Physics Of Fluid Flow Research Articles

The interpretation of amplitude changes in 4D seismic data arising from gas exsolution and dissolution

This study examines the four-dimensional (4D) seismic signatures from multiple seismic surveys shot during gas exsolution and dissolution in a producing hydrocarbon reservoir, and focuses in particular on what reservoir information may be extracted from their analysis. To aid in this process, hydrocarbon gas properties and behaviour are studied, and their relationship to the fluid-flow physics is understood using numerical simulation. This knowledge is then applied to interpret the seismic response of a turbidite field in the UK Continental Shelf (UKCS). It is concluded that for a repeat seismic survey shot 6 months or more after a pressure change above or below bubble point (as in our field case), the gas-saturation distribution during either exsolution or dissolution exists in two fixed saturation conditions defined by the critical and the maximum possible gas saturation. Awareness of this condition facilitates an interpretation of the data from our field example, which has surveys repeated at intervals of 12–24 months, to obtain an estimate of the critical gas saturation of between 0.6 and 4.0%. These low values are consistent with a range of measurements from laboratory and numerical studies in the open literature. Our critical gas-saturation estimate is also in qualitative agreement with the solution gas–oil ratios estimated in a material balance exercise using our data. It is not found possible to quantify the maximum gas saturation using the 4D seismic data alone, despite the advantage of having multiple surveys, owing to the insensitivity of the seismic amplitudes to the magnitude of this gas saturation. Assessment of the residual gas saturation left behind after secondary gas-cap contraction during the dissolution phase suggests that small values of less than a few per cent may be appropriate. The results are masked to some extent by an underlying water flood. It is believed that the methodology and approach used in this study may be readily generalized to other moderate- to high-permeability oil reservoirs, and used as input in simulation model updating.

Seismic attenuation in partially saturated rocks: Recent advances and future directions

The large amount of data collected with the broadband attenuation vessel (BBAV) and other laboratory devices and analyzed in the last five years sheds light on the physics of wave-induced fluid flow in Berea Sandstone. However, the knowledge is insufficient to fully exploit the physics of seismic wave attenuation in partially saturated rocks. In particular, some technical challenges have limited the depth of research. Soon these challenges will be overcome by the use of fluid-pressure sensors capable of measuring wave-induced fluid pressure in the seismic bandwidth when the sample is under high confining pressures. In addition, a new subresonance apparatus, paired with a micro-CT system, will be used to further investigate the influence of fluid distribution and microstructural features on attenuation.

Optic Imaging of Two-Phase-Flow Behavior in 1D Nanoscale Channels

Summary Gas in tight sand and shale exists in underground reservoirs with microdarcy (µd) or even nanodarcy (nd) permeability ranges; these reservoirs are characterized by small pore throats and crack-like interconnections between pores. The size of the pore throats in shale may differ from the size of the saturating-fluid molecules by only slightly more than one order of magnitude. The physics of fluid flow in these rocks, with measured permeability in the nanodarcy range, is poorly understood. Knowing the fluid-flow behavior in the nanorange channels is of major importance for stimulation design, gas-production optimization, and calculations of the relative permeability of gas in tight shale-gas systems. In this work, a laboratory-on-chip approach for direct visualization of the fluid-flow behavior in nanochannels was developed with an advanced epi-fluorescence microscopy method combined with a nanofluidic chip. Displacements of two-phase flow in 100-nm-depth slit-like channels were reported. Specifically, the two-phase gas-slip effect was investigated. Under experimental conditions, the gas-slippage factor increased as the water saturation increased. The two-phase flow mechanism in 1D nanoscale slit-like channels was proposed and proved by the flow-pattern images. The results are crucial for permeability measurement and understanding fluid-flow behavior for unconventional shale-gas systems with nanoscale pores.

An Approach for the Estimation of Dynamic Imbibition Capillary Pressure Curves

Capillary pressure is one of the most important parameters for reservoir engineering studies. Although different experimental methods are devised to measure capillary pressure, these methods do not represent the physics of fluid flow, which happens at reservoir conditions. Thus, it is attempted to extract the capillary pressure from spontaneous imbibition data, the common mechanism of oil production in water wet porous media. In this work, a new approach is developed to obtain the imbibition capillary pressure curve by using spontaneous water imbibition data in oil-water-rock systems. Comparison of calculated imbibition capillary pressure curves by the new approach with experimental values shows a good accordance with each other.

Optic Imaging of Two-Phase-Flow Behavior in Nanoscale Fractures

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164549, ’Optic Imaging of Two-Phase-Flow Behavior in Nanoscale Fractures,’ by Qihua Wu, Baojun Bai, SPE, and Yinfa Ma, Missouri University of Science and Technology; and Joeng Tai Ok, Keith Neeves, and Xiaolong Yin, SPE, Colorado School of Mines, prepared for the 2013 SPE Unconventional Resources Conference, The Woodlands, Texas, USA, 10-12 April. The paper has not been peer reviewed. Gas in tight sand and shale exists in underground reservoirs with microdarcy or even nanodarcy permeability ranges; these reservoirs are characterized by small pore throats and crack-like interconnections between pores. The physics of fluid flow in these rocks, with measured permeability in the nanodarcy range, is poorly understood. Knowing the fluid-flow behavior in the nanoscale channels is of major importance for both simulation studies and calculations of the relative permeability of gas in tight shale-gas systems. Introduction Shale-gas reservoirs have pore sizes in the range of 1 to 300 nm. Additionally, the matrix permeabilities of those unconventional gas reservoirs are in the microdarcy to nanodarcy range. When fluid (gas or water) flows in a shale pore, the molecule size is quite comparable to the flow diameter. When some gas molecules strike against the pore wall, they retain a certain velocity that causes them to “slip.” Under those conditions, Darcy’s equation may not be accurate or practical for describing the fluid-flow behavior because there may be other flow mechanisms at work such as slip flow and diffusive flow. Extensive studies have been conducted on single-phase flow in tight-sand and shale gas systems, and equations have been derived to measure the relative permeability of gas and to determine the single-phase gas-slippage effect. However, under real shale-gas-reservoir conditions, two phases (mostly water and gas) typically exist. It has been reported that in some ultralow-permeability shale-gas reservoirs, water saturation could be much greater than in conventional shale-gas plays. The effects of saturated water on gas permeability/relative permeability and gas slippage still have not been investigated sufficiently. For laboratory experiments, shale samples were used in most cases in order to represent the real pore structure and distribution in the reservoir. However, there are some limitations of using shale samples in laboratory experiments. For example, water saturation and saturation distribution are difficult to measure. Meanwhile, the laboratory-on-chip technique is becoming a suitable approach for investigating fluid flow in ultrasmall pores. Nano fluidics and microfluidics have been used in different subject areas for both fundamental research and application. Some micromodels are being used to study multiphase flow under both saturated and unsaturated conditions. Furthermore, the laboratory-on-chip technique provides a means by which to directly visualize fluid-flow behavior, such as the displacement of one fluid by another, because most micro-/nanofluidic chips are made of transparent materials. Micromodels have been used to simulate numerous porous-media-transport phenomena, including microorganism transport in unsaturated porous media. However, visualization studies of fluid flow in nanochannels are still lacking, especially for shale gas and tight gas.

Evidence of non-Darcy flow and non-Fickian transport in fractured media at laboratory scale

Abstract. During a risk assessment procedure as well as when dealing with cleanup and monitoring strategies, accurate predictions of solute propagation in fractured rocks are of particular importance when assessing exposure pathways through which contaminants reach receptors. Experimental data obtained under controlled conditions such as in a laboratory allow to increase the understanding of the fundamental physics of fluid flow and solute transport in fractures. In this study, laboratory hydraulic and tracer tests have been carried out on an artificially created fractured rock sample. The tests regard the analysis of the hydraulic loss and the measurement of breakthrough curves for saline tracer pulse inside a rock sample of parallelepiped shape (0.60 × 0.40 × 0.08 m). The convolution theory has been applied in order to remove the effect of the acquisition apparatus on tracer experiments. The experimental results have shown evidence of a non-Darcy relationship between flow rate and hydraulic loss that is best described by Forchheimer's law. Furthermore, in the flow experiments both inertial and viscous flow terms are not negligible. The observed experimental breakthrough curves of solute transport have been modeled by the classical one-dimensional analytical solution for the advection–dispersion equation (ADE) and the single rate mobile–immobile model (MIM). The former model does not properly fit the first arrival and the tail while the latter, which recognizes the existence of mobile and immobile domains for transport, provides a very decent fit. The carried out experiments show that there exists a pronounced mobile–immobile zone interaction that cannot be neglected and that leads to a non-equilibrium behavior of solute transport. The existence of a non-Darcian flow regime has showed to influence the velocity field in that it gives rise to a delay in solute migration with respect to the predicted value assuming linear flow. Furthermore, the presence of inertial effects enhance non-equilibrium behavior. Instead, the presence of a transitional flow regime seems not to exert influence on the behavior of dispersion. The linear-type relationship found between velocity and dispersion demonstrates that for the range of imposed flow rates and for the selected path the geometrical dispersion dominates the mixing processes along the fracture network.

Upscaling and microstructural analysis of the flow-structure relation perpendicular to random, parallel fiber arrays

Owing largely to multiscale heterogeneity in the underlying fibrous structure, the physics of fluid flow in and through fibrous media is incredibly complex. Using fully resolved finite element (FE) simulations of Newtonian, incompressible fluid flow perpendicular to the fibers, the macroscopic permeability is calculated in the creeping flow regime for arrays of random, ideal, perfectly parallel fibers.On the micro-scale, several order parameters, based on Voronoi and Delaunay tessellations, are introduced to characterize the structure of the randomly distributed, parallel, non-overlapping fiber arrays. In particular, by analyzing the mean and the distribution of the topological and metrical properties of Voronoi polygons, we observe a smooth transition from disorder to (partial) order with decreasing porosity, i.e., increasing packing fraction.On the macro-scale, the effect of fiber arrangement and local crystalline regions on the macroscopic permeability is discussed. For both permeability and local bond orientation order parameter, the deviation from a fully random configuration can be well represented by an exponential term as function of the mean gap width, which links the macro- and the micro-scales.Finally, we verify the validity of the, originally, macroscopic Darcy's law at various smaller length scales, using local Voronoi/Delaunay cells as well as uniform square cells, for a wide range of porosities. At various cell sizes, the average value and probability distributions of macroscopic quantities, such as superficial fluid velocity, pressure gradient or permeability, are obtained. These values are compared with the macroscopic permeability in Darcy's law, as the basis for a hierarchical upscaling methodology.

Production data analysis of unconventional gas wells: Workflow

Production data analysis techniques for unconventional reservoirs are in their infancy. These techniques continue to evolve according to our improved understanding of the physics of fluid storage and flow. Analytical methods, which include type-curves, flow-regime analysis and analytical simulation, have recently been modified to account for desorption of gas, multi-phase flow, non-Darcy flow (slip flow and diffusion), and non-static (stress-dependent) permeability. Further, adaptations have been made to account for complex wellbore and hydraulic fracture geometries encountered in some developments.Empirical methods, including the popular Arps decline-curve methodology, have been adopted to account for long-term transient and transitional flow associated with some unconventional plays. New empirical methods have been developed to address the limitations of the Arps curves. Unlike conventional reservoirs, however, where decades of application have led to “rules of thumb” and guidance for decline parameter ranges that can be used for different reservoir and production scenarios, application of empirical techniques to unconventional reservoirs can lead to significant uncertainty in production forecasts.In this article, a workflow is described for the integrated use of analytical and empirical production data analysis methods for the purpose of: 1) reservoir and hydraulic fracture characterization and 2) production forecasting/reserves determination. Details of the methodologies are provided in an accompanying review article (Clarkson, 2013). It is recommended that newly-developed empirical techniques not be applied on their own, and that decline parameters should be adjusted to match production forecasts generated using analytical techniques. Analytical methods better (although still imperfectly) account for the physics of fluid flow and storage in unconventional reservoirs, and can account for operational changes during the life of a well. Examples of the workflow are provided using a simulated and field example.

Aeroacoustics of Twin Supersonic Jets: A Review

Interaction of twin supersonic jets can dramatically alter the dynamic pressures in the near-field and cause fatigue of aircraft structures. This review paper focuses on the twin jet coupling situation that is rich in fluid flow physics, requires sophisticated analysis tools and is of relevance to aircraft with closely spaced engines and other industrial situations involving multiple jet flows. The review consists of four sections: (i) a historical survey of twin jet exhaust coupling, (ii) rectangular twin jets with both spanwise uniform and non-uniform geometry, (iii) a description of multi-modes and mode jumps using higher order spectral analysis, and (iv) the suppression of twin jet coupling. The parameters that affect twin jet coupling include nozzle geometry, internozzle spacing and nozzle operating conditions. Certain modes of resonant coupling increase the dynamic pressures drastically in the inter-nozzle region, whereas other coupling modes can suppress unsteady pressure levels. Since coupled resonances can cause fatigue failure of components, mitigation approaches need to be considered. Successful techniques include nozzle inserts, beveled nozzles, water injection, and miniature pins and cavities.

Numerical analysis of unsteady hydrodynamics and thermal transport in five-strand asymmetric tundish

In this work, a numerical study was carried out to characterise the hydrodynamics and heat transport in a five-strand asymmetric billet caster tundish. Employing a three-dimensional computational fluid dynamics model, several numerical experimentations were carried out to capture the exact physics of complex fluid flow and thermal transport in the tundish. Plant practices were simulated by considering seven distinct cases and analysed in detail. Tundish filling operation was tried out with volume of fluid methodology. The effects of thermal buoyancy, its effect on thermofluidic heat transfer and the abrupt change in thermal gradients at different zones in the tundish flow domain were explained after detailed analysis. Refractory heating simulations were performed, and results were analysed in detail. This is the first time that such an exhaustive numerical study on an asymmetric tundish has been reported.

An Experimental Investigation of the Free Jet Flow from a Radially Lobed Nozzle Using Hot-Wire Anemometry

Turbulence is a ubiquitous and important phenomenon in fluid mechanics and is also seen as a challenging topic of study in graduate education. In order for students to truly understand the physics of fluid flow and to use this knowledge to evaluate flow conditions, learning about the different measurement techniques employed for this purpose is essential. With this in mind, a graduate-level course in turbulence measurement techniques was introduced at the Department of Mechanical Engineering at Texas A&M University around 20 years ago. The idea was to expand undergraduate students' knowledge of instrumentation and merge it with concepts in fluid mechanics, to ensure that students have a chance to follow the theoretical and practical aspects of flow measurement. The course was recently revamped to incorporate a project that allows students to work with one of the measurement methods discussed in class – hot-wire anemometry (HWA). Different post-processing techniques and turbulence analysis methods are discussed in class and implemented in the project. The present paper reviews a project carried out by one group of graduate students and discusses its impact on their learning. The paper presents details of the project, including the design of the experiment, methodology and analysis of data (the raw data are available on the website of the corresponding author and can be used as a teaching aid for related courses).

Multiphysics borehole geophysical measurements, formation evaluation, petrophysics, and rock physics — Introduction

This special section showcases some emerging trends in the acquisition, processing, and interpretation of borehole geophysical measurements, with emphasis on multiphysics and multiscale applications that integrate geologic information, petrophysical properties, rock physics, and core measurements. Borehole geophysical measurements are routinely acquired to appraise, produce, and monitor subsurface resources, including fossil fuels, minerals, and water. They also are used in shallow reconnaissance projects, for civil-engineering studies, and for soil characterization and remediation, to cite a few salient applications. Wells usually contain the most dense and diverse types of information concerning geology, fluid flow, and rock physics, when assessing subsurface resources. During the last decade, borehole geophysical measurements have experienced significant developments in their acquisition, processing, and interpretation; they no longer can be viewed in isolation but rather as representing an important component of the quantitative description of petrophysical and rock physical properties under a geologic framework. Relatively recent entries to this endeavor are the petrophysical and geophysical appraisal/monitoring of subsurface CO 2 sequestration and the petrophysical/rock-physics characterization of hydrocarbon-bearing shale. It is expected that future interpretation challenges in borehole geophysics will consistently require the solid quantitative integration of measurements across disciplines and physical scales in formation-evaluation and rock-physics studies. The papers included in this issue consider topics as diverse as new multiphysics methods to combine electromagnetic and seismic amplitude measurements to estimate petrophysical properties between wells and the basis of Archie’s laws. Several of these contributions formally and rigorously integrate the physics of fluid flow in porous media with borehole geophysical measurements to estimate static and dynamic petrophysical properties. New rock-physics methods also are introduced to estimate elastic properties …

Simulation of tissue cutting and bleeding for laparoscopic surgery using auxiliary surfaces.

Realistic simulation of tissue cutting and bleeding is important components of a surgical simulator that are addressed in this study. Surgeons use a number of instruments to perform incision and dissection of tissues during minimally invasive surgery. For example, a coagulating hook is used to tear and spread the tissue that surrounds organs and scissors are used to dissect the cystic duct during laparoscopic cholecystectomy. During the execution of these procedures, bleeding may occur and blood flows over the tissue surfaces. We have developed computationally fast algorithms to display (1) tissue cutting and (2) bleeding in virtual environments with applications to laparoscopic surgery. Cutting through soft tissue generates an infinitesimally thin slit until the sides of the surface are separated from each other. Simulation of an incision through tissue surface is modeled in three steps: first, the collisions between the instrument and the tissue surface are detected as the simulated cutting tool passes through. Then, the vertices along the cutting path are duplicated. Finally, a simple elastic tissue model is used to separate the vertices from each other to reveal the cut. Accurate simulation of bleeding is a challenging problem because of the complexities of the circulatory system and the physics of viscous fluid flow. There are several fluid flow models described in the literature, but most of them are computationally slow and do not specifically address the problem of blood flowing over soft tissues. We have reviewed the existing models, and have adapted them to our specific task. The key characteristics of our blood flow model are a visually realistic display and real-time computational performance. To display bleeding in virtual environments, we developed a surface flow algorithm. This method is based on a simplified form of the Navier-Stokes equations governing viscous fluid flow. The simplification of these partial differential equations results in a wave equation that can be solved efficiently, in real-time, with finite difference techniques. The solution describes the flow of blood over the polyhedral surfaces representing the anatomical structures and is displayed as a continuous polyhedral surface drawn over the anatomy.

An Analytical Study for Fluid Flow in Porous Media Imbedded Inside a Channel With Moving or Stationary Walls Subjected to Injection/Suction

This paper reports a new analytical solution for 2D Darcy-Brinkman equations in porous channels filled with porous media subjected to various boundary conditions at walls. The governing equations of fluid flow through porous medium are reduced to a nonlinear ordinary differential equation (ODE) based on physics of fluid flow. The obtained ODE is solved analytically using homotopy perturbation method (HPM). The analytical models for velocity profile and pressure distribution along the length of channel are validated with data available in the open literature and an independent numerical study using finite volume method (FVM). It was shown that there is an excellent agreement between the presented models and the results of the CFD and previous works. Finally, the effects of Reynolds (Re) and Darcy (Da), numbers suction or injection parameters (α,β) and wall axial velocity coefficients (λ and γ) on velocity profiles and pressure drop in different cases are investigated. The models are applicable to analyze flow in channels filled with and without porous media for both moving and stationary walls and can be used to predict flow in micro and macro channels and over stretching sheets in porous medium as well as study of vapor flow in evaporator section of flat plate heat pipes.

Convective heat transfer and fluid flow physics in some ribbed ducts using liquid crystal thermography and PIV measuring techniques

Enhancement of forced convection is important in several engineering applications. Surface modifications like rib-roughening are commonly used in applications such as compact heat exchangers and internal cooling of gas turbine blades and vanes. This paper gives a brief summary of convective heat transfer and fluid flow in some ribbed ducts using liquid crystal thermography and PIV measuring techniques. Details of the flow pattern and the influence of rib configuration and arrangement on the heat transfer are presented. Nevertheless, the understanding of the flow and thermal physics in ribbed ducts is not yet complete and further studies are needed.

Estimating petrophysical parameters and average mud-filtrate invasion rates using joint inversion of induction logging and pressure transient data

We introduce an inversion approach for determining the water-based mud-filtrate invasion profile, as well as the formation porosity and horizontal permeability, from the induction logging data. The inversion is constrained by a multiphase fluid flow simulator that simulates the mud-filtrate invasion process to obtain the spatial distributions of the water saturation and the salt concentration, which are in turn transformed into the formation resistivity using a resistivity-saturation formula. By ignoring the diffusion effect, we assume that the mud-filtrate invasion process is mainly convective so that it can be equivalently simulated by providing an average invasion rate and the duration of invasion. The average invasion rate can be directly inverted from the fluid-flow-constrained inversion of induction logging data. We also obtain the mud-filtrate invasion profile, which is consistent with the fluid flow physics. The reconstructed mud-filtrate invasion profile benefits the interpretation of the formation test. When the pressure transient data are available, this approach can be also used to jointly invert both induction logging data and pressure transient data to obtain the mud-filtrate invasion profile, as well as a parametric distribution of the TI-anisotropic formation permeability and porosity. Assuming a vertical well penetrating horizontal formations, the fluid flow problem is solved using an implicit black oil finite-difference simulator with brine tracking option based on a cylindrical, axially symmetric grid, whereas the response of the induction logging tool is simulated using a frequency-domain finite-difference solver based on a Cartesian grid. A Gauss-Newton inversion scheme using the multiplicative regularization technique is used for either the fluid-flow-constrained inversion or the joint inversion. The reliability of the inversion results depends on the accuracy of a priori knowledge of the reservoir, which needs to be confirmed via sensitivity analysis.

Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

AbstractMolecular dynamics simulations of C60 bombardment of molecular solids suggest that there is a space–time divide between the fragmentation/ion creation process and the ejection of intact molecules via fluid flow physics. This space–time divide leads to the conclusion that molecular ions are preformed prior to ejection. Consequently, to increase the ion yield significantly, the sample must be altered to create more preformed ions. Copyright © 2010 John Wiley & Sons, Ltd.

Gas-Reserves Estimation in Resource Plays

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 130102, ’Gas-Reserves Estimation in Resource Plays,’ by W.J. Lee, SPE, Texas A&M University, and R.E. Sidle, SPE, Consultant, prepared for the 2010 SPE Unconventional Gas Conference, Pittsburgh, Pennsylvania, 23-25 February. See SPE Econ & Mgmt, October 2010, page 86. The petroleum industry’s lack of understanding of physical properties and the physics that control production from many important resource plays limits the ability to model and forecast production and reserves from these resources with confidence. While measurement technology and modeling accuracy are improving, the industry often is forced to resort to empirical methods that lack the validation usually required for high-confidence results. Some of the procedures in common use for forecasting are reviewed, and key strengths and limitations of the techniques are identified. Introduction Preferably, proper characterization of a resource play begins with production. When attempting to characterize a resource and to forecast production, it is important to know what can and cannot be determined. Thus, pilot tests, resource characterization, and analogs are favored over curve fitting or highly complex reservoir simulation. Analytical models not based on analogs are useful, but only to investigate the generalized incremental effects of different production conditions, such as horizontal vs. vertical wells or completion and well-operation methods. Analogs (usually based on older in-field wells) for decline analysis or type-curve techniques generally would be the preferred methods for high-confidence forecasts and reserves estimates. This approach has proved valuable in examples as diverse as the Antrim shale, Pinedale tight gas, and California diatomite. As a result, high-confidence reserves estimates begin with older wells—wells that have experienced any early-life transient-production effects and have reached a stage in which only stable, long-term trends are the dominant influence on production rate. The considerable complexities of production from resource plays make it important to isolate early effects from those that are fundamental to ultimate recovery. An incomplete understanding of the basic physics of fluid flow and stimulation results in complex-resource plays currently of interest has limited the ability to develop models that provide high confidence, particularly in shales. Because of this lack of understanding, empirical methods take on an unusually important role, but production histories from the most-modern completion and stimulation techniques are limited in duration, causing problems with validation of a forecasting methodology of any kind. The full-length paper provides a detailed critique of the methods used to forecast production and estimate reserves in poorly understood resource plays.

A Multiphysics Multiscale 3-D Computational Wave Basin Model for Wave Impact Load on a Cylindrical Structure

A multiphysics multiscale finite-element based nonlinear computational wave basin (CWB) model is developed using LS-DYNA. Its predictive capability is calibrated using a large-scale fluid-structure interaction experiment conducted in a 3-dimensional wave basin to determine wave impact on a cylindrical structure. This study focuses on evaluating CWB accuracy using two wave excitation conditions — plane and focused solitary waves — and two cylinder arrangements — single and multiple cylinders. Water surface elevation and water particle velocity are predicted numerically for the fluid domain, obtaining horizontal force, overturning moment, and dynamic pressure on the cylindrical structure and calibrated against experimental measurement. The CWB model predicts wave motion characteristics — water surface elevation and velocity, and integrated structural response — horizontal force and overturning moment, for the given wave conditions well. Computation time increases and the predictive accuracy decreases as nonlinear fluid-structure interaction becomes increasingly complex. A study of computation settings for improving computation performance showed that a high-performance parallel-computing hardware platform is needed to model details of highly nonlinear physics of fluid flow including wave breaking and turbulence.

Reliable addition of reagents into microfluidic droplets

This article reports a design that reliably adds reagents into droplets by exploiting the physics of fluid flow at a T-junction in the microchannel. An expanded section right after the T-junction enhances merging of a stream with a droplet, eliminates the drawbacks such as extra droplet formation and long mixing time. The expanded section reduces the pressure buildup at the T-junction and minimizes the tendency to form extra droplets; plays the role in creating low Laplace pressure jump across the interface of the droplet forming from the T-junction which reduces the probability of forming extra droplet in the merging process; provides space for droplet coalescence if there is an extra droplet due to droplet break-up before merging. In this design, after merging, the reactants are in axial arrangement inside the droplets which lead to faster mixing. Reliable addition of reagent to the droplets happens for the combination of flow rates in a broad range from 25 to 250 μl/h, for both DI water (Q DI) and fluorescent (Q fluo) streams.