scholarly journals Dynamical transitions during the collapse of inertial holes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jiakai Lu ◽  
Carlos M Corvalan
Keyword(s):  
High Fidelity ◽  
Fluid Viscosity ◽  
Governing Equations ◽  
Fluid Films ◽  
Small Viscosity ◽  
Dynamical Regimes ◽  
Capillary Collapse ◽  
Fundamental Physical ◽  
Practical Implications ◽  
Scaling Arguments

Abstract At the center of a collapsing hole lies a singularity, a point of infinite curvature where the governing equations break down. It is a topic of fundamental physical interest to clarify the dynamics of fluids approaching such singularities. Here, we use scaling arguments supported by high-fidelity simulations to analyze the dynamics of an axisymmetric hole undergoing capillary collapse in a fluid sheet of small viscosity. We characterize the transitions between the different dynamical regimes —from the initial inviscid dynamics that dominate the collapse at early times to the final Stokes dynamics that dominate near the singularity— and demonstrate that the crossover hole radii for these transitions are related to the fluid viscosity by power-law relationships. The findings have practical implications for the integrity of perforated fluid films, such as bubble films and biological membranes, as well as fundamental implications for the physics of fluids converging to a singularity.

“Never the first time on a patient”: the stakes of high-fidelity simulation for safety training

2018 ◽  
Vol 32 (5) ◽  
pp. 23-25 ◽  
Author(s):  
Lucie Cuvelier
Keyword(s):  
Case Studies ◽  
Design Methodology ◽  
Reading Time ◽  
Safety Training ◽  
High Fidelity ◽  
High Fidelity Simulation ◽  
Content Type ◽  
Pertinent Information ◽  
First Time ◽  
Practical Implications

Purpose This paper aims to review the latest management developments across the globe and pinpoint practical implications from cutting-edge research and case studies. Design/methodology/approach This briefing is prepared by an independent writer who adds their own impartial comments and places the articles in context. Findings An operative approach is described that is designed to structure the debriefing along three axes. Practical implications The paper provides strategic insights and practical thinking that have influenced some of the world’s leading organizations. Originality/value The briefing saves busy executives and researchers hours of reading time by selecting only the very best, most pertinent information and presenting it in a condensed and easy-to-digest format.

Viscoelectric Effect on the Electroosmotic Flow in Nanochannels With Heterogeneous Zeta Potentials

2018 ◽  
Author(s):  
Edson M. Jimenez ◽  
Federico Méndez ◽  
Juan P. Escandón
Keyword(s):  
Electroosmotic Flow ◽  
Fluid Velocity ◽  
Volumetric Flow Rate ◽  
Mass Conservation ◽  
Double Layers ◽  
Fluid Viscosity ◽  
Governing Equations ◽  
Flat Plates ◽  
Zeta Potentials ◽  
Poisson Boltzmann

In the present work, we realize a study about the influence of viscoelectric effect on the electroosmotic flow of Newtonian fluids in nanochannels formed by two parallel flat plates. In the problem, the channel walls have heterogeneous zeta potentials which follow a sinusoidal distribution; moreover, viscoelectric effects appear into the electric double layers when high zeta potentials are considered at the channel walls, modifying the fluid viscosity and the fluid velocity. To find the solution of flow field, the modified Poisson-Boltzmann, mass conservation and momentum governing equations, are solved numerically. In the results, combined effects from the zeta potential heterogeneities and viscosity changes yields different kind of flow recirculations controlled by the dephasing angle, amplitude and number of waves of the heterogeneities at the walls. The viscoelectric effect produces a decrease in the magnitude of velocity profiles and volumetric flow rate when the high zeta potentials are magnified. Additionally, the heterogeneous zeta potentials at the walls generate an induced pressure on the flow. This investigation extend the knowledge of electroosmotic flows under field effects for future mixing applications.

STUDY ON THE EFFECT OF VISCOSITY AND COMPRESSIBILITY ON ICE ACCRETION

2009 ◽  
Vol 23 (03) ◽  
pp. 481-484 ◽  
Author(s):  
CHENGXIANG ZHU ◽  
CHUNLING ZHU ◽  
BIN FU
Keyword(s):  
Flow Field ◽  
Numerical Method ◽  
Fluid Viscosity ◽  
Ice Accretion ◽  
Governing Equations ◽  
Different Parts

Ice accretion on aircraft is studied by a numerical method. By solving governing equations, the flow field is obtained for analyzing the icing zone and calculating the ice quantity on different parts. Influence of the fluid viscosity and compressibility on icing characters is extensively studied. And it can be found that the results agree well with those calculated by LEWICE program. This achievement could be helpful to further research on ice accretion.

Assessment centers vs situational judgment tests: longitudinal predictors of success

2016 ◽  
Vol 37 (7) ◽  
pp. 899-911 ◽  
Author(s):  
Carrie A. Blair ◽  
Brian J. Hoffman ◽  
Robert T. Ladd
Keyword(s):  
Career Success ◽  
High Fidelity ◽  
Assessment Centers ◽  
Situational Judgment Test ◽  
Situational Judgment ◽  
Situational Judgment Tests ◽  
Content Type ◽  
General Mental Ability ◽  
Utility Company ◽  
Practical Implications

Purpose The purpose of this paper is to provide an empirical comparison of a high-fidelity managerial simulation, assessment center (AC) ratings, to that of a lower fidelity managerial simulation, a video situational judgment test (SJT) in the prediction of manager career success. Design/methodology/approach Archival data were collected from a large utility company. A measure of general mental ability (GMA), an SJT, and an AC were examined as predictors of career success as measured by increases in salary. Findings The AC and the video SJT used in this study appeared to assess different constructs, extending previous findings that ACs and written SJTs measure distinct constructs. Furthermore, the AC dimensions and the SJT remained valid predictors of salary over a six year span following the test administration. In addition, the AC explained significant incremental variance beyond GMA and SJTs in career success six years after the assessment. Research limitations/implications The SJTs and AC used in this study are similar in psychological fidelity, yet the ACs remained a more valid predictor over time. The recommendation is that lower fidelity simulations should not be used as prerequisites for higher fidelity simulations. Practical implications The results lend general support to the value of high-fidelity instruments in predicting longitudinal success. Originality/value The paper offers a comparison of the validity of ACs and video SJTs.

Chaos in small-amplitude surface gravity waves over slowly varying bathymetry

1991 ◽  
Vol 227 ◽  
pp. 35-46 ◽  
Author(s):  
Michael G. Brown ◽  
Frederick D. Tappert ◽  
Sekhar E. R. B. Sundaram
Keyword(s):  
Gravity Waves ◽  
Small Amplitude ◽  
Equations Of Motion ◽  
Approximate Solutions ◽  
Surface Gravity ◽  
Governing Equations ◽  
Surface Gravity Waves ◽  
Extreme Sensitivity ◽  
Ray Trajectories ◽  
Practical Implications

We consider the motion of small-amplitude surface gravity waves over variable bathymetry. Although the governing equations of motion are linear, for general bathymetric variations they are non-separable and cannot be solved exactly. For slowly varying bathymetry, however, approximate solutions based on geometric (ray) techniques may be used. The ray equations are a set of coupled nonlinear ordinary differential equations with Hamiltonian form. It is argued that for general bathymetric variations, solutions to these equations - ray trajectories - should exhibit chaotic motion, i.e. extreme sensitivity to initial and environmental conditions. These ideas are illustrated using a simple model of bottom bathymetry, h(x,y) = h0(1 + εcos (2πx/L) cos (2πy/L)). The expectation of chaotic ray trajectories is confirmed via the construction of Poincaré sections and the calculation of Lyapunov exponents. The complexity of chaotic geometric wavefields is illustrated by considering the temporal evolution of (mostly) chaotic wavecrests. Some practical implications of chaotic ray trajectories are discussed.

scholarly journals Empennage sizing with the tail volume complemented with a method for dorsal fin layout

2021 ◽  
Vol 13 (3) ◽  
pp. 149-164
Author(s):  
Dieter SCHOLZ
Keyword(s):  
Statistical Method ◽  
Aircraft Design ◽  
Statistical Correlation ◽  
High Fidelity ◽  
Weak Correlation ◽  
Starting Values ◽  
Dorsal Fin ◽  
Lever Arm ◽  
Volume Coefficient ◽  
Practical Implications

Purpose: Provide good values for the tail volume coefficient and the lever arm as a percentage of the fuselage length. Provide a statistical method for dorsal fin layout. – Methodology: Based on an understanding of flight physics, the statistical correlation of real aircraft parameters is investigated. This is based on the firm conviction that high fidelity parameters for future aircraft need a checked against parameters of existing successful aircraft. – Findings: Typical tail volume coefficients are between 0.5 and 1.0 for the horizontal tail and between 0.03 and 0.08 for the vertical tail depending on aircraft category. Empennage statistics have clear trends. The often weak correlation shows that aircraft design allows for sufficient designer's choice. Only a minority of aircraft feature a dorsal fin. Designers see it as an added surface rather than as part of the vertical tail. It is used to limit the hypothetical risk of vertical tail stall due to high sideslip angles. – Research Limitations: Results obtained from statistics are close to reality, but not a proof to fulfill requirements. – Practical Implications: Methods from the paper can be used for quick initial sizing of a vertical tail with or without dorsal fin or sizing of a horizontal tail. These results can also be used as good starting values for optimization tools in aircraft design. – Originality: Estimation of the tail lever arm is necessary for sizing with the tail volume coefficient, but had not been investigated to any detail. A method for the layout of dorsal fins was missing.

Comparative study of multicomponent Lattice Boltzmann models for binary mixture flows

2021 ◽  
Author(s):  
M. Ho ◽  
S. Ammar ◽  
S. Leclaire ◽  
M. Reggio ◽  
J.-Y. Trépanier
Keyword(s):  
Binary Mixture ◽  
Lattice Boltzmann ◽  
Stokes Equations ◽  
Numerical Study ◽  
Flow Behavior ◽  
Fluid Viscosity ◽  
Incompressible Limit ◽  
Governing Equations ◽  
Mixture Flow ◽  
Pure Diffusion

Two lattice Boltzmann method (LBM) models for binary mixture flows are numerically compared. The first model solves the Navier–Stokes equations within the incompressible limit and considers the mixture as one single fluid. A multi relaxation time (MRT) collision operator tunes the fluid diffusivity independently of the fluid viscosity. The second model emerges from a different theoretical derivation of the kinetic theory, where the governing equations are recovered for each species of the mixture. A source term in the LBM defines the interspecies friction force and couples the species of the mixture. A pure diffusion flow and a 2D plane Poiseuille binary mixture flow verify both models in the incompressible limit where diffusive and viscous transport occurs. The influence of molecular mass ratio, dynamic viscosity ratio, and Schmidt number on species and mixture flow behavior is investigated. The numerical results show good agreement against their respective analytical solutions and capture the deviation between the velocity profiles according to the flow regime. The present numerical study underlines the difference between the models as a function of the flow regimes which was observed from the macroscopic governing equations.

Viscoelastic Effects on the Stability of Thin-Film Parallel Flow in Lubrication Applications

2000 ◽  
Author(s):  
Avraham Harnoy ◽  
Laksh. Shridhar ◽  
John Tavantzis
Keyword(s):  
Flow Instability ◽  
Hydrodynamic Lubrication ◽  
Fluid Model ◽  
Viscous Friction ◽  
Relaxation Effect ◽  
Parallel Flow ◽  
Fluid Viscosity ◽  
Fluid Films ◽  
Fluid Elasticity ◽  
The Stability

Abstract The analysis is concerned with the effect of fluid-elasticity on the stability of laminar parallel flow. The widely used multi-grade oils contain polymer additives that make them viscoelastic. These oils are widely used for high shear-rate laminar flow of hydrodynamic lubrication, where flow instability is undesirable because it significantly increases the viscous friction losses. A fluid model is applied where the stress-relaxation effect is considered in addition to the fluid viscosity. However, the normal stresses are disregarded. Extended Orr-Sommerfeld type analysis has been performed for elastic fluid films of lubrication. The conclusion is that the elasticity of the fluid has a destabilizing effect. For parallel flow, the transition to instability is at lower Reynolds number in comparison to Newtonian fluids.

Experimental study on penny-shaped fluid-driven cracks in an elastic matrix

2015 ◽  
Vol 471 (2182) ◽  
pp. 20150255 ◽  
Author(s):  
Ching-Yao Lai ◽  
Zhong Zheng ◽  
Emilie Dressaire ◽  
Jason S. Wexler ◽  
Howard A. Stone
Keyword(s):  
Elastic Matrix ◽  
Laboratory Model ◽  
Fluid Viscosity ◽  
Gelatin Matrix ◽  
Crack Shape ◽  
Elastic Stresses ◽  
Surrounding Matrix ◽  
Injection Flow ◽  
The Matrix ◽  
Scaling Arguments

When a pressurized fluid is injected into an elastic matrix, the fluid generates a fracture that grows along a plane and forms a fluid-filled disc-like shape. We report a laboratory study of such a fluid-driven crack in a gelatin matrix, study the crack shape as a function of time and investigate the influence of different experimental parameters such as the injection flow rate, Young’s modulus of the matrix and fluid viscosity. We choose parameters so that effects of material toughness are small. We find that the crack radius R ( t ) increases with time t according to t α with α =0.48±0.04. The rescaled experimental data at long times for different parameters collapse based on scaling arguments, available in the literature, showing R ( t )∝ t 4/9 from a balance of viscous stresses from flow along the crack and elastic stresses in the surrounding matrix. Also, we measure the time evolution of the crack shape, which has not been studied before. The rescaled crack shapes collapse at longer times and show good agreement with the scaling arguments. The gelatin system provides a useful laboratory model for further studies of fluid-driven cracks, which has important applications such as hydraulic fracturing.

Thermal radiation and buoyancy effects on MHD free convective heat generating flow over an accelerating permeable surface with temperature-dependent viscosity

2001 ◽  
Vol 79 (4) ◽  
pp. 725-732 ◽  
Author(s):  
M A Seddeek
Keyword(s):  
Thermal Radiation ◽  
Shooting Method ◽  
Skin Friction Coefficient ◽  
Permeable Surface ◽  
Fluid Viscosity ◽  
Governing Equations ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Thermal Buoyancy ◽  
Dependent Viscosity

The paper presents a study of the flow of a viscous incompressible fluid over an accelerating permeable surface with temperature-dependent viscosity, taking into account the effect of thermal radiation and thermal buoyancy in the presence of a magnetic field. The fluid viscosity is assumed to vary as an inverse linear function of temperature. The governing equations for laminar free convection of fluid are changed to dimensionless ordinary differential equations by similarity transformation. They are solved by a shooting method. The effects of various parameters on the velocity and temperature profiles as well as the skin friction coefficient and wall heat transfer are presented graphically and in tabulated form. PACS Nos.: 47.65ta, 52.30–q

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