Investigation of strongly ducted infrasonic dispersion using a vertical eigenfunction expansion of the Helmholtz equation in a modal broad band acoustic propagation code

Master's Project (M.S.) University of Alaska Fairbanks, 2015This 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

Hydrographic Products/Services as a Fundamental Component of the e-Navigation Concept of Operation

e-Navigation is a recent initiative aimed at moving traditional maritime navigation towards a connected digital environment. Defined by the International Maritime Organization (IMO) as “the harmonized collection, integration, exchange, presentation and analysis of maritime information onboard and ashore by electronic means to enhance birth-to-birth navigation and related services, for safety and security at sea and protection of the marine environment”, e-Navigation is not a new system of equipment but more an operational concept. Three significant outcomes are envisioned: 1) Shipboard navigation systems will benefit from the integration of own ship sensors, supporting information, standard user interface, and a comprehensive system for managing guard zones and alerts. Core elements include high-integrity electronic positioning, use of ENCs, and an analysis capability to reduce human error. 2) The management of vessel traffic and related services from ashore will be enhanced through better provision, coordination, and exchange of comprehensive data in formats that will be more easily understood and utilized. 3) A communications infrastructure designed to enable authorised seamless information transfer onboard ship, between ships, between ship and shore and between shore authorities. This paper discusses the main hydrographic-related components, implications for further standards development, some challenges/opportunities, and the role that IHO and others in the hydrographic community should play to facilitate the development and implementation of eNavigation

Splitting methods for constrained diffusion-reaction systems

We consider Lie and Strang splitting for the time integration of constrained partial differential equations with a nonlinear reaction term. Since such systems are known to be sensitive with respect to perturbations, the splitting procedure seems promising as we can treat the nonlinearity separately. This has some computational advantages, since we only have to solve a linear constrained system and a nonlinear ODE. However, Strang splitting suffers from order reduction which limits its efficiency. This is caused by the fact that the nonlinear subsystem produces inconsistent initial values for the constrained subsystem. The incorporation of an additional correction term resolves this problem without increasing the computational cost. Numerical examples including a coupled mechanical system illustrate the proven convergence results