Geometric modeling and processing

Formative assessment is an important element for supporting any learning process, with the provision of feedback being one of its most effective strategies. However, despite the extensive body of research on feedback and its importance to learning, its effectiveness and usefulness, and thus its expected effect, are not always guaranteed. This, in part, can be attributed to issues concerning how students make sense of and act upon feedback and the gap between how students receive and perceive feedback and how teachers structure and provide it. After the introduction of a newly developed feedback intervention aimed at improving the learning experience and, consequently, performance outcomes, it is now time to determine the next steps. This requires insight into and understanding of the usefulness and effectiveness of the recently introduced educational intervention, and this insight should be based on empirical evidence. This paper reports on the first part of an empirical study organized as a two-part project aimed at determining to what extent the new feedback intervention has had a positive impact on the learning experience and outcomes. The study also aims to determine the effect sizes and their relationships, along with the impact of the feedback characteristics on the goals in relation to the complex task of creating robust and best practice-compliant CAD models.

Keywords: CAD model alterability , design intent , dormant deficiency , Feedback effects , skill and competency development

Protein–protein interaction occurs on surface patches with some degree of complementary geometric and chemical features. Building on this understanding, this study endeavors to characterize the spike protein of the SARS-CoV-2 virus at the morphological and geometrical levels in its Alpha, Delta, and Omicron variants. In particular, the affinity between different SARS-CoV-2 spike proteins and the ACE2 receptor present on the membrane of the human respiratory system cells is investigated. To achieve an adequate degree of geometrical accuracy, the 3D depth maps of the proteins in exam are filtered by developing an ad-hoc convolutional filter with a kernel implemented as a sphere of varying radius, simulating a ball rolling on the surface (similar to the 'rolling ball' filter). This ball ideally models a hypothetical molecule that could interface with the protein and is inspired by the geometric approach to macromolecule–ligand interactions proposed by Kuntz et al. in 1982. The aim is to mitigate the imperfections and to obtain a smoother surface that could be studied from a geometrical perspective for binding purposes. A set of geometric descriptors, borrowed from the 3D face analysis context is then mapped point-by-point onto protein depth maps. Following a feature extraction phase inspired by Histogram of Oriented Gradients and Local Binary Patterns, the final histogram features are used as input for a Support Vector Machine classifier to automatically classify the proteins according to their surface affinity, where a similarity in shape is observed between ACE2 and the spike protein of the SARS-CoV-2 Omicron variant. Finally, Root Mean Square Error analysis is used to quantify the geometrical affinity between the ACE2 receptor and the respective Receptor Binding Domains of the three SARS-CoV-2 variants, culminating in a geometrical explanation for the higher contagiousness of Omicron relative to the other variants under study.

The Radial Neutron Camera (RNC) is a diagnostic system located in the ITER Equatorial Port 1 (EP01) composed by two sub-systems (i.e.: in-port and ex-port RNC) probing a poloidal section of the plasma through a set of fan-shaped Lines of Sight (LOS). The RNC is designed to provide a time resolved measurement of the neutron and alpha particles source profiles and of the total neutron source strength, through the application of reconstruction techniques to the line-integrated neutron fluxes. The Ex-port sub-system is composed by 16 LOS distributed in two different toroidal planes and enclosed in a massive shielding unit, extending from the EP01 closure plate through the Port Interspace, up to the Bioshield Plug. Neutrons, generated in the plasma core, stream through dedicated optical paths hollowed out in the central EP01 diagnostic shielding module and reach the detectors units located at the end of collimating structures. Each detector unit contains one 4He gas scintillator, one plastic scintillator as well as one single Crystal Diamond (sCD) matrix. The performed nuclear analysis allowed the selection of the SWX-277Z-5 castable borated hydrogenated mix as suitable material for the RNC shielding block; moreover, the evaluation of the nuclear heating on the ex-port RNC subcomponents, provided as input for structural analyses, highlighted that the impact of the radiation streaming is negligible with respect to the environmental thermal loads.

Keywords: ITER , MCNP , Neutron diagnostics , Neutronics , Radial Neutron Camera

This paper formulates quadrilateral elements for the NURBS-enhanced finite element method (NEFEM). The objective is to extend the application of NEFEM to problems where the use of quadrilateral elements is preferred. By leveraging a mapping, between reference and physical spaces, that encapsulates the exact boundary representation of the domain, a tight integration with computer aided design (CAD) systems is achieved. The contribution of this work is an enhanced quadrilateral finite element that incorporates the exact CAD geometry purely from the boundary representation (B-rep) from CAD and without the need for a whole volume representation (V-rep) as a NURBS entity. Numerical examples involving heat transfer and linear elastic problems are used to numerically demonstrate the optimal convergence properties of the method under mesh refinement.

Keywords: CAD integration , NEFEM , Quadrilateral elements

Additive Manufacturing (AM) technologies are widely spreading into multiple engineering sectors thanks to their flexibility to create complex geometries with virtual no material waste. AM technologies capabilities can be fully exploited when working with periodic lattices, creating topology-optimized structures through different cell types with different dimensions and volume fractions. Several factors (i.e., process parameters, quality and type of raw materials) can modify the mechanical properties of printed components and can be exploited to selectively create functionally graded materials or conventional laminated hybrid materials structures. This paper analyses and compares the mechanical properties of different additively manufactured lattice BCC structures through experimental and numerical means. At first, the manufacturing procedure followed by experimental tests is presented. The retrieved mechanical properties are then used as a benchmark for the numerical Finite Element Analyses and compared with analytical models available in the literature. The numerical simulation campaign includes the comparison of a full 3D model and a 1D/2D beam/shell formulation model. The research findings demonstrate a good correlation between the experimental tests and the numerical simulation results, indicating the potential for the proposed methodologies to be broadly implemented within various domains of structures and materials.

Keywords: 3D lattice , Additive Manufacturing , Design for Manufacturing , FEM , Periodicity

Nowadays the interest for improving methodologies to design customized external devices for the neck has considerably grown, considered that neck pathologies are widespread among the population. Their design for additive manufacturing starts by acquiring the body's part and, in order to achieve a satisfactory end result, the support of accurate reconstructed models from fast scans is relevant. At this aim, the availability of an average or statistical model could be potentially useful for reducing acquisition time and for upgrading low-resolution scans. This paper focuses on the application of a methodology for the creation of an average model of human neck. The method required the use of a set of scans, acquired by means of a structured light scanner, from which an accurate reconstruction of the neck surface was obtained. A number of healthy subjects of both genders was considered and the digital neck surfaces were used for creating an average digital model for males and for females. The methodology developed was based on mesh morphing and was applied to the sample considered with satisfactory results. The procedure is also suitable for the development of statistical models of the neck, that will cover future research

Keywords: Acquisition , Mesh morphing , Neck , Reverse Engineering

Aim: The objective of this research has been to apply a specific simulation to a patient to assess the biomechanical consequences of rotating an upper canine tooth through different attachment–aligner configurations and to predict the most efficient design using a three-dimensional finite element model of a full maxillary arch of a specific patient. Materials and methods: This was obtained by combining Cone-Beam Computed Tomography (CBCT) with the aim of reconstructing tooth roots and bone tissues, and Surface Structured-Light Scanning for creating digital tooth crown models from the patient's impressions. This model was imported into the finite element solver (Ansys® 17). Three different attachment–aligner combinations were created through the exploitation of computer-aided design (CAD) procedures, i.e., without attachments, with a couple of attachments and with an attachment and a pressure point. For each simulation, the resulting force–moment (MF) system applied by the aligner to the target tooth, as well as the tooth displacement and rotation, was computed using a workstation based on Intel Xeon CPU E3-1245 v3@3.40 GHz and 16 GB RAM. Simulations reported that by adding the pressure point and the attachment to the standard aligner the amount of Moment z (Mz) delivered to the tooth increased almost two times. Results and conclusions: The maximum tooth displacement (0.85 mm) was obtained with the attachment and pressure point aligner, while the lowest (0.058 mm) was obtained with use of a couple of attachments. Both the attachment and the pressure point have the potential to enhance the appliance's effectiveness. Particularly, the pressure point showed a higher influence on the load absolute value. The method applied in the present study should be used to retrieve the best design configuration for each patient and specific tooth movement

Keywords: aligners , digital workflow , finite element analysis , malocclusion , orthodontic movement , three-dimensional diagnosis and analysis , three-dimensional tooth movement

The presented study investigates differences in engineering designers' CAD performance when modelling from two types of projections in technical drawings – isometric and orthographic. The results revealed significant differences in the percentage of correctly replicated components' size and shape, indicating better CAD outcomes when generating CAD models from the orthographic projection. In addition, a comparison of duration, as well as the number and type of sketch entities, sketch relations, and CAD features, showed that CAD modelling processes were similar in both conditions.

Keywords: computer-aided design (CAD) , design representation , performance indicators

Objectives: Nowadays, a wide variety of software for 3D reconstruction from CT scans is available; they differ for costs, capabilities, a priori knowledge, and, it is not trivial to identify the most suitable one for specific purposes. The article is aimed to provide some more information, having set up various metrics for the evaluation of different software's performance. Methods: Metrics include software usability, segmentation quality, geometric accuracy, mesh properties and Dice Similarity Coefficient (DSC). Five different software have been considered (Mimics, D2P, Blue Sky Plan, Relu, and 3D Slicer) and tested on four cases; the mandibular bone was used as a benchmark. Results: Relu software, being based on AI, was able to solve some very intricate geometry and proved to have a very good usability. On the other side, the time required for segmentation was significantly higher than other software (reaching over twice the time required by Mimics). Geometric distances between nodes position calculated by different software usually kept below 2.5 mm, reaching 3.1 mm in some very critical area; 75th percentile q75 is generally less than 0.5 mm, with a maximum of 1.11 mm. Dealing with consistency among software, the maximum DSC value was observed between Mimics and Slicer, D2P and Mimics, and D2P and Slicer, reaching 0.96. Significance: This work has demonstrated how mandible segmentation performance among software was generally very good. Nonetheless, differences in geometric accuracy, usability, costs and times required can be significant so that information here provided can be useful to perform an informed choice.

Keywords: 3D reconstruction , CT scans , DSC , Geometric accuracy , Mandible , Segmentation , Usability

This work is aimed to set-up a methodology for foot shape prediction at different flexion angles, overcoming limitations encountered when different poses are required but a limited set of acquisitions can be performed. The basic idea was to identify a fitting law able to interpolate positions of foot anatomical landmarks, and then use this information to guide the deformation of an average foot shape. First of all, mesh correspondence between foot geometries was accomplished by an established procedure based on mesh morphing. Then Procrustes analysis was applied to the dataset to remove rigid motions and estimate the average shape. Two interpolation laws (linear and quadratic) were investigated and the best one in terms of prediction of 3D landmarks' coordinates was identified. Finally, shape geometries at any flexion angle were predicted performing a second mesh morphing guided by interpolated landmarks' displacements from the average shape. These analyses proved that a limited number of interpolation angles provides a prediction accuracy comparable to that obtained using all the angles available in the dataset. Moreover, predicted shapes have been compared to the actual scans in terms of root mean square error between corresponding nodes, obtaining a mean value of 4.03 ± 1.39 mm, in accordance with data reported in literature.

Keywords: Accurate geometric reconstruction , Foot model , Real-time acquisition , Statistical deformation model , Statistical shape model

In a technological context where, thanks to the additive manufacturing techniques, even sophisticated geometries as well as surfaces with specific micrometric features can be realized, we propose a mechano-regulation algorithm to determine the optimal microgeometric parameters of the surface of textured titanium devices for biomedical applications. A poroelastic finite element model was developed including a portion of bone, a portion of a textured titanium device and a layer of granulation tissue separating the bone from the device and occupying the space between them. The algorithm, implemented in the Matlab environment, determines the optimal values of the root mean square and the correlation length that the device surface must possess to maximize bone formation in the gap between the bone and the device. For low levels of compression load acting on the bone, the algorithm predicts low values of root mean square and high values of correlation length. Conversely, high levels of load require high values of root mean square and low values of correlation length. The optimal microgeometrical parameters were determined for various thickness values of the granulation tissue layer. Interestingly, the predictions of the proposed computational model are consistent with the experimental results reported in the literature. The proposed algorithm shows promise as a valuable tool for addressing the demands of precision medicine. In this approach, the device or prosthesis is no longer designed solely based on statistical averages but is tailored to each patient's unique anthropometric characteristics, as well as considerations related to their metabolism, sex, age, and more.

Keywords: Additive manufacturing techniques , Correlation length , Mechanobiology , Optimal surface roughness , Root mean square

This paper presents an image clustering algorithm that classifies parts to be fabricated using traditional and additive manufacturing (AM) technologies. The proposed algorithm is a MATLAB-based software tool that clusters 3D CAD models of parts considering their geometry only. The algorithm can classify image datasets, CAD datasets, and combined datasets that contain both images and CAD models. The software tool reduces the time and effort spent during process selection by offering a preselected set of parts that are more suitable for AM. The software tool is aimed at supporting decision-making for traditional manufacturing companies that consider expanding their production capability by introducing AM processes in their production facilities. The HICA software tool expands the scope of scientific applications in manufacturing process selection by providing an unsupervised approach that does not require data labelling. The tool is made available as a MATLAB function through a permanent link.

Keywords: Additive manufacturing , CAD , Hierarchical clustering , Image processing , MATLAB , Process selection , SolidWorks

Recent advancements in additive manufacturing technologies have significantly enhanced the capacity to accurately reproduce the shape and material properties found in nature. Furthermore, the behavior and functionality exhibited by natural systems can be effectively simulated using bio-inspired algorithms. An essential parameter that governs various life processes is the surface area to volume ratio. In industrial applications such as catalysis and heat exchange, this particular characteristic is intentionally augmented to enhance overall performance, thus fulfilling the functional requirements. In this study, a curve differential growth implementation was developed to obtain space-filling and self-avoiding paths. By applying successive iterations of the algorithm to an initial curve, a set of curves was generated. These curves were then organized in three-dimensional Euclidean space and combined into a NURBS surface. As a case study, the design of a coaxial counterflow heat exchanger employed the proposed modeling algorithm. The resulting model underwent a numerical simulation to assess the heat transfer rate and pressure drops. Material extrusion technology was used to manufacture a prototype for preliminary demonstration, although further studies are required to ensure watertight functional parts. Numerical results indicate that the proposed design exhibits a better heat transfer rate in a smaller size but leads to higher pressure drops when compared to three equivalent plain pipe solutions (with matching length, surface area, and heat transfer rate).

Keywords: Additive Manufacturing , Bioinspiration , Biomimicry , Differential Growth , Geometric Modeling , Space-Filling Curves

The present work proposes the use of point clouds differential entropy as a new method for reverse engineering quality assessment. This quality assessment can be used to measure the shape deviation of objects made with additive manufacturing or CNC techniques. The quality of the execution is intended as a measure of the deviation of the geometry of the obtained object compared to the original CAD model. The method exploits the quality index of the CorAl method. The advantages of CorAl are several, among them the use of a unique index of comparison, no problem of commutativity of the comparison, noise immunity, low influence of the presence of holes and of the point cloud densities. It is possible to plot quality maps showing the areas with the greatest deviation. In experiments, objects obtained by additive manufacturing with different print qualities are tested. The robustness of the method is also demonstrated. The quality index evaluated for each object, as defined in the CorAl method, turns out to be gradually closer to 0 as the quality of the piece's construction increases.

Keywords: Deviation Analysis , Differential Entropy , Point Clouds , Quality Assessment

Over the last few years, significant interest has been addressed in developing computer-based methods to document and analyze fragments of ceramics sherds in archaeology. This is because traditional manual processes do not allow for an objective, repeatable, and reproducible analysis of the large quantities of material needed to fully understand and explain human practices in various cultural contexts, such as the economy, daily life, and the material expression of religious beliefs. In that context, this paper proposes a fully digital methodology resulting from the constitution of an international research group coming from different scientific backgrounds: archaeologists with specific skills and experience in fast 3D geometry acquisition methods and researchers who developed and published the only available computer-based process for recognizing the geometric and morphological sherds features analyzed by archaeologists. The proposed methodology consists of two main parts: 1. 3D acquisition of sherds with the construction of the discrete 3D manifold model based on the Structure for Motion technologies; 2. recognition, segmentation, and dimensional characterization of morphological and geometrical features based on the codification and algorithmic implementation of the knowledge used by the archeologists in the traditional method. The method was applied to analyze a set of 133 sherds excavated at Tell el-Burak (Lebanon) to obtain, through the analysis of the namely Phoenician carinated-shoulder amphorae, new insights into the economic organization of the Phoenician homeland. The method demonstrated the potential for objectively, repeatedly, and reproducibly analyzing large quantities of sherds. Furthermore, it allowed studying sherds by generating new high-level knowledge from those acquired from 3D models; in particular, this paper introduces new morphological features that help the archaeologist classify fragments from an analysis of the rim's shape.

Keywords: 3D archeology , Automatic feature recognition , Hierarchical rims clusterization , Phoenician amphorae , Pottery , Structure from motion

The alignment of large datasets associated with 3D reconstructions is still an open issue in the scientific community. Among the several strategies available in the literature, some are based on using geometrical features. In this paper, the Authors have investigated the reliability of associating ideal planes with non-ideal roof features, which may be used to realign 3D terrestrial reconstructions. The obtained results underline a deep influence from noise, which affects the non-ideal roof feature and ideal plane association, and the necessity to define additional experiments to confirm the robustness of the solution.

Keywords: feature-based alignment , marker-less alignment , non-ideal feature approximation , terrestrial point-cloud

The paper proposes a new recognition rule to automatically identify the spine line by detecting vertebral apophyses from discrete models of human backs collected by 3D scanning. Unlike previous 3D optical approaches, the process described here aims to directly detect spinal apophyses, following the posturologist's method. These anatomical landmarks are identified not as areas of the back surface with specific shapes, but by searching for appropriate local shape perturbations. Except for vertebral prominences that are convex regions, spinal apophyses are generally unrelated to specific surface shapes. The rule has been tested on several human backs. For each, an experienced operator identified the spinal apophyses from palpation and indicated their position by applying an adhesive marker on the back surface. These positions are used as a reference to compare the vertebral apophyses automatically localized by the methodology proposed here. The experimental results show that the rule discriminates well even blurred vertebral prominences.

Keywords: 3D optical methods , Local shape analysis , Shape index , Spinal apophyses recognition , Spine line

The conceptual design stage is one of the main challenging phases in System Engineering. Starting from the High-Level Requirements (provided by the project needs), defining the broad features and conditions that a product must ensure, different design solutions are often implemented. Several methodologies can aid whenever a decision-making process has to be performed. Among these, the Fuzzy Analytic Hierarchy Process (Fuzzy AHP) stands out, providing a rational framework for a needed decision by quantifying its criteria and alternative options, and for relating those elements to the overall goal. Fuzzy AHP centralizes the opinion of experts who, through objective and subjective opinions, can rank the conceptual alternatives. The paper deals with the assessment of components for thermonuclear reactors, in particular the design of the DTT Divertor In-Vessel Fixation System. The main requirements that the Fixation System must guarantee are strictly related to the geometric-dimensional constraints concerning the presence of the various in-vessel components. Furthermore, the Fixation System must withstand the strong loads acting on the Divertor due to the partial or full loss of plasma confinement (Disruption Events). The aim is, therefore, to identify, through Fuzzy AHP, among different alternatives, the solution which best matches the functional requirements, geometrical constraints and Remote Handling compatibility.

Keywords: AHP , DTT Divertor , System Engineering

Over the decades, technical documentation has moved from paper to digital, until today in which operators, through Augmented Reality (AR), have the possibility to be helped in component location and recognition for different procedures. To support these activities, AR interfaces need to be developed with instructions provided through visual assets tailored to the information to convey. For localization tasks, auxiliary models, i.e., standard geometric shapes are the most suited. In this work, we propose ADAM (Automatic Development of Auxiliary Models): an authoring tool to support designers in generating various shapes of auxiliary models in the right dimensions and without modeling them in a CAD software. Thanks to this tool, the designer has a ready-to-use database of auxiliary models to choose from reusable in different AR technical documentations. In this way, ADAM allows to significantly reduce the time spent creating each auxiliary model from scratch. We validated our tool in a user study. A focus group of expert designers were asked to implement an AR interface, using auxiliary models for a localization task, with both ADAM Tool and the current authoring practice. The results confirmed that our tool outperforms the current authoring practice in terms of time performance and user experience.

Keywords: Augmented Reality , Authoring , Auxiliary Model , CAD , Technical Documentation

Extended Reality (XR) applications require Photorealistic Virtual Prototypes (PVPs), usually obtained by generating a polygon-based textured model of the original CAD (Computer Aided Design). Getting PVPs requires specific rendering and texturing software tools that experienced technicians use. Automatic simplification and conversion approaches from CAD to XR exist but are almost all focused on models without textures. The paper aims to establish a semi-automatic method for creating low-poly PVPs for XR starting from 3D CAD models. The process, implemented in Blender, consists of several steps. First, starting from a high-poly model imported from a 3D mechanical CAD system, the modelling cage (a low-poly simplified version) is designed. Second, a low-poly variety of the CAD geometries are generated using Blender modifiers (i.e., shrinkwrap, subdivision surface and Boolean). Texture mapping is carried out on the cage. Then, by combining Shrinkwrap, Boolean and Subdivision Surface modifiers, the cage is projected on the CAD-imported high-poly model. Thus, it becomes a low-poly version of the same geometry. Finally, the Normal Baking process adds high-frequency details (e.g., engravings). Thanks to the generation of a UV-Mapped cage wrapping up the component, in case of local modifications to the latter, Blender semi-automatically updates the PVP. The method was used on three stock versions of a sporting rifle. With an average duration of 23 min, the proposed approach more than halved the time required with manual modelling techniques.

Keywords: 3D Modelling , Extended Reality , Texture Mapping , Virtual Prototyping