kinetic energy in ocean currents, or marine hydrokinetic (MHK) energy, is a renewable energy resource that can help meet global energy requirements. An ocean circulation model-based census shows that subtropical surface western boundary currents (WBCs) are the only nearshore, large-scale currents swift enough to drive large electricity-generating ocean turbines envisioned for future use. We review several WBCs in the context of kinetic energy extraction. The power density in the Gulf Stream off North Carolina at times reaches several thousand watts per square meter at 75 m below the surface, and the annual average power is approximately 500-1,000 W m-2. Significant fluctuations occur with periods of 3-20 days (Gulf Stream meanders) and weeks to months (Gulf Stream path shifts). Interannual variations in annual average power occur because of year-to-year changes in these WBC motions. No large-scale turbines presently exist, and the road to establishing MHK facilities in WBCs will encounter challenges that are similar in many aspects to those associated with the development of offshore wind power.

Energy harvesting from human walking to power biomedical devices using oscillating generation.

This work summarizes the energy generation limits from walking employing a pendulum-based generation system. Self-winding wristwatches have exploited successfully this energy input technique for decades. Pendulum-based planar devices use the rotation to produce energy for inertial generators. Then the oscillations of body motion during locomotion present an opportunity to extract kinetic energy from planar generators. The sinusoidal motion of the center of gravity of the body, on the sagittal and frontal planes, and the limbs swinging are compliant with oscillating devices. Portable biomedical devices can extract energy from everyday walking to extend battery life or decrease battery size. Computer simulations suggest energy availability of 0.05-1.2 mJ on the chest, 0.5-2.5 mJ on the hip and 0.5-41 mJ on the elbow from walking.

Substantial Research Secures the Blue Future for our Blue Plant

Substantial Research Secures the Blue Future for our Blue Plant

Power conversion system for high altitude wind power generation with medium voltage AC transmission

High Altitude Wind Power (HAWP) generating system provides clean energy at low cost and high capacity factor due to reduced size of the turbine and high speed streamlined wind at high altitude. An air-borne wind turbine (AWT) at high altitude extracts kinetic energy from wind using buoyancy provided by the blimp/aerostat. The generated electrical power is then transmitted to the ground based station (without any power conditioning) using the transmission lines (tether). The power conversion system (PCS) for harnessing HAWP is proposed in this paper. The proposed PCS consists of a three-level neutral point clamped (NPC) rectifier, a three-level NPC DC–DC converter followed by a two-level inverter. Modelling, design and control of the PCS are presented and discussed. The PCS provides generation side maximum power-point tracking (MPPT) using sensorless optimal torque control technique. The DC–DC converter provides electrical isolation as well as voltage step-down functions. A modified proportional resonant (PR) control which can selectively eliminate lower order current harmonics of the grid-connected inverter is also presented. The proposed control scheme of the PCS is evaluated through simulation studies using software programs like PSIM and MATLAB. A scaled-down 1 kW laboratory prototype of the complete PCS is designed, built and tested. The experimental test results obtained validate the proposed control scheme for efficient power generation from high altitude wind and interface to the grid/load.

Kinetic energy extraction of a tidal stream turbine and its sensitivity to structural stiffness attenuation

The hydrodynamic forces imparted on a tidal turbine rotor, whilst causing it to rotate and hence generate power, will also cause the blades to deform. This deformation will affect the turbine's performance if not included in the early design phase and could lead to a decrease in power output and a reduction in operational life. Conversely, designing blades to allow them to deform slightly may reduce localised stress and therefore prolong the life of the blades and allow the blades to deform in to their optimum operational state. The aim of this paper is to better understand the kinetic energy extraction by varying the material modulus of a turbine blade. Shaft torque/power, blade tip displacement, and axial thrust results are presented for 2, 3 and 4 bladed rotor configurations at peak power extraction. For the rotor design studied the FSI model data show that there is a low sensitivity to blade deformation for the 2, 3 and 4 bladed rotors. However, the results reveal that the 3 bladed rotor displayed maximum hydrodynamic performance as a rigid structure which then decreased as the blade deformed. The 2 and 4 bladed rotor configurations elucidated a slight increase in hydrodynamic performance with deflection.

Optimal Inertial Support from the Variable Speed Wind Turbines using Particle Swarm Optimization

Variable Speed Wind Turbines (VSWT) are usually devoid of inertial response, a natural phenomenon observed in Synchronous Generators (SG). With increased generation share from wind energy, most of which employ VSWTs, the major concern for the utility operators is the reduction in grid inertia. Recently, various modifications in the outer control loop of VSWTs are suggested, which usually establish a link between the grid frequency deviations and the generator torque/active power to mimic the inertial response observed in SGs. Since the inertial support is synthetic and is the result of additional control loop, the parameters of the auxiliary control loop has profound effect on the emulated inertial response. In this work, a simple parameter selection approach based on Particle Swarm Optimization (PSO) is proposed. The objective is to enable the optimum extraction of stored kinetic energy while limiting the effects of consequent under-production period. The proposed approach for parameter setting is compared to two different approaches and found to be more effective in both limiting the frequency nadir and post-support disturbances.

Computational Examination of Utility Scale Wind Turbine Wake Interactions

Numerical simulations of small, utility scale wind turbine groupings were performed to determine how wakes generated by upstream turbines affect the performance of the small turbine group as a whole. Specifically, various wind turbine arrangements were simulated to better understand how turbine location influences small group wake interactions. The minimization of power losses due to wake interactions certainly plays a significant role in the optimization of wind farms. Since wind turbines extract kinetic energy from the wind, the air passing through a wind turbine decreases in velocity, and turbines downstream of the initial turbine experience flows of lower energy, resulting in reduced power output. This study proposes two arrangements of turbines that could generate more power by exploiting the momentum of the wind to increase velocity at downstream turbines, while maintaining low wake interactions at the same time. Simulations using Computational Fluid Dynamics are used to obtain results much more quickly than methods requiring wind tunnel models or a large scale experimental test.

Interaction of misaligned magnetospheres in the coalescence of binary neutron stars

We study the dependence of the electromagnetic luminosity --produced by interactions of force-free magnetospheres-- on dipole inclinations in binary neutron star systems. We show that this interaction extracts kinetic energy from the system and powers a Poynting flux with a strong dependence on the dipole orientations. This dependence can be linked to the reconnection and redistribution of magnetic field as the stars interact. Although the details of the Poynting luminosity are very much dependent on the orientation, all the cases considered here nevertheless radiate a large Poynting flux. This robust emission suggests that the pre-merger stage of binary neutron star systems can yield interesting electromagnetic counterparts to gravitational wave events.

Conversion of lowland river flow kinetic energy

Abstract This paper presents the analysis of possibilities and feasibilities of the extraction of kinetic energy from lowland rivers, which are slow and shallow and their water may contain organic fibres of water vegetation and solid particles of soil. In these rivers the existing hydrokinetic energy converters are not optimised for use because at small flow velocity the efficiency of such converters is very low. The depth of a shallow river flow may be not deep enough to install the converters. The latter are sensitive to jamming by water plant fibres. To overcome the difficulties in developing river flow kinetic energy the structures, the advantages and disadvantages of commonly used converters have been analysed A conveyor type converter has been found to be the most suitable for use in shallow rivers. Results of our field and laboratory studies of hydrokinetic energy converters have confirmed the anticipated difficulties when applying the commonly used converters in lowland rivers. The validity of our proposed method has allowed to reduce the number of mobile elements and friction couples in our novel converter and to increase its reliability. A particular approach to the principle of kinetic energy extraction from a river flow has been developed and a novel converter has been invented. To increase the efficiency of the river flow kinetic energy conversion a new conveyor technology has been proposed. This converter allows the extraction of kinetic energy from the river flow almost without affecting the river and the surrounding environment.

Three-Dimensional Structure and Evolution of the MJO and Its Relation to the Mean Flow

Abstract The two leading principal components of the daily 850- minus 150-hPa global velocity potential in the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) (1979–2011) data are used as time-varying Madden–Julian oscillation (MJO) indices. Regression maps and meridional cross sections based on these indices are used to document the structure and evolution of the zonal wind (u) and geopotential height (Z) anomalies in the MJO cycle. The data are daily, and they are not separated by season. At upper-tropospheric levels the MJO signature is dominated by eastward-propagating planetary wave packets consisting of equatorial Kelvin waves flanked by Rossby waves centered along 28°N/S, for which the westerly jet streams serve as waveguides. At lower-tropospheric levels the pattern more closely resembles the response to a pulsating heat source over the Maritime Continent, where the Andes block the eastward-propagating Kelvin wave pulse. The contrasting upper- and lower-tropospheric patterns are made up of the same building blocks: a deep, baroclinic modal structure with a node at the 400-hPa level, which dominates the tropical signature, and a barotropic residual field consisting mainly of extratropical wave trains oriented along great circles. The extratropical wave trains emanate from the flanking Rossby waves in the baroclinic modal structure. The strongest of them, which resembles the Pacific–North America (PNA) pattern, extracts kinetic energy from the climatological-mean flow in the jet exit region. At other longitudes the jet stream seems to act as a barrier to the poleward propagation of MJO-related wave activity.

Linking electromagnetic and gravitational radiation in coalescing binary neutron stars

We expand on our study of the gravitational and electromagnetic emissions from the late stage of an inspiraling neutron star binary as presented in Ref. \cite{Palenzuela:2013hu}. Interactions between the stellar magnetospheres, driven by the extreme dynamics of the merger, can yield considerable outflows. We study the gravitational and electromagnetic waves produced during the inspiral and merger of a binary neutron star system using a full relativistic, resistive MHD evolution code. We show that the interaction between the stellar magnetospheres extracts kinetic energy from the system and powers radiative Poynting flux and heat dissipation. These features depend strongly on the configuration of the initial stellar magnetic moments. Our results indicate that this power can strongly outshine pulsars in binaries and have a distinctive angular and time-dependent pattern. Our discussion provides more detail than Ref. \cite{Palenzuela:2013hu}, showing clear evidence of the different effects taking place during the inspiral. Our simulations include a few milliseconds after the actual merger and study the dynamics of the magnetic fields during the formation of the hypermassive neutron star. We also briefly discuss the possibility of observing such emissions.

Electromagnetic and Gravitational Outputs from Binary-Neutron-Star Coalescence

The late stage of an inspiraling neutron-star binary gives rise to strong gravitational wave emission due to its highly dynamic, strong gravity. Moreover, interactions between the stellar magnetospheres can produce considerable electromagnetic radiation. We study this scenario using fully general relativistic, resistive magnetohydrodynamic simulations. We show that these interactions extract kinetic energy from the system, dissipate heat, and power radiative Poynting flux, as well as develop current sheets. Our results indicate that this power can (i)outshine pulsars in binaries, (ii)display a distinctive angular- and time-dependent pattern, and (iii)radiate within large opening angles. These properties suggest that some binary neutron-star mergers are ideal candidates for multimessenger astronomy.

Parametric Study of Crowned Blade in Horizontal Axial Turbine

The horizontal axial turbine could extract kinetic energy from both wind and tidal stream. In this paper, a type of horizontal axial turbine was designed with a crown stalled on the blade tip and the turbine was analyzed in a tidal stream. Several turbines with different geometries of the crowns were compared, whose power coefficients were numerically simulated by the CFD method. Effects of the crown design parameters, such as crown setting directions and different widths on turbine efficiency were discussed. Furthermore, when the turbine worked at different tip speed ratio, the results were discussed, either. By analysis of the results, it is could be concluded that a circular crown was sufficient to eliminate blade tip loss caused by tip leakage flow. The upstream semicircle crown modified the corresponding side foil pressure distribution to the design value, and so did the downstream semicircle crown. In the ellipse crowns testing, turbine efficiency was approximately in line with the value of crowns width. When the turbine with the circular crown worked at a little higher tip speed ratio than the design value, the crown was effective as before.

Electrodynamic coupling of Jupiter’s thermosphere and stratosphere: A new source of thermospheric heating?

We investigate the vertical penetration of non-uniform electric fields in a planetary ionosphere. We develop a simple theoretical description of the vertical variation of electric fields with altitude in an ionosphere permeated with a vertical magnetic field. This framework is applied to the suggestion that winds in Jupiter’s stratosphere could drive currents in the thermosphere. In particular, we propose that wind structures in the upper region of Jupiter’s stratosphere (200–350km above the 1bar level) couple with the ionospheric plasma in this region to generate electric currents, some of which close by flowing vertically along magnetic field lines and then horizontally in the Pedersen conducting region of the thermosphere. These currents extract kinetic energy from the stratospheric winds and dissipate it, via Joule heating, as thermal energy in the thermosphere, thus providing a possible contribution to the observed high temperatures in this region. While the existence of significant wind structures in the upper stratosphere is speculative, the wind speeds that are required to generate significant heating (∼100ms−1) are not unreasonable in comparison to the observed tropospheric, lower stratospheric and thermospheric wind speeds. The scale size of the wind structures is critical to the degree of penetration of the induced electric fields. Wind structures with scale sizes less than ∼10km do not generate electric fields that penetrate significantly into the thermosphere, while those with scale sizes of greater than ∼100km (which includes very large, planetary-scale wind structures) generate electric fields that penetrate almost unmodified across the whole of the thermosphere. Sharp ionospheric layers or holes can prevent penetration of the electric fields to the thermosphere, doing so more effectively if they are of greater magnitude, of greater vertical width, or located at lower altitude. The timescale for damping of the stratospheric winds by ion drag is found to be strongly altitude-dependent, ranging from ∼1 planetary rotation at 350km altitude to >100 planetary rotations at 200km altitude. The timescales also vary strongly with the nature and scale size of the wind structures. If the timescales of the processes driving stratospheric winds are longer than these timescales, then our mechanism will damp the winds almost to zero, and supply negligible energy to the thermosphere. We also discuss the possible relevance of our results to magnetosphere–ionosphere coupling in the auroral regions of Jupiter and other planets.