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Empirical evaluation of hierarchical higher order face cluster radiosity
No full textThe report evaluates our implementation of the hiearchical higher order face cluster radiosity method and compares it with hierachical radiosity with volume clusters for input scenes composed of highly tessellated surfaces
An optimization problem of combustion in open flow
Get PDFDescription of a method for optimization of external combustion in linear formulation. This method can be used for different optimization problems related to combustion
Anatomical shape reconstruction and manufacturing: solving topological changes of lumen vessel trough geometric approach
Get PDFOver the last years there has been an increasing growth of interest in Rapid Prototyping (RP) techniques applied to various fields of medicine. RP makes it possible, in vascular surgery, to produce accurate anatomic replicas of patient vessels. These replicas can help the customization of surgical invasive interventions such as in situ stent-graft insertion in carotid region.
The main goal of this work is to obtain high quality in lumen reconstruction and manufacturing replicas by RP technique. This goal is achieved through the complete control of each phase of the generating process. We present a semi-automatic method for carotid lumen reconstruction based on Boundary Representation (BRep). All parameters influencing the quality of the shape reconstruction are presented and discussed: shape acquisition, shape reconstruction and shape manufacturing. The shape acquisition starts by extracting the points belonging to the boundary of the lumen
vessel, from Computer Tomography (CT) images. These points, parameterised in a vector, are the input data of the shape reconstruction algorithm based on B-Spline interpolation. The B-Spline type for representing curves and surfaces were chosen because of their properties of continuity and local control.
In the shape reconstruction stage we had to face problems due to the topological change on the vessel structure. For vessel regions where there are not changes of topology, we use the closed B-Spline curves (belonging to adjacent acquisition planes) as generating curves to build a B-Spline surface. For vessel regions with at least a change of topology (ex. bifurcation region) our algorithm split automatically the involved curves to obtain three rectangular B-Spline patches. Such patches are joined together to obtain the bifurcation vessel lumen. The set of lumen surfaces is then inserted in a Boundary Representation in order to get a valid solid. To analyse the quality of the reconstructed shapes, the final object is compared with the acquisition image. This solid is correctly tessellated in triangles to produce the data format used by the RP devices (STL)
Design of the hardware abstraction layer for the 3d acquisition system of AILUN and CRS4
Get PDFDuring development of software we’ve discovered that would be better divide
hardware management from all the other parts of code.
We needed to achieve many results:
a modular, manageable and portable code (from windows to Linux);
support of a loto of cameras and runtime choice of cameras;
de-coupling from management of different devices inside th acquisition system;
unified driver handling system (open, close, RTacquire e DSacquire) simplifies drivers development by people who do not belong to the team. To achieve these goals we have re-engineered the code that communicates with the hardware and we’ve developed a Hardware Abstraction Layer using techniques well known in software engineering (design patterns, petri nets, and so on)
Real-time haptic and visual simulation of bone dissection
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http://www.sherpa.ac.uk/romeo/search.phpBone dissection is an important component of many surgical procedures. In this paper, we discuss a haptic and visual simulation of a bone-cutting burr that is being developed as a component of a training system for temporal bone surgery. We use a physically motivated model to describe the burr-bone interaction, which includes haptic forces evaluation, the bone erosion process, and the resulting debris. The current implementation, directly operating on a voxel discretization of patient-specific 3D CT and MR imaging data, is efficient enough to provide real-time feedback on a low-end multiprocessing PC platform.110-122Pubblicat
Physical human lumen carotid reconstruction: life-size models by rapid prototyping
No full textPoster of SPIE Conference held in San Diego - CA, USA, 10/15 FebruaryRapid Prototyping (RP) is a technique used in industry for manufacturing prototypes. Its capability to physically reproduce geometrical complex shapes is getting increasing interest in many fields of medicine. In the field of vascular
surgery, replicas of artery lumen have utility in complex cases or when standard imaging is felt to be equivocal. Replicas can also facilitate experimental studies of computational vascular fluid-dynamics permitting in-vitro
reproductions of blood flow in living subjects before and after surgery.
The VIrtual VAscular (VIVA) project at CRS4, developed a system able to process three-dimensional (3D) datasets extracted from a Computer Tomography (CT) apparatus, visualize them, reconstruct the geometry of arteries of
specific patients, and simulate blood flow in them. In our work, the applicability of RP techniques to VIVA’s real size replicas of an autoptic carotid vessel lumen is presented and an overview of the RP based system developed is
provided. The techniques used in our prototype are discussed and experimental results for the creation of a human carotid lumen replica are analysed.
We discuss in detail the pipeline of the manufacturing process: 3D geometric reconstruction from segmented points, geometry tessellation, STL (Stereo Lithography format) conversion. Moreover we illustrate some technical details
of the specific RP technique called Fused Deposition Modelling (FDM), used to build the lumen replicas, the materials used for prototypes, throughput time and costs of the FDM models realized.
The system is totally based on open-source software. This enables us to control each step of the pipeline, from data acquisition to STL export file. In this context, we present main sources of error encountered during all
manufacturing process stages
Transport equations for an incompressible reactive flow with two separated phases
No full textThis report is devoted to the analysis of the premixed combustion modelling in the approximation leading to the sole use of a progress variable to characterize the mixture state. First, we shortly describe the TFC model to set the problematic. Then we recall the constitutive instantaneous equations and their averaged counterparts. We examine in details the limit case in which the reaction takes place in an infinitely thin sheet. This situation is formaly identical to the modelling of two separated fluids exchanging matter through their interface. In this case, there is an exact dependence of the so-called counter gradient transport term on the source term. The form of the dependence proves the counter gradient nature of the term which was up to now only intuited. It also shows that their is fundamentally only one unclosed term in the averaged progress variable equation. We examine the closure assumption of the source term in this framework and naturally re-derive the TFC model. We propose the basic idea for a slight improvement of the TFC model that takes into account the finite speed of the increasing brush width. The treatment of the limit case is done by use of generalized functions. They are quite delicate to manipulate and there is no strong familiarity with them in the combustion community leading to the effective difficulty in judging the correctness of the results. For this reason, we re-derive the corresponding results in the general case of regular functions
Fully compressible simulation of low-speed premixed reacting flows
Get PDFLow speed premixed combustion flows in industrial applications are generally simulated using the "incompressible" Navier-Stokes algorithms, which belong to the family of fractional step methods, or segregated methods. The approximations used for the combustion modelling in the framework of the segregated mathematical formulation, often represent important limitations for applying the combustion numerical simulation to a wider class of problems of engineering interest. Recent developments of preconditioning techniques allow to apply the same complete system of Navier-Stokes equations to a wide variety of fluid flow problems characterized by the whole range of Reynolds, Mach, Grashof, Prandtl and Damkoeler numbers. The present work describes the development of a fully "compressible" mathematical model for the simulation of low-speed turbulent premixed reactive flows. Issues on flow and fluid compressibility as well as on the two mathematical alternative formulations, are discussed. Also discussed are issues related to coupling the flamelet premixed combustion model (based on the solution of a transport equation for the progress variable) with one-equation turbulence models, instead of the classical two-equation K – ε model. In this work the model by Spalart & Allmaras is used. The several advantages brought about by the use of the fully compressible formulation are discussed based on the results obtained on a test case taken from literature
