Geometric modeling and processing

Images obtained in an underwater environment are often affected by colour casting and suffer from poor visibility and lack of contrast. In the literature, there are many enhancement algorithms that improve different aspects of the underwater imagery. Each paper, when presenting a new algorithm or method, usually compares the proposed technique with some alternatives present in the current state of the art. There are no studies on the reliability of benchmarking methods, as the comparisons are based on various subjective and objective metrics. This paper would pave the way towards the definition of an effective methodology for the performance evaluation of the underwater image enhancement techniques. Moreover, this work could orientate the underwater community towards choosing which method can lead to the best results for a given task in different underwater conditions. In particular, we selected five well-known methods from the state of the art and used them to enhance a dataset of images produced in various underwater sites with different conditions of depth, turbidity, and lighting. These enhanced images were evaluated by means of three different approaches: objective metrics often adopted in the related literature, a panel of experts in the underwater field, and an evaluation based on the results of 3D reconstructions.

Keywords: 3D reconstruction , Automatic colour equalization , Benchmark , CLAHE , Colour correction , Dehazing , Lab , Non-local dehazing , Screened poisson equation , Underwater image enhancement

Objectives To investigate the influence of specific resin-composite, glass ceramic and glass ionomer cement (GIC) material combinations in a “multi-layer” technique to replace enamel and dentin in class II mesio-occlusal-distal (MOD) dental restorations using 3D-Finite Element Analysis (FEA). Methods Four 3D-FE models (A–D) of teeth, adhesively restored with different filling materials, were created and analyzed in comparison with a 3D model (E) of a sound lower molar. Models A, B & C had “multilayer” constructions, consisting of three layers: adhesive, dentin replacement and enamel replacement. Model A: had a low modulus (8 GPa) composite replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model B: had a GI cement replacing dentin and a higher modulus (12 GPa) composite replacing enamel. Model C: had a low modulus (8 GPa) composite replacing dentin and a very high modulus (70 GPa) inlay replacing enamel. Model D: had a lithium disilicate inlay replacing both dentin and enamel with a luting cement base-layer. Polymerization shrinkage effects were simulated and a load of 600 N was applied. All the materials were assumed to behave elastically throughout the entire deformation. Results Model A showed the highest stress distribution along all the adhesive interfaces of the shrinking resin-based materials with a critical condition and failure risk marginally and internally. Model D, by contrast, showed a more favorable performance than either of the multilayer groups (A–C). Stress and displacement plots showed an elastic response similar to that obtained for the sound tooth model. Model B and Model C performed according to their bilayer material properties. The use of a non-shrink dentin component simulating a GIC clearly affected the shrinkage stress at the basis of the Model B; while the bulk resin composite having a 12 GPa Young's modulus and linear polymerization shrinkage of 1% strongly influenced the biomechanical response in the bucco-lingual direction. Significance Direct resin-based composite materials applied in multilayer techniques to large class II cavities, with or without shrinking dentin layers, produced adverse FEA stress distributions and displacements. An indirect lithium disilicate inlay used to replace lost dentin and enamel in posterior restored teeth generated lower stress levels, within the limits of the elastic FEA model.

Keywords: CAD , Class II restorations , Finite element analysis , Image analysis , Materials properties

Objective To assess the effect of a ferrule design with specific post material-shape combinations on the mechanical behavior of post-restored canine teeth. Methods Micro-CT scan images of an intact canine were used to create a 3-D tessellated CAD model, from which the shapes of dentin, pulp and enamel were obtained and geometric models of post-endodontically restored teeth were created. Two types of 15 mm post were evaluated: a quartz fiber post with conical–tapered shape, and a carbon (C) fiber post with conical–cylindrical shape. The abutment was created around the coronal portion of the posts and 0.1 mm cement was added between prepared crown and abutment. Cement was also added between the post and root canal and a 0.25 mm periodontal ligament was modeled around the root. Four models were analysed by Finite Element (FE) Analysis: with/without a ferrule for both types of post material and shape. A load of 50 N was applied at 45° to the longitudinal axis of the tooth, acting on the palatal surface of the crown. The maximum normal stress criterion was adopted as a measure of potential damage. Results Models without a ferrule showed greater stresses (16.3 MPa) than those for models with a ferrule (9.2 MPa). With a ferrule, stress was uniformly distributed along the abutment and the root, with no critical stress concentration. In all models, the highest stresses were in the palatal wall of the root. Models with the C-fiber post had higher stress than models with the quartz fiber posts. The most uniform stress distribution was with the combination of ferrule and quartz fiber post. Significance The FE analysis confirmed a beneficial ferrule effect with the combination of ferrule and quartz fiber post, with tapered shape, affording no critical stress concentrations within the restored system.

Keywords: CAD , Dental materials , Endodontic treatment , Finite element analysis , Image analysis , Materials properties

Objectives To study the influence of resin based and lithium disilicate materials on the stress and strain distributions in adhesive class II mesio-occlusal-distal (MOD) restorations using numerical finite element analysis (FEA). To investigate the materials combinations in the restored teeth during mastication and their ability to relieve stresses. Methods One 3D model of a sound lower molar and three 3D class II MOD cavity models with 95° cavity-margin-angle shapes were modelled. Different material combinations were simulated: model A, with a 10 μm thick resin bonding layer and a resin composite bulk filling material; model B, with a 70 μm resin cement with an indirect CAD-CAM resin composite inlay; model C, with a 70 μm thick resin cement with an indirect lithium disilicate machinable inlay. To simulate polymerization shrinkage effects in the adhesive layers and bulk fill composite, the thermal expansion approach was used. Shell elements were employed for representing the adhesive layers. 3D solid CTETRA elements with four grid points were employed for modelling the food bolus and tooth. Slide-type contact elements were used between the tooth surface and food. A vertical occlusal load of 600 N was applied, and nodal displacements on the bottom cutting surfaces were constrained in all directions. All the materials were assumed to be isotropic and elastic and a static linear analysis was performed. Results Displacements were different in models A, B and C. Polymerization shrinkage hardly affected model A and mastication only partially affected mechanical behavior. Shrinkage stress peaks were mainly located marginally along the enamel-restoration interface at occlusal and mesio-distal sites. However, at the internal dentinal walls, stress distributions were critical with the highest maximum stresses concentrated in the proximal boxes. In models B and C, shrinkage stress was only produced by the 70 μm thick resin layer, but the magnitudes depended on the Young's modulus (E) of the inlay materials. Model B mastication behavior (with E = 20 GPa) was similar to the sound tooth stress relief pattern. Model B internally showed differences from the sound tooth model but reduced maximum stresses than model A and partially than model C. Model C (with E = 70 GPa) behaved similarly to model B with well redistributed stresses at the occlusal margins and the lateral sides with higher stress concentrations in the proximal boxes. Models B and C showed a more favorable performance than model A with elastic biomechanics similar to the sound tooth model. Significance Bulk filling resin composite with 1% linear polymerization shrinkage negatively affected the mechanical behavior of class II MOD restored teeth. Class II MOD direct resin composite showed greater potential for damage because of higher internal and marginal stress evolution during resin polymerization shrinkage. With a large class II MOD cavity an indirect composite or a lithium disilicate inlay restoration may provide a mechanical response close to that of a sound tooth.

Keywords: CAD , Composite , FEA , Inlay , Lithium Disilicate , Micro-CT , Stress analysis

The use of polymer composites has been increasing over the years and nowadays the requirements for designing high performance and lightweight fabrics and laminates for sail manufacturing have become more stringent than ever. The present paper offers an effective methodology that enhances the understanding of the influence of fibres orientation and arrangement of panels on sail performance. Constitutive characteristics of the ten commonly used sail cloths are experimentally measured and their influence on sail dynamic performance is compared using an aerodynamic approach. As expected also in industry 4.0 the method allows to control the production process and final product optimization.

Keywords: Aerodynamic coefficient , Apparent wind angle (AWA) , Apparent Wind Speed (AWS) , CFD analysis , Digital photogrammetry , RE , Turbulence model

Objective To study the influence of the different class II mesio-occlusal-distal (MOD) cavity shape on the stress and strain distributions in adhesive indirect restorations, using numerical finite element analysis (FEA). To investigate the relationship between restored teeth failure and stiffness of food, three values of Young's modulus were used for the food. Methods A 3D model of a sound lower molar and three class II MOD cavities with different shape were created. Slide-type contact elements were used between tooth surface and food. An adhesive resin-based cement, modeled with fixed-type contact elements, and a single restorative filling materials were considered. To simulate polymerization shrinkage effect, which is basically restricted to the thin composite cement layer, shell elements were employed and the thermal expansion approach was used. A vertical occlusal load of 600 N was applied, while assigning fixed zero-displacements on the cutting surfaces below the crevices. All the materials were assumed to be isotropic and elastic. A static linear analysis was carried out. Results In the lingual cusp, the displacements increased as the values of the stiffness food increased. In the restored teeth, the stress near the restoration-tooth interface was strongly dependent on the MOD cavity shape. The stress peaks were mainly located along the enamel–dentin interface at the lingual side; wedge-shaped MOD cavity with a low angle, in combination with the lowest food stiffness provided the best results. Significance A more complex load application on the occlusal surfaces was introduced. Food stiffness slightly affected the stress distribution of the restored and sound teeth. Teeth with adhesive class II MOD indirect resin composite restorations were potentially more susceptible to damage if the class II MOD cavity-margin-angle was higher than 95°. Restored teeth with a higher cavity-margin-angle led to considerable stress concentration in the lingual cusp along the enamel–dentin interface. These models were more susceptible to fracture in the lingual cusps when compared to the buccal ones.

Keywords: CAD , Endodontics , Finite element analysis , Micro-computed tomography , Stress analysis

Sail manufacture has undergone significant development due to sailing races like the America's Cup and the Volvo around the World Race. These competitions require advanced technologies to help increase sail performance. Hull design is fundamentally important but the sails (the only propulsion instrument) play a key role in dynamic of sailboats. Under aerodynamic loads, sail cloth deforms, the aerodynamic interaction is modified and the pressure on the sails is variously distributed resulting in performance inconsistencies. The interaction between fluid and structure necessitates a solution which combines aerodynamic and structural numerical simulations. Furthermore, in numerical simulations the aeroelastic sail characteristics must be known accurately. In this paper, the dynamic performance of a Spinnaker was studied. Digital photogrammetry was used to acquire the images, make the 3D reconstruction of the sail and validate the models in Computational Fluid Dynamics (CFD) analysis. Orthotropic constitutive characteristics of ten different sail cloths were measured by experimental test. The methodology allowed to compare dynamic performance in terms of forces, pressure and vibration for the different sail cloths and different fiber orientations.

Keywords: CFD analysis , Detached eddy simulations , Pressure distributions , Sail aerodynamics , Turbulence models

A new method for secondary features segmentation, performed in highdensity acquired geometric models, is proposed. Four types of secondary features are considered: fillets, rounds, grooves and sharp edges. The method is based on an algorithm that analyzes the principal curvatures. The nodes, potentially attributable to a fillet of given geometry, are those with a certain value for maximum principal curvature. Since the deterministic application of this simple wor king principle shows several problems due to the uncertainties in the curvature estimation, a fuzzy approach is proposed. In order to segment the nodes of a tessellated model that pertain to the same secondary features, proper membership functions are evaluated as function of some parameters, which affect the quality of the curvature estimation. A region growing algorithm connects the nodes pertaining to the same secondary feature. The method is applied and verified for some test cases.

Keywords: Computational geometry , Features extractions , Fuzzy logic , Mechanical engineering computing , Region growing algorithm

The present paper deals with methods for product development aimed to support designing activities and to re-use company know-how. The work is addressed to complex products i.e. products characterized by several components and dependencies among them. Then, the paper presents both the methodological approach and the application to the 3D CAD modelling of an automotive car door assembly. The work uses directed graphs and a series of algorithms to provide a Graphical User Interface (GUI) able to support a designer by reducing the development time of new car door assemblies and increasing the accuracy of the design activities. According to a digital pattern approach, the GUI is used to determine the set of changes to 3D CAD models that typically occur in the automotive field, during the development of new car door assemblies.

Keywords: Automotive car door design and development , CAD modelling , Digital pattern for product development , Directed graphs

Aim of this work is to investigate the behaviour of a new reverse shoulder prosthesis, characterized by a humeral metaphysis with a variable offset, designed to increase the range of movements and to reduce the impingement. In particular, by means of virtual prototypes of the prosthesis, different offset values of the humeral metaphysis have been analysed in order to find the best positioning able to maximize the range of movements of the shoulder joint. The abduction force of the deltoid, at different offset values, has been also estimated. The study has been organized as follows. In the first step, the point clouds of the surfaces of the different components of the prosthesis have been acquired by a 3D scanner. This kind of scanner allows to convert camera images into three-dimensional models by analysing the moiré fringes. In the second step, the acquired point clouds have been post-processed and converted into CAD models. In the third step, all the 3D reconstructed models have been imported and assembled through a CAD system. After, a collision analysis has been performed to detect the maximum angular positions of the arm at different metaphysis offset values. In the last step, FEM models of shoulder joint with the new prosthesis have been created. Different analyses have been performed to estimate how the deltoid abduction force varies depending on the offset of the humeral tray. The study allowed to understand how the offset of the metaphysis affects the performances of the shoulder. The obtained results can be effectively used to give surgeons useful guidelines for the installation of these kinds of implants.

Keywords: CAD , Range of movements , Reverse engineering , Reverse shoulder prosthesis

This paper presents a nonlinear finite element formalism for modelling the dynamics of flexible manipulators using the special Euclidean group SE(3) framework. The method is based on a local description of the motion variables, and results in a singularity-free formulation which exhibits important advantages regarding numerical implementation. The motivation behind this work is the development of a new class of model-based control systems which may predict and thus avoid the deformations of a real flexible mechanism. Finite element methods based on the geometrically exact beam theory have been proven to be the most accurate to account for flexibility: in this paper we highlight the key aspects of this formulation deriving the equations of motion of a flexible constrained manipulator and we illustrate its potential in robotics through a simple case study, the dynamic analysis of a two-link manipulator, simulating different model assumptions in order to emphasize its real physical behavior as flexible mechanism.

Keywords: differential geometry , Flexible manipulators , motion formalism , nonlinear finite element , robot simulation , soft robots

The current trend in manufacturing is to obtain a flexible work cell in which human and robot can safely interact and collaborate. Virtual Reality (VR) represents an effective tool capable of simulating such complex systems with a high level of immersion. In order to take advantage of VR technologies to study Human-Robot Cooperation (HRC), a digital model of a redundant manipulator (KUKA LBR iiwa) has been developed starting with kinematic modeling and then coupled with the real robot. This approach allows simulating HRC in several scenarios, to reproduce the safe behavior on the real robot, as well as to train operators.

Keywords: Human-robot collaboration , Modelling , Simulation , Virtual reality

Transparent and removable aligners represent an effective solution to correct various orthodontic malocclusions through minimally invasive procedures. An aligner-based treatment requires patients to sequentially wear dentition-mating shells obtained by thermoforming polymeric disks on reference dental models. An aligner is shaped introducing a geometrical mismatch with respect to the actual tooth positions to induce a loading system, which moves the target teeth toward the correct positions. The common practice is based on selecting the aligner features (material, thickness, and auxiliary elements) by only considering clinician's subjective assessments. In this article, a computational design and engineering methodology has been developed to reconstruct anatomical tissues, to model parametric aligner shapes, to simulate orthodontic movements, and to enhance the aligner design. The proposed approach integrates computer-aided technologies, from tomographic imaging to optical scanning, from parametric modeling to finite element analyses, within a 3-dimensional digital framework. The anatomical modeling provides anatomies, including teeth (roots and crowns), jaw bones, and periodontal ligaments, which are the references for the down streaming parametric aligner shaping. The biomechanical interactions between anatomical models and aligner geometries are virtually reproduced using a finite element analysis software. The methodology allows numerical simulations of patient-specific conditions and the comparative analyses of different aligner configurations. In this article, the digital framework has been used to study the influence of various auxiliary elements on the loading system delivered to a maxillary and a mandibular central incisor during an orthodontic tipping movement. Numerical simulations have shown a high dependency of the orthodontic tooth movement on the auxiliary element configuration, which should then be accurately selected to maximize the aligner's effectiveness.

Keywords: Computational engineering , Computer-aided design , Finite element analysis , Orthodontic treatment , Patient-specific modeling , Polymeric aligner

The demand of new tools devoted to integrate aesthetic design into classic parametric CAD suites has undergone a raising interest from the user community. Industrial tools for reconstructing the 3D geometry of an object starting from 2D representations and for surfacing wireframe models according to designers intent, assumed a high relevance and have experienced a steady evolution. The problem of surfacing wireframe models with consistent closing surface patches is still a hot topic in the computer graphics as well as in the industrial field, as demonstrated by a number of recent works. In this paper, authors propose a procedure for enhancing the surfacing process by using shading information, together with the wireframe model. In particular, this work allows to use shading, represented either in a rendered 3D model or sketched by a designer, for retrieving consistent geometrical information related to the 3D object. The procedure is accompanied by some selected case studies, to highlight its strengths and weaknesses.

Keywords: 3D reconstruction , CAD , Hand-drawn sketches , Surfacing , Wireframe model

3D body scanners are nowadays used in a range of applications spanning from health, fashion and fitness to reverse engineering applications for robotics and computer vision. Nowadays very good performances are achievable when using commercial 3D body scanners; however, focusing on relative complex shape of some body details, the results still lack precision and acceptable accuracy. Such critical issue remains unsolved also when dealing with the instantaneous acquisition of the hand-wrist-arm (HWA) anatomy. In this paper, we present a new approach that leverages the emerging 3D depth cameras technologies to design a compact low cost 3D dedicated HWA scanner system capable of delivering almost instantaneous full 3D measurement.

Keywords: 3D body scanner , 3D surface , calibration , depth sensors , hand-wrist-arm anatomy

Cardiovascular diagnosis, surgical planning and intervention are among the most interested in recent developments in the field of 3D acquisition, modelling and rapid prototyping techniques. In case of complex heart disease, to provide an accurate planning of the intervention and to support surgical planning and intervention, an increasing number of Hospitals make use of physical 3D models of the cardiac structure, including heart, obtained using additive manufacturing starting from the 3D model retrieved with medical imagery. The present work aims in providing an overview on most recent approaches and methodologies for creating physical prototypes of patient-specific heart and cardiac structures, with particular reference to most critical phases such as segmentation and aspects concerning converting digital models into physical replicas through rapid prototyping techniques. First, recent techniques for image enhancement to highlight anatomical structures of interest are presented together with the current state of the art of semi-automatic image segmentation. Then, most suitable techniques for prototyping the retrieved 3D model are investigated so as to draft some hints for creating prototypes useful for planning the medical intervention.

Keywords: 3D modelling , 3D printing , Cardiovascular diseases , Heart , Medical imagery , Rapid prototyping , Surgical planning

This work presents Reverse Engineering and Computer Aided technologies to improve the inspection of injection moulded electro-mechanical parts. Through a strong integration and automation of these methods, tolerance analysis, acquisition tool-path optimization and data management are performed. The core of the procedure concerns the automation of the data measure originally developed through voxel-based segmentation. This paper discusses the overall framework and its integration made according to Smart Manufacturing requirements. The experimental set-up, now in operative conditions at ABB SACE, is composed of a laser scanner installed on a CMM machine able to measure components with lengths in the range of 5÷250 mm, (b) a tool path optimization procedure and (c) a data management both developed as CAD-based applications.

Keywords: Computer Aided Tolerancing & Inspection , Feature Recognition , Injection Moulding , Path Planning , Product Data Management , Quality Inspection , Reverse Engineering , Segmentation

Nowadays, the most updated CAE systems include structural optimization toolbox. This demonstrates that topological optimization is a mature technique, although it is not a well-established design practice. It can be applied to increase performance in lightweight design, but also to explore new topological arrangements. It is done through a proper definition of the problem domain, which means defining functional surfaces (interface surfaces with specific contact conditions), preliminary external lengths and geometrical conditions related to possible manufacturing constraints. In this sense, its applicability is possible for all kind of manufacturing, although, in Additive Manufacturing, its extreme solutions can be obtained. In this paper, we aim to present the general applicability of topological optimization in the design workflow together with a case study, exploited according to two design intents: the lightweight criterion and the conceptual definition of an enhanced topology. It demonstrates that this method may help to decrease the design efforts, which, especially in the case of additive manufacturing, can be reallocated for other kind of product optimization.

Keywords: Additive Manufacturing , Conceptual Design , Design Intent , Lightweight Design , Topological Optimization

This work describes an integrated method of 3D modelling algorithms with a modal approach in a multibody environment which provides a slimmer and more efficient simulation of flexible component contacts realistically reproducing system impacts and vibrations. A non-linear numerical model of the impulse contact forces based on the continuity approach of Lankarani and Nikravesh is developed. The model developed can evaluate deformation energy taking into account the material's characteristics, surface geometries and the velocity variations of the bodies in contact. ADAMS®-type modelling is applied to the sliding contacts of the links of a chain and its mechanical tensioner (“blade”) in the timing of an internal combustion engine. The blade was discretized by subdividing it into smaller components inter-connected with corresponding centres of gravity through 3D General Forces. Static and dynamic tests were performed to evaluate the stiffness, damping and friction parameters for the multibody model and to validate the methodology.

Keywords: Flexible body , Friction forces , Hysteresis damping , Impact , Slip

This work describes a simple, fast, and robust method for identifying, checking and managing the overlapping image keypoints for 3D reconstruction of large objects with numerous geometric singularities and multiple features at different lighting levels. In particular a precision 3D reconstruction of an extensive architecture captured by aerial digital photogrammetry using Unmanned Aerial Vehicles (UAV) is developed. The method was experimentally applied to survey and reconstruct the 'Saraceni' Bridge' at Adrano (Sicily), a valuable example of Roman architecture in brick of historical/cultural interest. The variety of features and different lighting levels required robust self-correlation techniques which would recognise features sometimes even smaller than a pixel in the digital images so as to automatically identify the keypoints necessary for image overlapping and 3D reconstruction. Feature Based Matching (FBM) was used for the low lighting areas like the intrados and the inner arch surfaces, and Area Based Matching (ABM) was used in conjunction to capture the sides and upper surfaces of the bridge. Applying SIFT (Scale Invariant Feature Transform) algorithm during capture helped find distinct features invariant to position, scale and rotation as well as robust for the affinity transformations (changes in scale, rotation, size and position) and lighting variations which are particularly effective in image overlapping. Errors were compared with surveys by total station theodolites, GPS and laser systems. The method can facilitate reconstruction of the most difficult to access parts like the arch intrados and the bridge cavities with high correlation indices.

Keywords: Architectural reconstruction , Area Based Matching , Feature Based Matching , Photogrammetry , SIFT algorithm