Probability of Occurrence of Extreme Waves in Three Dimensional Mechanically Generated Random Wave Fields: A Comparison With Numerical Simulations

2011 ◽  
Author(s):  
A. Toffoli ◽  
S. Chai ◽  
E. M. Bitner-Gregersen ◽  
F. Pistani
Keyword(s):  
Numerical Simulations ◽  
Quantitative Estimate ◽  
Numerical Models ◽  
Modulational Instability ◽  
Three Dimensional ◽  
Random Wave ◽  
Extreme Waves ◽  
Wave Fields ◽  
Numerical Investigations ◽  
Probability Of Occurrence

Experimental and numerical investigations reveal that nonlinear modulational instability can significantly affect the probability of occurrence of extreme waves, especially if waves are sufficiently steep and narrow banded both in the frequency and directional domain. However, it is not yet completely clear whether numerical simulations can provide an accurate quantitative estimate of experimental results. Here the potential Euler equations are used to assess the ability of numerical models to describe the evolution of statistical properties of mechanically generated directional, random wave fields and in particular the evolution of the kurtosis. Results show that simulations provide a good quantitative estimate of experimental observations within a broad range of wave directional width.

Experimental and Numerical Investigations of Tractive Performance of Off-Road Tires on Gravel Terrain

2019 ◽  
Vol 17 (08) ◽  
pp. 1950055 ◽  
Author(s):  
Haiyang Zeng ◽  
Wei Xu ◽  
Mengyan Zang ◽  
Peng Yang
Keyword(s):  
Finite Element ◽  
Numerical Models ◽  
Three Dimensional ◽  
Great Influence ◽  
Coupling Method ◽  
Experimental Device ◽  
Tractive Force ◽  
3D Finite Element ◽  
Numerical Investigations ◽  
Soil Bin

In this work, an indoor soil-bin is designed to investigate the tire–terrain interaction mechanisms for the off-road tires rolling on the gravel terrain. The soil-bin test is carried out by the indoor soil-bin experimental device and the three-dimensional (3D) finite element (FE) and discrete element (DE) coupling method under the same particles conditions, respectively. First, with the indoor soil-bin measurement system, the repeatability of the soil-bin experiments is employed to validate the experimental device and the numerical models. Moreover, the tractive performance experiments of the off-road tires with two tread patterns, smooth and grooved interacting with gravel terrain, are performed at the slip of 10%, 20% and 30%, respectively, to obtain the tractive force and the rim sinkage. Second, the corresponding numerical models are also established, and simulated by the FE–DE coupling method, where the FEM and the DEM are used to describe the off-road tires and the gravel terrain, respectively. The tractive mechanisms of the off-road tires in interaction with the gravel terrain such as the tractive force and the rim sinkage are investigated numerically. Meanwhile, The dynamics and discontinuity of the gravel assembly are described by the presented approach. Besides, both the results of the simulations and experiments indicate that tread patterns and slip conditions have great influence on the tire tractive performance. Finally, the numerical simulations and the experimental results qualitatively show good agreements, which certifies the effectiveness of the FE–DE coupling method in the tractive performance analysis of tire–gravel terrain interactions.

THREE-DIMENSIONAL ASPECTS OF RE-ENTRY IN EXPERIMENTAL AND NUMERICAL MODELS OF VENTRICULAR FIBRILLATION

1999 ◽  
Vol 09 (04) ◽  
pp. 695-704 ◽  
Author(s):  
V. N. BIKTASHEV ◽  
A. V. HOLDEN ◽  
S. F. MIRONOV ◽  
A. M. PERTSOV ◽  
A. V. ZAITSEV
Keyword(s):  
Ventricular Fibrillation ◽  
Numerical Simulations ◽  
Numerical Models ◽  
Three Dimensional ◽  
Spiral Waves ◽  
Excitable Media ◽  
Ventricular Wall ◽  
Two Dimensional ◽  
Key Features ◽  
Scroll Waves

Ventricular fibrillation is believed to be produced by the breakdown of re-entrant propagation waves of excitation into multiple re-entrant sources. These re-entrant waves may be idealized as spiral waves in two-dimensional, and scroll waves in three-dimensional excitable media. Optically monitored, simultaneously recorded endocardial and epicardial patterns of activation on the ventricular wall do not always show spiral waves. We show that numerical simulations, even with a simple homogeneous excitable medium, can reproduce the key features of the simultaneous endo- and epicardial visualizations of propagating activity, and so these recordings may be interpreted in terms of scroll waves within the ventricular wall.

Extreme Waves in Sea States Crossing an Oblique Current

2010 ◽  
Author(s):  
A. Toffoli ◽  
A. V. Babanin ◽  
F. Ardhuin ◽  
M. Benoit ◽  
E. M. Bitner-Gregersen ◽  
...  
Keyword(s):  
Nonlinear Dynamics ◽  
Gravity Waves ◽  
Laboratory Experiments ◽  
Random Wave ◽  
Extreme Waves ◽  
Regular Waves ◽  
Wave Fields ◽  
Surface Gravity Waves ◽  
Directional Wave ◽  
A Current

Laboratory experiments have been carried out in the directional wave tank at Marintek (Norway) to study the nonlinear dynamics of surface gravity waves and the occurrence of extreme events, when the wave field traverses obliquely an ambient current. A condition of partial opposition has been considered. Tests on regular waves have shown that the current can trigger the formation of large amplitude waves. In random wave fields, however, this only results in a weak deviation from the statistical properties observed in absence of a current.

Sediment transport and bed evolution in a 180∘ curved channel with lateral intake: Numerical simulations using Eulerian and Discrete Phase models

2020 ◽  
Vol 31 (08) ◽  
pp. 2050113
Author(s):  
H. Montaseri ◽  
K. Tavakoli ◽  
S. Evangelista ◽  
P. Omidvar
Keyword(s):  
Sediment Transport ◽  
Numerical Simulations ◽  
Numerical Models ◽  
Three Dimensional ◽  
Secondary Flows ◽  
The Other ◽  
Discrete Phase Model ◽  
Two Phase ◽  
Bed Topography ◽  
Discrete Phase

Lateral intakes are hydraulic structures used for domestic, agricultural and industrial water conveyance, characterized by a very complex three-dimensional morphodynamic behavior: since streamlines near the lateral intake are deflected, some vortices form, pressure gradient, shear and centrifugal forces at the intake generate flow separation and a secondary movement, responsible for local scour and sediment deposition. On the other side, the modeling of flows, besides the sediment transport, in curved channels implies some more complications in comparison with straight channels. In this research, this complex process has been investigated experimentally and numerically, with the mechanism of sediment transport, bed topography evolution, flow pattern and their interactions. Experiments were performed in the Laboratory of Tarbiat Modares University, Iran, where a U-shaped channel with a lateral intake was installed and dry sediment was injected at constant rate into a steady flow. Due to the spiral flow, the bed topography changes significantly and the bed forms in turn affect the sediment entering the intake. Different from the previous works on this topic which were mainly based on laboratory experiments, here, Computational Fluid Dynamics (CFD) numerical simulations with FLUENT software were also performed, specifically with the two-phase Eulerian Model (EM) and Discrete Phase Model (DPM), at the aim of evaluating their performance in reproducing the observed physical processes. This software is used for a large variety of CFD problems, but not much for simulating sediment transport phenomena and bed topography evolution. The comparison of the results obtained through the two models against the laboratory experimental data proved a good performance of both the models in reproducing the main features of the flow, for example, the longitudinal and vertical streamlines and the mechanism of particles movement. However, the EM reveals a better performance than DPM in the prediction of the secondary flows and, consequently, of the bed topography evolution, whereas the DPM well depicts the particles pattern, predicts the location of trapped particles and determines the percentage of sediment entering the intake. The numerical models so calibrated and validated were applied to other cases with different positions of the intake in the bend. The results show that mechanism of sediment entrance into the intake varies in different position. If the intake is installed in the second half of the bend, the sediment accumulates along the inner bank of the bend and enters the intake from downstream edge of intake; on the other side, if it is placed in the first half of the bend, the sediment accumulates along both the inner and the outer bends and, therefore, more sediment enters the intake. Also the results of the simulations performed with the DPM model for different positions of the lateral intake show that for all discharge ratios, the position of 120∘ is the one which guarantees the minimum ratio of sediment diverted to the intake (Gr).

scholarly journals Occurrence of extreme waves in three-dimensional mechanically generated wave fields propagating over an oblique current

2011 ◽  
Vol 11 (3) ◽  
pp. 895-903 ◽  
Author(s):  
A. Toffoli ◽  
L. Cavaleri ◽  
A. V. Babanin ◽  
M. Benoit ◽  
E. M. Bitner-Gregersen ◽  
...  
Keyword(s):  
Modulational Instability ◽  
Three Dimensional ◽  
Wave Direction ◽  
Subsequent Increase ◽  
Wave Fields ◽  
Wave Trains ◽  
Directional Wave ◽  
The Mean ◽  
Wave Maker ◽  
Non Gaussian

Abstract. Laboratory experiments were performed to study the dynamics of three- dimensional mechanically generated waves propagating over an oblique current in partial opposition. The flow velocity varied along the mean wave direction of propagation with an increasing trend between the wave-maker and the centre of the tank. Tests with regular wave packets traversing the area of positive current gradient showed that the concurrent increase of wave steepness triggered modulational instability on otherwise stable wave trains and hence induced the development of very large amplitude waves. In random directional wave fields, the presence of the oblique current resulted in a weak reinforcement of wave instability with a subsequent increase of the probability of occurrence of extreme events. This seems to partially compensate the suppression of strongly non-Gaussian properties due to directional energy distribution.

scholarly journals Approach to the numerical modelling of the chip temperatures in single grain scratching

2021 ◽  
Author(s):  
Thomas Bergs ◽  
Jannik Röttger ◽  
Sebastian Barth ◽  
Sebastian Prinz
Keyword(s):  
Experimental Validation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Sufficient Accuracy ◽  
Experimental Investigations ◽  
Fe Model ◽  
Numerical Investigations ◽  
Physical Mechanisms ◽  
Fundamental Understanding ◽  
Single Grain

AbstractTo achieve a fundamental understanding of the physical mechanisms and the heat generation in the contact zone during grinding, a large number of experimental and numerical investigations have been carried out to analyse the interaction of single grain and workpiece. Existing numerical models of the interaction between grain and workpiece do not represent the reality and especially the influence of the three-dimensional grain geometry on the temperatures during single grain scratching with sufficient accuracy. An experimental validation of the simulated temperatures has not been carried out yet as there is no appropriate method to measure them in experimental investigations. In this study, a three-dimensional FE-model of the interaction between CBN-grain and workpiece (100Cr6) in the grinding process is presented. The model predicts the chip temperatures for real grain geometries to investigate the interactions between grain and workpiece. The experiments to validate the model were carried out using a ratio pyrometer.

Modulational Instability in Directional Wave Fields, and Extreme Wave Events

2011 ◽  
Author(s):  
Alexander V. Babanin ◽  
Takuji Waseda ◽  
Igor Shugan ◽  
Hwung-Hweng Hwung
Keyword(s):  
Modulational Instability ◽  
Wave Train ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Wave Fields ◽  
Linear Evolution ◽  
Individual Wave ◽  
Wave Trains ◽  
Directional Wave

The paper is based on review of research articles by the authors, with the purpose to demonstrate that the modulational-instability mechanism is active in typical directional wave fields. If so, possible limits for the wave height due to such mechanism can be outlined. The modulational instability can lead to occurrence of very high waves, which either proceed to the breaking or appear as rogue events, but it was derived for and is usually associated with two-dimensional wave trains. There exists argument, both analytical and experimental, that this kind of instability is impaired or even suppressed in three-dimensional (directional) wave systems. The first part of the paper demonstrates indirect experimental evidences which relate the wave breaking in oceanic conditions to features of two-dimensional breaking waves due to modulational instability. The second section is dedicated to direct measurements of such instability-caused breaking in a directional wave tank with directional spread and mean steepness typical of those in the field. The last section provides conclusions on what is maximal height of an individual wave, depending on the mean wave steepness in a wave train/field, that can be achieved due to such non-linear evolution of wave trains.

Passive scalar transport by travelling wave fields

2000 ◽  
Vol 420 ◽  
pp. 147-200 ◽  
Author(s):  
PETER B. WEICHMAN ◽  
ROMAN E. GLAZMAN
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Diffusion Tensor ◽  
Numerical Models ◽  
Diffusion Constant ◽  
Spatial Inhomogeneity ◽  
General Nature ◽  
Random Wave ◽  
Climate Modelling ◽  
Wave Fields

We study turbulent transport of passive tracers by random wave fields of a rather general nature. A formalism allowing for spatial inhomogeneity and anisotropy of an underlying velocity field (such as that caused by a latitudinally varying Coriolis parameter) is developed, with the aim of treating problems of large-scale ocean transport by long internal waves. For the special case of surface gravity waves on deep water, our results agree with the earlier theory of Herterich & Hasselmann (1982), though even in that case we discover additional, off-diagonal elements of the diffusion tensor emerging in the presence of a mean drift. An advective diffusion equation including all components of the diffusion tensor D plus a mean, Stokes-type drift u is derived and applied to the case of baroclinic inertia–gravity (BIG) waves. This application is of particular interest for ocean circulation and climate modelling, as the mean drift, according to our estimates, is comparable to ocean interior currents. Furthermore, while on the largest (100 km and greater) scales, wave-induced diffusion is found to be generally small compared to classical eddy-induced diffusion, the two become comparable on scales below 10 km. These scales are near the present limit on the spatial resolution of eddy-resolving ocean numerical models. Since we find that uz and Dzz vanish identically, net vertical transport is absent in wave systems of this type. However, for anisotropic wave spectra the diffusion tensor can have non-zero off-diagonal vertical elements, Dxz and Dyz, and it is shown that their presence leads to non-positive definiteness of D, and a negative diffusion constant is found along a particular principal axis. However, the simultaneous presence of a depth-dependent mean horizontal drift u(z) eliminates any potential unphysical behaviour.

scholarly journals Numerical Investigations of Shape Memory Alloy Fatigue

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1558
Author(s):  
Vanderson M. Dornelas ◽  
Sergio A. Oliveira ◽  
Marcelo A. Savi ◽  
Pedro Manuel Calas Lopes Pacheco
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Numerical Simulations ◽  
Shape Memory ◽  
Three Dimensional ◽  
Macroscopic Model ◽  
Maximum Temperature ◽  
Structural Fatigue ◽  
Numerical Investigations ◽  
Cyclic Degradation

This work deals with numerical investigations of the functional and structural fatigue on shape memory alloys (SMAs). A thermodynamically consistent, three-dimensional constitutive model is employed, adopting a continuum damage perspective. Fatigue life is predicted by considering a macroscopic model. Numerical simulations are compared with experimental data taken from the literature to demonstrate the model’s ability to capture the general thermomechanical behavior of SMAs subjected to different loading conditions. Uniaxial and torsion tests are discussed; thermal loads are also analyzed considering the influence of the maximum temperature on the fatigue life of SMAs. Cyclic degradation of the shape memory effect is investigated in the sequence. Results show that numerical simulations are in good agreement with the experimental data, including the fatigue life estimation.

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