A novel hybrid approach for far-field characterization from near-field amplitude-only measurements on arbitrary scanning surfaces

2005 ◽  
Vol 53 (6) ◽  
pp. 1866-1874 ◽  
Author(s):  
S. Costanzo ◽  
G. Di Massa ◽  
M.D. Migliore
Keyword(s):  
Near Field ◽  
Hybrid Approach ◽  
Field Amplitude ◽  
Far Field

Average Q and yield estimates from the Pahute Mesa test site

1987 ◽  
Vol 77 (4) ◽  
pp. 1274-1294
Author(s):  
R. W. Burger ◽  
T. Lay ◽  
L. J. Burdick
Keyword(s):  
Time Domain ◽  
Near Field ◽  
Energy Levels ◽  
Source Model ◽  
Spectral Shape ◽  
Field Amplitude ◽  
Far Field ◽  
Source Models ◽  
Attenuation Models ◽  
Shape Data

Abstract Attenuation models, with and without frequency dependence, have been developed through analysis of time-domain amplitude measurements and teleseismic spectral shape data from Pahute Mesa nuclear explosions. The time-domain analysis is based on a near-field to far-field amplitude comparison. The near-field amplitude information is incorporated in two parameterized explosion source models (Mueller-Murphy and Helmberger-Hadley) based on analyses of near-field data. The teleseismic amplitude observations are from a large data set of WWSSN short-period analog recordings. For the narrow-band time-domain data, the various source and attenuation models are indistinguishable. We utilize the spectral shape data in the 0.5- to 4-Hz band as a constraint on the source-attenuation models at higher frequencies, concluding that either source model, when convolved with the appropriate frequency-dependent Q model, can be consistent with both the near-field and far-field time-domain amplitudes and the spectral shape data. Given the trade-off between source and attenuation models and the similarity of the different source models in the 0.5- to 4-Hz band, it is difficult to prefer clearly one source model over the other. The Mueller-Murphy model is more consistent with surface wave amplitude measurements because of larger predicted long-period energy levels. Whether or not frequency dependence is included in the attenuation model, the value of t* near 1 Hz is about 1.0 sec (assuming the Mueller-Murphy source model) or 0.8 sec (assuming the Helmberger-Hadley source model). This 0.2 sec difference results from greater 1-Hz energy levels for the Mueller-Murphy source model. Adopting an average attenuation model, predicted amplitudes and yields are shown to be within the uncertainty of the data for all the events analyzed.

Far-field pattern determination from the near-field amplitude on two surfaces

1990 ◽  
Vol 38 (11) ◽  
pp. 1772-1779 ◽  
Author(s):  
O.M. Bucci ◽  
G. D'Elia ◽  
G. Leone ◽  
R. Pierri
Keyword(s):  
Near Field ◽  
Field Amplitude ◽  
Field Pattern ◽  
Far Field ◽  
Pattern Determination ◽  
Far Field Pattern

Computational Analysis of Tonal Noise Generated High-Bypass Ratio Fan Stage

2005 ◽  
Author(s):  
Aleksey M. Sipatov ◽  
Michail V. Usanin ◽  
Valery G. Avgustinovich ◽  
Natalia O. Chuhlantseva
Keyword(s):  
Pressure Distribution ◽  
Acoustic Analysis ◽  
Stokes Equations ◽  
Near Field ◽  
Hybrid Approach ◽  
Leading Edge ◽  
Navier Stokes ◽  
Far Field ◽  
Unsteady Pressure ◽  
Acoustic Contribution

The paper shows the procedure of estimating different fan stage geometries from the point of the fan stage aerodynamic and acoustic efficiency by using CFX v.5.6 gas dynamics software. Two different fan stages were examined. The acoustic analysis was made based on unsteady pressure distribution along exit guide vanes. The unsteady pressure distribution was determined from 3-D calculations of rotor-stator interactions. An improved approach is suggested to estimate acoustic sources with the leading edge geometry considered. Three various grid models were analyzed to estimate the grid discretization influence on computational results. The hybrid approach was used to evaluate the acoustic contribution of fan stage rotor–stator interaction to a turbo-jet engine total noise level on first harmonic in a far field. This approach consists of three steps. The first step includes the solving of Navier-Stokes equations in fan stage, the second step includes the solving of linearized Euler’s equations (LEE) in a near field and, then, the third covers the calculation of Ffowcs Williams–Hawkings (FWH) integral in a far field. The first step marked the effect of strong attenuation of acoustics modes in the fan passage. The results of calculations in the far field were compared with experiment data.

Magnetic Tag Antenna for UHF Near-field and Far-Field RFID Applications

2015 ◽  
Vol 5 (2) ◽  
pp. 119
Author(s):  
Mondher Dhaouadi ◽  
M. Mabrouk ◽  
T. Vuong ◽  
A. Ghazel
Keyword(s):  
Near Field ◽  
Far Field ◽  
Rfid Applications

Far field modeling of the Mamala Bay outfalls

1998 ◽  
Vol 38 (10) ◽  
pp. 323-330
Author(s):  
Philip J. W. Roberts
Keyword(s):  
Field Model ◽  
Near Field ◽  
Far Field ◽  
Field Modeling ◽  
Visitation Frequency ◽  
Statistical Variation ◽  
Long Time ◽  
Harmonic Average ◽  
Ocean Outfall ◽  
Acoustic Doppler Current Profilers

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.

Direction of Arrival Estimation Under Near-Field Interference Using Matrix Filter

2015 ◽  
Vol 23 (04) ◽  
pp. 1540007 ◽  
Author(s):  
Guolong Liang ◽  
Wenbin Zhao ◽  
Zhan Fan
Keyword(s):  
Near Field ◽  
Direction Of Arrival ◽  
Doa Estimation ◽  
Direction Of Arrival Estimation ◽  
Far Field ◽  
Data Simulation ◽  
Estimation Algorithms ◽  
Simulation Results

Direction of arrival (DOA) estimation is of great interest due to its wide applications in sonar, radar and many other areas. However, the near-field interference is always presented in the received data, which may result in degradation of DOA estimation. An approach which can suppress the near-field interference and preserve the far-field signal desired by using a spatial matrix filter is proposed in this paper and some typical DOA estimation algorithms are adjusted to match the filtered data. Simulation results show that the approach can improve capability of DOA estimation under near-field inference efficiently.

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