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

2010 ◽  
Author(s):  
Jingbo Wang ◽  
Odd M. Faltinsen
Keyword(s):  
Free Surface ◽  
Boundary Element ◽  
High Speed ◽  
Surface Profile ◽  
Water Entry ◽  
Similarity Solutions ◽  
Surface Flow ◽  
Boundary Element Methods ◽  
Cavity Formation ◽  
Air Cavity

In this paper, a nonlinear boundary element method is developed for investigating the air cavity formation during the high speed water entry of wedges. A novel technique is introduced to remove the saw-tooth instability of the free surface profile, which is often encountered in solving violent free surface flow problems by boundary element methods. This technique applies to both the equally spaced grids and the non-equally spaced grids, and is demonstrated to be quite efficient and practical by numerical simulations. When the flow reaches the knuckle of the wedge, separation will occur. The authors develop a purely numerical method to simulate the non-viscous flow separation. This nonlinear BEM has been verified by comparisons with similarity solutions. We also compare the numerical results with experimental results.

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 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.

Validation of Open-Source SPH Code DualSPHysics for Numerical Simulations of Water Entry and Exit of a Rigid Body

2017 ◽  
Author(s):  
Sergei K. Buruchenko ◽  
Ricardo B. Canelas
Keyword(s):  
Free Surface ◽  
Rigid Body ◽  
Stokes Equations ◽  
Offshore Structures ◽  
Water Entry ◽  
Surface Flow ◽  
Rigid Body Dynamics ◽  
Structural Safety ◽  
Entry And Exit ◽  
Momentum Exchange

Water entry and exit of a body is an important topic in naval hydrodynamics as these phenomena play relevant roles both for offshore structures and vessels. Water entry and exit events are intrinsically transient and represent intense topological changes in the system, with large amounts of momentum exchange between phases. At its onset, they can be characterized by highly localized, both in space and time, loads on the vessel, influencing both the local structural safety of the structure and the global loads acting on it. The DualSPHysics code is proposed as a numerical tool for the simulation of fluid and floating object interaction. The numerical model is based on a Smoothed Particle Hydrodynamics discretization of the Navier-Stokes equations and Newton’s equations for rigid body dynamics. This paper examines the water impact, fluid motions, and movement of objects in the conventional case studies of object entry and exit from still water. A two dimensional body drop analysis was carried out demonstrating acceptable agreement of the movement of the object with published experimental and numerical results. The velocity field of the fluid is also captured and analyzed. Simulations for water entry and exit of a buoyant and neutral density cylinder compares well with previous experimental, numerical, and empirical studies in penetration, free surface evolution and object kinematics. These results provide a good foundation to evaluate the accuracy and stability of the DualSPHysics implementation for modeling the interaction between free surface flow and free moving floating objects.

scholarly journals SPH Open Boundary Simulation of Free-Surface Flow Over Ogee-crested Spillway

2021 ◽  
Vol 28 (2) ◽  
pp. 137-151
Author(s):  
Rizgar Karim ◽  
Jowhar Mohammad
Keyword(s):  
Free Surface ◽  
Open Source ◽  
Water Surface ◽  
Surface Profile ◽  
Free Surface Flow ◽  
The United States ◽  
Surface Flow ◽  
Absolute Difference ◽  
Open Boundary ◽  
Water Surface Profile

This study was conducted to compare water surface profiles with standard ogeecrested spillways. Different methods were used, such as (experimental models, numerical models, and design nomographs for the United States Army Corps of Engineers, USACE). In accordance with the USACE specifications, three different models were constructed from rigid foam and then installed in a testing flume. The water surface profile has been recorded for these models with different design heads. For modeling the experimental model configurations, a numerical model based on the smoothed particle hydrodynamics (SPH) technique was used and is developed to simulate the water surface profile of the flow over the ogee-crested spillway. A 2D SPHysics open-source software has been used in this study, using the SPH formulation to model fluid flow, developing the SPH boundary procedure to handle open-boundary simulations, and modifying the open-source SPHysics code for this purpose. The maximum absolute difference between the measured and computed results of the water surface profile for all head ratios of (H/Hd), does not exceed 4.63% at the crest region, the numerical results for the water surface profile showed good agreement with the physical model results. The results obtained experimentally and numerically by SPH are compared with the CFD results in order to be more reassuring from the results. Additional comparisons were made using interpolated data from USACE, Waterways Experiment Station (WES), and design nomographs. The SPH technique is considered very promising and effective for free surface flow applications.

Numerical analysis of high-speed liquid lithium free-surface flow

2012 ◽  
Vol 87 (5-6) ◽  
pp. 569-574 ◽  
Author(s):  
Sergej Gordeev ◽  
Volker Heinzel ◽  
Robert Stieglitz
Keyword(s):  
Free Surface ◽  
Numerical Analysis ◽  
High Speed ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Liquid Lithium

scholarly journals STUDY ON WATER ENTRY PROBLEM USING A LEVEL-SET IMMERSED BOUNDARY METHOD

2014 ◽  
Vol 34 ◽  
pp. 1460376
Author(s):  
WEI BAI ◽  
CHENGZHONG HUO
Keyword(s):  
Free Surface ◽  
Level Set ◽  
Immersed Boundary Method ◽  
Surface Profile ◽  
Water Entry ◽  
Navier Stokes ◽  
Immersed Boundary ◽  
Interface Evolution ◽  
Boundary Method ◽  
Moving Bodies

Water entry of a solid through the free surface is a persisting field of research in ship hydrodynamics applications. Indeed, the knowledge of pressure forces acting on structures is necessary to ensure the verification of safety criteria in the design and operation. However, in water entry problems, jets can be generated, thus an effective numerical model is needed to capture this complicated breaking water surface. In this paper, the level set method is adopted, which has been shown to be capable of capturing interface evolution when the topological change of shape is extremely large, or merging, breaking and pinching occur. Moreover, the incorporation of an immersed boundary method with this free surface capture scheme implemented in a Navier-Stokes solver allows the interaction between fluid flow with free surface and moving bodies of almost arbitrary shape to be modeled. The developed Level-Set Immersed Boundary Method is applied to simulate the water entry of a rectangular body with different velocities into the still water. The complicated surface profile, velocity field and pressure are obtained. The simulation is also carried out for the same body exiting the water, and some preliminary results are presented.

Optical Observation of the Supercavitation Induced by High-Speed Water Entry

2000 ◽  
Vol 122 (4) ◽  
pp. 806-810 ◽  
Author(s):  
Hong-Hui Shi ◽  
Motoyuki Itoh ◽  
Takuya Takami
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Shock Waves ◽  
High Speed ◽  
Bubbly Flow ◽  
Water Entry ◽  
Gas Pressure ◽  
Optical Observation ◽  
Water Tank ◽  
Experimental Facility

When a high-speed projectile penetrates into water, a cavity is formed behind the projectile. The gas enclosed in the cavity experiences a nonequilibrium process, i.e., the gas pressure decreases as the projectile moves more deeply into water. As a result, the cavity is sealed near the free surface (surface closure) and subsequently the cavity breaks up in water (deep closure). Accompanying the break-up of the cavity, secondary shock waves appear. This is the so-called supercavitation in water entry. This paper describes an experimental investigation into the water entry phenomenon. Projectiles of 342 m/s were generated from a small-bore rifle that was fixed vertically in the experimental facility. The projectiles were fired into a windowed water tank. A shadowgraph optical observation was performed to observe the entry process of the projectile and the formation and collapse of the cavity behind the projectile. A number of interesting observations relating to the motion of the free surface, the splash, the underwater bubbly flow and so on were found. [S0098-2202(00)00204-2]

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