arXiv subjects

Ali C. Kheirabadi

Publications and source records attributed to Ali C. Kheirabadi.

3 recordsLinked to original sources

arXiv2020

A Dynamic Parametric Wind Farm Model for Simulating Time-varying Wind Conditions and Floating Platform Motion

This paper introduces a dynamic parametric wind farm model that is capable of simulating floating wind turbine platform motion coupled with wake transport under time-varying wind conditions. The simulator is named FOWFSim-Dyn as it is a dynamic extension of the previously developed steady-state Floating Offshore Wind Farm Simulator (FOWFSim). One-dimensional momentum conservation is used to model dynamic propagation of wake centerline locations and average velocities, while momentum recovery is approximated with the assumption of a constant temporal wake expansion rate. Platform dynamics are captured by treating a floating offshore wind farm as a distribution of particles that are subject to aerodynamic, hydrodynamic, and mooring line forces. The finite difference method is used to discretize the momentum conservation equations to yield a nonlinear state-space model. Simulated data are validated against steady-state experimental wind tunnel results obtained from the literature. Predictions of wake centerlines differed from experimental results by at most 8.19% of the rotor diameter. Simulated wake velocity profiles in the far-wake region differed from experimental measurements by less than 3.87% of the free stream wind speed. FOWFSim-Dyn thus possesses a satisfactory level of fidelity for engineering applications. Finally, dynamic simulations are conducted to ensure that time-varying predictions match physical expectations and intuition.

physics.flu-dyn↗

arXiv2020

Distributed Economic Model Predictive Control -- Addressing Non-convexity Using Social Hierarchies

This paper introduces a novel concept for addressing non-convexity in the cost functions of distributed economic model predictive control (DEMPC) systems. Specifically, the proposed algorithm enables agents to self-organize into a hierarchy which determines the order in which control decisions are made. This concept is based on the formation of social hierarchies in nature. An additional feature of the algorithm is that it does not require stationary set-points that are known a priori. Rather, agents negotiate these targets in a truly distributed and scalable manner. Upon providing a detailed description of the algorithm, guarantees of convergence, recursive feasibility, and bounded closed-loop stability are also provided. Finally, the proposed algorithm is compared against a basic parallel distributed economic model predictive controller using an academic numerical example.

eess.SY↗

arXiv2020

Social Hierarchy-based Distributed Economic Model Predictive Control of Floating Offshore Wind Farms

This paper implements a recently developed social hierarchy-based distributed economic model predictive control (DEMPC) algorithm in floating offshore wind farms for the purpose of power maximization. The controller achieves this objective using the concept of yaw and induction-based turbine repositioning (YITuR), which minimizes the overlap areas between adjacent floating wind turbine rotors in real-time to minimize the wake effect. Floating wind farm dynamics and performance are predicted numerically using FOWFSim-Dyn. To ensure fast decision-making by the DEMPC algorithm, feed-forward neural networks are used to estimate floating wind turbine dynamics during the process of dynamic optimization. For simulated wind farms with layouts ranging from 1-by-2 to 1-by-5, an increase of 20% in energy production is predicted when using YITuR instead of greedy operation. Increased variability in wind speed and direction is also studied and is shown to diminish controller performance due to rising errors in neural network predictions.

eess.SY↗