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Topic for open discussion:
Tether Sag for a kite system
  • Wind force on tethers.   Changing winds. Changing directions of wind.
  • Gravity effect on tethers
  • Negative lift
  • Drag
  • Waves 
  • Oscillations
  • Turbulence
  • Changing tensions
  • Tension
  • Catenary
  • Tether slope at any tether station
  • Tether slope at wing's bridle convergence
  • Tether slope at ground base or line winch
  • Segmental environments along an active tether
  • Idealizations
  • Idealizations missing actuals  
  • Breakaway types and the effect of tehter sag just before breaks
  • Practical secondary uses of tehter sag
  • Tether sag effects on control systems
  • How tether sag may damp effects of gusts at the wing-set realm
  • Lateral stay lines
  • Downwind stay lines
  • Gain of moisture
  • Alighting birds
  • Insect impacts
  • Insolation effects, shadowing by clouds or other aircraft
  • Temperature of the air over tether segmeents
  • Effects of tether sag on AWES dedicated to producing electricity.
  • Effects of tether sag on AWES dedicated to towing ships, boats,
  • Effects of tether sag on AWES dedicated to pumping water.
  • Effects of tether sag on AWES dedicated to ____?______. 
Send AWE notes and topic replies to editor@upperwindpower.com
Sept. 22, 2020, post by Joe Faust
 Paper for study. Authors face kite-tether sag.

The Influence of Tether Sag on Airborne Wind Energy Generation  
Filippo Trevisi, Mac Gaunaa, and Michael Mcwilliam                 [d]
DTU Wind Energy         dtu.dk/english/about/profile/history
---------------------references state in the paper:
References [1] I. Argatov, P. Rautakorpi, R. Silvennoinen, Apparent wind load effects on the tether of a kite power generator, Journal of Wind Engineering and Industrial Aerodynamics 99 (10) (2011) 1079–1088. doi: 10.1016/j.jweia.2011.07.010.

[2] F. Bauer, R. M. Kennel, C. M. Hackl, F. Campagnolo, M. Patt, R. Schmehl, Drag power kite with very high lift coefficient, Renew. Energy 118 (2018) 290–305. doi:10.1016/j.renene.2017.10.073.

[3] F. Trevisi, M. Gaunaa, M. McWilliam, Unified engineering models for the performance and cost of Ground-Gen and Fly-Gen Crosswind Airborne Wind Energy Systems, Submitted to Renewable Energy (2020).

[4] F. Trevisi, Configuration Optimisation of Kite-Based Wind Turbines, Master’s thesis, Technical University of Denmark (2019). doi:10.13140/RG.2.2.24256.28160.

[5] R. van der Vlugt, A. Bley, M. Noom, R. Schmehl, Quasi-steady model of a pumping kite power system, Renewable Energy 131 (2019) 83–99. doi:10.1016/j.renene.2018.07.023.

[6] S. Dunker, Tether and bridle line drag in airborne wind energy applications, in: R. Schmehl (Ed.), Airborne Wind Energy. Green Energy and Technology. Springer, Singapore, 2018, pp. 29–56. doi: 10.1007/978-981-10-1947-0_2.

[7] N. Bigi, A. Nˆeme, K. Roncin, J.-B. Leroux, G. Bles, C. Jochum, Y. Parlier, Analytical tether model for static kite flight, in: R. Schmehl (Ed.), Airborne Wind Energy. Green Energy and Technology. Springer, Singapore, 2018, pp. 57–78. doi:10.1007/978-981-10-1947-0_3.

[8] H. Irvine, M. I. of Technology, Cable structures, Vol. 1, 1981.

[9] B. Houska, M. Diehl, Optimal control of towing kites, Proceedings of the 45th Ieee Conference on Decision and Control (2006) 2693–2697. doi:10.1109/CDC.2006.377210.
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