Modeling three-dimensional acoustic propagation in underwater waveguides using the longitudinally invariant finite element method

textThree-dimensional acoustic propagation in shallow water waveguides is studied using the longitudinally invariant finite element method. This technique is appropriate for environments with lateral variations that occur in only one dimension. In this method, a transform is applied to the three-dimensional Helmholtz equation to remove the range-independent dimension. The finite element method is employed to solve the transformed Helmholtz equation for each out-of-plane wavenumber. Finally, the inverse transform is used to transform the pressure field back to three-dimensional spatial coordinates. Due to the oscillatory nature of the inverse transform, two integration techniques are developed. The first is a Riemann sum combined with a wavenumber sampling method that efficiently captures the essential components of the integrand. The other is a modified adaptive Clenshaw-Curtis quadrature. Three-dimensional transmission loss is computed for a Pekeris waveguide, underwater wedge, and Gaussian canyon. For each waveguide, the two integration schemes are compared in terms of accuracy and efficiency.Mechanical Engineerin

Finite element investigation of tunable and non-reciprocal elastic wave metamaterials

This dissertation studies elastic wave propagation in metamaterials subjected to an externally-applied static or spatiotemporally-varying pre-strain. Elastic metamaterials are media with subwavelength structure that behave as effective materials displaying atypical effective dynamic properties that are used to directly control the propagation of macroscopic waves. One major design limitation of most metamaterial structures is that the dynamic response cannot be altered once the microstructure is manufactured. However, the ability to modify, or tune, wave propagation in the metamaterial with an external pre-strain that induces geometric nonlinearity is highly desirable for numerous applications. Acoustic and elastic metamaterials with time- and space-dependent effective material properties have also recently received significant attention as a means to induce non-reciprocal wave propagation. However, the modulation of effective material properties in space and time using mechanical deformation has been unexplored. Tunable elastic metamaterials that exhibit large effective material property changes under a varying external pre-strain are therefore strong candidates for a non-reciprocal medium. The complex geometry present in unit cells that exhibit large geometric nonlinearity necessitates the development of a numerical technique. In this dissertation, a finite element approach is derived and implemented to study elastic wave propagation in a static pre-strained metamaterial, then generalized to include the effects of a spatiotemporally-varying pre-strain. A honeycomb structure composed of a doubly-periodic array of curved beams, known as a negative stiffness honeycomb (NSH), is analyzed as a tunable and non-reciprocal elastic metamaterial. It is shown that NSH exhibits significant tunability and a high degree of anisotropic wave behavior when a static pre-strain is imposed. This behavior can be used to guide wave energy in different directions depending on static pre-strain levels. In addition, it is shown that partial band gaps exist where only longitudinal waves propagate. The NSH therefore behaves as a meta-fluid, or pentamode metamaterial, which may be of use for applications of transformation elastodynamics such as cloaking and gradient index lens devices. A negative stiffness chain, a quasi-one-dimensional representation of NSH, is also shown as a case example of a non-reciprocal medium. It is shown in this work that this structure displays a high degree of non-reciprocity for a small amount of modulation pre-strain. The utility of the finite element approach is further demonstrated by investigating the effects of chiral geometric asymmetry to enhance the non-reciprocal behavior of elastic wave propagation in NSH.Mechanical Engineerin

Collage Vol. I

JUDY COCHRAN: Editorial MICHAEL TANGEMAN: Haikus 2-5 ELISE ALBRECHT, CURTIS PLOWGIAN: French Calligrams 6 JASON VARDEN: Waiting 7 ALEXANDER GREEN: Photo 8 EDUARDO JARAMILLO: Formas violentas 9-11 GABRIELE DILLMANN: Photo 12 MICHAEL GOLDSBERG: Funf fur Ashley 13 MEGAN CARLSON: Fur Jared (German) 14 MAGGIE GLOVER: For Jared 14-15 CHRIS FAUR: Painting 16 LINDSEY ESHELMAN: Stuhl (The Chair) 17 HALLE THOMPSON, GWENN DOBOS: Les Bouches 18 JILL BOO: Lacheln (A Smile) 19 ALEXANDER GREEN: Photo 20 JULIA GRAWEMEYER: Villanelle 21, Expressions francaises (French Figures) 22-23, Pour me rappeler (So that I\u27d remember) 24 MICHEL CLIQUET: Photo 25 CHARLES O\u27KEEFE: Photos 26-28 LINE LERYCKE: Photos 29-32 MICHEL CLIQUET: Pierre docile (Docile Stone) 29-32 LOGAN FAVIA: Ataraxia 33 AVRITA SINGH: Absence 34 RACHEL GROTHEER: Compassion 35, Ligne (Line) 36, Nuit, douce nuit (Night, gentle night) 37, Rouge (Red) 38, Bonjour Bleu (Hello Blue) 39, Ligne courbe (Curved Line) 40 AMELIA DUNLAP: Compassion 41-42 KYLE SIMPSON: Separation 43 ALEXANDER GREEN: Photo 44 GWENN DOBOS: Ataraxia 45 SARAH SLOTKIN: Separation 46 CURTIS PLOWGIAN: Absence 47 ELISA VER MERRIS: Photo 48, Attachement (Attachment) 49 JENNIFER JOHNSON: Attachement (Attachment)50 ANNA KELLY: Compassion 51 RICHARD BANAHAN: Photo 52, Mon grand-pere et moit (My grandfather and me) 53 MEREDITH KATZ: Separation 54 BRENDA HEATER: Compassion 55 ZACHARY WALSH: Ataraxia 56 MICHEL CLIQUET: Photos 57-5

Worcester Hydro Station

https://digitalcommons.wpi.edu/gps-posters/1539/thumbnail.jp

Vertical Take-off and Landing Autonomous Aircraft Design

This project addresses the design, analysis, and and construction of an autonomous fixed-wing/rotorcraft hybrid aircraft capable of vertical take-off and landing. Autonomy is addressed to enable obstacle avoidance, visual detection of a landing target area, and accurate landing. The designed aircraft consists of a ducted main rotor and two smaller tilt-rotors, and is based on a similar design from the literature. This report provides detailed analyses of the aircraft's aerodynamic and structural properties, dynamics and stability, propulsion, and power. The development of onboard autonomy using a 3D depth sensor is presented. Simulations of stabilizing controllers are presented. The construction of a prototype aircraft and its preliminary flight test results are reported

Vertical Take-off and Landing Autonomous Aircraft Design

This project addresses the design, analysis, and and construction of an autonomous fixed-wing/rotorcraft hybrid aircraft capable of vertical take-off and landing. Autonomy is addressed to enable obstacle avoidance, visual detection of a landing target area, and accurate landing. The designed aircraft consists of a ducted main rotor and two smaller tilt-rotors, and is based on a similar design from the literature. This report provides detailed analyses of the aircraft's aerodynamic and structural properties, dynamics and stability, propulsion, and power. The development of onboard autonomy using a 3D depth sensor is presented. Simulations of stabilizing controllers are presented. The construction of a prototype aircraft and its preliminary flight test results are reported