Cavity ripple dynamics after pinch-off

2018 ◽  
Vol 850 ◽  
pp. 611-623 ◽  
Author(s):  
Jean-François Louf ◽  
Brian Chang ◽  
Javad Eshraghi ◽  
Austin Mituniewicz ◽  
Pavlos P. Vlachos ◽  
...  
Keyword(s):  
Impact Velocity ◽  
Water Entry ◽  
Pressure Variation ◽  
Acoustic Model ◽  
Force Amplitude ◽  
Air Cavity ◽  
Ripple Formation ◽  
Ripple Amplitude ◽  
Measured Force

During water entry, a projectile can entrain an air cavity that trails behind it. Most previous studies focus on the formation and pinch-off dynamics of the air cavity, but only a few have investigated the long-term cavity dynamics after pinch-off. In this study, we examine the ripple formation following the pinch-off of an air cavity generated by a cone, with different cone angles and impact velocities. The amplitude and wavelength of these ripples are measured, and the force on the cone is experimentally determined. It was observed that the ripple amplitude and wavelength increase linearly with the cone impact velocity, which is predicted by our acoustic model of the compressible air cavity. In addition, the measured force exhibits distinct amplitudes and wavelengths. By measuring the length of the cavity, the resulting pressure variation was averaged inside the air cavity leading to a theoretical force amplitude, which matched our observations. We noted that the force wavelength also follows the same acoustic model, which agrees very well with the wavelength of the ripples.

Long Term Dynamics of Water-Entry Cavity

2010 ◽  
Author(s):  
Roderick R. La Foy ◽  
Sunghwan Jung ◽  
Pavlos Vlachos
Keyword(s):  
Surface Tension ◽  
Internal Pressure ◽  
Potential Flow ◽  
Water Entry ◽  
Cavity Volume ◽  
Fluid Interface ◽  
Simple Analysis ◽  
Liquid Pressure ◽  
Air Cavity

Many engineering applications involve the motion of objects crossing a fluid interface. The dynamics of this process are often complicated due to the interplay of surface tension, gravity, and inertia. Nevertheless, a simple analysis using potential flow theory works well to predict the interfacial profile of the air cavity formed during an impact. Most current theories however, cannot predict the behavior of the air cavity after pinch off occurs. We therefore investigated the long term dynamics of water entry in both experiment and theory. It was found that shortly after pinch off the cavity dynamics become governed primarily by thermodynamic gas relations. The internal pressure slowly rises due to the cavity volume decreasing while the ambient liquid pressure quickly increases as a result of the descent of the projectile. This effect is incorporated into our model to correctly predict the cavity geometry.

Modification of water entry (xylem vessels) and water exit (stomata) orchestrates long term drought acclimation of wheat leaves

2011 ◽  
Vol 347 (1-2) ◽  
pp. 179-193 ◽  
Author(s):  
Panagiota Bresta ◽  
Dimosthenis Nikolopoulos ◽  
Garifalia Economou ◽  
Petros Vahamidis ◽  
Dionyssia Lyra ◽  
...  
Keyword(s):  
Water Entry ◽  
Drought Acclimation ◽  
Wheat Leaves ◽  
Water Exit

Water Entry of a Wedge by Hydroelastic Orthotropic Plate Theory

1999 ◽  
Vol 43 (03) ◽  
pp. 180-193 ◽  
Author(s):  
Odd M. Faltinsen
Keyword(s):  
Impact Velocity ◽  
Cross Sections ◽  
Orthotropic Plate ◽  
Plate Theory ◽  
Three Dimensional ◽  
Water Entry ◽  
Natural Period ◽  
Cross Sectional ◽  
Flow Effects ◽  
The Impact

Water entry of a hull with wedge-shaped cross sections is analyzed. The stiffened platings between two transverse girders on each side of the keel are separately modeled. Orthotropic plate theory is used. The effect of structural vibrations on the fluid flow is incorporated by solving the two-dimensional Laplace equation in the cross-sectional fluid domain by a generalized Wagner's theory. The coupling with the plate theory provides three-dimensional flow effects. The theory is validated by comparison with full-scale experiments and drop tests. The importance of global ship accelerations is pointed out. Hydrodynamic and structural error sources are discussed. Systematic studies on the importance of hydroelasticity as a function of deadrise angle and impact velocity are presented. This can be related to the ratio between the wetting time of the structure and the greatest wet natural period of the stiffened plating. This ratio is proportional to the deadrise angle and inversely proportional to the impact velocity. A small ratio-means that hydroelasticity is important and a large ratio means that hydroelasticity is not important.

scholarly journals The Hydrodynamics of High Diving

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 73
Author(s):  
Thibault Guillet ◽  
Mélanie Mouchet ◽  
Jérémy Belayachi ◽  
Sarah Fay ◽  
David Colturi ◽  
...  
Keyword(s):  
Water Surface ◽  
High Speed ◽  
Water Entry ◽  
Air Cavity ◽  
Initial Height

Diving consists of jumping into water from a platform, usually while performing acrobatics. During high diving competitions, the initial height reaches 27 m. From this height, the crossing of the water surface occurs at 85 km/h, and as such it is very technical to avoid injuries. Major risks occur due to the violent impact at the water entry and the formation and collapse of the air cavity around the diver. In this study, we investigate experimentally the dynamics of the jumper underwater and the hydrodynamic causes of injuries in high dives by monitoring dives from different heights with high-speed cameras and accelerometers in order to understand the physics underlying diving.

Slam induced loads on a 3D bow with various pitch angles

2019 ◽  
pp. 1-18 ◽  
Author(s):  
Yiwen Wang ◽  
Weiguo Wu ◽  
Shan Wang ◽  
Carlos Guedes Soares
Keyword(s):  
Impact Velocity ◽  
Pitch Angle ◽  
Water Entry ◽  
Model Tests ◽  
Experimental Measurements ◽  
Pressure Distributions ◽  
Slamming Load

Abstract A 3D water entry of a typical bow model of River-to-Sea ship is studied experimentally. A large number of systematic experiments have been performed for the bow model with different pitch angles. Considering various pitch angles and impact velocities in the model tests, the slamming pressure distributions on the bottom of the bow are presented and discussed. The measured slamming pressures on the bow are identified in terms of the maximum slamming coefficient. The effects of the pitch angle and impact velocity on slamming pressure are discussed as well, based on the experimental measurements. It is shown that the slamming load on the bottom of the model increases as the pitch angle decreases in most cases. With a higher impact velocity, the coefficient of the maximum slamming pressure is smaller for most of the tested cases.

Numerical Investigation of Air Cavity Formation During the High-Speed Vertical Water Entry of Wedges

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Jingbo Wang ◽  
Odd M. Faltinsen
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Nonlinear Boundary ◽  
Water Entry ◽  
Similarity Solutions ◽  
Free Surface Flows ◽  
Cavity Formation ◽  
Air Cavity ◽  
Numerical Instabilities ◽  
Entry Velocity

In this paper, a nonlinear boundary element method (BEM) is developed for investigating air cavity formation during the high-speed water entry of wedges. A technique is proposed for dynamic re-gridding of free surface boundaries. This technique applies to both equally and nonequally spaced grids, and it is able to suppress the numerical instabilities encountered using a BEM for simulating free surface flows. The authors also develop a purely numerical method to simulate nonviscous flow separation, which occurs when the flow reaches the knuckle of the wedge. The present nonlinear BEM has been verified by comparisons with similarity solutions. We also compare numerical results with experimental results. Finally, we give a numerical prediction of the evolution of the cavity until the closure of the cavity, and the influence of the initial entry velocity, wedge mass, and deadrise angle on the characteristics of the transient cavities is investigated.

scholarly journals Unsteady forces on spheres during free-surface water entry

2012 ◽  
Vol 704 ◽  
pp. 173-210 ◽  
Author(s):  
Tadd T. Truscott ◽  
Brenden P. Epps ◽  
Alexandra H. Techet
Keyword(s):  
Free Surface ◽  
Surface Water ◽  
High Speed ◽  
Accurate Determination ◽  
Water Entry ◽  
High Speed Imaging ◽  
Air Cavity ◽  
Unsteady Forces ◽  
Unsteady Force ◽  
Low Mass

AbstractWe present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments.

scholarly journals Parametric Study on the Free-Fall Water Entry of a Sphere by Using the RANS Method

2019 ◽  
Vol 7 (5) ◽  
pp. 122
Author(s):  
Pengyao Yu ◽  
Cong Shen ◽  
Chunbo Zhen ◽  
Haoyun Tang ◽  
Tianlin Wang
Keyword(s):  
Impact Velocity ◽  
Impact Force ◽  
Free Fall ◽  
Water Entry ◽  
Time Step ◽  
Measuring Device ◽  
Mesh Density ◽  
The Impact ◽  
Peak Value ◽  
Rans Method

Motivated by the application of water-entry problems in the air-drop deployment of a spherical oceanographic measuring device, the free-fall water entry of a sphere was numerically investigated by using the transient Reynolds-averaged Navier–Stokes (RANS) method. A convergence study was carried out, which accounts for the mesh density and time-step independence. The present model was validated by the comparison of non-dimensional impact force with previous experimental and numerical results. Effects of parameters, such as impact velocity, radius, and mass of the sphere on the impact force and the acceleration of the sphere, are discussed. It is found that the peak value of the non-dimensional impact force is independent of the impact velocity and the radius of the sphere, while it depends on the mass of the sphere. By fitting the relationship between the peak value of the non-dimensional impact force and the non-dimensional mass, simplified formulas for the prediction of peak values of the impact force and the acceleration were achieved, which will be useful in the design of the spherical oceanographic measuring device.

Slam Induced Loads on a 3D Bow With Various Pitch Angles

2016 ◽  
Author(s):  
Yiwen Wang ◽  
Weiguo Wu ◽  
C. Guedes Soares
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Impact Velocity ◽  
Pitch Angle ◽  
Water Entry ◽  
Experimental Measurements ◽  
Numerical Predictions ◽  
Element Method

A 3D water entry of a typical bow model of sea-river link ship is studied using both experimental measurements and numerical predictions. A large number of systematic experiments have been performed with different pitch angles. The slamming process is simulated through finite element method with LS-DYNA. The distribution and magnitude of slam induced loads is determined from experiments and is calculated. The effect of the pitch angle and impact velocity is discussed based on the comparison between the predicted results and the experiments values.

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