The exploitation of cyclostationarity properties of vibratory signals is now more widelyused for monitoring rotating machinery and especially for diagnosing bearing defects. Theacoustic emission (AE) technology has also emerged as a reliable tool for preventivemaintenance of rotating machines. In this study, we propose an experimental study thatcharacterizes the cyclostationary aspect of acoustic emission (AE) signals recorded from adefective bearing (40 μm on the outer race) to see its efficiency to detecta defect at its very early stage of degradation. An industrial sensor (UE10 000) is used.An electrical circuit converts the high frequency signal into an audible signal byheterodyning. The cyclic spectral density, which is a tool dedicated that put intoevidence the presence of cyclostationarity, is used for characterizing thecyclostationary. Two new indicators based on this cyclostationary technique are proposedand compared for early detection of defective bearings.

Floods through inundated urban environments constitute a hazard to the population andinfrastructure. A series of field measurements were performed in an inundated section ofthe City of Brisbane (Australia) during a major flood in January 2011. Using an acousticDoppler velocimeter (ADV), detailed velocity and suspended sediment concentrationmeasurements were conducted about the peak of the flood. The results are discussed with afocus on the safety of individuals in floodwaters and the sediment deposition during theflood recession. The force of the floodwaters in Gardens Point Road was deemed unsafe forindividual evacuation. A comparison with past laboratory results suggested that previousrecommendations could be inappropriate and unsafe in real flood flows.

Since a few years, a new wind measurement instrument has been competing with standard cupanemometers: the LiDAR. The performances of this instrument over complex terrain are stilla matter of debate and this is mainly due to the flow homogeneity assumption made by theinstrument. In this work, the error caused by this hypothesis was evaluated with the helpof OpenFOAM 1.7, MeteoDyn WT 4.0 and WAsP Engineering for a LiDAR deployed on a complexsite covered with dense forest. The assessment of the CFD model firstly revealed thesignificant impact of both the location and nature of the inlet boundary condition.Despite the presence of terrain complexity within a radius of 340 m around the remotesensor, an averaged error of less than 3% was observed, suggesting that the LiDAR is onlyaffected by topographic variations in the immediate vicinity of the scanned volume.

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.

An international benchmark has been organized by EDF R&D during 2008–2010, gathering 11 partners. Its main objective is to quantify the confidence in numericalmodels. The built-up dynamical system considered is a pump actually in service in powerplants, considered in its work environment. Blind eigenfrequency numerical values relativeto the pump assembly fixed in concrete present a larger variability than the 5% roughvariability concerning the separate parts, essentially due to the modeling of the boundaryconditions and interfaces at macro level. For the nine first eigenmodes considered, experimental-numerical correlation shows a frequency error less than 15% for the freesub-structures and nearly 30% for the free five-component system. Though the first overallmodes are correctly identified, the frequency error is significantly larger for theclamped pump assembly, with however MAC coefficients higher than 0.9 for two modes; butthe frequency error can be reduced to less than 9% for the four first modes after updatingprocedure. A lesson to draw is that measurement information is needed to improve thequality of theoretical built-up structure. After this benchmark, a more ambitious researchprogram will follow as a FUI project, gathering the observation of numerical andexperimental variabilities, updating model improvement and numerical quantification of thetotal uncertainty.

Vibrations in buildings impact the behaviour of structures and humans, for sourcesdefined as internal or external to the building. Besides the comparison of vibrations tofixed limits, the choice of a relevant indicator is unavoidable and this indicator isdefined differently according to the selected reference text. Various standards (ordirectives similar to standards) exist and this paper focuses on the most important andthe most used ones, for ground vibrations induced to buildings or for human exposureinside buildings. In addition to the interest of comparing values to well-defined andwell-known limits, the knowledge of these standards allows the use of suitable indicators.Various vibration signals are used, from a simple harmonic signal to complex vibrationsgenerated by railway traffic, in order to present a relevant analysis of severity of eachnorm. It turns out that criteria noticeably vary from one reference to another one, andthat the thresholds are different for each standard.

Impeller tip clearance is a key parameter in design process of a centrifugal compressor which has influential effects on its aerodynamic and thermodynamic performances. Interaction of tip leakage flow with the main stream could be the major source for occurrence of stall phenomenon. In the present investigation, two impeller tip clearances of small and large sizes are investigated under different flow coefficients assigned to “design”, “low flow” and “high flow” conditions. Flow field is precisely simulated utilizing solution of the Reynolds-Averaged Navier-Stokes equations. Influence of the impeller stall on the volute flow field is studied. Structure of vortical flows within the impeller passages and volute are demonstrated in details. Numerical results showed that the flow within the volute becomes stall-prone while the flow within the impeller stalls. In contrast to the high flow case, the low flow condition was more prone for the stall occurrence. Performance tests were also conducted on Iran University of Science and Technology (IUST) centrifugal compressor test rig for validation of the numerical results.

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.

This work deals with the application of the fuzzy logic to automate diagnosis of bearing defects in rotating machines based on vibration signals. The classification tool used is a fuzzy inference system (FIS) of Mamdani type. The vector form of input contains parameters extracted from the signals collected from the test bench studied. The output vector contains the classes for the different operating modes of the experimental study. The results show that; pretreatment data (filtering, decimation,...), the choice of parameters of fuzzy inference system (input variables and output, types and parameters of membership functions associated with different input and output variables of the system, the generation of fuzzy inference rules,...) are of major importance for the performance of fuzzy inference system used as a tool for fault diagnosis of rotating machinery.

Nowadays, backache risks due to professional activities remain high, while theirquantitative estimation is not well-known. Different methods have been developed todetermine the exposure of the spinal column to risk of damage. In Belgium, the “Fond desMaladies professionnelles” (FMP) suggests to use the “Mainz Dortmund Dosis” (MDD) methodto compute the exposure dose accumulated during the whole professional life. This methoduses the so-called biomechanical model “The Dortmunder” where the skeleton of the humanbody is represented by 30 rigid bodies to which certain abdominal and back muscles arelinked. This paper presents an implementation of the Dortmunder model with EasyDyn, aC++ library developed by theDepartment of Theoretical Mechanics, Dynamics and Vibrations of the University of Mons forsolving multibody problems, among others. Our model is first validated by comparing theobtained results with the one found in the literature. It is then used in a posture thatis not considered yet by the FMP. It is shown that working on ones knees can induce forcesin the back that increase the risk of backage.

An experimental investigation of the Marangoni convection around a single vapor bubble ofFC-72 on a downward-facing heated surface was reported. The boiling cell used for thisstudy was equipped with an optical measurement system which was dedicated to the ParticleTracking Velocimetry (PTV) method. This method allowed us to obtain the velocity fields inthe liquid around the vapor bubble. From the velocity fields obtained, we verified thepresence of Marangoni convection rolls in the vicinity of the liquid-vapor interface.Lastly, the influence of levels of subcooling on the velocity of convective rolls relatedto the Marangoni effect was investigated.

This paper presents the comparison of results obtained from two codes with different degrees of accuracy and computational time on the case of a contra-rotating open rotor (AI-PX7). The main goal is to assess the capacity of a code based on singularity methods to predict global open rotor performance, the in-plane loads (also called 1P loads), and the blade load distribution during a full blade cycle. Moreover, installation and unsteady correction models have been implemented in this code in order to evaluate the possible improvements of initial predictions. Finally, a numerical method to quantify some of the mechanisms governing open rotor thrust and 1P loads is proposed.

The aim of this study is to approach the possibilities of stimulated infraredthermography to the carpal tunnel syndrome diagnosis. Eleven patients were studied. Six ofthem were affected by the carpal tunnel syndrome. The five others were healthy. The studyconsists in exciting the patients’ hands and in analyzing their thermal response. Theinfrared thermograms obtained show that the hands infected by the carpal tunnel syndromegive a different thermal response.

The early detection of gear faults remains a major problem, especially when the gears aresubjected to non stationary phenomena due to defects. In industrial applications, thecrack of tooth is a default very difficult to detect whether using the time descriptors orthe frequency analysis. In this work and based on a numerical model, we prove that thecrack default affects directly the phase of the frequency component of the defective wheel(frequency modulation). To properly estimate the phases, we suggest two high-resolutiontechniques (Estimation of Signal Parameters via Rotational Invariance Techniques ESPRITwith a sliding window and Weighted Least Squares Estimator WLSE). The results of bothmethods are compared to the phase obtained by Hilbert transform. The three techniques arethen applied on a multiplicative signal with a frequency modulation to show the influenceof the amplitude modulation on the quality of phase estimation. We note that the ESPRITmethod is much better in the estimation of frequencies while WLSE shows much efficiency inthe estimation of phases if we keep the frequencies almost stables.

Subsystems of rotary-wing aircrafts, such as helicopters for instance, are strongly interrelated due to their intrinsic specificities. Convergence to a feasible design is then not ensured and implies an iterative process. Moreover, rotorcrafts must cover a much wider range of missions than their fixed-wing counterparts. For those reasons a correctly sized rotorcraft is difficult to obtain and finding the best design for a defined set of missions needs numerous iterations. This article presents the application of a multi-objective optimization approach from the predesign stage. The standard predesign approach has been reformulated to highlight sizing constraints and three strategies are then proposed to solve those constraints: the first one is the basic transcription of the standard predesign approach; the second one leaves the problem solving to the genetic optimizer through penalization; the third one is a hybrid of both previous methods based on a constraint repairing approach. Those strategies also involved the adaptation of the helicopter modelling. Here, the focus is on two components of that new model: namely the main rotor polar and the weight assessment model.

An algorithm of operational modal analysis in time domain is presented for thediscrimination between structural modes, harmonic excitations and spurious modes. Aclassification factor is developed and based on the construction of the damped signal- to-noise ratio which separates the physical modes from the numerical ones. The harmonicexcitations are then recognized at very high power indexes and zero damping. Furthermore, after the modal discrimination, the harmonic spectrum and the estimated frequency responsefunction can be derived. The method can be updated in the time domain either by a shorttime sliding window or a recursive technique to provide the modal monitoring in bothstationary and non-stationary process. An industrial application on a hydro-electricalgenerator is discussed to identify the machine frequencies under operational workingconditions.

Sustainability is one of the challenging issues in electricity production systems.Recently, solid oxide fuel cell (SOFC) has been suggested for use in combined heat andpower (CHP) systems. This application is introduced as a promisingenvironmentally-friendly system according to the thermodynamic and electrochemical models.In this paper, an atmospheric SOFC/CHP cycle was analysed based on integrating exergyconcepts, energy and mass balance equations. In this regard, a zero-dimensional energy andmass balance model was developed in engineering equation solver (EES) software. Twodimensionless parameters (the exergetic performance coefficient (EPC) for investigatingthe whole cycle, and exergetic efficiency for investigating the exergy efficiency of themain component of this cycle) were applied. Results show that efficiencies of the systemhave been increased substantially. The electrical efficiency, total efficiency and EPC ofthis cycle were ~54%,~79% and~58% respectively.Moreover, the CO2emission is 19% lower than when compared with a conventional combined power cycle fed bynatural gas. In addition, a dynamic economic evaluation was performed to extract the mostsensitive parameters affecting the outputs: electricity sales price (ESP), equipmentpurchase cost and fuel cost. Furthermore, an electricity production cost of~125 $MW.h-1 wasattributed to our model, resulting in yet further cost reduction for widespreadapplications of this cycle.

For the unsteady simulation of compressible subsonic flows (Large Eddy Simulation orDirect Numerical Simulation), the proper handling of the inlet boundary is a challengingtask. Indeed, inflow generation through imposition of the velocity may lead to anon-physical reflection of the upstream acoustic waves. In the present contribution, amethod that allows both filtering of these waves and proper imposition of the requiredvariables is proposed. This method is based on identification of the roles of the temporalrate of change of wave amplitudes at the inlet in the low Mach number regime. Theformulation obtained is tested numerically on unsteady one-dimensional flows at low Machnumber for which the unsteady inlet velocity signal is purely harmonic or harmonic withthe superimposition of synthetic turbulence.

This paper presents the analysis of the instabilities inception in a transoniccentrifugal compressor for different rotation speeds. The analysis was conducted fromexperimental results obtained with unsteady pressure sensors implanted in the inducer,vaneless diffuser and vaned diffuser. Beyond the stability limit the compressor entersinto a deep surge without any precursor, whatever the speed. The surge process isinitiated in the vaned diffuser by a massive boundary layer separation. For low speeds,together with the surge which remains triggered in the diffuser, aerodynamic instabilitiesare detected in the inducer. These instabilities can be understood as “tip clearancerotating disturbances” because they are generated at the leading edge of the impeller mainblades and move along the tip clearance trajectory.

Impact wear can be defined as the wear of a solid surface due to percussion, which is arepetitive exposure to dynamic contact by another solid body. It has not been studied asextensive as other wear mechanisms and the information on causes and actual data is quitescarce. In the present work an experimental wear tester is designed and used to study theimpact wear phenomenon experimentally. It creates the consecutive impacts between ballsand flat plate. The different ball sizes (up to 30 mm), impact velocities (up to 6m.s-1) and impactangle (10°− 80°) can be tried by tester. The mass lossof plate is measured as the wear parameter. These measurements for different specimensrevealed some aspects of their wearing behaviors. The obtained results could be helpful inoptimal practical designs and explanation of some phenomena associated with impact wear.