PT-Stokes wall shear stress model implementation

This software implements the new wall shear stress model put forward in Alpresa et al. (2018a, b)  for orbital shakers. The main script is PTStokesInput, which demonstrates how to use the two main functions PT and PTStokes.  

PT provides the velocity and surface elevation in an orbital shaker at a given location (x,y) and time t as a function of the depth z according to the potential flow solution in Reclari et al. (2014). 

PTStokes computes the wall shear stress in an orbital shaker as a given location as a function of time according to Alpresa et al (2018b).

----

Paola Alpresa, Peter Weinberg, Spencer Sherwin, Maarten van Reeuwijk (2018a),  Orbitally shaken shallow fluid layers. Part 1. Regime classification, Physics of Fluids, https://doi.org/10.1063/1.4996916.

Paola Alpresa, Peter Weinberg, Spencer Sherwin, Maarten van Reeuwijk (2018b), Orbitally shaken shallow fluid layers. Part 2. An improved wall shear stress model. Physics of Fluids, https://doi.org/10.1063/1.5016343.

M. Reclari, M. Dreyer, S. Tissot, D. Obreschkow, F. M. Wurm, and M. Farhat (2014), Surface wave dynamics in orbital shaken cylindrical containers, Physics of Fluids 26, 052104.