Interaction Between the Underwater Explosion Bubble and the Structure

2008 ◽  
Author(s):  
A. M. Zhang ◽  
X. L. Yao ◽  
D. Y. Shi ◽  
J. Li
Keyword(s):  
Free Surface ◽  
Flat Plate ◽  
Dynamic Characteristics ◽  
Potential Flow ◽  
Underwater Explosion ◽  
Wall Pressure ◽  
Severe Damage ◽  
Plastic Structure ◽  
Pressure Peak ◽  
Great Damage

Based on the potential-flow assumption, BEM is applied to simulate the dynamic characteristics of underwater explosion bubble near boundaries and solve the interaction of bubble and elastic-plastic structure by coupling with FEM. A complete 3D program of underwater bubble analysis (UBA) is developed and the calculated error is within 10%. With this program, flat plate, cylinder and other simple structures are analyzed; the damages caused by retarded flow, pulsating pressure and jet and other loads on the structures are calculated, including different cases with free surface or without free surface. Results show that bubbles can cause great damage, and the specific cases can even cause greater damage. From the wall pressure and the stress curves of typical elements on the structure, it can be seen that the pressure peak occurs when the bubble collapses, which proves that the pressures caused by the bubble’s collapse and jet can result in great structure’s severe damage. It can provide reference for the research on the dynamic characteristics. The research in this paper aims to provide references for the correlated research on the dynamics of the underwater bubble.

Explicit Coupling Methods in Hydrodynamic Impacts

2005 ◽  
Author(s):  
N. Aquelet ◽  
M. Souli
Keyword(s):  
Free Surface ◽  
Penalty Method ◽  
Underwater Explosion ◽  
Industrial Applications ◽  
Local Pressure ◽  
Oil Platforms ◽  
Coupling Methods ◽  
Eulerian Formulation ◽  
Pressure Peak ◽  
Industrial Designers

The purpose of this paper is to study and compare two finite element coupling methods to simulate the problem of a body penetrating a free surface. The hydrodynamic impact problem concerns industrial designers in shipbuilding domain. In rough seas, sometimes ships suffer local damages from large water impact loads called slamming impacts. In the framework of a collaboration with a french research company in shipbuilding (Principia Marine) a numerical prediction of the local impulse load on a wedge striking a free surface is investigated by using two methods: penalty and Lagrange multiplier formulations. These methods of coupling, which makes it possible to transmit the efforts in pressure from the Eulerian formulation to the Lagrangian formulation and conversely are relatively recent algorithmic developments. The Euler/Lagrange penalty method was successfully used in many scientific and industrial applications: the modeling of the attack of birds on the fuselage of a Jet for the Boeing Corporation, the underwater explosion shaking the oil platforms, the airbag simulation... The explicit coupling based on multiplier approach is a new development, which is compared to the penalty method. For both methods, a parametric study of the local pressure peak is investigated for impact angles from 0 to 30 degrees.

Research on the Bubble Motion near Free Surface in Underwater Explosion

2011 ◽  
Vol 52-54 ◽  
pp. 1086-1091
Author(s):  
Jian Li ◽  
Ji Li Rong ◽  
Da Lin Xiang
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Energy Equation ◽  
Equations Of Motion ◽  
Underwater Explosion ◽  
Engineering Calculation ◽  
Bubble Motion ◽  
Hamilton Principle ◽  
Time Histories ◽  
Theory Research

A model for a moderately deep underwater explosion bubble was developed in inviscid and irrotational fluid. Considering the effects of gravity, buoyancy, drag to the motion of bubble, the equations of motion (EOM) for bubble in inviscid and irrotational fluid near a free surface were established by introducing the potential-flow theory, energy equation and Hamilton principle. The displacement of the center of bubble, the radius-time histories and impulse periods of bubble were acquired by solving the EOM. The calculated results were compared with the experimental and numerical results. The compared results show that the former is consistent with the latter. The research has value to correlative theory research and engineering calculation.

Linear and non-linear potential-flow calculations of free-surface waves with lift and induced drag

2000 ◽  
Vol 214 (6) ◽  
pp. 801-812
Author(s):  
C-E Janson
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Lift Force ◽  
Radiation Condition ◽  
Linear Potential ◽  
Surface Boundary ◽  
Model Approximation ◽  
Non Linear ◽  
Lifting Surfaces ◽  
The Waves

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.

On the choice of CFD codes in the design process of planing sailing yachts

2009 ◽  
Author(s):  
Jérémie Raymond ◽  
Jean-Marie Finot ◽  
Jean-Michel Kobus ◽  
Gérard Delhommeau ◽  
Patrick Queutey ◽  
...  
Keyword(s):  
Free Surface ◽  
Design Process ◽  
Finite Differences ◽  
Potential Flow ◽  
Surface Condition ◽  
Cpu Time ◽  
Free Surface Condition ◽  
Finite Differences Method ◽  
Non Linear ◽  
Ranse Solver

The discussion is based on results gathered during the first two years of a 3 years research program for the benefits of Groupe Finot-Conq, Naval Architects. The introduction presents the objectives of the program: Setting up a practical method using numerical and experimental available tools to design fast planing sailing yachts. The aim of this paper is to compare advantages and disadvantages of four different kinds of CFD codes which are linear and non-linear potential flow approach, RANSE solver using finite differences method and RANSE solver using volume of fluid method. The Fluid Mechanics Laboratory of the Ecole Centrale de Nantes (France) has developed those three approaches so those homemade codes will be used for this study. The first one is REVA, a potential flow code with a linearised free surface condition. ICARE is a RANSE solver using finite differences method with a non linear free surface condition. It is extensively used for industrial projects as for sailing yachts projects (ACC for example). ISIS-CFD is a RANSE solver using finite volume method to build the spatial discretization of the transport equations with unstructured mesh. The latter is able to compute sprays for fast planing ships but is also the slower in terms of CPU time. In addition, we had the opportunity to test FS-FLOW which is a potential flow code with a non linear free surface condition distributed by FRIENDSHIP CONSULTING. Numerical results for the four codes are compared with the other codes' results as with tank tests data. Those tank tests were made using captive model test technique on two Open60' models. Reasons of the choice of the captive model technique are explained and experimental procedures are briefly described. Comparisons between codes are mainly based on the easiness of use, the cost in CPU time and the confidence we can have in the results as a function of the boat speed. Flow visualizations, pressure maps, free surface deformation are shown and compared. Analysis of local quantities integrated or by zone is also presented. Results are analyzed focusing on the ability of each code to represent flow dynamics for every speed with a special attention to high speeds. The practical question raised is to know which kind of answers each code can bring in terms of tendencies evaluation or sensitivity to hull geometry modifications. The main goal is to be able to judge if those codes are able to make reliable and consistent comparisons of different designs. Conclusion is that none of the codes is perfect and gather all the advantages. It is still difficult to propose a definitive methodology to estimate hydrodynamic performances at every speed and at every stage of the design process. Knowing each code limitations, it appears more coherent to use each of them at different stages of the design process: the quickest and less reliable to understand the main tendencies and the longest and more precise to validate the final options.

scholarly journals A Lab-Scale Experiment Approach to the Measurement of Wall Pressure from Near-Field under Water Explosions by a Hopkinson Bar

2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Xiongwei Cui ◽  
Xiongliang Yao ◽  
Yingyu Chen
Keyword(s):  
Shock Wave ◽  
Near Field ◽  
Underwater Explosion ◽  
Experimental System ◽  
Hopkinson Bar ◽  
Wall Pressure ◽  
Pressure Loading ◽  
Target Plate ◽  
Wave Pressure ◽  
Shock Wave Pressure

Direct measurement of the wall pressure loading subjected to the near-field underwater explosion is of great difficulty. In this article, an improved methodology and a lab-scale experimental system are proposed and manufactured to assess the wall pressure loading. In the methodology, a Hopkinson bar (HPB), used as the sensing element, is inserted through the hole drilled on the target plate and the bar’s end face lies flush with the loaded face of the target plate to detect and record the pressure loading. Furthermore, two improvements have been made on this methodology to measure the wall pressure loading from a near-field underwater explosion. The first one is some waterproof units added to make it suitable for the underwater environment. The second one is a hard rubber cylinder placed at the distal end, and a pair of ropes taped on the HPB is used to pull the HPB against the cylinder hard to ensure the HPB’s end face flushes with loaded face of the target plate during the bubble collapse. To validate the pressure measurement technique based on the HPB, an underwater explosion between two parallelly mounted circular target plates is used as the validating system. Based on the assumption that the shock wave pressure profiles at the two points on the two plates which are symmetrical to each other about the middle plane of symmetry are the same, it was found that the pressure obtained by the HPB was in excellent agreement with pressure transducer measurements, thus validating the proposed technique. To verify the capability of this improved methodology and experimental system, a series of minicharge underwater explosion experiments are conducted. From the recorded pressure-time profiles coupled with the underwater explosion evolution images captured by the HSV camera, the shock wave pressure loading and bubble-jet pressure loadings are captured in detail at 5  mm, 10  mm, …, 30  mm stand-off distances. Part of the pressure loading of the experiment at 35  mm stand-off distance is recorded, which is still of great help and significance for engineers. Especially, the peak pressure of the shock wave is captured.

Pressure and velocity measurements of an incompressible moderate Reynolds number jet interacting with a tangential flat plate

2015 ◽  
Vol 770 ◽  
pp. 247-272 ◽  
Author(s):  
A. Di Marco ◽  
M. Mancinelli ◽  
R. Camussi
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Scaling Laws ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Theoretical Modelling ◽  
Wall Pressure Fluctuations ◽  
Moderate Reynolds Number ◽  
The Mean ◽  
Pressure And Velocity Measurements

The statistical properties of wall pressure fluctuations generated on a rigid flat plate by a tangential incompressible single stream jet are investigated experimentally. The study is carried out at moderate Reynolds number and for different distances between the nozzle axis and the flat plate. The overall aerodynamic behaviour is described through hot wire anemometer measurements, providing the effect of the plate on the mean and fluctuating velocity. The pressure field acting on the flat plate was measured by cavity-mounted microphones, providing point-wise pressure signals in the stream-wise and span-wise directions. Statistics of the wall pressure fluctuations are determined in terms of time-domain and Fourier-domain quantities and a parametric analysis is conducted in terms of the main geometrical length scales. Possible scaling laws of auto-spectra and coherence functions are presented and implications for theoretical modelling are discussed.

Surface Ship Total Resistance Prediction Based on a Nonlinear Free Surface Potential Flow Solver and a Reynolds-Averaged Navier-Stokes Viscous Correction

2007 ◽  
Vol 51 (01) ◽  
pp. 47-64
Author(s):  
James C. Huan ◽  
Thomas T. Huang
Keyword(s):  
Free Surface ◽  
Surface Potential ◽  
Potential Flow ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Total Resistance ◽  
Flow Solver ◽  
Resistance Prediction ◽  
Nonlinear Free Surface

A fast turnaround and an accurate computational fluid dynamics (CFD) approach for ship total resistance prediction is developed. The approach consists of a nonlinear free surface potential flow solver (PShip code) with a wet-or-dry transom stern model, and a Reynolds-averaged Navier-Stokes (RANS) equation solver that solves viscous free surface flow with a prescribed free surface given from the PShip. The prescribed free surface RANS predicts a viscous correction to the pressure resistance (viscous form) and viscous flow field around the hull. The viscous free surface flow solved this way avoids the time-consuming RANS iterations to resolve the free surface profile. The method, however, requires employing a flow characteristic-based nonreflecting boundary condition at the free surface. The approach can predict the components of ship resistance, the associated wave profile around the hull, and the sinkage and trim of the ship. Validation of the approach is presented with Wigley, Series 60 (CB = 0.6), and NSWCCD Model 5415 hulls. An overall accuracy of ±2% for ship total resistance prediction is achieved. The approach is applied to evaluating the effects of a stern flap on a DD 968 model on ship performance. An empirical viscous form resistance formula is also devised for a quick ship total resistance estimate.

On the Cushioning of Water Impact by Entrapped Air

1968 ◽  
Vol 12 (02) ◽  
pp. 116-130 ◽  
Author(s):  
Grant Lewison ◽  
W. M. Maclean
Keyword(s):  
Free Surface ◽  
Flat Plate ◽  
Water Surface ◽  
Peak Pressure ◽  
Water Movement ◽  
Theoretical Work ◽  
Two Dimensional ◽  
Water Impact ◽  
Entrapped Air

Impact between a rigid flat plate and the free surface of water has been investigated experimentally and theoretically. Under two-dimensional conditions, the experiments give values of peak pressure of the same order as those recorded on ships slamming at sea, but very much smaller than would be expected from existing theories. New theoretical work is presented which takes account of the air trapped between the model and the water surface, and of both compressible and incompressible water movement. This shows good general agreement with the experiments, though further work is needed to confirm some of the assumptions made.

A Two-Dimensional Potential Flow Model of the Wave Field Generated by a Semisubmerged Body in Heaving Motion

1988 ◽  
Vol 32 (02) ◽  
pp. 83-91
Author(s):  
X. M. Wang ◽  
M. L. Spaulding
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Potential Flow ◽  
Flow Model ◽  
Second Order ◽  
Two Dimensional ◽  
Third Order ◽  
The Third ◽  
Potential Flow Model ◽  
Good Agreement

A two-dimensional potential flow model is formulated to predict the wave field and forces generated by a sere!submerged body in forced heaving motion. The potential flow problem is solved on a boundary fitted coordinate system that deforms in response to the motion of the free surface and the heaving body. The full nonlinear kinematic and dynamic boundary conditions are used at the free surface. The governing equations and associated boundary conditions are solved by a second-order finite-difference technique based on the modified Euler method for the time domain and a successive overrelaxation (SOR) procedure for the spatial domain. A series of sensitivity studies of grid size and resolution, time step, free surface and body grid redistribution schemes, convergence criteria, and free surface body boundary condition specification was performed to investigate the computational characteristics of the model. The model was applied to predict the forces generated by the forced oscillation of a U-shaped cylinder. Numerical model predictions are generally in good agreement with the available second-order theories for the first-order pressure and force coefficients, but clearly show that the third-order terms are larger than the second-order terms when nonlinearity becomes important in the dimensionless frequency range 1≤ Fr≤ 2. The model results are in good agreement with the available experimental data and confirm the importance of the third order terms.

Effect of free surface on a flat plate translating normal to the flow

2019 ◽  
Vol 171 ◽  
pp. 458-468 ◽  
Author(s):  
Sukruth Satheesh ◽  
Francisco J. Huera-Huarte
Keyword(s):  
Free Surface ◽  
Flat Plate
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