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High power pulsed underwater electrical discharge can be used for different applications in medecine (destructions of kidney stones, decontamination of bacteria), industry (grinding of materials, forming, etc.) and recycling of multi-material wastes (separation and fragmentation of materials). An electric arc between two electrodes creates a plasma channel generating a pressure wave which propagates into water. This wave is followed by expansion of a gaseous volume of water vapor. The amplitude of the shock wave depends on the electrical generator parameters, electrodes geometry, distance between them etc., and can be varied to obtain desired physical effects. Velocity measurements and Shlieren technique allow to visualize the waves propagation and characterize the shock waves and vapor bubble evolution. The experimental results are compared with corresponding RADIOSS numerical simulations in order to assess the code ability to physically reproduce this ultra-short high-intense phenomenon. After calibration, we utilized the series of simulations to analyze the mechanical and structural effects into objects placed in the water not far from the electrodes. The numerical modeling permit to design a new optimized concept for shock generation yielding to an improved efficiency in multi-material separation and fragmentation.
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02/07/2014 titre présentation 1
Ekaterina Mazanchenko, Julien Deroy, Alain Claverie,
Michel Boustie, Yannick Chauveau, Gilles Avrillaud,
Boni Dramane, Gauthier Demol, Charles Kofyan
Experimental and numerical simulation of shock waves generated by pulsed underwater electrical discharges
2014 European Altair Technology Conference, Academic & Industry Collaboration Day,
Munich, Germany
June 26th, 2014 1
International Technologies for High Pulsed Power, Thégra: Realization of the prototypes for clients tests in research and defence.
Bmax (I-Cube research), Toulouse: Expertise and research in forming, welding and crimping using extreme deformation speeds.
AIDER project: «Application Industrielles des Décharges dans l’Eau pour le Recyclage»
PPRIME Institute (CNRS-ENSMA), Poitiers: LMPM + LCD
PAPREC Groupe, La Courneuve: Independent French specialist in recycling (papers, cartons, confidential archives, plastic, industrial garbage, metals, wood, batteries, vehicles etc.)
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Introduction
High power electrical discharge in water:
• generation of shock waves, • waves propagation and interaction with
materials.
Applications:
• medical, • separation of materials, • recycling.
Fig. from PhD thesis of Gilles Touya
Lithotripter and fragments of a 1-cm calcium oxalate stone
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Outline
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1) Discharge characterization
2) Shock waves propagation
3) Interaction with an object
4) Optimization
Shock waves generated by laser, PPRIME (Poitiers)
Preparation of Schlieren and shadowgraph diagnostics for the series of experiments at Bmax.
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Shock waves generated by underwater electrical discharge, Bmax (Toulouse)
• Modular electrical discharge generator:
• Capacitive storage of electrical energy
• 1 to 9 capacitors of 1.85µF, maximum voltage of 40kV
• Stored energy capability : approx. 1-10 kJ
• Discharge circuit:
• Point-Point or Point-Plane electrodes configuration
• Variable inter electrodes gap
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• Available diagnostics:
• Current and voltage probes
• Pressure gauge
• High speed cameras
• Velocimetry measurement
Pressure wave propagation observation
Ultra High Speed Camera (by LCD): Shimadzu HPV-2 camera up to 1M frames/s (312x260 pixels)
Spherical mirror
Hg lamp
Spherical
lens
Knife
Spherical
lens
High speed camera
Experimentation tank
Filter
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Bubble expansion, ITHPP (Thégra)
Gap 15 mm U0=25 kV C=1.85 µF E0=327 J Pressure diagnostic - PVDF
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Velocity measurements
0,000
0,002
0,004
0,006
0,008
0,010
0,012
0,014
0,016
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000
ns
km
/s
9 David Assous (Société IDIL)
Pressure simulation by inverse analysis
2D model with hydro water law and alu 50 µm: pressure varied to fit experimental velocity profile, and then initial energy E0.
0,000
0,002
0,004
0,006
0,008
0,010
0,012
0,014
0,016
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000
nskm
/s
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Experiment to simulate (ITHPP)
Tests were carried out at the tank 60x60x53 cm (LxWxH). Gap between electrodes: 5 to 15 mm. Max stored energy - to 35 kJ. Time (shock risetime): 530 ns. 11
Model definition
• 2D axisymmetric
• QUAD elements 0.5x0.5 mm
• Gap is 15 mm
Material laws:
• water – law 26 SESAME #7150 ,
• discharge zone - law 26 SESAME #7150 with initial energy,
• outlet zone – law 11 type 3 (silent boundary).
For all 3 materials ALE description has been used.
SESAME law presentation 12
Pressure wave propagation
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Pressure max ~ 26 GPa
Interaction with aluminium foil
14 Pressure max ~ 2 GPa
Optimization: reflector
Possible mechanical amplification of shock waves – an ellipsoidal reflector.
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Pressure inside the foil
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Evolution of the bubble
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Conclusions and perspectives
• Ability of RADIOSS to simulate ultra-short high intense shock waves propagation in water.
• Satisfactory correlation between experiments and simulation.
• Improvements by correlation with new experiments (velocity measurements, structure effects…).
• Further optimization.
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Acknowledgements
The work supported by ADEME (AIDER project 2010-2013).
Thanks for Altair Engineering France for training seminars and online support.
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Annexes
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0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1
km/s
GP
a
alu w a w a mirror contact w a 90 mm w a just before
Pressure near contact zone
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Theoretical pressure for the flyer
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Evolution of the bubble
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
5
10
15
20
25
0
50
100
150
200
250
300
radius(mm)
Time (ms)
Rad
ius
(mm
)
Ve
loci
ty (
m/s
)
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