Extraction Of Kinetic Energy Research Articles

Mapping Kinetic Energy Hotspots in the Persian Gulf and Oman Sea Using Surface Current Derived by Geodetic Observations and Data Assimilation

Harnessing ocean kinetic energy has emerged as a promising renewable energy solution in recent years. However, identifying optimal locations for extracting this energy remains a significant challenge. This study presents a novel scheme to estimate the total surface current (TSC) as permanent surface current by integrating geodetic data and in-situ measurements. The TSC is typically a combination of the geostrophic current, derived from dynamic topography, and the Ekman current. We utilize NOAA’s Ekman current data to complement the geostrophic current and obtain the TSC. To further enhance the accuracy of the TSC estimates, we employ a 3DVAR data assimilation method, incorporating local current meter observations. The results are verified against two control current meter stations. The data-assimilation process resulted in an improvement of 4 to 15 cm/s in the precision of calculated TSC. Using the assimilated TSC data, we then assess the kinetic energy potential and identify six regions with the most significant promise for marine kinetic energy extraction. This innovative approach can assist researchers and policymakers in targeting the most suitable locations for harnessing renewable ocean energy.

Energy Budget Characterisation of the Optimal Disturbance in Stratified Shear Flow

Stratified Taylor–Couette flow (STCF) undergoes transient growth. Recent studies have shown that there exists transient amplification in the linear regime of counter-rotating STCF. The kinetic budget of the optimal transient perturbation is analysed numerically to simulate the interaction of the shear production (SP), buoyancy flux (BP), and other energy components that contributes to the total optimal transient kinetic energy. These contributions affect the total energy by influencing the perturbation to extract kinetic energy (KE) from the mean flow. The decay of the amplification factor resulted from the positive amplification of both BP and SP, while the growth is attributed to the negative and positive amplification of BP and SP, respectively. The optimal SP is positively amplified, implying that there is the possibility of constant linear growth. These findings agree with the linear growth rate for increasing values of Grashof number.

Energy budget characteristics of the subseasonal Scandinavian pattern

Based on daily Japanese 55-year reanalysis data, this study analysed the daily energy budget characteristics of 94 Scandinavian (SCA) events in the positive phase during 62 winters from 1958 to 2020. Low-frequency circulation anomalies characterize the SCA events. The maintenance of low-frequency anomalies mainly comes from the extraction of both available potential energy (APE) and kinetic energy (KE) from the background field during both the developing stage and the decaying stage. This energy conversion characteristic is related to the “locking” effect of the background field. During the developing stage, the interactions among the low-frequency circulation anomalies continuously generate KE, which is the main source for initiating the primary circulation anomalies around western Europe and the Scandinavian Peninsula. Meanwhile, the horizontal KE advection maintains the KE of the circulation anomalies around Lake Baikal. The decay process of the SCA events is mainly related to the damping effect on the APE due to diabatic heating and the interactions among the low-frequency circulation anomalies. The SCA event is a type of atmospheric internal dynamic pattern.

Adaptive Droop Gain Control for Optimal Kinetic Energy Extraction From Wind Turbines to Support System Frequency

Adaptive Droop Gain Control for Optimal Kinetic Energy Extraction From Wind Turbines to Support System Frequency

CFD-based design optimization of ducted hydrokinetic turbines

Hydrokinetic turbines extract kinetic energy from moving water to generate renewable electricity, thus contributing to sustainable energy production and reducing reliance on fossil fuels. It has been hypothesized that a duct can accelerate and condition the fluid flow passing the turbine blades, improving the overall energy extraction efficiency. However, no substantial evidence has been provided so far for hydrokinetic turbines. To investigate this problem, we perform a CFD-based optimization study with a blade-resolved Reynolds-averaged Navier–Stokes (RANS) solver to explore the design of a ducted hydrokinetic turbine that maximizes the efficiency of energy extraction. A gradient-based optimization approach is utilized to effectively deal with the high-dimensional design space of the blade and duct geometry, with gradients being calculated through the adjoint method. The final design is re-evaluated through higher-fidelity unsteady RANS (URANS) simulations. Our optimized ducted turbine achieves an efficiency of about 54% over a range of operating conditions, higher than the typical 46% efficiency of unducted turbines.

Using spectral modeling to break light-curve degeneracies of type II supernovae interacting with circumstellar material

A large fraction of red-supergiant stars seem to be enshrouded by circumstellar material (CSM) at the time of explosion. Relative to explosions in a vacuum, this CSM causes both a luminosity boost at early times as well as the presence of symmetric emission lines with a narrow core and electron-scattering wings typical of type IIn supernovae (SNe). For this study, we performed radiation-hydrodynamics and radiative transfer calculations for a variety of CSM configurations (i.e., compact, extended, and detached) and documented the resulting ejecta and radiation properties. We find that models with a dense, compact, and massive CSM on the order of 0.5 M⊙ can match the early luminosity boost of type II-P SNe but fail to produce type IIn-like spectral signatures (also known as “flash features”). These only arise if the photon mean free path in the CSM is large enough (i.e., if the density is low enough) to allow for a radiative precursor through a long-lived (i.e., a day to a week), radially extended unshocked optically thick CSM. The greater radiative losses and kinetic-energy extraction in this case boost the luminosity even for modest CSM masses – this boost comes with a delay for a detached CSM. The inadequate assumption of high CSM density, in which the shock travels essentially adiabatically, overestimates the CSM mass and associated mass-loss rate. Our simulations also indicate that type IIn-like spectral signatures last as long as there is optically-thick unshocked CSM. Constraining the CSM structure therefore requires a combination of light curves and spectra, rather than photometry alone. We emphasize that for a given total energy, the radiation excess fostered by the presence of CSM comes at the expense of kinetic energy, as evidenced by the disappearance of the fastest ejecta material and the accumulation of mass in a dense shell. Both effects can be constrained from spectra well after the interaction phase.

Performance evaluation and shape improvement of a novel vertical-axis autorotation current turbine

A new type of vertical-axis turbine called the vertical-axis autorotation current turbine (VAACT) has been investigated experimentally and numerically. This novel turbine utilizes the autorotation phenomenon to extract kinetic energy and is characterized by a higher moment of inertia and a flapped blade. The main objective of the present work is to further improve the efficiency of this turbine type by improving the original shape. First, through a comparison of experimental and numerical results under specific conditions, the accuracy of the three-dimensional (3D) detached eddy simulation (DES) used in the present study is validated. The free surface effect on the average rotation velocity and efficiency is found to be insignificant when the fluctuation of the free surface is small. Then, shape improvement based on response surface methodology (RSM) incorporated into computational fluid dynamics (CFD) simulations is performed. The inner length and flapped angle are selected as shape variation parameters. Finally, the optimal parameters of an inner length of 10.8 cm and a flapped angle of 47.2°, corresponding to a maximum mean power coefficient of 0.1545, are found and verified. The improvement methodology adopted in this paper greatly reduces the number of required sampling points compared to other optimization algorithms, such as genetic algorithms, which confirms the potential of the resource-intensive 3D DES method as a computational tool.

Design and Evaluation of a Load Control System for Biomechanical Energy Harvesters and Energy-Removing Exoskeletons

Controlling the timing and magnitude of electricity production is a critical factor in reducing the metabolic cost of walking with an energy-removing exoskeleton. This article outlines a novel power electronic control system designed to apply a mechanical loading profile onto the user that extracts kinetic energy. This energy extraction assists the user's muscles, thereby providing metabolic assistance while simultaneously producing electrical power. This open-loop control system estimates the state of both the exoskeleton and the user's lower limbs and uses this estimation to identify and apply a desired knee flexion moment during the terminal swing phase. The control system was evaluated using human treadmill walking experiments and benchtop testing, which determined that the system could identify the user's stride period, ground contact timing, and the device's moment arm with high accuracy and precision. Furthermore, the system could apply the desired cable force within +2.6 and −2.3 N and the muscle-centric knee moment profile within +0.05 and −0.04 N·m. Through proper load control, a user would benefit from walking with an energy-removing exoskeleton, regardless of the need for portable power.

Aerodynamic Characterization of Darrieus Turbines during Self-Start at different Azimuthal Quadrants

One key technology to extract kinetic energy from wind and water is the vertical-axis turbines. However, these flows and currents often fluctuate, forcing the turbine rotors to operate in transient modes. To improve rotor performance, the transient aerodynamic characteristics across the four quadrants of the rotor sweep must be well-understood. We address this need by simulating the transient process of a 3-bladed Darrieus turbine rotor during self-start using the dedicated turbine aerodynamics software QBlade. The simulated transient evolution of the rotor compares well against the experimental and computational-fluid-dynamics data from previous studies. When the rotor self-starts within its first three cycles, its torque is contributed differently from each of the four quadrants. Respectively, its windward and upwind quadrant positively contributes by up to 43% and 326% each to the overall torque, and the leeward and downwind quadrant negatively reduces by up to -346% and -85% each from the overall torque. However, upon reaching steady state, these roles change where the positive torques are contributed by the upwind and leeward quadrants by up to 120% and 10%, respectively, while the negative torques are caused by the downwind and windward quadrants by up to -18% and -13%, respectively. Insights into these rotor dynamics can be later used to propose newer rotor designs or operations to improve the transient performance of the turbine

Experimental evaluation of power performance and wake characteristics of twin flanged duct turbines in tandem under bi-directional tidal flows

Ducted turbines have the potential to generate large-scale electricity when placed in tidal farms. Understanding the fluid-duct interaction would provide vital information for tidal farm projects. This paper describes flume experiments to investigate the performance and far wake impact on flanged duct turbines in bi-directional tidal flows. Results showed that ducted turbines generate 40% more power per rotor unit area than bare turbines. The turbines underperformed for each device in tandem configurations. However, ducted turbines outperformed bare turbines by 15%. The decreasing range of wake velocities and increasing turbulence intensities of the devices were shown to be greater in the ducted turbines. The drop in wake velocity is caused by kinetic energy extraction, and duct and rotor blockage effects. For the isolated bare and ducted turbines, full flow recovery occurs at around 13 and 20 rotor diameters, respectively. In tandem arrangements, while the bare turbine operated as if it was in isolation from 24 rotor diameters downstream, the wake flow in the ducted turbines persisted beyond. However, in terms of power output per rotor unit area, the deployment of additional ducted turbines may be advantageous. Though in the present state of development, precise economic estimates of energy costs are unavailable.

Submesoscale Dynamics in the Upper Ocean

Oceanic motions with spatial scales of 200 m–20 km, called submesoscales, are ubiquitous in the upper ocean and serve as a key intermediary between larger-scale balanced dynamics and unbalanced turbulence. Here, we introduce the fluid dynamics of submesoscales and contrast them with motions at larger and smaller scales. We summarize the various ways in which submesoscales develop due to instabilities that extract potential or kinetic energy from larger-scale balanced currents; some instabilities have counterparts at larger scales, while others are distinct to the submesoscale regime. Submesoscales modify the density stratification in the upper ocean and redistribute energy between scales. These energy transfers are complex, having both up-scale and down-scale components. Submesoscale eddies and fronts also contribute to a spatially heterogeneous distribution of shear and restratification that leave an imprint on upper ocean turbulence. The impact of submesoscales on the Earth's climate remains an exciting research frontier.

Coupled BEM and two-phase mixture model for surrounding flow of horizontal axial turbine over sediment seabed

Horizontal axial turbine (HAT) is widely used to extract kinetic energy from tidal current. The power absorption of HAT is largely decided by the surrounding flow. A two-phase, sediment-laden mixture model is coupled with the blade element momentum method (BEM) for the impact of HAT on surrounding flow over sediment seabed. The mixture model incorporates theoretical relative velocity, turbulence enhancement from particle wake flow and turbulence damping from high concentration sediment. A blade-induced turbulence (BIT) term is introduced into the mixture model to represent the turbulence production at blade edge. The computed velocity and turbulence are improved by the BIT term in the wake region of HAT. Three turbine hub heights are adopted to investigate the impact of the turbine on sediment seabed and the surrounding flow. Results show that with low turbine hub height, long wake region is generated after the turbine, force exerted on the turbine is asymmetric vertically and thrust and power coefficients decrease. The pattern of bed shear stress is highly dependent on the turbine hub height. The bed shear stress is enhanced under the turbine and strong scour and sediment transport tend to occur on the sediment seabed with low turbine hub height.

Chasing the offshore wind farm wind-wake-induced upwelling/downwelling dipole

The operational principle of offshore wind farms (OWF) is to extract kinetic energy from the atmosphere and convert it into electricity. Consequently, a region of reduced wind speed in the shadow zone of an OWF, the so-called wind-wake, is generated. As there is a horizontal wind speed deficit between the wind-wake and the undisturbed neighboring regions, the locally reduced surface stress results in an adjusted Ekman transport. Subsequently, the creation of a dipole pattern in sea surface elevation induces corresponding anomalies in the vertical water velocities. The dynamics of these OWF wind-wake induced upwelling/downwelling dipoles have been analyzed in earlier model studies, and strong impacts on stratified pelagic ecosystems have been predicted. Here we provide for the first time empirical evidence of the existence of such upwelling/downwelling dipoles. The data were obtained by towing a remotely operated vehicle (TRIAXUS ROTV) through leeward regions of operational OWFs in the summer stratified North Sea. The undulating TRIAXUS transects provided high-resolution CTD data which enabled the characterization of three different phases of the ephemeral life cycle of a wind-wake-induced upwelling/downwelling dipole: development, operation, and erosion. We identified two characteristic hydrographic signatures of OWF-induced dipoles: distinct changes in mixed layer depth and potential energy anomaly over a distance < 5 km and a diagonal excursion of the thermocline of ~10–14 m over a dipole dimension of ~10–12 km. Whether these anthropogenically induced abrupt changes are significantly different from the corridor of natural variability awaits further investigations.

Dynamic response of hybrid energy storage based virtual inertial support in wind application

The replacement of conventional synchronous generator (SG) with wind energy conversion system (WECS) greatly reduces the available inertial support in the electrical network. In order to avoid mechanical stress on wind turbine (WT) which is caused by kinetic energy (KE) extraction in providing the virtual inertial support (VIS), this paper proposed an improved technique in converting a hybrid energy storage (HES) into VIS during disturbances for wind turbine systems. The complementary behaviour of supercapacitor (SC) and battery energy storage (BES) offers a great deal of faster and limitless VIS. The trade-off between SC and BES has been achieved through a modified formulation of total available inertial time constant for HES-based VIS. To realize this, the new SC's voltage and BES's voltage are kept updated before being used to form the SC's and BES's reference current in the proposed model. Alongside in operating the HES-based VIS, this paper also introduced a modified energy management system (EMS) by fully utilizing the advantages of the high-power density of SC and the high-energy density of BES in handling disturbances. This modified control technique greatly provides faster and continuous VIS throughout the disturbances compared to the sole energy storage of SC and BES. In addition, based on the tested system of fixed wind speed and variable loads, the proposed HES-based VIS significantly improved the frequency nadir and peak frequency by 3.5 % and 2.7 % respectively. Additionally, the proposed HES-based VIS shows a significant improvement during variable wind speed and load conditions.

Asymmetric Impacts of El Niño and La Niña on the Pacific–South America Teleconnection Pattern

Abstract El Niño–Southern Oscillation (ENSO) has a huge influence on Antarctic climate variability via Rossby wave trains. In this study, the asymmetry of the ENSO teleconnection in the Southern Hemisphere, together with the mechanisms involved, is systematically investigated. In four reanalysis datasets, the composite atmospheric circulation anomaly in austral winter over the Amundsen Sea during La Niña is situated more to the west than during El Niño. This asymmetric feature is reproduced by ECHAM5.3.2 forced with both composite and idealized symmetric sea surface temperature anomalies. Utilizing a linear baroclinic model, we find that ENSO-triggered circulation anomalies in the subtropics can readily extract kinetic energy from the climatological mean flow and develop efficiently at the exit of the subtropical jet stream (STJ). The discrepancy in the location of the STJ between El Niño and La Niña causes asymmetric circulation responses by affecting the energy conversion. During El Niño years, anomalous tropical convective precipitation increases the meridional temperature gradient, which in turn leads to the strengthening of the STJ and the eastward movement of the jet core and jet exit in the Pacific. With the movement of the STJ exit, the wave train tends to develop over the eastern region. The opposite is the case during La Niña when the westward shift of the jet exit favors the development of the wave train in the western region. Our findings expand the current understanding regarding ENSO teleconnection.

Asymmetric impacts of El Niño and La Niña on the Pacific–North American teleconnection pattern: the role of subtropical jet stream

The asymmetric impacts of El Niño and La Niña on the Pacific–North American teleconnection pattern in boreal winter have important implications for the surface air temperature and precipitation anomalies in North America. Previous studies have shown that the varying tropical convective heating contributes to the zonal shift of the teleconnection pattern during different El Niño/Southern Oscillation phases. In this study, using reanalysis, atmospheric general circulation model (AGCM) simulations, and a linear baroclinic model, we further present that the discrepancy of the subtropical jet stream (STJ) during El Niño and La Niña also contributes to the asymmetry. The atmospheric anomalies readily extract kinetic energy and effectively develop at the exit of the STJ. During El Niño (La Niña) years, as the central-eastern tropical Pacific warms up (cools down), the meridional temperature gradient in central subtropical Pacific increases (decreases), leading to the eastward (westward) shift of the STJ. The movement of the STJ leads to the shift of the location where disturbance develops most efficiently, ultimately contributing to the asymmetry of the teleconnection pattern.

Energy extraction of oscillating foil with an active deflecting trailing-edge flap

The method of oscillating-foil energy extraction can be used to extract kinetic energy from the surrounding flow by a combined pitching and heaving motion of the foil. In order to improve the efficiency of energy extraction, a slotted foil with an active deflecting trailing-edge flap—inspired by the structure of the tail edge of bird wings—is designed. In this study, the unsteady Reynolds-averaged Navier–Stokes equation is solved to investigate the energy extraction performance of an oscillating foil at a Reynolds number of 5.0 × 105. In the numerical simulation, the dynamic overset mesh technology is used in order to ensure the accuracy and convergence of numerical solution. The effect of the deflecting motion of trailing-edge flaps on the efficiency of energy extraction is studied at a range of oscillating frequencies. In addition, the flow control mechanisms of slots on the oscillating foil are revealed by comparing the flow fields of the slotted foil and the NACA0015 foil. The result shows that active deflecting trailing-edge flaps can improve the efficiency of energy extraction over a wide range of oscillation frequencies. The active deflection of trailing-edge flaps increases the energy extraction efficiency of oscillating foils by 21.1% relative to conventional foils under a specific operating condition of oscillating frequency f* = 0.18. A detailed analysis of the flow fields indicates that the slot on the foil can suppress flow separation, while it has a negative effect on the attachment of leading-edge vortices. The deflecting trailing-edge flap enhances the heaving force. Therefore, the energy output and the efficiency of the oscillating foil are enhanced especially at the operating conditions of the oscillating foil without leading-edge vortex shedding.

Statistical Analysis of Wind Speed Distribution Based on Five Weibull Methods for Wind Power Evaluation in Maan, Jordan

Due to the increasing environmental and economic cost of fossil fuels, alternative sources of energy are needed. One of these sources is wind energy. The wind-turbines extract kinetic energy from the wind to convert it to mechanical energy and then transfer to electrical energy. Wind speed is the most important parameter for an efficient wind energy system. In this work the Microsoft excel software used to analysis of wind speed data and evaluate the wind speed distribution. the wind speed probability estimated and analyzed by using five methods of Weibull and Rayleigh distributions and evaluated the best methods to represent the actual data based on monthly mean wind speed data of the Ma'an city site, Jordan. furthermore, from the analysis, it has been found that the energy pattern factor method EPFM is the best method to represent the actual data and the EPFM is the best and most accurate and efficient method to determine the Weibull distribution parameters ( k ) and ( c ). In addition, in this work, the annual average shape parameter ( k ) is 3.4 and the annual average scale parameter ( c ) is 4.0 m/s. The most probable wind speed is 4.4 m/s in August and the maximum wind speed carrying maximum energy is 5.2 m/s occurs in October. Meanwhile, the maximum power and energy density are 57.5 W/m 2 , 42.8 kWh/m 2 respectively in August. Moreover, the site has annual power density 39.3W/m 2 and 345.5 kWh/m 2 of energy density. Keywords : Renewable energy, Wind energy, Wind speed, Weibull distributions, Power density, Energy density DOI: 10.7176/JETP/11-4-05 Publication date: September 30th 2021

Study of a Bi-Vertical Axis Turbines Farm Using the Actuator Cylinder Method

Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present large variation of direction during tide. Methods for representing vertical axis turbines in tidal farms should be implemented in order to predict correctly power production with an acceptable time cost. The Actuator Cylinder (AC) is one of them. Numerical results in terms of wakes, with the study of velocity profiles, and efforts are compared to experiences, as well as showed that the method is sufficiently accurate and for a reasonable computing time, which is of prime importance for tidal turbines farms studies. The Actuator Cylinder method is implemented in ANSYS Fluent in a 2D stationary resolution. The method is then applied to a double levels of two counter-rotating rotors marine turbine designed by Hydroquest. Wake and power production of a single turbine and several farm configurations are studied under different current conditions (magnitude and direction).

OPTIMIZATION OF FLOATING HORIZONTAL AXIS WIND TURBINE (FHAWT) BLADES FOR AERODYNAMIC PERFORMANCE MEASUREMENT

Wind power is one of the most important sources of renewable energy which extract kinetic energy from the wind. Currently much research has concentrated on improving the aerodynamic performance of wind turbine blade through wind tunnel testing and theoretical studies. However, wind turbine simulation through Computational Fluid Dynamics (CFD) software offers inexpensive solutions to aerodynamic blade analysis problem. The purpose of this paper is to find the effect of angle of attack towards the blade of Floating Horizontal Axis Wind Turbine (FHAWT) and optimize to get the best blade performance in between twisted and untwisted blade which will give maximum lift and drag force ratio. The optimization of the FHAWT blades are carried out by analysing, modelling and simulation by using simplified spreadsheet method, CFD analysis in ANSYS WORKBENCH 2020 R1 software and wind tunnel testing. The blades are evaluated regarding their lift and drag force ratio in different angle of attack and wind speed. The results, obtained from both computer programs, wind tunnel testing and the initial hand calculations, are comparable and satisfying. Finally, the model was implemented to optimize blades performance, especially at low wind velocities, which is crucial to produce power during operating in offshore environment.