# J. Gregory McdanielBoston University | BU · Department of Mechanical Engineering

J. Gregory Mcdaniel

PhD

## About

181

Publications

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Introduction

Sound and vibration.

## Publications

Publications (181)

Synopsis
Arboreal embryos of phyllomedusine treefrogs hatch prematurely to escape snake predation, cued by vibrations in their egg clutches during attacks. However, escape success varies between species, from ∼77% in Agalychnis callidryas to just ∼9% in A. spurrelli at 1 day premature. Both species begin responding to snake attacks at similar devel...

Purpose
Eigenvalues are the natural frequencies of system squared. When designing a system it is important to know the natural frequencies, because if the system is forced near one of these natural frequencies the magnitude of vibration becomes very large. The eigenvalues are typically determined by solving an eigenvalue problem, which is an iterat...

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ABSTRACT
Engineers who design complex dynamic systems do not have the luxury of iteration. Numerical analysis of a single design, typically by finite element analysis, requires enormous amounts of CPU time. Therefore, improving a design by trying out many design modifications is impossible. Moreover, it is also impossible to identi...

Calculating the displacement vector for a harmonically vibrating structure becomes computationally expensive for larger Degree of Freedom (DOF) systems. If a portion of the system is modified, then the stiffness and mass of the system are perturbed and a new displacement vector must be calculated. In cases where an optimal solution must be determin...

The oscillatory dynamics of nanoelectromechanical systems (NEMS) is at the heart of many emerging applications in nanotechnology. For common NEMS, such as beams and strings, the oscillatory dynamics is formulated using a dissipationless wave equation derived from elasticity. Under a harmonic ansatz, the wave equation gives an undamped free vibratio...

Stereotyped signals can be a fast, effective means of communicating danger, but animals assessing predation risk must often use more variable incidental cues. Red eyed-treefrog, Agalychnis callidryas, embryos hatch prematurely to escape from egg predators, cued by vibrations in attacks, but benign rain generates vibrations with overlapping properti...

Mechanosensory-cued hatching (MCH) is widespread, diverse, and important for survival in many animals. Disturbance by predators elicits escape-hatching. Agitation by hosts stimulates parasite hatching. Sibling movements and parental vibrations synchronize hatching. Abiotic vibrations inform embryos of habitat conditions. Tests for MCH often use man...

Over the past century, a number of scalar metrics have been proposed to measure the damping of a complex system. The present work explores these metrics in the context of finite element models. Perhaps the most common is the system loss factor, which is proportional to the ratio of energy dissipated over a cycle to the total energy of vibration. Ho...

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ABSTRACT
A harmonically vibrating structure is considered for this study and divided into segments. The objective of the proposed research is to use knowledge from the nominal structure to make predictions as to how the root mean squared (RMS) displacement of the structure will change when either the mass or stiffness of a segment...

As animals develop, their capacities to sense cues, assess threats, and perform actions change, as do the relative costs and benefits that underlie behavioural decisions. We presented ambiguous cues to test if hatching decisions of red-eyed treefrogs, Agalychnis callidryas, change developmentally following adaptive predictions based on changing cos...

No PDF available
ABSTRACT
In 1930, Kimball wrote a paper entitled "The damping factor in vibrations" that appeared in the journal Product Engineering. That paper proposed a damping factor based on the decrement of a vibrating system with exponential decay. Kimball showed that the proposed damping factor was proportional to the ratio of the energy d...

No PDF available
ABSTRACT
In structural vibrations, the Rayleigh quotient may be used to calculate the natural frequency (or eigenvalue) of a structure given the corresponding mode shape (or eigenvector). Previous works have shown that the eigenvalue may be calculated relatively accurately using the Rayleigh quotient as long as an appropriate guess...

Here, we study the acoustic radiation generated by the vibration of miniaturized doubly clamped and cantilever beam resonators in viscous fluids. Acoustic radiation results in an increase in dissipation and consequently a decrease in the resonator’s quality factor. We find that dissipation due to acoustic radiation is negligible when the acoustic w...

Here we study viscous oscillatory nanoflows generated in a fluid by mechanical oscillations of miniaturized resonators. In particular, we focus on the limits of two-dimensional cylinder theory, which approximates a slender nanoresonator, such as an atomic force microscopy microcantilever or a nanobeam resonator, as a cylinder oscillating in a fluid...

Vibration testing is a critical aspect in the qualification of fieldable hardware as dynamic environments are typically design drivers, especially in the case of airborne and space-borne systems. However, when testing components or small subassemblies, it is challenging to match the boundary conditions presented by the true installation interface,...

Metallic foam metamaterials consist of an open-cell metallic microstructure completely saturated by a viscous material. In this chapter, dynamic responses of metamaterials containing foams with two distinct pore sizes as well as six different saturating materials are measured in controlled laboratory settings. The vibration damping and isolation ch...

The natural frequencies of a structure are the square roots of its eigenvalues. Traditionally, determining the eigenvalues for a structure requires an iterative procedure. This becomes expensive for larger Degrees of Freedom (DOF) systems, and increasingly more expensive if several modifications of the structure are tested. An additional way to det...

No PDF available
ABSTRACT
Richard Lyon's pioneering work on the statistics of vibration produced significant insights and tools that profoundly improved our world. This work and its impact will be reviewed. This lecture begins with his 1955 Doctoral Dissertation at the Massachusetts Institute of Technology, which was entitled The Response of Contin...

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ABSTRACT
This work proposes a method for accelerating generalized polynomial chaos (gPC) expansions, using Neumann series, for uncertainty quantification of complex structures with uncertain damping and spring parameters. Often, classical Monte Carlo simulations are used for uncertainty quantification, however, for larger systems a...

A method for estimating acoustic absorption in porous materials is presented in which the thermal and viscous boundary layers are modeled through boundary conditions to the Helmholtz equation for the acoustic pressure. The method is proposed for rigid-framed porous materials in which vibration of the frame is negligible compared to pressure fluctua...

An engineering method for triaxial hydrostatic compression of metallic foam is presented to preferentially alter the foam's microstructure. The method is demonstrated on an assortment of open-cell aluminum foams with varying pore size and porosity. Measurements of acoustic absorption indicate that the compressed samples absorb significantly more so...

A composite foam consisting of open-cell metallic foam embedded with polyurethane foam is fabricated and evaluated for sound absorbing properties. The best performing composite foam increased the sound absorption by a factor of 6 (from .1 to .6) in the low frequency test range and by a factor of 2 (from .2 to .4) broadband compared to the original...

This paper presents a method to simultaneously predict the elastic modulus, axial load, and boundary conditions of a NMES beam from a minimum of two measured natural frequencies. The proposed method addresses the challenges of the inverse problem at the nano scale which include high natural frequencies, small geometric beam dimensions, and measurem...

This paper presents a new method for evaluating the Neumann series approximation for the response of a dynamic system perturbed by two parameters. The proposed method will be valuable for iterative model updating methods, where major computational savings are gained when the approximation is evaluated multiple times. The method is based on the bino...

No PDF available
ABSTRACT
This presentation surveys a variety of representative case studies in an effort to better understand and predict the accuracy of the light damping approximation. For viscously damped systems, the light damping approximation ignores the off-diagonal elements of the transformed damping matrix. When the approximation is valid...

No PDF available
ABSTRACT
A composite foam consisting of polyurethane foam embedded in metallic foam is fabricated and evaluated for sound absorbing properties. The normal incidence sound absorption coefficient is measured in an impedance tube for three different types of foams including the composite foam, a rigid framed metallic foam, and an elas...

This paper presents a new method for efficiently computing the response of a perturbed dynamic system. The method is based on predicting the convergence of a Neumann series expansion that approximates the displacement response of a perturbed system. The Neumann series is often faster than a direct solve, but only converges when the spectral radius...

A method for estimating acoustic absorption in foams is presented using a combination of micro-computed tomography, finite element analysis, and boundary layer loss theory. In the method, the foam is assumed to be rigid framed and the viscous and thermal boundary layers at the fluid and frame interface are assumed to be small compared to foam dimen...

As animals develop, their abilities and needs change, altering cost/benefit trade-offs and optimal behavior responses to cues. We tested if ontogenetic changes in information use and environmentally cued hatching decisions of embryos match adaptive predictions, using red-eyed treefrogs, Agalychnis callidryas. These arboreal embryos hatch rapidly an...

A method is presented to improve the estimates of material properties, dimensions, and other model parameters for linear vibrating systems. The method improves the estimates of a single model parameter of interest by finding parameter values that bring model predictions into agreement with experimental measurements. A truncated Neumann series is us...

Algorithms that enable acoustic sensing vehicles to autonomously map acoustic fields are being developed, but some require an analytical representation of the data collected from the acoustic field with specific continuity properties. One optimal control technique that has these requirements and has been used in autonomous acoustic sensing algorith...

This presentation discusses historical developments of damping models most commonly used in the analysis of structural acoustics and vibrations today. This presentation represents all damping models as frequency-dependent complex-valued matrices that appear in the equations of motion. The historical development of damping models has benefited from...

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....

A method for correcting multiple mechanical and acoustical properties in a finite element model using the Neumann series is presented and demonstrated with numerical examples. In previous work, the authors developed a method for estimating a model parameter in a complex structure using a Neumann series as an approximation to system response. The me...

A method is presented to improve the estimates of material properties, dimensions, and other model parameters for linear vibrating systems. The method improves the estimates of a single model parameter of interest by finding parameter values that bring model predictions into agreement with experimental measurements. A truncated Neumann series is us...

Analyses and examples are presented that explore the limits and accuracies of a technique for improving acoustic and vibration models by temporal comparisons to data. In a previous paper, the authors proposed the use of impulsive excitations followed by time windowing of responses. This approach allows comparisons between experimental data and mode...

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 ar...

A new method is proposed for estimating the material properties of a component in a complex system, given vibration measurements taken at points on the system. The method begins by identifying a set of unknown material parameters for each material. A finite element model is constructed using initial estimates of these parameters. A set of error met...

Cellular solids are of large interest in structural vibration due to their high strength-to-weight ratio and ability for high energy absorption. This presentation describes concepts for digitally designing cellular solids and demonstrates the ability of this design method for tuning effective material properties for noise and vibration mitigation a...

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. He...

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 Padé approximants or implicitly interpolatory subspaces, the main advantage of these methods is that their structure is adaptively determined, m...

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 experi...

The goal of this work is to investigate how the combination of 3D computer graphics and finite elementsoftware 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 art...

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...

One of the visions for Acoustically enabled Autonomous UnderwaterVehicles(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 lo...

A new method is developed to estimate road profile in order to estimate IRI based on the ASTM standard. This method utilizes an accelerometer and a Dynamic Tire Pressure Sensor (DTPS) to estimate road roughness. The accelerometer measures the vertical axle acceleration. The DTPS, which is mounted on the tire's valve stem, measures dynamic pressure...

A new method is proposed for estimating the material properties of a component in a complex system given vibration measurements taken at points on the system. The method begins by identifying a set of unknown material parameters for each material. A finite element model is constructed using initial estimates of these parameters. A set of error metr...

Cellular solids are of large interest in structural vibration due to their high strength-to-weight ratio and ability for high energy absorption. This presentation describes concepts for digitally designing cellular solids, and demonstrates the ability of this design method for tuning effective material properties for noise and vibration mitigation...

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...

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 tra...

Cellular materials have recently found attention in structural applications to buffer impacts and for energy absorption. In order to choose the most suitable cellular material based on its intended application, one must understand its mechanical response either through experimentation and/or modeling. Accurate modeling of the response of a material...

This paper develops and demonstrates a strategy for identifying the lack of dynamic interaction, or coupling, between potential design modifications to a vibrating base structure. Such decoupling may be exploited to efficiently compare the performance of competing engineering designs. In particular, it is shown how different design modifications ma...

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 system&apos...

This presentation describes the use of video imaging to estimate material properties of a structure within a region of interest. The first technology examined is video magnification, which is a technique that magnifies motions that are mathematically present in a video but often not visible to the human eye. The second technology examined is digita...

Spectral Analysis of Surface Wave (SASW) is widely used in nondestructive subsurface profiling for geological sites. The air-coupled SASW is an extension from conventional SASW methods by replacing ground-mounted accelerometers with non-contact microphones, which acquire a leaky surface wave instead of ground vibration. The air-coupled SASW is a go...

A method is developed to estimate pavement macrotexture depth (MTD), using measurements from a microphone mounted underneath a moving vehicle. The acoustic energy is assumed to have positive linear correlation with MTD of the pavement. However, the acoustic measurements will include tire-generated sound that carries information about the road featu...

The present work proposes and demonstrates a method for improving the accuracy of large finite element models using measurements. Finite element analysis routinely allows for the construction of dynamic models with millions of degrees of freedom. The models often involve a large number of parameters, such as material properties and dimensions, that...

The present work investigates the causal and passive interpolation of structural acoustic matrices in the frequency domain. Interpolations significantly ease computational burdens involved in computing these matrices from models. For example, one may wish to compute a small admittance matrix, relating forces to velocities at points on a structure,...

This paper presents high order modal methods that increase the accuracy of the standard modal truncation scheme with an emphasis on frequency-domain accuracy. The existing Mode Acceleration and Modal Truncation Augmentation methods are compared alongside a new interpretation utilizing the interpolating polynomial. This technique is motivated by tak...

The goal of this work is to examine the efficacy of interpolatory model order reduction on frequency sweep problems with many forcing vectors. The adaptive method proposed relies on the implicit interpolatory properties of subspace projection with basis vectors spanning the forced response of the system and its derivatives. The algorithm is similar...

As material fabrication advances, new materials with special properties will be possible to accommodate new design boundaries. An emerging and promising field of investigation is to study the basic phenomena of materials with a negative Poisson ratio (NPR). This work seeks to develop zero Poisson ratio (ZPR) metamaterials for use in reducing acoust...

Acoustic scattering from a cylindrical shell is required to be causal, so that the incident wave must precede the scattered wave that it creates. In the frequency domain, this statement may be explored by forming a frequency-dependent complex-valued reflection coefficient that relates the scattered wave to the incident wave. The real and imaginary...

This paper outlines a strategy for identifying and exploiting the lack of dynamic coupling between potential modifications to a vibroacoustic system. Often a designer develops a set of modifications and wishes to determine those that perform the best relative to some metric, in particular, we consider performance metrics that rely on the steady sta...

An investigation on the prediction of macrotexture Mean Texture Depth (MTD) of pavement from a moving vehicle is conducted. The MTD was predicted by using the tire/road noise measured from a microphone mounted underneath a moving vehicle. Principal Component Analysis (PCA) is used to filter noise from microphone data prioer to estimating its energy...

In order to best prioritize road maintenance, the level of deterioration must be known for all roads in a city's network. Pavement Condition Index (PCI) and International Roughness Index (IRI) are two standard methods for obtaining this information. However, IRI is substantially easier to measure. Significant time and money could be saved if a meth...

A method is developed to estimate the mean texture depth (MTD) value, which to some extent represents pavement quality, using measurements from a microphone mounted underneath a moving vehicle. Such measurements will include tire-generated sound that carries information about the road macrotexture as well as noise generated by the wind and vehicle....

An analytic approximation is derived for the far-field response of a generally anisotropic plate subject to a time-harmonic point force acting normal to the plate. This approximation quantifies the directivity of the flexural wave field that propagates away from the force, which is expected to be useful in the design and testing of anisotropic plat...

The present work is concerned with the design of composite plates that are optimized with respect to their wave propagation characteristics. For example, one may wish to design a composite plate such that the attenuation of a dominant wave is maximized. The optimization proposed here considers a composite plate with a specified number of layers. Th...

The present work investigates the physics of constrained layer damping treatments for plates and beams by a semi-analytical finite element method and presents applications of the method to the optimization of damping treatments. The method uses finite element discretizations in the thickness coordinate and propagating wave solutions in the remainin...

Surface waves are commonly used for vibration-based nondestructive testing for infrastructure. Spectral Analysis of Surface Waves (SASW) has been used to detect subsurface properties for geologic inspections. Recently, efforts were made to scale down these subsurface detection approaches to see how they perform on small-scale structures such as con...

This work presents a non-destructive and non-contact acoustic sensing approach for measuring road profile of road and bridge deck with vehicles running at normal speed without stopping traffic. This approach uses an instantaneous and real-time dynamic tire pressure sensor (DTPS) that can measure dynamic response of the tire-road interaction and inc...

Pavement condition surveys are typically done manually by inspection teams. They can be expensive and can take several months to complete. This paper considers a vehicle-mounted pavement inspection system that aims to be more affordable and faster than manual surveys. The system is comprised of a vehicle outfitted with a multi-modal sensor array th...

Classifications of road conditions are crucial because officials prioritize road maintenance decisions based on them.
Pavement condition index (PCI) surveys are performed manually and used by many cities in the U.S. to evaluate road
surface conditions. In this research, a more efficient method is used to detect road surface conditions. This method...

A road is considered safe when it provides adequate friction between the tire and pavement surface interaction to avoid accidents. The current manual methods of evaluating surface friction of roads are not only dangerous for the inspectors and motorists on the road but are very time-consuming and subject to the inspector's judgment. This paper conf...

The United States is facing a challenge on repairing aging civil infrastructures because of limited resources allocation. The international roughness index (IRI) is a key quantity of road inspection data to aid officials in prioritizing road maintenance decisions, which allows them to be efficient with their resources. IRI measures both the road ro...

Various sensor systems are wildly used in inspecting the nation's civil infrastructure of roads and bridges. Unfortunately, infrastructure integrity cannot be conveniently evaluated in an economically or a time efficient way using these existing systems. This work presents a non-destructive and non-contact acoustic sensing approach for fast inspect...

A method is developed to assess the pavement condition, using measurements from a microphone mounted behind the tire of a moving vehicle. Such measurements will include tire/road noise that carries information about the road feature. The proposed method uses standard deviation (STD) of the amplitudes of frequency spectra from the acoustic measureme...

This work presents a convenient and non-contact acoustic sensing approach for measuring ground vibration. This approach, which uses an instantaneous dynamic tire pressure sensor (DTPS), possesses the capability to replace the accelerometer or directional microphone currently being used for inspecting pavement conditions. By measuring dynamic pressu...

In 1955, Preston Smith wrote a landmark paper on free waves in a cylindrical shell. That paper described the displacement components and dispersions of the flexural, shear, and longitudinal waves that propagate in helical directions in the wall of the cylinder. The present author first met Preston over forty years later, when the hand calculations...

The present work seeks to optimize the spatial distribution of damping in structures with boundary damping. This work is motivated by design considerations, such as weight and cost, that often limit the amount of damping that can be used. In such cases, the designer must choose the spatial distribution of damping in order to reduce the structural v...

This work presents an application of the Ritz Method to the optimization of vibrating structures. The optimization problems considered here involve local design choices made in various regions of the structure in hopes of improving the vibration characteristics of the structure. In order to find the global optimum, one must perform an exhaustive se...

Cylindrical shells composed of concentric layers may be designed to affect the way that elastic waves are generated and propagated, particularly when some layers are anisotropic. To aid the design process, the present work develops a wave based analysis of the Green's function for a layered cylindrical shell in which the response is given as a sum...

This work presents a method for assessing pavement surface condition
using measurements from a microphone mounted underneath a moving
vehicle. Such measurements will include tire-generated sound, which
carries much information about the road condition, as well as noise
generated by the wind and vehicle. The proposed method uses Principal
Component...

This work presents an alternative design of a rotating energy harvester,
which possesses the capability of powering electronic sensors and
wireless sensor networks within vehicle. This energy harvester design is
based on magnetostatic coupling between a stationary circular-arc hard
magnet array and rotating magnetic solenoids, which consists of a u...

SASW (Spectral Analysis of Surface Waves) is practical and relatively effective in characterizing subsurface ground truth. According to the surface wave in the interesting range of frequency, some criteria for source-receiver configuration are employed and limit the applications. Challenges emerge when SASW is applied to study the surface wave invo...

Spectral Analysis for Surface Wave (SASW) is a widely practiced NDT
method due to its ability to identify the shear velocity profile of
subsurface layers. However, the SASW method is limited to point-to-point
inspection because all data has to go through an inversion process,
which is iterative and manual. Some automated iteration techniques were
d...

This work investigates composite plates and their ability to direct flexural intensity, which has important implications for noise and vibration control. It is well known that a composite plate supports a flexural wave whose wavenumber depends strongly on its angle of propagation. This suggests that a composite plate will direct more flexural inten...

Approaches are currently being developed for converting ocean wave energy by creating mechanical rotations within buoys. These devices benefit from the absence of mechanical stops that may destroy devices that utilize mechanical translations within buoys. In the present work, an analysis is developed that quantifies the mechanical coupling of ocean...

Available technologies for producing thermal images promise temperature sensitivity on the order of 25 mK. This sensitivity prompts the present investigation, which is concerned with defining circumstances in which thermal images may be used to detect and perhaps measure damping effects. Ultimately, thermal images may lead to a spatial map of dampi...

Sensitivity to substrate-borne vibrations is widespread in animals and evolutionarily precedes hearing but, compared with other sensory modalities, we know little about vibrational communication, particularly in vertebrates. For plant-dwelling arthropods, vibrations are likely as important as sound. Arboreal vertebrates excite plant vibrations with...

A large scale finite element model with high mesh resolution is established to simulate the ground truth of regular highway pavement structure with subsurface debonding defects. The simulation is motivated by non-destructive testing methods that derive information from the acoustic radiation of the surface wave. These NDT (Non-Destructive Testing)...

This work considers passive damping treatments that dynamically interact with plates over areas that are much smaller than a flexural wavelength. Each treatment is modeled as a frequency-dependent admittance presented to the plate at a point. The frequency-dependence is required to satisfy the causality and minimum phase conditions, which are impli...

Some of the most challenging vibration control problems involve the selection and placement of frequency-dependent damping devices, such as multilayered viscoelastic materials. In complex structures involving the simultaneous use of several passive damping devices, it is difficult to determine the effectiveness of each device directly from measurem...

Prey use predator cues to inform defensive decisions. Detecting these cues is often complicated by benign stimuli that resemble and can be mistaken for predators, leading prey to display costly defences incorrectly. One strategy that prey have evolved to reduce these ‘false alarms’ is to respond only to stimuli with characteristics consistent with...

Effective design and placement of damping treatments for complex structures benefit greatly from a knowledge of where the vibrational energy is being dissipated. Previously, the authors presented a method for spatially mapping contributions to the modal loss factor of a viscously damped structure [McDaniel et al., J. Acoust. Soc. Am. 125, 2603 (200...

A method is proposed for constructing spatial maps of modal damping for viscously damped structures. These maps are intended to be useful in assessing the effectiveness of spatially distributed damping, particularly in complex structures that are damped by a variety of mechanisms. The method uses frequency response measurements and modal analysis t...

Incidental acoustic and vibrational cues generated by predators are a potential source of information for prey assessing risk. Substrate vibrations should be excited by most predators, and frequency, amplitude or temporal properties could allow prey to distinguish predator from benign-source vibrations. Red-eyed treefrog embryos detect egg predator...

While the causality statement in the time domain is quite simple, the corresponding statement in the frequency domain involves Hilbert transform relations between the real and imaginary parts of the relevant transfer function. If the transfer function is minimum phase, one can go further and develop Hilbert transform relations between the amplitude...