ON THE APPLICATION OF A NOVEL ALGORITHM TO HYDRODYNAMIC DIFFUSION AND VELOCITY FLUCTUATIONS IN SEDIMENTING SYSTEMS

1996 ◽  
Vol 07 (04) ◽  
pp. 543-561 ◽  
Author(s):  
WOLFGANG KALTHOFF ◽  
STEFAN SCHWARZER ◽  
GERALD RISTOW ◽  
HANS J. HERRMANN
Keyword(s):  
Numerical Simulations ◽  
Numerical Method ◽  
Incompressible Fluids ◽  
Strong Anisotropy ◽  
Velocity Fluctuations ◽  
Drag Forces ◽  
Large Numbers ◽  
Spatial Dimensions ◽  
Experimental Findings ◽  
Novel Algorithm

We present a numerical method to deal efficiently with large numbers of particles in incompressible fluids. The interactions between particles and fluid are taken into account by a physically motivated ansatz based on locally defined drag forces. We demonstrate the validity of our approach by performing numerical simulations of sedimenting non-Brownian spheres in two spatial dimensions and compare our results with experiments. Our method reproduces qualitatively important aspects of the experimental findings, in particular the strong anisotropy of the hydrodynamic bulk self-diffusivities.

scholarly journals Lagrangian controllability of inviscid incompressible fluids: a constructive approach

2017 ◽  
Vol 23 (3) ◽  
pp. 1179-1200
Author(s):  
Thierry Horsin ◽  
Otared Kavian
Keyword(s):  
Numerical Simulations ◽  
Euler Equation ◽  
Approximate Controllability ◽  
Holomorphic Functions ◽  
Rational Functions ◽  
Incompressible Fluids ◽  
Constructive Method ◽  
Constructive Approach ◽  
Density Result

We present here a constructive method of Lagrangian approximate controllability for the Euler equation. We emphasize on different options that could be used for numerical recipes: either, in the case of a bi-dimensionnal fluid, the use of formal computations in the framework of explicit Runge approximations of holomorphic functions by rational functions, or an approach based on the study of the range of an operator by showing a density result. For this last insight in view of numerical simulations in progress, we analyze through a simplified problem the observed instabilities.

The transient start of supersonic jets

2007 ◽  
Vol 578 ◽  
pp. 331-369 ◽  
Author(s):  
MATEI I. RADULESCU ◽  
CHUNG K. LAW
Keyword(s):  
Numerical Simulations ◽  
Ambient Air ◽  
Hydrogen Gas ◽  
Shock Interactions ◽  
Round Jets ◽  
Reactive Gases ◽  
Acoustic Instabilities ◽  
Diffusive Fluxes ◽  
Experimental Findings ◽  
Good Agreement

This study investigates the initial transient hydrodynamic evolution of highly under-expanded slit and round jets. A closed-form analytic similarity solution is derived for the temporal evolution of temperature, pressure and density at the jet head for vanishing diffusive fluxes, generalizing a previous model of Chekmarev using Chernyi's boundary-layer method for hypersonic flows. Two-dimensional numerical simulations were also performed to investigate the flow field during the initial stages over distances of ~ 1000 orifice radii. The parameters used in the simulations correspond to the release of pressurized hydrogen gas into ambient air, with pressure ratios varying between approximately 100 and 1000. The simulations confirm the similarity laws derived theoretically and indicate that the head of the jet is laminar at early stages, while complex acoustic instabilities are established at the sides of the jet, involving shock interactions within the vortex rings, in good agreement with previous experimental findings. Very good agreement is found between the present model, the numerical simulations and previous experimental results obtained for both slit and round jets during the transient establishment of the jet. Criteria for Rayleigh–Taylor instability of the decelerating density gradients at the jet head are also derived, as well as the formulation of a model addressing the ignition of unsteady expanding diffusive layers formed during the sudden release of reactive gases.

scholarly journals Dynamical Simulation and Statistical Analysis of Velocity Fluctuations of a Turbulent Flow behind a Cube

2007 ◽  
Vol 2007 ◽  
pp. 1-28 ◽  
Author(s):  
T. F. Oliveira ◽  
R. B. Miserda ◽  
F. R. Cunha
Keyword(s):  
Turbulent Flow ◽  
Numerical Simulations ◽  
Compressible Flows ◽  
Statistical Approach ◽  
Power Spectra ◽  
Flow Simulation ◽  
Scaling Analysis ◽  
Velocity Fluctuations ◽  
Ergodic Hypothesis ◽  
Time Average

A statistical approach for the treatment of turbulence data generated by computer simulations is presented. A model for compressible flows at large Reynolds numbers and low Mach numbers is used for simulating a backward-facing step airflow. A scaling analysis has justified the commonly used assumption that the internal energy transport due to turbulent velocity fluctuations and the work done by the pressure field are the only relevant mechanisms needed to model subgrid-scale flows. From the numerical simulations, the temporal series of velocities are collected for ten different positions in the flow domain, and are statistically treated. The statistical approach is based on probability averages of the flow quantities evaluated over several realizations of the simulated flow. We look at how long of a time average is necessary to obtain well-converged statistical results. For this end, we evaluate the mean-square difference between the time average and an ensemble average as the measure of convergence. This is an interesting question since the validity of the ergodic hypothesis is implicitly assumed in every turbulent flow simulation and its analysis. The ergodicity deviations from the numerical simulations are compared with theoretical predictions given by scaling arguments. A very good agreement is observed. Results for velocity fluctuations, normalized autocorrelation functions, power spectra, probability density distributions, as well as skewness and flatness coefficients are also presented.

Investigation of the Asymptotic Behavior of Stresses at the Tip of Wedge- and Cone-Shaped Cracks

2012 ◽  
Vol 528 ◽  
pp. 119-126
Author(s):  
T. Korepanova ◽  
V.P. Matveenko ◽  
N. Sevodina
Keyword(s):  
Asymptotic Behavior ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Numerical Method ◽  
Stress Singularity ◽  
Singular Solutions ◽  
Different Boundary Conditions ◽  
Crack Faces ◽  
Made In

Numerical method is proposed for construction of singular solutions for spatial crossing wedge-and cone-shaped cracks. The results of numerical simulations made in the study allowed us to estimate the stress singularity indices at the tip of wedge-shaped cracks for different boundary conditions on the crack faces and at the tip of crossing cone cracks. The stress singularity at the tips of cone-shaped cracks is investigated.

A Numerical Method for Penetration into Concrete Target Using SPH-Lagrange Coupling Method

2010 ◽  
Vol 163-167 ◽  
pp. 1217-1221 ◽  
Author(s):  
Xi Cheng Huang ◽  
Yi Xia Yan ◽  
Wei Zhou Zhong ◽  
Yu Ze Chen ◽  
Jian Shi Zhu
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Numerical Method ◽  
Empirical Equation ◽  
Maximum Depth ◽  
Coupling Method ◽  
Depth Of Penetration ◽  
Lagrange Method ◽  
Concrete Target

This paper demonstrates the application of both numerical simulation and empirical equation in predicting the penetration of a concrete target by an ogive-nosed projectile. The results from the experiment performed by Gran and Frew are used as a benchmark for comparison. In the numerical simulations a 3.0-caliber radius-head steel ogival-nose projectile with a mass of 47 kg is fired against cylindrical concrete target with a striking velocity of 315 m/s. In the simulation the smooth particles hydrodynamics SPH-Lagrange coupling method is applied to predict the maximum depth of penetration. For calculation of DoP and response of projectile the SPH-Lagrange method can give satisfactory results.

The Bigger, The Better? – Paleomagnetic recording fidelity of weakly interacting clusters of particles, and implications for micro-scale paleomagnetism

2021 ◽  
Author(s):  
Thomas Berndt ◽  
Chen Han ◽  
Jose Devienne
Keyword(s):  
Numerical Simulations ◽  
Recent Trend ◽  
Single Domain ◽  
Magnetic Interactions ◽  
Small Samples ◽  
Microscopic Imaging ◽  
Micro Scale ◽  
Thermoremanent Magnetization ◽  
Weakly Interacting ◽  
Large Numbers

<p>A recent trend in paleomagnetism is the study of samples of ever decreasing sizes, going down to (sub)millimeter scales and even microscopic scales, including single-silicate-crystals and meteorites. Microscopic imaging has shown that some of these micro-scale samples appear to be much closer to ideal single-domain (SD) paleomagnetic recorders than bulk rocks. Small samples with large numbers of SD particles do, however, pose the problem of magnetic interactions affecting their paleomagnetic recording fidelity. We show that clusters of particles are common in micro-scale samples and that these interactions do affect thermoremanent magnetization (TRM) acquisition. We further show through numerical simulations that such interacting clusters may be difficult to detect in traditional experiments (such as FORC diagrams), but may nonetheless lead to over- or underestimates in paleointensities.</p>

A Novel Method for Indirect Estimation of Tire Pressure

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Selim Solmaz
Keyword(s):  
Numerical Simulations ◽  
Failure Modes ◽  
Estimation Method ◽  
Multiple Models ◽  
Tire Pressure ◽  
Lateral Dynamics ◽  
Novel Method ◽  
Switching Method ◽  
Dynamics Models ◽  
Novel Algorithm

In this paper, a novel algorithm for indirect tire failure indication is described. The estimation method is based on measuring changes in the lateral dynamics behavior resulting from certain types of tire failure modes including excessive deflation or significant thread loss in a combination of tires. Given the fact that both failures will notably affect the lateral dynamics behavior, quantifying these changes constitutes the basis of the estimation method. In achieving this, multiple models and switching method are utilized based on lateral dynamics models of the vehicle that are parametrized to account for the uncertainty in tire pressure levels. The results are demonstrated using representative numerical simulations.

Theoretical and numerical structure of unstable detonations

1995 ◽  
Vol 350 (1692) ◽  
pp. 29-68 ◽  
Keyword(s):  
Numerical Simulations ◽  
Numerical Method ◽  
Recent Progress ◽  
Simplified Models ◽  
One Dimensional ◽  
Numerical Predictions ◽  
Theoretical Predictions ◽  
Linear And Nonlinear ◽  
Physical Phenomena ◽  
Insight Into

In this review, we emphasize the recent progress achieved in understanding the behaviour of unstable detonations through the interaction of theoretical, asymp­ totic, and numerical ideas. Theoretical predictions and numerical simulations for unstable one-dimensional detonations are described in detail as an important testing ground for the more complex ideas and phenomena that occur in several space dimensions. The linear and nonlinear theories for unstable detonations are generalized to several space dimensions. A new dedicated numerical method leads to better insight into the physical phenomena of unstable detonations, such as the nature of the turbulence generated in the wake of the front. Simplified models derived through asymptotics and comparisons between theoretical and numerical predictions are stressed throughout this paper.

scholarly journals Velocity statistics inside coherent vortices generated by the inverse cascade of 2-D turbulence

2016 ◽  
Vol 809 ◽  
Author(s):  
I. V. Kolokolov ◽  
V. V. Lebedev
Keyword(s):  
Velocity Profile ◽  
Structure Function ◽  
Correlation Functions ◽  
Two Dimensional ◽  
Strong Anisotropy ◽  
Velocity Fluctuations ◽  
Inverse Cascade ◽  
Velocity Statistics ◽  
Flow Fluctuations ◽  
Coherent Vortices

We analyse velocity fluctuations inside coherent vortices generated as a result of the inverse cascade in the two-dimensional (2-D) turbulence in a finite box. As we demonstrated in Kolokolov & Lebedev (Phys. Rev. E, vol. 93, 2016, 033104), the universal velocity profile, established in Laurie et al. (Phys. Rev. Lett., vol. 113, 2014, 254503), corresponds to the passive regime of the flow fluctuations. This property enables one to calculate correlation functions of the velocity fluctuations in the universal region. We present the results of the calculations that demonstrate a non-trivial scaling of the structure function. In addition the calculations reveal strong anisotropy of the structure function.

scholarly journals Coexistence of synchronization and anti-synchronization in chaotic systems

2016 ◽  
Vol 26 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Ling Ren ◽  
Rongwei Guo ◽  
Uchechukwu E. Vincent
Keyword(s):  
Numerical Simulations ◽  
Chaotic System ◽  
Chaotic Systems ◽  
Control Strategies ◽  
System Control ◽  
Slave System ◽  
Unified Chaotic System ◽  
Master System ◽  
Novel Algorithm

The coexistence of anti-synchronization and synchronization in chaotic systems is investigated. A novel algorithm is proposed to determine the variables of the master system that should anti-synchronize with corresponding variables of the slave system. Control strategies that guarantee the coexistence of synchronization and anti-synchronization in the unified chaotic system are presented; while numerical simulations are employed to validate and illustrate the effectiveness of the proposed method.

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