MABS21 Israel 2010 Julius Mezaros Lecture 53 Years of Blast Wave Research A Personal History by John M. Dewey Dewey McMillin & Associates Professor Emeritus, University of Victoria

MABS21 Israel 2010 The Entropy Problem G. I. Taylor (1950) ΔSΔS ΔSΔS ΔSΔS

MABS21 Israel 2010 The Entropy Problem G. I. Taylor (1950) In Eulerian co-ordinates the air passing a fixed measurement point is non-isentropic

MABS21 Israel 2010 The Entropy Problem G. I. Taylor (1950) In Eulerian co-ordinates the air passing a fixed measurement point is non-isentropic The simple thermodynamic relationships do not apply

MABS21 Israel 2010 The Entropy Problem G. I. Taylor (1950) In Eulerian co-ordinates the air passing a fixed measurement point is non-isentropic The simple thermodynamic relationships do not apply Measured P = f(t) ρ = f(t) u = f(t) T = f(t)

MABS21 Israel 2010 The Solution Work in Lagrangian co-ordinates, viz. trace the physical properties along the particle paths instead of in x,y,z space.

MABS21 Israel 2010 The Solution Work in Lagrangian co-ordinates, viz. trace the physical properties along the particle paths instead in x,y,z space Along the particle paths between the primary and secondary shocks the entropy is constant and the simple thermodynamic relationships can be used

MABS21 Israel 2010 Smoke Tracers on Snowball (500 t TNT, 1964)

MABS21 Israel 2010 Particle Trajectory Analysis Radius Time Primary Shock Particle Trajectories ΔRo ΔRΔR

MABS21 Israel 2010 The Spherical Piston G. I. Taylor (1946)

MABS21 Israel 2010

Piston Path compared to gauge MINOR UNCLE 2 kt ANFO Hydrostatic pressure

MABS21 Israel 2010 Piston Path compared to gauge MINOR UNCLE 2 kt ANFO Dynamic Pressure

MABS21 Israel 2010 SCALING For most explosives, the physical properties of blast waves scale with great precision over wide ranges of charge mass and atmospheric conditions using Hopkinson’s (1915) and Sachs’ (1944) scaling laws

MABS21 Israel 2010 SCALING For most explosives, the physical properties of blast waves scale with great precision over wide ranges of charge mass and atmospheric conditions using Hopkinson’s (1915) and Sachs’ (1944) scaling laws A 1950s Tripartite (US, UK & Canada) agreement recommended all blast results be scaled to a unit charge mass at NTP

MABS21 Israel 2010 Hopkinson’s & Sachs’ Scaling

MABS21 Israel 2010 Scaling Peak Values Dewey, 1964 TNT Surface Burst 30 kg 100 tonne

MABS21 Israel 2010 Scaling Time Histories TNT Surface Burst 30 kg 100 tonnes (Dewey, 1964)

MABS21 Israel 2010 Scaling Not Being Used Experimenters are not taking advantage of the scaling laws

MABS21 Israel 2010 Scaling Not Being Used Experimenters are not taking advantage of the scaling laws Charge mass, and ambient atmospheric conditions frequently are not measured or recorded

MABS21 Israel 2010 Scaling Not Being Used Experimenters are not taking advantage of the scaling laws Charge mass, and ambient atmospheric conditions frequently are not measured or recorded This makes it impossible to validate results

MABS21 Israel 2010 Shock Reflection (HOB) H RS PS MS Regular ReflectionMach Reflection TP

MABS21 Israel 2010 Von Neumann 2 & 3 Shock (1943)

MABS21 Israel 2010 Hydrostatic Pressure 1.25 kg TNT at 1.7 m HOB (AirBlast)

MABS21 Israel 2010 Dynamic Pressure 1.25 kg TNT HOB 1.7 m (AirBlast) RR MR Transition

MABS21 Israel 2010 Over-emphasis on Hydrostatic Pressure Most blast wave properties are expressed in terms of hydrostatic overpressure This was because it was the only physical property of a blast wave that could be measured with adequate time resolution

MABS21 Israel 2010 Over-emphasis on Hydrostatic Pressure Hydrostatic pressure is the least sensitive of all the physical propertiese.g. contact surfaces, boundary layer

MABS21 Israel 2010 Over-emphasis on Hydrostatic Pressure Hydrostatic pressure is the least sensitive of all the physical propertiese.g. contact surfaces, boundary layer Hydrostatic pressure is not the primary cause of damage by a blast wave. Most damage and injury is caused by the drag forces, i.e. drag coeff. x dynamic pressure

MABS21 Israel 2010 Dynamic Pressure P D = ½ ρ u * |u| Dynamic pressure is a mathematical, not a physical property of a compressible flow i.e. it is not directly measureable.

MABS21 Israel 2010 Dynamic Pressure P D = ½ ρ u * |u| Dynamic pressure is a mathematical, not a physical property of a compressible flow i.e. it is not directly measureable. Most analyses now use numerical simulation techniques from which dynamic pressure is as easily derived as any other property.

MABS21 Israel 2010 Example: Entrance Labyrinths & Blast Wave Mitigation

MABS21 Israel 2010 Energy Loss is Minimal Energy in a blast wave is essentially

MABS21 Israel 2010 Energy Loss is Minimal Energy in a blast wave is essentially If the hydrostatic pressure is decreased then the dynamic pressure must increase

MABS21 Israel 2010 MABS Results At the last three MABS, twenty papers dealt with blast mitigation

MABS21 Israel 2010 MABS Results At the last three MABS, twenty papers dealt with blast mitigation Only one discussed the energy relationship between hydrostatic and dynamic pressure

MABS21 Israel 2010 MABS Results At the last three MABS, twenty papers dealt with blast mitigation Only one discussed the energy relationship between hydrostatic and dynamic pressure Only two attempted to measure or report the dynamic pressures

MABS21 Israel 2010 MABS Results At the last three MABS, twenty papers dealt with blast mitigation Only one discussed the energy relationship between hydrostatic and dynamic pressure Only two attempted to measure or report the dynamic pressures Two report that although the side-wall pressures were reduced the end-wall pressure was enhanced

MABS21 Israel 2010 Concluding Remarks Thanks to my MABS colleagues and friends

MABS21 Israel 2010 Concluding Remarks Thanks to my MABS colleagues and friends Thanks to Spiez Labor for Spiez-base and the web site.

MABS21 Israel 2010 Concluding Remarks Thanks to my MABS colleagues and friends Thanks to Spiez Labor for Spiez-base and the web site. I shall miss the thrill of the count-down and the smell of detonation products

MABS21 Israel 2010

The Solution Work in Lagrangian co-ordinates Along the particle paths between the primary and secondary shocks the entropy is constant and the simple thermodynamic relationships can be used Thus the measurement of one physical property allows all the others to be calculated

MABS21 Israel 2010 Rankine-Hugoniot Equations Conservation of mass, momentum and energy for a compressible flow Created before the existence of a shock was known More precise than experimental accuracy Ms < 3 (OP 7 atm) gamma = Ms > 3 use real gas gamma

MABS21 Israel 2010 MABS Results At the last three MABS, twenty papers dealt with blast mitigation Only one discussed the energy relationship between hydrostatic and dynamic pressure Only two attempted to measure or report the dynamic pressures Two report that although the side-wall pressures were reduced the end-wall pressure was enhanced

MABS21 Israel 2010 Energy Loss is Minimal Energy in a blast wave is essentially If the overpressure is decreased then the dynamic pressure must increase The energy may also be spread in time and distancethus decreasing the peak pressures

MABS21 Israel 2010 Dynamic Pressure P D = ½ ρ u * |u| Dynamic pressure is a mathematical, not a physical property of a compressible flow i.e. it is not directly measureable. Most analyses now use numerical simulation techniques from which dynamic pressure is as easily derived as any other property. P D is better related to the drag forces which cause most of the damage & injury.

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg Uncased ANFO < several 100 kg

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg Uncased ANFO < several 100 kg ANFO yield increases with loading density

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg Uncased ANFO < several 100 kg ANFO yield increases with loading density AgN3 valid to 0.5 mg

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg Uncased ANFO < several 100 kg ANFO yield increases with loading density AgN3 valid to 0.5 mg Scaling limits for most explosives have not been reported

MABS21 Israel 2010 Limitation of Scaling Cast uncased TNT < about 4 kg Uncased ANFO < several 100 kg ANFO yield increases with loading density AgN3 valid to 0.5 mg Scaling limits for most explosives has not been reported In the M tonne range, atmospheric stratification becomes important

MABS21 Israel 2010 Energy Loss is Minimal Energy in a blast wave is essentially If the overpressure is decreased then the dynamic pressure must increase The energy may also be spread in time and distancethus decreasing the peak pressures