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At least 91 records · Page 5Linked to original sources
arXiv2013

Direct solutions for normal depths in curved irrigation canals

The normal depth is an important hydraulic element for canal design, operation and management. Curved irrigation canals including parabola, U-shaped and catenary canals have excellent hydraulic performance and strong ability of anti-frost heave, while the normal depths in the governing equations of the current common methods have no explicit analytical solution. They are only indirect methods by using trial procedures, numerical methods, and graphical tools. This study presents new direct formulas for normal depth in curved irrigation canals by applying for Marquardt method. The maximum relative error of the proposed formulas is less than 1% within the practice range by comparative analysis, and they are simple and convenient for manual calculations. The results may provide the reliable theoretical basis and useful reference for the design and operation management of irrigation canals.

physics.flu-dyn↗
arXiv2013

Variational Approach to Necessary and Sufficient Stability Conditions for Inviscid Shear Flow

A necessary and sufficient condition for linear stability of inviscid parallel shear flow is formulated by a novel variational method, where the velocity profile is assumed to be monotonic and analytic. Unstable eigenvalues of the Rayleigh equation are shown to be associated with positive eigenvalues of a certain selfadjoint operator. The stability is therefore simply determined by maximizing a quadratic form, which is theoretically and numerically more tractable than directly solving the Rayleigh equation. This variational approach is based on the Hamiltonian nature of the inviscid fluid and will be applicable to other hydrodynamic stability problems.

physics.flu-dyn↗
arXiv2018

Microfluidics Development at Berkeley

Richard A. Mathies is professor emeritus of Chemistry at the University of California, Berkeley. In this contribution he summarizes his journey through microfluidics over the past 30 years from the invention of Capillary Array Electrophoresis in the 1990s to recent attempts to launch a microfluidic system into space.

physics.flu-dyn↗
arXiv2018

Microfluidics for Biofabrication

Shoji Takeushi is professor in and the Director of the Center for International Research on Integrative Biomedical Systems (CIBiS), Institute of Industrial Science (IIS) at the University of Tokyo. Here he describes his attempts to use inherent function of living materials in engineered systems by reconstructing the biological structure using microfluidic technology.

physics.flu-dyn↗
arXiv2018

Microfluidic tools for assaying immune cell function

Joel Voldman is a professor in the Electrical Engineering and Computer Science Department at MIT. Here he describes his labs efforts to develop microfluidic devices for cell manipulation and analysis.

physics.flu-dyn↗
arXiv2018

Centrifugal Microfluidics for Biomedical Applications

Yoon-Kyoung Cho is a full professor in Biomedical Engineering at UNIST. In this contribution she describes a fully integrated and automated lab-on-a-disc using centrifugal microfluidics to provide a "sample-in and answer-out" type of biochemical analysis solution with simple, size-reduced, and cost-efficient instrumentation. She also gives various examples of the fully integrated "lab-on-a-disc" developed for broad applications ranging from medical diagnostics to food, environment, and energy applications.

physics.flu-dyn↗
arXiv2018

Microfluidics for Chemical Synthesis: Flow Chemistry

Klavs F. Jensen is Warren K. Lewis Professor in Chemical Engineering and Materials Science and Engineering at the Massachusetts Institute of Technology. Here he describes the use of microfluidics for chemical synthesis, from the early demonstration examples to the current efforts with automated droplet microfluidic screening and optimization techniques.

physics.flu-dyn↗
arXiv2018

When Streams of Optofluidics Meet the Sea of Life

Luke P. Lee is a Tan Chin Tuan Centennial Professor at the National University of Singapore. In this contribution he describes the power of optofluidics as a research tool and reviews new insights within the areas of single cell analysis, microphysiological analysis, and integrated systems.

physics.flu-dyn↗
arXiv2018

Fractal mesh refinement, rare events and type Ia supenova

Fractal mesh refinement enables mesh refinement regimes to the Gibson scale and beyond. Conventional multifractal subgrid models have cost considerations which also lead to local mesh refinement, but more importantly, the application of these models to compressible turbulent deflagration fronts is a topic for future research, while subgrid models tuned to this complex physics lack a multifractal search focus, and for cost reasons do not allow the large search volumes required to find the sought for rare event to trigger a DDT. Here we propose methods to resolve fine scales and locate rare possible DDT trigger events within large volumes while addressing multifractal issues at a feasible computational cost. We are motivated by the goal of confirming or assessing the hypothesis of a delayed detonation in type Ia supernova and to assessing the delay in this event if it is found to occur.

physics.comp-ph↗
arXiv2018

Structure and Persistence of Ship Wakes and the Role of Langmuir-Type Circulations

Surface ships operating in ocean waves are shown to generate transverse surface currents which persist long after the initial ship-induced currents have decayed. These surface currents are due to the formation of large-scale Langmuir-type circulations and are suggested to be the mechanism for the concentration of surface-active substance into streaks or bands, which are regularly seen in synthetic aperture radar imagery of the ocean surface. These circulations are generated by the Craik-Leibovich vortex force, which results from interaction of ship-induced current with ambient surface waves. Once generated, the circulations persist due to their large-scale nearly-inviscid nature. Numerical simulations of the wake behind a surface ship in calm, head, and following seas are presented and show good agreement with radar imagery from at-sea experiments. It is demonstrated that surface currents do not persist in the absence of surface waves, but can persist for tens of kilometers through the formation of Langmuir-type circulations. Since the circulations are driven by the cross product of the Stokes drift and the wake vorticity, the structure of the persistent wake is a function of relative heading of the ship with respect to the direction of surface-wave propagation.

physics.flu-dyn↗
arXiv2022

Ferrofluid drop impacts and Rosensweig peak formation in a non-uniform magnetic field

Vertical drop impacts of ferrofluids onto glass slides in a non-uniform magnetic field have been studied using high-speed photography. Outcomes have been classified based on the motion of the fluid-surface contact lines, and formation of peaks (Rosensweig instabilities) which affect the height of the spreading drop. The largest peaks are nucleated at the edge of a spreading drop, similarly to crown-rim instabilities in drop impacts with conventional fluids, and remain there for an extended time. Impact Weber numbers ranged from 18.0 to 489, and the vertical component of the B-field was varied between 0 and 0.37 T at the surface by changing the vertical position of a simple disc magnet placed below the surface. The falling drop was aligned with the vertical cylindrical axis of the 25 mm diameter magnet, and the impacts produced Rosensweig instabilities without splashing. At high magnetic field strengths a stationary ring of ferrofluid forms approximately above the outer edge of the magnet.

physics.flu-dyn↗
arXiv2013

Interacting length scales in the reactive-infiltration instability

The reactive-infiltration instability, which develops when a porous matrix is dissolved by a flowing fluid, contains two important length scales. Here we outline a linear stability analysis that simultaneously incorporates both scales. We show that the commonly used "thin-front" model is a limiting case of a more general theory, which also includes convection-dominated dissolution as another special case. The wavelength of the instability is bounded from below, and lies in the range 1mm to 1km for physically reasonable flow rates and reaction rates. We obtain a closed form for the growth rate when the change in porosity is small.

physics.geo-ph↗
arXiv2013

Influence of asperities on fluid and thermal flow in a fracture: a coupled Lattice Boltzmann study

The characteristics of the hydro-thermal flow which occurs when a cold fluid is injected into a hot fractured bedrock depend on the morphology of the fracture. We consider a sharp triangular asperity, invariant in one direction, perturbing an otherwise flat fracture. We investigate its influence on the macroscopic hydraulic transmissivity and heat transfer efficiency, at fixed low Reynolds number. In this study, numerical simulations are done with a coupled lattice Boltzmann method that solves both the complete Navier-Stokes and advection-diffusion equations in three dimensions. The results are compared with those obtained under lubrication approximations which rely on many hypotheses and neglect the three-dimensional (3D) effects. The lubrication results are obtained by analytically solving the Stokes equation and a two-dimensional (integrated over the thickness) advection-diffusion equation. We use a lattice Boltzmann method with a double distribution (for mass and energy transport) on hypercubic and cubic lattices. Beyond some critical slope for the boundaries, the velocity profile is observed to be far from a quadratic profile in the vicinity of the sharp asperity: the fluid within the triangular asperity is quasi-static. We find that taking account of both the 3D effects and the cooling of the rock, are important for the thermal exchange. Neglecting these effects with lubrication approximations results in overestimating the heat exchange efficiency. The evolution of the temperature over time, towards steady state, also shows complex behavior: some sites alternately reheat and cool down several times, making it difficult to forecast the extracted heat.

physics.geo-ph↗
arXiv2013

Velocity measurements in the liquid metal flow driven by a two-phase inductor

We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two-phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0 to 90 degrees. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.

physics.flu-dyn↗
arXiv2024

Interaction between corner and bulk flows during drainage in granular porous media

Drainage in porous media can be broken down into two main mechanisms: a primary piston-like displacement of the interfaces through the bulk of pore bodies and throats, and a secondary slow flow through corners and films in the wake of the invasion front. In granular porous media, this secondary drainage mechanism unfolds in connected pathways of pendular structures, such as capillary bridges and liquid rings, formed between liquid clusters. To represent both mechanisms, we proposed a dynamic dual-network model for drainage, considering that a gas displaces a wetting liquid from quasi-2D granular porous media. For this model, dedicated analyses of the capillary bridge shapes and hydraulic conductivity were conducted so that the secondary drainage mechanism could be properly quantified at finite speeds. With the model, an investigation of the wetting-phase connectivity and flow during drainage was carried out, covering a broad range of flow conditions. Results indicate that the span of liquid-connected structures in the unsaturated region, as well as their ability to contribute to flow, varies significantly with Capillary and Bond numbers.

cond-mat.soft↗
arXiv2013

Lagrangian Descriptors: A Method for Revealing Phase Space Structures of General Time Dependent Dynamical Systems

In this paper we develop new techniques for revealing geometrical structures in phase space that are valid for aperiodically time dependent dynamical systems, which we refer to as Lagrangian descriptors. These quantities are based on the integration, for a finite time, along trajectories of an intrinsic bounded, positive geometrical and/or physical property of the trajectory itself. We discuss a general methodology for constructing Lagrangian descriptors, and we discuss a "heuristic argument" that explains why this method is successful for revealing geometrical structures in the phase space of a dynamical system. We support this argument by explicit calculations on a benchmark problem having a hyperbolic fixed point with stable and unstable manifolds that are known analytically. Several other benchmark examples are considered that allow us the assess the performance of Lagrangian descriptors in revealing invariant tori and regions of shear. Throughout the paper "side-by-side" comparisons of the performance of Lagrangian descriptors with both finite time Lyapunov exponents (FTLEs) and finite time averages of certain components of the vector field ("time averages") are carried out and discussed. In all cases Lagrangian descriptors are shown to be both more accurate and computationally efficient than these methods. We also perform computations for an explicitly three dimensional, aperiodically time-dependent vector field and an aperiodically time dependent vector field defined as a data set. Comparisons with FTLEs and time averages for these examples are also carried out, with similar conclusions as for the benchmark examples.

nlin.CD↗