First Advisor

Martin Siderius

Term of Graduation

Fall 2025

Date of Publication

12-16-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Electrical and Computer Engineering

Department

Electrical and Computer Engineering

Language

English

Subjects

Finite-difference Time-domain, Rough dynamic sea-surface, Signal processing, Underwater acoustic modeling

Physical Description

1 online resource (xiii, 123 pages)

Abstract

This dissertation presents a two-dimensional (2D) Finite-difference Time-domain (FDTD) model for simulating underwater acoustic propagation and scattering from a one-dimensional (1D) time-evolving rough sea-surface. The techniques discussed are extendable to three spatial dimensions. Traditional acoustic modeling techniques often rely on a "frozen" sea-surface assumption, which proves inadequate for long-duration signals interacting with the time-evolving boundary at many different wave height displacements during its transit. To address this, a new FDTD update equation incorporating a variable subgrid is developed, significantly enhancing spatial accuracy at the boundary without increasing computational cost or compromising stability.

The model's accuracy is rigorously validated against established methods for various boundary conditions: the Image Method (IM) for static smooth surfaces, the Modified Image Method (MIM) for dynamic (evolving over time) smooth surfaces, and the Helmholtz Integral Equation (HIE) for static rough surfaces. Quantitative signal similarity metrics, including the normalized correlation coefficient and mean squared error, demonstrate the FDTD model's ability to accurately capture both scattering due to roughness and time contraction/dilation effects caused by motion. Notably, the model reveals that discrepancies in reflected signals from traditional methods that stem from the "frozen" sea-surface assumption, which can be mitigated by accounting for ray path length differences due to boundary translation.

Furthermore, this dissertation details the development of a high-performance cloud computing (HPCC) architecture for acoustic modeling simulations and an accompanying framework with a user-friendly extensible Underwater Acoustic Modeling (UAM) package written in Matlab, Python and BASH. This infrastructure facilitates distributed simulations, drastically reducing computation times for large-scale, realistic underwater modeling scenarios. The validated FDTD model, coupled with the HPCC framework, offers a robust tool for investigating the complex interactions of broadband acoustic signals with dynamic ocean environments, providing crucial insights for the design of next-generation sound navigation and ranging (SONAR) systems.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/44409

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