In this paper, a computational investigation of thermohydrodynamic performance andmechanical deformations of a fixed-geometry thrust bearing with artificial surfacetexturing is presented. A parallel eight-pad bearing is considered; the surface of eachpad is partially textured with square dimples. Here, a CFD-based thermohydrodynamicmodeling approach, recently introduced by the authors, is used to calculate theperformance of the bearing; the THD results are then used to quantify the deformations ofthe bearing mechanical parts. The bearing is modelled as a sector-shaped channel,consisting of a smooth rotating wall (thrust collar) and a partially textured stationarywall (bearing pad). The bearing performance characteristics are computed by means ofnumerical simulations, based on the numerical solution of the Navier-Stokes and energyequations for incompressible flow, as well as on the solution of the elasticity equationsfor the bearing solid parts. Here, a reference texture geometry is considered, whileproper thermal and structural boundary conditions are implemented. For representative filmthickness values, the effect of rotational speed and collar thickness on bearingperformance is quantified, and the resulting pad and rotor deformation fields arecomputed. It is found that, due to oil heating, the load carrying capacity decreases withrotational speed for values higher that approximately 2000 rpm. The computed rotordeformation field is representative of a fixed support beam, characterized bysubstantially higher levels than those of the bearing pad. Rotor deformations increasesubstantially at low values of collar thickness.

This study presents a finite element (FE) model of the human hand-arm system to derivenatural frequencies and mode shapes. The FE model is calibrated by considering modalparameters obtained from experimental vibration analyzed by using operational modalanalysis (OMA) and transmissibility. Modal and harmonic analyses of the FE model areperformed for two boundary conditions. The first one considers fixed shoulder conditionwhile the second one introduces the trunk in order to permit motion of the shoulder. Theresults show that the natural frequencies of the second model that permits shoulder motionare comparable with those determined from measurements. Especially, the natural frequencyabout 12 Hz, which is corresponding to the frequency of maximum weight in ISO-5349-1(2001), is not present in the model with fixed shoulder condition, while it appears in thesecond model. The results of the present study suggest that improved finite element modelsof the human hand-arm system may reveal hand-arm injury mechanism, the understanding ofwhich may assist in deriving appropriate frequency weightings for the assessment ofdifferent components of the hand-arm vibration syndrome.

This paper presents experimental and numerical studies of drop tests of corrugatedcardboard packaging containing different foam cushions. An efficient homogenization modelfor the corrugated cardboard has been developed. In our homogenized model, the corrugatedcardboard is represented by a 2D plate. Instead of using a local constitutive law(relating the strains to the stresses) at each material point, the homogenization givesthe global rigidities (relating the generalized strains to the resultant forces) for theequivalent homogeneous plate. This model was implemented into the FE software ABAQUS. Thefoam behaviour was experimentally determined and modelled using a crushable foam model ofABAQUS. The packages are tested in free fall from a given height on a rigid floor. Thedeceleration of the packed product was recorded using a triaxial accelerometer. Thenumerical results obtained using the FE simulation with the homogenized model agree wellwith the experimental results. We have also shown that the contribution of the corrugatedcardboard box to the shock response could not be neglected in the design of cushioningpackage.

In order to overcome the loss of performances issue when scaling resonant sensors down toNEMS, it proves extremely useful to study the behavior of resonators up to largedisplacements and hence high nonlinearities. A comprehensive nonlinear multiphysics modelbased on the Euler-Bernoulli equation which includes both mechanical and electrostaticnonlinearities in the case of a capacitive doubly clamped beam is presented. This purelyanalytical model captures all the nonlinear phenomena present in NEMS resonatorselectrostatically actuated including bistability, multistability which can lead to severalphysical limitations such as noise mixing, frequency stability deterioration as well asdynamic pull-in. Moreover, close-form expressions of the critical amplitudes and pull-indomain initiation amplitude are provided which can potentially serve for NEMS designers asquick design rules.

Virtual reality shows to be of use in several domains of manufacturing as a complementary tool to CAD/CAM environment. Design review is one of the very first application of VR in product design, but assembly/disassembly studies are also existing though they require some more specific work. But it can also be useful beyond the scope of common CAD software such as ergonomic studies. We will show an example from the RNTL PERF-RV project where we study the ergonomics of a car dashboard and more specifically of a push-button. We will discuss the issues raised by studying ergonomics thanks to Virtual Reality and force-feedback systems which are both hardware and software.

In order to improve digital mock-up, a tolerancing phase should be integrated in thegeometric models. However, in CAD software, tolerances are represented by annotations,which are neglected as well as the tolerance impact. Thus, the system malfunction isgenerated. For these reasons, in this paper a tolerancing phase is integrated in thenumerical model to form a realistic model, where worst case configurations of assembliesare determined from the tolerances assigned to the nominal model. The proposed modelincorporates tolerances on CAD models in the case of planar face, cylindrical face andplanar face with non quadratic loop. In addition, the model ability to respect the maximummaterial condition (MMC) and the requirement of datum priority order in the CAD models isshown. Finally, functional requirement of a linear guide mechanism is inspected by usingthe proposed model.

Nous présentons une méthode d'interaction fluide-structure basée sur une approche monolithique eulérienne permettant d'étudier à différentes échelles les procédés de mélange sous leur aspect dispersif et distributif. Une première approche macroscopique traitant de la résolution mécanique dans le procédé, où interviennent des outils tournants, est présentée, puis une approche microscopique modélisant la dispersion d'un agglomérat, et enfin une approche couplée via une théorie cinétique.

Magnetic bearings are oil-free bearings that are widely employed in turbo machineries such as turbo refrigerant compressors in order to eliminate lubrication systems, avoid contamination, and increase efficiency. We have developed a 145 refrigerant ton (RT)-class turbo refrigerant compressor using homopolar-type radial hybrid magnetic bearings (HMBs) and thrust magnetic bearings. The thrust magnetic bearing comprises a thrust HMB and a permanent magnet that generate downward forces to overcome high upward thrust forces of 2000 N at 21 000 rpm. A test rig and controller for the compressor with magnetic bearings were fabricated, and rotordynamics such as the unbalance response and axial displacement were investigated. Rotordynamics analyses using the finite element method predicted that the 1st bending mode is located at a high frequency with sufficient margin from the operating speeds. Further, the zero-to-peak displacement caused by the unbalanced response was sufficiently small. The rotor was stably supported with few vibrations across the entire range of the operational speeds. Our results demonstrate that the advantages of oil-free bearings can be easily exploited in turbo machineries such as turbo refrigerant compressors by adopting HMBs.

The transient dynamics of evacuated and fluid-filled circular elastic shells, submerged in an infinite fluid medium and subjected to an external weak shock wave,is considered in this paper. This circular shell/acoustic medium interaction problem has already been tackled with simplified thin shell models, based on the Love-Kirchhoff hypotheses for thestructural dynamics. In this case, the resulting radiated pressure field displays some discrepancies related to the A0/S0 waves when compared to the experimental data available inthe literature for the evacuated case. These drawbacks are overcome here by the use of an isotropic elastic model for the structural dynamics and an inviscid acoustic flow for the fluid dynamics,in a two-dimensional framework. The approach is based on the methods of Laplace transform in time, Fourier series expansions and separation of variables in space. For the fluid-filled case,the transient thick shell-weak shock wave interaction problem is explored and the radiated acoustic field described.

The use of natural fibers in the development of composite materials is a sector in full expansion. These fibers were used for their low cost, their availability and their renewable character. The fibers of the palm (palm tree) were used as reinforcement in polypropylene (PP). The date palm fibers have some potential because of their ecological and economic interest. Both unmodified and compatibilized fibers are used. Compatibilization was carried out with the use of maleic anhydride copolymers. The morphology and mechanical properties were characterized by electron microscopy scanning (SEM) and tensile tests. The influence of fiber content on mechanical properties of composite PP/date palm has been evaluated and demonstrated, that the maximum stress and elongation decreases with increasing fiber volume rate. On the other hand, an increase of the tensile modulus has been noticed, but after the fibers improvement, the maximum stress increases significantly up to 25% weight.

We present the results of a numerical simulation of a mixing process of two parallel streams of nitrogen (N2) and carbon monoxide (CO), in a microchannel with a splitter plate mounted at the inlet. As an attempt to enhance mixing efficiency, bumps are added on the channel walls, downstream the splitter. Typically, in such a passive micro device, the gas flow is laminar, rarefied, and characterized by a Knudsen number in the range of about 0.01 to 0.5, that is in the transition flow regime. The Direct Simulation Monte Carlo (DSMC) method is employed to explore the influence of the bumps and the splitter plate, and to analyze the sensitivity of the gas mixing length to parameters such as the inlet velocity as well as the height and location of the bumps. For a selected range of parameters, quantitative analytical and numerical results are in very good agreement.

Passive control of the entrainment phenomenon in the turbulent jets is a mixing enhancement economical method of wide interest in the industrial field. A lobed nozzle without lobes inclinations allows improving mixing in the generated flow compared to a reference circular jet. A second lobed nozzle, having the same exit plane geometry but with inclined lobes intensifies, in a considerable manner, the entrainment which reaches up to four times the one in the reference circular jet. The lobed jets vortical dynamics analysis shows that the azimuthal structures are not annular like in the case of a circular jet, but discontinuous, due to the shear of the transverse flow induced by the curvature variation of the exit plane. The streamwise structures development at the discontinuities locations is probably explaining the entrainment benefit observed in the lobed jet without inclination angles. The lobed jet issued from the second nozzle presents like the first lobed jet, discontinuous azimuthal structures, but its remarkable induction benefit is not merely owed to the previous phenomenon. The intensification and organisation of the streamwise vorticity field into large scale structures, resulting in a consequent mixing enhancement, are connected to the increased shear produced by the lobes inclinations.

In recent years, the adaptive decomposition methods have become the center of interest of researchers in many fields and especially in the vibration diagnosis of rotating machines. This paper compares the sensitivity of defect detection of two adaptive methods: local mean decomposition (L.M.D) and empirical mode decomposition (E.M.D). The efficiency of L.M.D and E.M.D methods for detecting defects is investigated for two cases, one from numerical signals and the other from signals recorded during a fatigue test on gear bench. The time descriptors Kurtosis, Thalaf and Thikat are applied on the signal and on its Hilbert transform. The results reveal that both techniques seem to be suitable and have good efficiency for the fault detection. From experimental signals, the comparative results reveal that both methods allow for monitoring wear, but that L.M.D is more sensitive to detect rapid changes of degradation than E.M.D method for the considered case. Consequently these features have potential to become powerful tools for the monitoring of rotating machinery.

The stability properties of the rotating free surface flow in a cylindrical container isstudied using a global stability approach, considering successively three models. For thecase of solid body rotation (Newton’s bucket), all eigenmodes are found to be stable, andare classified into three families: gravity waves, singular inertial modes, and Rossbywaves. For the case of a potential flow, an instability is found. The mechanism isexplained as a resonance between gravity waves and centrifugal waves, and is thought to beat the origin of the “rotating polygon instability” observed in experiments where the flowis driven by rotation of the bottom plate (see L. Tophøj, J. Mougel, T. Bohr, D. Fabre,The Rotating Polygon Instability of a Swirling Free Surface Flow, Phys. Rev. Lett. 110(2013) 194502). Finally, in the case of the Rankine vortex which in fact consists in thecombination of the two first cases, we report a new instability mechanism involving Rossbyand gravity waves.

Cette étude est concernée par le tournage dur de l'acier de roulement 100Cr6 en utilisant un outil en nitrure de bore cubique (CBN7020). Des essais de laboratoire ont été planifiés pour investiguer l'effet de la vitesse de coupe sur les différentes formes de l'usure de l'outil. Ensuite, une autre série d'expériences a été dédiée à l'étude de la rugosité obtenue en fonction des paramètres de coupe. La relation entre la rugosité de la surface usinée et l'usure en dépouille correspondante de l'outil a été mise sous la forme d'équations puissance pour décrire l'évolution de la rugosité à différentes vitesses de coupe allant jusqu'à 350 m.min-1. La comparaison des rugosités (Ra et Rt) en fonction de l'avance en tant que paramètre d'influence prépondérante a montré que le modèle à une variable (f) décrit d'une manière excellente les résultats expérimentaux alors que le modèle général à trois variables (Vc, f, ap) reste satisfaisant et très bien apprécié par le coefficient de détermination. Pour la rugosité moyenne, le modèle théorique surestime les valeurs de Ra avec une divergence notable à 0,2 mm.tr-1 alors que la rugosité totale est sous-estimée aux faibles valeurs de l'avance, ce qui donne lieu à des prédictions théoriques en deçà des attentes et conforte expérimentalement les modèles sous forme puissance proposés. Bien que la quantité de chaleur dégagée soit importante au vu des températures mesurées sur le copeau, la surface usinée n'a pas été thermiquement affectée.

When operational modal analysis (OMA) is conducted on operating machines or structureswithout knowing excitations and perturbations neither the number of concerned frequencies,one problem raises on the validity of modal parameters identification (especially dampingratios) and on the precision of results obtained. This paper presents an OMA methodallowing for the evaluation of uncertainties of modal parameters (frequencies, dampingratios and mode shapes). The method is based on the vector autoregressive model (VAR) formultiple numbers of measured channels. It is seen that the uncertainty of modal parametersdecreases with higher model orders; the calculation of uncertainty allows also for theconstruction of an objective criterion for the selection of computing model order based ona threshold of confidence interval. The derivation confirms also that the identificationof natural frequencies deals with a smaller uncertainty compared with the damping ratioestimation, and hence it can be conducted with a lower computing model order. Numericalsimulations and experiments on a steel plate show the feasibility and the effectiveness ofthe developed OMA method.

For qualitative prediction of chip morphology and quantitative prediction of burr size,2D and 3D finite element (FE) based turning models have been developed in this paper.Coupled temperature-displacement machining simulations exploiting the capabilities ofAbaqus® with a particular industrial turning insert and a newly proposed geometricalversion of this insert have been performed. Limitations of 2D models in defining the chipmorphologies and surface topologies have been discussed. The phenomenological findings onthe Poisson burr (Side burr) formation using 3D cutting models have been highlighted.Bespoke geometry of the turning insert has been found helpful in reducing the Poisson burrformation, as it reduces the contact pressures at the edges of tool rake face-workpieceinterface. Lower contact pressures serve to decrease the material flow towards workpieceedges (out of plane deformation). In contrast, higher contact pressures at tool rakeface-workpiece interface lead to more material flow towards workpiece edges resulting inlonger burr. Simulation results of chip morphologies and cutting forces for turning analuminum alloy A2024-T351 have been compared with the experimental ones. Finally, it hasbeen concluded that the newly proposed geometry of the insert not only decreases the burrbut also helpful in lessening the magnitude of tool-workpiece initial impact.

Several studies have been carried out in order to describe the impact ofwater-contaminated lubricants on lubrication performance. One approach considers thewater-contaminated oil as a homogeneous lubricant with physical characteristics varyingwith water concentration. The presented work is being achieved in order to experimentallyvalidate this theory. First investigations showed that the variation of contaminatedlubricant viscosity has the most significant effect on lubricating performance.Consequently, the lubricant viscosity is the only parameter taken into account in thisstudy. Thus, based on the rheological measurements, water-in-oil emulsion viscosity hasbeen modelled according to water concentration and temperature. Water concentration wasconsidered relatively to total mass of oil: the mass concentration varied then from 0 to7% and temperature from 10 to 80 °C. Viscosity modelling was then used to perform thenumerical simulations of a hydrodynamic thrust bearing supplied with water contaminatedoil. Finally, the experimental validation will be done by measuring various bearingcharacteristics like the film/pad temperature, the film thickness and the friction torqueon a tilting pad thrust bearing test rig.

In this study, vibration of helical compression springs, excited axially, is discussed. The mathematical formulation of the dynamic behavior of the springs is composed of a system of four partial differential equations of first order hyperbolic type, which are the equations of momentum and the laws of constitution. The principle unknown variables are angular and axial deformations and velocities. In small deformations, the coefficients of the equation system are constant and the model describes the linear dynamic behavior of coil springs. The impedance method is applied to calculate the frequency spectrum and to study the natural frequency response. The study takes into account the dynamic coupling between the axial and angular waves due to the effects of Poisson’s ratio. The results show two fundamental frequencies corresponding to the two wave speeds: fast angular waves and slow axial waves. The numerical resolution is performed by the conservative finite difference scheme of Lax-Wendroff and the finite element method. The results were used to analyze the evolution in time of deformations and velocities in different sections of the spring due to a sinusoidal excitation of the axial velocity applied at the end of the spring and to show the effect of the interaction between the axial and angular waves. These results clearly show the resonance and other phenomena related to wave propagations such as wave reflections and beat.

The process of ultrasonic shot peening has been studied from two aspects: (a) a 3D numerical model of shot motion in the peening chamber based on the theory of granular gases, (b) an experimental setup developed for measuring shot velocity distribution in the chamber and impact locations on the peened surface. The aim of such study is to propose an experimental method providing shot trajectories in order to validate the 3D model for the process parameter optimization, used for example in the aeronautic industry. The presented results illustrate the value of the model in the understanding and mastering of the process, as well as its usefulness, on one hand for the design of peening chambers, and on the other hand for a better definition of numerical models that help to predict residual stresses generated in the peened material.