Explosive performance of the new helicopter borne system DaisyBell - Comparison of different gas mixture effects

Transcription

1 WORKSHOP ARTIFICIAL AVALANCHE RELEASE Explosive performance of the new helicopter borne system DaisyBell - Comparison of different gas mixture effects Dr. Philippe Berthet-Rambaud, Fanny Bourjaillat, Ernesto Bassetti MND Group, France 1

2 The M.N.D Group Preventive systems and services for natural hazards Ski area equipement and safety strutures Research, development and engineering for natural risk prevention 2

3 TAS Keypoints - Created in the French Alps in Leader for 20 years in remote avalanche release system with Gazex - Helicopter-born DaisyBell Gazex and 35 DaisyBell in 15 countries for over 500 customers - New GazFlex and O Bellx systems -Patents on every system and R&D programs 3

4 TAS Solutions - Surface to be treated + FIXED SYSTEMS MOBILE SYSTEM Removable + Availability all conditions - 4

5 Gas properties Gas Flame speed in the air(m/s) Comparaison des énergies spécifiques des expolosifs et mélanges gazeux Hydrogene 3,5 Propan 0,52 Butan 0,5 Energie libérée (unités US) E 25,0 20,0 15,0 10,0 5,0 0,0 14,1 19,1 18,2 18,6 22,3 Methan 0,45 - Hydrogen and propan with the highest combustion flame speed and interesting relative energy in comparison to TNT - Before ignition, different possibilities depending on Gas + O2 mixture density (vs air): - Propan/O2 at the bottom of the Gazex exploder - H2/O2 at the top of the DaisyBell bell - H2 and O2 available with high pressure bottles 5

6 Gas systems Advantages: - Safer for operators thanks to remote shooting - Safer for the environment: no unexploded charges or pollution -Less regulation constraints compared to solid explosives - Explosion above the snow mantle - Shock wave on the slope, (vibrations in the ground) - Power depending on the capacity, type of gas and position THE CHALLENGE 6

7 GAS SYSTEMS VS EXPLOSIVES 7

8 GAS SYSTEMS VS EXPLOSIVES Photos sources: web 8

9 HELIBOMBING some possible safety improvements! 9

10 The DaisyBell project Helicopter mobility Solid explosives constraints Gas systems safety and efficiency 10

11 - Gas choice : high potential energy, high pressure storage - Explosive mixture: injection discharge with good ratio, homogeneity of the mixture, low density Stoechiometric mixture of hydrogen / oxygen (2/3 H 2, 1/3 O 2 ) H 2 +½O 2 H 2 0 Low density of hydrogen naturally concentrated at the top of a bell-shape vessel Confinement by a rigid, metallic vessel: no consumables, free-standing volume, simplified mechanical system completely autonomous, remotely controlled with a large number of reproducible shots and safe thanks to a semi-automatic procedure 11

12 Keypoints - Cone: high elastic limit S690 steel, 4mm thickness - Laser telemeter for a correct vertical positioning (4 to 10m depending on the snow) - Total weight: 350 kg without bottles to 150 kg depending on the bottle types: lighted, B50 or B20 - Radio remote control system from helicopter cockpit with a semi-automatic procedure 12

13 EFFICIENCY CFD optimised mixer-spreader unit at the top of the explosion chamber to get the most homogenous filling after some seconds injection! Numerical simulation by Renuda UK 13

14 Operations Operations at least until 4000 m asl with all type of helicopters 14

15 Operations 15

16 3 problematics CONFINED and ORIENTED EXPLOSION A) Induced effects on the system B) Direct effect on the snowpack (layers) C) Indirect / long distance influence? 16

17 3 problematics CONFINED and ORIENTED EXPLOSION A) Induced effects on the system B) Direct effect on the snowpack (layers) C) Indirect / long distance influence? 17

18 A) Induced effects in the structure Extreme loading scenario: pure chapman-jouguet detonation (Renuda UK) 18

19 - Numerical evaluation of the maximum internal pressure due to a theoretical perfect detonation (Renuda UK) - Pressure measurements - Modeling and strain gages measures of the deformation : the minimum safety factor is at least 3! - Database of the initial frequencies for aging control High elastic limit S690 steel, 4mm thickness A) Induced effects in the structure u cône MPa Von Mises au sein du Distance au sommet du cône t=0.1ms t=0.35ms t=0.6ms t=0.85ms 19

20 A) Induced effects on the supporting system Helicopter flight compatibility Limited impact on the helicopter due to the vertical jump: equivalent overweight of 20 to 30% during a very short time with a 10 to 20 meter sling and the included 2-meters damper.. 20

21 3 problematics CONFINED and ORIENTED EXPLOSION A) Induced effects on the system B) Direct effect on the snowpack (layers) C) Indirect / long distance influence? 21

22 B) Direct effect on the snow Experimental protocol -Total autonomy and helicopter-borne design: usable hung under a mobile crane - Parameters: distance (5s injection duration) - Shock wave characterization: - high speed camera (at least 1000 fps) - Free-Field ICP Blast Pressure Sensors 137A22 PCBpiezotronics - data acquisition Hz - Safety distance for operators: 30 meters (+ears protection) - Delay between two shots: 10 seconds - Number of shots with usual bottles: 60 22

23 B) Direct effect on the snow Measurements 23

24 B) Direct effect on the snow Measurements 24

25 B) Direct effect on the snow Incident shockwave Reflexion on the ground 25

26 B) Direct effect on the snow Incident shockwave Perfect reproductibility 26

27 B) Direct effect on the snow Incident shockwave 27

28 B) Direct effect on the snow Incident shockwave Maxi: 2 bars 28

29 B) Direct effect on the snow Incident shockwave Collapse of cylindric shells: - Φ160 - H=200 - thickness=0.1 or 0.2mm - material: aluminium or copper - closures at extremity, - bottom pinned to the ground 29

30 B) Direct effect on the snow Max incident shockwave Maxi: 2 bars 30

31 B) Direct effect on the snow Others shockwave sources 31

32 Solid explosive B) Direct effect on the snow Others shockwave sources Distance=10m Distance=5m Crucial parameter vs type of snow : Maximum overpressure? 32

33 B) Direct effect on the snow Others shockwave sources mbars Gazex O.8 m3 Daisy Bell temps Crucial parameter vs type of snow : Positive impulse? Depression phasis? 33

34 B) Direct effect on the snow Transmitted shockwave Explosion source 15cm thick spring snow slab at 550kg/m3 34

35 3 problematics CONFINED and ORIENTED EXPLOSION A) Induced effects on the system B) Direct effect on the snowpack (layers) C) Indirect / long distance influence? 35

36 C) Indirect effect on the snow Reflected shockwave Effective range?? 36

37 Effects on the snowpack Solid explosives Gas explosion H2 + O2 C3H8+O2 Height 0 to h m Fresh snow: h(~10m ) Surface Spring snow: h (~3m ) Pmax Lateral effect?? shockwave Incident effect BEST/Internal effect?? amplitude, impulse, wave speed?? TNT Equivalence Topography Snowpack Properties 37

38 Cbis) Long distance effect Experiments for Airap: Association pour l'information sur les Risques d'avalanches Urbaines et leur Prévention / Association for information about urban avalanches hazards and prevention 38

39 Cbis) Long distance effect Experiments for Airap: Association pour l'information sur les Risques d'avalanches Urbaines et leur Prévention / Association for information about urban avalanches hazards and prevention 39

40 - Shockwave sound Cbis) Long distance effect Experiments for Sound ICP sensor Y378B02 PCBpiezotronics Airap: Association pour l'information sur les Risques d'avalanches Urbaines et leur Prévention / Association for information about urban avalanches hazards and prevention 40

41 -1 millibar = 100 Pascals Cbis) Long distance effect Experiments for Opération A Opération B Opération C Opération D L=2400m L=180m L=220m L=4350m H=1200m H=60m H=70m H=600m Gazex 1.5m3 Explosif 1 Explosif 2 DaisyBell1 DaisyBell2 Gazex 1.5m3 explosif Gazex 1.5m3 Gazex 3m Pa 3.6 Pa 2.5 Pa 37.0 Pa 55.0 Pa 70.0 Pa 16.0 Pa 16.0 Pa 14.0 Pa Weather dependant: wind, temperature/air density?, humidity? Anyway, < 1 mbar unable to release any almost ready avalanche Airap: Association pour l'information sur les Risques d'avalanches Urbaines et leur Prévention / Association for information about urban avalanches hazards and prevention 41

42 Conclusions H shockwave Topography BEST EFFECT?? Snowpack Properties (ρ, C??) 42

43 43

44 Thank you for your attention 44