Evaluation of Seafloor Microseism Energy Availability
Abstract
The Office of Naval Research launched a collaborative research effort (entitled ?microseism energy harvesting study?) at the Johns H,opkins University and the Naval Information Warfare Center-Atlantic in July 2020, with the goal of estimating the amount of energy a,vailable at the seafloor due to nonlinear interactions of multidirectional irregular waves on the ocean surface. The study was motiv,ated by a recent renewal of interest in the work of Longuet-Higgins in 1950, which proposed that the 5?7 micron microseisms frequent,ly observed on ocean floors are caused by a nonlinear interaction of likefrequency waves from opposite directions. Other workers in,recent years have provided numerical and experimental support for this theory.The goal of the 2020 effort was to use the Longuet-Hig,gins theory to estimate the magnitudes of the vertically non-attenuating second-order pressure and the amount of energy transmitted,to the seafloor due to the nonlinear interaction of surface waves. In orderto assess the geographic variability of this potential so,urce, five locations with depths ranging from 3000m to 5000m and distributed in the Pacific and Atlantic oceans were selected in con,sultation with the ONR Program Office, and available power amounts were calculated over a chosen one-year period spanning 2019 and 2,020. Hindcast wave data for the five locations were downloaded from the ERDDAP data interface. Spectral density and predominant dire,ctions for wind seas and swells at 30-minute intervals were used. The results for these sites showed available average seafloor powe,r amounts ranging from 5 W/m2 to 100 W/m2, depending on the geographic location.These power amounts make microseism energy an attrac,tive potential source for a number of deep-sea applications of interest to the Science and Defense communities. This is our primary,motivation for proposing a follow-on investigation aimed at improving our understanding of seafloor energy availability, with a view, to making this source more amenable to practical utilization. Thus, for the next phase of this research, our objectives are:1.To ex,tend our seafloor energy availability calculations to include several locations in shallow and littoral depths in the range ? 200m.,This is in response to ONR?s interest in additionally quantifying the seafloor energy amounts in shallower depths.2.To investigate i,nfrasonic pressure wave dynamics through the water column using an acoustic pressure-wave propagation model, allowing for more gener,al boundary conditions. This study will also include numerical modeling based on full (rather than approximated) nonlinear expressio,ns for the pressure magnitudes at each point beneath the interacting waves (as opposed to areal averages as used thus far).3.To quan,tify fundamental limits on amounts of available power that can theoretically be converted, and to determine optimum shapes, sizes, a,nd depth-wise locations for best conversion at given sites. This step is essential because energy converters need to satisfy conditi,ons of impedance matching with the oscillatory energy source.4.For validation, to investigate vertical second-order pressure waves i,n a wave tank with multidirectional irregular wave capability where sufficient repeatability and precision are available.5.To prepar,e microseism energy availability world maps for ready visualization and assessment of available energy (second order and first order,), convertible energy, etc. These maps will help to synthesize the findings of most of the work carried out as part of this research,.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 08, 2022
- Source ID
- N000142212700
Entities
People
- Umesh A. Korde
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy