Effect of the blade number on the marine propeller performance

This paper deals with numerical simulation of stationary flow around a marine propeller. The aim is to reproduce the hydrodynamic turbulent flow around the Wageningen B serie propellers in open water using the ANSYS FLUENT code and the RANS approach. The computational domain consists of an inter-blade channel with periodic boundaries, meshed with tetrahedral cells. The turbulence is modeled with the k-ω. The obtained results provide good agreement with the available experimental data and show that the blades number affects considerably the marine propellers performances. It is interesting to notice that the six blades propeller is the best adapted one for the open water flows.

The Generation of 3D Trimmed Elements for NURBS-Based Isogeometric Analysis

In conventional 3D NURBS-based isogeometric analysis (IGA), it is required to generate a discretized 3D model from the imported CAD model. Since a CAD file only contains surface information of the 3D object, generation of 3D mesh and trivariate basis functions are required for the IGA. In CAD system, the Boolean difference operation, so-called “trimming” is frequently employed for creating complex objects. To directly utilize the trimming information into analysis, trimmed elements need to be defined and their integration schemes are also needed. In this paper, trimmed elements searching, classification, decomposition and integration rules are presented. In the process, seven types of generalized trimmed elements are defined. Since covering all possible 3D geometries is not possible, three out of seven types of trimmed elements formed by extrusion are treated. The decomposition rule of trimmed elements is introduced and curved tetrahedral cells are adopted to integrate the trimmed elements. For numerical integration of curved tetrahedral cells, 3D NEFEM-like integration scheme has been developed. For the demonstration of the usage of the developed elements, two numerical examples of trimmed volume are treated.

SNUB 24-CELL DERIVED FROM THE COXETER–WEYL GROUP W(D4)

Snub 24-cell is the unique uniform chiral polytope in four dimensions consisting of 24 icosahedral and 120 tetrahedral cells. The vertices of the four-dimensional semiregular polytope snub 24-cell and its symmetry group (W(D4)/C2): S3 of order 576 are obtained from the quaternionic representation of the Coxeter–Weyl group W(D4). The symmetry group is an extension of the proper subgroup of the Coxeter–Weyl group W(D4) by the permutation symmetry of the Coxeter–Dynkin diagram D4. The 96 vertices of the snub 24-cell are obtained as the orbit of the group when it acts on the vector Λ = (τ, 1, τ, τ) or on the vector Λ = (σ, 1, σ, σ) in the Dynkin basis with [Formula: see text] and [Formula: see text]. The two different sets represent the mirror images of the snub 24-cell. When two mirror images are combined it leads to a quasiregular four-dimensional polytope invariant under the Coxeter–Weyl group W(F4). Each vertex of the new polytope is shared by one cube and three truncated octahedra. Dual of the snub 24-cell is also constructed. Relevance of these structures to the Coxeter groups W(H4) and W(E8) has been pointed out.

Decomposition of Hexahedral Block Topology to Generate Initial Tetrahedral Grids for Complex Configurations

Most three dimensional tetrahedral grid generators can refine an initial grid in matter of seconds. But making an initial tetrahedral grid for complex geometry can be a tedious and time consuming task. This paper describes a novel procedure for generation of starting tetrahedral cells using hexahedral block topology. Hexahedral blocks are arranged around an aerodynamic body to fill-up a computational flow domain. Each of the hexahedral blocks is then decomposed into six tetrahedral elements to obtain an initial tetrahedral grid around the same aerodynamic body. This resulted in an algorithm that enables users to produce starting tetrahedral grids for variety of aerodynamic configurations. To construct an initial starting tetrahedral grid suitable for computational flow simulations, representing a solid surface geometry (fuselage or a wing section) attached to a plane-of-symmetry, a topology containing at least 5 hexahedral blocks is required. This results in an initial starting grid consisting of 30 tetrahedral cells with 74 faces and 16 vertices, which is the same number of vertices as for the hexahedral blocks. Since the number of vertices and their coordinate locations are kept the same, a connectivity matrix can be produced to describe the forming faces of the tetrahedral grid. This procedure was performed for a single block, 5-block, and 9-block topologies to produce starting tetrahedral cells for numerous domain size and shapes.