Safran (United Kingdom)

Abstract In this paper we propose a representative simulation test-case of E × B discharges accounting for plasma wall interactions with the presence of both the electron cyclotron drift instability and the modified-two-stream-instability. Seven independently developed particle-in-cell (PIC) codes have simulated this benchmark case, with the same specified conditions. The characteristics of the different codes and computing times are given. Results show that both instabilities were captured in a similar fashion and good agreement between the different PIC codes is reported as main plasma parameters were closely related within a 5% interval. The number of macroparticles per cell was also varied and statistical convergence was reached. Detailed outputs are given in the supplementary data, to be used by other similar groups in the perspective of code verification.

CONTEXT: Treatment for depression can be expensive and depression can affect the use of other medical services, yet there is little information on how depression affects the prevalence of cost-related medication nonadherence (CRN) in elderly patients and patients with disabilities. OBJECTIVE: To quantify the presence of CRN in depressed and nondepressed elderly Medicare beneficiaries and nonelderly Medicare beneficiaries with disabilities prior to the implementation of the Medicare Drug Benefit. DESIGN AND SETTING: 2004 Medicare Current Beneficiary Survey. PARTICIPANTS: Depressed and nondepressed elderly Medicare beneficiaries and beneficiaries with disabilities. MAIN OUTCOME MEASURES: Cost-related medication nonadherence included taking smaller doses or skipping doses of a prescription to make it last longer, or failing to fill a prescription because of cost, controlling for health insurance status, comorbid conditions, age, race, sex, and functional status. RESULTS: In a nationally representative sample of 13 835 noninstitutionalized elderly Medicare enrollees and Medicare enrollees with disabilities, 44% of beneficiaries with disabilities and 13% of elderly beneficiaries reported being depressed during the previous year. Among enrollees with disabilities reporting depressive symptoms, 38% experienced CRN compared with 22% of enrollees with disabilities who did not report depressive symptoms. Among elderly enrollees who reported depressive symptoms, 19% experienced CRN, compared with 12% of elderly enrollees who did not report such symptoms. In adjusted analyses, depressive symptoms remained a significant predictor of CRN in both groups (persons with disabilities: odds ratio, 1.7; 95% confidence interval, 1.3-2.3; elderly persons: odds ratio, 1.4; 95% confidence interval, 1.1-1.7). CONCLUSIONS: Depressive symptoms were associated with CRN in elderly Medicare enrollees and Medicare enrollees with disabilities. Providers should elicit information on economic barriers that might interfere with treatment of Medicare beneficiaries with depression.

Purpose – The purpose of this paper is to suggest a solution to the problem of implementing a full “Lean” methodology for small-/medium-sized enterprises (SMEs) in a developing economy. Design/methodology/approach – This is a reflective paper that looks at an illustrative case study against the wider perspectives of the financial and resource costs of implementing a full lean programme in a developing country and suggests that using a “Lean Lite” approach may help the consultant/manager introduce lean concepts into a manufacturing organisation in a developing country. Findings – The paper concludes that “Lean Lite” as an approach that can be used to introduce lean initiatives in an SME in a developing economy by allowing a company with very limited resources to engage not only in business improvement but also in improving working conditions and education for employees. Research limitations/implications – The observations are limited to a single case study, although tempered by the authors’ wider experience. Further empirical research and critique of the original research is required to validate the observations and conclusions. Practical implications – The proposed “Lean Lite” initiative can help to introduce lean concepts to an organisation with limited financial and other resources. This helps organisations to increase productivity and assists the adoption of the lean philosophy and principles in a developing economy. The approach may also be used to engage in a wider corporate social responsibility strategy at ground level. Social implications – The social benefits as a result of implementing a Lean Lite approach include improving working conditions and educating employees. Originality/value – The paper proposes an approach that can be used to widen organisational involvement in lean initiatives in a developing economy by allowing a company with limited resources to engage not only in business improvement but also in improving working conditions and education for employees. As such the approach has both economic and social benefits.

This article presents an optimal carrier-based voltage balancing scheme for three-phase three-level converters. The proposed scheme utilizes two available degrees of freedom, i.e., zero-sequence signal injection and virtual zero-level modulation (VZM), to eliminate the low-frequency neutral-point voltage oscillation. It is universally effective over the full power factor and modulation index range and easy to implement in digital controllers. The hybrid algorithm combines the merits of both approaches, which offers the optimal performance regarding controllability, switching device power losses, and output harmonics. The main drawbacks of VZM, i.e., the increased switching loss and high-frequency harmonics due to additional switching transitions, have been minimized in the proposed scheme. The performance of the proposed scheme is evaluated through simulation and experiment.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destine au dpt et la diffusion de documents scientifiques de niveau recherche, publis ou non, manant des tablissements d'enseignement et de recherche franais ou trangers, des laboratoires publics ou privs.

Purpose: Rubber is widely used in tires, mechanical parts, and user goods where elasticity is necessary. Some essential features persist unsolved, primarily if they function in excessive mechanical properties. It is required to study elastomeric Rubber's performance, which is operational in high-level dynamic pressure and high tensile strength. These elastomeric aims to increase stress breaking and preserve highly pressurised tensile strength. Design/methodology/approach: The effects of carbon black polymer matrix on the tensile feature of different Rubber have been numerically investigated in this research. Rubber's material characteristics properties were measured using three different percentages (80%, 90%and 100%) of carbon black filler parts per Hundreds Rubber (pphr). Findings: This study found that the tensile strength and elongation are strengthened as the carbon black filler proportion increases by 30%. Practical implications: This research study experimental tests for Rubber within four hyperelastic models: Ogden's Model, Mooney-Rivlin Model, Neo Hooke Model, Arruda- Boyce Model obtain the parameters for the simulation of the material response using the finite element method (FEM) for comparison purposes. These four models have been extensively used in research within Rubber. The hyperelastic models have been utilised to predict the tensile test curves—the accurate description and prediction of elastomer rubber models. For four models, elastomeric material tensile data were used in the FEA package of Abaqus. The relative percentage error was calculated when predicting fitness in selecting the appropriate model—the accurate description and prediction of elastomer rubber models. For four models, elastomeric material tensile data were used in the FEA package of Abaqus. The relative percentage error was calculated when predicting fitness in selecting the appropriate model. Numerical Ogden model results have shown that the relative fitness error was the case with large strains are from 1% to 2.04%. Originality/value: In contrast, other models estimate parameters with fitting errors from 2.3% to 49.45%. The four hyperelastic models were tensile test simulations conducted to verify the efficacy of the tensile test. The results show that experimental data for the uniaxial test hyperelastic behaviour can be regenerated effectively as experiments. Ultimately, it was found that Ogden's Model demonstrates better alignment with the test data than other models.

International audience

International audience

In the present study, we analyze the broadband noise of an ultra high by-pass ratio fan/OGV stage developed at Ecole Centrale de Lyon. Wall-modeled large eddy simulations (LES) of a periodic fan/OGV sector are performed at approach conditions on an unstructured grid that is well refined for direct noise propagation. Comparisons between wall-resolved and wall-modeled computations are performed using a 2.5D simplified configuration of the fan/OGV stage, and show a good agreement. This justifies the use of wall-modeled simulations for the full-span configuration. A good agreement is found between LES and RANS aerodynamic results. However, some differences can be found in the tip gap region and near the hub, where large coherent structures appear. Additionally, a small recirculation bubble can be observed from approximately 60% of the fan blade span in the LES. In this study, the broadband noise is directly computed from the fully-compressible LES solver and compared with predictions from available analytical models. The input data for the analytical models, such as mean and turbulent flow statistics, are obtained from the LES computation. A good agreement is found for the predicted sound power levels between direct LES noise predictions and the LES-informed analytical models. This confirms the capability of the LES numerical setup to directly predict far-field noise. However, some discrepancies can be observed at low frequencies. These might be attributed to the additional noise sources that are present in the LES, which are not considered by the analytical models.

A methodology to include flow–acoustic interactions in a Helmholtz solver is proposed and used to quantify their impact on the thermoacoustic modes of a real industrial combustor. This methodology takes advantage of the compactness of flow–acoustic interactions, modeling the regions of interest by matrices included in the Helmholtz computation thanks to a dedicated boundary condition. The one-dimensional formulation introduced in Ni et al. (“Accounting for Acoustic Damping in a Helmholtz Solver,” AIAA Journal, Vol. 55, No. 4, 2017, pp. 1205–1220) is extended to three-dimensional configurations so that the dissipation of dilution holes, swirlers, and perforated plates can be accounted for. The potential of the method is illustrated by performing the thermoacoustic analysis of an annular combustor from SAFRAN. The Helmholtz solution corresponding to an azimuthal mode is analyzed and shows that flow–acoustic interactions dissipate an important part of the acoustic energy but also limit the amplification created by the flame.

The determination of high cycle fatigue (HCF) properties of a material with standard method requires a lot of specimens, and could be really time consuming. The self-heating method has been developed in order to predict S–N–P curves ( i.e. , amplitude stress – number of cycles to failure – probability of failure) with only a few specimens. So the time-saving advantage of this method has been demonstrated on several materials, at room temperature. In order to reduce the cost and time of fatigue characterization at high temperature, the self-heating method is adapted to characterize HCF properties of a titanium alloy, the Ti-6Al-4V (TA6V), at different temperatures. So the self-heating procedure is adjusted to conduct tests with a furnace. Two dissipative phenomena can be observed on self-heating curves. Because of this, a two-scale probabilistic model with two dissipative mechanisms is used to describe them. The first one is observed for low amplitudes of cyclic loading, under the fatigue limit, and the second one for higher amplitudes where the mechanisms of fatigue damage are activated and are dissipating more energy. This model was developed on steel at room temperature. Even so, it is used to describe the self-heating curves of the TA6V at several temperatures.

<div class="section abstract"><div class="htmlview paragraph">The aim of this work is to develop a semi-empirical model for erosion phenomena under ice crystal condition, which is one of the major phenomena for ice crystal accretion. Such a model would be able to calculate the erosion rate caused by impinging ice crystals on accreted ice layer.</div><div class="htmlview paragraph">This model is based on Finnie [<span class="xref">1</span>] and Bitter [<span class="xref">2</span>] [<span class="xref">3</span>] solid/solid collision theory which assumes that metal erosion due to sand impingement is driven by two phenomena: cutting wear and deformation wear. These two phenomena are strongly dependent on the particle density, velocity and shape, as well as on the surface physical properties such as Young modulus, Poisson ratio, surface yield strength and hardness. Moreover, cutting wear is mostly driven by tangential velocity and is more effective for ductile eroded body, whereas deformation wear is driven by normal velocity and is more effective for brittle eroded body. Several researchers based their erosion modelling on these two phenomena such as Hutchings et al. [<span class="xref">4</span>] for deformation erosion, or Huang et al. [<span class="xref">5</span>] and Arabnejad et al. [<span class="xref">6</span>] for cutting and deformation erosion.</div><div class="htmlview paragraph">The main work of this paper is to develop an erosion model for ice crystal impingement based on these two phenomena, and to show its capability to predict accretion shape by simulating experimental cases from the National Research Council of Canada (NRC). NRC’s Currie et al. ice crystal experiments [<span class="xref">7</span>] [<span class="xref">8</span>] realized in warm aerodynamic conditions, such as the one encountered in high icing severity areas of a turbofan engine, show accretion severity for a large range of liquid water content to total water content. In order to validate the erosion model based on solid/solid collision, this paper presents the simulation of the lower melting rate experiment. Results show fair agreement with experimental data and allow us to propose pertinent further work.</div></div>

Vibration analysis is an important component of industrial equipment health monitoring. Aircraft engines in particular are complex rotating machines where vibrations, mainly caused by unbalance, misalignment, or damaged bearings, put engine parts under dynamic structural stress. Thus, monitoring the vibratory behavior of engines is essential to detect anomalies and trends, avoid faults and improve availability. Intrinsic properties of parts can be described by the evolution of vibration as function of rotation speed, called a vibration signature. This work presents a methodology for large-scale vibration monitoring on operating civil aircraft engines, based on unsupervised learning algorithms and a flight recorder database. Firstly, we present a pipeline for massive extraction of vibration signatures from raw flight data, consisting in time-domain medium-frequency sensor measurements. Then, signatures are classified and visualized using interpretable self-organized clustering algorithms, yielding a visual cartography of vibration profiles. Domain experts can then extract various insights from resulting models. An abnormal temporal evolution of a signature gives early warning before failure of an engine. In a post-finding situation after an event has occurred, similar at-risk engines are detectable. The approach is global, end-to-end and scalable, which is yet uncommon in our industry, and has been tested on real flight data.

This paper highlights the link between the unsteady aerodynamics and Open Fan tonal noise generation prediction using the hybrid computational methodology combining the unsteady Reynolds Averaged Navier-Stokes (uRANS) simulation with Ffowcs-Williams and Hawkings (FWH) acoustic analogy. Among the various causes of noise, interaction noise emerges as a major noise source. Thus, an accurate evaluation of the interaction noise is consequently indispensable to correctly estimate the overall acoustic properties of an Open Fan. Careful attention must be paid to the computation of the aerodynamic flowfield to ensure that noise sources resulting from aerodynamic interactions are well captured, and their propagation up to the FWH coupling surface is accurate. Different acoustic prediction results are obtained between the FWH formulations (surface impermeable and permeable) as well as between the considered numerical schemes. This study emphasizes the sensitivities of numerical set-up for Open Fan noise prediction.

This paper concerns the design of a high efficiency and high torque density machine developed for a direct-drive aircraft application. Minimizing the active material in electrical machines can be achieved by attaining higher electric frequencies (> 1.5 kHz). The increasing global losses need to be addressed and minimized as the heat exchange surfaces are limited. Higher slot fill factor allows reducing the active materials (i.e. shorter tooth) and then minimizing the iron loss. Bar-wound winding shows several advantages such as reduced end-winding volume and loss. Aluminium solid conductors are in this work identified to be an intriguing solution for the given specifications. The higher resistivity reduce its vulnerability to eddy currents linked phenomena. Furthermore, aluminium powder alloys such as AlSi10Mg are nowadays widely employed in additive manufacturing and their mass density is about three times less than copper.

International audience

ÖzBu çalışmadaki amaç

The recent development of a numerical strategy dedicated to the simulation of rotor/stator interactions stemming from structural contacts in modern aircraft engines led to the first optimization of a high-pressure compressor blade profile accounting for criteria related to non-linear contact simulations. This optimization procedure revealed very significant improvements in terms of amplitudes of vibration but failed to identify key design parameters. Satisfying numerical results were obtained by a minor modification of a combination of many design parameters. Based on this observation, this contribution intends to shed a new light on this previous redesign operation focusing on one key quantity: the clearance consumption. This quantity is presented in the first section. In the second section, results of the redesign operation are recalled before the presentation of original results, featuring detailed interaction maps in the frequency domain, on which focuses the third section of the article. Finally, the blade profiles are extensively compared based on their specific clearance consumption and presented results suggest that this quantity may be key in discriminating acceptable from unacceptable blade profiles with respect to their vibratory behaviour when structural contacts occur.

View Video Presentation: https://doi.org/10.2514/6.2021-0388.vid With more complex aircraft architectures, fast and cost-effective design iterations are key to improve overall fuel efficiency. This paper proposes to revisit a low-order unsteady modeling approach to replace costly full annulus URANS simulation. Unsteady Body Force Methods (UBFM) could allow a significant cost reduction for fan distortion ingestion and operability assessment. In this approach, the bladed area in the computational domain is replaced by source terms in the Navier–Stokes equations, and the cost of the simulation is reduced by a factor of 26. The operability of the fan is evaluated with and without distortion in order to assess the accuracy of the model. Previously published results of URANS simulations performed on the same fan subject to an unsteady vortex ingestion are used as reference. The results show that our UBFM is able to predict rotating stall cells, with patterns and rotating speed similar to the URANS data.

This paper presents an analytical model to provide a rapid estimation of the steady-state averaged power loss of a T-type STATCOM with Virtual Zero level Modulation (VZM) to balance the neutral point voltage. A case study is then conducted on a 54kVA rated T-type STATCOM system to investigate the power loss distribution over power devices and variations over switching frequency. A comparison is made in the case study between Silicon IGBT and Silicon Carbide MOSFETs considering the power losses. Downscaled experimental verification is then conducted and shows good consistency with the analytical model. The loss model indicates that VZM reduces the conduction losses of the power converter, but increases the switching losses at the same time.