2015-08-01
information systems (GIS) software. A smaller 6.25 square kilometer area around the Southern Methodist University was extracted from the larger...area and analyzed using an acoustic finite- difference time-domain (FDTD) code. The procedures to model the area using GIS software, extract required...create directories. .................................................. 127 Figure 8.4. Choose section cut to extract data
Finite difference time domain grid generation from AMC helicopter models
NASA Technical Reports Server (NTRS)
Cravey, Robin L.
1992-01-01
A simple technique is presented which forms a cubic grid model of a helicopter from an Aircraft Modeling Code (AMC) input file. The AMC input file defines the helicopter fuselage as a series of polygonal cross sections. The cubic grid model is used as an input to a Finite Difference Time Domain (FDTD) code to obtain predictions of antenna performance on a generic helicopter model. The predictions compare reasonably well with measured data.
Finite difference time domain calculations of antenna mutual coupling
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Kunz, Karl S.
1991-01-01
The Finite Difference Time Domain (FDTD) technique was applied to a wide variety of electromagnetic analysis problems, including shielding and scattering. However, the method has not been exclusively applied to antennas. Here, calculations of self and mutual admittances between wire antennas are made using FDTD and compared with results obtained during the method of moments. The agreement is quite good, indicating the possibilities for FDTD application to antenna impedance and coupling.
Finite difference time domain calculations of antenna mutual coupling
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Kunz, Karl S.
1991-01-01
The Finite Difference Time Domain (FDTD) technique has been applied to a wide variety of electromagnetic analysis problems, including shielding and scattering. However, the method has not been extensively applied to antennas. In this short paper calculations of self and mutual admittances between wire antennas are made using FDTD and compared with results obtained using the Method of Moments. The agreement is quite good, indicating the possibilities for FDTD application to antenna impedance and coupling.
Finite difference time domain modeling of spiral antennas
NASA Technical Reports Server (NTRS)
Penney, Christopher W.; Beggs, John H.; Luebbers, Raymond J.
1992-01-01
The objectives outlined in the original proposal for this project were to create a well-documented computer analysis model based on the finite-difference, time-domain (FDTD) method that would be capable of computing antenna impedance, far-zone radiation patterns, and radar cross-section (RCS). The ability to model a variety of penetrable materials in addition to conductors is also desired. The spiral antennas under study by this project meet these requirements since they are constructed of slots cut into conducting surfaces which are backed by dielectric materials.
Finite difference time domain analysis of chirped dielectric gratings
NASA Technical Reports Server (NTRS)
Hochmuth, Diane H.; Johnson, Eric G.
1993-01-01
The finite difference time domain (FDTD) method for solving Maxwell's time-dependent curl equations is accurate, computationally efficient, and straight-forward to implement. Since both time and space derivatives are employed, the propagation of an electromagnetic wave can be treated as an initial-value problem. Second-order central-difference approximations are applied to the space and time derivatives of the electric and magnetic fields providing a discretization of the fields in a volume of space, for a period of time. The solution to this system of equations is stepped through time, thus, simulating the propagation of the incident wave. If the simulation is continued until a steady-state is reached, an appropriate far-field transformation can be applied to the time-domain scattered fields to obtain reflected and transmitted powers. From this information diffraction efficiencies can also be determined. In analyzing the chirped structure, a mesh is applied only to the area immediately around the grating. The size of the mesh is then proportional to the electric size of the grating. Doing this, however, imposes an artificial boundary around the area of interest. An absorbing boundary condition must be applied along the artificial boundary so that the outgoing waves are absorbed as if the boundary were absent. Many such boundary conditions have been developed that give near-perfect absorption. In this analysis, the Mur absorbing boundary conditions are employed. Several grating structures were analyzed using the FDTD method.
Finite difference time domain implementation of surface impedance boundary conditions
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Yee, Kane S.; Kunz, Karl S.
1991-01-01
Surface impedance boundary conditions are employed to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In a finite difference solution, they also can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. Two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a 2-D demonstration. Extensions to 3-D should be straightforward.
Finite-difference time-domain simulation of GPR data
NASA Astrophysics Data System (ADS)
Chen, How-Wei; Huang, Tai-Min
1998-10-01
Simulation of digital ground penetrating radar (GPR) wave propagation in two-dimensional (2-D) media is developed, tested, implemented, and applied using a time-domain staggered-grid finite-difference (FD) numerical method. Three types of numerical algorithms for constructing synthetic common-shot, constant-offset radar profiles based on an actual transmitter-to-receiver configuration and based on the exploding reflector concept are demonstrated to mimic different types of radar survey geometries. Frequency-dependent attenuation is also incorporated to account for amplitude decay and time shift in the recorded responses. The algorithms are based on an explicit FD solution to Maxwell's curl equations. In addition, the first-order TE mode responses of wave propagation phenomena are considered due to the operating frequency of current GPR instruments. The staggered-grid technique is used to sample the fields and approximate the spatial derivatives with fourth-order FDs. The temporal derivatives are approximated by an explicit second-order difference time-marching scheme. By combining paraxial approximation of the one-way wave equation ( A2) and the damping mechanisms (sponge filter), we propose a new composite absorbing boundary conditions (ABC) algorithm that effectively absorb both incoming and outgoing waves. To overcome the angle- and frequency-dependent characteristic of the absorbing behaviors, each ABC has two types of absorption mechanism. The first ABC uses a modified Clayton and Enquist's A2 condition. Moreover, a fixed and a floating A2 ABC that operates at one grid point is proposed. The second ABC uses a damping mechanism. By superimposing artificial damping and by alternating the physical attenuation properties and impedance contrast of the media within the absorbing region, those waves impinging on the boundary can be effectively attenuated and can prevent waves from reflecting back into the grid. The frequency-dependent characteristic of the damping
Finite-difference time-domain simulation of spacetime cloak.
Cornelius, Jason; Liu, Jinjie; Brio, Moysey
2014-05-19
In this work, we present a numerical method that remedies the instabilities of the conventional FDTD approach for solving Maxwell's equations in a space-time dependent magneto-electric medium with direct application to the simulation of the recently proposed spacetime cloak. We utilize a dual grid FDTD method overlapped in the time domain to provide a stable approach for the simulation of a magneto-electric medium with time and space varying permittivity, permeability and coupling coefficient. The developed method can be applied to explore other new physical possibilities offered by spacetime cloaking, metamaterials, and transformation optics.
Finite difference time domain implementation of surface impedance boundary conditions
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Yee, Kane S.; Kunz, Karl S.
1991-01-01
Surface impedance boundary conditions are employed to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In the finite difference solution, they also can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. Here, two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a two dimensional demonstration. Extensions to three dimensions should be straightforward.
Transient analysis of printed lines using finite-difference time-domain method
Ahmed, Shahid
2012-03-29
Comprehensive studies of ultra-wideband pulses and electromagnetic coupling on printed coupled lines have been performed using full-wave 3D finite-difference time-domain analysis. Effects of unequal phase velocities of coupled modes, coupling between line traces, and the frequency dispersion on the waveform fidelity and crosstalk have been investigated in detail. To discriminate the contributions of different mechanisms into pulse evolution, single and coupled microstrip lines without (ϵ_{r} = 1) and with (ϵ_{r} > 1) dielectric substrates have been examined. To consistently compare the performance of the coupled lines with substrates of different permittivities and transients of different characteristic times, a generic metric similar to the electrical wavelength has been introduced. The features of pulse propagation on coupled lines with layered and pedestal substrates and on the irregular traces have been explored. Finally, physical interpretations of the simulation results are discussed in the paper.
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.; Yee, Kane S.
1991-01-01
Surface impedance boundary conditions are employed to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In a finite difference solution, they also can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media, throughout the solution volume. A 1-D implementation for a surface impedance boundary condition for good conductors in the Finite Difference Time Domain (FDTD) technique.
Parallel electromagnetic simulator based on the Finite-Difference Time Domain method
NASA Astrophysics Data System (ADS)
Walendziuk, Wojciech
2006-03-01
In the following paper the parallel tool for electromagnetic field distribution analysis is presented. The main simulation programme is based on the parallel algorithm of the Finite-Difference Time-Domain method and use Message Passing Interface as a communication library. In the paper also ways of communications among computation nodes in a parallel environment and efficiency of the parallel algorithm are presented.
Parallel 3-D viscoelastic finite difference seismic modelling
NASA Astrophysics Data System (ADS)
Bohlen, Thomas
2002-10-01
Computational power has advanced to a state where we can begin to perform wavefield simulations for realistic (complex) 3-D earth models at frequencies of interest to both seismologists and engineers. On serial platforms, however, 3-D calculations are still limited to small grid sizes and short seismic wave traveltimes. To make use of the efficiency of network computers a parallel 3-D viscoelastic finite difference (FD) code is implemented which allows to distribute the work on several PCs or workstations connected via standard ethernet in an in-house network. By using the portable message passing interface standard (MPI) for the communication between processors, running times can be reduced and grid sizes can be increased significantly. Furthermore, the code shows good performance on massive parallel supercomputers which makes the computation of very large grids feasible. This implementation greatly expands the applicability of the 3-D elastic/viscoelastic finite-difference modelling technique by providing an efficient, portable and practical C-program.
NASA Technical Reports Server (NTRS)
Beggs, John H.; Luebbers, Raymond J.; Kunz, Karl S.; Yee, Kane S.
1991-01-01
Surface impedance boundary conditions are used to reduce the solution volume during the analysis of scattering from lossy dielectric objects. In a finite difference solution, they also can be used to avoid using small cells, made necessary by shorter wavelengths in conducting media, throughout the solution volume. A one dimensional implementation is presented for a surface impedance boundary condition for good conductors in the Finite Difference Time Domain (FDTD) technique. In order to illustrate the FDTD surface impedance boundary condition, a planar air-lossy dielectric interface is considered.
Gabran, S R I; Saad, J H; Salama, M M A; Mansour, R R
2009-01-01
This paper demonstrates the electromagnetic modeling and simulation of an implanted Medtronic deep brain stimulation (DBS) electrode using finite difference time domain (FDTD). The model is developed using Empire XCcel and represents the electrode surrounded with brain tissue assuming homogenous and isotropic medium. The model is created to study the parameters influencing the electric field distribution within the tissue in order to provide reference and benchmarking data for DBS and intra-cortical electrode development.
Accurate finite-difference time-domain simulation of anisotropic media by subpixel smoothing.
Oskooi, Ardavan F; Kottke, Chris; Johnson, Steven G
2009-09-15
Finite-difference time-domain methods suffer from reduced accuracy when discretizing discontinuous materials. We previously showed that accuracy can be significantly improved by using subpixel smoothing of the isotropic dielectric function, but only if the smoothing scheme is properly designed. Using recent developments in perturbation theory that were applied to spectral methods, we extend this idea to anisotropic media and demonstrate that the generalized smoothing consistently reduces the errors and even attains second-order convergence with resolution.
NASA Technical Reports Server (NTRS)
Lansing, Faiza S.; Rascoe, Daniel L.
1993-01-01
This paper presents a modified Finite-Difference Time-Domain (FDTD) technique using a generalized conformed orthogonal grid. The use of the Conformed Orthogonal Grid, Finite Difference Time Domain (GFDTD) enables the designer to match all the circuit dimensions, hence eliminating a major source o error in the analysis.
3D finite-difference seismic migration with parallel computers
Ober, C.C.; Gjertsen, R.; Minkoff, S.; Womble, D.E.
1998-11-01
The ability to image complex geologies such as salt domes in the Gulf of Mexico and thrusts in mountainous regions is essential for reducing the risk associated with oil exploration. Imaging these structures, however, is computationally expensive as datasets can be terabytes in size. Traditional ray-tracing migration methods cannot handle complex velocity variations commonly found near such salt structures. Instead the authors use the full 3D acoustic wave equation, discretized via a finite difference algorithm. They reduce the cost of solving the apraxial wave equation by a number of numerical techniques including the method of fractional steps and pipelining the tridiagonal solves. The imaging code, Salvo, uses both frequency parallelism (generally 90% efficient) and spatial parallelism (65% efficient). Salvo has been tested on synthetic and real data and produces clear images of the subsurface even beneath complicated salt structures.
Finite difference time domain analysis of microwave ferrite devices and mobile antenna systems
NASA Astrophysics Data System (ADS)
Yildirim, Bahadir Suleyman
This dissertation presents analysis and design of shielded mobile antenna systems and microwave ferrite devices using a finite-difference time-domain method. Novel shielded antenna structures suitable for cellular communications have been analyzed and designed with emphasize on reducing excessive radiated energy absorbed in user's head and hand, while keeping the antenna performance at its peak in the presence of user. These novel antennas include a magnetically shielded antenna, a dual-resonance shielded antenna and, a shorted and truncated microstrip antenna. The effect of magnetic coating on the performance of a shielded monopole antenna is studied extensively. A parametric study is performed to analyze the dual-resonance phenomenon observed in the dual-resonance shielded antenna, optimize the antenna design within the cellular communications band, and improve the antenna performance. Input impedance, near and far fields of the dual-resonance shielded antenna are calculated using the finite-difference time-domain method. Experimental validation is also presented. In addition, performance of a shorted and truncated microstrip antenna has been investigated over a wide range of substrate parameters and dimensions. Objectives of the research work also include development of a finite-difference time-domain technique to accurately model magnetically anisotropic media, including the effect of non-uniform magnetization within the finite-size ferrite material due to demagnetizing fields. A slow wave thin film isolator and a stripline disc junction circulator are analyzed. An extensive parametric study calculates wide-band frequency-dependent parameters of these devices for various device dimensions and material parameters. Finally, a ferrite-filled stripline configuration is analyzed to study the non- linear behaviour of ferrite by introducing a modified damping factor.
Polarization-current-based, finite-difference time-domain, near-to-far-field transformation.
Zeng, Yong; Moloney, Jerome V
2009-05-15
A near-to-far-field transformation algorithm for three-dimensional finite-difference time-domain is presented in this Letter. This approach is based directly on the polarization current of the scatterer, not the scattered near fields. It therefore eliminates the numerical errors originating from the spatial offset of the E and H fields, inherent in the standard near-to-far-field transformation. The proposed method is validated via direct comparisons with the analytical Lorentz-Mie solutions of plane waves scattered by large dielectric and metallic spheres with strong forward-scattering lobes.
NASA Astrophysics Data System (ADS)
Adhikari, Achyut; Dev, Kapil; Asundi, Anand
2016-11-01
Wire grid polarizers (WGP), are sub-wavelength gratings with applications in display projection system due to their compact size, wide field of view and long-term stability. Measurement and testing of these structures are important to optimize their use. This is done by first measuring the Mueller matrix of the WGP using a Mueller matrix polarimeter. Next the finite difference time domain (FDTD) method is used to simulate a similar Mueller matrix thus providing the period and step height of the WGP. This approach may lead to more generic determination of sub-wavelength structures including diffractive optical structures.
The electromagnetic modeling of thin apertures using the finite-difference time-domain technique
NASA Technical Reports Server (NTRS)
Demarest, Kenneth R.
1987-01-01
A technique which computes transient electromagnetic responses of narrow apertures in complex conducting scatterers was implemented as an extension of previously developed Finite-Difference Time-Domain (FDTD) computer codes. Although these apertures are narrow with respect to the wavelengths contained within the power spectrum of excitation, this technique does not require significantly more computer resources to attain the increased resolution at the apertures. In the report, an analytical technique which utilizes Babinet's principle to model the apertures is developed, and an FDTD computer code which utilizes this technique is described.
NASA Astrophysics Data System (ADS)
Yamamoto, Kaho; Iwai, Yosuke; Uchida, Yoshiaki; Nishiyama, Norikazu
2016-08-01
We numerically analyzed the light propagation in cholesteric liquid crystalline (CLC) droplet array by the finite-difference time-domain (FDTD) method. The FDTD method successfully reproduced the experimental light path observed in the complicated photonic structure of the CLC droplet array more accurately than the analysis of CLC droplets by geometric optics with Bragg condition, and this method help us understand the polarization of the propagating light waves. The FDTD method holds great promise for the design of various photonic devices composed of curved photonic materials like CLC droplets and microcapsules.
Finite Difference Time Domain Electromagnetic Scattering from Frequency-Dependent Lossy Materials
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
During this effort the tasks specified in the Statement of Work have been successfully completed. The extension of Finite Difference Time Domain (FDTD) to more complicated materials has been made. A three-dimensional FDTD code capable of modeling interactions with both dispersive dielectric and magnetic materials has been written, validated, and documented. This code is efficient and is capable of modeling interesting targets using a modest computer work station platform. However, in addition to the tasks in the Statement of Work, a significant number of other FDTD extensions and calculations have been made. RCS results for two different plate geometries have been reported. The FDTD method has been extended to computing far zone time domain results in two dimensions. Finally, the capability to model nonlinear materials has been incorporated into FDTD and validated. The FDTD computer codes developed have been supplied, along with documentation, and preprints describing the other FDTD advances have been included with this report as attachments.
Finite-difference time-domain simulation of thermal noise in open cavities
Andreasen, Jonathan; Cao Hui; Taflove, Allen; Kumar, Prem |; Cao Changqi
2008-02-15
A numerical model based on the finite-difference time-domain (FDTD) method is developed to simulate thermal noise in open cavities owing to output coupling. The absorbing boundary of the FDTD grid is treated as a blackbody, whose thermal radiation penetrates the cavity in the grid. The calculated amount of thermal noise in a one-dimensional dielectric cavity recovers the standard result of the quantum Langevin equation in the Markovian regime. Our FDTD simulation also demonstrates that in the non-Markovian regime the buildup of the intracavity noise field depends on the ratio of the cavity photon lifetime to the coherence time of thermal radiation. The advantage of our numerical method is that the thermal noise is introduced in the time domain without prior knowledge of cavity modes.
Kemp, Jonathan A; Bilbao, Stefan; McMaster, James; Smith, Richard A
2013-08-01
Wave separation within a trumpet is presented using three high pressure microphones to measure pressure waves within the curved, constant cross-section tuning slide of the instrument while the instrument was being played by a virtuoso trumpet player. A closer inter-microphone spacing was possible in comparison to previous work through the use of time domain windowing on non-causal transfer functions and performing wave separation in the frequency domain. Time domain plots of the experimental wave separation were then compared to simulations using a physical model based on a time domain finite difference simulation of the trumpet bore coupled to a one mass, two degree of freedom lip model. The time domain and frequency spectra of the measured and synthesized sounds showed a similar profile, with the sound produced by the player showing broader spectral peaks in experimental data. Using a quality factor of 5 for the lip model was found to give greater agreement between the simulated and experimental starting transients in comparison to the values in the range 1-3 often assumed. Deviations in the spectral content and wave shape provide insights into the areas where future research may be directed in improving the accuracy of physical modeling synthesis.
NASA Technical Reports Server (NTRS)
Ryan, Deirdre A.; Langdon, H. Scott; Beggs, John H.; Steich, David J.; Luebbers, Raymond J.; Kunz, Karl S.
1992-01-01
The approach chosen to model steady state scattering from jet engines with moving turbine blades is based upon the Finite Difference Time Domain (FDTD) method. The FDTD method is a numerical electromagnetic program based upon the direct solution in the time domain of Maxwell's time dependent curl equations throughout a volume. One of the strengths of this method is the ability to model objects with complicated shape and/or material composition. General time domain functions may be used as source excitations. For example, a plane wave excitation may be specified as a pulse containing many frequencies and at any incidence angle to the scatterer. A best fit to the scatterer is accomplished using cubical cells in the standard cartesian implementation of the FDTD method. The material composition of the scatterer is determined by specifying its electrical properties at each cell on the scatterer. Thus, the FDTD method is a suitable choice for problems with complex geometries evaluated at multiple frequencies. It is assumed that the reader is familiar with the FDTD method.
3D Finite Difference Modelling of Basaltic Region
NASA Astrophysics Data System (ADS)
Engell-Sørensen, L.
2003-04-01
The main purpose of the work was to generate realistic data to be applied for testing of processing and migration tools for basaltic regions. The project is based on the three - dimensional finite difference code (FD), TIGER, made by Sintef. The FD code was optimized (parallelized) by the author, to run on parallel computers. The parallel code enables us to model large-scale realistic geological models and to apply traditional seismic and micro seismic sources. The parallel code uses multiple processors in order to manipulate subsets of large amounts of data simultaneously. The general anisotropic code uses 21 elastic coefficients. Eight independent coefficients are needed as input parameters for the general TI medium. In the FD code, the elastic wave field computation is implemented by a higher order FD solution to the elastic wave equation and the wave fields are computed on a staggered grid, shifted half a node in one or two directions. The geological model is a gridded basalt model, which covers from 24 km to 37 km of a real shot line in horizontal direction and from the water surface to the depth of 3.5 km. The 2frac {1}{2}D model has been constructed using the compound modeling software from Norsk Hydro. The vertical parameter distribution is obtained from observations in two wells. At The depth of between 1100 m to 1500 m, a basalt horizon covers the whole sub surface layers. We have shown that it is possible to simulate a line survey in realistic (3D) geological models in reasonable time by using high performance computers. The author would like to thank Norsk Hydro, Statoil, GEUS, and SINTEF for very helpful discussions and Parallab for being helpful with the new IBM, p690 Regatta system.
Finite-difference time-domain analysis for the dynamics and diffraction of exciton-polaritons.
Chen, Minfeng; Chang, Yia-Chung; Hsieh, Wen-Feng
2015-10-01
We adopted a finite-difference time-domain (FDTD) scheme to simulate the dynamics and diffraction of exciton-polaritons, governed by the coupling of polarization waves with electromagnetic waves. The polarization wave, an approximate solution to the Schrödinger's equation at low frequencies, essentially captures the exciton behavior. Numerical stability of the scheme is analyzed and simple examples are provided to prove its validity. The system considered is both temporally and spatially dispersive, for which the FDTD analysis has attracted less attention in the literature. Here, we demonstrate that the FDTD scheme could be useful for studying the optical response of the exciton-polariton and its dynamics. The diffraction of a polariton wave from a polaritonic grating is also considered, and many sharp resonances are found, which manifest the interference effect of polariton waves. This illustrates that the measurement of transmittance or reflectance near polariton resonance can reveal subwavelength features in semiconductors, which are sensitive to polariton scattering.
Finite difference time domain method for simulation of damage initiation in thin film coatings
NASA Astrophysics Data System (ADS)
Smalakys, Linas; Momgaudis, Balys; Grigutis, Robertas; Melninkaitis, Andrius
2016-12-01
Time resolved digital holography (TRDH) is a versatile tool that provides valuable insights into the dynamics of femtosecond damage initiation by providing spatiotemporal information of excited material. However, interpreting of TRDH data in thin film dielectric coatings is rather complicated without appropriate theoretical models that are able to correctly describe underlying nature of damage formation. Therefore, a model based on finite difference time domain (FDTD) method with complete Keldysh theory for nonlinear ionization of atoms and multiple rate equation (MRE) method for conduction band electrons was developed. The model was used to reproduce both temporal and spatial characteristics of TRDH experiment performed on Ta2O5 dielectric coating. Fitted material parameters were then applied to indirectly estimate LIDT of the coating.
Application of the symplectic finite-difference time-domain scheme to electromagnetic simulation
Sha, Wei . E-mail: ws108@ahu.edu.cn; Huang, Zhixiang; Wu, Xianliang; Chen, Mingsheng
2007-07-01
An explicit fourth-order finite-difference time-domain (FDTD) scheme using the symplectic integrator is applied to electromagnetic simulation. A feasible numerical implementation of the symplectic FDTD (SFDTD) scheme is specified. In particular, new strategies for the air-dielectric interface treatment and the near-to-far-field (NFF) transformation are presented. By using the SFDTD scheme, both the radiation and the scattering of three-dimensional objects are computed. Furthermore, the energy-conserving characteristic hold for the SFDTD scheme is verified under long-term simulation. Numerical results suggest that the SFDTD scheme is more efficient than the traditional FDTD method and other high-order methods, and can save computational resources.
A finite difference-time domain technique for modeling narrow apertures in conducting scatterers
NASA Technical Reports Server (NTRS)
Demarest, Kenneth R.
1987-01-01
The finite difference-time domain (FDTD) technique has proven to be a valuable tool for the calculation of the transient and steady state scattering characteristics of relatively complex scatterer and source configurations. In spite of its usefulness, it exhibits serious deficiencies when used to analyze geometries that contain fine detail. An FDTD technique is described that utilizes Babinet's principle to decouple the regions on both sides of the aperture. The result is an FDTD technique that is capable of modeling apertures that are much smaller than the spatial grid used in the analysis and yet is not perturbed by numerical noise when used in the 'scattered field' mode. Numerical results are presented that show the field penetration through cavity-backed apertures that are much smaller than the spatial grid used during the solution.
Finite difference time domain calculation of transients in antennas with nonlinear loads
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.; Kunz, Karl S.; Chamberlin, Kent
1991-01-01
In this paper transient fields for antennas with more general geometries are calculated directly using Finite Difference Time Domain methods. In each FDTD cell which contains a nonlinear load, a nonlinear equation is solved at each time step. As a test case the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed using this approach. The results agree well with both calculated and measured results previously published. The approach given here extends the applicability of the FDTD method to problems involving scattering from targets including nonlinear loads and materials, and to coupling between antennas containing nonlinear loads. It may also be extended to propagation through nonlinear materials.
The analysis of reactively loaded microstrip antennas by finite difference time domain modelling
NASA Technical Reports Server (NTRS)
Hilton, G. S.; Beach, M. A.; Railton, C. J.
1990-01-01
In recent years, much interest has been shown in the use of printed circuit antennas in mobile satellite and communications terminals at microwave frequencies. Although such antennas have many advantages in weight and profile size over more conventional reflector/horn configurations, they do, however, suffer from an inherently narrow bandwidth. A way of optimizing the bandwidth of such antennas by an electronic tuning technique using a loaded probe mounted within the antenna structure is examined, and the resulting far-field radiation patterns are shown. Simulation results from a 2D finite difference time domain (FDTD) model for a rectangular microstrip antenna loaded with shorting pins are given and compared to results obtained with an actual antenna. It is hoped that this work will result in a design package for the analysis of microstrip patch antenna elements.
Samak, M. Mosleh E. Abu; Bakar, A. Ashrif A.; Kashif, Muhammad; Zan, Mohd Saiful Dzulkifly
2016-01-01
This paper discusses numerical analysis methods for different geometrical features that have limited interval values for typically used sensor wavelengths. Compared with existing Finite Difference Time Domain (FDTD) methods, the alternating direction implicit (ADI)-FDTD method reduces the number of sub-steps by a factor of two to three, which represents a 33% time savings in each single run. The local one-dimensional (LOD)-FDTD method has similar numerical equation properties, which should be calculated as in the previous method. Generally, a small number of arithmetic processes, which result in a shorter simulation time, are desired. The alternating direction implicit technique can be considered a significant step forward for improving the efficiency of unconditionally stable FDTD schemes. This comparative study shows that the local one-dimensional method had minimum relative error ranges of less than 40% for analytical frequencies above 42.85 GHz, and the same accuracy was generated by both methods.
Development of the Finite Difference Time Domain Method on a Lebedev Grid for Anisotropic Materials
NASA Astrophysics Data System (ADS)
Nauta, Marcel D.
The finite-difference time-domain (FDTD) method is derived on a Lebedev grid, instead of the standard Yee grid, to better represent the constitutive relations in anisotropic materials. The Lebedev grid extends the Yee grid by approximating Maxwell's equations with tensor constitutive relations using only central differences. A dispersion relation with stability criteria is derived and it is proven that the Lebedev grid has a consistent calculus. An integral derivation of the update equations illustrates how to appropriately excite the grid. This approach is also used to derive the update equations at planar material interfaces and domain edge PEC. Lebedev grid results are compared with analytical and Yee grid solutions using an equal memory comparison. Numerical results show that the Lebedev grid suffers greater dispersion error but better represents material interfaces. Focus is given to generalizing the concepts that make the Yee grid robust for isotropic materials. Keywords: FDTD, anisotropic materials, Lebedev grid, collocated grids.
Inclusion of lumped elements in finite difference time domain electromagnetic calculations
Thomas, V.A.; Jones, M.E.; Mason, R.J.
1994-12-31
A general approach for including lumped circuit elements in a finite difference, time domain (FD-TD) solution of Maxwell`s equations is presented. The methodology allows the direct access to SPICE to model the lumped circuits, while the full 3-Dimensional solution to Maxwell`s equations provides the electromagnetic field evolution. This type of approach could be used to mode a pulsed power machine by using a SPICE model for the driver and using an electromagnetic PIC code for the plasma/electromagnetics calculation. The evolution of the driver can be made self consistent with the behavior of the plasma load. Other applications are also possible, including modeling of nonlinear microwave circuits (as long as the non-linearities may be expressed in terms of a lumped element) and self-consistent calculation of very high speed computer interconnections and digital circuits.
NASA Astrophysics Data System (ADS)
Matsui, Tatsunosuke; Okajima, Akiko
2014-01-01
The photonic nanojet (PNJ) from a microcylinder with liquid crystals (LCs) showing tangential molecular alignment inside the microcylinder has been numerically analyzed on the basis of the finite-difference time-domain method. By introducing a small degree of birefringence, the characteristics of the PNJ, such as propagation length and polarization state, can be drastically changed. The azimuth angle and the ellipticity of the elliptically polarized PNJ obtained from the LC microcylinder changes within the propagation lengths in the micrometer range even in the isotropic matrix, which might be attributed to the jet like spatial profile of the PNJ. By using LC microcylinders or microspheres, we may obtain a rich variety of PNJs with unique polarization characteristics, which might open a new avenue for the development of novel optical devices with electrical tunability.
Finite difference time domain calculation of transients in antennas with nonlinear loads
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.; Kunz, Karl S.; Chamberlin, Kent
1991-01-01
Determining transient electromagnetic fields in antennas with nonlinear loads is a challenging problem. Typical methods used involve calculating frequency domain parameters at a large number of different frequencies, then applying Fourier transform methods plus nonlinear equation solution techniques. If the antenna is simple enough so that the open circuit time domain voltage can be determined independently of the effects of the nonlinear load on the antennas current, time stepping methods can be applied in a straightforward way. Here, transient fields for antennas with more general geometries are calculated directly using Finite Difference Time Domain (FDTD) methods. In each FDTD cell which contains a nonlinear load, a nonlinear equation is solved at each time step. As a test case, the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed using this approach. The results agree well with both calculated and measured results previously published. The approach given here extends the applicability of the FDTD method to problems involving scattering from targets, including nonlinear loads and materials, and to coupling between antennas containing nonlinear loads. It may also be extended to propagation through nonlinear materials.
Consistent modeling of boundaries in acoustic finite-difference time-domain simulations.
Häggblad, Jon; Engquist, Björn
2012-09-01
The finite-difference time-domain method is one of the most popular for wave propagation in the time domain. One of its advantages is the use of a structured staggered grid, which makes it simple and efficient on modern computer architectures. A drawback, however, is the difficulty in approximating oblique boundaries, having to resort to staircase approximations. In many scattering problems this means that the grid resolution required to obtain an accurate solution is much higher than what is dictated by propagation in a homogeneous material. In this paper zero boundary data are considered, first for the velocity and then the pressure. These two forms of boundary conditions model perfectly rigid and pressure-release boundaries, respectively. A simple and efficient method to consistently model curved rigid boundaries in two dimensions was developed in Tornberg and Engquist [J. Comput. Phys. 227, 6922-6943 (2008)]. Here this treatment is generalized to three dimensions. Based on the approach of this method, a technique to model pressure-release surfaces with second order accuracy and without additional restriction on the timestep is also introduced. The structure of the standard method is preserved, making it easy to use in existing solvers. The effectiveness is demonstrated in several numerical tests.
NASA Technical Reports Server (NTRS)
Sun, W.; Loeb, N. G.; Fu, Q.
2002-01-01
The three-dimensional (3-D) finite-difference time-domain (FDTD) technique has been extended to simulate light scattering and absorption by nonspherical particles embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition is used to truncate the computational domain. When computing the single-scattering properties of a particle in an absorbing dielectric medium, we derive the single-scattering properties including scattering phase functions, extinction, and absorption efficiencies using a volume integration of the internal field. A Mie solution for light scattering and absorption by spherical particles in an absorbing medium is used to examine the accuracy of the 3-D UPML FDTD code. It is found that the errors in the extinction and absorption efficiencies from the 3-D UPML FDTD are less than similar to 2%. The errors in the scattering phase functions are typically less than similar to 5%. The errors in the asymmetry factors are less than similar to 0.l%. For light scattering by particles in free space, the accuracy of the 3-D UPML FDTD scheme is similar to a previous model.
Finite-difference Time-domain Modeling of Laser-induced Periodic Surface Structures
NASA Astrophysics Data System (ADS)
Römer, G. R. B. E.; Skolski, J. Z. P.; Oboňa, J. Vincenc; Veld, A. J. Huis in't.
Laser-induced periodic surface structures (LIPSSs) consist of regular wavy surface structures with amplitudes the (sub)micrometer range and periodicities in the (sub)wavelength range. It is thought that periodically modulated absorbed laser energy is initiating the growth of LIPSSs. The "Sipe theory" (or "Efficacy factor theory") provides an analytical model of the interaction of laser radiation with a rough surface of the material, predicting modulated absorption just below the surface of the material. To address some limitations of this model, the finite-difference time-domain (FDTD) method was employed to numerically solve the two coupled Maxwell's curl equations, for linear, isotropic, dispersive materials with no magnetic losses. It was found that the numerical model predicts the periodicity and orientation of various types of LIPSSs which might occur on the surface of the material sample. However, it should be noted that the numerical FDTD model predicts the signature or "fingerprints" of several types of LIPSSs, at different depths, based on the inhomogeneously absorbed laser energy at those depths. Whether these types of (combinations of) LIPSSs will actually form on a material will also depend on other physical phenomena, such as the excitation of the material, as well as thermal-mechanical phenomena, such as the state and transport of the material.
NASA Astrophysics Data System (ADS)
Ibey, Bennett L.; Payne, Jason A.; Mixon, Dustin G.; Thomas, Robert J.; Roach, William P.
2008-02-01
Assessing the biological reaction to electromagnetic (EM) radiation of all frequencies and intensities is essential to the understanding of both the potential damage caused by the radiation and the inherent mechanisms within biology that respond, protect, or propagate damage to surrounding tissues. To understand this reaction, one may model the electromagnetic irradiation of tissue phantoms according to empirically measured or intelligently estimated dielectric properties. Of interest in this study is the terahertz region (0.2-2.0 THz), ranging from millimeter to infrared waves, which has been studied only recently due to lack of efficient sources. The specific interaction between this radiation and human tissue is greatly influenced by the significant EM absorption of water across this range, which induces a pronounced heating of the tissue surface. This study compares the Monte Carlo Multi-Layer (MCML) and Finite Difference Time Domain (FDTD) approaches for modeling the terahertz irradiation of human dermal tissue. Two congruent simulations were performed on a one-dimensional tissue model with unit power intensity profile. This works aims to verify the use of either technique for modeling terahertz-tissue interaction for minimally scattering tissues.
Kooijman, Gerben; Ouweltjes, Okke
2009-04-01
A lumped element electroacoustic model for a synthetic jet actuator is presented. The model includes the nonlinear flow resistance associated with flow separation and employs a finite difference scheme in the time domain. As opposed to more common analytical frequency domain electroacoustic models, in which the nonlinear resistance can only be considered as a constant, it allows the calculation of higher harmonics, i.e., distortion components, generated as a result of this nonlinear resistance. Model calculations for the time-averaged momentum flux of the synthetic jet as well as the radiated sound power spectrum are compared to experimental results for various configurations. It is shown that a significantly improved prediction of the momentum flux-and thus flow velocity-of the jet is obtained when including the nonlinear resistance. Here, the current model performs slightly better than an analytical model. For the power spectrum of radiated sound, a reasonable agreement is obtained when assuming a plausible slight asymmetry in the nonlinear resistance. However, results suggest that loudspeaker nonlinearities play a significant role as well in the generation of the first few higher harmonics.
Udagedara, Indika; Premaratne, Malin; Rukhlenko, Ivan D; Hattori, Haroldo T; Agrawal, Govind P
2009-11-09
Finite-difference time-domain (FDTD) simulations of any electromagnetic problem require truncation of an often-unbounded physical region by an electromagnetically bounded region by deploying an artificial construct known as the perfectly matched layer (PML). As it is not possible to construct a universal PML that is non-reflective for different materials, PMLs that are tailored to a specific problem are required. For example, depending on the number of dispersive materials being truncated at the boundaries of a simulation region, an FDTD code may contain multiple sets of update equations for PML implementations. However, such an approach is prone to introducing coding errors. It also makes it extremely difficult to maintain and upgrade an existing FDTD code. In this paper, we solve this problem by developing a new, unified PML algorithm that can effectively truncate all types of linearly dispersive materials. The unification of the algorithm is achieved by employing a general form of the medium permittivity that includes three types of dielectric response functions, known as the Debye, Lorentz, and Drude response functions, as particular cases. We demonstrate the versatility and flexibility of the new formulation by implementing a single FDTD code to simulate absorption of electromagnetic pulse inside a medium that is adjacent to dispersive materials described by different dispersion models. The proposed algorithm can also be used for simulations of optical phenomena in metamaterials and materials exhibiting negative refractive indices.
Evaluation of a thin-slot formalism for finite-difference time-domain electromagnetics codes
Turner, C.D.; Bacon, L.D.
1987-03-01
A thin-slot formalism for use with finite-difference time-domain (FDTD) electromagnetics codes has been evaluated in both two and three dimensions. This formalism allows narrow slots to be modeled in the wall of a scatterer without reducing the space grid size to the gap width. In two dimensions, the evaluation involves the calculation of the total fields near two infinitesimally thin coplanar strips separated by a gap. A method-of-moments (MoM) solution of the same problem is used as a benchmark for comparison. Results in two dimensions show that up to 10% error can be expected in total electric and magnetic fields both near (lambda/40) and far (1 lambda) from the slot. In three dimensions, the evaluation is similar. The finite-length slot is placed in a finite plate and an MoM surface patch solution is used for the benchmark. These results, although less extensive than those in two dimensions, show that slightly larger errors can be expected. Considering the approximations made near the slot in incorporating the formalism, the results are very promising. Possibilities also exist for applying this formalism to walls of arbitrary thickness and to other types of slots, such as overlapping joints. 11 refs., 25 figs., 6 tabs.
Transfer-matrix approach for finite-difference time-domain simulation of periodic structures.
Deinega, Alexei; Belousov, Sergei; Valuev, Ilya
2013-11-01
Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment.
Transfer-matrix approach for finite-difference time-domain simulation of periodic structures
NASA Astrophysics Data System (ADS)
Deinega, Alexei; Belousov, Sergei; Valuev, Ilya
2013-11-01
Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment.
Simulation of optical devices using parallel finite-difference time-domain method
NASA Astrophysics Data System (ADS)
Li, Kang; Kong, Fanmin; Mei, Liangmo; Liu, Xin
2005-11-01
This paper presents a new parallel finite-difference time-domain (FDTD) numerical method in a low-cost network environment to stimulate optical waveguide characteristics. The PC motherboard based cluster is used, as it is relatively low-cost, reliable and has high computing performance. Four clusters are networked by fast Ethernet technology. Due to the simplicity nature of FDTD algorithm, a native Ethernet packet communication mechanism is used to reduce the overhead of the communication between the adjacent clusters. To validate the method, a microcavity ring resonator based on semiconductor waveguides is chosen as an instance of FDTD parallel computation. Speed-up rate under different division density is calculated. From the result we can conclude that when the decomposing size reaches a certain point, a good parallel computing speed up will be maintained. This simulation shows that through the overlapping of computation and communication method and controlling the decomposing size, the overhead of the communication of the shared data will be conquered. The result indicates that the implementation can achieve significant speed up for the FDTD algorithm. This will enable us to tackle the larger real electromagnetic problem by the low-cost PC clusters.
Finite-difference time-domain synthesis of infrasound propagation through an absorbing atmosphere.
de Groot-Hedlin, C
2008-09-01
Equations applicable to finite-difference time-domain (FDTD) computation of infrasound propagation through an absorbing atmosphere are derived and examined in this paper. It is shown that over altitudes up to 160 km, and at frequencies relevant to global infrasound propagation, i.e., 0.02-5 Hz, the acoustic absorption in dB/m varies approximately as the square of the propagation frequency plus a small constant term. A second-order differential equation is presented for an atmosphere modeled as a compressible Newtonian fluid with low shear viscosity, acted on by a small external damping force. It is shown that the solution to this equation represents pressure fluctuations with the attenuation indicated above. Increased dispersion is predicted at altitudes over 100 km at infrasound frequencies. The governing propagation equation is separated into two partial differential equations that are first order in time for FDTD implementation. A numerical analysis of errors inherent to this FDTD method shows that the attenuation term imposes additional stability constraints on the FDTD algorithm. Comparison of FDTD results for models with and without attenuation shows that the predicted transmission losses for the attenuating media agree with those computed from synthesized waveforms.
Finite-difference time-domain approach to acoustic radiation force problems
NASA Astrophysics Data System (ADS)
Silva, Glauber T.
2005-09-01
Acoustic radiation force plays a major role in elastography methods such as vibro-acoustography, acoustic radiation force, shear wave elasticity, and supersonic shear wave imaging. The radiation force (dynamic or static) exerted on an object by an incident wave can be obtained by solving the acoustic scattering problem for the object. However, only in rather simple cases the scattering of waves can be described by exact analytical expressions. In this work, we developed an algorithm based on the finite-difference time-domain (FDTD) method to compute the radiation force exerted on arbitrary shaped objects. The algorithm simulates the wave propagation in a finite extended medium with an embedded object. The radiation force is obtained by numerically calculating a surface integral of the momentum flux, which depends on the incident and scattered fields. Absorbing boundary conditions are used to truncate the medium. We compute the radiation force exerted on a rigid and soft cylinder by a plane wave. Results are in agreement with the theoretical predictions. Discrepancies due to numerical dispersion in the algorithm are under investigation. The presented method might be used to calculate the radiation force on complex objects present in elastography techniques. [Work supported by FAPEAL/CNPq, Brazil.
Light Scattering by Gaussian Particles: A Solution with Finite-Difference Time Domain Technique
NASA Technical Reports Server (NTRS)
Sun, W.; Nousiainen, T.; Fu, Q.; Loeb, N. G.; Videen, G.; Muinonen, K.
2003-01-01
The understanding of single-scattering properties of complex ice crystals has significance in atmospheric radiative transfer and remote-sensing applications. In this work, light scattering by irregularly shaped Gaussian ice crystals is studied with the finite-difference time-domain (FDTD) technique. For given sample particle shapes and size parameters in the resonance region, the scattering phase matrices and asymmetry factors are calculated. It is found that the deformation of the particle surface can significantly smooth the scattering phase functions and slightly reduce the asymmetry factors. The polarization properties of irregular ice crystals are also significantly different from those of spherical cloud particles. These FDTD results could provide a reference for approximate light-scattering models developed for irregular particle shapes and can have potential applications in developing a much simpler practical light scattering model for ice clouds angular-distribution models and for remote sensing of ice clouds and aerosols using polarized light. (copyright) 2003 Elsevier Science Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Bohlen, Thomas; Wittkamp, Florian
2016-03-01
We analyse the performance of a higher order accurate staggered viscoelastic time-domain finite-difference method, in which the staggered Adams-Bashforth (ABS) third-order and fourth-order accurate time integrators are used for temporal discretization. ABS is a multistep method that uses previously calculated wavefields to increase the order of accuracy in time. The analysis shows that the numerical dispersion is much lower than that of the widely used second-order leapfrog method. Numerical dissipation is introduced by the ABS method which is significantly smaller for fourth-order than third-order accuracy. In 1-D and 3-D simulation experiments, we verify the convincing improvements of simulation accuracy of the fourth-order ABS method. In a realistic elastic 3-D scenario, the computing time reduces by a factor of approximately 2.4, whereas the memory requirements increase by approximately a factor of 2.2. The ABS method thus provides an alternative strategy to increase the simulation accuracy in time by investing computer memory instead of computing time.
Use of the finite-difference time-domain method in electromagnetic dosimetry
Sullivan, D.M.
1987-01-01
Although there are acceptable methods for calculating whole body electromagnetic absorption, no completely acceptable method for calculating the local specific absorption rate (SAR) at points within the body has been developed. Frequency domain methods, such as the method of moments (MoM) have achieved some success; however, the MoM requires computer storage on the order of (3N)/sup 2/, and computation time on the order of (3N)/sup 3/ where N is the number of cells. The finite-difference time-domain (FDTD) method has been employed extensively in calculating the scattering from metallic objects, and recently is seeing some use in calculating the interaction of EM fields with complex, lossy dielectric bodies. Since the FDTD method has storage and time requirements proportional to N, it presents an attractive alternative to calculating SAR distribution in large bodies. This dissertation describes the FDTD method and evaluates it by comparing its results with analytic solutions in 2 and 3 dimensions. The results obtained demonstrate that the FDTD method is capable of calculating internal SAR distribution with acceptable accuracy. The construction of a data base to provide detailed, inhomogeneous man models for use with the FDTD method is described. Using this construction method, a model of 40,000 1.31 cm. cells is developed for use at 350 MHz, and another model consisting of 5000 2.62 cm. cells is developed for use at 100 MHz. To add more realism to the problem, a ground plane is added to the FDTD software. The needed changes to the software are described, along with a test which confirms its accuracy. Using the CRAY II supercomputer, SAR distributions in human models are calculated using incident frequencies of 100 MHz and 350 MHz for three different cases: (1) A homogeneous man model in free space, (2) an inhomogeneous man model in free space, and (3) an inhomogeneous man model standing on a ground plane.
High-performance finite-difference time-domain simulations of C-Mod and ITER RF antennas
Jenkins, Thomas G. Smithe, David N.
2015-12-10
Finite-difference time-domain methods have, in recent years, developed powerful capabilities for modeling realistic ICRF behavior in fusion plasmas [1, 2, 3, 4]. When coupled with the power of modern high-performance computing platforms, such techniques allow the behavior of antenna near and far fields, and the flow of RF power, to be studied in realistic experimental scenarios at previously inaccessible levels of resolution. In this talk, we present results and 3D animations from high-performance FDTD simulations on the Titan Cray XK7 supercomputer, modeling both Alcator C-Mod’s field-aligned ICRF antenna and the ITER antenna module. Much of this work focuses on scans over edge density, and tailored edge density profiles, to study dispersion and the physics of slow wave excitation in the immediate vicinity of the antenna hardware and SOL. An understanding of the role of the lower-hybrid resonance in low-density scenarios is emerging, and possible implications of this for the NSTX launcher and power balance are also discussed. In addition, we discuss ongoing work centered on using these simulations to estimate sputtering and impurity production, as driven by the self-consistent sheath potentials at antenna surfaces.
High-performance finite-difference time-domain simulations of C-Mod and ITER RF antennas
NASA Astrophysics Data System (ADS)
Jenkins, Thomas G.; Smithe, David N.
2015-12-01
Finite-difference time-domain methods have, in recent years, developed powerful capabilities for modeling realistic ICRF behavior in fusion plasmas [1, 2, 3, 4]. When coupled with the power of modern high-performance computing platforms, such techniques allow the behavior of antenna near and far fields, and the flow of RF power, to be studied in realistic experimental scenarios at previously inaccessible levels of resolution. In this talk, we present results and 3D animations from high-performance FDTD simulations on the Titan Cray XK7 supercomputer, modeling both Alcator C-Mod's field-aligned ICRF antenna and the ITER antenna module. Much of this work focuses on scans over edge density, and tailored edge density profiles, to study dispersion and the physics of slow wave excitation in the immediate vicinity of the antenna hardware and SOL. An understanding of the role of the lower-hybrid resonance in low-density scenarios is emerging, and possible implications of this for the NSTX launcher and power balance are also discussed. In addition, we discuss ongoing work centered on using these simulations to estimate sputtering and impurity production, as driven by the self-consistent sheath potentials at antenna surfaces.
3D Vectorial Time Domain Computational Integrated Photonics
Kallman, J S; Bond, T C; Koning, J M; Stowell, M L
2007-02-16
The design of integrated photonic structures poses considerable challenges. 3D-Time-Domain design tools are fundamental in enabling technologies such as all-optical logic, photonic bandgap sensors, THz imaging, and fast radiation diagnostics. Such technologies are essential to LLNL and WFO sponsors for a broad range of applications: encryption for communications and surveillance sensors (NSA, NAI and IDIV/PAT); high density optical interconnects for high-performance computing (ASCI); high-bandwidth instrumentation for NIF diagnostics; micro-sensor development for weapon miniaturization within the Stockpile Stewardship and DNT programs; and applications within HSO for CBNP detection devices. While there exist a number of photonics simulation tools on the market, they primarily model devices of interest to the communications industry. We saw the need to extend our previous software to match the Laboratory's unique emerging needs. These include modeling novel material effects (such as those of radiation induced carrier concentrations on refractive index) and device configurations (RadTracker bulk optics with radiation induced details, Optical Logic edge emitting lasers with lateral optical inputs). In addition we foresaw significant advantages to expanding our own internal simulation codes: parallel supercomputing could be incorporated from the start, and the simulation source code would be accessible for modification and extension. This work addressed Engineering's Simulation Technology Focus Area, specifically photonics. Problems addressed from the Engineering roadmap of the time included modeling the Auston switch (an important THz source/receiver), modeling Vertical Cavity Surface Emitting Lasers (VCSELs, which had been envisioned as part of fast radiation sensors), and multi-scale modeling of optical systems (for a variety of applications). We proposed to develop novel techniques to numerically solve the 3D multi-scale propagation problem for both the microchip
Study of two-dimensional transient cavity fields using the finite-difference time-domain technique
Crisp, J.L.
1988-06-01
This work is intended to be a study into the application of the finite-difference time-domain, or FD-TD technique, to some of the problems faced by designers of equipment used in modern accelerators. In particular it discusses using the FD-TD algorithm to study the field distribution of a simple two-dimensional cavity in both space and time. 18 refs.
3D time-domain airborne EM forward modeling with topography
NASA Astrophysics Data System (ADS)
Yin, Changchun; Qi, Yanfu; Liu, Yunhe; Cai, Jing
2016-11-01
The time-domain finite-difference method has been widely used in simulation of the electromagnetic field diffusion. However, this method is severely restricted by the mesh size and time step. To overcome the defect, we adopted edge finite-element method for unstructured grid with Backward Euler method to conduct 3D airborne electromagnetic forward modeling directly in time-domain. The tetrahedral meshes provide the flexibility required for representing the rugged topography and complex-shape anomalous bodies. We simulated the practical shape, size and attitude of transmitting source by directly setting the loop into the well-generated grids. The characteristic properties of vector basic functions guarantee automatic satisfaction of divergence-free property of electric fields. The Galerkin's method is used to discretize the governing equations and a direct solver is adopted to solve the large sparse linear system. We adopted an algorithm with constant step in each time segment to speed up the forward modeling. Further we introduced the local mesh strategy to reduce the calculations, in which an optimized grid is designed for each sounding station. We check the accuracy of our 3D modeling results against the solution for a homogenous half-space and those for a buried vertical plate model using integral equation. The numerical experiments for a hill, a valley or undulating topography model with buried anomalous bodies were further studied that show that the topography has a serious effect on airborne EM data.
Double absorbing boundaries for finite-difference time-domain electromagnetics
NASA Astrophysics Data System (ADS)
LaGrone, John; Hagstrom, Thomas
2016-12-01
We describe the implementation of optimal local radiation boundary condition sequences for second order finite difference approximations to Maxwell's equations and the scalar wave equation using the double absorbing boundary formulation. Numerical experiments are presented which demonstrate that the design accuracy of the boundary conditions is achieved and, for comparable effort, exceeds that of a convolution perfectly matched layer with reasonably chosen parameters. An advantage of the proposed approach is that parameters can be chosen using an accurate a priori error bound.
Finite difference time domain electromagnetic scattering from frequency-dependent lossy materials
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Four different FDTD computer codes and companion Radar Cross Section (RCS) conversion codes on magnetic media are submitted. A single three dimensional dispersive FDTD code for both dispersive dielectric and magnetic materials was developed, along with a user's manual. The extension of FDTD to more complicated materials was made. The code is efficient and is capable of modeling interesting radar targets using a modest computer workstation platform. RCS results for two different plate geometries are reported. The FDTD method was also extended to computing far zone time domain results in two dimensions. Also the capability to model nonlinear materials was incorporated into FDTD and validated.
3D frequency-domain finite-difference modeling of acoustic wave propagation
NASA Astrophysics Data System (ADS)
Operto, S.; Virieux, J.
2006-12-01
We present a 3D frequency-domain finite-difference method for acoustic wave propagation modeling. This method is developed as a tool to perform 3D frequency-domain full-waveform inversion of wide-angle seismic data. For wide-angle data, frequency-domain full-waveform inversion can be applied only to few discrete frequencies to develop reliable velocity model. Frequency-domain finite-difference (FD) modeling of wave propagation requires resolution of a huge sparse system of linear equations. If this system can be solved with a direct method, solutions for multiple sources can be computed efficiently once the underlying matrix has been factorized. The drawback of the direct method is the memory requirement resulting from the fill-in of the matrix during factorization. We assess in this study whether representative problems can be addressed in 3D geometry with such approach. We start from the velocity-stress formulation of the 3D acoustic wave equation. The spatial derivatives are discretized with second-order accurate staggered-grid stencil on different coordinate systems such that the axis span over as many directions as possible. Once the discrete equations were developed on each coordinate system, the particle velocity fields are eliminated from the first-order hyperbolic system (following the so-called parsimonious staggered-grid method) leading to second-order elliptic wave equations in pressure. The second-order wave equations discretized on each coordinate system are combined linearly to mitigate the numerical anisotropy. Secondly, grid dispersion is minimized by replacing the mass term at the collocation point by its weighted averaging over all the grid points of the stencil. Use of second-order accurate staggered- grid stencil allows to reduce the bandwidth of the matrix to be factorized. The final stencil incorporates 27 points. Absorbing conditions are PML. The system is solved using the parallel direct solver MUMPS developed for distributed
NASA Astrophysics Data System (ADS)
Chun, Kyungwon; Kim, Huioon; Hong, Hyunpyo; Chung, Youngjoo
GMES which stands for GIST Maxwell's Equations Solver is a Python package for a Finite-Difference Time-Domain (FDTD) simulation. The FDTD method widely used for electromagnetic simulations is an algorithm to solve the Maxwell's equations. GMES follows Object-Oriented Programming (OOP) paradigm for the good maintainability and usability. With the several optimization techniques along with parallel computing environment, we could make the fast and interactive implementation. Execution speed has been tested in a single host and Beowulf class cluster. GMES is open source and available on the web (http://www.sf.net/projects/gmes).
Sprague, Mark W; Luczkovich, Joseph J
2016-01-01
This finite-difference time domain (FDTD) model for sound propagation in very shallow water uses pressure and velocity grids with both 3-dimensional Cartesian and 2-dimensional cylindrical implementations. Parameters, including water and sediment properties, can vary in each dimension. Steady-state and transient signals from discrete and distributed sources, such as the surface of a vibrating pile, can be used. The cylindrical implementation uses less computation but requires axial symmetry. The Cartesian implementation allows asymmetry. FDTD calculations compare well with those of a split-step parabolic equation. Applications include modeling the propagation of individual fish sounds, fish aggregation sounds, and distributed sources.
Finite-difference time-domain methods to analyze ytterbium-doped Q-switched fiber lasers.
Hattori, Haroldo T; Khaleque, Abdul
2016-03-01
Q-switched lasers are widely used in material processing, laser ranging, medicine, and nonlinear optics--in particular, Q-switched lasers in optical fibers are important since they cannot only generate high peak powers but can also concentrate high peak powers in small areas. In this paper, we present new finite-difference time-domain methods that analyze the dynamics of Q-switched fiber lasers, which are more flexible and robust than previous methods. We extend the method to analyze fiber ring lasers and compare the results with our experiments.
Poroelastic Wave Propagation With a 3D Velocity-Stress-Pressure Finite-Difference Algorithm
NASA Astrophysics Data System (ADS)
Aldridge, D. F.; Symons, N. P.; Bartel, L. C.
2004-12-01
Seismic wave propagation within a three-dimensional, heterogeneous, isotropic poroelastic medium is numerically simulated with an explicit, time-domain, finite-difference algorithm. A system of thirteen, coupled, first-order, partial differential equations is solved for the particle velocity vector components, the stress tensor components, and the pressure associated with solid and fluid constituents of the two-phase continuum. These thirteen dependent variables are stored on staggered temporal and spatial grids, analogous to the scheme utilized for solution of the conventional velocity-stress system of isotropic elastodynamics. Centered finite-difference operators possess 2nd-order accuracy in time and 4th-order accuracy in space. Seismological utility is enhanced by an optional stress-free boundary condition applied on a horizontal plane representing the earth's surface. Absorbing boundary conditions are imposed on the flanks of the 3D spatial grid via a simple wavefield amplitude taper approach. A massively parallel computational implementation, utilizing the spatial domain decomposition strategy, allows investigation of large-scale earth models and/or broadband wave propagation within reasonable execution times. Initial algorithm testing indicates that a point force density and/or moment density source activated within a poroelastic medium generates diverging fast and slow P waves (and possibly an S-wave)in accord with Biot theory. Solid and fluid particle velocities are in-phase for the fast P-wave, whereas they are out-of-phase for the slow P-wave. Conversions between all wave types occur during reflection and transmission at interfaces. Thus, although the slow P-wave is regarded as difficult to detect experimentally, its presence is strongly manifest within the complex of waves generated at a lithologic or fluid boundary. Very fine spatial and temporal gridding are required for high-fidelity representation of the slow P-wave, without inducing excessive
NASA Astrophysics Data System (ADS)
Beker, B.
1992-12-01
Numerical modeling of electromagnetic (EM) interaction is normally performed by using either differential or integral equation methods. Both techniques can be implemented to solve problems in frequency or time domain. The method of moments (MOM) approach to solving integral equations has matured to the point where it can be used to solve complex problems. In the past, MOM has only been applied to scattering and radiation problems involving perfectly conducting or isotropic penetrable, lossy or lossless objects. However, many materials, (e.g., composites that are used on the Navy's surface ships in practical applications) exhibit anisotropic properties. To account for these new effects, several integral equation formulations for scattering and radiation by anisotropic objects have been developed recently. The differential equation approach to EM interaction studies has seen the emergence of the finite-difference time-domain (FD-TD) method as the method of choice in many of today's scattering and radiation applications. This approach has been applied to study transient as well as steady-state scattering from many complex structures, radiation from wire antennas, and coupling into wires through narrow apertures in conducting cavities. It is important to determine whether or not, and how effectively, the FD-TD can be used to solve EM interaction problems of interest to the Navy, such as investigating potential EM interference in shipboard communication systems. Consequently, this report partly addresses this issue by dealing exclusively with FD-TD modeling of time-domain EM scattering and radiation.
NASA Astrophysics Data System (ADS)
Zhang, Di; Capoglu, Ilker; Li, Yue; Cherkezyan, Lusik; Chandler, John; Spicer, Graham; Subramanian, Hariharan; Taflove, Allen; Backman, Vadim
2016-06-01
Combining finite-difference time-domain (FDTD) methods and modeling of optical microscopy modalities, we previously developed an open-source software package called Angora, which is essentially a "microscope in a computer." However, the samples being simulated were limited to nondispersive media. Since media dispersions are common in biological samples (such as cells with staining and metallic biomarkers), we have further developed a module in Angora to simulate samples having complicated dispersion properties, thereby allowing the synthesis of microscope images of most biological samples. We first describe a method to integrate media dispersion into FDTD, and we validate the corresponding Angora dispersion module by applying Mie theory, as well as by experimentally imaging gold microspheres. Then, we demonstrate how Angora can facilitate the development of optical imaging techniques with a case study.
Silva, F. da
2008-10-15
The EU will supply the plasma position reflectometer for ITER. The system will have channels located at different poloidal positions, some of them obliquely viewing a plasma which has a poloidal density divergence and curvature, both adverse conditions for profile measurements. To understand the impact of such topology in the reconstruction of density profiles a full-wave two-dimensional finite-difference time domain O-mode code with the capability for frequency sweep was used. Simulations show that the reconstructed density profiles still meet the ITER radial accuracy specifications for plasma position (1 cm), except for the highest densities. Other adverse effects such as multireflections induced by the blanket, density fluctuations, and MHD activity were considered and a first understanding on their impact obtained.
NASA Astrophysics Data System (ADS)
Huang, Shi-Hao; Wang, Shiang-Jiu; Tseng, Snow H.
2015-03-01
Optical coherence tomography (OCT) provides high resolution, cross-sectional image of internal microstructure of biological tissue. We use the Finite-Difference Time-Domain method (FDTD) to analyze the data acquired by OCT, which can help us reconstruct the refractive index of the biological tissue. We calculate the refractive index tomography and try to match the simulation with the data acquired by OCT. Specifically, we try to reconstruct the structure of melanin, which has complex refractive indices and is the key component of human pigment system. The results indicate that better reconstruction can be achieved for homogenous sample, whereas the reconstruction is degraded for samples with fine structure or with complex interface. Simulation reconstruction shows structures of the Melanin that may be useful for biomedical optics applications.
NASA Astrophysics Data System (ADS)
Ojima, Masayoshi; Ogawa, Yasuhiro; Ozaki, Ryotaro; Moritake, Hiroshi; Yoshida, Hiroyuki; Fujii, Akihiko; Ozaki, Masanori
2010-03-01
The photonic band structure and circular-polarization dependence of the transmission properties of cholesteric blue phase II were analyzed using a finite-difference time-domain method based on a double-twist cylinder model. The polarization dependence of the calculated band structure was not recognized in the same manner as that in previous studies. However, it can be clearly observed that the calculated transmission spectra depend on the circular polarization; this result agrees well with experimental results. On the basis of the circular-polarization dependence of the transmission spectra in the case of a thick sample, it can be indicated that a total reflection band appears in the selective reflection band.
NASA Technical Reports Server (NTRS)
Vinh, Hoang; Dwyer, Harry A.; Van Dam, C. P.
1992-01-01
The applications of two CFD-based finite-difference methods to computational electromagnetics are investigated. In the first method, the time-domain Maxwell's equations are solved using the explicit Lax-Wendroff scheme and in the second method, the second-order wave equations satisfying the Maxwell's equations are solved using the implicit Crank-Nicolson scheme. The governing equations are transformed to a generalized curvilinear coordinate system and solved on a body-conforming mesh using the scattered-field formulation. The induced surface current and the bistatic radar cross section are computed and the results are validated for several two-dimensional test cases involving perfectly-conducting scatterers submerged in transverse-magnetic plane waves.
Aldridge, David Franklin; Collier, Sandra L.; Marlin, David H.; Ostashev, Vladimir E.; Symons, Neill Phillip; Wilson, D. Keith
2005-05-01
This document is intended to serve as a users guide for the time-domain atmospheric acoustic propagation suite (TDAAPS) program developed as part of the Department of Defense High-Performance Modernization Office (HPCMP) Common High-Performance Computing Scalable Software Initiative (CHSSI). TDAAPS performs staggered-grid finite-difference modeling of the acoustic velocity-pressure system with the incorporation of spatially inhomogeneous winds. Wherever practical the control structure of the codes are written in C++ using an object oriented design. Sections of code where a large number of calculations are required are written in C or F77 in order to enable better compiler optimization of these sections. The TDAAPS program conforms to a UNIX style calling interface. Most of the actions of the codes are controlled by adding flags to the invoking command line. This document presents a large number of examples and provides new users with the necessary background to perform acoustic modeling with TDAAPS.
NASA Astrophysics Data System (ADS)
Lu, Jia; Zhou, Huaichun
2016-09-01
To deal with the staircase approximation problem in the standard finite-difference time-domain (FDTD) simulation, the two-dimensional boundary condition equations (BCE) method is proposed in this paper. In the BCE method, the standard FDTD algorithm can be used as usual, and the curved surface is treated by adding the boundary condition equations. Thus, while maintaining the simplicity and computational efficiency of the standard FDTD algorithm, the BCE method can solve the staircase approximation problem. The BCE method is validated by analyzing near field and far field scattering properties of the PEC and dielectric cylinders. The results show that the BCE method can maintain a second-order accuracy by eliminating the staircase approximation errors. Moreover, the results of the BCE method show good accuracy for cylinder scattering cases with different permittivities. Project supported by the National Natural Science Foundation of China (Grant No. 51025622).
NASA Astrophysics Data System (ADS)
Nagatani, Yoshiki; Imaizumi, Hirotaka; Fukuda, Takashi; Matsukawa, Mami; Watanabe, Yoshiaki; Otani, Takahiko
2006-09-01
In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. We have, therefore, simulated wave propagation in such a complex medium by the finite-difference time-domain (FDTD) method, using a three-dimensional X-ray computer tomography (CT) model of an actual cancellous bone. In this simulation, experimentally observed acoustic constants of the cortical bone were adopted. As a result, the generation of fast and slow waves was confirmed. The speed of fast waves and the amplitude of slow waves showed good correlations with the bone volume fraction. The simulated results were also compared with the experimental results obtained from the identical cancellous bone.
A 3D staggered-grid finite difference scheme for poroelastic wave equation
NASA Astrophysics Data System (ADS)
Zhang, Yijie; Gao, Jinghuai
2014-10-01
Three dimensional numerical modeling has been a viable tool for understanding wave propagation in real media. The poroelastic media can better describe the phenomena of hydrocarbon reservoirs than acoustic and elastic media. However, the numerical modeling in 3D poroelastic media demands significantly more computational capacity, including both computational time and memory. In this paper, we present a 3D poroelastic staggered-grid finite difference (SFD) scheme. During the procedure, parallel computing is implemented to reduce the computational time. Parallelization is based on domain decomposition, and communication between processors is performed using message passing interface (MPI). Parallel analysis shows that the parallelized SFD scheme significantly improves the simulation efficiency and 3D decomposition in domain is the most efficient. We also analyze the numerical dispersion and stability condition of the 3D poroelastic SFD method. Numerical results show that the 3D numerical simulation can provide a real description of wave propagation.
HEMP 3D -- a finite difference program for calculating elastic-plastic flow
Wilkins, M.L.
1993-05-26
The HEMP 3D program can be used to solve problems in solid mechanics involving dynamic plasticity and time dependent material behavior and problems in gas dynamics. The equations of motion, the conservation equations, and the constitutive relations are solved by finite difference methods following the format of the HEMP computer simulation program formulated in two space dimensions and time. Presented here is an update of the 1975 report on the HEMP 3D numerical technique. The present report includes the sliding surface routines programmed by Robert Gulliford.
Silva, F. da; Hacquin, S.
2005-03-01
We present a novel numerical signal injection technique allowing unidirectional injection of a wave in a wave-guiding structure, applicable to 2D finite-difference time-domain electromagnetic codes, both Maxwell and wave-equation. It is particularly suited to continuous wave radar-like simulations. The scheme gives an unidirectional injection of a signal while being transparent to waves propagating in the opposite direction (directional coupling). The reflected or backscattered waves (returned) are separated from the probing waves allowing direct access to the information on amplitude and phase of the returned wave. It also facilitates the signal processing used to extract the phase derivative (or group delay) when simulating radar systems. Although general, the technique is particularly suited to swept frequency sources (frequency modulated) in the context of reflectometry, a fusion plasma diagnostic. The UTS applications presented here are restricted to fusion plasma reflectometry simulations for different physical situations. This method can, nevertheless, also be used in other dispersive media such as dielectrics, being useful, for example, in the simulation of plasma filled waveguides or directional couplers.
NASA Technical Reports Server (NTRS)
Ryan, Deirdre A.; Luebbers, Raymond J.; Nguyen, Truong X.; Kunz, Karl S.; Steich, David J.
1992-01-01
Prediction of anechoic chamber performance is a difficult problem. Electromagnetic anechoic chambers exist for a wide range of frequencies but are typically very large when measured in wavelengths. Three dimensional finite difference time domain (FDTD) modeling of anechoic chambers is possible with current computers but at frequencies lower than most chamber design frequencies. However, two dimensional FDTD (2D-FTD) modeling enables much greater detail at higher frequencies and offers significant insight into compact anechoic chamber design and performance. A major subsystem of an anechoic chamber for which computational electromagnetic analyses exist is the reflector. First, an analysis of the quiet zone fields of a low frequency anechoic chamber produced by a uniform source and a reflector in two dimensions using the FDTD method is presented. The 2D-FDTD results are compared with results from a three dimensional corrected physical optics calculation and show good agreement. Next, a directional source is substituted for the uniform radiator. Finally, a two dimensional anechoic chamber geometry, including absorbing materials, is considered, and the 2D-FDTD results for these geometries appear reasonable.
NASA Technical Reports Server (NTRS)
Sun, W.; Loeb, N. G.; Tanev, S.; Videen, G.
2004-01-01
The two-dimensional (2-D) finite-difference time domain (FDTD) method is applied to calculate light scattering and absorption by an arbitrarily shaped infinite column embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition (ABC) is used to truncate the computational domain. The single-scattering properties of the infinite column embedded in the absorbing medium, including scattering phase functions, extinction and absorption efficiencies, are derived using an area integration of the internal field. An exact solution for light scattering and absorption by a circular cylinder in an absorbing medium is used to examine the accuracy of the 2-D UPML FDTD code. With use of a cell size of 1/120 incident wavelength in the FDTD calculations, the errors in the extinction and absorption efficiencies and asymmetry factors from the 2-D UPML FDTD are generally smaller than approx .1%. The errors in the scattering phase functions are typically smaller than approx .4%. Using the 2-D UPML FDTD technique, light scattering and absorption by long noncircular columns embedded in absorbing media can be accurately solved.
NASA Astrophysics Data System (ADS)
Maryana, Okky Fajar Tri; Hidayat, Rahmat
2016-08-01
Finite Difference Time Domain (FDTD) method has been much employed for studying light propagation in various structures, from simple one-dimensional structures up to three-dimensional complex structures. One of challenging problems is to implement this method for the case of light propagation in amplifying medium or structures, such as optical amplifier and lasers. The implementation is hindered by the fact that the dielectric constant becomes a complex number when optical gain parameter is involved in the calculation. In general, complex dielectric constant is related to complex susceptibility, in which the imaginary part is related to optical gain. Here, we then modify the formulation for updating electric field in the calculation algorithm. Using this approach, we then finally can calculate light amplification in laser active medium of Nd3+ ion doped glass. The calculation result shows an agreement with the result from the calculation using differential equation for intensity. Although this method is more time consuming, the method seem promising for optical complex micro- and nano-structures, such quantum dot lasers, micro-ring lasers, etc.
NASA Astrophysics Data System (ADS)
Wei, Xiao-Kun; Shao, Wei; Shi, Sheng-Bing; Zhang, Yong; Wang, Bing-Zhong
2015-07-01
An efficient conformal locally one-dimensional finite-difference time-domain (LOD-CFDTD) method is presented for solving two-dimensional (2D) electromagnetic (EM) scattering problems. The formulation for the 2D transverse-electric (TE) case is presented and its stability property and numerical dispersion relationship are theoretically investigated. It is shown that the introduction of irregular grids will not damage the numerical stability. Instead of the staircasing approximation, the conformal scheme is only employed to model the curve boundaries, whereas the standard Yee grids are used for the remaining regions. As the irregular grids account for a very small percentage of the total space grids, the conformal scheme has little effect on the numerical dispersion. Moreover, the proposed method, which requires fewer arithmetic operations than the alternating-direction-implicit (ADI) CFDTD method, leads to a further reduction of the CPU time. With the total-field/scattered-field (TF/SF) boundary and the perfectly matched layer (PML), the radar cross section (RCS) of two 2D structures is calculated. The numerical examples verify the accuracy and efficiency of the proposed method. Project supported by the National Natural Science Foundation of China (Grant Nos. 61331007 and 61471105).
NASA Astrophysics Data System (ADS)
Lo, F. S.; Lu, P. S.; Ragan-Kelley, B.; Minnich, A. J.; Lee, T. H.; Lin, M. C.; Verboncoeur, J. P.
2014-02-01
A thermionic energy converter (TEC) is a static device that converts heat directly into electricity by boiling electrons off a hot emitter surface across a small inter-electrode gap to a cooler collector surface. The main challenge in TECs is overcoming the space charge limit, which limits the current transmitted across a gap of a given voltage and width. We have verified the feasibility of studying and developing a TEC using a bounded finite-difference time-domain particle-in-cell plasma simulation code, OOPD1, developed by Plasma Theory and Simulation Group, formerly at UC Berkeley and now at Michigan State University. In this preliminary work, a TEC has been modeled kinetically using OOPD1, and the accuracy has been verified by comparing with an analytically solvable case, giving good agreement. With further improvement of the code, one will be able to quickly and cheaply analyze space charge effects, and seek designs that mitigate the space charge effect, allowing TECs to become more efficient and cost-effective.
Riley, D.J.
1993-04-01
A technique to integrate a dense, locally non-uniform mesh into finite-difference time-domain (FDTD) codes is presented. The method is designed for the full-wave analysis of multi-material layers that are physically thin, but perhaps electrically thick. Such layers are often used for the purpose of suppressing electromagnetic reflections from conducting surfaces. Throughout the non-uniform local mesh, average values for the conductivity and permittivity are used, where as variations in permeability are accommodated by splitting H-field line integrals and enforcing continuity of the normal B field. A unique interpolation scheme provides accuracy and late-time stability for mesh discontinuities as large as 1000 to 1. Application is made to resistive sheets, the absorbing Salisbury screen, crosstalk on printed circuit boards, and apertures that are narrow both in width and depth with regard to a uniform cell. Where appropriate, comparisons are made with the MoM code CARLOS and transmission-line theory. The hybrid mesh formulation has been highly optimized for both vector and parallel-processing on Cray YMP architectures.
Zhao, Huawei; Crozier, Stuart; Liu, Feng
2002-12-01
Numerical modeling of the eddy currents induced in the human body by the pulsed field gradients in MRI presents a difficult computational problem. It requires an efficient and accurate computational method for high spatial resolution analyses with a relatively low input frequency. In this article, a new technique is described which allows the finite difference time domain (FDTD) method to be efficiently applied over a very large frequency range, including low frequencies. This is not the case in conventional FDTD-based methods. A method of implementing streamline gradients in FDTD is presented, as well as comparative analyses which show that the correct source injection in the FDTD simulation plays a crucial rule in obtaining accurate solutions. In particular, making use of the derivative of the input source waveform is shown to provide distinct benefits in accuracy over direct source injection. In the method, no alterations to the properties of either the source or the transmission media are required. The method is essentially frequency independent and the source injection method has been verified against examples with analytical solutions. Results are presented showing the spatial distribution of gradient-induced electric fields and eddy currents in a complete body model.
Ibrahim, T S; Lee, R; Baertlein, B A; Yu, Y; Robitaille, P M
2000-09-01
In this work, a finite difference time domain (FDTD) algorithm is validated at 1.5 tesla using the standard GE Signa quadrature head coil and a muscle phantom. The electrical characteristics of the birdcage head coil are then calculated for the linear and quadrature cases. Unlike previous computational analysis which assume idealized currents on the end rings and the struts of the resonator, a complete computational analysis is provided. This treatment considers the coupling between the resonator and the sample and includes a real coil excitation, a complete current derivation, and a thorough description of both B(1) fields and RF radiation. With this improvement, electromagnetic phenomena such as radiation, standing wave currents on the wires, and field inhomogeneities due to interactions between the coil and the load inside the coil are observed. At 200 MHz, it is demonstrated that this particular coil does not work well due to radiation and non-uniformities on the struts of the device. Also, at this frequency magnetic field inhomogeneities become large when the coil is loaded with a phantom.
NASA Astrophysics Data System (ADS)
Large, Nicolas; Cao, Yang; Manjavacas, Alejandro; Nordlander, Peter
2015-03-01
Electron energy-loss spectroscopy (EELS) is a unique tool that is extensively used to investigate the plasmonic response of metallic nanostructures since the early works in the '50s. To be able to interpret and theoretically investigate EELS results, a myriad of different numerical techniques have been developed for EELS simulations (BEM, DDA, FEM, GDTD, Green dyadic functions). Although these techniques are able to predict and reproduce experimental results, they possess significant drawbacks and are often limited to highly symmetrical geometries, non-penetrating trajectories, small nanostructures, and free standing nanostructures. We present here a novel approach for EELS calculations using the Finite-difference time-domain (FDTD) method: EELS-FDTD. We benchmark our approach by direct comparison with results from the well-established boundary element method (BEM) and published experimental results. In particular, we compute EELS spectra for spherical nanoparticles, nanoparticle dimers, nanodisks supported by various substrates, and gold bowtie antennas on a silicon nitride substrate. Our EELS-FDTD implementation can be easily extended to more complex geometries and configurations and can be directly implemented within other numerical methods. Work funded by the Welch Foundation (C-1222, L-C-004), and the NSF (CNS-0821727, OCI-0959097).
3D parallel inversion of time-domain airborne EM data
NASA Astrophysics Data System (ADS)
Liu, Yun-He; Yin, Chang-Chun; Ren, Xiu-Yan; Qiu, Chang-Kai
2016-12-01
To improve the inversion accuracy of time-domain airborne electromagnetic data, we propose a parallel 3D inversion algorithm for airborne EM data based on the direct Gauss-Newton optimization. Forward modeling is performed in the frequency domain based on the scattered secondary electrical field. Then, the inverse Fourier transform and convolution of the transmitting waveform are used to calculate the EM responses and the sensitivity matrix in the time domain for arbitrary transmitting waves. To optimize the computational time and memory requirements, we use the EM "footprint" concept to reduce the model size and obtain the sparse sensitivity matrix. To improve the 3D inversion, we use the OpenMP library and parallel computing. We test the proposed 3D parallel inversion code using two synthetic datasets and a field dataset. The time-domain airborne EM inversion results suggest that the proposed algorithm is effective, efficient, and practical.
3D finite-difference modeling algorithm and anomaly features of ZTEM
NASA Astrophysics Data System (ADS)
Wang, Tao; Tan, Han-Dong; Li, Zhi-Qiang; Wang, Kun-Peng; Hu, Zhi-Ming; Zhang, Xing-Dong
2016-09-01
The Z-Axis tipper electromagnetic (ZTEM) technique is based on a frequency-domain airborne electromagnetic system that measures the natural magnetic field. A survey area was divided into several blocks by using the Maxwell's equations, and the magnetic components at the center of each edge of the grid cell are evaluated by applying the staggered-grid finite-difference method. The tipper and its divergence are derived to complete the 3D ZTEM forward modeling algorithm. A synthetic model is then used to compare the responses with those of 2D finite-element forward modeling to verify the accuracy of the algorithm. ZTEM offers high horizontal resolution to both simple and complex distributions of conductivity. This work is the theoretical foundation for the interpretation of ZTEM data and the study of 3D ZTEM inversion.
NASA Astrophysics Data System (ADS)
Cassidy, Nigel J.; Millington, Tim M.
2009-04-01
Numerical modelling has recently established itself as an important, near-surface GPR interpretation tool with the finite-difference, time-domain (FDTD) method becoming one of the most popular techniques. Robust, flexible and accurate, the FDTD technique is capable of simulating GPR wave propagation in complex, three-dimensional, heterogeneous, lossy, subsurface environments to a high degree of realism. Unfortunately, many of the current FDTD methods still consider the subsurface materials as being 'non magnetic' and, as such, do not include the propagation and loss effects associated with magnetic materials (e.g., basic igneous rocks, iron-rich sands, corroded steel reinforced concrete, smelting wastes, etc). For magnetically lossy materials, the inclusion of a complex magnetic permeability into the FDTD scheme can result in smeared or 'fuzzy' interface problems, increased computational demand and equation-level coding changes. Therefore, it is prudent to describe the magnetically derived loss and propagation characteristics in a more generic manner where the 'electric' (e.g., permittivity and conductivity) properties of the material incorporate the magnetic loss effects explicitly. In this paper, we present a "generalised complex effective permittivity" approach to the FDTD material descriptors that allows for the true loss and propagation characteristics of the magnetic materials to modelled fully, regardless of their individual magnetic or electric field relaxation mechanisms. In doing so, we are able to incorporate the lossy, dispersive effects directly into existing FDTD schemes without modification, additional error or increased computational demand. To demonstrate its application, a three-dimensional, 450 MHz, near-surface model of GPR data simulation over a rusty pipe has been included that illustrates how the FDTD modelling can be used to evaluate subtle changes in the spectral nature of the reflected signals. The modelling results show that, for
NASA Astrophysics Data System (ADS)
Panayappan, Kadappan
With the advent of sub-micron technologies and increasing awareness of Electromagnetic Interference and Compatibility (EMI/EMC) issues, designers are often interested in full- wave solutions of complete systems, taking to account a variety of environments in which the system operates. However, attempts to do this substantially increase the complexities involved in computing full-wave solutions, especially when the problems involve multi- scale geometries with very fine features. For such problems, even the well-established numerical methods, such as the time domain technique FDTD and the frequency domain methods FEM and MoM, are often challenged to the limits of their capabilities. In an attempt to address such challenges, three novel techniques have been introduced in this work, namely Dipole Moment (DM) Approach, Recursive Update in Frequency Domain (RUFD) and New Finite Difference Time Domain ( vFDTD). Furthermore, the efficacy of the above techniques has been illustrated, via several examples, and the results obtained by proposed techniques have been compared with other existing numerical methods for the purpose of validation. The DM method is a new physics-based approach for formulating MoM problems, which is based on the use of dipole moments (DMs), as opposed to the conventional Green's functions. The absence of the Green's functions, as well as those of the vector and scalar potentials, helps to eliminate two of the key sources of difficulties in the conventional MoM formulation, namely the singularity and low-frequency problems. Specifically, we show that there are no singularities that we need to be concerned with in the DM formulation; hence, this obviates the need for special techniques for integrating these singularities. Yet another salutary feature of the DM approach is its ability to handle thin and lossy structures, or whether they are metallic, dielectric-type, or even combinations thereof. We have found that the DM formulation can handle these
A time-space domain stereo finite difference method for 3D scalar wave propagation
NASA Astrophysics Data System (ADS)
Chen, Yushu; Yang, Guangwen; Ma, Xiao; He, Conghui; Song, Guojie
2016-11-01
The time-space domain finite difference methods reduce numerical dispersion effectively by minimizing the error in the joint time-space domain. However, their interpolating coefficients are related with the Courant numbers, leading to significantly extra time costs for loading the coefficients consecutively according to velocity in heterogeneous models. In the present study, we develop a time-space domain stereo finite difference (TSSFD) method for 3D scalar wave equation. The method propagates both the displacements and their gradients simultaneously to keep more information of the wavefields, and minimizes the maximum phase velocity error directly using constant interpolation coefficients for different Courant numbers. We obtain the optimal constant coefficients by combining the truncated Taylor series approximation and the time-space domain optimization, and adjust the coefficients to improve the stability condition. Subsequent investigation shows that the TSSFD can suppress numerical dispersion effectively with high computational efficiency. The maximum phase velocity error of the TSSFD is just 3.09% even with only 2 sampling points per minimum wavelength when the Courant number is 0.4. Numerical experiments show that to generate wavefields with no visible numerical dispersion, the computational efficiency of the TSSFD is 576.9%, 193.5%, 699.0%, and 191.6% of those of the 4th-order and 8th-order Lax-Wendroff correction (LWC) method, the 4th-order staggered grid method (SG), and the 8th-order optimal finite difference method (OFD), respectively. Meanwhile, the TSSFD is compatible to the unsplit convolutional perfectly matched layer (CPML) boundary condition for absorbing artificial boundaries. The efficiency and capability to handle complex velocity models make it an attractive tool in imaging methods such as acoustic reverse time migration (RTM).
DNS of Sheared Particulate Flows with a 3D Explicit Finite-Difference Scheme
NASA Astrophysics Data System (ADS)
Perrin, Andrew; Hu, Howard
2007-11-01
A 3D explicit finite-difference code for direct simulation of the motion of solid particulates in fluids has been developed, and a periodic boundary condition implemented to study the effective viscosity of suspensions in shear. The code enforces the no-slip condition on the surface of spherical particles in a uniform Cartesian grid with a special particle boundary condition based on matching the Stokes flow solutions next to the particle surface with a numerical solution away from it. The method proceeds by approximating the flow next to the particle surface as a Stokes flow in the particle's local coordinates, which is then matched to the finite difference update in the bulk fluid on a ``cage'' of grid points near the particle surface. (The boundary condition is related to the PHYSALIS method (2003), but modified for explicit schemes and with an iterative process removed.) Advantages of the method include superior accuracy of the scheme on a relatively coarse grid for intermediate particle Reynolds numbers, ease of implementation, and the elimination of the need to track the particle surface. For the sheared suspension, the effects of fluid and solid inertia and solid volume fraction on effective viscosity at moderate particle Reynolds numbers and concentrated suspensions will be discussed.
NASA Astrophysics Data System (ADS)
Zhou, Dong
2005-11-01
Modeling and simulation play increasingly more important roles in the development and commercialization of optical devices and integrated circuits. The current trend in photonic technologies is to push the level of integration and to utilize materials and structures of increasing complexity. On the other hand, the superb characteristics of free-space and fiber-optics continue to hold strong position to serve a wide range of applications. All these constitute significant challenges for the computer-aided modeling, simulation, and design of such optical devices and systems. The research work in this thesis deals with investigation and development of advanced finite-difference time-domain (FDTD) methods with focus on emerging optical devices and integrated circuits with complex material and/or structural properties. On the material aspects, we consider in a systematic fashion the dispersive and anisotropic characteristics of different materials (i.e., insulators, semiconductors, and conductors) in a broad wavelength range. The Lorentz model is examined and adapted as a general model for treating the material dispersion in the context of FDTD solutions. A dispersive FDTD method based on the multi-term Lorentz dispersive model is developed and employed for the modeling and design of the optical devices. In the FDTD scheme, the perfectly matched layer (PML) boundary condition is extended to the dispersive medium with arbitrary high order Lorentz terms. Finally, a parameter extraction scheme that links the Lorentz model to the experimental results is established. Further, the dispersive FDTD method is then applied to modeling and simulation of magneto-optical (MO) disk system, in combination of the vector diffraction theory. While the former is used for analysis of the interaction of the focused optical field interacting with the conducting materials on the surface of disk, the latter is to simulate the beam propagation from the objective lens to the disk surface. The
Ground motion simulations in Marmara (Turkey) region from 3D finite difference method
NASA Astrophysics Data System (ADS)
Aochi, Hideo; Ulrich, Thomas; Douglas, John
2016-04-01
In the framework of the European project MARSite (2012-2016), one of the main contributions from our research team was to provide ground-motion simulations for the Marmara region from various earthquake source scenarios. We adopted a 3D finite difference code, taking into account the 3D structure around the Sea of Marmara (including the bathymetry) and the sea layer. We simulated two moderate earthquakes (about Mw4.5) and found that the 3D structure improves significantly the waveforms compared to the 1D layer model. Simulations were carried out for different earthquakes (moderate point sources and large finite sources) in order to provide shake maps (Aochi and Ulrich, BSSA, 2015), to study the variability of ground-motion parameters (Douglas & Aochi, BSSA, 2016) as well as to provide synthetic seismograms for the blind inversion tests (Diao et al., GJI, 2016). The results are also planned to be integrated in broadband ground-motion simulations, tsunamis generation and simulations of triggered landslides (in progress by different partners). The simulations are freely shared among the partners via the internet and the visualization of the results is diffused on the project's homepage. All these simulations should be seen as a reference for this region, as they are based on the latest knowledge that obtained during the MARSite project, although their refinement and validation of the model parameters and the simulations are a continuing research task relying on continuing observations. The numerical code used, the models and the simulations are available on demand.
NASA Astrophysics Data System (ADS)
de Larquier, S.; Pasko, V. P.; Stenbaek-Nielsen, H. C.; Wilson, C. R.; Olson, J. V.
2009-12-01
Atmospheric infrasonic waves are acoustic waves with frequencies ranging from 0.02 to 10 Hz, slightly higher than the acoustic cut-off frequency (approximately 0.032 Hz), but lower than the audible frequencies (typically 20 Hz-15 kHz) [e.g., Blanc, Ann. Geophys., 3, 673, 1985]. A number of natural events have been identified as generating atmospheric infrasound, such as volcanoes, tornadoes, avalanches, earthquakes [e.g., Bedard and Georges, Physics Today, S3, 32, 2000], ocean surfaces [e.g., Gossard and Hooke, Waves in the Atmosphere, Elsevier, 1975, Ch. 9], lightning [e.g., Assink et al., GRL, 35, L15802, 2008; Pasko, JGR, 114, D08205, 2009], or transient luminous events in the middle atmosphere termed sprites [e.g., Farges, Lightning: Principles, Instruments and Applications, H.D. Betz et al. (eds), Springer, 2009, Ch. 18]. The importance of infrasound studies has been emphasized in the past ten years from the Comprehensive Nuclear-Test-Ban Treaty verification perspective [e.g., Le Pichon et al., JGR, 114, D08112, 2009]. A proper understanding of infrasound propagation in the atmosphere is required for identification and classification of different infrasonic waves and their sources [Drob et al., JGR, 108, D21, 4680, 2003]. The goal of the present work is to provide a quantitative interpretation and explanation of infrasonic signatures from pulsating auroras reported recently by Wilson et al. [GRL, 32, L14810, 2005]. The infrasound signals observed with an infrasonic array at Fairbanks, Alaska had a mean amplitude of 0.05 Pa, a delay of about 5 minutes from the pulsating aurora, and an almost normal incidence on the ground plane [Wilson et al., 2005]. We employ a finite-difference time-domain (FDTD) model of infrasound propagation in a realistic atmosphere. We use the absorption model of infrasound introduced by Sutherland and Bass [J. Acoust. Soc. Am., 115, 1012, 2004]. Classical absorption mechanisms as well as molecular relaxation mechanisms are taken into
Greene, Jethro H; Taflove, Allen
2003-10-01
We report the initial three-dimensional finite-difference time-domain modeling of a vertically coupled photonic racetrack. The modeling reveals details of the full suite of space-time behavior of electromagnetic-wave phenomena involved in guiding, coupling, multimoding, dispersion, and radiation. This behavior is not easily obtainable by analytical or full-vector frequency-domain methods, measurements of terminal properties, or near-field scanning optical microscopy.
3D Finite-Difference Modeling of Scattered Teleseismic Wavefields in a Subduction Zone
NASA Astrophysics Data System (ADS)
Morozov, I. B.; Zheng, H.
2005-12-01
For a teleseismic array targeting subducting crust in a zone of active subduction, scattering from the zone underlying the trench result in subhorizontally-propagating waves that could be difficult to distinguish from converted P- and S- wave backscattered from the surface. Because back-scattered modes often provide the most spectacular images of subducting slabs, it is important to understand their differences from the arrivals scattered from the trench zone. To investigate the detailed teleseismic wavefield in a subduction zone environment, we performed a full-waveform, 3-D visco-elastic finite-difference modeling of teleseismic wave propagation using a Beowulf cluster. The synthetics show strong scattering from the trench zone, dominated by the mantle and crustal P-waves propagating at 6.2-8.1.km/s and slower. These scattered waves occupy the same time and moveout intervals as the backscattered modes, and also have similar amplitudes. Although their amplitude decay characters are different, with the uncertainties in the velocity and density structure of the subduction zone, unambiguous distinguishing of these modes appears difficult. However, under minimal assumptions (in particular, without invoking slab dehydration), recent observations of receiver function amplitudes decreasing away from the trench favor the interpretation of trench-zone scattering.
NASA Astrophysics Data System (ADS)
Dou, Hu; Ma, Hongmei; Sun, Yu-Bao
2016-09-01
The finite-difference time-domain method is used to simulate the optical characteristics of an in-plane switching blue phase liquid crystal display. Compared with the matrix optic methods and the refractive method, the finite-difference time-domain method, which is used to directly solve Maxwell’s equations, can consider the lateral variation of the refractive index and obtain an accurate convergence effect. The simulation results show that e-rays and o-rays bend in different directions when the in-plane switching blue phase liquid crystal display is driven by the operating voltage. The finite-difference time-domain method should be used when the distribution of the liquid crystal in the liquid crystal display has a large lateral change. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304074, 61475042, and 11274088), the Natural Science Foundation of Hebei Province, China (Grant Nos. A2015202320 and GCC2014048), and the Key Subject Construction Project of Hebei Province University, China.
3-D Finite-Difference Modeling of Earthquakes in the City of Rome, Italy
NASA Astrophysics Data System (ADS)
Akinci, A.; Olsen, K. B.; Rovelli, A.; Marra, F.; Malagnini, L.
2002-12-01
The goal of this study is to estimate 3-D amplification effects from regional and local earthquakes in the city of Rome. Mainly, two distinct seismogenic districts may affect the city of Rome: the (1) Alban Hills region, located about 25 km from downtown Rome, and (2) the Central Apennines, located 80-100 km from Rome where the most recent event occurred on January 13, 1915 (M=6.8) which was felt in Rome with a VII degree intensity. To address the seismic hazard in Rome from such sources we have simulated 0-1 Hz viscoelastic wave propagation in a three-dimensional model of the Tiber Valley, Rome, for an M5.5 scenario earthquake (1 Hz) in the seismogenic area of Alban Hills about 25 km from downtown Rome and an M7.0 earthquake (0.5 Hz) about 100 km east of the valley using a fourth-order staggered-grid finite-difference method. We used a basin model (~ 6 km by 6 km by 0.050 km) which includes sediments with shear-wave velocities as low as 250 m/s in the Tiber River sediments, constrained by more than 3000 borehole measurements. We have also estimated the amplification of the 3D model due to a 1-Hz vertically-incident planar SH wave. Our results suggest that the strongest ground motion amplification in Rome is restricted to the Holocene alluvial areas with a significant concentration close to the edges of the Tiber River valley, in agreement with the results by Tertulliani and Riguzzi (1995). In particular, the fill deposits in the Tiber River generate amplification by up to a factor of 2 with respect to the surrounding volcanics, largest near the contact between the alluvial sediments and the surrounding volcanic deposits for the incident plane wave source. We find 1-Hz peak ground velocities of up to 30 cm/sec for the M5.5, Alban Hills earthquake, largest near the northwestern edges of the Tiber River. The largest 0.5-Hz peak velocity is 24 cm/s for the M7.0 earthquake with extended durations up to about 1 min. The lower maximum frequency for this scenario is
NASA Technical Reports Server (NTRS)
Yefet, Amir; Petropoulos, Peter G.
1999-01-01
We consider a divergence-free non-dissipative fourth-order explicit staggered finite difference scheme for the hyperbolic Maxwell's equations. Special one-sided difference operators are derived in order to implement the scheme near metal boundaries and dielectric interfaces. Numerical results show the scheme is long-time stable, and is fourth-order convergent over complex domains that include dielectric interfaces and perfectly conducting surfaces. We also examine the scheme's behavior near metal surfaces that are not aligned with the grid axes, and compare its accuracy to that obtained by the Yee scheme.
Accurate 2D/3D electromagnetic modeling for time-domain airborne EM systems
NASA Astrophysics Data System (ADS)
Yin, C.; Hodges, G.
2012-12-01
The existing industry software cannot deliver correct results for 3D time-domain airborne EM responses. In this paper, starting from the Fourier transform and convolution, we compare the stability of different modeling techniques and analyze the reason for instable calculations of the time-domain airborne EM responses. We find that the singularity of the impulse responses of EM systems at very early time that are used in the convolution is responsible for the instability of the modeling (Fig.1). Based on this finding, we put forward an algorithm that uses step response rather than impulse response of the airborne EM system for the convolution and create a stable algorithm that delivers precise results and maintains well the integral/derivative relationship between the magnetic field B and the magnetic induction dB/dt. A three-step transformation procedure for the modeling is proposed: 1) output the frequency-domain EM response data from the existing software; 2) transform into step-response by digital Fourier/Hankel transform; 3) convolve the step response with the transmitting current or its derivatives. The method has proved to be working very well (Fig. 2). The algorithm can be extended to the modeling of other time-domain ground and airborne EM system responses.Fig. 1: Comparison of impulse and step responses for an airborne EM system Fig. 2: Bz and dBz/dt calculated from step (middle panel) and impulse responses (lower panel) for the same 3D model as in Fig.1.
Finite-Difference Algorithm for Simulating 3D Electromagnetic Wavefields in Conductive Media
NASA Astrophysics Data System (ADS)
Aldridge, D. F.; Bartel, L. C.; Knox, H. A.
2013-12-01
Electromagnetic (EM) wavefields are routinely used in geophysical exploration for detection and characterization of subsurface geological formations of economic interest. Recorded EM signals depend strongly on the current conductivity of geologic media. Hence, they are particularly useful for inferring fluid content of saturated porous bodies. In order to enhance understanding of field-recorded data, we are developing a numerical algorithm for simulating three-dimensional (3D) EM wave propagation and diffusion in heterogeneous conductive materials. Maxwell's equations are combined with isotropic constitutive relations to obtain a set of six, coupled, first-order partial differential equations governing the electric and magnetic vectors. An advantage of this system is that it does not contain spatial derivatives of the three medium parameters electric permittivity, magnetic permeability, and current conductivity. Numerical solution methodology consists of explicit, time-domain finite-differencing on a 3D staggered rectangular grid. Temporal and spatial FD operators have order 2 and N, where N is user-selectable. We use an artificially-large electric permittivity to maximize the FD timestep, and thus reduce execution time. For the low frequencies typically used in geophysical exploration, accuracy is not unduly compromised. Grid boundary reflections are mitigated via convolutional perfectly matched layers (C-PMLs) imposed at the six grid flanks. A shared-memory-parallel code implementation via OpenMP directives enables rapid algorithm execution on a multi-thread computational platform. Good agreement is obtained in comparisons of numerically-generated data with reference solutions. EM wavefields are sourced via point current density and magnetic dipole vectors. Spatially-extended inductive sources (current carrying wire loops) are under development. We are particularly interested in accurate representation of high-conductivity sub-grid-scale features that are common
Saarelma, Jukka; Savioja, Lauri
2016-12-01
The finite-difference time-domain method has gained increasing interest for room acoustic prediction use. A well-known limitation of the method is a frequency and direction dependent dispersion error. In this study, the audibility of dispersion error in the presence of air absorption is measured. The results indicate that the dispersion error in the worst-case direction of the studied scheme gets masked by the air absorption at a phase velocity error percentage of 0.28% at the frequency of 20 kHz.
NASA Astrophysics Data System (ADS)
Palka, N.; Panowicz, R.; Ospald, F.; Beigang, R.
2015-08-01
An ultra-high molecular weight polyethylene composite sample totally punctured by a projectile was examined by THz TDS raster scanning method in reflection configuration. The scanning results correctly match the distribution of delaminations inside the sample, which was proven with cross-sectional and frontal views after waterjet cutting. For further analysis, a signal-processing algorithm based on the deconvolution method was developed and the modified reference signal was used to reduce disturbances. The complex refractive index of the sample was determined by transmission TDS technique and was later used for the simulation of pulse propagation by the finite difference time domain method. These simulations verified the correctness of the proposed method and showed its constraints. Using the proposed algorithm, the ambiguous raw THz image was converted into a binary 3D image of the sample, which consists only of two areas: sample—polyethylene and delamination—air. As a result, a clear image of the distribution of delaminations with their spatial extent was obtained which can be used for further comparative analysis. The limitation of the proposed method is that parts of the central area of the puncture cannot be analyzed because tilted layers deflect the incident signal.
Crack identification by 3D time-domain elastic or acoustic topological sensitivity
NASA Astrophysics Data System (ADS)
Bellis, Cédric; Bonnet, Marc
2009-03-01
The topological sensitivity analysis, based on the asymptotic behavior of a cost functional associated with the creation of a small trial flaw in a defect-free solid, provides a computationally-fast, non-iterative approach for identifying flaws embedded in solids. This concept is here considered for crack identification using time-dependent measurements on the external boundary. The topological derivative of a cost function under the nucleation of a crack of infinitesimal size is established, in the framework of time-domain elasticity or acoustics. The simplicity and efficiency of the proposed formulation is enhanced by the recourse to an adjoint solution. Numerical results obtained on a 3-D elastodynamic example using the conventional FEM demonstrate the usefulness of the topological derivative as a crack indicator function. To cite this article: C. Bellis, M. Bonnet, C. R. Mecanique 337 (2009).
Finite-difference model for 3-D flow in bays and estuaries
Smith, Peter E.; Larock, Bruce E.; ,
1993-01-01
This paper describes a semi-implicit finite-difference model for the numerical solution of three-dimensional flow in bays and estuaries. The model treats the gravity wave and vertical diffusion terms in the governing equations implicitly, and other terms explicitly. The model achieves essentially second-order accurate and stable solutions in strongly nonlinear problems by using a three-time-level leapfrog-trapezoidal scheme for the time integration.
Improvements to the ICRH antenna time-domain 3D plasma simulation model
NASA Astrophysics Data System (ADS)
Smithe, David N.; Jenkins, Thomas G.; King, J. R.
2015-12-01
We present a summary of ongoing improvements to the 3D time-domain plasma modeling software that has been used to look at ICRH antennas on Alcator C-Mod, NSTX, and ITER [1]. Our past investigations have shown that in low density cases where the slow wave is propagating, strong amplitude lower hybrid resonant fields can occur. Such a scenario could result in significant parasitic power loss in the SOL. The primary resonance broadening in this case is likely collisions with neutral gas, and thus we are upgrading the model to include realistic neutral gas in the SOL, in order to provide a better understanding of energy balance in these situations. Related to this, we are adding a temporal variation capability to the local plasma density in front of the antenna in order to investigate whether the near fields of the antenna could modify the local density sufficiently to initiate a low density situation. We will start with a simple scalar ponderomotive potential density expulsion model [2] for the density evolution, but are also looking to eventually couple to a more complex fluid treatment that would include tensor pressures and convective physics and sources of neutrals and ionization. We also review continued benchmarking efforts, and ongoing and planned improvements to the computational algorithms, resulting from experience gained during our recent supercomputing runs on the Titan supercomputer, including GPU operations.
Kitamura, Kyoko; Sakai, Kyosuke; Noda, Susumu
2011-07-18
Radially polarized focused beams have attracted a great deal of attention because of their unique properties characterized by the longitudinal field. Although this longitudinal field is strongly confined to the beam axis, the energy flow, i.e., the Poynting vector, has null intensity on the axis. Hence, the interaction of the focused beam and matter has thus far been unclear. We analyzed the interactions between the focused beam and a subwavelength metal block placed at the center of the focus using three-dimensional finite-difference time-domain (FDTD) calculation. We found that most of the Poynting energy propagates through to the far-field, and that a strong enhancement of the electric field appeared on the metal surface. This enhancement is attributed to the constructive interference of the symmetric electric field and the coupling to the surface plasmon mode.
Potravkin, N N; Perezhogin, I A; Makarov, V A
2012-11-01
We propose an alternative method of integration of Maxwell equations. This method is the generalization of a finite-difference time-domain method with an auxiliary differential equation for the case of a linear optical medium with a frequency dispersion and an arbitrary source of spatial dispersion. We apply this method to the problem of the propagation of short plane-wave linearly polarized light pulses in such a medium. It is shown that some features of their propagation are completely different from those that are generally recognized for the linear optical activity phenomenon. For example, in some cases an initially linearly polarized light pulse becomes elliptically polarized during the propagation. This effect is more prominent in the front part of the pulse.
Asakura, T; Ishizuka, T; Miyajima, T; Toyoda, M; Sakamoto, S
2014-09-01
Due to limitations of computers, prediction of structure-borne sound remains difficult for large-scale problems. Herein a prediction method for low-frequency structure-borne sound transmissions on concrete structures using the finite-difference time-domain scheme is proposed. The target structure is modeled as a composition of multiple plate elements to reduce the dimensions of the simulated vibration field from three-dimensional discretization by solid elements to two-dimensional discretization. This scheme reduces both the calculation time and the amount of required memory. To validate the proposed method, the vibration characteristics using the numerical results of the proposed scheme are compared to those measured for a two-level concrete structure. Comparison of the measured and simulated results suggests that the proposed method can be used to simulate real-scale structures.
NASA Astrophysics Data System (ADS)
Jarem, John M.
1991-03-01
A multifilament method of moments (MOM) analysis and a finite-difference time-domain (FE-TD) analysis are used to numerically calculate the input impedance of a probe-sleeve fed rectangular waveguide which has been short-circuited on one side. The input impedance of the system is determined by using the above methods for several probe-sleeve configurations, and reasonable agreement between the two methods for the cases studied is found. An MOM Green's function formulation which is based on scattering superposition and which allows the input impedance of a probe-sleeve feed to be calculated when the waveguide is terminated in a given load is derived. The MOM results and FD-TD numerical results are compared for this loaded waveguide input impedance case, and reasonable agreement between the methods is found. A comparison of theory and experiment is given for when the waveguide is terminated in a ground plane aperture.
NASA Astrophysics Data System (ADS)
Lacombe, Jürgen; Sergeev, Oleg; Chakanga, Kambulakwao; von Maydell, Karsten; Agert, Carsten
2011-07-01
In this paper, modeling of light propagation in silicon thin film solar cells without using any fitting parameter is presented. The aim is to create a realistic view of the light trapping effects and of the resulting optical generation rate in the absorbing semiconductor layers. The focus is on real three dimensional systems. Our software Sentaurus tcad, developed by Synopsys, has the ability to import real topography measurements and to model the light propagation using the finite-difference time-domain method. To verify the simulation, we compared the measured and simulated angular distribution functions of a glass/SnO2:F transparent conducting oxide system for different wavelengths. The optical generation rate of charge carriers in amorphous silicon thin film solar cells including rough interfaces is calculated. The distribution of the optical generation rate is correlated with the shape of the interface, and the external quantum efficiencies are calculated and compared to experimental data.
NASA Astrophysics Data System (ADS)
Bogatyrev, I. B.; Grojo, D.; Delaporte, P.; Leyder, S.; Sentis, M.; Marine, W.; Itina, T. E.
2011-11-01
We present a theoretical model, which describes local energy deposition inside IR-transparent silicon and gallium arsenide with focused 1.3-μm wavelength femtosecond laser pulses. Our work relies on the ionization rate equation and two temperature model (TTM), as we simulate the non-linear propagation of focused femtosecond light pulses by using a 3D finite difference time domain method. We find a strong absorption dependence on the initial free electron density (doping concentration) that evidences the role of avalanche ionization. Despite an influence of Kerr-type self-focusing at intensity required for non-linear absorption, we show the laser energy deposition remains confined when the focus position is moved down to 1-mm below the surface. Our simulation results are in agreement with the degree of control observed in a simple model experiment.
3-D geoelectrical modelling using finite-difference: a new boundary conditions improvement
NASA Astrophysics Data System (ADS)
Maineult, A.; Schott, J.-J.; Ardiot, A.
2003-04-01
Geoelectrical prospecting is a well-known and frequently used method for quantitative and non-destructive subsurface exploration until depths of a few hundreds metres. Thus archeological objects can be efficiently detected as their resistivities often contrast with those of the surrounding media. Nevertheless using the geoelectrical prospecting method has long been restricted due to inhability to model correctly arbitrarily-shaped structures. The one-dimensional modelling and inversion have long been classical, but are of no interest for the majority of field data, since the natural distribution of resistivity is rarely homogeneous or tabular. Since the 1970's some authors developed discrete methods in order to solve the two and three-dimensional problem, using mathematical tools such as finite-element or finite-difference. The finite-difference approach is quite simple, easily understandable and programmable. Since the work of Dey and Morrison (1979), this approach has become quite popular. Nevertheless, one of its major drawbacks is the difficulty to establish satisfying boundary conditions. Recently Lowry et al. (1989) and Zhao and Yedlin (1996) suggested some refinements on the improvement of the boundary problem. We propose a new betterment, based on the splitting of the potential into two terms, the potential due to a reference tabular medium and a secondary potential caused by a disturbance of this medium. The surface response of a tabular medium has long been known (see for example Koefoed 1979). Here we developed the analytical solution for the electrical tabular potential everywhere in the medium, in order to establish more satisfying boundary conditions. The response of the perturbation, that is to say the object of interest, is then solved using volume-difference and preconditioned conjugate gradient. Finally the grid is refined one or more times in the perturbed domain in order to ameliorate the precision. This method of modelling is easy to implement
Fitzgerald, Anthony J.; Pickwell-MacPherson, Emma; Wallace, Vincent P.
2014-01-01
The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues. PMID:25010734
NASA Technical Reports Server (NTRS)
Sun, W.; Loeb, N. G.; Videen, G.; Fu, Q.
2004-01-01
Natural particles such as ice crystals in cirrus clouds generally are not pristine but have additional micro-roughness on their surfaces. A two-dimensional finite-difference time-domain (FDTD) program with a perfectly matched layer absorbing boundary condition is developed to calculate the effect of surface roughness on light scattering by long ice columns. When we use a spatial cell size of 1/120 incident wavelength for ice circular cylinders with size parameters of 6 and 24 at wavelengths of 0.55 and 10.8 mum, respectively, the errors in the FDTD results in the extinction, scattering, and absorption efficiencies are smaller than similar to 0.5%. The errors in the FDTD results in the asymmetry factor are smaller than similar to 0.05%. The errors in the FDTD results in the phase-matrix elements are smaller than similar to 5%. By adding a pseudorandom change as great as 10% of the radius of a cylinder, we calculate the scattering properties of randomly oriented rough-surfaced ice columns. We conclude that, although the effect of small surface roughness on light scattering is negligible, the scattering phase-matrix elements change significantly for particles with large surface roughness. The roughness on the particle surface can make the conventional phase function smooth. The most significant effect of the surface roughness is the decay of polarization of the scattered light.
Chaudhury, Bhaskar; Chaturvedi, Shashank
2006-12-15
Power-flow trajectories of electromagnetic waves through a spatially nonuniform plasma have been computed using direct solutions of Maxwell's equations using the three-dimensional finite-difference time-domain (FDTD) method. This method yields accurate information on refraction as well as absorption effects. The method can be used to compute power-flow trajectories for plasmas with arbitrarily varying density profiles, including effects due to arbitrarily shaped conducting or dielectric surfaces bounding the plasma. Furthermore, since FDTD is computationally expensive, especially for parametric studies, it is desirable to use ray tracing to estimate refraction effects. A quantitative comparison is performed between two different methods of obtaining exact and approximate solutions of Maxwell's equations in order to assess their relative utility in different situations. In the present work, we limit ourselves to a cold, collisional, unmagnetized plasma, where the response to electromagnetic waves is fully specified by a dispersion relation based on magnetoionic theory. It is shown that ray tracing in such plasmas yields accurate results only when two conditions are satisfied. Firstly, the density scale length should be long as compared to the free-space wavelength of the incident wave. Secondly, the conduction current should be small as compared to the displacement current in the medium. The second condition is one which has been identified for the first time.
Gao, YingJie; Yang, HongWei
2014-01-01
An explicit high-order, symplectic, finite-difference time-domain (SFDTD) scheme is applied to a bioelectromagnetic simulation using a simple model of a pregnant woman and her fetus. Compared to the traditional FDTD scheme, this scheme maintains the inherent nature of the Hamilton system and ensures energy conservation numerically and a high precision. The SFDTD scheme is used to predict the specific absorption rate (SAR) for a simple model of a pregnant female woman (month 9) using radio frequency (RF) fields from 1.5 T and 3 T MRI systems (operating at approximately 64 and 128 MHz, respectively). The results suggest that by using a plasma protective layer under the 1.5 T MRI system, the SAR values for the pregnant woman and her fetus are significantly reduced. Additionally, for a 90 degree plasma protective layer, the SAR values are approximately equal to the 120 degree layer and the 180 degree layer, and it is reduced relative to the 60 degree layer. This proves that using a 90 degree plasma protective layer is the most effective and economical angle to use. PMID:25493433
Liu, Gui-qiang; Hu, Ying; Liu, Zheng-qi; Chen, Yuan-hao; Cai, Zheng-jie; Zhang, Xiang-nan; Huang, Kuan
2014-03-07
We propose a robust multispectral transparent plasmonic structure and calculate its transparency response by using the three-dimensional finite-difference time-domain (FDTD) method. The proposed structure is composed of a continuous ultrathin metal film sandwiched by double two-dimensional (2D) hexagonal non-close-packed metal-dielectric multilayer core-shell nanoparticle arrays. The top and bottom plasmonic arrays in such a structure, respectively, act as the light input and output couplers to carry out the efficient trapping and release of light. Near-perfect multispectral optical transparency in the visible and near-infrared regions is achieved theoretically. The calculated electric field distribution patterns show that the near-perfect multispectral optical transparency mainly originates from the excitation and hybridization of shell and core plasmon modes, strong near-field coupling of dipole plasmon modes between adjacent nanoparticles as well as the excitation of surface plasmon waves of the metal film. The robust transparency bands can be efficiently tuned in a large range by varying the structural parameters and the surrounding dielectric environment. The proposed structure also shows additional merits such as a deep sub-wavelength size and fully retained electrical and mechanical properties of the natural metal. These features might provide promising applications in highly integrated optoelectronic devices including plasmonic filters, nanoscale multiplexers, and non-linear optics.
NASA Astrophysics Data System (ADS)
Francés, Jorge; Bleda, Sergio; Álvarez, Mariela Lázara; Martínez, Francisco Javier; Márquez, Andres; Neipp, Cristian; Beléndez, Augusto
2014-01-01
The implementation of split-field finite difference time domain (SF-FDTD) applied to light-wave propagation through periodic media with arbitrary anisotropy method in graphics processing units (GPUs) is described. The SF-FDTD technique and the periodic boundary condition allow the consideration of a single period of the structure reducing the simulation grid. Nevertheless, the analysis of the anisotropic media implies considering all the electromagnetic field components and the use of complex notation. These aspects reduce the computational efficiency of the numerical method compared with the isotropic and nonperiodic implementation. Specifically, the implementation of the SF-FDTD in the Kepler family of GPUs of NVIDIA is presented. An analysis of the performance of this implementation is done, and several applications have been considered in order to estimate the possibilities provided by both the formalism and the implementation into GPU: binary phase gratings and twisted-nematic liquid crystal cells. Regarding the analysis of binary phase gratings, the validity of the scalar diffraction theory is evaluated by the comparison of the diffraction efficiencies predicted by SF-FDTD. The analysis for the second order of diffraction is extended, which is considered as a reference for the transmittance obtained by the SF-FDTD scheme for periodic media.
Kinefuchi, K.; Funaki, I.; Shimada, T.; Abe, T.
2012-10-15
Under certain conditions during rocket flights, ionized exhaust plumes from solid rocket motors may interfere with radio frequency transmissions. To understand the relevant physical processes involved in this phenomenon and establish a prediction process for in-flight attenuation levels, we attempted to measure microwave attenuation caused by rocket exhaust plumes in a sea-level static firing test for a full-scale solid propellant rocket motor. The microwave attenuation level was calculated by a coupling simulation of the inviscid-frozen-flow computational fluid dynamics of an exhaust plume and detailed analysis of microwave transmissions by applying a frequency-dependent finite-difference time-domain method with the Drude dispersion model. The calculated microwave attenuation level agreed well with the experimental results, except in the case of interference downstream the Mach disk in the exhaust plume. It was concluded that the coupling estimation method based on the physics of the frozen plasma flow with Drude dispersion would be suitable for actual flight conditions, although the mixing and afterburning in the plume should be considered depending on the flow condition.
Yang, Li; Ge, Manling; Guo, Jia; Wang, Qingmeng; Jiang, Xiaochi; Yan, Weili
2007-01-01
Finite-difference time-domain (FDTD) method and specific absorption rate (SAR) are employed here to study the relationship between the radiation of a mobile handset and the human being health. Nowadays, much more attention has been paid to the simulations for the effects of RF radiation on the particular organs, such as the eyes or the ears because they are more sensitive and more near to the working mobile. In the paper, the simulation of the RF fields is focused on the eyes model and the eyes with glasses of metal frame respectively. A planar inverted F antenna is used as an exposure source at 900 MHz. Under this case, the intensity of the electrical field is calculated and analyzed. Also, SAR is utilized to evaluate the absorption of the organs to the radiation. Through the simulation, the peak values of SAR per 1G tissue at the radiating power being 600mW are obtained. It is concluded that when people are wearing glasses of metal framework, the peak value of SAR is shown to be a little higher than the safety limits. It is suggested that the radiation from the mobile handset do more harmful effect on the eyes with the glasses of metal frameworks.
Gao, YingJie; Yang, HongWei
2014-01-01
An explicit high-order, symplectic, finite-difference time-domain (SFDTD) scheme is applied to a bioelectromagnetic simulation using a simple model of a pregnant woman and her fetus. Compared to the traditional FDTD scheme, this scheme maintains the inherent nature of the Hamilton system and ensures energy conservation numerically and a high precision. The SFDTD scheme is used to predict the specific absorption rate (SAR) for a simple model of a pregnant female woman (month 9) using radio frequency (RF) fields from 1.5 T and 3 T MRI systems (operating at approximately 64 and 128 MHz, respectively). The results suggest that by using a plasma protective layer under the 1.5 T MRI system, the SAR values for the pregnant woman and her fetus are significantly reduced. Additionally, for a 90 degree plasma protective layer, the SAR values are approximately equal to the 120 degree layer and the 180 degree layer, and it is reduced relative to the 60 degree layer. This proves that using a 90 degree plasma protective layer is the most effective and economical angle to use.
NASA Astrophysics Data System (ADS)
Ogino, Akihisa; Naito, Katsutoshi; Terashita, Fumie; Nanko, Shohei; Nagatsu, Masaaki
2005-02-01
In this paper, we presented experimental results on the production of volume wave plasma (VWP) using an internally mounted cylindrical planar microwave launcher, for application to novel plasma processings, such as inner wall coating, impurity-free etching or internal sterilization of medical instruments using VWP. It was demonstrated that the ellipsoidal VWP is produced in front of a microwave launcher in He or Ar gas atmosphere. Numerical analyses of microwave fields radiated from a planar launcher have been carried out using the two-dimensional finite difference time domain (FDTD) method to determine the mechanism of VWP production in middle of the chamber. It was shown that the calculation results showed fairly good agreements with the experimental results measured using a dipole antenna probe. The spatial distributions of plasma density and the temperature of VWP were also measured using a double probe. It was found that the electron density is comparable to or slightly less than cutoff density of 7.4 × 1010 cm-3 corresponding to the microwave frequency of fm=2.45 GHz, and that the electron temperature is approximately 6 eV at the plasma center.
NASA Astrophysics Data System (ADS)
Li, Y.; Han, B.; Métivier, L.; Brossier, R.
2016-09-01
We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.
Wakefield Simulation of CLIC PETS Structure Using Parallel 3D Finite Element Time-Domain Solver T3P
Candel, A.; Kabel, A.; Lee, L.; Li, Z.; Ng, C.; Schussman, G.; Ko, K.; Syratchev, I.; /CERN
2009-06-19
In recent years, SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic time-domain code T3P. Higher-order Finite Element methods on conformal unstructured meshes and massively parallel processing allow unprecedented simulation accuracy for wakefield computations and simulations of transient effects in realistic accelerator structures. Applications include simulation of wakefield damping in the Compact Linear Collider (CLIC) power extraction and transfer structure (PETS).
Iterative methods for 3D implicit finite-difference migration using the complex Padé approximation
NASA Astrophysics Data System (ADS)
Costa, Carlos A. N.; Campos, Itamara S.; Costa, Jessé C.; Neto, Francisco A.; Schleicher, Jörg; Novais, Amélia
2013-08-01
Conventional implementations of 3D finite-difference (FD) migration use splitting techniques to accelerate performance and save computational cost. However, such techniques are plagued with numerical anisotropy that jeopardises the correct positioning of dipping reflectors in the directions not used for the operator splitting. We implement 3D downward continuation FD migration without splitting using a complex Padé approximation. In this way, the numerical anisotropy is eliminated at the expense of a computationally more intensive solution of a large-band linear system. We compare the performance of the iterative stabilized biconjugate gradient (BICGSTAB) and that of the multifrontal massively parallel direct solver (MUMPS). It turns out that the use of the complex Padé approximation not only stabilizes the solution, but also acts as an effective preconditioner for the BICGSTAB algorithm, reducing the number of iterations as compared to the implementation using the real Padé expansion. As a consequence, the iterative BICGSTAB method is more efficient than the direct MUMPS method when solving a single term in the Padé expansion. The results of both algorithms, here evaluated by computing the migration impulse response in the SEG/EAGE salt model, are of comparable quality.
Preliminary simulation of a M6.5 earthquake on the Seattle Fault using 3D finite-difference modeling
Stephenson, William J.; Frankel, Arthur D.
2000-01-01
A three-dimensional finite-difference simulation of a moderate-sized (M 6.5) thrust-faulting earthquake on the Seattle fault demonstrates the effects of the Seattle Basin on strong ground motion in the Puget lowland. The model area includes the cities of Seattle, Bremerton and Bellevue. We use a recently developed detailed 3D-velocity model of the Seattle Basin in these simulations. The model extended to 20-km depth and assumed rupture on a finite fault with random slip distribution. Preliminary results from simulations of frequencies 0.5 Hz and lower suggest amplification can occur at the surface of the Seattle Basin by the trapping of energy in the Quaternary sediments. Surface waves generated within the basin appear to contribute to amplification throughout the modeled region. Several factors apparently contribute to large ground motions in downtown Seattle: (1) radiation pattern and directivity from the rupture; (2) amplification and energy trapping within the Quaternary sediments; and (3) basin geometry and variation in depth of both Quaternary and Tertiary sediments
NASA Astrophysics Data System (ADS)
Schultz, A.
2010-12-01
describe our ongoing efforts to achieve massive parallelization on a novel hybrid GPU testbed machine currently configured with 12 Intel Westmere Xeon CPU cores (or 24 parallel computational threads) with 96 GB DDR3 system memory, 4 GPU subsystems which in aggregate contain 960 NVidia Tesla GPU cores with 16 GB dedicated DDR3 GPU memory, and a second interleved bank of 4 GPU subsystems containing in aggregate 1792 NVidia Fermi GPU cores with 12 GB dedicated DDR5 GPU memory. We are applying domain decomposition methods to a modified version of Weiss' (2001) 3D frequency domain full physics EM finite difference code, an open source GPL licensed f90 code available for download from www.OpenEM.org. This will be the core of a new hybrid 3D inversion that parallelizes frequencies across CPUs and individual forward solutions across GPUs. We describe progress made in modifying the code to use direct solvers in GPU cores dedicated to each small subdomain, iteratively improving the solution by matching adjacent subdomain boundary solutions, rather than iterative Krylov space sparse solvers as currently applied to the whole domain.
Okamura, Yoshimasa; Yamamoto, Yoshito; Fujita, Kazuhiro; Miyoshi, Taiki; Teramoto, Koji; Kawaguchi, Hideki; Kagami, Shin; Furukawa, Masakazu
2007-07-15
Numerical studies of microwave propagation properties in a conical horn and an adjustable waveguides, and for plasmas generated under disk-plate windows of a 220 mm diameter and in a vacuum chamber are studied by a finite-difference time-domain (FDTD) method including plasma equations. In the numerical studies, a TM01-mode microwave of 2.45 GHz at a power of 1 kW is supplied from the top of the conical horn waveguide. In addition, numerical results by the FDTD method are compared with experimental results, and a validity of the numerical results is investigated. From the numerical results, it is found that the TM01-mode microwave changes its field shape and propagates along inner surfaces of the conical horn and the adjustable waveguides. Then electromagnetic fields of the TM01-mode microwave concentrate at the center surfaces of the disk-plate windows [quartz ({epsilon}{sub r}=3.8), alumina ({epsilon}{sub r}=9.7), and WG20 ({epsilon}{sub r}=20.0)]. A diameter of higher concentration is within 80 mm, and the orientation of electric field is almost vertical to the disk-plate window. The diameters within 80 mm are equivalent to a diameter at a higher electron density in an oxygen plasma experiment in the volume mode at 1 kW and 133 Pa with a quartz window. When heights of the adjustable waveguide are changed from 64 to 244 mm, peaks of electric fields in the heights, where microwave power is estimated to be strongly absorbed into the plasmas, appear and peak positions of the electric fields are observed periodically in surface-wave mode plasmas as well as the volume mode plasmas. Heights of the peaks increase with increasing dielectric constant and peak-to-peak distances of the peak positions decrease with increasing dielectric constant. The peak positions agree to the minimum microwave power reflections tuned by a combination of an autotuning unit and adjustable waveguide heights in experiments. Furthermore, peak positions of relatively absorbed microwave powers in
NASA Astrophysics Data System (ADS)
Kawabe, H.; Kamae, K.
2005-12-01
There is high possibility of the occurrence of the Tonankai and Nankai earthquakes which are capable of causing immense damage. During these huge earthquakes, long period ground motions may strike mega-cities Osaka and Nagoya located inside the Osaka and Nobi basins in which there are many long period and low damping structures (such as tall buildings and oil tanks). It is very important for the earthquake disaster mitigation to predict long period strong ground motions of the future Tonankai and Nankai earthquakes that are capable of exciting long-period strong ground motions over a wide area. In this study, we tried to predict long-period ground motions of the future Tonankai and Nankai earthquakes using 3D finite difference method. We construct a three-dimensional underground structure model including not only the basins but also propagation field from the source to the basins. Resultantly, we can point out that the predominant periods of pseudo-velocity response spectra change basin by basin. Long period ground motions with periods of 5 to 8 second are predominant in the Osaka basin, 3 to 6 second in the Nobi basin and 2 to 5 second in the Kyoto basin. These characteristics of the long-period ground motions are related with the thicknesses of the sediments of the basins. The duration of long period ground motions inside the basin are more than 5 minutes. These results are very useful for the earthquake disaster mitigation of long period structures such as tall buildings and oil tanks.
NASA Astrophysics Data System (ADS)
Perrin, A.; Hu, H.
2006-11-01
We have extended previous work on an 2D explicit finite-difference code for direct simulation of the motion of solid particles in a fluid to 3D. It is challenging to enforce the no-slip condition on the surface of spherical particles in a uniform Cartesian grid. We have implemented a treatment of the boundary condition similar to that in the PHYSALIS method of Takagi et. al. (2003), which is based on matching the Stokes flow solutions next to the particle surface with a numerical solution away from it. The original PHYSALIS method was developed for implicit flow solvers, and required an iterative process to match the Stokes flow solutions with the numerical solution. However, it was easily adapted to work with the present explicit scheme, and found to be more efficient since no iterative process is required in the matching. The method proceeds by approximating the flow next to the particle surface as a Stokes flow in the particle’s local coordinates, which is then matched to the numerically computed external flow on a ``cage'' of grid points near the particle surface. Advantages of the method include superior accuracy of the scheme on a relatively coarse grid for intermediate Reynolds numbers, ease of implementation, and the elimination of the need to track the particle surface. Several examples are presented, including flow over a stationary sphere in a square tube, sedimentation of a particle, and dropping, kissing, and tumbling of two particles. This research is supported by a GAANN fellowship from the U.S. Dept. of Education.
NASA Astrophysics Data System (ADS)
Tobón, Luis E.; Ren, Qiang; Liu, Qing Huo
2015-02-01
A new Discontinuous Galerkin Time Domain (DGTD) method for solving the 3D time dependent Maxwell's equations via the electric field intensity E and magnetic flux density B fields is proposed for the first time. It uses curl-conforming and divergence-conforming basis functions for E and B, respectively, with the same order of interpolation. In this way, higher accuracy is achieved at lower memory consumption than the conventional approach based on the field variables E and H. The centered flux and Riemann solver are both used to treat interfaces with non-conforming meshes, and both explicit Runge-Kutta method and implicit Crank-Nicholson method are implemented for time integration. Numerical examples for realistic cases will be presented to verify that the proposed method is a non-spurious and efficient DGTD scheme.
Wada, Yuji; Koyama, Daisuke; Nakamura, Kentaro
2014-12-01
The direct finite-difference fluid simulation of acoustic streaming on a fine-meshed three-dimensional model using a graphics processing unit (GPU)-based calculation array is discussed. Airflows are induced by an acoustic traveling wave when an intense sound field is generated in a gap between a bending transducer and a reflector. The calculation results showed good agreement with measurements in a pressure distribution. Several flow vortices were observed near the boundary layer of the reflector and the transducer, which have often been observed near the boundary of acoustic tubes, but have not been observed in previous calculations for this type of ultrasonic air pump.
NASA Astrophysics Data System (ADS)
da Silva, F.; Heuraux, S.; Ricardo, E.; Quental, P.; Ferreira, J.
2016-11-01
We conducted a first assessment of the measurement performance of the in-vessel components at gap 6 of the ITER plasma position reflectometry with the aid of a synthetic Ordinary Mode (O-mode) broadband frequency-modulated continuous-wave reflectometer implemented with REFMUL, a 2D finite-difference time-domain full-wave Maxwell code. These simulations take into account the system location within the vacuum vessel as well as its access to the plasma. The plasma case considered is a baseline scenario from Fusion for Energy. We concluded that for the analyzed scenario, (i) the plasma curvature and non-equatorial position of the antenna have neglectable impact on the measurements; (ii) the cavity-like space surrounding the antenna can cause deflection and splitting of the probing beam; and (iii) multi-reflections on the blanket wall cause a substantial error preventing the system from operating within the required error margin.
Baran, A J; Yang, P; Havemann, S
2001-08-20
We calculated the scattering and absorption properties of randomly oriented hexagonal ice columns using T-matrix theory, employing analytic orientation averaging, and the finite-difference time-domain method, which uses a numerical procedure to simulate random orientation. The total optical properties calculated are the extinction efficiency, absorption efficiency, single-scattering albedo, and the asymmetry parameter. The optical properties are calculated at the wavelengths of 0.66, 8.5, and 12 mum, up to a size parameter of 20 at 0.66 mum and 15 at the two other wavelengths. The phase-matrix elements P11, P12, and P22 are also calculated and compared, up to a size parameter of 20 at 0.66 mum and 15 at 12.0 mum. The scattering and absorption solutions obtained from the two independent electromagnetic methods are compared and contrasted, as well as the central processing unit time and memory load for each size parameter. It is found that the total optical properties calculated by the two methods are well within 3% of each other for all three wavelengths and size parameters. In terms of the phase-matrix elements it is found that there are some differences between the T-matrix and the finite-difference time-domain methods appearing in all three elements. Differences between the two methods for the P11 element are seen particularly at scattering angles from approximately 120 degrees to 180 degrees ; and at the scattering angle of 180 degrees , relative differences are less than 16%. At scattering angles less than 100 degrees , agreement is generally within a few percent. Similar results are also found for the P12 and P22 elements of the phase matrix. The validity of approximating randomly oriented hexagonal ice columns by randomly oriented equal surface area circular cylinders is also investigated in terms of the linear depolarization ratio.
NASA Technical Reports Server (NTRS)
Kraft, R. E.
1999-01-01
Single-degree-of-freedom resonators consisting of honeycomb cells covered by perforated facesheets are widely used as acoustic noise suppression liners in aircraft engine ducts. The acoustic resistance and mass reactance of such liners are known to vary with the intensity of the sound incident upon the panel. Since the pressure drop across a perforated liner facesheet increases quadratically with the flow velocity through the facesheet, this is known as the nonlinear resistance effect. In the past, two different empirical frequency domain models have been used to predict the Sound Pressure Level effect of the incident wave on the perforated liner impedance, one that uses the incident particle velocity in isolated narrowbands, and one that models the particle velocity as the overall velocity. In the absence of grazing flow, neither frequency domain model is entirely accurate in predicting the nonlinear effect that is measured for typical perforated sheets. The time domain model is developed in an attempt to understand and improve the model for the effect of spectral shape and amplitude of multi-frequency incident sound pressure on the liner impedance. A computer code for the time-domain finite difference model is developed and predictions using the models are compared to current frequency-domain models.
NASA Astrophysics Data System (ADS)
Moczo, Peter; Kristek, Jozef; Galis, Martin; Chaljub, Emmanuel; Etienne, Vincent
2011-12-01
We analyse 13 3-D numerical time-domain explicit schemes for modelling seismic wave propagation and earthquake motion for their behaviour with a varying P-wave to S-wave speed ratio (VP/VS). The second-order schemes include three finite-difference, three finite-element and one discontinuous-Galerkin schemes. The fourth-order schemes include three finite-difference and two spectral-element schemes. All schemes are second-order in time. We assume a uniform cubic grid/mesh and present all schemes in a unified form. We assume plane S-wave propagation in an unbounded homogeneous isotropic elastic medium. We define relative local errors of the schemes in amplitude and the vector difference in one time step and normalize them for a unit time. We also define the equivalent spatial sampling ratio as a ratio at which the maximum relative error is equal to the reference maximum error. We present results of the extensive numerical analysis. We theoretically (i) show how a numerical scheme sees the P and S waves if the VP/VS ratio increases, (ii) show the structure of the errors in amplitude and the vector difference and (iii) compare the schemes in terms of the truncation errors of the discrete approximations to the second mixed and non-mixed spatial derivatives. We find that four of the tested schemes have errors in amplitude almost independent on the VP/VS ratio. The homogeneity of the approximations to the second mixed and non-mixed spatial derivatives in terms of the coefficients of the leading terms of their truncation errors as well as the absolute values of the coefficients are key factors for the behaviour of the schemes with increasing VP/VS ratio. The dependence of the errors in the vector difference on the VP/VS ratio should be accounted for by a proper (sufficiently dense) spatial sampling.
Dharmaraj, Christopher D.; Thadikonda, Kishan; Fletcher, Anthony R.; Doan, Phuc N.; Devasahayam, Nallathamby; Matsumoto, Shingo; Johnson, Calvin A.; Cook, John A.; Mitchell, James B.; Subramanian, Sankaran; Krishna, Murali C.
2009-01-01
Three-dimensional Oximetric Electron Paramagnetic Resonance Imaging using the Single Point Imaging modality generates unpaired spin density and oxygen images that can readily distinguish between normal and tumor tissues in small animals. It is also possible with fast imaging to track the changes in tissue oxygenation in response to the oxygen content in the breathing air. However, this involves dealing with gigabytes of data for each 3D oximetric imaging experiment involving digital band pass filtering and background noise subtraction, followed by 3D Fourier reconstruction. This process is rather slow in a conventional uniprocessor system. This paper presents a parallelization framework using OpenMP runtime support and parallel MATLAB to execute such computationally intensive programs. The Intel compiler is used to develop a parallel C++ code based on OpenMP. The code is executed on four Dual-Core AMD Opteron shared memory processors, to reduce the computational burden of the filtration task significantly. The results show that the parallel code for filtration has achieved a speed up factor of 46.66 as against the equivalent serial MATLAB code. In addition, a parallel MATLAB code has been developed to perform 3D Fourier reconstruction. Speedup factors of 4.57 and 4.25 have been achieved during the reconstruction process and oximetry computation, for a data set with 23 × 23 × 23 gradient steps. The execution time has been computed for both the serial and parallel implementations using different dimensions of the data and presented for comparison. The reported system has been designed to be easily accessible even from low-cost personal computers through local internet (NIHnet). The experimental results demonstrate that the parallel computing provides a source of high computational power to obtain biophysical parameters from 3D EPR oximetric imaging, almost in real-time. PMID:19672315
Xin, Xuegang; Wang, Di; Han, Jijun; Feng, Yanqiu; Feng, Qianjin; Chen, Wufan
2012-07-01
The numerical optimization of a three-channel radiofrequency (RF) coil with a physical aperture for the open, vertical-field, MR-guided, focused ultrasound surgery (MRgFUS) system using the hybrid method of moment (MoM)/finite difference time domain (FDTD) method is reported. The numerical simulation of the current density distribution on an RF coil with a complicated irregular structure was performed using MoM. The electromagnetic field simulation containing the full coil-tissue interactions within the region of interest was accomplished using the FDTD method. Huygens' equivalent box with six surfaces smoothly connected the MoM and FDTD method. An electromagnetic model of the human pelvic region was reconstructed and loaded in the FDTD zone to optimize the three-channel RF coil and compensate for the lower sensitivity at the vertical field. In addition, the numerical MoM was used to model the resonance, decoupling and impedance matching of the RF coil in compliance with engineering practices. A prototype RF coil was constructed to verify the simulation results. The results demonstrate that the signal-to-noise ratio and the homogeneity of the B(1) field were both greatly improved compared with previously published results.
Hosokawa, Atsushi
2015-06-01
Using a finite-difference time-domain method, ultrasound backscattered waves inside cancellous bone were numerically analyzed to investigate the backscatter mechanism. Two bone models with different thicknesses were modeled with artificial absorbing layers positioned at the back surfaces of the model, and an ultrasound pulse wave was transmitted toward the front surface. By calculating the difference between the simulated waveforms obtained using the two bone models, the backscattered waves from a limited range of depths in cancellous bone could be isolated. The results showed that the fast and slow longitudinal waves, which have previously been observed only in the ultrasound waveform transmitted through the bone, could be distinguished in the backscattered waveform from a deeper bone depth when transmitting the ultrasound wave parallel to the main orientation of the trabecular network. The amplitudes of the fast and slow backscattered waves were more closely correlated with the bone porosity [R2 = 0.84 and 0.66 (p < 0.001), respectively] than the amplitude of the whole (nonisolated) backscattered waves [R2 = 0.48 (p < 0.001)]. In conclusion, the nonisolated backscattered waves could be regarded as the superposition of the fast and slow waves reflected from various bone depths, returning at different times.
NASA Astrophysics Data System (ADS)
Liu, Zhen; Teng, Bin; Ning, De-Zhi; Sun, Liang
2010-06-01
To study wave-current actions on 3-D bodies a time-domain numerical model was established using a higher-order boundary element method (HOBEM). By assuming small flow velocities, the velocity potential could be expressed for linear and higher order components by perturbation expansion. A 4th-order Runge-Kutta method was applied for time marching. An artificial damping layer was adopted at the outer zone of the free surface mesh to dissipate scattering waves. Validation of the numerical method was carried out on run-up, wave exciting forces, and mean drift forces for wave-currents acting on a bottom-mounted vertical cylinder. The results were in close agreement with the results of a frequency-domain method and a published time-domain method. The model was then applied to compute wave-current forces and run-up on a Seastar mini tension-leg platform.
NASA Astrophysics Data System (ADS)
Weng, W.; Taylor, P. A.
2010-09-01
Based on the early linear and Non-Linear Mixed Spectral Finite-Difference (MSFD and NLMSFD) models, a 3-D non-linear model of planetary boundary-layer flow (NLMSFD-PBL) was developed to study neutral PBL flow over complex terrain. The model assumes upwind or zero-order profiles of mean and turbulence variables about which perturbation quantities are calculated due to the effects of the terrain. In early models, the mean zero-order wind profile was assumed to be a simple logarithmic surface-layer profile and Reynolds stresses were constant throughout the depth of the model domain. This formally limits the applications of model to the surface-layer flow. The new model utilizes the results of early 1-D planetary boundary layer model of Weng and Taylor as the zero-order or upstream profiles of mean and turbulent quantities. The limitations associated with the original MSFD/NLMSFD model (e.g. logarithmic wind profile and constant shear stress layer) are relaxed. The effect of earth's rotation is also included in the model. Model results for planetary boundary-layer flow over complex terrain are discussed, particularly, the flow over Askervein hill - the site of a detailed and much referenced field study of flow over hills in the 1980s. This type of modelling of flow over complex terrain has important applications for wind energy resource assessment and wind farm design.
Turovets, Sergei; Volkov, Vasily; Zherdetsky, Aleksej; Prakonina, Alena; Malony, Allen D
2014-01-01
The Electrical Impedance Tomography (EIT) and electroencephalography (EEG) forward problems in anisotropic inhomogeneous media like the human head belongs to the class of the three-dimensional boundary value problems for elliptic equations with mixed derivatives. We introduce and explore the performance of several new promising numerical techniques, which seem to be more suitable for solving these problems. The proposed numerical schemes combine the fictitious domain approach together with the finite-difference method and the optimally preconditioned Conjugate Gradient- (CG-) type iterative method for treatment of the discrete model. The numerical scheme includes the standard operations of summation and multiplication of sparse matrices and vector, as well as FFT, making it easy to implement and eligible for the effective parallel implementation. Some typical use cases for the EIT/EEG problems are considered demonstrating high efficiency of the proposed numerical technique.
2015-08-01
CONTRACT NUMBER Form Approved OMB NO. 0704-0188 3. DATES COVERED (From - To) - UU UU UU UU 01-08-2015 1-Apr-2011 31- Mar -2014 Approved for Public Release...Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 landscape dynamics, lidar time series, space time cube, tangible interface...2701 Sullivan Drive Suite 240 Raleigh, NC 27695 -7514 31- Mar -2014 ABSTRACT Terrain Dynamics Analysis Using Space-Time Domain Hypersurfaces and
2007-10-01
from) in earth -fixed axes ν mean wave direction (from) in earth -fixed axes νi mean wave direction (from) for spectral component i ρ water density {σ...Kennedy Abstract This report serves as a user manual for simulating ship motions in waves and in calm water using ShipMo3D Version 1.0. ShipMo3D is...with associated user applica- tions for predicting ship motions in calm water and in waves. Motion predictions are available in both the frequency
Time-Domain Simulation of RF Couplers
Smithe, David; Carlsson, Johan; Austin, Travis
2009-11-26
We have developed a finite-difference time-domain (FDTD) fluid-like approach to integrated plasma-and-coupler simulation [1], and show how it can be used to model LH and ICRF couplers in the MST and larger tokamaks.[2] This approach permits very accurate 3-D representation of coupler geometry, and easily includes non-axi-symmetry in vessel wall, magnetic equilibrium, and plasma density. The plasma is integrated with the FDTD Maxwell solver in an implicit solve that steps over electron time-scales, and permits tenuous plasma in the coupler itself, without any need to distinguish or interface between different regions of vacuum and/or plasma. The FDTD algorithm is also generalized to incorporate a time-domain sheath potential [3] on metal structures within the simulation, to look for situations where the sheath potential might generate local sputtering opportunities. Benchmarking of the time-domain sheath algorithm has been reported in the references. Finally, the time-domain software [4] permits the use of particles, either as field diagnostic (test particles) or to self-consistently compute plasma current from the applied RF power.
A two-dimensional time domain near zone to far zone transformation
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Ryan, Deirdre; Beggs, John H.; Kunz, Karl S.
1991-01-01
In a previous paper, a time domain transformation useful for extrapolating 3-D near zone finite difference time domain (FDTD) results to the far zone was presented. In this paper, the corresponding 2-D transform is outlined. While the 3-D transformation produced a physically observable far zone time domain field, this is not convenient to do directly in 2-D, since a convolution would be required. However, a representative 2-D far zone time domain result can be obtained directly. This result can then be transformed to the frequency domain using a Fast Fourier Transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time domain far zone result is required it can be obtained by inverse Fourier transform of the final frequency domain result.
Finite Difference Time Domain Modeling at USA Instruments, Inc.
NASA Astrophysics Data System (ADS)
Curtis, Richard
2003-10-01
Due to the competitive nature of the commercial MRI industry, it is essential for the financial health of a participating company to innovate new coil designs and bring product to market rapidly in response to ever-changing market conditions. However, the technology of MRI coil design is still early in its stage of development and its principles are yet evolving. As a result, it is not always possible to know the relevant electromagnetic effects of a given design since the interaction of coil elements is complex and often counter-intuitive. Even if the effects are known qualitatively, the quantitative results are difficult to obtain. At USA Instruments, Inc., the acquisition of the XFDTDâ electromagnetic simulation tool from REMCOM, Inc., has been helpful in determining the electromagnetic performance characteristics of existing coil designs in the prototype stage before the coils are released for production. In the ideal case, a coil design would be modeled earlier at the conceptual stage, so that only good designs will make it to the prototyping stage and the electromagnetic characteristics better understood very early in the design process and before the testing stage has begun. This paper is a brief overview of using FDTD modeling for MRI coil design at USA Instruments, Inc., and shows some of the highlights of recent FDTD modeling efforts on Birdcage coils, a staple of the MRI coil design portfolio.
NAFDTD - A Near-field Finite Difference Time Domain Solver
2012-09-01
SAR Mode ......................................................28 5. Generating the Sources and Receivers 33 6. Code Validation and Examples 38...by NAFDTD and FEKO showing (a) magnitude at h = 12 cm; (b) phase at h = 12 cm; (c) magnitude at h = 2 m; and (d) phase at h = 2m...project_name.savenear). ................25 Figure 26. Example of PBS job submission script for the Harold system running the NAFDTD code in the SAR mode
Seafloor Scattering in Three Dimensions by Time Domain Finite Differences
2006-02-13
the first two years we would have liked to address the following tasks: 1) A version of Spectral Element Method (SEM) code which runs on a Beowulf ...computer architectures like Beowulf clusters and grids. Some issues that will need to be addressed in transitioning the SEM code to high frequency bottom
NASA Astrophysics Data System (ADS)
Komatitsch, Dimitri; Michéa, David; Erlebacher, Gordon; Göddeke, Dominik
2010-05-01
We first accelerate a three-dimensional finite-difference in the time domain (FDTD) wave propagation code by a factor of about 50 using Graphics Processing Unit (GPU) computing on a cheap NVIDIA graphics card with the CUDA programming language. We implement the code in CUDA in the case of the fully heterogeneous elastic wave equation. We also implement Convolution Perfectly Matched Layers (CPMLs) on the graphics card to efficiently absorb outgoing waves on the fictitious edges of the grid. We show that the code that runs on the graphics card gives the expected results by comparing our results to those obtained by running the same simulation on a classical processor core. The methodology that we present can be used for Maxwell's equations as well because their form is similar to that of the seismic wave equation written in velocity vector and stress tensor. We then implement a high-order finite-element (spectral-element) application, which performs the numerical simulation of seismic wave propagation resulting for instance from earthquakes at the scale of a continent or from active seismic acquisition experiments in the oil industry, on a cluster of NVIDIA Tesla graphics cards using the CUDA programming language and non blocking message passing based on MPI. We compare it to the implementation in C language and MPI on a classical cluster of CPU nodes. We use mesh coloring to efficiently handle summation operations over degrees of freedom on an unstructured mesh, and we exchange information between nodes using non blocking MPI messages. Using non-blocking communications allows us to overlap the communications across the network and the data transfer between the GPU card and the CPU node on which it is installed with calculations on that GPU card. We perform a number of numerical tests to validate the single-precision CUDA and MPI implementation and assess its accuracy. We then analyze performance measurements and in average we obtain a speedup of 20x to 25x.
Accurate Finite Difference Algorithms
NASA Technical Reports Server (NTRS)
Goodrich, John W.
1996-01-01
Two families of finite difference algorithms for computational aeroacoustics are presented and compared. All of the algorithms are single step explicit methods, they have the same order of accuracy in both space and time, with examples up to eleventh order, and they have multidimensional extensions. One of the algorithm families has spectral like high resolution. Propagation with high order and high resolution algorithms can produce accurate results after O(10(exp 6)) periods of propagation with eight grid points per wavelength.
Time domain simulation and sound synthesis for the snare drum.
Bilbao, Stefan
2012-01-01
The snare drum is a complex system, relying on the interaction of multiple components: the drumheads, or membranes, a set of snares, the surrounding acoustic field and an internal cavity. Because these components are multidimensional, and due to a strong distributed non-linearity (the snare interaction), many techniques used frequently in physical modeling synthesis applications, such as digital waveguides and modal methods are difficult to apply. In this article, finite difference time domain techniques are applied to a full 3D system, and various features of interest, such as the coupling between membranes, and the interaction between the membranes and the snares, are examined in detail. Also discussed are various numerical features, such as spurious splitting of degenerate modes and bandwidth limitation, and estimates of computational complexity are provided. Sound examples are presented.
Casimir forces in the time domain: Theory
Rodriguez, Alejandro W.; McCauley, Alexander P.; Joannopoulos, John D.; Johnson, Steven G.
2009-07-15
We present a method to compute Casimir forces in arbitrary geometries and for arbitrary materials based on the finite-difference time-domain (FDTD) scheme. The method involves the time evolution of electric and magnetic fields in response to a set of current sources, in a modified medium with frequency-independent conductivity. The advantage of this approach is that it allows one to exploit existing FDTD software, without modification, to compute Casimir forces. In this paper, we focus on the derivation, implementation choices, and essential properties of the time-domain algorithm, both considered analytically and illustrated in the simplest parallel-plate geometry.
3D nanopillar optical antenna photodetectors.
Senanayake, Pradeep; Hung, Chung-Hong; Shapiro, Joshua; Scofield, Adam; Lin, Andrew; Williams, Benjamin S; Huffaker, Diana L
2012-11-05
We demonstrate 3D surface plasmon photoresponse in nanopillar arrays resulting in enhanced responsivity due to both Localized Surface Plasmon Resonances (LSPRs) and Surface Plasmon Polariton Bloch Waves (SPP-BWs). The LSPRs are excited due to a partial gold shell coating the nanopillar which acts as a 3D Nanopillar Optical Antenna (NOA) in focusing light into the nanopillar. Angular photoresponse measurements show that SPP-BWs can be spectrally coincident with LSPRs to result in a x2 enhancement in responsivity at 1180 nm. Full-wave Finite Difference Time Domain (FDTD) simulations substantiate both the spatial and spectral coupling of the SPP-BW / LSPR for enhanced absorption and the nature of the LSPR. Geometrical control of the 3D NOA and the self-aligned metal hole lattice allows the hybridization of both localized and propagating surface plasmon modes for enhanced absorption. Hybridized plasmonic modes opens up new avenues in optical antenna design in nanoscale photodetectors.
THE PSTD ALGORITHM: A TIME-DOMAIN METHOD REQUIRING ONLY TWO CELLS PER WAVELENGTH. (R825225)
A pseudospectral time-domain (PSTD) method is developed for solutions of Maxwell's equations. It uses the fast Fourier transform (FFT), instead of finite differences on conventional finite-difference-time-domain (FDTD) methods, to represent spatial derivatives. Because the Fourie...
Upwind Compact Finite Difference Schemes
NASA Astrophysics Data System (ADS)
Christie, I.
1985-07-01
It was shown by Ciment, Leventhal, and Weinberg ( J. Comput. Phys.28 (1978), 135) that the standard compact finite difference scheme may break down in convection dominated problems. An upwinding of the method, which maintains the fourth order accuracy, is suggested and favorable numerical results are found for a number of test problems.
Quasi-Wollaston-Prism for Terahertz Frequencies Fabricated by 3D Printing
NASA Astrophysics Data System (ADS)
Hernandez-Serrano, A. I.; Castro-Camus, E.
2017-01-01
In this letter, we present the design, fabrication, and characterization of a quasi-Wollaston prism for terahertz frequencies based on form birefringence. The prism uses the birefringence induced in a sub-wavelength layered plastic-air structure that produces refraction in different directions for different polarizations. The component was simulated using the finite-difference-time-domain method, fabricated by 3D printing and subsequently tested by terahertz time-domain spectroscopy showing a polarization separation around of 23° for frequencies below 400 GHz, exhibiting cross polarization power extinction ratios better than 1.6 × 10-3 at 200 GHz.
Implicit time-domain simulation of metamaterials on GPUs
NASA Astrophysics Data System (ADS)
Cooke, Simon; Levush, Baruch
2010-11-01
Metamaterials present a challenge to 3D electromagnetic simulation due to their sub-wavelength structural features, demanding spatial grid cell sizes typically λ/50. This is similar to the situation found modeling conventional slow-wave structures, such as TWTs. For explicit, finite-difference time-domain (FDTD) techniques, numerical stability further dictates the use of very small time steps, leading to long simulation times for wave propagation in metamaterials. We present simulations using a new alternating direction implicit (ADI) FDTD algorithm [1,2] implemented efficiently for high performance graphics processing units (GPUs). Our method uses a complex-envelope representation for the field amplitudes to factor out the rf timescale, and is absolutely stable. Consequently, we are able to use time steps comparable to the rf period for narrow-bandwidth simulations, and reduce simulation times by orders of magnitude compared to conventional FDTD on CPUs. Simulation results will be presented for a number of metamaterial structures. [1] S. J. Cooke et al., Int. J. Numer. Model., 22, 187 (2009) [2] M. Botton et al., IEEE Trans. Plasma Sci., 38 (6), 1439 (2010)
Finite-Difference, Time-Domain Simulation of Sound Propagation in a Dynamic Atmosphere
2004-05-01
Tech- nology Laboratory, David Aldridge and Neill Symons of the Sandia National Laboratory, David Marlin and Sandra Collier of the Army Research...above. [The reader may refer to Attenborough et al. (1995) and Salomons (2001) for detailed discussions of the FFP and PE methods.] On the other hand...small pores and/or low frequencies. Subsequent authors, such as Attenborough (1983), have shown that when the properties of the material are considered
Prospects for Finite-Difference Time-Domain (FDTD) Computational Electrodynamics
NASA Astrophysics Data System (ADS)
Taflove, Allen
2002-08-01
FDTD is the most powerful numerical solution of Maxwell's equations for structures having internal details. Relative to moment-method and finite-element techniques, FDTD can accurately model such problems with 100-times more field unknowns and with nonlinear and/or time-variable parameters. Hundreds of FDTD theory and applications papers are published each year. Currently, there are at least 18 commercial FDTD software packages for solving problems in: defense (especially vulnerability to electromagnetic pulse and high-power microwaves); design of antennas and microwave devices/circuits; electromagnetic compatibility; bioelectromagnetics (especially assessment of cellphone-generated RF absorption in human tissues); signal integrity in computer interconnects; and design of micro-photonic devices (especially photonic bandgap waveguides, microcavities; and lasers). This paper explores emerging prospects for FDTD computational electromagnetics brought about by continuing advances in computer capabilities and FDTD algorithms. We conclude that advances already in place point toward the usage by 2015 of ultralarge-scale (up to 1E11 field unknowns) FDTD electromagnetic wave models covering the frequency range from about 0.1 Hz to 1E17 Hz. We expect that this will yield significant benefits for our society in areas as diverse as computing, telecommunications, defense, and public health and safety.
Numerical analysis of curved frequency selective surface by finite-difference time-domain
NASA Astrophysics Data System (ADS)
Chen, Xin-yi; Wang, Jian-bo; Chen, Gui-bo; Sun, Guan-cheng; Lu, Jun
2011-08-01
Frequency selective surface is a monolayer or multilayer 2D periodic structure which is composed of multiple resonance units scattering by a two-dimensional periodic array on dielectric layer. FSS can't absorb radio frequency energy, but can filter the frequency which is therefore applied in microwave technique or stealth technology. The relative research on curved FSS is relatively scarce since the curved FSS structure can be obtained only when FSS is attached on the materials surfaces of curved structures in engineering application. However, curved FSS is widely applied in practical engineering; therefore, the research on curved FSS structure has important significance. In this paper, a curved FSS structure model of Y-pore unit is established and numerical simulated by means of FDTD. The influence of curvature on FSS transmission characteristics is studied according to the analysis on the changing of radar cross section (RCS). The results show: the center frequency point of the plane band pass FSS structure drifts after the curve surface deformation of the structure; the center frequency point of the curved band pass FSS structure drifts with the changing of the curvature radius, i. e. with the decreasing of curvature radius, the frequency point drifts towards high points and the transmittance decreases. The design of FSS radome demands of accurate and stable center resonance frequency; therefore, the actual situation of curved surface should be considered in practical engineering application when band pass FSS is made into frequency selection filtering radome. The curvature radius should be long enough to avoid center frequency drifting and transmittance deceasing.
Chen, Hao; Tang, Juming; Liu, Fang
2007-01-01
Due to the complexity of interactions between microwaves and food products, a reliable and efficient simulation model can be a very useful tool to guide the design of microwave heating systems and processes. This research developed a model to simulate coupled phenomena of electromagnetic heating and conventional heat transfer by combining commercial electromagnetic software with a customer built heat transfer model. Simulation results were presented and compared with experimental results for hot water and microwave heating in a single mode microwave system at 915 MHz. Good agreement was achieved, showing that this model was able to provide insight into industrial electromagnetic heating processes.
Finite Difference Time Domain (FDTD) Analysis of a Leaky Traveling Wave Microstrip Antenna
2007-11-02
aviobj = avifile([name,’.avi’],’ fps ’,12,’quality’,100); end; %*********************************************************************** % FREQUENCY...Joachim and Rolf H. Jansen . “Spectral Domain Investigation of Surface Wave Excitation and Radiation by Microstrip Lines and Microstrip Disk Resonators
2008-02-01
frequency electromagnetic exposure: tutorial review on experimental dosimetry.” Bioelectromagnetics . 1996;17(3):195-208. [8] Chou, C. K., G. W...Chen, A. W. Guy, and K. H. Luk, “Formulas for Preparing Phantom Muscle Tissue at Various Radiofrequencies,” Bioelectromagnetics , 1984, 5, 435-441
NASA Astrophysics Data System (ADS)
Holt, Jennifer Jane
Ground Penetrating Radar (GPR) is a common technique for locating buried objects in the near surface. The near surface is never perfectly homogeneous due to different moisture levels, grain packing, and types of material that influence the properties in the subsurface. This dissertation examines the influence of heterogeneity on GPR measurements, its influence on spatial dispersion, and defining the GPR response from a range of standard deviations of different numerical models. Most modeling in GPR concentrates on antenna patterns or dispersion caused by complex permittivity in homogeneous blocks of material. The forward model developed in this dissertation incorporates heterogeneity by replacing the traditional homogenous spatial regions with a distribution of physical properties. The models in this dissertation maintain the major spatial model boundaries, but the physical model values within each boundary are determined by a statistical distribution. Statistical approximations of heterogeneity of the physical property distributions can provide an approximation of the geologic noise that influences GPR measurements. This dissertation presents a numerical modeling analysis of random property variation, where the variations occur in one, two, and three directions. The models are developed for a half space and a two layered earth model where the input is a Ricker wavelet. Most of the visible spatial dispersion of the electrical field in both the half space and the layered earth models studied in this dissertation, occurred in the near region of the electromagnetic field. However, the largest average dispersion occurred in the far field at 1.0 m distance from a dipole source. The presence of horizontal layers increased the dispersive effects of the random distribution of electrical property values. There was also a measurable change in the dispersed field when the layers were vertical. There was more change with thin horizontal layers than with tubes or three dimensional variations of heterogeneous material. A practical conclusion of this study is that lateral variation in physical properties must be taken into account when interpreting GPR data.
Finite difference neuroelectric modeling software.
Dang, Hung V; Ng, Kwong T
2011-06-15
This paper describes a finite difference neuroelectric modeling software (FNS), written in C and MATLAB, which can be executed as a standalone program or integrated with other packages for electroencephalography (EEG) analysis. The package from the Oxford Center for Functional MRI of the Brain (FMRIB), FMRIB Software Library (FSL), is used to segment the anatomical magnetic resonance (MR) image for realistic head modeling. The EEG electrode array is fitted to the realistic head model using the Bioelectromagnetism MATLAB toolbox. The finite difference formulation for a general inhomogeneous anisotropic body is used to obtain the system matrix equation, which is then solved using the conjugate gradient algorithm. The reciprocity theorem is utilized to limit the number of required forward solutions to N-1, where N is the number of electrodes. Results show that the forward solver only requires 500 MB of random-access memory (RAM) for a realistic 256×256×256 head model and that the software can be conveniently combined with inverse algorithms such as beamformers and MUSIC. The software is freely available under the GNU Public License.
NASA Astrophysics Data System (ADS)
Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.
2015-12-01
The acoustic and gravity waves propagating in the planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to the atmosphere dynamics. To get a better understanding of the physic behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground to the upper thermosphere. Thus, In order to provide an efficient numerical tool at the regional or the global scale a high order finite difference time domain (FDTD) approach is proposed that relies on the linearized compressible Navier-Stokes equations (Landau 1959) with non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). One significant benefit from this code is its versatility. Indeed, it handles both acoustic and gravity waves in the same simulation that enables one to observe correlations between the two. Simulations will also be performed on 2D/3D realistic cases such as tsunamis in a full MSISE-00 atmosphere and gravity-wave generation through atmospheric explosions. Computations are validated by comparison to well-known analytical solutions based on dispersion relations in specific benchmark cases (atmospheric explosion and bottom displacement forcing).
A parallel algorithm for solving the 3d Schroedinger equation
Strickland, Michael; Yager-Elorriaga, David
2010-08-20
We describe a parallel algorithm for solving the time-independent 3d Schroedinger equation using the finite difference time domain (FDTD) method. We introduce an optimized parallelization scheme that reduces communication overhead between computational nodes. We demonstrate that the compute time, t, scales inversely with the number of computational nodes as t {proportional_to} (N{sub nodes}){sup -0.95} {sup {+-} 0.04}. This makes it possible to solve the 3d Schroedinger equation on extremely large spatial lattices using a small computing cluster. In addition, we present a new method for precisely determining the energy eigenvalues and wavefunctions of quantum states based on a symmetry constraint on the FDTD initial condition. Finally, we discuss the usage of multi-resolution techniques in order to speed up convergence on extremely large lattices.
Time-domain boundary conditions for outdoor ground surfaces
NASA Astrophysics Data System (ADS)
Collier, Sandra L.; Ostashev, Vladimir E.; Wilson, D. Keith; Marlin, David H.
2003-10-01
Finite-difference time-domain techniques are promising for detailed dynamic simulations of sound propagation in complex atmospheric environments. Success of such simulations requires the development of new techniques to accurately handle the reflective and absorptive properties of a porous ground. One method of treating the ground boundary condition in the time domain [Salomons et al., Acta Acust. 88, 483-492 (2002)] is to use modified fluid dynamic equations, where the ground is considered as a porous medium described by its physical properties. However, this approach significantly increases computation time, as the domain must be extended into the ground and a large number of grid points are needed. Standard impedance models for the ground boundary condition are frequency-domain models, which generally are non-causal [Y. H. Berthelot, J. Acoust. Soc. Am. 109, 1736-1739 (2001)]. The development of a time-domain boundary condition from these models requires removing the singularity from the impedance equation when transforming from the frequency domain to the time domain. Alternatively, as the impedance boundary condition is a flux equation, a time-domain boundary condition can be derived from first principles, using the physical properties of the ground. We report on our development of a time-domain ground boundary condition.
NASA Astrophysics Data System (ADS)
Bodin, Jacques
2015-03-01
In this study, new multi-dimensional time-domain random walk (TDRW) algorithms are derived from approximate one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) analytical solutions of the advection-dispersion equation and from exact 1-D, 2-D, and 3-D analytical solutions of the pure-diffusion equation. These algorithms enable the calculation of both the time required for a particle to travel a specified distance in a homogeneous medium and the mass recovery at the observation point, which may be incomplete due to 2-D or 3-D transverse dispersion or diffusion. The method is extended to heterogeneous media, represented as a piecewise collection of homogeneous media. The particle motion is then decomposed along a series of intermediate checkpoints located on the medium interface boundaries. The accuracy of the multi-dimensional TDRW method is verified against (i) exact analytical solutions of solute transport in homogeneous media and (ii) finite-difference simulations in a synthetic 2-D heterogeneous medium of simple geometry. The results demonstrate that the method is ideally suited to purely diffusive transport and to advection-dispersion transport problems dominated by advection. Conversely, the method is not recommended for highly dispersive transport problems because the accuracy of the advection-dispersion TDRW algorithms degrades rapidly for a low Péclet number, consistent with the accuracy limit of the approximate analytical solutions. The proposed approach provides a unified methodology for deriving multi-dimensional time-domain particle equations and may be applicable to other mathematical transport models, provided that appropriate analytical solutions are available.
Casimir forces in the time domain: Applications
McCauley, Alexander P.; Rodriguez, Alejandro W.; Joannopoulos, John D.; Johnson, Steven G.
2010-01-15
Our previous article [Phys. Rev. A 80, 012115 (2009)] introduced a method to compute Casimir forces in arbitrary geometries and for arbitrary materials that was based on a finite-difference time-domain (FDTD) scheme. In this article, we focus on the efficient implementation of our method for geometries of practical interest and extend our previous proof-of-concept algorithm in one dimension to problems in two and three dimensions, introducing a number of new optimizations. We consider Casimir pistonlike problems with nonmonotonic and monotonic force dependence on sidewall separation, both for previously solved geometries to validate our method and also for new geometries involving magnetic sidewalls and/or cylindrical pistons. We include realistic dielectric materials to calculate the force between suspended silicon waveguides or on a suspended membrane with periodic grooves, also demonstrating the application of perfectly matched layer (PML) absorbing boundaries and/or periodic boundaries. In addition, we apply this method to a realizable three-dimensional system in which a silica sphere is stably suspended in a fluid above an indented metallic substrate. More generally, the method allows off-the-shelf FDTD software, already supporting a wide variety of materials (including dielectric, magnetic, and even anisotropic materials) and boundary conditions, to be exploited for the Casimir problem.
Finite-difference computations of rotor loads
NASA Technical Reports Server (NTRS)
Caradonna, F. X.; Tung, C.
1985-01-01
The current and future potential of finite difference methods for solving real rotor problems which now rely largely on empiricism are demonstrated. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advanced-ratio flight. Comparisons are made with experimental pressure data.
Finite-difference computations of rotor loads
NASA Technical Reports Server (NTRS)
Caradonna, F. X.; Tung, C.
1985-01-01
This paper demonstrates the current and future potential of finite-difference methods for solving real rotor problems which now rely largely on empiricism. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advance-ratio flight. Comparisons are made with experimental pressure data.
Flexible time domain averaging technique
NASA Astrophysics Data System (ADS)
Zhao, Ming; Lin, Jing; Lei, Yaguo; Wang, Xiufeng
2013-09-01
Time domain averaging(TDA) is essentially a comb filter, it cannot extract the specified harmonics which may be caused by some faults, such as gear eccentric. Meanwhile, TDA always suffers from period cutting error(PCE) to different extent. Several improved TDA methods have been proposed, however they cannot completely eliminate the waveform reconstruction error caused by PCE. In order to overcome the shortcomings of conventional methods, a flexible time domain averaging(FTDA) technique is established, which adapts to the analyzed signal through adjusting each harmonic of the comb filter. In this technique, the explicit form of FTDA is first constructed by frequency domain sampling. Subsequently, chirp Z-transform(CZT) is employed in the algorithm of FTDA, which can improve the calculating efficiency significantly. Since the signal is reconstructed in the continuous time domain, there is no PCE in the FTDA. To validate the effectiveness of FTDA in the signal de-noising, interpolation and harmonic reconstruction, a simulated multi-components periodic signal that corrupted by noise is processed by FTDA. The simulation results show that the FTDA is capable of recovering the periodic components from the background noise effectively. Moreover, it can improve the signal-to-noise ratio by 7.9 dB compared with conventional ones. Experiments are also carried out on gearbox test rigs with chipped tooth and eccentricity gear, respectively. It is shown that the FTDA can identify the direction and severity of the eccentricity gear, and further enhances the amplitudes of impulses by 35%. The proposed technique not only solves the problem of PCE, but also provides a useful tool for the fault symptom extraction of rotating machinery.
3-D FDTD simulation of shear waves for evaluation of complex modulus imaging.
Orescanin, Marko; Wang, Yue; Insana, Michael
2011-02-01
The Navier equation describing shear wave propagation in 3-D viscoelastic media is solved numerically with a finite differences time domain (FDTD) method. Solutions are formed in terms of transverse scatterer velocity waves and then verified via comparison to measured wave fields in heterogeneous hydrogel phantoms. The numerical algorithm is used as a tool to study the effects on complex shear modulus estimation from wave propagation in heterogeneous viscoelastic media. We used an algebraic Helmholtz inversion (AHI) technique to solve for the complex shear modulus from simulated and experimental velocity data acquired in 2-D and 3-D. Although 3-D velocity estimates are required in general, there are object geometries for which 2-D inversions provide accurate estimations of the material properties. Through simulations and experiments, we explored artifacts generated in elastic and dynamic-viscous shear modulus images related to the shear wavelength and average viscosity.
Finite-difference modeling of commercial aircraft using TSAR
Pennock, S.T.; Poggio, A.J.
1994-11-15
Future aircraft may have systems controlled by fiber optic cables, to reduce susceptibility to electromagnetic interference. However, the digital systems associated with the fiber optic network could still experience upset due to powerful radio stations, radars, and other electromagnetic sources, with potentially serious consequences. We are modeling the electromagnetic behavior of commercial transport aircraft in support of the NASA Fly-by-Light/Power-by-Wire program, using the TSAR finite-difference time-domain code initially developed for the military. By comparing results obtained from TSAR with data taken on a Boeing 757 at the Air Force Phillips Lab., we hope to show that FDTD codes can serve as an important tool in the design and certification of U.S. commercial aircraft, helping American companies to produce safe, reliable air transportation.
Applications of an exponential finite difference technique
NASA Technical Reports Server (NTRS)
Handschuh, Robert F.; Keith, Theo G., Jr.
1988-01-01
An exponential finite difference scheme first presented by Bhattacharya for one dimensional unsteady heat conduction problems in Cartesian coordinates was extended. The finite difference algorithm developed was used to solve the unsteady diffusion equation in one dimensional cylindrical coordinates and was applied to two and three dimensional conduction problems in Cartesian coordinates. Heat conduction involving variable thermal conductivity was also investigated. The method was used to solve nonlinear partial differential equations in one and two dimensional Cartesian coordinates. Predicted results are compared to exact solutions where available or to results obtained by other numerical methods.
Calculation of nonzero-temperature Casimir forces in the time domain
Pan, Kai; Reid, M. T. Homer; McCauley, Alexander P.; Rodriguez, Alejandro W.; White, Jacob K.; Johnson, Steven G.
2011-04-15
We show how to compute Casimir forces at nonzero temperatures with time-domain electromagnetic simulations, for example, using a finite-difference time-domain (FDTD) method. Compared to our previous zero-temperature time-domain method, only a small modification is required, but we explain that some care is required to properly capture the zero-frequency contribution. We validate the method against analytical and numerical frequency-domain calculations, and show a surprising high-temperature disappearance of a nonmonotonic behavior previously demonstrated in a pistonlike geometry.
Optimized Finite-Difference Coefficients for Hydroacoustic Modeling
NASA Astrophysics Data System (ADS)
Preston, L. A.
2014-12-01
Responsible utilization of marine renewable energy sources through the use of current energy converter (CEC) and wave energy converter (WEC) devices requires an understanding of the noise generation and propagation from these systems in the marine environment. Acoustic noise produced by rotating turbines, for example, could adversely affect marine animals and human-related marine activities if not properly understood and mitigated. We are utilizing a 3-D finite-difference acoustic simulation code developed at Sandia that can accurately propagate noise in the complex bathymetry in the near-shore to open ocean environment. As part of our efforts to improve computation efficiency in the large, high-resolution domains required in this project, we investigate the effects of using optimized finite-difference coefficients on the accuracy of the simulations. We compare accuracy and runtime of various finite-difference coefficients optimized via criteria such as maximum numerical phase speed error, maximum numerical group speed error, and L-1 and L-2 norms of weighted numerical group and phase speed errors over a given spectral bandwidth. We find that those coefficients optimized for L-1 and L-2 norms are superior in accuracy to those based on maximal error and can produce runtimes of 10% of the baseline case, which uses Taylor Series finite-difference coefficients at the Courant time step limit. We will present comparisons of the results for the various cases evaluated as well as recommendations for utilization of the cases studied. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Seismic imaging using finite-differences and parallel computers
Ober, C.C.
1997-12-31
A key to reducing the risks and costs of associated with oil and gas exploration is the fast, accurate imaging of complex geologies, such as salt domes in the Gulf of Mexico and overthrust regions in US onshore regions. Prestack depth migration generally yields the most accurate images, and one approach to this is to solve the scalar wave equation using finite differences. As part of an ongoing ACTI project funded by the US Department of Energy, a finite difference, 3-D prestack, depth migration code has been developed. The goal of this work is to demonstrate that massively parallel computers can be used efficiently for seismic imaging, and that sufficient computing power exists (or soon will exist) to make finite difference, prestack, depth migration practical for oil and gas exploration. Several problems had to be addressed to get an efficient code for the Intel Paragon. These include efficient I/O, efficient parallel tridiagonal solves, and high single-node performance. Furthermore, to provide portable code the author has been restricted to the use of high-level programming languages (C and Fortran) and interprocessor communications using MPI. He has been using the SUNMOS operating system, which has affected many of his programming decisions. He will present images created from two verification datasets (the Marmousi Model and the SEG/EAEG 3D Salt Model). Also, he will show recent images from real datasets, and point out locations of improved imaging. Finally, he will discuss areas of current research which will hopefully improve the image quality and reduce computational costs.
A two-dimensional time domain near zone to far zone transformation
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Ryan, Deirdre; Beggs, John H.; Kunz, Karl S.
1991-01-01
A time domain transformation useful for extrapolating three dimensional near zone finite difference time domain (FDTD) results to the far zone was presented. Here, the corresponding two dimensional transform is outlined. While the three dimensional transformation produced a physically observable far zone time domain field, this is not convenient to do directly in two dimensions, since a convolution would be required. However, a representative two dimensional far zone time domain result can be obtained directly. This result can then be transformed to the frequency domain using a Fast Fourier Transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time domain far zone result is required, it can be obtained by inverse Fourier transform of the final frequency domain result.
NASA Astrophysics Data System (ADS)
Takenaka, H.; Komatsu, M.; Toyokuni, G.; Nakamura, T.; Okamoto, T.
2015-12-01
A simple and efficient finite-difference scheme is developed to compute seismic wave propagation for a partial spherical shell model of a three-dimensionally (3-D) heterogeneous global earth structure. This new scheme solves the elastodynamic equations in the "quasi-Cartesian" coordinate system similar to a local Cartesian one, instead of the spherical coordinate system, with a staggered-grid finite-difference method in time domain (FDTD) which is one of the most popular numerical methods in seismic motion simulations for local to regional scale models. The proposed scheme may be useful for modeling seismic wave propagation in a very large region of sub-global scale beyond regional and less than global ones, where the effects of roundness of earth cannot be ignored. In "quasi-Cartesian" coordinates, x, y, and z are set to be locally in directions of latitude, longitude and depth, respectively. The stencil for each of the x-derivatives then depends on the depth coordinate at the evaluation point, while the stencil for each of the y-derivatives varies with both coordinates of the depth and latitude. In order to reduce lateral variations of the horizontal finite-difference stencils over the computational domain, we move the target area to a location around the equator of the computational spherical coordinate system using a way similar to the conversion from equatorial coordinates to ecliptic coordinates. The developed scheme can be easily implemented in 3-D Cartesian FDTD codes for local to regional scale modeling by changing a very small part of the codes. Our scheme may be able to open a window for multi-scale modeling of seismic wave propagation in scales from sub-global to local one.
Finite-difference migration to zero offset
Li, Jianchao.
1992-01-01
Migration to zero offset (MZO), also called dip moveout (DMO) or prestack partial migration, transforms prestack offset seismic data into approximate zero-offset data so as to remove reflection point smear and obtain quality stacked results over a range of reflector dips. MZO has become an important step in standard seismic data processing, and a variety of frequency-wavenumber (f-k) and integral MZO algorithms have been used in practice to date. Here, I present a finite-difference MZO algorithm applied to normal-moveout (NMO)-corrected, common-offset sections. This algorithm employs a traditional poststack 15-degree finite-difference migration algorithm and a special velocity function rather than the true migration velocity. This paper shows results of implementation of this MZO algorithm when velocity varies with depth, and discusses the possibility of applying this algorithm to cases where velocity varies with both depth and horizontal distance.
Finite-difference migration to zero offset
Li, Jianchao
1992-07-01
Migration to zero offset (MZO), also called dip moveout (DMO) or prestack partial migration, transforms prestack offset seismic data into approximate zero-offset data so as to remove reflection point smear and obtain quality stacked results over a range of reflector dips. MZO has become an important step in standard seismic data processing, and a variety of frequency-wavenumber (f-k) and integral MZO algorithms have been used in practice to date. Here, I present a finite-difference MZO algorithm applied to normal-moveout (NMO)-corrected, common-offset sections. This algorithm employs a traditional poststack 15-degree finite-difference migration algorithm and a special velocity function rather than the true migration velocity. This paper shows results of implementation of this MZO algorithm when velocity varies with depth, and discusses the possibility of applying this algorithm to cases where velocity varies with both depth and horizontal distance.
Second Order Accurate Finite Difference Methods
1984-08-20
a study of the idealized material has direct applications to some polymer structures (4, 5). Wave propagation studies in hyperelastic materials have...34Acceleration Wave Propagation in Hyperelastic Rods of Variable Cross- section. Wave Motion, V4, pp. 173-180, 1982. 9. M. Hirao and N. Sugimoto...Waves in Hyperelastic Road," Quart. Appl. Math., V37, pp. 377-399, 1979. 11. G. A. Sod. "A Survey of Several Finite Difference Methods for Systems of
2005-02-01
Ostashev NOAA/Environmental Technology Laboratory, Boulder, Colorado 80305, and Department of Physics, New Mexico State University, Las Cruces, New... Mexico 88003 D. Keith Wilson and Lanbo Liu U.S. Army Engineer Research and Development Center, Hanover, New Hampshire 03755 David F. Aldridge and...Neill P. Symons Department of Geophysical Technology, Sandia National Labs., Albuquerque, New Mexico 87185 David Marlin U.S. Army Research Laboratory
3D EFT imaging with planar electrode array: Numerical simulation
NASA Astrophysics Data System (ADS)
Tuykin, T.; Korjenevsky, A.
2010-04-01
Electric field tomography (EFT) is the new modality of the quasistatic electromagnetic sounding of conductive media recently investigated theoretically and realized experimentally. The demonstrated results pertain to 2D imaging with circular or linear arrays of electrodes (and the linear array provides quite poor quality of imaging). In many applications 3D imaging is essential or can increase value of the investigation significantly. In this report we present the first results of numerical simulation of the EFT imaging system with planar array of electrodes which allows 3D visualization of the subsurface conductivity distribution. The geometry of the system is similar to the geometry of our EIT breast imaging system providing 3D conductivity imaging in form of cross-sections set with different depth from the surface. The EFT principle of operation and reconstruction approach differs from the EIT system significantly. So the results of numerical simulation are important to estimate if comparable quality of imaging is possible with the new contactless method. The EFT forward problem is solved using finite difference time domain (FDTD) method for the 8×8 square electrodes array. The calculated results of measurements are used then to reconstruct conductivity distributions by the filtered backprojections along electric field lines. The reconstructed images of the simple test objects are presented.
NASA Astrophysics Data System (ADS)
Fahlke, J.; Buchner, J.; Ippisch, O.; Roth, K.; Bastian, P.
2012-04-01
The simulation of ground-penetrating radar (GPR) measurements requires the solution of Maxwell's equations. While finite-differences time-domain (FDTD) solvers are faster on structured grids, finite-element time-domain (FETD) and discontinuous Galerkin time-domain (DGTD) allow to resolve complicated structures and avoid staircase approximations. Soil horizon boundaries can be resolved exactly by the finite element mesh. In this contribution 3D simulations are compared with measurements from the ASSESS-GPR test site which is an artificial GPR testbed with a well known geometry and ground-truth on volumetric water content provided by 32 TDR probes. For the simulations a DGTD method is used in a dual-field formulation and compared to a standard FETD method with conforming edge-based finite elements. The software for the simulation has been developed using the Distributed and Unified Numerics Environment (DUNE) and its PDELab discretization module. The programs have been parallelized using MPI to make computations on the size of 108 unknowns feasible.
Finite difference methods for approximating Heaviside functions
NASA Astrophysics Data System (ADS)
Towers, John D.
2009-05-01
We present a finite difference method for discretizing a Heaviside function H(u(x→)), where u is a level set function u:Rn ↦ R that is positive on a bounded region Ω⊂Rn. There are two variants of our algorithm, both of which are adapted from finite difference methods that we proposed for discretizing delta functions in [J.D. Towers, Two methods for discretizing a delta function supported on a level set, J. Comput. Phys. 220 (2007) 915-931; J.D. Towers, Discretizing delta functions via finite differences and gradient normalization, Preprint at http://www.miracosta.edu/home/jtowers/; J.D. Towers, A convergence rate theorem for finite difference approximations to delta functions, J. Comput. Phys. 227 (2008) 6591-6597]. We consider our approximate Heaviside functions as they are used to approximate integrals over Ω. We prove that our first approximate Heaviside function leads to second order accurate quadrature algorithms. Numerical experiments verify this second order accuracy. For our second algorithm, numerical experiments indicate at least third order accuracy if the integrand f and ∂Ω are sufficiently smooth. Numerical experiments also indicate that our approximations are effective when used to discretize certain singular source terms in partial differential equations. We mostly focus on smooth f and u. By this we mean that f is smooth in a neighborhood of Ω, u is smooth in a neighborhood of ∂Ω, and the level set u(x)=0 is a manifold of codimension one. However, our algorithms still give reasonable results if either f or u has jumps in its derivatives. Numerical experiments indicate approximately second order accuracy for both algorithms if the regularity of the data is reduced in this way, assuming that the level set u(x)=0 is a manifold. Numerical experiments indicate that dependence on the placement of Ω with respect to the grid is quite small for our algorithms. Specifically, a grid shift results in an O(hp) change in the computed solution
NASA Astrophysics Data System (ADS)
Jian, Wang; Xiaohong, Meng; Hong, Liu; Wanqiu, Zheng; Yaning, Liu; Sheng, Gui; Zhiyang, Wang
2017-03-01
Full waveform inversion and reverse time migration are active research areas for seismic exploration. Forward modeling in the time domain determines the precision of the results, and numerical solutions of finite difference have been widely adopted as an important mathematical tool for forward modeling. In this article, the optimum combined of window functions was designed based on the finite difference operator using a truncated approximation of the spatial convolution series in pseudo-spectrum space, to normalize the outcomes of existing window functions for different orders. The proposed combined window functions not only inherit the characteristics of the various window functions, to provide better truncation results, but also control the truncation error of the finite difference operator manually and visually by adjusting the combinations and analyzing the characteristics of the main and side lobes of the amplitude response. Error level and elastic forward modeling under the proposed combined system were compared with outcomes from conventional window functions and modified binomial windows. Numerical dispersion is significantly suppressed, which is compared with modified binomial window function finite-difference and conventional finite-difference. Numerical simulation verifies the reliability of the proposed method.
3D modelling of the electromagnetic response of geophysical targets using the FDTD method
Debroux, P.S.
1996-05-01
A publicly available and maintained electromagnetic finite-difference time domain (FDTD) code has been applied to the forward modelling of the response of 1D, 2D and 3D geophysical targets to a vertical magnetic dipole excitation. The FDTD method is used to analyze target responses in the 1 MHz to 100 MHz range, where either conduction or displacement currents may have the controlling role. The response of the geophysical target to the excitation is presented as changes in the magnetic field ellipticity. The results of the FDTD code compare favorably with previously published integral equation solutions of the response of 1D targets, and FDTD models calculated with different finite-difference cell sizes are compared to find the effect of model discretization on the solution. The discretization errors, calculated as absolute error in ellipticity, are presented for the different ground geometry models considered, and are, for the most part, below 10% of the integral equation solutions. Finally, the FDTD code is used to calculate the magnetic ellipticity response of a 2D survey and a 3D sounding of complicated geophysical targets. The response of these 2D and 3D targets are too complicated to be verified with integral equation solutions, but show the proper low- and high-frequency responses.
Recent advances on a DGTD method for time-domain electromagnetics
NASA Astrophysics Data System (ADS)
Descombes, Stéphane; Durochat, Clément; Lanteri, Stéphane; Moya, Ludovic; Scheid, Claire; Viquerat, Jonathan
2013-11-01
During the last ten years, the discontinuous Galerkin time-domain (DGTD) method has progressively emerged as a viable alternative to well established finite-difference time-domain (FDTD) and finite-element time-domain (FETD) methods for the numerical simulation of electromagnetic wave propagation problems in the time-domain. In this paper, we review the historical development of the DGTD method and emphasize its recent adoption by the nanophotonic research community. In addition, we discuss about some of our recent efforts aiming at improving the accuracy, flexibility and efficiency of a non-dissipative order DGTD method, and also report on some preliminary works towards its extension to the numerical treatment of physical models and problems that are relevant to nanophotonics.
TUNED FINITE-DIFFERENCE DIFFUSION OPERATORS
Maron, Jason; Low, Mordecai-Mark Mac E-mail: mordecai@amnh.org
2009-05-15
Finite-difference simulations of fluid dynamics and magnetohydrodynamics generally require an explicit diffusion operator, either to maintain stability by attenuating grid-scale structure, or to implement physical diffusivities such as viscosity or resistivity. If the goal is stability only, the diffusion must act at the grid scale, but should affect structure at larger scales as little as possible. For physical diffusivities the diffusion scale depends on the problem, and diffusion may act at larger scales as well. Diffusivity can undesirably limit the computational time step in both cases. We construct tuned finite-difference diffusion operators that minimally limit the time step while acting as desired near the diffusion scale. Such operators reach peak values at the diffusion scale rather than at the grid scale, but behave as standard operators at larger scales. These operators will be useful for simulations with high magnetic diffusivity or kinematic viscosity such as in the simulation of astrophysical dynamos with magnetic Prandtl number far from unity, or for numerical stabilization using hyperdiffusivity.
Time Domain Switched Accelerometer Design and Fabrication
2014-09-01
TECHNICAL REPORT 2052 September 2014 Time -Domain Switched Accelerometer Design and Fabrication Paul Swanson Andrew Wang...Approved for public release. SSC Pacific San Diego, CA 92152-5001 TECHNICAL REPORT 2052 September 2014 Time ...objective of this report is to record the decision-making process for developing the device design and fabrication workflow for the time -domain switched
A Fourier collocation time domain method for numerically solving Maxwell's equations
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1991-01-01
A new method for solving Maxwell's equations in the time domain for arbitrary values of permittivity, conductivity, and permeability is presented. Spatial derivatives are found by a Fourier transform method and time integration is performed using a second order, semi-implicit procedure. Electric and magnetic fields are collocated on the same grid points, rather than on interleaved points, as in the Finite Difference Time Domain (FDTD) method. Numerical results are presented for the propagation of a 2-D Transverse Electromagnetic (TEM) mode out of a parallel plate waveguide and into a dielectric and conducting medium.
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. We present the application of the Finite Difference Time Domain (FDTD) Technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and disclosed.
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
Radar cross section (RCS) calculations for flat, perfectly conducting plates are readily available through the use of conventional frequency domain techniques such as the Method of Moments (MOM). However, if the plate is covered with a dielectric material that is relatively thick in comparison with the wavelength in the material, these frequency domain techniques become increasingly difficult to apply. The application is presented of the Finite Difference Time Domain (FDTD) technique to the problem of electromagnetic scattering and RCS calculations from a thin, perfectly conducting plate that is coated with a thick layer of lossless dielectric material. Both time domain and RCS calculations are presented and discussed.
Application of a novel finite difference method to dynamic crack problems
NASA Technical Reports Server (NTRS)
Chen, Y. M.; Wilkins, M. L.
1976-01-01
A versatile finite difference method (HEMP and HEMP 3D computer programs) was developed originally for solving dynamic problems in continuum mechanics. It was extended to analyze the stress field around cracks in a solid with finite geometry subjected to dynamic loads and to simulate numerically the dynamic fracture phenomena with success. This method is an explicit finite difference method applied to the Lagrangian formulation of the equations of continuum mechanics in two and three space dimensions and time. The calculational grid moves with the material and in this way it gives a more detailed description of the physics of the problem than the Eulerian formulation.
Xu, Jiajie; Kvasnička, Pavel; Idso, Matthew; Jordan, Roger W; Gong, Heng; Homola, Jiří; Yu, Qiuming
2011-10-10
The local electric field distribution and the effect of surface-enhanced Raman spectroscopy (SERS) were investigated on the quasi-3D (Q3D) plasmonic nanostructures formed by gold nanohole and nanodisc array layers physically separated by a dielectric medium. The local electric fields at the top gold nanoholes and bottom gold nanodiscs as a function of the dielectric medium, substrate, and depth of Q3D plasmonic nanostructures upon the irradiation of a 785 nm laser were calculated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The intensity of the maximum local electric fields was shown to oscillate with the depth and the stronger local electric fields occurring at the top or bottom gold layer strongly depend on the dielectric medium, substrate, and depth of the nanostructure. This phenomenon was determined to be related to the Fabry-Pérot interference effect and the interaction of localized surface plasmons (LSPs). The enhancement factors (EFs) of SERS obtained from the 3D-FDTD simulations were compared to those calculated from the SERS experiments conducted on the Q3D plasmonic nanostructures fabricated on silicon and ITO coated glass substrates with different depths. The same trend was obtained from both methods. The capabilities of tuning not only the intensity but also the location of the maximum local electric fields by varying the depth, dielectric medium, and substrate make Q3D plasmonic nanostructures well suited for highly sensitive and reproducible SERS detection and analysis.
Adaptive finite difference for seismic wavefield modelling in acoustic media.
Yao, Gang; Wu, Di; Debens, Henry Alexander
2016-08-05
Efficient numerical seismic wavefield modelling is a key component of modern seismic imaging techniques, such as reverse-time migration and full-waveform inversion. Finite difference methods are perhaps the most widely used numerical approach for forward modelling, and here we introduce a novel scheme for implementing finite difference by introducing a time-to-space wavelet mapping. Finite difference coefficients are then computed by minimising the difference between the spatial derivatives of the mapped wavelet and the finite difference operator over all propagation angles. Since the coefficients vary adaptively with different velocities and source wavelet bandwidths, the method is capable to maximise the accuracy of the finite difference operator. Numerical examples demonstrate that this method is superior to standard finite difference methods, while comparable to Zhang's optimised finite difference scheme.
Adaptive finite difference for seismic wavefield modelling in acoustic media
Yao, Gang; Wu, Di; Debens, Henry Alexander
2016-01-01
Efficient numerical seismic wavefield modelling is a key component of modern seismic imaging techniques, such as reverse-time migration and full-waveform inversion. Finite difference methods are perhaps the most widely used numerical approach for forward modelling, and here we introduce a novel scheme for implementing finite difference by introducing a time-to-space wavelet mapping. Finite difference coefficients are then computed by minimising the difference between the spatial derivatives of the mapped wavelet and the finite difference operator over all propagation angles. Since the coefficients vary adaptively with different velocities and source wavelet bandwidths, the method is capable to maximise the accuracy of the finite difference operator. Numerical examples demonstrate that this method is superior to standard finite difference methods, while comparable to Zhang’s optimised finite difference scheme. PMID:27491333
Finite difference computation of Casimir forces
NASA Astrophysics Data System (ADS)
Pinto, Fabrizio
2016-09-01
In this Invited paper, we begin by a historical introduction to provide a motivation for the classical problems of interatomic force computation and associated challenges. This analysis will lead us from early theoretical and experimental accomplishments to the integration of these fascinating interactions into the operation of realistic, next-generation micro- and nanodevices both for the advanced metrology of fundamental physical processes and in breakthrough industrial applications. Among several powerful strategies enabling vastly enhanced performance and entirely novel technological capabilities, we shall specifically consider Casimir force time-modulation and the adoption of non-trivial geometries. As to the former, the ability to alter the magnitude and sign of the Casimir force will be recognized as a crucial principle to implement thermodynamical nano-engines. As to the latter, we shall first briefly review various reported computational approaches. We shall then discuss the game-changing discovery, in the last decade, that standard methods of numerical classical electromagnetism can be retooled to formulate the problem of Casimir force computation in arbitrary geometries. This remarkable development will be practically illustrated by showing that such an apparently elementary method as standard finite-differencing can be successfully employed to numerically recover results known from the Lifshitz theory of dispersion forces in the case of interacting parallel-plane slabs. Other geometries will be also be explored and consideration given to the potential of non-standard finite-difference methods. Finally, we shall introduce problems at the computational frontier, such as those including membranes deformed by Casimir forces and the effects of anisotropic materials. Conclusions will highlight the dramatic transition from the enduring perception of this field as an exotic application of quantum electrodynamics to the recent demonstration of a human climbing
Choi, Kyongsik; Chon, James W; Gu, Min; Lee, Byoungho
2007-08-20
In this paper, a simple confocal laser scanning microscopic (CLSM) image mapping technique based on the finite-difference time domain (FDTD) calculation has been proposed and evaluated for characterization of a subwavelength-scale three-dimensional (3D) void structure fabricated inside polymer matrix. The FDTD simulation method adopts a focused Gaussian beam incident wave, Berenger's perfectly matched layer absorbing boundary condition, and the angular spectrum analysis method. Through the well matched simulation and experimental results of the xz-scanned 3D void structure, we first characterize the exact position and the topological shape factor of the subwavelength-scale void structure, which was fabricated by a tightly focused ultrashort pulse laser. The proposed CLSM image mapping technique based on the FDTD can be widely applied from the 3D near-field microscopic imaging, optical trapping, and evanescent wave phenomenon to the state-of-the-art bio- and nanophotonics.
Numerical stability analysis of the pseudo-spectral analytical time-domain PIC algorithm
Godfrey, Brendan B.; Vay, Jean-Luc; Haber, Irving
2014-02-01
The pseudo-spectral analytical time-domain (PSATD) particle-in-cell (PIC) algorithm solves the vacuum Maxwell's equations exactly, has no Courant time-step limit (as conventionally defined), and offers substantial flexibility in plasma and particle beam simulations. It is, however, not free of the usual numerical instabilities, including the numerical Cherenkov instability, when applied to relativistic beam simulations. This paper derives and solves the numerical dispersion relation for the PSATD algorithm and compares the results with corresponding behavior of the more conventional pseudo-spectral time-domain (PSTD) and finite difference time-domain (FDTD) algorithms. In general, PSATD offers superior stability properties over a reasonable range of time steps. More importantly, one version of the PSATD algorithm, when combined with digital filtering, is almost completely free of the numerical Cherenkov instability for time steps (scaled to the speed of light) comparable to or smaller than the axial cell size.
Time domain reflectometry in time variant plasmas
NASA Technical Reports Server (NTRS)
Scherner, Michael J.
1992-01-01
The effects of time-dependent electron density fluctuations on a synthesized time domain reflectometry response of a one-dimensional cold plasma sheath are considered. Numerical solutions of the Helmholtz wave equation, which describes the electric field of a normally incident plane wave in a specified static electron density profile, are used. A study of the effects of Doppler shifts resulting from moving density fluctuations in the electron density profile of the sheath is included. Varying electron density levels corrupt time domain and distance measurements. Reducing or modulating the electron density levels of a given electron density profile affects the time domain response of a plasma and results in motion of the turning point, and the effective motion has a significant effect on measuring electron density locations.
3D-Printed Broadband Dielectric Tube Terahertz Waveguide with Anti-Reflection Structure
NASA Astrophysics Data System (ADS)
Vogt, Dominik Walter; Leonhardt, Rainer
2016-11-01
We demonstrate broadband, low loss, and close-to-zero dispersion guidance of terahertz (THz) radiation in a dielectric tube with an anti-reflection structure (AR-tube waveguide) in the frequency range from 0.2 to 1.0 THz. The anti-reflection structure (ARS) consists of close-packed cones in a hexagonal lattice arranged on the outer surface of the tube cladding. The feature size of the ARS is in the order of the wavelength between 0.2 and 1.0 THz. The waveguides are fabricated with the versatile and cost efficient 3D-printing method. Terahertz time-domain spectroscopy (THz-TDS) measurements as well as 3D finite-difference time-domain simulations (FDTD) are performed to extensively characterize the AR-tube waveguides. Spectrograms, attenuation spectra, effective phase refractive indices, and the group-velocity dispersion parameters β 2 of the AR-tube waveguides are presented. Both the experimental and numerical results confirm the extended bandwidth and smaller group-velocity dispersion of the AR-tube waveguide compared to a low loss plain dielectric tube THz waveguide. The AR-tube waveguide prototypes show an attenuation spectrum close to the theoretical limit given by the infinite cladding tube waveguide.
Anderson localization in the time domain
NASA Astrophysics Data System (ADS)
Sacha, Krzysztof; Delande, Dominique
2016-08-01
In analogy with the usual Anderson localization taking place in time-independent disordered quantum systems where the disorder acts in configuration space, systems exposed to temporally disordered potentials can display Anderson localization in the time domain. We demonstrate this phenomenon with one-dimensional examples where a temporally disordered potential induces localization during the quantum evolution of wave packets, in contrast with a fully delocalized classical dynamics. This is an example of a time crystal phenomenon, i.e., a crystalline behavior in the time domain.
Efficient fabrication method of nano-grating for 3D holographic display with full parallax views.
Wan, Wenqiang; Qiao, Wen; Huang, Wenbin; Zhu, Ming; Fang, Zongbao; Pu, Donglin; Ye, Yan; Liu, Yanhua; Chen, Linsen
2016-03-21
Without any special glasses, multiview 3D displays based on the diffractive optics can present high resolution, full-parallax 3D images in an ultra-wide viewing angle. The enabling optical component, namely the phase plate, can produce arbitrarily distributed view zones by carefully designing the orientation and the period of each nano-grating pixel. However, such 3D display screen is restricted to a limited size due to the time-consuming fabricating process of nano-gratings on the phase plate. In this paper, we proposed and developed a lithography system that can fabricate the phase plate efficiently. Here we made two phase plates with full nano-grating pixel coverage at a speed of 20 mm^{2}/mins, a 500 fold increment in the efficiency when compared to the method of E-beam lithography. One 2.5-inch phase plate generated 9-view 3D images with horizontal-parallax, while the other 6-inch phase plate produced 64-view 3D images with full-parallax. The angular divergence in horizontal axis and vertical axis was 1.5 degrees, and 1.25 degrees, respectively, slightly larger than the simulated value of 1.2 degrees by Finite Difference Time Domain (FDTD). The intensity variation was less than 10% for each viewpoint, in consistency with the simulation results. On top of each phase plate, a high-resolution binary masking pattern containing amplitude information of all viewing zone was well aligned. We achieved a resolution of 400 pixels/inch and a viewing angle of 40 degrees for 9-view 3D images with horizontal parallax. In another prototype, the resolution of each view was 160 pixels/inch and the view angle was 50 degrees for 64-view 3D images with full parallax. As demonstrated in the experiments, the homemade lithography system provided the key fabricating technology for multiview 3D holographic display.
NASA Astrophysics Data System (ADS)
Kowalski, Adam; Hawley, Suzanne; Davenport, James; Berlicki, Arkadiusz; Cauzzi, Gianna; Fletcher, Lyndsay; Heinzel, Petr; Notsu, Yuta; Loyd, Parke; Martinez Oliveros, Juan Carlos; Pugh, Chloe; Schmidt, Sarah Jane; Karmakar, Subhajeet; Pye, John; Flaccomio, Ettore
2016-07-01
Proceedings for the splinter session "Flares in Time-Domain Surveys" convened at Cool Stars 19 on June 07, 2016 in Uppsala, Sweden. Contains a two page summary of the splinter session, links to YouTube talks, and a PDF copy of the slides from the presenters.
Time-domain flicker measurement technique
NASA Astrophysics Data System (ADS)
Miseli, Joseph
1999-04-01
The visibility of flicker on a display depends upon many factors, including the observer's sensitivity to flicker. Whenever flicker is observed, it is probably undesirable and often unacceptable. Much has been written about flicker, its perception, and its variability. Methods have been presented to the industry that use frequency domain analysis of measured flicker response. Here we prose an alternate method to quantify flicker in the time domain, just as people see it, and we will try to understand how the measurements relate to what people see. Both the frequency domain and time domain flicker measurements can be found in the Video Electronics Standards Association Flat Panel Display Measurements Standard. An attempt is made to compare the two methods and show how the simpler measurement can be employed for many display technologies.
LHC RF System Time-Domain Simulation
Mastorides, T.; Rivetta, C.; /SLAC
2010-09-14
Non-linear time-domain simulations have been developed for the Positron-Electron Project (PEP-II) and the Large Hadron Collider (LHC). These simulations capture the dynamic behavior of the RF station-beam interaction and are structured to reproduce the technical characteristics of the system (noise contributions, non-linear elements, and more). As such, they provide useful results and insight for the development and design of future LLRF feedback systems. They are also a valuable tool for the study of diverse longitudinal beam dynamics effects such as coupled-bunch impedance driven instabilities and single bunch longitudinal emittance growth. Results from these studies and related measurements from PEP-II and LHC have been presented in multiple places. This report presents an example of the time-domain simulation implementation for the LHC.
Time-Domain Stability Margin Assessment
NASA Technical Reports Server (NTRS)
Clements, Keith
2016-01-01
The baseline stability margins for NASA's Space Launch System (SLS) launch vehicle were generated via the classical approach of linearizing the system equations of motion and determining the gain and phase margins from the resulting frequency domain model. To improve the fidelity of the classical methods, the linear frequency domain approach can be extended by replacing static, memoryless nonlinearities with describing functions. This technique, however, does not address the time varying nature of the dynamics of a launch vehicle in flight. An alternative technique for the evaluation of the stability of the nonlinear launch vehicle dynamics along its trajectory is to incrementally adjust the gain and/or time delay in the time domain simulation until the system exhibits unstable behavior. This technique has the added benefit of providing a direct comparison between the time domain and frequency domain tools in support of simulation validation.
Time Domain Stability Margin Assessment Method
NASA Technical Reports Server (NTRS)
Clements, Keith
2017-01-01
The baseline stability margins for NASA's Space Launch System (SLS) launch vehicle were generated via the classical approach of linearizing the system equations of motion and determining the gain and phase margins from the resulting frequency domain model. To improve the fidelity of the classical methods, the linear frequency domain approach can be extended by replacing static, memoryless nonlinearities with describing functions. This technique, however, does not address the time varying nature of the dynamics of a launch vehicle in flight. An alternative technique for the evaluation of the stability of the nonlinear launch vehicle dynamics along its trajectory is to incrementally adjust the gain and/or time delay in the time domain simulation until the system exhibits unstable behavior. This technique has the added benefit of providing a direct comparison between the time domain and frequency domain tools in support of simulation validation.
Magnified time-domain ghost imaging
NASA Astrophysics Data System (ADS)
Ryczkowski, Piotr; Barbier, Margaux; Friberg, Ari T.; Dudley, John M.; Genty, Goëry
2017-04-01
Ghost imaging allows the imaging of an object without directly seeing this object. Originally demonstrated in the spatial domain, it was recently shown that ghost imaging can be transposed into the time domain to detect ultrafast signals, even in the presence of distortion. We propose and experimentally demonstrate a temporal ghost imaging scheme which generates a 5× magnified ghost image of an ultrafast waveform. Inspired by shadow imaging in the spatial domain and building on the dispersive Fourier transform of an incoherent supercontinuum in an optical fiber, the approach overcomes the resolution limit of standard time-domain ghost imaging generally imposed by the detectors speed. The method can be scaled up to higher magnification factors using longer fiber lengths and light source with shorter duration.
Finite-difference numerical simulations of underground explosion cavity decoupling
NASA Astrophysics Data System (ADS)
Aldridge, D. F.; Preston, L. A.; Jensen, R. P.
2012-12-01
Earth models containing a significant portion of ideal fluid (e.g., air and/or water) are of increasing interest in seismic wave propagation simulations. Examples include a marine model with a thick water layer, and a land model with air overlying a rugged topographic surface. The atmospheric infrasound community is currently interested in coupled seismic-acoustic propagation of low-frequency signals over long ranges (~tens to ~hundreds of kilometers). Also, accurate and efficient numerical treatment of models containing underground air-filled voids (caves, caverns, tunnels, subterranean man-made facilities) is essential. In support of the Source Physics Experiment (SPE) conducted at the Nevada National Security Site (NNSS), we are developing a numerical algorithm for simulating coupled seismic and acoustic wave propagation in mixed solid/fluid media. Solution methodology involves explicit, time-domain, finite-differencing of the elastodynamic velocity-stress partial differential system on a three-dimensional staggered spatial grid. Conditional logic is used to avoid shear stress updating within the fluid zones; this approach leads to computational efficiency gains for models containing a significant proportion of ideal fluid. Numerical stability and accuracy are maintained at air/rock interfaces (where the contrast in mass density is on the order of 1 to 2000) via a finite-difference operator "order switching" formalism. The fourth-order spatial FD operator used throughout the bulk of the earth model is reduced to second-order in the immediate vicinity of a high-contrast interface. Current modeling efforts are oriented toward quantifying the amount of atmospheric infrasound energy generated by various underground seismic sources (explosions and earthquakes). Source depth and orientation, and surface topography play obvious roles. The cavity decoupling problem, where an explosion is detonated within an air-filled void, is of special interest. A point explosion
Time-domain robotic vision application
NASA Technical Reports Server (NTRS)
Tolliver, C. L.
1987-01-01
The quest for the highest resolution microwaves imaging and the principle of time-domain imaging is the primary motivation for recent developments in time-domain techniques. With the present technology fast time varying signals can now be measured and recorded both in magnitude and in phase. It has also enhanced the ability to extract relevant details concerning the scattering object. In the past, the inference of object geometry or shape from scattered signals has received substantial attention in radar technology. Various inverse scattering theories were proposed to develop analytical solutions to this problem. Furthermore, the random inversion, frequenty swept holography, and the synthetic radar imaging, all of which have two things in common: the physical optic far-field approximation and the utilization of the channels as an extra physical dimension, were also advanced significantly. Despite the inherent vectorial nature of electromagnetic waves, these scalar treatments have brought forth some promising results in practice with notable examples in subsurface and structure sounding. The use of time-domain imaging for space robotic vision applications was proposed. A multisensor approach to vision was shown to have several advantages over the video-only approach.
Time-Domain Filtering of Metasurfaces
Wakatsuchi, Hiroki
2015-01-01
In general electromagnetic response of each material to a continuous wave does not vary in time domain if the frequency component remains the same. Recently, it turned out that integrating several circuit elements including schottky diodes with periodically metallised surfaces, or the so-called metasurfaces, leads to selectively absorbing specific types of waveforms or pulse widths even at the same frequency. These waveform-selective metasurfaces effectively showed different absorbing performances for different widths of pulsed sine waves by gradually varying their electromagnetic responses in time domain. Here we study time-filtering effects of such circuit-based metasurfaces illuminated by continuous sine waves. Moreover, we introduce extra circuit elements to these structures to enhance the time-domain control capability. These time-varying properties are expected to give us another degree of freedom to control electromagnetic waves and thus contribute to developing new kinds of electromagnetic applications and technologies, e.g. time-windowing wireless communications and waveform conversion. PMID:26564027
NASA Astrophysics Data System (ADS)
Hamano, Yozo
2002-09-01
We present a new time-domain approach to the forward modelling of 3-D electromagnetic induction in a heterogeneous conducting sphere excited by external and internal sources. This method utilizes the standard decomposition of the magnetic field into toroidal and poloidal parts, and spherical harmonic expansions of both the magnetic fields and the conductivity heterogeneity. Resulting induction equations for the spherical harmonics are solved simultaneously in the time domain. Coupling terms between the electromagnetic fields and the conductivity structure are re-expanded in spherical harmonics, so that the terms can be calculated by matrix multiplications at each time step of the computation. A finite difference approximation was used to solve the set of diffusion equations for the spherical harmonics up to degree 20. This method can be efficiently used to analyse transient geomagnetic variations to estimate the 3-D conductivity structure of the Earth. In order to validate the present approach, we solved an induction problem in simple four-layer mantle models, which consist of the surface layer (r= 6371 - 6351 km, σ=1 S m-1), the upper mantle (r= 6351 - 5971 km, σ= 0.01 S m-1), the transition layer (r= 5971 - 5671 km, σ= 0.01-1 S m-1), and the lower mantle (r= 5671 - 3481 km, σ= 1 S m-1). Conductivity heterogeneities are considered in the surface layer or the transition layer. For these models, temporal variations of the Gauss coefficients in response to a sudden application of P10-type external field were calculated, and the impulse response function of each harmonic component was obtained by differentiating the calculated variations with time. The response functions of the primary induced components, g10, have large initial values and monotonously decay with time. Changes of the decay rate reflect the radial distribution of the electrical conductivity. For the surface heterogeneous models, temporal variations of other secondary induced components have two
Optical identification based on time domain optical coherence tomography.
Gandhi, Vishal; Semenov, Dmitry; Honkanen, Seppo; Hauta-Kasari, Markku
2015-09-01
We present a novel method for optical identification, i.e., authenticating valuable documents such as a passport, credit cards, and bank notes, using optical coherence tomography (OCT). An OCT system can capture three-dimensional (3D) images and visualize the internal structure of an object. In our work, as an object, we consider a multilayered optical identification tag composed of a limited number of thin layers (10-100 μm thick). The thickness, width, and location of the layers in the tag encode a unique identification information. Reading of the tag is done using a time domain OCT (TD-OCT) system. Typically, a TD-OCT system requires continuous mechanical scanning in one or more directions to get a 3D volume image of an object. The continuous scanning implies a complicated optical setup, which makes an OCT system fragile and expensive. We propose to avoid the conventional scanning by (1) not requiring 3D imaging, and (2) utilizing the motion of the optical tag itself. The motion is introduced to the tag reader, for example, by a user, which replaces the need for conventional scanning. The absence of a conventional scanning mechanism makes the proposed OCT method very simple and suited for identification purposes; however, it also puts some constraints to the construction of the optical tag, which we discuss in this paper in detail.
NASA Astrophysics Data System (ADS)
Viquerat, Jonathan; Lanteri, Stéphane
2016-01-01
During the last ten years, the discontinuous Galerkin time-domain (DGTD) method has progressively emerged as a viable alternative to well established finite-difference time-domain (FDTD) and finite-element time-domain (FETD) methods for the numerical simulation of electromagnetic wave propagation problems in the time-domain. The method is now actively studied in various application contexts including those requiring to model light/matter interactions on the nanoscale. Several recent works have demonstrated the viability of the DGDT method for nanophotonics. In this paper we further demonstrate the capabilities of the method for the simulation of near-field plasmonic interactions by considering more particularly the possibility of combining the use of a locally refined conforming tetrahedral mesh with a local adaptation of the approximation order.
Early Results and Plans for the Time Domain Spectroscopic Survey
NASA Astrophysics Data System (ADS)
Green, Paul J.; Anderson, S. F.; Morganson, E.; Ruan, J. J.; PS1; SDSS-III; SDSS-IV
2014-01-01
With PanSTARRS-1 just finishing and LSST over the horizon, time-domain astronomy is a celestial tsunami just now hitting our shores. We outline the Time Domain Spectroscopic Survey (TDSS) - the first large-scale, all-sky spectroscopic survey of celestial variables. As part of SDSS-IV eBOSS program, the TDSS has begun obtaining BOSS-quality spectroscopy of variable objects selected primarily from the PS1 3pi survey. During the duration of SDSS-IV (2014-2020), TDSS should garner of order 1E+05 first-ever spectra of variables to i-band mag about 21. While AGN will dominate the sample, all kinds of variable stars will also be revealed, including RR Lyr, flare stars, eclipsing binaries, pulsating white dwarfs and more. We will outline target selection, and discuss early results. We also describe a TDSS subprogram testing for spectroscopic variability by obtaining 2d or 3d epoch spectra of several carefully chosen source classes.
Xie, Yuliang; Yang, Shikuan; Mao, Zhangming; Li, Peng; Zhao, Chenglong; Cohick, Zane; Huang, Po-Hsun; Huang, Tony Jun
2014-12-23
In this work, we develop an in situ method to grow highly controllable, sensitive, three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrates via an optothermal effect within microfluidic devices. Implementing this approach, we fabricate SERS substrates composed of Ag@ZnO structures at prescribed locations inside microfluidic channels, sites within which current fabrication of SERS structures has been arduous. Conveniently, properties of the 3D Ag@ZnO nanostructures such as length, packing density, and coverage can also be adjusted by tuning laser irradiation parameters. After exploring the fabrication of the 3D nanostructures, we demonstrate a SERS enhancement factor of up to ∼2×10(6) and investigate the optical properties of the 3D Ag@ZnO structures through finite-difference time-domain simulations. To illustrate the potential value of our technique, low concentrations of biomolecules in the liquid state are detected. Moreover, an integrated cell-trapping function of the 3D Ag@ZnO structures records the surface chemical fingerprint of a living cell. Overall, our optothermal-effect-based fabrication technique offers an effective combination of microfluidics with SERS, resolving problems associated with the fabrication of SERS substrates in microfluidic channels. With its advantages in functionality, simplicity, and sensitivity, the microfluidic-SERS platform presented should be valuable in many biological, biochemical, and biomedical applications.
2015-01-01
In this work, we develop an in situ method to grow highly controllable, sensitive, three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrates via an optothermal effect within microfluidic devices. Implementing this approach, we fabricate SERS substrates composed of Ag@ZnO structures at prescribed locations inside microfluidic channels, sites within which current fabrication of SERS structures has been arduous. Conveniently, properties of the 3D Ag@ZnO nanostructures such as length, packing density, and coverage can also be adjusted by tuning laser irradiation parameters. After exploring the fabrication of the 3D nanostructures, we demonstrate a SERS enhancement factor of up to ∼2 × 106 and investigate the optical properties of the 3D Ag@ZnO structures through finite-difference time-domain simulations. To illustrate the potential value of our technique, low concentrations of biomolecules in the liquid state are detected. Moreover, an integrated cell-trapping function of the 3D Ag@ZnO structures records the surface chemical fingerprint of a living cell. Overall, our optothermal-effect-based fabrication technique offers an effective combination of microfluidics with SERS, resolving problems associated with the fabrication of SERS substrates in microfluidic channels. With its advantages in functionality, simplicity, and sensitivity, the microfluidic-SERS platform presented should be valuable in many biological, biochemical, and biomedical applications. PMID:25402207
On the Analysis Methods for the Time Domain and Frequency Domain Response of a Buried Objects*
NASA Astrophysics Data System (ADS)
Poljak, Dragan; Šesnić, Silvestar; Cvetković, Mario
2014-05-01
There has been a continuous interest in the analysis of ground-penetrating radar systems and related applications in civil engineering [1]. Consequently, a deeper insight of scattering phenomena occurring in a lossy half-space, as well as the development of sophisticated numerical methods based on Finite Difference Time Domain (FDTD) method, Finite Element Method (FEM), Boundary Element Method (BEM), Method of Moments (MoM) and various hybrid methods, is required, e.g. [2], [3]. The present paper deals with certain techniques for time and frequency domain analysis, respectively, of buried conducting and dielectric objects. Time domain analysis is related to the assessment of a transient response of a horizontal straight thin wire buried in a lossy half-space using a rigorous antenna theory (AT) approach. The AT approach is based on the space-time integral equation of the Pocklington type (time domain electric field integral equation for thin wires). The influence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The obtained results for the transient current induced along the electrode due to the transmitted plane wave excitation are compared to the numerical results calculated via an approximate transmission line (TL) approach and the AT approach based on the space-frequency variant of the Pocklington integro-differential approach, respectively. It is worth noting that the space-frequency Pocklington equation is numerically solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transient response is obtained by the aid of inverse fast Fourier transform (IFFT). The results calculated by means of different approaches agree satisfactorily. Frequency domain analysis is related to the assessment of frequency domain response of dielectric sphere using the full wave model based on the set of coupled electric field integral
Metrology for terahertz time-domain spectrometers
NASA Astrophysics Data System (ADS)
Molloy, John F.; Naftaly, Mira
2015-12-01
In recent years the terahertz time-domain spectrometer (THz TDS) [1] has emerged as a key measurement device for spectroscopic investigations in the frequency range of 0.1-5 THz. To date, almost every type of material has been studied using THz TDS, including semiconductors, ceramics, polymers, metal films, liquid crystals, glasses, pharmaceuticals, DNA molecules, proteins, gases, composites, foams, oils, and many others. Measurements with a TDS are made in the time domain; conversion from the time domain data to a frequency spectrum is achieved by applying the Fourier Transform, calculated numerically using the Fast Fourier Transform (FFT) algorithm. As in many other types of spectrometer, THz TDS requires that the sample data be referenced to similarly acquired data with no sample present. Unlike frequency-domain spectrometers which detect light intensity and measure absorption spectra, a TDS records both amplitude and phase information, and therefore yields both the absorption coefficient and the refractive index of the sample material. The analysis of the data from THz TDS relies on the assumptions that: a) the frequency scale is accurate; b) the measurement of THz field amplitude is linear; and c) that the presence of the sample does not affect the performance characteristics of the instrument. The frequency scale of a THz TDS is derived from the displacement of the delay line; via FFT, positioning errors may give rise to frequency errors that are difficult to quantify. The measurement of the field amplitude in a THz TDS is required to be linear with a dynamic range of the order of 10 000. And attention must be given to the sample positioning and handling in order to avoid sample-related errors.
Time-domain multiple-quantum NMR
Weitekamp, D.P.
1982-11-01
The development of time-domain multiple-quantum nuclear magnetic resonance is reviewed through mid 1982 and some prospects for future development are indicated. Particular attention is given to the problem of obtaining resolved, interpretable, many-quantum spectra for anisotropic magnetically isolated systems of coupled spins. New results are presented on a number of topics including the optimization of multiple-quantum-line intensities, analysis of noise in two-dimensional spectroscopy, and the use of order-selective excitation for cross polarization between nuclear-spin species.
3D Modeling of Antenna Driven Slow Waves Excited by Antennas Near the Plasma Edge
NASA Astrophysics Data System (ADS)
Smithe, David; Jenkins, Thomas
2016-10-01
Prior work with the 3D finite-difference time-domain (FDTD) plasma and sheath model used to model ICRF antennas in fusion plasmas has highlighted the possibility of slow wave excitation at the very low end of the SOL density range, and thus the prudent need for a slow-time evolution model to treat SOL density modifications due to the RF itself. At higher frequency, the DIII-D helicon antenna has much easier access to a parasitic slow wave excitation, and in this case the Faraday screen provides the dominant means of controlling the content of the launched mode, with antenna end-effects remaining a concern. In both cases, the danger is the same, with the slow-wave propagating into a lower-hybrid resonance layer a short distance ( cm) away from the antenna, which would parasitically absorb power, transferring energy to the SOL edge plasma, primarily through electron-neutral collisions. We will present 3D modeling of antennas at both ICRF and helicon frequencies. We've added a slow-time evolution capability for the SOL plasma density to include ponderomotive force driven rarefaction from the strong fields in the vicinity of the antenna, and show initial application to NSTX antenna geometry and plasma configurations. The model is based on a Scalar Ponderomotive Potential method, using self-consistently computed local field amplitudes from the 3D simulation.
Eigenvalues of singular differential operators by finite difference methods. II.
NASA Technical Reports Server (NTRS)
Baxley, J. V.
1972-01-01
Note is made of an earlier paper which defined finite difference operators for the Hilbert space L2(m), and gave the eigenvalues for these operators. The present work examines eigenvalues for higher order singular differential operators by using finite difference methods. The two self-adjoint operators investigated are defined by a particular value in the same Hilbert space, L2(m), and are strictly positive with compact inverses. A class of finite difference operators is considered, with the idea of application to the theory of Toeplitz matrices. The approximating operators consist of a good approximation plus a perturbing operator.
NASA Astrophysics Data System (ADS)
Kohno, Nanase; Itakura, Ryuji; Tsubouchi, Masaaki
2016-10-01
We applied terahertz (THz) time-domain spectroscopy to reveal the mechanism of the relativistic Doppler reflection of THz light from a photoinduced plasma front in a silicon wafer. The frequency upshift caused by the Doppler reflection was identified by measurement of the reflected THz waveforms and compared to the calculated results obtained using the one-dimensional finite-difference time-domain method. The relation between the energy density of the pump light and the frequency upshift was also explored. We found that the interaction time of the moving plasma front and the reflected THz pulse is a key factor in understanding the mechanism of the relativistic Doppler reflection.
Time-domain representation of frequency-dependent foundation impedance functions
Safak, E.
2006-01-01
Foundation impedance functions provide a simple means to account for soil-structure interaction (SSI) when studying seismic response of structures. Impedance functions represent the dynamic stiffness of the soil media surrounding the foundation. The fact that impedance functions are frequency dependent makes it difficult to incorporate SSI in standard time-history analysis software. This paper introduces a simple method to convert frequency-dependent impedance functions into time-domain filters. The method is based on the least-squares approximation of impedance functions by ratios of two complex polynomials. Such ratios are equivalent, in the time-domain, to discrete-time recursive filters, which are simple finite-difference equations giving the relationship between foundation forces and displacements. These filters can easily be incorporated into standard time-history analysis programs. Three examples are presented to show the applications of the method.
Time-domain reconstruction using sensitivity coefficients for limited view ultrawide band tomography
NASA Astrophysics Data System (ADS)
Abdullah, M. Z.; Yin, W.; Bilal, M.; Armitage, D. W.; Mackin, R.; Peyton, A. J.
2007-08-01
This article addresses time-domain ultrawide band (UWB) electromagnetic tomography for reconstructing the unknown spatial characteristic of an object from observations of the arrivals of short electromagnetic (EM) pulses. Here, the determination of the first peak arrival of the EM traces constitutes the forward problem, and the inverse problem aims to reconstruct the EM property distribution of the media. In this article, the finite-difference time-domain method implementing a perfectly matched layer is used to solve the forward problem from which the system sensitivity maps are determined. Image reconstruction is based on the combination of a linearized update and regularized Landweber minimization algorithm. Experimental data from a laboratory UWB system using targets of different contrasts, sizes, and shapes in an aqueous media are presented. The results show that this technique can accurately detect and locate unknown targets in spite of the presence of significant levels of noise in the data.
Hybrid finite element-finite difference method for thermal analysis of blood vessels.
Blanchard, C H; Gutierrez, G; White, J A; Roemer, R B
2000-01-01
A hybrid finite-difference/finite-element technique for the thermal analysis of blood vessels embedded in perfused tissue has been developed and evaluated. This method provides efficient and accurate solutions to the conjugated heat transfer problem of convection by blood coupled to conduction in the tissue. The technique uses a previously developed 3D automatic meshing method for creating a finite element mesh in the tissue surrounding the vessels, coupled iteratively with a 1-D marching finite difference method for the interior of the vessels. This hybrid technique retains the flexibility and ease of automated finite-element meshing techniques for modelling the complex geometry of blood vessels and irregularly shaped tissues, and speeds the solution time by using a simple finite-difference method to calculate the bulk mean temperatures within all blood vessels. The use of the 1D finite-difference technique in the blood vessels also eliminates the large computer memory requirements needed to accurately solve large vessel network problems when fine FE meshes are used in the interior of vessels. The accuracy of the hybrid technique has been verified against previously verified numerical solutions. In summary, the hybrid technique combines the accuracy and flexibility found in automated finite-element techniques, with the speed and reduction of computational memory requirements associated with the 1D finite-difference technique, something which has not been done before. This method, thus, has the potential to provide accurate, flexible and relatively fast solutions for the thermal analysis of coupled perfusion/blood vessel problems, and large vessel network problems.
The Relation of Finite Element and Finite Difference Methods
NASA Technical Reports Server (NTRS)
Vinokur, M.
1976-01-01
Finite element and finite difference methods are examined in order to bring out their relationship. It is shown that both methods use two types of discrete representations of continuous functions. They differ in that finite difference methods emphasize the discretization of independent variable, while finite element methods emphasize the discretization of dependent variable (referred to as functional approximations). An important point is that finite element methods use global piecewise functional approximations, while finite difference methods normally use local functional approximations. A general conclusion is that finite element methods are best designed to handle complex boundaries, while finite difference methods are superior for complex equations. It is also shown that finite volume difference methods possess many of the advantages attributed to finite element methods.
A Finite Difference-Augmented Peridynamics Method for Wave Dispersion
2014-10-21
ARL-RP-0531 ● AUG 2015 US Army Research Laboratory A Finite Difference- Augmented Peridynamics Method for Wave Dispersion by...AUG 2015 US Army Research Laboratory A Finite Difference- Augmented Peridynamics Method for Wave Dispersion by Raymond A Wildman and George...Difference- Augmented Peridynamics Method for Wave Dispersion 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S
Wang, Zhaojun; Zhou, Xiaoming
2016-12-01
The authors study the wave propagation in continuum acoustic metamaterials whose all or not all of the principal elements of the mass tensor or the scalar compressibility can be negative due to wave dispersion. Their time-domain wave characteristics are particularly investigated by the finite-difference time-domain (FDTD) method, in which algorithms for the Drude and Lorentz dispersion pertinent to acoustic metamaterials are provided necessarily. Wave propagation nature of anisotropic acoustic metamaterials with all admissible material parameters are analyzed in a general manner. It is found that anomalous negative refraction phenomena can appear in several dispersion regimes, and their unique time-domain signatures have been discovered by the FDTD modeling. It is further proposed that two different metamaterial layers with specially assigned dispersions could comprise a conjugate pair that permits wave propagation only at specific points in the wave vector space. The time-domain pulse simulation verifies that acoustic directive radiation capable of modulating radiation angle with the wave frequency can be realized with this conjugate pair. The study provides the detailed analysis of wave propagation in anisotropic and dispersive acoustic mediums, which makes a further step toward dispersion engineering and transient wave control through acoustic metamaterials.
Gravitational Waves and Time Domain Astronomy
NASA Technical Reports Server (NTRS)
Centrella, Joan; Nissanke, Samaya; Williams, Roy
2012-01-01
The gravitational wave window onto the universe will open in roughly five years, when Advanced LIGO and Virgo achieve the first detections of high frequency gravitational waves, most likely coming from compact binary mergers. Electromagnetic follow-up of these triggers, using radio, optical, and high energy telescopes, promises exciting opportunities in multi-messenger time domain astronomy. In the decade, space-based observations of low frequency gravitational waves from massive black hole mergers, and their electromagnetic counterparts, will open up further vistas for discovery. This two-part workshop featured brief presentations and stimulating discussions on the challenges and opportunities presented by gravitational wave astronomy. Highlights from the workshop, with the emphasis on strategies for electromagnetic follow-up, are presented in this report.
Time domain para hydrogen induced polarization.
Ratajczyk, Tomasz; Gutmann, Torsten; Dillenberger, Sonja; Abdulhussaein, Safaa; Frydel, Jaroslaw; Breitzke, Hergen; Bommerich, Ute; Trantzschel, Thomas; Bernarding, Johannes; Magusin, Pieter C M M; Buntkowsky, Gerd
2012-01-01
Para hydrogen induced polarization (PHIP) is a powerful hyperpolarization technique, which increases the NMR sensitivity by several orders of magnitude. However the hyperpolarized signal is created as an anti-phase signal, which necessitates high magnetic field homogeneity and spectral resolution in the conventional PHIP schemes. This hampers the application of PHIP enhancement in many fields, as for example in food science, materials science or MRI, where low B(0)-fields or low B(0)-homogeneity do decrease spectral resolution, leading to potential extinction if in-phase and anti-phase hyperpolarization signals cannot be resolved. Herein, we demonstrate that the echo sequence (45°-τ-180°-τ) enables the acquisition of low resolution PHIP enhanced liquid state NMR signals of phenylpropiolic acid derivatives and phenylacetylene at a low cost low-resolution 0.54 T spectrometer. As low field TD-spectrometers are commonly used in industry or biomedicine for the relaxometry of oil-water mixtures, food, nano-particles, or other systems, we compare two variants of para-hydrogen induced polarization with data-evaluation in the time domain (TD-PHIP). In both TD-ALTADENA and the TD-PASADENA strong spin echoes could be detected under conditions when usually no anti-phase signals can be measured due to the lack of resolution. The results suggest that the time-domain detection of PHIP-enhanced signals opens up new application areas for low-field PHIP-hyperpolarization, such as non-invasive compound detection or new contrast agents and biomarkers in low-field Magnetic Resonance Imaging (MRI). Finally, solid-state NMR calculations are presented, which show that the solid echo (90y-τ-90x-τ) version of the TD-ALTADENA experiment is able to convert up to 10% of the PHIP signal into visible magnetization.
Finite-difference and finite-volume methods for nonlinear standing ultrasonic waves in fluid media.
Vanhille, C; Conde, C; Campos-Pozuelo, C
2004-04-01
In the framework of the application of high-power ultrasonics in industrial processing in fluid media, the mathematical prediction of the acoustical parameters inside resonators should improve the development of practical systems. This can be achieved by the use of numerical tools able to treat the nonlinear acoustics involved in these phenomena. In particular, effects like nonlinear distortion and nonlinear attenuation are fundamental in applications. In this paper, three one-dimensional numerical models in the time domain for calculating the nonlinear acoustic field inside a one-dimensional resonant cavity are presented and compared. They are based on the finite-difference and the finite-volume methods. These different algorithms solve the differential equations, from the linear up to the strongly nonlinear case (including weak shock). Some physical results obtained from the modelling of ultrasonic waves and a comparison of the efficiency of the different algorithms are presented.
NASA Astrophysics Data System (ADS)
Imamura, N.; Schultz, A.
2015-12-01
Recently, a full waveform time domain solution has been developed for the magnetotelluric (MT) and controlled-source electromagnetic (CSEM) methods. The ultimate goal of this approach is to obtain a computationally tractable direct waveform joint inversion for source fields and earth conductivity structure in three and four dimensions. This is desirable on several grounds, including the improved spatial resolving power expected from use of a multitude of source illuminations of non-zero wavenumber, the ability to operate in areas of high levels of source signal spatial complexity and non-stationarity, etc. This goal would not be obtainable if one were to adopt the finite difference time-domain (FDTD) approach for the forward problem. This is particularly true for the case of MT surveys, since an enormous number of degrees of freedom are required to represent the observed MT waveforms across the large frequency bandwidth. It means that for FDTD simulation, the smallest time steps should be finer than that required to represent the highest frequency, while the number of time steps should also cover the lowest frequency. This leads to a linear system that is computationally burdensome to solve. We have implemented our code that addresses this situation through the use of a fictitious wave domain method and GPUs to speed up the computation time. We also substantially reduce the size of the linear systems by applying concepts from successive cascade decimation, through quasi-equivalent time domain decomposition. By combining these refinements, we have made good progress toward implementing the core of a full waveform joint source field/earth conductivity inverse modeling method. From results, we found the use of previous generation of CPU/GPU speeds computations by an order of magnitude over a parallel CPU only approach. In part, this arises from the use of the quasi-equivalent time domain decomposition, which shrinks the size of the linear system dramatically.
NASA Astrophysics Data System (ADS)
Yu, Peicheng; Li, Fei; Dalichaouch, Thamine; Fiuza, Frederico; Decyk, Viktor; Davidson, Asher; Tableman, Adam; An, Weiming; Tsung, Frank; Fonseca, Ricardo; Lu, Wei; Vieira, Jorge; Silva, Luis; Mori, Warren
2016-10-01
we present a finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm, which is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control the EM dispersion curve in the direction of the plasma drift of a FDTD Maxwell solver by using a customized higher order finite difference operator for the spatial derivative along the direction of the drift (1& circ; direction). We show that this eliminates the main NCI modes with moderate | k1 | , while keeps additional main NCI modes well outside the range of physical interest with higher | k1 | . These main NCI modes can be easily filtered out along with first spatial aliasing NCI modes which are also at the edge of the fundamental Brillouin zone. The customized solver has the possible advantage of improved parallel scalability because it can be easily partitioned along 1& circ; which typically has many more cells than other directions for the problems of interest.
Subresolution Displacements in Finite Difference Simulations of Ultrasound Propagation and Imaging.
Pinton, Gianmarco F
2017-03-01
Time domain finite difference simulations are used extensively to simulate wave propagation. They approximate the wave field on a discrete domain with a grid spacing that is typically on the order of a tenth of a wavelength. The smallest displacements that can be modeled by this type of simulation are thus limited to discrete values that are integer multiples of the grid spacing. This paper presents a method to represent continuous and subresolution displacements by varying the impedance of individual elements in a multielement scatterer. It is demonstrated that this method removes the limitations imposed by the discrete grid spacing by generating a continuum of displacements as measured by the backscattered signal. The method is first validated on an ideal perfect correlation case with a single scatterer. It is subsequently applied to a more complex case with a field of scatterers that model an acoustic radiation force-induced displacement used in ultrasound elasticity imaging. A custom finite difference simulation tool is used to simulate propagation from ultrasound imaging pulses in the scatterer field. These simulated transmit-receive events are then beamformed into images, which are tracked with a correlation-based algorithm to determine the displacement. A linear predictive model is developed to analytically describe the relationship between element impedance and backscattered phase shift. The error between model and simulation is λ/ 1364 , where λ is the acoustical wavelength. An iterative method is also presented that reduces the simulation error to λ/ 5556 over one iteration. The proposed technique therefore offers a computationally efficient method to model continuous subresolution displacements of a scattering medium in ultrasound imaging. This method has applications that include ultrasound elastography, blood flow, and motion tracking. This method also extends generally to finite difference simulations of wave propagation, such as electromagnetic or
NASA Astrophysics Data System (ADS)
Fabien-Ouellet, Gabriel; Gloaguen, Erwan; Giroux, Bernard
2017-03-01
Full Waveform Inversion (FWI) aims at recovering the elastic parameters of the Earth by matching recordings of the ground motion with the direct solution of the wave equation. Modeling the wave propagation for realistic scenarios is computationally intensive, which limits the applicability of FWI. The current hardware evolution brings increasing parallel computing power that can speed up the computations in FWI. However, to take advantage of the diversity of parallel architectures presently available, new programming approaches are required. In this work, we explore the use of OpenCL to develop a portable code that can take advantage of the many parallel processor architectures now available. We present a program called SeisCL for 2D and 3D viscoelastic FWI in the time domain. The code computes the forward and adjoint wavefields using finite-difference and outputs the gradient of the misfit function given by the adjoint state method. To demonstrate the code portability on different architectures, the performance of SeisCL is tested on three different devices: Intel CPUs, NVidia GPUs and Intel Xeon PHI. Results show that the use of GPUs with OpenCL can speed up the computations by nearly two orders of magnitudes over a single threaded application on the CPU. Although OpenCL allows code portability, we show that some device-specific optimization is still required to get the best performance out of a specific architecture. Using OpenCL in conjunction with MPI allows the domain decomposition of large models on several devices located on different nodes of a cluster. For large enough models, the speedup of the domain decomposition varies quasi-linearly with the number of devices. Finally, we investigate two different approaches to compute the gradient by the adjoint state method and show the significant advantages of using OpenCL for FWI.
Convergence of finite difference transient response computations for thin shells.
NASA Technical Reports Server (NTRS)
Sobel, L. H.; Geers, T. L.
1973-01-01
Numerical studies pertaining to the limits of applicability of the finite difference method in the solution of linear transient shell response problems are performed, and a computational procedure for the use of the method is recommended. It is found that the only inherent limitation of the finite difference method is its inability to reproduce accurately response discontinuities. This is not a serious limitation in view of natural constraints imposed by the extension of Saint Venant's principle to transient response problems. It is also found that the short wavelength limitations of thin shell (Bernoulli-Euler) theory create significant convergence difficulties in computed response to certain types of transverse excitations. These difficulties may be overcome, however, through proper selection of finite difference mesh dimensions and temporal smoothing of the excitation.
Time-domain diffuse correlation spectroscopy
Sutin, Jason; Zimmerman, Bernhard; Tyulmankov, Danil; Tamborini, Davide; Wu, Kuan Cheng; Selb, Juliette; Gulinatti, Angelo; Rech, Ivan; Tosi, Alberto; Boas, David A.; Franceschini, Maria Angela
2016-01-01
Physiological monitoring of oxygen delivery to the brain has great significance for improving the management of patients at risk for brain injury. Diffuse correlation spectroscopy (DCS) is a rapidly growing optical technology able to non-invasively assess the blood flow index (BFi) at the bedside. The current limitations of DCS are the contamination introduced by extracerebral tissue and the need to know the tissue’s optical properties to correctly quantify the BFi. To overcome these limitations, we have developed a new technology for time-resolved diffuse correlation spectroscopy. By operating DCS in the time domain (TD-DCS), we are able to simultaneously acquire the temporal point-spread function to quantify tissue optical properties and the autocorrelation function to quantify the BFi. More importantly, by applying time-gated strategies to the DCS autocorrelation functions, we are able to differentiate between short and long photon paths through the tissue and determine the BFi for different depths. Here, we present the novel device and we report the first experiments in tissue-like phantoms and in rodents. The TD-DCS method opens many possibilities for improved non-invasive monitoring of oxygen delivery in humans. PMID:28008417
Reengineering observatory operations for the time domain
NASA Astrophysics Data System (ADS)
Seaman, Robert L.; Vestrand, W. T.; Hessman, Frederic V.
2014-07-01
Observatories are complex scientific and technical institutions serving diverse users and purposes. Their telescopes, instruments, software, and human resources engage in interwoven workflows over a broad range of timescales. These workflows have been tuned to be responsive to concepts of observatory operations that were applicable when various assets were commissioned, years or decades in the past. The astronomical community is entering an era of rapid change increasingly characterized by large time domain surveys, robotic telescopes and automated infrastructures, and - most significantly - of operating modes and scientific consortia that span our individual facilities, joining them into complex network entities. Observatories must adapt and numerous initiatives are in progress that focus on redesigning individual components out of the astronomical toolkit. New instrumentation is both more capable and more complex than ever, and even simple instruments may have powerful observation scripting capabilities. Remote and queue observing modes are now widespread. Data archives are becoming ubiquitous. Virtual observatory standards and protocols and astroinformatics data-mining techniques layered on these are areas of active development. Indeed, new large-aperture ground-based telescopes may be as expensive as space missions and have similarly formal project management processes and large data management requirements. This piecewise approach is not enough. Whatever challenges of funding or politics facing the national and international astronomical communities it will be more efficient - scientifically as well as in the usual figures of merit of cost, schedule, performance, and risks - to explicitly address the systems engineering of the astronomical community as a whole.
How Swift is redefining time domain astronomy
NASA Astrophysics Data System (ADS)
Gehrels, N.; Cannizzo, J. K.
2015-09-01
NASA's Swift satellite has completed ten years of amazing discoveries in time domain astronomy. Its primary mission is to chase gamma-ray bursts (GRBs), but due to its scheduling flexibility it has subsequently become a prime discovery machine for new types of behavior. The list of major discoveries in GRBs and other transients includes the long-lived X-ray afterglows and flares from GRBs, the first accurate localization of short GRBs, the discovery of GRBs at high redshift (z > 8), supernova shock break-out from SN Ib, a jetted tidal disruption event, an ultra-long class of GRBs, high energy emission from flare stars, novae and supernovae with unusual characteristics, magnetars with glitches in their spin periods, and a short GRB with evidence of an accompanying kilonova. Swift has developed a dynamic synergism with ground based observatories. In a few years gravitational wave observatories will come on-line and provide exciting new transient sources for Swift to study.
NASA Astrophysics Data System (ADS)
He, Zi; Chen, Ru-Shan
2016-03-01
An efficient three-dimensional time domain parabolic equation (TDPE) method is proposed to fast analyze the narrow-angle wideband EM scattering properties of electrically large targets. The finite difference (FD) of Crank-Nicolson (CN) scheme is used as the traditional tool to solve the time-domain parabolic equation. However, a huge computational resource is required when the meshes become dense. Therefore, the alternating direction implicit (ADI) scheme is introduced to discretize the time-domain parabolic equation. In this way, the reduced transient scattered fields can be calculated line by line in each transverse plane for any time step with unconditional stability. As a result, less computational resources are required for the proposed ADI-based TDPE method when compared with both the traditional CN-based TDPE method and the finite-different time-domain (FDTD) method. By employing the rotating TDPE method, the complete bistatic RCS can be obtained with encouraging accuracy for any observed angle. Numerical examples are given to demonstrate the accuracy and efficiency of the proposed method.
Nondestructive Evaluation of Aircraft Composites Using Terahertz Time Domain Spectroscopy
2008-12-10
Taday, P. F., Pepper , M. (2008). Elimination of scattering effects in spectral measurement of granulated materials using terahertz time domain...W., Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Material parameter extraction for terahertz time-domain spectroscopy using... Ferguson , B., Rainsford, T., Mickan, S. P., & Abbott, D. (2005). Simple material parameter estimation via terahertz time-domain spectroscopy
Compact finite difference method for American option pricing
NASA Astrophysics Data System (ADS)
Zhao, Jichao; Davison, Matt; Corless, Robert M.
2007-09-01
A compact finite difference method is designed to obtain quick and accurate solutions to partial differential equation problems. The problem of pricing an American option can be cast as a partial differential equation. Using the compact finite difference method this problem can be recast as an ordinary differential equation initial value problem. The complicating factor for American options is the existence of an optimal exercise boundary which is jointly determined with the value of the option. In this article we develop three ways of combining compact finite difference methods for American option price on a single asset with methods for dealing with this optimal exercise boundary. Compact finite difference method one uses the implicit condition that solutions of the transformed partial differential equation be nonnegative to detect the optimal exercise value. This method is very fast and accurate even when the spatial step size h is large (h[greater-or-equal, slanted]0.1). Compact difference method two must solve an algebraic nonlinear equation obtained by Pantazopoulos (1998) at every time step. This method can obtain second order accuracy for space x and requires a moderate amount of time comparable with that required by the Crank Nicolson projected successive over relaxation method. Compact finite difference method three refines the free boundary value by a method developed by Barone-Adesi and Lugano [The saga of the American put, 2003], and this method can obtain high accuracy for space x. The last two of these three methods are convergent, moreover all the three methods work for both short term and long term options. Through comparison with existing popular methods by numerical experiments, our work shows that compact finite difference methods provide an exciting new tool for American option pricing.
Direct simulations of turbulent flow using finite-difference schemes
NASA Technical Reports Server (NTRS)
Rai, Man Mohan; Moin, Parviz
1989-01-01
A high-order accurate finite-difference approach is presented for calculating incompressible turbulent flow. The methods used include a kinetic energy conserving central difference scheme and an upwind difference scheme. The methods are evaluated in test cases for the evolution of small-amplitude disturbances and fully developed turbulent channel flow. It is suggested that the finite-difference approach can be applied to complex geometries more easilty than highly accurate spectral methods. It is concluded that the upwind scheme is a good candidate for direct simulations of turbulent flows over complex geometries.
Finite-Difference Algorithms For Computing Sound Waves
NASA Technical Reports Server (NTRS)
Davis, Sanford
1993-01-01
Governing equations considered as matrix system. Method variant of method described in "Scheme for Finite-Difference Computations of Waves" (ARC-12970). Present method begins with matrix-vector formulation of fundamental equations, involving first-order partial derivatives of primitive variables with respect to space and time. Particular matrix formulation places time and spatial coordinates on equal footing, so governing equations considered as matrix system and treated as unit. Spatial and temporal discretizations not treated separately as in other finite-difference methods, instead treated together by linking spatial-grid interval and time step via common scale factor related to speed of sound.
Tan, Sirui; Huang, Lianjie
2014-11-01
For modeling scalar-wave propagation in geophysical problems using finite-difference schemes, optimizing the coefficients of the finite-difference operators can reduce numerical dispersion. Most optimized finite-difference schemes for modeling seismic-wave propagation suppress only spatial but not temporal dispersion errors. We develop a novel optimized finite-difference scheme for numerical scalar-wave modeling to control dispersion errors not only in space but also in time. Our optimized scheme is based on a new stencil that contains a few more grid points than the standard stencil. We design an objective function for minimizing relative errors of phase velocities of waves propagating in all directions within a given range of wavenumbers. Dispersion analysis and numerical examples demonstrate that our optimized finite-difference scheme is computationally up to 2.5 times faster than the optimized schemes using the standard stencil to achieve the similar modeling accuracy for a given 2D or 3D problem. Compared with the high-order finite-difference scheme using the same new stencil, our optimized scheme reduces 50 percent of the computational cost to achieve the similar modeling accuracy. This new optimized finite-difference scheme is particularly useful for large-scale 3D scalar-wave modeling and inversion.
NASA Astrophysics Data System (ADS)
Pletinckx, D.
2011-09-01
The current 3D hype creates a lot of interest in 3D. People go to 3D movies, but are we ready to use 3D in our homes, in our offices, in our communication? Are we ready to deliver real 3D to a general public and use interactive 3D in a meaningful way to enjoy, learn, communicate? The CARARE project is realising this for the moment in the domain of monuments and archaeology, so that real 3D of archaeological sites and European monuments will be available to the general public by 2012. There are several aspects to this endeavour. First of all is the technical aspect of flawlessly delivering 3D content over all platforms and operating systems, without installing software. We have currently a working solution in PDF, but HTML5 will probably be the future. Secondly, there is still little knowledge on how to create 3D learning objects, 3D tourist information or 3D scholarly communication. We are still in a prototype phase when it comes to integrate 3D objects in physical or virtual museums. Nevertheless, Europeana has a tremendous potential as a multi-facetted virtual museum. Finally, 3D has a large potential to act as a hub of information, linking to related 2D imagery, texts, video, sound. We describe how to create such rich, explorable 3D objects that can be used intuitively by the generic Europeana user and what metadata is needed to support the semantic linking.
Time Domain Viscoelastic Full Waveform Inversion
NASA Astrophysics Data System (ADS)
Fabien-Ouellet, Gabriel; Gloaguen, Erwan; Giroux, Bernard
2017-03-01
Viscous attenuation can have a strong impact on seismic wave propagation, but it is rarely taken into account in full waveform inversion (FWI). When viscoelasticity is considered in time domain FWI, the displacement formulation of the wave equation is usually used instead of the popular velocity-stress formulation. However, inversion schemes rely on the adjoint equations, which are quite different for the velocity-stress formulation than for the displacement formulation. In this paper, we apply the adjoint state method to the isotropic viscoelastic wave equation in the velocity-stress formulation based on the generalized standard linear solid rheology. By applying linear transformations to the wave equation before deriving the adjoint state equations, we obtain two symmetric sets of partial differential equations for the forward and adjoint variables. The resulting sets of equations only differ by a sign change and can be solved by the same numerical implementation. We also investigate the crosstalk between parameter classes (velocity and attenuation) of the viscoelastic equation. More specifically, we show that the attenuation levels can be used to recover the quality factors of P- and S- waves, but that they are very sensitive to velocity errors. Finally, we present a synthetic example of viscoelastic FWI in the context of monitoring CO2 geological sequestration. We show that FWI based on our formulation can indeed recover P- and S- wave velocities and their attenuation levels when attenuation is high enough. Both changes in velocity and attenuation levels recovered with FWI can be used to track the CO2 plume during and after injection. Further studies are required to evaluate the performance of viscoelastic FWI on real data.
NASA Astrophysics Data System (ADS)
Zehner, Björn; Hellwig, Olaf; Linke, Maik; Görz, Ines; Buske, Stefan
2016-01-01
3D geological underground models are often presented by vector data, such as triangulated networks representing boundaries of geological bodies and geological structures. Since models are to be used for numerical simulations based on the finite difference method, they have to be converted into a representation discretizing the full volume of the model into hexahedral cells. Often the simulations require a high grid resolution and are done using parallel computing. The storage of such a high-resolution raster model would require a large amount of storage space and it is difficult to create such a model using the standard geomodelling packages. Since the raster representation is only required for the calculation, but not for the geometry description, we present an algorithm and concept for rasterizing geological models on the fly for the use in finite difference codes that are parallelized by domain decomposition. As a proof of concept we implemented a rasterizer library and integrated it into seismic simulation software that is run as parallel code on a UNIX cluster using the Message Passing Interface. We can thus run the simulation with realistic and complicated surface-based geological models that are created using 3D geomodelling software, instead of using a simplified representation of the geological subsurface using mathematical functions or geometric primitives. We tested this set-up using an example model that we provide along with the implemented library.
Direct Finite-Difference Simulations Of Turbulent Flow
NASA Technical Reports Server (NTRS)
Rai, Man Mohan; Moin, Parviz
1991-01-01
Report discusses use of upwind-biased finite-difference numerical-integration scheme to simulate evolution of small disturbances and fully developed turbulence in three-dimensional flow of viscous, incompressible fluid in channel. Involves use of computational grid sufficiently fine to resolve motion of fluid at all relevant length scales.
Jones, Stacy; Sinha, Sudarson Sekhar; Pramanik, Avijit; Ray, Paresh Chandra
2016-11-03
Drug resistant superbug infection is one of the foremost threats to human health. Plasmonic nanoparticles can be used for ultrasensitive bio-imaging and photothermal killing by amplification of electromagnetic fields at nanoscale "hot spots". One of the main challenges to plasmonic imaging and photothermal killing is design of a plasmonic substrate with a large number of "hot spots". Driven by this need, this article reports design of a three-dimensional (3D) plasmonic "hot spot"-based substrate using gold nanoparticle attached hybrid graphene oxide (GO), free from the traditional 2D limitations. Experimental results show that the 3D substrate has capability for highly sensitive label-free sensing and generates high photothermal heat. Reported data using p-aminothiophenol conjugated 3D substrate show that the surface enhanced Raman spectroscopy (SERS) enhancement factor for the 3D "hot spot"-based substrate is more than two orders of magnitude greater than that for the two-dimensional (2D) substrate and five orders of magnitude greater than that for the zero-dimensional (0D) p-aminothiophenol conjugated gold nanoparticle. 3D-Finite-Difference Time-Domain (3D-FDTD) simulation calculations indicate that the SERS enhancement factor can be greater than 10(4) because of the bent assembly structure in the 3D substrate. Results demonstrate that the 3D-substrate-based SERS can be used for fingerprint identification of several multi-drug resistant superbugs with detection limits of 5 colony forming units per mL. Experimental data show that 785 nm near infrared (NIR) light generates around two times more photothermal heat for the 3D substrate with respect to the 2D substrate, and allows rapid and effective killing of 100% of the multi-drug resistant superbugs within 5 minutes.
3d-3d correspondence revisited
Chung, Hee -Joong; Dimofte, Tudor; Gukov, Sergei; ...
2016-04-21
In fivebrane compactifications on 3-manifolds, we point out the importance of all flat connections in the proper definition of the effective 3d N = 2 theory. The Lagrangians of some theories with the desired properties can be constructed with the help of homological knot invariants that categorify colored Jones polynomials. Higgsing the full 3d theories constructed this way recovers theories found previously by Dimofte-Gaiotto-Gukov. As a result, we also consider the cutting and gluing of 3-manifolds along smooth boundaries and the role played by all flat connections in this operation.
Time-Domain Terahertz Computed Axial Tomography NDE System
NASA Technical Reports Server (NTRS)
Zimdars, David
2012-01-01
NASA has identified the need for advanced non-destructive evaluation (NDE) methods to characterize aging and durability in aircraft materials to improve the safety of the nation's airline fleet. 3D THz tomography can play a major role in detection and characterization of flaws and degradation in aircraft materials, including Kevlar-based composites and Kevlar and Zylon fabric covers for soft-shell fan containment where aging and durability issues are critical. A prototype computed tomography (CT) time-domain (TD) THz imaging system has been used to generate 3D images of several test objects including a TUFI tile (a thermal protection system tile used on the Space Shuttle and possibly the Orion or similar capsules). This TUFI tile had simulated impact damage that was located and the depth of damage determined. The CT motion control gan try was designed and constructed, and then integrated with a T-Ray 4000 control unit and motion controller to create a complete CT TD-THz imaging system prototype. A data collection software script was developed that takes multiple z-axis slices in sequence and saves the data for batch processing. The data collection software was integrated with the ability to batch process the slice data with the CT TD-THz image reconstruction software. The time required to take a single CT slice was decreased from six minutes to approximately one minute by replacing the 320 ps, 100-Hz waveform acquisition system with an 80 ps, 1,000-Hz waveform acquisition system. The TD-THZ computed tomography system was built from pre-existing commercial off-the-shelf subsystems. A CT motion control gantry was constructed from COTS components that can handle larger samples. The motion control gantry allows inspection of sample sizes of up to approximately one cubic foot (.0.03 cubic meters). The system reduced to practice a CT-TDTHz system incorporating a COTS 80- ps/l-kHz waveform scanner. The incorporation of this scanner in the system allows acquisition of 3D
Structural organization of human replication timing domains.
Boulos, Rasha E; Drillon, Guénola; Argoul, Françoise; Arneodo, Alain; Audit, Benjamin
2015-10-07
Recent analysis of genome-wide epigenetic modification data, mean replication timing (MRT) profiles and chromosome conformation data in mammals have provided increasing evidence that flexibility in replication origin usage is regulated locally by the epigenetic landscape and over larger genomic distances by the 3D chromatin architecture. Here, we review the recent results establishing some link between replication domains and chromatin structural domains in pluripotent and various differentiated cell types in human. We reconcile the originally proposed dichotomic picture of early and late constant timing regions that replicate by multiple rather synchronous origins in separated nuclear compartments of open and closed chromatins, with the U-shaped MRT domains bordered by "master" replication origins specified by a localized (∼200-300 kb) zone of open and transcriptionally active chromatin from which a replication wave likely initiates and propagates toward the domain center via a cascade of origin firing. We discuss the relationships between these MRT domains, topologically associated domains and lamina-associated domains. This review sheds a new light on the epigenetically regulated global chromatin reorganization that underlies the loss of pluripotency and the determination of differentiation properties.
NASA Astrophysics Data System (ADS)
Gorunmez, Zohre; Jana, Debrina; He, Jie; Sagle, Laura; Beck, Thomas
Core-shell (CS) nanostructures have received attention in recent years due to their usefulness in applications ranging from catalysis to cancer treatment. SERS has been shown to be one of the most sensitive techniques for molecular detection, achieving single molecule detection. It has been established that the electromagnetic mechanism (EM) provides the main contribution to SERS enhancement due to the normal Raman spectroscopy arising from coupling of both the incident and re-emitted fields. The FDTD technique has been developed to provide numerical solutions to Maxwell's time-dependent curl equations in order to promise modeling capabilities for EM enhancement of SERS. Herein, we apply this method to the study of three morphologically different gold core-shell nanoparticles to investigate their contributions to SERS. In these structures, the dye/probe molecule resides in between the shell and the core and only the shell morphology is altered. The data shows that the surface plasmon resonances (PRs) influencing the SERS of the probe molecules, due to the coupling of the core and shell, are tunable by changing the shell morphologies and CS structures with sharp features on their surfaces highlight larger enhancements due to stronger localized surface PRs. University of Cincinnati start-up funds, NSF, Ohio Supercomputer Center, and the Ministry of National Education of the Republic of Turkey.
2006-12-01
the environment that causes the sound scattering (such as buildings) can be modeled on a computer and adequate sensor data can be collected, one can...way, for example, high-energy ultrasound can be precisely focused to break up a gallstone or kidney stone.6, 7 In the process of locating a sound
Elastic wave modelling in 3D heterogeneous media: 3D grid method
NASA Astrophysics Data System (ADS)
Jianfeng, Zhang; Tielin, Liu
2002-09-01
We present a new numerical technique for elastic wave modelling in 3D heterogeneous media with surface topography, which is called the 3D grid method in this paper. This work is an extension of the 2D grid method that models P-SV wave propagation in 2D heterogeneous media. Similar to the finite-element method in the discretization of a numerical mesh, the proposed scheme is flexible in incorporating surface topography and curved interfaces; moreover it satisfies the free-surface boundary conditions of 3D topography naturally. The algorithm, developed from a parsimonious staggered-grid scheme, solves the problem using integral equilibrium around each node, instead of satisfying elastodynamic differential equations at each node as in the conventional finite-difference method. The computational cost and memory requirements for the proposed scheme are approximately the same as those used by the same order finite-difference method. In this paper, a mixed tetrahedral and parallelepiped grid method is presented; and the numerical dispersion and stability criteria on the tetrahedral grid method and parallelepiped grid method are discussed in detail. The proposed scheme is successfully tested against an analytical solution for the 3D Lamb problem and a solution of the boundary method for the diffraction of a hemispherical crater. Moreover, examples of surface-wave propagation in an elastic half-space with a semi-cylindrical trench on the surface and 3D plane-layered model are presented.
Asymptotic analysis of numerical wave propagation in finite difference equations
NASA Technical Reports Server (NTRS)
Giles, M.; Thompkins, W. T., Jr.
1983-01-01
An asymptotic technique is developed for analyzing the propagation and dissipation of wave-like solutions to finite difference equations. It is shown that for each fixed complex frequency there are usually several wave solutions with different wavenumbers and the slowly varying amplitude of each satisfies an asymptotic amplitude equation which includes the effects of smoothly varying coefficients in the finite difference equations. The local group velocity appears in this equation as the velocity of convection of the amplitude. Asymptotic boundary conditions coupling the amplitudes of the different wave solutions are also derived. A wavepacket theory is developed which predicts the motion, and interaction at boundaries, of wavepackets, wave-like disturbances of finite length. Comparison with numerical experiments demonstrates the success and limitations of the theory. Finally an asymptotic global stability analysis is developed.
Time dependent wave envelope finite difference analysis of sound propagation
NASA Technical Reports Server (NTRS)
Baumeister, K. J.
1984-01-01
A transient finite difference wave envelope formulation is presented for sound propagation, without steady flow. Before the finite difference equations are formulated, the governing wave equation is first transformed to a form whose solution tends not to oscillate along the propagation direction. This transformation reduces the required number of grid points by an order of magnitude. Physically, the transformed pressure represents the amplitude of the conventional sound wave. The derivation for the wave envelope transient wave equation and appropriate boundary conditions are presented as well as the difference equations and stability requirements. To illustrate the method, example solutions are presented for sound propagation in a straight hard wall duct and in a two dimensional straight soft wall duct. The numerical results are in good agreement with exact analytical results.
Selecting step sizes in sensitivity analysis by finite differences
NASA Technical Reports Server (NTRS)
Iott, J.; Haftka, R. T.; Adelman, H. M.
1985-01-01
This paper deals with methods for obtaining near-optimum step sizes for finite difference approximations to first derivatives with particular application to sensitivity analysis. A technique denoted the finite difference (FD) algorithm, previously described in the literature and applicable to one derivative at a time, is extended to the calculation of several simultaneously. Both the original and extended FD algorithms are applied to sensitivity analysis for a data-fitting problem in which derivatives of the coefficients of an interpolation polynomial are calculated with respect to uncertainties in the data. The methods are also applied to sensitivity analysis of the structural response of a finite-element-modeled swept wing. In a previous study, this sensitivity analysis of the swept wing required a time-consuming trial-and-error effort to obtain a suitable step size, but it proved to be a routine application for the extended FD algorithm herein.
Finite difference seismic modeling of axial magma chambers
Swift, S.A.; Dougherty, M.E.; Stephen, R.A. )
1990-11-01
The authors tested the feasibility of using finite difference methods to model seismic propagation at {approximately}10 Hx through a two-dimensional representation of an axial magma chamber with a thin, liquid lid. This technique produces time series of displacement or pressure at seafloor receivers to mimic a seismic refraction experiment and snapshots of P and S energy propagation. The results indicate that the implementation is stable for models with sharp velocity contrasts and complex geometries. The authors observe a high-energy, downward-traveling shear phase, observable only with borehole receivers, that would be useful in studying the nature and shape of magma chambers. The ability of finite difference methods to model high-order wave phenomena makes this method ideal for testing velocity models of spreading axes and for planning near-axis drilling of the East Pacific Rise in order to optimize the benefits from shear wave imaging of sub-axis structure.
Finite elements and finite differences for transonic flow calculations
NASA Technical Reports Server (NTRS)
Hafez, M. M.; Murman, E. M.; Wellford, L. C.
1978-01-01
The paper reviews the chief finite difference and finite element techniques used for numerical solution of nonlinear mixed elliptic-hyperbolic equations governing transonic flow. The forms of the governing equations for unsteady two-dimensional transonic flow considered are the Euler equation, the full potential equation in both conservative and nonconservative form, the transonic small-disturbance equation in both conservative and nonconservative form, and the hodograph equations for the small-disturbance case and the full-potential case. Finite difference methods considered include time-dependent methods, relaxation methods, semidirect methods, and hybrid methods. Finite element methods include finite element Lax-Wendroff schemes, implicit Galerkin method, mixed variational principles, dual iterative procedures, optimal control methods and least squares.
Finite difference schemes for long-time integration
NASA Technical Reports Server (NTRS)
Haras, Zigo; Taasan, Shlomo
1993-01-01
Finite difference schemes for the evaluation of first and second derivatives are presented. These second order compact schemes were designed for long-time integration of evolution equations by solving a quadratic constrained minimization problem. The quadratic cost function measures the global truncation error while taking into account the initial data. The resulting schemes are applicable for integration times fourfold, or more, longer than similar previously studied schemes. A similar approach was used to obtain improved integration schemes.
NASA Astrophysics Data System (ADS)
Meulien Ohlmann, Odile
2013-02-01
Today the industry offers a chain of 3D products. Learning to "read" and to "create in 3D" becomes an issue of education of primary importance. 25 years professional experience in France, the United States and Germany, Odile Meulien set up a personal method of initiation to 3D creation that entails the spatial/temporal experience of the holographic visual. She will present some different tools and techniques used for this learning, their advantages and disadvantages, programs and issues of educational policies, constraints and expectations related to the development of new techniques for 3D imaging. Although the creation of display holograms is very much reduced compared to the creation of the 90ies, the holographic concept is spreading in all scientific, social, and artistic activities of our present time. She will also raise many questions: What means 3D? Is it communication? Is it perception? How the seeing and none seeing is interferes? What else has to be taken in consideration to communicate in 3D? How to handle the non visible relations of moving objects with subjects? Does this transform our model of exchange with others? What kind of interaction this has with our everyday life? Then come more practical questions: How to learn creating 3D visualization, to learn 3D grammar, 3D language, 3D thinking? What for? At what level? In which matter? for whom?
Introduction to finite-difference methods for numerical fluid dynamics
Scannapieco, E.; Harlow, F.H.
1995-09-01
This work is intended to be a beginner`s exercise book for the study of basic finite-difference techniques in computational fluid dynamics. It is written for a student level ranging from high-school senior to university senior. Equations are derived from basic principles using algebra. Some discussion of partial-differential equations is included, but knowledge of calculus is not essential. The student is expected, however, to have some familiarity with the FORTRAN computer language, as the syntax of the computer codes themselves is not discussed. Topics examined in this work include: one-dimensional heat flow, one-dimensional compressible fluid flow, two-dimensional compressible fluid flow, and two-dimensional incompressible fluid flow with additions of the equations of heat flow and the {Kappa}-{epsilon} model for turbulence transport. Emphasis is placed on numerical instabilities and methods by which they can be avoided, techniques that can be used to evaluate the accuracy of finite-difference approximations, and the writing of the finite-difference codes themselves. Concepts introduced in this work include: flux and conservation, implicit and explicit methods, Lagrangian and Eulerian methods, shocks and rarefactions, donor-cell and cell-centered advective fluxes, compressible and incompressible fluids, the Boussinesq approximation for heat flow, Cartesian tensor notation, the Boussinesq approximation for the Reynolds stress tensor, and the modeling of transport equations. A glossary is provided which defines these and other terms.
Algorithmic vs. finite difference Jacobians for infrared atmospheric radiative transfer
NASA Astrophysics Data System (ADS)
Schreier, Franz; Gimeno García, Sebastián; Vasquez, Mayte; Xu, Jian
2015-10-01
Jacobians, i.e. partial derivatives of the radiance and transmission spectrum with respect to the atmospheric state parameters to be retrieved from remote sensing observations, are important for the iterative solution of the nonlinear inverse problem. Finite difference Jacobians are easy to implement, but computationally expensive and possibly of dubious quality; on the other hand, analytical Jacobians are accurate and efficient, but the implementation can be quite demanding. GARLIC, our "Generic Atmospheric Radiation Line-by-line Infrared Code", utilizes algorithmic differentiation (AD) techniques to implement derivatives w.r.t. atmospheric temperature and molecular concentrations. In this paper, we describe our approach for differentiation of the high resolution infrared and microwave spectra and provide an in-depth assessment of finite difference approximations using "exact" AD Jacobians as a reference. The results indicate that the "standard" two-point finite differences with 1 K and 1% perturbation for temperature and volume mixing ratio, respectively, can exhibit substantial errors, and central differences are significantly better. However, these deviations do not transfer into the truncated singular value decomposition solution of a least squares problem. Nevertheless, AD Jacobians are clearly recommended because of the superior speed and accuracy.
NASA Astrophysics Data System (ADS)
Simpson, J. J.; Taflove, A.
2005-12-01
We report a finite-difference time-domain (FDTD) computational solution of Maxwell's equations [1] that models the possibility of detecting and characterizing ionospheric disturbances above seismic regions. Specifically, we study anomalies in Schumann resonance spectra in the extremely low frequency (ELF) range below 30 Hz as observed in Japan caused by a hypothetical cylindrical ionospheric disturbance above Taiwan. We consider excitation of the global Earth-ionosphere waveguide by lightning in three major thunderstorm regions of the world: Southeast Asia, South America (Amazon region), and Africa. Furthermore, we investigate varying geometries and characteristics of the ionospheric disturbance above Taiwan. The FDTD technique used in this study enables a direct, full-vector, three-dimensional (3-D) time-domain Maxwell's equations calculation of round-the-world ELF propagation accounting for arbitrary horizontal as well as vertical geometrical and electrical inhomogeneities and anisotropies of the excitation, ionosphere, lithosphere, and oceans. Our entire-Earth model grids the annular lithosphere-atmosphere volume within 100 km of sea level, and contains over 6,500,000 grid-points (63 km laterally between adjacent grid points, 5 km radial resolution). We use our recently developed spherical geodesic gridding technique having a spatial discretization best described as resembling the surface of a soccer ball [2]. The grid is comprised entirely of hexagonal cells except for a small fixed number of pentagonal cells needed for completion. Grid-cell areas and locations are optimized to yield a smoothly varying area difference between adjacent cells, thereby maximizing numerical convergence. We compare our calculated results with measured data prior to the Chi-Chi earthquake in Taiwan as reported by Hayakawa et. al. [3]. Acknowledgement This work was suggested by Dr. Masashi Hayakawa, University of Electro-Communications, Chofugaoka, Chofu Tokyo. References [1] A
NASA Astrophysics Data System (ADS)
Yang, Fang; Gao, Feng; Jiao, Yuting; Zhao, Huijuan
2010-02-01
It is generally believed that the inverse problem in diffuse optical tomography (DOT) is highly ill-posed and its solution is always under-determined and sensitive to noise, which is the main problem in the application of DOT. In this paper, we propose a method on image reconstruction for time-domain diffuse optical tomography based on panel detection and Finite-Difference Method, and introduce an approach to reduce the number of unknown parameters in the reconstruction process. We propose a multi-level scheme to reduce the number of unknowns by parameterizing the spatial distribution of optical properties via wavelet transform and then reconstruct the coefficients of this transform. Compared with previous traditional uni-level full spatial domain algorithm, this method can efficiently improve the reconstruction quality. Numerical simulations show that wavelet-based multi-level inversion is superior to the uni-level algebraic reconstruction technique.
Scalar self-force on eccentric geodesics in Schwarzschild spacetime: A time-domain computation
Haas, Roland
2007-06-15
We calculate the self-force acting on a particle with scalar charge moving on a generic geodesic around a Schwarzschild black hole. This calculation requires an accurate computation of the retarded scalar field produced by the moving charge; this is done numerically with the help of a fourth-order convergent finite-difference scheme formulated in the time domain. The calculation also requires a regularization procedure, because the retarded field is singular on the particle's world line; this is handled mode-by-mode via the mode-sum regularization scheme first introduced by Barack and Ori. This paper presents the numerical method, various numerical tests, and a sample of results for mildly eccentric orbits as well as ''zoom-whirl'' orbits.
Chandra, Rohit; Balasingham, Ilangko
2015-01-01
A microwave imaging-based technique for 3D localization of an in-body RF source is presented. Such a technique can be useful for localization of an RF source as in wireless capsule endoscopes for positioning of any abnormality in the gastrointestinal tract. Microwave imaging is used to determine the dielectric properties (relative permittivity and conductivity) of the tissues that are required for a precise localization. A 2D microwave imaging algorithm is used for determination of the dielectric properties. Calibration method is developed for removing any error due to the used 2D imaging algorithm on the imaging data of a 3D body. The developed method is tested on a simple 3D heterogeneous phantom through finite-difference-time-domain simulations. Additive white Gaussian noise at the signal-to-noise ratio of 30 dB is added to the simulated data to make them more realistic. The developed calibration method improves the imaging and the localization accuracy. Statistics on the localization accuracy are generated by randomly placing the RF source at various positions inside the small intestine of the phantom. The cumulative distribution function of the localization error is plotted. In 90% of the cases, the localization accuracy was found within 1.67 cm, showing the capability of the developed method for 3D localization.
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Kreider, K. L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in ducts. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
NASA Astrophysics Data System (ADS)
Kaus, Boris; Popov, Anton; Püsök, Adina
2014-05-01
In order to solve high-resolution 3D problems in computational geodynamics it is crucial to use multigrid solvers in combination with parallel computers. A number of approaches are currently in use in the community, which can broadly be divided into coupled and decoupled approaches. In the decoupled approach, an algebraic or geometric multigrid method is used as a preconditioner for the velocity equations only while an iterative approach such as Schur complement reduction used to solve the outer velocity-pressure equations. In the coupled approach, on the other hand, a multigrid approach is applied to both the velocity and pressure equations. The coupled multigrid approaches are typically employed in combination with staggered finite difference discretizations, whereas the decoupled approach is the method of choice in many of the existing finite element codes. Yet, it is unclear whether there are differences in speed between the two approaches, and if so, how this depends on the initial guess. Here, we implemented both approaches in combination with a staggered finite difference discretization and test the robustness of the two approaches with respect to large jumps in viscosity contrast, as well as their computational efficiency as a function of the initial guess. Acknowledgements. Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on JUQUEEN of the Jülich high-performance computing center.
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.; Kreider, Kevin L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
ERIC Educational Resources Information Center
Hastings, S. K.
2002-01-01
Discusses 3 D imaging as it relates to digital representations in virtual library collections. Highlights include X-ray computed tomography (X-ray CT); the National Science Foundation (NSF) Digital Library Initiatives; output peripherals; image retrieval systems, including metadata; and applications of 3 D imaging for libraries and museums. (LRW)
An Exponential Finite Difference Technique for Solving Partial Differential Equations.
1987-06-01
density , kg/N 3 (lbm/ft 3) 91.*,e separation variables (At dimensionless timelAX) 2 vi -W sNiv W- NiW.4%1 1. INTRODUCTION Partial differential equations...competing numerical analysis were run in double precision on either the IBM-3033 or the Cray X-MP mainframes. The computer codes developed for the...is increased. - R P~p~ 15 Effect of Initial and Boundary Conditions on the Exponential Finite Difference Method In this section the effect of
Macroscopic traffic modeling with the finite difference method
Mughabghab, S.; Azarm, A.; Stock, D.
1996-03-15
A traffic congestion forecasting model (ATOP), developed in the present investigation, is described briefly. Several macroscopic models, based on the solution of the partial differential equation of conservation of vehicles by the finite difference method, were tested using actual traffic data. The functional form, as well as the parameters, of the equation of state which describes the relation between traffic speed and traffic density, were determined for a section of the Long Island Expressway. The Lax method and the forward difference technique were applied. The results of extensive tests showed that the Lax method, in addition to giving very good agreement with the traffic data, produces stable solutions.
Time-domain implementation of an impedance boundary condition with boundary layer correction
NASA Astrophysics Data System (ADS)
Brambley, E. J.; Gabard, G.
2016-09-01
A time-domain boundary condition is derived that accounts for the acoustic impedance of a thin boundary layer over an impedance boundary, based on the asymptotic frequency-domain boundary condition of Brambley (2011) [25]. A finite-difference reference implementation of this condition is presented and carefully validated against both an analytic solution and a discrete dispersion analysis for a simple test case. The discrete dispersion analysis enables the distinction between real physical instabilities and artificial numerical instabilities. The cause of the latter is suggested to be a combination of the real physical instabilities present and the aliasing and artificial zero group velocity of finite-difference schemes. It is suggested that these are general properties of any numerical discretization of an unstable system. Existing numerical filters are found to be inadequate to remove these artificial instabilities as they have a too wide pass band. The properties of numerical filters required to address this issue are discussed and a number of selective filters are presented that may prove useful in general. These filters are capable of removing only the artificial numerical instabilities, allowing the reference implementation to correctly reproduce the stability properties of the analytic solution.
Tian, Yuan; Han, Yiping; Ai, Xia; Liu, Xiuxiang
2014-12-15
In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.
Finite Difference Elastic Wave Field Simulation On GPU
NASA Astrophysics Data System (ADS)
Hu, Y.; Zhang, W.
2011-12-01
Numerical modeling of seismic wave propagation is considered as a basic and important aspect in investigation of the Earth's structure, and earthquake phenomenon. Among various numerical methods, the finite-difference method is considered one of the most efficient tools for the wave field simulation. However, with the increment of computing scale, the power of computing has becoming a bottleneck. With the development of hardware, in recent years, GPU shows powerful computational ability and bright application prospects in scientific computing. Many works using GPU demonstrate that GPU is powerful . Recently, GPU has not be used widely in the simulation of wave field. In this work, we present forward finite difference simulation of acoustic and elastic seismic wave propagation in heterogeneous media on NVIDIA graphics cards with the CUDA programming language. We also implement perfectly matched layers on the graphics cards to efficiently absorb outgoing waves on the fictitious edges of the grid Simulations compared with the results on CPU platform shows reliable accuracy and remarkable efficiency. This work proves that GPU can be an effective platform for wave field simulation, and it can also be used as a practical tool for real-time strong ground motion simulation.
OBTAINING POTENTIAL FIELD SOLUTIONS WITH SPHERICAL HARMONICS AND FINITE DIFFERENCES
Toth, Gabor; Van der Holst, Bart; Huang Zhenguang
2011-05-10
Potential magnetic field solutions can be obtained based on the synoptic magnetograms of the Sun. Traditionally, a spherical harmonics decomposition of the magnetogram is used to construct the current- and divergence-free magnetic field solution. This method works reasonably well when the order of spherical harmonics is limited to be small relative to the resolution of the magnetogram, although some artifacts, such as ringing, can arise around sharp features. When the number of spherical harmonics is increased, however, using the raw magnetogram data given on a grid that is uniform in the sine of the latitude coordinate can result in inaccurate and unreliable results, especially in the polar regions close to the Sun. We discuss here two approaches that can mitigate or completely avoid these problems: (1) remeshing the magnetogram onto a grid with uniform resolution in latitude and limiting the highest order of the spherical harmonics to the anti-alias limit; (2) using an iterative finite difference algorithm to solve for the potential field. The naive and the improved numerical solutions are compared for actual magnetograms and the differences are found to be rather dramatic. We made our new Finite Difference Iterative Potential-field Solver (FDIPS) a publicly available code so that other researchers can also use it as an alternative to the spherical harmonics approach.
Pencil: Finite-difference Code for Compressible Hydrodynamic Flows
NASA Astrophysics Data System (ADS)
Brandenburg, Axel; Dobler, Wolfgang
2010-10-01
The Pencil code is a high-order finite-difference code for compressible hydrodynamic flows with magnetic fields. It is highly modular and can easily be adapted to different types of problems. The code runs efficiently under MPI on massively parallel shared- or distributed-memory computers, like e.g. large Beowulf clusters. The Pencil code is primarily designed to deal with weakly compressible turbulent flows. To achieve good parallelization, explicit (as opposed to compact) finite differences are used. Typical scientific targets include driven MHD turbulence in a periodic box, convection in a slab with non-periodic upper and lower boundaries, a convective star embedded in a fully nonperiodic box, accretion disc turbulence in the shearing sheet approximation, self-gravity, non-local radiation transfer, dust particle evolution with feedback on the gas, etc. A range of artificial viscosity and diffusion schemes can be invoked to deal with supersonic flows. For direct simulations regular viscosity and diffusion is being used. The code is written in well-commented Fortran90.
[Size dependent SERS activity of gold nanoparticles studied by 3D-FDTD simulation].
Li, Li-mei; Fang, Ping-ping; Yang, Zhi-lin; Huang, Wen-da; Wu, De-yin; Ren, Bin; Tian, Zhong-qun
2009-05-01
By synthesizing Au nanoparticles with the controllable size from about 16 to 160 nm and measuring their SERS activity, the authors found that Au nanoparticles film with a size in the range of 120-135 nm showed the highest SERS activity with the 632.8 nm excitation, which is different from previous experimental results and theoretical predictions. The three dimensional finite difference time domain (3D-FDTD)method was employed to simulate the size dependent SERS activity. At the 632.8 nm excitation, the particles with a size of 110 nm shows the highest enhancement under coupling condition and presents an enhancement as high as 10(9) at the hot site. If the enhancement is averaged over the whole surface, the enhancement can still be as high as 10(7), in good agreement with our experimental data. For Au nanoparticles with a larger size such as 220 nm, the multipolar effect leads to the appearance of the second maximum enhancement with the increase in particles size. The averaged enhancement for the excitation line of 325 nm is only 10(2).
Probing the intrinsic optical Bloch-mode emission from a 3D photonic crystal
NASA Astrophysics Data System (ADS)
Hsieh, Mei-Li; Bur, James A.; Du, Qingguo; John, Sajeev; Lin, Shawn-Yu
2016-10-01
We report experimental observation of intrinsic Bloch-mode emission from a 3D tungsten photonic crystal at low thermal excitation. After the successful removal of conventional metallic emission (normal emission), it is possible to make an accurate comparison of the Bloch-mode and the normal emission. For all biases, we found that the emission intensity of the Bloch-mode is higher than that of the normal emission. The Bloch-mode emission also exhibits a slower dependence on (\\hslash ω /{k}bT) than that of the normal emission. The observed higher emission intensity and a different T-dependence is attributed to Bloch-mode assisted emission where emitters have been located into a medium having local density of states different than the isotropic case. Furthermore, our finite-difference time-domain (FDTD) simulation shows the presence of localized spots at metal-air boundaries and corners, having intense electric field. The enhanced plasmonic field and local non-equilibrium could induce a strong thermally stimulated emission and may be the cause of our unusual observation.
Spong, Donald A
2016-06-20
AE3D solves for the shear Alfven eigenmodes and eigenfrequencies in a torodal magnetic fusion confinement device. The configuration can be either 2D (e.g. tokamak, reversed field pinch) or 3D (e.g. stellarator, helical reversed field pinch, tokamak with ripple). The equations solved are based on a reduced MHD model and sound wave coupling effects are not currently included.
NASA Astrophysics Data System (ADS)
Liu, Dong; Chen, Chuansong; Man, Baoyuan; Meng, Xue; Sun, Yanna; Li, Feifei
2015-12-01
The femtosecond laser ablated morphology on titanium surface is investigated theoretically and experimentally. A three dimensional two temperature model (3D-TTM) is used to simulate the surface morphology of titanium sample which is irradiated by femtosecond laser pulses. The electron heat capacity and electron-phonon coupling coefficient of titanium (transition metal) are complex temperature dependent, so the two parameters are corrected based on the theory of electron density of states (DOS). The model is solved by the finite difference time domain (FDTD) method. The 3D temperature field near the target surface is achieved. The radius and depth of the ablated crater are obtained based on the temperature field. The evolutions of the crate's radius and depth with laser fluence are discussed and compared with the experimental results. It is found that the back-flow of the molten material and the deposition of the material vapor should be responsible for the little discrepancy between the simulated and experimental results. The present work makes a better understanding of the thermodynamic process of femtosecond laser ablating metal and meanwhile provides an effective method tool to predict the micro manufacturing process on metals with femtosecond laser.
Comparison of a 3-D GPU-Assisted Maxwell Code and Ray Tracing for Reflectometry on ITER
NASA Astrophysics Data System (ADS)
Gady, Sarah; Kubota, Shigeyuki; Johnson, Irena
2015-11-01
Electromagnetic wave propagation and scattering in magnetized plasmas are important diagnostics for high temperature plasmas. 1-D and 2-D full-wave codes are standard tools for measurements of the electron density profile and fluctuations; however, ray tracing results have shown that beam propagation in tokamak plasmas is inherently a 3-D problem. The GPU-Assisted Maxwell Code utilizes the FDTD (Finite-Difference Time-Domain) method for solving the Maxwell equations with the cold plasma approximation in a 3-D geometry. Parallel processing with GPGPU (General-Purpose computing on Graphics Processing Units) is used to accelerate the computation. Previously, we reported on initial comparisons of the code results to 1-D numerical and analytical solutions, where the size of the computational grid was limited by the on-board memory of the GPU. In the current study, this limitation is overcome by using domain decomposition and an additional GPU. As a practical application, this code is used to study the current design of the ITER Low Field Side Reflectometer (LSFR) for the Equatorial Port Plug 11 (EPP11). A detailed examination of Gaussian beam propagation in the ITER edge plasma will be presented, as well as comparisons with ray tracing. This work was made possible by funding from the Department of Energy for the Summer Undergraduate Laboratory Internship (SULI) program. This work is supported by the US DOE Contract No.DE-AC02-09CH11466 and DE-FG02-99-ER54527.
Viscoelastic Finite Difference Modeling Using Graphics Processing Units
NASA Astrophysics Data System (ADS)
Fabien-Ouellet, G.; Gloaguen, E.; Giroux, B.
2014-12-01
Full waveform seismic modeling requires a huge amount of computing power that still challenges today's technology. This limits the applicability of powerful processing approaches in seismic exploration like full-waveform inversion. This paper explores the use of Graphics Processing Units (GPU) to compute a time based finite-difference solution to the viscoelastic wave equation. The aim is to investigate whether the adoption of the GPU technology is susceptible to reduce significantly the computing time of simulations. The code presented herein is based on the freely accessible software of Bohlen (2002) in 2D provided under a General Public License (GNU) licence. This implementation is based on a second order centred differences scheme to approximate time differences and staggered grid schemes with centred difference of order 2, 4, 6, 8, and 12 for spatial derivatives. The code is fully parallel and is written using the Message Passing Interface (MPI), and it thus supports simulations of vast seismic models on a cluster of CPUs. To port the code from Bohlen (2002) on GPUs, the OpenCl framework was chosen for its ability to work on both CPUs and GPUs and its adoption by most of GPU manufacturers. In our implementation, OpenCL works in conjunction with MPI, which allows computations on a cluster of GPU for large-scale model simulations. We tested our code for model sizes between 1002 and 60002 elements. Comparison shows a decrease in computation time of more than two orders of magnitude between the GPU implementation run on a AMD Radeon HD 7950 and the CPU implementation run on a 2.26 GHz Intel Xeon Quad-Core. The speed-up varies depending on the order of the finite difference approximation and generally increases for higher orders. Increasing speed-ups are also obtained for increasing model size, which can be explained by kernel overheads and delays introduced by memory transfers to and from the GPU through the PCI-E bus. Those tests indicate that the GPU memory size
Time domain solutions for a coasting beam with impedance feedback
Blaskiewicz, M.
1993-06-01
Time domain solutions for a coasting beam interacting with a longitudinal or transverse impedance are presented. The treatment is limited to first order perturbation theory, but it includes Landau damping.
Time domain solutions for a coasting beam with impedance feedback
Blaskiewicz, M.
1993-01-01
Time domain solutions for a coasting beam interacting with a longitudinal or transverse impedance are presented. The treatment is limited to first order perturbation theory, but it includes Landau damping.
Study on the After Cavity Interaction in a 140 GHz Gyrotron Using 3D CFDTD PIC Simulations
NASA Astrophysics Data System (ADS)
Lin, M. C.; Illy, S.; Avramidis, K.; Thumm, M.; Jelonnek, J.
2016-10-01
A computational study on after cavity interaction (ACI) in a 140 GHz gryotron for fusion research has been performed using a 3-D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method. The ACI, i.e. beam wave interaction in the non-linear uptaper after the cavity has attracted a lot of attention and been widely investigated in recent years. In a dynamic ACI, a TE mode is excited by the electron beam at the same frequency as in the cavity, and the same mode is also interacting with the spent electron beam at a different frequency in the non-linear uptaper after the cavity while in a static ACI, a mode interacts with the beam both at the cavity and at the uptaper, but at the same frequency. A previous study on the dynamic ACI on a 140 GHz gyrotron has concluded that more advanced numerical simulations such as particle-in-cell (PIC) modeling should be employed to study or confirm the dynamic ACI in addition to using trajectory codes. In this work, we use a 3-D full wave time domain simulation based on the CFDTD PIC method to include the rippled-wall launcher of the quasi-optical output coupler into the simulations which breaks the axial symmetry of the original model employing a symmetric one. A preliminary simulation result has confirmed the dynamic ACI effect in this 140 GHz gyrotron in good agreement with the former study. A realistic launcher will be included in the model for studying the dynamic ACI and compared with the homogenous one.
Time domain referencing in intensity modulation fiber optic sensing systems
NASA Technical Reports Server (NTRS)
Adamovsky, Grigory
1986-01-01
Intensity modulation sensors are classified by the way in which the reference and signal channels are separated: in space, wavelength, or time domains. To implement the time-domain referencing, different types of fiber-optic loops have been used. A pulse of short duration sent into the loop results in a series of pulses of different amplitudes. The information about the measured parameter is retrieved from the relative amplitudes of pulses in the same train.
Time domain referencing in intensity modulation fiber optic sensing systems
NASA Technical Reports Server (NTRS)
Adamovsky, G.
1986-01-01
Intensity modulation sensors are classified depending on the way in which the reference and signal channels are separated: in space, wavelength (frequency), or time domains. To implement the time domain referencing different types of fiber optic (FO) loops have been used. A pulse of short duration sent into the loop results in a series of pulses of different amplitudes. The information about the measured parameter is retrieved from the relative amplitudes of pulses in the same train.
A parallel finite-difference method for computational aerodynamics
NASA Technical Reports Server (NTRS)
Swisshelm, Julie M.
1989-01-01
A finite-difference scheme for solving complex three-dimensional aerodynamic flow on parallel-processing supercomputers is presented. The method consists of a basic flow solver with multigrid convergence acceleration, embedded grid refinements, and a zonal equation scheme. Multitasking and vectorization have been incorporated into the algorithm. Results obtained include multiprocessed flow simulations from the Cray X-MP and Cray-2. Speedups as high as 3.3 for the two-dimensional case and 3.5 for segments of the three-dimensional case have been achieved on the Cray-2. The entire solver attained a factor of 2.7 improvement over its unitasked version on the Cray-2. The performance of the parallel algorithm on each machine is analyzed.
Parallelization of implicit finite difference schemes in computational fluid dynamics
NASA Technical Reports Server (NTRS)
Decker, Naomi H.; Naik, Vijay K.; Nicoules, Michel
1990-01-01
Implicit finite difference schemes are often the preferred numerical schemes in computational fluid dynamics, requiring less stringent stability bounds than the explicit schemes. Each iteration in an implicit scheme involves global data dependencies in the form of second and higher order recurrences. Efficient parallel implementations of such iterative methods are considerably more difficult and non-intuitive. The parallelization of the implicit schemes that are used for solving the Euler and the thin layer Navier-Stokes equations and that require inversions of large linear systems in the form of block tri-diagonal and/or block penta-diagonal matrices is discussed. Three-dimensional cases are emphasized and schemes that minimize the total execution time are presented. Partitioning and scheduling schemes for alleviating the effects of the global data dependencies are described. An analysis of the communication and the computation aspects of these methods is presented. The effect of the boundary conditions on the parallel schemes is also discussed.
Finite difference modeling of Biot's poroelastic equations atseismic frequencies
Masson, Y.J.; Pride, S.R.; Nihei, K.T.
2006-02-24
Across the seismic band of frequencies (loosely defined as<10 kHz), a seismic wave propagating through a porous material willcreate flow in the pore space that is laminar; that is, in thislow-frequency "seismic limit," the development of viscous boundary layersin the pores need not be modeled. An explicit time steppingstaggered-grid finite difference scheme is presented for solving Biot'sequations of poroelasticity in this low-frequency limit. A key part ofthis work is the establishment of rigorous stability conditions. It isdemonstrated that over a wide range of porous material properties typicalof sedimentary rock and despite the presenceof fluid pressure diffusion(Biot slow waves), the usual Courant condition governs the stability asif the problem involved purely elastic waves. The accuracy of the methodis demonstrated by comparing to exact analytical solutions for both fastcompressional waves and slow waves. Additional numerical modelingexamples are also presented.
Accurate finite difference methods for time-harmonic wave propagation
NASA Technical Reports Server (NTRS)
Harari, Isaac; Turkel, Eli
1994-01-01
Finite difference methods for solving problems of time-harmonic acoustics are developed and analyzed. Multidimensional inhomogeneous problems with variable, possibly discontinuous, coefficients are considered, accounting for the effects of employing nonuniform grids. A weighted-average representation is less sensitive to transition in wave resolution (due to variable wave numbers or nonuniform grids) than the standard pointwise representation. Further enhancement in method performance is obtained by basing the stencils on generalizations of Pade approximation, or generalized definitions of the derivative, reducing spurious dispersion, anisotropy and reflection, and by improving the representation of source terms. The resulting schemes have fourth-order accurate local truncation error on uniform grids and third order in the nonuniform case. Guidelines for discretization pertaining to grid orientation and resolution are presented.
Visualization of elastic wavefields computed with a finite difference code
Larsen, S.; Harris, D.
1994-11-15
The authors have developed a finite difference elastic propagation model to simulate seismic wave propagation through geophysically complex regions. To facilitate debugging and to assist seismologists in interpreting the seismograms generated by the code, they have developed an X Windows interface that permits viewing of successive temporal snapshots of the (2D) wavefield as they are calculated. The authors present a brief video displaying the generation of seismic waves by an explosive source on a continent, which propagate to the edge of the continent then convert to two types of acoustic waves. This sample calculation was part of an effort to study the potential of offshore hydroacoustic systems to monitor seismic events occurring onshore.
Stability of finite difference models containing two boundaries or interfaces
NASA Technical Reports Server (NTRS)
Trefethen, L. N.
1984-01-01
The stability of finite difference models of hyperbolic initial boundary value problems is connected with the propagation and reflection of parasitic waves. Wave propagation ideas are applied to models containing two boundaires or interfaces, where repeated reflection of trapped wave packets is a potential new source of instability. Various known instability phenomena are accounted for in a unified way. Results show: (1) dissipativity does not ensure stability when three or more formulas are concatenated at a boundary or internal interface; (2) algebraic GKS instabilities can be converted by a second boundary to exponential instabilities only when an infinite numerical reflection coefficient is present; and (3) GKS-stability and P-stability can be established in certain problems by showing that all numerical reflection coefficients have modulus less than 1.
High order accurate finite difference schemes based on symmetry preservation
NASA Astrophysics Data System (ADS)
Ozbenli, Ersin; Vedula, Prakash
2016-11-01
A new algorithm for development of high order accurate finite difference schemes for numerical solution of partial differential equations using Lie symmetries is presented. Considering applicable symmetry groups (such as those relevant to space/time translations, Galilean transformation, scaling, rotation and projection) of a partial differential equation, invariant numerical schemes are constructed based on the notions of moving frames and modified equations. Several strategies for construction of invariant numerical schemes with a desired order of accuracy are analyzed. Performance of the proposed algorithm is demonstrated using analysis of one-dimensional partial differential equations, such as linear advection diffusion equations inviscid Burgers equation and viscous Burgers equation, as our test cases. Through numerical simulations based on these examples, the expected improvement in accuracy of invariant numerical schemes (up to fourth order) is demonstrated. Advantages due to implementation and enhanced computational efficiency inherent in our proposed algorithm are presented. Extension of the basic framework to multidimensional partial differential equations is also discussed.
Aberration correction for time-domain ultrasound diffraction tomography.
Mast, T Douglas
2002-07-01
Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to "gold standard" ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction.
Contact-free fault location and imaging with on-chip terahertz time-domain reflectometry.
Nagel, Michael; Michalski, Alexander; Kurz, Heinrich
2011-06-20
We demonstrate in a first experimental study the application of novel micro-machined optoelectronic probes for a time-domain reflectometry-based localization of discontinuities and faults in electronic structures at unprecedented resolution and accuracy (± 0.55 µm). Thanks to the THz-range bandwidth of our optoelectronic system--including the active probes used for pulse injection and detection--the spatial resolution and precision of high-end all-electronic detection systems is surpassed by more than one order of magnitude. The new analytic technology holds great promise for rapid and precise fault detection and location in advanced (3D) integrated semiconductor chips and packages.
Azimuthally Anisotropic 3D Velocity Continuation
Burnett, William; Fomel, Sergey
2011-01-01
We extend time-domain velocity continuation to the zero-offset 3D azimuthally anisotropic case. Velocity continuation describes how a seismic image changes given a change in migration velocity. This description turns out to be of a wave propagation process, in which images change along a velocity axis. In the anisotropic case, the velocity model is multiparameter. Therefore, anisotropic image propagation is multidimensional. We use a three-parameter slowness model, which is related to azimuthal variations in velocity, as well as their principal directions. This information is useful for fracture and reservoir characterization from seismic data. We provide synthetic diffraction imaging examples to illustratemore » the concept and potential applications of azimuthal velocity continuation and to analyze the impulse response of the 3D velocity continuation operator.« less
Three-dimensional finite difference viscoelastic wave modelling including surface topography
NASA Astrophysics Data System (ADS)
Hestholm, Stig
1999-12-01
I have undertaken 3-D finite difference (FD) modelling of seismic scattering fromfree-surface topography. Exact free-surface boundary conditions for arbitrary 3-D topographies have been derived for the particle velocities. The boundary conditions are combined with a velocity-stress formulation of the full viscoelastic wave equations. A curved grid represents the physical medium and its upper boundary represents the free-surface topography. The wave equations are numerically discretized by an eighth-order FD method on a staggered grid in space, and a leap-frog technique and the Crank-Nicholson method in time. I simulate scattering from teleseismic P waves by using plane incident wave fronts and real topography from a 60 x 60 km area that includes the NORESS array of seismic receiver stations in southeastern Norway. Synthetic snapshots and seismograms of the wavefield show clear conversion from P to Rg (short-period fundamental-mode Rayleigh) waves in areas of rough topography, which is consistent with numerous observations. By parallelization on fast supercomputers, it is possible to model higher frequencies and/or larger areas than before.
NASA Astrophysics Data System (ADS)
Moore, Gregory F.
2009-05-01
This volume is a brief introduction aimed at those who wish to gain a basic and relatively quick understanding of the interpretation of three-dimensional (3-D) seismic reflection data. The book is well written, clearly illustrated, and easy to follow. Enough elementary mathematics are presented for a basic understanding of seismic methods, but more complex mathematical derivations are avoided. References are listed for readers interested in more advanced explanations. After a brief introduction, the book logically begins with a succinct chapter on modern 3-D seismic data acquisition and processing. Standard 3-D acquisition methods are presented, and an appendix expands on more recent acquisition techniques, such as multiple-azimuth and wide-azimuth acquisition. Although this chapter covers the basics of standard time processing quite well, there is only a single sentence about prestack depth imaging, and anisotropic processing is not mentioned at all, even though both techniques are now becoming standard.
NASA Astrophysics Data System (ADS)
Oldham, Mark
2015-01-01
Radiochromic materials exhibit a colour change when exposed to ionising radiation. Radiochromic film has been used for clinical dosimetry for many years and increasingly so recently, as films of higher sensitivities have become available. The two principle advantages of radiochromic dosimetry include greater tissue equivalence (radiologically) and the lack of requirement for development of the colour change. In a radiochromic material, the colour change arises direct from ionising interactions affecting dye molecules, without requiring any latent chemical, optical or thermal development, with important implications for increased accuracy and convenience. It is only relatively recently however, that 3D radiochromic dosimetry has become possible. In this article we review recent developments and the current state-of-the-art of 3D radiochromic dosimetry, and the potential for a more comprehensive solution for the verification of complex radiation therapy treatments, and 3D dose measurement in general.
Iliesiu, Luca; Kos, Filip; Poland, David; ...
2016-03-17
We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge CT. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-17
We study the conformal bootstrap for a 4-point function of fermions <ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C_{T}. We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N. Finally, we also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
2011-09-01
time to forward model a travel-time data set when a fully 3D raytracing methods is used. An efficient alternative to full 3D raytracing is travel...when a fully 3D raytracing methods is used. An efficient alternative to full 3D raytracing is travel-time linearization, which approximates the...numerical methods are available for raytracing and travel-time calculation in 3D Earth models, such as the finite-difference eikonal method (e.g
NASA Technical Reports Server (NTRS)
Plaut, Jeffrey J.
1993-01-01
Stereographic images of the surface of Venus which enable geologists to reconstruct the details of the planet's evolution are discussed. The 120-meter resolution of these 3D images make it possible to construct digital topographic maps from which precise measurements can be made of the heights, depths, slopes, and volumes of geologic structures.
NASA Astrophysics Data System (ADS)
Carson, Jeffrey J. L.; Roumeliotis, Michael; Chaudhary, Govind; Stodilka, Robert Z.; Anastasio, Mark A.
2010-06-01
Our group has concentrated on development of a 3D photoacoustic imaging system for biomedical imaging research. The technology employs a sparse parallel detection scheme and specialized reconstruction software to obtain 3D optical images using a single laser pulse. With the technology we have been able to capture 3D movies of translating point targets and rotating line targets. The current limitation of our 3D photoacoustic imaging approach is its inability ability to reconstruct complex objects in the field of view. This is primarily due to the relatively small number of projections used to reconstruct objects. However, in many photoacoustic imaging situations, only a few objects may be present in the field of view and these objects may have very high contrast compared to background. That is, the objects have sparse properties. Therefore, our work had two objectives: (i) to utilize mathematical tools to evaluate 3D photoacoustic imaging performance, and (ii) to test image reconstruction algorithms that prefer sparseness in the reconstructed images. Our approach was to utilize singular value decomposition techniques to study the imaging operator of the system and evaluate the complexity of objects that could potentially be reconstructed. We also compared the performance of two image reconstruction algorithms (algebraic reconstruction and l1-norm techniques) at reconstructing objects of increasing sparseness. We observed that for a 15-element detection scheme, the number of measureable singular vectors representative of the imaging operator was consistent with the demonstrated ability to reconstruct point and line targets in the field of view. We also observed that the l1-norm reconstruction technique, which is known to prefer sparseness in reconstructed images, was superior to the algebraic reconstruction technique. Based on these findings, we concluded (i) that singular value decomposition of the imaging operator provides valuable insight into the capabilities of
Cao, Jie; Hao, Qun; Cheng, Yang; Peng, Yuxin; Zhang, Kaiyu; Mu, Jiaxing; Wang, Peng
2016-01-10
A ranging method based on the differential time domain method (DTDM) is proposed in order to improve ranging accuracy and the range of active measurement based on peak discriminator (PD). We develop mathematical models and deduce that zero-crossing sensitivity is an important factor, which affects the ranging error of DTDM. Additionally, zero-crossing sensitivity is determined by delayed time. We carried out relative experiments and obtained the smallest ranging error when delayed time is receiving pulse width. We also compare ranging, three-dimensional (3D) point clouds and depth images based on two methods under same testing conditions. The results show that DTDM is beneficial in improving performance of pulse laser ranging and 3D imaging.
Improved time-space method for 3-D heat transfer problems including global warming
Saitoh, T.S.; Wakashima, Shinichiro
1999-07-01
In this paper, the Time-Space Method (TSM) which has been proposed for solving general heat transfer and fluid flow problems was improved in order to cover global and urban warming. The TSM is effective in almost all-transient heat transfer and fluid flow problems, and has been already applied to the 2-D melting problems (or moving boundary problems). The computer running time will be reduced to only 1/100th--1/1000th of the existing schemes for 2-D and 3-D problems. However, in order to apply to much larger-scale problems, for example, global warming, urban warming and general ocean circulation, the SOR method (or other iterative methods) in four dimensions is somewhat tedious and provokingly slow. Motivated by the above situation, the authors improved the speed of iteration of the previous TSM by introducing the following ideas: (1) Timewise chopping: Time domain is chopped into small peaches to save memory requirement; (2) Adaptive iteration: Converged region is eliminated for further iteration; (3) Internal selective iteration: Equation with slow iteration speed in iterative procedure is selectively iterated to accelerate entire convergence; and (4) False transient integration: False transient term is added to the Poisson-type equation and the relevant solution is regarded as a parabolic equation. By adopting the above improvements, the higher-order finite different schemes and the hybrid mesh, the computer running time for the TSM is reduced to some 1/4600th of the conventional explicit method for a typical 3-D natural convection problem in a closed cavity. The proposed TSM will be more efficacious for large-scale environmental problems, such as global warming, urban warming and general ocean circulation, in which a tremendous computing time would be required.
Elastic finite-difference method for irregular grids
Oprsal, I.; Zahradnik, J.
1999-01-01
Finite-difference (FD) modeling of complicated structures requires simple algorithms. This paper presents a new elastic FD method for spatially irregular grids that is simple and, at the same time, saves considerable memory and computing time. Features like faults, low-velocity layers, cavities, and/or nonplanar surfaces are treated on a fine grid, while the remaining parts of the model are, with equal accuracy, represented on a coarse grid. No interpolation is needed between the fine and coarse parts due to the rectangular grid cells. Relatively abrupt transitions between the small and large grid steps produce no numerical artifacts in the present method. Planar or nonplanar free surfaces, including underground cavities, are treated in a way similar to internal grid points but with consideration of the zero-valued elastic parameters and density outside the free surface (vacuum formalism). A theoretical proof that vacuum formalism fulfills the free-surface conditions is given. Numerical validation is performed through comparison with independent methods, comparing FD with explicitly prescribed boundary conditions and finite elements. Memory and computing time needed in the studied models was only about 10 to 40% of that employing regular square grids of equal accuracy. A practical example of a synthetic seismic section, showing clear signatures of a coal seam and cavity, is presented. The method can be extended to three dimensions.
QED multi-dimensional vacuum polarization finite-difference solver
NASA Astrophysics Data System (ADS)
Carneiro, Pedro; Grismayer, Thomas; Silva, Luís; Fonseca, Ricardo
2015-11-01
The Extreme Light Infrastructure (ELI) is expected to deliver peak intensities of 1023 - 1024 W/cm2 allowing to probe nonlinear Quantum Electrodynamics (QED) phenomena in an unprecedented regime. Within the framework of QED, the second order process of photon-photon scattering leads to a set of extended Maxwell's equations [W. Heisenberg and H. Euler, Z. Physik 98, 714] effectively creating nonlinear polarization and magnetization terms that account for the nonlinear response of the vacuum. To model this in a self-consistent way, we present a multi dimensional generalized Maxwell equation finite difference solver with significantly enhanced dispersive properties, which was implemented in the OSIRIS particle-in-cell code [R.A. Fonseca et al. LNCS 2331, pp. 342-351, 2002]. We present a detailed numerical analysis of this electromagnetic solver. As an illustration of the properties of the solver, we explore several examples in extreme conditions. We confirm the theoretical prediction of vacuum birefringence of a pulse propagating in the presence of an intense static background field [arXiv:1301.4918 [quant-ph
The geometry of finite difference discretizations of semilinear elliptic operators
NASA Astrophysics Data System (ADS)
Teles, Eduardo; Tomei, Carlos
2012-04-01
Discretizations by finite differences of some semilinear elliptic equations lead to maps F(u) = Au - f(u), u \\in {{R}}^n , given by nonlinear convex diagonal perturbations of symmetric matrices A. For natural nonlinearity classes, we consider the equation F(u) = y - tp, where t is a large positive number and p is a vector with negative coordinates. As the range of the derivative f'i of the coordinates of f encloses more eigenvalues of A, the number of solutions increases geometrically, eventually reaching 2n. This phenomenon, somewhat in contrast with behaviour associated with the Lazer-McKenna conjecture, has a very simple geometric explanation: a perturbation of a multiple fold gives rise to a function which sends connected components of its critical set to hypersurfaces with large rotation numbers with respect to vectors with very negative coordinates. Strictly speaking, the results have nothing to do with elliptic equations: they are properties of the interaction of a (self-adjoint) linear map with increasingly stronger nonlinear convex diagonal interactions.
A hybrid finite-difference and analytic element groundwater model.
Haitjema, H M; Feinstein, D T; Hunt, R J; Gusyev, M A
2010-01-01
Regional finite-difference models tend to have large cell sizes, often on the order of 1-2 km on a side. Although the regional flow patterns in deeper formations may be adequately represented by such a model, the intricate surface water and groundwater interactions in the shallower layers are not. Several stream reaches and nearby wells may occur in a single cell, precluding any meaningful modeling of the surface water and groundwater interactions between the individual features. We propose to replace the upper MODFLOW layer or layers, in which the surface water and groundwater interactions occur, by an analytic element model (GFLOW) that does not employ a model grid; instead, it represents wells and surface waters directly by the use of point-sinks and line-sinks. For many practical cases it suffices to provide GFLOW with the vertical leakage rates calculated in the original coarse MODFLOW model in order to obtain a good representation of surface water and groundwater interactions. However, when the combined transmissivities in the deeper (MODFLOW) layers dominate, the accuracy of the GFLOW solution diminishes. For those cases, an iterative coupling procedure, whereby the leakages between the GFLOW and MODFLOW model are updated, appreciably improves the overall solution, albeit at considerable computational cost. The coupled GFLOW-MODFLOW model is applicable to relatively large areas, in many cases to the entire model domain, thus forming an attractive alternative to local grid refinement or inset models.
Assessment of Linear Finite-Difference Poisson-Boltzmann Solvers
Wang, Jun; Luo, Ray
2009-01-01
CPU time and memory usage are two vital issues that any numerical solvers for the Poisson-Boltzmann equation have to face in biomolecular applications. In this study we systematically analyzed the CPU time and memory usage of five commonly used finite-difference solvers with a large and diversified set of biomolecular structures. Our comparative analysis shows that modified incomplete Cholesky conjugate gradient and geometric multigrid are the most efficient in the diversified test set. For the two efficient solvers, our test shows that their CPU times increase approximately linearly with the numbers of grids. Their CPU times also increase almost linearly with the negative logarithm of the convergence criterion at very similar rate. Our comparison further shows that geometric multigrid performs better in the large set of tested biomolecules. However, modified incomplete Cholesky conjugate gradient is superior to geometric multigrid in molecular dynamics simulations of tested molecules. We also investigated other significant components in numerical solutions of the Poisson-Boltzmann equation. It turns out that the time-limiting step is the free boundary condition setup for the linear systems for the selected proteins if the electrostatic focusing is not used. Thus, development of future numerical solvers for the Poisson-Boltzmann equation should balance all aspects of the numerical procedures in realistic biomolecular applications. PMID:20063271
A finite difference model for free surface gravity drainage
Couri, F.R.; Ramey, H.J. Jr.
1993-09-01
The unconfined gravity flow of liquid with a free surface into a well is a classical well test problem which has not been well understood by either hydrologists or petroleum engineers. Paradigms have led many authors to treat an incompressible flow as compressible flow to justify the delayed yield behavior of a time-drawdown test. A finite-difference model has been developed to simulate the free surface gravity flow of an unconfined single phase, infinitely large reservoir into a well. The model was verified with experimental results in sandbox models in the literature and with classical methods applied to observation wells in the Groundwater literature. The simulator response was also compared with analytical Theis (1935) and Ramey et al. (1989) approaches for wellbore pressure at late producing times. The seepage face in the sandface and the delayed yield behavior were reproduced by the model considering a small liquid compressibility and incompressible porous medium. The potential buildup (recovery) simulated by the model evidenced a different- phenomenon from the drawdown, contrary to statements found in the Groundwater literature. Graphs of buildup potential vs time, buildup seepage face length vs time, and free surface head and sand bottom head radial profiles evidenced that the liquid refills the desaturating cone as a flat moving surface. The late time pseudo radial behavior was only approached after exaggerated long times.
Time-Domain Filtering for Spatial Large-Eddy Simulation
NASA Technical Reports Server (NTRS)
Pruett, C. David
1997-01-01
An approach to large-eddy simulation (LES) is developed whose subgrid-scale model incorporates filtering in the time domain, in contrast to conventional approaches, which exploit spatial filtering. The method is demonstrated in the simulation of a heated, compressible, axisymmetric jet, and results are compared with those obtained from fully resolved direct numerical simulation. The present approach was, in fact, motivated by the jet-flow problem and the desire to manipulate the flow by localized (point) sources for the purposes of noise suppression. Time-domain filtering appears to be more consistent with the modeling of point sources; moreover, time-domain filtering may resolve some fundamental inconsistencies associated with conventional space-filtered LES approaches.
Time domain averaging based on fractional delay filter
NASA Astrophysics Data System (ADS)
Wu, Wentao; Lin, Jing; Han, Shaobo; Ding, Xianghui
2009-07-01
For rotary machinery, periodic components in signals are always extracted to investigate the condition of each rotating part. Time domain averaging technique is a traditional method used to extract those periodic components. Originally, a phase reference signal is required to ensure all the averaged segments are with the same initial phase. In some cases, however, there is no phase reference; we have to establish some efficient algorithms to synchronize the segments before averaging. There are some algorithms available explaining how to perform time domain averaging without using phase reference signal. However, those algorithms cannot eliminate the phase error completely. Under this background, a new time domain averaging algorithm that has no phase error theoretically is proposed. The performance is improved by incorporating the fractional delay filter. The efficiency of the proposed algorithm is validated by some simulations.
Wind-instrument reflection function measurements in the time domain.
Keefe, D H
1996-04-01
Theoretical and computational analyses of wind-instrument sound production in the time domain have emerged as useful tools for understanding musical instrument acoustics, yet there exist few experimental measurements of the air-column response directly in the time domain. A new experimental, time-domain technique is proposed to measure the reflection function response of woodwind and brass-instrument air columns. This response is defined at the location of sound regeneration in the mouthpiece or double reed. A probe assembly comprised of an acoustic source and microphone is inserted directly into the air column entryway using a foam plug to ensure a leak-free fit. An initial calibration phase involves measurements on a single cylindrical tube of known dimensions. Measurements are presented on an alto saxophone and euphonium. The technique has promise for testing any musical instrument air columns using a single probe assembly and foam plugs over a range of diameters typical of air-column entryways.
On-Time 3D Time-Domain EMI and Tensor Magnetic Gradiometry for UXO Detection and Discrimination
2008-06-04
Acquisition System DFC Denver Federal Center DoD Department of Defense DOE Department of Energy EMI Electromagnetic Induction HFS High-Frequency...I I YPG BTG2 -ALL TEM ZZM 9/26/06 ~_iiii: ....U ... _SGS_ l~ t : .§._E -=RDP Processed Data 05/23/06 Ei -~ MINC gridded at 0.2 meter o = original...about T = 53635.5 sec. The cart oscillated on its balloon tires with a frequency of about 2.9 Hz, causing the Head 1 X-component to register
New frontiers in time-domain diffuse optics, a review
NASA Astrophysics Data System (ADS)
Pifferi, Antonio; Contini, Davide; Mora, Alberto Dalla; Farina, Andrea; Spinelli, Lorenzo; Torricelli, Alessandro
2016-09-01
The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity.
Time-Domain Impedance Boundary Conditions for Computational Aeroacoustics
NASA Technical Reports Server (NTRS)
Tam, Christopher K. W.; Auriault, Laurent
1996-01-01
It is an accepted practice in aeroacoustics to characterize the properties of an acoustically treated surface by a quantity known as impedance. Impedance is a complex quantity. As such, it is designed primarily for frequency-domain analysis. Time-domain boundary conditions that are the equivalent of the frequency-domain impedance boundary condition are proposed. Both single frequency and model broadband time-domain impedance boundary conditions are provided. It is shown that the proposed boundary conditions, together with the linearized Euler equations, form well-posed initial boundary value problems. Unlike ill-posed problems, they are free from spurious instabilities that would render time-marching computational solutions impossible.
Time domain finite element analysis of multimode microwave applicators
Dibben, D.C.; Metaxas, R.
1996-05-01
Analysis of multimode applicators in the frequency domain via the finite element technique produces a set of very ill-conditioned equations. This paper outlines a time domain finite element method (TDFE) for analyzing three dimensional microwave applicators where this ill-conditioning is avoided. Edge elements are used in order to handle sharp metal edges and to avoid spurious solutions. Analysis in the time domain allows field distributions at a range of different frequencies to be obtained with a single calculation. Lumping is investigated as a means of reducing the time taken for the calculation. The reflection coefficient is also obtained.
Discretizing delta functions via finite differences and gradient normalization
NASA Astrophysics Data System (ADS)
Towers, John D.
2009-06-01
In [J.D. Towers, Two methods for discretizing a delta function supported on a level set, J. Comput. Phys. 220 (2007) 915-931] the author presented two closely related finite difference methods (referred to here as FDM1 and FDM2) for discretizing a delta function supported on a manifold of codimension one defined by the zero level set of a smooth mapping u :Rn ↦ R . These methods were shown to be consistent (meaning that they converge to the true solution as the mesh size h → 0) in the codimension one setting. In this paper, we concentrate on n ⩽ 3 , but generalize our methods to codimensions other than one - now the level set function is generally a vector valued mapping u → :Rn ↦Rm, 1 ⩽ m ⩽ n ⩽ 3 . Seemingly reasonable algorithms based on simple products of approximate delta functions are not generally consistent when applied to these problems. Motivated by this, we instead use the wedge product formalism to generalize our FDM algorithms, and this approach results in accurate, often consistent approximations. With the goal of ensuring consistency in general, we propose a new gradient normalization process that is applied before our FDM algorithms. These combined algorithms seem to be consistent in all reasonable situations, with numerical experiments indicating O (h2) convergence for our new gradient-normalized FDM2 algorithm. In the full codimension setting (m = n) , our gradient normalization processing also improves accuracy when using more standard approximate delta functions. This combination also yields approximations that appear to be consistent.
NASA Astrophysics Data System (ADS)
Sparrow, Victor Ward
1990-01-01
This study has concerned the propagation of finite amplitude, i.e. weakly non-linear, acoustical blast waves from explosions over hard and porous media models of outdoor ground surfaces. The nonlinear acoustic propagation effects require a numerical solution in the time domain. To model a porous ground surface, which in the frequency domain exhibits a finite impedance, the linear phenomenological porous model of Morse and Ingard was used. The phenomenological equations are solved in the time domain for coupling with the time domain propagation solution in the air. The numerical solution is found through the method of finite differences. The second-order in time and fourth -order in space MacCormack method was used in the air, and the second-order in time and space MacCormack method was used in the porous medium modeling the ground. Two kinds of numerical absorbing boundary conditions were developed for the air propagation equations to truncate the physical domain for solution on a computer. Radiation conditions first were used on those sides of the domain where there were outgoing waves. Characteristic boundary conditions secondly are employed near the acoustic source. The numerical model agreed well with the Pestorius algorithm for the propagation of electric spark pulses in the free field, and with a result of Pfriem for normal plane reflection off a hard surface. In addition, curves of pressure amplification versus incident angle for waves obliquely incident on the hard and porous surfaces were produced which are similar to those in the literature. The model predicted that near grazing finite amplitude acoustic blast waves decay with distance over hard surfaces as r to the power -1.2. This result is consistent with the work of Reed. For propagation over the porous ground surface, the model predicted that this surface decreased the decay rate with distance for the larger blasts compared to the rate expected in the linear acoustics limit.
Time domain measurement of frequency stability: A tutorial introduction
NASA Technical Reports Server (NTRS)
Vanier, J.; Tetu, M.
1978-01-01
The theoretical basis behind the definition of frequency stability in the time domain is outlined. Various types of variances were examined. Their differences and interrelation are pointed out. Systems that are generally used in the measurement of these variances are described.
Frequency calibration of terahertz time-domain spectrometers
Naftaly, M.; Dudley, R. A.; Bernard, F.; Thomson, C.; Tian, Z.; Fletcher, J. R.
2009-07-15
We present three techniques of calibrating frequency and spectral profile measurements of terahertz time-domain spectrometers. The first utilizes the etalon effect generated by multiple reflections in thin nonabsorbing samples. The second employs a CO gas cell to provide multiple narrow absorption lines at known frequencies. The third aims to use a grating monochromator to produce an independently measured comparable spectrum.
Application of Time Domain Reflectometers to Urban Settings
Time domain reflectometers (TDRs) are in-situ monitoring probes that produce a temperature-compensated signal proportional to soil moisture content of the surrounding material when calibrated to a particular media. Typically used in agricultural settings, TDRs may also be applied...
Advanced propeller noise prediction in the time domain
NASA Technical Reports Server (NTRS)
Farassat, F.; Dunn, M. H.; Spence, P. L.
1992-01-01
The time domain code ASSPIN gives acousticians a powerful technique of advanced propeller noise prediction. Except for nonlinear effects, the code uses exact solutions of the Ffowcs Williams-Hawkings equation with exact blade geometry and kinematics. By including nonaxial inflow, periodic loading noise, and adaptive time steps to accelerate computer execution, the development of this code becomes complete.
Data Management, Infrastructure and Archiving for Time-Domain Astronomy
NASA Astrophysics Data System (ADS)
Schade, David
2012-04-01
The workshop on Data Management issues for Time-Domain Astronomy was conceived as a forward-looking discussion of the primary issues that need to be addressed for science in the time domain. The very broad diversity of the science areas presented in the main Symposium made it clear that most of the general issues for astronomy data management-for example, large data volumes, the need for timely processing and network performance-would be pertinent in the time domain. In addition, there might be other tight time constraints on data processing when the output was required to trigger rapid follow-up observations, while science based on very long time-baselines might require careful consideration of long-term data preservation and availability issues. But broadly speaking, data management challenges in the time domain are not at variance to any significant degree with those for astronomy or data-intensive research in general. The workshop framed and debated a number of questions: What is the biggest challenge faced by future projects? How do grid and cloud computing figure in data management plans? Is the Virtual Observatory important to future projects? How are the issues of data life cycle being addressed?
Application of Time Domain Reflectometers in Urban Settings
Time domain reflectometers (TDRs) are sensors that measure the volumetric water content of soils and porous media. The sensors consist of stainless steel rods connected to a circuit board in an epoxy housing. An electromagnetic pulse is propagated along the rods. The time, or per...
The coating curing properties study using terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
Ren, Jiaojiao; Zhao, Duo; Li, Lijuan
2015-10-01
Coating curing curve is one of the most important methods to reflect the coating curing properties. It is of great significance for the coating curing properties. In this paper, by using the reflective Terahertz (THz) time-domain spectroscope technique, the curing properties of coating with different thicknesses are studied. Three different parameters used for studying the properties of coating curing curve are proposed in this paper. They are respectively the differential time of flight, power spectrum and amplitude for reflective THz time-domain waveform. In this paper, two kinds of coating (with different thicknesses) curing properties curves are established and the relative errors from three parameter analysis methods are compared respectively. This study shows that the study on coating curing properties curves by using the power spectrum of reflective THz time-domain waveform is superior to the amplitude parameter method. But for the thick coating, the differential time of flight for the reflective THz time-domain waveform can also better reflect the coating curing properties.
Directly coupled vs conventional time domain reflectometry in soils
Technology Transfer Automated Retrieval System (TEKTRAN)
Time domain reflectometry (TDR), a technique for estimation of soil water, measures the travel time of an electromagnetic pulse on electrodes embedded in the soil, but has limited application in commercial agriculture due to costs, labor, and sensing depth. Conventional TDR systems have employed ana...
Application of Time Domain Reflectometers in Urban Settings
This is a poster for the Million Trees NYC research symposium in New York City, NY, March 5-6, 2010. The poster gives a summary of how time domain reflectometers can be installed in urban fill soil, engineered bioretention media, and recycled concrete aggregate to document the ...
Wakefield Computations for the CLIC PETS using the Parallel Finite Element Time-Domain Code T3P
Candel, A; Kabel, A.; Lee, L.; Li, Z.; Ng, C.; Schussman, G.; Ko, K.; Syratchev, I.; /CERN
2009-06-19
In recent years, SLAC's Advanced Computations Department (ACD) has developed the high-performance parallel 3D electromagnetic time-domain code, T3P, for simulations of wakefields and transients in complex accelerator structures. T3P is based on advanced higher-order Finite Element methods on unstructured grids with quadratic surface approximation. Optimized for large-scale parallel processing on leadership supercomputing facilities, T3P allows simulations of realistic 3D structures with unprecedented accuracy, aiding the design of the next generation of accelerator facilities. Applications to the Compact Linear Collider (CLIC) Power Extraction and Transfer Structure (PETS) are presented.
Time-Domain Simulation of Three Dimensional Quantum Wires
Mossman, Sean; Kuzyk, Mark G.
2016-01-01
A method is presented to calculate the eigenenergies and eigenfunctions of quantum wires. This is a true three-dimensional method based on a direct implementation of the time-dependent Schrödinger equation. It makes no approximations to the Schrödinger equation other than the finite-difference approximation of the space and time derivatives. The accuracy of our method is tested by comparing it to analytical results in a cylindrical wire. PMID:27124603
NASA Technical Reports Server (NTRS)
1997-01-01
The two hills in the distance, approximately one to two kilometers away, have been dubbed the 'Twin Peaks' and are of great interest to Pathfinder scientists as objects of future study. 3D glasses are necessary to identify surface detail. The white areas on the left hill, called the 'Ski Run' by scientists, may have been formed by hydrologic processes.
The IMP is a stereo imaging system with color capability provided by 24 selectable filters -- twelve filters per 'eye.
Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right
NASA Astrophysics Data System (ADS)
Fung, Y. C.
1995-05-01
This conference on physiology and function covers a wide range of subjects, including the vasculature and blood flow, the flow of gas, water, and blood in the lung, the neurological structure and function, the modeling, and the motion and mechanics of organs. Many technologies are discussed. I believe that the list would include a robotic photographer, to hold the optical equipment in a precisely controlled way to obtain the images for the user. Why are 3D images needed? They are to achieve certain objectives through measurements of some objects. For example, in order to improve performance in sports or beauty of a person, we measure the form, dimensions, appearance, and movements.
NASA Technical Reports Server (NTRS)
1992-01-01
Ames Research Center research into virtual reality led to the development of the Convolvotron, a high speed digital audio processing system that delivers three-dimensional sound over headphones. It consists of a two-card set designed for use with a personal computer. The Convolvotron's primary application is presentation of 3D audio signals over headphones. Four independent sound sources are filtered with large time-varying filters that compensate for motion. The perceived location of the sound remains constant. Possible applications are in air traffic control towers or airplane cockpits, hearing and perception research and virtual reality development.
Cevidanes, Lucia; Tucker, Scott; Styner, Martin; Kim, Hyungmin; Chapuis, Jonas; Reyes, Mauricio; Proffit, William; Turvey, Timothy; Jaskolka, Michael
2009-01-01
This paper discusses the development of methods for computer-aided jaw surgery. Computer-aided jaw surgery allows us to incorporate the high level of precision necessary for transferring virtual plans into the operating room. We also present a complete computer-aided surgery (CAS) system developed in close collaboration with surgeons. Surgery planning and simulation include construction of 3D surface models from Cone-beam CT (CBCT), dynamic cephalometry, semi-automatic mirroring, interactive cutting of bone and bony segment repositioning. A virtual setup can be used to manufacture positioning splints for intra-operative guidance. The system provides further intra-operative assistance with the help of a computer display showing jaw positions and 3D positioning guides updated in real-time during the surgical procedure. The CAS system aids in dealing with complex cases with benefits for the patient, with surgical practice, and for orthodontic finishing. Advanced software tools for diagnosis and treatment planning allow preparation of detailed operative plans, osteotomy repositioning, bone reconstructions, surgical resident training and assessing the difficulties of the surgical procedures prior to the surgery. CAS has the potential to make the elaboration of the surgical plan a more flexible process, increase the level of detail and accuracy of the plan, yield higher operative precision and control, and enhance documentation of cases. Supported by NIDCR DE017727, and DE018962 PMID:20816308
NASA Technical Reports Server (NTRS)
1997-01-01
An area of rocky terrain near the landing site of the Sagan Memorial Station can be seen in this image, taken in stereo by the Imager for Mars Pathfinder (IMP) on Sol 3. 3D glasses are necessary to identify surface detail. This image is part of a 3D 'monster' panorama of the area surrounding the landing site.
Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.
Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right
NASA Astrophysics Data System (ADS)
Choi, S. J.; Kim, J.; Shin, S.
2014-12-01
In this presentation, a new non-hydrostatic (NH) dynamical core using the spectral element method (SEM) in the horizontal discretization and the finite difference method (FDM) in the vertical discretization will be presented. By using horizontal SEM, which decomposes the physical domain into smaller pieces with a small communication stencil, we can achieve a high level of scalability. Also by using vertical FDM, we provide an easy way for coupling the dynamics and existing physics packages. The Euler equations used here are in a flux form based on the hybrid sigma hydrostatic pressure vertical coordinate, which are similar to those used in the Weather Research and Forecasting (WRF) model. Within these Euler equations, we use a time-split third-order Runge-Kutta (RK3) for the time discretization. In order to establish robustness, firstly the NH dynamical core is verified in a simplified two dimensional (2D) slice framework by conducting widely used standard benchmark tests, and then we verify the global three dimensional (3D) dynamical core on the cubed-sphere grid with several test cases introduced by Dynamical Core Model Intercomparison Project (DCMIP).
Finite-difference modeling of SH-wave conversions in shallow shear-wave refraction surveying
NASA Astrophysics Data System (ADS)
Mi, Binbin; Xia, Jianghai; Xu, Yixian
2015-08-01
The shallow shear-wave refraction method works successfully in an area with a series of horizontal layers. Complex near-surface geology, however, may not fit into the assumption of a series of horizontal layers. It is theoretically inevitable that a plane SH-wave undergoes wave-type conversions along an interface in an area of non-horizontal layers. One real example has shown that the shallow SH-wave refraction method provides velocities of a converted wave rather than SH-wave. Moreover, it is impossible to identify the converted wave by refraction data itself. In this paper, we implement numerical simulation for conversion of SH- to P-wave in 3D heterogeneous medium with the finite-difference method. An SH-wave source excitation method that we give in the numerical simulation is testified, which can only generate SH-wave without P-wave. The numerical modeling results demonstrate that the conversion of the SH-wave to other wave-types will occur in an area of non-horizontal layers. All the converted P-wave arrivals are shown reversed polarity like S-wave arrivals in the modeling of reverse of the source and we have clarified the peculiar properties of converted P-waves from the S-wave. Our numerical simulation results confirm that velocities calculated from an SH-wave refraction survey are velocities of converted waves. Therefore, special attention should be paid to this pitfall in the real world.
Caspi, S.; Helm, M.; Laslett, L.J.
1991-03-30
We have developed an harmonic representation for the three dimensional field components within the windings of accelerator magnets. The form by which the field is presented is suitable for interfacing with other codes that make use of the 3D field components (particle tracking and stability). The field components can be calculated with high precision and reduced cup time at any location (r,{theta},z) inside the magnet bore. The same conductor geometry which is used to simulate line currents is also used in CAD with modifications more readily available. It is our hope that the format used here for magnetic fields can be used not only as a means of delivering fields but also as a way by which beam dynamics can suggest correction to the conductor geometry. 5 refs., 70 figs.
Rodgers, Arthur J.; Dreger, Douglas S.; Pitarka, Arben
2015-06-15
We performed three-dimensional (3D) anelastic ground motion simulations of the South Napa earthquake to investigate the performance of different finite rupture models and the effects of 3D structure on the observed wavefield. We considered rupture models reported by Dreger et al. (2015), Ji et al., (2015), Wei et al. (2015) and Melgar et al. (2015). We used the SW4 anelastic finite difference code developed at Lawrence Livermore National Laboratory (Petersson and Sjogreen, 2013) and distributed by the Computational Infrastructure for Geodynamics. This code can compute the seismic response for fully 3D sub-surface models, including surface topography and linear anelasticity. We use the 3D geologic/seismic model of the San Francisco Bay Area developed by the United States Geological Survey (Aagaard et al., 2008, 2010). Evaluation of earlier versions of this model indicated that the structure can reproduce main features of observed waveforms from moderate earthquakes (Rodgers et al., 2008; Kim et al., 2010). Simulations were performed for a domain covering local distances (< 25 km) and resolution providing simulated ground motions valid to 1 Hz.
A first-order time-domain Green's function approach to supersonic unsteady flow
NASA Technical Reports Server (NTRS)
Freedman, M. I.; Tseng, K.
1985-01-01
A time-domain Green's Function Method for unsteady supersonic potential flow around complex aircraft configurations is presented. The focus is on the supersonic range wherein the linear potential flow assumption is valid. The Green's function method is employed in order to convert the potential-flow differential equation into an integral one. This integral equation is then discretized, in space through standard finite-element technique, and in time through finite-difference, to yield a linear algebraic system of equations relating the unknown potential to its prescribed co-normalwash (boundary condition) on the surface of the aircraft. The arbitrary complex aircraft configuration is discretized into hyperboloidal (twisted quadrilateral) panels. The potential and co-normalwash are assumed to vary linearly within each panel. Consistent with the spatial linear (first-order) finite-element approximations, the potential and co-normalwash are assumed to vary linearly in time. The long range goal of our research is to develop a comprehensive theory for unsteady supersonic potential aerodynamics which is capable of yielding accurate results even in the low supersonic (i.e., high transonic) range.
Broadband Trailing Edge Noise Predictions in the Time Domain. Revised
NASA Technical Reports Server (NTRS)
Casper, Jay; Farassat, Fereidoun
2003-01-01
A recently developed analytic result in acoustics, "Formulation 1B," is used to compute broadband trailing edge noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Willliams-Hawkings equation with the loading source term, and has been shown in previous research to provide time domain predictions of broadband noise that are in excellent agreement with experimental results. Furthermore, this formulation lends itself readily to rotating reference frames and statistical analysis of broadband trailing edge noise. Formulation 1B is used to calculate the far field noise radiated from the trailing edge of a NACA 0012 airfoil in low Mach number flows, by using both analytical and experimental data on the airfoil surface. The acoustic predictions are compared with analytical results and experimental measurements that are available in the literature. Good agreement between predictions and measurements is obtained.
Time Domain Partitioning of Electricity Production Cost Simulations
Barrows, C.; Hummon, M.; Jones, W.; Hale, E.
2014-01-01
Production cost models are often used for planning by simulating power system operations over long time horizons. The simulation of a day-ahead energy market can take several weeks to compute. Tractability improvements are often made through model simplifications, such as: reductions in transmission modeling detail, relaxation of commitment variable integrality, reductions in cost modeling detail, etc. One common simplification is to partition the simulation horizon so that weekly or monthly horizons can be simulated in parallel. However, horizon partitions are often executed with overlap periods of arbitrary and sometimes zero length. We calculate the time domain persistence of historical unit commitment decisions to inform time domain partitioning of production cost models. The results are implemented using PLEXOS production cost modeling software in an HPC environment to improve the computation time of simulations while maintaining solution integrity.
Technical and Observational Challenges for Future Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Bloom, Joshua S.
2012-04-01
By the end of the last decade, robotic telescopes were established as effective alternatives to the traditional role of astronomer in planning, conducting and reducing time-domain observations. By the end of this decade, machines will play a much more central role in the discovery and classification of time-domain events observed by such robots. While this abstraction of humans away from the real-time loop (and the nightly slog of the nominal scientific process) is inevitable, just how we will get there as a community is uncertain. I discuss the importance of machine learning in astronomy today, and project where we might consider heading in the future. I will also touch on the role of people and organisations in shaping and maximising the scientific returns of the coming data deluge.
Time domain responses of a prestressed beam and prestress identification
NASA Astrophysics Data System (ADS)
Law, S. S.; Lu, Z. R.
2005-12-01
The time-domain response of a prestressed Euler-Bernoulli beam under external excitation is studied based on modal superposition. The prestress force is then identified in the time domain by a system identification approach and Tikhonov regularization technique is used to provide bounds to the ill-conditioned results in the identified problem. Both measured displacements and strains are used. The noise effect is improved using the orthogonal polynomial function, and cases with either sinusoidal or impulsive excitations are illustrated to give very good results from the lower three measured modes and data obtained from three measurement points. Work in this paper demonstrates the feasibility of indirectly identifying the prestress force in a beam.
Raman-assisted vector Brillouin optical time domain analysis
NASA Astrophysics Data System (ADS)
Angulo-Vinuesa, X.; Bacquet, D.; Martin-Lopez, S.; Corredera, P.; Szriftgiser, P.; Gonzalez-Herraez, M.
2013-05-01
Raman-assistance (RA) has become a promising technique to enhance the sensing range of standard Brillouin Optical Time Domain Analysis (BOTDA) fiber sensors due to its ability to amplify in a distributed way all the interacting signals within the fiber. Unfortunately, Raman amplification introduces a great amount of Relative Intensity Noise (RIN) to the detected low-frequency probe wave. This RIN transfer problem has been widely identified as a major limitation in RABOTDA. In Vector Brillouin Optical Time Domain Analysis (VBOTDA) the detected signal is transferred to a highfrequency carrier where the Raman RIN transfer turns out to be much less harmful. In this work we demonstrate, for the first time to our knowledge, Raman-assistance in a VBOTDA. Our results show significant reduction of the RIN transfer effect in RA-VBOTDA compared to standard RA-BOTDA, making this type of scheme particularly interesting for long range distributed sensing.
THz time-domain spectroscopy imaging for mail inspection
NASA Astrophysics Data System (ADS)
Zhang, Liquan; Wang, Zhongdong; Ma, Yanmei; Hao, Erjuan
2011-08-01
Acquiring messages from the mail but not destroying the envelope is a big challenge in the war of intelligence. If one can read the message of the mail when the envelope is closed, he will benefit from the message asymmetry and be on a good wicket in the competition. In this paper, we presented a transmitted imaging system using THz time-domain spectroscopy technology. We applied the system to image the mail inside an envelope by step-scanning imaging technology. The experimental results show that the THz spectroscopy can image the mail in an envelope. The words in the paper can be identified easily from the background. We also present the THz image of a metal blade in the envelope, in which we can see the metal blade clearly. The results show that it is feasible of THz Time-Domain Spectroscopy Imaging for mail inspection applications.
Coupling Between Microstrip Lines Embedded in Polyimide Layers for 3D-MMICs on Si
NASA Technical Reports Server (NTRS)
Ponchak, George E.; Tentzeris, Emmanouil M.; Papapolymerou, John
2001-01-01
Three-dimensional circuits built upon multiple layers of polyimide are required for constructing Si/SiGe monolithic microwave/millimeter-wave integrated circuits on CMOS (low resistivity) Si wafers. However, the closely spaced transmission lines are susceptible to high levels of coupling, which degrades circuit performance. In this paper, Finite Difference Time Domain (FDTD) analysis and measured characteristics of novel shielding structures that significantly reduce coupling between embedded microstrip lines are presented.
Parallel computation of the SAR distribution in a 3D human head model
NASA Astrophysics Data System (ADS)
Walendziuk, Wojciech
2008-01-01
This work presents a way of parallel computation of the Specific Absorption Rate distribution. The parallel program used in the computation was based on the FDTD (Finite-Difference Time-Domain) method [1,2,3]. In order to establish communication among the computational nodes, the MPI (Message Passing Interface) standard was used [4,5,6]. The presented example of a human head numerical model was built with the use of MRI (Magnetic Resonance Image) pictures.
NASA Astrophysics Data System (ADS)
Marquet, F.; Pernot, M.; Aubry, J.-F.; Montaldo, G.; Marsac, L.; Tanter, M.; Fink, M.
2009-05-01
A non-invasive protocol for transcranial brain tissue ablation with ultrasound is studied and validated in vitro. The skull induces strong aberrations both in phase and in amplitude, resulting in a severe degradation of the beam shape. Adaptive corrections of the distortions induced by the skull bone are performed using a previous 3D computational tomography scan acquisition (CT) of the skull bone structure. These CT scan data are used as entry parameters in a FDTD (finite differences time domain) simulation of the full wave propagation equation. A numerical computation is used to deduce the impulse response relating the targeted location and the ultrasound therapeutic array, thus providing a virtual time-reversal mirror. This impulse response is then time-reversed and transmitted experimentally by a therapeutic array positioned exactly in the same referential frame as the one used during CT scan acquisitions. In vitro experiments are conducted on monkey and human skull specimens using an array of 300 transmit elements working at a central frequency of 1 MHz. These experiments show a precise refocusing of the ultrasonic beam at the targeted location with a positioning error lower than 0.7 mm. The complete validation of this transcranial adaptive focusing procedure paves the way to in vivo animal and human transcranial HIFU investigations.
Time domains of the hypoxic ventilatory response in ectothermic vertebrates.
Porteus, Cosima; Hedrick, Michael S; Hicks, James W; Wang, Tobias; Milsom, William K
2011-04-01
Over a decade has passed since Powell et al. (Respir Physiol 112:123-134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123-134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O(2) supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more 'holistic' fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind.
Historical Time-Domain: Data Archives, Processing, and Distribution
NASA Astrophysics Data System (ADS)
Grindlay, Jonathan E.; Griffin, R. Elizabeth
2012-04-01
The workshop on Historical Time-Domain Astronomy (TDA) was attended by a near-capacity gathering of ~30 people. From information provided in turn by those present, an up-to-date overview was created of available plate archives, progress in their digitization, the extent of actual processing of those data, and plans for data distribution. Several recommendations were made for prioritising the processing and distribution of historical TDA data.
Analysis of time-domain scattering by periodic structures
NASA Astrophysics Data System (ADS)
Gao, Yixian; Li, Peijun
2016-11-01
This paper is devoted to the mathematical analysis of a time-domain electromagnetic scattering by periodic structures which are known as diffraction gratings. The scattering problem is reduced equivalently into an initial-boundary value problem in a bounded domain by using an exact transparent boundary condition. The well-posedness and stability of the solution are established for the reduced problem. Moreover, a priori energy estimates are obtained with minimum regularity requirement for the data and explicit dependence on the time.
Characteristic Based Methods for the Time-Domain Maxwell Equations
1993-08-09
2-D results on Cartesian frame demonstrated a potential for numerical efficiency improvement. 14. SUBJECT TERMS 15. NUMBER OF PAGES Time-domain...11 4 Discussion of Numerical Results ........................ 19 5 C onclusion...l ill tiit, pruIcIt a1lyis lder this’ Iranirwurk. Ilulilerical results it’lect tfi heIcst puss,’ibk 1)1(2pefon~lI liace of t he iiew aiiuiirical j
Time Domain Reflectometry for Damage Detection of Laminated CFRP plate
2011-08-18
Final Report PROJECT ID: AOARD-10-4112 Title: Time Domain Reflectometry for damage detection of laminated CFRP plate Researcher: Professor Akira...From July/2010 To July/2011 Abstract Recently, high toughness Carbon Fiber Reinforced Polymer ( CFRP ) laminates are used to primary structures. The...tough CFRP yields small fiber breakages when delamination crack is made in many cases. This requires a detection system of fiber breakages at low cost for
Time-domain Ramsey interferometry with interacting Rydberg atoms
NASA Astrophysics Data System (ADS)
Sommer, Christian; Pupillo, Guido; Takei, Nobuyuki; Takeda, Shuntaro; Tanaka, Akira; Ohmori, Kenji; Genes, Claudiu
2016-11-01
We theoretically investigate the dynamics of a gas of strongly interacting Rydberg atoms subject to a time-domain Ramsey interferometry protocol. The many-body dynamics is governed by an Ising-type Hamiltonian with long-range interactions of tunable strength. We analyze and model the contrast degradation and phase accumulation of the Ramsey signal and identify scaling laws for varying interrogation times, ensemble densities, and ensemble dimensionalities.
High-Order Entropy Stable Finite Difference Schemes for Nonlinear Conservation Laws: Finite Domains
NASA Technical Reports Server (NTRS)
Fisher, Travis C.; Carpenter, Mark H.
2013-01-01
Developing stable and robust high-order finite difference schemes requires mathematical formalism and appropriate methods of analysis. In this work, nonlinear entropy stability is used to derive provably stable high-order finite difference methods with formal boundary closures for conservation laws. Particular emphasis is placed on the entropy stability of the compressible Navier-Stokes equations. A newly derived entropy stable weighted essentially non-oscillatory finite difference method is used to simulate problems with shocks and a conservative, entropy stable, narrow-stencil finite difference approach is used to approximate viscous terms.
Anderson localization and Mott insulator phase in the time domain
Sacha, Krzysztof
2015-01-01
Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. There is an intriguing question if solid state phenomena can be observed in the time domain. Here we show that wave-packets localized on resonant classical trajectories of periodically driven systems are ideal elements to realize Anderson localization or Mott insulator phase in the time domain. Uniform superpositions of the wave-packets form stationary states of a periodically driven particle. However, an additional perturbation that fluctuates in time results in disorder in time and Anderson localization effects emerge. Switching to many-particle systems we observe that depending on how strong particle interactions are, stationary states can be Bose-Einstein condensates or single Fock states where definite numbers of particles occupy the periodically evolving wave-packets. Our study shows that non-trivial crystal-like phenomena can be observed in the time domain. PMID:26074169
High frequency resolution terahertz time-domain spectroscopy
NASA Astrophysics Data System (ADS)
Sangala, Bagvanth Reddy
2013-12-01
A new method for the high frequency resolution terahertz time-domain spectroscopy is developed based on the characteristic matrix method. This method is useful for studying planar samples or stack of planar samples. The terahertz radiation was generated by optical rectification in a ZnTe crystal and detected by another ZnTe crystal via electro-optic sampling method. In this new characteristic matrix based method, the spectra of the sample and reference waveforms will be modeled by using characteristic matrices. We applied this new method to measure the optical constants of air. The terahertz transmission through the layered systems air-Teflon-air-Quartz-air and Nitrogen gas-Teflon-Nitrogen gas-Quartz-Nitrogen gas was modeled by the characteristic matrix method. A transmission coefficient is derived from these models which was optimized to fit the experimental transmission coefficient to extract the optical constants of air. The optimization of an error function involving the experimental complex transmission coefficient and the theoretical transmission coefficient was performed using patternsearch algorithm of MATLAB. Since this method takes account of the echo waveforms due to reflections in the layered samples, this method allows analysis of longer time-domain waveforms giving rise to very high frequency resolution in the frequency-domain. We have presented the high frequency resolution terahertz time-domain spectroscopy of air and compared the results with the literature values. We have also fitted the complex susceptibility of air to the Lorentzian and Gaussian functions to extract the linewidths.
Uzayisenga, Viviane; Lin, Xiao-Dong; Li, Li-Mei; Anema, Jason R; Yang, Zhi-Lin; Huang, Yi-Fan; Lin, Hai-Xin; Li, Song-Bo; Li, Jian-Feng; Tian, Zhong-Qun
2012-06-19
Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.
Joint inversions of two VTEM surveys using quasi-3D TDEM and 3D magnetic inversion algorithms
NASA Astrophysics Data System (ADS)
Kaminski, Vlad; Di Massa, Domenico; Viezzoli, Andrea
2016-05-01
In the current paper, we present results of a joint quasi-three-dimensional (quasi-3D) inversion of two versatile time domain electromagnetic (VTEM) datasets, as well as a joint 3D inversion of associated aeromagnetic datasets, from two surveys flown six years apart from one another (2007 and 2013) over a volcanogenic massive sulphide gold (VMS-Au) prospect in northern Ontario, Canada. The time domain electromagnetic (TDEM) data were inverted jointly using the spatially constrained inversion (SCI) approach. In order to increase the coherency in the model space, a calibration parameter was added. This was followed by a joint inversion of the total magnetic intensity (TMI) data extracted from the two surveys. The results of the inversions have been studied and matched with the known geology, adding some new valuable information to the ongoing mineral exploration initiative.
NASA Astrophysics Data System (ADS)
Kühmstedt, Peter; Bräuer-Burchardt, Christian; Munkelt, Christoph; Heinze, Matthias; Palme, Martin; Schmidt, Ingo; Hintersehr, Josef; Notni, Gunther
2007-09-01
Here a new set-up of a 3D-scanning system for CAD/CAM in dental industry is proposed. The system is designed for direct scanning of the dental preparations within the mouth. The measuring process is based on phase correlation technique in combination with fast fringe projection in a stereo arrangement. The novelty in the approach is characterized by the following features: A phase correlation between the phase values of the images of two cameras is used for the co-ordinate calculation. This works contrary to the usage of only phase values (phasogrammetry) or classical triangulation (phase values and camera image co-ordinate values) for the determination of the co-ordinates. The main advantage of the method is that the absolute value of the phase at each point does not directly determine the coordinate. Thus errors in the determination of the co-ordinates are prevented. Furthermore, using the epipolar geometry of the stereo-like arrangement the phase unwrapping problem of fringe analysis can be solved. The endoscope like measurement system contains one projection and two camera channels for illumination and observation of the object, respectively. The new system has a measurement field of nearly 25mm × 15mm. The user can measure two or three teeth at one time. So the system can by used for scanning of single tooth up to bridges preparations. In the paper the first realization of the intraoral scanner is described.
NASA Technical Reports Server (NTRS)
2004-01-01
This 3-D, microscopic imager mosaic of a target area on a rock called 'Diamond Jenness' was taken after NASA's Mars Exploration Rover Opportunity ground into the surface with its rock abrasion tool for a second time.
Opportunity has bored nearly a dozen holes into the inner walls of 'Endurance Crater.' On sols 177 and 178 (July 23 and July 24, 2004), the rover worked double-duty on Diamond Jenness. Surface debris and the bumpy shape of the rock resulted in a shallow and irregular hole, only about 2 millimeters (0.08 inch) deep. The final depth was not enough to remove all the bumps and leave a neat hole with a smooth floor. This extremely shallow depression was then examined by the rover's alpha particle X-ray spectrometer.
On Sol 178, Opportunity's 'robotic rodent' dined on Diamond Jenness once again, grinding almost an additional 5 millimeters (about 0.2 inch). The rover then applied its Moessbauer spectrometer to the deepened hole. This double dose of Diamond Jenness enabled the science team to examine the rock at varying layers. Results from those grindings are currently being analyzed.
The image mosaic is about 6 centimeters (2.4 inches) across.
NASA Technical Reports Server (NTRS)
1997-01-01
Many prominent rocks near the Sagan Memorial Station are featured in this image, taken in stereo by the Imager for Mars Pathfinder (IMP) on Sol 3. 3D glasses are necessary to identify surface detail. Wedge is at lower left; Shark, Half-Dome, and Pumpkin are at center. Flat Top, about four inches high, is at lower right. The horizon in the distance is one to two kilometers away.
Mars Pathfinder is the second in NASA's Discovery program of low-cost spacecraft with highly focused science goals. The Jet Propulsion Laboratory, Pasadena, CA, developed and manages the Mars Pathfinder mission for NASA's Office of Space Science, Washington, D.C. JPL is an operating division of the California Institute of Technology (Caltech). The Imager for Mars Pathfinder (IMP) was developed by the University of Arizona Lunar and Planetary Laboratory under contract to JPL. Peter Smith is the Principal Investigator.
Click below to see the left and right views individually. [figure removed for brevity, see original site] Left [figure removed for brevity, see original site] Right
NASA Astrophysics Data System (ADS)
Wang, Chongwen; Li, Ping; Wang, Junfeng; Rong, Zhen; Pang, Yuanfeng; Xu, Jiawen; Dong, Peitao; Xiao, Rui; Wang, Shengqi
2015-11-01
Precise fabrication of subtle nanogaps amid individual nanoparticles or between adjacent ones to obtain the highest SERS enhancement is still a challenge. Here, we reported a novel approach for fabricating core-shell-satellite 3D magnetic microspheres (CSSM), that easily form a porous 1.5 nm PEI interlayer to accommodate molecules and create sufficient hotspots between the inner Fe3O4@Ag core and outer assembled Au@Ag satellites. Experiments and finite-difference time-domain (FDTD) simulation demonstrated that the enhancement factor (EF) was about 2.03 × 108 and 6.25 × 106, respectively. In addition, the micro-scale magnetic core endowed the CSSM with a superior magnetic nature, which enabled easy separation and further enhanced Raman signals due to enrichment of targeted analytes and abundant interparticle hotspots created by magnetism-induced aggregation. Our results further demonstrated that the CSSM is expected to be a versatile SERS substrate, which has been verified by the detection of the adsorbed pesticide thiram and the non-adsorbed pesticide paraquat with a detection limit as low as 5 × 10-12 M and 1 × 10-10 M, respectively. The novel CSSM can overcome the long-standing limitations of SERS for the trace characterization of various analytes in different solutions and promises to transform SERS into a practical analytical technique.Precise fabrication of subtle nanogaps amid individual nanoparticles or between adjacent ones to obtain the highest SERS enhancement is still a challenge. Here, we reported a novel approach for fabricating core-shell-satellite 3D magnetic microspheres (CSSM), that easily form a porous 1.5 nm PEI interlayer to accommodate molecules and create sufficient hotspots between the inner Fe3O4@Ag core and outer assembled Au@Ag satellites. Experiments and finite-difference time-domain (FDTD) simulation demonstrated that the enhancement factor (EF) was about 2.03 × 108 and 6.25 × 106, respectively. In addition, the micro
NASA Astrophysics Data System (ADS)
Salazar Rodriguez, J. M.; Vargas Jiménez, C. A.
2015-12-01
In this research, various configurations of reservoirs were simulated using finite elements in 3D, in order to analyze the subsoil electromagnetic responses in the time domain. Apparent resistivity curves both early and late time and their respective sensitivities in detecting hydrocarbon reservoirs are found. The maximum sensitivity obtained in the early and late times was 55.72% and 49.32% respectively. The separation of 1km between the transmitter and receiver was used in the simulations, because at shorter distances problems were encountered in in determining the resistivity curves. In addition, it was determined that the current dipole transmitter must be over 800A • m to overcome the level of noise instrumental of the receptor coil.
Non-linear Conjugate Gradient Time-Domain Controlled Inversion Source
Newman, Gregory A.; Commer, Michael
2006-11-16
Software that simulates and inverts time-domain electromagnetic field data for subsurface electrical properties (electrical conductivity) of geological media. The software treats data produced by a step-wise source signal from either galvanic (grounded wires) or inductive (magnetic loops) sources. The inversion process is carried inductive (magnetic loops) sources. The inversion process is carried out using a non-linear conjugate gradient optimization scheme, which minimizes the misfit between field data and model data using a least squares criteria. The software is an upgrade from the code TEM3D ver. 2.0. The upgrade includes the following components: (1) Improved (faster)memory access during gradient computation. (2) Data parellelization scheme: Multiple transmitters (sources) can be distributed accross several banks of processors (daa-planes). Similarly, the receivers of each source are also distributed accross the corresponding data-plane. (3) Improved data-IO.
NASA Astrophysics Data System (ADS)
Vincenti, H.; Vay, J.-L.
2016-03-01
Very high order or pseudo-spectral Maxwell solvers are the method of choice to reduce discretization effects (e.g. numerical dispersion) that are inherent to low order Finite-Difference Time-Domain (FDTD) schemes. However, due to their large stencils, these solvers are often subject to truncation errors in many electromagnetic simulations. These truncation errors come from non-physical modifications of Maxwell's equations in space that may generate spurious signals affecting the overall accuracy of the simulation results. Such modifications for instance occur when Perfectly Matched Layers (PMLs) are used at simulation domain boundaries to simulate open media. Another example is the use of arbitrary order Maxwell solver with domain decomposition technique that may under some condition involve stencil truncations at subdomain boundaries, resulting in small spurious errors that do eventually build up. In each case, a careful evaluation of the characteristics and magnitude of the errors resulting from these approximations, and their impact at any frequency and angle, requires detailed analytical and numerical studies. To this end, we present a general analytical approach that enables the evaluation of numerical errors of fully three-dimensional arbitrary order finite-difference Maxwell solver, with arbitrary modification of the local stencil in the simulation domain. The analytical model is validated against simulations of domain decomposition technique and PMLs, when these are used with very high-order Maxwell solver, as well as in the infinite order limit of pseudo-spectral solvers. Results confirm that the new analytical approach enables exact predictions in each case. It also confirms that the domain decomposition technique can be used with very high-order Maxwell solvers and a reasonably low number of guard cells with negligible effects on the whole accuracy of the simulation.
Numerical computation of transonic flows by finite-element and finite-difference methods
NASA Technical Reports Server (NTRS)
Hafez, M. M.; Wellford, L. C.; Merkle, C. L.; Murman, E. M.
1978-01-01
Studies on applications of the finite element approach to transonic flow calculations are reported. Different discretization techniques of the differential equations and boundary conditions are compared. Finite element analogs of Murman's mixed type finite difference operators for small disturbance formulations were constructed and the time dependent approach (using finite differences in time and finite elements in space) was examined.
Shi, Xiaowei; Lou, Zaizhu; Zhang, Peng; Fujitsuka, Mamoru; Majima, Tetsuro
2016-11-23
Nowadays, how to convert solar energy efficiently to other energies, such as chemical energy, is an important subject. In the present work, gold nanosphere (AuNS) monoencapsulated in TiO2 hollow nanosphere (Au-TiO2) and three-dimensional assembled array of Au-TiO2 (3D-array) were fabricated to carefully explore the multiscattering effect on the photocatalytic activity of H2 generation under simulated solar light and visible light irradiation, respectively. Au-TiO2 with the inner cavity diameter of 176 nm was uniformly synthesized via SiO2 protection method and then was used as building blocks for construction of 3D-array. The 3D-array exhibited a much higher photocatalytic activity of H2 generation (3.5 folds under visible light irradiation, 1.4 folds under solar light irradiation) than Au-TiO2. Single-particle plasmonic photoluminescence measurement and computational simulation of finite difference time domain (FDTD) were performed to elucidate the detailed mechanisms of photocatalysis. It was suggested that the hot electrons generated by AuNS under visible light irradiation play a significant role during the photocatalysis process. The higher activity of 3D-array is due to the elongation of light path length because of the multiscattering in-between Au-TiO2 and the reflection inside of the TiO2 shell. Therefore, the AuNS has more opportunity to absorb light and more hot electrons are expected to be generated through the electron transfer from AuNS to TiO2 shell, leading to an increment in the H2 generation. This result gives us a new perspective of constructing structures for efficient light utilization.
Using time domain characteristics to discriminate physiologic and parkinsonian tremors.
Edwards, R; Beuter, A
2000-01-01
Tremor amplitude and frequency do not always clearly differentiate subjects with particular pathologies from control subjects or from subjects with other pathologies, especially in early stages of a disease. For patients with early stages of Parkinson's disease (PD) the discriminative power of amplitude was compared with that of other time domain characteristics of tremor recordings that are probably not evident clinically. Postural tremor with and without visual feedback and rest tremor were recorded in both hands of a group of patients with Parkinson's disease (n = 21) and a group of healthy control subjects (n = 30) using displacement lasers. Velocity and acceleration data were derived from displacement data. Twelve time domain characteristics were calculated on each recording and the discriminating power of each was evaluated using the worse hand in each case. Postural tremor with no visual feedback separates the two groups of subjects most efficiently, especially in velocity and acceleration. Tremor in Parkinson's disease (in comparison to normal physiologic tremor) has a specific morphology, has a distinctive histogram, is more periodic, and contains indications of nonlinearity in the underlying dynamics. There may also be greater difference in amplitude between the two hands and time asymmetry in tremor of patients with PD. A series of finger flexions seems to enhance normal tremor but not tremor in PD and may thus aid in discrimination. Discrimination of tremor attributable to PD from normal physiologic tremor can be enhanced by measuring time domain characteristics subtler than amplitude, particularly when amplitude itself is not large. Tremor measurement should not be limited to acceleration data because some information is more visible in other variables.
The Benard problem: A comparison of finite difference and spectral collocation eigen value solutions
NASA Technical Reports Server (NTRS)
Skarda, J. Raymond Lee; Mccaughan, Frances E.; Fitzmaurice, Nessan
1995-01-01
The application of spectral methods, using a Chebyshev collocation scheme, to solve hydrodynamic stability problems is demonstrated on the Benard problem. Implementation of the Chebyshev collocation formulation is described. The performance of the spectral scheme is compared with that of a 2nd order finite difference scheme. An exact solution to the Marangoni-Benard problem is used to evaluate the performance of both schemes. The error of the spectral scheme is at least seven orders of magnitude smaller than finite difference error for a grid resolution of N = 15 (number of points used). The performance of the spectral formulation far exceeded the performance of the finite difference formulation for this problem. The spectral scheme required only slightly more effort to set up than the 2nd order finite difference scheme. This suggests that the spectral scheme may actually be faster to implement than higher order finite difference schemes.
A time domain, weighted residual formulation of Maxwell's equations
NASA Technical Reports Server (NTRS)
Young, Jeffrey L.; Brueckner, Frank P.
1993-01-01
A finite element model is developed and used to simulate two-dimensional electromagnetic wave propagation and scattering. The spatial discretization of the time-domain electrodynamic equations is accomplished by a Galerkin approach. The semi-discrete equations are solved explicitly using a second-order Runge-Kutta scheme. Both the electric and magnetic fields are discretized using a single grid, with the divergence-free conditions satisfied through a correction approach. Examples depicting the scattering of plane waves in 2D geometries are given to demonstrate the validity of the methodology.
Selecting Variables for the Time Domain Spectroscopic Survey
NASA Astrophysics Data System (ADS)
Morganson, Eric; TDSS; SDSS; Pan-STARRS1
2014-01-01
The Time Domain Spectroscopic Survey is an eBOSS subprogram that will obtain spectroscopy for 400,000 objects that vary more than 0.1 magnitudes. 100,000 of these objects will be unique to TDSS and 300,000 will be shared with other subprograms. We use a combination of Pan-STARRS1 and SDSS photometry to select a sample of variables that is 95% pure and 60% complete. This sample is obtained with three dimension Kernel Density Analysis. Our data and method are particularly effective at selecting long term variables, and more than 300,000 of our variables will be quasars.
Radar target imaging by time-domain inverse scattering
NASA Astrophysics Data System (ADS)
Morag, M.
1981-03-01
This thesis describes the study and development of a workable inverse scattering method for imaging and identification of radar targets. The space-time integral approach is used for iterative target shape reconstruction. Following an overview of transient electromagnetics, the integral equation is applied for thin-wire transient response computation. The analytical time domain integral equation is derived and solved numerically, for general conducting bodies of revolution. Finally the algorithm for an inverse scattering computer solution is derived and tested under simulation of physical environments.
New Flutter Analysis Technique for Time-Domain Computational Aeroelasticity
NASA Technical Reports Server (NTRS)
Pak, Chan-Gi; Lung, Shun-Fat
2017-01-01
A new time-domain approach for computing flutter speed is presented. Based on the time-history result of aeroelastic simulation, the unknown unsteady aerodynamics model is estimated using a system identification technique. The full aeroelastic model is generated via coupling the estimated unsteady aerodynamic model with the known linear structure model. The critical dynamic pressure is computed and used in the subsequent simulation until the convergence of the critical dynamic pressure is achieved. The proposed method is applied to a benchmark cantilevered rectangular wing.
Astrophysics in the Era of Massive Time-Domain Surveys
NASA Astrophysics Data System (ADS)
Djorgovski, G.
Synoptic sky surveys are now the largest data producers in astronomy, entering the Petascale regime, opening the time domain for a systematic exploration. A great variety of interesting phenomena, spanning essentially all subfields of astronomy, can only be studied in the time domain, and these new surveys are producing large statistical samples of the known types of objects and events for further studies (e.g., SNe, AGN, variable stars of many kinds), and have already uncovered previously unknown subtypes of these (e.g., rare or peculiar types of SNe). These surveys are generating a new science, and paving the way for even larger surveys to come, e.g., the LSST; our ability to fully exploit such forthcoming facilities depends critically on the science, methodology, and experience that are being accumulated now. Among the outstanding challenges, the foremost is our ability to conduct an effective follow-up of the interesting events discovered by the surveys in any wavelength regime. The follow-up resources, especially spectroscopy, are already and, for the predictable future, will be severely limited, thus requiring an intelligent down-selection of the most astrophysically interesting events to follow. The first step in that process is an automated, real-time, iterative classification of events, that incorporates heterogeneous data from the surveys themselves, archival and contextual information (spatial, temporal, and multiwavelength), and the incoming follow-up observations. The second step is an optimal automated event prioritization and allocation of the available follow-up resources that also change in time. Both of these challenges are highly non-trivial, and require a strong cyber-infrastructure based on the Virtual Observatory data grid, and the various astroinformatics efforts. Time domain astronomy is inherently an astronomy of telescope-computational systems, and will increasingly depend on novel machine learning and artificial intelligence tools
Fast Brillouin Optical Time Domain Analysis for dynamic sensing.
Peled, Yair; Motil, Avi; Tur, Moshe
2012-04-09
A new technique for the fast implementation of Brillouin Optical Time Domain Analysis (BOTDA) is proposed and demonstrated, carrying the classical BOTDA method to the dynamic sensing domain. By using a digital signal generator which enables fast switching among 100 scanning frequencies, we demonstrate a truly distributed and dynamic measurement of a 100 m long fiber with a sampling rate of ~10 kHz, limited only by the fiber length and the frequency granularity. With 10 averages the standard deviation of the measured strain was ~5 µε.
Balanced detection in Brillouin optical time domain analysis
NASA Astrophysics Data System (ADS)
Dominguez-Lopez, Alejandro; Lopez-Gil, Alexia; Martin-Lopez, Sonia; Gonzalez-Herraez, Miguel
2014-05-01
We propose the use of balanced detection in Brillouin Optical Time Domain Analysis (BOTDA) sensors. Balanced detection can be effectively accomplished among the Stokes and anti-Stokes bands in the probe signal. This type of detection leads to a doubling of the trace amplitude and at least a √2 increase in signal to noise ratio over the conventional configuration. Moreover, it leads to a complete cancellation of the common-mode noise in the probe signal, including relative intensity noise in Raman-assisted configurations. We show all these benefits both theoretically and experimentally.
Sources of noise in Brillouin optical time-domain analyzers
NASA Astrophysics Data System (ADS)
Urricelqui, Javier; Soto, Marcelo A.; Thévenaz, Luc
2015-09-01
This paper presents a thorough study of the different sources of noise affecting Brillouin optical time-domain analyzers (BOTDA), providing a deep insight into the understanding of the fundamental limitations of this kind of sensors. Analytical and experimental results indicate that the noise source ultimately fixing the sensor performance depends basically on the fiber length and the input pump-probe powers. Thus, while the phase-to-intensity noise conversion induced by stimulated Brillouin scattering can have a dominating effect at short distances, a combination of sources determines the noise in longrange sensing, basically dominated by probe double Rayleigh scattering.
Time-domain simulation of nonlinear radiofrequency phenomena
Jenkins, Thomas G.; Austin, Travis M.; Smithe, David N.; Loverich, John; Hakim, Ammar H.
2013-01-15
Nonlinear effects associated with the physics of radiofrequency wave propagation through a plasma are investigated numerically in the time domain, using both fluid and particle-in-cell (PIC) methods. We find favorable comparisons between parametric decay instability scenarios observed on the Alcator C-MOD experiment [J. C. Rost, M. Porkolab, and R. L. Boivin, Phys. Plasmas 9, 1262 (2002)] and PIC models. The capability of fluid models to capture important nonlinear effects characteristic of wave-plasma interaction (frequency doubling, cyclotron resonant absorption) is also demonstrated.
NASA Technical Reports Server (NTRS)
Kreider, Kevin L.; Baumeister, Kenneth J.
1996-01-01
An explicit finite difference real time iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for future large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable for a harmonic monochromatic sound field, a parabolic (in time) approximation is introduced to reduce the order of the governing equation. The analysis begins with a harmonic sound source radiating into a quiescent duct. This fully explicit iteration method then calculates stepwise in time to obtain the 'steady state' harmonic solutions of the acoustic field. For stability, applications of conventional impedance boundary conditions requires coupling to explicit hyperbolic difference equations at the boundary. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Fiber laser hydrogen sensor codified in the time domain
NASA Astrophysics Data System (ADS)
Barmenkov, Yuri O.; Ortigosa-Blanch, Arturo; Diez, Antonio; Cruz Munoz, Jose Luis; Andres, Miguel V.
2004-10-01
A novel scheme for a fiber optic hydrogen sensor is presented. The sensor is based on an erbium-doped fiber laser with a Pd-coated tapered fiber within the laser cavity acting as the hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases changing the cavity losses, which leads to a modification of the switching-on laser transient. The hydrogen concentration can be obtained by a simple measurement of the build-up time of the laser. This technique translates the measurement of hydrogen concentration into the time domain. Sensing techniques translating the measurement to the time domain offer the possibility to acquire and process the information very easily and accurately using reliable and low-cost electronics. We have also studied the influence of the pumping conditions. We have found that changing from a 100% modulation depth of the pump to biasing the laser with a certain pump power (being this value always below the laser threshold) the sensitivity of the sensor is substantially enhanced. Hence the sensitivity of the fiber laser sensor can be adjusted to certain requirements by simply controlling the pump. Relative build-up times variations of up to 55% for 10% hydrogen concentration are demonstrated.
Quantifying Airborne Induced Polarization effects in helicopter time domain electromagnetics
NASA Astrophysics Data System (ADS)
Macnae, James
2016-12-01
This paper derives the Airborne Induced Polarization (AIP) response of an airborne electromagnetic (AEM) system to a horizontal, thin sheet conductor. A vertical component double-dipole approximates helicopter systems with towed concentric horizontal transmitter and receiver loops in frequency- or time-domain. In time domain, the AIP effect typically shows up as late-time negative data with amplitude 4 to 5 orders of magnitude smaller than the early-time peak of the positive AEM responses. Because of limited bandwidth from the short sample time after the decay of inductive responses, accurate extraction of intrinsic AIP parameters other than a minimum chargeability is almost impossible. Modelling further suggests that AIP effects in double-dipole AEM systems can only be reliably detected from polarizable material in the top few tens of metres. A titanium mineral exploration case history from the Lac Brûlé area, Quebec, Canada illustrates strong spatial coherence of AIP minimum chargeability estimates and their independence from other effects such as conductivity and magnetic susceptibility.
[Aging explosive detection using terahertz time-domain spectroscopy].
Meng, Kun; Li, Ze-ren; Liu, Qiao
2011-05-01
Detecting the aging situation of stock explosive is essentially meaningful to the research on the capability, security and stability of explosive. Existing aging explosive detection techniques, such as scan microscope technique, Fourier transfer infrared spectrum technique, gas chromatogram mass spectrum technique and so on, are either not able to differentiate whether the explosive is aging or not, or not able to image the structure change of the molecule. In the present paper, using the density functional theory (DFT), the absorb spectrum changes after the explosive aging were calculated, from which we can clearly find the difference of spectrum between explosive molecule and aging ones in the terahertz band. The terahertz time-domain spectrum (THz-TDS) system as well as its frequency spectrum resolution and measured range are analyzed. Combined with the existing experimental results and the essential characters of the terahertz wave, the application of THz-TDS technique to the detection of aging explosive was demonstrated from the aspects of feasibility, veracity and practicability. On the base of that, the authors advance the new method of aging explosive detection using the terahertz time-domain spectrum technique.
Time-domain spectroscopy in the mid-infrared.
Lanin, A A; Voronin, A A; Fedotov, A B; Zheltikov, A M
2014-10-20
When coupled to characteristic, fingerprint vibrational and rotational motions of molecules, an electromagnetic field with an appropriate frequency and waveform offers a highly sensitive, highly informative probe, enabling chemically specific studies on a broad class of systems in physics, chemistry, biology, geosciences, and medicine. The frequencies of these signature molecular modes, however, lie in a region where accurate spectroscopic measurements are extremely difficult because of the lack of efficient detectors and spectrometers. Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared. In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain. These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase.
Terahertz time-domain spectroscopy and application on peanut oils
NASA Astrophysics Data System (ADS)
Li, Jiusheng; Yao, Jianquan; Li, Jianrui
2008-12-01
Many materials were previously studied using far-infrared Fourier transform spectroscopy (FTS) in transmission and reflection modes. Recently, there has been a remarkable effort in employing terahertz time-domain spectroscopy (THz-TDS) for investigating material properties, including environment pollutants, semiconductors, polymers, explosive materials, and gases, etc. Since the absorption coefficient and the refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted field, both parts of the complex permittivity can be obtained by THz-TDS. In this letter, the optical properties of peanut oils in the frequency range from 0.2 to 2.5 THz were studied by employing terahertz time-domain spectroscopy. Several peanut oils, such as clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling were tested. The time delays of clean unused peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling are 8.33ps, 8.46ps and 8.46ps, respectively. The refractive indices of the three oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range.
Time domain Rankine-Green panel method for offshore structures
NASA Astrophysics Data System (ADS)
Li, Zhifu; Ren, Huilong; Liu, Riming; Li, Hui
2017-02-01
To solve the numerical divergence problem of the direct time domain Green function method for the motion simulation of floating bodies with large flare, a time domain hybrid Rankine-Green boundary element method is proposed. In this numerical method, the fluid domain is decomposed by an imaginary control surface, at which the continuous condition should be satisfied. Then the Rankine Green function is adopted in the inner domain. The transient free surface Green function is applied in the outer domain, which is used to find the relationship between the velocity potential and its normal derivative for the inner domain. Besides, the velocity potential at the mean free surface between body surface and control surface is directly solved by the integration scheme. The wave exciting force is computed through the convolution integration with wave elevation, by introducing the impulse response function. Additionally, the nonlinear Froude-Krylov force and hydrostatic force, which is computed under the instantaneous incident wave free surface, are taken into account by the direct pressure integration scheme. The corresponding numerical computer code is developed and first used to compute the hydrodynamic coefficients of the hemisphere, as well as the time history of a ship with large flare; good agreement is obtained with the analytical solutions as well as the available numerical results. Then the hydrodynamic properties of a FPSO are studied. The hydrodynamic coefficients agree well with the results computed by the frequency method; the influence of the time interval and the truncated time is investigated in detail.
Time-domain analysis of scrotal thermoregulatory impairment in varicocele.
Ismail, Enas; Orlando, Giuseppe; Pompa, Paolo; Gabrielli, Daniela; Di Donato, Luigino; Cardone, Daniela; Merla, Arcangelo
2014-01-01
Varicocele is a common male disease defined as the pathological dilatation of the pampiniform plexus and scrotal veins with venous blood reflux. Varicocele usually impairs the scrotal thermoregulation via a hemodynamic alteration, thus inducing an increase in cutaneous temperature. The investigation of altered scrotal thermoregulation by means of thermal infrared imaging has been proved to be useful in the study of the functional thermal impairment. In this study, we use the Control System Theory to analyze the time-domain dynamics of the scrotal thermoregulation in response to a mild cold challenge. Four standard time-domain dynamic parameters of a prototype second order control system (Delay Time, Rise Time, closed poles locations, steady state error) and the static basal temperatures were directly estimated from thermal recovery curves. Thermal infrared imaging data from 31 healthy controls (HCS) and 95 varicocele patients were processed. True-positive predictions, by comparison with standard echo color Doppler findings, higher than 87% were achieved into the proper classification of the disease stage. The proposed approach could help to understand at which specific level the presence of the disease impacts the scrotal thermoregulation, which is also involved into normal spermatogenesis process.
Time-domain fitting of battery electrochemical impedance models
NASA Astrophysics Data System (ADS)
Alavi, S. M. M.; Birkl, C. R.; Howey, D. A.
2015-08-01
Electrochemical impedance spectroscopy (EIS) is an effective technique for diagnosing the behaviour of electrochemical devices such as batteries and fuel cells, usually by fitting data to an equivalent circuit model (ECM). The common approach in the laboratory is to measure the impedance spectrum of a cell in the frequency domain using a single sine sweep signal, then fit the ECM parameters in the frequency domain. This paper focuses instead on estimation of the ECM parameters directly from time-domain data. This may be advantageous for parameter estimation in practical applications such as automotive systems including battery-powered vehicles, where the data may be heavily corrupted by noise. The proposed methodology is based on the simplified refined instrumental variable for continuous-time fractional systems method ('srivcf'), provided by the Crone toolbox [1,2], combined with gradient-based optimisation to estimate the order of the fractional term in the ECM. The approach was tested first on synthetic data and then on real data measured from a 26650 lithium-ion iron phosphate cell with low-cost equipment. The resulting Nyquist plots from the time-domain fitted models match the impedance spectrum closely (much more accurately than when a Randles model is assumed), and the fitted parameters as separately determined through a laboratory potentiostat with frequency domain fitting match to within 13%.
Time-domain diffuse optics: towards next generation devices
NASA Astrophysics Data System (ADS)
Contini, Davide; Dalla Mora, Alberto; Arridge, Simon; Martelli, Fabrizio; Tosi, Alberto; Boso, Gianluca; Farina, Andrea; Durduran, Turgut; Martinenghi, Edoardo; Torricelli, Alessandro; Pifferi, Antonio
2015-07-01
Diffuse optics is a powerful tool for clinical applications ranging from oncology to neurology, but also for molecular imaging, and quality assessment of food, wood and pharmaceuticals. We show that ideally time-domain diffuse optics can give higher contrast and a higher penetration depth with respect to standard technology. In order to completely exploit the advantages of a time-domain system a distribution of sources and detectors with fast gating capabilities covering all the sample surface is needed. Here, we present the building block to build up such system. This basic component is made of a miniaturised source-detector pair embedded into the probe based on pulsed Vertical-Cavity Surface-Emitting Lasers (VCSEL) as sources and Single-Photon Avalanche Diodes (SPAD) or Silicon Photomultipliers (SiPM) as detectors. The possibility to miniaturized and dramatically increase the number of source detectors pairs open the way to an advancement of diffuse optics in terms of improvement of performances and exploration of new applications. Furthermore, availability of compact devices with reduction in size and cost can boost the application of this technique.
A Time Domain Fluorescence Tomography System for Small Animal Imaging
Raymond, Scott B.; Dunn, Andrew K.; Bacskai, Brian J.; Boas, David A.
2010-01-01
We describe the application of a time domain diffuse fluorescence tomography system for whole body small animal imaging. The key features of the system are the use of point excitation in free space using ultrashort laser pulses and noncontact detection using a gated, intensified charge-coupled device (CCD) camera. Mouse shaped epoxy phantoms, with embedded fluorescent inclusions, were used to verify the performance of a recently developed asymptotic lifetime-based tomography algorithm. The asymptotic algorithm is based on a multiexponential analysis of the decay portion of the data. The multiexponential model is shown to enable the use of a global analysis approach for a robust recovery of the lifetime components present within the imaging medium. The surface boundaries of the imaging volume were acquired using a photogrammetric camera integrated with the imaging system, and implemented in a Monte-Carlo model of photon propagation in tissue. The tomography results show that the asymptotic approach is able to separate axially located fluorescent inclusions centered at depths of 4 and 10 mm from the surface of the mouse phantom. The fluorescent inclusions had distinct lifetimes of 0.5 and 0.95 ns. The inclusions were nearly overlapping along the measurement axis and shown to be not resolvable using continuous wave (CW) methods. These results suggest the practical feasibility and advantages of a time domain approach for whole body small animal fluorescence molecular imaging, particularly with the use of lifetime as a contrast mechanism. PMID:18672432
Study on the Before Cavity Interaction in a Second Harmonic Gyrotron Using 3D CFDTD PIC Simulations
NASA Astrophysics Data System (ADS)
Lin, M. C.; Illy, S.; Thumm, M.; Jelonnek, J.
2016-10-01
A computational study on before cavity interaction (BCI) in a 28 GHz second harmonic (SH) gryotron for industrial applications has been performed using a 3-D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) method. On the contrary to the after cavity interaction (ACI), i.e. beam wave interaction in the non-linear uptaper after the cavity, which has been widely investigated, the BCI, i.e. beam wave interaction in the non-linear downtaper before the cavity connected to the beam tunnel with an entrance, is less noticed and discussed. Usually the BCI might be considered easy to be eliminated. However, this is not always the case. As the SH gyrotron had been designed for SH TE12 mode operation, the first harmonic (FH) plays the main competition. In the 3-D CFDTD PIC simulations, a port boundary has been employed for the gyro-beam entrance of the gyrotron cavity instead of a metallic short one which is not reflecting a realistic situation as an FH backward wave oscillation (BWO) is competing with the desired SH generation. A numerical instability has been found and identified as a failure of the entrance port boundary caused by an evanescent wave or mode conversion. This indicates the entrance and downtaper are not fully cut-off for some oscillations. A further study shows that the undesired oscillation is the FH TE11 BWO mode concentrated around the beam tunnel entrance and downtaper. A mitigation strategy has been found to suppress this undesired BCI and avoid possible damage to the gun region.
3-D Acoustic Scattering from 2-D Rough Surfaces Using A Parabolic Equation Model
2013-12-01
acoustic propagation signals, especially at mid- frequencies and higher (e.g., acoustic communications systems). For many years, the effects of rough...of the effect of surface scattering on 3-D propagation , which is critical in evaluating the variability in underwater acoustic propagation . Results...14. SUBJECT TERMS Acoustic Propagation , Acoustic Scattering, Sea Surface Perturbations, Split- Step Fourier Algorithm, Finite Difference Algorithm
Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics
NASA Astrophysics Data System (ADS)
Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.
2014-02-01
Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model [1], using the finite-difference electromagnetic Vorpal/Vsim software [2]. This model has been augmented with a non-linear rf-sheath sub-grid model [3], which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves [4] in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques [5] to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion
Quantitative modeling of ICRF antennas with integrated time domain RF sheath and plasma physics
Smithe, David N.; D'Ippolito, Daniel A.; Myra, James R.
2014-02-12
Significant efforts have been made to quantitatively benchmark the sheath sub-grid model used in our time-domain simulations of plasma-immersed antenna near fields, which includes highly detailed three-dimensional geometry, the presence of the slow wave, and the non-linear evolution of the sheath potential. We present both our quantitative benchmarking strategy, and results for the ITER antenna configuration, including detailed maps of electric field, and sheath potential along the entire antenna structure. Our method is based upon a time-domain linear plasma model, using the finite-difference electromagnetic Vorpal/Vsim software. This model has been augmented with a non-linear rf-sheath sub-grid model, which provides a self-consistent boundary condition for plasma current where it exists in proximity to metallic surfaces. Very early, this algorithm was designed and demonstrated to work on very complicated three-dimensional geometry, derived from CAD or other complex description of actual hardware, including ITER antennas. Initial work with the simulation model has also provided a confirmation of the existence of propagating slow waves in the low density edge region, which can significantly impact the strength of the rf-sheath potential, which is thought to contribute to impurity generation. Our sheath algorithm is based upon per-point lumped-circuit parameters for which we have estimates and general understanding, but which allow for some tuning and fitting. We are now engaged in a careful benchmarking of the algorithm against known analytic models and existing computational techniques to insure that the predictions of rf-sheath voltage are quantitatively consistent and believable, especially where slow waves share in the field with the fast wave. Currently in progress, an addition to the plasma force response accounting for the sheath potential, should enable the modeling of sheath plasma waves, a predicted additional root to the dispersion, existing at the
Theory of mirrored time domain sampling for NMR spectroscopy.
Ghosh, Arindam; Wu, Yibing; He, Yunfen; Szyperski, Thomas
2011-12-01
A generalized theory is presented for novel mirrored hypercomplex time domain sampling (MHS) of NMR spectra. It is the salient new feature of MHS that two interferograms are acquired with different directionality of time evolution, that is, one is sampled forward from time t=0 to the maximal evolution time tmax, while the second is sampled backward from t=0 to -tmax. The sampling can be accomplished in a (semi) constant time or non constant-time manner. Subsequently, the two interferograms are linearly combined to yield a complex time domain signal. The manifold of MHS schemes considered here is defined by arbitrary settings of sampling phases ('primary phase shifts') and amplitudes of the two interferograms. It is shown that, for any two given primary phase shifts, the addition theorems of trigonometric functions yield the unique linear combination required to form the complex signal. In the framework of clean absorption mode (CAM) acquisition of NMR spectra being devoid of residual dispersive signal components, 'secondary phase shifts' represent time domain phase errors which are to be eliminated. In contrast, such secondary phase shifts may be introduced by experimental design in order to encode additional NMR parameters, a new class of NMR experiments proposed here. For generalization, it is further considered that secondary phase shifts may depend on primary phase shifts and/or sampling directionality. In order to compare with MHS theory, a correspondingly generalized theory is derived for widely used hypercomplex ('States') sampling (HS). With generalized theory it is shown, first, that previously introduced 'canonical' schemes, characterized by primary phases being multiples of π/4, afford maximal intensity of the desired absorptive signals in the absence of secondary phase shifts, and second, how primary phases can be adjusted to maximize the signal intensity provided that the secondary phase shifts are known. Third, it is demonstrated that theory enables
3D-spectral CDIs: a fast alternative to 3D inversion?
NASA Astrophysics Data System (ADS)
Macnae, James
2015-09-01
Virtually all airborne electromagnetic (AEM) data is interpreted using stitched 1D conductivity sections, derived from constrained inversion or fast but fairly accurate approximations. A small subset of this AEM data recently has been inverted using either block 3D models or thin plates, which processes have limitations in terms of cost and accuracy, and the results are in general strongly biased by the choice of starting models. Recent developments in spectral modelling have allowed fast 3D approximations of the EM response of both vortex induction and current gathering for simple geological target geometries. Fitting these spectral responses to AEM data should be sufficient to accurately locate current systems within the ground, and the behaviour of these local current systems can in theory approximately define a conductivity structure in 3D. This paper describes the results of initial testing of the algorithm in fitting vortex induction in a small target at the Forrestania test range, Western Australia, using results from a versatile time-domain electromagnetic (VTEM)-Max survey.
NASA Astrophysics Data System (ADS)
Kabakian, Adour Vahe
1998-12-01
Most time-domain solvers of Maxwell's equations that are applied to electromagnetic wave scattering problems are based on second- or third-order finite-difference and finite-volume schemes. Since linear wave propagation phenomena tend to be very susceptible to numerical dissipation and dispersion errors, they place high accuracy demands on the numerical methods employed. Starting with the premise that the required accuracy can be achieved more efficiently with high-order methods, a new numerical scheme based on spectral collocation is developed for solving Maxwell's equations in the time domain. The three-dimensional method is formulated over generalized curvilinear coordinates. It employs Fourier and Chebyshev spectral collocation for the spatial derivatives, while time advancement is achieved by the explicit third-order Adams-Moulton-Bashforth scheme. A domain decomposition method supplementing the spectral solver is also developed, extending its range of applications to geometries more complex than those traditionally associated with spectral methods. Reflective and absorbing boundary conditions are developed specifically for the spectral scheme. Finally, a grid stretching function is incorporated into the solver, which can be used, when needed, to relieve the stability restriction associated with the Chebyshev spacing of the collocation points, at the expense of only moderate loss in accuracy. The numerical method is applied to solve electromagnetic wave scattering problems from perfectly conducting solid targets, using both single and multi-domain grids. The geometries considered are the circular cylinder, the square cylinder, and the sphere. Solutions are evaluated and validated by the accuracy of the radar cross-section and, in some instances, the surface currents. Compared to commonly used finite-difference and finite-volume solvers, the spectral scheme produces results that are one to two orders of magnitude more accurate, using grids that are an order of
NASA Astrophysics Data System (ADS)
Cole, James B.
2014-09-01
The finite difference time domain (FDTD) algorithm is a popular tool for photonics design and simulations, but it also can yield deep insights into the fundamental nature of light and - more speculatively - into the discretization and connectivity and geometry of space-time. The CFL stability limit in FDTD can be interpreted as a limit on the speed of light. It depends not only on the dimensionality of space-time, but also on its connectivity. Thus the speed of light not only tells us something about the dimensionality of space-time but also about its connectivity. The computational molecule in conventional 2-D FDTD is (х +/- h,y)-(x,+/- y h)-(x-y), where h= triangle x = triangle y . It yields the CFL stability limit ctriangle/h<= t/h 1 √2 . Including diagonal nodes (x+/- h, y +/- h) in the computational molecule changes the connectivity of the space and changes the CFL limit. The FDTD model also predicts precursor signals (which physically exist). The Green's function of the FDTD model, which differs from that of the wave equation, may tell us something about underlying periodicities in space-time. It may be possible to experimentally observe effects of space-time discretization and connectivity in optics experiments.
Fujii, Masafumi
2010-12-20
We analyze light-induced forces on metal nano-spheres by using the three-dimensional finite-difference time-domain method with the Lorentz force formulation. Convergent analysis of the force on metal nano-particle clusters has been achieved by integrating the Lorentz and the Coulomb forces over the volume of the metal particles. Comparison to the Mie theory of radiation pressure on metal spheres under a plane wave illumination has verified rigorously the accuracy of the numerical method. We also analyze separate two metal spheres in close proximity and the results of the induced forces are compared to those in previous publications. The present method allows analysis of forces on various irregular structures; we apply the method to touching metal spheres, forming a simple cluster with a slight deformation at the contact point, to analyze the forces induced by the plasmonic resonance of the clusters. We show that the fundamental resonance modes, which newly appear in an infrared range when spheres are touching, exhibit strong binding forces within the clusters. Based on the numerical analyses we identify the resonance modes and evaluate quantitatively the infrared-induced forces on metal nano-sphere clusters.
MESA: A 3-D Eulerian hydrocode for penetration mechanics studies
Mandell, D.A.; Holian, K.S.; Henninger, R.
1991-01-01
We describe an explicit, finite-difference hydrocode, called MESA, and compare calculations to metal and ceramic plate impacts with spall and to Taylor cylinder tests. The MESA code was developed with support from DARPA, the Army and the Marine Corps for use in armor/anti-armor problems primarily, but the code has been used for a number of other applications. MESA includes 2-D and 3-D Eulerian hydrodynamics, a number of material strength and fracture models, and a programmed burn high explosives model. 15 refs., 4 figs.
NASA Astrophysics Data System (ADS)
Mediavilla, Evencio; Arribas, Santiago; Roth, Martin; Cepa-Nogué, Jordi; Sánchez, Francisco
2011-09-01
Preface; Acknowledgements; 1. Introductory review and technical approaches Martin M. Roth; 2. Observational procedures and data reduction James E. H. Turner; 3. 3D Spectroscopy instrumentation M. A. Bershady; 4. Analysis of 3D data Pierre Ferruit; 5. Science motivation for IFS and galactic studies F. Eisenhauer; 6. Extragalactic studies and future IFS science Luis Colina; 7. Tutorials: how to handle 3D spectroscopy data Sebastian F. Sánchez, Begona García-Lorenzo and Arlette Pécontal-Rousset.
Spherical 3D isotropic wavelets
NASA Astrophysics Data System (ADS)
Lanusse, F.; Rassat, A.; Starck, J.-L.
2012-04-01
Context. Future cosmological surveys will provide 3D large scale structure maps with large sky coverage, for which a 3D spherical Fourier-Bessel (SFB) analysis in spherical coordinates is natural. Wavelets are particularly well-suited to the analysis and denoising of cosmological data, but a spherical 3D isotropic wavelet transform does not currently exist to analyse spherical 3D data. Aims: The aim of this paper is to present a new formalism for a spherical 3D isotropic wavelet, i.e. one based on the SFB decomposition of a 3D field and accompany the formalism with a public code to perform wavelet transforms. Methods: We describe a new 3D isotropic spherical wavelet decomposition based on the undecimated wavelet transform (UWT) described in Starck et al. (2006). We also present a new fast discrete spherical Fourier-Bessel transform (DSFBT) based on both a discrete Bessel transform and the HEALPIX angular pixelisation scheme. We test the 3D wavelet transform and as a toy-application, apply a denoising algorithm in wavelet space to the Virgo large box cosmological simulations and find we can successfully remove noise without much loss to the large scale structure. Results: We have described a new spherical 3D isotropic wavelet transform, ideally suited to analyse and denoise future 3D spherical cosmological surveys, which uses a novel DSFBT. We illustrate its potential use for denoising using a toy model. All the algorithms presented in this paper are available for download as a public code called MRS3D at http://jstarck.free.fr/mrs3d.html
Time domain analysis of the weighted distributed order rheological model
NASA Astrophysics Data System (ADS)
Cao, Lili; Pu, Hai; Li, Yan; Li, Ming
2016-11-01
This paper presents the fundamental solution and relevant properties of the weighted distributed order rheological model in the time domain. Based on the construction of distributed order damper and the idea of distributed order element networks, this paper studies the weighted distributed order operator of the rheological model, a generalization of distributed order linear rheological model. The inverse Laplace transform on weighted distributed order operators of rheological model has been obtained by cutting the complex plane and computing the complex path integral along the Hankel path, which leads to the asymptotic property and boundary discussions. The relaxation response to weighted distributed order rheological model is analyzed, and it is closely related to many physical phenomena. A number of novel characteristics of weighted distributed order rheological model, such as power-law decay and intermediate phenomenon, have been discovered as well. And meanwhile several illustrated examples play important role in validating these results.
Time domain simulations of preliminary breakdown pulses in natural lightning.
Carlson, B E; Liang, C; Bitzer, P; Christian, H
2015-06-16
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism.
Opening the 100-Year Window for Time-Domain Astronomy
NASA Astrophysics Data System (ADS)
Grindlay, Jonathan; Tang, Sumin; Los, Edward; Servillat, Mathieu
2012-04-01
The large-scale surveys such as PTF, CRTS and Pan-STARRS-1 that have emerged within the past 5 years or so employ digital databases and modern analysis tools to accentuate research into Time Domain Astronomy (TDA). Preparations are underway for LSST which, in another 6 years, will usher in the second decade of modern TDA. By that time the Digital Access to a Sky Century @ Harvard (DASCH) project will have made available to the community the full sky Historical TDA database and digitized images for a century (1890-1990) of coverage. We describe the current DASCH development and some initial results, and outline plans for the ``production scanning'' phase and data distribution which is to begin in 2012. That will open a 100-year window into temporal astrophysics, revealing rare transients and (especially) astrophysical phenomena that vary on time-scales of a decade. It will also provide context and archival comparisons for the deeper modern surveys.
Time domain BEM for sound radiation of tires
NASA Astrophysics Data System (ADS)
Banz, Lothar; Gimperlein, Heiko; Nezhi, Zouhair; Stephan, Ernst P.
2016-07-01
This work investigates a time domain boundary element method for the acoustic wave equation in an exterior domain in the half-space mathbb {R}^3_+. The Neumann problem is formulated as a boundary integral equation of the second kind, and the convergence and stability of conforming Galerkin approximations is studied in the complex geometry of a car or truck tire above a street. After a validation experiment, numerical results are presented in time or frequency domain for realistic benchmarks in traffic noise: the sound emission of vibrating tires, noise amplification in the horn-like geometry between the tire and the road, as well as the Doppler effect of a moving tire. The results are compared with calculations in frequency domain.
Time Domain Reflectometric and spectroscopic studies on toluene + butyronitrile solution
NASA Astrophysics Data System (ADS)
Karthick, N. K.; Arivazhagan, G.; Kumbharkhane, A. C.; Joshi, Y. S.; Kannan, P. P.
2016-03-01
The dielectric parameters of toluene + butyronitrile solution have been obtained by time domain reflectometry (TDR) technique in the frequency range from 10 MHz to 30 GHz at 298 K. Spectroscopic (FTIR and 13C NMR) studies have also been carried out on the solution and the results of the studies show that neat butyronitrile is self-associative through C-H⋯N contacts and weak intermolecular forces of C-H⋯N and C-H⋯π type are operative in the solution. The obtained dielectric parameters such as Kirkwood correlation factor g, relaxation time τ etc. have been analyzed in view of these weak intermolecular forces. The weak non-covalent interactions between heteromolecules appear to have no influence on the ideality of ɛm vs X2 curve of the solution. Heteromolecular entities with weak intermolecular forces experience larger hindrance leading to longer relaxation time τ.
Time domain simulations of preliminary breakdown pulses in natural lightning
NASA Astrophysics Data System (ADS)
Carlson, B. E.; Liang, C.; Bitzer, P.; Christian, H.
2015-06-01
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism.
Time domain analysis of coherent terahertz synchrotron radiation
NASA Astrophysics Data System (ADS)
Hübers, H.-W.; Semenov, A.; Holldack, K.; Schade, U.; Wüstefeld, G.; Gol'tsman, G.
2005-10-01
The time structure of coherent terahertz synchrotron radiation at the electron storage ring of the Berliner Elektronensynchrotron und Speicherring Gesellschaft has been analyzed with a fast superconducting hot-electron bolometer. The emission from a single bunch of electrons was found to last ˜1500ps at frequencies around 0.4THz, which is much longer than the length of an electron bunch in the time domain (˜5ps). It is suggested that this is caused by multiple reflections at the walls of the beam line. The quadratic increase of the power with the number of electrons in the bunch as predicted for coherent synchrotron radiation and the transition from stable to bursting radiation were determined from a single storage ring fill pattern of bunches with different populations.
Characterization of Wheat Varieties Using Terahertz Time-Domain Spectroscopy
Ge, Hongyi; Jiang, Yuying; Lian, Feiyu; Zhang, Yuan; Xia, Shanhong
2015-01-01
Terahertz (THz) spectroscopy and multivariate data analysis were explored to discriminate eight wheat varieties. The absorption spectra were measured using THz time-domain spectroscopy from 0.2 to 2.0 THz. Using partial least squares (PLS), a regression model for discriminating wheat varieties was developed. The coefficient of correlation in cross validation (R) and root-mean-square error of cross validation (RMSECV) were 0.985 and 1.162, respectively. In addition, interval PLS was applied to optimize the models by selecting the most appropriate regions in the spectra, improving the prediction accuracy (R = 0.992 and RMSECV = 0.967). Results demonstrate that THz spectroscopy combined with multivariate analysis can provide rapid, nondestructive discrimination of wheat varieties. PMID:26024421
SVD compression for magnetic resonance fingerprinting in the time domain.
McGivney, Debra F; Pierre, Eric; Ma, Dan; Jiang, Yun; Saybasili, Haris; Gulani, Vikas; Griswold, Mark A
2014-12-01
Magnetic resonance (MR) fingerprinting is a technique for acquiring and processing MR data that simultaneously provides quantitative maps of different tissue parameters through a pattern recognition algorithm. A predefined dictionary models the possible signal evolutions simulated using the Bloch equations with different combinations of various MR parameters and pattern recognition is completed by computing the inner product between the observed signal and each of the predicted signals within the dictionary. Though this matching algorithm has been shown to accurately predict the MR parameters of interest, one desires a more efficient method to obtain the quantitative images. We propose to compress the dictionary using the singular value decomposition, which will provide a low-rank approximation. By compressing the size of the dictionary in the time domain, we are able to speed up the pattern recognition algorithm, by a factor of between 3.4-4.8, without sacrificing the high signal-to-noise ratio of the original scheme presented previously.
Nonlinear ultrasonic resonators: a numerical analysis in the time domain.
Vanhille, Christian; Campos-Pozuelo, Cleofé
2006-12-22
In the framework of the study of nonlinear acoustic phenomena arising in high-power ultrasonic resonators, this paper deals with the numerical prediction of the behaviour of strongly nonlinear waves in resonators. In particular three-dimensional cavities in complex modal configurations are analyzed. The main motivation of this work is the understanding and optimisation of high-power ultrasonic applications in fluids. Based on conservation laws written in Lagrangian coordinates and the isentropic state equation, several evolution equations (one-dimensional, two-dimensional, three-dimensional and axisymmetric) are proposed and numerically solved in the time domain. No restriction on nonlinearity level is imposed. These developments allow the simulation of the time evolution of the pressure distribution inside the cavity, as well as the harmonics distribution. Distortion, nonlinear attenuation and rms pressure can be studied. Periodic (continue) and pulsed signal excitation are possible. Some results referred to complicated nonlinear waves are presented.
Uncertainty in Terahertz Time-Domain Spectroscopy Measurement of Liquids
NASA Astrophysics Data System (ADS)
Yang, Fei; Liu, Liping; Song, Maojiang; Han, Feng; Shen, Li; Hu, Pengfei; Zhang, Fang
2017-02-01
Terahertz time-domain spectroscopy (THz-TDS) is a significant technique for characterizing materials as it allows fast and broadband measurement of optical constants in the THz regime. The measurement precision of the constants is highly influenced by the complicated measurement procedure and data processing. Taking THz transmission measurement of liquids into account, the sources of error existing in THz-TDS process are identified. The contributions of each source to the uncertainty of optical constants in THz-TDS process are formulated, with particular emphasis on the effect of multilayer reflections and plane wave assumption. As a consequence, an analytical model is proposed for uncertainty evaluation in a THz-TDS measurement of liquids. An actual experiment with a Di 2-Ethyl Hexyl Phthalate (DEHP) sample is carried out to show that the proposed model could be a basis to evaluate the measurement precision of optical constants of liquids.
Time-domain response of the ARIANNA detector
NASA Astrophysics Data System (ADS)
Barwick, S. W.; Berg, E. C.; Besson, D. Z.; Duffin, T.; Hanson, J. C.; Klein, S. R.; Kleinfelder, S. A.; Piasecki, M.; Ratzlaff, K.; Reed, C.; Roumi, M.; Stezelberger, T.; Tatar, J.; Walker, J.; Young, R.; Zou, L.
2015-03-01
The Antarctic Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a high-energy neutrino detector designed to record the Askaryan electric field signature of cosmogenic neutrino interactions in ice. To understand the inherent radio-frequency (RF) neutrino signature, the time-domain response of the ARIANNA RF receiver must be measured. ARIANNA uses Create CLP5130-2N log-periodic dipole arrays (LPDAs). The associated effective height operator converts incident electric fields to voltage waveforms at the LDPA terminals. The effective height versus time and incident angle was measured, along with the associated response of the ARIANNA RF amplifier. The results are verified by correlating to field measurements in air and ice, using oscilloscopes. Finally, theoretical models for the Askaryan electric field are combined with the detector response to predict the neutrino signature.
Detecting Rare Events in the Time-Domain
Rest, A; Garg, A
2008-10-31
One of the biggest challenges in current and future time-domain surveys is to extract the objects of interest from the immense data stream. There are two aspects to achieving this goal: detecting variable sources and classifying them. Difference imaging provides an elegant technique for identifying new transients or changes in source brightness. Much progress has been made in recent years toward refining the process. We discuss a selection of pitfalls that can afflict an automated difference imagine pipeline and describe some solutions. After identifying true astrophysical variables, we are faced with the challenge of classifying them. For rare events, such as supernovae and microlensing, this challenge is magnified because we must balance having selection criteria that select for the largest number of objects of interest against a high contamination rate. We discuss considerations and techniques for developing classification schemes.
Discontinuous Galerkin time-domain computations of metallic nanostructures.
Stannigel, Kai; König, Michael; Niegemann, Jens; Busch, Kurt
2009-08-17
We apply the three-dimensional Discontinuous-Galerkin Time-Domain method to the investigation of the optical properties of bar- and V-shaped metallic nanostructures on dielectric substrates. A flexible finite element-like mesh together with an expansion into high-order basis functions allows for an accurate resolution of complex geometries and strong field gradients. In turn, this provides accurate results on the optical response of realistic structures. We study in detail the influence of particle size and shape on resonance frequencies as well as on scattering and absorption efficiencies. Beyond a critical size which determines the onset of the quasi-static limit we find significant deviations from the quasi-static theory. Furthermore, we investigate the influence of the excitation by comparing normal illumination and attenuated total internal reflection setups. Finally, we examine the possibility of coherently controlling the local field enhancement of V-structures via chirped pulses.
Synthetic Spectrum Approach for Brillouin Optical Time-Domain Reflectometry
Nishiguchi, Ken'ichi; Li, Che-Hsien; Guzik, Artur; Kishida, Kinzo
2014-01-01
We propose a novel method to improve the spatial resolution of Brillouin optical time-domain reflectometry (BOTDR), referred to as synthetic BOTDR (S-BOTDR), and experimentally verify the resolution improvements. Due to the uncertainty relation between position and frequency, the spatial resolution of a conventional BOTDR system has been limited to about one meter. In S-BOTDR, a synthetic spectrum is obtained by combining four Brillouin spectrums measured with different composite pump lights and different composite low-pass filters. We mathematically show that the resolution limit, in principle, for conventional BOTDR can be surpassed by S-BOTDR and experimentally prove that S-BOTDR attained a 10-cm spatial resolution. To the best of our knowledge, this has never been achieved or reported. PMID:24608011
Time Domain Simulations of Arm Locking in LISA
NASA Technical Reports Server (NTRS)
Thorpe, J. I.; Maghami, P.; Livas, Jeff
2011-01-01
Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA). a gravitational-wave observatory sensitive' in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise. spacecraft jitter noise. and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and associated "pulling" of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency.
3D Elevation Program—Virtual USA in 3D
Lukas, Vicki; Stoker, J.M.
2016-04-14
The U.S. Geological Survey (USGS) 3D Elevation Program (3DEP) uses a laser system called ‘lidar’ (light detection and ranging) to create a virtual reality map of the Nation that is very accurate. 3D maps have many uses with new uses being discovered all the time.
The time domain response of some systems for sound reproduction
NASA Astrophysics Data System (ADS)
Nelson, P. A.; Rose, J. F. W.
2006-09-01
The perception in a listener of the existence of a "virtual" source of sound at a prescribed spatial position can be produced by ensuring that the acoustic signals at the listener's ears faithfully replicate those that would be produced by a "real" source at the same position. When loudspeakers are used to transmit the signals, it is necessary to pass the signals intended for presentation at the listener's ears through a matrix of filters that provide the inverse of the matrix of transfer functions that relates the loudspeaker input signals to the listener's ear signals. The characteristics of such filter matrices are profoundly influenced by the conditioning of the matrix to be inverted. This filter design problem is reviewed here by representing the loudspeakers as simple point monopole sources the head of the listener as a rigid sphere. The case of a virtual acoustic imaging system that uses two loudspeakers in order to reproduce the signals at the two ears is first described in some detail and previous work is reviewed. It is confirmed that the time domain response of the reproduced field is of long duration at frequencies where the inversion problem is ill-conditioned. The influence of the presence of the listener's head on this time domain behaviour is also evaluated. The principle is then extended to four input-four output reproduction systems and the computational model is used to explain some previous experimental observations. Finally, the conditioning of five input-four output systems is also examined and shown to have some potentially desirable characteristics.
Applications of pattern classification to time-domain signals
NASA Astrophysics Data System (ADS)
Bertoncini, Crystal Ann
Many different kinds of physics are used in sensors that produce time-domain signals, such as ultrasonics, acoustics, seismology, and electromagnetics. The waveforms generated by these sensors are used to measure events or detect flaws in applications ranging from industrial to medical and defense-related domains. Interpreting the signals is challenging because of the complicated physics of the interaction of the fields with the materials and structures under study. Often the method of interpreting the signal varies by the application, but automatic detection of events in signals is always useful in order to attain results quickly with less human error. One method of automatic interpretation of data is pattern classification, which is a statistical method that assigns predicted labels to raw data associated with known categories. In this work, we use pattern classification techniques to aid automatic detection of events in signals using features extracted by a particular application of the wavelet transform, the Dynamic Wavelet Fingerprint (DWFP), as well as features selected through physical interpretation of the individual applications. The wavelet feature extraction method is general for any time-domain signal, and the classification results can be improved by features drawn for the particular domain. The success of this technique is demonstrated through four applications: the development of an ultrasonographic periodontal probe, the identification of flaw type in Lamb wave tomographic scans of an aluminum pipe, prediction of roof falls in a limestone mine, and automatic identification of individual Radio Frequency Identification (RFID) tags regardless of its programmed code. The method has been shown to achieve high accuracy, sometimes as high as 98%.
A Time Domain Along-Track SAR Interferometry Method
NASA Astrophysics Data System (ADS)
Cao, N.; Lee, H.; Jung, H. C.
2015-12-01
Differential interferometric synthetic aperture radar (DInSAR) has already been proven to be a useful technique for measuring ground displacement at millimeter level. One major drawback of traditional DInSAR technique is that only 1-D deformation in slant range direction can be detected. In order to obtain along-track displacement using a single InSAR pair, two major attempts have been made. The first one is based on cross-correlation between two SAR amplitude images. The second attempt is based on split-beam processing to generate two SAR images from forward- and backward-looking beams. Comparing with the former method, this multiple-aperture SAR interferometry (MAI) can achieve much better measurement accuracy. The major drawback of the MAI method is degraded signal to noise ratio (SNR) and along-track resolution since total along-track integration time decreases in the split-beam procedure. In order to improve the SNR and along-track resolution as well as to extract the terrain displacement in the along-track direction, a time domain along-track SAR interferometry method is proposed in this study. Using traditional time domain backprojection method, the phase component corresponding to slant range direction offset can be estimated and removed from the range compressed SAR signal. Then a phase estimation procedure is implemented to obtain the phase component in the along-track direction. Using ALOS PALSAR data over Kilauea Volcano area in Hawai'i, our experimental results demonstrate the improved performance of the proposed method in extracting 2-D terrain deformation map from one pair of SAR images.
NASA Technical Reports Server (NTRS)
Mickens, Ronald E.
1989-01-01
A family of conditionally stable, forward Euler finite difference equations can be constructed for the simplest equation of Schroedinger type, namely u sub t - iu sub xx. Generalization of this result to physically realistic Schroedinger type equations is presented.
Finite-difference scheme for the numerical solution of the Schroedinger equation
NASA Technical Reports Server (NTRS)
Mickens, Ronald E.; Ramadhani, Issa
1992-01-01
A finite-difference scheme for numerical integration of the Schroedinger equation is constructed. Asymptotically (r goes to infinity), the method gives the exact solution correct to terms of order r exp -2.
NASA Technical Reports Server (NTRS)
Fix, G. J.; Rose, M. E.
1983-01-01
A least squares formulation of the system divu = rho, curlu = zeta is surveyed from the viewpoint of both finite element and finite difference methods. Closely related arguments are shown to establish convergence estimates.
A non-linear constrained optimization technique for the mimetic finite difference method
Manzini, Gianmarco; Svyatskiy, Daniil; Bertolazzi, Enrico; Frego, Marco
2014-09-30
This is a strategy for the construction of monotone schemes in the framework of the mimetic finite difference method for the approximation of diffusion problems on unstructured polygonal and polyhedral meshes.
Lisitsa, Vadim; Tcheverda, Vladimir; Botter, Charlotte
2016-04-15
We present an algorithm for the numerical simulation of seismic wave propagation in models with a complex near surface part and free surface topography. The approach is based on the combination of finite differences with the discontinuous Galerkin method. The discontinuous Galerkin method can be used on polyhedral meshes; thus, it is easy to handle the complex surfaces in the models. However, this approach is computationally intense in comparison with finite differences. Finite differences are computationally efficient, but in general, they require rectangular grids, leading to the stair-step approximation of the interfaces, which causes strong diffraction of the wavefield. In this research we present a hybrid algorithm where the discontinuous Galerkin method is used in a relatively small upper part of the model and finite differences are applied to the main part of the model.
Kim, S.
1994-12-31
Parallel iterative procedures based on domain decomposition techniques are defined and analyzed for the numerical solution of wave propagation by finite element and finite difference methods. For finite element methods, in a Lagrangian framework, an efficient way for choosing the algorithm parameter as well as the algorithm convergence are indicated. Some heuristic arguments for finding the algorithm parameter for finite difference schemes are addressed. Numerical results are presented to indicate the effectiveness of the methods.
Exact finite difference schemes for the non-linear unidirectional wave equation
NASA Technical Reports Server (NTRS)
Mickens, R. E.
1985-01-01
Attention is given to the construction of exact finite difference schemes for the nonlinear unidirectional wave equation that describes the nonlinear propagation of a wave motion in the positive x-direction. The schemes constructed for these equations are compared with those obtained by using the usual procedures of numerical analysis. It is noted that the order of the exact finite difference models is equal to the order of the differential equation.
None
2016-07-12
This video provides an overview of the Sandia National Laboratories developed 3-D World Model Building capability that provides users with an immersive, texture rich 3-D model of their environment in minutes using a laptop and color and depth camera.
NASA Astrophysics Data System (ADS)
van Hecke, Martin; de Reus, Koen; Florijn, Bastiaan; Coulais, Corentin
2014-03-01
We present a class of elastic structures which exhibit collective buckling in 3D, and create these by a 3D printing/moulding technique. Our structures consist of cubic lattice of anisotropic unit cells, and we show that their mechanical properties are programmable via the orientation of these unit cells.
2013-10-30
This video provides an overview of the Sandia National Laboratories developed 3-D World Model Building capability that provides users with an immersive, texture rich 3-D model of their environment in minutes using a laptop and color and depth camera.
2013-10-01
Earth3D is a computer code designed to allow fast calculation of seismic rays and travel times through a 3D model of the Earth. LLNL is using this for earthquake location and global tomography efforts and such codes are of great interest to the Earth Science community.
NASA Technical Reports Server (NTRS)
1977-01-01
A market study of a proposed version of a 3-D eyetracker for initial use at NASA's Ames Research Center was made. The commercialization potential of a simplified, less expensive 3-D eyetracker was ascertained. Primary focus on present and potential users of eyetrackers, as well as present and potential manufacturers has provided an effective means of analyzing the prospects for commercialization.
NASA Astrophysics Data System (ADS)
Walsh, J. R.
2004-02-01
The Euro3D RTN is an EU funded Research Training Network to foster the exploitation of 3D spectroscopy in Europe. 3D spectroscopy is a general term for spectroscopy of an area of the sky and derives its name from its two spatial + one spectral dimensions. There are an increasing number of instruments which use integral field devices to achieve spectroscopy of an area of the sky, either using lens arrays, optical fibres or image slicers, to pack spectra of multiple pixels on the sky (``spaxels'') onto a 2D detector. On account of the large volume of data and the special methods required to reduce and analyse 3D data, there are only a few centres of expertise and these are mostly involved with instrument developments. There is a perceived lack of expertise in 3D spectroscopy spread though the astronomical community and its use in the armoury of the observational astronomer is viewed as being highly specialised. For precisely this reason the Euro3D RTN was proposed to train young researchers in this area and develop user tools to widen the experience with this particular type of data in Europe. The Euro3D RTN is coordinated by Martin M. Roth (Astrophysikalisches Institut Potsdam) and has been running since July 2002. The first Euro3D science conference was held in Cambridge, UK from 22 to 23 May 2003. The main emphasis of the conference was, in keeping with the RTN, to expose the work of the young post-docs who are funded by the RTN. In addition the team members from the eleven European institutes involved in Euro3D also presented instrumental and observational developments. The conference was organized by Andy Bunker and held at the Institute of Astronomy. There were over thirty participants and 26 talks covered the whole range of application of 3D techniques. The science ranged from Galactic planetary nebulae and globular clusters to kinematics of nearby galaxies out to objects at high redshift. Several talks were devoted to reporting recent observations with newly
3D GPR Modeling and Imaging of Burials: Mueschke Historic Cemetery, Houston, Texas
NASA Astrophysics Data System (ADS)
Abdul Aziz, A.; Stewart, R.; Green, S. L.
2014-12-01
3D ground-penetrating radar (GPR) surveys consisting of 6 grids were conducted from October 2013 until April 2014 to delineate burials at the historic Mueschke Cemetery in Houston, Texas. The surveys were primarily to assist historians and archeologists from the Mueschke Cemetery Association and Lone Star College in locating some 13 postulated unmarked burials. Antenna with three frequencies were used: 100 MHz, 250 MHz and 1000 MHz. Most surveys were conducted with the 250 MHz Sensors and Software NOGGIN System which has a maximum penetration of about 3 m. Three methods were used to estimate the soil velocity for time-to-depth conversion: Common mid-point (CMP) surveys, time-to-known depth matching, and hyperbola fitting. All three methods gave an average velocity of 0.06 m/ns in the upper 2 m of the soil. The time-to-known depth method was accomplished by digging a trench (1.5 m deep by 1.5 m wide by 3 m long) about 10 m from the cemetery entrance using a back-hoe. Rebar was hammered horizontally into the trench wall at 0.25 m increments from depths of 1.5 m to 0.25 m. The excavation also allowed us to observe soil strata which transitions from loam, to silty clay to mostly clay with increasing depth. We used finite-difference, time-domain computer modeling to synthesize the response of two types of burials: vaulted or concrete enclosed (post-1940) and non-vaulted or casket only (pre-1940). Modeling results indicate that vaulted burials have a flattened apex signature while non-vaulted burials have signatures that are more hyperbolic. The data were processed using gain, dewow, background removal, filtering, and migration. Survey data over known burials show distinct diffractions and a rectangular shape-correspondent to the computer modeling results. Burials before 1940 have weaker diffractions which complicates their detection. Tree roots, clay patches, and rocks can also present anomalies that must be carefully investigated. Nonetheless, several strong burial
NASA Astrophysics Data System (ADS)
Pezzaniti, J. Larry; Edmondson, Richard; Vaden, Justin; Hyatt, Bryan; Chenault, David B.; Kingston, David; Geulen, Vanilynmae; Newell, Scott; Pettijohn, Brad
2009-02-01
In this paper, we report on the development of a 3D vision system consisting of a flat panel stereoscopic display and auto-converging stereo camera and an assessment of the system's use for robotic driving, manipulation, and surveillance operations. The 3D vision system was integrated onto a Talon Robot and Operator Control Unit (OCU) such that direct comparisons of the performance of a number of test subjects using 2D and 3D vision systems were possible. A number of representative scenarios were developed to determine which tasks benefited most from the added depth perception and to understand when the 3D vision system hindered understanding of the scene. Two tests were conducted at Fort Leonard Wood, MO with noncommissioned officers ranked Staff Sergeant and Sergeant First Class. The scenarios; the test planning, approach and protocols; the data analysis; and the resulting performance assessment of the 3D vision system are reported.
Dawood, A; Marti Marti, B; Sauret-Jackson, V; Darwood, A
2015-12-01
3D printing has been hailed as a disruptive technology which will change manufacturing. Used in aerospace, defence, art and design, 3D printing is becoming a subject of great interest in surgery. The technology has a particular resonance with dentistry, and with advances in 3D imaging and modelling technologies such as cone beam computed tomography and intraoral scanning, and with the relatively long history of the use of CAD CAM technologies in dentistry, it will become of increasing importance. Uses of 3D printing include the production of drill guides for dental implants, the production of physical models for prosthodontics, orthodontics and surgery, the manufacture of dental, craniomaxillofacial and orthopaedic implants, and the fabrication of copings and frameworks for implant and dental restorations. This paper reviews the types of 3D printing technologies available and their various applications in dentistry and in maxillofacial surgery.
NASA Technical Reports Server (NTRS)
Walatka, Pamela P.; Buning, Pieter G.; Pierce, Larry; Elson, Patricia A.
1990-01-01
PLOT3D is a computer graphics program designed to visualize the grids and solutions of computational fluid dynamics. Seventy-four functions are available. Versions are available for many systems. PLOT3D can handle multiple grids with a million or more grid points, and can produce varieties of model renderings, such as wireframe or flat shaded. Output from PLOT3D can be used in animation programs. The first part of this manual is a tutorial that takes the reader, keystroke by keystroke, through a PLOT3D session. The second part of the manual contains reference chapters, including the helpfile, data file formats, advice on changing PLOT3D, and sample command files.
EM modeling for GPIR using 3D FDTD modeling codes
Nelson, S.D.
1994-10-01
An analysis of the one-, two-, and three-dimensional electrical characteristics of structural cement and concrete is presented. This work connects experimental efforts in characterizing cement and concrete in the frequency and time domains with the Finite Difference Time Domain (FDTD) modeling efforts of these substances. These efforts include Electromagnetic (EM) modeling of simple lossless homogeneous materials with aggregate and targets and the modeling dispersive and lossy materials with aggregate and complex target geometries for Ground Penetrating Imaging Radar (GPIR). Two- and three-dimensional FDTD codes (developed at LLNL) where used for the modeling efforts. Purpose of the experimental and modeling efforts is to gain knowledge about the electrical properties of concrete typically used in the construction industry for bridges and other load bearing structures. The goal is to optimize the performance of a high-sample-rate impulse radar and data acquisition system and to design an antenna system to match the characteristics of this material. Results show agreement to within 2 dB of the amplitudes of the experimental and modeled data while the frequency peaks correlate to within 10% the differences being due to the unknown exact nature of the aggregate placement.
PLOT3D/AMES, APOLLO UNIX VERSION USING GMR3D (WITHOUT TURB3D)
NASA Technical Reports Server (NTRS)
Buning, P.
1994-01-01
PLOT3D is an interactive graphics program designed to help scientists visualize computational fluid dynamics (CFD) grids and solutions. Today, supercomputers and CFD algorithms can provide scientists with simulations of such highly complex phenomena that obtaining an understanding of the simulations has become a major problem. Tools which help the scientist visualize the simulations can be of tremendous aid. PLOT3D/AMES offers more functions and features, and has been adapted for more types of computers than any other CFD graphics program. Version 3.6b+ is supported for five computers and graphic libraries. Using PLOT3D, CFD physicists can view their computational models from any angle, observing the physics of problems and the quality of solutions. As an aid in designing aircraft, for example, PLOT3D's interactive computer graphics can show vortices, temperature, reverse flow, pressure, and dozens of other characteristics of air flow during flight. As critical areas become obvious, they can easily be studied more closely using a finer grid. PLOT3D is part of a computational fluid dynamics software cycle. First, a program such as 3DGRAPE (ARC-12620) helps the scientist generate computational grids to model an object and its surrounding space. Once the grids have been designed and parameters such as the angle of attack, Mach number, and Reynolds number have been specified, a "flow-solver" program such as INS3D (ARC-11794 or COS-10019) solves the system of equations governing fluid flow, usually on a supercomputer. Grids sometimes have as many as two million points, and the "flow-solver" produces a solution file which contains density, x- y- and z-momentum, and stagnation energy for each grid point. With such a solution file and a grid file containing up to 50 grids as input, PLOT3D can calculate and graphically display any one of 74 functions, including shock waves, surface pressure, velocity vectors, and particle traces. PLOT3D's 74 functions are organized into
PLOT3D/AMES, APOLLO UNIX VERSION USING GMR3D (WITH TURB3D)
NASA Technical Reports Server (NTRS)
Buning, P.
1994-01-01
PLOT3D is an interactive graphics program designed to help scientists visualize computational fluid dynamics (CFD) grids and solutions. Today, supercomputers and CFD algorithms can provide scientists with simulations of such highly complex phenomena that obtaining an understanding of the simulations has become a major problem. Tools which help the scientist visualize the simulations can be of tremendous aid. PLOT3D/AMES offers more functions and features, and has been adapted for more types of computers than any other CFD graphics program. Version 3.6b+ is supported for five computers and graphic libraries. Using PLOT3D, CFD physicists can view their computational models from any angle, observing the physics of problems and the quality of solutions. As an aid in designing aircraft, for example, PLOT3D's interactive computer graphics can show vortices, temperature, reverse flow, pressure, and dozens of other characteristics of air flow during flight. As critical areas become obvious, they can easily be studied more closely using a finer grid. PLOT3D is part of a computational fluid dynamics software cycle. First, a program such as 3DGRAPE (ARC-12620) helps the scientist generate computational grids to model an object and its surrounding space. Once the grids have been designed and parameters such as the angle of attack, Mach number, and Reynolds number have been specified, a "flow-solver" program such as INS3D (ARC-11794 or COS-10019) solves the system of equations governing fluid flow, usually on a supercomputer. Grids sometimes have as many as two million points, and the "flow-solver" produces a solution file which contains density, x- y- and z-momentum, and stagnation energy for each grid point. With such a solution file and a grid file containing up to 50 grids as input, PLOT3D can calculate and graphically display any one of 74 functions, including shock waves, surface pressure, velocity vectors, and particle traces. PLOT3D's 74 functions are organized into
NASA Astrophysics Data System (ADS)
Gualtieri, L.; Serretti, P.; Morelli, A.
2014-01-01
We present a 3-D P wave velocity model of the crust and shallowest mantle under the Italian region, that includes a revised Moho depth map, obtained by regional seismic travel time tomography. We invert 191,850 Pn and Pg wave arrival times from 6850 earthquakes that occurred within the region from 1988 to 2007, recorded by 264 permanent seismic stations. We adopt a high-resolution linear B-spline model representation, with 0.1° horizontal and 2 km vertical grid spacing, and an accurate finite-difference forward calculation scheme. Our nonlinear iterative inversion process uses the recent European reference 3-D crustal model EPcrust as a priori information. Our resulting model shows two arcs of relatively low velocity in the crust running along both the Alps and the Apennines, underlying the collision belts between plates. Beneath the Western Alps we detect the presence of the Ivrea body, denoted by a strong high P wave velocity anomaly. We also map the Moho discontinuity resulting from the inversion, imaged as the relatively sharp transition between crust and mantle, where P wave velocity steps up to values larger than 8 km/s. This simple condition yields an image quite in agreement with previous studies that use explicit representations for the discontinuity. We find a complex lithospheric structure characterized by shallower Moho close by the Tyrrhenian Sea, intermediate depth along the Adriatic coast, and deepest Moho under the two mountain belts.
Unassisted 3D camera calibration
NASA Astrophysics Data System (ADS)
Atanassov, Kalin; Ramachandra, Vikas; Nash, James; Goma, Sergio R.
2012-03-01
With the rapid growth of 3D technology, 3D image capture has become a critical part of the 3D feature set on mobile phones. 3D image quality is affected by the scene geometry as well as on-the-device processing. An automatic 3D system usually assumes known camera poses accomplished by factory calibration using a special chart. In real life settings, pose parameters estimated by factory calibration can be negatively impacted by movements of the lens barrel due to shaking, focusing, or camera drop. If any of these factors displaces the optical axes of either or both cameras, vertical disparity might exceed the maximum tolerable margin and the 3D user may experience eye strain or headaches. To make 3D capture more practical, one needs to consider unassisted (on arbitrary scenes) calibration. In this paper, we propose an algorithm that relies on detection and matching of keypoints between left and right images. Frames containing erroneous matches, along with frames with insufficiently rich keypoint constellations, are detected and discarded. Roll, pitch yaw , and scale differences between left and right frames are then estimated. The algorithm performance is evaluated in terms of the remaining vertical disparity as compared to the maximum tolerable vertical disparity.
Application of Time Domain Reflectometers in Urban Settings ...
Time domain reflectometers (TDRs) are sensors that measure the volumetric water content of soils and porous media. The sensors consist of stainless steel rods connected to a circuit board in an epoxy housing. An electromagnetic pulse is propagated along the rods. The time, or period, required for the signal to travel down the rods and back varies with the volumetric water content of the surrounding media and temperature. A calibration curve is needed for the specific media. TDRs were developed mostly for agricultural applications; however, the technology has also been applied to forestry and ecological research. This study demonstrates the use of TDRs for quantifying drainage properties in low impact development (LID) stormwater controls, specifically permeable pavement and rain garden systems. TDRs were successfully used to monitor the responses of urban fill, engineered bioretention media, and the aggregate storage layer under permeable pavement to multiple rain events of varying depth, intensity, and duration. The hydrologic performance of permeable pavement and rain garden systems has previously been quantified for underdrain systems, but there have been few studies of systems that drain to the underlying soils. We know of no published studies outlining the use of TDR technology to document drainage properties in media other than soil. In this study TDRs were installed at multiple locations and depths in underlying urban fill soils, engineered bior
TIME-DOMAIN METHODS FOR DIFFUSIVE TRANSPORT IN SOFT MATTER
Fricks, John; Yao, Lingxing; Elston, Timothy C.; Gregory Forest, And M.
2015-01-01
Passive microrheology [12] utilizes measurements of noisy, entropic fluctuations (i.e., diffusive properties) of micron-scale spheres in soft matter to infer bulk frequency-dependent loss and storage moduli. Here, we are concerned exclusively with diffusion of Brownian particles in viscoelastic media, for which the Mason-Weitz theoretical-experimental protocol is ideal, and the more challenging inference of bulk viscoelastic moduli is decoupled. The diffusive theory begins with a generalized Langevin equation (GLE) with a memory drag law specified by a kernel [7, 16, 22, 23]. We start with a discrete formulation of the GLE as an autoregressive stochastic process governing microbead paths measured by particle tracking. For the inverse problem (recovery of the memory kernel from experimental data) we apply time series analysis (maximum likelihood estimators via the Kalman filter) directly to bead position data, an alternative to formulas based on mean-squared displacement statistics in frequency space. For direct modeling, we present statistically exact GLE algorithms for individual particle paths as well as statistical correlations for displacement and velocity. Our time-domain methods rest upon a generalization of well-known results for a single-mode exponential kernel [1, 7, 22, 23] to an arbitrary M-mode exponential series, for which the GLE is transformed to a vector Ornstein-Uhlenbeck process. PMID:26412904
Closed-loop quantum control utilizing time domain maps
NASA Astrophysics Data System (ADS)
Biteen, Julie S.; Geremia, J. M.; Rabitz, Herschel
2003-05-01
Closed-loop laser control of quantum dynamics phenomena may be accomplished through frequency domain manipulations in the laboratory guided by a learning algorithm. This paper presents an alternative method based on the use of nonlinear input→output maps generated in the time domain, although the actual experiments and control optimization are carried out in the frequency domain. The procedure first involves the construction of input→output maps relating the field structure to the observed control performance. These maps are utilized as a substitute for actual experiments in the subsequent optimization stage in order to find the field that drives the system to a specified target. This closed-loop learning process is repeated with a sufficient number of maps until a control field is found that yields the target observable as best as possible. The overall algorithm is simulated with two model quantum systems. It is shown that excellent quality control can be achieved through this sequential learning procedure, even with individual maps that have only modest global accuracy.
A New Time Domain Formulation for Broadband Noise Predictions
NASA Technical Reports Server (NTRS)
Casper, J.; Farassat, F.
2002-01-01
A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specified from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.
A New Time Domain Formulation for Broadband Noise Predictions
NASA Technical Reports Server (NTRS)
Casper, Jay H.; Farassat, Fereidoun
2002-01-01
A new analytic result in acoustics called "Formulation 1B," proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specied from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.
Interpretation of time domain electromagnetic soundings near geological contacts
Wilt, M.J.
1991-12-01
Lateral changes in geology pose a serious problem in data interpretation for any surface geophysical method. Although many geophysical techniques are designed to probe vertically, the source signal invariably spreads laterally, so any lateral variations in geology will affect the measurements and interpretation. This problem is particularly acute for controlled source electromagnetic soundings because only a few techniques are available to interpret the data if lateral effects are present. In this thesis we examine the effects of geological contacts for the time domain electromagnetic sounding method (TDEM). Using two simple two-dimensional models, the truncated thin-sheet and the quarter-space, we examine the system response for several commonly used TDEM sounding configurations. For each system we determine the sensitivity to the contact, establish how to the contact anomaly may be distinguished from other anomalies and, when feasible, develop methods for interpreting the contact geometry and for stripping the contact anomaly from the observed data. Since no numerical models were available when this work was started, data were collected using scale models with a system designed at the University of California at Berkeley. The models were assembled within a table-top modeling tank from sheets or blocks of metal using air or mercury as a host medium. Data were collected with a computer-controlled acquisition system.
Statistical and Mathematical Methods for Synoptic Time Domain Surveys
NASA Astrophysics Data System (ADS)
Mahabal, Ashish A.; SAMSI Synoptic Surveys Time Domain Working Group
2017-01-01
Recent advances in detector technology, electronics, data storage, and computation have enabled astronomers to collect larger and larger datasets, and moreover, pose interesting questions to answer with those data. The complexity of the data allows data science techniques to be used. These have to be grounded in sound techniques. Identify interesting mathematical and statistical challenges and working on their solutions is one of the aims of the year-long ‘Statistical, Mathematical and Computational Methods for Astronomy (ASTRO)’ program of SAMSI. Of the many working groups that have been formed, one is on Synoptic Time Domain Surveys. Within this we have various subgroups discussing topics such as Designing Statistical Features for Optimal Classification, Scheduling Observations, Incorporating Unstructured Information, Detecting Outliers, Lightcurve Decomposition and Interpolation, Domain Adaptation, and also Designing a Data Challenge. We will briefly highlight some of the work going on in these subgroups along with their interconnections, and the plans for the near future. We will also highlight the overlaps with the other SAMSI working groups and also indicate how the wider astronomy community can both participate and benefit from the activities.
Demonstration of Time Domain Multiplexed Readout for Magnetically Coupled Calorimeters
NASA Technical Reports Server (NTRS)
Porst, J.-P.; Adams, J. S.; Balvin, M.; Bandler, S.; Beyer, J.; Busch, S. E.; Drung, D.; Seidel, G. M.; Smith, S. J.; Stevenson, T. R.
2012-01-01
Magnetically coupled calorimeters (MCC) have extremely high potential for x-ray applications due to the inherent high energy resolution capability and being non-dissipative. Although very high energy-resolution has been demonstrated, until now there has been no demonstration of multiplexed read-out. We report on the first realization of a time domain multiplexed (TDM) read-out. While this has many similarities with TDM of transition-edge-sensors (TES), for MGGs the energy resolution is limited by the SQUID read-out noise and requires the well established scheme to be altered in order to minimize degradation due to noise aliasing effects. In cur approach, each pixel is read out by a single first stage SQUID (SQ1) that is operated in open loop. The outputs of the SQ1 s are low-pass filtered with an array of low cross-talk inductors, then fed into a single-stage SQUID TD multiplexer. The multiplexer is addressed from room temperature and read out through a single amplifier channel. We present results achieved with a new detector platform. Noise performance is presented and compared to expectations. We have demonstrated multiplexed X-ray spectroscopy at 5.9keV with delta_FWHM=10eV. In an optimized setup, we show it is possible to multiplex 32 detectors without significantly degrading the Intrinsic detector resolution.
Nitrocellulose membrane sample holder using for terahertz time domain spectroscopy
NASA Astrophysics Data System (ADS)
Zhao, Xiaojing; Liu, Shangjian; Wang, Cuicui; Zuo, Jian; Zhang, Cunlin
2016-11-01
Terahertz (THz) technology has promising applications for the detection and identification of materials because it has a great advantage in measuring material fingerprint spectrum. Terahertz time-domain spectroscopy (THz-TDS) is a key technique that is applied to spectroscopic measurement of materials. However, it is difficult to press a pellet with small mass of sample and a bulking medium such as polyethylene (PE) powder usually need to be added. Characteristic absorption peaks of the solution in liquid cell is hard to be observed due to the interaction between materials and water molecules. Therefore, one method using the hydrophilic nitrocellulose (NC) membrane as a sample holder was applied to detect samples in an aqueous medium by THz-TDS. In this study, the α-lactose samples were mixed with 20 μl of deionized water and then applied directly onto the double-layered NC membrane sample holder. This mixture is located on the gap of two piece of NC membranes. Firstly the NC membranes with different pore sizes were tested in the experiment. And then the α-lactose solutions with different concentrations were measured on the NC with different pore sizes. Consequently, the small mass of samples can be detected and the characteristic absorption peaks become stronger with the increase of NC pore size. Moreover, compared to the traditional pellet-making and liquid cell detection, this membrane method is more convenient and easy to operate.
Determining Phthalic Acid Esters Using Terahertz Time Domain Spectroscopy
NASA Astrophysics Data System (ADS)
Liu, L.; Shen, L.; Yang, F.; Han, F.; Hu, P.; Song, M.
2016-09-01
In this report terahertz time domain spectroscopy (THz-TDS) is applied for determining phthalic acid esters (PAEs) in standard materials. We reported the THz transmission spectrum in the frequency range of 0.2 to 2.0 THz for three PAEs: di-n-butyl phthalate (DBP), di-isononyl phthalate (DINP), and di-2-ethylhexyl phthalate ester (DEHP). The study provided the refractive indices and absorption features of these materials. The absorption spectra of three PAEs were simulated by using Gaussian software with Density Functional Theory (DFT) methods. For pure standard PAEs, the values of the refractive indices changed between 1.50 and 1.60. At 1.0 THz, the refractive indices were 1.524, 1.535, and 1.563 for DINP, DEHP, and DBP, respectively. In this experiment different concentrations of DBP were investigated using THz-TDS. Changes were measured in the low THz frequency range for refractive indices and characteristic absorption. The results indicated that THz-TDS is promising as a new method in determining PAEs in many materials. The results of this study could be used to support the practical application of THz-TDS in quality detection and food monitoring. In particular, this new technique could be used in detecting hazardous materials and other substances present in wine or foods.
Time-domain measurement of broadband coherent Cherenkov radiation
Miocinovic, P.; Gorham, P. W.; Guillian, E.; Milincic, R.; Field, R. C.; Walz, D.; Saltzberg, D.; Williams, D.
2006-08-15
We report on further analysis of coherent microwave Cherenkov impulses emitted via the Askaryan mechanism from high-energy electromagnetic showers produced at the Stanford Linear Accelerator Center (SLAC). In this report, the time-domain based analysis of the measurements made with a broadband (nominally 1-18 GHz) log periodic dipole array antenna is described. The theory of a transmit-receive antenna system based on time-dependent effective height operator is summarized and applied to fully characterize the measurement antenna system and to reconstruct the electric field induced via the Askaryan process. The observed radiation intensity and phase as functions of frequency were found to agree with expectations from 0.75-11.5 GHz within experimental errors on the normalized electric field magnitude and the relative phase; {sigma}{sub RvertcalbarEverticalbar}=0.039 {mu}V/MHz/TeV and {sigma}{sub {phi}}=17 deg. This is the first time this agreement has been observed over such a broad bandwidth, and the first measurement of the relative phase variation of an Askaryan pulse. The importance of validation of the Askaryan mechanism is significant since it is viewed as the most promising way to detect cosmogenic neutrino fluxes at E{sub {nu}}(greater-or-similar sign)10{sup 15} eV.
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
Miocinovic, P.; Field, R.C.; Gorham, P.W.; Guillian, E.; Milincic, R.; Saltzberg, D.; Walz, D.; Williams, D.; /UCLA
2006-03-13
We report on further analysis of coherent microwave Cherenkov impulses emitted via the Askaryan mechanism from high-energy electromagnetic showers produced at the Stanford Linear Accelerator Center (SLAC). In this report, the time-domain based analysis of the measurements made with a broadband (nominally 1-18 GHz) log periodic dipole antenna (LPDA) is described. The theory of a transmit-receive antenna system based on time-dependent effective height operator is summarized and applied to fully characterize the measurement antenna system and to reconstruct the electric field induced via the Askaryan process. The observed radiation intensity and phase as functions of frequency were found to agree with expectations from 0.75-11.5 GHz within experimental errors on the normalized electric field magnitude and the relative phase; {sigma}{sub R|E|} = 0.039 {micro}V/MHz/TeV and {sigma}{sub {phi}} = 17{sup o}. This is the first time this agreement has been observed over such a broad bandwidth, and the first measurement of the relative phase variation of an Askaryan pulse. The importance of validation of the Askaryan mechanism is significant since it is viewed as the most promising way to detect cosmogenic neutrino fluxes at E{sub v} {ge} 10{sup 15} eV.
Time domain simulations of arm locking in LISA
Thorpe, J. I.; Livas, J.; Maghami, P.
2011-06-15
Arm locking is a proposed laser frequency stabilization technique for the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that compose LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of a Kalman-filter-based arm-locking system that includes the expected limiting noise sources as well as the effects of imperfect a priori knowledge of the constellation geometry on which the design is based. We use the simulation to study aspects of the system performance that are difficult to capture in a steady-state frequency-domain analysis such as frequency pulling of the master laser due to errors in estimates of heterodyne frequency. We find that our implementation meets requirements on both the noise and dynamic range of the laser frequency with acceptable tolerances and that the design is sufficiently insensitive to errors in the estimated constellation geometry that the required performance can be maintained for the longest continuous measurement intervals expected for the LISA mission.
A 128 Multiplexing Factor Time-Domain SQUID Multiplexer
NASA Astrophysics Data System (ADS)
Prêle, D.; Voisin, F.; Piat, M.; Decourcelle, T.; Perbost, C.; Chapron, C.; Rambaud, D.; Maestre, S.; Marty, W.; Montier, L.
2016-07-01
A cryogenic 128:1 Time-Domain Multiplexer (TDM) has been developed for the readout of kilo-pixel Transition Edge Sensor (TES) arrays dedicated to the Q&U Bolometric Interferometer for Cosmology (QUBIC) instrument which aims to measure the B-mode polarization of the Cosmic Microwave Background. Superconducting QUantum Interference Devices (SQUIDs) are usually used to read out TESs. Moreover, SQUIDs are used to build TDM by biasing sequentially the SQUIDs connected together—one for each TES. In addition to this common technique which allows a typical 32 multiplexing factor, a cryogenic integrated circuit provides a 4:1 second multiplexing stage. This cryogenic integrated circuit is one of the original part of our TDM achieving an unprecedented 128 multiplexing factor. We present these two dimension TDM stages: topology of the SQUID multiplexer, operation of the cryogenic integrated circuit, and integration of the full system to read out a TES array dedicated to the QUBIC instrument. Flux-locked loop operation in multiplexed mode is also discussed.
Time domain simulations of preliminary breakdown pulses in natural lightning
Carlson, B E; Liang, C; Bitzer, P; Christian, H
2015-01-01
Lightning discharge is a complicated process with relevant physical scales spanning many orders of magnitude. In an effort to understand the electrodynamics of lightning and connect physical properties of the channel to observed behavior, we construct a simulation of charge and current flow on a narrow conducting channel embedded in three-dimensional space with the time domain electric field integral equation, the method of moments, and the thin-wire approximation. The method includes approximate treatment of resistance evolution due to lightning channel heating and the corona sheath of charge surrounding the lightning channel. Focusing our attention on preliminary breakdown in natural lightning by simulating stepwise channel extension with a simplified geometry, our simulation reproduces the broad features observed in data collected with the Huntsville Alabama Marx Meter Array. Some deviations in pulse shape details are evident, suggesting future work focusing on the detailed properties of the stepping mechanism. Key Points Preliminary breakdown pulses can be reproduced by simulated channel extension Channel heating and corona sheath formation are crucial to proper pulse shape Extension processes and channel orientation significantly affect observations PMID:26664815
Time-domain simulation of a guitar: model and method.
Derveaux, Grégoire; Chaigne, Antoine; Joly, Patrick; Bécache, Eliane
2003-12-01
This paper presents a three-dimensional time-domain numerical model of the vibration and acoustic radiation from a guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard, and the sound radiation. A specific spectral method is used for solving the Kirchhoff-Love's dynamic top plate model for a damped, heterogeneous orthotropic material. The air-plate interaction is solved with a fictitious domain method, and a conservative scheme is used for the time discretization. Frequency analysis is performed on the simulated sound pressure and plate velocity waveforms in order to evaluate quantitatively the transfer of energy through the various components of the coupled system: from the string to the soundboard and from the soundboard to the air. The effects of some structural changes in soundboard thickness and cavity volume on the produced sounds are presented and discussed. Simulations of the same guitar in three different cases are also performed: "in vacuo," in air with a perfectly rigid top plate, and in air with an elastic top plate. This allows comparisons between structural, acoustic, and structural-acoustic modes of the instrument. Finally, attention is paid to the evolution with time of the spatial pressure field. This shows, in particular, the complex evolution of the directivity pattern in the near field of the instrument, especially during the attack.
Time domain functional NIRS imaging for human brain mapping.
Torricelli, Alessandro; Contini, Davide; Pifferi, Antonio; Caffini, Matteo; Re, Rebecca; Zucchelli, Lucia; Spinelli, Lorenzo
2014-01-15
This review is aimed at presenting the state-of-the-art of time domain (TD) functional near-infrared spectroscopy (fNIRS). We first introduce the physical principles, the basics of modeling and data analysis. Basic instrumentation components (light sources, detection techniques, and delivery and collection systems) of a TD fNIRS system are described. A survey of past, existing and next generation TD fNIRS systems used for research and clinical studies is presented. Performance assessment of TD fNIRS systems and standardization issues are also discussed. Main strengths and weakness of TD fNIRS are highlighted, also in comparison with continuous wave (CW) fNIRS. Issues like quantification of the hemodynamic response, penetration depth, depth selectivity, spatial resolution and contrast-to-noise ratio are critically examined, with the help of experimental results performed on phantoms or in vivo. Finally we give an account on the technological developments that would pave the way for a broader use of TD fNIRS in the neuroimaging community.
Time domain reflectometry as a rock mass monitoring technique
Francke, J.L.; Terrill, L.J.; Allen, W.W.
1996-06-01
This paper describes the practices and methods used in a study of Time Domain Reflectometry (TDR) as an inexpensive deformation monitoring tool in underground excavations at the Waste Isolation Pilot Plant (WIPP). The WIPP is being developed near Carlsbad, New Mexico, for the disposal of transuranic nuclear wastes in bedded salt 655 m (2150 ft) below the surface. Data collected from WIPP geomechanical monitoring are used to characterize conditions, confirm design assumptions, and understand and predict the performance of the deep salt excavation. The geomechanical monitoring techniques ranging from inspection of observation boreholes to advanced radar surveys. In 1989 TDR was introduced as a monitoring tool with the installation of 12.7 mm (0.5 in) diameter TDR cables in the underground excavations. In 1993, a new TDR system was installed in a separate location. Based on experience with the previous installation, enhancements were implemented into the new TDR system that: (1) extended the period of performance by increasing cable diameter to 22. 2 mm (0.875 in), (2) increased accuracy in locating areas of deformation by aligning cables with nearby observation boreholes, and (3) improved data acquisition and analyses using a standard laptop computer, eliminating the chart recorder previously used. In summary, the results of a correlation between the TDR signatures to nearby observation boreholes and geomechanical instrumentation will be presented.
Towards next generation time-domain diffuse optics devices
NASA Astrophysics Data System (ADS)
Dalla Mora, Alberto; Contini, Davide; Arridge, Simon R.; Martelli, Fabrizio; Tosi, Alberto; Boso, Gianluca; Farina, Andrea; Durduran, Turgut; Martinenghi, Edoardo; Torricelli, Alessandro; Pifferi, Antonio
2015-03-01
Diffuse Optics is growing in terms of applications ranging from e.g. oximetry, to mammography, molecular imaging, quality assessment of food and pharmaceuticals, wood optics, physics of random media. Time-domain (TD) approaches, although appealing in terms of quantitation and depth sensibility, are presently limited to large fiber-based systems, with limited number of source-detector pairs. We present a miniaturized TD source-detector probe embedding integrated laser sources and single-photon detectors. Some electronics are still external (e.g. power supply, pulse generators, timing electronics), yet full integration on-board using already proven technologies is feasible. The novel devices were successfully validated on heterogeneous phantoms showing performances comparable to large state-of-the-art TD rack-based systems. With an investigation based on simulations we provide numerical evidence that the possibility to stack many TD compact source-detector pairs in a dense, null source-detector distance arrangement could yield on the brain cortex about 1 decade higher contrast as compared to a continuous wave (CW) approach. Further, a 3-fold increase in the maximum depth (down to 6 cm) is estimated, opening accessibility to new organs such as the lung or the heart. Finally, these new technologies show the way towards compact and wearable TD probes with orders of magnitude reduction in size and cost, for a widespread use of TD devices in real life.
THz Time-Domain Spectroscopy of Complex Interstellar Ice Analogs
NASA Astrophysics Data System (ADS)
Ioppolo, Sergio; McGuire, Brett A.; Allodi, Marco A.; de Vries, Xander; Finneran, Ian; Carroll, Brandon; Blake, Geoffrey
2014-06-01
It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 - 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, and CH4) compared to more complex molecules (e.g., HCOOH, CH3COOH, CH3CHO, (CH3)2CO, HCOOCH3, and HCOOC2H5). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.
Time domain simulations of arm locking in LISA
NASA Astrophysics Data System (ADS)
Thorpe, J. I.; Maghami, P.; Livas, J.
2011-06-01
Arm locking is a proposed laser frequency stabilization technique for the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that compose LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of a Kalman-filter-based arm-locking system that includes the expected limiting noise sources as well as the effects of imperfect a priori knowledge of the constellation geometry on which the design is based. We use the simulation to study aspects of the system performance that are difficult to capture in a steady-state frequency-domain analysis such as frequency pulling of the master laser due to errors in estimates of heterodyne frequency. We find that our implementation meets requirements on both the noise and dynamic range of the laser frequency with acceptable tolerances and that the design is sufficiently insensitive to errors in the estimated constellation geometry that the required performance can be maintained for the longest continuous measurement intervals expected for the LISA mission.
Seismic analysis of wind turbines in the time domain
NASA Astrophysics Data System (ADS)
Witcher, D.
2005-01-01
The analysis of wind turbine loading associated with earthquakes is clearly important when designing for and assessing the feasibility of wind farms in seismically active regions. The approach taken for such analysis is generally based on codified methods which have been developed for the assessment of seismic loads acting on buildings. These methods are not able to deal properly with the aeroelastic interaction of the dynamic motion of the wind turbine structure with either the wind loading acting on the rotor blades or the response of the turbine controller. This article presents an alternative approach, which is to undertake the calculation in the time domain. In this case a full aeroelastic model of the wind turbine subject to turbulent wind loading is further excited by ground motion corresponding to the earthquake. This capability has been introduced to the GH Bladed wind turbine simulation package. The software can be used to compute the combined wind and earthquake loading of a wind turbine given a definition of the external conditions for an appropriate series of load cases. This article discusses the method and presents example results. Copyright
Time-domain simulation of a guitar: Model and method
NASA Astrophysics Data System (ADS)
Derveaux, Grégoire; Chaigne, Antoine; Joly, Patrick; Bécache, Eliane
2003-12-01
This paper presents a three-dimensional time-domain numerical model of the vibration and acoustic radiation from a guitar. The model involves the transverse displacement of the string excited by a force pulse, the flexural motion of the soundboard, and the sound radiation. A specific spectral method is used for solving the Kirchhoff-Love's dynamic top plate model for a damped, heterogeneous orthotropic material. The air-plate interaction is solved with a fictitious domain method, and a conservative scheme is used for the time discretization. Frequency analysis is performed on the simulated sound pressure and plate velocity waveforms in order to evaluate quantitatively the transfer of energy through the various components of the coupled system: from the string to the soundboard and from the soundboard to the air. The effects of some structural changes in soundboard thickness and cavity volume on the produced sounds are presented and discussed. Simulations of the same guitar in three different cases are also performed: ``in vacuo,'' in air with a perfectly rigid top plate, and in air with an elastic top plate. This allows comparisons between structural, acoustic, and structural-acoustic modes of the instrument. Finally, attention is paid to the evolution with time of the spatial pressure field. This shows, in particular, the complex evolution of the directivity pattern in the near field of the instrument, especially during the attack.
A finite-difference frequency-domain code for electromagnetic induction tomography
Sharpe, R M; Berryman, J G; Buettner, H M; Champagne, N J.,II; Grant, J B
1998-12-17
We are developing a new 3D code for application to electromagnetic induction tomography and applications to environmental imaging problems. We have used the finite-difference frequency- domain formulation of Beilenhoff et al. (1992) and the anisotropic PML (perfectly matched layer) approach (Berenger, 1994) to specify boundary conditions following Wu et al. (1997). PML deals with the fact that the computations must be done in a finite domain even though the real problem is effectively of infinite extent. The resulting formulas for the forward solver reduce to a problem of the form Ax = y, where A is a non-Hermitian matrix with real values off the diagonal and complex values along its diagonal. The matrix A may be either symmetric or nonsymmetric depending on details of the boundary conditions chosen (i.e., the particular PML used in the application). The basic equation must be solved for the vector x (which represents field quantities such as electric and magnetic fields) with the vector y determined by the boundary conditions and transmitter location. Of the many forward solvers that could be used for this system, relatively few have been thoroughly tested for the type of matrix encountered in our problem. Our studies of the stability characteristics of the Bi-CG algorithm raised questions about its reliability and uniform accuracy for this application. We have found the stability characteristics of Bi-CGSTAB [an alternative developed by van der Vorst (1992) for such problems] to be entirely adequate for our application, whereas the standard Bi-CG was quite inadequate. We have also done extensive validation of our code using semianalytical results as well as other codes. The new code is written in Fortran and is designed to be easily parallelized, but we have not yet tested this feature of the code. An adjoint method is being developed for solving the inverse problem for conductivity imaging (for mapping underground plumes), and this approach, when ready, will
2007-11-02
AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 5 Feb 98 4. TITLE AND SUBTITLE 3D Scan Systems Integration REPORT TYPE AND DATES COVERED...2-89) Prescribed by ANSI Std. Z39-1 298-102 [ EDO QUALITY W3PECTEDI DLA-ARN Final Report for US Defense Logistics Agency on DDFG-T2/P3: 3D...SCAN SYSTEMS INTEGRATION Contract Number SPO100-95-D-1014 Contractor Ohio University Delivery Order # 0001 Delivery Order Title 3D Scan Systems
3D seismic imaging on massively parallel computers
Womble, D.E.; Ober, C.C.; Oldfield, R.
1997-02-01
The ability to image complex geologies such as salt domes in the Gulf of Mexico and thrusts in mountainous regions is a key to reducing the risk and cost associated with oil and gas exploration. Imaging these structures, however, is computationally expensive. Datasets can be terabytes in size, and the processing time required for the multiple iterations needed to produce a velocity model can take months, even with the massively parallel computers available today. Some algorithms, such as 3D, finite-difference, prestack, depth migration remain beyond the capacity of production seismic processing. Massively parallel processors (MPPs) and algorithms research are the tools that will enable this project to provide new seismic processing capabilities to the oil and gas industry. The goals of this work are to (1) develop finite-difference algorithms for 3D, prestack, depth migration; (2) develop efficient computational approaches for seismic imaging and for processing terabyte datasets on massively parallel computers; and (3) develop a modular, portable, seismic imaging code.
Simon, Carl G; Yang, Yanyin; Dorsey, Shauna M; Ramalingam, Murugan; Chatterjee, Kaushik
2011-01-01
We have developed a combinatorial platform for fabricating tissue scaffold arrays that can be used for screening cell-material interactions. Traditional research involves preparing samples one at a time for characterization and testing. Combinatorial and high-throughput (CHT) methods lower the cost of research by reducing the amount of time and material required for experiments by combining many samples into miniaturized specimens. In order to help accelerate biomaterials research, many new CHT methods have been developed for screening cell-material interactions where materials are presented to cells as a 2D film or surface. However, biomaterials are frequently used to fabricate 3D scaffolds, cells exist in vivo in a 3D environment and cells cultured in a 3D environment in vitro typically behave more physiologically than those cultured on a 2D surface. Thus, we have developed a platform for fabricating tissue scaffold libraries where biomaterials can be presented to cells in a 3D format.
NASA Astrophysics Data System (ADS)
Lee-Elkin, Forest
2008-04-01
Three dimensional (3D) autofocus remains a significant challenge for the development of practical 3D multipass radar imaging. The current 2D radar autofocus methods are not readily extendable across sensor passes. We propose a general framework that allows a class of data adaptive solutions for 3D auto-focus across passes with minimal constraints on the scene contents. The key enabling assumption is that portions of the scene are sparse in elevation which reduces the number of free variables and results in a system that is simultaneously solved for scatterer heights and autofocus parameters. The proposed method extends 2-pass interferometric synthetic aperture radar (IFSAR) methods to an arbitrary number of passes allowing the consideration of scattering from multiple height locations. A specific case from the proposed autofocus framework is solved and demonstrates autofocus and coherent multipass 3D estimation across the 8 passes of the "Gotcha Volumetric SAR Data Set" X-Band radar data.
NASA Astrophysics Data System (ADS)
Moczo, P.; Kristek, J.; Galis, M.; Chaljub, E.; Chen, X.; Zhang, Z.
2012-04-01
Numerical modeling of earthquake ground motion in sedimentary basins and valleys often has to account for the P-wave to S-wave speed ratios (VP/VS) as large as five and even larger, mainly in sediments below groundwater level. The ratio can attain values larger than 10 - the unconsolidated lake sediments in Ciudad de México are a good example. At the same time, accuracy of the numerical schemes with respect to VP/VS has not been sufficiently analyzed. The numerical schemes are often applied without adequate check of the accuracy. We present theoretical analysis and numerical comparison of 18 3D numerical time-domain explicit schemes for modeling seismic motion for their accuracy with the varying VP/VS. The schemes are based on the finite-difference, spectral-element, finite-element and discontinuous-Galerkin methods. All schemes are presented in a unified form. Theoretical analysis compares accuracy of the schemes in terms of local errors in amplitude and vector difference. In addition to the analysis we compare numerically simulated seismograms with exact solutions for canonical configurations. We compare accuracy of the schemes in terms of the local errors, grid dispersion and full wavefield simulations with respect to the structure of the numerical schemes.
NASA Astrophysics Data System (ADS)
Reimer, Ashton S.; Cheviakov, Alexei F.
2013-03-01
A Matlab-based finite-difference numerical solver for the Poisson equation for a rectangle and a disk in two dimensions, and a spherical domain in three dimensions, is presented. The solver is optimized for handling an arbitrary combination of Dirichlet and Neumann boundary conditions, and allows for full user control of mesh refinement. The solver routines utilize effective and parallelized sparse vector and matrix operations. Computations exhibit high speeds, numerical stability with respect to mesh size and mesh refinement, and acceptable error values even on desktop computers. Catalogue identifier: AENQ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AENQ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License v3.0 No. of lines in distributed program, including test data, etc.: 102793 No. of bytes in distributed program, including test data, etc.: 369378 Distribution format: tar.gz Programming language: Matlab 2010a. Computer: PC, Macintosh. Operating system: Windows, OSX, Linux. RAM: 8 GB (8, 589, 934, 592 bytes) Classification: 4.3. Nature of problem: To solve the Poisson problem in a standard domain with “patchy surface”-type (strongly heterogeneous) Neumann/Dirichlet boundary conditions. Solution method: Finite difference with mesh refinement. Restrictions: Spherical domain in 3D; rectangular domain or a disk in 2D. Unusual features: Choice between mldivide/iterative solver for the solution of large system of linear algebraic equations that arise. Full user control of Neumann/Dirichlet boundary conditions and mesh refinement. Running time: Depending on the number of points taken and the geometry of the domain, the routine may take from less than a second to several hours to execute.
Combinatorial 3D Mechanical Metamaterials
NASA Astrophysics Data System (ADS)
Coulais, Corentin; Teomy, Eial; de Reus, Koen; Shokef, Yair; van Hecke, Martin
2015-03-01
We present a class of elastic structures which exhibit 3D-folding motion. Our structures consist of cubic lattices of anisotropic unit cells that can be tiled in a complex combinatorial fashion. We design and 3d-print this complex ordered mechanism, in which we combine elastic hinges and defects to tailor the mechanics of the material. Finally, we use this large design space to encode smart functionalities such as surface patterning and multistability.
SOME NEW FINITE DIFFERENCE METHODS FOR HELMHOLTZ EQUATIONS ON IRREGULAR DOMAINS OR WITH INTERFACES.
Wan, Xiaohai; Li, Zhilin
2012-06-01
Solving a Helmholtz equation Δu + λu = f efficiently is a challenge for many applications. For example, the core part of many efficient solvers for the incompressible Navier-Stokes equations is to solve one or several Helmholtz equations. In this paper, two new finite difference methods are proposed for solving Helmholtz equations on irregular domains, or with interfaces. For Helmholtz equations on irregular domains, the accuracy of the numerical solution obtained using the existing augmented immersed interface method (AIIM) may deteriorate when the magnitude of λ is large. In our new method, we use a level set function to extend the source term and the PDE to a larger domain before we apply the AIIM. For Helmholtz equations with interfaces, a new maximum principle preserving finite difference method is developed. The new method still uses the standard five-point stencil with modifications of the finite difference scheme at irregular grid points. The resulting coefficient matrix of the linear system of finite difference equations satisfies the sign property of the discrete maximum principle and can be solved efficiently using a multigrid solver. The finite difference method is also extended to handle temporal discretized equations where the solution coefficient λ is inversely proportional to the mesh size.
Improving sub-grid scale accuracy of boundary features in regional finite-difference models
NASA Astrophysics Data System (ADS)
Panday, Sorab; Langevin, Christian D.
2012-06-01
As an alternative to grid refinement, the concept of a ghost node, which was developed for nested grid applications, has been extended towards improving sub-grid scale accuracy of flow to conduits, wells, rivers or other boundary features that interact with a finite-difference groundwater flow model. The formulation is presented for correcting the regular finite-difference groundwater flow equations for confined and unconfined cases, with or without Newton Raphson linearization of the nonlinearities, to include the Ghost Node Correction (GNC) for location displacement. The correction may be applied on the right-hand side vector for a symmetric finite-difference Picard implementation, or on the left-hand side matrix for an implicit but asymmetric implementation. The finite-difference matrix connectivity structure may be maintained for an implicit implementation by only selecting contributing nodes that are a part of the finite-difference connectivity. Proof of concept example problems are provided to demonstrate the improved accuracy that may be achieved through sub-grid scale corrections using the GNC schemes.
Improving sub-grid scale accuracy of boundary features in regional finite-difference models
Panday, Sorab; Langevin, Christian D.
2012-01-01
As an alternative to grid refinement, the concept of a ghost node, which was developed for nested grid applications, has been extended towards improving sub-grid scale accuracy of flow to conduits, wells, rivers or other boundary features that interact with a finite-difference groundwater flow model. The formulation is presented for correcting the regular finite-difference groundwater flow equations for confined and unconfined cases, with or without Newton Raphson linearization of the nonlinearities, to include the Ghost Node Correction (GNC) for location displacement. The correction may be applied on the right-hand side vector for a symmetric finite-difference Picard implementation, or on the left-hand side matrix for an implicit but asymmetric implementation. The finite-difference matrix connectivity structure may be maintained for an implicit implementation by only selecting contributing nodes that are a part of the finite-difference connectivity. Proof of concept example problems are provided to demonstrate the improved accuracy that may be achieved through sub-grid scale corrections using the GNC schemes.
Minimum divergence viscous flow simulation through finite difference and regularization techniques
NASA Astrophysics Data System (ADS)
Victor, Rodolfo A.; Mirabolghasemi, Maryam; Bryant, Steven L.; Prodanović, Maša
2016-09-01
We develop a new algorithm to simulate single- and two-phase viscous flow through a three-dimensional Cartesian representation of the porous space, such as those available through X-ray microtomography. We use the finite difference method to discretize the governing equations and also propose a new method to enforce the incompressible flow constraint under zero Neumann boundary conditions for the velocity components. Finite difference formulation leads to fast parallel implementation through linear solvers for sparse matrices, allowing relatively fast simulations, while regularization techniques used on solving inverse problems lead to the desired incompressible fluid flow. Tests performed using benchmark samples show good agreement with experimental/theoretical values. Additional tests are run on Bentheimer and Buff Berea sandstone samples with available laboratory measurements. We compare the results from our new method, based on finite differences, with an open source finite volume implementation as well as experimental results, specifically to evaluate the benefits and drawbacks of each method. Finally, we calculate relative permeability by using this modified finite difference technique together with a level set based algorithm for multi-phase fluid distribution in the pore space. To our knowledge this is the first time regularization techniques are used in combination with finite difference fluid flow simulations.
The Time Domain Spectroscopic Survey: Variable Selection and Anticipated Results
NASA Astrophysics Data System (ADS)
Morganson, Eric; Green, Paul J.; Anderson, Scott F.; Ruan, John J.; Myers, Adam D.; Eracleous, Michael; Kelly, Brandon; Badenes, Carlos; Bañados, Eduardo; Blanton, Michael R.; Bershady, Matthew A.; Borissova, Jura; Nielsen Brandt, William; Burgett, William S.; Chambers, Kenneth; Draper, Peter W.; Davenport, James R. A.; Flewelling, Heather; Garnavich, Peter; Hawley, Suzanne L.; Hodapp, Klaus W.; Isler, Jedidah C.; Kaiser, Nick; Kinemuchi, Karen; Kudritzki, Rolf P.; Metcalfe, Nigel; Morgan, Jeffrey S.; Pâris, Isabelle; Parvizi, Mahmoud; Poleski, Radosław; Price, Paul A.; Salvato, Mara; Shanks, Tom; Schlafly, Eddie F.; Schneider, Donald P.; Shen, Yue; Stassun, Keivan; Tonry, John T.; Walter, Fabian; Waters, Chris Z.
2015-06-01
We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an Sloan Digital Sky Survey (SDSS)-IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable stars and active galactic nuclei across 7500 deg2 selected from a combination of SDSS and multi-epoch Pan-STARRS1 photometry. TDSS will be the largest spectroscopic survey to explicitly target variable objects, avoiding pre-selection on the basis of colors or detailed modeling of specific variability characteristics. Kernel Density Estimate analysis of our target population performed on SDSS Stripe 82 data suggests our target sample will be 95% pure (meaning 95% of objects we select have genuine luminosity variability of a few magnitudes or more). Our final spectroscopic sample will contain roughly 135,000 quasars and 85,000 stellar variables, approximately 4000 of which will be RR Lyrae stars which may be used as outer Milky Way probes. The variability-selected quasar population has a smoother redshift distribution than a color-selected sample, and variability measurements similar to those we develop here may be used to make more uniform quasar samples in large surveys. The stellar variable targets are distributed fairly uniformly across color space, indicating that TDSS will obtain spectra for a wide variety of stellar variables including pulsating variables, stars with significant chromospheric activity, cataclysmic variables, and eclipsing binaries. TDSS will serve as a pathfinder mission to identify and characterize the multitude of variable objects that will be detected photometrically in even larger variability surveys such as Large Synoptic Survey Telescope.
Integral ceramic superstructure evaluation using time domain optical coherence tomography
NASA Astrophysics Data System (ADS)
Sinescu, Cosmin; Bradu, Adrian; Topala, Florin I.; Negrutiu, Meda Lavinia; Duma, Virgil-Florin; Podoleanu, Adrian G.
2014-02-01
Optical Coherence Tomography (OCT) is a non-invasive low coherence interferometry technique that includes several technologies (and the corresponding devices and components), such as illumination and detection, interferometry, scanning, adaptive optics, microscopy and endoscopy. From its large area of applications, we consider in this paper a critical aspect in dentistry - to be investigated with a Time Domain (TD) OCT system. The clinical situation of an edentulous mandible is considered; it can be solved by inserting 2 to 6 implants. On these implants a mesostructure will be manufactured and on it a superstructure is needed. This superstructure can be integral ceramic; in this case materials defects could be trapped inside the ceramic layers and those defects could lead to fractures of the entire superstructure. In this paper we demonstrate that a TD-OCT imaging system has the potential to properly evaluate the presence of the defects inside the ceramic layers and those defects can be fixed before inserting the prosthesis inside the oral cavity. Three integral ceramic superstructures were developed by using a CAD/CAM technology. After the milling, the ceramic layers were applied on the core. All the three samples were evaluated by a TD-OCT system working at 1300 nm. For two of the superstructures evaluated, no defects were found in the most stressed areas. The third superstructure presented four ceramic defects in the mentioned areas. Because of those defects the superstructure may fracture. The integral ceramic prosthesis was send back to the dental laboratory to fix the problems related to the material defects found. Thus, TD-OCT proved to be a valuable method for diagnosing the ceramic defects inside the integral ceramic superstructures in order to prevent fractures at this level.