Browsing University of Alaska Fairbanks by Subject "Temperature inversions"
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Investigation of strongly ducted infrasonic dispersion using a vertical eigenfunction expansion of the Helmholtz equation in a modal broad band acoustic propagation codeThis study investigates an infrasound propagation model created by the National Center for Physical Acoustics (NCPA) which is applied to atmospheric data with a strong temperature inversion in the lower atmosphere. This temperature inversion is believed to be the primary cause of a dispersed infrasonic signal recorded by an infrasound sensor array located on the Southern California coast in August, 2012. The received signal is characterized by initial low frequency content followed by a high frequency content tail. It is shown the NCPA model is hindered by limited atmospheric data and no ground truth for the source function which generated the received signal. The results of the NCPA model are shown to not reproduce the recorded signal and provide inconclusive evidence for infrasonic dispersion.
Two dimensional computational fluid dynamics model of pollutant transport in an open pit mine under Arctic inversionA better understanding of the microscale meteorology of deep, open pit mines is important for mineral exploitation in arctic and subarctic regions. During strong temperature inversions in the atmospheric boundary layer--which are common in arctic regions during the winter--the concentrations of gaseous pollutants in open pit mines can reach dangerous levels. In this research, a two dimensional computational fluid dynamics (CFD) model was used to study the atmosphere of an open pit mine. The natural airflow patterns in an open pit mine are strongly dependent on the geometry of the mine. Generally, mechanical turbulence created by the mine topography results in a recirculatory region at the bottom of the mine that is detached from the freestream. The presence of a temperature inversion further inhibits natural ventilation in open pit mines, and the air can quickly become contaminated if a source of pollution is present. Several different exhaust fan configurations were modeled to see if the pollution problem could be mitigated. The two dimensional model suggests that mitigation is possible, but the large quantity of ventilating air required would most likely beimpractical in an industrial setting.