Emmanuel Mermoz

Normal signature characterization for system health assessment

Helicopter is a system on which operates a large number of specialities from electrical domain to mechanical domain. Today, diagnosis methods are segmented by field of expertise. Each expert treats the sub-system whose he is responsible for regardless of the results of other specialities. Therefore, there is no relation between specialities. Thus, diagnosis at system level is efficient but, due to the lack of correlation between subsystems, it is incomplete. Within the framework of a helicopter, the operator of maintenance uses all the data recorded during the flight, the results of expert treatments, but also his knowledge, his experience and his capacities of observation and analysis to provide an effective global diagnosis. In order to build relation between fields of expertise and so, to obtain a diagnosis at aircraft level which could be relevant, we try to set up a concept which gets closer, at most, to human judgment but which is not well adapted to industrial environment: the normality. During our study, we established that to reach our objective and to stick at best with the concept of normality, the most relevant solution consists in building a global normal signature. This signature could be illustrated as the image of the aircraft health, qualified as normal. This paper defines the normal signature and explains, in part, the process of its building.

Computational Design Synthesis Using Model-Driven Engineering and Constraint Programming

This paper introduces a new process for computational design synthesis. It starts from functional requirements to generate one or more topologies of components. This process is implemented using Model-Driven Engineering techniques and Constraint Programming solving capabilities. Model transformations are used to transform functions and available components to a CSP. This problem is solved with a CSP solver, which solutions are transformed to topological architectures. The process is successfully applied on the design synthesis of an autonomous generator. It produces about 60 relevant solutions from which we found some existing product architectures.

Study of Bearing Modelling in the Helicopter Gearbox

In trying to incessantly reduce gearboxes weight, designers can negatively impact the service reliability, particularly in the aeronautic industry, where a weight reduction is often linked with stiffness decrease. Looking for weight savings, gearbox casings are classically made of magnesium or aluminium alloy. In addition, helicopter gearbox design is included the integration of several functions within the same part (like the shafts which gather one or more gears, splines and integrated bearings raceways). These particularities in the design are requiring some specific methodologies for Power Transmission bearing modelling. In this paper, a comparison between tests and simulations results of the aforementioned gearboxes is presented. The first section of the article focuses on the helicopter gearbox description and associated finite elements modelling. Then, the second section provides a comparison between the experimental observations with the results of both FEM simulation and classical analytical simulation. This comparison demonstrates the interest of using FEM simulation to analyze gearboxes behaviour.

Contact Pressure Calculation Methodologies in Aeronautic Gearboxes in the CAD Process

This paper deals with the various methodologies usable in a CAD environment for the calculation of contact pressures in aeronautic gearbox bearings. These methodologies may be analytical (Hertz theory), numerical (F.E.M.) or hybrid. They are analyzed and compared according to their precision, calculation time and readiness to be integrated in the industrial design process. An optimum contact pressure calculation methodology will be presented based upon the results of this analysis.

A framework for automatic architectural synthesis in conceptual design phase

ABSTRACT Architectural synthesis is a key phase of the conceptual design process. In the constant evolution of complex systems, architects have found it difficult to carry out an exhaustive search of all the feasible architectural solutions for a set of given requirements. This paper proposes a computational synthesis framework that automatically generates, from a set of formatted requirements and a sub-systems database, all architectures that are requirement consistent, minimalist regarding the number of components and non-redundant. The resolution principles are based on graph theory representations and Constraint Programming solving techniques. Key features of the framework and an application example are also detailed. Abbreviations: AO: architectural object; BPMN: business process model and notation; CSP: constraint satisfaction problem; DSM: design structure matrix; SE: systems engineering.