scholarly journals Falling styles of disks

2013 ◽  
Vol 719 ◽  
pp. 388-405 ◽  
Author(s):  
Franck Auguste ◽  
Jacques Magnaudet ◽  
David Fabre
Keyword(s):  
Complex Dynamics ◽  
Three Dimensional ◽  
Relative Magnitude ◽  
The Body ◽  
Fluid Inertia ◽  
Viscous Effects ◽  
Fluid Medium ◽  
Body Experiences ◽  
Set Up ◽  
Thin Disks

AbstractWe numerically investigate the dynamics of thin disks falling under gravity in a viscous fluid medium at rest at infinity. Varying independently the density and thickness of the disk reveals the influence of the disk aspect ratio which, contrary to previous belief, is found to be highly significant as it may completely change the route to non-vertical paths as well as the boundaries between the various path regimes. The transition from the straight vertical path to the planar fluttering regime is found to exhibit complex dynamics: a bistable behaviour of the system is detected within some parameter range and several intermediate regimes are observed in which, although the wake is unstable, the path barely deviates from vertical. By varying independently the body-to-fluid inertia ratio and the relative magnitude of inertial and viscous effects over a significant range, we set up a comprehensive map of the corresponding styles of path followed by an infinitely thin disk. We observe the four types of planar regimes already reported in experiments but also identify two additional fully three-dimensional regimes in which the body experiences a slow horizontal precession superimposed onto zigzagging or tumbling motions.

scholarly journals Path oscillations and enhanced drag of light rising spheres

2018 ◽  
Vol 841 ◽  
pp. 228-266 ◽  
Author(s):  
Franck Auguste ◽  
Jacques Magnaudet
Keyword(s):  
Density Ratio ◽  
Reynolds Numbers ◽  
Relative Magnitude ◽  
The Body ◽  
Sphere Diameter ◽  
Viscous Effects ◽  
Flow Parameters ◽  
Route To Chaos ◽  
Set Up ◽  
Equivalent Conditions

The dynamics of light spheres rising freely under buoyancy in a large expanse of viscous fluid at rest at infinity is investigated numerically. For this purpose, the computational approach developed by Mougin & Magnaudet (Intl J. Multiphase Flow, vol. 28, 2002, pp. 1837–1851) is improved to account for the instantaneous viscous loads induced by the translational and rotational sphere accelerations, which play a crucial role in the dynamics of very light spheres. A comprehensive map of the rise regimes encountered up to Reynolds numbers (based on the sphere diameter and mean rise velocity) of the order of $10^{3}$ is set up by varying independently the body-to-fluid density ratio and the relative magnitude of inertial and viscous effects in approximately 250 distinct combinations. These computations confirm or reveal the presence of several distinct periodic regions on the route to chaos, most of which only exist within a finite range of the sphere relative density and Reynolds number. The wake structure is analysed in these various regimes, evidencing the existence of markedly different shedding modes according to the style of path. The variation of the drag force with the flow parameters is also examined, revealing that only one of the styles of path specific to very light spheres yields a non-standard drag behaviour, with drag coefficients significantly larger than those measured on a fixed sphere under equivalent conditions. The outcomes of this investigation are compared with available experimental and numerical results, evidencing points of consensus and disagreement.

Direct Numerical Simulations of Planar and Cylindrical Density Currents

2005 ◽  
Vol 73 (6) ◽  
pp. 923-930 ◽  
Author(s):  
Mariano I. Cantero ◽  
S. Balachandar ◽  
Marcelo H. García ◽  
James P. Ferry
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Boussinesq Approximation ◽  
The Body ◽  
Density Current ◽  
Density Currents ◽  
Mean Flow ◽  
Viscous Effects ◽  
Spreading Velocity ◽  
Slip Boundary

The collapse of a heavy fluid column in a lighter environment is studied by direct numerical simulation of the Navier-Stokes equations using the Boussinesq approximation for small density difference. Such phenomenon occurs in many engineering and environmental problems resulting in a density current spreading over a no-slip boundary. In this work, density currents corresponding to two Grashof (Gr) numbers are investigated (105 and 1.5×106) for two very different geometrical configurations, namely, planar and cylindrical, with the goal of identifying differences and similarities in the flow structure and dynamics. The numerical model is capable of reproducing most of the two- and three-dimensional flow structures previously observed in the laboratory and in the field. Soon after the release of the heavier fluid into the quiescent environment, a density current forms exhibiting a well-defined head with a hanging nose followed by a shallower body and tail. In the case of large Gr, the flow evolves in a three-dimensional fashion featuring a pattern of lobes and clefts in the intruding front and substantial three-dimensionality in the trailing body. For the case of the lower Gr, the flow is completely two dimensional. The dynamics of the current is visualized and explained in terms of the mean flow for different phases of spreading. The initial phase, known as slumping phase, is characterized by a nearly constant spreading velocity and strong vortex shedding from the front of the current. Our numerical results show that this spreading velocity is influenced by Gr as well as the geometrical configuration. The slumping phase is followed by a decelerating phase in which the vortices move into the body of the current, pair, stretch and decay as viscous effects become important. The simulated dynamics of the flow during this phase is in very good agreement with previously reported experiments.

scholarly journals Direct numerical simulation of the autoignition of a hydrogen plume in a turbulent coflow of hot air

2013 ◽  
Vol 720 ◽  
pp. 424-456 ◽  
Author(s):  
S. G. Kerkemeier ◽  
C. N. Markides ◽  
C. E. Frouzakis ◽  
K. Boulouchos
Keyword(s):  
Complex Dynamics ◽  
Mixture Fraction ◽  
A Priori ◽  
Three Dimensional ◽  
Scalar Dissipation ◽  
Detailed Chemistry ◽  
History Of ◽  
Reactive Mixture ◽  
Set Up ◽  
Flame Sheet

AbstractThe autoignition of an axisymmetric nitrogen-diluted hydrogen plume in a turbulent coflowing stream of high-temperature air was investigated in a laboratory-scale set-up using three-dimensional numerical simulations with detailed chemistry and transport. The plume was formed by releasing the fuel from an injector with bulk velocity equal to that of the surrounding air coflow. In the ‘random spots’ regime, autoignition appeared randomly in space and time in the form of scattered localized spots from which post-ignition flamelets propagated outwards in the presence of strong advection. Autoignition spots were found to occur at a favourable mixture fraction close to the most reactive mixture fraction calculated a priori from considerations of homogeneous mixtures based on inert mixing of the fuel and oxidizer streams. The value of the favourable mixture fraction evolved in the domain subject to the effect of the scalar dissipation rate. The hydroperoxyl radical appeared as a precursor to the build-up of the radical pool and the ensuing thermal runaway at the autoignition spots. Subsequently, flamelets propagated in all directions with complex dynamics, without anchoring or forming a continuous flame sheet. These observations, as well as the frequency of and scatter in appearance of the spots, are in good agreement with experiments in a similar set-up. In agreement with experimental observations, an increase in turbulence intensity resulted in a downstream shift of autoignition. An attempt is made to understand the key processes that control the mean axial and radial locations of the spots, and are responsible for the observed scatter. The advection of the most reactive mixture through the domain, and hence the history of evolution of the developing radical pools were considered to this effect.

The Influence of Viscous Effects on the Motion of a Body Floating in Waves

1993 ◽  
Vol 115 (1) ◽  
pp. 40-45 ◽  
Author(s):  
M. J. Downie ◽  
J. M. R. Graham ◽  
X. Zheng
Keyword(s):  
Three Dimensional ◽  
Vortex Method ◽  
Inviscid Flow ◽  
The Body ◽  
Viscous Effects ◽  
Local Flow ◽  
Discrete Vortex ◽  
Outer Flow ◽  
Viscous Forces ◽  
Singularity Distribution

This paper describes a method for calculating the forces experienced by a body floating in waves, including those due to vortex shedding from its surface. The method uses a purely theoretical approach, incorporating viscous forces, for calculating the motions of the body in the frequency domain. It involves the matching of an outer inviscid flow with the local flow in the regions of flow separation on the body, which must be well defined. The outer flow is computed by a three-dimensional singularity distribution technique and the inner flow by the discrete vortex method. The technique has been applied to the prediction of the motion response of barges floating in waves. The results compare favorably with experimental data.

scholarly journals Particles, Drops, and Bubbles Moving Across Sharp Interfaces and Stratified Layers

2020 ◽  
Vol 52 (1) ◽  
pp. 61-91 ◽  
Author(s):  
Jacques Magnaudet ◽  
Matthieu J. Mercier
Keyword(s):  
Relative Magnitude ◽  
Immiscible Fluids ◽  
The Body ◽  
Body Motion ◽  
Physical Parameters ◽  
Viscous Effects ◽  
Fluid Resistance ◽  
Wide Range ◽  
Deformable Bodies ◽  
Sharp Interfaces

Rigid or deformable bodies moving through continuously stratified layers or across sharp interfaces are involved in a wide variety of geophysical and engineering applications, with both miscible and immiscible fluids. In most cases, the body moves while pulling a column of fluid, in which density and possibly viscosity differ from those of the neighboring fluid. The presence of this column usually increases the fluid resistance to the relative body motion, frequently slowing down its settling or rise in a dramatic manner. This column also exhibits specific dynamics that depend on the nature of the fluids and on the various physical parameters of the system, especially the strength of the density/viscosity stratification and the relative magnitude of inertia and viscous effects. In the miscible case, as stratification increases, the wake becomes dominated by the presence of a downstream jet, which may undergo a specific instability. In immiscible fluids, the viscosity contrast combined with capillary effects may lead to strikingly different evolutions of the column, including pinch-off followed by the formation of a drop that remains attached to the body, or a massive fragmentation phenomenon. This review discusses the flow organization and its consequences on the body motion under a wide range of conditions, as well as potentialities and limitations of available models aimed at predicting the body and column dynamics.

Scanning electron microscopy of freeze-fractured prescapular lymph node of caprine

1984 ◽  
Vol 42 ◽  
pp. 244-245
Author(s):  
O. Faroon ◽  
F. Al-Bagdadi ◽  
T. G. Snider ◽  
C. Titkemeyer
Keyword(s):  
Lymph Node ◽  
Lymph Nodes ◽  
Lymphatic System ◽  
Three Dimensional ◽  
Meat Products ◽  
The Body ◽  
Morphological Data ◽  
The World ◽  
Cellular Constituent ◽  
Scanning Electron

The lymphatic system is very important in the immunological activities of the body. Clinicians confirm the diagnosis of infectious diseases by palpating the involved cutaneous lymph node for changes in size, heat, and consistency. Clinical pathologists diagnose systemic diseases through biopsies of superficial lymph nodes. In many parts of the world the goat is considered as an important source of milk and meat products.The lymphatic system has been studied extensively. These studies lack precise information on the natural morphology of the lymph nodes and their vascular and cellular constituent. This is due to using improper technique for such studies. A few studies used the SEM, conducted by cutting the lymph node with a blade. The morphological data collected by this method are artificial and do not reflect the normal three dimensional surface of the examined area of the lymph node. SEM has been used to study the lymph vessels and lymph nodes of different animals. No information on the cutaneous lymph nodes of the goat has ever been collected using the scanning electron microscope.

scholarly journals Vibration characteristics of triple-gear-rotor system in compressed air energy storage under variable torque load

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042098705
Author(s):  
Xinran Wang ◽  
Yangli Zhu ◽  
Wen Li ◽  
Dongxu Hu ◽  
Xuehui Zhang ◽  
...  
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Element Model ◽  
Rotor System ◽  
Dynamic Responses ◽  
System Response ◽  
Rotating Speed ◽  
Torque Load ◽  
Set Up ◽  
Two Stages

This paper focuses on the effects of the off-design operation of CAES on the dynamic characteristics of the triple-gear-rotor system. A finite element model of the system is set up with unbalanced excitations, torque load excitations, and backlash which lead to variations of tooth contact status. An experiment is carried out to verify the accuracy of the mathematical model. The results show that when the system is subjected to large-scale torque load lifting at a high rotating speed, it has two stages of relatively strong periodicity when the torque load is light, and of chaotic when the torque load is heavy, with the transition between the two states being relatively quick and violent. The analysis of the three-dimensional acceleration spectrum and the meshing force shows that the variation in the meshing state and the fluctuation of the meshing force is the basic reasons for the variation in the system response with the torque load. In addition, the three rotors in the triple-gear-rotor system studied show a strong similarity in the meshing states and meshing force fluctuations, which result in the similarity in the dynamic responses of the three rotors.

Optimum Design for the Frame of Open Type Abrasive Flow Polish Machine

2012 ◽  
Vol 497 ◽  
pp. 89-93
Author(s):  
Liang Liang Yuan ◽  
Ke Hua Zhang ◽  
Li Min
Keyword(s):  
Finite Element ◽  
Natural Frequency ◽  
Finite Element Methods ◽  
Optimization Design ◽  
Low Cost ◽  
Three Dimensional ◽  
Force Model ◽  
Optimization Analysis ◽  
Open Type ◽  
Set Up

In order to process heterotype hole of workpiece precisely, an open abrasive flow polish machine is designed, and the optimization design of machine frame is done for low cost. Firstly, basing on the parameters designed with traditional ways, three-dimensional force model is set up with the soft of SolidWorks. Secondly, the statics and modal analysis for machine body have been done in Finite element methods (FEM), and then the optimization analysis of machine frame has been done. At last, the model of rebuild machine frame has been built. Result shows that the deformation angle value of machine frame increased from 0.72′ to 1.001′, the natural frequency of the machine decreased from 75.549 Hz to 62.262 Hz, the weight of machine decreased by 74.178 Kg after optimization. It meets the strength, stiffness and angel stiffness requirement of machine, reduces the weight and cost of machine.

Clinical Utility of an Exoskeleton Robot Using 3-Dimensional Scanner Modeling in Burn Patient: A Case Report

2021 ◽  
Author(s):  
So Young Joo ◽  
Seung Yeol Lee ◽  
Yoon Soo Cho ◽  
Sangho Yi ◽  
Cheong Hoon Seo
Keyword(s):  
Burn Injury ◽  
Hand Function ◽  
Three Dimensional ◽  
The Body ◽  
3D Technology ◽  
Early Management ◽  
3 Dimensional ◽  
Exoskeleton Robot ◽  
Physical Abilities ◽  
Upper Limb Dysfunction

Abstract Hands are the part of the body that are most commonly involved in burns, and the main complications are finger joint contractures and nerve injuries. Hypertrophic scarring cannot be avoided despite early management of acute hand burn injuries, and some patients may need application of an exoskeleton robot to restore hand function. To do this, it is essential to individualize the customization of the robot for each patient. Three-dimensional (3D) technology, which is widely used in the field of implants, anatomical models, and tissue fabrication, makes this goal achievable. Therefore, this report is a study on the usefulness of an exoskeleton robot using 3D technology for patients who lost bilateral hand function due to burn injury. Our subject was a 45-year-old man with upper limb dysfunction of 560 days after a flame and chemical burn injury, with resultant impairment of manual physical abilities. After wearing an exoskeleton robot made using 3D printing technology, he could handle objects effectively and satisfactorily. This innovative approach provided considerable advantages in terms of customization of size and reduction in manufacturing time and costs, thereby showing great potential for use in patients with hand dysfunction after burn injury.

scholarly journals Virtual Archaeology of Death and Burial: A Procedure for Integrating 3D Visualization and Analysis in Archaeothanatology

2021 ◽  
Vol 7 (1) ◽  
pp. 540-555
Author(s):  
Hayley L. Mickleburgh ◽  
Liv Nilsson Stutz ◽  
Harry Fokkens
Keyword(s):  
Spatial Information ◽  
3D Visualization ◽  
Rapid Development ◽  
Three Dimensional ◽  
3D Models ◽  
The Body ◽  
Test Case ◽  
Archaeology Of Death ◽  
Human Burials ◽  
3D Information

Abstract The reconstruction of past mortuary rituals and practices increasingly incorporates analysis of the taphonomic history of the grave and buried body, using the framework provided by archaeothanatology. Archaeothanatological analysis relies on interpretation of the three-dimensional (3D) relationship of bones within the grave and traditionally depends on elaborate written descriptions and two-dimensional (2D) images of the remains during excavation to capture this spatial information. With the rapid development of inexpensive 3D tools, digital replicas (3D models) are now commonly available to preserve 3D information on human burials during excavation. A procedure developed using a test case to enhance archaeothanatological analysis and improve post-excavation analysis of human burials is described. Beyond preservation of static spatial information, 3D visualization techniques can be used in archaeothanatology to reconstruct the spatial displacement of bones over time, from deposition of the body to excavation of the skeletonized remains. The purpose of the procedure is to produce 3D simulations to visualize and test archaeothanatological hypotheses, thereby augmenting traditional archaeothanatological analysis. We illustrate our approach with the reconstruction of mortuary practices and burial taphonomy of a Bell Beaker burial from the site of Oostwoud-Tuithoorn, West-Frisia, the Netherlands. This case study was selected as the test case because of its relatively complete context information. The test case shows the potential for application of the procedure to older 2D field documentation, even when the amount and detail of documentation is less than ideal.

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