Air entrapment by a falling water mass

1995 ◽  
Vol 294 ◽  
pp. 181-207 ◽  
Author(s):  
Hasan N. Oguz ◽  
Andrea Prosperetti ◽  
Ali R. Kolaini
Keyword(s):  
High Speed ◽  
Water Mass ◽  
Boundary Integral ◽  
Surface Shape ◽  
Water Tank ◽  
Air Entrapment ◽  
Free Surface Shape ◽  
Large Water ◽  
The Impact ◽  
Good Agreement

The impact of a nearly cylindrical water mass on a water surface is studied both experimentally and theoretically. The experiments consist of the rapid release of water from the bottom of a cylindrical container suspended above a large water tank and of the recording of the free-surface shape of the resulting crater with a high-speed camera. A bubble with a diameter of about twice that of the initial cylinder remains entrapped at the bottom of the crater when the aspect ratio and the energy of the falling water mass are sufficiently large. Many of the salient features of the phenomenon are explained on the basis of simple physical arguments. Boundary-integral potential-flow simulations of the process are also described. These numerical results are in fair to good agreement with the observations.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

scholarly journals The impact on global magnetohydrodynamic simulations from varying initialisation methods: results from GUMICS-4

2017 ◽  
Vol 35 (4) ◽  
pp. 907-922 ◽  
Author(s):  
Antti Lakka ◽  
Tuija I. Pulkkinen ◽  
Andrew P. Dimmock ◽  
Adnane Osmane ◽  
Ilja Honkonen ◽  
...  
Keyword(s):  
High Speed ◽  
Synthetic Data ◽  
Constant Density ◽  
Satellite Measurements ◽  
Wind Measurements ◽  
Sinusoidal Functions ◽  
Magnetohydrodynamic Simulations ◽  
The Impact ◽  
Different Parts ◽  
Good Agreement

Abstract. We investigate the effects of different initialisation methods of the GUMICS-4 global magnetohydrodynamic (MHD) simulation to the dynamics in different parts of the Earth's magnetosphere and hence compare five 12 h simulation runs that were initiated by 3 h of synthetic data and followed by 9 h of solar wind measurements using the OMNI data as input. As a reference, we use a simulation run that includes nearly 60 h of OMNI data as input prior to the 9 h interval examined with different initialisations. The selected interval is a high-speed stream event during a 10-day interval (12–22 June 2007). The synthetic initialisations include stepwise, linear and sinusoidal functions of the interplanetary magnetic field with constant density and velocity values. The results show that the solutions converge within 1 h to give a good agreement in both the bow shock and the magnetopause position. However, the different initialisation methods lead to local differences which should be taken into consideration when comparing model results to satellite measurements.

Experimental Investigation of the Green Water Loads on a Wave-Piercing Tumblehome Ship

2017 ◽  
Author(s):  
Hui Li ◽  
Bao-Li Deng ◽  
Shu-Zheng Sun ◽  
Wen-Lei Du ◽  
Hao-Dong Zhao
Keyword(s):  
Experimental Investigation ◽  
High Speed ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Green Water ◽  
Strong Nonlinearity ◽  
Water Tank ◽  
Water Tank Experiment ◽  
The Impact ◽  
Ship Speed

This paper presents the results of an experimental investigation of green water loads on a wave-piercing tumblehome ship. A water tank experiment was carried out in head regular waves by using a self-propelling segmented ship model. Wave probes and pressure sensors were arranged on the bow deck along the longitudinal and transverse directions. The height of water and the impact pressure on the deck were measured and their distributions in different wave conditions studied. The motion of the water flowing on the deck was recorded by a high-speed video system. Based on the experimental results, it was found that the green water is more serious with the increase of incident wave height and ship speed. The bow shape has little effects on the occurrence of green water, but it influences the green water loads to some extent. The distribution of green water pressure is different from that of green water height due to the strong nonlinearity of green water pressure.

scholarly journals Growth and instability of the liquid rim in the crown splash regime

2014 ◽  
Vol 752 ◽  
pp. 485-496 ◽  
Author(s):  
G. Agbaglah ◽  
R. D. Deegan
Keyword(s):  
Thin Film ◽  
High Speed ◽  
Unstable Mode ◽  
Linear Stability Theory ◽  
Scaling Relations ◽  
X Ray ◽  
X Ray Imaging ◽  
Secondary Droplets ◽  
The Impact ◽  
Good Agreement

AbstractWe study the formation, growth and disintegration of jets following the impact of a drop on a thin film of the same liquid for $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{We}<1000$ and $\mathit{Re}<2000$ using a combination of numerical simulations and linear stability theory (Agbaglah, Josserand & Zaleski, Phys. Fluids, vol. 25, 2013, 022103). Our simulations faithfully capture this phenomena and are in good agreement with experimental profiles obtained from high-speed X-ray imaging. We obtain scaling relations from our simulations and use these as inputs to our stability analysis. The resulting predictions for the most unstable wavelength are in excellent agreement with experimental data. Our calculations show that the dominant destabilizing mechanism is a competition between capillarity and inertia but that deceleration of the rim provides an additional boost to growth. We also predict over the entire parameter range of our study the number and timescale for formation of secondary droplets formed during a splash, based on the assumption that the most unstable mode sets the droplet number.

Impact of artificial monolayer application on stored water quality at the air–water interface

2015 ◽  
Vol 72 (7) ◽  
pp. 1250-1256 ◽  
Author(s):  
P. Pittaway ◽  
V. Martínez-Alvarez ◽  
N. Hancock ◽  
B. Gallego-Elvira
Keyword(s):  
Water Quality ◽  
Oxygen Demand ◽  
Cost Effective ◽  
Subsurface Water ◽  
Water Tank ◽  
Water Interface ◽  
Field Investigations ◽  
Air Water Interface ◽  
Large Water ◽  
The Impact

Evaporation mitigation has the potential to significantly improve water use efficiency, with repeat applications of artificial monolayer formulations the most cost-effective strategy for large water storages. Field investigations of the impact of artificial monolayers on water quality have been limited by wind and wave turbulence, and beaching. Two suspended covers differing in permeability to wind and light were used to attenuate wind turbulence, to favour the maintenance of a condensed monolayer at the air/water interface of a 10 m diameter tank. An octadecanol formulation was applied twice-weekly to one of two covered tanks, while a third clean water tank remained uncovered for the 14-week duration of the trial. Microlayer and subsurface water samples were extracted once a week to distinguish impacts associated with the installation of covers, from the impact of prolonged monolayer application. The monolayer was selectively toxic to some phytoplankton, but the toxicity of hydrocarbons leaching from a replacement liner had a greater impact. Monolayer application did not increase water temperature, humified dissolved organic matter, or the biochemical oxygen demand, and did not reduce dissolved oxygen. The impact of an octadecanol monolayer on water quality and the microlayer may not be as detrimental as previously considered.

Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces

2015 ◽  
Author(s):  
Bulent Guzel ◽  
Fatih C. Korkmaz
Keyword(s):  
Experimental Investigation ◽  
Flow Separation ◽  
High Speed ◽  
Water Entry ◽  
Air Entrapment ◽  
Hydrophobic Surfaces ◽  
Blunt Bodies ◽  
Drop Tests ◽  
Set Up ◽  
The Impact

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces. In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.

The role of ‘splashing’ in the collapse of a laser-generated cavity near a rigid boundary

1999 ◽  
Vol 380 ◽  
pp. 339-361 ◽  
Author(s):  
R. P. TONG ◽  
W. P. SCHIFFERS ◽  
S. J. SHAW ◽  
J. R. BLAKE ◽  
D. C. EMMONY
Keyword(s):  
High Speed ◽  
Vital Role ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Liquid Jet ◽  
Rigid Boundary ◽  
Jet Impact ◽  
Pressure Peak ◽  
Peak Pressures ◽  
The Impact

Vapour cavities in liquid flows have long been associated with cavitation damage to nearby solid surfaces and it is thought that the final stage of collapse, when a high- speed liquid jet threads the cavity, plays a vital role in this process. The present study investigates this aspect of the motion of laser-generated cavities in a quiescent liquid when the distance (or stand-off) of the point of inception from a rigid boundary is between 0.8 and 1.2 times the maximum radius of the cavity. Numerical simulations using a boundary integral method with an incompressible liquid impact model provide a framework for the interpretation of the experimental results. It is observed that, within the given interval of the stand-off parameter, the peak pressures measured on the boundary at the first collapse of a cavity attain a local minimum, while at the same time there is an increase in the duration of the pressure pulse. This contrasts with a monotonic increase in the peak pressures as the stand-off is reduced, when the cavity inception point is outside the stated interval. This phenomenon is shown to be due to a splash effect which follows the impact of the liquid jet. Three cases are chosen to typify the splash interaction with the free surface of the collapsing cavity: (i) surface reconnection around the liquid jet; (ii) splash impact at the base of the liquid jet; (iii) thin film splash. Hydrodynamic pressures generated following splash impact are found to be much greater than those produced by the jet impact. The combination of splash impact and the emission of shock waves, together with the subsequent re-expansion, drives the flow around the toroidal cavity producing a distinctive double pressure peak.

scholarly journals Generation and breakup of Worthington jets after cavity collapse. Part 1. Jet formation

2010 ◽  
Vol 663 ◽  
pp. 293-330 ◽  
Author(s):  
STEPHAN GEKLE ◽  
J. M. GORDILLO
Keyword(s):  
Flow Structure ◽  
High Speed ◽  
Liquid Surface ◽  
Circular Disk ◽  
Boundary Integral ◽  
Analytical Modelling ◽  
Acceleration Region ◽  
Jet Formation ◽  
Cavity Collapse ◽  
The Impact

At the beginning of the last century Worthington and Cole discovered that the high-speed jets ejected after the impact of an axisymmetric solid on a liquid surface are intimately related to the formation and collapse of an air cavity created in the wake of the impactor. In this paper, we combine detailed boundary-integral simulations with analytical modelling to describe the formation of such Worthington jets after the impact of a circular disk on water. We extend our earlier model in Gekle et al. (Phys. Rev. Lett., vol. 102, 2009a, 034502), valid for describing only the jet base dynamics, to describe the whole jet. We find that the flow structure inside the jet may be divided into three different regions: the axial acceleration region, where the radial momentum of the incoming liquid is converted to axial momentum; the ballistic region, where fluid particles experience no further acceleration and move constantly with the velocity obtained at the end of the acceleration region; and the jet tip region, where the jet eventually breaks into droplets. From our modelling of the ballistic region we conclude that, contrary to the case of other physical situations where high-speed jets are also ejected, the types of Worthington jets studied here cannot be described using the theory of hyperbolic jets of Longuet-Higgins (J. Fluid Mech., vol. 127, 1983, p. 103). Most importantly, we find that the velocity and the shape of the ejected jets can be well predicted at any instant in time with the only knowledge of quantities obtained before pinch-off occurs. This fact allows us to provide closed expressions for the jet velocity and the sizes of the ejected droplets as a function of the velocity and the size of the impactor. We show that our results are also applicable to Worthington jets emerging after the collapse of a bubble growing from an underwater nozzle, although this system creates thicker jets than the disk impact.

scholarly journals Experimental And Numerical Study Of Single And Multiple Imapcts Of Angular particles On Ductile Metals

2021 ◽  
Author(s):  
Mahdi Takaffoli
Keyword(s):  
Solid Particle ◽  
High Speed ◽  
Numerical Study ◽  
Solid Particle Erosion ◽  
Fe Model ◽  
Particle Erosion ◽  
Erosion Mechanisms ◽  
The Impact ◽  
Good Agreement ◽  
Angular Particles

Solid particle erosion occurs when small high speed particles impact surfaces. It can be either destructive such as in the erosion of oil pipelines by corrosion byproducts, or constructive such as in abrasive jet machining processes. Two dimensional finite element (FE) models of single rhomboid particles impact on a copper target were developed using two different techniques to deal with the problem of element distortion: (i) element deletion, and (ii) remeshing. It was found that the chip formation and the material pile-up, two phenomena that cannot be simulated using a previously developed rigid-plastic model, could be simulated using the FE models, resulting in a good agreement with experiments performed using a gas gun. However, remeshing in conjunction with a failure model caused numerical instabilities. The element deletion approach also induced errors in mass loss due to the removal of distorted elements. To address the limitations of the FE approach, smoothed particle hydrodynamics (SPH) which can better accommodate large deformations, was used in the simulation of the impact of single rhomboid particles on an aluminum alloy target. With appropriate constitutive and failure parameters, SPH was demonstrated to be suitable for simulating all of the relevant damage phenomena observed during impact experiments. A new methodology was developed for generating realistic three dimensional particle geometries based on measurements of the size and shape parameter distributions for a sample of 150 µm nominal diameter angular aluminum oxide powder. The FE models of these generated particles were implemented in a SPH/FE model to simulate non-overlapping particle impacts. It was shown that the simulated particles produced distributions of crater and crater lip dimensions that agreed well with those measured from particle blasting experiments. Finally, a numerical model for simulating overlapping impacts of angular particles was developed and compared to experimental multi-particle erosion tests, with good agreement. An investigation of the simulated trajectory of the impacting particles revealed various erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off crater lips which were consistent with previously noted ductile solid particle erosion mechanisms in the literature.

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