Robust design of spacecraft structures under lack of knowledge

International audienceIn robust design, lacks of knowledge are rarely taken into account explicitly, but this is the case in the RRDO-IG. This paper summarises the ongoing developments and perspectives for the use of the RRDO-IG methodology in a spatial industrial context, where non-linearities have to be treated. After shortly describing the RRDO-IG methodology and the actual encountered problems, we will construct an improvement strategy based on a state of the art in metamodelisation and failure probability computation

PHARAO Laser Source Flight Model: Design and Performances

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.Comment: Accepted for publication in Review of Scientific Instrument

Design of an uncertain prestressed space structure: an info-gap approach

Uncertainty quantification is an integral part of the model validation process and is important to take into account during the design of mechanical systems. Sources of uncertainty are diverse but generally fall into two categories: aleatory uncertainties due to random processes and epistemic uncertainty resulting from a lack of knowledge or erroneous assumptions. This work focuses on the impact of uncertain levels of prestress on the behavior of solar arrays in their stowed configuration. In this context, snubbers are inserted between two adjacent panels to maintain contact and absorb vibrations during launch. However, under high excitation loads, a loss of contact between the two panels may occur. This results in impacts that can cause extensive damages to fragile elements. In practice, the specific load configuration for which the separation of the two panels occurs is difficult to determine precisely since the exact level of prestress applied to the structure is unknown. An info-gap robustness analysis is applied to study the impact of this lack of knowledge on the prestress safety factor required to avoid loss of contact. The proposed methodology is illustrated using a simplified model of a solar array

Robust design of notching profiles under epistemic model uncertainties

International audienceThe notching profile defines the loading conditions for satellite subsystem shake tests. Its model-based design is a critical issue in the space field and must be defined early in order to initiate as soon as possible discussions between launch authorities and subcontractors. This discussion revolves around the following dilemma: how conservative can the loading be and still be safe for the subsystem interfaces? Indeed, the significant lack of knowledge present in the non-validated model can result in overloading conditions. This paper will propose a global strategy for the model-based design of notching profiles which accounts for epistemic modeling uncertainties using an info-gap approach. The latter provides a generic framework for evaluating and comparing the performances of competing profile designs as well as addressing issues of lack of knowledge in both deterministic and probabilistic model parameters. The proposed methodologies will be illustrated on an academic test case

Metrics for nonlinear model updating in structural dynamics

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Metrics For Non-linear Model Updating In Mechanical Systems

This paper proposes a comparative study between differents metrics for non-linear model updating based on vibration test data. Four approaches in the frequency and time domain are implemented: harmonic balance method, constitutive relation error, restoring force surface and Karhunen-Loève decomposition. Firstly, each non-linear updating metric is succinctly reviewed. We then define an academic benchmark which is used to compare the performance of metric function based on the form of the objective function and calculation time. Finally, we conclude with a discussion of the applicability, limitations and differences between the investigated approaches.Friswell, M.I., Mottershead, J.E., (1995) Finite Element Model Updating in Structural Dynamics, , Kluwer Academy PublishersMeyer, S., Link, M., Modelling and updating of local non-linearities using frequency response residuals (2003) Mechanical Systems and Signal Processing, 17 (1), pp. 219-226Deraemaeker, A., Ladevèze, P., Leconte, Reduced bases for model updating in structural dynamics based on constitutive relation error (2002) Computer Methods in Applied Mechanics and Engineering, 191, pp. 2427-2444Puel, G., (2001) Mise en Évidence et Recalage des Non-linéarités Locales en Dynamique des Structures, , Master's thesis, Université Paris VIWorden, K., Tomlinson, G.R., (2001) Nonlinearity in Structural Dynamics, , London: Institute of Physics PublishingKerschen, G., Golinval, J.C., Worden, K., Theoretical and experimental identification of a non-linear beam (2001) Journal of Sound and Vibration, 244 (4), pp. 597-613Silva, S., Dias Junior, M., Lopes Jr., V., Damage detection in a benchmark structure using ar-arx models and statistical pattern recognition (2007) Journal of the Brazilian Society of Mechanical Sciences and Engineering, 29 (2), pp. 174-184Lenaerts, V., Kerschen, G., Golinval, J.C., Proper orthogonal decomposition for model updating of non-linear mechanical system (2001) Mechanical Systems and Signal Processing, 15 (1), pp. 31-4

Metrics for non-linear model updating in mechanical systems

February 4-7International audienc