James G. McDaniel

Finite element modeling of fluid-saturated metallic foams from micro-computed tomography

Open-cell metallic foams are high stiffness-to-weight cellular materials whose microstructure allows for saturation of viscous liquid. Such a composite has advantages for underwater sound absorption over traditional rubbers due to minimal compression from hydrostatic pressure, composite tunability, and potential for specific gravity less than one. Semi-phenomenological and hybrid numerical models have been shown to predict sound absorption performance of metallic foams, however difficulty arises in determining parameters for the numerical models such as tortuosity, viscous characteristic length, thermal characteristic length, and flow resistivity. Such models also assume that the porous frame is rigid, an assumption valid for only a limited frequency range. In this presentation, finite element models of fluid-saturated metallic foams are created from micro-computed tomography scans and analyzed to determine sound absorption performance. The advantage of this method is that the entire foam microstructure and surrounding fluid can be accurately modeled through a finite element mesh. In addition, experimental measurement of model parameters is not required and the rigid frame assumption can be removed.Open-cell metallic foams are high stiffness-to-weight cellular materials whose microstructure allows for saturation of viscous liquid. Such a composite has advantages for underwater sound absorption over traditional rubbers due to minimal compression from hydrostatic pressure, composite tunability, and potential for specific gravity less than one. Semi-phenomenological and hybrid numerical models have been shown to predict sound absorption performance of metallic foams, however difficulty arises in determining parameters for the numerical models such as tortuosity, viscous characteristic length, thermal characteristic length, and flow resistivity. Such models also assume that the porous frame is rigid, an assumption valid for only a limited frequency range. In this presentation, finite element models of fluid-saturated metallic foams are created from micro-computed tomography scans and analyzed to determine sound absorption performance. The advantage of this method is that the entire foam microstructure a...

Design of tunable acoustic metamaterials using 3D computer graphics

The goal of this work is to investigate how the combination of 3D computer graphics and finite element software can be used to rapidly design materials with tunable properties for noise and vibration mitigation applications. Algorithms and software that create three-dimensional objects, known collectively as 3D computer graphics, are widely used artistically for rendering, animation, and game creation. These approaches allow for the design of complex topological structures such as cellular solids. This presentation describes the use of 3D computer graphics to design cellular structures, which can be imported into finite element software in order to determine effective vibrational properties. This approach is advantageous for several reasons. It allows for quick variation of parameters of cellular solids such as porosity and void fraction. It also is time efficient compared to alternative methods such as performing computed tomography scans on physical samples and analyzing the imaged files. Furthermore, r...

Quiet micro boats: An inexpensive acoustic sensing suite

The Quiet Micro Boat [QMB] is an inexpensive acoustic sensing platform constructed from off-the-shelf hardware and software components to allow for a fleet of acoustic sensors that can be deployed into real-world sensing scenarios at a low cost. The QMBs operate using a Beaglebone Black as a central processor, with jet propulsion generated by bilge pumps for robust ocean operation. Acoustic data are collected through a hydrophone which interfaces with the BBB, and data is centralized using the XBee and Zigbee radio mesh configuration. The talk will focus on the hardware costs and performance, discuss the design cycle and decisions, and feature some of the acoustics projects that have been tested on the devices. [Work sponsored by the Naval Sea Systems Command (NAVSEA) Naval Engineering Education Consortium (NEEC) Contract Number N00174-15-C-0022 and by the Raytheon Advanced Studies Fellowship.]

Observer-feedback control based acoustic homing beacon for autonomous underwater vehicles

One of the visions for Acoustically enabled Autonomous Underwater Vehicles (AUVs) is a fleet of these vehicles to be held on a ship, deployed for a specific mission and then recovered by the ship. A component of this mission is finding the ship after deployment to be recovered, since both the ship and AUVs have probably drifted from their original locations and intended deployments. While many vehicles can surface, utilize radio and GPS to relocate the ship and navigate towards it, the method presented allows the ship to be found by deploying an acoustic beacon, while the AUVs utilize an observer system to navigate towards the ship. The spatial decay of spreading sound waves provides a spatially dependent variable for the AUV to measure. Then, utilizing a linear model of the dynamics, a linear observer is constructed. The absolute value of the sound pressure readings are fit to a spatial decay model, which is then linearized to form the observer equation. By tuning the observer gain, the AUV can directly ...

Motion planning based on matched field processing with Bayesian filtering

Matched Field Processing (MFP) has often been used with stationary arrays as a method for developing source location information, but potentially with large amounts of uncertainty. This has been overcome in some cases by using Bayesian Filtering to improve estimates over time of the source location by treating this quantity as a random variable. Here we show how these methods can be applied to an autonomous vehicle for motion planning. The vehicle moving through an acoustic field can provide spatially separated data that can be used in an MFP algorithm to generate an estimated source location, which can be integrated utilizing Bayesian Filtering. Motion planning methods are shown which aim to move the vehicle to the maxima of this probability distribution. This method is demonstrated using ocean acoustic simulations. [Work supported by Raytheon Advanced Studies Fellowship.]

Adaptive interpolation techniques for structural acoustic system response

In recent years, several new techniques for interpolating the response of structural acoustic systems have been developed. Besides the various underlying approximation schemes that utilize concepts such as Pade approximants or implicitly interpolatory subspaces, the main advantage of these methods is that their structure is adaptively determined, meaning that they select interpolation points and, when appropriate, interpolation order as the algorithm proceeds. This allows users to have little to no a priori knowledge of the system response and yet still achieve approximations of a desired accuracy. Furthermore, the interpolation is generated at minimal cost giving rise to approximations that are efficient as well as accurate. A variety of these techniques are introduced and discussed with emphasis on the trade-offs between the methods. Then, a numerical test bed is developed to evaluate the performance of the interpolation schemes giving each access to the same computational resources. Recommendations are...

Improvement of acoustic and vibration models by temporal error metrics

Analyses and examples are presented that explore the limits and accuracies of a technique for improving acoustic and vibration models by temporal comparisons to experimental data. In a previous presentation, the authors proposed the use of impulsive excitations followed by time windowing of responses. This approach allows comparisons between experimental data and model predictions over an isolated spatial region whose volume is a fraction of the entire system volume. The advantage of this spatial isolation is that it significantly reduces the number of model parameters that must be varied to bring the model predictions into agreement with the experimental data. In the present work, the method is analyzed in detail to quantify the limits and accuracies of the method relative to window size, number of measurement locations, and excitation. Two types of examples will be presented to illustrate these findings. The first involves the improvement of material properties for a homogeneous region. The second invol...

Direct and transient analyses of the Schur complement for complex vibrating systems

We are interested in computing the steady-state response of coupled vibrating systems over a frequency band. For each system, the present coupling analysis requires the impedance matrix that relates forces and velocities at the coupled or externally forced degrees of freedom at all frequencies of interest. Algebraic manipulation of each systems full impedance matrix yields the desired impedance matrix in the form of a Schur complement. The present work surveys and compares two approaches for computing the Schur complement, with a particular focus on the effects of damping. The direct analysis computes the Schur complement in the frequency domain, which requires a linear solve of a large system with several forcing vectors at each frequency. The transient analysis computes the impulse responses of the coupled degrees of freedom by numerical integration. This is followed by a Fourier transform that yields the Schur complement. Approaches for choosing the most efficient analysis are presented, along with nu...

Estimation of material properties using vibration magnification

This presentation describes the use of video magnification to estimate material properties of a structure within a region of interest. Video magnification is a recently introduced technique that magnifies motions which are mathematically present in a video but often not visible to the human eye. Several recent papers have shown that this technique may be used to derive quantitative information about vibration without contacting the structure. Furthermore, the technique amplifies all components of the three-dimensional vibration field that are present in the plane of the video. In the present work, a mechanical excitation is applied to the center of a region of interest on a structure. The excitation is concentrated in space and time. The response of the structure is captured at high temporal and spatial resolution by a video camera focused on the area of interest. Material properties are then estimated by adjusting values in a model of the region until agreement is obtained throughout the temporal and spa...

Multi-agent acoustic noise field characterization using optimal control

Investigations of acoustic-driven control schemes have stayed away from traditional Optimal Control methods because of the computational load and lack of direct solution methods. The method presented here overcomes these challenges and learns a spatially varying noise field by applying the Pontryagin Maximum Principle (PMP) to solve for optimal trajectories over a changing estimate of the noise field. The resulting control drives the agents to the regions of the estimated field with the most uncertainty. This optimization is conducted with multiple agents interested in the noise field for a single frequency as well as for multiple agents simultaneously optimizing over multiple frequencies of interest. The challenges of finding a solution to the mixed boundary value problems is achieved through an eigenvalue decomposition method. The selected cost function is designed to minimize time and thus bound error introduced by the open loop control derived through the PMP methodology. Simulations and preliminary e...