Blast-resistant vehicle hull

A vehicle hull has a longitudinal blast mitigation duct formed between left and right hull portions. The duct includes a first section oriented at a first angle to a longitudinal reference line, and a second section adjacent to the first section and oriented at a second angle to the reference line. The second angle is greater than the first angle to form a diverging surface for a shock wave travelling from the first to the second section. The blast mitigation duct further comprises a second, rearward-oriented diverging surface for a shock wave travelling rearward along the hull. A rib projects generally perpendicular from a joint between the first and second sections and is configured to initiate separation of the shock wave from the hull, thereby reducing the amount of energy transferred to the hull.

TECHNICAL FIELD

The disclosure relates to vehicles, such as military vehicles, that may be subjected to blasts originating beneath or closely adjacent to the vehicle. More specifically, the disclosure relates to a vehicle hull geometry and method of construction providing improved protection from such blasts.

BACKGROUND

Military vehicles used in combat zones must provide ballistic and blast protection for occupants of the vehicle's crew compartment. One of the challenges in designing a military vehicle is to achieve the proper balance between crew protection (survivability) and mobility.

Good mobility generally calls for a vehicle to be lightweight and to have a relatively low center-of-gravity. To achieve a low center-of-gravity, the vehicle should sit as low to the ground as possible while still providing required ground clearance.

Survivability, on the other hand, drives vehicle design towards more armor, resulting in more weight and therefore a higher center-of-gravity. One way to improve survivability versus a detonation originating close to or below the crew compartment (such as detonation of a lane mine or IED) is to increase the clearance between the bottom of the crew compartment and ground. Increased armor weight and greater ground clearance may result in the vehicle center-of-gravity being so high as to cause an unacceptable roll-over risk when travelling over uneven terrain.

Improved vehicle survivability has recently been demonstrated by what is referred to as a Double-V hull configuration, the general concept of which is shown inFIGS. 1aand1b. In the Double-V configuration, sloping or angled outward-facing surfaces extending along both sides of the lower portion of the vehicle hull form the first “V” (when viewed from the front or rear of the vehicle,FIG. 1a). The second “V” (when viewed in transverse cross-section,FIG. 1b) is formed by upward-sloping surfaces between the two outboard portions of the hull (sometimes referred to as “pontoons”) and extending to the front and rear along the approximated longitudinal centerline of the vehicle. The sloped lateral surfaces of the first “V” direct detonation energy outward and away from the vehicle if an explosion occurs close to the side of the vehicle. The second, central “V” deals with detonations originating directly beneath the vehicle, between the pontoons, by directing the energy of the detonation forward and/or rearward to reduce the amount of kinetic energy transferred to the hull and its occupants.

SUMMARY

In a disclosed embodiment, a vehicle hull has a longitudinal blast mitigation duct between left and right hull portions. The duct comprises a first section oriented at a first angle to a longitudinal reference line, and a second section adjacent to the first section and oriented at a second angle to the reference line. The second angle is greater than the first angle to form a diverging surface for a shock wave travelling from the first to the second section.

In another embodiment, a rib projects generally perpendicular from a joint between the first and second sections. The rib is configured to initiate separation of the shock wave from the hull, thereby reducing the amount of energy transferred to the hull.

In another embodiment, the diverging surface formed by the first and second sections diverges toward a forward end of the hull, and the blast mitigation duct further comprises a two-section, rearward diverging surface for a shock wave travelling rearward along the hull.

In another embodiment, a vehicle hull comprises a left portion, a right portion, and a central portion between the left and right portions. The central portion is raised relative to the left and right portions to form a downward-opening duct having a first section oriented at first angle to a longitudinal reference line and a second section adjacent to the first section and oriented at a second angle to the reference line. The second angle is greater than the first angle to form a diverging surface.

In another embodiment, a vehicle hull comprises a first plate, a second plate attached to the first plate along a joint, and a rib attached to the first and second plates. The rib projects generally perpendicular from the second plate a distance sufficient to cause a shock wave to separate from the hull after passing the joint, thereby reducing energy transfer from the shock wave

DETAILED DESCRIPTION

As seen inFIGS. 2-5, a military vehicle10intended for use in a combat zone includes a blast-resistant hull12mounted to a frame14. Suspension and powertrain components are schematically indicated at16, and may include any number and combination of wheels and/or tracks (not shown). Hull12is depicted equipped with four crew seats such as may be the case if the hull forms a crew cab of a light general purpose vehicle, but a blast-resistant hull may be of any size necessary to house the required number of occupants and related mission equipment. Hull12may be formed of any appropriate high-strength material that provides the required degree of blast and ballistic protection for the occupants.

Terms such as up, down, horizontal, and vertical, as used herein, assume that vehicle10is in a normal running condition, with its wheels/tracks resting on a relatively flat and level surface. As such, this disclosure assumes that the longitudinal and lateral axes of vehicle10are generally parallel with the horizontal plane and the vertical axis of the vehicle is normal to the horizontal plane.

The lower section of hull12generally comprises a left hull portion20, a right hull portion22, and a central hull portion24disposed between the left and right portions. Left and right hull portions20,22may extend along substantially the full length of the vehicle and substantially parallel to the longitudinal centerline of the hull. As best seen inFIG. 5, left and right hull portions20,22include outboard-facing lateral surfaces20a,22athat may be angled upward and outward in order to mitigate the effects of an explosion originating outboard of the vehicle. Depending upon the exact position of the detonation relative to the vehicle, the angled surfaces20a,22a(along with other features of the hull geometry) will reduce the amount of kinetic energy transferred to the hull from the detonation shock wave.

As best seen inFIG. 6, the lower or exterior surfaces of central hull portion24are angled with respect to a reference line L to form a pair of blast mitigation ducts26,28. Duct26slopes upward and forward while duct28slopes upward and to the rear, the two ducts meeting at a vertex30. Vertex30is shown located at the approximate longitudinal center of the hull12, but the fore/aft location of the vertex may vary as dictated by mission requirements without departing from the scope of the present invention.

Forward blast mitigation duct26comprises a first duct section32extending forward from vertex30and sloping upward at an angle α1from longitudinal reference line L (which in this view is horizontal), and a diverging duct section34joined to and extending forwardly from the first duct section. Diverging duct section34makes an angle β1with longitudinal centerline L as shown, and β1is greater than α1so that a convex corner36having a divergence angle δ1is formed at the intersection or joint between the two duct sections32,34.

Duct sections32,34may be arched or curved to have downward-facing concave surfaces, as best seen inFIGS. 5 and 6. The forward edge of first duct section32and rear edge of diverging duct section34form may overlap one another along the joint between the two sections, thereby providing a joint having improved resistance to ballistic and blast effects of a detonation.

Rear blast mitigation duct28is generally similar in geometry to forward duct26, comprising a first duct section38extending rearward from vertex30and sloping upward at an angle α2from longitudinal reference line L, and a diverging duct section40joined to and extending rearward from the first duct section38. Diverging duct section40makes an angle β2with reference line L as shown, and β2is greater than α2so that a convex corner42having a divergence angle δ2is formed at the intersection or joint between the two duct sections38,40.

Corresponding angles of forward and rear blast mitigation ducts26,28(α1/α2, β1/β2, and δ1/δ2) may be equal or non-equal to one another depending upon design requirements and/or constraints (interior volume, for example) related to hull12.

Front and rear blast mitigation ducts26,28combine to form a downward-opening channel extending generally parallel with the longitudinal axis of hull12. The channel may coincide with the vehicle centerline, or it may be offset from the centerline if vehicle design objectives so dictate. Components of the vehicle powertrain (drive shafts, transmissions, motors, batteries, etc.) or other essential equipment (not shown) may be located in the channel, but such components are not shown since they are incidental to this disclosure.

Detonation of an explosive device (such as mine or IED) generates a high-intensity wave front and related supersonic shock wave that radiates outward in all directions from the origin of the detonation. If the detonation origin is directly beneath hull12(between the left and right lower hull portions20,22), the energy of the detonation is directed against the surfaces of blast mitigation ducts26,28and so is directed forward and/or rearward. The relative proportion of the energy of the detonation directed forward versus rearward depends on where relative to vertex30the detonation originates. For example, if the detonation origin is forward of the vertex30, a larger portion of the detonation energy is directed forward (by forward blast mitigation duct26) rather than to the rear.

Referring now toFIG. 11, a schematic depiction of the interaction between the supersonic flow/shock wave and the surface of the forward blast mitigation duct26. The direction of travel of the shock wave and related fluid flow being are by arrows F. As the shock wave travels past convex corner36at the joint between duct sections32and34, the effect on the flow is similar to that occurring in a divergent nozzle and may be analyzed using the Prandtl-Meyer equation, as is well known in the in the fluid dynamics field. The Prandtl-Meyer equation predicts that a divergence angle δ greater than or equal to a critical value (known as the Prandtl-Meyer angle) will result in the shock wave separating from the surface and the formation of an expansion fan emanating from the corner of the diverging angle. Separation of the shock wave from the surface of the hull results in a reduced amount of kinetic energy being transferred to the hull structure as compared with the shock wave remaining attached to the surface.

The Prandtl-Meyer angle δ required to achieve shock wave separation depends upon many factors, including the speed of the shock wave (expressed in Mach number), which in turn depends upon the power of the explosive device and the distance of the detonation from the hull surface. Computer simulations have been run utilizing Mach numbers ranging from M=2.9 to M=5.2, with the corresponding δ values of between 11.1 degrees and 20.2 degrees effective to cause shock wave separation.

Simulations using computer models of hull designs featuring the diverging duct contour as described herein have resulted in significant reductions in the amount of kinetic energy transferred to the vehicle. This reduction is depicted inFIG. 12, where the upper, dashed-line shows the amount of kinetic energy transferred to a hull without the diverging duct effect (δ=0) whereas the lower, solid-line shows energy transferred to a hull featuring a diverging duct.

FIGS. 13aand13bare graphic depictions of computer model simulations showing the reduction in the level of kinetic energy transferred from the detonation to the hull.FIG. 13ais a vehicle hull210having a prior art geometry (δ=0) being subjected to a detonation directly below the vehicle. Blast/shock wave220is shown striking the underside of hull210, with the heavily stippled area230indicating the area over which the highest levels of kinetic energy transfer are predicted.FIG. 13bshows the results of the same detonation blast/shock wave320applied to a vehicle hull310having a diverging blast mitigation duct as disclosed herein. The significant reduction in energy transfer is clearly indicated by the reduced size of the area330of highest kinetic energy transfer.

A rib50(best seen inFIGS. 7-10) may extend along the joint between first duct section32and divergent duct section34. In the disclosed embodiment, rib50is arch-shaped to follow the curved joint between the duct sections. A rib50may also be joined to rear duct sections38,40at convex corner42, and the following description of the forward rib50also applies to a rear rib if present.

Rib50has a width substantially greater than the thickness t1of first duct section32so that the lower edge50aof the rib extends a distance w below the lower/outer surface of duct section32. Rib50thus projects into the flow travelling from duct section32toward duct section34(indicated by arrows F). Computer simulations of detonations have shown that a rib50extending a significant distance beyond the surface of duct32enhances the desired separation of the shock wave as the wave transitions from first duct section32to divergent duct section34.

For example, computer simulations have shown that a rib projection distance w ranging from approximately 5 mm (millimeters) to 19 mm enhances or initiates separation of the shock wave from the hull surface. A rib projection distance w=10 mm has, under simulated test conditions, shown a significant reduction in energy transferred to the vehicle.

The projecting rib50has the beneficial effect of achieving the desired shock wave separation when used in combination with a duct geometry in which divergence angle δ is smaller than would otherwise be required (per the discussion of the Prandtl-Meyer equation above) if the rib were not present. Rib50thus allows a hull design in which the advantageous effects of shock wave separation may be achieved using a smaller divergence angle δ, i.e. the angle β1of the divergent section34may be smaller/shallower, thereby increasing the amount of usable volume inside of hull12.

Addition of rib50to the overlapping joint between duct sections32and40(as best seen inFIG. 11) also provides additional strength to the hull structure. Rib50and duct sections32and34may be joined by welding along one or more of the continuous lines of contact between the components, as indicated by l1, l2, and l3. Multiple weld lines along the three lines of contact l1, l2, and l3increases the section modulus at the joint between the duct sections, making the joint very rigid and resistant to blast and ballistic effects of a detonation. An additional weld line l4may also be used at the location shown inFIG. 10to further increase the strength of joint and/or to aid in the fabrication process.

The term “welding” is used herein to refer to any of the many joining techniques known in the materials field and is not meant to restrict the type of material used for the structure in any way. For example, components of the hull may be formed of high-strength aluminum alloy, as is well-known in the military vehicle industry. If such an alloy is used, the joints may be formed by friction stir welding, or some other suitable welding method. Full-penetration welds, where such welds are practical, generally provide superior strength. If non-metallic and/or metal-composite materials are used in the hull structure, other appropriate joining/bonding techniques such as adhesives and/or ultrasonic welding may be used.

FIG. 14shows another embodiment of a blast-resistant hull112in which the central hull portion124is formed by flat plates rather than the curved plates (32,34,38,40) used in the embodiment shown inFIGS. 1-10. This configuration may be advantageous depending upon the material(s) and/or the construction methods used to construct the hull. First duct section132extends upward and forwardly to meet diverging duct section134, and rib150extends along at least the horizontal line of the joint where the duct sections meet one another. Additional sections of rib150may also extend along the vertical portions of the joint between the duct sections. The rear diverging duct (not shown) may have a similar geometry and construction. It should be noted that a transverse cross-sectional view taken along line6′-6′ would appear substantially similar toFIG. 6, since the surfaces of duct sections132,134, are also arranged at angles α, β, and δ.

In summary, the diverging duct causes the shock wave from a detonation to separate from the vehicle hull surface, reducing or negating the ability of the shock wave to transfer kinetic energy to the structure. The rib protruding from the surface at or near the convex joint or corner further enhances/enables shock wave separation and the resulting reduction in kinetic energy transfer.