Facilities
Hydroacoustics Lab
Water Tank and Filter
UR10e Robots
Data Acquisition
Temperature Probes
The Underwater Acoustics Laboratory at Brigham Young University (BYU) was designed and constructed during the years 2019-2021 to facilitate high quality research. Because of the priority on mentored undergraduate student research at BYU, each component was selected with considerations for high levels of safety, automation, and reliability. These features give students the opportunity to learn to perform effective acoustical measurements and data analysis in a mentored environment.
In addition to providing opportunities to train students, this lab provides a way to test algorithms that can be applied to open-water data. Obtaining large open-water data sets for underwater acoustics research and validating measurements has high economic and temporal costs. A laboratory system saves on those costs, especially for researchers without ease of access to large bodies of water. Open-water tests are often noisy and unpredictable with ever changing environmental concerns, but the tank allows for better control of the environment. Measurement automation allows data to be collected quickly and efficiently, with high precision.
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C.T. Vongsawad et al. "Design of an Underwater Acoustics Lab", 181st Meeting of the Acoustical Society of America, Seattle, Washington, December 2021. (https://pubs.aip.org/asa/poma/article/45/1/070005/830044/Design-of-an-underwater-acoustics-lab)
The open-air rectangular parallelepiped water tank, was made by Engineering Laboratory Design Inc. (Lake City, Minnesota, USA) and is constructed of scratch resistance acrylic panels that are solvent-welded together, with a steel frame on adjustable leveling pads. The tank material, acrylic, was also chosen for its visual transparency and non-corrosive nature. Acoustical reflections from these walls are reduced compared to tanks made of steel, concrete, or glass since the acoustic impedance of acrylic is closer to that of water than those other materials. The tank’s dimensions were chosen to allow scaled acoustical measurements and designed to maximize usable laboratory space. The 3.66 m long by 1.22 m wide rectangular tank has a maximum water depth of 0.91 m, corresponding to a maximum fill volume of 4077.6 liters.
Water quality is maintained by a system that provides for filtration, sanitization, temperature control, and bubble reduction. Acoustic disturbances caused by thru wall plumbing penetrations of the tank are avoided by siphoning water out of the tank over the wall and returning it after treatment over the wall. The pickup (inlet) and return (outlet) siphon pipes are removable so the filtration system can be separated from the tank entirely. Control of pumps, valves, and heating is automated using a programmable logic controller (PLC). Tap water is used to fill the tank, with the water level replenished using distilled water as gradual evaporation occurs in order to maintain control over the water properties and thus the speed of sound. Distilled water replaces the evaporated water without introducing increased calcium hardness or other changes to water properties.
To reduce the reflections from the side walls, panels of attenuating material (polyurethane) are used. The attenuating material from Precision Acoustics was chosen to reduce side-wall reflections especially for ultrasonic frequencies. The 50 mm thick, 60 cm tall, square Apltile SF5048 panels, are optimized for 20-200 kHz and advertise an echo reduction greater than 30 dB.
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C.T. Vongsawad et al. "Design of an Underwater Acoustics Lab", 181st Meeting of the Acoustical Society of America, Seattle, Washington, December 2021. (https://pubs.aip.org/asa/poma/article/45/1/070005/830044/Design-of-an-underwater-acoustics-lab)
The three-dimensional positioning system uses two UR10e collaborative robots from Universal-Robots (universal-robots.com), with one on a Vention (vention.io) 7th axis extender track. The robots, were chosen for their intuitive programming language, high level of programmable safety, and 0.01 mm precision for repeatability. Each robot operates using six axes of motion and has a maximum reach of 1.3 m. Both robots are mounted level with the top of the tank: one on a simple pedestal and the other on the Vention 7th-axis extender track with a rack and pinion motor providing an additional 1.4 m reach along the length of the tank. The extender track has an added positioning error of ±0.01 mm. The Universal-Robots website contains an interactive online academy which allows students to learn robot functionality, safety, and programming in a quick, simple, and thorough way.
Transducers may be attached to the UR10e in any orientation via custom-designed mounts, referred to as tools. This feature allows for more flexibility than traditional two or three axis positioning systems while maintaining similar precision. The custom transducer mounts allow for multiple configurations including an added wire PTFE/FEP Tip Probe (K-37X-T) thermocouple from ThermoWorks to measure temperature without significant increased scattering. The automated positioning is controlled through TCP/IP by custom LabVIEW software used for the data acquisition. Users input coordinates or grids of coordinates in the LabVIEW software, ESAU; if the requested locations fit within defined safety limits, the locations are sequentially sent to the robot and a recording is made at each location. Each robot’s software then interpolates between available robot arm/tool orientations to maintain consistent orientation relative to the transducer directivity.
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C.T. Vongsawad et al. "Design of an Underwater Acoustics Lab", 181st Meeting of the Acoustical Society of America, Seattle, Washington, December 2021. (https://pubs.aip.org/asa/poma/article/45/1/070005/830044/Design-of-an-underwater-acoustics-lab)
Sensor positioning, signal generation, and data acquisition are controlled via custom LabVIEW soft-ware, referred to as Easy Spectrum Acoustics Underwater, or ESAU. ESAU, created by author ADK, facilitates user communication with the Spectrum data acquisition cards and the UR10e robotic arms. The data acquisition cards have relatively high resolution (16-bit) and high sampling rate (40 MS/s). Using the Star-Hub module, the arbitrary waveform generator (AWG) (M2p.6546-x4) and digitizer (M2p.5932-x4) cards are accurately synchronized while housed inside an external PCIe chassis. As implemented, the shared memory allows for 128 mega samples for each of the four input and four output channels.
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C.T. Vongsawad et al. "Design of an Underwater Acoustics Lab", 181st Meeting of the Acoustical Society of America, Seattle, Washington, December 2021. (https://pubs.aip.org/asa/poma/article/45/1/070005/830044/Design-of-an-underwater-acoustics-lab)
At room temperature, a water tank tends to have a spatially uniform water temperature producing constant sound speed throughout the water. Temperature measurements are made with two LMP 307T depth and temperature transmitters,
which specify an accuracy of less than or equal to 1 degree Celsius. During a calibration test of the two sensors in a bath of ice water, the temperature sensors measured about 0.05°C different. This difference in calibration corresponds to a difference of sound speed of 0.15 m/s for water at 20°C. During the experiments, the temperature is sampled every 5 sec and saved to Excel spreadsheets. These data are then plotted and converted to water sound speed with Python.
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A. M. Hopps-McDaniel et al. "Temperature-induced sound speed variability in a laboratory water tank". 184th Meeting of the Acoustical Society of America, Chicago, Illinois, May 2023. (https://pubs.aip.org/asa/poma/article/51/1/070001/2904030/Temperature-induced-sound-speed-variability-in-a)