Aim of this work is the analysis of the flow in the stern region of a fully appended twin-screw hull by an URANSE simulation. The numerical tool consists of a finite volume code, where the convective terms are integrated by a third-order algorithm that, introducing a very small numerical diffusivity, permits to follow the evolution of the tip vortices and their interaction with the rudder. The movement of the propeller is resolved by a dynamic overlapping grids method. The numerical data are first verified and validated by comparison with measurements and then exploited in order to get a deep insight of both the velocity field and the pressure oscillation on the stern vault.
A complementary experimental and numerical study of the interference eect for a fast catamaran is presented. Resistance, sinkage and trim are collected by towing tank experiments for Froude number in the range from 0:2 to 0:8 for several separation distances and for the monohull. Resistance coefficient curves reveal the presence of two humps, the second one strongly depending on the separation length; high interference is observed in correspondence of the second hump. To gain a deeper insight into these behaviors, a complementary analysis is carried out by a numerical campaign; simulations are performed by means of an in-house unsteady RANS solver. Verication of numerical results is provided, together with validation, which is made by the comparison with both present and other experimental data. Agreement in terms of resistance coefficient is rather good, comparison error being always smaller than 2.2%.
We present a work in progress about extracting words from images of historical printed documents by using fast marching method. Segmentation is a process that allows an image to be divided into disjoint zones, so that extracted areas contain homogeneous characteristics. The numerical method, we used to segment images, is based on the theory of interface evolution, described by the eikonal equation. We adopted the fast marching technique to solve the upwind finite difference approximation of the eikonal equation. Segmentation of ancient documents is generally acknowledged as a very complicated problem because this kind of documents can be low quality, presenting local skew and several degradations due to old printing or ink stains.
