PartialVolume damping

[RaphaelGebhart]

The definition/use of:

• d = k_volume_damping*sqrt(abs(2*L/(V*max(density_derp_h, 1e-10)))) "Friction factor for coupled boundaries"
• k_volume_damping "Damping factor multiplicator"
• density_derp_h "Partial derivative of density by pressure at constant specific enthalpy"

in ThermofluidStream.Boundaries.Internal.PartialVolume is in my opinion not fully intuitive/not complete correct:

• For an incompressible fluid + ThermofluidStream.Boundaries.Reservoir one can obtain k_volume_damping = sqrt(2)*D, with damping ratio D, i.e. k_volume_damping = sqrt(2) yields critical damping.
• For an ideal gas, i.e. ThermofluidStream.Media.myMedia.Air.DryAirNasa, + ThermofluidStream.Boundaries.Volume one can obtain density_derp_h = cp/(R^2*T) = kappa/((kappa-1)*R*T) = kappa^2/((kappa-1)*a^2), with velocity of sound a, such that
  k_volume_damping = sqrt(2)*D*sqrt(density_derp_h/a^2) = sqrt(2)*D*kappa/(kappa-1), i.e. k_volume_damping = sqrt(2)*kappa/sqrt(kappa-1) yields critical damping.

Hence i would change:

• k_volume_damping to damping ratio D
• density_derp_h to velocity of sound a (partial derivative of pressure by density (commonly at constant specific entropy))

Of course we could also try to use Bessel filter or other filter characteristics.

And i would recommend to enhance the docu....

[RaphaelGebhart]

One more remark: Note that the TFS damping approach yields (for a single DOF system) the same equations as mentioned in Maheo [1] (compare with equation (30) and (31)) of the socalled Bulk Velocity Method (Von Neumann, Richtmeyer (1950) [2] and extended by Landshoff (1955) [3]), that is said to be used " in most commercially available software programs developed for solving dynamic problems (such as Abaqus, Ls-Dyna)" [1, page 6].

[1] Maheo https://link.springer.com/article/10.1007/s00466-012-0708-8
[2] Van Neumann, Richtmeyer https://pubs.aip.org/aip/jap/article/21/3/232/159292/A-Method-for-the-Numerical-Calculation-of
[3] Landshoff https://www.osti.gov/search/author:%22Landshoff,%20R%22)https://www.osti.gov/biblio/4364774