Dean E. Capone

Divergence of a stereotyped call in northern resident killer whales

Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes. This study suggests that new stereotyped calls may result from the gradual modification of existing call types through subtypes. Vocalizations of individuals and small groups of killer whales were collected using a bottom-mounted hydrophone array in Johnstone Strait, British Columbia in 2006 and 2007. Discriminant analysis of slope variations of a predominant call type, N4, revealed the presence of four distinct call subtypes. Similar to previous studies, there was a divergence of the N4 call between members of different matrilines of the same pod. However, this study reveals that individual killer whales produced multiple subtypes of the N4 call, indicating that divergence in the N4 call is not the result of individual differences, but rather may indicate the gradual evolution of a new stereotyped call.

Calculation of turbulent boundary layer wall pressure spectra

The suitability of various wave‐vector–frequency spectral models for predicting the point wall pressure spectrum due to developed turbulent boundary layer flow over planar, rigid surfaces is investigated. The early Corcos model [G. Corcos, J. Fluid Mech. 18, 353–378 (1964)] along with the incompressible and compressible models developed by Chase [D. Chase, J. Sound Vib. 112, 124–147 (1987)] are given particular attention. The effect of finite‐sized measurement transducers is included in the integration of the theoretical wave‐vector–frequency spectrum over the in‐plane wave numbers in order to arrive at an attenuated point pressure frequency spectrum that can be compared directly to existing experimental data obtained in air, water, and glycerine. The selected experiments cover a wide range of fluid properties and Reynolds numbers. It is found that the Corcos model does not predict the measured data as well as the Chase model. An optimum set of empirical constants needed to exercise the Chase models are p...

Unsteady Lift of Thick Airfoils in Turbulent Flow

Measurements of the unsteady lift forces acting on airfoils in turbulent flow were made to determine the effect of thickness on the gust response and validate a previously developed analytical model. A family of NACA 65-series uncambered airfoils with a range of thickness-to-chord ratios were tested in a water tunnel with grid-generated turbulence. Piezoelectric force gages were used to measure the spectral density of the unsteady lift, and the system was calibrated using an impulse force hammer. An accelerometer-based multiple coherence noise removal technique was employed to eliminate background noise contamination from the facility. The experimental results are shown to agree well with an analytical model of the unsteady lift based on turbulence ingestion theory and an incompressible gust response which accounts for airfoil thickness.Copyright

Structural-acoustic tailoring of metal structures by laser free-forming

Laser Free-Forming (LFF) is a manufacturing process that facilitates the mixture of different metal alloys and provides new opportunities in structural-acoustic tailoring. In this paper, a brief introduction is given to the LFF manufacturing process and the potential benefits, in terms of process cost and strength and reliability, are discussed. A hydrofoil for an underwater vehicle is used as an example problem to explore strategies for structural-acoustic design optimization and noise mitigation. It is shown through numerical studies that the sound radiation of a hydrofoil can be appreciably reduced by spatially varying its material properties.

Modeling the unsteady forces on a finite‐length circular cylinder in cross‐flow

Semi‐empirical models, for unsteady lift, drag, and axial forces, are developed to predict the spectral features of the unsteady forces on a finite‐length, right circular cylinder in cross‐flow. In general, the models consist of two parts; the spatial variation of rms wall pressure on the cylinder, and the correlation lengths, or areas, which describe the spatial extent of the correlation of the unsteady pressures. Experiments were conducted in a low‐noise wind tunnel to measure the statistics of the unsteady wall pressures on a model cylinder. The results from the measurements are incorporated into the theoretical models, and predictions are made for the spectral characteristics of the theoretical lift, drag, and axial forces. The unsteady lift and drag predictions using the models developed in this work agree well with previously measured unsteady force data measured on gradient hyrdophones exposed to flow. Below St=0.8 the unsteady lift and drag are found to be the dominant force on the cylinder, while above St=0.8 the unsteady axial force dominates.

Low‐wavenumber turbulent boundary layer wall‐pressure measurements from vibration data on smooth and rough cylinders in pipe flow.

The vibration response of a thin cylindrical shell excited by a fully‐developed turbulent boundary layer is measured and used to extract the fluctuating pressure levels generated by the boundary layer. Parameters used to extract the turbulent boundary layer pressure levels are determined via experimental modal analysis of the water‐filled pipe and measured vibration levels from flow through the pipe at 6 m/s. Hydrostatic head from a large reservoir provides the low‐noise source of steady flow for measuring the low‐wavenumber fluctuating pressure levels. Measurements are reported for smooth, transitionally rough, and fully rough conditions and are compared to the turbulent boundary layer pressure models of Chase, Smol’yakov, and Howe.

Underwater acoustic ground cloak development and demonstration

Acoustic ground cloaks, which conceal an object on a rigid surface, utilize a linear coordinate transformation to map the flat surface to a triangular void by compressing space into two triangular cloaking regions consisting of a homogeneous anisotropic acoustic metamaterial. Transformation acoustics allows for the realization of a coordinate transformation through a reinterpretation of the scale factors as a new material in the original coordinate system. An underwater acoustic ground cloak was constructed from perforated steel plates and experimentally tested to conceal an object on a pressure release surface. The perforated plate acoustic ground cloak successfully cloaked the scattered object. There was excellent agreement between the phase of the surface reflection and cloak reflection with a small amplitude difference. Above 15 [kHz], the cloaking performance decreased as the effective material parameters of the perforated plate metamaterial deviated from the required material parameters.Acoustic ground cloaks, which conceal an object on a rigid surface, utilize a linear coordinate transformation to map the flat surface to a triangular void by compressing space into two triangular cloaking regions consisting of a homogeneous anisotropic acoustic metamaterial. Transformation acoustics allows for the realization of a coordinate transformation through a reinterpretation of the scale factors as a new material in the original coordinate system. An underwater acoustic ground cloak was constructed from perforated steel plates and experimentally tested to conceal an object on a pressure release surface. The perforated plate acoustic ground cloak successfully cloaked the scattered object. There was excellent agreement between the phase of the surface reflection and cloak reflection with a small amplitude difference. Above 15 [kHz], the cloaking performance decreased as the effective material parameters of the perforated plate metamaterial deviated from the required material parameters.

Development of a multi-material underwater anisotropic acoustic metamaterial

Previous work in the open literature has described three potential ways to create an acoustic metamaterial with anisotropic mass density and isotropic bulk modulus: (1) alternating layers of homogeneous isotropic materials, (2) perforated plates, and (3) solid inclusions. The primary focus of this work will be to experimentally demonstrate the anisotropic behavior of a metamaterial comprised of a multi-solid inclusion unit cell in water. The two material design of the unit cell consists of one material more dense and one less dense than the background fluid, which results in an effective mass density tensor for the unit cell where one component is more dense and one component is less dense than the background fluid. Successful demonstration of an anisotropic metamaterial with these effective parameters is an important step in the development of structures based on transformational acoustics.

Wave propagation through additive manufactured phononic crystals

Obtaining the effective parameters is an important step in designing a unit cell for a variety of metamaterial applications. The effective parameters including the density and bulk modulus govern how a wave propagates through a medium constructed from unit cells. Additive manufacturing has created the potential to change the static density of materials by encapsulating metallic powder inside the produced component. This work will use modal analysis to extract the bulk modulus from additive manufactured rods. After the material properties are determined, numerical and experimental results will be compared for wave propagation through a phononic crystal constructed from additive manufactured rods of different densities.

Acoustic ground cloaks revisited

The unique material properties now obtainable with acoustic metamaterials have led to unprecedented control of acoustic wave propagation, resulting in many applications including acoustic cloaking. The two fundamental approaches in the development of a ground cloak are quasiconformal mapping [Li et al. Phys. Rev. Lett. 101, 203901 (2008)] and coordinate transformations [Popa et al. Phys. Rev. B. 83, 224304 (2011)]. The differences in the required material properties prescribed by these two approaches lie in the amount of anisotropy and inhomogeneity, as well as the size of the cloak relative to object. The coordinate transformation approach has been used to produce a realizable anisotropic homogeneous ground cloak in the acoustic domain. This presentation will highlight the findings of work that examined how advances in metamaterial development could lead to the realization of required material properties for ground cloaks, and explore alternative transformations to expand the applications for acoustic gr...