Real-Time and Real-Fast Performance of General-Purpose and Real-Time Operating Systems in Multithreaded Physical Simulation of Complex Mechanical Systems

Physical simulation is a valuable tool in many fields of engineering for the tasks of design, prototyping, and testing. General-purpose operating systems (GPOS) are designed for real-fast tasks, such as offline simulation of complex physical models that should finish as soon as possible. Interfacing hardware at a given rate (as in a hardware-in-the-loop test) requires instead maximizing time determinism, for which real-time operating systems (RTOS) are designed. In this paper, real-fast and real-time performance of RTOS and GPOS are compared when simulating models of high complexity with large time steps. This type of applications is usually present in the automotive industry and requires a good trade-off between real-fast and real-time performance. The performance of an RTOS and a GPOS is compared by running a tire model scalable on the number of degrees-of-freedom and parallel threads. The benchmark shows that the GPOS present better performance in real-fast runs but worse in real-time due to nonexplicit task switches and to the latency associated with interprocess communication (IPC) and task switch

Multi-Objective Optimization of a Vehicle Body by Combining Gradient-based Methods and Vehicle Concept Modelling

Abstract In the automotive field, size optimization procedures can be combined with concept modelling approaches, in order to design a vehicle Body-In-White (BIW) model with optimal static and dynamic performances already in the early design stages. However, this specific optimization problem, with hundreds of design variables, limited design space and often conflicting objectives, makes the choice of the appropriate optimization method really difficult. The aim of this paper is to show an industrial case study, where two different implementations of the classical gradient-based (GB) method are used in combination with a technique for vehicle body concept modelling to achieve a multi-objective BIW optimization of a passenger car

Design and Prototyping of Miniaturized Straight Bevel Gears for Biomedical Applications

This paper presents a semi-automated design algorithm for computing straight bevel gear involute profiles. The proposed formulation is based on the Tredgold approximation method. It allows the design of a pair of bevel gears with any desired number of teeth and relative axes inclination angles by implementing additive manufacturing technology. A specific case study is discussed to calculate the profiles of two straight bevel gears of a biomedical application. Namely, this paper illustrates the design of the bevel gears for a new laparoscopic robotic system, EasyLap, under development with a grant from POR Calabria 2014–2020 Fesr-Fse. A meshing analysis is carried out to identify potential design errors. Moreover, finite element-based tooth contact analysis is fulfilled for determining the vibrational performances of the conjugate tooth profiles throughout a whole meshing cycle. Simulation results and a built prototype are reported to show the engineering feasibility and effectiveness of the proposed design approach

Real-Time and Real-Fast Performance of General-Purpose and Real-Time Operating Systems in Multithreaded Physical Simulation of Complex Mechanical Systems

Physical simulation is a valuable tool in many fields of engineering for the tasks of design, prototyping, and testing. General-purpose operating systems (GPOS) are designed for real-fast tasks, such as offline simulation of complex physical models that should finish as soon as possible. Interfacing hardware at a given rate (as in a hardware-in-the-loop test) requires instead maximizing time determinism, for which real-time operating systems (RTOS) are designed. In this paper, real-fast and real-time performance of RTOS and GPOS are compared when simulating models of high complexity with large time steps. This type of applications is usually present in the automotive industry and requires a good trade-off between real-fast and real-time performance. The performance of an RTOS and a GPOS is compared by running a tire model scalable on the number of degrees-of-freedom and parallel threads. The benchmark shows that the GPOS present better performance in real-fast runs but worse in real-time due to nonexplicit task switches and to the latency associated with interprocess communication (IPC) and task switch

On the Benefits of Using Object-Oriented Programming for the Objective Evaluation of Vehicle Dynamic Performance in Concurrent Simulations

Assessing passenger cars’ dynamic performance is a critical aspect for car industries, due to its impact on the overall vehicle safety evaluation and the subjective nature of the involved handling and comfort metrics. Accordingly, ISO standards, such as ISO 4138 and ISO 3888, define several specific driving tests to assess vehicle dynamics performance objectively. Consequently, proper evaluation of the dynamic behaviour requires measuring several physical quantities, including accelerations, speed, and linear and angular displacements obtained after instrumenting a vehicle with multiple sensors. This experimental activity is highly demanding in terms of hardware costs, and it is also significantly time-consuming. Several approaches can be considered for reducing vehicle development time. In particular, simulation software can be exploited to predict the approximate behaviour of a vehicle using virtual scenarios. Moreover, motion platforms and detail-scalable numerical vehicle models are widely implemented for the purpose. This paper focuses on a customized simulation environment developed in C++, which exploits the advantages of object-oriented programming. The presented framework strives to perform concurrent simulations of vehicles with different characteristics such as mass, tyres, engine, suspension, and transmission systems. Within the proposed simulation framework, we adopted a hierarchical and modular representation. Vehicles are modelled by a 14 degree-of-freedom (DOF) full-vehicle model, capable of capturing the dynamics and complemented by a set of scalable-detail models for the remaining sub-systems such as tyre, engine, and steering system. Furthermore, this paper proposes the usage of autonomous virtual drivers for a more objective evaluation of vehicle dynamic performances. Moreover, to further evaluate our simulator architecture’s efficiency and assess the achieved level of concurrency, we designed a benchmark able to analyse the scaling of the performances with respect to the number of different vehicles during the same simulation. Finally, the paper reports the proposed simulation environment’s scalability resulting from a set of different and varying driving scenarios

Efficient modelling methodologies for multibody simulations of vehicle dynamics

Dottorato di Ricerca in Igegneria Meccanica, Ciclo XXVII, a.a. 2014Università della Calabri

Reduced Basis method for closed-form affine dependent second order systems

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIXThis thesis proposes the use of Reduced Basis (RB) methods to improve the computational efficiency of simulations in the field of elastodynamics and acoustics including poroelastic materials. RB methods are Model Order Reduction techniques used to generate parametric Reduced Order Models (ROM). The are many reasons for current researchers to focus on MOR for computational improvements. The technological development of computers and hardware has led to using brute force for calculations of large matrices projected onto simple shape-functions rather than, as it was normally done in the 60s and 70s, trying shrink the size of the matrices using special shapefunctions (i.e., specific for the different systems) [1]. The purpose of MOR techniques is to use these enormously detailed but slow (to compute and even to read) data to generate those smart shape functions. Hence, the resulting ROM contain the level of detail of those huge models, referred to as high fidelity models or full order models (FOM), offering high computational performances. These characteristics of ROM can strongly enlarge the horizons of optimization techniques enabling repeated simulation at high rate or, in some cases, allow real-time simulations paving the way for e.g. virtual sensing, haptic technology, computer graphics. A common strategy to do MOR is to use projection-based techniques that apply to semi-discretised models (e.g. finite element models). A projection transforms the basis that describes the multidimensional space of the model to be much smaller. Thus, a projection of the model into a subspace that contains all and only the dimensions necessary to describe the model will minimize the computation effort. The field of MOR includes dozens of methodologies and this thesis does not pretend to cover all of them. The focus of the work is to develop methods based on projection that are able to generate ROM with explicit parametric dependency typically indicated under the category Parametric Model Order Reduction (PMOR). Changes of the parameters configuration affect the shape of the multidimensional space. Therefore, to obtain a reduced parametric solution, a manifold of all the basis corresponding to the different parameter configurations is needed. Among the possible approaches available to do PMOR, the RB methods achieve efficient results separating the parametric dependent and parametric independent quantities in the FOM. This enable an efficient reduction and originates ROM whose operations are independent from the size of the former FOM. The research brought to a parametric approach in the frequency domain that can take into account the nonlinear frequency dependent characteristics of poroelastic materials (PEM). Also this methodology is verified using few numerical examples. In addition, a parametric approach to study elastodynamic problems of linear structures made of beams is presented and applied. The results of the study are discussed and validated with direct comparison to direct FE simulations. In addition to the original contribution, the research reported in this thesis raises some new questions that could set the start of new research projects in the field of PMOR and are discussed in the conclusion to this work.Università della Calabria

Finite Element models for the dynamic analysis of composite and sandwich structures

Dottorato di Ricerca in Igegneria Meccanica, Ciclo XXVIII, a.a. 2015-2016The use of lightweight multi-layered materials is dramatically changing the design process and criteria in many engineering fields. The transportation industry, for example, is facing major challenges in order to replace traditional materials while keeping at least the same level of passengers’ comfort and safety. In particular, the Noise, Vibration and Harshness (NVH) performances are affected by the novel combination of high stiffness and low density. If the aeronautic industry still heavily relies on testing to assess designs’ validity, such an approach cannot be applied to the automotive industry for the development costs would be too high. It is therefore necessary to identify CAE tools capable of giving realistic, reliable and cost-effective predictions of multi-layered structures’ behaviour under dynamic loadings. An often overlooked problem is that of damping which is generally higher in composite and sandwich structure but rarely it is also efficiently exploited, so that in most cases the classic approach of applying NVH treatments is followed. However, this procedure has a detrimental effect on the attained weight saving and on the global dynamic performance of lightweight structures, therefore leading to unsatisfactory results. Moreover, the variability of mechanical properties due to the low repeatability of some manufacturing processes can also have an impact on the global behaviour of the as-manufactured component. An early integration of damping prediction and an estimate of possible stiffness variations due to the manufacturing can actually lead to better designs in less time. In this thesis these challenges are tackled from the Computer Aided Engineering (CAE) point of view, thanks to the introduction of a novel finite element for the prediction of the damped response of generic multi-layered structures and the proposition of a CAMCAE approach to introduce manufacturing simulations at an early stage in the design and analysis process. In the first chapters, different analytical and numerical approaches for the modelling of multi-layered structures are presented and used for the development of a 1D finite element. The results of the mono-dimensional analysis show that zigzag theories are a cost-effective and accurate alternative to solid finite element models, motivating the development of a 2D element for the analysis of plates and shells. With respect to previous investigations on zigzag theories, the current study focus on their use for modal parameters prediction, i.e. eigenfrequencies, mode shapes and damping. It will be shown that compared to classic models, the zigzag elements are able to predict the dynamic response, damped and undamped, of beam, plates and shells with the same accuracy of 3D models but at a much lower computational cost. In the last chapter, the available homogenisation methods for the analysis of long fibres composites are reviewed and compared to more refined models based on manufacturing simulation algorithms. Results show that changes in manufacturing parameters lead to substantially different results. The goal is to show that CAM/FE coupling is possible already at an early design stage and that manufacturing simulations can be used as a mean to further optimise the performance of composite structures. As a final stage, an example of coupling between zigzag theories and manufacturing simulations is presented. Despite some limitations, the proposed methods increase the accuracy of the analysis and gives a better understanding of lightweight multi-layered structures. Further research could focus on the use of the developed zigzag elements for fatigue analysis and delamination modelling as well as detailed modelling of drop-off regions in the framework of CAM tools improvementsUniversità della Calabri

Advanced techniques for numerical contact analysis in spiral bevel gears

Dottorato di Rocerca in Ingegneria Civile ed Industriale. Ciclo XXXThe research presented in this dissertation treats the subject of efficient gear contact simulation and is applied to the contact analysis of spiral bevel gears. In today’s competitive environment getting better products to market faster is essential to win a customer’s interest and loyalty. Therefore, engineers are evermore in need of the correct solutions to rapidly predict, analyze and improve their designs if they want to meet the tight development schedules and budgets. Within the current development cycle of mechanical transmissions, computerized tooth contact analysis (TCA) has proven to be an invaluable tool to predict a gear pair’s key contact performance characteristics, while reducing the need for expensive physical prototyping and labor-intensive experimental testing. However, the geometrical complexity of the gear teeth still pose significant computational challenges to the tooth contact simulation for spiral bevel gears. Correctly capturing the spatial nature of the motion transfer and the resulting contact load distribution requires a three-dimensional gear contact model. Finite element method (FEM) based contact simulations are usually conducted, especially in an industrial context, while various tailor-made solutions also exist. When performing the contact detection, many of these solutions tend to apply a general contact detection method (e.g. node-to-surface) that treats the contacting gear teeth flanks as arbitrary surfaces. Not realizing that the gear flanks are designed to transmit motion in a near-conjugate way, leads to inefficient contact searches for which the associated computational cost not only limits TCA’s application to static component-level analysis but also hinders extension towards full-system level analysis or dynamic gear contact simulation. Building upon the existing concept of the surface of roll angles to efficiently detect contact, this dissertation develops a new penetration-based contact model to compute the three-dimensional contact loads from the actual position and orientation of the real tooth surfaces, whether misaligned or not. The proposed methods show to correctly predict component behavior at a computational cost that enables further application in system-level or dynamic analyses. An accurate description of the spiral bevel gear tooth surfaces is deep-rooted in the presented methodologies, since this proves vital to precisely describe the gear pair kinematics but also to correctly include all the relevant complex contact phenomena. However, a reference tooth profile, similar to the involute for cylindrical gears, does not exist for spiral bevel gears. Therefore, a mathematical model that simulates the cutting kinematics of the manufacturing process, proves to be indispensable to correctly capture both the gear teeth’s macro- and microgeometry. In this work the five-cut face-milling cutting process is adopted to create a representative geometry of a face-milled spiral bevel gear set. Contact detection based on the tooth flank’s surface of roll angles, combined with the ease-off topography, has been proposed in the gear literature to reduce the computational load, associated with the contact search. Yet, the ease-off topography, which quantifies the geometrical mismatch of a pair of contacting gear tooth surfaces, shows to hold limitations when moving beyond componentlevel contact analysis, as it is sensitive to the instantaneous gear pair installment. With the underlying idea of potential application of the presented methodologies within multibody system simulation, the usage of ease-off topography concept for contact detection is abandoned and replaced by a penetration-based contact model. An analytical compliance model is formulated to translate the detected penetrations into appropriate contact loads. The compliance model separates the linear gear tooth deflection components from a tooth pair’s local nonlinear deformation, which arises around the contact zone. The developed gear contact model with surfaces of roll angles, computed for the gear pair’s actual tooth flanks in the absence of misalignments, is then shown to be well capable of predicting a misaligned gear pair’s contact performance. In contrast, ease-off based contact models would require an update of the (misaligned) ease-off topography, each time the gear pair’s configuration changes (e.g. due to system-induced deflections), reducing their otherwise excellent computational efficiency. The proposed penetration-based gear contact model identifies the contact locations based on the surface of roll angles but computes the flank mismatch based on the instantaneous position and orientation of the real gear tooth surfaces, showing to be more robust to configurational changes. Finally, a strategy to parametrically redefine the gear contact model’s surfaces of roll angles in function of the instantaneous misaligned state of the gear pair, is proposed to further increase the accuracy of the contact detection. A prototype toolchain is created around the presented techniques for contact modeling, covering the various analyses for unloaded and loaded tooth contact analysis that are an essential part of today’s spiral bevel gear design process. Automated finite element model creation routines are developed to support the validation of the methods against nonlinear FEM-based contact simulations. These tools will greatly support future research into methodological advancesUniversità della Calabria