Trial lecture
“Green's functions for compressional and shear waves in lossless and lossy media”
Time and place: March 25, 2026 11:15 AM. Kristen Nygaards sal (5370), Ole-Johan Dahls hus.
Main research findings
Modeling How Sound Travels Through the Seabed
The seabed is a complex, sponge-like medium where seawater permeates the spaces between solid grains. We rely on sound waves for underwater navigation, communication, and offshore energy exploration, but the seabed can strongly influence how these waves propagate. Accurate modeling of the seabed’s geoacoustic behavior is therefore important for reliable marine operations.
However, a definitive understanding of how sound speed and attenuation vary with propagation frequency, even in simple sediments, has not yet been achieved. The problem becomes more challenging when sediments are layered or uneven. Existing models work under limited conditions, and their physical consistency and reliability across the full frequency range remain uncertain.
We develop a physically consistent and unified mathematical framework to describe how sound waves travel through seabed sediments across a wide range of frequencies. The framework uses fractional calculus, a mathematical approach that captures the material’s “memory,” to derive corresponding wave equations. It also enables incorporation of different physical mechanisms within sediments that influence sound attenuation.
The proposed approach improves the accuracy and reliability of seabed acoustic modeling, supporting enhanced sonar performance, precise seabed characterization, and improved tools for marine research and offshore engineering, while providing a foundation for studying wave propagation in complex materials.
Adjudication committee
- Professor Robert McGough, Michigan State University, USA
- Professor Hefeng Dong, NTNU, Norway
- Professor Anne Helene Schistad Solberg, Department of Informatics, University of Oslo, Norway
Supervisors
Professor Sverre Holm, University of Oslo, Norway
Professor Sven Peter Näsholm University of Oslo, Norway
Chair of defence
- Professor Andreas Austeng, Department of Informatics, University of Oslo
Contact information at Department: Mozhdeh Sheibani Harat