30 research outputs found
Polynomial cubic splines with tension properties
In this paper we present a new class of spline functions with tension properties. These splines are composed by polynomial cubic pieces and therefore are conformal to the standard, NURBS based CAD/CAM systems
VELOS: A VR Platform for Ship-Evacuation Analysis
“Virtual Environment for Life On Ships” (VELOS) is a multi-user Virtual Reality
(VR) system that aims to support designers to assess (early in the design
Process) passenger and crew activities on a ship for both normal and hectic
Conditions of operations and to improve ship design accordingly. This paper focuses
On presenting the novel features of VELOS related to both its VR and
Evacuation-specific functionalities. These features include: i) capability of multiple
Users’ immersion and active participation in the evacuation process, ii)
Real-time interactivity and capability for making on-the-fly alterations of environment
Events and crowd-behavior parameters, iii) capability of agents and
Avatars to move continuously on decks, iv) integrated framework for both the
Simplified and the advanced method of analysis according to the IMO/MSC 1033
Circular, v) enrichment of the ship geometrical model with a topological model
Suitable for evacuation analysis, vi) efficient interfaces for the dynamic specification and handling of the required heterogeneous input data, and vii) post
Processing of the calculated agent trajectories for extracting useful information
For the evacuation process. VELOS evacuation functionality is illustrated using
Three evacuation test cases for a ro-ro passenger ship
Shape-optimization of 2D hydrofoils using an Isogeometric BEM solver
In this paper, an optimization procedure, based on an Isogeometric BEM solver for the potential
ow, is developed and used for the shape optimization of hydrofoils. The formulation of the
exterior potential-
ow problem reduces to a Boundary-Integral Equation (BIE) for the associated
velocity potential exploiting the null-pressure jump Kutta condition at the trailing edge. The
numerical solution of the BIE is performed by an Isogeometric Boundary-Element Method (BEM)
combining a generic B-splines parametric modeler for generating hydrofoil shapes, using a set of
eight parameters, the very same basis of the geometric representation for representing the velocity
potential and collocation at the Greville abscissas of the knot vector of the hydrofoil's B-splines
representation. Furthermore, the optimization environment is developed based on the geometric
parametric modeler for the hydrofoil, the Isogeometric BEM solver and an optimizer employing
a controlled elitist genetic algorithm. Multi-objective hydrofoil shape optimization examples are
demonstrated with respect to the criteria i) maximum lift coefficient and ii) minimum deviation
of the hydrofoil area from a reference area
Ship-Hull Shape Optimization with a T-spline based BEM-Isogeometric Solver
In this work, we present a ship-hull optimization process combining a T-spline based parametric ship-hull model and an Isogeometric Analysis (IGA) hydrodynamic solver for the calculation of ship wave resistance. The surface representation of the ship-hull instances comprise one cubic T-spline with extraordinary points, ensuring C2C2 continuity everywhere except for the vicinity of extraordinary points where G1G1 continuity is achieved. The employed solver for ship wave resistance is based on the Neumann–Kelvin formulation of the problem, where the resulting Boundary Integral Equation is numerically solved using a higher order collocated Boundary Element Method which adopts the IGA concept and the T-spline representation for the ship-hull surface. The hydrodynamic solver along with the ship parametric model are subsequently integrated within an appropriate optimization environment for local and global ship-hull optimizations against the criterion of minimum resistance
VELOS : a VR platform for ship-evacuation analysis
Virtual Environment for Life On Ships (VELOS) is a multi-user Virtual Reality (VR) system that aims to support designers to assess (early in the design process) passenger and crew activities on a ship for both normal and hectic conditions of operations and to improve ship design accordingly. This article focuses on presenting the novel features of VELOS related to both its VR and evacuation-specific functionalities. These features include: (i) capability of multiple users’ immersion and active participation in the evacuation process, (ii) real-time interactivity and capability for making on-the-fly alterations of environment events and crowd-behavior parameters, (iii) capability of agents and avatars to move continuously on decks, (iv) integrated framework for both the simplified and advanced method of analysis according to the IMO/MSC 1033 Circular, (v) enrichment of the ship geometrical model with a topological model suitable for evacuation analysis, (vi) efficient interfaces for the dynamic specification and handling of the required heterogeneous input data, and (vii) post-processing of the calculated agent trajectories for extracting useful information for the evacuation process. VELOS evacuation functionality is illustrated using three evacuation test cases for a ro–ro passenger ship
Shape-preserving interpolation on surfaces via variable-degree splines
This paper proposes two, geodesic-curvature based, criteria for shape-preserving interpolation on smooth surfaces, the first criterion being of non-local nature, while the second criterion is a local (weaker) version of the first one. These criteria are tested against a family of on-surface C2 splines obtained by composing the parametric representation of the supporting surface with variable-degree (≥3) splines amended with the preimages of the shortest-path geodesic arcs connecting each pair of consecutive interpolation points. After securing that the interpolation problem is well posed, we proceed to investigate the asymptotic behaviour of the proposed on-surface splines as degrees increase. Firstly, it is shown that the local-convexity sub-criterion of the local criterion is satisfied. Second, moving to non-local asymptotics, we prove that, as degrees increase, the interpolant tends uniformly to the spline curve consisting of the shortest-path geodesic arcs. Then, focusing on isometrically parametrized developable surfaces, sufficient conditions are derived, which secure that all criteria of the first (strong) criterion for shape-preserving interpolation are met. Finally, it is proved that, for adequately large degrees, the aforementioned sufficient conditions are satisfied. This permits to build an algorithm that, after a finite number of iterations, provides a C2 shape-preserving interpolant for a given data set on a developable surface
A BEM-ISOGEOMETRIC method for the ship wave-resistance problem
In the present work IsoGeometric Analysis is applied to the solution of the Boundary
Integral Equation associated with the Neumann-Kelvin problem and the calculation of the
wave resistance of ships. As opposed to low-order panel methods, where the body is
represented by a large number of quadrilateral panels and the velocity potential is assumed
to be piecewise constant (or approximated by low degree polynomials) on each panel, the
isogeometric concept is based on exploiting the same NURBS basis, used for representing
exactly the body geometry, for approximating the singularity distribution (and, in general,
the dependent physical quantities). In order to examine the accuracy of the present method,
numerical results obtained in the case of submerged and surface piercing bodies are
* Corresponding author. Tel: (+30) 2107721138, Fax: (+30) 2107721397, e-mail: [email protected]
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compared against analytical solutions, experimental data and predictions provided by the
low-order panel or other similar methods appeared in the pertinent literature, illustrating
the superior efficiency of the isogeometric approach. The present approach by applying
Isogeometric Analysis and Boundary Element Method to the linear NK problem has the
novelty of combining modern CAD systems for ship-hull design with computational
hydrodynamics tools
An Isogeometric Boundary Element Method for 3D lifting flows using T-splines
In this paper an Isogeometric Boundary Element Method for three-dimensional lifting flows based on Morino’s (Morino and Kuo, 1974) formulation is presented. Analysis-suitable T-splines are used for the representation of all boundary surfaces and the unknown perturbation potential is approximated by the same T-spline basis used for the geometry. A novel numerical application of the so-called Kutta condition is introduced that utilises the advantages of isogeometric analysis with regard to the smoothness of the trailing edge curve basis functions. The method shows good agreement with existing experimental results and superior behaviour when compared to a low order panel method. The effect of the tip singularity on Kutta condition is also investigated for different levels of refinement and positions of the trailing edge collocation points
Isogeometric Boundary-Element Analysis for the Wave-Resistance Problem using T-splines
In this paper we couple collocated Boundary Element Methods (BEM) with unstructured analysis suitable
T-spline surfaces for solving a linear Boundary Integral Equation (BIE) arising in the
context of a ship-hydrodynamic problem, namely the so-called Neumann-Kelvin problem, following
the formulation by Brard (1972) [1] and Baar & Price (1988) [2]. The local-refinement capabilities
of the adopted T-spline bases, which are used for representing both the geometry of the hull and
approximating the solution of the associated BIE, in accordance with the Isogeometric concept
proposed by Hughes et al. (2005) [3], lead to a solver that achieves the same error level for many
fewer degrees of freedom as compared with the corresponding NURBS-based Isogeometric-BEM
solver recently developed in Belibassakis et al. (2013) [4]. In this connection, this paper makes a
step towards integrating modern CAD representations for ship-hulls with hydrodynamic solvers of
improved accuracy and efficiency, which is a prerequisite for building efficient ship-hull optimizers
Shape optimization of conductive-media interfaces using an IGA-BEM solver
In this paper, we present a method that combines the Boundary Element Method (BEM) with IsoGeometric Analysis (IGA) for numerically solving the system of Boundary Integral Equations (BIE) arising in the context of a 2-D steady-state heat conduction problem across a periodic interface separating two conducting and conforming media. Our approach leads to a fast solver with high convergence rate when compared with low-order BEM. Additionally, an optimization framework comprising a parametric model for the interface’s shape, our IGA-BEM solver, and evolutionary and gradient-based optimization algorithms is developed and tested. The optimization examples demonstrate the efficiency of the framework in generating optimum interfaces for maximizing heat transfer under various geometric constraints