Naval Undersea Warfare Center Research Articles

Using before-after control-impact methodology to quantify effects of full ship shock trial explosions on marine fauna

In the summer of 2021, the US Navy conducted a Full Ship Shock Trial (FSST) for the USS Gerald R. Ford. This involved three large underwater explosions off the coast of Florida, USA. We collected underwater acoustic recordings, using low-sensitivity recorders, for the Naval Undersea Warfare Center to validate their underwater acoustic propagation models. We also deployed SoundTraps on the shallow moorings to collect additional acoustical biologics data in hopes of measuring any acoustic responses of marine fauna to the explosions. The acoustic energy of the explosions did not propagate up the continental slope and were hence not captured by the SoundTraps on the shallow moorings. However, our analyses did yield some notable changes in acoustic behavior after as compared to before the explosions. Here, we describe how our field plan was designed for before-after control-impact (BACI) hypothesis testing and discuss our analyses and findings of the few significant cases. These results lend insight for improving the impact assessments and conducting behavioral response studies during a future FSST or other large underwater explosions.

Performance of a MEMS IMU for Localizing a Seaglider AUV on an Acoustic Tracking Range

A Seaglider instrumented with an inertial attitude and heading reference system was tracked for three days on an acoustic tracking range in Dabob Bay, Washington, operated by the Naval Undersea Warfare Center, Keyport, WA, USA. Inertial measurements were integrated to yield estimates of position and compared with tracked positions. Within 3 min, the integrated positioning results deviated from tracked positions by more than a kilometer. The addition of a depth constraint from pressure sensor measurements slowed the error growth over time, but even with this constraint, measurements were too noisy to accurately determine position without aid from additional sensors. Inertial data did contribute to accurate localization when used to estimate vehicle attitude and incorporated into an existing flight model; however, results did not demonstrate marked improvement over existing flight models. Although not a decisive demonstration of vehicle positioning with a standalone low-cost, low-power sensor, the results presented here provide a benchmark for comparison as MEMS inertial sensors continue to evolve using a valuable ground-truth of subsea Seaglider position not previously available.

Comparing Acoustic Measurements of Underwater Materials in Pressure Tanks Using a Calibration Panel

Researchers in the United Kingdom and the United States worked together to compare acoustic panel measurement methods and equipment using a calibration test panel. Underwater testing can be used to calibrate various transducers or to measure acoustic properties of materials, from which material properties can then be derived. The calibration panel used in this study consisted of a rubber material. Tests were initially conducted in the Acoustic Pressure Vessel (APV) at the National Physical Laboratory (NPL) in Teddington, UK and were subsequently performed in the Acoustic Pressure Tank Facility (APTF) at the Naval Undersea Warfare Center (NUWC) in Newport, Rhode Island, USA. The UK tank is a smaller-scale version of the US tank. However, the measurement approaches developed by the two groups of researchers differs. The UK utilized a parametric source with a baffle and a planar hydrophone array for reflection and transmission measurements. The US used a spherical source, a linear pseudo-array along with coherent subtraction for reflection, and a single hydrophone for transmission measurements. Early results indicated that the measurement methods showed significant discrepancies, but refurbishment of the US facility and subsequent re-testing of the panel delivered results that were in good agreement between the two groups.

Graduate education in acoustic engineering, transduction, and signal processing University of Massachusetts Dartmouth

The University of Massachusetts Dartmouth has an established graduate program of study with a concentration in Applied Acoustics leading to the M.S. and Ph.D. degree in Electrical Engineering. The program offers courses and research opportunities in the area of electroacoustic transduction, underwater acoustics, and signal processing. Courses include the Fundamentals of Acoustics, Random Signals, Underwater Acoustics, Introduction to Transducers, Electroacoustic Transduction, Medical Ultrasonics, Digital Signal Processing, Detection Theory, and Estimation Theory. The ECE department established the university’s indoor underwater acoustic test and calibration facility which is one of the largest academic facilities supporting undergraduate and graduate thesis and sponsored research. The department has collaborations with many marine acoustic related companies including nearby Naval Undersea Warfare Center in Newport, RI and Woods Hole Oceanographic Institute in Cape Cod, MA. The presentation will highlight recent theses and dissertations, course offerings, and industry and government collaborations that support acoustical engineering, transduction, and signal processing.

Ed Sullivan: Mentor, scientist, colleague, and friend

I had the great fortune of meeting Ed Sullivan in 1989 when he was the Manager of Basic Research at the Naval Undersea Warfare Center and, to his dismay, was spending almost all of his time managing rather than researching. Ed hired me as a part-time student associate to analyze and implement passive synthetic aperture sonar, the core of our collaborative efforts for over twenty years and the technical focus of this presentation. Conversations with Ed, whether technical or not, were intellectually stimulating, fun, or mostly a combination of the two. Importantly though and through Ed’s confident and unique lens, he provided me – and many of you – with insights into highly relevant areas such as matched field and model based signal processing, music, history, and physics!I had the great fortune of meeting Ed Sullivan in 1989 when he was the Manager of Basic Research at the Naval Undersea Warfare Center and, to his dismay, was spending almost all of his time managing rather than researching. Ed hired me as a part-time student associate to analyze and implement passive synthetic aperture sonar, the core of our collaborative efforts for over twenty years and the technical focus of this presentation. Conversations with Ed, whether technical or not, were intellectually stimulating, fun, or mostly a combination of the two. Importantly though and through Ed’s confident and unique lens, he provided me – and many of you – with insights into highly relevant areas such as matched field and model based signal processing, music, history, and physics!

Measurement of Sounds Emitted by Certain High-Resolution Geophysical Survey Systems

Scientific questions regarding the impact of anthropomorphic noise in the marine environment have resulted in an increasing number of regulatory requirements and precautionary mitigation strategies to reduce the risks associated with high-resolution marine geophysical surveys performed in waters subjected to government jurisdiction. An example of regulatory frameworks includes the Marine Mammal Protection Act in the United States and the Marine Strategy Framework Directive 2008/56/EC in the European Union. Regulatory compliance often requires an assessment of the potential ecological risks before initiating a marine geophysical survey. However, the acoustic source data needed to estimate the risk associated with the operation of a given high-resolution survey system are frequently lacking. A comprehensive measurement program was performed to quantify the characteristics of sounds radiated by a variety of commercial marine geophysical survey systems, including boomers, sparkers, airguns, chirp sub-bottom profilers, sidescan sonars, and swath-bathymetric sonars [Crocker and Fratantonio, “Characteristics of high-frequency sounds emitted during high-resolution marine geophysical surveys,” Naval Undersea Warfare Center, Newport, RI, USA, NUWC-NPT Tech. Rep. 12, 203, 2016]. Calibrated acoustic source data, including source levels, source spectra, and beam patterns, were acquired for a total of 18 different marine geophysical survey systems. The data support modeling to estimate the potential ecological impacts resulting from the operation of certain high-resolution marine geophysical survey systems.

A review of single crystal underwater transducers

The unique material properties of lead magnesium niobate-lead titanate (PMN-PT) single crystals enable compact, broadband, high power sound projectors that cannot be realized using conventional ceramics. This paper shall highlight single crystal transducer prototypes developed at the Naval Undersea Warfare Center, Division Newport, and elsewhere demonstrating that the broadband, high power performance promised by single crystal’s material properties can be realized in practical underwater transducers. Various single crystal transducer designs for underwater applications, including longitudinal vibrators, fully active and active-passive air-backed cylinder transducers, free-flooded ring transducers and bender bar transducers, will be shown. These transducer designs cover a wide span of frequencies, and utilize both 33- and 32- operating modes. Tuned bandwidths of up to 2.5 octaves of frequency, as well as source level increases of up to 15 dB at the band edges, will be demonstrated. t will also be shown that these technologies provide stable performance under high drive and duty cycle conditions. Finally, the impact of using these single crystal sources on the drive electronics and power consumption shall also be discussed.

Asymptotic stepwise coupled modes for horizontally-variable acoustic media

Efficient and accurate mathematical codes for the prediction of underwater sound propagation are a critical component of SONAR system development and operation. The goal of the research presented herein is to develop, implement, and verify an efficient and rigorous coupled-mode solution for acoustic wave propagation in shallow water range-dependent environments. A theoretical framework involving a range-expanded inner product for capturing the coupling between modes as they propagate through a horizontally-variable medium is presented. This framework includes a novel discretization of the range-dependent acoustic medium. A difference equations approach, which implements the inner product to account for non-adiabatic energy transfer between modes, is used to recursively compute reflection and transmission coefficients throughout the discretized environment. Increased efficiency is gained in the method due to the ability to compute coupling via closed-form algebraic expressions and in the application of asymptotic analysis to simplify the transmission and reflection coefficients. Results will be shown for a sample of waveguides with horizontally-variable bottom depth, along with comparable results from R. Evans’ COUPLE model and an FEM solution produced by ARL-UT. [This work was funded by the Naval Undersea Warfare Center, Newport Rhode Island.]

Exploring phononic crystal tunability using dielectric elastomers

Tunable phononic crystals give rise to interesting opportunities such as variable-frequency vibration filters. By using soft dielectric elastomers, which undergo large deformations when acted upon by an external electric field, the frequency ranges of these band gaps may be adjusted, or new band gaps may be created through electrical stimuli. In this talk, we will discuss our finite-element-based numerical simulation capability for designing electrically-tunable, soft phononic crystals. The key ingredients of our finite-element tools are (i) the incorporation of electro-mechanical coupling, (ii) large-deformation capability, and (iii) an accounting for inertial effects. We present a demonstration of our simulation capability to the design of phononic crystals consisting of both square and hexagonal arrays of circular-cross-section threads embedded in a dielectric elastomeric matrix. Finally, we will consider electro-mechanical instabilities as alternative route for enhanced tunability. [This work was currently funded through the Naval Undersea Warfare Center Research program.]

Lithium Battery Casualty Detection and Mitigation Developments for Navy Platforms

The growing need for large lithium batteries and lithium battery powered equipment aboard submarines provides major challenges to the US Navy; two of these challenges include (1) early battery casualty detection and (2) containment or mitigation of hazards associated from lithium-based battery casualties. Lithium ion rechargeable batteries used within research unmanned undersea vehicles (UUV) was abusively tested inside of its vehicle and was instrumented with water mitigation and various types of presumptive pre/post casualty onset detection sensors. These efforts were conducted under the requirements for the Navy’s Lithium Battery Safety Program, Naval Sea Systems Command Instruction 9310.1C and related documents as guidance for need. This effort followed similar recent works for the storage and carriage of large form lithium and lithium-ion batteries conducted preciously. This paper will review the results of these tests conducted by the Naval Surface Warfare Center, Carderock Division (NSWCCD), Naval Undersea Warfare Center, Newport (NUWC NWPT) and the Naval Research Center (NRL) over the past six years. These efforts have enabled the carriage and deployment of lithium battery powered systems from surface platforms and are expected to enable the deployment from undersea platforms.

Implementation of moving magnet actuation in very low frequency underwater acoustic transduction

The Naval Undersea Warfare Center’s Underwater Sound Reference Division (USRD) is designing a very low frequency sound source to calibrate line arrays in the 1–100Hz band at their Leesburg Facility. For calibrations below 20 Hz, the low frequency cutoff of their J15-3 standard projector, the USRD currently uses a passive method where the sound source is the ambient noise in the spring. A limitation of this method is a low signal-to-noise ratio. By designing, building, and implementing the aforementioned sound source, the USRD looks to increase the signal-to-noise ratio of their recorded data, and consequently increase the reliability of measurements at very low frequencies. This presentation explores the idea of implementing moving magnet technology in a very low frequency transducer. Although moving coil projectors have been used since 1914 as low frequency sound sources, their acoustic output at very low frequencies is limited. The potential benefits of a moving magnet projector over moving coil projectors are discussed. Acoustic performance estimates for a moving magnet projector are calculated based on specifications of an off-the-shelf moving magnet actuator. Lastly, the presentation will cover current efforts being made to design an underwater housing for the projector.

Reverberation characterization inside an anechoic test chamber at the weapon sonar test facility at Naval Undersea Warfare Center Keyport Division

The Weapon Sonar Test Facility (WSTF) at NUWC Keyport, WA, is a 34 500 gallon pressure tank currently used for test and evaluation of torpedo sonar arrays. The tank has many more possible uses and complete characterization of the testing environment needs to be performed. One of the methods of characterization being used is the determination of the reverberation time of the anechoic chamber. Applying Sabine-Franklin-Jaeger theory of reverberant rooms, an experimentally determined reverberation time T60 for a “live room” can be used to provide an upper bound for the reverberation time in the chamber. Utilizing the Eyring theory of “dead” rooms will provide a better determination of T60 for the anechoic chamber, hence provide a lower bound characterization. The experimental method involves determining the spatially averaged acoustic energy of an initial tone and the corresponding reflection from the chamber wall seen in a recorded signal. These values determined from the root mean square signal voltage determine the wave decay time, τ. The decay time is directly related to the reverberation time through T60 = 6τ×loge10. The reverberation was determined to be within an acceptable tolerance for testing and evaluation.

Experimental verification of acoustic trace wavelength enhancement.

Directivity is essentially a measure of a sonar array's beamwidth that can be obtained in a spherically isotropic ambient noise field; narrow array mainbeam widths are more directive than broader mainbeam widths. For common sonar systems, the directivity factor (or directivity index) is directly proportional to the ratio of an incident acoustic trace wavelength to the sonar array's physical length (which is always constrained). Increasing this ratio, by creating additional trace wavelengths for a fixed array length, will increase array directivity. Embedding periodic structures within an array generates Bragg scattering of the incident acoustic plane wave along the array's surface. The Bragg scattered propagating waves are shifted in a precise manner and create shorter wavelength replicas of the original acoustic trace wavelength. These replicated trace wavelengths (which contain identical signal arrival information) increase an array's wavelength to length ratio and thus directivity. Therefore, a smaller array, in theory, can have the equivalent directivity of a much larger array. Measurements completed in January 2015 at the Naval Undersea Warfare Center's Acoustic Test Facility, in Newport, RI, verified, near perfectly, these replicated, shorter, trace wavelengths.

Liquid Catholyte Investigations for Safer Storage of a Li Primary Battery

The close proximity of the electrode materials is a design risk for commercial off the shelf (COTS) Li batteries. COTS Li batteries can off gas and ignite if the electroactive materials are inadvertently mixed by events such as thermal abuse, crush, penetration, and shock. Crew safety on US Navy ships and submarines critically depends on minimizing the probability of exposure to toxic gases and fire. The Naval Undersea Warfare Center (NUWC) is investigating a primary Li battery design for undersea applications that is, in principle, safer to store and transport than COTS batteries. In this approach a liquid catholyte is stored separately from a Li metal anode. The catholyte is added to the anode housing immediately prior to off board deployment of the energy section. With this configuration the electroactive materials can be stored separately and more safely than in COTS batteries. NUWC has recently begun investigating slurry catholytes1 comprised of solid redox active cathode materials and electronically conductive carbon powders dispersed in a nonaqueous electrolyte. Our goals are high volumetric charge capacity, high voltage, good power density and a “pumpable” rheology. These properties are significantly affected by the formulation of the slurry such as the choice of redox active material, the volumetric solids concentration of the redox active and carbon materials, the interaction between the particles, and the particle size distributions. This talk will discuss NUWC’s separated anode / catholyte battery concept, the tradeoffs of various electroactive cathode materials, and the results of catholyte investigations and their expected impact on the performance of a Li-slurry catholyte primary battery. 1) M.Duduta., B.Ho, V.C. Wood, P. Limthongkul, V. E. Brunini, W. C. Carter, and Y-M Chiang, Semi-Solid Lithium Rechargeable Flow Battery , Adv. Energy Mater. 2011, 1, 511–516

3D Finite Element Modeling of Single Bolt Connections under Static and Dynamic Tension Loading

The Naval Undersea Warfare Center has funded research to examine a range of finite element approaches used for modeling bolted connections subjected to various loading conditions. Research focused on developing finite element bolt representations that were accurate and computationally efficient. A variety of finite element modeling approaches, from detailed models to simplified ones, were used to represent the behavior of single solid bolts under static and dynamic tension loading. Test cases utilized models of bolted connection test arrangements (static tension and dynamic tension) developed for previous research and validated against test data for hollow bore bolts (Behan et al., 2013). Simulation results for solid bolts are validated against experimental data from physical testing of bolts in these load configurations.

Communication and Collaboration Among Heterogeneous Unmanned Systems Using SAE JAUS Standard Formats and Protocols

The Naval Undersea Warfare Center Division Newport (NUWCDIVNPT) and Georgia Tech Research Institute (GTRI) completed a successful at-sea exercise with autonomous UAS and UUV systems demonstrating communication and collaboration. The exercise represented for the first time the use of standard protocols and formats that effectively support cross-domain unmanned system operations. Four man-portable Iver2 UUVs operating in coordinated missions autonomously collected environmental data, which was compressed in-stride, re-formatted, and exfiltrated via UAS relay for display and tactical decision making. Two UAS with autonomous flight take-off and mission execution were sequenced to serve as ISR platforms and to support communications as RF relays for the UUVs performing Intelligence Preparation of the Environment missions. Two Command and Control nodes ashore provided unmanned system tasking and re-tasking, and they served to host and display both geo-positional data and status for UAS and UUV vehicles during the operational scenarios run during the exercise. The SAE Joint Architecture for Unmanned Systems (JAUS) standards were used for all message traffic between shore-based C2 nodes, UAS, and UUVs active in the exercise area. Development for this project highlighted both the strengths and shortfalls of JAUS and captured the requirements for moving forward in effective cross-domain communications that support distributed, agile C2 nodes to meet evolving CONOPS for growing unmanned system presence and mission roles. The JAUS architecture was introduced to the NUWC and GTRI unmanned systems though an instantiation of the Mission Oriented Operating Suite (MOOS) autonomy framework on secondary CPUs integrated into the Iver2 UUVs and the GTRI UAS. This work represents a critical step in communications for networking of heterogeneous unmanned systems and establishes a solid platform for alignment of development and ongoing programs.

Graduate education in underwater acoustics, transduction, and signal processing at UMass Dartmouth

The University of Massachusetts Dartmouth established a Ph.D. degree in Electrical Engineering with a specialization in Marine Acoustics in 1996, building on the strength of the existing M.S. program. Current enrollment in these programs include 26 M.S. students and 16 Ph.D. students. The program offers courses and research opportunities in the area of underwater acoustics, transduction, and signal processing. Courses include the Fundamentals of Acoustics, Random Signals, Underwater Acoustics, Introduction to Transducers, Electroacoustic Transduction, Digital Signal Processing, Detection Theory, and Estimation Theory. The university’s indoor underwater acoustic test and calibration facility is one of the largest in academia and supports undergraduate and graduate thesis and sponsored research. The university also owns three Iver-2 fully autonomous underwater vehicles. The graduate program capitalizes on collaborations with many marine technology companies resident at the university’s Advanced Technology and Manufacturing Center (ATMC) and the nearby Naval Undersea Warfare Center in Newport, RI. The presentation will highlight recent theses and dissertations, course offerings, and industry and government collaborations that support underwater acoustics research.

Very low frequency acoustic vector sensor calibration

In-water calibration of Acoustic Vector Sensors (AVS) operating at very low frequencies (fraction of Hz to hundreds of Hz) presents a set of unique challenges as the acoustic wavelengths are much longer than any existing laboratory calibration facilities. The developed calibration approach utilizes existing Naval Undersea Warfare Center’s pressurized horizontal calibrating steel tube equipped with two independently controlled sound sources located at the opposite ends of the tube. Controlling the phase and amplitude of these sources allows for creating of pressure or velocity fields inside the tube. Respective pressure and particle velocity complex amplitudes are measured and calculated, respectively, with two reference hydrophones. Experimental results of this calibration approach is presented for a newly developed very low frequency AVS comprising of pressure and non-inertial velocity sensors built into an acoustic velocity horn.

Carbon nanotube thermoacoustic projectors for undersea vehicles

Renewed interest in the thermophone has developed with the recently demonstrated capability to manufacture carbon nanotube thin films and capacity to emit sound through the thermoacoustic effect. High fidelity broadband sound generation is attributed to the ultra-low heat capacity and low thermal inertia of these films. Motivated by the need for low-frequency, broad-bandwidth, compact sonar projectors to be embedded in the hull of unmanned sea vehicles or in the outer coating of a surface combatant or submarine as a conformal array, a team of researchers from Virginia Tech, The University of Texas at Dallas, and the Naval Undersea Warfare Center are evaluating these novel materials and devices both theoretically and experimentally. Analytical and numerical simulations support mechanical, thermal and acoustic experimentation. Correlated results will be presented. [Work supported by Office of Naval Research, code 321MS.]

Long term passive acoustics monitoring reveals differences in deep diving Odontocetes foraging strategies

Beaked whales, sperm whales, pilot whales, and Risso's dolphins perform deep dives to feed on prey in the deep sea. They use echolocation to detect prey, and echolocation can be monitor as a proxy of their foraging activities. Ecological acoustic recorders were deployed to monitor in time the echolocation signals of pilot whales, Risso's dolphins, beaked whales, and sperm whales near Josephine Seamount (Portugal), in the Ligurian Sea (Italy), and along the Kona coast of the island of Hawaii. Data analysis was performed using two automatic detector/classification systems: Marine Mammal Monitoring on Navy Ranges (M3R), developed at the Naval Undersea Warfare Center Division in Newport, USA, and a custom MATLAB program. An operator-supervised custom MATLAB program was used to validate the classification performance, which was higher than 85% for each category. Results show that pilot whales and Risso's dolphins concentrate their feeding effort mainly during the night. The foraging activity of beaked and sperm whales is variable, and different patterns are observed at different locations. Prey behavior might play a central role in driving the foraging activity of deep divers, but to date, the reasons why such activity varies between species that might feed on similar food resources remains unknown.