Add a new improved version of the kp penstock image

[dietmarw]

This is a follow-up from #21. It would be nice to have a better quality image for the explanation of the KP method currently stored in besad.png:

[pandeysudan1]

I think the initial figure was produced/referenced from MSc thesis workout and presented at B. R. Sharefi, ‘Modeling for Control of Hydropower Systems’, Master’s thesis, Telemark University College, Porsgrunn, Norway, 2011.

This figure was created for "Staggered-grid spatial discretization of the penstock for mass and momentum balance." The penstock of length L_pvis divided into N segments where pressure nodes X_1, X_2, ..... X_N-1 are located at the centers of control volumes, and mass-flow nodes S_1, S_2, ....., S_N are located at the interfaces between them. The upper row represents the momentum-balance control volumes, while the lower row corresponds to the mass-balance (continuity) control volumes. Inputs from the headwater and tailwater define the hydraulic boundary conditions p_i, mdot_i. This staggered arrangement eliminates pressure–velocity decoupling and provides numerical stability for solving the one-dimensional compressible-elastic flow equations used in the OpenHPL.Waterway.Penstock model. However, there exists a better numerical solution than this for the penstock modeling. The model is from KP numerical scheme and is modeled as PenstockKP on OpenHPL.

The svg version is created now at:

[pandeysudan1]

This SVG was made in Mathcha.io, so it might not render correctly in OpenModelica. If that happens, we can recreate it in Inkscape, but it takes much longer and is a bit tedious.

[dietmarw]

Thanks @pandeysudan1 I added a slightly cleaned up version of the file you provided. Due to it's rather experimental nature of the model I doubt it has much practical use at the moment. But we'll keep the model for the time being.