The Experts below are selected from a list of 345 Experts worldwide ranked by ideXlab platform
James Ward - One of the best experts on this subject based on the ideXlab platform.
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space time adaptive processing for airborne radar
Space-Time Adaptive Processing (Ref. No. 1998 241) IEE Colloquium on, 1998Co-Authors: James WardAbstract:Advanced airborne radar systems are required to detect targets in the presence of both clutter and jamming. Ground clutter is extended in both angle and range, and is spread in Doppler frequency because of the Platform Motion. Space-time adaptive processing (STAP) refers to the simultaneous processing of the signals from an array antenna during a multiple pulse coherent waveform. STAP can provide improved detection of targets obscured by mainlobe clutter, sidelobe clutter, and jamming. This paper provides an overview of partially adaptive STAP approaches. Analysis of the clutter covariance matrix rank provides insight and conditions for preprocessor design. As the filters used for detection in a STAP radar depend on the background interference estimates, the approaches used for parameter estimation must be modified for a STAP radar. The effect of STAP on angle and Doppler accuracy is described, and an approach for joint angle and Doppler estimation in a STAP radar is described.
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space time adaptive processing for airborne radar
International Conference on Acoustics Speech and Signal Processing, 1995Co-Authors: James WardAbstract:Advanced airborne radar systems are required to detect targets in the presence of both clutter and jamming. Ground clutter is extended in both angle and range, and is spread in Doppler frequency because of the Platform Motion. Space-time adaptive processing (STAP) refers to the simultaneous processing of the signals from an array antenna during a multiple pulse coherent waveform. STAP can provide improved detection of targets obscured by mainlobe clutter, defection of targets obscured by sidelobe clutter, and detection in combined clutter and jamming environments. Fully adaptive STAP is impractical for reasons of computational complexity and estimation with limited data, so partially adaptive approaches are required. The paper presents a taxonomy of partially adaptive STAP approaches that are classified according to the type of preprocessor, or equivalently, by the domain in which adaptive weighting occurs. Analysis of the rank of the clutter covariance matrix in each domain provides insight and conditions for preprocessor design.
B.l. Douglas - One of the best experts on this subject based on the ideXlab platform.
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Synthetic aperture active sonar imaging
[Proceedings] ICASSP-92: 1992 IEEE International Conference on Acoustics Speech and Signal Processing, 1992Co-Authors: B.l. DouglasAbstract:The main problems involved in synthetic aperture sonar imaging are medium instability, slow mapping rate, and Platform Motion. Proposed solutions to these problems are reviewed, and a new technique for synthetic aperture sonar imaging is presented which allows a fast mapping rate and improved Motion compensation. This technique involves using multiple receivers to form a complex-valued preliminary image for each pulse. The preliminary images are used to estimate translation and rotation, and then they are registered, phase corrected, and superimposed to form high-resolution synthetic aperture sonar images. >
Moan Torgeir - One of the best experts on this subject based on the ideXlab platform.
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A comparative study of different methods for predicting the long-term extreme structural responses of the combined wind and wave energy concept semisubmersible wind energy and flap-type wave energy converter
'Academy of Traumatology', 2018Co-Authors: Li Qinyuan, Michailides Constantine, Gao Zhen, Moan TorgeirAbstract:The combined wind and wave concept semisubmersible wind energy and flap-type wave energy converter was developed in the EU FP7 project MARINA Platform. It consists of a four-column semisubmersible with a 5-MW wind turbine placed on top of the central column and three flap-type wave energy converters on top of three pontoons that connect the four columns. Numerical and experimental studies have been performed to demonstrate the functionality and the survivability of the combined concept. In extreme conditions, both wind turbine and wave energy converters are set in a protection mode which reduces the dynamic loads and responses. In this article, different methods for predicting long-term (50-year) extreme responses considering the wind and wave conditions at two given European offshore sites are carried out, and structural response quantities are calculated, compared and presented. The full long-term analysis was performed and regarded as the reference method, and the corresponding results are compared with the modified environmental contour method and the environmental contour method. The response quantities studied here are the axial forces and bending moments of the semisubmersible wind energy and flap-type wave energy converter, including those of the wind turbine (blade, shaft and tower), arms of the flap-type wave energy converters and mooring lines, as well as the Platform Motion in 6 degrees of freedom. The extreme responses that are dominated by the aerodynamic loadings are effectively calculated either by the full long-term analysis or the modified environmental contour method. Compared to the full long-term analysis, the environmental contour method gives an under-prediction of the long-term extreme responses of quantities related to the wind turbine (e.g. internal loads of blades and tower). For the extreme responses that are dominated by the hydrodynamic loadings, all the three methods provide similar results
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A comparative study of different methods for predicting the long-term extreme structural responses of the combined wind and wave energy concept semisubmersible wind energy and flap-type wave energy converter
SAGE Publications, 2018Co-Authors: Li Qinyuan, Michailides Constantine, Gao Zhen, Moan TorgeirAbstract:The combined wind and wave concept semisubmersible wind energy and flap-type wave energy converter was developed in the EU FP7 project MARINA Platform. It consists of a four-column semisubmersible with a 5-MW wind turbine placed on top of the central column and three flap-type wave energy converters on top of three pontoons that connect the four columns. Numerical and experimental studies have been performed to demonstrate the functionality and the survivability of the combined concept. In extreme conditions, both wind turbine and wave energy converters are set in a protection mode which reduces the dynamic loads and responses. In this article, different methods for predicting long-term (50-year) extreme responses considering the wind and wave conditions at two given European offshore sites are carried out, and structural response quantities are calculated, compared and presented. The full long-term analysis was performed and regarded as the reference method, and the corresponding results are compared with the modified environmental contour method and the environmental contour method. The response quantities studied here are the axial forces and bending moments of the semisubmersible wind energy and flap-type wave energy converter, including those of the wind turbine (blade, shaft and tower), arms of the flap-type wave energy converters and mooring lines, as well as the Platform Motion in 6 degrees of freedom. The extreme responses that are dominated by the aerodynamic loadings are effectively calculated either by the full long-term analysis or the modified environmental contour method. Compared to the full long-term analysis, the environmental contour method gives an under-prediction of the long-term extreme responses of quantities related to the wind turbine (e.g. internal loads of blades and tower). For the extreme responses that are dominated by the hydrodynamic loadings, all the three methods provide similar results.acceptedVersion© 2018. This is the authors' accepted and refereed manuscript to the article. The final authenticated version is available online at: https://doi.org/10.1177%2F147509021772688
Vinhtan Nguyen - One of the best experts on this subject based on the ideXlab platform.
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aerodynamic simulations of offshore floating wind turbine in Platform induced pitching Motion
Wind Energy, 2017Co-Authors: Vinhtan NguyenAbstract:Forfloating offshore wind turbines, rotors are under coupled Motions of rotating and Platform-induced Motions because of hydrodynamics impacts. Notably, the coupled Motion of Platform pitching and rotor rotating induces unsteadiness and nonlinear aerodynamics in turbine operations; thus having a strong effect on the rotor performances including thrust and power generation. The present work aims at developing a computational fluid dynamics model for simulations of rotor under floating Platform induced Motions. The rotor Motion is realized using arbitrary mesh interface, and wind flows are modelled by incompressible Navier-Stokes flow solver appended by the k − ω shear stress transport turbulence model to resolve turbulence quantities. In order to investigate the fully coupled Motion of floating wind turbine, the six degree of freedom solid body Motion solver is extended to couple with multiple Motions, especially for the Motion of rotor coupled with the prescribed surge-heave-pitch Motion of floating Platform. The detailed methodology of multiple Motion coupling is also described and discussed in this work. Both steady and unsteady simulations of offshore floating wind turbine are considered in the present work. The steady aerodynamic simulation of offshore floating wind turbine is implemented by the multiple reference frames approach and for the transient simulation, the rotor Motion is realized using arbitrary mesh interface. A rigorous benchmark of the present numerical model is performed by comparing to the reported literatures. The detailed elemental thrust and power comparisons of wind turbine are carried out by comparing with the results from FAST developed by National Renewable Energy Laboratory and various existing numerical data with good agreement. The proposed approach is then applied for simulations of National Renewable Energy Laboratory 5MW turbine in coupled Platform Motion at various wind speeds under a typical load case scenario. Transient effect of flows over turbines rotor is captured with good prediction of turbine performance as compared with existing data from FAST. Copyright © 2016 John Wiley & Sons, Ltd.
Abdulqadir Aziz Singapore Wala - One of the best experts on this subject based on the ideXlab platform.
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numerical validation of floating offshore wind turbine scaled rotors for surge Motion
Energies, 2018Co-Authors: Krishnamoorthi Sivalingam, Steven Martin, Abdulqadir Aziz Singapore WalaAbstract:Aerodynamic performance of a floating offshore wind turbine (FOWT) is significantly influenced by Platform surging Motions. Accurate prediction of the unsteady aerodynamic loads is imperative for determining the fatigue life, ultimate loads on key components such as FOWT rotor blades, gearbox and power converter. The current study examines the predictions of numerical codes by comparing with unsteady experimental results of a scaled floating wind turbine rotor. The influence of Platform surge amplitude together with the tip speed ratio on the unsteady aerodynamic loading has been simulated through unsteady CFD. It is shown that the unsteady aerodynamic loads of FOWT are highly sensitive to the changes in frequency and amplitude of the Platform Motion. Also, the surging Motion significantly influences the windmill operating state due to strong flow interaction between the rotating blades and generated blade-tip vortices. Almost in all frequencies and amplitudes, CFD, LR-BEM and LR-uBEM predictions of mean thrust shows a good correlation with experimental results.