TECHNOLOGY AREAS: Sensors, Electronics

ACQUISITION PROGRAM: The improved hose described herein is potentially applicable to each of the

OBJECTIVE: Develop and demonstrate a reduced density towed array hose that is able to temporarily alter its shape during turns. This hose will improve array ruggedness by being thicker, while simultaneously reducing damaging strum-induced vibration. Develop and demonstrate a reduced density towed array hose for passive submarine towed arrays that has the ability to reduce or eliminate turn induced strum vibrations.

DESCRIPTION: Current generation towed array outer hoses are circular in cross section and have a relatively thin wall thickness. This circular shape optimizes self-noise performance, interaction with the handling equipment, and ease of manufacturing. The drawback of having an array with a circular cross-section is that it causes strum (Strouhal vortex shedding) whenever water flows across its longitudinal axis at angles of attack of greater than 4 degrees. Crosswise flow occurs whenever the SSN towing anthe array turns.

Additionally, the hosewall thickness is constrained by the need for the array to tow horizontally which is achieved with neutral buoyancy. The ideal hose would be thicker and lighter. A thicker hose will permit internal fill pressures in excess of 30 psi instead of the 12-15 psi currently used. HSMS measurements show that a hose filled to 30 psi prevents most handler-induced forces from being imparted onto the internal wiring and connectors of the array. A rugged hose made of lower density can bring both ruggedness and neutral buoyancy to the array.

Strum suppression techniques such as temporarily changing the hose shape during turns have to a more hydrodynamic cross section, growing some "hairy fairing" to keep the flow attached, or some other method of adding a virtual or physical tail would diminish strum and support the Navy�s need. It would be necessary for the hose to return to circular shape (or retract hairy fairing) upon completion of the turn. Such an addition to the towed array would serve three purposes:
1. The strum reduction would greatly reduce damaging stresses on the array internal structure, improving reliability and lowering repair costs.
2. Reducing strum during turns would also allow improved hydrophone performance, (which are presently swampoverloaded at important low frequencies) allowing the array to support SSN use during turns.
3. Strum reduction will also improve the heading sensor performance which presently is diminished during periods of vibration. Improved heading sensor performance during turns would also contribute to improved array performance during SSN maneuvers have a specific gravity in the 1.1 to 1.2 range. Towed arrays must be near neutrally buoyant (specific gravity = 1.02). As the Navy seeks to reduce towed array diameter, the heavy hose takes up more of the relative array volume and comes to have a major impact on maintaining array buoyancy.

The Navy seeks innovative hose material or design alternatives to reduce hose specific gravity while meeting other mechanical and acoustic requirements. A reasonable goal would be the reduction of the hose specific gravity to the 0.9 to 1.0 range. Current hoses use thermoplastic urethane and approaches should provide a mechanical stiffness equivalent to 80 Shore-A durometer. Materials must be compatible with extrusion of the array hose. Materials must be capable of 40% elongation. The hose must be acoustically transparent. The hose should be fully compatible (no property changes) with Exxon Isopar L. The extruded viscosity and extrusion process should be capable of encapsulating small diameter twisted or braided polyester strands running longitudinally. Temporarily changing hose shape or growing "hairy fairing" is seen as challenging, but will have substantial benefit. Techniques that reduce strum over all cross-flow angles up to 30 degrees are desired, but even suppressing strum up to 10 degrees cross-flow would improve towed array performance and reliability.

Hosewall density has been driven by the urethanes presently used (BF Goodrich 58881 for example) that support excellent self-noise performance and moderate mechanical ruggedness. The ideal hose would preserve key parameters such as static Young�s modulus, tan delta, and dynamic Young�s modulus; while reducing specific gravity from 1.12 to 1.0. Candidate approaches are seen as those that modify the BF Goodrich 58881 with a co-extrusion or injection of micro-spheres or development of a new material.
within the hose wall. Mechanical and acoustic properties should not change more than 10% over a temperature range of 0�C to 40�C.

PHASE I: Demonstrate the proof of concept by selecting one or more materials or design approaches, assessing applicable Navy requirements, and conducting research, modeling, and testing to prove design feasibility. Several key features to be considered are specific gravity, acoustic evaluating the benefits of conceptual shapes or added "hairy fairing.", Strum reduction as a function of characterizing the cross-flow angle (compared to a circular cross-section baseline) is seen as a metric for performance of candidates. Added drag must also be measured and used to evaluate the benefits of candidate configurations.
Hosewall specific gravity (contrasted to the 1.12 of the baseline material) while measuring the key static and dynamic material properties will also be part of concept demonstration.
at which strum is induced as well as characterizing any added drag. Additionally, a demonstration of a feasible approach for altering the strum suppression, while returning to the original circular cross section is needed. transparency, producibility, and iso-thermal mechanical properties.

PHASE II: Design, fabricate, and demonstrate a prototype hose that is capable of being used to "boot" a typical TB-29A module. This prototype will be used to evaluate the effectiveness of the proposed solution. Strum suppression feasibility of the prototype will be shown through a demonstration of the contractor�s choice.

The contractor will also provide an assessment of the prototype design�s ability to provide mechanical interface between the array and the OA-9070B SSN handling system.

Recommendations for improvements will be submitted as part of the final test report.

PHASE III: The contractor will use the prototype hose developed under Phase II and use it to house a TB-29A acoustic module. This module will be used to perform three key capability demonstrations. A) The prototype will be tested at the NSWC Carderock tow basin to confirm its ability to reduce strum at SSN towed array angles of attack.
B) The prototype will be tested at the Navy�s towed array evaluation facility at Lake Pend Oreille, Idaho. There the prototype hose�s acoustic impact on towed array performance will be assessed.
C) The prototype will then be tested at the NUWC OA-9070B land based SSN handler facility to determine its effectiveness when exposed to the stresses imparted by this equipment.
Upon successful completion of these key demonstrations, the contractor will provide this hose to the submarine twin-Thinline line advanced development program and participate in the development of an Engineering Change Proposal (ECP) to incorporate this new hose into the program baseline.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This technology may find application in commercial seismic exploration and arrays monitoring systems.

REFERENCES:

KEYWORDS: towed, towed array; low density Strouhal vortex shedding; array hose; acoustic; strum; fairing, low-density buoyancy

** TOPIC AUTHOR (TPOC) **

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