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

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

A model-based rams estimation methodology for innovative aircraft on-board systems supporting mdo applications

The reduction of aircraft operating costs is one of the most important objectives addressed by aeronautical manufactures and research centers in the last decades. In order to reach this objective, one of the current ways is to develop innovative on-board system architectures, which can bring to lower fuel and maintenance costs. The development and optimization of these new aircraft on-board systems can be addressed through a Multidisciplinary Design Optimization (MDO) approach, which involves different disciplines. One relevant discipline in this MDO problem is Reliability, Availability, Maintainability and Safety (RAMS), which allows the assessment of the reliability and safety of aircraft systems. Indeed the development of innovative systems cannot comply with only performance requirements, but also with reliability and safety constraints. Therefore, the RAMS discipline plays an important role in the development of innovative on-board systems. In the last years, different RAMS models and methods have been defined, considering both conventional and innovative architectures. However, most of them rely on a document-based approach, which makes difficult and time consuming the use of information gained through their analysis to improve system architectures. On the contrary, a model-based approach would make easier and more accessible the study of systems reliability and safety, as explained in several studies. Model Based Systems Engineering (MBSE) is an emerging approach that is mainly used for the design of complex systems. However, only a few studies propose this approach for the evaluation of system safety and reliability. The aim of this paper is therefore to propose a MBSE approach for model-based RAMS evaluations. The paper demonstrates that RAMS models can be developed to quickly and more effectively assess the reliability and safety of conventional and innovative on-board system architectures. In addition, further activities for the integration of the model-based RAMS methodology within MDO processes are described in the paper

A model based approach to design for reliability and safety of critical aeronautic systems

This paper explores how the safety engineering practices applied to the aircraft design can be effectively associated to the MBSE. Requirements and procedures of the ARP4754/ED-79 and ARP4761 were considered. As an example the fuel system of a civil aircraft was used. Some key issues were found relevant, whilst modeling the system through the MBSE tools. The management of both the functional and dysfunctional analysis, leading to the Functional Hazard Analysis (FHA) of the whole aircraft, within the same modeling environment was tested. The elicitation of safety requirements with a direct link to the FTA and FMEA used to quantify the risk of failure was performed. The software tools which can be interoperated for those tasks were tested. As a result, the integration between the two above mentioned analyses looks fairly easy. In fact, further efforts are required to make fully interoperable the tools currently available to perform this activity and to include the human interaction with the analyzed syste