Experimental Identification of an Advanced Spar’s Low Frequency Drag Damping in Waves

Abstract Climate change and increasing population growth are accelerating the need for new clean renewable energy generation. One such proposed type of renewable energy is offshore floating wind, which has yet to reach a convergence as to the optimum type of floating platform to support a wind turbine. To date there has been numerous proposals of novel floating platforms with unique hull characteristics. One such type is the advanced spar, which has a large area of sharp edges and therefore considerably different hydrodynamic viscous effects than typical cylindrical platforms. Prediction of a floating body’s low frequency drag damping is crucial to successfully predicting the horizontal motions. Calculation of the viscous effects have been seen to have the most uncertainty. Published literature shows that the viscous drag effects of floating bodies either increase or decrease with increasing wave severity as compared to still water decay tests. In this paper a combined experimental and numerical method for identifying low frequency viscous damping effects on the hull of a moored platform is introduced. An initial offset is applied to the platform, which is then released in still water and regular sinusoidal waves. The experimental results will then be compared to a weakly nonlinear time domain model in order to identify how the drag coefficients vary with wave conditions. Discussions on Keulegan–Carpenter (KC) number dependent damping are given. Finally simulations using results from these experiments are compared against a full scale deployed floating platform in multi-directional waves, current and wind.

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Using CFD to Assess Low Frequency Damping

Volume 5: Ocean Engineering; CFD and VIV ◽

10.1115/omae2012-83326 ◽

2012 ◽

Author(s):

Alessio Pistidda ◽

Harald Ottens ◽

Richard Zoontjes

Keyword(s):

Standard Procedure ◽

Low Frequency ◽

Added Mass ◽

Model Tests ◽

Viscous Damping ◽

Viscous Effects ◽

Floating Bodies ◽

Time Step ◽

Damping Coefficients ◽

Quadratic Component

During offshore installation operations, floating bodies are often moored using soft mooring which are designed to withstand the environmental forces. Large amplitude motions often occur due to excitation by slowly varying wind and wave drift forces. To analyze these motions the dynamic system has to be accurately described, which includes an estimation of the added mass and damping coefficients. In general, the added mass can be accurately calculated with traditional potential theory. However for the damping this method is not adequate because viscous effects play an important role. Generally these data are obtained using model tests. This paper validates the CFD methodology as an alternative to model tests to evaluate the viscous damping. The aim is to define a standard procedure to derive viscous damping coefficients for surge, sway and yaw motion of floating bodies. To estimate viscous damping in CFD, a 3D model of the launch and float-over barge H-851 was used. For this barge, model test data is available which could be compared with the results of the CFD analysis. For the simulations, the commercial package STAR-CCM+ with the implicit unsteady solver for Reynolds-Averaged Navier-Stokes (RANS) equations was used. The turbulence model implemented was the k-Omega-SST. Numerical errors have been assessed performing sensitivity analysis on time step and grid size. Damping has been investigated by performing decay simulations as in the model tests, taking the effect of coupling among all motions into account. The P-Q fitting method has been used to determine the linear and quadratic component of the damping. Numerical results are validated with those obtained from the towing tank. Results show that CFD is an adequate tool to estimate the low frequency damping in terms of equivalent damping. More investigations are required to determine the linear and quadratic component.

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THE ANALYSIS OF OPERATION MODES OF ENERGY STORES IN AUTONOMOUS HYBRID POWER PLANTS WITH RENEWABLE ENERGY RESOURCES

Alternative Energy and Ecology (ISJAEE) ◽

10.15518/isjaee.2018.13-15.055-067 ◽

2018 ◽

pp. 55-67

Author(s):

S. G. Obukhov ◽

I. A. Plotnikov ◽

V. G. Masolov

Keyword(s):

Renewable Energy ◽

Power Systems ◽

Low Frequency ◽

Rechargeable Batteries ◽

Energy Resources ◽

Renewable Energy Resources ◽

Hybrid Power ◽

Operation Modes ◽

Energy Stores ◽

Energy Store

The paper presents the results of the comparative analysis of operation modes of an autonomous hybrid power complex with/without the energy store. We offere the technique which defines the power characteristics of the main components of a hybrid power complex: the consumers of the electric power, wind power and photo-electric installations (the last ones have been constructed). The paper establishes that, in order to compensate the seasonal fluctuations of power in autonomous power systems with renewable energy resources, the accumulative devices are required, with a capacity of tens of MWh including devices that are capable to provide energy storage with duration about half a year. This allows abandoning the storage devices for smoothing the seasonal fluctuations in the energy balance.The analysis of operation modes of energy stores has shown that for a stock and delivery of energy on time intervals, lasting several hours, the accumulative devices with rather high values of charging and digit power aren't required. It allows using the lead-acid rechargeable batteries of the deep category for smoothing the daily peaks of surplus and a capacity shortage. Moreover, the analysis of operation modes of energy stores as a part of the hybrid complexes has demonstrated that in charging/digit currents of the energy store the low-frequency and high-frequency pulsations of big amplitude caused by changes of size of output power of the renewable power installations and loading are inevitable. If low-frequency pulsations (the period of tens of minutes) can partially be damped due to the restriction of size of the maximum charging current of rechargeable batteries, then it is essentially impossible to eliminate high-frequency pulsations (the period of tens of seconds) in the power systems with the only store of energy. The paper finds out that the combined energy store having characteristics of the accumulator in the modes of receiving and delivery of power on daily time intervals, and at the same time having properties of the supercondenser in the modes of reception and return of impulses of power on second intervals of time is best suited to requirements of the autonomous power complexes with renewable energy resources.

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Impact of High Penetration Renewable Energy Systems on Low-Frequency Oscillations

2021 International Conference on Electric Power Engineering – Palestine (ICEPE- P) ◽

10.1109/icepe-p51568.2021.9423472 ◽

2021 ◽

Author(s):

Hasan Ali Abumeteir ◽

Ahmet Mete Vural

Keyword(s):

Renewable Energy ◽

Low Frequency ◽

Energy Systems ◽

Renewable Energy Systems ◽

Low Frequency Oscillations ◽

High Penetration

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Experiment Investigation of Bistable Vibration Energy Harvesting with Random Wave Environment

Applied Sciences ◽

10.3390/app11093868 ◽

2021 ◽

Vol 11 (9) ◽

pp. 3868

Author(s):

Qiong Wu ◽

Hairui Zhang ◽

Jie Lian ◽

Wei Zhao ◽

Shijie Zhou ◽

...

Keyword(s):

Renewable Energy ◽

Energy Harvesting ◽

Cantilever Beam ◽

Large Scale ◽

Low Frequency ◽

Vibration Energy ◽

Random Wave ◽

Periodic Signal ◽

Vibration Energy Harvesting ◽

Motion Activity

The energy harvested from the renewable energy has been attracting a great potential as a source of electricity for many years; however, several challenges still exist limiting output performance, such as the package and low frequency of the wave. Here, this paper proposed a bistable vibration system for harvesting low-frequency renewable energy, the bistable vibration model consisting of an inverted cantilever beam with a mass block at the tip in a random wave environment and also develop a vibration energy harvesting system with a piezoelectric element attached to the surface of a cantilever beam. The experiment was carried out by simulating the random wave environment using the experimental equipment. The experiment result showed a mass block’s response vibration was indeed changed from a single stable vibration to a bistable oscillation when a random wave signal and a periodic signal were co-excited. It was shown that stochastic resonance phenomena can be activated reliably using the proposed bistable motion system, and, correspondingly, large-scale bistable responses can be generated to realize effective amplitude enlargement after input signals are received. Furthermore, as an important design factor, the influence of periodic excitation signals on the large-scale bistable motion activity was carefully discussed, and a solid foundation was laid for further practical energy harvesting applications.

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Chaos in positive ion–negative ion magnetized plasmas

Journal of Plasma Physics ◽

10.1017/s0022377820001348 ◽

2020 ◽

Vol 86 (6) ◽

Author(s):

Samiran Ghosh ◽

Biplab Maity ◽

Swarup Poria

Keyword(s):

Nonlinear Wave ◽

Low Frequency ◽

Negative Ions ◽

Dynamical Behaviour ◽

Negative Ion ◽

Sound Waves ◽

Weakly Nonlinear ◽

Positive Ions ◽

Experimental Parameters ◽

Map Analysis

The dynamical behaviour of weakly nonlinear, low-frequency sound waves are investigated in a plasma composed of only positive and negative ions incorporating the effects of a weak external uniform magnetic field. In the plasma model the mass (temperature) of the positive ions is smaller (larger) than that of the negative ions. The dynamics of the nonlinear wave is shown to be governed by a novel nonlinear equation. The stationary plane wave (analytical and numerical) nonlinear analysis on the basis of experimental parameters reveals that the nonlinear wave does have quasi-periodic and chaotic solutions. The Poincarè return map analysis confirms these observed complex structures.

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Differential Recordings of Local Field Potential:A Genuine Tool to Quantify Functional Connectivity

10.1101/270439 ◽

2018 ◽

Author(s):

Meyer Gabriel ◽

Caponcy Julien ◽

Paul A. Salin ◽

Comte Jean-Christophe

Keyword(s):

Functional Connectivity ◽

Local Field ◽

Signal To Noise Ratio ◽

Field Potential ◽

Low Frequency ◽

Large Area ◽

Signal To Noise ◽

Cortical Areas ◽

Electrophysiological Method ◽

Local Field Potential Lfp

AbstractLocal field potential (LFP) recording is a very useful electrophysiological method to study brain processes. However, this method is criticized for recording low frequency activity in a large area of extracellular space potentially contaminated by distal activity. Here, we theoretically and experimentally compare ground-referenced (RR) with differential recordings (DR). We analyze electrical activity in the rat cortex with these two methods. Compared with RR, DR reveals the importance of local phasic oscillatory activities and their coherence between cortical areas. Finally, we show that DR provides a more faithful assessment of functional connectivity caused by an increase in the signal to noise ratio, and of the delay in the propagation of information between two cortical structures.

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Prediction of Steady Propeller Performance with a Nonlinear Slipstream and Boundary-Layer Effect

Journal of Ship Research ◽

10.5957/jsr.1995.39.4.297 ◽

1995 ◽

Vol 39 (04) ◽

pp. 297-312

Author(s):

You-Hua Liu

Keyword(s):

Boundary Layer ◽

Three Dimensional ◽

Leading Edge ◽

Viscous Drag ◽

Viscous Effects ◽

Lattice Method ◽

Suction Force ◽

Layer Effect ◽

Dimensional Boundary ◽

Propeller Performance

Both slipstream deformation and viscous effects are factors that affect the performance of a rotating marine propeller but neither of them has been properly treated in most of the current lifting-surface methods and surface panel theories. With the introduction of a partial roll-up wake model that is flexible to various cases of propeller geometry and loading condition, this paper presents a vortex-lattice method that can improve propeller performance prediction especially at heavy loading conditions. Some observations on the calculation of the blade leading-edge suction force and how to deduct it to account for the viscous drag increasing are given. The scale effect of propeller performance can be readily predicted by the quasi-three-dimensional boundary-layer calculation presented in this paper. Some patterns of the limiting streamlines on blade surfaces are also illustrated and compared with experimental results.

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Development of an Improved LMD Method for the Low-Frequency Elements Extraction from Turbine Noise Background

Energies ◽

10.3390/en13040805 ◽

2020 ◽

Vol 13 (4) ◽

pp. 805

Author(s):

Lida Liao ◽

Bin Huang ◽

Qi Tan ◽

Kan Huang ◽

Mei Ma ◽

...

Keyword(s):

Renewable Energy ◽

Wind Turbine ◽

Condition Monitoring ◽

Renewable Energy Sources ◽

Near Field ◽

Low Frequency ◽

Aerodynamic Noise ◽

Frequency Noise ◽

Human Society ◽

Noise Background

Given the prejudicial environmental effects of fossil-fuel based energy production, renewable energy sources can contribute significantly to the sustainability of human society. As a clean, cost effective and inexhaustible renewable energy source, wind energy harvesting has found a wide application to replace conventional energy productions. However, concerns have been raised over the noise generated by turbine operating, which is helpful in fault diagnose but primarily identified for its adverse effects on the local ecosystems. Therefore, noise monitoring and separation is essential in wind turbine deployment. Recent developments in condition monitoring provide a solution for turbine noise and vibration analysis. However, the major component, aerodynamic noise is often distorted in modulation, which consequently affects the condition monitoring. This study is conducted to explore a novel approach to extract low-frequency elements from the aerodynamic noise background, and to improve the efficiency of online monitoring. A framework built on the spline envelope method and improved local mean decomposition has been developed for low-frequency noise extraction, and a case study with real near-field noises generated by a mountain-located wind turbine was employed to validate the proposed approach. Results indicate successful extractions with high resolution and efficiency. Findings of this research are also expected to further support the fault diagnosis and the improvement in condition monitoring of turbine systems.

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Spillovers to Renewable Energy Stocks in the US and Europe: Are They Different?

Energies ◽

10.3390/en13123162 ◽

2020 ◽

Vol 13 (12) ◽

pp. 3162 ◽

Cited By ~ 2

Author(s):

Tiantian Liu ◽

Shigeyuki Hamori

Keyword(s):

Renewable Energy ◽

Stock Markets ◽

Low Frequency ◽

Investment Horizon ◽

Stock Market Index ◽

Energy Investment ◽

Time Frequency ◽

Volatility Spillovers ◽

Financial Variables ◽

The Us

This paper examines the spillovers of return and volatility transmitted from fossil energies (crude oil and natural gas) and several important financial variables (stock market index, bonds, and the volatility index) to renewable stock markets in the US and Europe under the time-frequency domain frameworks. The total spillovers of return and volatility from all variables to renewable stock markets in the US are higher than those in Europe. Stock markets transmit the highest return spillovers to renewable energy stocks, which far exceed the spillovers from fossil energy to renewable energy stocks in both regions. In addition, both return and volatility spillovers could be enhanced, possibly due to specific events or sudden changes in prices. In particular, extreme events such as the Brexit referendum in 2016 influenced mostly the volatility spillovers across European markets. Moreover, the spillovers of return and volatility are contingent on frequency, and most return spillovers are concentrated at the high frequency, whereas most volatility spillovers are concentrated at the low frequency. These results remind investors that it is necessary to consider the investment horizon when making their financial decisions on renewable energy investment.

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