1. Behavior of bubble pulse in food processing using underwater shock wave
Hideki Hamashima*, Manabu Shibuta**, Yosuke Nishimura**, Shigeru Itoh**
*Kumamoto Industrial Research Institute
**Shock Wave and Condensed Matter Research Center, Kumamoto University
Thank you very much, Chairperson. I’m Hideki Hamashima, Kumamoto Industrial Research Institute, in Japan.
I would like to talk you about “Behavior of bubble pulse in food processing using underwater shock wave”.

2. Content Background and Purpose Experiment Numerical simulation
Conclusion
This is content of my presentation.

3. Background (1/2) Explosive processing Food processing
Conventional Techniques for Explosive and Shock wave …
Explosive processing
(Except for Destruction technique!)
Explosive forming, Explosive welding, Explosive synthesis,
Explosive cutting(Shaped charge) etc.
Recent years…
Explosive and Shock wave are used for
Food processing
Shock processing of Apple
This is background.
In conventional techniques for Explosive and Shock wave etc.,There is an Explosive processing. It is not destruction technique.
There are explosive forming, Explosive welding, Explosive synthesis, Explosive cutting etc. in this technique.
In recent years, Explosive and Shock wave are used for Food processing.
For example, this is shock processing of apple.
Apple become very soft.
If the apple with the load of the shock wave is extracted by hand, fruit juice will overflow. Fruit juice can be very directly drunk for a straw to an apple.
Apple subjected to shock load

4. Background (2/2) Food processing using shock wave However…
New Food Processing!
Food processing using shock wave
Attract attention!
Shock wave is generated from the explosion of explosive
and pulse power of a high voltage.
Excellent Features!
Processing time is very short.
There is little influence of heat to food.
Deterioration of food does not take place easily.
Bactericidal effect etc.
However…
The details of shock processing are not clarified.
The food processing using the shock wave as such a new food processing attracts attention.
Shock wave is generated from explosion of explosive and pulse power of a high voltage.
Excellent features of this technique are
Processing time is very short.
There is little influence of heat to food.
Deterioration of food does not take place easily.
Bactericidal effect etc.
However, the details of shock processing are not clarified.
Because, the shock wave which processes food has
Shock wave generated by early explosion and
Shock wave generated by expansion contraction of detonation product gas.
Generally, this is called Bubble pulse.
The shock wave which processes food has
Apple subjected to shock load
Shock wave generated by early explosion
Shock wave generated by expansion contraction of detonation product gas(Bubble pulse).

5. Purpose Development of Food processing device using shock wave
Final Goal!
Development of Food processing device using shock wave
Therefore…
In this research,
Shock wave generated by early explosion
Shock wave generated by expansion contraction of detonation product gas(Bubble pulse).
Investigation!
fundamental investigation
Our final goal is development of food processing device using shock wave.
Therefore,
In order to reach our goal, in this research, bubble pulse was investigated.
It is fundamental investigation.
In order to investigate the behavior of a bubble pulse, it was investigated by two research methods.
They are optical observation and numerical simulation.
In order to investigate the behavior of Bubble pulse,
Research method
・Optical observation using a high-speed video camera
・Numerical simulation

6. Bubble Pulse
There are shock wave and explosion product gas in the fundamental phenomenon of underwater explosion. A gas bubble shows the complicated action which repeats expansion and contraction. The pressure called a Bubble pulse occurs at the time of contraction (when becoming the minimum radius).
Although the maximum pressure of a bubble pulse is small compared with a shock wave, there is the feature that duration of shock is long. It is considered that it is important when calculating the shock response of marine structures, such as a ship.
There are shock wave and explosion product gas in the fundamental phenomenon of underwater explosion.
A gas bubble shows the complicated action which repeats expansion and contraction.
The pressure called a bubble pulse occurs at the time of contraction (when becoming the minimum radius).
Although the maximum pressure of a bubble pulse is small compared with a shock wave,
there is the feature that duration of shock is long.
It is considered that it is important when calculating the shock response of marine structures, such as a ship.

7. Experiment
Next is experiment.

8. Experimental Setup Water Container Water Pressure Gauge
Width : 1.2m
Length : 3.2m
Depth : 1.8m
Water
Water is poured from
the bottom to 1.6m.
Pressure Gauge
Observation Window
1.8m
This is the schematic experimental setup.
The experiment was conducted with a water container of this size.
Explosive was exploded in water like this,
and the explosion phenomenon was observed with the high-speed video camera through the observation window.
Bubble
Explosive
High-speed
Video Camera
1.2m
3.2m

9. Experimental Water Container
Width : 1.2m
Length : 3.2m
Depth : 1.8m
Water is poured from the bottom to 1.6m.
High-speed Video Camera
Phantom　V7.3
Vision Research, Inc.
Resolution : 800x600 pix
Rates : 2000fps
This is experimental scenery photograph.
The experiment was conducted with this container.
High-speed video camera was used.
This is phantom V7.3. Framing speed is 2000fps.

10. Experimental Condition
Explosive
Depth of Water (mm) ED
200
300
400
ED : No.6 Electrical Detonator
Observation Window
Depth
Water
This is experimental condition.
Depth of explosive was changed into three stages, 200mm, 300mm and 400mm.
It was used No. 6 electrical detonator for explosive.
1.6m
Explosive
High-speed
Video Camera

11. Experimental Results
Next is experimental result.

12. Movie (ED, Water Depth:200mm,300mm)
This is a movie at 200mm in depth of the explosive.
I will show the movie.
Detonation product gas repeated the expansion contraction like this.
The bubble collapsed when time passes and it didn't expand and contract.
These are movies at 200mm and 300mm in depth of the explosive.
Detonation product gas repeated the expansion contraction like this.
In the both experiments, the bubble at the first cycle expanded and contracted spherically. However, the bubble at the 2nd and 3rd cycle didn’t become spherical.

13. Movie (ED, Water Depth:400mm)
This is a movie at 400mm in depth of the explosive.
Detonation product gas similarly repeated the expansion contraction as for this.
This is a movie at 400mm in depth of the explosive.
Detonation product gas similarly repeated the expansion contraction as for this.

14. Bubble Diameter (Experiment)
This is a time change of the bubble diameter obtained from the movies ahead.
All almost were the same diameters for the first cycle.
The bubble diameter became small at the second cycle as depth of explosive became deep.
Because the bubble had collapsed, the third cycle was not able to be measured well.
Therefore, It is considered that the diameter at 300mm in the depth of explosive was greatly measured.
This is a time change of the bubble diameter obtained from the movies ahead.
All experiments had the same diameters of the bubble for the first cycle.
The bubble diameter became small by attenuation as the cycle progressed. And it became small at the 2nd cycle as depth of explosive became deep.

15. Fall of Bubble (Experiment)
This is figure where the amount of the fall displacement of the bubble was shown.
As you can see, the amount of the fall displacement of the bubble has decreased as the position of explosion becomes deep.
This is figure where the amount of the fall displacement of the bubble was shown.
The amount of the fall displacement of the bubble has decreased as the position of explosion becomes deep.

16. Fall of Bubble (ED:200mm:Experiment)
This is figure where the bubble diameter and the amount of fall of the bubble were shown.
This is a result at 200mm.
The bubble fell intensely when the bubble contracted.
Fall of Bubble
This is figure where the bubble diameter and the amount of fall of the bubble were shown. This is a result at 200mm. The bubble fell intensely when the bubble contracted.

17. Fall of Bubble (ED:Experiment)
ED:200mm
ED:300mm
Fall of Bubble
The bubble fell intensely when the bubble contracted at all the experiments.
The bubble fell intensely when the bubble contracted at all the experiments.
ED:400mm

18. Consideration of Fall of Bubble
(a)Expansion (b)Contraction
(a) In a expansion process, the gas bag near a rigid body wall expands to the position of a dotted line.
(b) In a contraction process, water does not return from the circumference uniformly. Water follows the streamline at which it turned from the wall side, and the side which does not have a wall is easier to return.
This is the consideration of the fall phenomenon of the bubble.
In a expansion process, the gas bag near a rigid body wall expands to the position of a dotted line.
In a contraction process, water does not return from the circumference uniformly.
Water follows the streamline at which it turned from the wall side, and the side which does not have a wall is easier to return.

19. Consideration of Fall of Bubble
Air
It is considered that a big flow of water is generated because it is easy to move in water on explosive below, and the bubble fell in these experiments.
Water
Gas
It is considered that a big flow of water is generated because it is easy to move in water on explosive below, and the bubble fell in these experiments.
Contraction

20. Pressure History (ED:300mm)
-10 10 20 30 40 50 60 70 80 90
This is a pressure measurement result obtained from a past experiment.
After the bubble contracted, the shock wave has been generated.
-10 10 20 30 40 50 60 70 80 90
This is a pressure measurement result obtained from a past experiment.
As you can see, after the bubble contracts, the shock wave has been generated.
In an optical observation, it was understood that the shock wave reached the window from whitening of the window.

21. Pressure History (ED:300mm)
When a shock wave reacheｄ
an observation window
Usual framing photographs
0.5ms
23.5ms
42.0ms
0.0ms
11.5ms
-10 10 20 30 40 50 60 70 80 90
In an optical observation, it was understood that the shock wave reached the window from whitening of the window.
This is a pressure measurement result obtained from a past experiment.
As you can see, after the bubble contracts, the shock wave has been generated.
In an optical observation, it was understood that the shock wave reached the window from whitening of the window. .

22. Simulation
Next is simulation.

23. Simulation Model Quarter model
Simulation was performed using LS-DYNA (SMP Edition ;smp971）.
Quarter model
Simplification!
Air
Air
100mm
Water
Water
400mm
400mm
Explosive
1000mm
900mm
Explosive Z
Simulation was performed using LS-DYNA.
Quarter model as the symmetry problem was analyzed.
This is a simulation model at 400mm in depth of explosive.
Here is water, here is air and here is explosive.
500mm
500mm
500mm X

24. Calculation Method
Calculation method
Euler method: Explosive, Air, Water
Burn technique
CJ volume burn + Programmed burn
(point ignition)
Mesh size
Euler element : 10 x 10 x 10 (mm)
The multi-material Euler method was used for the simulation.
This is size of element.
The number of elements is 250,000.
Number of elements
Euler element : 250,000

25. Equation of States (EOS)
Calculation method
Euler method: Explosive, Air, Water
Explosive
Detonation Products EOS: JWL EOS
0.6g SEP was used instead of ED.
Air
Density: 1.252kg/m3
EOS: Ideal gas EOS
Equations of state was used for the analysis.
Water
Density: 1000kg/m3
EOS: Gruneisen EOS

26. Calculation Results
Next is calculation results.

27. Movie (ED, Water Depth:200mm)
This is a numerical result when the position of the explosive is 200mm in depth.
Although the bubble of the first cycle spread spherically, the bubble of the 2nd and 3rd cycle burst.
This is a numerical result when the position of the explosive is 200mm in depth.
As you can see, although the bubble of the first cycle spread spherically, the bubble of the 2nd and 3rd cycle burst.

28. Movie (ED, Water Depth:300mm)
This is a numerical result in case the position of the explosive is 300mm in depth.
Only the bubble of the first cycle carried out expansion contraction spherically like the case of 200mm.
This is a numerical result in case the position of the explosive is 300mm in depth.
Only the bubble of the first cycle carried out expansion contraction spherically like the case of 200mm.

29. Movie (ED, Water Depth:400mm)
This is a numerical result in 400mm. It differed in 200mm and 300mm, and the bubble of the 2nd and 3rd cycle was able to be expressed.
This is a numerical result in 400mm.
It differed in 200mm and 300mm, and the bubble of the 2nd and 3rd cycle was able to be expressed.

30. Bubble Diameter (Calculation)
This is a time history of the bubble diameter obtained from the numerical result.
As you can see, in the three condition, the outside diameter of the bubble at the first cycle became the same size as about 280mm.
This is a time history of the bubble diameter obtained from the numerical result. In the three condition, the outside diameter of the bubble at the first cycle became the same size as about 280mm.

31. Fall of Bubble (Calculation)
This figure is shown about the fall of the bubble.
An extreme fall was not obtained too much like this.
This figure is shown about the fall of the bubble.
An intense fall was not obtained too much like this.

32. Fall of Bubble (ED:200mm:Calculation)
This is figure where the bubble diameter and the amount of fall of the bubble obtained from numerical analysis were shown.
This is a result at 200mm.
The bubble when the bubble contracted has not fallen intensely compare with the case of the experiment.
This is figure where the bubble diameter and the amount of fall of the bubble obtained from numerical analysis were shown. This is a result at 200mm. The bubble when the bubble contracted has not fallen intensely compare with the case of the experiment.

33. Fall of Bubble (ED:Calculation)
ED:200mm
ED:300mm
No Fall of Bubble
Thus, at all the analyses, an intense fall of the bubble like the experiment was not obtained when the bubble contracted.
Thus, at all the simulations, an intense fall of the bubble like the experiment was not obtained when the bubble contracted.
ED:400mm

34. Comparison between Experimental and Calculation Results
Next is Comparison between Experimental and Calculation Results

35. Comparison of Bubble Diameter (ED200mm)
This is a comparison of the experimental result and the numerical result at 200mm in depth.
As you can see, the history at the first cycle was almost corresponding.
This is a comparison of the experimental result and the numerical result at 200mm and 300mm in depth.
The histories at the first cycle was almost corresponding.

36. Comparison of Bubble Diameter (ED400mm)
This is a comparison at 400mm in depth of the explosive.
The bubble history at the first cycle was almost corresponding.
The bubble outside diameter of the numerical result did not attenuate compared with the experiment result.
Moreover, the analysis repeated the expansion contraction at a slightly short cycle.
It is considered that this is because the analysis greatly reflects the influence of water in the upper part of explosive.
Moreover, the water container of limited was used in the experiment.
The analysis was conducted in the infinite waters in the analysis.
It is considered that these differences influenced the difference of behavior.
This is a comparison at 400mm in depth of the explosive. The bubble history at the first cycle was almost corresponding. The bubble outside diameter of the numerical result did not attenuate compared with the experiment result. Moreover, the analysis repeated the expansion contraction at a slightly short cycle.

37. Comparison of Fall of Bubble
This is figure where the falls of the bubble were compared.
The analysis was small the bubble fall.
It is considered that this is because the condition of the analysis was an analysis in the infinite waters.
This is figure where the falls of the bubble were compared.
The analysis was small the bubble fall. It is considered that this is because the condition of the analysis was an analysis in the infinite waters.

38. Comparison of Pressure History (ED:300mm)
-10 10 20 30 40 50 60 70 80 90
1st Pulse
EXP: 8.1 (MPa)
CAL: 8.7 (MPa)
This is a comparison of the pressure histories at 300mm.
As you can see, the peak value of an initial shock wave hardly changed.
However, the time that reached the gauge at the analysis became early.
It is considered that this appeared by the difference between the infinite waters and the limited waters, too.
This is a comparison of the pressure histories at 300mm. The peak value of an initial shock wave hardly changed. However, the time that reached the gauge at the analysis became early. It is considered that this appeared by the difference between the infinite waters and the limited waters, too.

39. Conclusion
・It succeeded in the high-speed photography of the bubble within a limited container. The data of the variation with time of the maximum diameter of a bubble or the cycle of a bubble pulse was able to be obtained.
・It turned out that the maximum bubble diameter becomes small by attenuation as the cycle progressed.
・In the underwater explosion near the water surface, it demonstrated that involved in and a high-speed flow was made to the bottom. The fall phenomenon of the bubble has been confirmed.
・Also in the numerical simulation, it could be simulated about the reduction of the maximum bubble diameter and the fall phenomenon of the bubble.
It succeeded in the high-speed photography of the bubble within a limited tank.
The data of the variation with time of the maximum diameter of a bubble or the cycle of a bubble pulse was able to be obtained.
It turned out that the the maximum bubble diameter becomes small by attenuation as the cycle progressed.
In the underwater explosion near the water surface, it demonstrated that involved in and a high-speed flow was made to the bottom.
The fall phenomenon of the bubble has been confirmed.
Also in the numerical simulation,
it could be simulated about the reduction of the maximum bubble diameter and the fall phenomenon of the bubble.

40. Future Work
・The simulation that models even the water container is conducted. Whether the amount of fall of the bubble becomes larger when an analytical model with limited waters is used is investigated.
・The simulation of a Bubble pulse is conducted by more fine mesh. We constructed a parallel computer recently.

41. Thank you for your attention.