Heterogeneous simulation and interoperability of tools applied to the design, integration and development of safety critical systems

A key issue of the assessment of the Model Based Systems Engineering (MBSE) is the integration between the requirement, functional and physical analyses. It turns out into a full capability of correlation and data exchange among the tools currently available to manage those three activities and, in particular, into a tight cooperation between the functional modeling and the physical one, being based on several methods of engineering, widely applied since longtime (mathematical, analytical, numerical and experimental). A successful accomplishment of this task within the frame of the development of the MBSE represents a milestone for both the methodology and the tools of the Systems Engineering. The application of models and simulations to support the engineering activities has spread over different domains and is strictly related to the decision making process applied to finalize an effective system design. Many kind of models are often performed to develop the systems currently populating the wide scenario of complex and smart products. When the product is a result of a material processing, some geometrical models allow describing shape and properties of the manufactured product, whose behavior is then predicted by resorting to some numerical discretization funded on a set of equations to be solved. Those models mainly describe the real nature of system, not only as is designed but even as is manufactured, thus allowing the required verification and validation activities. Due to this motivation those models belong the so–called physical modeling, whose key targets are both a mathematical modeling and a quantitative evaluation of performance. According to the MBSE the above described activity is never sufficient to completely define the details of the system under design and development. Moreover, to face the inherent complexity of new systems, being characterized by a number of functions, components and interfaces, a clear traceability from requirement to numbered part is needed. A bright allocation of each requirement to the system functions first, and to its logical blocks then, is definitely a key issue of the proposed approach. Those two main goals require a preliminary functional modeling activity, never characterized by numbers, while is dominant a prediction of system operation, behavior, interaction with other systems and stakeholders, and even a preliminary definition of well assessed requirements to motivate a consequent set of proposed layouts, based on some selected technolog

Digital Twin: towards the integration between System Design and RAMS assessment through the Model–Based Systems Engineering

The design of a safety-critical system requires an effective prediction of its reliability, availability, maintainability and safety (RAMS). Anticipating the RAMS analysis at the concept design helps the designer in the trade-off of the system architecture and technologies, reduces cost of product development and the time to market. This action is rather difficult, because the RAMS analysis deals with the hazard assessment of system components, whose abstraction at concept level is never simple. Therefore, to integrate the system design and RAMS assessment, a clear path to follow is required. The paper investigates how the Model Based Systems Engineering (MBSE) supports this task and drives the system reliability allocation, through the functional and dysfunctional analyses. The implementation of the proposed approach needs to set up the tool chain. In the industrial context it must be compatible with practices, standards and tools currently used in product development. Defining a suitable process of integration of tools used for the System Design and the Safety Engineering is a need of industry. Therefore, this task is also discussed, in this paper, dealing with some examples of industrial test case

Smart Manufacturing in Rolling Process Based on Thermal Safety Monitoring by Fiber Optics Sensors Equipping Mill Bearings

The steel rolling process is critical for safety and maintenance because of loading and thermal operating conditions. Machinery condition monitoring (MCM) increases the system’s safety, preventing the risk of fire, failure, and rupture. Equipping the mill bearings with sensors allows monitoring of the system in service and controls the heating of mill components. Fiber optic sensors detect loading condition, vibration, and irregular heating. In several systems, access to machinery is rather limited. Therefore, this paper preliminarily investigates how fiber optics can be effectively embedded within the mill cage to set up a smart manufacturing system. The fiber Bragg gratings (FBG) technology allows embedding sensors inside the pins of backup bearings and performing some prognosis and diagnosis activities. The study starts from the rolling mill layout and defines its accessibility, considering some real industrial cases. Testing of an FBG sensor prototype checks thermal monitoring capability inside a closed cavity, obtained on the surface of either the fixed pin of the backup bearing or the stator surrounding the outer ring. Results encourage the development of the whole prototype of the MCM system to be tested on a real mill cage in full operation

Geodesic domes for planetary exploration

Venus and the Ocean Worlds are emerging areas of interest for space exploration, as they can potentially host, or have hosted, conditions compatible with life. Landers and probes for in-situ exploration, however, must deal with very high external pressure, due to the environmental conditions, often resulting in thick and heavy structures. Robust, reinforced shell structures can provide a lightweight solution for the primary structure. In this frame, the isogrid layout is already a standard in aerospace, especially for flat panels or cylindrical shells. In this paper, isogrid-stiffened hemispherical shells, or "geodesic domes", are described, focusing on the case of a concept of a Venus lander. Early design methods for both plain and geodesic domes subjected to external pressure are presented, providing design equations. Additive Manufacturing is identified as the key technology for fabricating metallic geodesic domes, due to the complexity of the internal features.Moreover, it allows to fabricate ports and integrated thermostructural systems in the same process, potentially resulting in improved performance or cost and schedule savings

Numerical modeling and testing of mechanical behavior of AM Titanium alloy bracket for aerospace applications

A key issue in designing a new product made through the Additive Manufacturing (AM) is the prediction of mechanical properties of material. Several experimental results show that AM-based products are often affected by widespread porosity, low density regions within their volume and anisotropy. Those effects are due to the manufacturing process, despite of efforts spent to improve the process parameters. This paper presents the numerical modelling of a geometrically complex structural bracket for aerospace application, which was re-designed through a topological optimization and produced in Ti-6Al-4V by means of the AM. The design activity herein described required to resort to a suitable model of constitutive properties of material by facing the problem of a large number of porosity/low density areas, as detected by a tomographic analysis of the mechanical component. According to some references an equivalent isotropic and homogeneous model of material was applied. Nevertheless the limitations of that approach were investigated through a validation of the numerical model and a testing activity. It was demonstrated that the Finite Element model based upon the assumptions of homogeneous and isotropic material might be effective in predicting the material and component strength, at least in static design, but even in case of design against fatigue, provided that a suitable experimental characterization of material was performed. The procedure of optimization was then assessed and compared to some preliminary tests performed on the real component, thus providing a preliminary good practice to the industrial partner involved in this research activity

On the Vibration Analysis of Coupled Transverse and Shear Piezoelectric FG Porous Beams with Higher-Order Theories

This investigation aims to perform a detailed natural frequency analysis of functionally graded porous beams integrated with transverse (d31) and shear (d15) piezoelectric layers under short circuit and open circuit electrical conditions. It is assumed that the core layer is made of functionally graded materials containing porosities. Due to the existence of internal pores, the mechanical properties of functionally graded materials are considered according to the modified powerlaw rule which includes the effect of porosity. The distribution of electric potential within the d31 and d15 piezoelectric layers is modeled based on nonlinear variation for both short circuit and open circuit conditions. Employing the classical, the first-order, and the higher-order beam theories incorporated with the virtual work principle as well as Maxwell’s equation, the electromechanical equations of motion are derived. The governing equations are then solved analytically for simply supported boundary condition and a parametric study is presented. After validation of the results, some new interesting conclusions covering the effects of porosity volume fraction, porosity distribution, various piezoelectricity modes, power-law index, and the beam theories on short circuit and open circuit resonance frequencies are reported. It is believed that the presented numerical results could provide a benchmark to check the accuracy of the approximated approaches

The Effects of Oil Film Shape on Piston Ring and Liner Tribology Under Mixed Lubrication

Mechanical power loss reduction at lubricated reciprocating and rotating components is recognized as an approach to improve the efficiency and to reduce the emissions of Internal Combustion Engines (ICEs). To achieve these goals, the instantaneous investigation of lubrication characteristics is required. Piston ring pack is of paramount importance as it is known as major contributor to frictional losses and energy dissipation. Applying Reynolds equation and lubrication theory to study piston ring tribology, requires specifying of boundary conditions. Oil film characteristics (shape and thickness) and generated hydrodynamic pressure are under influence of considered boundary conditions. Besides, the type of selected boundary conditions affects analysis robustness and sensitivity. During engine strokes, piston ring enjoys hydrodynamic and mixed lubrication regimes. The principle aim of the current study is to examine the effects of alternative boundary conditions: Half Sommerfeld, oil separation and Reynolds cavitation and reformation conditions on piston ring tribology under isothermal mixed and hydrodynamic lubrication regimes. This article demonstrates that different boundary conditions are suited to different operating conditions with respect to load, speed and temperature as well as crank angle, i.e., relative position of ring with respect to the liner. Thicker oil film thickness has been calculated applying half Sommerfeld boundary conditions under either hydrodynamic or mixed lubrication regimes followed by oil separation due to larger effective of the ring width. It was observed that considering oil separation boundary conditions results in lower deviation from experimental data, followed by Sommerfeld boundary conditions under mixed lubrication

Validation of compact models of microcantilever actuators for RF-MEMS application

Microcantilever specimens for in-plane and out-ofplane bending tests are here analyzed. Experimental validation of 2D and 3D numerical models is performed. Main features of in-plane and out-of-plane layouts are then discussed. Effectiveness of plane models to predict pull-in in presence of geometric nonlinearity due to a large tip displacement and initial curvature of microbeam is investigated. The paper is aimed to discuss the capability of 2D models to be used as compact tools to substitute some model order reduction techniques, which appear unsuitable in presence of both electromechanical and geometric nonlinearities.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838