Noise mitigation measures to be used for the explosive cladding in open air

Transcription

1 Noise mitigation measures to be used for the explosive cladding in open air Erik Carton Frank van den Berg Frits van der Eerden 1 Mei 2012

2 Mitigation Open Air Explosions 1 Simulation of the blast wave shape Ø 2 m plate of detonating TNT (0.1 m thick)

3 Mitigation Open Air Explosions 2 Video images of detonation of 50 kg cladding explosive without (left) and with water foam Foam: Reduction in peak pressure 28% Reduction in impulse 22%

4 Mitigation Open Air Explosions 3 Overview of presentation Objective Numerical techniques & Validation Muzzle blast mitigation (Ministry of Defense) Mitigations of open air explosions Conclusions

5 Mitigation Open Air Explosions 4 Objective: Reduction of blast noise from explosive cladding in open air Open air explosions burden for people in the surroundings Comparable with problems military training area Common approach not applicable: Shielding measures (like for traffic) do not work Sound propagation different due to high noise levels (non-linear effects)

6 Mitigation Open Air Explosions 5 Background: Reduction of blast noise Initialized by: - US-Army - the Netherlands Ministry of Defense Objective: Mitigation of blast noise from large weapons (armor, artillary) - Propagation over large distances - By means of barriers and sound absorbing material - Close to the source (non-linear acoustics) gabion or Hesco s

7 Mitigation Open Air Explosions 6 Numerical hybrid model: FCT NPE PE FCT: Flux-Corrected Transport technique strong shock wave NPE: Non-linear progressive wave equation weak shock wave PE: Parabolic Equation linear acoustic

8 Mitigation Open Air Explosions 7 Validated at Aberdeen Test Centre, MD, USA A large pile of gravel 15x15 m2, 1.5m high, coarse gravel (3cm) Three source locations, C-4 bricks (0.57 kg) Hz 3m 1m 1.5m -5m +2m

9 Mitigation Open Air Explosions 8 Numerical FCT results (compared to measurements)

10 Mitigation Open Air Explosions 9 Case study: Shielding Howitzer blast noise

11 Mitigation Open Air Explosions 10 Case study: Barrier with absorption added Gravel filled gabions/bastions (1 m 3 ): - absorb shock wave energy - suppress ground reflection (behind barrier)

12 Mitigation Open Air Explosions 11 Case study: Barrier with absorption added Two movies: blast mitigation behind barrier

13 Mitigation Open Air Explosions 12 Calculation results for different configurations

14 Mitigation Open Air Explosions 13 A balcony construction for increased reduction

15 Mitigation Open Air Explosions 14 Numerical results (sound exposure level, in db) With balcony

16 Mitigation Open Air Explosions 15 Study to reduce open air explosions from cladding Absorbing material (broken stones)

17 Mitigation Open Air Explosions 16 Simulations: 8 variants (500 kg source) Variant 0 = slope without gabions Variant 1a, 1b = slope with 1m high gabions Variant 2a,2b,2c = slope with 2m or 3m high gabions Variant 3a,3b = barrier in front of slope Variant 4, combination 3b & 2c variant2b microphones at 80m slope

18 Mitigation Open Air Explosions 17 Levels at end of slope (at 80m, 1/5/10/20m high) Variant0: Pa Variant2b: 6000 Pa Result: 6 db (20log2) Measurement at 90m: 174 db Simulation at 80m: 176 db

19 Mitigation Open Air Explosions 18 Levels at 300m (beyond slope) Small effects for all variants! No noticable effect of mitigation measures

20 Mitigation Open Air Explosions 19 Explanation variant2b At 80m: variant Pa, variant2b 6000 Pa At 90m: variant Pa, variant2b 5000 Pa propagation into shadow zone, easy for low frequencies shadow variant2b, already smooth wave with low-frequency content (higher freq s are damped) variant0, only low-frequencies propagate into shadow zone Variant0 Variant2b

21 Mitigation Open Air Explosions 20 Balcony results: increased screening

22 Mitigation Open Air Explosions 21 Balcony results: increased screening

23 Balcony results at 300 m Mitigation Open Air Explosions 22

24 Mitigation Open Air Explosions 23 Conclusions Hybrid FCT-NPE-PE method presented for shock wave propagation non-linear interaction with barrier / absorbing material; Standard barrier has limited effect for explosions; Adding absorbing material increases shielding effect; For strong explosions special constructions (balcony) are needed to increase barrier effect significantly.