A fast method of material, design and process eco-selection via topology optimization, for additive manufactured structures

We propose an innovative approach to minimize the greenhouse gas impacts of additive manufactured structures over their entire life cycle. The novelty of our method lies in its simultaneous optimization of material selection, process selection, and design optimization. To fully leverage the potential benefits of additive manufacturing, we use topology optimization and compile a comprehensive database of printed materials and printing processes, which we share with the wider community. To account for the complex interdependence between materials and processes, our method employs a pairing system, which we efficiently reduce using topology optimization properties and a generalized form of Ashby indices. To enhance computational efficiency, we employ a meta-model. We validate our proposed method through successful testing on an aeronautical case and a pedestrian bridge, demonstrating its robustness even in the presence of environmental data uncertainty. The optimal material-process pair for the aeronautical structure is the cobalt-based super-alloy with the LENS process. Despite this pair having the highest material and processing emissions, the resulting lighter part lowers the use phase emissions. It appears that precise mechanical data is needed for the method to give accurate results: a 20% drop of Young's modulus totally disrupts the material-process pair ranking

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

ASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater

Physics-Informed Proper Orthogonal Decomposition for Data Reconstruction

Many engineering problems are governed by complex governing equations that are difficult and typically require high computational costs to solve. Machine learning and surrogate modelling aid such an endeavour by providing a cheap-to-evaluate prediction model that acts as a replacement of the original model. While most research focuses on predicting scalar values (e.g., lift and drag), predicting the solution field is also of interest in many practical engineering and scientific applications. This paper proposes a Physics-Informed Proper Orthogonal Decomposition (POD) technique that improves the solution field prediction by enforcing governing equations as a loss penalty. The proposed idea utilizes a reduced-order modeling technique based on POD to decompose solution snapshots into singular vectors and values. A Gaussian Process Regression is then utilized to predict the singular values from variable parameters. The predicted singular values from the data of the problem are then adjusted via optimization to minimize the physics-informed loss and achieve better prediction. In this paper, we illustrate the efficacy of the proposed method on simple two-dimensional partial differential equations. The result clearly shows that the proposed physics-informed POD outperforms the conventional POD in terms of approximation error

Fast Nonlinear Static Aeroelasticity Method for High-Aspect-Ratio Wings at Different Mach Regimes

A low-computational-cost method is proposed in this paper to predict steady-state nonlinear aeroelastic response for high-aspect-ratio wings. This fast nonlinear static aeroelasticity method relies on a simple but robust mathematical approach. The work presented in this paper evaluates the accuracy of a nonlinear aerodynamic method on a large range of Mach numbers for a geometry representative of a typical industrial high-aspect-ratio-wing aircraft. The robustness of the method relies on the accurate estimation of the local pressure field based on an aerodynamic database using a local incidence estimated with a vortex lattice method. The database can be filled with flight test, wind tunnel test, or high-fidelity numerical simulation. The structural deformation is provided by a coupled aeroelastic high-fidelity numerical simulation, and so this paper focuses mainly on the development and validation of the aerodynamic model. Then, the flexible coefficients of the wing are compared to the high-fidelity aeroelastic numerical simulations for a set of Mach numbers ranging from subsonic to transonic conditions. The results presented in this paper show that the present method is very accurate for low-Mach-number regimes (error is lower than 1% on lift), and it is also adapted to transonic flow regimes because the error on lift is lower than 5%. For high Mach numbers, the current solution commits larger errors on drag and pitching moment coefficients

Urban Air Vehicle Mission Sizing and Performance Estimation Using Pacelab APD

Modern aviation has been focusing on hybrid-electric propulsion in recent years, aiming for concepts with lower atmospheric and acoustic pollution to improve social acceptance of the sector. Development of such new enabling technologies results in emergence of whole new aircraft concepts like Electric Vertical Take-Off and Landing (eVTOL) for urban air mobility. The present work focuses on the preliminary design of a hybrid-electric Vertical Take-Off and Landing (VTOL) air vehicle with multiple ducted fans. A theoretical preliminary sizing model is proposed and then implemented in Pacelab APDTM, a commercial preliminary design tool developed by PACE Aerospace Engineering and Information Technology GmbH. The performance deck for electric ducted fans is developed in parallel using PROOSISTM, a separate dedicated propulsive system simulation software, using flight conditions as input and providing appropriate performance characteristics as output. The targeted powertrain is completed with a turbogenerator, also modelled in PROOSIS as a generic turboshaft engine with an additional electric generator efficiency accounting. After having sized it at cruise condition, a specific fuel consumption map is retrieved. A typical urban air mobility operational framework is considered when building the design mission - composed of vertical take-off, hover, cruise and vertical landing - as well as a range of off-design use case scenarios. Power requirement in vertical flight segments is also estimated. An example of the developed model application in Pacelab APD is provided; it is inspired by existing concepts on the market. It presents a hybrid-electric powertrain with eight ducted fans and a fully composite airframe. The model is implemented in a customized version of APD, along with coding of the missing engineering objects and the propulsive system performance decks exported from PROOSIS. The design mission is then simulated and analysed, suggesting a feasible aircraft solution, which is later subject to sensitivity studies

Stability of high-density trailing vortices

The three dimensional modal linear stability of the radially stratified q-vortex is investigated. The presence of a radial density gradient in the vortex core biases the vortex stability features over the whole parameter space, i.e. varying the swirl number q, the axial k and azimuthal m wavenumbers and the density-to-vorticity radius ratio ε. The high swirl vortex, known to be stable in the constant-density situation becomes unstable to the Rayleigh–Taylor instability (RTI) with high amplification rates for vortex cores denser than the ambient. Hence we carry out a comprehensive stability analysis to measure the consequences of the onset of the RTI on the q-vortex linear stability. The damping effect of viscosity saturates beyond a threshold Reynolds number and we mean to address high Reynolds number situations such as those found in aircraft trailing vortices. Hence we place ourselves in the high Reynolds numbers regime for which vortices with a dense core exhibit a significant increase of the global maximum of the amplification rate. The effect of the radius ratio ε is twofold. In the high swirl number regime where the homogeneous modes are stable or weakly amplified, the concentration of denser fluid at the vortex core promotes instabilities. In regions of the (k, q)-plane favouring both the homogeneous instability and the RTI mechanism, the amplification rate peaks for a radius ratio around ε≈2

Comparison of control strategies for hysteresis attenuation in electromechanical actuators subject to dispersion

This paper addresses the difficulties of designing highly efficient robust controllers for a class of systems exhibiting high hysteresis with parameters dispersion that limits control accuracy and performance homogene- ity over the parametric uncertainties range. Two control strategies to solve the problem are assessed. First, a Reference Model Sliding Mode Control (RMSMC) feedback controller known to be robust to parametric uncertainty is designed to compensate for hysteresis, regardless of the hysteresis quantity. Secondly, a strategy based on a feedforward controller with a Neural Network inverse model and a PID feedback controller is proposed. In this case, hysteresis dispersion is addressed by integrating a backlash estimator for computing the Neural Network inverse model. The control strategies are implemented for position control of a Limited-Angle Torque Motor (LATM) exhibiting uncertain hysteresis. Experimental tests demonstrated the very good accuracy and robustness of the Neural Network inverse model and the PID controller for position tracking when the LATM is subject to dispersion and the benefits of the Reference Model Sliding Mode Control (RMSMC) feedback controller for the rejection of external disturbances

Simulations numériques d'allumages des moteurs aéronautiques en conditions réalistes de hautes altitudes

La capacité de rallumage est un aspect critique de la conception des moteurs aéronautiques et les normes de sureté exigent l'allumage du moteur en conditions de haute altitude (basse pression : P = 0.3 bar et basse température : T = 233 K ). Ainsi, l'influence des conditions de basse pression et de basse temperature doit être mieux comprise. Pour cela, l'effet de ces conditions sur les phenomènes chimiques a tout d'abord été étudié en configurations purement gazeuses. Les résultats ont alors montré que les conditions sub-atmosphériques étaient désavantageuses à cause d'un ralentissement de la réactivité chimique et donc d'une réduction de la puissance dégagée. De plus, des simulations numériques directes ont été réalisées en utilisant une chimie ARC multi-composante ce qui a permis de comparer le développement des noyaux de flamme en fonction des conditions de pression et de température. Les résultats indiquent alors que les noyaux formés en condition de basse pression sont moins robustes aux phénomènes d'extinctions. D'autre part, l'influence des conditions de haute altitude sur le diphasique a aussi été évaluée. Premièrement, au niveau de l'injection de carburant, les données expérimentales disponibles ont montré que les basses pressions réduisent les processus d'atomisation ce qui conduit à la formation d'un spray composé de gouttes plus larges et moins nombreuses. Des simulations d'allumage diphasique ont alors été réalisées en prenant en compte la modification de la distribution de goutte induite par les conditions de haute altitude. Un changement complet du régime de combustion a alors été observé par rapport au cas gazeux. Pour finir, ce travail a permis de développer de nouvelles méthodes numériques qui ont pu être utilisées pour simuler l'allumage en condition réaliste de haute altitude dans le banc MERCATO. Ce calcul a mis en évidence le rôle critique des phénomènes diphasiques dans la formation et le développement du noyau. De plus, l'effet néfaste des basses pressions et des basses températures sur l'allumage a été retrouvé. The relight capability is a critical aspect of the aeronautical engine design and safety standards require the ignition of the engine under high altitude conditions (low pressure: P = 0.3 bar and low temperature: T = 233 K). Therefore the influence of low pressure and low temperature conditions on the ignition processes must be better understood. For this purpose, the effect of these conditions on the chemical phenomena has been first evaluated with purely gaseous configurations. The results have shown the detrimental effect of sub-atmospheric conditions via a slowing down of the chemical reactivity and thus a reduction of the power released. In addition, direct numerical simulations performed using a multi-component ARC chemistry enable to compare the kernel developments depending on the pressure and temperature conditions and indicate that low pressure kernels are less robust to extinction phenomena. On the other hand, the influences of high altitude conditions on the two-phase flow have also been evaluated. Firstly, at the fuel injection, the available experimental measurements have shown that low pressure reduces the atomization phenomenon resulting in a spray with larger and fewer droplets. Two-phase ignition simulations have thus been performed taking into account the different droplet distribution due to the high altitude conditions. A complete modification of the combustion regime has then been observed compared to the gaseous case. Finally, this work enables to develop new numerical methods which have been used to simulate the ignition under realistic high altitude conditions in the MERCATO configuration. This computation highlighted the critical role of the two-phase phenomena in the formation and development of the kernel. Furthermore, the detrimental effect of low pressure and low temperature on the ignition has been recovered once again

On the Equivalence between Kalman Filter at Steady State and DPLL

Fundamental results in the literature previously showed that a class of Kalman filter converges to a digital phase lock loop (DPLL) structure at the second and third order. We generalize these results at any order and give the closed-form linear relation, and its inverse, between the steady-state Kalman gains and the loop filter constants. Both relations are simple and only involve Stirling numbers of the first and second kind. This new result may help in a deeper understanding of the equivalence between Kalman filter and DPLL and be of practical interest in high dynamic scenarios

Mutation of Formally Verified SysML Models

Model checking of SysML models contributes to detect design errors and to check design decisions against user requirements. Yet, each time a model is modified, formal verification must be performed again, which makes model evolution costly and hampers the use of agile development methods. Based on former contri- butions on dependency graphs, the paper proposes to facilitate updates (also called mutations) on models: whenever a mutation is performed on a model, the algorithms introduced in this paper can determine which proofs remain valid and which ones must be performed again. In this latter case, our algorithm reuses as much as possible previous proofs results in order to lower the proof complexity. The paper focuses on reachability proofs, and relies on a real-time communication architecture based on TSN (Time Sensitive Network) to exemplify the approach and give performance results