scholarly journals Nano-wrinkles, compactons, and wrinklons associated with laser-induced Rayleigh–Taylor instability: I. Bubble environment

2020 ◽  
Vol 38 (2) ◽  
pp. 101-113
Author(s):  
Stjepan Lugomer
Keyword(s):  
Fluid Layer ◽  
Nonlinear Differential Equations ◽  
Fluid Velocity ◽  
Target Surface ◽  
Elementary Excitation ◽  
Sudden Increase ◽  
New Paradigm ◽  
Lateral Tension ◽  
Rayleigh Taylor Instability ◽  
Elastic Sheets

ABSTRACTWe study dynamics, structure and organization of the new paradigm of wavewrinkle structures associated with multipulse laser-induced RayleighTaylor (RT) instability in the plane of a target surface in the circumferential zone (C-zone) of the spot. Irregular target surface, variation of the fluid layer thickness and of the fluid velocity affect the nonlinearity and dispersion. The fluid layer inhomogeneity establishes local domains arranged (organized) in the «domain network». The traveling wavewrinkles become solitary waves and latter on become transformed into stationary soliton wavewrinkle patterns. Their morphology varies in the radial direction ofaussian-like spot ranging from the compacton-like solitons to the aperiodic rectangular waves (with rounded top surface) and to the periodic ones. These wavewrinkles may be successfully juxtapositioned with the exact solution of the nonlinear differential equations formulated in the KadomtsevPetviashvili sense taking into account the fluid conditions in particular domain. The cooling wave that starts at the periphery by the end of the pulse causes sudden increase of density and surface tension: the wavewrinkle structures become unstable what causes their break-up. The onset of solidification causes formation of an elastic sheet which starts to shrink generating lateral tension on the wavewrinkles. The focusing of energy at the constrained boundary causes the formation of wrinklons as the new elementary excitation of the elastic sheets.

scholarly journals Experiments on generation of surface waves by an underwater moving bottom

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150069 ◽  
Author(s):  
Timothée Jamin ◽  
Leonardo Gordillo ◽  
Gerardo Ruiz-Chavarría ◽  
Michael Berhanu ◽  
Eric Falcon
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Surface Deformation ◽  
Fluid Layer ◽  
Fluid Velocity ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Low Pass ◽  
Spatio Temporal ◽  
Experimental Findings

We report laboratory experiments on surface waves generated in a uniform fluid layer whose bottom undergoes an upward motion. Simultaneous measurements of the free-surface deformation and the fluid velocity field are focused on the role of the bottom kinematics (i.e. its spatio-temporal features) in wave generation. We observe that the fluid layer transfers bottom motion to the free surface as a temporal high-pass filter coupled with a spatial low-pass filter. Both filter effects are often neglected in tsunami warning systems, particularly in real-time forecast. Our results display good agreement with a prevailing linear theory without any parameter fitting. Based on our experimental findings, we provide a simple theoretical approach for modelling the rapid kinematics limit that is applicable even for initially non-flat bottoms: this may be a key step for more realistic varying bathymetry in tsunami scenarios.

Instability and Transition of a Plane Bubble Plume

2002 ◽  
Author(s):  
Ophe´lie Caballina ◽  
Eric Climent ◽  
Jan Dusˇek
Keyword(s):  
Stokes Equations ◽  
Fluid Layer ◽  
Fluid Velocity ◽  
Continuous Phase ◽  
Collective Effects ◽  
Recent Experimental Data ◽  
Fluid Viscosity ◽  
Bubble Plume ◽  
Carrier Fluid ◽  
Bubble Cloud

When bubbles are continuously released from a located source at the bottom of a fluid layer initially at rest, a plume is produced. The motion of the carrier fluid is initiated and driven by buoyancy of the bubble cloud. In the present study, a detailed analysis of the bubble plume transition is investigated. The continuous phase flow is obtained by direct numerical resolution of Navier-Stokes equations forced by the presence of bubbles. Collective effects induced by the presence of bubbles are modelled by a spatio-temporal distribution of momentum. Time evolution of the dispersed phase is solved by lagrangian tracking of all the bubbles. Focused on the description of plume transition, several configurations (plume widths, fluid viscosity, injection rate) are investigated. During the laminar ascension of the plume, fluid velocity profiles can be non-dimensionalised on a single auto-similar evolution. Dimensional analysis provides a prediction of the limit rising velocity of the plume top. This prediction has been confirmed by our numerical simulations. Furthermore, our first results point out the symmetry breaking induced by plume instability which appears beyond a critical transition height. Various data show that the Grashof number based on injection conditions is the key parameter to predict the transition of the plume. Our results agree very well with recent experimental data. Comparison with experiments on thermal plumes in air shows that the bubble plume is more unstable. This feature should be related to the lack of diffusion in the lagrangian transport of density gradient by the bubble cloud and to the slip velocity between the two phases.

Fluid Flow Characteristics of a Confined Slot Jet Without or With a Target Surface

2005 ◽  
Author(s):  
L. K. Liu ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. Y. Lee ◽  
Y. H. Hung
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Fluid Velocity ◽  
Flow Characteristics ◽  
Target Surface ◽  
Streamwise Velocity ◽  
Separation Distance ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Fluid Flow Characteristics

A series of experimental investigations with a stringent measurement method on the fluid flow characteristics of slot jet without or with a target surface have been successfully conducted. From all the fluid velocity data measured in the present study, the experimental conditions have been verified to be spanwise-symmetrically maintained and the results have been achieved in a spanwise-symmetric form. Three types of jet configuration without or with target surface are investigated: (A) Confined Slot Jet without Target Surfaces – the fluid flow parameters studied in the present investigation is the jet Reynolds number (ReD). Its ranges are ReD=506-1517. (B) Confined Slot Jet with Smooth Surfaces – the fluid flow parameters studied in the present investigation include the ratio of jet separation distance (H) to nozzle width (W) and the jet Reynolds number (ReD). The ranges of the relevant parameters are H/W=2–10 and ReD=504–1526. (C) Confined Slot Jet with Extended Surfaces – the fluid flow parameters studied include the ratio of jet separation distance (H) to nozzle width (W), the Reynolds number (ReD) and the ratio of extended surface height (Hes) to nozzle width (W). Their ranges are H/W=3–10, Hes/W=0.74-3.40 and ReD=501–1547. The flow characteristics such as the local mean streamwise velocity distribution, mean streamwise velocity decay along jet centerline, local jet turbulence intensity distribution, and turbulence intensities along jet centerline have been presented and discussed in the study.

Pulsatile Blood Flow Through a Constricted Porous Artery

2020 ◽  
Vol 17 (2) ◽  
pp. 743-749
Author(s):  
Salah Uddin ◽  
Obaid Ullah Mehmood ◽  
Mahathir Mohamad ◽  
Mahmod Abd Hakim Mohmad ◽  
D. F. Jamil ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Blood Flow ◽  
Flow Velocity ◽  
Nonlinear Differential Equations ◽  
Fluid Velocity ◽  
Volumetric Flow Rate ◽  
Physical Parameters ◽  
Porosity Parameter ◽  
Arterial Blood ◽  
Flow Through

In this paper a speculative study of an incompressible Newtonian blood flow through a constricted porous channel and pulsatile nature is inspected. Porosity parameter λ is incorporated in the momentum equation. Governing nonlinear differential equations are numerically evaluated by employing the perturbation method technique for a very small perturbation parameter ε 1 such that ε ≠ 0 and with conformable boundary conditions. Numerical results of the flow velocity profile and volumetric flow rate have been derived numerically and detailed graphical analysis for different physical parameters porosity, Reynolds number and stenosis has been presented. It is found that arterial blood velocity is dependent upon all of these factors and that the relationship of fluid velocity and flow is more complex and nonlinear than heretofore generally believe. Furthermore the flow velocity enhanced with Reynolds number, porosity parameter and at maximum position of the stenosis/constriction.

scholarly journals Laser generated Richtmyer–Meshkov instability and nonlinear wave paradigm in turbulent mixing: I. Central region of Gaussian spot

2016 ◽  
Vol 34 (4) ◽  
pp. 687-704 ◽  
Author(s):  
Stjepan Lugomer
Keyword(s):  
Flow Field ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Pressure Field ◽  
Three Dimensional ◽  
Target Surface ◽  
Kp Equation ◽  
New Paradigm ◽  
Shape Oscillations ◽  
The Individual

AbstractA three-dimensional Richtmyer–Meshkov instability (RMI) was generated on metal target by the laser pulse of Gaussian-like power profile in the semiconfined configuration (SCC). The SCC enables the extended lifetime of a hot vapor/plasma plume above the target surface as well as the fast multiple reshocks. The oscillatory pressure field of the reshocks causes strong bubble shape oscillations giving rise to the complex wave-vortex phenomena. The irregularity of the pressure field causes distortion of the shock wave front observed as deformed waves. In a random flow field the waves solidified around the bubbles form the broken “egg-karton” structure – or the large-scale chaotic web. In the coherent flow field the shape oscillations and collapse of the large bubbles generate nonlinear waves as the line- and the horseshoe-solitons. The line solitons are organized into a polygonal web, while the horseshoe solitons make either the rosette-like web or appear as the individual parabolic-like solitons. The configurations of the line solitons are juxtapositioned with solitons simulated by the Kadomtsev–Petviashvili (KP) equation. For the horseshoe solitons it was mentioned that it can be obtained by the simulation based on the cylindrical KP equation. The line and the horseshoe solitons represent the wave-vortex phenomena in which the fluid accelerated by the shock and exposed to a subsequent series of fast reshocks follows more complex scenario than in the open configuration. The RMI environment in the SCC generates complex fluid dynamics and the new paradigm of wave vortex phenomena in turbulent mixing.

CFD Simulations of Flow and Heat Transfer Through the Porous Interface of a Metal Foam Heat Exchanger

2014 ◽  
Author(s):  
Emilie Sauret ◽  
Kamel Hooman ◽  
Suvash C. Saha
Keyword(s):  
Numerical Modelling ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Metal Foam ◽  
Waste Heat ◽  
Fluid Layer ◽  
Fluid Velocity ◽  
Numerical Results ◽  
Waste Heat Recovery System ◽  
Porous Interface

This paper offers numerical modelling of a waste heat recovery system. A thin layer of metal foam is attached to a cold plate to absorb heat from hot gases leaving the system. The heat transferred from the exhaust gas is then transferred to a cold liquid flowing in a secondary loop. Two different foam PPI (Pores Per Inch) values are examined over a range of fluid velocities. Numerical results are then compared to both experimental data and theoretical results available in the literature. Challenges in getting the simulation results to match those of the experiments are addressed and discussed in detail. In particular, interface boundary conditions specified between a porous layer and a fluid layer are investigated. While physically one expects much lower fluid velocity in the pores compared to that of free flow, capturing this sharp gradient at the interface can add to the difficulties of numerical simulation. The existing models in the literature are modified by considering the pressure gradient inside and outside the foam. Comparisons against the numerical modelling are presented. Finally, based on experimentally-validated numerical results, thermo-hydraulic performance of foam heat exchangers as waste heat recovery units is discussed with the main goal of reducing the excess pressure drop and maximising the amount of heat that can be recovered from the hot gas stream.

scholarly journals CHANGING THE PARADIGM OF MODELING AND FORECASTING SOCIO-ECONOMIC SYSTEMS

2021 ◽  
Author(s):  
Svitlana Kolomiiets ◽  
Ruslan Dinits
Keyword(s):  
Differential Equations ◽  
Nonlinear Differential Equations ◽  
Economic Research ◽  
Economic Systems ◽  
Nonlinear Phenomena ◽  
New Paradigm ◽  
Evolutionary Processes ◽  
Principle Of Superposition ◽  
General Law ◽  
Modeling And Forecasting

Modern socio-economic systems demonstrate instability, chaos, and unpredictability. What methodology should be used to modeling modern socio-economic systems? Constant changes and crises in the development of socio-economic systems require new approaches to the research of these systems. The feature of the approach to the study of socio-economic systems in modern conditions is the conversion from a linear to a nonlinear paradigm. The models of socio-economic systems are systems of nonlinear differential equations. Nonlinear differential equations demonstrate different modes of functioning of complex socio-economic systems. Nonlinear equations can have several qualitatively different solutions. This explains the existence of different ways of evolution of nonlinear socio-economic systems. Nonlinearity is a fundamental position of new paradigm of cognition and development. Nonlinearity is a general law of nature and means, first of all, non-observance of the principle of superposition. The whole cannot be the sum of its parts; the result cannot be the sum of efforts, the quality of the whole is not determined by the sum of the qualities of its parts, the reaction of the system is not proportional to the influence. For nonlinear phenomena, knowledge about the behavior of a part of an object does not yet guarantee correct ideas about the behavior of the object as a whole, and its response to changes in conditions may qualitatively depend on the magnitude of these changes. Non-linearity is the multivariance of the evolutionary paths, the presence of a choice of alternative paths and determining the rate of evolution. Nonlinearity is the irreversibility of evolutionary processes; nonlinear, indirect dependence of evolutionary processes on external influences. The article examines the topical issue of changing the paradigm of modeling and forecasting socio-economic systems. The necessity of transition from linear to nonlinear paradigm in economic research is theoretically substantiated. The features of the application of methods of nonlinear dynamics to the modeling of socio-economic systems are considered. The phenomenon of nonlinearity of socio-economic systems is studied.

scholarly journals Inherent Irreversibility of Mixed Convection within Concentric Pipes in a Porous Medium with Thermal Radiation

2021 ◽  
Vol 53 (3) ◽  
pp. 395-414
Author(s):  
Oluwole Daniel Makinde ◽  
Adetayo Samuel Eegunjobi
Keyword(s):  
Porous Medium ◽  
Nusselt Number ◽  
Boundary Value Problem ◽  
Mixed Convection ◽  
Thermal Radiation ◽  
Nonlinear Differential Equations ◽  
Fluid Velocity ◽  
Entropy Generation Rate ◽  
Integration Scheme ◽  
Bejan Number

This work investigated the thermal putrefaction and inherent irreversibility in a steady flow of an incompressible inconstant viscosity radiating fluid within two concentric pipes filled with a porous medium. Following the Brinkmann-Darcy-Forchheimer approach, the nonlinear differential equations governing the model were obtained. The model boundary value problem was addressed numerically via a shooting quadrature with the Runge-Kutta-Fehlberg integration scheme. The effects of diverse emerging parameters on the fluid velocity, temperature, skin friction, Nusselt number, entropy generation rate and the Bejan number are provided in graphs and discussed in this paper.

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