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Inflatable Deployable Sail Systems for Future Submarines


RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Ground / Sea Vehicles

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop technology that will advance traditional submarine design toward accommodating an Inflatable Deployable Sail System (IDSS) for future submarines.

DESCRIPTION: A submarine designed without a sail would have inherent advantages in submerged operations over a design with a sail in the areas of speed, maneuverability, and acoustic stealth. However, until a solution can be found to safely navigate a submarine without the height of eye and visibility afforded by a sail, no such design can be entertained. Advances in inflatable structures can provide the freeboard needed for surface transit with a temporary and reusable structure. Maturation of this technology will open up the SSN(X) design space to entertain submarines that can operate submerged without the impediments of a sail.

The submarine sail is an integrated structural platform that hosts various Undersea Warfare (USW) systems and equipment including periscopes; communication antenna masts; acoustic, electromagnetic and radar sensor systems; exhaust ports; and crew access/escape trunks. The sail connects the bridge to a secondary (non-pressure) hull that, in turn, connects to the pressure (primary) hull. Crew hatches are positioned at each boundary interface along the sail access/escape trunk. The sail vertically offsets the bridge from the primary hull to provide a specified freeboard. Each submarine class in today’s USN Fleet incorporates a fixed rigid sail structure. These traditional sail structures provide a manned bridge that enables the crew to command, communicate and control operations remotely from the internal control room while affording necessary height of eye and on-ship visibility to facilitate surface transits. The sail structure also provides freeboard necessary to enable vertical and underway replenishment (VERTREP and UNREP, respectively) operations without flooding the primary hull.

Sail geometries are optimized for their hydrodynamic performance to minimize flow-induced noise, vibrations and wake effects by using faired leading and trailing edges and, for specific class variants, optional cusp fairings. Unlike the Seawolf, Virginia, and improved Los Angeles class submarines, variants such as the Ohio, original Los Angeles, and Columbia classes incorporate articulating dive planes external to the sail.

The structural loadings, deployment/retrieval operations and stability mechanisms required present significant design and material challenges for an inflatable and deployable sail. NAVSEA’s design objectives for future submarines are to explore and innovate sail concepts, including development toward achieving an Inflatable and on-demand Deployable Sail System (IDSS) that is capable of controlled deployment from and stowage inside the secondary hull. The IDSS shall primarily be used for manned bridge operations with a crew access/escape trunk only and will not house the aforementioned USW systems and related equipment.

There are many dimensional and configuration constraints exist for IDSS: The sail dimensions for deployable assembly should have a minimum 16-ft freeboard (other dimensions as necessary for manned bridge capabilities that match current submarine sails); Crew bridge capacity should be at a minimum of 2 crew shoulder-to-shoulder forward of bridge hatch with minimum of 2 crew shoulder-to-shoulder rear of bridge hatch; Bridge and pressure hull hatches should be 30-inch inner diameter; Bridge should have power, lighting and communications (from pressure hull to bridge) and conduits, flip-up windshield, storage lockers, etc.; Crew access/escape trunk (connects pressure hull hatch to bridge hatch), include ladder system; Wave slap should have uniform pressure loading; Bridge weight should be 4,000-lbs maximum; Sail external vertical loads must include weight of ice, etc.; Ice and foreign object impact protection; Ballistic protection (small arms fire); Positive locking stowage configuration.

The minimum operational constraints for IDSS are: Inflatable actuation (potable water, seawater, air/water combination); Operational cycles of 10,000, Deploy/stow at 0.0 knots from periscope depth with cross flow of 5.0 knots; Maintain shape at periscope depth in cross flow velocity of 5 knots; Deploy/stow at surface at vessel speed of 5.0 knots; Deploy/stow during range of sea states (operational to SS6, survivable to SS8); Provide pressure relief for internal pressure exceeding 2.5x ambient pressure within 5.0 seconds; Safety factors for inflatable components: 4.0; Deployment time of 1.0 minute; Stowage time of 1.0 minute; Deflection limits at full deployment shall be 5.0-inches yaw, pitch, roll with respect from bridge to secondary hull (existing fixed sails are stress-limited); and Temperature range of -60°F to 150°F.

The current state of inflatable soft structures technologies can provide unique solutions to the many challenges limiting today’s USW operations, capabilities and system designs. Inflatable soft structures have been successfully developed for DoD, NASA, and industry and are generally categorized in the following sectors: Inflatable control surfaces, deployable energy absorbers, and temporary on-demand structures.

Successful design and performance of soft inflatable structures is attributed to technological advancements derived from: High Performance Fibers (HPF) including, but not limited to, Vectran®, DSP® (dimensionally stable polyester), PEN (polyethylene napthalate), Spectra® (ultra-high molecular weight polyethylene), Kevlar®; Novel fabric architectures and 3-dimensional woven preforms capable of unique mechanical behaviors; Continuous weaving processes for elimination of seams in inflatable structures; Robust Physics-Based Modeling (PBM) methods with Fluid-Structure Interaction (FSI) capabilities including FEA and CFD; and material test methods for characterization of multi-axial and pressure-dependent mechanical behaviors for inputs to numerical models.

Collectively, these advancements have established a sound technology base; one that can be leveraged for innovative solutions to soft structure designs requiring significant load-carrying capacities, shock mitigation, dynamic energy absorption, rapid deployment, large deployed-to-stowed volume ratios, and fail-safe modes of operations.

The Inflatable Deployable Sail Structure (IDSS) shall consist of a generally soft or soft/rigid hybrid inflatable structure with a rigid or hybrid rigid/inflatable bridge. The IDSS will connect to the submarine’s seawater pump interface (SPI) and air flask interface (AFI). The tube seawater pump and air flask shall be used to control inflation and deflation of the IDSS with seawater and air as the possible inflation media.

The soft structures considered for use in developing the IDSS may include, but are not limited to, control volumes constructed of inflated membranes, 3-D woven preforms, flexible bladders, coated fabrics, and hybrid (soft/rigid) material systems, and hard goods-to-soft goods connections. Hybrid inflatables may include inflatable elements with semi- or fully-rigid reinforcements serving as deployment shaping controls, and abrasion resistant contact surfaces. The pressurization media for all inflatable components will be limited to seawater and air.

Structural testing of the IDSS concept shall be required to validate the operational performance and resistance to wave slap loading using a full-scale IDSS prototype and in accordance with stated objectives using air, water, or both as the inflation media. The tests shall demonstrate:

Test-1: deployment from the stowed to the fully deployed (operational) configuration.

Test-2: resistance to wave slap and impact loadings along the port and starboard athwart ship directions and the fore and aft longitudinal directions when fully deployed.

Test-3: retrieval from the fully deployed configuration to the stowed configuration.

The company shall identify recognized issues and propose resolutions affecting operational performance and reliability, crew and system safety, environmental exposure effects (temperature, cyclic fatigue, UV, abrasion, puncture, impact, biofouling, chemical/biological, etc.) and maintenance concerns including crew accessibility and repair methods. Failure modes effects analyses (FMEA) shall be performed for the primary structural and inflatable components.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. Owned and Operated with no Foreign Influence as defined by DOD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence Security Agency (DCSA). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DCSA and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advance phases of this contract.

PHASE I: Create a virtual design concept for an IDSS including a Concept Feasibility Analysis (CFA). The CFA shall assess the IDSS concept using Finite Element Analysis (FEA) to characterize the structural response and stability for hydrostatic, hydrodynamic, wave slap, ice and foreign object impact loading events. Additionally, Computational Fluid Dynamics (CFD) modeling shall analyze the hydrodynamic and flow noise/vibrations responses. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build and test a prototype solution in Phase II.

PHASE II: Optimize the IDSS design based on the results of the Phase I and Phase II Statement of Work (SOW) including material selections for the soft structural components, pneumatic/hydraulic layout design and manifolding, inflation/deflation sequencing, porting to the submarine’s seawater interface pump and air supply flask, hard-to-soft-goods connections, power, data and lighting connections to the pressure hull, environmental factors. Identify and document all operational, safety, environmental and maintenance issues as recognized during development of the proposed IDSS design. Perform risk identifications, risk assessments, and risk mitigation plans from the concept development stage.

Build a full-scale structural prototype of the proposed IDSS and test to validate the above requirements. Correlate the results of models developed to those obtained from the prototype tests, including deflections, reaction forces and the pressure-time histories for each inflated component and loading direction.

Deliver the prototype IDSS to the NAVSEA designated Warfare Center(s) for testing in accordance with the stated operational requirements.

It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III DUAL USE APPLICATIONS: The technologies are applicable to future underwater weapons, Unmanned Underwater Vehicles (UUVs), Unmanned Surface Vehicles (USVs), and commercial/industrial dual use. All technologies including designs, material data, manufacturing methods, prototype test results, etc. developed under this topic shall be transferred to the Navy for transition to future submarines, UUVs, USVs and underwater weapons. Potential commercial applications include adaptable and deployable structures for the construction industry, Lighter-Than-Air (LTA) ships, space vehicle structures (including deployable control surfaces) and habitats, civil infrastructure protective systems (land, air and port barriers; levee sealing and erosion repair), chemical/biological containment systems for internal use aboard aircraft and mass transit ground vehicles, blast/shock mitigation and impact energy absorption devices), and maritime safety systems (rescue and buoyant recovery platforms).


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