Un approccio all'integrazione di mesh e nurbs

Viene sviluppata in XCSurf, un pacchetto di XCModel, una struttura dati chiamata B-Rep il cui scopo è quello di poter accogliere sia geometrie mesh che nurbs. La struttura B-Rep è stata progettata nel lavoro di tesi di F.Pelosi a seguito del riscontro di diverse analogie fra la struttura winged-edge (per mesh) e la struttura B-Rep (per nurbs). In questa tesi viene sviluppata ed integrata ulteriormente. Il punto di arrivo è la possibilità di attaccare due modelli qualsiasi (Nurbs + Nurbs, Mesh + Nurbs, Mesh + Mesh), deformando opportunamente le parti da attaccare, ma mantenendo tutte le informazioni in un'unica struttura.

Add-on in blender per la deformazione di mesh poligonali

L’idea da cui nasce questa tesi è quella di introdurre in Blender un Add-on in linguaggio Python che permetta di applicare alcune deformazioni di tipo surface-based a mesh poligonali. Questa tipologia di deformazioni rappresentano l’alternativa alle deformazioni di mesh poligonali tramite rigging ( cioè l’aggiunta di uno scheletro per controllare e per animare la mesh) e caging (cioè l’utilizzo di una struttura di controllo di tipo reticolare che propaga la sua deformazione su un oggetto in essa immerso), che di solito sono le prescelte in computer animation e in modellazione. Entrambe le deformazioni indicate sono già estremamente radicate in Blender, prova ne è il fatto che esiste più di un modificatore che le implementa, già integrato in codice nativo. Si introduce inizialmente la tecnica di deformazione di mesh poligonali tramite elasticità discreta, che è stata realizzata, quindi, presenteremo diverse metodologie di deformazione. Illustreremo poi come modellare, creare ed editare delle mesh in Blender. Non ci soffermeremo su dettagli puramente dettati dall’interfaccia utente, cercheremo invece di addentrarci nei concetti e nelle strutture teoriche, allo scopo di avere le basi logiche per definire una Add-on che risulti veramente efficace e utile all’interno del sistema di modellazione. Approfondiremo la struttura di due modificatori chiave per la deformazioni di mesh : Lattice Modifier e Mesh Deform Modifier che implementano una metodologia di tipo space-based. Infine ci concentreremo sulla parte di scripting Python in Blender. Daremo un’idea delle strutture dati, dei metodi e delle funzioni da utilizzare per interagire con l’ambiente circostante, con i singoli oggetti ed in particolare con le Mesh e daremo un esempio di script Python. Andremo infine a descrivere l’implementazione della deformazione elastica mediante add-on Python in Blender.

Una libreria OpenGL per la selezione e editing di mesh poligonali

Nel mondo Open Source, la libreria grafica OpenGL è oggi ampiamente utilizzata in svariati settori come l'animazione 2D/3D, la modellazione CAD o nello sviluppo di videogiochi. A causa dei suoi innumerevoli usi e dell'astrazione che OpenGL permette di ottenere su diversi ambienti grafici, lo sviluppatore - che la utilizza - è vincolato a cercare librerie di supporto al fine di sfruttarne al meglio le potenzialità. Questa tesi si configura su questi presupposti, presentando una libreria di selezione e editing di mesh 3D basata su OpenGL. La libreria, chiamata libEditMesh, sfrutta il meccanismo geometrico del RayPicking permettendo all'utilizzatore di identificare col mouse punti, facce e lati di solidi in scena. La tesi si articola sostanzialmente in due parti: nella prima vengono proposte alcune soluzioni ad-hoc sviluppate su applicazioni già esistenti nel panorama openSource, e non; nella seconda vengono esposti gli algoritmi e funzioni implementate in libEditMesh.

"Offshore tower or platform foundations: numerical analysis of a laterally loaded single pile or pile group in soft clay and analysis of actions on a jacket structure"

Laterally loaded piles are a typical situation for a large number of cases in which deep foundations are used. Dissertation herein reported, is a focus upon the numerical simulation of laterally loaded piles. In the first chapter the best model settings are largely discussed, so a clear idea about the effects of interface adoption, model dimension, refinement cluster and mesh coarseness is reached. At a second stage, there are three distinct parametric analyses, in which the model response sensibility is studied for variation of interface reduction factor, Eps50 and tensile cut-off. In addition, the adoption of an advanced soil model is analysed (NGI-ADP). This was done in order to use the complex behaviour (different undrained shear strengths are involved) that governs the resisting process of clay under short time static loads. Once set a definitive model, a series of analyses has been carried out with the objective of defining the resistance-deflection (P-y) curves for Plaxis3D (2013) data. Major results of a large number of comparisons made with curves from API (America Petroleum Institute) recommendation are that the empirical curves have almost the same ultimate resistance but a bigger initial stiffness. In the second part of the thesis a simplified structural preliminary design of a jacket structure has been carried out to evaluate the environmental forces that act on it and on its piles foundation. Finally, pile lateral response is studied using the empirical curves.

Envy: A Psychometric Refinement of the Construct

The noticeable differences in the theoretical and operative definitions of envy across studies and approaches have produced a fragmentary representation and understanding of the envious emotion. The present dissertation aimed to clarify the inherent nature of the construct of envy through the integration of findings from three independent studies. We focused on malicious envy, and investigated it from both a dispositional and an episodic perspective. Studies 1 and 2 investigated the dimensionality of envy as a stable individual characteristic and an episodic emotional state, respectively. In order to elicit episodic envy, a scenario-based experiment was conducted. Results indicated that, in both its dispositional and episodic facets, envy is a bidimensional construct composed by an inner-directed dimension of inferiority and helplessness, and an outer-directed dimension of feelings of anger and ill will. Moreover, findings from Study 1 allowed to establish boundaries between envy and competing constructs that have often been included in conceptualizations of envy. The psychometrically validated definition of envy provided by Studies 1 and 2 represents a valuable contribution to empirical research. Implications for envy research concern the promotion of a shared operationalization of envy in future studies, which will arguably facilitate the comparison of findings between studies and between approaches. Study 3 examined the mechanisms through which dispositional envy affects individuals’ social adjustment and psychological wellbeing. Findings revealed that the detrimental effects of envy on perceived social support and subjective well-being are mostly mediated by other personal characteristics, such as neuroticism and self-esteem. By reducing global self-esteem, the envious disposition may damage supportive social networks via antisocial direct and indirect behaviors that may arise from envy and that are likely to drive others away. On the other hand, by damaging both emotional stability and self-worth, dispositional envy leads to reduced subjective well-being. Implications for clinical practice are discussed.

High precision swept volume approximation with conservative error bounds

In technical design processes in the automotive industry, digital prototypes rapidly gain importance, because they allow for a detection of design errors in early development stages. The technical design process includes the computation of swept volumes for maintainability analysis and clearance checks. The swept volume is very useful, for example, to identify problem areas where a safety distance might not be kept. With the explicit construction of the swept volume an engineer gets evidence on how the shape of components that come too close have to be modified.rnIn this thesis a concept for the approximation of the outer boundary of a swept volume is developed. For safety reasons, it is essential that the approximation is conservative, i.e., that the swept volume is completely enclosed by the approximation. On the other hand, one wishes to approximate the swept volume as precisely as possible. In this work, we will show, that the one-sided Hausdorff distance is the adequate measure for the error of the approximation, when the intended usage is clearance checks, continuous collision detection and maintainability analysis in CAD. We present two implementations that apply the concept and generate a manifold triangle mesh that approximates the outer boundary of a swept volume. Both algorithms are two-phased: a sweeping phase which generates a conservative voxelization of the swept volume, and the actual mesh generation which is based on restricted Delaunay refinement. This approach ensures a high precision of the approximation while respecting conservativeness.rnThe benchmarks for our test are amongst others real world scenarios that come from the automotive industry.rnFurther, we introduce a method to relate parts of an already computed swept volume boundary to those triangles of the generator, that come closest during the sweep. We use this to verify as well as to colorize meshes resulting from our implementations.

Improvement of photon transport model by including coupled photon-electron transport and kernel refinement

The first part of this work deals with the inverse problem solution in the X-ray spectroscopy field. An original strategy to solve the inverse problem by using the maximum entropy principle is illustrated. It is built the code UMESTRAT, to apply the described strategy in a semiautomatic way. The application of UMESTRAT is shown with a computational example. The second part of this work deals with the improvement of the X-ray Boltzmann model, by studying two radiative interactions neglected in the current photon models. Firstly it is studied the characteristic line emission due to Compton ionization. It is developed a strategy that allows the evaluation of this contribution for the shells K, L and M of all elements with Z from 11 to 92. It is evaluated the single shell Compton/photoelectric ratio as a function of the primary photon energy. It is derived the energy values at which the Compton interaction becomes the prevailing process to produce ionization for the considered shells. Finally it is introduced a new kernel for the XRF from Compton ionization. In a second place it is characterized the bremsstrahlung radiative contribution due the secondary electrons. The bremsstrahlung radiation is characterized in terms of space, angle and energy, for all elements whit Z=1-92 in the energy range 1–150 keV by using the Monte Carlo code PENELOPE. It is demonstrated that bremsstrahlung radiative contribution can be well approximated with an isotropic point photon source. It is created a data library comprising the energetic distributions of bremsstrahlung. It is developed a new bremsstrahlung kernel which allows the introduction of this contribution in the modified Boltzmann equation. An example of application to the simulation of a synchrotron experiment is shown.

Modellazione di mesh tramite operatori booleani

Nella computer grafica, nell’ambito della modellazione geometrica, si fa uso delle operazioni booleane tra solidi per la manipolazione e la creazione di nuovi oggetti. Queste operazioni, quali unione, intersezione e differenza, vengono applicate alle superfici degli oggetti 3D esattamente come si fa su altri insiemi. In questo modo si riescono ad ottenere nuove forme complesse come combinazione delle altre, che sono in genere più semplici. Ciò che è stato realizzato in questo lavoro di tesi si colloca all’interno di un progetto preesistente, realizzato per consentire la manipolazione di modelli tridimensionali mediante l’utilizzo di operatori booleani: Mesh Glue. In questo lavoro, si è estesa la logica dell’applicazione degli operatori booleani, presente in Mesh Glue, per poter gestire anche scenari con mesh che presentano facce in tangenza. Inoltre, si è inserito Mesh Glue all’interno di un progetto più grande: Mesh Craft. Mesh Craft è un progetto che consiste in un ambiente di modellazione che utilizza come sistema di input il Leap Motion Controller, un dispositivo capace di identificare le dita di una mano e seguirne i movimenti con alta precisione.

Mesh shrinkage and pain in laparoscopic ventral hernia repair: a randomized clinical trial comparing suture versus tack mesh fixation

Mesh fixation during laparoscopic ventral hernia repair can be performed using transfascial sutures or metal tacks. The aim of the present study is to compare mesh shrinkage and pain between two different techniques of mesh fixation in a prospective randomized trial.

Sexual health of ethnic minority MSM in Britain (MESH project): design and methods

Background Men who have sex with men (MSM) remain the group most at risk of acquiring HIV infection in Britain. HIV prevalence appears to vary widely between MSM from different ethnic minority groups in this country for reasons that are not fully understood. The aim of the MESH project was to examine in detail the sexual health of ethnic minority MSM living in Britain. Methods/Design The main objectives of the MESH project were to explore among ethnic minority MSM living in Britain: (i) sexual risk behaviour and HIV prevalence; (ii) their experience of stigma and discrimination; (iii) disclosure of sexuality; (iv) use of, and satisfaction with sexual health services; (v) the extent to which sexual health services (for treatment and prevention) are aware of the needs of ethnic minority MSM. The research was conducted between 2006 and 2008 in four national samples: (i) ethnic minority MSM living in Britain; (ii) a comparison group of white British MSM living in Britain; (iii) NHS sexual health clinic staff in 15 British towns and cities with significant ethnic minority communities and; (iv) sexual health promotion/HIV prevention service providers. We also recruited men from two "key migrant" groups living in Britain: MSM born in Central or Eastern Europe and MSM born in Central or South America. Internet-based quantitative and qualitative research methods were used. Ethnic minority MSM were recruited through advertisements on websites, in community venues, via informal networks and in sexual health clinics. White and "key migrant" MSM were recruited mostly through Gaydar, one of the most popular dating sites used by gay men in Britain. MSM who agreed to take part completed a questionnaire online. Ethnic minority MSM who completed the online questionnaire were asked if they would be willing to take part in an online qualitative interview using email. Service providers were identified through the British Association of Sexual Health and HIV (BASHH) and the Terrence Higgins Trust (THT) CHAPS partnerships. Staff who agreed to take part were asked to complete a questionnaire online. The online survey was completed by 1241 ethnic minority MSM, 416 men born in South and Central America or Central and Eastern Europe, and 13,717 white British MSM; 67 ethnic minority MSM took part in the online qualitative interview. In addition 364 people working in sexual health clinics and 124 health promotion workers from around Britain completed an online questionnaire. Discussion The findings from this study will improve our understanding of the sexual health and needs of ethnic minority MSM in Britain.

Influence of Smoothing on Voxel-Based Mesh Accuracy in Micro-Finite Element

The interest in automatic volume meshing for finite element analysis (FEA) has grown more since the appearance of microfocus CT (μCT), due to its high resolution, which allows for the assessment of mechanical behaviour at a high precision. Nevertheless, the basic meshing approach of generating one hexahedron per voxel produces jagged edges. To prevent this effect, smoothing algorithms have been introduced to enhance the topology of the mesh. However, whether smoothing also improves the accuracy of voxel-based meshes in clinical applications is still under question. There is a trade-off between smoothing and quality of elements in the mesh. Distorted elements may be produced by excessive smoothing and reduce accuracy of the mesh. In the present work, influence of smoothing on the accuracy of voxel-based meshes in micro-FE was assessed. An accurate 3D model of a trabecular structure with known apparent mechanical properties was used as a reference model. Virtual CT scans of this reference model (with resolutions of 16, 32 and 64 μm) were then created and used to build voxel-based meshes of the microarchitecture. Effects of smoothing on the apparent mechanical properties of the voxel-based meshes as compared to the reference model were evaluated. Apparent Young’s moduli of the smooth voxel-based mesh were significantly closer to those of the reference model for the 16 and 32 μm resolutions. Improvements were not significant for the 64 μm, due to loss of trabecular connectivity in the model. This study shows that smoothing offers a real benefit to voxel-based meshes used in micro-FE. It might also broaden voxel-based meshing to other biomechanical domains where it was not used previously due to lack of accuracy. As an example, this work will be used in the framework of the European project ContraCancrum, which aims at providing a patient-specific simulation of tumour development in brain and lungs for oncologists. For this type of clinical application, such a fast, automatic, and accurate generation of the mesh is of great benefit.

Mesh-based vs. Image-based Statistical Appearance Model of the Human Femur: a Preliminary Comparison Study for the Creation of Finite Element Meshes

Statistical models have been recently introduced in computational orthopaedics to investigate the bone mechanical properties across several populations. A fundamental aspect for the construction of statistical models concerns the establishment of accurate anatomical correspondences among the objects of the training dataset. Various methods have been proposed to solve this problem such as mesh morphing or image registration algorithms. The objective of this study is to compare a mesh-based and an image-based statistical appearance model approaches for the creation of nite element(FE) meshes. A computer tomography (CT) dataset of 157 human left femurs was used for the comparison. For each approach, 30 finite element meshes were generated with the models. The quality of the obtained FE meshes was evaluated in terms of volume, size and shape of the elements. Results showed that the quality of the meshes obtained with the image-based approach was higher than the quality of the mesh-based approach. Future studies are required to evaluate the impact of this finding on the final mechanical simulations.