Patent Grant
8646373
Not applicable.
1. The Field of the Invention
The invention relates to blast wave absorption systems and more specifically to blast wave absorption systems that effectively suppress Mach reflections of a supersonic blast wave.
2. The Relevant Technology
When a bomb or other explosive device is detonated, the area around the explosion becomes overpressurized, resulting in highly compressed air particles that travel outward from the explosion at a high rate of speed, thereby forming a blast wave. This blast wave will dissipate over time and distance and will exist generally only for a matter of milliseconds at any one distance from the explosion. However, in that short amount of time the blast wave can create a tremendous amount of force against anything with which it comes in contact, typically causing a great deal of damage. Furthermore, a transonic flow can follow the shock wave front, which causes a secondary force that can also cause damage.
The faster a blast wave propagates the more damage it potentially can inflict. At the speed of sound in the air (Mach (M)=1 or approximately 330 m/s) the equivalent excess pressure caused by the blast wave is close to 0.6 bars. This pressure is dangerous for most buildings, but typically not sufficient to damage an armored vehicle. At larger blast wave velocities (i.e., at supersonic speeds (M>1)), however, the waves become damaging to practically any man-made structure.
To protect against such a blast wave, devices have been designed to absorb the energy caused by these blast waves. Some typical areas where the energy absorbing devices have been used include explosive ordnance disposal (EOD) suits, vehicle armor, supersonic aircraft engine linings, and building protection. One feature that is common to these current designs is the use of energy absorbing elements. One example of a current use of an energy absorbing element is a blast door. The typical blast door is suspended on springs so that the springs can absorb the impact energy when the blast wave hits the door. Another example is chalk panels, which fracture on impact and friction between the particles absorbs energy. Another energy absorbing scheme is described in U.S. Pat. No. 6,200,664, where energy is absorbed by liquid contained within collapsible structures. Still another example is described in U.S. Pat. No. 7,017,705, which deals with incident and reflected waves by incorporating an evacuated layer in a wave-absorbing device.
While energy absorbing devices have been effective for blast waves traveling at lower velocities, they have not been able to withstand the higher velocity blast waves. What is needed in the art, therefore, are systems that can increase dissipation or deflection of the higher velocity blast waves, with or without the use of energy absorbing materials or devices.
Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope.
a-13b are cross-sectional views of a blast panel having a deformable layer according to an embodiment of the present invention;
a-17d are cross-sectional views showing what happens when an incident blast wave propagates toward the blast panel shown in
a-18g depict various types of structures having inventive blast panels attached thereto or integrated therewith.
The present invention relates to blast wave absorption systems capable of dissipating or deflecting blast wave energy due to the shape of the surface of armor plating associated therewith. More specifically, the embodiments described herein have armor plating with surfaces that include peaks and valleys formed thereon in such a manner that much of the energy is deflected or otherwise dissipated.
A “shock wave” as used herein is defined as a region of abrupt change of pressure and density moving as a wave front at or above the velocity of sound, such as that caused by an intense explosion or supersonic flow over a body. A “blast wave” as used herein is a type of shock wave that is a violent propagating disturbance, produced by an explosion in air, that consists of an abrupt rise in pressure followed by a drop in pressure to or below atmospheric pressure. A blast wave can also be considered a single shock wave that propagates through a medium over time. That is, a blast wave as used herein does not refer to a steady state condition but to a one time “pulse.” Although the discussion herein is directed to blast waves, it is appreciated that embodiments of the present invention can also be used with other types of shock waves, including steady state shock waves.
As noted above, when a bomb or other explosive device is detonated, a blast wave is generated that emanates out from the explosion at a high rate of speed. For large explosives this blast wave is typically supersonic. As is known in the art, when a supersonic flow or wave impinges on a wedge or at an angle to a flat wall, a reflection occurs. The type of reflection depends on the velocity of the flow or wave (also known as the Mach number M, where M=1 corresponds to the speed of sound in the medium) and the angle α between the wall or the wedge and the direction of the supersonic flow. There are three distinctive types of reflections caused by supersonic flows in gases (see, e.g., B. W. Skews, J. T. Ashworth, The Physical Nature of Weak Shock Wave Reflection, Journal of Fluid Mechanics, 2005, vol. 542, pp. 105-114). At small angles α and/or small Mach values M, regular reflections occur. At larger angles and Mach numbers, a connector is formed between incoming and reflecting supersonic flow called a Mach stem, and this type of reflection is called Mach reflection. Finally, in a very narrow range of Mach numbers, Von Neumann types of reflection exist, but will not be considered herein.
An example of areas corresponding to regular and Mach reflection, and transition areas therebetween, is shown in the graph of
For example, in a system corresponding to
As can be seen from
Regular and Mach reflections are known in the art. Because of this only a cursory, explanation of each will be given herein. Turning to
As shown in
Although not completely eliminating Mach reflections, embodiments of the present application minimize the amount of Mach reflection caused by the incident supersonic flow against the blast panel. Specifically, the surface profile is designed to reduce the overall Mach reflection of an incident supersonic flow by use of peaks and valleys formed thereon.
A first peak 146 is formed on outer surface 144. First peak 146 comprises two side surfaces 150 and 152 that both extend out to a first apex 148 on opposite sides of a longitudinal axis 154. In some embodiments, longitudinal axis 154 bisects the angle formed between side surfaces 150 and 152 at first apex 148. In some embodiments, longitudinal axis 154 is orthogonal to inner surface 142 of blast panel 140. In any event, longitudinal axis 154 is designed to be generally aligned with the propagation direction 147 of incident blast wave 145 when the portion of blast panel 140 that contains first peak 146 is “face on” to incident blast wave 145.
As depicted in the cross-sectional view of
Various values can be used for angles α1a and α1b, as long as those angle values will cause a regular reflection to occur. For example, in a system that conforms to the values shown in
In some embodiments, the combined angle between side surfaces 150 and 152 (i.e., α1a+α1b) can be less than about 80 degrees, less than about 60 degrees, or less than about 40 degrees. Other ranges of combined angles are also possible.
A second peak 156 is formed on outer surface 144 adjacent to first peak 146. Second peak 156, which is shorter than first peak 146, comprises two side surfaces 160 and 162 that both extend out to a second apex 158 on opposite sides of a longitudinal axis 164. In some embodiments, longitudinal axis 164 bisects the angle formed between side surfaces 160 and 162 at second apex 158. In some embodiments, longitudinal axis 164 is orthogonal to inner surface 142 of blast panel 140. In any event, longitudinal axis 164 is designed to be generally aligned with the propagation direction 147 of blast wave 145 when the portion of blast panel 140 that contains second peak 156 is “face on” to blast wave 145. In some embodiments, longitudinal axis 164 is generally parallel to longitudinal axis 154.
As depicted in the cross-sectional view of
In the depicted embodiment, surfaces 160 and 162 are substantially symmetrical about the peak's longitudinal axis 164 (i.e., angles α2a and α2b, are substantially the same), although this is not required. Also, in some embodiments, a line drawn tangential to the slope of the shorter second peak 156 at apex 158 (see dashed line 166) does not intersect adjacent taller first peak 146. This helps to avoid reflected wave trappings, thus minimizing the pressure against the blast panel.
Unlike angles α1a and α1b of first peak 146, angles α2a and α2b are not constrained by the type of reflection they will cause to occur. That is, angles α2a and α2b can be sized such that a regular or Mach reflection or a combination thereof will occur on each side of second peak 156 when an incident supersonic flow, such as blast wave 145, moving in the direction of the longitudinal axis 164 contacts the side surfaces 160 and 162 near second apex 158. Thus, a wide range of values can be used for angles α2a and α2b. For example, in a system that conforms to the values shown in
As shown in
As noted above, first peak 146 is taller than second peak 156. That is, the distance d1 between the bottom of the first valley 168 and apex 148 in the direction of longitudinal axis 154 is greater than the distance d2 between the bottom of the first valley 168 and apex 158. As discussed below, the value of d1 can be affected by whether transonic flow suppression is desired. Distance d1, generally varies between about 0.5 microns to about 100 cm, with higher and lower values also possible. In some embodiments d1 can vary between about 0.2 mm to about 50 mm, with about 1 mm to about 10 mm being common. In other embodiments, d1 can vary between about 1 cm to about 100 cm, with about 1 cm to about 10 cm being common. In other embodiments, d1 can be greater than about 0.3 mm, greater than about 1 mm, or greater than about 1 cm. Smaller values for d1 can also be used for other embodiments, as discussed in more detail below.
As noted above, distance d2 is less than d1. In some embodiments, d1 can be between about 2 and about 10 times greater than d2, while in other embodiments d1 can be between about 5 and about 10 times greater than d2. In other embodiments, d1 can be at least 2 times greater than d2, at least 5 times greater than d2, or at least 10 times greater than d2. Other comparative sizes of d1 and d2 are also possible.
The distance between the first peak 146 and the second peak 156, represented by d4 in
In some embodiments, d4 can vary as a proportion of d1. For example, in some embodiments, d4 can be between about 0.5 to about 2 times the measurement of d1, with about 0.5 to about 0.9 being common. In other embodiments, d4 can be equal to or less than d1; and in other embodiments substantially less than d1. Other comparative sizes of d1 and d4 are also possible.
In some embodiments, a third peak 176 is formed on outer surface 144 adjacent to second peak 156. As shown in
As depicted in the cross-sectional view of
As with angles α1a and α1b, various values can be used for angles α3a and α3b, as long as those angle values will cause a regular reflection to occur. For example, in a system that conforms to the values shown in
As shown in
As noted above, third peak 176 is generally the same height as first peak 146. That is, the distance d3 between the bottom of the second valley 188 and apex 178 in the direction of longitudinal axis 184 is generally the same as the distance d1 between the bottom of the first valley 168 and apex 148. As such, distance d3 can conform to the same ranges as discussed above regarding d1. In some embodiments, third peak 176 is the same height as first peak 146 and has substantially the same attributes as first peak 146.
Similarly, the distance d5 between second peak 156 and third peak 176 is generally the same as the distance d4 between first peak 146 and second peak 156. That is, the orthogonal distance d5 between longitudinal axis 164 of the second peak and the longitudinal axis 184 of the third peak 176 is generally the same as the distance d4 between the longitudinal axis 154 of the first peak and the longitudinal axis 164 of the second peak 156. As such, distance d5 can conform to the same general ranges as discussed above regarding d4.
Blast panel 140 can be made of a variety of materials that can withstand the forces of a blast wave. For example, blast panel 140 can be made of metals (such as aluminum, titanium, steel, or alloys), plastics, ceramics, composites (such as fiber reinforced materials), rubber, and concrete. Other materials can also be used. In some embodiments, blast panel 140 is made from a material able to withstand a dynamic pressure of at least 0.1 MPa.
With the novel peaks and valleys construction described above, the blast panel 140 is able to better deflect and/or dissipate energy from the incoming incident blast wave and the subsequent transonic flow. As noted above in conjunction with
Furthermore, as shown in
As shown in
As shown in
As noted above, a transonic flow typically follows the incident blast wave to cause a secondary force against the blast panel. When the shock wave propagates at high Mach speeds, such as above 1.5, the transonic flow can generate close to 0.6 bars of pressure or higher against the blast panel, which can add to damage incurred as a result of the blast wave. The curved shapes of side surfaces 152, 160, 162, 180 that form valleys 168 and 188 of blast panel 140 help to alleviate this problem.
For example, as shown in
Transonic flow suppression can impose size limitations. For example, to obtain a high efficiency, the size of the profile elements should not be less than the thickness of the boundary layer. For a typical transonic flow, the boundary layer is approximately 0.2 to 0.3 mm. As such, an efficient profile should be at least that tall. That is, the distances d1 and d3 between the bottom of the valleys 168 and 188 and the apexes 148 and 178 of the highest peaks 146 and 176 (see
In many cases, the suppression of the transonic flow associated with a blast wave is not a concern. For example, thick reinforced concrete structures or poles are typically strong enough to ignore transonic flow pressure contributions. In these cases, the valleys between the peaks can be formed without curved surfaces, thus making manufacturing easier. For example,
As noted above, blast panel 200 is similar to blast panel 140 except that instead of first and second valleys 168 and 188 being continuously curved, blast panel 200 has first and second valleys 202 and 204 that are substantially v-shaped. In this embodiment, side surfaces 150, 152, 160, 162, 180, and 182 are all substantially linear. Side surfaces 152 of first peak 146 and 160 of second peak 156 come together to form a first vertex 206 at the bottom of the first valley 202, and side surfaces 162 of second peak 146 and 180 of third peak 176 come together to form a second vertex 208 at the bottom of the second valley 204. Although side surfaces 150, 152, 160, 162, 180, and 182 are depicted as being substantially straight, other non-linear shapes can also be used. For example, side surfaces 150, 152, 160, 162, 180, and 182 can have multiple angles or can have a combination of straight and curved sections. Other shapes are also possible.
Although part of the flow may become trapped in the valleys, blast panels having v-shaped, valleys offer some advantages over blast panels with curved valleys if suppression of the transonic flow is not a concern. For example, manufacturing of blast panels having v-shaped valleys may be easier and cheaper than the manufacture of blast panels having curved surfaces. Tolerances for the v-shaped surfaces can typically be much more forgiving than with the parabolic or other curved surfaces, especially when using concrete and the like.
Furthermore, the profile of the blast panel surface can be much smaller. As noted above, to have a high efficiency when attempting to suppress the transonic flow, the thickness of the boundary layer of the flow is a limiting factor, requiring the height of the tall peaks to be at least 0.2 to 0.3 mm. However, if transonic flow suppression is not a concern, the main limiting factor for efficiency is the thickness of the shock wave front which is much thinner than the boundary layer. At M=1, a shock wave front in air has a thickness of about 0.05 microns. The thickness is even smaller at higher Mach numbers. Therefore, if transonic flow suppression is not a concern, a micron-size profile can be efficient, which is about a thousand times smaller than the profile required for high efficiency of the blast panel attempting to suppress transonic flow. As such, d1 can have other values and ranges of values than those discussed above if transonic flow is not an issue. For example, in some embodiments distance d1 can vary between about 0.1 micron to about 100 microns with about 1 to about 10 microns or about 1 to about 5 microns being common. In some embodiments, d1 can be less than about 1 micron, less than about 10 microns or greater than about 0.5 microns. Other values for d1 are also possible.
In some embodiments, the tall and short peaks are included in a repeating pattern of peak structures, with each peak structure including a taller peak and a shorter peak positioned with respect to each other as discussed above. For example,
Furthermore, each of the peaks 146 and 156 can be linearly formed on the outer surface 144 of the blast panel. For example,
It is also appreciated that the ridges, peaks and valleys can be arranged so as to form other linear and non-linear geometric patterns on the armor plating surface 144. For example,
Although the blast panel having non-linear ridges can be somewhat harder to manufacture, aesthetics or other reasons may dictate using such a structure.
In some embodiments, the blast panel includes a thin deformable or compressible layer positioned next to the outer surface of the blast panel so as to follow the contours of the peaks and valleys. For example,
Deformable layer 232 needs to be thin enough to be able to conform to and keep the same general shape as the profile of outer surface 144. In some embodiments, deformable layer 232 has a thickness that can vary between about 10 microns to about 100 microns, with about 20 microns to about 50 microns being common. In other embodiments, deformable layer 232 has a thickness that is less than about 50 microns, less than about 20 microns, or less than about 10 microns. For larger peaks and valleys, deformable layer 232 can have a thickness up to about 5 cm or up to about 1 cm.
Using a deformable layer can yield additional benefits to the blast panel. For example, as shown in
In some embodiments, space 252 has a thickness that can vary between about 10 microns to about 100 microns, with about 20 microns to about 50 microns being common. In other embodiments, space 252 has a thickness that is less than about 50 microns, less than about 20 microns, or less than about 10 microns. For larger peaks and valleys, space 252 can have a thickness up to about 5 cm or up to about 1 cm.
In many cases it is desired that the blast panel profile be protected from the elements. For example, mud or other debris can coat the profile or get stuck within the valleys. Furthermore, in many cases protection is desired against the sharp edges of the peaks of the profile, such as on wearable armor or a helmet. For these and other reasons, in some embodiments the blast panel includes a covering positioned over the blast panel. For example,
Of course it is noted that while each of the particular embodiments of blast panels described above may show either only curved valleys or only V-shaped valleys, this is by no means meant to limit the scope of the invention. That is, any of the embodiments described above could use either type of valley depending on the desire of the user. Furthermore, if so desired by the user, both types of valleys can be incorporated into the same blast panel.
The various embodiments of blast panels described herein can be attached to or integrated with many different types of structures, such as those shown, for example, in
c shows an aircraft 284 comprising an airframe 286 onto which one or more engines are mounted. The airframe 286 typically includes a fuselage 288 having wings 290 and a tail section 292 extending therefrom. The airframe 286 has an inner surface 294 designed to face the interior of the airframe 286, and an opposing outer surface 296 designed to face the exterior of the aircraft. An inventive blast panel 298 is incorporated on at least a portion of the inner surface 294 of the aircraft to protect the aircraft structure against a bomb or other explosive device that is detonated on the inside of the aircraft, for example by terrorists. Of course, it is appreciated that one or more inventive blast panels can also be incorporated on the outer surface 296 of the aircraft.
d shows a building structure 300 having an exterior wall 302. The exterior wall 302 has an outer surface 304 configured to face away from the interior of the building structure 300. A plurality of inventive blast panels 306 are disposed on or integrated with the outer surface 304 of the exterior wall 302. The blast panels 306 are disposed side by side and the rows are offset from adjacent rows although this is not necessary. Of course, instead of multiple blast panels 306, a single blast panel covering the outer surface 304 can alternatively be used. Inventive blast panels can also be used with other structures, such as towers, bunkers, walls, and the like.
e through g show various articles that can be worn that include an inventive blast panel incorporated thereon.
Testing has confirmed the reduction in force felt by a structure that uses the inventive profiled blast panel. In one test, panels made from 7075 aluminum alloy plates were machined with profiled parabolic mills so as to have the surface profile shown in
Both sets of panels were tested concurrently in each test to determine the difference in force felt by each type of panel due to an explosive blast. For each test, the profiled and non-profiled panels were mounted side-by-side on identical ballistic pendulums with accelerometers so that the panels would be facing the blast wave, and the ballistic pendulums were disposed behind the panels to measure the force from the blast wave. The ballistic pendulums weighed 2.7 kg, which can be thought to represent part of the mass of a typical man's head, and the panel area corresponded to the normal projection of roughly the same part of the head. The test measurements were taken in the open field at a distance of four meters from the blasts. Tests were performed using different masses of explosive charges. Electric detonators with 5 ms delay were used to detonate explosive charges of composition C-4 with masses of 2, 3.75 and 5 kg. The charges were positioned 1.2 m above the ground. The charges had a cylindrical shape and were oriented with the cylinder axis vertical relative to the ground. Panels on the ballistic pendulums were also positioned approximately 1.2 m above the ground, assuring that any interference from the blast wave reflected from the ground could be easily differentiated. Accelerometer data was recorded at 1 Ms/s with 25-50 ms of data obtained and stored for each test.
Using the data obtained from each test, the ratio of the maximum force on the blank panel to the maximum force on the profiled panel was determined as a function of the shock wave Mach number, and is shown in
Each data point in
As shown in
Extrapolating from
It is appreciated that the tests described above were performed using nearly ideal profile shapes at particular Mach numbers. As noted above, the profile can be adjusted to any shock wave front velocities, corresponding to a variety of expected threats. Within the scope of this invention the profile can be used as is, or somewhat simplified for easier manufacturability. While non-ideal shapes may not yield the same spectacular results, they will still be able to provide a substantial increase of protection over conventional blast panels.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract No. N00173-07-C-2055 awarded by U.S. Naval Research Laboratory.
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