In armed conflicts, land mines are a serious threat to people or vehicles traveling on the ground. In recent conflicts around the world, attacks from improvised explosive devices (IED) are becoming more common. IEDs may also include some form of armored penetrator, including explosively formed penetrators (EFP). Armored vehicles, such as the Mine Resistant Ambush Protected (MRAP) vehicle, have been designed to help withstand these attacks and minimize harm to the vehicle's occupants.
A vehicle is provided with one or more structural channels that help to dissipate blast energy and debris from explosions. In one embodiment, the channel, which is open at both ends, extends vertically through the vehicle. The channel thereby provides a passage through the vehicle for blast energy and gas and debris from an explosion beneath the vehicle. The soldiers in the crew compartment remain isolated and protected from damaging effects of the explosion.
The channel can have a variety of configurations. For example, the channel can be in the configuration of a straight-sided cylinder with a round, rectangular, or other cross-section. The channel can include a converging section and/or a diverging section to provide a nozzle to further accelerate debris through the passage. The channel can be in the configuration of a slot open toward the rear, sides, or front of the vehicle. Multiple channels can be provided in a single vehicle.
The channel is structurally attached to the structure of the vehicle, becoming another structural component of the vehicle. In particular, the channel is structurally attached to the hull floor, thereby strengthening and adding rigidity to the hull floor. This further increases the ability of the vehicle to withstand an explosion from underneath. The hull floor can be shaped to function cooperatively with the channel. For example, the hull floor can be V-shaped, which further redirects outwardly from the vehicle any blast energy and debris that is not directed into the channel. In one embodiment, the hull floor is formed with multiple pyramid shapes nested within a base of a larger truncated pyramid shape. The channel can also serve as a mount for a platform or accessories, or as a pick point for lifting or picking the vehicle off the ground.
In another embodiment, the channel is formed from one or more elements having a surface shaped to redirect a blast flow originating beneath the structural enclosure, the surface attached to the structural enclosure adjacent a side of the hull floor.
In another aspect, the channel can serve as a storage compartment for objects that would be sacrificed during a blast. The objects can be mounted within, above, or below the channel with breakaway mounting fixtures.
The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
The disclosures of U.S. Provisional Patent Application No. 61/284,488, filed Dec. 18, 2009, and U.S. patent application Ser. No. 12/807,818, filed Sep. 14, 2010, are incorporated by reference herein.
A vehicle 10, generally an armored vehicle such as an MRAP (mine resistant ambush protected) vehicle or HMMWV (high mobility multipurpose vehicle), is provided with one or more structural channels 20 that extend fully through the vehicle from the floor 12 to the roof 14 of the vehicle. See
The channel 20 vents energy from an explosive blast through the vehicle early in the event. The vertical vector component of the directed energy from the blast is often the most damaging. Thus, the vertical orientation of the channel transmits the energy and gas and debris through and out the top of the vehicle before they can do more serious damage to the vehicle and its crew. The channel operates nearly instantaneously, allowing blast gas and debris to pass through the vehicle structure with minimal redirection or drag. The vehicle's occupants are substantially separated and insulated from the event.
The channel wall or walls 24 also form a structural element of the vehicle 10 by supporting the hull floor 12 or underbelly pan and transferring the load from the underbelly pan into the upper structure 18 of the vehicle. The channel thus provides another load path through the vehicle in addition to the vehicle's structural pillars. As a structural supporting element, the channel shortens the unsupported span length of the floor and roof in the vehicle. The channel wall or walls can also be designed to buckle to absorb un-vented energy that is transferred to the vehicle.
The channel 20 is structurally connected directly to the structural enclosure of the vehicle in any suitable manner. In particular, the channel is structurally attached to the hull floor 12 (the portion of the vehicle structure between the compartment 16 and the ground), thereby strengthening and adding rigidity to the hull floor. For example, the channel can be formed from a tube open at the top and bottom ends 26, 28 and attached to the floor 12 by welding or other suitable attachment mechanism. The tube is generally attached to the roof 14 of the vehicle. However, the channel can also be provided with vehicles having a non-structural roof or rag top. The channel can also be integrally formed with the structural enclosure of the vehicle. The channel can be used with any type of structural enclosure for a vehicle, such as a body-on-frame, body-frame integral, unibody or monocoque.
The channel 20 can be located in any suitable location within the vehicle. The center of the vehicle is generally a suitable location, because this interior space may be less used. The channel may have any suitable cross section in plan view. For example, the channel can be circular (see
The channel can have a straight wall or walls, as shown in
In another embodiment, the channel 520 can be in the form of one or more slots in the vehicle 510. The slots can be oriented toward the front, sides or rear of the vehicle.
The channel can be used with a variety of hull bottom shapes. For example, the hull bottom can be flat or V-shaped. The V-shaped hull can also aid in redirecting the blast energy and debris away from the vehicle.
Non-flat, angled vehicle bottoms (the so-called “V” bottom hull design) have been employed with some success in an effort to divert or guide the blast away from the vehicle, rather than taking the blast directly. However, as vehicles have gotten wider, while a significant angle to the ground needs to be maintained to make the “V” hull effective, the ground clearance has been reduced. Two problems with reduced ground clearance are: 1) reduced ground clearance from obstacles, causing the vehicles to hit the ground more easily, and 2) reduced ground clearance moves the vehicle closer to the explosion source, greatly increasing the local forces (pressures) on the hull. “Double-V” designs have been developed to help reduce the ground clearance problem, but such designs tend to trap the blast if it is centered on the vehicle. The present channel(s) can be used with an otherwise conventional “Double-V” design to reduce the vehicle's vulnerability to blasts centered under the vehicle, while preserving desired ground clearance.
The structural blast channel forms a stiff structural support to the floor. This stiff structural support helps to reduce blast effects, even without a vent, by supporting the floor or hull and increasing the mass presented to the blast. For example, a hollow box beam or tube or a non-hollow structural beam, such as an I-beam or C-channel, connected from the hull bottom to the roof or near the roof line stiffens the floor/hull.
While the present discussion has been focused on blasts centered under the vehicle, the present vented channel designs have also proved effective for off-center blasts. Generally, for non-vented designs, the effects of the blast are reduced as the blast moves away from the center of the vehicle. For the vented design, however, within a small area around the vent, the lowest effects are experienced if the blast is directly under the vent, and increases slightly away from the vent, but the effects are still much lower than the unvented case. Once outside the vicinity of the vent, the blast is sufficiently off center that the blast effects are reduced anyway (i.e. even for the unvented design).
The channel does two things that work together to reduce the effects on the occupants: First, the channel reduces the vertical explosive load on the vehicle hull bottom, especially at the center of the hull. Second, the channel provides a structural support to the hull bottom, reducing bottom side deflection. Directing energy into the entire vehicle, not just the hull floor, reduces the energy transferred and the effect on the crew.
A model of an expanding hemispherical debris field 840 impacting a circular plate 842 with a hole (vent) 844 at the center illustrates the reduction in vertical explosive load on the vehicle hull bottom. See
Consider a circular hull 842 of diameter Do, with a center vent hole 844 of diameter Di, placed a height h above an expanding debris field 840 of radius r as shown in
The absolute momentum per unit surface area of the debris hemisphere is given by
The component of momentum per unit hemisphere area normal to the hull bottom (i.e. in a vertical direction) is then
Integrating over the portion of the hemisphere that will interact with the hull bottom, using spherical coordinates, yields the total vertical momentum transfer. The vertical fraction of the absolute momentum that can be transferred to the hull is then:
Carrying out the integration yields:
The ratio of the momentum transferred with a vent to that without a vent gives an indication of the effectiveness of the vent. The fraction of vertical momentum that is transferred to the vented plate in comparison to the unvented case is then:
Assuming the plate with the vent has the same mass as the plate without the vent, then the fraction of kinetic energy transferred for the vented case in comparison to the unvented case is just the Momentum Fraction squared. The equal mass assumption is reasonable because the mass of the vehicle with the vent would be close to that without the vent. The Energy Fraction is then:
Test results have shown that the reduction may be further improved because the debris field is more energetic in the center where the vent is located, something that the uniform debris field model dose not account for. Also, test results have shown a further improvement in the reduction by tapering of the vent tube, and by shaping the hull bottom, from that of a flat plate.
As noted above and as discussed in conjunction with the models below, the present channel is effective in combination with a rigid hull. To investigate benefits of a rigid hull floor, consider a simplified vehicle under an applied impulse pressure loading from the bottom. Before the vehicle has had a chance to displace substantially, the impulse has come and gone, leaving the structure in a state of motion (i.e. velocity). It is this state of motion that the structure needs to deal with, and protect the occupants.
Consider first an idealized completely rigid vehicle as illustrated in
where a is the vertical acceleration and t is time. The resulting kinetic energy is then:
As an example, consider a 21,000 pound vehicle with a 44 ft2 hull area acted on by a pressure impulse of 500 psi-ms. The resulting velocity, using the rigid assumption, is 4.9 ft/sec (3.3 mph). The vehicle is moving upward and on a collision course with the occupants who have not yet been acted on. Fortunately, the velocity is low, and the impact will be similar to dropping the occupants into their seats from a height of 4 inches (i.e. dropping an object from a height of 4 inches results in a velocity of 4.9 ft/s). The total kinetic energy in the body is about 7,700 ft-lb.
Consider next a vehicle with a compliant hull bottom acted on by the same pressure impulse loading as the rigid hull, illustrated in
In order to simplify the flexible nature of the hull bottom, consider a rigid hull bottom connected to the body with springs, illustrated in
and the kinetic energy is given by:
If the hull bottom weighs 1000 pounds (of the total 21,000 lb), the velocity just after the impulse is 102 fps (about 70 mph) and the kinetic energy in the hull bottom is 162,000 ft-lb. This is now roughly equivalent to dropping the occupants into their seats from a height of 160 feet. This is a worse situation for the occupants compared to the rigid case.
This model demonstrates the so-called “slapping” effect of a compliant hull bottom into the vehicle (and occupants), which is a real effect and can be detrimental. The occupants need to be completely isolated from the hull bottom under this condition.
An increasingly rigid floor design can also, however, increase the likelihood of hull breach under the explosive load. Thus, a rigid hull floor in combination with a channel(s) to vent blast energy and gas and debris minimizes this possibility and can provide a beneficial synergy.
It is also useful to understand the effect of an off center blast and to look at the effectiveness of the vent channel with less than optimum placement, since the location of a blast cannot be determined in advance. Referring to
x=R sin φ cos θ+S
y=R sin φ sin θ
z=R cos φ
For the condition Z=h:
and
x=h tan φ cos θ+S
y=h tan φ sin θ
z=h
This yields a function of two variables for integration. The integration is done differently than for the centered case. Here, the integration is over the entire field of the expanding hemisphere, but the integrand is set to zero if the debris is outside of the annulus defined by Ri≦r≦Ro
Calculating the fraction of momentum and energy for the vented versus unvented case, in a similar manner to the centered case, results in the Energy Fraction plot shown in
Structural blast channels can also be taken as any pathway that vents blast waves and debris around the vehicle to lower the blast effects and improve survivability. Thus, redirecting blast channels can be provided to lower blast effects and improve survivability. The force resulting from redirecting the flow with a redirecting blast channel can counteract the effects of other forces resulting from the blast. The force is generated by changing the momentum of the blast effluent, which can be accomplished without changing the magnitude of the velocity, or speed, of the flow. Changing the direction of the flow is all that is needed to create a force. This is beneficial, because the device does not need to meet the blast effluent head on, but rather from the side. Force F is defined by Newton's second law of motion as the time rate of change of momentum P with respect to time t:
Force F and momentum P are both vectors. Thus, as illustrated schematically in
The redirecting blast channel can also form a thin shell 990 that extends over a large portion of the hull bottom and up along the sides to an extent. See
In a further aspect of the mitigating effect of a blast on a vehicle, referring to
In another aspect of mitigating the effects of a blast on a vehicle, the vehicle can include a mechanism to produce an upward force to hold the vehicle down during an explosion located beneath the vehicle. For example, referring to
In a further aspect, the vehicle can include a mechanism to produce an additional downward force to counter the upward force produced by the explosion and subsequent landing back on the ground. For example, referring to
Any suitable sensing device, such as an accelerometer, can be used to sense when the vehicle is accelerating upwardly or downwardly, and any suitable control mechanism can be provided to actuate either the downward force or the upward force, as necessary to counteract the blast lifting the vehicle up and the subsequent landing.
The structural blast channel or channels described above can also serve as a mount for a platform or for accessories. For example,
The structural blast channel can be used as a single pick point to lift or service the vehicle. A device 1430, 1440 can be inserted into the channel 1420 from either the top or the bottom of the vehicle 1410 to pick or to lift the vehicle off the ground, as illustrated schematically in
In another aspect, the blast channel can be flexible and stored out of the way most of the time, such as by folding or rolling, and it can open or inflate when a blast occurs. A flexible channel can be made from, for example, a reinforced rubber or another composite material. It can be incorporated within other structural elements to provide structural support to the vehicle.
In a further aspect, test results have shown that one or more objects can be located within, below, or above the blast channel such that the object(s) blocks at least a portion of the blast channel, without adversely altering the effectiveness of reducing the blast effects on the vehicle occupants from explosive events under the vehicle. The test results were surprising in that blocking the blast path through the blast channel would be expected to reduce the effectiveness of the blast channel in directing blast products through the channel. Thus, the blast channel can serve as a storage compartment during normal operation of the vehicle. The objects in the storage compartment can be sacrificed in the event of an explosion, the primary goal being the safety of the human occupants in the vehicle.
Referring to
Objects 1522 located within the blast channel 1520 can include, as examples and without limitation, electronic components, batteries, food, water, water tanks, explosives and/or ammunition. Such items can also be stored in a storage container mounted within the blast channel.
Objects 1524 located above the opening of the blast channel 1520 can include, as examples and without limitation, batteries; generators and related components; and/or cooling components such as radiators, fans, and reservoirs. The object can also form a cover that fits over the opening of the blast channel 1520. The objects located above the opening of the blast channel can be located directly above the opening or can be offset to the side while covering at least partially the opening.
Objects 1526 located below the opening of the blast channel 1520 can include, as examples and without limitation, transmission components, such as a transfer case; batteries; engines and related components; generators and related components; and/or cooling components such as radiators, fans, and reservoirs. The object can also form a cover that fits over the opening of the blast channel 1520. The objects located below the opening of the blast channel can be located directly below the opening or can be offset to the side while covering at least partially the opening.
Objects can be mounted within, above, or beneath the blast channel using break-away or breakable mounting fixtures. For example, in one embodiment, referring to
It will be appreciated that the embodiments and aspects of the present invention can be combined with each other in various ways. The invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims.
This application is a continuation-in-part of and claims the benefit under 35 U.S.C. §120 of U.S. patent application Ser. No. 12/807,818, filed Sep. 14, 2010, the disclosure of which is incorporated by reference herein. This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/284,488, filed Dec. 18, 2009, the disclosure of which is incorporated by reference herein.
This invention was made with Government support under Agreement No. HR-0011-09-9-0001, by DARPA. The Government has certain rights in the invention.
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Child | 13066243 | US |