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Particle Motion (particle + motion)
Selected AbstractsCharacterization of flow regime transition and particle motion using acoustic emission measurement in a gas-solid fluidized bedAICHE JOURNAL, Issue 5 2010Wang Jingdai Abstract Particle motion is a major determinant of the dynamical performance of a fluidized bed. It plays an important role in determining and optimizing the complex correlation of fluidization condition between particle-particle and particle-environment in a system. A passive acoustic emission (AE) technique is applied to monitor, characterize, and control the fluidization condition of polyethylene particles in a gas-solid fluidized bed. Experimental results show that AE signals are very sensitive to the particle movements by analyzing energy distribution, which can help to understand the status of the system. The AE energy temporal analysis is further used to identify the transition of flow regimes. Moreover, the activity of particle motion can be quantitatively determined by using a combination of granular temperature and AE spatial energy analysis. This work provides valuable insights into the dynamic behavior of particles in a gas-solid fluidized bed based on AE technique. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Absolute S -velocity estimation from receiver functionsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007L. Svenningsen SUMMARY We present a novel method to recover absolute S velocities from receiver functions. For a homogeneous half-space the S velocity can be calculated from the horizontal slowness and the angle of surface particle motion for an incident P wave. Generally, the calculated S velocity is an apparent half-space value which depends on model inhomogeneity and P -waveform. We therefore, suggest to calculate such apparent half-space S velocities from low-pass filtered (smoothed) receiver functions using a suite of filter-parameters, T. The use of receiver functions neutralize the influence of the P -waveform, and the successive low-pass filterings emphasize the variation of S velocity with depth. We apply this VS,app.(T) technique to teleseismic data from three stations: FUR, BFO and SUM, situated on thick sediments, bedrock and the Greenland ice cap, respectively. The observed VS,app.(T) curves indicate the absolute S velocities from the near surface to the uppermost mantle beneath each station, clearly revealing the different geological environments. Application of linearized, iterative inversion quantify these observations into VS(z) models, practically independent of the S -velocity starting model. The obtained models show high consistency with independent geoscientific results. These cases provide also a general validation of the VS,app.(T) method. We propose the computation of VS,app.(T) curves for individual three-component broad-band stations, both for direct indication of the S velocities and for inverse modelling. [source] Improved microseismic event location by inclusion of a priori dip particle motion: a case study from EkofiskGEOPHYSICAL PROSPECTING, Issue 5 2010G.A. Jones ABSTRACT Microseismic monitoring in petroleum settings provides insights into induced and naturally occurring stress changes. Such data are commonly acquired using an array of sensors in a borehole, providing measures of arrival times and polarizations. Events are located using 1D velocity models, P- and S-wave arrival times and the azimuths of P-wave particle motions. However in the case of all the sensors being deployed in a vertical or near-vertical borehole, such analysis leads to an inherent 180° ambiguity in the source location. Here we present a location procedure that removes this ambiguity by using the dip of the particle motion as an a priori information to constrain the initial source location. The new procedure is demonstrated with a dataset acquired during hydraulic fracture stimulation, where we know which side of the monitoring well the events are located. Using a 5 -step location procedure, we then reinvestigate a microseismic data set acquired in April 1997 at the Ekofisk oilfield in the North Sea. Traveltimes for 2683 candidate events are manually picked. A noise-weighted analytic-signal polarization analysis is used to estimate the dip and azimuth of P-wave particle motions. A modified t-test is used to statistically assess the reliability of event location. As a result, 1462 events are located but 627 are deemed to be statistically reliable. The application of a hierarchal cluster analysis highlights coherent structures that cluster around wells and inferred faults. Most events cluster at a depth of roughly 3km in the Ekofisk chalk formation but very little seismicity is observed from the underlying Tor chalk formation, which is separated from the Ekofisk formation by an impermeable layer. We see no evidence for seismicity in the overburden but such events may be too distant to detect. The resulting picture of microseismicity at Ekofisk is very different from those presented in previous studies. [source] A spectral projection method for the analysis of autocorrelation functions and projection errors in discrete particle simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2008André Kaufmann Abstract Discrete particle simulation is a well-established tool for the simulation of particles and droplets suspended in turbulent flows of academic and industrial applications. The study of some properties such as the preferential concentration of inertial particles in regions of high shear and low vorticity requires the computation of autocorrelation functions. This can be a tedious task as the discrete point particles need to be projected in some manner to obtain the continuous autocorrelation functions. Projection of particle properties on to a computational grid, for instance, the grid of the carrier phase, is furthermore an issue when quantities such as particle concentrations are to be computed or source terms between the carrier phase and the particles are exchanged. The errors committed by commonly used projection methods are often unknown and are difficult to analyse. Grid and sampling size limit the possibilities in terms of precision per computational cost. Here, we present a spectral projection method that is not affected by sampling issues and addresses all of the above issues. The technique is only limited by computational resources and is easy to parallelize. The only visible drawback is the limitation to simple geometries and therefore limited to academic applications. The spectral projection method consists of a discrete Fourier-transform of the particle locations. The Fourier-transformed particle number density and momentum fields can then be used to compute the autocorrelation functions and the continuous physical space fields for the evaluation of the projection methods error. The number of Fourier components used to discretize the projector kernel can be chosen such that the corresponding characteristic length scale is as small as needed. This allows to study the phenomena of particle motion, for example, in a region of preferential concentration that may be smaller than the cell size of the carrier phase grid. The precision of the spectral projection method depends, therefore, only on the number of Fourier modes considered. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratiosINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004M. A. Habib Abstract Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd. [source] A numerical approach revealing the impact of rheological properties on mouthfeel caused by foodINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2007Katrin Mathmann Summary In contrast to the static chemoreceptor-related flavour perception, texture of food capable of flow is detected dynamically with oral mechanoreceptors while the food is manipulated in the mouth. The resulting sensation called mouthfeel strongly depends on the different physical properties of food. Aim of the current study is to determine numerically the occurring fluid mechanical forces in food suspensions using a simplified tongue-palate model system consisting of two parallel plates. For this purpose, the equations of fluid and particle motion are numerically solved by using structured overlapping grids. In the computational experiment, a density neutral fluid system between the plates is compressed by moving the upper plate with constant velocity down to the other one. It has been found that suspended particles move with the fluid flow but have only minor effect on the global flow field in the applied concentration. [source] Quantitative evaluation of the prosthetic head damage induced by microscopic third-body particles in total hip replacementJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 4 2001Manuela Teresa Raimondi Abstract The increase of the femoral head roughness in artificial hip joints is strongly influenced by the presence of abrasive particulate entrapped between the articulating surfaces. The aim of the present study is to evaluate the dependence of such damage on the geometry of the particles entrapped in the joint, with reference to the UHMWPE/chrome-cobalt coupling. Five chrome-cobalt femoral heads and their coupled UHMWPE acetabular cups, retrieved at revision surgery after a short period of in situ functioning, have been investigated for the occurrence of third-body damage. This was found on all the prosthetic heads, where the peak-to-valley height of the scratches, as derived from profilometry evaluations, ranged from 0.3,1.3 ,m. The observed damage has been divided into four classes, related to the particle motion while being embedded into the polymer. Two kinds of particle morphology have been studied, spherical and prismatic, with size ranging from 5,50 ,m. In order to provide an estimation of the damage induced by such particles, a finite element model of the third-body interaction was set up. The peak-to-valley height of the impression due to the particle indentation on the chrome-cobalt surface is assumed as an index of the induced damage. The calculated values range from 0.1,0.5 ,m for spherical particles of size ranging from 10,40 ,m. In the case of prismatic particles, the peak-to-valley height can reach 1.3 ,m and depends both on the size and width of the particle's free corner, indenting the chrome-cobalt. As an example, a sharp-edged particle of size 30 ,m can induce on the chrome-cobalt an impression with peak-to-valley height of 0.75 ,m, when embedded into the polyethylene with a free edge of 5 ,m facing the metallic surface. Negligible damage is induced, if a free edge of 7.5 ,m is indenting the counterface. Our findings offer new support to the hypothesis that microscopic third-body particles are capable of causing increased roughening of the femoral head and provide a quantitative evaluation of the phenomenon. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 436,448, 2001 [source] Characterization of flow regime transition and particle motion using acoustic emission measurement in a gas-solid fluidized bedAICHE JOURNAL, Issue 5 2010Wang Jingdai Abstract Particle motion is a major determinant of the dynamical performance of a fluidized bed. It plays an important role in determining and optimizing the complex correlation of fluidization condition between particle-particle and particle-environment in a system. A passive acoustic emission (AE) technique is applied to monitor, characterize, and control the fluidization condition of polyethylene particles in a gas-solid fluidized bed. Experimental results show that AE signals are very sensitive to the particle movements by analyzing energy distribution, which can help to understand the status of the system. The AE energy temporal analysis is further used to identify the transition of flow regimes. Moreover, the activity of particle motion can be quantitatively determined by using a combination of granular temperature and AE spatial energy analysis. This work provides valuable insights into the dynamic behavior of particles in a gas-solid fluidized bed based on AE technique. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Stochastic modeling of particle motion along a sliding conveyorAICHE JOURNAL, Issue 1 2010Kevin Cronin Abstract The sliding conveyor consists of a plane surface, known as the track, along which particles are induced to move by vibrating the bed sinusoidal with respect to time. The forces on the particle include gravity, bed reaction force and friction. Because friction coefficients are inherently variable, particle motion along the bed is erratic and unpredictable. A deterministic model of particle motion (where friction is considered to be known and invariant) is selected and its output validated by experiment. Two probabilistic solution techniques are developed and applied to the deterministic model, in order to account for the randomness that is present. The two methods consider particle displacement to be represented by discrete time and continuous time random processes, respectively, and permits analytical solutions for mean and variance in displacement versus time to be found. These are compared with experimental measurements of particle motion. Ultimately this analysis can be employed to calculate residence-time distributions for such items of process equipment. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Characterization of granular flow of wet solids in a bladed mixerAICHE JOURNAL, Issue 8 2006Azzeddine Lekhal Abstract In this study, we measure instantaneous, average, and fluctuating velocity fields at exposed surfaces for dry and wet grains in a vertical cylindrical mixer, agitated by four pitched blades. When the material is dry, the free surface of the granular bed deforms, rising where the blades are present, and falling between blade passes. Although average velocities are predominantly azimuthal, instantaneous velocities tracked in time reveal three-dimensional particle circulations, including significant periods of particle motion in the opposite direction to that of the blades, indicative of bed penetration. When moisture is added to the solid particles, the flow dynamics change from a regime dominated by the motion of individual grains to a regime controlled by the motion of small clumps that form as a result of the cohesive forces. This transition is characterized by a reduced particle,particle collision frequency and exhibits a sharp decrease in the granular temperature at the free surface. This transition is also characterized by an increase in bed porosity, which is attributed to increased cohesiveness arising from liquid bridges. A Fourier transform analysis conducted on the tangential component of the velocities (dominant flow) shows that a group of high frequencies exceeding the blade rotation frequency become significant with added moisture. These are characteristics of the large number of wet agglomerates flowing between successive blade passes. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Fluid dynamic simulation of O3 decomposition in a bubbling fluidized bedAICHE JOURNAL, Issue 11 2003Madhava Syamlal Recent advances in dense, multiphase, computational fluid dynamics (CFD) have allowed accurate simulation of the gas and particle motion in bubbling and circulating fluidized beds. Since fluidized-bed reactors are used for many chemical processes, a simulation must also be able to accurately couple chemical reactions to bed hydrodynamics. The catalytic decomposition of ozone (O3) often has been used to study experimentally the contacting behavior of catalytic reactors. Simulations of laboratory-scale experiments of premixed O3 decomposition in a bubbling fluidized bed using the multiphase CFD code MFIX were conducted. The grid-independent results are in very good agreement with reported experimental data on total conversion over a range of fluidization velocities and initial bed heights. This confirms the ability of multiphase hydrodynamic models to capture quantitatively the effect of hydrodynamics on chemical reactions in a bubbling fluidized bed. [source] Modeling and Simulation of Elementary Processes in Ideal SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Fumihiro Wakai Three-dimensional numerical simulation of sintering was performed to illustrate the interplay between shapes and forces in particle scale. Elementary rules for topological transition of triple lines were derived from the analysis of micromechanical models of sintering: bond formation, pore channel closure, and pore disappearance. The particle motion was driven by the force acting on a particle, i.e., a vector sum of sintering forces. The non-equilibrium sintering stress was defined to analyze the pore shrinkage. A particle changed its own shape through interaction with neighbor particles; then, the coordination number affected particle motion, pore shrinkage, coarsening, and grain growth. [source] Gas-solid Two-phase Mixtures Flowing Upward through a Confined Packed Bed,PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3-4 2006Yurong He Abstract This paper deals with flows of a gas-solid two-phase mixture through a confined packed bed. Both experimental work and numerical modelling are performed on the behaviour of suspended particles within the packed bed. The experimental work is carried out with a non-intrusive Positron Emission Particle Tracking (PEPT) technique, which tracks particle motion at the single particle level for a prolonged period thus allows both the microscopic and macroscopic solids behaviour to be analysed under the steady-state conditions. A continuous based model is used to simulate the flow behaviour. The model uses a newly proposed porosity model and treats the suspended and packed particles as a binary mixture with the packed particles being at zero velocity. The results show that the model captures the main features of solids behaviour in terms of the radial distributions of the suspended particle concentration and the axial solids velocity. Both the experiments and modelling suggest that the wall effect on the motion of suspended particles be limited to a small region close to the wall (,0.5,1 packed particle diameter). However, deviations exist between the model predictions and experiments; more work is therefore proposed to improve the interaction terms in the model between the suspended and packed particles. [source] Positron Imaging Studies of Rotating DrumsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2005David J. Parker Abstract The potential of the radioisotope tracer technique of positron emission tomography (PET) and the related techniques of positron emission projection imaging (PEPI) and positron emission particle tracking (PEPT) is illustrated with reference to laboratory scale studies of particulate motion in rotating drums, operating either in batch or continuous flow modes. Sand grains, glass beads and TiO2 granules down to 0.5mm diameter were labelled. Using PEPT the transition between rolling and slumping modes has been identified and the velocity profile within the active layer has been determined for a range of drum diameters. PEPI has been used to measure and explain residence time distributions, while all three techniques have been used to study segregation based on particle size, both radially and axially within the drum. Data on particle motion within a novel baffled drum is also presented. Le potentiel de la technique de traçage par radio-isotopes en tomographie par émission de positrons (PET) et les techniques associées de l'imagerie par projection des émissions de positrons (PEPI) ou le traçage des particules par émission de positrons (PEPT), est illustré en référence à des études à l'échelle de laboratoire du déplacement de particules dans des tambours rotatifs, fonctionnant soit en mode d'écoulement discontinu ou continu. Des grains de sable, des billes de verre et des granules de TiO2 aussi petits que 0,5 mm de diamètre ont été marqués. À l'aide de la technique PEPT, la transition entre les modes roulant et glissant a été identifiée et le profil de vitesse à l'intérieur de la couche active a été déterminé pour une gamme de diamètres de tambours. La technique PEPI a été utilisée pour mesurer et expliquer les distributions de temps de séjour, tandis que les trois techniques ont servi pour l'analyse de la ségrégation d'après la taille des particules, à la fois radialement et axialement dans le tambour. Des données sur le déplacement des particules dans un nouveau tambour à chicanes sont également présentées. [source] Measurement of Solid Circulation Patterns in Liquid,Solid and Gas,Liquid,Solid Fluidized BedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Shahzad Barghi Abstract Solid circulation patterns were determined by measuring collisions between tracer particles and cylindrical probes in liquid,solid and gas,liquid,solid fluidized beds. Special probes were used to obtain two- and three-dimensional views of particle motion. Circulation patterns for 3 and 5 mm glass beads were studied. Mixing cells, which had been formed at low liquid velocities, grew in size and eventually merged as the liquid velocity increased. The flow patterns of smaller particles having the same density as bed particles and particles lighter than bed particles (graphite particles) with the same size were also measured. On a déterminé des profils de circulation des solides en mesurant les collisions entre des traceurs particulaires et des sondes cylindriques dans des lits fluidisés liquide, solide et gaz,liquide,solide. Des sondes spéciales ont été employées pour obtenir des images bidimensionnelle et tridimensionnelle du déplacement des particules. Les profils de circulation pour des billes de verre de 3 mm et 5 mm ont été étudiés. Les cellules de mélange, qui se forment à de faibles vitesses de liquide, augmentent en taille et finissent par fusionner à mesure que la vitesse du liquide augmente. On a également mesuré les profils d'écoulement des particules plus petites ayant la même masse volumique que les particules de lit et des particules plus légères que les particules de lit (particules de graphite) ayant la même taille. [source] The eastward displacement of a freely falling body on the rotating Earth: Newton and Hooke's debate of 1679ANNALEN DER PHYSIK, Issue 8 2010W. Dittrich Abstract In this article I would like to tell the story of the beginning of modern theoretical physics, freed from all kinds of questionable anecdotes which have entered the scientific literature over the centuries. It all began in the seventeenth century when the mathematical theory of astronomy began to take shape. A major step in the history of modern science was taken when a few members of The Royal Society in London realized that the laws ruling the motions of heavenly bodies as manifested in Kepler's three laws are also effective in the dynamics of Earth-bound particle motion. Everything started, not with I. Newton, but with R. Hooke. Not Newton's falling apple (Voltaire's invention), but a far-reaching response by R. Hooke to a letter by I. Newton, dated November 28, 1679, ignited Newton's interest in gravity. That letter contained the famous spiral which a falling body would follow when released from a certain height above the surface of the Earth. Hooke's answer, based on Keplerian orbits, expressed the opinion that the body's trajectory would rather follow an elliptical path. In his spiral sketch Newton, however, predicted correctly that the falling body would be found to suffer an eastward deviation from the vertical in consequence of the Earth's rotation. In the course of time, many a researcher, including Hooke himself, was able to verify this conjecture. But it took until 1803 for the first satisfactory calculation of the eastward displacement of a freely falling body to be performed, and was provided by C.F. Gauss. [source] Non-Volkov solutions for a charge in a plane waveANNALEN DER PHYSIK, Issue 8 2005V. Bagrov Abstract As it is known, a set of solutions of the Klein-Gordon and Dirac equations with a plane-wave field was found for the first time by Volkov. We construct new solutions of these equations different from the Volkov ones. In particular, the new solutions are characterized by quantum numbers different from Volkov solutions. In fact, our result is based on the demonstration that the transversal charge motion in a plane wave can be mapped by a special quantum transformation to transversal free particle motion. Similarly, we find new sets of solutions of the Klein-Gordon and Dirac equations with the combined electromagnetic field. [source] A new look at the derivation of the Schrödinger equation from Newtonian mechanicsANNALEN DER PHYSIK, Issue 6 2003L. Fritsche Abstract We present a modified version of Nelson's seminal paper on the derivation of the time-dependent Schrödinger equation which draws on the equation of motion of a particle that moves under the influence of a classical force field and additional stochastic forces. The emphasis of our elaboration is focused on the implication of allowing stochastic forces to occur, viz. that the energy E of the particle is no longer conserved on its trajectory in a conservative force field. We correlate this departure , E from its classical energy with the energy/time uncertainty relation where , t is the average time for , E to persist. The stability of atoms, the zero-point energy of oscillators, the tunneling effect and the diffraction at slits are shown to be directly connected with the occurrence of such energy fluctuations. We discuss and rederive Nelson's theory entirely from this point of view and generalize his approach to systems of N particles which interact via pair forces. Achieving reversibility in a description of particle motion that is akin to Brownian motion, represents a salient point of the derivation. We demonstrate that certain objections raised against Nelson's theory are without substance. We also try to put the particular worldview of this version of stochastic quantum mechanics into perspective with regard to the established Copenhagen interpretation. [source] Electrohydrodynamic-mediated dielectrophoretic separation and transport based on asymmetric electrode pairsELECTROPHORESIS, Issue 24 2008E. Du Abstract This paper presents a system for continuous separation and transport of micron and submicron particles in fluidic environment based on dielectrophoretic fractionation in concert with AC electrothermal (AC ET)-induced fluidic pumping action. In this system, high frequency AC signals are used to energize asymmetric electrode pairs. AC ET-driven fluidic pumping is utilized as an alternative to the commonly used external pressure-driven fluid flow. Distinct collection sites for negative-dielectrophoretic and positive-dielectrophoretic particle populations are identified. The coupling effects of dielectrophoretic force and viscous drag from AC ET fluid flow on particle motions are investigated theoretically and numerically. We demonstrate that these two forces can be efficiently coupled to achieve continuous separation and transport of particle mixture in a fluidic medium when the dielectric properties of the particles and the fluidic environment are different. The combination of dielectrophoretic separation and AC ET pumping function provides a promising approach to further miniaturize and integrate these mechanisms into lab-on-chip devices. [source] Improved microseismic event location by inclusion of a priori dip particle motion: a case study from EkofiskGEOPHYSICAL PROSPECTING, Issue 5 2010G.A. Jones ABSTRACT Microseismic monitoring in petroleum settings provides insights into induced and naturally occurring stress changes. Such data are commonly acquired using an array of sensors in a borehole, providing measures of arrival times and polarizations. Events are located using 1D velocity models, P- and S-wave arrival times and the azimuths of P-wave particle motions. However in the case of all the sensors being deployed in a vertical or near-vertical borehole, such analysis leads to an inherent 180° ambiguity in the source location. Here we present a location procedure that removes this ambiguity by using the dip of the particle motion as an a priori information to constrain the initial source location. The new procedure is demonstrated with a dataset acquired during hydraulic fracture stimulation, where we know which side of the monitoring well the events are located. Using a 5 -step location procedure, we then reinvestigate a microseismic data set acquired in April 1997 at the Ekofisk oilfield in the North Sea. Traveltimes for 2683 candidate events are manually picked. A noise-weighted analytic-signal polarization analysis is used to estimate the dip and azimuth of P-wave particle motions. A modified t-test is used to statistically assess the reliability of event location. As a result, 1462 events are located but 627 are deemed to be statistically reliable. The application of a hierarchal cluster analysis highlights coherent structures that cluster around wells and inferred faults. Most events cluster at a depth of roughly 3km in the Ekofisk chalk formation but very little seismicity is observed from the underlying Tor chalk formation, which is separated from the Ekofisk formation by an impermeable layer. We see no evidence for seismicity in the overburden but such events may be too distant to detect. The resulting picture of microseismicity at Ekofisk is very different from those presented in previous studies. [source] Dynamical modeling of chaos single-screw extruder and its three-dimensional numerical analysisPOLYMER ENGINEERING & SCIENCE, Issue 3 2000W. R. Hwang The Chaos Screw (CS) nonlinear dynamical model is proposed to describe the development of chaos in a single-screw extrusion process and the model is verified by three-dimensional numerical simulations. The only-barrier channel is the unperturbed Hamiltonian system, which consists of two homoclinic orbits and nested elliptic tori of nonlinear oscillation in periodic (extended) state space. A periodically inserted no-barrier zone represents a perturbation. For small perturbations, homoclinic tangle leads to the Cantor set near the homoclinic fixed point and elliptic rotations are changed into the resonance bands or KAM tori, depending on the commensurability of frequency ratio of the corresponding orbits. A finite element method of multivariant Q,1+PO elements is applied to solve the velocity fields and a 4th order Runge-Kutta method is used for the particle tracing. The resulting Poincaré section verifies the proposed dynamical model, showing the resonance band corresponding to rotation number 1/3 under small perturbations. As the strength of perturbation increases, the Poincaré sections indicate wider stochastic regions in which random particle motions take place. [source] Resolution of structure characteristics of AE signals in multiphase flow system,From data to informationAICHE JOURNAL, Issue 10 2009Yi-Jun He Abstract This investigation was performed to study the underlying structure characteristics of acoustic emission (AE) signals, which could be helpful not only to understand a relatively complete picture of hydrodynamics in multiphase flow systems, but also to extract the most useful information from the original signals with respect to a particular measurement requirement. However, due to AE signals are made up of emission from many acoustic sources at different scales, the resolution of AE signals is often very complicated and appears to be relatively poorly researched. In this study, the structure characteristics of AE signals measured both in gas,solid fluidized bed and liquid,solid stirred tank were researched in detail by resorting to wavelet transform and rescaled range analysis. A general criterion was proposed to resolve AE signals into three physical-related characteristic scales, i.e., microscale, mesoscale, and macroscale. Multiscale resolution of AE signals implied that AE signals in microscale represented totally the dynamics of solid phase and could be applied to measure particle-related properties. Furthermore, based on the structure characteristics of AE signals, useful features related to particles motion were extracted to establish two new prediction models, one for on-line measurements of particle size distribution (PSD) and average particle size in gas,solid fluidized bed and the other for on-line measurement of the suspension height in liquid,solid stirred tank. The prediction results indicated that (1) measurements of PSD and average particle size using AE method showed a fairly good agreement with that using sieve method both for laboratory scale and plant scale fluidized beds, and (2) measurements of the suspension height using AE method showed a fairly good agreement with that using visual method. The results thus validated that the extracted features based on analyses of structure characteristics of AE signals were very useful for establishing effective on-line measurement models with respect to some particular applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | ||||||||||||||||