A Naval Undersea Warfare Center Division Newport team of oceanographers, marine biologists and engineers is studying the melons of odontocetes, or toothed whales, to provide the U.S. Navy with more information about mammal exposure to noise and shock loads from underwater explosions. Principal investigator Monica DeAngelis (center) holds a mammal skull of a harbor porpoise, with team members Lauren Marshall (left) and University of Rhode Island intern Catherine Eno (right).

Story by Public Affairs Office, Naval Undersea Warfare Center Division Newport

A Naval Undersea Warfare Center (NUWC) Division Newport team of oceanographers, marine biologists and engineers is determined to collect new data on marine mammals in an effort to provide the U.S. Navy with more applicable test plan information when it comes to mammal exposure to noise and shock loads.

Navy operations and exercises may expose marine mammals to manmade noise and shock loads, such as underwater explosions. Currently, the protection and mitigation measures that are in place are based on data collected from the lung and gastrointestinal (GI) tract of terrestrial mammals. This information is used to establish monitoring zones to protect marine mammals during testing and training. The team is looking for new data that would be focused solely on marine mammals.

The team united for the project “Investigating Marine Mammal Melon Response to Underwater Explosions,” which is in its second year of a three-year in-house laboratory independent research effort. Principal investigators Monica DeAngelis, Environmental Branch, and Dr. Emily Guzas, Applied Sciences and Structural Mechanics Branch, worked with a team that includes Lauren Marshall, Tom Fetherston, Dan Perez, Rachel Hesse, Eric Warner, A.J. Paolero, Jesse Belden, Joe Legris, Dave Bamford, Drew Canfield, Craig Urian, Carlos Javier and University of Rhode Island interns Catherine Eno and Irine Chenwi.

A 3D printer in Division Newport’s Rapid Innovation Center helped develop models for the project.

“As you can imagine, there are differences between a terrestrial mammal and a marine mammal — yet we are still using data collected from terrestrial mammals to determine [non-auditory injury and mortality] thresholds for marine mammals. So, at the very least, our model will be tested using actual marine mammal tissue,” DeAngelis said.

For this study, the team is focusing on the forehead of odontocetes, or toothed whales, which holds an organ called the melon. According to National Oceanographic and Atmospheric Administration, “the melon acts like an acoustic lens, aiding in sound recognition. In addition to the melon, the dolphin’s teeth are arranged in a way that they function like antenna, receiving incoming sound.”

This study is based on the belief that the marine mammal melon is very important in the animal’s ability to echolocate. If the melon is somehow compromised or damaged and the animal is not killed immediately, how is the mammal adversely affected?

The Division Newport team is asking the following questions:

Are the current non-auditory explosive criteria (developed for the lungs and GI tract) inclusive for other tissues?
Is damage to melon below criteria developed for the lung and GI tract?
Could trauma induced by underwater explosions, concussive impact or oscillation of nearby air-filled structures affect the melon similarly to impulsive forces on human skull and brain?
Do underwater explosions affect the melon’s functionality (an important organ for echolocation)?
Do underwater explosions compromise an animal’s ability to navigate, communicate, hunt, and, ultimately, survive?
The team’s goal is to create validated numerical models of underwater explosions on marine mammal melons to attempt to establish whether the current non-auditory criteria are adequate to assess the potential impact of underwater explosions to other tissues besides the lung and GI tract. DeAngelis was able to collect the marine mammals’ samples through a permit and some assistance from the International Fund for Animal Welfare and Mystic Aquarium.

“We were fortunate enough to get the entire skull of a harbor porpoise and an entire carcass of a fresh dead common dolphin,” DeAngelis said. “I was able to remove the melon from both animals and then preserve the skull for both species. The melon sits on top of the skull, so getting the actual melon and the actual skull from the animal is very fortunate. We worked with Drew Canfield [Sensors and Sonar Systems Department] who used the Advanced Concepts Mechanical Engineering [ACME] lab’s FARO arm laser for 3D measurement of the skull and a cast of the melon that I made. We will then use this in our model to see how it compares to research that has been previously done on the dolphin skull and the orientation of the melon to the skull itself. These measurements define the melon and the skull’s external geometry for our specific specimens. It also makes a great addition to our presentations when we can use these images to explain our research.”

The team started working with Eric Warner, manager of the Mechanics of Materials Laboratory in the Advanced Technology Modeling and Simulation Division, about a year ago. Warner developed the team’s drop test tower that they used to simulate an impulsive loading similar to the shockwave from an explosion. Small weights “drop” on the melon tissue to simulate certain target impulse levels [in units of pound-force per square inch-milliseconds] that the team hypothesized will cause no damage to the melon or will cause damage to the melon. Warner and his machinists also developed sampling tools to make it easier to extract small cylindrical samples from the actual melon itself.

“He’s an absolute magician when it comes to creating materials that we can use,” DeAngelis said. “Here I am a biologist working with my team of engineers and we’re all trying to explain to Eric what we need and somehow he interprets it all and makes it for us.”

The team’s main research program objectives include building a fluid-structure interaction numerical model of the marine mammal melon, taking into account the spatially varying acoustic and mechanical material properties.

DeAngelis explained that the melon is a mass of adipose tissue that is unique to certain marine mammals. The exact composition varies throughout the melon, but is a mixture of triglycerides and wax esters. Structurally, the melon is part of the nasal apparatus and comprises most of the mass of tissue between the blowhole and tip of snout.

“Of particular interest is the composition of the melon,” DeAngelis said. “The core has a higher wax content than the outer parts and conducts sound slower. Therefore, we have leveraged published material properties and geometry to develop a ‘bare’ melon model. Based on those results, we were able to obtain the spatially varying material properties —the shell, which is stiff, and the core, which is soft.”

“Trying to create a numerical model of something as squishy as a marine mammal melon that can accurately represent its movement to external stimuli is really difficult and thus super interesting,” Guzas added. “Its stiffness response is similar to breast tissue, but yet its acoustic properties vary throughout the organ, due to its specialized function. Should we model the melon material as a fluid or as a solid? What modeling techniques best meet our needs, to try to model its motion and deformation accurately but without so much computational expense that it would take us a prohibitively long time to simulate the melon’s response to a single [underwater explosion] scenario (when there are infinitely many cases to choose from)?”

The team also conducted an extensive literature search to determine which underwater explosions they wanted to simulate.

DeAngelis said the team is beginning its testing by incorporating their information on material properties of the melon tissue itself and their information on selected underwater explosions with the synthetic samples they developed using EcoFlex, a silicone-based material that they embedded with 3D-printed material to simulate the vasculature of the marine mammal melon. The team will use surrogate biological tissue to test their methods and then will test all of these scenarios using the melon tissue itself.

Once the team gains a better understanding of the marine mammal melon and melon-like material response to dynamic shock loading, they plan to investigate the high- and low-density cores, their potential function, and vulnerability to impulsive loading and evaluate whether the shell acts as some sort of “shield” to the inner core.

Based on their results, the team may be able to provide recommendations to modify the current non-auditory criteria as well as to necropsy protocols. Necropsies are autopsies performed on marine mammals and current protocols do not include examination of the marine mammal melon.

“Currently, it’s not standard practice to collect samples from the melon or other non-auditory tissues and organs, so it’s not clear if cause of death may be caused by [underwater explosions],” said DeAngelis. “We’d also like to eventually see if there is a possible correlation to humans and CTE [chronic traumatic encephalopathy]. Our long-term goal is to create a synthetic marine mammal that would include organ structures like the melon, lungs, GI-tract, etc., maybe even test on a synthetic human.”

“After all of this, we are hoping to demonstrate no damage and potential damage to the melon based on the severity of the underwater explosions and then re-evaluate the current thresholds, or criteria, that are used to protect marine mammals from exposure to underwater explosions,” said DeAngelis.

“It’s a gut check on the current criteria for testing around marine mammals,” added Guzas.

“The Navy, as well as other entities, incurs costs associated with monitoring the zones of influence. If we can refine the thresholds, this may provide a cost savings to the Navy because it would reduce the uncertainty that exists now using terrestrial mammals as surrogates,” said DeAngelis. “Also, it could be important information on the potential susceptibility to humans to shockwave exposure, such as divers, and would position NUWC as leaders in this research. We’re trying to make the uncertain more certain and we’re hoping to refine what people are thinking.”

Interns assist in marine mammal impacts research

As part of a summer internship program, Catherine Eno and Irine Chenwi from the University of Rhode Island (URI) worked on the marine mammal melon project with the Division Newport team.

Chenwi is a doctorate student in URI’s Department of Mechanical Engineering who heard about Division Newport’s internship program from her professor and fellow students who had previously completed the internship. Chenwi has been able to work on a variety of projects including a creep peel test with Dr. Thomas Ramotowski, and a Split-Hopkinson pressure bar with Eric Warner and Mike Galuska. She conducted battery testing with Dr. Charles Patrissi, soft tissue drop weight testing with Dr. Emily Guzas and examined low-temperature effects on saturated composites with Dr. James Leblanc. Chenwi has completed her doctoral course work and is working exclusively on her research.

“Most of the projects I am working on are very educative and a learning experience for me,” Chenwi said. “Getting to know how research can improve on the structures of the Navy is pretty exciting. Also, NUWC is very welcoming, with friendly people everywhere. Getting to talk with people who have so much hands-on experience is great.

“I am definitely considering working at NUWC after graduation.” Chenwi said. “Material characterization has been one domain I have much interest in. I believe every other research starts from knowing the materials you are working with and understanding their behavior under different conditions.”

Eno is in her third year of a five-year program where she is majoring in both ocean engineering and marine biology. Following her Division Newport internship, she returned to URI’s campus to take a combination of online and in-person courses.

“I like this project because it was exactly something I was interested in studying – the effects of technology on marine mammals,” Eno said. “When Emily called and asked what I was interested in, it was a perfect fit to their project.”

In addition to the marine mammal project, Eno also worked with Patrissi on his research on seawater batteries.

“My goal was to learn as much as possible and get a feel for research projects,” Eno said. “I’d definitely consider NUWC [for employment] because it has so many opportunities beyond marine mammal research.”

NUWC Division Newport is a shore command of the U.S. Navy within the Naval Sea Systems Command, which engineers, builds and supports America’s fleet of ships and combat systems. NUWC Newport provides research, development, test and evaluation, engineering and fleet support for submarines, autonomous underwater systems, undersea offensive and defensive weapons systems, and countermeasures associated with undersea warfare.

NUWC Newport is the oldest warfare center in the country, tracing its heritage to the Naval Torpedo Station established on Goat Island in Newport Harbor in 1869. Commanded by Capt. Chad Hennings, NUWC Newport maintains major detachments in West Palm Beach, Florida, and Andros Island in the Bahamas, as well as test facilities at Seneca Lake and Fisher’s Island, New York, Leesburg, Florida, and Dodge Pond, Connecticut.

Schematic of melon composition and location, with inset of a finite element model of a Cuvier’s beaked whale melon derived from published material properties and geometry. The graphic is part of a Naval Undersea Warfare Center Division Newport research project about mammal exposure to noise and shock loads from underwater explosions.