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Airborne Wind Energy is an emerging field in which simulation has an important role to play with system being more complex than encountered in classical wind power.

The first step toward simulation is defining a model, which can then be used for analytical computations or for simulation based on numerical computations.

The first level corresponds to static flight.

The second level enables to make some power estimation based on simple formula. The most famous one is Lloyds' formula based on a quasi-static approach.

The third level corresponds to kinematic simulator, for which parts of the effects of mass is neglected (inertia, but not necessarily weight).

The fourth level corresponds to dynamic simulator in which inertia are taken into account.

Simulators can also be categorized by the number of degrees of freedom or the number of bodies in the case of multibody simulation.

Multibody simulation might be needed for some aspects of system which are using flying pods for example.

Multibody simulation might be needed as well.

== Static flight ==

=== Static symmetric flight. ===

==== Equilibrium ====
When in static flight, the forces are balanced.

Aerodynamic force and line tension have to be considered. Weight might be neglected.

If weight and wind gradient are neglected, the behavior of the system is invariant by rotation around the wind axis.

The system can then be reduced to only two degrees of freedom which are the pitch of the kite and position with respect to the center of the wind window.

If gravity is taken into account, a symmetric kite has only two equilibrium positions which are at zenith or at nadir.

==== Stability analysis ====
Stability analysis was [https://forum.awesystems.info/uploads/short-url/qhbxF0hpdlMSesTwZ75ckJPDnaV.pdf conducted by Bryan] back in 1915<ref>The small oscillations of a kite, The aeronautical journal, October/December 1915 by Bryan</ref>

=== Asymmetric static flight on the side of the wind window ===

Other equilibrium positions can be reached if an asymmetry is created, either by moving mass away from plane of symmetry of kite, or if kite is not symmetric anymore.

== Quasi-static model ==
Mile Lloyds studied in 1980 the crosswind flight using a quasi-static model.<ref>[https://awesco.eu/awe-explained/Loyd1980.pdf Crosswind kite power], Miles Lloyds, The journal of Energy 1980</ref>

http://edge.rit.edu/edge/P15462/public/CAD/crosswind_kite.pdf

== Dynamic flight ==

=== 2D model ===
Nonlinear dynamics of a kite in flight was studied by Monica Geist in her master of science at University of Colorado Denver<ref>Non linear dynamics of a kite in flight, Monica Geist, Master of science. University of Colorado 1996</ref>

http://digital.auraria.edu/AA00003180/00001

A more recent study was done by Gonzalo Sanchez in 2006<ref>[https://www.researchgate.net/publication/262685061_Dynamics_and_Control_of_Single-Line_Kites Dynamics and Control of Single-Line Kites] , Gonzalo Sanchez-Arriaga 2006</ref>, and results applied in the field of Airborne Wind Energy by Filipo Trevesi<ref>[https://www.mdpi.com/1996-1073/14/22/7704 Flight Stability of Rigid Wing Airborne Wind Energy Systems] by Filipo Trevesi in Energies, 2021</ref>

=== 3D model ===
Moritz Diehl proposed a 3D model in 2001.<ref>[https://archiv.ub.uni-heidelberg.de/volltextserver/1659/ Real-Time Optimization for Large Scale Nonlinear Processes], Moritz Diehl, Phd thesis at University of Heidelberg, 2001</ref>

== Simulators ==
Here are a few open sources simulators which can be used to model AWE systems:

Specialized simulator:

* [https://bitbucket.org/ufechner/freekitesim/src/master/ FreeKiteSim], by Uwe Fechner
* [https://github.com/aenarete/KiteSimulators.jl KiteSimulators.jl] by Uwe Fechner
* [https://github.com/awegroup/MegAWES megAWES]: 3DoF & 6DoF kite dynamics, initially developed by Dylan Eijkelhof
* [https://github.com/awebox/awebox awebox]<ref>"''De Schutter, J.; Leuthold, R.; Bronnenmeyer, T.; Malz, E.; Gros, S.; Diehl, M. AWEbox: An Optimal Control Framework for Single- and Multi-Aircraft Airborne Wind Energy Systems. Energies 2023, 16, 1900. https://doi.org/10.3390/en16041900''[https://doi.org/10.3390/en16041900 "]</ref>
* [https://github.com/PREDICT-EPFL/openkite openkite]: OpenKITE is a ROS package for simulation, estimation and control of rigid-wing airborne wind energy kites. Developed at the Automatic Control laboratory EPFL as part of the AWESCO project.
* [https://github.com/kitextech/kitesim kitesim]: real time dynamic model of a tethered kite which can be useful for visualisation, parameter estimation, flight controller development and so forth for airborne wind turbines.
* [https://github.com/apastor3/laksa laksa]: LAgrangian Kite SimulAtor, developed at Universidad Carlos III de Madrid by Gonzalo Sánchez-Arriaga and Alejandro Pastor-Rodríguez
* [https://github.com/AlsonLee87/KiteEnergySystems KiteEnergySystems]: simulation framework for kite energy system using C++ language
* '''[https://github.com/ufechner7/TetheredKiteUAV_Simulink TetheredKiteUAV_Simulink]'''
* [https://github.com/ghorn/rawesome rawsome] : RAWESOME Airborne Wind Energy Simulation, Optimization and Modeling Environment

{| class="wikitable"
|+
!Simulator
!Degrees of freedom
!Language
!Winch model
!Kite network
|-
|megaAWES
|3/6
|Matlab/simulink
|Yes
|No
|-
|FreeKiteSim
|
|Python
|Yes
|No
|-
|KiteSimulators.jl
|
|Julia
|Yes
|No
|-
|
|
|
|
|
|-
|
|
|
|
|
|-
|
|
|
|
|
|}
General purpose simulators:

* Bullet
* Mujoco
* Exudyn<br />
<references />

Simulation for Airborne Wind Energy - Revision history

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