The KW-boundary hybrid digital waveguide mesh for room acoustics applications

The digital waveguide mesh is a discrete-time simulation used to model acoustic wave propagation through a bounded medium. It can be applied to the simulation of the acoustics of rooms through the generation of impulse responses suitable for auralization purposes. However, large-scale three-dimensional mesh structures are required for high quality results. These structures must therefore be efficient and also capable of flexible boundary implementation in terms of both geometrical layout and the possibility for improved mesh termination algorithms. The general one-dimensional N-port boundary termination is investigated, where N depends on the geometry of the modeled domain and the mesh topology used. The equivalence between physical variable Kirchoff-model, and scattering-based wave-model boundary formulations is proved. This leads to the KW-hybrid one-dimensional N-port boundary-node termination, which is shown to be equivalent to the Kirchoff- and wave-model cases. The KW-hybrid boundary-node is implemented as part of a new hybrid two-dimensional triangular digital waveguide mesh. This is shown to offer the possibility for large-scale, computationally efficient mesh structures for more complex shapes. It proves more accurate than a similar rectilinear mesh in terms of geometrical fit, and offers significant savings in processing time and memory use over a standard wave-based model. The new hybrid mesh also has the potential for improved real-world room boundary simulations through the inclusion of additional mixed modeling algorithms

A Novel Millimeter-Wave Channel Simulator and Applications for 5G Wireless Communications

This paper presents details and applications of a novel channel simulation software named NYUSIM, which can be used to generate realistic temporal and spatial channel responses to support realistic physical- and link-layer simulations and design for fifth-generation (5G) cellular communications. NYUSIM is built upon the statistical spatial channel model for broadband millimeter-wave (mmWave) wireless communication systems developed by researchers at New York University (NYU). The simulator is applicable for a wide range of carrier frequencies (500 MHz to 100 GHz), radio frequency (RF) bandwidths (0 to 800 MHz), antenna beamwidths (7 to 360 degrees for azimuth and 7 to 45 degrees for elevation), and operating scenarios (urban microcell, urban macrocell, and rural macrocell), and also incorporates multiple-input multiple-output (MIMO) antenna arrays at the transmitter and receiver. This paper also provides examples to demonstrate how to use NYUSIM for analyzing MIMO channel conditions and spectral efficiencies, which show that NYUSIM is an alternative and more realistic channel model compared to the 3rd Generation Partnership Project (3GPP) and other channel models for mmWave bands.Comment: 7 pages, 8 figures, in 2017 IEEE International Conference on Communications (ICC), Paris, May 201

Frequency Domain Modeling of SAW Devices

New SAW sensors for integrated vehicle health monitoring of aerospace vehicles are being investigated. SAW technology is low cost, rugged, lightweight, and extremely low power. However, the lack of design tools for MEMS devices in general, and for Surface Acoustic Wave (SAW) devices specifically, has led to the development of tools that will enable integrated design, modeling, simulation, analysis and automatic layout generation of SAW devices. A frequency domain model has been created. The model is mainly first order, but it includes second order effects from triple transit echoes. This paper presents the model and results from the model for a SAW delay line device

A 3-D Model of the Auroral Ionosphere

A new 3-D model of the high latitude ionosphere is developed to study the coupling of the ionosphere with the magnetosphere and neutral atmosphere. The model consists of equations describing conservations of mass, momentum and energy for the six ionospheric constituents (O+, NO+, N+2 , O+2 , N+ and e-) and an electrostatic potential equation. This 3-D model is used to examine interrelated processes of ion heating, plasma structuring due to perpendicular transport, ion upflow, molecular ion generation, and neutral wave forcing. It is first validated by comparisons with a 2-D model, which uses similar mathematical and numerical approaches, and is additionally compared against incoherent scatter radar data. Results from a simulation of ionospheric response to a large amplitude acoustic wave also suggests an important role for these waves in generating local dynamo currents and density variations. Results of this model also shed some light on the interplay of perpendicular and parallel transports of plasma in producing structures in density and drift velocity profiles

Caractérisation de la génération et la propagation d'ondes de pressions dans des tissus biologiques pour la conception d'appareils médicaux

Therapies using so called extracorporeal shock waves (Extracorporeal Shock Wave Therapy ESWT) have become current medical practice in orthopedy and traumatology. In order to understand and to optimize the effect of shock waves in clinical applications, medical results must be correlated with well characterized mechanical stimuli. This thesis has an industrial scope. It contributes to the comprehension of the generation and propagation of pressure waves in human tissues with the aim of improving existing ESWT therapies and of providing the industrial partner with tools for the design of a new generation of extracorporeal shock waves devices. The adopted general approach is based on a combination of experimental characterization and analytical and numerical modeling of wave generation and propagation phenomena in a medical treatment device and in biological tissues. Firstly, the characterization of a wave generator is based, on the one hand, on measurements of the dynamic behavior of the moving parts coupled with rigid body simulation, and on the other hand on measurements of wave propagation by means of a Hopkinson bar coupled with finite elements simulations. This characterization has shown that the generator produces very reproducible stress pulses. The simulation technique allows designing a new wave generator with a higher energy range and with well controlled operating parameters. The new design is covered by a patent. Secondly, a measurement technique for generation and propagation of pressure waves in soft animal tissues has been developed that is based on PVDF gages. The applicability of these gages has been qualitatively validated by comparative measurements with a Hopkinson bar. The perturbation effect of the gage, acting as an inclusion in the medium to be characterized, has been evaluated by means of simulations of wave propagation in water. Comparison with measurements in soft tissues suggests that it is negligible for pressure measurement in this type of materials. An independent calibration of the gage could however not be performed. Finally, measurements of wave propagation in pig skin and fat using PVDF gauges showed good reproducibility for a given sample. They highlighted the influence of the supply pressure of the wave generator on the amplitude and on the attenuation of the wave in tissues. Moreover, the dependence between the amplitude of the wave and its propagation velocity suggests a non-linear viscoelastic behavior of soft tissues as well as the need of a constitutive model for high strain rates. Simulations of wave propagation using a known hyperelastic constitutive model highlighted the difficulty of modeling such soft tissues. A viscoelastic non-linear constitutive model based on power laws was considered and is an interesting candidate for future simulations. The simulation technique for wave generation and propagation in a solid (aluminum) and a liquid (water) has been validated by comparing its results with measurements performed in these materials (strain gages and PVDF hydrophone respectively). Simulations of pressure wave propagation validated for solids and liquids showed that they can be applied to biological tissues modeled using a known constitutive model; they are a tool for any other simulation using more complex constitutive models. This work contributes to a broader study aimed at establishing and validating constitutive models for biological materials suitable for use in simulations of wave propagation

Landslide tsunami case studies using a Boussinesq model and a fully nonlinear tsunami generation model

International audienceCase studies of landslide tsunamis require integration of marine geology data and interpretations into numerical simulations of tsunami attack. Many landslide tsunami generation and propagation models have been proposed in recent time, further motivated by the 1998 Papua New Guinea event. However, few of these models have proven capable of integrating the best available marine geology data and interpretations into successful case studies that reproduce all available tsunami observations and records. We show that nonlinear and dispersive tsunami propagation models may be necessary for many landslide tsunami case studies. GEOWAVE is a comprehensive tsunami simulation model formed in part by combining the Tsunami Open and Progressive Initial Conditions System (TOPICS) with the fully non-linear Boussinesq water wave model FUNWAVE. TOPICS uses curve fits of numerical results from a fully nonlinear potential flow model to provide approximate landslide tsunami sources for tsunami propagation models, based on marine geology data and interpretations. In this work, we validate GEOWAVE with successful case studies of the 1946 Unimak, Alaska, the 1994 Skagway, Alaska, and the 1998 Papua New Guinea events. GEOWAVE simulates accurate runup and inundation at the same time, with no additional user interference or effort, using a slot technique. Wave breaking, if it occurs during shoaling or runup, is also accounted for with a dissipative breaking model acting on the wave front. The success of our case studies depends on the combination of accurate tsunami sources and an advanced tsunami propagation and inundation model

Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 47 (2012): 65-95, doi:10.1016/j.ocemod.2012.01.003.The coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST) enables simulations that integrate oceanic, atmospheric, wave and morphological processes in the coastal ocean. Within the modeling system, the three-dimensional ocean circulation module (ROMS) is coupled with the wave generation and propagation model (SWAN) to allow full integration of the effect of waves on circulation and vice versa. The existing wave-current coupling component utilizes a depth dependent radiation stress approach. In here we present a new approach that uses the vortex force formalism. The formulation adopted and the various parameterizations used in the model as well as their numerical implementation are presented in detail. The performance of the new system is examined through the presentation of four test cases. These include obliquely incident waves on a synthetic planar beach and a natural barred beach (DUCK’ 94); normal incident waves on a nearshore barred morphology with rip channels; and wave-induced mean flows outside the surf zone at the Martha’s Vineyard Coastal Observatory (MVCO). Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK’ 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from Garcez-Faria et al. (1998, 2000). Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar / rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non- breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).The first two authors were supported by a NOAA/IOOS Grant (Integration of Coastal Observations and Assets in the Carolinas in Support of Regional Coastal Ocean Observation System Development in the Southeast Atlantic) and a cooperative agreement between U.S. Geological Survey and University of South Carolina as part of the Carolinas Coastal Change Processes Project. Also G. Voulgaris was partially supported by the National Science Foundation (Awards: OCE-0451989 and OCE-0535893)

A semi-analytical decomposition analysis of surface plasmon generation and the optimal nanoledge plasmonic device

Surface plasmon resonance (SPR) of nanostructured thin metal films (so-called nanoplasmonics) has attracted intense attention due to its versatility for optical sensing and chip-based device integration. Understanding the underlying physics and developing applications of nanoplasmonic devices with desirable optical properties, e.g. intensity of light scattering and high refractive index (RI) sensitivity at the perforated metal film, is crucial for practical uses in physics, biomedical detection, and environmental monitoring. This work presents a semi-analytical model that enables decomposition and quantitative analysis of surface plasmon generation at a new complex nanoledge aperture structure under plane-wave illumination, thus providing insight on how to optimize plasmonic devices for optimal plasmonic generation efficiencies and RI sensitivity. A factor analysis of parameters (geometric, dielectric-RI, and incident wavelength) relevant to surface plasmon generation is quantitatively investigated to predict the surface plasmon polariton (SPP) generation efficiency. In concert with the analytical treatment, a finite-difference time-domain (FDTD) simulation is used to model the optical transmission spectra and RI sensitivity as a function of the nanoledge device's geometric parameters, and it shows good agreement with the analytical model. Further validation of the analytical approach is provided by fabricating subwavelength nanoledge devices and testing their optical transmission and RI sensitivity

On the theory and modelling of the fourth generation light source

This thesis reports research carried out to develop a non-averaged 3D simulation code written using minimal approximation to model a Free Electron Laser (FEL) amplifier, the so-called fourth generation light source. Previous generations of light source use synchrotron which has poor temporal coherence. The current race to build the next generation of coherent light sources, FELs, has started and the work carried out in this thesis aims to provide a new simulation code to give insight on the behaviour of the electrons and radiation interaction below the radiation wavelength limit. The numerical simulation was written in Fortran 90 for use on parallel architecture computers to model a Free Electron Laser in three spatial dimensions and including time dependent effects. The Maxwell wave equation and Lorentz equation were used to describe the radiation field evolution and the electrons' propagation. These equations were scaled to become dimensionless. A finite element method, linear solver and Runge-Kutta method were applied to solve these equations. Previous results were reproduced in the 1D limit. Coherent Spontaneous Emission (CSE) was reproduced; this can not be done by other current 3D simulators. Other numerical studies include the FEL interaction, electron shot-noise and modelling of the energy spread and emittance of the electron beam. A final simulation demonstrates radiation difractive effects in a full nonlinear FEL interaction including all 3D effects. This code is the first of its type to be developed and will allow a completely new range of physics of the FEL to be investigated and exploited