U.S. patent application number 15/098026 was filed with the patent office on 2016-10-13 for system and method for protecting a vessel and vessel.
This patent application is currently assigned to Fyfe Co. LLC. The applicant listed for this patent is Fyfe Co. LLC. Invention is credited to Scott Arnold, Trevor Gerard, Tomas Jimenez.
Application Number | 20160297594 15/098026 |
Document ID | / |
Family ID | 57111254 |
Filed Date | 2016-10-13 |
United States Patent
Application |
20160297594 |
Kind Code |
A1 |
Gerard; Trevor ; et
al. |
October 13, 2016 |
SYSTEM AND METHOD FOR PROTECTING A VESSEL AND VESSEL
Abstract
A protective casing for a vessel includes an outer shell
surrounding the vessel wall. A spacer extends from adjacent the
vessel wall toward the outer shell and spaces the outer shell away
from the vessel wall. The spacer permits substantially uninhibited
deformation of the outer shell to failure inward toward the vessel
wall when a missile impact is imparted on the outer shell such that
the outer shell substantially dampens the transmission of the
energy of the missile impact to the exterior vessel wall. The
spacer can position the outer shell to allow reinforcing fibers of
the outer shell to elongate to the yield point to maximize energy
absorption. Embodiments of the protective casing and a protected
vessel, as well as a kit and method for forming the protective
casing, are disclosed.
Inventors: |
Gerard; Trevor; (San Diego,
CA) ; Arnold; Scott; (Solana Beach, CA) ;
Jimenez; Tomas; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fyfe Co. LLC |
San Diego |
CA |
US |
|
|
Assignee: |
Fyfe Co. LLC
San Diego
CA
|
Family ID: |
57111254 |
Appl. No.: |
15/098026 |
Filed: |
April 13, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62146704 |
Apr 13, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F41H 5/04 20130101; F42B
39/14 20130101; F42D 5/045 20130101; F41H 5/00 20130101; B65D
81/022 20130101 |
International
Class: |
B65D 81/02 20060101
B65D081/02 |
Claims
1. A vessel protected to inhibit the vessel from perforating when a
missile impact is imparted on the vessel, the vessel comprising; an
exterior vessel wall; an outer shell surrounding the exterior
vessel wall, the outer shell comprising an energy absorbing
material deformable when the missile impact is imparted thereupon
to absorb energy of the missile impact; a spacer extending from
adjacent the exterior vessel wall toward the outer shell and
spacing the outer shell away from the exterior vessel wall, the
spacer being configured to permit substantially uninhibited
deformation of the outer shell inward toward the vessel wall when
the missile impact is imparted on the outer shell such that the
outer shell substantially dampens the transmission of the energy of
the missile impact to the exterior vessel wall.
2. A vessel as set forth in claim 1 wherein the spacer is
configured to permit the outer shell to deform to failure prior to
engaging the exterior vessel wall.
3. A vessel as set forth in claim 2 wherein the spacer comprises a
cellular formation oriented transverse to the vessel wall and
extending from an inner end located adjacent the vessel wall to an
outer end located adjacent the outer shell.
4. A vessel as set forth in claim 3 wherein the cellular formation
defines a plurality of honeycomb cells extending axially between
the vessel wall and the outer shell.
5. A vessel as set forth in claim 4 wherein the cellular formation
surrounds the vessel wall.
6. A vessel as set forth in claim 3 further comprising at least one
anchor anchoring the cellular formation to the vessel wall.
7. A vessel as set forth in claim 6 wherein the anchor comprises a
dowel have a threaded end threadably received in the vessel wall
and a free end secured to the cellular formation.
8. A vessel as set forth in claim 3 wherein the cellular formation
is configured to compressively deform when the outer shell deforms
inward toward the exterior wall in response to the missile
impact.
9. A vessel as set forth in claim 1 wherein the deformation of the
outer shell is configured to absorb from about 85% to about 95% of
the energy of the missile impact and wherein the spacer is
configured to absorb from about 5% to about 15% of the energy of
the missile impact.
10. A vessel as set forth in claim 8 wherein the deformation of the
outer shell is configured to absorb at least about nine-times as
much of the energy of the missile impact as the deformation of the
spacer.
11. A vessel as set forth in claim 3 wherein the cellular formation
comprises paper.
12. A vessel as set forth in claim 1 further comprising an inner
shell surrounding the vessel wall and located between the vessel
wall and the outer shell.
13. A vessel as set forth in claim 12 wherein the spacer is
disposed between the inner shell and the outer shell.
14. A vessel as set forth in claim 12 wherein the inner shell is
bonded to the vessel wall.
15. A vessel as set forth in claim 12 wherein the inner shell
comprises fiber-reinforced polymer.
16. A vessel as set forth in claim 1 wherein the outer shell
comprises fiber-reinforced polymer.
17. A vessel as set forth in claim 16 wherein the outer shell
comprises a first layer of fiber-reinforced polymer having fibers
oriented substantially in a first direction and a second layer of
fiber-reinforced polymer having fibers oriented substantially in a
second direction transverse to the first direction.
18. A vessel as set forth in claim 16 wherein the fiber-reinforced
polymer comprises glass fibers and resin.
19. A kit for protecting an exterior wall of a vessel to inhibit
the vessel from perforating when a missile impact is imparted on
the vessel, the kit comprising: a spacer configured to be mounted
on the exterior wall of the vessel and to extend away from the
exterior wall a spacer thickness when mounted thereupon; and an
outer shell configured to be mounted on the spacer when the spacer
is mounted on the exterior wall of the vessel such that the spacer
spaces the outer shell apart from the exterior wall by the spacer
thickness, the outer shell comprising an energy absorbing material
when mounted on the spacer, the energy absorbing material being
deformable inward toward the vessel wall when the missile impact is
imparted thereupon to absorb energy of the missile impact.
20. A method of protecting an exterior wall of a vessel to inhibit
the vessel from perforating when a missile impact is imparted on
the vessel, the method comprising: mounting a spacer on the
exterior wall of the vessel; and mounting an outer covering on the
spacer such that the spacer spaces the outer covering from the
exterior vessel wall, the outer covering forming an outer shell
around the exterior wall when mounted on the spacer, the outer
shell comprising an energy absorbing material that is deformable
inward toward the vessel in response the missile impact being
imparted thereupon to absorb energy of the missile impact.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 62/146,704, entitled SYSTEM AND METHOD FOR
PROTECTING A VESSEL AND VESSEL, which was filed on Apr. 13, 2015
and is hereby incorporated by reference for all purposes.
FIELD
[0002] The present invention generally relates to protecting
vessels against missile impacts, and more specifically to
positioning an outer shell of deformable energy absorbing material
around a vessel wall to absorb energy of a missile impact imparted
thereupon.
BACKGROUND
[0003] Vessels that store materials (e.g., hazardous materials) are
often located in regions where, due to the weather conditions in
the region, they may be at risk of missile impacts. A missile
impact occurs when a projectile moving at a high rate of speed
impacts a vessel wall. Oftentimes, during a large storm, such as a
tornado or hurricane, storm winds carry loose debris through the
storm area at sufficiently high speeds to impart missile impacts on
a vessel located in the storm area. The Nuclear Regulatory
Commission defines several categories of missile objects capable of
imparting a missile impact upon a vessel when traveling at missile
velocities. Representative missile objects include a 6.625-inch
(16.8275 cm) diameter schedule 40 steel pipe that is 15 feet (4.572
meters) in length, a full-sized automobile, and a one-inch (2.54
cm) diameter steel sphere. The Nuclear Regulatory Commission's
design basis for tornado missiles assumes the steel pipe and
automobile travel at missile velocities of 135 ft/s (41.148 m/sec),
112 ft/s (34.1376 m/sec), and 79 ft/s (24.0792 m/sec) and assumes
that the solid steel sphere travels at missile velocities of 26
ft/s (7.9248 m/sec), 23 ft/s (7.0140 m/sec), and 20 ft/s (6.096
m/sec). Likewise the American Society for Testing and Materials
defines several categories of missiles capable of imparting a
missile impact upon a vessel. The American Society for Testing and
Materials' "Missile Levels" include a two-gram (0.00440925 lb.)
steel ball traveling at 130 ft/sec (39.624 m/sec) (Missile Level
A), a two-pound (0.907185 kg) piece of lumber traveling at 50
ft/sec (15.24 m/s) (Missile Level B), a 4.5-pound (2.04117 kg)
piece of lumber traveling at 40 ft/sec (12.192 m/sec) (Missile
Level C), a nine-pound (4.08233 kg) piece of lumber traveling at 50
ft/sec (15.24 m/sec) (Missile Level D), and a nine-pound piece
(4.08233 kg) of lumber traveling at 80 ft/sec (24.384 m/sec)
(Missile Level A). Those skilled in the art will appreciate that
the Missile Levels are merely exemplary of representative types of
missiles and that missile impacts can be imparted by projectiles of
various sizes and shapes traveling at various rates of speed.
[0004] Most vessels are not constructed to withstand missile
impacts. When a missile impact is imparted on a vessel, the missile
can perforate the vessel wall, thereby negating the vessel's
ability to contain its contents. It is known to use concrete and
steel barriers to protect vessels against missile impacts. However,
these systems are costly, heavy, and difficult to install, and in
some instances require additional regulatory involvement.
Accordingly, an improved system and method for protecting a vessel
against missile impacts is desired. Likewise, a vessel that is
protected against perforation when a missile impact is imparted on
the vessel is desired.
SUMMARY
[0005] In one aspect, a vessel is protected to inhibit the vessel
from perforating when a missile impact is imparted on the vessel.
The vessel comprises an exterior vessel wall. An outer shell
surrounds the exterior vessel wall. The outer shell comprises an
energy absorbing material deformable when the missile impact is
imparted thereupon to absorb energy of the missile impact. A spacer
extends from adjacent the exterior vessel wall toward the outer
shell and spaces the outer shell away from the exterior vessel
wall. The spacer is configured to permit substantially uninhibited
deformation of the outer shell inward toward the vessel wall when
the missile impact is imparted on the outer shell such that the
outer shell substantially dampens the transmission of the energy of
the missile impact to the exterior vessel wall.
[0006] In another aspect, a kit for protecting an exterior wall of
a vessel to inhibit the vessel from perforating when a missile
impact is imparted on the vessel comprises a spacer configured to
be mounted on the exterior wall of the vessel and to extend away
from the exterior wall a spacer thickness when mounted thereupon.
An outer shell is configured to be mounted on the spacer when the
spacer is mounted on the exterior wall of the vessel such that the
spacer spaces the outer shell apart from the exterior wall by the
spacer thickness. The outer shell comprises an energy absorbing
material when mounted on the spacer. The energy absorbing material
is deformable inward toward the vessel wall when the missile impact
is imparted thereupon to absorb energy of the missile impact.
[0007] In another aspect, a method of protecting an exterior wall
of a vessel to inhibit the vessel from perforating when a missile
impact is imparted on the vessel comprises mounting a spacer on the
exterior wall of the vessel and mounting an outer covering on the
spacer such that the spacer spaces the outer covering from the
exterior vessel wall. The outer covering forms an outer shell
around the exterior wall when mounted on the spacer. The outer
shell comprises an energy absorbing material that is deformable
inward toward the vessel in response the missile impact being
imparted thereupon to absorb energy of the missile impact.
[0008] Other aspects, features, and embodiments will be, in part,
apparent and, in part, pointed out in this disclosure and the
associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective of a conventional storage tank;
[0010] FIG. 2 is a perspective of a protected tank;
[0011] FIG. 3 is a fragmentary horizontal section of the protected
tank;
[0012] FIG. 4 is like FIG. 3, illustrating the protected tank after
a missile impact is imparted to the tank; and
[0013] FIG. 5 is a magnified fragmentary perspective of a wall of
the protected tank with layers broken away and illustrating
reinforcing fiber bundles schematically with broken lines.
[0014] Corresponding reference characters indicate corresponding
parts throughout the drawings.
DETAILED DESCRIPTION
[0015] Referring to FIG. 1, a conventional vessel for storing
industrial liquid is generally designated by reference number 10.
In the illustrated embodiment, the vessel 10 is a contaminated
water storage tank with a steel exterior wall 12, such as may be
used to store contaminated water at a nuclear power plant. The tank
10 is not constructed to withstand a missile impact, and when a
missile impact is imparted upon the tank wall 12 the missile can
perforate the wall, causing leakage or loss of the tank's contents.
The tank 10 is merely exemplary of one type of vessel for which
there is a need for protection against missile impacts. Other types
of vessels for storing other types of materials can also be used
without departing from the scope of the invention. A vessel that is
protected against missile impacts according to the principles
described below can have an exterior vessel wall of any suitable
material and that is arranged to define any suitable vessel shape.
As will be apparent to those skilled in the art, the present
disclosure describes systems and methods for protecting vessels
such as the tank 12 against missile impacts. Thus, aspects of the
present disclosure can be implemented with the tank 10 or another
type of unprotected vessel to construct a protected vessel that is
protected against impacts imparted on the vessel by a projectile
driven by, for example, storm winds during a tornado or other
storm. It is also envisioned that the protection may be used on
objects over than vessels.
[0016] Referring to FIG. 2, a protected contaminated water storage
tank that is protected to withstand missile impacts is generally
designated by reference number 110. The protected tank 110 includes
the steel-walled tank 10, which is substantially sheathed in a
protective casing, generally designated by reference number 112. As
is evident from FIGS. 1 and 2, the protected tank 110 can be
constructed from a tank 10 that is manufactured conventionally
prior to installation of the protective casing 112. Thus, the
protective casing may be applied to the steel wall 12 of the tank
10 as a retrofit addition to the tank in the field. Alternatively,
the protective casing 112 may be applied to the steel wall 12 of
the tank 10 as part of a tank 110 that is protected against missile
impacts as originally manufactured. As shown in FIG. 3, the
protective casing 112 includes, in the illustrated embodiment, an
inner shell, generally designated by 114, a spacer generally
designated by 116, and an outer shell generally designated by
118.
[0017] The inner shell 114 is bonded to and substantially covers
the tank wall 12. Although the inner shell 114 is bonded to the
tank wall 12, in other embodiments the inner shell can be secured
to the tank wall in other ways (e.g., mechanical fasteners, etc.)
without departing from the scope of the invention. The inner shell
114 is located between the tank wall 12 and outer shell 118 and
surrounds the tank wall. The inner shell 114 is preferably made
from a high-strength, energy absorbing material, such as
fiber-reinforced polymer. The inner shell 114 is configured to
absorb energy from a missile impact, thereby limiting the
transmission of missile impact energy to the tank wall 12. As
discussed in further detail below, the inner shell also provides a
bonding surface for bonding the spacer 116 to the tank 10.
[0018] In the illustrated embodiment, the inner shell 114 comprises
a single layer of unidirectional fiber-reinforced polymer.
Unidirectional fiber-reinforced polymer has reinforcing fibers
oriented substantially in a single direction. For example, a
unidirectional fiber-reinforced polymer can include bundles of
reinforcing fiber that are stitched together into a fabric and
suspended within a polymer matrix. Unidirectional fiber-reinforced
polymers have high tensile strength in a direction parallel to
their reinforcing fibers.
[0019] As shown in FIG. 5, the illustrated unidirectional material
includes fiber bundles 120 that form a fabric sheet suspended in a
polymeric material. The fiber bundles 120 are arranged so that,
when the fabric is wetted with a curable liquid, the fabric holds
(e.g., is saturated with) the curable liquid. The reinforcing fiber
bundles 120 are oriented parallel to one another. Each of the fiber
bundles 120 extends circumferentially around the tank wall 12 in a
horizontal direction. Although the illustrated embodiment uses
unidirectional reinforcing fabric, other inner shell architectures
(e.g., bi-directional, woven, braided, knit, or stitched) may also
be used without departing from the scope of the invention.
Moreover, the inner shell may include multiple layers and/or layers
of material that are not "fabrics." Preferably, each of the bundles
120 is made of one of glass fibers and carbon fibers. Other types
of fiber materials (e.g., basalt, carbon, and aramid) may also be
used without departing from the scope of the invention. The
polymeric material can be an epoxy, a resin, or any other suitable
material. However, in preferred embodiments, the polymer comprises
a curable material. In one or more preferred embodiments, the inner
shell 114 comprises Tyfo.RTM. SEH-51A unidirectional glass fiber
suspended in a matrix of cured Tyfo.RTM. S Epoxy. In one or more
additional embodiments, the inner shell 114 comprises, Tyfo.RTM.
SCH-41 unidirectional carbon fiber suspended in a matrix of cured
Tyfo .RTM. S Epoxy.
[0020] The inner shell 114 may include multiple layers of
unidirectional fiber-reinforced polymer, successively bonded to and
covering the adjacent inner layer. Preferably, when multiple layers
of unidirectional fiber-reinforced polymer are used to form the
inner shell 114, the directional fiber bundles in adjacent layers
are oriented transverse to one another, so that the directional
strength characteristics of successive layers can be combined to
enhance the overall strength of the inner shell. For example, the
directional fiber bundles in a first layer of the inner shell 114
can be oriented at about 0.degree. (e.g., substantially
horizontally) and the directional fiber bundles in a second layer
of the inner shell can be oriented at about 90.degree.. Successive
layers preferably alternate between directional fibers oriented at
about 0.degree. and about 90.degree.. Each layer of the inner shell
can, for example, have a thickness from about 0.01 inches (0.0254
cm) to about 0.10 inches (0.254 cm). In total, the inner shell can
include from one layer to about 4 layers of unidirectional
fiber-reinforced polymer.
[0021] The spacer 116 is bonded to the inner shell 114 and extends
outward from adjacent the exterior tank wall 12 toward to outer
shell 118 to space the outer shell away from the tank wall. As
shown in FIG. 3, the spacer 116 extends outwardly a spacer
thickness T from an inner end located adjacent the tank wall 12 to
an outer end located adjacent an outer shell 118. The spacer
thickness T is preferably from about 0.1 inches (0.254 cm) to about
5 inches (12.7 cm) and, more preferably, from about 0.5 inches
(1.27 cm) to about 2 inches (5.08 cm). The spacer 116 is disposed
between the inner shell 114 and outer shell 118. The spacer 116
comprises one or more sheets of pliable material wrapped around the
perimeter of the tank wall 12. The spacer material is configured to
bend to conform to the shape of the tank wall 12 while
substantially retaining the spacer thickness T. As will be
discussed in greater detail below, the spacer 12 is preferably
configured to space the outer shell 118 apart from the tank wall 12
so that the outer shell can deform inward in response to a missile
impact. Thus, the spacer 116 is configured for compressive
deformation when a missile impact is imparted upon the reinforced
vessel 110. Various materials can be used for the spacer 116,
including plastic, aluminum, foam, paper, fiber-reinforced
composite, or any other suitable material.
[0022] Referring to FIG. 5, the spacer 116 preferably comprises a
cellular formation oriented transverse to the tank wall 12 and
surrounding the tank wall. The cellular formation defines a
plurality of honeycomb cells 122 extending between the tank wall 12
and the outer shell 118. In the illustrated embodiment, the cells
120 are defined by alternating walls of flat and corrugated
material that are joined together along axially extending joints.
Other cellular architectures can also be used without departing
from the scope of the invention. In a preferred embodiment, the
cellular formation 116 comprises paper. The paper cellular
formation 116 is inexpensive to manufacture and can be bent to
conform to the shape of a vessel 10, while being robust enough to
support the outer shell 118 in spaced apart relation with the tank
wall 12. In addition, paper cellular formation 116 readily deforms
when energy of a missile impact is imparted thereupon. In some
embodiments, where it is desirable for the spacer to absorb a
significant portion of the energy of the missile impact, it may be
preferable to use a cellular formation comprising a higher strength
material (e.g., plastic, aluminum, fiber-reinforced polymer, etc.).
But the spacer should preferably not be so strong that it
substantially inhibits the outer shell from deforming inward. It is
envisioned that deformable spacers having other than a honeycomb
structure may be used.
[0023] Referring again to FIG. 3, the spacer 116 is anchored to the
tank wall 12 using one or more anchors 124. In the illustrated
embodiment, the anchors 124 include threaded dowels that are
threadably received in the tank wall 12. It will also be understood
that the dowels can be attached to the tank wall 12 by an adhesive
material, welding, or other methods of attachment. These attachment
methods may be preferable to coring and tapping threaded openings
in the tank wall for threadably receiving the dowels therein. Free
ends of the dowels 124 extend outward from the tank wall 12 to form
radially extending lugs for anchoring the spacer 116 to the tank
wall. The spacer 116 is installed on the tank wall 12 so that the
lugs 124 extend into the honeycomb cells 122 and engage the
honeycomb formation, thereby inhibiting the spacer from shifting in
position relative to the tank wall. Other anchoring mechanisms can
also be used, or an anchoring system may be omitted altogether,
without departing from the scope of the invention.
[0024] The outer shell 118 surrounds the tank wall 12 and is spaced
away from the tank wall by the spacer 116. The outer shell 118 is
preferably bonded to the spacer 116 to form the protective casing
112, although the outer shell can be mounted on the spacer in other
ways without departing from the scope of the invention. The outer
shell 118 comprises energy absorbing material that is deformable
when a missile impact is imparted thereupon. In a preferred
embodiment, the outer shell 118 comprises a fiber-reinforced
polymer material. As will be discussed in further detail below, the
fiber-reinforced polymer is capable of absorbing energy of a
missile impact imparted thereupon to protect the tank 10 from
perforating when a missile impact is imparted on the protected tank
110.
[0025] In the illustrated embodiment, the outer shell 118 comprises
two layers 118A, 1186 of unidirectional fiber-reinforced polymer.
As shown in FIG. 5, the inner layer 118A comprises bundles of
reinforcing fibers 130 (e.g., carbon, glass, basalt, or aramid
fibers) oriented vertically and extending parallel to a vertical
axis of the tank 110, and the outer layer 1186 comprises bundles of
reinforcing fibers 132 oriented horizontally and extending
circumferentially around the tank 10. Preferably, the bundles 130,
132 comprise reinforcing fibers that have a high tensile strength
and are at least somewhat ductile so that when a missile impact is
imparted upon the shell the reinforcing fibers absorb impact energy
through elongation prior to failure. Although the illustrated outer
shell 118 includes inner and outer layers 118A, 1186 with
unidirectional reinforcing fibers oriented perpendicular to one
another, in other embodiments the reinforcing fibers of adjacent
layers of unidirectional fiber-reinforced polymer can be oriented
at other transverse angles without departing from the scope of the
invention. In addition, the orientation of the reinforcing fiber
bundles 130, 132 in the inner and outer layers 118A, 118B could be
reversed or otherwise reoriented without departing from the scope
of the invention.
[0026] Preferably, each set of reinforcing bundles 130, 132 is
arranged in a sheet of fabric adapted to carry (e.g., be saturated
with) a curable polymeric material. Likewise the fiber bundles 130,
132 are preferably suspended in a polymeric material that is
curable. In one or more preferred embodiments, each of the outer
shell layers 118A, 118B comprises Tyfo.RTM. SEH-51A unidirectional
glass fiber fabric suspended in a matrix of cured Tyfo.RTM. S
Epoxy. In one or more additional embodiments each of the outer
shell layers 118A, 118B comprises Tyfo.RTM. SCH-41 unidirectional
carbon fiber suspended in a matrix of cured Tyfo.RTM. S Epoxy.
[0027] Additional layers (not shown) of unidirectional
fiber-reinforced polymer can also be added to the outer shell 118
to increase the strength of the outer shell. The layering of
unidirectional fiber-reinforced polymer layers enables strength to
be added to the outer shell in discrete amounts, one layer at time.
Thus, a user can optimize the strength characteristics of the
protective casing 112 without wasting material. In one or more
embodiments, each additional layer is bonded to the adjacent inner
layer. The reinforcing fibers in one layer are preferably oriented
transverse to the reinforcing fibers in the adjacent inner layer
and an adjacent outer layer bonded thereto. In certain embodiments,
successive layers alternate between having reinforcing fibers
oriented in a first direction (e.g., horizontally) and having
reinforcing fibers oriented in a second direction (e.g.,
vertically), transverse (e.g., perpendicular) to the first
direction. As discussed above, unidirectional fiber-reinforced
polymer is known to have high tensile strength in the direction
parallel to the orientation of its reinforcing fibers. By orienting
successive layers in transverse directions, the overall strength of
the outer shell is improved since the layers impart strength in
different directions. Each layer of unidirectional fiber-reinforced
polymer in the outer layer can, for example, have a nominal
thickness of from about 0.01 inches (0.0254 cm) to about 0.05
inches (0.127 cm). In total, the outer shell 118 can, for example,
comprise from about 1 to about 8 layers.
[0028] Although the illustrated embodiment of the protected tank
110 uses two layers 118A, 118B of unidirectional fiber-reinforced
polymer to form the outer shell 118, it will be understood that the
outer shell could be formed from other materials without departing
from the scope of the invention. For example, it is contemplated
that the outer shell 118 could be formed from a single layer of
fiber-reinforced polymer, with any suitable fiber architecture
(e.g., bi-directional, woven, braided, knit, or stitched). It is
also contemplated that other materials besides fiber-reinforced
polymer could be used for the outer shell without departing from
the scope of the invention.
[0029] In a preferred embodiment the outer shell 118 is configured
to absorb significantly more of the energy of a missile impact than
the spacer 116. As discussed above, the outer shell 118 preferably
comprises reinforcing fibers having high tensile strength and some
ductility (e.g., less ductility than the steel tank wall 12, but
enough ductility to permit elongation of the reinforcing fibers
when a missile impact is imparted to the outer shell). As a result,
when a missile impact is imparted upon the outer shell 118 and
causes deformation of the outer shell, the reinforcing fibers
absorb a significant amount of impact energy as they deform
longitudinally prior to failing. By comparison, in the illustrated
embodiment the spacer 116 is a paper cellular formation with
relatively low compressive strength. As shown in FIG. 4, in a
preferred embodiment, the spacer 116 spaces the outer shell 118
apart from the tank wall 12 a sufficient distance to permit the
outer shell to deform to failure prior to engaging the tank wall.
The missile impact causes lengthwise deformation of the reinforcing
fibers that exceeds the tensile strength of the fibers and causes
them to fracture or otherwise fail. However, the deformation and
fracturing of the reinforcing fibers absorbs a significant amount
of the energy of the missile impact such that the missile impact
does not perforate the tank 110. In some cases, the missile impact
may cause deformation (e.g., denting) of the tank wall 12 without
causing perforation. The denting of the tank wall 12 will also
absorb a portion of the missile impact energy.
[0030] In one or more embodiments, the protected tank 110 is
configured so that the tank wall 12 is not perforated when the
protected tank is subjected to a missile impact. For example, the
outer shell 118 is configured to absorb enough of the kinetic
energy of the missile impact so that the tank wall 10 has
sufficient strength to absorb any additional kinetic energy of the
missile impact without perforation. Where a protected vessel 110 is
to be designed to withstand a predetermined missile impact having a
total kinetic energy of E.sub.K, the outer shell 118 is preferably
configured to absorb energy E.sub.S that is greater than the
difference between the total kinetic energy of the missile impact
and the critical kinetic energy E.sub.T of the tank wall 12 (i.e.,
E.sub.S>E.sub.K-E.sub.T). The critical kinetic energy E.sub.T of
the tank wall is the maximum kinetic energy the tank wall can
absorb before being perforated.
[0031] Using the critical kinetic energy E.sub.T of the tank wall
12, a minimum energy absorption E.sub.S(min) of the outer shell 118
can be determined from Equation 1.
E.sub.S(min)=E.sub.K-E.sub.T (1)
[0032] In order for the outer shell 118 to be capable of absorbing
kinetic energy equal to its critical energy E.sub.S, the fibers
130, 132 in the outer shell must be spaced apart from the tank wall
12 as sufficient distance to allow elongation to tensile failure.
Thus, the protective covering 112 can be designed to prevent the
tank 10 from perforating when impacted by a missile impact having a
kinetic energy E.sub.K when two design criteria are met: (1) the
number of reinforcing layers used forms an outer shell 118 having a
thickness great enough to absorb E.sub.S(min) and, (2) the outer
shell material is spaced apart from the tank wall 12 a sufficient
distance to allow the fiber reinforcement 130, 132 to elongate to
failure. One skilled in the art will appreciate that the thickness
of the spacer material 116 may be determined based on the
elongation at failure of the reinforcing fibers 130, 132 to satisfy
the second design criteria.
[0033] Compressive deformation of the cellular formation 116
absorbs relatively little impact energy in comparison to the
deformation of the outer shell 118. For example, in one or more
embodiments, deformation of the outer shell 118 is configured to
absorb from about 85% to about 95% of the energy of the missile
impact, whereas deformation of the cellular formation is configured
to absorb from about 5% to about 15% of the energy of the missile
impact. Likewise, the outer shell can be configured to absorb at
least about nine-times as much of the energy of the missile impact
as the deformation of the cellular formation.
[0034] For particularly high risk or high value applications, a
protected vessel can comprise more than one protective casing 112.
A second spacer (not shown) is bonded to or otherwise mounted on
the outermost layer 1186 of the outer shell 118, and a second outer
shell (not shown) is bonded to or otherwise mounted on the second
spacer. Additional spacers and outer shells can also be added as
needed to achieve the desired protection. Each additional
protective casing 112 adds greater protection against missile
impact because each successive outer shell is spaced apart by a
spacer, which enables each outer shell to absorb impact energy as
it deforms inward into the space occupied by the spacer.
[0035] In one embodiment, the protected tank 110 is manufactured
from a kit that includes unidirectional fiber fabric, a pliable
cellular formation (e.g., a sheet of cellular material), and a
curable epoxy. The fiber fabric is configured to be cut into a
first sheet sized to substantially cover the exterior wall 12 of
the tank. The first sheet is adapted to be saturated with the
curable epoxy, applied to the tank wall 12, and cured to form the
inner shell 112. In one or more embodiments, the kit includes
additional fiber fabric sheets configured to be saturated with
epoxy and bonded to the first fabric sheet to form a multi-layer
inner shell. The cellular formation is configured to be mounted on
the tank to form the spacer 114. Preferably, the cellular formation
bends to conform to the shape of the tank 12 when mounted on the
tank. In certain embodiments, the kit comprises threaded anchoring
dowels 124 configured to be installed in the tank wall 12 and
positioned within the cells 122 of the spacer 114 to position the
spacer on the tank wall 12. The unidirectional fiber fabric is
further configured to be cut into second and third sheets sized to
substantially cover the spacer 114. The second sheet is adapted to
be saturated with the curable epoxy, applied to the outer end of
the spacer 114 with its reinforcing fibers oriented in a first
fiber direction, and allowed to cure, thereby forming the inner
layer 118A of the outer shell 118. The third sheet is adapted to be
saturated with the curable epoxy, applied to the inner layer 118A
of the outer shell 118 so that the reinforcing fibers are oriented
transverse (e.g., perpendicular to) the reinforcing fibers in the
inner layer, and allowed to cure, thereby forming the outer layer
1186. Additional sheets may also be included in the kit to create
an outer shell of more than two layers.
[0036] In one method of protecting a tank 10 against missile
impacts, the inner shell 114 is installed on the tank by saturating
at least a first sheet of unidirectional fiber fabric with a
curable epoxy, applying the saturated fabric to the wall 12 of the
tank, and allowing the fabric to cure. The first sheet is installed
as an inner covering on the tank that, when cured, forms the inner
shell 114. A spacer 116 is mounted on the tank 10 by bending a
cellular formation with a spacer thickness T to conform to the
shape of the tank while the epoxy in the inner shell is curing,
thereby bonding the spacer material to the inner shell 112. In
certain embodiments, threaded dowels 124 are received in the cells
124 to position the cellular formation on the tank wall 12. An
outer shell 118 is installed by saturating a second sheet of
unidirectional fiber fabric with a curable epoxy, applying the
second sheet as a covering over the spacer with the reinforcing
fibers in the fabric oriented in a first direction, and allowing
the second sheet to cure. A third sheet of unidirectional fiber
fabric is saturated with curable epoxy, applied as a covering over
the second sheet with the reinforcing fibers in the third sheet
oriented transverse to the reinforcing fibers in the second sheet,
and allowed to cure. Together, the second and third sheets are
installed as an outer covering on the spacer that, when cured,
forms the outer shell 118.
[0037] Having described the invention in detail, it will be
apparent that modifications and variations are possible without
departing from the scope of the invention defined in the appended
claims.
[0038] As various changes could be made in the above constructions
and methods without departing from the scope of the invention, it
is intended that all matter contained in the above description and
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
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