TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

OBJECTIVE: Develop a low cost enabling manufacturing technology for the production of Physical Scale Models (PSMs) for signature reduction from full-scale drawings of Navy ships. Address all technical issues related to full-scale drawing conversions, and PSM design, fabrication and testing.

DESCRIPTION: Typical models of ships and submarines focus on the aesthetic quality of the model and its ability to visually relate the major features of the vessel without regard for physics-based effects. Physical Scale Models (PSMs), on the other hand, are designed not only to accurately reproduce the form of the vessel, but also to reproduce the effects of structure and materials in response to physical stimuli [e.g. wave action, vibration, acoustic and electromagnetic (EM) propagation, etc.]. This requires the development of high fidelity reproductions of features in the model. Since the 1940�s, when PSMs were first employed routinely to model electromagnetic (EM) behavior, these features have been meticulously designed and constructed by hand in model-making machine shops. While providing an accurate representation of the magnetic signature, this process has nonetheless been labor intensive, requiring many hours of skilled craftsmanship to complete a PSM. In many cases, the PSM was developed while new construction vessel designs were still being modified. Significant design changes often resulted in increased rework of the model or, more likely, fabrication of an entirely new model. The result is that, under current fabrication procedures, the manufacture of PSMs is expensive, labor intensive, and slow to respond to design changes. With today�s advanced design, modeling and fabrication tools, the techniques used in developing PSMs are ripe for modernization. Rapid and efficient manufacturing techniques are needed to go from concept to design to fabrication of a physical product in a short time. New technologies such as solid freeform fabrication and direct digital manufacturing, which are suitable for "art-to-part" approaches, mass customization, flexibility in design changes, and robotic assembly, can be exploited to impact PSM development.

PHASE I: Develop proof-of-concept of a technique to design, model and manufacture PSM for EM signature reduction. The PSM can be 1/30 to 1/60 of full-scale and should have EM signature corresponding to the full-scale structure. Current PSMs use manually assembled sheet metal and manually laid degaussing coils. The proposed PSM could be made of any material or combination of materials as long as it has the desired EM signature and has a means to include coils, either in situ, or later installed. Demonstrate manufacturing cost reduction of 1/4 to 1/2 of current costs, which can be as high as $500K to $1M per PSM. Demonstrate significant reduction in product realization time, few days or few weeks. Using the developed fabrication concepts, build a simple shape, such as a cylinder, for testing and validation by the Navy. An example could be reduced scale ship steel cylinder with inserts and partitions to serve as decks or bulkheads.

PHASE II: In cooperation with the Navy, construct a PSM prototype as a testable product. The Navy will perform the signature tests and validate the model. An example could be a coast guard boat scaled to 1/48 or 1/24, whose drawings are available in autoCAD, CATIA or other forms.

PHASE III: Transition the PSM manufacturing technology to critical military use and the civilian sector. Build marketable manufacturing units and demonstrate the fabrication of a test model. For example, construct a PSM of a complex Navy ship with degaussing coils.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A successful PSM fabrication system would be useful for a variety of commercial applications. Its affordability and versatility will result in new businesses and industries, and high value jobs.

REFERENCES:
1. John J. Holmes, Application of Models in the Design of Underwater Electromagnetic Signature Reduction Systems, Naval Engineers Journal, vol. 119, no. 4, (2007), pp. 19-29.

2. John J. Holmes, Modeling a Ship's Ferromagnetic Signatures, 1st ed., Morgan & Claypool, 2007.

3. ASNE Ships & Ship Systems Technology (S3T) Symposium, "The Role of Physical Scale Models in the Design of Ship Degaussing Systems in the Age of Computer Modeling" (Mr. William Gay & Mr. Robert Wingo), 13-14 November 2006.

KEYWORDS: Physical Scale Model; EM Signature; Rapid Manufacturing; Cost Reduction.