Design methods for mobility

Rapid development in vehicular technology has caused more automated vehicle control to increase on the roads. Studies showed that driving in mixed traffic with an autonomous vehicle (AV) had a negative impact on the time headway (THW) of conventional vehicles (CVs) (i.e., driven by humans). To address this issue, there is a need to equip CV with visual advanced driver assistance systems (ADASs) that helps the driver maintain safe headway when driving near AVs. This study examines the perception of drivers using visual ADAS and their associated risk while driving behind the AV at constant and varying speeds. The preliminary results showed that while visual ADAS could help drivers keep the safe THW, it could affect drivers' ability to react to emergencies. This implies that visual modality alone might not be sufficient and therefore requires some other feedback or intelligent transport systems to help drivers maintain safe driving in a mixed-Traffic condition.

Keywords: car-following , sustainable transport management platooning , virtual realtiy , visual advanced driver assistance system

In response to the many social impacts of automated mobility, in September 2020 the European Commission published “Ethics of Connected and Automated Vehicles,” a report in which recommendations on road safety, privacy, fairness, explainability, and responsibility are drawn from a set of eight overarching principles. This paper presents the results of an interdisciplinary research where philosophers and engineers joined efforts to operationalize the guidelines advanced in the report. To this aim, the authors endorse a function-based working approach to support the implementation of values and recommendations into the design of automated vehicle technologies. Based on this, they develop methodological tools to tackle issues related to personal autonomy, explainability, and privacy as domains that most urgently require fine-grained guidance due to the associated ethical risks. Even though each tool still requires further inquiry, they believe that the work might already prove the productivity of the function-based approach and foster its adoption in the CAV scientific community.

Keywords: Application , Autonomy , Connected and Automated Vehicles , Ethics , Explainability , Principles , Privacy

Additive manufacturing is even more capturing the interest of vehicle manufactures. Its adoption enables design potentials such as parts customization, lightweighting or functional integration. Deep adoption of additive manufacturing and integration of topology optimization design techniques enable the calculation of light components, while additive manufacturing makes it feasible by adding subsequent layers of material. Design for additive manufacturing guidelines address these challenges by enabling the build of such complex shapes thanks to parts consolidation and features integration. Several prototypes of such lightweight design concerning chassis, body, and structures have been provided, but the lack of structured and objective approaches limits the application in normal production. This work integrates Key Performance Indexes (KPIs) into the Design for Additive Manufacturing (DfAM) approach for an effective adoption of selection of trade-off studies for the selection of best product variant and process setup. The trade-off involves KPIs related to structural product requirements and laser Powder Bed Fusion process cost estimation, to return functional components that address the best ratio between weight reduction and expected manufacturing cost. Proof of the method effectiveness and its application to lighten real components is demonstrated by applying the approach to reduce the weight of a steering support system for a Formula SAE race car. The objectivity of the trade-off promotes the extensive adoption to other vehicle components for substantial fuel efficiency improvement and emissions reduction perspectives.

Keywords: Additives , Cost estimating , Economic and social effects , Emission control , Product design

BACKGROUND: Aircraft seating comfort has a significant impact on passenger on-board experience. Its assessment requires the adoption of well-designed strategies for data collection as well as appropriate data analysis methods in order to obtain accurate and reliable results. OBJECTIVES: This paper focuses on the assessment of aircraft seating comfort based on subjective comfort responses collected during laboratory experiments and taking into account seat features and passenger characteristics. METHODS: The subjective comfort evaluations have been analyzed using a model-based approach to investigate the relationship between overall seating comfort and specific seat/user characteristics. RESULTS: The results show that the overall seating comfort perception is significantly influenced by the thickness of the seat pan, the backrest position (upright or reclined), the age of the passenger and the passenger perception of being comfortably supported at the lumbar region. CONCLUSIONS: The adopted model-based approach allows the analysis of subjective seating comfort data taking into account their ordinal nature as well as the dependency between evaluations provided by the same subject.

Keywords: laboratory experiments , ordinal regression , repeated evaluations , Seat comfort

The process of designing a sail can be a challenging task because of the difficulties in predicting the real aerodynamic performance. This is especially true in the case of downwind sails, where the evaluation of the real shapes and aerodynamic forces can be very complex because of turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical methods are very useful and reliable tools to investigate sail performances, and their use, also as a result of the exponential growth of computational resources at a very low cost, is spreading more and more, even in not highly competitive fields. This paper presents a new methodology to support sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind sails. The proposed method is parametric and automated and allows for investigating multiple kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is presented as a case study. Based on the numerical results obtained, an analytical formulation for calculating the sail corner loads has been also proposed. The novel proposed methodology could represent a promising approach to allow for the widespread and effective use of numerical methods in the design and manufacturing of yacht sails.

Keywords: Computational fluid dynamics , Finite element method , FSI , Gennaker , Sail design , Sail loads

This paper presents a nonlinear model of an inversion-based generalized cross-spring pivot (IG-CSP) using the beam constraint model (BCM), which can be employed for the geometric error analysis and the characteristic analysis of an inversion-based symmetric cross-spring pivot (IS-CSP). The load-dependent effects are classified in two ways, including structure load-dependent effects and beam load-dependent effects, where the loading positions, geometric parameters of elastic flexures, and axial forces are the main contributing factors. The closed-form load-rotation relations of an IS-CSP and a non-inversion-based symmetric cross-spring pivot (NIS-CSP) are derived with consideration of the three contributing factors for analyzing the load-dependent effects. The load-dependent effects of IS-CSP and NIS-CSP are compared when the loading position is fixed. The rotational stiffness of the IS-CSP or NIS-CSP can be designed to increase, decrease, or remain constant with axial forces, by regulating the balance between the loading positions and the geometric parameters. The closed-form solution of the center shift of an IS-CSP is derived. The effects of axial forces on the IS-CSP center shift are analyzed and compared with those of a NIS-CSP. Finally, based on the nonlinear analysis results of IS-CSP and NIS-CSP, two new compound symmetric cross-spring pivots are presented and analyzed via analytical and FEA models.

Keywords: Center shift , Compliant cross-spring pivot , Load-dependent effects , Loading positions , Nonlinear analysis

The tyre-suspension-seat dynamic system, driveline and engine vibrations are generally considered in the vibrational field as the main factors that influence the particular feeling of comfort perceived by passengers on a vehicle. Hence, the development of several criteria and models for the optimal estimation of the design parameters of such systems. Among these parameters, the most detrimental impacting on the passenger comfort are undoubtedly acceleration and its variation. The two types of suspension systems (conventional passive suspension system and active suspension system) differ as the first foresees the spring-damper characteristics to be adjusted so that only one of several conflicting objectives (such as passenger comfort, road holding, and suspension deflection) is followed. In active suspension systems, instead, these objectives are balanced by the designer in a more efficient manner thanks to the feedback-controller actuator assembly. However, this approach presents some limitations linked to the extremely wide spectrum of magnitude and frequency of external forces that the tyre-suspension-seat system has to efficiently control and mitigate. It remains that in the existing optimisation models and systems time exposure limits established by unification agencies and road authorities are not generally considered. This paper illustrates the development of an active tyre-suspension-seat system control for passenger cars, using both a non-linear multibody model and Genetic Algorithm (GA) controls. A benefit of the proposed active tyre-suspension-seat system control is also to consider various time exposure limits and an active damping element. The main innovative element introduced by this work consists in having coupled an active control to passive mechanical parameters in order to minimize the seat acceleration. The 3 DoF multibody model, applied to a quarter body for symmetry reasons, treated road roughness as an input variable in the GA control so as to determine the vertical component of acceleration. The numerical and experimental applications of the proposed model to a specific case study allowed to validate the effectiveness of the active system towards the vibrations transmitted to the passenger.

Keywords: Acceleration variation , Active suspension system , Genetic algorithm , Passenger comfort , Vibrations

BACKGROUND: Nowadays, the ergonomic study of the driving position is a critical aspect of automotive design. Indeed, due to the rising needs on the market, one focus for car industries is to improve the perceived comfort related to the cars' interior. Driving a car for a prolonged time could cause complaints in some body-regions, especially in the lumbar-sacral area. Thus, special lumbar-sacral supports for driver seat has been proposed for reducing this kind of complaints. OBJECTIVE: Development of two virtual and physical models of lumbar-sacral support for improving both the lumbar/sacral and overall perceived comfort while driving. METHODS: Two prototypes of lumbar/sacral support have been realized: the first one was integrated into the seat, and the second one was shaped as a removable pillow (removable support). Fifty participants were asked to rate the perceived comfort in lab tests performed on a seating-buck by comparing three configurations (5 min each): a standard seat, seat with the removable support, seat with integrated support. Subjective data (by questionnaires) and objective data (interface pressure between backrest and driver) have been acquired and statistically processed. In addition, real driving tests have been performed to test the actual performance of the removable support in term of perceived comfort comparing it with the standard seat. RESULTS: Statistical correlations between subjective and objective data showed interesting results in comfort improvement through the adopted solutions. Real driving tests showed an improvement in comfort perception with the lumbar-sacral support towards the standard seat. CONCLUSIONS: Thanks to the virtual prototyping and the application of previous knowledge, coming from literature and experience, a solution for improving the overall comfort and reduce the lumbar/sacral pain while driving has been developed, tested, and assessed.

Keywords: body-shaped pillow , Car seat comfort , lumbar-sacral support , seat design

The high power demanding in many emerging power electronic applications requires innovative solutions in semiconductor field. One of the possible keys to satisfy this requirement is the use of more paralleled devices. For traction applications, parallel connection of Silicon Carbide (SiC) MOSFETs is widely employed. In this framework, the power devices are housed in module packages. This paper presents a parametric analysis of a SiC power module for traction inverters, with a three-phase topology, containing many paralleled dice for each swich. The scope of the work is to study this phenomenon with a numerical investigation based on a circuit simulation, evaluating the junction temperature in a case study. The parameters varied in the simulations are the threshold voltage and the drain-source on-state resistance.

Si- and SiC-based fast on-board chargers require very special thermal strategies, to ensure high reliability in order to assess long life in harsh environments, such as the automotive one. Indeed, the power losses in the switches may lead to a severe temperature rise in the enclosed cabinet, causing a reduce lifetime of the system. In this paper, we propose a scalable fast charger for automotive applications able to manage a 7 kW power flow. A thermal simulation based on COMSOL Multiphysics is performed in this work. The study allows us to get a realistic evaluation of the higher temperatures reached by the active Si and SiC devices of the converter during the normal operation, at the steady state and at the maximum allowed power.

Keywords: automotive , DC/DC converter , fast charger , LLC , OBC , PFC , thermal simulation

The Silicon Carbide (SiC) semiconductor material is playing a fundamental role in the development of new power modules. Due to its excellent physical properties, the power devices based on this novel compound improve the traction inverter performance in electric vehicles. This work presents a 3D Finite Element Model (FEM) and fluid dynamics simulation to investigate the behavior of a directly cooled SiC module structure. Furthermore, a two-step experimental procedure to thermally characterize the module is also reported. It comprises a calibration and, subsequently, the thermal impedance computation. The proposed FEM model is compared with experimental test results in order to demonstrate its effectiveness.

This study aims to evaluates how an adaptive winglet during flight can improve aircraft aerodynamic characteristics of the CRJ700. The aircraft geometry was slightly modified to integrate a one-rotation axis adaptive winglet. Aerodynamic characteristics of the new adaptive design were computed using a validated high-fidelity aerodynamic model developed with the open-source code OpenFoam. The aerodynamic model successively uses the two solvers simpleFoam and rhoSimple-Foam based on Reynold Averaged Navier Stokes equations. Characteristics of the adaptive winglet design were studied for 16 flight conditions, representative of climb and cruise usually considered by the CRJ700. The adaptive winglet can increase the lift-to-drag ratio by up to 6.10% and reduce the drag coefficient by up to 2.65%. This study also compared the aerodynamic polar and pitching moment coefficients variations of the Bombardier CRJ700 equipped with an adaptive versus a fixed winglet.

Keywords: Adaptive , Aerodynamic , Longitudinal , Morphing , OpenFoam , Optimization , Subsonic , Transonic , Winglet

A numerical investigation is conducted in order to identify a PID control loop feedback scheme able to return dynamics augmentation and superior seakeeping characteristics in the application of high speed flying yacht hulls. An existing lumped parameters model based on general unsteady equations of motion is extended and implemented in combination with a regular basic ocean waves model, to conduct parametric studies and predict the overall performances of a specific engine-propelled flying yacht hull, both in calm and rough water conditions. The unsteady behavior of six foiling/maneuvering appendages is investigated, the hydrodynamic characteristics being based on a database generated through the use of computational fluid dynamics methods (CFD) coupled with static/dynamic-mesh schemes. Equations of motion and hydrodynamics are solved numerically by explicit time-integration method. By comparison with control open-loop conditions, the results show the effects of the use of PID controllers in such dynamic systems in terms of seakeeping performances and dynamics augmentation.

Keywords: Flying yacht , Foiling , Hydrodynamic performances , Lumped parameters model , Ocean waves , PID control

This study is focused on the development of longitudinal aerodynamic models for steady flight conditions. While several commercial solvers are available for this type of work, we seek to evaluate the accuracy of an open source software. This study aims to verify and demonstrate the accuracy of the OpenFoam solver when it is used on basic computers (32-64GB of RAM and eight cores). A new methodology was developed to show how an aerodynamic model of an aircraft could be designed using OpenFoam software. The mesh and the simulations were designed only using OpenFoam utilities, such as blockMesh, snappyHexMesh, simpleFoam and rhoSimpleFoam. For the methodology illustration, the process was applied to the Bombardier CRJ700 aircraft and simulations were performed for its flight envelope, up to M0.79. Forces and moments obtained with the OpenFoam model were compared with an accurate flight data source (level D flight simulator). Excellent results in data agreement were obtained with a maximum absolute error of 0.0026 for the drag coefficient, thus validating a high-fidelity aerodynamic model for the Bombardier CRJ-700 aircraft.

Keywords: Aerodynamics , Compressible flow , CRJ-700 aircraft , Incompressible flow , OpenFoam software

This paper provides a comprehensive revision of the working principles and limitations of the mechanical limited-slip differential (LSD), a passive device used to improve traction capabilities and to extend the performance envelope of high-performance road cars, racing and rally cars. The LSD has been in use for decades. However, according to the authors' experience, its impact on vehicle dynamics appears to be somewhat neglected in the literature and often misunderstood, especially in the semi-pro racing community. Current research on the subject is usually focused on side aspects and/or on modern control applications such as active differentials and torque-vectoring systems. These state-of-the-art technologies still rely on the same principles of the LSD, which should therefore be fully explained. The authors intend to fill this gap by starting with a comprehensive literature review. Then, an intuitive explanation of the impact of limited slip systems on vehicle behaviour is proposed with simple mathematical models and examples to integrate what seems to be missing. The peculiar shape of the torque-sensitive LSD working zone on the torque bias diagram is explained to an unprecedented level of detail. Real-world application examples are provided, including data recorded on a single-seater racecar integrated with examples based on a virtual model.

Keywords: Limited slip differential , Torque bias diagram , Vehicle dynamics , Vehicle stability , Yaw moment control

Understanding the amount of energy a tire is subjected to is one of the key elements to perform in motorsport competitions, especially in Formula 1 feeder categories, where the number of tires is limited over the race weekend to contain costs. This forces teams to use worn tires towards the end of the event. Therefore, tires are usually chosen only relying on their external shape or based on the kilometers traveled. Moreover, being aware of how a setup change impacts tires can be a breakthrough in tire management, especially in tracks where tire wear is limiting the overall performance. This paper provides a scientific method aimed at helping race engineers in tire management to maintain a high performance level through the entire race weekend.

Keywords: Racing tires , Tire management , Tire sensitivity , Tire sliding power

Vehicle sideslip angle estimation is still one of the most challenging research topics in the automotive industry. Many papers can be found on this topic, where authors propose varied methods to reach the goal. Which is the most effective? After an extensive literature review, two very different methods have been identified as the most used: Extended Kalman Filter with dynamic model and Artificial Neural Network. In this work a comparison among these methods is presented. A fully instrumented car has been used to gather typical vehicle dynamics data and feed the models required for a model-based design approach. Results showed that each method has either positive aspects or drawbacks.

Due to problems related to environmental pollution and fossil fuels consumption that have not infinite availability, the automotive sector is increasingly moving towards electric powertrains. The most limiting aspect of this category of vehicles is certainly the battery pack, regarding the difficulty in obtaining high range with good performance and low weights. The aim of this work is to provide a simulation tool, which allows for the analysis of the performance of different types of electric and hybrid powertrains, concerning both mechanical and electrical aspects. Through this model it is possible to test different vehicle configurations before prototype realization or to investigate the impact that subsystems' modifications may have on a vehicle under development. This will allow to speed-up the model-based design process typical for fully electric and hybrid vehicles. The model aims to be at the same time complete but simple enough to lower the simulation time and computational burden so that it can be used in real-time applications, such as driving simulators. All this reduces the time and costs of vehicle design. Validation is also provided, based on a real vehicle and comparison with another consolidated simulation tool. Maximum error on mechanical quantities is proved to be within 5% while on electrical quantities it is always lower than 10%.

Keywords: Alternative propulsion , Balance of forces , Electric powertrain , Energy consumption , Energy consumption prediction , Hybrid powertrain , Mathematical modelling , Performance prediction

To implement the CAD platform-based approach of Design for Additive Manufacturing (DfAM) and validate it in a real case, an entire design optimization process of a Formula SAE front brake caliper has been performed, to be printed by Powder Bed Fusion (PBF) process. The DfAM consists in the use of a Ti6Al4V titanium alloy to better resist at high temperatures and a topology optimized shape allowed by the technology to save weight despite the density increase. Structural and thermal behavior has been discussed. DfAM process-specific techniques have been implemented for internal geometrical features and optimized shapes. The design for additive workflow is presented and finally the exploited design approach based on a CAD platform is synthesized.

Keywords: Automotive , Brake caliper , CAD platform , DfAM , Topology optimization

This paper presents a project proposal about the design of an innovative and futuristic transport system that aims to replace highways and major roads with a fast, safe and ecological new arrangement. The aim was to conceive an innovative new infrastructure of transport that fits into a future city scenery. In the current historical period we are invested by fast, frenetic and unstoppable evolution that leads to the continuous replacement of products and technologies that in a few years went from being innovative to become obsolete and outdated. Moreover, this process has inevitably affected the whole world of transport: It has assisted and is still witnessing the replacement of diesel and petrol engines with hybrid and electric ones. These evolution and change have led us into the research and understanding of increasingly innovative technologies such as the ones with zero impact motors or magnetic levitation, which in the near future will probably become a valid alternative, or even the new pioneers of transport around the world. At the beginning, the methodology used for the present case study was adopted to analyze how people used to move in the current period (i.e. 2019-20); then, it was taken into consideration the problems linked to the main means of transport diffused, with clean and green technologies; later, it was carried out a market analysis for each category, with related Benchmarking, in order to find the most significant technical characteristics of each one. According to the emerged results, a concept of an innovative transport system was developed, in order to guarantee the safety and privacy of passengers in addition to other performance items, as high speed or integration with other means. The intention was to create a transport network that could connect many cities with direct and easily practicable routes that could replace highways.

Keywords: Ecological , Future city , Future transport , High Speed , Magnetic Levitation , Safe