FleetMon is currently supporting the research project of Dr. Alexandra Muscalus from the Georgia Institute of Technology (“Georgia Tech”) in Atlanta, Georgia. She uses AIS data from FleetMon to investigate the impact of low-frequency ship wake on shorelines in the far-field.
Dr. Alexandra Muscalus just completed her Ph.D. in the Ocean Science & Engineering program at Georgia Tech and plans to pursue a career in coastal engineering research. Her goals were to identify where low-frequency ship wake propagated out of the shipping channel, how far away from the channel its hydrodynamic signature could be detected, and how much power it contributed to shorelines in the far-field. Low-frequency ship wake is important, she says, because it can cause erosion, pose public safety hazards, damage coastal structures, and affect coastal ecosystems that are sensitive to hydrodynamics.
This project tracks the propagation of low-frequency ship wake from a shipping channel into a “far-field” system of connected secondary tidal waterways. Pressure and velocity sensors are deployed both in the main shipping channel and the far-field network, and AIS data is combined from multiple sources to create high-resolution vessel tracks for shipping channel traffic. The tracks are used to identify precise times at which large vessels pass over multiple source points, or breaks in the shipping channel that may allow wake to propagate into the far-field. Linear long wave theory is then applied to predict when wake propagating along various pathways through the network is expected to reach the far-field instrument sites. These predictions are compared to the measured time series to confirm which source points and pathways do transmit wake. The study finds that wake propagates out of the channel at all source points studied and can travel at least 11 km away from the shipping channel.
Low-frequency ship wake, sometimes called “primary wake” or the “drawdown and surge,” is a 1-3 minute mini tsunami-like wake effect produced at the shorelines near shipping channels. A prior study from my Ph.D. work found that low-frequency ship wake is the dominant source of hydrodynamic power near a rapidly-eroding shoreline along the shipping channel in the Savannah River, Georgia. This study also noted that ship wake was the dominant source of power on the backside of an island facing the shipping channel, implying that wake effects extended beyond the shipping channel shorelines. Given the relative importance of the power associated with the wake, a follow-up study was designed to investigate the sources and extents of low-frequency ship wake propagating outside the shipping channel.
Which Data Have You Received From FleetMon?
I received vessel position, time, speed, dimensions, and identification numbers during the time period I was collecting field measurements. I combined the provided data with other AIS sources to produce very high-resolution ship tracks. This allowed me to determine precisely when each ship passed over each “source points, ” which is essentially the start time of the propagation process from that source. Obtaining accurate start times was critical to successfully tracking wake propagation through the far-field waterway network and linking far-field hydrodynamics to vessel traffic in the shipping channel.
Which Challenges Occurred?
Initially, we expected only one source point: a break in the channel directly adjacent to the far-field waterway network. However, our field measurements showed that wake was also reaching the far-field from two additional source points, both several kilometers up/down the river from the main entrance to the network. Additionally, because the far-field consisted of a network of connected waterways, there were multiple possible propagation paths from each source. This added complexity to the process of predicting when the wake from a given ship would reach the far-field instrumentation. For the network we studied, each vessel passage could produce up to four sets of wake in the far-field.
What Is the Conclusion?
Low-frequency ship wake readily propagated out of breaks in the shipping channel and into a far-field waterway network. It is capable of traveling at least 11 km, the spatial extent of the study, and its far-field power at the shoreline is similar to that of tidal currents.
Publication supported in part by an Institutional Grant (NA18OAR4170084) to the Georgia Sea Grant College Program from the National Sea Grant Office, National Oceanic and Atmospheric Administration, U.S. Department of Commerce. All views, opinions, findings, conclusions, and recommendations expressed in this material are those of the author(s) and do not necessarily reflect the opinions of the Georgia Sea Grant College Program or the National Oceanic and Atmospheric Administration.
Research & Development at FleetMon
At FleetMon, we have not only created the world’s first vessel database, but we are also very passionate about research and development. We motivate scientists, institutes, and universities to use our powerful and customized API solutions and provide access to our historical vessel position database.
Providing AIS data is incredibly important for research projects around the world. We will continue to keep you informed about Alexandra’s research.