A History of Research and a Review of Recent Developments

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Blast simulation 127 long, and a further expansion cone connected this section to a 4.86 m diameter section 66 m long. This was followed by a semi-circular 10.7 m diameter extension. The development and calibration of the simulator has been reviewed by Tate [6.20] who noted that the guns were removed and the blast wave was eventually generated in the 1.82 m tube by the detonation of up to 100 m of detonating cord (59 g of PETN/m) wound vertically on an expanded polystyrene former. The use of explosives rather than compressed air meant that the diaphragms of the early small shock tubes were no longer required. The blast wave shape was found to be very similar to the ‘Friedlander’ shape discussed earlier (see Figure 1.1), although for economic reasons the larger tubular sections were shorter in length than would be normally adopted in shock tube work. The complete facility is shown in Figure 6.3, taken from ref. [6.20]. We have already noted that a rarefaction wave is produced at the open end of a shock tube, and considerable research has taken place to support the development of suitable Rarefaction Wave Eliminators (RWE). In the Foulness tube the eliminators take the form of metal grids that give partial blockages at the open end of the final tunnel and at the end of the 4.86 m diameter section. The blockage due to the grid at any section is about 40% of the total crosssectional area, and Tate points out that a restriction less than this would allow too strong a rarefaction wave to propagate back into the preceding tube; a greater restriction would limit the peak pressure attainable in the final semicircular test section. The ratio of the peak instantaneous pressures in the sections of the tube are, to a first approximation, inversely proportional to the ratio of the cross-sectional areas. At the time of Tate’s paper the peak pressure in the final semi-circular tube was limited to less than 55 psi. Figure 6.3 Explosive-driven blast-wave simulator, Foulness, UK (from Tate, ref. 6.20).
128 Pressure measurement and blast simulation The development of the Foulness simulator demonstrates the various aspects of detail design, equipment and instrumentation that must be taken into account in the construction and operation of large shock tubes. For example, there was considerable experimentation and discussion before the method used to drive the simulator was finally evolved, as reported by Clare [6.21]. The ‘smoothing’ of high-frequency perturbations that affect the shock wave/duration profile was important, and research was devoted to the use of an aqueous foam plug in the 2.4 m diameter section to attenuate the ‘spikes’ in the wave form. The ‘side-on’ pressure gauges to measure static pressures in the main test sections have been described by Leys [6.19] and dynamic differential pressure gauges were developed and described by Ethridge et al. [6.22]. The Foulness facility simulates an equivalent free-air high explosive yield of 1.5 kt of TNT, which has a peak overpressure of up to 50 psi and a positive phase duration of 350 msec. The simulator reaches the required pressure, but the positive phase durations are somewhat less than 350 msec. Depending on the use of smoothing and rarefaction eliminators, the durations are between 150 and 300 msec. The compressed air system, rather than the explosive methods of driving shock tubes, has been retained by the French and German authorities in their blast simulator development. In the 1970s the French installed an air-driven simulator at the Centre d’Etudes de Gramat, which consisted of a single large semi-circular tube, 100 m long, 70 m 2 in cross-sectional area, driven by a bank of single shock tubes of less than 1m in diameter. The shock fronts emerging from the individual driver tubes are mixed and diffracted, and this causes a very spiky pressure/duration relationship. This must be smoothed as far as possible in a zone of the tube between the driver tubes and the test section as indicated in Figure 6.4. At the far end of the tube a reflection wave eliminator in the form of a grid is used. The conception and performance of this simulator has been described by Gratias and Monzac [6.23], and research into methods of damping or eliminating the perturbations in the pressure/time curves by the use of perforated tunnels and extension cones has been reported by Hoffman [6.24]. The driver tubes were originally separated from the driven zone by metal diaphragms, which were broken instantaneously by pyrotechnic devices. The safety rules associated with the installation of these devices, and the possibility that pieces of the diaphragms might break off and become projectiles down the tube, led to research in diaphragm replacement, reported in 1985 by Gratias [6.25]. It was proposed that a valve system be used with a very short opening time of about 20 msec. A parallel study on fast acting valve systems was made at the same time by Osofsky and Mason [6.26], as part of the feasibility study for a US military large shock tube test facility. They concluded that heated driver gas was required to produce good wave forms if the diaphragm system was used. In the diaphragm system unheated driver gas produced dynamic pressure discontinuities, particularly at high overpressures (735 psi). If, however, fast acting valves were used in place of diaphragms, it was found possible to
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EXPLOSIVE LOADING OF ENGINEERING ST
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Explosive Loading of Engineering St
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Contents Preface vii Acknowledgemen
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Preface A long time ago I walked ov
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Acknowledgements The reports from w
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xii Notation m mass of projectile m
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xiv Notation Q work done during exp
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Introduction Explosions can threate
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Introduction xix Bertram Hopkinson
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Introduction xxi in the seventeenth
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Introduction xxiii own versions of
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Introduction xxv indoor shelters an
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Introduction xxvii explosions/ stru
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Introduction xxix particularly dama
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Introduction xxxi but the feeling i
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2 The nature of explosions propelli
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4 The nature of explosions or rathe
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6 The nature of explosions ogive, a
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8 The nature of explosions mass, an
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10 The nature of explosions Figure
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12 4 lb cylinders, TNT, 3.75 lb sph
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14 The nature of explosions As Figu
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16 The nature of explosions of the
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18 1.4 THE DECAY OF INSTANTANEOUS O
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20 The nature of explosions Figure
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22 The nature of explosions where I
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24 sometimes written in psi as The
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26 The nature of explosions 1.20 Ki
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28 The detonation of explosive char
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50 Figure 2.18 Radius/time curve of
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54 and 50%, rather than by a factor
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3 Propellant, dust, gas and vapour
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Dust explosions 61 as the period 19
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Gas explosions 63 reported by Palme
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Gas explosions 65 workings in very
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Vapour cloud explosions 67 the leak
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References 69 in Los Angeles Harbou
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4 Structural loading from distant e
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Uniformly distributed pressures 73
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Table 4.1 Loading/time relationship
Page 110 and 111: Loading/time relationships 77 overp
Page 112 and 113: Loading/time relationships 79 side
Page 114 and 115: Loads on underground structures 81
Page 120 and 121: Loads on underwater structures 87 c
Page 122: References 89 4.12 Allgood, J. (197
Page 125 and 126: 92 Structural loading from local ex
Page 131 and 132: 98 The general empirical equation f
Page 133 and 134: 100 Structural loading from local e
Page 145 and 146: 112 Figure 5.16 Relationship betwee
Page 153 and 154: 120 Pressure measurement and blast
Page 159: 126 Pressure measurement and blast
Page 175 and 176: 142 Penetration and fragmentation r
Page 177 and 178: 144 Penetration and fragmentation p
Page 179 and 180: 146 Penetration and fragmentation w
Page 181 and 182: 148 Penetration and fragmentation T
Page 183 and 184: 152 Penetration and fragmentation F
Page 185 and 186: 152 Penetration and fragmentation n
Page 191 and 192: 158 Figure 7.16 Penetration simulat
Page 195 and 196: 162 Penetration and fragmentation b
Page 197 and 198: 164 Table 7.1 Penetration and fragm
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Page 203 and 204: 170 Penetration and fragmentation l
Page 207 and 208: 174 Penetration and fragmentation p
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178 Penetration and fragmentation o
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180 Penetration and fragmentation 7
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182 Penetration and fragmentation 7
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184 The effects of explosive loadin
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188 Table 8.1 It is worth noting th
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200 Table 8.5 The effects of explos
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216 Response, safety and evolution
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224 In the log-normal distribution
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230 Cole, R.H. 46, 48, 53, 55, 99 C
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232 Petry 143 Philip, E.B. 13, 14,
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Subject index Aircraft damage 207 A
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A History of Research and a Review of Recent Developments

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