In this paper, we present the static and dynamic structural characterisation of alow-mobility parallel kinematic manipulator, involving analysis of its stiffness andvibrational dynamic behaviour. The study starts by building numerical models of thebehaviour of the manipulator to be compared to experimental measurements from a prototype.For the case study, we consider a four-degree-of-freedom(x, y, z, θz) manipulatorwith prismatic actuators designed by the COMPMECH research group at the University of theBasque Country. The characterisation allows the behaviour of the static and dynamicstiffness, as well as the natural frequencies of the manipulator, to be mapped in themanipulator workspace. These maps together with kinematic, static and dynamic constraintslead to the definition of operational, static, dynamic and structural workspaces,respectively. Further, we analyse the modes of the manipulator to determine dynamicdisplacements, these being key in the performance in the machining tasks for which therobot was designed.

The aerodynamic drag of simplified car geometry with small span and strongly separatedwake can be reduced up 20% by using pulsed jet distributed along the rear window. Resultsshow an enhancement of transversal wake size in the control region, a displacement of themean positions of vortex wake structures, a decrease of velocities near the rear part anda reduction of vortex structure recirculation in the wake. These modifications produced bythe control are analyzed, commented and model based on simple strategy to build efficientand suitable separation control strategy is proposed.

Les jonctions tubulaires, fréquemment employées dans l’industrie offshore, sont soumisesen service à des contraintes résultant de chargements élémentaires detraction-compression, flexion dans le plan et flexion hors plan. Ce travail porte surl’analyse des recommandations classiquement utilisées pour le dimensionnement en fatiguedes jonctions soudées lors de l’application de sollicitations combinées. Plusparticulièrement, il a porté sur l’étude du comportement en fatigue d’une jonction soudéeen T soumise à un chargement de type flexion déviée. Tout d’abord, sur leplan numérique, par la réalisation d’un modèle éléments-finis et la mise en œuvre deméthodes telles que celle proposée par l’IIS, puis, sur le plan expérimental, à travers laréalisation d’essais de fatigue sur ce type de jonctions. Les comparaisons essais/calculsont montré que l’application de ce type de recommandations ne s’avérait passystématiquement sécuritaire. Aussi, une démarche visant à prendre en compte le caractèremultiaxial des contraintes en pied de cordon de soudure a été mise en œuvre afin decompléter les recommandations visant au dimensionnement des jonctions tubulaires soudées.

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.

In this paper, an analytical solution is developed for free vibration analysis of conicalfiber metal shells. In order to find constitutive relations, the assumptions of thinshells are used and the governing equations are based on Love’s theory. The Galerkin methodis employed to solve the governing equations in which beam functions are used toapproximate the mode shapes. Using beam functions enables us to assess the effects ofdifferent boundary conditions on the frequency response of the shells. Numericalcomparisons of the present and previously published results confirm the accuracy of thecurrent approach. Additionally, the influences of geometrical parameters and embeddingaluminum plies in different layers of the structure on natural frequency of the conicalshells with various boundary conditions are investigated. It can be observed that the morethe aluminum plies are used, the greater natural frequency of the structure will bereached. Except the clamped-free boundary conditions, the results also indicate that ifthe aluminum plies are embedded in the top and bottom layers of the laminate, naturalfrequency reaches its maximum value.

Fiber metal laminates (FMLs) are widely used in aerospace industries nowadays. Repairingof the cracks in these advanced materials was first done by some aeronautical laboratoriesin early 1970s. In this study, experimental investigations were done on the effect ofrepairing the center-cracked aluminum plates using the FML patches. The repairingprocesses were conducted to characterize the response of the repaired structures totensile tests. The composite patches were made of one aluminum layer and two wovenglass-epoxy composite layers. Three different crack lengths in three crack angles anddifferent patch lay-ups were examined. It was observed that no matter what the cracklength was, the more the crack angle is larger, the more ultimate tensile strength of thestructure became. It was also indicated that the patch lay-up had an important effect onthe tensile response of the repaired specimens. When the aluminum layer of the patches wasfarther from the repair zone, the ultimate tensile strength reached to its maximum value.

Large thrust bearings are highly loaded machine elements and their failures cause seriouslosses. Start ups and stoppages of the bearing under load are specially critical regimesof operation. Load carrying capacity depends on the profile of the oil gap. In transientstates this profile is also changing. In the design of large thrust bearings minimizingthermo-elastic deformations is an important goal, which can be accomplished due toapplication of advanced models of the bearing. Modeling of transient states becomes evenmore complex since there is a dynamic development of temperature distribution anddeformations. Often hydrostatic jacking systems are also used. It seems to the authorsthat advanced bearing models are applied only in research and development of the bearingswhile very simple modeling is applied in on-line analysis of data from monitoring systems.Analysis of the measurement data with the use of more sophisticated models may be helpfulin assessment of current bearing status – especially in early warning. Material issuescreate a separate problem for modeling, being more important nowadays as polymer linedbearings come into use. The models used for polymer lined bearings require realistictreatment of heat exchange and resilience of the bearing surface layer.

L’objectif principal de cet article est la mise au point d’une méthodologie numérique deprévision du comportement local d’un procédé de renforcement des poteaux en bois par lafibre de carbone. En particulier, on s’intéresse à l’étude du comportementélasto-plastique du matériau bois avec effet du renforcement. Une modélisation basée surla thermodynamique des processus irréversibles avec variables d’état est utilisée pourtraduire le couplage entre le comportement plastique à écrouissage isotrope et l’effet durenforcement. Les aspects théoriques et numériques de cette formulation sont décrits endétail. La résolution du problème d’équilibre global est assurée par un schéma DynamiqueExplicite. La validation de la procédure de calcul implémentée dans ABAQUS/Explicit estfaite sur la simulation d’un essai de compression des éprouvettes circulaires en boisrenforcées par la fibre de carbone. Les résultats des simulations sont confrontés à ceuxde l’expérience.

Thanks to infrared thermography, we have studied the mechanisms of CO2 captureby solid adsorbents (CO2 capture via gas adsorption on various types of poroussubstrates) to better understand the physico-chemical mechanisms that controlCO2-surface interactions. In order to develop in the future an efficientprocess for post-combustion CO2 capture, it is necessary to quantify the energyof adsorption of the gas on the adsorbent (exothermic process). The released heat (heat ofadsorption) is a key parameter for the choice of materials and for the design of captureprocesses. Infrared thermography is used, at first approach, to detect the temperaturefields on a thin-layer of adsorbent during CO2 adsorption. An analytical heattransfer model was developed to evaluate the adsorption heat flux and to estimate, via aninverse technique, the heat of adsorption. The main originality of our method is toestimate heat losses directly from the heat generated during the adsorption process. Then,the estimated heat loss is taken for an a posteriori calculation of the adsorption heatflux. Finally, the heat of adsorption may be estimated. The interest in using infraredthermography is also its ability to quickly change the experimental setup, for example, toswitch from the adsorbent thin-layer to the adsorbent bed configuration. We present thefirst results tempting to link the thin-layer data to the propagation speed of the thermalfront in a millifluidics adsorption bed, also observed by IR thermography.

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.

Rotating machines monitoring in a non-stationary regime, characterized by the operating parameters (speed, load) variation, presents a particular challenge. The speed variation has an impact on the vibratory response given by the accelerometers and therefore masks any defect that may be detected by classical indicators (for example RMS value). To overcome this problem, a new indicator is proposed. For this, a signal accelerometer and a signal from an optical encoder are acquired simultaneously. An algorithm to estimate the instantaneous speed from the signal delivered by the optical encoder is applied. Then, each sample of the accelerometer signal is divided by its corresponding instantaneous speed sample. The RMS value is then applied to the resulting signal. A model simulation signal is used to test the proposed method. A test rig is performed to extract signals of different degradation states of thrust bearings in variable speed regime. The results show a correlation between the proposed RMS value and the thrust bearings state in variable regime.

The problem of the squeezing of a fluid film with a complex rheology is studied. Thefluid is represented by the Phan-Tien and Tanner (PTT) constitutive equation. The goal ofthe paper is to develop an analytical approach which allows one to describe and quantifythis process, which is often present in classical lubrication problems, but particularlyin human joints. The present approach can potentially supplement time-consuming and costlypurely numerical methods which are also susceptible to misleading artifacts. A parametricstudy reveals the effect of fluid elasticity compared to viscous effects and someexplanation is suggested as to their possible links with joint diseases.

This paper presents a numerical study about lubricant inertia effect onthermohydrodynamic (THD) characteristics of Rayleigh step bearings running under steady,incompressible and laminar condition. To reach this goal, the set of governing equationsis solved numerically with and without considering the inertia terms. The discretizedforms of the momentum and energy equations are obtained by the finite volume method andsolved using the Computational Fluid Dynamic (CFD) technique. These equations are solvedsimultaneously because the dependency of lubricant viscosity with temperature. Thehydrodynamic and thermal behaviors of the slider step bearings are demonstrated bypresenting several figures including the lubricant pressure and temperature distributionswith and without considering the fluid inertia effect. Numerical results show that inertiaterm has considerable effect on THD characteristics of step bearings, especially when theyrun with high velocity of runner surface.

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.

In this paper, a two modular zeolite water adsorption heat pump (AHP) based on thethermal wave concept has been experimentally investigated. Each module composes of twoheat exchangers contained in a hermetic stainless steel vessel. The first heat exchangeris the adsorber/desorber located on the top of the vessel, while the second is theevaporator/condenser heat exchanger located on the bottom of the vessel. Throughout thiswork, the effect of the non-dimensional switching frequency, which has been introduced andtheoretically investigated by Alam et al. [Int. J. Heat Mass Transfer 43 (2000)4419–4431], on COP and the mean heating power of an adsorption heat pump has beenexperimentally investigated under one typical working condition of AHPs. The resultsshowed that the switching frequency and adsorber/desorber flow rate have strong influenceson both COP and the mean heating power. It has been also found that there is an optimumswitching frequency corresponding to each flow rate, at which the COP attains its maximumvalue. The obtained optimum switching frequencies vary slightly from 0.28 at an adsorberfluid flow rate of 0.6 l.min-1 to 0.32 at 1 l.min-1.

In the present paper an experimental investigation of drag reduction on in-line tubebundles with a configuration of seven by seven with a pitch ratio of 1.44 has beenperformed. Two longitudinal grooves are placed on the external surface of the circularcylinders as a passive control. The experiment is carried out using a subsonic windtunnel. The pressure distributions for various azimuthal angles along the tubes aremeasured using a multi-channel differential pressure. Drag forces are also determinedusing a combined wire-strain gauge balance. The pressure drops are deduced from theresulting drag forces. The results obtained show an unexpected reduction in the pressuredrop for the tube bundles. A reduction of 36.5% in the pressure drop for a Reynolds numberof 1.33 × 104 is found compared to the configuration without grooves. Somecorrelations for the pressure drop are proposed.

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.

Among the primary phenomena observed when studying fire suppression are fuel surfacecooling, fire plume cooling and inerting effects. The last two result from waterevaporation generating a significant vapor concentration, thus leading to an importantheat sink as well as displacement and dilution of both oxygen and fuel vapor. FireDynamics Simulator (FDS.v6) is expected to be able to reproduce these effects.Extinguishment criterion focusing on plume cooling and inerting effects is based on adedicated heat balance, whereas suppression model related to fuel surface coolingevaluates the burning rate decrease according to an exponential law taking into accountlocal water mass reaching the fuel surface per unit area and an empirical constant whichpenalizes the prediction ability. Therefore, a new model derived from an Arrheniusequation has been implemented, which links the burning rate to the fuel surfacetemperature. Numerical simulations are conducted and compared with experimental data forall extinguishing mechanisms.

Hydrodynamic dispersion is a key controlling factor of solute transport in heterogeneousporous media. It critically depends on dimensionality. The asymptotic macrodispersion,transverse to the mean velocity direction, vanishes only in 2D and not in 3D. Using theclassical Gaussian correlated permeability fields with a lognormal distribution ofvariance σY2, thelongitudinal and transverse dispersivities are determined numerically as a function ofheterogeneity and dimensionality. We show that the transverse macrodispersion steeplyincreases with σY2 underlyingthe essential role of flow lines braiding, a mechanism specific to 3D systems. Thetransverse macrodispersion remains however at least two orders of magnitude smaller thanthe longitudinal macrodispersion, which increases even more steeply withσY2. At moderateto high levels of heterogeneity, the transverse macrodispersion also converges much fasterto its asymptotic regime than do the longitudinal macrodispersion. Braiding cannot be thustaken as the sole mechanism responsible for the high longitudinal macrodispersions. Itcould be either supplemented or superseded by stronger velocity correlations in 3D than in2D. This assumption is supported by the much larger longitudinal macrodispersions obtainedin 3D than in 2D, up to a factor of 7 for σY2 = 7.56.