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A bi-level co-design approach for multicopters
Full text linkOver the last few decades, multicopters have become significantly popular because of their various applications.
However, multicopters suffer from poor endurance performance as compared to other aircraft configurations with lifting surfaces.
In this paper, a co-design approach for the multicopter structure and propulsive system is presented with the objective of improving the energetic efficiency of the vehicle, while respecting dynamic performance requirements. For this purpose, the approach uses a bi-level formulation to optimize concurrently the design and the control. The methodology offers the possibility to activate or not a passive fault tolerant strategy in the controller synthesis to be tolerant to single rotor failure. In contrast to conventional design approaches that sequentially design each part, the co-design approach leads to a better optimal solution due to the consideration of the interactions and couplings between design and control.
With the proposed co-design approach, the results show the soundness of the proposed design methodology and a significant reduction in the consumed energy compared to a reference non-optimal design, while maintaining the same requirements in terms of dynamic performance
Toward a Real-Time Index of Pupillary Activity as an Indicator of Cognitive Load
Full text linkThe Low/High Index of Pupillary Activity (LHIPA), an eye-tracked measure of pupil diameter oscillation, is redesigned and implemented to function in real-time. The novel Real-time IPA (RIPA) is shown to discriminate cognitive load in re-streamed data from earlier experiments. Rationale for the RIPA is tied to the functioning of the human autonomic nervous system yielding a hybrid measure based on the ratio of Low/High frequencies of pupil oscillation. The paper's contribution is drawn from provision of documentation of the calculation of the RIPA. As with the LHIPA, it is possible for researchers to apply this metric to their own experiments where a measure of cognitive load is of interest
Epsilon v3: exergy-based aerodynamic analysis tool for cfd and wtt data
Full text linkIn 2020, ISAE-SUPAERO has released the first version of Epsilon: an open source tool for the aerodynamic analysis of CFD data with Paraview [1]. Several methods were available: near-field, far-field, Lamb vector and exergy. In the original release, CFD data could be fully analyzed but the analysis of wind tunnel data was very limited. That is why a development effort was undertaken in order to improve the posttreatment capabilities of wind tunnel data. Several tools were created to properly perform an aerodynamic analysis from PIV and 5HP data. These developments were implemented and verified in a recent wind tunnel campaign and the resulting feedback was used to perform a further upgrade to the software. The resulting new version of Epsilon is released to the public along with this conference paper
Numerical modelling of parts distortion and beam supports breakage during selective laser melting (SLM) additive manufacturing
Full text linkThe Selective Laser Melting (SLM) process has been progressively endorsed as an industrial manufacturing technique to produce high value-added components. However, one of the main obstacles to its wide application is the uncertainty regard- ing the successful completion of the manufacturing process. Mechanical stresses are generated and accumulated during the process, which may lead to the parts warping and cracking. Support structures may also detach from the part but it is not certain that these cracks conduct to the manufacturing failure. The process simulations currently available do not consider the cracking of the supports and the ongoing part’s deflection. The aim of this study is to investigate cone supports fracture behaviour comparing the results from a numerical model and the manufacturing of an industrial part. A model using 1D-beam elements to mesh the supports has been developed to consider the damage of the supports, their breakage and the ongoing deflection. Some numerical convergence issues are identified and solutions are proposed. Specific experimental set-ups are developed to characterise the behaviour of the supports individually and as a group. Significant improvements are denoted while injecting the measured characteristics within the model. Some key parameters of the supports damage behaviour are identified. It is shown that the supports mechanical characteristics are significantly different from the parts due to their manufacturing conditions and environment. Also, limitations regarding the characterisation of the supports as well as strong numerical convergence issues brought by multiple supports cracking are discussed
Physical and dynamic mechanical properties of continuous bamboo reinforcement/bio-based epoxy composites
Full text linkUnidirectional bamboo reinforced cardanol-based epoxy composites were prepared by a close mould method. Two morphologies of reinforcements were used in this research: bamboo fibres and bamboo strips. The present article investigates the influence of bamboo reinforcements on the thermal and mechanical properties of the bio based matrix. Differential Scanning Calorimetry analyses showed that the introduction of bamboo does not modify the physical properties of the matrix. DMA analyses in shear mode showed an improvement of the shear conservative modulus that reaches 1.7 ± 0.1 GPa. This value that is independent from the morphology of reinforcements, indicates the existence of physical interactions. The continuity of matter between bamboo strips or bamboo fibres and the matrix observed by SEM confirms this result. Nevertheless, in tensile mode, the improvement of the tensile conservative modulus is specific to the used morphology. Indeed, for bamboo strips composites, it is 7.7 ± 0.8 GPa, while for bamboo fibres composites, it reaches 9.6 ± 0.8 GPa. This result is explained by the optimisation of stress transfer thanks to the specific morphology of bamboo fibres. A significant increase is also observed for the rubbery modulus due to entanglements specific of bamboo reinforcement
Spectral Proper Orthogonal Decomposition of coupled hydrodynamic and acoustic fields: application to impinging jet configurations
Full text linkA large variety of flow configurations involve an aero-acoustic coupling and the complexity of the interaction can make the analysis difficult. In the purpose to decompose these flows in simpler phenomena, the spectral proper orthogonal decomposition (SPOD) algorithm can be used. Compared to POD, this method adds up a discrete Fourier transform before the singular value decomposition. A theoretical framework for the weighting of the flow field variables used in the SPOD has been proposed to identify hydrodynamic modes by Schmidt et al. However, in flow configurations where both the hydrodynamic and acoustic fields interact, without additional data processing, only hydrodynamic modes that are generally dominants would be identified by the SPOD. This paper proposes a general framework based on a few pre-processing steps applied to the input aero-acoustic fields to facilitate the identification of both the hydrodynamic and acoustic fields by the SPOD, the purpose being to analyze how the hydrodynamic waves lead to the acoustic ones and the possible feedback process. This framework is applied to large-eddy simulations of supersonic ideally expanded impinging planar jet of infinite extent characterized by different nozzle-to-plate distances and incidence angles of the flat plate. The analysis shows that the SPOD algorithm is able to capture two important aero-acoustic feedback loops of impinging jet configurations: the one closed by sound waves traveling upstream (related to the jet impingement on the flat plate) and the one characterized by neutral wave modes of the jet shear layer itself. The analysis has also shown that the symmetrical/anti-symmetrical acoustic patterns radiated with respect to the jet main axis and due to the jet impingement are mainly correlated to the axial velocity fluctuations structures in the jet for the normally impinging cases. For the cases
with flat plate incidence, the acoustic radiated is mainly correlated to vertical velocity fluctuations structures developing in the upper shear layer of the jet
Three-dimensional dynamics of a pair of deformable bubbles rising initially in line. Part 2. Highly inertial regimes
Full text linkThe buoyancy-driven dynamics of a pair of gas bubbles released in line is investigated numerically, focusing on highly inertial conditions under which isolated bubbles follow non-straight paths. In an early stage, the second bubble always drifts out of the wake of the leading one. Then, depending on the ratios of the buoyancy, viscous and capillary forces which de ne the Galilei (Ga) and Bond (Bo) numbers of the system, ve distinct regimes speci c to such conditions are identi ed, in which the two bubbles may rise independently or continue to interact and possibly collide in the end. In the former case, they usually perform large-amplitude planar zigzags within the same plane or within two distinct planes, depending on the oblateness of the leading bubble. However, for large enough Ga and low enough Bo, they follow nearly vertical paths with small-amplitude erratic horizontal deviations. Increasing Bo makes the wake-induced attraction toward the leading bubble stronger, forcing the two bubbles to realign vertically one or more times along their ascent. During such sequences, wake vortices may hit the trailing bubble, deflecting its path and, depending on the case, promoting or hindering further possibilities of interaction. In some regimes, varying the initial distance separating the two bubbles modifies their lateral separation beyond the initial stage. Similarly, minute initial angular deviations favour the selection of a single vertical plane of rise common to both bubbles. These changes may dramatically a ect the fate of the tandem as, depending on Bo, they promote or prevent future vertical realignments
An inverse identification procedure for the evaluation of equivalent loading conditions for simplified numerical models in Abaqus
Full text linkIn the finite element simulation process, it is very common to use simplified models to replace the original complex models to reduce the computational cost. To improve the accuracy of simulation with simplified numerical models in Abaqus Explicit, we propose an inverse identification procedure to evaluate the equivalent loading conditions to be applied to these simplified models. We construct an objective function to test the correlation between the final deformed shape obtained by simulation on the full models and the simplified models. A Python identification program using the Levenberg-Marquardt algorithm is implemented to optimize this objective function. In parallel to this approach, we propose a data processing step, validated by a dynamic tensile test, to obtain more accurate numerical responses, including data extraction and estimation. Full numerical models for the Taylor test, dynamic tensile test, and dynamic shear test were constructed using Abaqus Explicit FEM code. The complete models were then replaced by simplified models, in which some non-essential parts were removed and some boundary conditions were modified. In order to obtain the same results in terms of the final geometry, the proposed inverse identification procedure is then used to calculate the equivalent impact velocities for the simplified models
Development of new surface treatments for the adhesive bonding of aluminum surfaces
Full text linkBi-functional water-soluble polymers have been investigated as bonding layers (BL) on aluminum surfaces to promote the adhesion of adhesives for structural bonding applications in the automotive sector. The BLs are located at the interface between two parts: the aluminum substrate and the adhesive (an epoxy-dicyandiamide). The formation and the morphology are studied mainly by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Many process parameters have been investigated such as: i) long or short immersion time in the treatment baths containing the polymers, ii) formulation using three different concentrations. The performances of the BLs under these different operating conditions are evaluated via several mechanical tests: micro-scratch, three-point bending, single lap shear. Results were compared with results obtained with already existing products, launched for the same application, surface treatment prior to structural adhesive bonding of aluminum in transportation
Development of a 3D finite element model at mesoscale for the crushing of unidirectional composites: Application to plates crushing
Full text linkThis paper presents the development of a new 3D finite element model for the simulation of UD composites
materials under crushing, at the mesoscale. It is based on the Discrete Ply Model (DPM), enhanced with a new
damage law to represent compression at constant stress due to localised crushing and its propagation from one
element to another. The model aims to take into account the various damage types involved in UD laminates
during crushing and the associated absorbed energies: delamination, splitting, ply rupture in tension or bending,
compression due to localised fragmentation and friction. The model is confronted with experimental results
obtained on laminated plates crushing: not only global metrics (force, energy absorbed…) but especially key
morphological aspects of the crushing front (delamination lengths, splaying, number of plies under localised
crushing, debris wedge…) thanks to high speed camera pictures