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A simplified modal analysis of a single lap bonded joint using the macro-element technique
Get PDFModal analyses are essential steps in structural design. Simple and quick numerical procedures and design tools for modal and dynamic analysis of bonded joints would be an attractive option to increase the efficiency of the design process in its early phases. This paper offers a simple and quick numerical tool dedicated to the modal analysis of single lap bonded joints with balanced and unbalanced adherends with various boundary conditions. Based on the macro-element technique developed with Taylor expansion in power series, this paper gives all the steps to develop the mass matrix associated with a macro-element. The mass matrix has been developed so far for 1D-bar and 1D-beam kinematic frameworks. The results obtained with the macro-element technique and a Finite Element analysis give similar results
A generalized non-linear flow law based on modified Zerilli-Armstrong model and its implementation into Abaqus/Explicit FEM Code
Get PDFNon-linear numerical modeling, widely used in research and development to understand many complex processes such as forming or machining, does not guarantee the success of a study to be performed. Indeed, the numerical simulation uses finite element codes where the models already integrated are not based on shapes adjustable to any type of study. In this study, a new form of non-linear constitutive flow law based on the Modified Zerilli-Armstrong model, which can answer the above problem, has been developed to apply it to the numerical simulation of two different tests (a quasi-static compression test, the necking of a circular bar). This flow law is based on the modified Zerilli-Armstrong model, which, together with the new modified Johnson-Cook model, has been compared to appreciate the relevance of the proposal. For that, an implementation of this new law via the VUHARD subroutine into the Abaqus/Explicit finite element code was made to model the two tests. The comparison of the results obtained (from identification) by our proposed law with those obtained using the NMJC shows that this new law better approaches the experiments than the other one. This is also shown through the numerical results using the Abaqus software. It can be said that this way of formulating a flow law allows highlighting the great performance of the proposed approach. Although this law has been only used for quasi-static tests, we can say that it can also be used in dynamic tests
Improving user experience of SSVEP BCI through low amplitude depth and high frequency stimuli design
Get PDFSteady-States Visually Evoked Potentials (SSVEP) refer to the sustained rhythmic activity observed in surface electroencephalography (EEG) in response to the presentation of repetitive visual stimuli (RVS). Due to their robustness and rapid onset, SSVEP have been widely used in Brain Computer Interfaces (BCI). However, typical SSVEP stimuli are straining to the eyes and present risks of triggering epileptic seizures. Reducing visual stimuli contrast or extending their frequency range both appear as relevant solutions to address these issues. It however remains sparsely documented how BCI performance is impacted by these features and to which extent user experience can be improved. We conducted two studies to systematically characterize the effects of frequency and amplitude depth reduction on SSVEP response. The results revealed that although high frequency stimuli improve visual comfort, their classification performance were not competitive enough to design a reliable/responsive BCI. Importantly, we found that the amplitude depth reduction of low frequency RVS is an effective solution to improve user experience while maintaining high classification performance. These findings were further validated by an online T9 SSVEP-BCI in which stimuli with 40% amplitude depth reduction achieved comparable results (>90% accuracy) to full amplitude stimuli while significantly improving user experience
A methodology to integrate reliability into the conceptual design of safety-critical multirotor unmanned aerial vehicles
Get PDFThis article introduces a new conceptual design methodology to evaluate and explore underactuated electric multirotor unmanned aerial vehicle (UAV) designs for safety-critical applications. A case study focusing on medical transport in an urban environment demonstrates the methodology's effectiveness. The current state of the art does not provide conceptual design methodologies that integrate reliability considerations for multirotor UAVs. The proposed methodology addresses this gap by developing systematic reliability calculation and introducing sizing based on failure cases. For this purpose, controllability and reliability analysis methods are developed and linked to an analytical sizing methodology. The controllability analysis is based on the available control authority index adapted for failure case assessment and reliability analysis. The link between the controllability analysis and the sizing methodology is achieved by introducing failure case sizing factors. The sizing relies on a modern analytical database-free methodology with multidisciplinary design optimization for design customization and computational efficiency. This methodology is developed with new design models to cover failure cases in forward flights. When applied to the case study, the methodology efficiently evaluates and compares five concepts and indicates that only two comply with both the safety and reliability requirements and mission specifications (payload and range). More specifically, the methodology shows the major impact of reliability considerations on the case study with sizing factors that almost double or triple the required rotor thrusts depending on the design. This methodology is applicable to challenging future multirotor UAV applications that require to demonstrate high safety levels and redundancies, such as urban air taxis, flying ambulances, and search and rescue and medical equipment transport
Grafting Copper Atoms and Nanoparticles on Double-Walled Carbon Nanotubes: Application to Catalytic Synthesis of Propargylamine
Get PDFThe decoration of carbon nanotubes (CNTs) by metal nanoparticles (NPs) combines the advantages of a high specific surface material with catalytic properties of metal nanocrystals. Little work has been devoted to the decoration of CNTs with copper NPs, and no evidence of copper atomic decoration of CNTs has shown up until now. Herein, we demonstrate that the strong acidic oxidation of double-walled CNTs (dwCNTs) is very efficient for the decoration of the carbon surface by copper NPs and atoms. This treatment severely degraded the CNT walls and generated a large amount of disordered sp3 carbon. This amorphous carbon film bears many chemically active functions like carboxyl and hydroxyl ones. In such conditions, the CNT walls behave as very efficient ligands for the stabilization of copper obtained by the thermolysis of the mesityl precursor in organic solution under mild dihydrogen pressure. In addition to copper NPs, we evidenced the presence of a regular coverage with copper atoms over the dwCNTs. This nanocomposite catalyzes the quantitative synthesis of propargylamines via one A3-type coupling reaction. Five consecutive catalytic cycles with 100% yield could be performed with no loss of activity, and the combination of Cu supported on dwCNTs allows a facile recycling of the catalytic material
The sound of a Martian dust devil
Get PDFDust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam microphone. The dust devil encounter was also simultaneously imaged by the Perseverance rover’s Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we shown that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m/s. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars
After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission
Get PDFAfter DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future
Planetary Defense Mission
Thomas S. Statler 1 , Sabina D. Raducan 2 , Olivier S. Barnouin 3 , Mallory E. DeCoster 3 , Steven R. Chesley 4 ,
Brent Barbee 5
, Harrison F. Agrusa 6 , Saverio Cambioni 7 , Andrew F. Cheng 3 , Elisabetta Dotto 8
, Siegfried Eggl9 ,
Eugene G. Fahnestock 4
, Fabio Ferrari 2 , Dawn Graninger 3 , Alain Herique 10
, Isabel Herreros 11
, Masatoshi Hirabayashi 12,13 ,
Stavro Ivanovski 14
, Martin Jutzi 2
, Özgür Karatekin 15
, Alice Lucchetti 16
, Robert Luther 17 , Rahil Makadia 9 ,
Francesco Marzari 18 , Patrick Michel 19 , Naomi Murdoch 20
, Ryota Nakano13 , Jens Ormö 11 , Maurizio Pajola 16 ,
Andrew S. Rivkin3 , Alessandro Rossi 21 , Paul Sánchez 22 , Stephen R. Schwartz 23
, Stefania Soldini 24
, Damya Souami 19
,
Angela Stickle 3 , Paolo Tortora 25
, Josep M. Trigo-Rodríguez 26,27 , Flaviane Venditti 28 , Jean-Baptiste Vincent 29
, and
Kai Wünnemann 17,30
1 Planetary Defense Coordination Office and Planetary Science Division, NASA Headquarters, 300 Hidden Figures Way SW, Washington, DC 20546, USA
[email protected]
2 Space Research and Planetary Sciences, Physics Institute, University of Bern, Bern, 3012, Switzerland
3 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
4 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
5 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
6 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
7 Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
8 INAF-Osservatorio Astronomico di Roma, Rome, I-00078, Italy
9 Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
10 Univ. Grenoble Alpes, CNRS, CNES, IPAG, F-38000 Grenoble, France
11 Centro de Astrobiología CSIC-INTA, Instituto Nacional de Técnica Aeroespacial, E-28850 Torrejón de Ardoz, Spain
12 Department of Geosciences, Auburn University, Auburn, AL 36849, USA
13 Department of Aerospace Engineering, Auburn University, Auburn, AL 36849, USA
14 INAF- Osservatorio Astronomico di Trieste, Trieste I-34143, Italy
15 Royal Observatory of Belgium, Belgium
16 INAF-Astronomical Observatory of Padova, Padova I-35122, Italy
17 Museum für Naturkunde—Leibniz Institute for Evolution and Biodiversity Science, Germany
18 University of Padova, Padova, Italy
19 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice F-06304, France
20 Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
21 IFAC-CNR, Sesto Fiorentino I-50019, Italy
22 Colorado Center for Astrodynamics Research, University of Colorado Boulder, Boulder, CO 80303, USA
23 Planetary Science Institute, Tucson, AZ 85719, USA
24 Department of Mechanical, Materials and Aerospace Engineering, University of Liverpool, Liverpool, UK
25 Alma Mater Studiorum—Università di Bologna, Department of Industrial Engineering, Interdepartmental Center for Industrial Research in Aerospace, Via
Fontanelle 40—Forlì (FC)—I-47121, Italy
26 Institute of Space Sciences (ICE, CSIC), Cerdanyola del Vallès, E-08193 Barcelona, Catalonia, Spain
27 Institut d’Estudis Espacials de Catalunya (IEEC), Ed. Nexus, E-08034 Barcelona, Catalonia, Spain
28 Arecibo Observatory, University of Central Florida, HC-3 Box 53995, Arecibo, PR 00612, USA
29 German Aerospace Center, DLR Berlin, Germany
30 Freie Universität Berlin, Germany
Received 2022 August 9; revised 2022 September 18; accepted 2022 September 22; published 2022 October 28
Abstract
NASA’s Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology.
Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later
Hera mission, will result in measurement of the momentum transfer efficiency accurate to ∼10% and
characterization of the Didymos binary system. But DART is a single experiment; how could these results be used
in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos’s
response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge
of the physical properties of asteroidal materials and predictive power of impact simulations; what information
about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection
mission should be informed by this understanding. We generalize the momentum enhancement factor β, showing
that a particular direction-specific β will be directly determined by the DART results, and that a related direction-
specific β is a figure of merit for a kinetic impact mission. The DART β determination constrains the ejecta
momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos’s near-
surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered
asteroid will require Earth-based observations and benefit from in situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to
optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction
Robust integrated control/structure co-design for stratospheric balloons
Get PDFStratospheric balloons offer cost-effective platforms for optical payloads in the context of astronomy missions. During the 2018 flight of the Faint Intergalactic medium Redshifted Emission Balloon (FIREBall) experiment, the moon light was scattered from the surface of the balloon and re-directed into the telescope which resulted in degraded optical performance. To reduce this parasite effect, it is sought to increase the length of the fight train. However, this change in the mechanical design significantly modifies the dynamics of the system and the pointing performance must not be altered. In this purpose, a robust integrated control/structure co-design method is proposed. After deriving a Linear Fractional Transformation (LFT) model of the system, the co-design is tackled as a multi-objective, structured, robust H2/H∞ problem that is solved with a non-smooth optimization algorithm to maximize the train's length under constraints of pointing performance. By optimizing in a single iteration the controllers along with the structural parameter with regard to the worst-case configurations of the uncertain parameters, time-consuming procedures requiring not only to iterate between control and mechanical design, but also to analyze the robustness based on Monte-Carlo simulations, are avoided
Model-checking for TASTE designed space software systems: results and lessons learned
Get PDFModel-Based Systems Engineering (MBSE) is an adopted modelling and development approach for correct-by- construction of complex software systems, such as space applications. TASTE [1] is a pragmatic and mature MBSE toolset supported by ESA that enables and provides automation for most of the phases of software system development: (i) heterogeneous system design through several modelling and programming languages (e.g., ASN.1, AADL, SDL, C/C++), (ii) code generation, build and deployment of the binary application(s), (iii) validation through static analysis and simulation, and (iv) formal verification of properties by model-checking. The formal verification capabilities have been recently added to the TASTE toolset in the ESA project Model-Checking for Formal Verification of Space Systems (MoC4Space) and validated on two real-life case studies. Within this paper we report on the results and lessons learned during the project
A Partitioned Finite Element Method (PFEM) for power-preserving discretization of port-Hamiltonian systems (pHs) with polynomial nonlinearity
Get PDFThe Partitioned Finite Element Method introduced in [IMA J. MCIControl and Information, 2021]. provides a structure-preserving discretization for the solution
of systems of boundary controlled and observed Partial Differential Equations (PDEs), formulated as distributed-parameter port-Hamiltonian systems (pHs). In particular, the energy balance is preserved at the discrete level. This method, already well-developped for linear systems, is also suitable for nonlinear systems with polynomial nonlinearity, such as the 2D Shallow Water Equations, or the full von-Kármán plate equations