Resistance results

The forces data can be accessed trough the menu options View results>Forces on Boundaries and View results>Forces Graph or by using the corresponding icons of the Tdyn toolbar (see Figure 65).

Figure 65. Forces on boundaries and Forces graph icons.

The resulting data can be compared with the resistance values of the model, using the standard decomposition given by:

 

CT = Cv + Cw = (1+kCf  + Cw

Being CT the total resistance coeficient, Cv = 0.5·VFx/(r·S·ν2) the viscous drag coefficient and Cw = 0.5·PFx/(r·S· ν2) the wave resistance coefficient. Where r is the fluid density, S is the wetted area and ν the velocity of the analysis.

We can obtain the viscous drag coefficient by,

 

Cv = (1+k)*0.075/(log10(Re)-2)2

Experimentally a value of k» 0.09 is obtained, and since  Re = ρ·ν·L/μ = 1.45·107, we can estimate Cv = 3.07·10-3, while the result of our calculation[1] is Cv  = 2.90·10-3.

The experimental data of the wave drag Cw» 1.5·10-3, can be compared1 with the pressure force obtained in the simulation Cw = 1.40·10-3.

As can be seen both values are very similar to the experimental ones.