The Experts below are selected from a list of 12393 Experts worldwide ranked by ideXlab platform
John Young - One of the best experts on this subject based on the ideXlab platform.
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a novel geometry adaptive cartesian grid based immersed boundary lattice boltzmann method for fluid structure interactions at moderate and high reynolds numbers
Journal of Computational Physics, 2018Co-Authors: Lincheng Xu, Fangbao Tian, John YoungAbstract:Abstract A novel computational framework which combines the lattice Boltzmann method (LBM) and an improved immersed boundary method (IBM) based on a dynamic geometry-adaptive Cartesian grid system is introduced for the fluid–structure interaction (FSI) problems at moderate and high Reynolds numbers. In this framework, the fluid dynamics is obtained by solving the discrete lattice Boltzmann equation. The boundary conditions at the fluid–structure interfaces are handled by an improved IBM based on a Feedback scheme, which drives the predicted flow velocity (calculated after the LBM stream process without the IBM body force) near the immersed boundaries to match the solid velocity. In the present IBM, the Feedback Coefficient is mathematically derived and explicitly approximated. The Lagrangian force density is divided into two parts: one is the traction caused by the predicted flow velocity, and the other is caused by the acceleration of the immersed boundary. Such treatment significantly enhances the numerical stability for modelling FSI problems involving small structure-to-fluid mass ratios. A novel dynamic geometry-adaptive refinement is applied to provide fine resolution around the immersed geometries and coarse resolution in the far field. The overlapping grids between two adjacent refinements consist of two layers. In order to enhance the numerical stability, two-layer “ghost nodes” are generated within the immersed body domain which is a non-fluid area. The movement of fluid–structure interfaces only causes adding or removing grids at the boundaries of refinements and consequently a high mesh-update efficiency is guaranteed. Finally, large eddy simulation models are incorporated into the framework to model turbulent flows at relatively high Reynolds numbers. Several validation cases, including an impulsively started flow over a vertical plate, flow over stationary and oscillating cylinders, flow over flapping foils, flexible filaments in a uniform flow, turbulent flow over a wavy boundary, flow over a stationary sphere and a dragonfly in hovering flight, are conducted to verify the accuracy and fidelity of the present solver over a range of Reynolds numbers.
Lincheng Xu - One of the best experts on this subject based on the ideXlab platform.
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a novel geometry adaptive cartesian grid based immersed boundary lattice boltzmann method for fluid structure interactions at moderate and high reynolds numbers
Journal of Computational Physics, 2018Co-Authors: Lincheng Xu, Fangbao Tian, John YoungAbstract:Abstract A novel computational framework which combines the lattice Boltzmann method (LBM) and an improved immersed boundary method (IBM) based on a dynamic geometry-adaptive Cartesian grid system is introduced for the fluid–structure interaction (FSI) problems at moderate and high Reynolds numbers. In this framework, the fluid dynamics is obtained by solving the discrete lattice Boltzmann equation. The boundary conditions at the fluid–structure interfaces are handled by an improved IBM based on a Feedback scheme, which drives the predicted flow velocity (calculated after the LBM stream process without the IBM body force) near the immersed boundaries to match the solid velocity. In the present IBM, the Feedback Coefficient is mathematically derived and explicitly approximated. The Lagrangian force density is divided into two parts: one is the traction caused by the predicted flow velocity, and the other is caused by the acceleration of the immersed boundary. Such treatment significantly enhances the numerical stability for modelling FSI problems involving small structure-to-fluid mass ratios. A novel dynamic geometry-adaptive refinement is applied to provide fine resolution around the immersed geometries and coarse resolution in the far field. The overlapping grids between two adjacent refinements consist of two layers. In order to enhance the numerical stability, two-layer “ghost nodes” are generated within the immersed body domain which is a non-fluid area. The movement of fluid–structure interfaces only causes adding or removing grids at the boundaries of refinements and consequently a high mesh-update efficiency is guaranteed. Finally, large eddy simulation models are incorporated into the framework to model turbulent flows at relatively high Reynolds numbers. Several validation cases, including an impulsively started flow over a vertical plate, flow over stationary and oscillating cylinders, flow over flapping foils, flexible filaments in a uniform flow, turbulent flow over a wavy boundary, flow over a stationary sphere and a dragonfly in hovering flight, are conducted to verify the accuracy and fidelity of the present solver over a range of Reynolds numbers.
Xuehua Wang - One of the best experts on this subject based on the ideXlab platform.
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optimized controller design for lcl type grid connected inverter to achieve high robustness against grid impedance variation
IEEE Transactions on Industrial Electronics, 2015Co-Authors: Xinbo Ruan, Weiwei Li, Xuehua WangAbstract:Capacitor-current-Feedback active damping is an effective method to suppress the $LCL$ -filter resonance in grid-connected inverters. However, due to the variation of grid impedance, the $LCL$ -filter resonance frequency will vary in a wide range, which challenges the design of the capacitor-current-Feedback Coefficient. Moreover, if the resonance frequency is equal to one-sixth of the sampling frequency $(f_{s}/6)$ , the digitally controlled $LCL$ -type grid-connected inverter can be hardly stable no matter how much the capacitor-current-Feedback Coefficient is. In this paper, the optimal design of the capacitor-current-Feedback Coefficient is presented to deal with the wide-range variation of grid impedance. First, the gain margin requirements for system stability are derived under various resonance frequencies. By evaluating the effect of grid impedance on gain margins, an optimal capacitor-current-Feedback Coefficient is obtained. With this Feedback Coefficient, stable operations will be retained for all resonance frequencies except $f_{s} /6$ . Second, in order to improve system stability for a resonance frequency of $f_{s} /6$ , a phase-lag compensation for the loop gain is proposed. Finally, a 6-kW prototype is tested to verify the proposed design procedure.
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design of the pi regulator and Feedback Coefficient of capacitor current for grid connected inverter with an lcl filter in discrete time domain
European Conference on Cognitive Ergonomics, 2012Co-Authors: Xuehua Wang, Xinbo Ruan, Lin XuAbstract:The LCL filter is widely used in grid-connected inverter due to its powerful ability of attenuating the switching-frequency harmonics. However, the frequency response of the LCL filter has a resonance peak, which would amplify the harmonics around the resonant frequency or even cause the inverter to be unstable. Active damping based on the Feedback of capacitor current is an effective solution to damp the resonance oscillation. Since the one-timestep delay of the digital signal processor (DSP) can hardly be avoided, the stable margin of the inverter will be weakened. Besides, the optional range of the capacitor-current Feedback Coefficient will be shrunk. This paper discusses the effect of the one-timestep delay firstly, and proposes a step-by-step design method to choose the parameters of the PI-based current regulator and the capacitor-current Feedback Coefficient. Based on Jury stability criterion, the selectable 3D region surrounded by the parameters of PI-based regulator and capacitor-current Feedback Coefficient can be plotted. Further, some specific constraints such as steady-state error and phase margin etc. will decide the suitable values of PI regulator and capacitor-current Feedback Coefficient. A 6-kW single-phase grid-connected inverter is built to verify the proposed design method.
Fangbao Tian - One of the best experts on this subject based on the ideXlab platform.
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a novel geometry adaptive cartesian grid based immersed boundary lattice boltzmann method for fluid structure interactions at moderate and high reynolds numbers
Journal of Computational Physics, 2018Co-Authors: Lincheng Xu, Fangbao Tian, John YoungAbstract:Abstract A novel computational framework which combines the lattice Boltzmann method (LBM) and an improved immersed boundary method (IBM) based on a dynamic geometry-adaptive Cartesian grid system is introduced for the fluid–structure interaction (FSI) problems at moderate and high Reynolds numbers. In this framework, the fluid dynamics is obtained by solving the discrete lattice Boltzmann equation. The boundary conditions at the fluid–structure interfaces are handled by an improved IBM based on a Feedback scheme, which drives the predicted flow velocity (calculated after the LBM stream process without the IBM body force) near the immersed boundaries to match the solid velocity. In the present IBM, the Feedback Coefficient is mathematically derived and explicitly approximated. The Lagrangian force density is divided into two parts: one is the traction caused by the predicted flow velocity, and the other is caused by the acceleration of the immersed boundary. Such treatment significantly enhances the numerical stability for modelling FSI problems involving small structure-to-fluid mass ratios. A novel dynamic geometry-adaptive refinement is applied to provide fine resolution around the immersed geometries and coarse resolution in the far field. The overlapping grids between two adjacent refinements consist of two layers. In order to enhance the numerical stability, two-layer “ghost nodes” are generated within the immersed body domain which is a non-fluid area. The movement of fluid–structure interfaces only causes adding or removing grids at the boundaries of refinements and consequently a high mesh-update efficiency is guaranteed. Finally, large eddy simulation models are incorporated into the framework to model turbulent flows at relatively high Reynolds numbers. Several validation cases, including an impulsively started flow over a vertical plate, flow over stationary and oscillating cylinders, flow over flapping foils, flexible filaments in a uniform flow, turbulent flow over a wavy boundary, flow over a stationary sphere and a dragonfly in hovering flight, are conducted to verify the accuracy and fidelity of the present solver over a range of Reynolds numbers.
Josep M Guerrero - One of the best experts on this subject based on the ideXlab platform.
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analysis and design of improved weighted average current control strategy for lcl type grid connected inverters
IEEE Transactions on Energy Conversion, 2017Co-Authors: Yang Han, Ping Yang, Congling Wang, Josep M GuerreroAbstract:The LCL grid-connected inverter has the ability to attenuate the high-frequency current harmonics. However, the inherent resonance of the LCL filter affects the system stability significantly. To damp the resonance effect, the dual-loop current control can be used to stabilize the system. The grid current plus capacitor current Feedback system is widely used for its better transient response and high robustness against the grid impedance variations. The weighted average current (WAC) Feedback scheme is capable to provide a wider bandwidth at higher frequencies but show poor stability characteristics under weak grid scenarios. To overcome this shortcoming, the improved WAC damping method is proposed with an additional capacitor current Feedback loop. In this paper, a systematic parameter design guideline for the optimal selection of the current loop proportional resonant controller and the additional capacitor current Feedback Coefficient are presented for the improved WAC Feedback control strategy. The satisfactory range of the system control parameters can be obtained under different delay conditions to meet the system performance specifications. The improved WAC method enhances system robustness under weak grid scenarios, and the stability and robustness have been enhanced under control delay. Finally, the experimental results are presented to validate the effectiveness of the proposed improved WAC control strategy and the parameter design method.
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resonance damping and parameter design method for lcl lc filter interfaced grid connected photovoltaic inverters
International Power Electronics and Motion Control Conference, 2016Co-Authors: Aiting Jiang, Pan Shen, Yang Han, Josep M GuerreroAbstract:In order to attenuate PWM harmonics effectively and reduce filter cost and volume, LCL-LC filter is proposed using a combination of LCL filter and an LC series resonant part. Compared with LCL filter, LCL-LC filter is characterized with decreased total inductance and better switch-frequency harmonics attenuation ability, but the resonant problem affects the system stability remarkably. In this paper, active damping based on the capacitor voltage Feedback is proposed using the concept of the equivalent virtual impedance in parallel with the capacitor. With the consideration of system delay, this paper presents a systematic design method for the LCL-LC filtered grid-connected photovoltaic (PV) system. With this method, controller parameters and the active damping Feedback Coefficient are easily obtained by specifying the system stability and dynamic performance indices, and it is more convenient to optimize the system performance according to the predefined satisfactory region. Finally, the simulation results are presented to validate the proposed design method and control scheme.
