Virtual prototyping and digital twin

Open-cell foams offer several interesting possibilities in numerous technological fields. In fact, they present high surface area to volume ratio as well as enhanced flow mixing and attractive stiffness and strength. However, their complete and reliable characterization has not been completed yet. In fact, there is still no a comprehensive work that relates all the foam geometrical characteristics to their heat transfer and pressure drop features. This paper is the very first outcome of a larger study that aims at realizing open-cell foams via additive manufacturing, testing them, then generating a simulation model based on the real geometries to numerically optimize each parameter. The present manuscript presents the construction of the open-foam via 3D printing and the experimental pressure drop measurements when water flows through the foam.

A 3D numerical model aimed at predicting the deformations of a S355 steel T-joint in both as-welded and post-welding heat treated conditions was developed. Experimental tests were carried out with the objective to collect data necessary to the heat source calibration and model validation in terms of microstructure and joint distortions. All metallurgical phenomena were taken into account such as specific volume change and transformation plasticity induced by solid-state phase transformations. A viscoplasticity model for stress relief processing implemented in Sysweld finite elements code was used. Numerical results showed a satisfactory agreement with experimental ones. Further investigations will be necessary to consider also the validation of residual stress relief effects.

Keywords: Distortions , Microstructure , Steel , Stress relief heat trewatment , Welding simulation

Complexity of dynamical systems are increasing more and more as well as their mathematical models. At the same time, simulation of system behaviour assumes a key role to assure the fulfillment of requirements as performances, quality, safety, and robustness. Therefore, due to model complexity, it is often very complex to assess a system behaviour but a reduction of model complexity could enhance the simulation aimed to specific characteristics of the system. Several useful model order reduction (MOR) techniques exist but each of them is often powerful for specific applications. This review paper deals with MOR by critically comparing the most popular MOR techniques from the fields of structural dynamics, numerical mathematics and systems and control. In particular, after different reduction techniques have been presented, a table summarizing their most important features is proposed, for comparison purpose. The motivation for such comparison stems from the fact that the insight obtained by the comparison allows to make a motivated choice for a particular model reduction technique, on the basis of the desired properties retained in the reduced model. Particular attention is paid on reduction techniques from the area of structural dynamics. Finally, the differences among some of the presented reduction techniques are illustrated, on a quantitative level, by means of their application to the case of a slewing flexible beam. In particular, in the application of the different reduction techniques, a consistent-mass finite element model, with only translational degrees of freedom, is employed as beam full model.

Nowadays companies have to face a competitive market that requires small volumes with a high level of customisations. In this context, assembly quality and timeliness is crucial. To guarantee flexibility and personalization, manual operations still have a crucial role for a lot of manufacturing sectors, so that workers' conditions and ergonomics are important factors to achieve a better product quality and overall cost reduction. Ergonomics evaluation in manufacturing is a challenging and expensive activity that requires a transdisciplinary approach, to merge technical and social sciences to finally have a consolidated and reliable evaluation. This paper compared two digital human simulations tools offered by Siemens Tecnomatix: Jack and Process Simulate. They were applied on the same industrial case study, concerning the hood assembly of an agricultural machine, comparing results on ergonomics reports and usage time. Results confirmed the advantage of adopting a digital approach to predict the human effort and ergonomic risk related to a series of tasks. At the same time, they showed the major strengths and weaknesses of the two analysed tools and defined how they can be successfully adopted by companies. The paper finally provided guidelines to drive companies in choosing the best tool according to their needs.

Keywords: Digital human simulations , Digital manufacturing , Ergonomics , Human-centered design , Transdisciplinary engineering

Virtual reality (VR) offers a promising set of technologies to digitally simulate industrial processes and interaction between humans and machines. However, the use of immersive VR simulations is still limited in industry due to the uncertainty of benefits in respect with traditional digital tools, and the lack of structured methodologies to effectively implement immersive virtual simulations in practice. This paper deals with the application of VR to create virtual manufacturing simulations with the aim to design assembly lines in compliance with factory ergonomics. It proposes a methodology to allow the virtualization and simulation of assembly tasks using a combination of VR tools by replicating, or rather anticipating, what would happen at the shop floor. The adopted tools are Unity 3D for virtual environment generation, HTC VIVE to immerse the user in the virtual factory layout, Xsens as tracking system, and Leap Motion for gesture recognition. The paper also compares the new VR-based procedure with a more traditional desktop-based digital simulation on industrial cases. Results show that the new methodology is more precise to detect the operator's comfort angles and more powerful to predict process criticalities and optimize factory layout design. At the same time, it is less sensitive to errors during ergonomic assessment related to the expert's subjectivity during the analysis. © 2020, Springer-Verlag London Ltd.

Keywords: Human-centered design , Industrial ergonomics , Virtual manufacturing , Virtual reality

Product and process digitalization is pervading numerous areas in the industry to improve quality and reduce costs. In particular, digital models enable virtual simulations to predict product and process performances, as well as to generate digital contents to improve the general workflow. Digital models can also contain additional contents (e.g., model-based design (MBD)) to provide online and on-time information about process operations and management, as well as to support operator activities. The recent developments in augmented reality (AR) offer new specific interfaces to promote the great diffusion of digital contents into industrial processes, thanks to flexible and robust applications, as well as cost-effective devices. However, the impact of AR applications on sustainability is still poorly explored in research. In this direction, this paper proposed an innovative approach to exploit MBD and introduce AR interfaces in the industry to support human intensive processes. Indeed, in those processes, the human contribution is still crucial to guaranteeing the expected product quality (e.g., quality inspection). The paper also analyzed how this new concept can benefit sustainability and define a set of metrics to assess the positive impact on sustainability, focusing on social aspects. © 2021 by the authors.

Keywords: Augmented reality , Humancentered design , Model-based design , Product development , Quality inspection , Social sustainability

Latest trends and developments in digital technologies have enabled a new manufacturing model. Digital systems can monitor, optimize and control processes by creating a virtual copy of the physical world and making decentralized decisions. This paradigm relies on the development of a digital counterpart, the Digital Twin, for each production resource taking part to the whole manufacturing process. Although real applications of Digital Twin may differ in technical and operational details, in the past years, a huge effort has been done in order to identify and define focal functionalities and properties, as well as main challenges for the practical implementation within real factories. This paper is intended to review and analyse principles, ideas and technological solutions of the Digital Twin vision for production processes focusing on the practical industrial implementation. The purpose of this document is therefore to summarize the current state-of-art on Digital Twin concepts, and to draw their up-to-date state for application and deployment in real industrial processes. Finally, future directions for further research are discussed.

Keywords: Digital twin , digital twin industrial architecture , industrial implementation , industry 4.0 , smart manufacturing

In recent years, the use and demand of bicycles have increased thanks to the growing attention to the environment and due to the COVID-19 pandemic situation. At the same time, the design of the bicycles has remained substantially unchanged, improving in materials and components technology. In the off-road sector, two diametrically opposed categories have emerged in terms of comfort and pedalling efficiency. The goal of this research is to introduce a first methodological approach for the optimization of a mountain bike frame. The behaviour of the developed frame aims to combine the pedalling benefits now available only in different and non-comparable bicycle configurations. The first step concerns the modelling of a generic off-road bicycle frame, then its behaviour has been simulated for specific load cases. Subsequently, the part of the bicycle that best performed the double function of compliance and rigidity has been sought through an analysis of the strain energy using FE simulations. Hence, the reference region has been topologically optimized to provide adequate chassis travel performance. The analysis scheme has been iteratively repeated also on other parts of the frame until an acceptable solution is obtained for the utilize presented. The final configuration permits a rear tube and bottom bracket displacement of 10.4 mm and 2.4 mm compared to the 0.5 mm and 0.4 mm of the original frame respectively. The approach described can be proposed as a support for the search for an innovative design for products with unchanged geometries due to the inertia of the designers. At the same time, this methodology aims to expand the possible use of topological optimization, moving away from the classic constraint schemes present in various software.

The miniscrew-assisted rapid palatal expansion approach has given new opportu-nities for the treatment of maxilla transverse deficiency by providing an alternative to the surgical approach for adult patients. However, the presence of a thin palatal bone can compromise the success of such approach. Recently, the digital planning of the miniscrew-assisted appliances has offered unique advantages in terms of safety and accuracy of the overall process. The aim of this study is to describe the digital planning and MSE fabrication with cad-cam technology using 6 mini-screws in cases with a palatal bone thickness of less than 2.5 mm.

Keywords: Digital orthodontics , MARPE , Maxillary transverse deficiency , MSE , Palatal expansion

The quality and acoustic comfort of agricultural tractor cabins are nowadays highly valued by the market. For this reason, tractor manufacturers are more and more interested in improving the behaviour of their vehicles also from an acoustics point of view. A tractor cabin is an unusual environment, with a space mainly developed in the vertical direction, characterised by a relatively small volume of air and surrounded by windows, which can be considered as large reflecting surfaces. This feature causes strong standing waves that, when coupled with an acoustic source, can generate high sound pressure levels resulting in reduced comfort for the driver. This paper investigates, through measurements and simulations, the low frequency acoustic behaviour of a small tractor cabin. The technique adopted for the measurements is based on a multiple transfer function analysis. Measured frequency response functions are processed for the cabin's acoustic mode parameters. The results of the experiments are validated through a finite-element model allowing the reconstruction of the sound pressure contours inside the volume and further analyses.

Keywords: Finite element , Sound absorption , Standing waves , Tractor cabin , Transfer function

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

This paper describes a mechanics–based framework for virtual prototyping of soft robots, i.e. robots with deformable bodies and flexible joints. The framework builds on top of the screw theory, and uses geometrically exact nonlinear beam models for describing the behavior of deformable bodies, as well as the finite element method for space discretization. The computer implementation of this framework results in SimSOFT, a physics engine for soft robots. The capabilities of the framework are illustrated with one general example, an articulated chain of rigid and soft links connected through rigid and flexible joints. Furthermore, several case studies are shown for industrial and medical applications.

Keywords: Continuum mechanics , Design methods , Multibody dynamics , Soft robotics , Virtual prototyping

Within the era of smart factories, concerning the ergonomics related to production processes, the Digital Twin (DT) is the key to set up novel models for monitoring the performance of manual work activities, which are able to provide results in near real time and to support the decision-making process for improving the working conditions. This paper aims to propose a methodological framework that, by implementing a human DT, and supports the monitoring and the decision making regarding the ergonomics performances of manual production lines. A case study, carried out in a laboratory, is presented for demonstrating the applicability and the effectiveness of the proposed framework. The results show how it is possible to identify the operational issues of a manual workstation and how it is possible to propose and test improving solutions.

Keywords: Digital Twin , Ergonomics , Manufacturing , Production process

The paper discusses the application of Reinforcement Learning to the control of an onshore Wave Energy Converter (WEC). The proposed WEC features a simple and low-cost architecture. It is characterized by an oscillating floating rocker arm which moves a four bar linkage in the vertical plane. A mechanical rectifier, based on two one-way clutches and a multiplier gearbox, transforms the low speed oscillating motion of the four bar into a higher-speed unidirectional rotation of the electrical generator. The dynamic model of the WEC, based on multibody approach and Linear Wave Theory, is presented. Then a Reinforcement Learning (RL) algorithm, a Q-learning method, is applied to dynamically adjust the generator speed-torque ratio as a function of the sea state. Simulation results show the effectiveness of this model-free adaptive control in tuning the system in order to maximize the generated power. Starting from a simple monochromatic model of the sea, the presented approach is verified according to sea conditions of increasing complexity, and finally to long term time series, obtained from measurements of real sea states in the considered geographical region. The tuning of the hyper-parameters of RL algorithm with respect to the speed of convergence and optimality of generated power is also discussed.

Keywords: Linear Wave Theory , Oscillating arm , Q-learning , Reinforcement Learning , WEC

This paper reports the study of a planar Cross-Axis Flexural Pivot (CAFP) comprising an additional contact pair. The proposed device may be useful for applications requiring a revolute joint that behaves differently when deflecting clockwise/anti-clockwise. The presence of the contact pair reduces the free length of one flexures, resulting in a considerable increment of the overall joint stiffness. The pivot behaviour is investigated, for different load cases, via the Chained-Beam-Constraint Model (CBCM), namely an accurate method to be applied in large deflection problems. A framework comprising Matlab and ANSYS is developed for testing the CAFP performances in terms of rotational stiffness, parasitic shift and maximum stress, with different combinations of geometrical aspect ratios and contact extensions. Results achieved via CBCM for a pure rotation applied to the CAFP's output link are then verified through Finite Element Analysis. The resulting performance maps show good agreement between the numerical results. Furthermore, the CBCM shows an improved computational efficiency, which is a crucial aspect for preliminary design steps. At last, direct comparison between simulations and experiments, developed by means of two custom test rigs, confirms the efficacy of the proposed design method for the modeling of contacts in large deflection problems.

Keywords: Chained-beam-constraint model , Contact-aided compliant mechanism , Cross-Axis Flexural Pivot , Multi software framework

The research on the use of virtual reality (VR) in the design domain has been conducted in a fragmentary way so far, and some misalignments have emerged among scholars. In particular, the actual support of VR in early design phases and the diffusion of practices involving VR in creative design stages are argued. In the present paper, we reviewed VR applications in design and categorized each of the collected 86 sources into multiple classes. These range from supported design functions to employed VR technologies and the use of systems complementing VR. The identified design functions include not only design activities traditionally supported by VR, such as 3D modelling, virtual prototyping, and product evaluation, but also co-design and design education beyond the early design phases. The possibility to support early design phases by means of VR is mirrored by the attention on products that involve an emotional dimension beyond functional aspects, which are particularly focused on in virtual assemblies and prototypes. Relevant matches between VR technologies and specific design functions have been individuated, although a clear separation between VR devices and supported design tasks cannot be claimed.

Keywords: 3D modelling , Co-design , Early design phases , Engineering design , Industrial design , Product design , Product evaluation , Technological development , Virtual prototyping , Virtual reality

The present work illustrates the dynamization of an orthopaedic plate for internal fracture fixation which is thought to shorten healing times and enhance the quality of the new formed bone. The dynamization is performed wirelessly thanks to a magnetic coupling. The paper shows the peculiarities of the design and manufacturing of this system: it involves two components, sliding with respect to each other with an uncertain coefficient of friction, and with a specific compounded geometry; there are stringent limits on component size, and on the required activation energy. Finally, the device belongs to medical devices and, as such, it must comply with the respective regulation (EU 2017/745, ASTM F382). The design of the dynamizable fracture fixation plate has required verifying the dynamic of the unlocking mechanism through the development of a parametric multibody model which has allowed us to fix the main design variables. As a second step, the fatigue strength of the device and the static strength of the whole bone-plate system was evaluated by finite element analysis. Both analyses have contributed to defining the final optimized geometry and the constitutive materials of the plate; finally, the respective working process was set up and its performance was tested experimentally on a reference fractured femur. As a result of these tests, the flexural stiffness of the bone-plate system resulted equal to 370 N/mm, while a maximum bending moment equal to 75.3 kNmm can be withstood without plate failure. On the whole, the performance of this dynamic plate was proved to be equal or superior to those measured for static plates already on the market, with excellent clinical results. At the same time, pre-clinical tests will be an interesting step of the future research, for which more prototypes are now being produced.

Keywords: Dynamizable plate , Fracture synthesis , Internal fixation , Mechanical tests , Medical device manufacturing , Stress analysis

This paper proposes a replicable methodology based on virtual prototyping design in multibody environment to optimize the functionality of Mechanical Spring Devices (MSD). These devises are assembled to control the shaft angular velocity in medium-voltage (MV) switch disconnector. The angular velocity of switch disconnector, moving the contact fingers, is directly linked to arcing time, which is the parameter that mainly influences accuracy, safety drives and a longer service life of device. Design of experiment (DoE) techniques, integrated with tridimensional geometric parametrization, were used in multibody environment to optimize the displacement of switch disconnector shaft. The best values of shape, stiffness and preload of the main cylindrical helical spring of MSD were obtained in every functional condition. Optimization results were compared with the limits values measured in homologation and with the acceptance limits values released by ENEL technical specifications for the MSD studied proving the effective methodology and the improvement obtained in terms of the safety of the system.

Keywords: Arcing time , DoE , Multibody model , MV electromechanical compartments , Parameterization