International Shipbuilding Progress - Volume 33, issue 386

Authors: Lewkowicz, A.K. | Das, D.K.

Article Type: Research Article

Abstract: A wind tunnel simulation of two boundary layer flows (with and without an adverse pressure gradient) on two surfaces with different roughness was carried out. One of the surfaces was covered throughout with an irregular coarse roughness and the other was identical but additionally overlaid with a large number of deformable nylon on tufts (to simulate the growth of biological fouling on a marine object). Detailed mean flow and turbulence measurements were carried out to perceive the effect of the overlayer on the boundary layer development with different pressure gradient conditions. Generally, the overlayer affected significantly a majority of …the monitored quantities, i.e., the physical growth, displacement, momemtum loss, wall friction, normal and shear turbulent stresses, mixing length, eddy viscosity, etc. However, with the pressure gradient (of nearly constant second derivative) the effect on the physical growth and the displacement thickness parameters was somewhat reduced. The latter flow resulted in a near equilibrium boundary layer at the rear of the test plate. Macro- and micro-scales of turbulence were hardly affected by the overlayer, but the dissipation length was reduced by it. A lag-entrainment method (modified here for the particular surface roughnesses) predicted the present experimental data well. Another family of integral methods did worse. Show more

DOI: 10.3233/ISP-1986-3338601

Citation: International Shipbuilding Progress, vol. 33, no. 386, pp. 174-186, 1986

Authors: Hills, W. | Welsh, M.

Article Type: Research Article

Abstract: Recent developments in computing technology and reduced hardware costs have encouraged the use of micro-based CAD workstations. The need for effective design procedures which utilize the attributes of such workstations is recognised. A system for generating a hull form of sufficient accuracy and fairness for use in preliminary design is described. The surface is defined using a set of bi-cubic B-spline surface patches although intermediate forms can be examined via a cubic spline 2-D or 3-D representation. While the mathematical methodology is less sophisticated than that which forms the basis of some of the more advanced systems, fundamental procedures are …adapted and structured in a way that ensures accurate and reliable results. This facilitates the rapid generation of hull forms at relatively low cost. These features provide the designer with a flexible and effective design tool which can be used in an environment where frequent changes may be necessary or a large number of alternative designs have to be examined e.g. at the conceptual or preliminary design stage. An application of the system to the design of a Ro-Ro type form is given. Show more

DOI: 10.3233/ISP-1986-3338602

Citation: International Shipbuilding Progress, vol. 33, no. 386, pp. 187-194, 1986