Wireless Power Transfer…Underwater (Web Exclusive)

Wireless 1A underwater wireless power system coil built using additive manufacturing at Naval Surface Warfare Center Carderock Division.










By Margaret Zavarelli

Cross-functional engineering teams across the Navy are working on underwater wireless energy transfer systems that charge unmanned underwater vehicles (UUVs) to continue the service’s dominance of undersea warfare.

“We’re constantly being challenged by our adversaries,” said Alex Askari, a lead engineer on the team from Naval Surface Warfare Center Carderock Division. “We need to look at new concepts and maybe change the way we operate our unmanned systems.” Operating in new ways intrinsically leads to technology challenges the Navy can address, he said.

Safety concerns, energy storage, and the way the unmanned underwater vehicles are deployed add to the ship’s operational considerations. “The Navy asset that deploys the unmanned system has to stay around in the area when it could be off conducting other missions,” Askari said. “Right now, the unmanned vehicle is deployed, conducts its mission, comes back, and then we have to retrieve it to download the data it has collected and recharge or swap out its batteries. That’s a fairly lengthy process. Imagine if we could keep all those unmanned vehicles in the operational area and autonomously charge them underwater so they didn’t have to come back to the mother ship to get charged—that could change the game completely.” Doing so would allow the UUVs to stay on station longer, increasing the persistence and, therefore, the mission effectiveness, Askari said. Underwater docking and energy transfer is relatively new to the Navy compared with how operations have historically been conducted.

Various Navy platforms can deploy UUVs for a multitude of operations. Unmanned systems are becoming much more prevalent because of their low cost, advancements in technology, and elimination of safety concerns associated with having humans aboard. The number and type of unmanned assets carried aboard Navy platforms depend on the purpose and available space. Unmanned systems can be used as force multipliers, carrying out tasks autonomously while the manned assets continue their own parts of the operation in a different location.

How long the UUV could be away from a ship is one aspect being studied, as is its relation to the rate at which energy could be autonomously transferred to the UUV in the operational area. “One of the Navy’s goals is having persistent presence underwater, and we believe wireless power transfer is one of the enabling technologies that could help us achieve that goal,” Askari said.

Askari said the concept can be explained by imagining how some cell phones are charged. “You place it on a pad that has a coil embedded,” he said. “A coil is just like your antenna that sends your power to the receiver.” Wireless energy transfer can allow higher reliability because there aren’t hard mechanical connections involved and can reduce current spatial alignment requirements. In addition, biofouling—a critical challenge of any underwater operation— potentially can be diminished.

For the past several years, most of what Carderock has been doing within the realm of wireless power transfer has been studying the fundamental science—conducting modeling and simulation and running experiments in laboratories to understand the scientific laws behind the application, knowing it was the precursor to implementation. To better understand how the energy is transferred wirelessly, the team investigated the factors that affect the system’s efficiency, as well as the system’s sensitivity to those factors.

The modeling and simulation enabled the team to start developing system designs that led to experimentation within the laboratory. They verified the modeling and simulation with real-world results so that further theoretical designs could be trusted prior to fabrication. In terms of fabrication, the Carderock team is leveraging state-of-the-art additive manufacturing methods in 3-D printing, coupled with computer-assisted design software, to rapidly and cost effectively manufacture different coil designs before settling on the final system. This allows the team to prototype and test a wide variety of coil system design considerations—such as the number of turns, wire gauge, form factor, shape, and other parameters—before settling on an optimum design.

Carderock is currently participating in a cross-systems command demonstration effort with the Naval Undersea Warfare Center Division Newport and Space and Naval Warfare Systems Center Pacific. The engineering teams from the three labs have decided to pool resources to execute a system of systems demonstration—wirelessly transferring data and energy autonomously to an underwater unmanned vehicle.

Carderock is developing and providing the wireless power transfer system, including the energy system’s power electronics requirements and a state-of-charge algorithm indicator developed by some of its engineers at the Ship Systems Engineering Station that shows the state of the battery during charge and discharge. The Naval Undersea Warfare Center Division team is providing the vehicle for the demonstration, as well as designing an underwater docking station for the vehicle. Carderock’s wireless energy system will be incorporated into both, as will the underwater communications systems from Space and Naval Warfare Systems Center Pacific, which will allow the entire system to transfer data and communicate underwater.

This summer the teams will test their work at two demonstrations. First, Carderock team members will test their energy system at their headquarters in West Bethesda, Maryland. This initial demo will be conducted in a 6,000-gallon tank. “We’ve made the water murky, and we’re going to add salt to it to simulate the actual ocean environment,” Askari said referring to the water from the base’s test pond, where underwater explosives are detonated. The energy-centric demonstration will showcase the energy system prototype before integrating it with the technologies provided by the other commands for the second, larger demonstration in Narragansett Bay, Rhode Island, at the Naval Undersea Warfare Center.

“Getting all the players together is like a well-orchestrated choreography,” said Mayer Nelson, a technical project manager at Carderock. “Each lab is designing its own system, and in the second phase when we go to Rhode Island we are going to integrate all the systems and test them in a relevant environment, which is the Bay.

“With [the Naval Undersea Warfare Center Division] and [Space and Naval Warfare Systems Command], all of us are starting to really look at the integration efforts and say, ‘OK, how does what’s in the lab differ from actually putting it into a vehicle or platform?’ because a lot of engineering challenges arise when you do that, especially when you’re combining it with other systems with different functions, all of which have to work together,” Nelson said. “It’s not necessarily a physics thing at that point—of course that’s always present—it’s more of a systems engineering problem, and sometimes the physical environment in the real world may seem to go against some of the things you’ve seen on a bread board or in modeling and simulation.” Carderock will be able to use those previous years’ efforts in fundamental research to troubleshoot any engineering problems.

The team is designing a system prototype that could be used in many platforms, not just the current vehicle. “A lot of technology out there now is vendor proprietary,” Nelson said. “The Navy wants to invest in a lot of different types of unmanned assets, so a more open system is inherently appropriate.” Carderock’s design philosophy is to keep the system scalable and modular. “We call it vehicle agnostic,” Askari said.

Part of what Carderock is working on can be explained in the context of the “undersea constellation”—the cumulative collection of undersea vehicles and systems. Both engineers were optimistic about interoperability, a facet all three labs find paramount. If Carderock’s wireless energy transfer system is designed smartly, it could be used on different-sized vehicles and platforms. The challenge is to understand how a wireless power transfer system would scale, because one system configuration that gets great results won’t work as seamlessly on another system or platform. “A lot of that goes into the entire system design,” Nelson said. “It’s not just the coil; it’s also the stuff that’s behind the coil and the interactions with the rest of the system that matters.”

Each of the labs has been working in their respective areas for many years. With the summer demonstrations the teams are starting to see what the integration effects and challenges are. “Just like Carderock is learning a lot from this collaborative effort, so are the other teams,” Nelson said. “And it’s even better for the Navy, because through these types of collaborative projects, you start to interact with other warfare centers and systems commands—with other people from different backgrounds and systems. We start to get a common language. Part of [the project’s] funding is meant for workforce development, so the fact that we can all collaborate and work on something technical motivated by operational considerations that’s good for the Navy is a home run.”

About the author:

Margaret Zavarelli is a public affairs specialist with the Naval Surface Warfare Center Carderock Division.

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