1,008 research outputs found
Topological and Structural Design of Optimized Lattice Models for Mechanical Simulation and Applications in Mechanobiology
No full textNumerical simulations represent a powerful tool for supporting scientific research by adopting the best knowledge from engineering disciplines such as computer science, numerical analysis, and computer graphics. The current computational technologies enable the development of interactive and collaborative design workflows, based on the simulation of multiple scenarios (what-if approach), and the possibility of implementing iterative optimization cycles in acceptable response times with affordable costs.
Mechanical simulation for engineering applications is principally founded on mesh-based approaches as Finite Element Methods, for studying the behavior of deformable solids, and Computational Fluid Dynamics for analyses on fluid domains. An interesting research field is currently represented by the simulation methods based on discrete elements approaches, and in particular by Lattice Models, which typically demonstrate a high potential when dealing with large deformations and topological changes as plasticity or fracture.
The principal focus of this Ph.D. thesis is the investigation of the possibility to employ lattice modelling approaches to study the mechanical responses at mesoscale of highly deformable elastic objects. This choice was made to exploit the main advantages offered by this class of methods, i.e. a fast and stable formulation capable of providing approximate solutions in reasonable times (and often near real-time) with a pre-defined level of accuracy. These features are ideal for analyzing parallel design configurations at a glance or to implement advanced optimization algorithms in which the fundamental parameters of the simulations are continuously perturbed until reaching a specific goal. The main idea behind this thesis work is to create and test novel simulation frameworks based on discrete lattice models, to be adopted in early design stages for the conceptualization of a particular embodiment or for the preliminary screening of multiple solutions, in order to filter and identify suitable design configurations to be further validated, in a subsequent phase, into rigorous FEM environments or by experimental testing procedures.
The general principles of discrete lattice models were deeply analyzed, and different strategies to generate homogeneous, isotropic, and conformal topologies for optimized networks of elastic elements to model deformable surfaces and volumetric objects, were proposed and discussed, thus contributing to the minimization of the variability associated to mesh-dependent mechanical responses. In parallel, a set of topological metrics to assess the overall quality of a specific deformable lattice was defined, along with a series of design guidelines for optimal lattice models generation. Moreover, a series of trials for implementing complete lattice model frameworks into CAD environments were performed, with the aim of creating interactive design workflows. The proposed frameworks were tested and validated on a set of relevant case studies, in the fields of advanced biomedicine and mechanobiology. In detail, lattice spring models were employed to contribute in the understanding of the relationships linking external mechanical stimuli and adaptive biophysical responses of living cells, by extracting the elastic constants of subcellular components in mesenchymal stem cells adhered to a flat substrate. This work started from a series of experimental campaigns conducted in collaboration with researchers from Max Planck Institute for Medical Research, Heidelberg, and from CNRS, Grenoble. In another case study, wireframe-based lattice beam models were adopted to conceive a complete interactive workflow for the modelling and the mechanical simulation of customized biomimetic porous implants to be employed in the field of regenerative medicine. At last, a series of support activities for experimental procedures were carried out. The design and the nanofabrication of a set of rigid substrates presenting variable curvatures, with the aim of assessing the response of adhered mesenchymal stem cells in terms of differentiation to a specific phenotype, were carried out. Moreover, the design of an electro-mechanic cyclic loading device necessary for assessing the response of adhered mesenchymal stem cells to specific mechanical stimuli, in terms of maximization of newly formed bone tissue, was performed.
From the present thesis work emerged that lattice models should be considered as a class of powerful methods, characterized by a simple numerical implementation and a fast and stable response, to be effectively adopted in preliminary design phases, or within numerical optimization algorithms, or for the interactive study of highly deformable materials and porous lattices, often present in advanced biomedical applications. The principal results of the research reported in this Ph.D. thesis were published in scientific journals and presented in international conferences
Preliminary Study of a 3D-Printed High-Fidelity Simulator for the Training on the EBUS TBNA Procedure
No full text[ITA] Il cancro del polmone è la seconda neoplasia per incidenza e la principale causa di morte per neoplasia nel mondo. Una pratica consolidata per la diagnosi precoce e la stadiazione del cancro del polmone è l'EBUS TBNA (EndoBronchial UltraSound-guided TransBronchial Needle Aspiration).
Nonostante sia una procedura a basso rischio, il suo successo dipende in larga misura dalle competenze del personale medico, che necessita pertanto di una formazione adeguata.
Con l'obiettivo futuro di sviluppare un nuovo simulatore realistico di TBNA EBUS che consenta anche il campionamento dei tessuti, in questo lavoro gli autori propongono una rappresentazione semplificata del mediastino per definire un layout adeguato.
Per quanto ne sanno gli autori, i simulatori fisici disponibili in commercio hanno scarse proprietà ecogene, non consentono il campionamento dei tessuti e possono essere piuttosto costosi.
Il progetto è stato realizzato all'interno di Custom3D, un laboratorio congiunto tra l'Ospedale Careggi di Firenze e il Dipartimento di Ingegneria Industriale dell'Università di Firenze, su richiesta del reparto di pneumologia interventistica. Il modello è stato validato da un medico esperto che ne ha valutato l'accuratezza anatomica e l'adeguatezza delle proprietà meccaniche e acustiche.
Inoltre, la possibilità di eseguire l'agoaspirazione linfonodale è un valore aggiunto che promette di portare la simulazione della TBNA EBUS a un nuovo livello di realismo.
[ENG] Lung cancer is the second neoplasia for incidence and the leading cause of death from neoplasia in the world. A consolidated practice for lung cancer early diagnosis and staging is EBUS TBNA (EndoBronchial UltraSound-guided TransBronchial Needle Aspiration).
Despite being a low-risk procedure, its success highly depends on the medical staff’s skills, who therefore require appropriate training.
With the future aim of developing a novel realistic EBUS TBNA simulator that also allows tissue sampling, in this paper, the authors propose a simplified representation of the mediastinum to define a suitable layout.
As far as the authors know, the physical commercially-available simulators have poor echogenic properties, do not allow tissue sampling, and can be quite expensive.
The project was carried out within Custom3D, a joint laboratory between Careggi Hospital of Florence and the Department of Industrial Engineering of the University of Florence, under the request of the interventional pneumology ward. The model was validated by an expert medical doctor who assessed its anatomical accuracy and the suitability of its mechanical and acoustic properties.
Moreover, the possibility of performing lymph node needle aspiration is an added value that promises to bring the EBUS TBNA simulation to a new level of realism
Computer Aided Design Tool for GT Ventilation System Ductworks
No full textThe proper design of a ventilation system (VS) is an important requirement in the Gas Turbine (GT) and energy production industry in general. In fact, ventilation systems are designed to provide a continuous source of cooling air so as to: remove heat and maintain the air temperature in the compartment below the operating limit; prevent the accumulation of hazardous gases; preserve a constant and uniform airflow through the ducts, independently from the environmental conditions; avoid accidental dust and sand contamination in gas turbines, especially when these are located in regions prone to sandstorm conditions. When compared to typical Heating, Ventilating and Air Conditioning (HVAC) systems, the design of VSs results particularly challenging since many requirements, generally involving different engineering aspects such as fluid-dynamic, acoustic and structural, have to be fulfilled. Generally speaking, a VS is composed by a number of elements such as linear ducts, expansion joints, transition duct sections, elbows, outlets to the atmosphere, supports, saddles and brackets. Shape and dimensions of these elements may significantly vary depending on the kind of application. Basically, the elements may have circular/oval or rectangular/square section. In the first case, they are manufactured by employing calendaring process followed by welding. Otherwise, the component is realized by cutting and welding metal sheets. Elements are coupled by using bolted flanges or welded joints in order to obtain the entire VS ductwork
A Semi-Automatic CAD Procedure to Design Custom-made Surgical Cutting Guides
No full textThe present paper presents the development of a novel procedure for the modeling of Surgical Cutting Guides (SCGs) exploiting an implicit modeling approach. As discussed in the text, this approach allows for a streamlined and efficient design of this type of medical device. A procedural approach based on the application of a series of a priori-known implicit modeling function allows the generation of personalized surgical guides starting from the i) patient’s anatomy and ii) clinical decisions made by the medical staff. The CAD procedure is detailed in the text; achieved results are discussed and compared with a traditional CAD modeling approach on three case studies
Scene Acquisition with Multiple 2D and 3D Optical Sensors: A PSO-Based Visibility Optimization
No full textDesigning an acquisition system for 2D or 3D information, based on the integration of data provided by different sensors is a task that requires a labor-intensive initial design phase. Indeed, the definition of the architecture of such acquisition systems needs to start from the identification of the position and orientation of the sensors observing the scene. Their placement is carefully studied to enhance the efficacy of the system. This often coincides with the need to maximize the surfaces observed by the sensors or some other metric. An automatic optimization procedure based on the Particle Swarm Optimization (PSO) algorithm, to seek the most convenient setting of multiple optical sensors observing a 3D scene, is proposed. The procedure has been developed to provide a fast and efficient tool for 2D and 3D data acquisition. Three different objective functions of general validity, to be used in future applications, are proposed and described in the text. Various filters are introduced to reduce computational times of the whole procedure. The method is capable of handling occlusions from undesired obstacle in the scene. Finally, the entire method is discussed with reference to 1) the development of a body scanner for the arm-wrist-hand district and 2) the acquisition of an internal environment as case studies
Statistical Shape Model: comparison between ICP and CPD algorithms on medical applications
No full textThe increasing availability of 3D anatomical models obtained from diagnostic images exploiting Reverse Engineering techniques allows the application of statistical analysis in the quantitative investigation of anatomical shapes variability. Statistical Shape Models are a well-established method for representing such variability, especially for complex forms like the anatomical ones. Not by chance, these models are widely used for medical applications, such as guiding segmentation of the diagnostic image and virtual reconstruction of incomplete anatomic region. The application of a statistical analysis on a set of shapes representing the same anatomical region essentially requires that shapes must be in correspondence, i.e. constituted by the same number of points in corresponding position. This work aims to compare two established algorithms, namely a modified version of the Iterative Closest Point and the non-rigid version of the Coherent Point Drift, to solve the correspondences’ problem in the construction of a Statistical Shape Model of the human cranium. The comparison is carried out on the models using the standard evaluation criteria: generalization, specificity and compactness. The modified version of the Iterative Closest Point delivers a better Statistical Shape Model in terms of generalization and specificity, but not for compactness, than the Coherent Point Drift-based model
A RGB-D based instant body-scanning solution for compact box installation
No full textBody scanning presents unique value in delivering the first digital asset of a human body thus resulting a fundamental device for a range of applications dealing with health, fashion and fitness. Despite several body scanners are in the market, recently depth cameras such as Microsoft Kinect® have attracted the 3D community; compared with conventional 3D scanning systems, these sensors are able to capture depth and RGB data at video rate and even if quality and depth resolution are not optimal for this kind of applications, the major benefit comes from the overall acquisition speed and from the IR pattern that allows poor lighting conditions optimal acquisition. When dealing with non-rigid bodies, unfortunately, the use of a single depth camera may lead to inconsistent results mainly caused by wrong surfaces registration. With the aim of improving existing systems based on low-resolution depth cameras, the present paper describes a novel scanning system for capturing 3D full human body models by using multiple Kinect® devices in a compact setup. The system consists of an instantaneous scanning system using eight depth cameras, appropriately arranged in a compact wireframe. To validate the effectiveness of the proposed architecture, a comparison of the obtained 3D body model with the one obtained using a professional Konica Minolta Range Seven 3D scanner is also presented and possible drawbacks are hinted at
Comparison of Mesh Simplification tools in a 3D Watermarking framework
No full textGiven a to-be-watermarked 3D model, a transformed domain analy-sis is needed to guarantee a robust embedding without compromising the visual quality of the result. A multiresolution remeshing of the model allows to repre-sent the 3D surface in a transformed domain suitable for embedding a robust and imperceptible watermark signal. Simplification of polygonal meshes is the basic step for a multiresolution remeshing of a 3D model; this step is needed to obtain the model approximation (coarse version) from which a refinement framework (i.e. 3D wavelet analysis, spectral analysis, ...) able to represent the model at multiple resolution levels, can be performed. The simplification algo-rithm should satisfy some requirements to be used in a watermarking system: the repeatability of the simplification, and the robustness of it to noise or, more generally, to slight modifications of the full resolution mesh. The performance of a number of software packages for mesh simplification, including both commercial and academic offerings, are compared in this survey. We defined a benchmark for testing the different software in the watermarking scenario and reported a comprehensive analysis of the software performances based on the geometric distortions measurement of the simplified versions
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