Geometric modeling and processing

Purpose: The current study aimed to propose a Deep Learning (DL) and Augmented Reality (AR) based solution for a in-vivo robot-assisted radical prostatectomy (RARP), to improve the precision of a published work from our group. We implemented a two-steps automatic system to align a 3D virtual ad-hoc model of a patient's organ with its 2D endoscopic image, to assist surgeons during the procedure. Methods: This approach was carried out using a Convolutional Neural Network (CNN) based structure for semantic segmentation and a subsequent elaboration of the obtained output, which produced the needed parameters for attaching the 3D model. We used a dataset obtained from 5 endoscopic videos (A, B, C, D, E), selected and tagged by our team's specialists. We then evaluated the most performing couple of segmentation architecture and neural network and tested the overlay performances. Results: U-Net stood out as the most effecting architectures for segmentation. ResNet and MobileNet obtained similar Intersection over Unit (IoU) results but MobileNet was able to elaborate almost twice operations per seconds. This segmentation technique outperformed the results from the former work, obtaining an average IoU for the catheter of 0.894 (σ = 0.076) compared to 0.339 (σ = 0.195). This modifications lead to an improvement also in the 3D overlay performances, in particular in the Euclidean Distance between the predicted and actual model's anchor point, from 12.569 (σ= 4.456) to 4.160 (σ = 1.448) and in the Geodesic Distance between the predicted and actual model's rotations, from 0.266 (σ = 0.131) to 0.169 (σ = 0.073). Conclusion: This work is a further step through the adoption of DL and AR in the surgery domain. In future works, we will overcome the limits of this approach and finally improve every step of the surgical procedure.

Keywords: Deep learning , Intra-operative , Neural network , Semantic segmentation

The design process of industrial products considers different aspects of the product lifecycle to make decisions about the functionality, manufacturability, usability, among other aspects related to the user interaction. Assembly sequence definition is an important phase of the product development process that is normally defined during the detailed design stage, and it is mainly based on skill and experience of manufacturing designers. The prospect to automatically identify possible assembly sequences at early stages of the design process, starting from contact or liaison information between components extracted from 3D CAD models would lead up to reduce time and costs, and would give interactive information for support designers during decision making activities. In this way, authors propose a computer application, so called Automatic Sequence Planner for Industrial Products (ASPIP), to automatically identify assembly sequences of an industrial product. The core of the application is based on an existent approach for Assembly Sequence Analysis, which is followed and presented step by step to enable the designer to create the assembly sequence. The tool enables the analysis of the liaison graph of the components of the product, which is automatically obtained from a kinematically stable CAD model, and automatically obtains a list of assembly sequences with at least one feasible sequence. The assembly sequence analysis of an industrial product is presented as a validation of the functionality of the application ASPIP.

Keywords: Assembly Modeling Liaisons , Assembly Sequence Analysis , Assembly Sequence Planning , Computer Aided Systems , Feasible Assembly Sequence

In the previous Design for Sintering Club Project the design procedure developed in previous studies has been applied to real industrial parts, aiming at verifying the reliability in predicting the anisotropic dimensional changes on sintering. Satisfactory results were obtained, and directions for further improvements were also highlighted, so that a new Club Project was proposed to the industrial partners involved in the first one. Design for Sintering 2 Club Project aims at improving the effectiveness and reliability of the design procedure, both enlarging the reference database, and investigating in depth the mechanisms responsible for anisotropic dimensional change on sintering. In the first part of the three years project the influence of geometry and green density is studied, considering different materials representing both solid-state sintering and liquid-phase sintering. New anisotropy parameter describing anisotropic dimensional changes is proposed based on the analysis of results. © European Powder Metallurgy Association (EPMA)

Keywords: anisotropy , design for sintering , dimensional change

Rail–wheel interaction is one of the most significant and studied aspects of rail vehicle dynamics. The vibrations caused by rail–wheel interaction can become critical when the radial, lateral and longitudinal loads of the vehicle, cargo and passengers are experienced while the vehicle is in motion along winding railroad paths. This mainly causes an excessive production of vibrations that may lead to discomfort for the passengers and shortening of the life span of the vehicle's body parts. The use of harmonic response analysis (HRA) shows that the wheel experiences high vibrational amplitudes from both radial and lateral excitation. The present study describes a numerical and experimental design procedure that allows mitigation of the locomotive wheel resonance during radial and lateral excitations through viscoelastic layers. It is proven that these high frequencies can be reduced through the proper design of damping layer mechanisms. In particular, three parametric viscoelastic damping layer arrangements were analyzed (on the web of both wheel sides, under the rim of both wheel sides and on the web and under the rim of both wheel sides). The results demonstrate that the correct design and dimensions of these viscoelastic damping layers reduce the high-amplitude resonance peaks of the wheel successfully during both radial and lateral excitation.

Keywords: harmonic response analysis , lateral excitation , modal analysis , radial excitation , viscoelastic damping layers , web and rim parametric design

Assembly process of aeronautical skin panels deals with large, thin and compliant components, which are usually joined with rivets. A leading challenge is the control of part-to-part gaps prior to riveting operation, which must be maintained below tight design specification limits to avoid excessive pretensions of the rivets which, if exceeded, impair the durability of the whole skin assembly. Gaps are compensated by number of time consuming and costly manual inspection-repair quality loops, which involve measuring gaps, disassembling parts, adding be-spoke shims, re-assembling parts. This paper proposes a novel methodology to support the inspection-repair quality loops with the aim to model and optimise the shape of the shims with the ultimate goal of reducing/eliminating manual and trial-and-error measurements as per today best practice. The methodology will be discussed in two steps: (1) physics-based variation simulation to model generation and propagation of dimensional and geometrical variations (by using scanning data o morphing mesh model) during multi-stage assembly operations; (2) virtual shimming simulator to model and optimise shimming condition between parts being assembled. The proposed methodology is presented and validated using the assembly process of the vertical stabiliser for commercial aircrafts.

Keywords: Aircraft Skin Assembly , Morphing Mesh , Physics-based Modelling , Scanning Data , Virtual Shimming Simulator

In this work is analyzed the possibility to use optical techniques for the characterization of airless radial tire. Electronic Speckle Pattern Interferometry (ESPI), laser scanner based on principle of triangulation and Digital Image Correlation (DIC) have been used to acquire and study this kind of tire. A MICHELIN® X® TWEEL® UTV has been considered as case study. The acquisitions have been used for the measurement of the shape for testing junction areas and to evaluate the structure behavior under a vertical load.

Keywords: Composite laminates , Laser scanner , NDI , Tire

The aim of the current work was to analyze the influence of the ferrule effect for hybrid composite endodontic post designs consisting of carbon (C) and glass (G) fiber-reinforced polyetherimide (PEI), in upper canine teeth. Starting from theoretical designs of C-G/PEI hybrid composite posts with different Young's moduli (Post A-57.7 GPa, Post B-31.6 GPa, Post C-graduated from 57.7 to 9.0 GPa in the coronal-apical direction) in endodontically treated anterior teeth, the influence of the ferrule effect was determined through finite element analysis (FEA). On the surface of the crown, a load of 50 N was applied at 45° to the longitudinal axis of the tooth. Maximum principal stresses were evaluated along the C-G/PEI post as well as at the interface between the surrounding tooth structure and the post. Maximum stress values were lower than those obtained for the corresponding models without a ferrule. The presence of a ferrule led to a marked decrease of stress and gradients especially for posts A and B. A less marked effect was globally found for Post C, except in a cervical margin section along a specific direction, where a significant decrease of the stress was probably due to local geometric features, compared to the model without a ferrule. The presence of a ferrule did not generally provide a marked benefit in the case of the graduated Post C, in comparison to other C-G/PEI posts. The outcomes suggest how such a hybrid composite post alone should be sufficient to optimize the stress distribution, dissipating stress from the coronal to the apical end.

Keywords: Computer-Aided Design , Endodontic post design , Finite element analysis , Polyetherimide composites , Reverse engineering

Industry 4.0 promises to increase the efficiency of production plants and the quality of the final product. Consequently, companies that implement advanced solutions in production systems will have a competitive advantage in the future. The principles of Industry 4.0 can also be applied to shipyards to transform them into “smart shipyards” (Shipyard 4.0). The aim of this research is to implement an interactive approach by Internet of Things on a closed power-loop test bench equipped with sophisticated sensors that is specifically designed to test high-power thrusters before they are installed on high-speed crafts, which are used in passenger transport. The preliminary results of the proposed Internet of Things-platform demonstrates the efficacy of the decision-making support tool in improving the design of propulsion systems and increasing their efficiency compared to traditional systems.

Keywords: CAD modelling , Experimental tests , Industry 4.0 , Internet of Things (IoT) , Test bench

Total elbow arthroplasty (TEA) is an effective and frequently used treatment for patients with debilitating elbow pathology. Total elbow prostheses have lagged behind those of the knee, hip and shoulder for different reasons, such as the high failure rate of the early designs. Concern remains regarding the longevity of TEA implants, especially in younger patients. The main cause of revision of the implant is usually related to the phenomenon of aseptic loosening mainly due to the cement-bone interface failure. Aim of this work is the biomechanical analysis of a new elbow prosthesis to investigate the mechanical behaviour at the cement-bone interface. For this reason, a musculoskeletal model has been developed by modelling the forces of the muscles and after FEM analyses have been performed. Obtained results confirm the validity of the implemented model and can provide guidelines for surgeons regarding the implant configurations with the aim to reduce the aseptic loosening.

Keywords: CAD , FEM , Reverse engineering , Total elbow arthroplasty

Potteries are the most numerous finds found in archaeological excavations; they are often used to get information about the history, economy, and art of a site. Archaeologists rarely find complete vases but, generally, damaged and in fragments, often mixed with other pottery groups. By using the traditional manual method, the analysis and reconstruction of sherds are performed by a skilled operator. Reviewed papers provided evidence that the traditional method is not reproducible, not repeatable, time-consuming and its results have great uncertainties. To overcome the aforementioned limits, in the last years, researchers have made efforts to develop computer-based methods for archaeological ceramic sherds analysis, aimed at their reconstruction. To contribute to this field of study, in this paper, a comprehensive analysis of the most important available publications until the end of 2019 is presented. This study, focused on pottery fragments only, is performed by collecting papers in English by the Scopus database using the following keywords: "computer methods in archaeology", "3D archaeology", "3D reconstruction", "automatic feature recognition and reconstruction", "restoration of pottery shape relics". The list is completed by additional references found through the reading of selected papers. The 53 selected papers are divided into three periods of time. According to a detailed review of the performed studies, the key elements of each analyzed method are listed based on data acquisition tools, features extracted, classification processes, and matching techniques. Finally, to overcome the actual gaps some recommendations for future researches are proposed.

Keywords: 3D archaeology , 3D reconstruction , Automatic feature recognition and reconstruction , Computer methods in archaeology , Restoration of pottery shape relics

Secondary features, such as fillets, rounds, chamfers and grooves, are simple transitions between primary features, generally introduced in order to remove the sharp edges created by the intersection of primary features. Being able to distinguish secondary from primary features is important in various application contexts, such as reverse engineering, automatic geometric inspection of real scanned objects, and for preparation of models for FEM analysis and CNC tool-path generation. The process for the recognition of secondary features from high-density tessellated models of real work-pieces is intrinsically complex for several reasons. This explains why, currently, there are no methodologies able to recognize automatically secondary features and the investigation on secondary features is mostly focused on B-Rep models. In a previous paper, the authors proposed a method for secondary features recognition from discrete geometric models synthetically generated. Here the methodology is extended to discrete geometric models experimentally acquired, for which the recognition is a very complex process, due to the object discretization, to its non-ideal geometry and to measurement errors.

Keywords: Blending features , Feature recognition , Fuzzy logic , Point cloud segmentation

Sports equipment design is a young and evolving engineering discipline focused on the best simultaneous optimization of user and product as a system. In motorsports, in particular, the final performance during a race depends on many parameters related to the vehicle, circuit, weather, and tyres and the personal feelings of every single driver. Top teams in high-tech categories can invest huge amounts of money in developing simulators, but such economic commitment is not sustainable for all those teams that operate in minor but very popular categories, such as karts or mini-motorcycles. In these fields, the most common design approach is trial and error on physical prototypes. Such an approach leads to high costs, long optimization times, poor innovation, and inefficient management of the design knowledge. The present paper proposes a driver centred methodology for the design of an innovative mini racing motorcycle frame. It consists of two main phases: the drivers' feelings translation into engineering requirements and constraints, and the exploration of the design solution space. Expected effects of the application of the proposed methodology are an overall increase in the degree of innovation, time compression, and cost reduction during the development process, with a significant impact on the competitiveness of small racing teams in minor categories.

Keywords: Design methodology , Racing motorcycle frame design , Topological optimization

The aim of this work is the design of a new customised elbow orthosis completely realized by Additive Manufacturing and the development of generative algorithms for parametric modelling and creation of 3D patterns to be adapted to the CAD model. This work describes a method to perfect the design of a custom elbow orthosis. A reverse engineering approach has been used to digitalize the patient's arm and the subsequent CAD modelling of the structure of the custom elbow orthosis has been performed. In particular, two algorithms have been implemented for the creation of 3D patterns and Voronoi tessellations. Subsequently, FEM analyses have been carried out to validate the design. Finally, a prototype of the elbow orthosis with Voronoi tessellation has been realized by means of the SLS technology. The results obtained have demonstrated that the implemented algorithm solved the problems found during CAD modelling with conventional software. Furthermore, the results of FEM analyses have validated the design choices. All this allowed realizing the prototype by AM technologies without problems. Moreover, the new proposed modelling approaches allows creating, in an interactive way, patterns on complex surfaces. The results of this research activity present innovative elements of originality in the CAD modelling sector, which can contribute to solving problems related to the modelling for Additive Manufacturing. Furthermore, another innovative characteristic of the device is the use of torsion springs that simulate the action of physiotherapists during exercises for patient rehabilitation.

Keywords: Additive manufacturing , Computer aided design , Elbow orthosis , Generative design , Reverse engineering

Tibial fractures are common injuries in people. The proper treatment of these fractures is important in order to recover complete mobility. The aim of this work was to investigate if screw positioning in plates for proximal tibial fractures can affect the stability of the system, and if it can consequently influence the patient healing time. In fact, a more stable construct could allow the reduction of the non-weight-bearing period and consequently speed up the healing process. For that purpose, virtual models of fractured bone/plate assemblies were created, and numerical simulations were performed to evaluate the reaction forces and the maximum value of the contact pressure at the screw/bone interface. A Schatzker type I tibial fracture was considered, and four different screw configurations were investigated. The obtained results demonstrated that, for this specific case study, screw orientation affected the pressure distribution at the screw/bone interface. The proposed approach could be used effectively to investigate different fracture types in order to give orthopaedists useful guidelines for the treatment of proximal tibial fractures.

Keywords: CAD , FEM , Implant stability , Locking plates , Reverse engineering , Tibial fracture

Purpose: The purpose of this paper is to implement a new process aimed at the design and production of orthopaedic devices fully manufacturable by additive manufacturing (AM). In this context, the use of generative algorithms for parametric modelling of additively manufactured textiles (AMTs) also has been investigated, and new modelling solutions have been proposed. Design/methodology/approach: A new method for the design of customised elbow orthoses has been implemented. In particular, to better customise the elbow orthosis, a generative algorithm for parametric modelling and creation of a flexible structure, typical of an AMT, has been developed. Findings: To test the developed modelling algorithm, a case study based on the design and production of an elbow orthosis made by selective laser sintering was investigated. The obtained results have demonstrated that the implemented algorithm overcomes many drawbacks typical of the traditional computer aided design (CAD) modelling approaches. The parametric CAD model of the orthosis obtained through the new approach is characterised by a flexible structure with no deformations or mismatches and has been effectively used to produce the prototype through AM technologies. Originality/value: The obtained results present innovative elements of originality in the CAD modelling sector, which can contribute to solving problems related to modelling for AM in different application fields.

Keywords: Additive manufacturing , Additively manufactured textiles , AM technologies , CAD modeling , Elbow orthosis , Generative algorithms

Tooth loss is a common pathology that affects many people. Dental osseointegrated implants are the ideal solution to restore normal functionality in partially or completely edentulous patients. The not perfect osseointegration and the fixture fracture are the main causes of failure for these kinds of implant. To avoid these drawbacks, several studies have been conducted to analyse the behaviour of dental implants. Aim of this work is to analyse the biomechanical behaviour of three different endosseous dental implants. For this purpose, a new numerical model has been developed to simulate different levels of osseointegration and to evaluate the stress values on the bone at different times. In this way, it can be investigated the possibility of anticipating the use of dental implants that usually is delayed three months after surgery. Obtained results confirm the validity of the proposed approach and can provide useful guidelines for dentists.

Keywords: CAD , Dental implant , FEM , Osseointegration , Virtual simulation

In the last two decades, osseointegrated prostheses have been shown to be a good alternative for lower limb amputees experiencing complications in using a traditional socket-type prosthesis; however, restraining biomechanical issues, such as peri-prosthetic bone fractures or loosening, are present. To better understand and overcome these limiting issues, and thus reduce the number of implant failures, many studies have investigated the stress distribution on bone and implant during normal daily activities. The aim of this study was a biomechanical analysis of two different osseointegrated implants, a screw-type (OPRA) and a press fit system (OPL, Osseointegrated Prosthetic Limb), to evaluate the stresses generated in bone and prosthesis during a fall. In particular, four scenarios have been experimentally reproduced to determine the loads on the limb during different kinds of fall. For this purpose, a motion capture system and a force plate have been used. Numerical FEM (Finite Element Method) simulations have been performed to compare the behaviour of the OPRA and OPL systems in different fall scenarios. The obtained results showed that a fall backwards due to balance loss is the most stressful scenario among the ones analysed. As regards the comparison between OPRA and OPL devices, it emerged they have similar behaviours in terms of peak values of the stress, but the OPL implant generates larger high-stress areas in the distal femur as compared with the OPRA system.

Keywords: CAD , Finite element analysis , OPL osseointegrated prosthesis , OPRA , Transfemoral amputee

The current generation of transcatheter heart valves (THV), as the Edwards SAPIEN 3 Ultra (S3), is not specifically designed for mitral position implantation and has intrinsic design geometry that may make mitral implantation suboptimal. This study aimed to develop a computed-tomography (CT) based CAD workflow for the preoperative planning of transcatheter mitral valve replacement (TMVR) by evaluating the resulting obstruction in the left ventricular outflow tract (LVOT). Specifically, the computational framework to reconstruct heart anatomy and virtually deploy the THV into mitral valve annulus was developed and successively applied to the cases of two patients who experienced annuloplasty ring failure. Planimetric assessment of the cross-sectional area of the neo-LVOT was quantified at different anatomic levels of implanted THV. Findings revealed the importance of the proposed CAD modeling workflow to enable more informative pre-operative assessments of the risk related to the development of the neo-LVOT obstruction and even to guide the Heart Team regarding device selection, sizing and intended positioning for TMVR.

Keywords: CAD , Medical imaging , Reverse engineering , Transcatheter mitral valve replacement , Virtual simulation

Parallel-sided foil sections are used for centerboards and rudders in sailing dinghy classes and also for struts placed in a fluid flow. The objective of this work is to create a systematic series of parallel-sided sections to be used under different conditions, with an emphasis on the sailing dinghies 470, 420 and Optimist. The loss, and surprisingly the gain, in performance relative to 4-digit NACA sections are also investigated. A 2D Reynolds-averaged Navier-Stokes solver is used with the k-ω SST turbulence model and the gamma transition criterion. A verification study is carried out based on four grids of systematically varied density, and results compared with experimental data on a NACA 64-006 section. The parallel-sided sections are modeled with rational Bézier curves whose geometrical parameters permit to link the shape of the profile to physical variables, which are systematically varied. Three Reynolds numbers and two angles of attack are investigated. Systematic plots show the influence of the trailing edge angle and nose radius for the different section families, and the optimum combination is presented in a table. Physical explanations of the trends, and of the exceptions, are given in the paper, using flow visualizations as well as pressure and friction plots.

Keywords: Bézier curves , CAD , Centerboard , Gamma transition criterion , Low Reynolds number , NACA , Parallel-sided , Sailing , Systematic investigation

One of the main challenges in the roadmap to the realization of fusion energy is to develop a heat and power exhaust system able to withstand the large loads expected in the divertor of a fusion power plant. The challenge of reducing the heat load on the divertor targets is addressed, within the mission 2 ‘Heat-exhaust systems', through the investigation of divertor configurations alternative to the standard Single Null (SN), such as the Snowflake (SF), Double Null (DN), X and Super-X (SX) divertors. This paper focuses on a preliminary engineering assessment of the alternative configurations proposed for the EU DEMO reactor. Starting from the description of the optimized plasma shape developed for each configuration, the 3D geometrical description of the Magnet System and of the main Mechanical Structures (Vacuum Vessel and in-vessel components) is presented. Based on the 3D geometry, the compatibility of the location and dimensions of ports with Remote Maintenance needs is discussed and possible design optimizations are proposed both for the Magnets system and the mechanical structures design. Finally, the various configurations are compared with regard to the engineering and feasibility aspects.

Keywords: Alternative magnetic configurations , CAD , Conceptual design , DEMO , Divertor concept