Add moment coefficient calculations around specified point

[1-Bart-1]

[ufechner7]

Which reference frame shall be used to define the point?

[1-Bart-1]

The principal kite body frame: https://en.wikipedia.org/wiki/Euler%27s_equations_(rigid_body_dynamics). Centered in the center of mass of the kite.

[ufechner7]

So which name would you give it? We already have the Kite reference frame, short K, and the kite sensor reference frame, short KS. See: https://ufechner7.github.io/KiteUtils.jl/stable/reference_frames/

By the way, the origin of the Kite reference frame is NOT the center of mass, but P_C, the midpoint between the two outer points. And it is not really attached to the kite, because it stays constant when the depower settings change.

And how is it defined?

See also: #52

[1-Bart-1]

For the dynamics to be correct the reference frame has to be centered in the center of mass.
KP would be the name then.

[1-Bart-1]

From the python development branch:

            # (1) Panel aerodynamic center in global frame:
            panel_ac_global = panel_i.aerodynamic_center  # 3D [x, y, z]

            # (2) Convert local (2D) pitching moment to a 3D vector in global coords.
            #     Use the axis around which the moment is defined,
            #     which is the z-axis pointing "spanwise"
            moment_axis_global = panel_i.z_airf

            # Scale by panel width if your 'moment[i]' is 2D moment-per-unit-span:
            M_local_3D = moment[i] * moment_axis_global * panel_i.width

            # (3) Vector from panel AC to the chosen reference point:
            r_vector = panel_ac_global - reference_point  # e.g. CG, wing root, etc.

            # (4) Cross product to shift the force from panel AC to ref. point:
            force_global_3D = np.array([fx_global_3D, fy_global_3D, fz_global_3D])
            M_shift = np.cross(r_vector, force_global_3D)

            # (5) Total panel moment about the reference point:
            M_ref_panel = M_local_3D + M_shift

[ufechner7]

Do you suggest to introduce a CAD reference frame? If yes, how would it be defined?