TECHNOLOGY AREA(S): Ground/Sea Vehicles

ACQUISITION PROGRAM: PMS 406, Undersea Vehicles

OBJECTIVE: Develop modeling tools to design a new integrated propulsion system to increase the overall propulsion efficiency and reduce the acoustic noise signature of Unmanned Underwater Vehicles (UUVs).

DESCRIPTION: With the Navy�s focus on the development and fielding of UUVs, there is a heightened need for efficient vehicle propulsion systems.� These systems will allow the respective UUV to realize and achieve its maximum range, duration, and capability.� As a result, energy management and efficient propulsion remains a fundamental limitation of UUVs.� As more stress is placed on autonomy requiring more power intense sensors and computing, not having to compromise range and duration will necessitate the most efficient use of power for propulsion.� What is performed currently to design a UUV propulsion system is a market survey and piecing together the adequate components.� This methodology might provide a propulsion system for the UUV, but it is often far from optimized for the UUVs structure, mission, and size, weight, and power (SWaP) requirements.

Due to this increased Navy need, the subject Broad Agency Announcement (BAA) seeks the development of a propulsion system design toolkit that is parametrically validated through prototype evaluation and resulting in a Fleet-delivered design.� The intention of the design tool and ultimate propulsion system design is to optimize and increase the overall propulsion efficiency and reduce the noise signature of underwater vehicles.� The new propulsion system design tool will ensure scalable performance when applied to different UUVs sizes, from micro-UUVs to Large Diameter Unmanned Underwater Vehicles (LDUUVs).� The model will integrate the following components into a single simulated system: electrical energy storage (batteries or equivalent) system, transformation and distribution (electrical/electronic components) systems, conversion into mechanical energy (harmonic drive), including any energy transfer losses, and final conversion into effective thrust and vehicle operation.

It is expected that the model will provide a multi-objective optimization algorithm that will iteratively act on the physical and geometrical parameters of each virtual prototype component converging onto the optimum characteristics of the propulsion plant as a whole.� This type of approach is fundamentally different from a traditional design approach, where each component is designed and optimized individually, but when assembled as a system, it does not provide the most efficient and lowest radiated noise approach.� Additionally, this traditional approach methodology ignores important interaction effects that may prevent the convergence on the best overall performance of the system.� The proposed integrated co-simulation approach is the key to enable the evaluation of several non-linear interactions, such as dynamic effects due to transients, which are typically neglected in traditional design approaches based on steady-state performance characteristics.� The use of widely recognized, open-source, high-level interface protocols will ensure the best compatibility and interfacing capability of the numerical propulsion system simulator with existing and future modules/components.

The system development capability will be based upon high-fidelity physics-based dynamic simulation models of the whole propulsion chain, starting from the propulsion power supply, and continuing to, and including, the propeller.� In using the modeling capability, it is expected that it will facilitate the investigation of new propulsor technology using unconventional blade designs, including either open or ducted propellers.� Some possible propeller solutions include those with high rake and tip skew, tip loaded propellers, and newer unconventional blade sections with reverse camber.� The basis for the decision for which propeller design is included in the system will be based on optimum and efficient performance in transitional flow.� Further, it is expected that the model will also facilitate the investigation of prime movers offering high torque at low speed, and ensuring high efficiency and silent operation, including those prime movers (i.e., motors) custom designed for the particular applications.� Some examples of the applicable recipient systems include the current Knifefish vehicle being used for mine detection, localization, and identification; and the Large Diameter UUV, which is 48� in diameter and offers a payload capacity that lends the vehicle to multiple missions.

PHASE I: Developing the structure for a physics-based numerical simulation model capable of designing and predicting the performance of a UUV propulsion system.� Demonstrate the feasibility of that concept by presenting l analyses aimed at developing a prototype propulsion system design to replace an existing UUV design, or of a new UUV, depending on the availability of vehicles.� The analyses can be seen as trade studies, where the propulsion system design is optimized for range, duration, and low noise, yet leaving adequate power for the sensors intended for the vehicle.

The Phase I Option, if awarded, will address the structure of the model that includes all aspect of a UUV propulsion system.� The model structure will integrate the electrical energy storage (batteries or equivalent) system, transformation and distribution (electrical/electronic components) systems, conversion into mechanical energy (harmonic drive), including any energy transfer losses, and final conversion into effective thrust and vehicle operations.� Phase I will include plans for a prototype to be developed during Phase II.

PHASE II: Build upon the model structure deliverable from Phase I and refine it to provide the capability for optimizing the efficiency of UUV.� If the design is prototyped on an existing UUV prototype, the new design shall show measurable improvement in propulsion efficiency approximately two to four-fold from existing propulsor designs of comparable power.� If the design is prototyped on a new UUV design, the performance comparison will be made with the closest existing replica.� If the prototype design is installed on an existing design or forms the basis of a new vehicle design, the prototype will be scrutinized to validate the predictions of the model.� The company will prepare a Phase III development plan to transition the technology for Navy validation and accreditation.

PHASE III DUAL USE APPLICATIONS: Support the Navy in evaluating the prototype delivered in Phase II and the transition of the technology to Navy use.� To validate the final optimal design, a full-size prototype UUV propulsion system will be built and integrated to a Government-furnished vehicle.� The propulsion system and vehicle will be evaluated through a set of qualifying tests based on expected operational areas, and desired missions.� Testing will include those needed for qualifying a system ready for Fleet issue, or at least ready for Fleet turnover allowing for Sailor evaluation.� Further, commercial use could span to improving marketed UUVs used for oil and gas, and historical exploration.

The expected deliverable from the subject effort will lead to efficient and low-noise UUVs regardless if the vehicle is used for military use or not.

REFERENCES:

1. Brown M., et al., �Improving Propeller Efficiency Through Tip Loading,� 30th Symposium on Naval Hydrodynamics, Hobart, Tasmania, Australia, 2-7 November 2014; https://www.researchgate.net/publication/272021083_Improving_Propeller_Efficiency_Through_Tip_Loading

2. Gaggero S., et al. �Design and analysis of a new generation of CLT propellers.� Applied Ocean Research, 59: 424�450, 2016. http://www.sciencedirect.com/science/article/pii/S0141118716302279

3. Farhoo, Fariba. �Enabling Quantification of Uncertainty in Physical Systems (EQUiPS).� Defense Applied Research Projects Agency (DARPA).� http://www.darpa.mil/program/equips

KEYWORDS: Unmanned Undersea Vehicle (UUV); Propulsor Design; Hydrodynamics; Radiated Acoustic Noise; Propulsor Efficiency; Propeller Design