It was recently shown that blind source separation (BSS), as originally developed in the signal processing community, can be used in operational modal analysis to separate the responses of a structure into its individual modal contributions. This, in turn, allows the application of simple single-of-degree-freedom techniques to identify the modal parameters of interest. Several publications have recently attempted to give a posteriori physical interpretations to BSS – as initially developed in telecommunication signal processing – when applied to the field of structural dynamics. This paper proposes to follow the route the other way round. It shows that several separation criteria purposely dedicated to operational modal analysis can be deduced from general physical considerations. Three such examples are introduced, based on very different properties that uniquely characterise a structural mode. The first criterion, coined the “principle of shortest envelope”, conjectures that the envelope of a modal response has, among all possible envelopes, the shortest length. That such a principle leads to the governing differential equation of a single-degree-of-freedom oscillator is proved from calculus of variation. The second criterion, coined the “principle of minimum spectral variance”, conjectures that the frequency spectrum of a structural mode is maximally concentrated around its central frequency. Finally, the third criterion, coined the “principle of least spectral complexity”, states that a structural mode has the lowest possible entropy in the frequency domain. All three criteria can be expressed in terms of a mixing matrix whose columns contain the unknown mode shapes. The recovery of the latter is then trivially achieved by minimising the criteria. Extensive simulations show that the proposed criteria lead to figures of merit very similar to those of the state-of-the-art, while at the same time providing physical insight that other algorithms issued form the signal processing community may dramatically lack.

This paper deals with analysis of the cutting process, on a macro and micro scale, in the deep hole drilling with BTA system. An experimental procedure is developed to highlight the impact of cutting speed and feed rate on the cutting process when machining the 18MND5 steel. Parameters based on dimensional characteristics of chips are introduced to quantify the morphology of chips generated by central, intermediate and external inserts of the complex BTA drilling tool. From observation of the chips morphology (flat, curved and spiral) and the measurement of the chips width, the provenance of each chip with respect to cutting inserts is identified. Then, the Chip Compression Ratio is evaluated for each cutting condition, indicating the amount of plastic strain in chips. Thanks to the introduction of a new parameter, denoted as Chip Fragmentation Ratio, it is found that the cutting speed has a little influence, compared to the feed rate, on the chips size. Based on this quantitative analysis, the optimal range of cutting conditions for the BTA deep hole drilling is discussed. It is mentioned that although increasing the feed rate promotes the chips fragmentation and increases the material removal rate (increasing productivity), an upper limit is to determine to prevent excessive flank wear. Also, the cutting speed should be limited to avoid excessive crater wear.

Reinforced Poly Ether Ether Ketone with 30% of Carbon Fiber (PEEK CF30) offer several thermo-mechanical advantages over standard materials and alloys which make them better candidates in different applications. However, the hard and abrasive nature of the reinforcement fiber is responsible for rapid tool wear and high machining costs. It is very important to find highly effective ways to machine that material. Accordingly, it is important to predict forces when machining fiber matrix composites because this will help to choose perfect tools for machining and ultimately save both money and time. In this study, Artificial Neural Network (ANN) was applied to predict the cutting force components in turning operations of PEEK CF30 using TiN coated cutting tools under dry conditions where the machining parameters are cutting speed ranges, feed rate, and depth of cut. For this study, the experiments have been conducted using full factorial design experiments (DOEs) on CNC turning machine. The results indicated that the well-trained (ANN) model could be able to predict the cutting force components in turning of Carbon Fiber Reinforcement Polymer (CFRP) composites. Complementary results that were not used during derivation of the ANN model have enabled one to assess the validity of the obtained predictions.

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.

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.

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.

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.