From FLP or "COMPUTATIONAL FLUID DYNAMICS", by John D. Anderson, Jr.
- Body forces, which act directly on the volumetric mass of the fluid element. These forces "act at a distance"; examples are gravitational, electric, and magnetic forces.
- Surface forces, which act directly on the surface of the fluid element.
This definition for me is not clear for whether it should be mathematically strict or physically correct. If the former then all calculations if following this integral should be called body force.
$$\mathbf{F}_{\mathrm{body}}=\int\limits_{V}\mathbf{f}(\mathbf{r})\mathrm{d}V$$
I believe that the Froude–Krylov force (in fluid dynamics) is a valid nature of body force and is normally in hydrodynamic communities called Archimedes force due to the acceleration field has no difference with Archimedes (buoyancy) force except direction.
But from Wiki:
A body force is distinct from a contact force in that the force does not require contact for transmission. Thus, common forces associated with pressure gradients and conductive and convective heat transmission are not body forces as they require contact between systems to exist.
Would this statement be inaccurate?
In case the body is fixed underwater but with ambient incident waves. So we only talk about the excitation force (no radiation here, for radiation is another similar topic), then, the current velocity field can induce acceleration field due to waves, which obviously has the nature of Froude-Krylove force. However for this force to be evaluated, the pressure has to be integrated over the body surface which again involves contact force.
So where I am lost in classification of the forces? Or should we decompose the total load into different components due to different mechanism like Froude-Krylove, scattering (some call scattering diffraction excluding FK-force).
