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| Aug. 18, 2017
Sediment Research is a Large, Yet Granular Exercise at NRL
By Michael Hart
STENNIS SPACE CENTER, Miss. -- It’s an unseasonably warm February afternoon at the U.S. Naval Research Laboratory, Stennis Space Center (SSC), Mississippi, where three men are tinkering with a 7-foot tall, four-legged instrument platform, preparing it for an upcoming research experiment off the coast of Virginia.
The rugged apparatus known as a “quadpod,” was built to withstand being on the bottom of the ocean for weeks at a time, measuring waves, currents, and seafloor change.
“It’s equipped with imaging sonar to capture the motion and burial of munitions on the seafloor,” said Joseph Calantoni, head of NRL’s Sediment Dynamics Section at SSC.
Calantoni, a research physicist, leads a team of 12 scientists and engineers. Their mission is to make predictions of the subaqueous environment for the Navy, “and exploit these predictions to improve underwater acoustic communications, improve our ability to find buried objects and the Navy’s capacity to put troops on the beach.
“We spend a significant amount of time determining what conditions can move unexploded ordnances (UXOs) around the seafloor. That’s where the quadpod comes in,” he said.
To accomplish their munitions research, Calantoni and his team fabricate replica UXOs with the same shape, size, and density of real ordnances found unexploded on the seafloor.
“The focus of this research is to understand how the waves and currents either transfer or bury these unexploded bombs,” Calantoni said.
Understanding how Mother Nature’s fluctuating weather conditions affect underwater munitions is an important focus of NRL’s sediment research, but the team’s primary mission is to quantify how the sediment on the seafloor, river bed and estuaries around the world is affected by the forces of nature – hurricanes, typhoons and heavy storms, or even the daily ebb and flow of tides, waves and currents.
“We are focused on sediment properties as they apply to problems of interest for the Navy,” Calantoni said. “One of the Navy’s many missions is to put Marines and special forces on the beach.”
Calantoni emphasized why it’s critical to understand how the beach behaves during a storm.
“Clearing sea lanes to bring troops from ship to shore is of great importance to the Navy’s mission, but that process requires a lot of instrumentation and personnel,” he said.
“We provide the R&D (research and development) to help operators make informed, tactical decisions.”
According to Calantoni, mine warfare is and has been a significant concern of the Navy for centuries, to ensure safe sea lanes and at-sea operations.
“You can go all the way back to World War II during the Normandy Invasion, where there were problems with transports getting stuck on sand bars,” Calantoni said. “Understanding how storms, waves and currents affect sand bars, for example, is still a challenge for the Navy.”
His section’s research illustrates how satellites provide useful images of waterways, rivers and other bodies of water, but sometimes the images can be unclear and few days old.
“Can we tell how those sand bars have changed in those few days? That’s a big focus of our work,” said Calantoni.
The group’s research also involves modeling and simulating potential and current naval operating areas, with models ranging from grains of sand up to kilometers of coastline.
“This simulation is useful in predicting how a sand bar on a beach might change during the course of a Nor’easter off the coast of North Carolina, for example,” Calantoni said.
“The Navy’s ability to communicate under water is strongly dependent on the shape of the sea floor,” he continued. “Being able to predict the roughness of the sea floor – the presence of ripples or not – is very valuable for the Navy to conduct operations.”
Those operations are also dependent on the research conducted in the field, where highly sensitive instruments are used in the ocean, rivers and estuaries.
“We make a lot of predictions using remote sensing techniques,” said Calantoni.
According to Meg Palmsten, an oceanographer in NRL Stennis’ Sediment Dynamics Section, remote sensing, using video cameras attached to unmanned aircrafts, towers, or even other researchers, is used to observe and study waves and currents moving toward the shore.
“Our work is important because waves and currents move the sediment around on the ocean floor, which can create navigation hazards” said Palmsten. “We conduct our research all around the world in many different environments. The goal is to have the data we collect incorporated into a tactical decision aid.”
Tactical decision aids help the warfighter make informed decisions given the best available data. Combining the lab work, along with numerical and field observations together is a key element in providing the warfighter information about their environment.
Allison Penko, a coastal engineer also on Calantoni’s team, and an expert in analyzing the movement of sand in the ocean, uses laboratory equipment to study small-scale processes occurring on the seafloor. The Small-Oscillatory Flow Tunnel (S-OFT) at NRL simulates the forcing on the seafloor from waves and currents. The rectangular, acrylic tunnel has several instruments to measure the flow over a sand bed at high-resolution.
Penko spends much of her time developing numerical models and laboratory experiments to study a large range of flow conditions causing turbulent interactions on the seafloor.
“We’re using the information collected in the laboratory, field, and from models to examine processes on the sea bed to learn how those processes affect large-scale sand movement.”
Remote sensing also plays a key role in Penko’s work.
“They Navy is interested in operational time frames, so we focus on forecasting up to four days,” Penko said. “Remote sensing helps to make our predictions more accurate by incorporating those observations into our models.”
Penko expressed the importance of providing accurate information to the warfighter. “If we have to send Marines up a river and then a storm occurs, we need to be able to tell them if it’s safe to navigate back.”
Calantoni and his team are fully aware of the complexity of their research and how a team effort is a driving force toward success.
“We have physicists, oceanographers and all sorts of engineers – civil, ocean, mechanical, electrical and technical – as well as computer scientists who are very important to the work we do,” said Calantoni. “This is the fun part, merging multiple disciplines and working on challenging problems.
“If it’s not a hard problem, then we shouldn’t be working on it here at the U.S. Naval Research Laboratory.”
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