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

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

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

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 flow, is developed and used for the shape optimization of hydrofoils. The formulation of the exterior potential-flow 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

Shape optimization and inverse problems in heat transfer employing an IGA-BEM approach

This work focuses on the 2-D steady-state heat conduction problem across the periodic interface separating two conducting and conforming material strips of infinite length. Our solver combines the Boundary Element Method (BEM) with the Iso-Geometric Analysis (IGA) concept and exhibits, as it will be demonstrated, superior convergence characteristics compared to classical panel methods. In this presentation, emphasis will be placed on the application of the developed IGABEM solver in shape optimization of these separating interfaces, under various geometric constraints, with the aim of heat transfer maximization. Additionally, handling of inverse problems, where we seek the interface shape achieving a given heat transfer value, will be also discussed and presented

HIGH FRICTION COEFFICIENT OF VERTICALLY ALIGNED CARBON-NANOTUBES: A MOLECULAR DYNAMICS SIMULATION

In this study, we perform non-equilibrium molecular dynamics simulations to study the friction coefficient between two carbon nanotubes grown vertically on two separate graphene layers, which are placed parallel to each other with one set in motion. Significantly high values of approximately 3 and 1.5 are computed for the static and dynamic friction coefficients, respectively. The effects of nanotubes overlapping length, speed of relative movement on the dynamic friction coefficient are also studied in our work. According to our results, and in agreement with the standard model of friction, dynamic friction between the two carbon nanotubes remains constant, regardless of the relative speed of their movement

Construction of smooth branching surfaces using T-splines

Abstract The request for designing or reconstructing objects from planar cross sections arises in various applications, ranging from CAD to GIS and Medical Imaging. The present work focuses on the “one-to-many” branching problem, where one of the planes can be populated with many, possibly tortuous and densely packed, contours. The proposed method combines the proximity information offered by the Euclidean Voronoi diagram with the concept of surrounding curve, introduced in Gabrielides et al. (2007), and T-splines technology Sederberg et al. (2003) for securing a flexible and portable representation. Our algorithm delivers a single cubic T-spline that deviates from the given contours less than a user-specified tolerance, measured via the so-called discrete Fréchet distance Eiter and Mannila (1994) and is C2 everywhere except from a finite set of point-neighborhoods. Subject to minor enrichment, the algorithm is also capable to handle the “many-to-many” configuration as well as the global reconstruction problem involving contours on several planes

PHONON HEAT TRANSPORT IN TWO-DIMENSIONAL PHAGRAPHENE-GRAPHENE SUPERLATTICE

In this study, we perform non-equilibrium molecular dynamics simulations to investigate phonon heat transport in a two-dimensional superlattice with equal-sized domains of graphene and phagraphene. Ef fects on conductivity are examined in relation to modifications of domain sizes, the length of employed nanoribbons and temperature differences between the thermal baths used with the superlattices. We have determined that effective thermal conductivity reaches a minimum value of 155 W/mK for ribbons with a superlattice period of 12.85 nm. This minimum thermal conductivity of graphene-phagraphene superlattices at infinite length is approximately 5%, of pure graphene thermal conductivity, and ≈ 50% of phagraphene thermal conductivity. Minimum thermal conductivity occurs at the transition from coherent to incoherent phonon transport, where the superlattice period is comparable to the phonon coherence lengt

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) and Baar and Price (1988). 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), 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). 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

An isogeometric BEM for exterior potential-flow problems around lifting bodies

In this paper, the Isogeometric Analysis (IGA) concept is combined with the Boundary Element Method (BEM) for solving the exterior Neumann problem associated with the steady lifting flow around a hydrofoil. The formulation of the problem is based on a Boundary Integral Equation for the associated velocity potential combined with the null-pressure jump Kutta condition at the trailing edge. The developed Isogeometric-BEM is based on a parametric NURBS representation of the hydrofoil and employs the very same basis for representing the velocity potential. The Boundary Integral Equation is numerically solved by collocating at the Greville abscissas of the knot vector of the hydrofoil's parametric representation. Numerical error analysis of the Isogeometric-BEM using h-renement is performed and compared with classical low-order panel methods