C. G. Politis

An isogeometric BEM for exterior potential-flow problems in the plane

In this paper, the isogeometric concept introduced by Hughes, in the context of Finite Element Method, is applied to Boundary Element Method (BEM), for solving an exterior planar Neumann problem. The developed isogeometric-BEM concept is based on NURBS, for representing the exact body geometry and employs the same basis for representing the potential and/or the density of the single layer. In order to examine the accuracy of the scheme, numerical results for the case of a circle and a free-form body are presented and compared against analytical solutions. This enables performing a numerical error analysis, verifying the superior convergence rate of the isogeometric BEM versus low-order BEM. When starting from the initial NURBS representation of the geometry and then using knot insertion for refinement of the NURBS basis, the achieved rate of convergence is O(DoF-4). This rate may be further improved by using a degree-elevated initial NURBS representation of the geometry (kh-refinement).

A BEM-ISOGEOMETRIC METHOD WITH APPLICATION TO THE WAVEMAKING RESISTANCE PROBLEM OF SHIPS AT CONSTANT SPEED

In the present work IsoGeometric Analysis (IGA), initially proposed by Hughes et al (2005), is applied to the solution of the boundary integral equation associated with the Neumann-Kelvin (NK) problem and the calculation of the wave resistance of ships, following the formulation by Brard (1972) and Baar & Price (1988). 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 NURBS basis, which is used for representing exactly the body geometry and adopts the very same basis functions for approximating the singularity distribution (or in general the dependent physical quantities). In order to examine the accuracy of the present method, in a previous paper Belibassakis et al (2009), numerical results obtained in the case of submerged bodies are compared against analytical and benchmark solutions and low-order panel method predictions, illustrating the superior efficiency of the isogeometric approach. In the present paper we extent previous analysis to the case of wavemaking resistance problem of surface piercing bodies. The present approach, although focusing on the linear NK problem which is more appropriate for thin ship hulls, it carries the IGA novelty of integrating CAD systems for ship-hull design with computational hydrodynamics solvers.Copyright

VELOS - A VR environment for ship applications: current status and planned extensions

Virtual Environment for Life On Ships (VELOS) is a multi-user Virtual Reality (VR) system that supports 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 the ship design accordingly [10]. Realistic simulations of behavioral aspects of crowd in emergency conditions require modeling of panic aspects and social conventions of inter-relations. The present paper provides a description of the enhanced crowd modeling approach employed in VELOS for the performance of ship evacuation assessment and analysis based on the guidelines provided by IMO’s Circular MSC 1238/2007 [20].

Motions Effect for Crowd Modeling Aboard Ships

Pre-computed ship-motion history has been used in the multi-user Virtual Reality (VR) system VELOS in conjunction with a kinematically-oriented inclination steering behavior as simple means for considering the effects of ship motion on simulated passengers’ movement. This first approach does not account for the dynamic nature of the phenomenon, thus ignoring motion accelerations. Ship-motion accelerations, however, are critical to the assessment of a person’s balancing and/or sliding aboard ships and consequently to its capability of performing an assigned task. In this work, we are focusing on the exploitation of pre-computed ship motions and accelerations and we investigate the usage of the concepts of Motion-Induced Interruptions (MIIs) and tipping coefficients in modeling the effects of ship-motion accelerations on passengers.