Numerical Simulation of a CT-Scanned Counter-Current Flow Experiment

Counter-current flow occurs in many reservoir processes and it is important to understand and model these processes in order to operate them effectively. Both drainage and imbibition processes exist simultaneously during counter-current flow. It has thus proven difficult to model this type of flow using conventional techniques because of the impossibility of assigning a single capillary pressure curve applicable over the entire sample. In the current paper, a new saturation-history-dependent approach has been developed to simulate a counter-current flow experiment done with an X-ray CT scanner. Hysteresis in both capillary pressure and relative permeabilities is considered during simulation. Capillary hysteresis loop and relative permeabilities are extracted through history matching and a family of scanning curves is constructed connecting the two branches of the capillary hysteresis loop. Each gridblock of the sample is assigned a different scanning curve according to the local saturation history. History-dependent modeling of the experiment reproduced two-dimensional saturation distributions over time with good accuracy, which cannot be obtained with traditional simulation using only one capillary pressure curve.     

EFFECT OF VERTICAL BAFFLES ON PARTICLE MIXING AND DRYING IN FLUIDIZED BEDS OF GROUP D PARTICLES

This study reports the effect of vertical baffles on the group D powder mixing and drying characteristics in a batch fluidized bed dryer. Results obtained in this study showed that operating the fluidized bed dryer with vertical baffles gave better particle mixing. This is due to the fact that the vertical baffles acted to limit the growth of small bubbles into large bubbles and the small bubbles caused more vigorous mixing in the bed of particles before finally erupting at the bed surface. Thus, insertion of vertical baffles is a useful way to process group D particles in a fluidized bed, especially when the fluidized bed is large.     

Rheological aspects of dense lignite–water suspensions; structure development on consecutive flow loops

Aspects of dense lignite–water slurries (LWS) rheology were investigated using controlled stress and controlled strain rheometers with parallel disks and Couette geometries. During the preparation of the slurries, the achieved solids volume fractions were up to 0.425 and the particle size distributions were polydispersed with sizes up to 300 μm. In the ascending parts of consecutive flow loops, a slope transition of the flow curve was observed and studied in relation to the solids volume fraction. The obtained results with the different geometries and rheometers were qualitatively the same. By following the model proposed by Cheng (Rheol Acta 42:372–382, 2003) for thixotropic fluids, and taking into account the yield stress appearance, a suitable correlation for LWS is proposed, which is consistent with the experimental flow curves.     

Seismic Evaluation of Multi-Storey RC Frame Using Modal Pushover Analysis

The recently developed pushover analysis procedure has led a new dimension to performance-based design in structural engineering practices. With the increase in the magnitude of monotonic loading, weak links and failure modes in the multi-storey RC frames are usually formed. The force distribution and storey displacements are evaluated using static pushover analysis based on the assumption that the response is controlled by fundamental mode and no mode shift takes place. Himalayan-Nagalushai region, Indo-Gangetic plain, Western India, Kutch and Kathiawar regions are geologically unstable parts of India and some devastating earthquakes of remarkable intensity have occurred here. In view of the intensive construction activity in India, where even a medium intensity tremor can cause a calamity, the authors feel that a completely up-to-date, versatile method of aseismic analysis and design of structures are essential. A detailed dynamic analysis of a 10-storey RC frame building is therefore performed using response spectrum method based on Indian Standard Codal Provisions and base shear, storey shear and storey drifts are computed. A modal pushover analysis (MPA) is also carried out to determine the structural response of the same model for the same acceleration spectra used in the earlier case. The major focus of study is to bring out the superiority of pushover analysis method over the conventional dynamic analysis method recommended by the code. The results obtained from the numerical studies show that the response spectrum method underestimates the response of the model in comparison with modal pushover analysis. It is also seen that modal participation of higher modes contributes to better results of the response distribution along the height of the building. Also pushover curves are plotted to illustrate the displacement as a function of base shear.     

Evolutive and nonlinear vibrations of rotor on aerodynamic bearings

The use of air as a lubricant in aerodynamic bearings is advantageous, particularly in the food industry. Aerodynamic bearings with tilting pads have complicated stiffness and damping properties and need a very detailed theoretical and experimental research. Response curves of rigid rotor supported on aerodynamic bearings are presented for a linear but evolutive mathematical model. Due to non-monotone properties of stiffness and damping matrices at variable revolutions, a new resonance appears. The mathematical model of rotor vibrations in the whole area of bearing clearance is also developed in the consideration of strongly nonlinear properties of aerodynamic bearing.     

Normal form for librational curves of the standard map

We present a method for constructing analytic expansions approximating librational invariant curves in the case of the so-called generalized standard map. After some preliminary changes of variables, we apply a direct Birkhoff normal form to a fixed order. The resulting system describes homotopically trivial invariant curves close to a periodic orbit. We investigate the stability of the librational curves applying a numerical method developed by J. Greene.

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Sommario Presentiamo un metodo per la costruzione di espansioni analitiche, adatte a descrivere le curve invarianti di librazione nel caso della standard map generalizzata. Dopo aver effettuato alcuni cambiamenti preliminari di variabili, calcoliamo la forma normale di Birkhoff ad un ordine fissato. Il sistema risultante descrive curve invarianti attorno ad orbite periodiche. Studiamo la stabilità di tali curve di librazione tramite un metodo numerico sviluppato da J. Greene.

     

Defect assessment procedure based on ductile tearing process

Strain hardening, crack growth resistance and nonuniform load distribution have significant effects on the ductile tearing process. A defect assessment procedure incorporating with the above features is proposed in the present paper, with the final appearance of “design curves” to facilitate engineering applications.     

Transition to escape in a system of coupled oscillators

We study a Hamiltonian system of coupled oscillators derived from two forced pendulums, connected with a torsional spring. The uncoupled limit is described by two identical oscillators, each possessing a homoclinic orbit separating bounded from unbounded motion. We focus on intermediate energy levels which lead to detained motions, defined as trajectories that, though unbounded as t → ∞, oscillate within the region defined by the homoclinic orbit of the unperturbed system for a long but finite time. We analyze the existence and behavior of these motions in terms of equipotential surfaces. These curves provide bounds on the motion of the system and are shown to be closed for low energies. However, above some critical energy level the equipotential curves become open. The detained trajectories are shown to arise from the region of phase space that was, for appropriate energies, stochastic. These motions remain within this region for long times before finally “leaking out” of the opening in the equipotential curves and proceeding to infinity.     

Modeling the Formation of Fluid Banks During Counter-Current Flow in Porous Media

Fluid banks sometimes form during gravity-driven counter-current flow in certain natural reservoir processes. Prediction of flow performance in such systems depends on our understanding of the bank-formation process. Traditional modeling methods using a single capillary pressure curve based on a final saturation distribution have successfully simulated counter-current flow without fluid banks. However, it has been difficult to simulate counter-current flow with fluid banks. In this paper, we describe the successful saturation-history-dependent modeling of counter-current flow experiments that result in fluid banks. The method used to simulate the experiments takes into account hysteresis in capillary pressure and relative permeabilities. Each spatial element in the model follows a distinct trajectory on the capillary pressure versus saturation map, which consists of the capillary hysteresis loop and the associated capillary pressure scanning curves. The new modeling method successfully captured the formation of the fluid banks observed in the experiments, including their development with time. Results show that bank formation is favored where the p_c-versus-saturation slope is low. Experiments documented in the literature that exhibited formation of fluid banks were also successfully simulated.