Prediction of vertical flows in large diameter pipes

There is an increasing interest in multiphase flows in large diameter vertical pipes (typically with diameters greater that 100 mm) in the context of hydrocarbon production systems. There are strong indications that flows in such pipes differ greatly from those in smaller diameter pipes on which most of the prediction methodologies are based. In small diameter pipes, an important mechanism for the bubble flow to slug flow transition is the formation of void waves. This research reveal this wave growth and also predict the breakdown points from bubble-to-slug flow transition using Biesheuvel and Gorissen (1990) approximate void wave model based on Harwell small tube bubble flow experiments. As the gas velocity is further increased, the slug flow itself breaks down into churn flow by a process of flooding in the Taylor bubbles. In large diameter pipes, it appears that conventional slug flow does not occur; this is probably due to the fact that there is a size limit on spherical cap bubbles. Thus, this study reviews most of literatures in terms of bubble coalescence and breakup kernels in order to evaluate dynamic bubble size changes by applying population balance model. Unfortunately, these kernels have their own problems to be solved. Therefore we establish a simplified two-group bubble interaction model by taking into account mechanisms of large bubble shearing-off breakup and small bubble coalescence in large bubble wakes, respectively, assuming small bubbles do not coalesce to each other. In large diameter pipes, the bubble/slug and slug/churn transitions appear to be by-passed in favour of a direct transition from bubble to churn flow with increasing gas mass flux. Note that the churn flow studied here is emphasized by a continuous path for the gas phase. This study also describes work aimed at developing a phenomenological understanding of the bubble/churn and churn/annular transition regions in large diameter pipes. Investigation of the liquid transport mechanisms has led to the definition of two new flow regime transition criteria, namely liquid upflow potential and minimum entrained fraction. To estimate the bubble-to-churn flow transition, the liquid upflow potential of a churn flow at the particular local set of gas and liquid flow rates is estimated by using axial view experiments and the existing adiabatic equilibrium data. In churn flow, liquid upflow is achieved by the net upward flow in the film (bearing in mind that both upflow and downflow are occurring in the film, though the net value must be positive) and by droplet transport in the gas core. Once the Kutateladse flooding is reached, suggested by Pushkina and Sorokin (1969), then it is postulated that the transition to churn flow occurs. As the gas velocity is further increased, the flow rate of entrained drops in the gas core decreases to a minimum and then rises again. This minimum is observed to occur at a dimensionless gas velocity approximately equal to one and this serves as a possible criterion for the churn-to-annular flow transition. As a framework for prediction, an existing one-dimensional steady state modelling code (GRAMP2) has been selected. This code takes account of regime changes and predicts void fraction and pressure gradient using phenomenological models. Work on connecting the void wave growth, bubble size evaluation and GRAMP2 code for large diameter pipes will be the main target for the nearly future. In the meantime, CFD simulation is also being undertaken using a finite volume method based the STARCD software in order to numerically predict the evaluations of dynamic bubble size and flow regime changes in large diameter pipes

Buoyancy-driven plumes in a layered porous medium

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Helix vs. Sheet Formation in a Small Peptide

Segments with the amino acid sequence EKAYLRT appear in natural occurring proteins both in $\alpha$-helices and $\beta$-sheets. For this reason, we have use this peptide to study how secondary structure formation in proteins depends on the local environment. Our data rely on multicanonical Monte Carlo simulations where the interactions among all atoms are taken into account. Results in gas phase are compared with that in an implicit solvent. We find that both in gas phase and solvated EKAYLRT forms an $\alpha$-helix when not interacting with other molecules. However, in the vicinity of a $\beta$-strand, the peptide forms a $\beta$-strand. Because of this change in secondary structure our peptide may provide a simple model for the $\alpha \to \beta$ transition that is supposedly related to the outbreak of Prion diseases and similar illnesses.Comment: to appear in Physical Review

Critical Scale-invariance in Healthy Human Heart Rate

We demonstrate the robust scale-invariance in the probability density function (PDF) of detrended healthy human heart rate increments, which is preserved not only in a quiescent condition, but also in a dynamic state where the mean level of heart rate is dramatically changing. This scale-independent and fractal structure is markedly different from the scale-dependent PDF evolution observed in a turbulent-like, cascade heart rate model. These results strongly support the view that healthy human heart rate is controlled to converge continually to a critical state.Comment: 9 pages, 3 figures. Phys. Rev. Lett., to appear (2004

Advances in Plant-Derived Scaffold Proteins

Scaffold proteins form critical biomatrices that support cell adhesion and proliferation for regenerative medicine and drug screening. The increasing demand for such applications urges solutions for cost effective and sustainable supplies of hypoallergenic and biocompatible scaffold proteins. Here, we summarize recent efforts in obtaining plant-derived biosynthetic spider silk analogue and the extracellular matrix protein, collagen. Both proteins are composed of a large number of tandem block repeats, which makes production in bacterial hosts challenging. Furthermore, post-translational modification of collagen is essential for its function which requires co-transformation of multiple copies of human prolyl 4-hydroxylase. We discuss our perspectives on how the GAANTRY system could potentially assist the production of native-sized spider dragline silk proteins and prolyl hydroxylated collagen. The potential of recombinant scaffold proteins in drug delivery and drug discovery is also addressed

Applying Deep Learning for Phase-Array Antenna Design

Master of Engineering (Electrical Engineering), 2021Hybrid beamforming (HBF) can provide rapid data transmission rates while reducing the complexity and cost of massive multiple-input multiple-output (MIMO) systems. However, channel state information (CSI) is imperfect in realistic downlink channels, introducing challenges to hybrid beamforming (HBF) design. For HBF designs, we had a hard time finding the proper labels. If we use the optimized output based on the traditional algorithm as the label, the neural network can only be trained to approximate the traditional algorithm, but not better than the traditional algorithm. This thesis proposes a hybrid beamforming neural network based on unsupervised deep learning (USDNN) to prevent the labeling overhead of supervised learning and improve the achievable sum rate based on imperfect CSI. Compared with the traditional HBF method, the unsupervised learning-based method can avoid the labeling overhead as well as obtain better performance than the traditional algorithm. The network consists of 5 dense layers, 4 batch normalization (BN) layers and 5 activation functions. After training, the optimized beamformer can be obtained, and the optimized beamforming vector can be directly output. The simulation results show that our proposed method is 74% better than manifold optimization (MO) and 120% better than orthogonal match pursuit (OMP) systems. Furthermore, our proposed USDNN can achieve near-optimal performance

Viscous fingering in a radial elastic-walled Hele-Shaw cell

We study the viscous fingering instability in a radial Hele-Shaw cell in which the top boundary has been replaced by a thin elastic sheet. The introduction of wall elasticity delays the onset of the fingering instability to much larger values of the injection flow rate. Furthermore, when the instability develops, the fingers that form on the expanding air-liquid interface are short and stubby, in contrast with the highly-branched patterns observed in rigid-walled cells (Pihler-Puzovi c et al. 2012). We report the outcome of a comprehensive experimental study of this problem and compare the experimental observations to the predictions from a theoretical model that is based on the solution of the Reynolds lubrication equations, coupled to the F oppl-von-K arm an equations which describe the deformation of the elastic sheet. We perform a linear stability analysis to study the evolution of small-amplitude non-axisymmetric perturbations to the time-evolving base flow. We then derive a simpli ed model by exploiting the observations (i) that the non-axisymmetric perturbations to the sheet are very small and (ii) that perturbations to the flow occur predominantly in a small wedge-shaped region ahead of the air-liquid interface. This allows us to identify the various physical mechanisms by which viscous fi ngering is weakened (or even suppressed) by the presence of wall elasticity. We show that the theoretical predictions for the growth rate of small amplitude perturbations are in good agreement with experimental observations for injection flow rates that are slightly larger than the critical flow rate required for the onset of the instability. We also characterize the large-amplitude fingering patterns that develop at larger injection flow rates. We show that the wavenumber of these patterns is still well predicted by the linear stability analysis, and that the length of the fingers is set by the local geometry of the compliant cell.EPSR