Determination of the Viscous Drag of a Ship Model

Abstract

In recent years, experimental results obtained by means of the wake survey method have indicated that the viscous drag of a ship model varies with the Froude number; later studies have tended to confirm these findings. The present work was undertaken to establish the validity of this variation. In order to avoid the principal sources of inaccuracy of previous work, modifications to the equipment were made. Also, to obtain viscous drag, the authors applied a refinement of the Betz-Tulin formula.

On irrotational flows equivalent to the boundary layer and wake

“…The data given in Reference m E - [8] indicate, however, that, at a section at 0.6 of the length behind the stern of a ship model, u_, is zero within the accuracy of the measurements.…”

“…Comparison with the form of ( 16) now shows that, to the second order of accuracy, the irrotational flow about the displaced surface satisfies the specified boundary condition (8) at the edge of the boundary layer and wake.…”

“…Because u., occurs both in the integrand and in the denominator of the expression for the drag, it is not immediately evident which of the two bounds is the larger. Denoting these bounds by D^when u = and D" when u = u » and applying the aforementioned approximations, we obtain from (87), The latter form was given by Tzou and Landweber [8].…”

Developing methods of decomposing the physical resistance components acting on a hydrofoil

“…Per the method, the velocity field in the rotational wake region (with non-zero vorticity) must be replaced with an irrotational one. This may be done by interpolating into the rotational flow region [19] using the surrounding irrotational velocity field. To do this, the rotational wake was first identified using the criterion on the vorticity magnitude |ω| > 0.1s −1 (small value chosen to filter out cells with non-zero vorticity due to numerical diffusion).…”

“…The momentum deficit in the wake may be integrated over a wake plane that is perpendicular to the foil's direction of motion to yield a value of viscous resistance -an idea first put forth in [21]. Many different formulations have since been developed and used in naval and yachting contexts [19,[22][23][24]. A summary of formulas is given in [25].…”