Ships – Submersible device
Reexamination Certificate
2002-02-04
2003-03-25
Avila, Stephen (Department: 3617)
Ships
Submersible device
C114S382000
Reexamination Certificate
active
06536366
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for testing the response of a structure to an explosive event, more particularly for testing the response of a submerged hull structure such as a submarine to an underwater explosive event.
During a typical underwater explosion (UNDEX) test, the target is a hull model which is initially struck by a shock wave. Typically, the shock wave results from conversion of about half the chemical potential (explosive charge) energy into kinetic energy in the water surrounding the charge. The explosion products form a bubble which expands to maximum size in a span of ~100 times the time constant of the steep fronted, exponentially decaying, free field incident shock wave. The shock wave response of the target to this later, more slowly applied pressure load is characterized by lower frequency and longer wavelength motion. This is in comparison with the shock wave response of the target to the earlier, more rapidly applied pressure load which is characterized by higher frequency and shorter wavelength motion.
Submersible hulls are tested, particularly with respect to internal/external equipment survival, in underwater explosion environments. This testing includes UNDEX model testing, often at reduced scale, but in some cases at full scale. Various test vehicles (“targets”) have been designed, fabricated and tested over the past half century. Most of these have been short (length/diameter ratio of
−
1), therefore responding primarily in early shock deformational modes involving higher frequencies and shorter wavelengths. Longer models (length/diameter ratios of
−
9) have been employed when special circumstances have demanded additional kinds of response, such as the bending (“whipping”) motion associated with later shock deformational modes involving lower frequencies and longer wavelengths. Such vehicles, even at reduced scale, but large enough to allow inclusion of essential details, can become heavy (e.g., about 64 long tons dry with about 80 long tons displacement), and expensive (e.g., about two million dollars).
For a particular project, the inventor and his colleagues considered a mechanically excited (e.g., via impact) “dry land” approach. However, such approach was dismissed as untenable in view of the huge mass required to simulate the dynamic participation of the adjacent ballasting structure and fluid in addition to that of the hull test section itself and the equipment within. Other factors also pointed to the preferability of a “submerged” approach to testing. According to a “dry land” approach, the simulated fluid “added” mass would have to be absolutely devoid of shear stiffness, a difficult proposition. Furthermore, it would be difficult to simulate UNDEX loading “in the dry.”
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for simulating submarine hull target response to UNDEX (underwater explosion) excitation.
Another object of the present invention is to provide method and apparatus for measuring both high and low frequency response components to UNDEX load in submersible hulls and equipment.
A further object of the present invention is to provide method and apparatus, characterized by reusability, for deducing velocities and stresses in submarine hulls and in internal equipment for purposes of assessing the survivability of novel or extant hull, equipment or equipment-support designs.
Yet another object of the present invention is to provide method and apparatus, characterized by cost-effectiveness, for determining hull and equipment UNDEX response and survivability.
In accordance with typical embodiments of the present invention, a vehicle comprises three hollow, axially aligned, axially symmetrical sections, viz., a hull section and two bellows sections. The hull section has two hull section ends. Each bellows section generally describes a peripherally (e.g., approximately perimetrically or approximately circumferentially) pleated shape and is attached at a hull section end. The vehicle is adaptable to use in association with explosion means for testing response to underwater explosion. Each bellows section attributes the vehicle with axial flexibility responsive to the underwater explosion.
The terms “bellows” and “concertina,” as used herein, each synonymously refer to any apparatus generally characterized by a geometric axis and a plurality of generally parallel and generally peripheral (e.g., perimetric or circumferential) folds, bends or pleats which attribute the apparatus with a degree of flexibility in the generally axial direction. A typical bellows or concertina apparatus in accordance with the present invention is analogous to a bellows or concertina apparatus which is included in, part of or associated with a type of musical instrument commonly known as an “accordion.”
In accordance with the present invention, a vessel is provided which may be used as a test model for evaluating the response of a full-scale version thereof to an underwater explosive event. In particular, a submarine test vehicle is provided by the present invention to determine both early (high frequency) and late (low frequency) UNDEX hull and equipment response. Of particular note is the present invention's capability of determining late (low frequency) UNDEX hull and equipment response. Associated with late (low frequency) UNDEX hull response is a hull “whipping” motion. In the past, when “whipping” motion required study, long models (e.g., length/diameter ratios of ~9) were employed. As previously pointed out herein, such vehicles, albeit at reduced scale but nevertheless large enough to enclose essential details, tend to be massive and costly. The present invention's test vehicle can be excited, without damage, up to design severities, in “accordion” modes previously inattainable in any vehicle having a length/diameter ratio as low as 3. Hence, the present invention's test submersible is typically characterized by a relatively low length/diameter ratio, and yet affords test information comparable in value to that afforded by a conventional test submersible characterized by a much higher length/diameter ratio (e.g., ~9) as well as realistic flexural/longitudinal modes. Accordingly, the present invention is a “short” UNDEX model whose submerged vibration characteristics simulate those of a “long” prototype.
The inventive submarine model vehicle subjected to inventive testing has been dubbed by the inventor the “Poisson Blanc” (PB) in contradistinction to a like diameter generic submarine pressure hull model prototype which is three times longer, named the “Whitefish.” The inventive testing demonstrated that the inventive Poisson Blanc's response to underwater explosion loading simulates or mimics that of the Whitefish. The inventive PB thus represents a dynamic surrogate of the longer prototype. The inventive PB's middle or central part is a generic ring-stiffened (e.g., cylindrical) pressure hull test section, of arbitrary design, which houses equipment. At each end of the middle test section is a perforated (bolt ring) flange. Bolted to each flange is a “concertina” or “bellows” apparatus which is just over a quarter of the test section in length. Each bellows apparatus has two manhole-equipped (hatch-equipped) end plates (bulkheads). Further, each bellows apparatus has one or more valves (located at the outboard bulkheads, only) for intake and scavenging (expulsion) of liquid (e.g., water) or gas (e.g., air). Accordingly, the bellows (concertina) apparati pair provides for: (i) submergence (diving) ballast for the inventive model vehicle; and, (ii) the combination of low stiffness and large inertia of the inventive model vehicle, thereby together enabling low frequency bending (i.e., axial and bending, or according to this invention “beam/accordion” deformation) to take place. The UNDEX loading external to the inventive PB vehicle is measured by pressure gauges, while response measureme
Avila Stephen
Kaiser Howard
The United States of America as represented by the Secretary of
LandOfFree
Underwater explosion test vehicle does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Underwater explosion test vehicle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Underwater explosion test vehicle will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074749