Solutions of EM problems using finite element & complex frequency hopping techniques

1995 ◽  
Author(s):  
M A Kolbehdari ◽  
M S Nak ◽  
Q J Zhang
Keyword(s):  
Finite Element ◽  
Frequency Hopping ◽  
Complex Frequency

Complex Frequency Hopping

1994 ◽  
pp. 103-127
Author(s):  
Eli Chiprout ◽  
Michel S. Nakhla
Keyword(s):  
Frequency Hopping ◽  
Complex Frequency

Coupling Sound Absorbing Materials With an Air Cavity Using Frequency Dependent Bulk Material Properties

2016 ◽  
Author(s):  
Shung H. Sung ◽  
Donald J. Nefske
Keyword(s):  
Finite Element ◽  
Frequency Response ◽  
Material Properties ◽  
Complex Frequency ◽  
Air Cavity ◽  
Frequency Dependent ◽  
Absorbing Materials ◽  
Mode Method ◽  
Modal Solution ◽  
Solution Methodology

This paper presents the acoustic finite element method and the modal solution method for coupling sound absorbing materials with an air cavity to predict the sound pressure frequency response. The sound absorbing materials are represented with complex, frequency-dependent, effective mass-density and bulk-modulus properties obtained from the acoustic impedance of material samples. To couple the sound absorber cavity and air cavity, the boundary conditions at the interface between the cavities requires equality of pressure and equality of acoustic volume flow. Two modal solution methods are developed to compute the frequency response of the coupled system with frequency dependent material properties: the component mode method and the coupled mode method. The finite element and modal solution methodology is developed in a form readily adaptable for implementation in commercially available codes. The accuracy of the modal solution methodology is assessed for modeling a one-dimensional air tube terminated with absorbent material and the seats in an automobile passenger compartment.

Prediction Capabilities of Damped Updated Finite Element Models

2011 ◽  
Author(s):  
Vikas Arora
Keyword(s):  
Finite Element ◽  
Model Updating ◽  
Dynamic Properties ◽  
Detailed Comparison ◽  
Element Model ◽  
Mode Shapes ◽  
Finite Element Models ◽  
Complex Frequency ◽  
Structural Modifications ◽  
The Finite Element Model

Model updating techniques are used to correct the finite element model of a structure using experimental data such that the updated model more correctly describes the dynamic properties of the structure. One of the applications of such an updated model is to predict the effects of making modifications to the structure. These modifications may be imposed by design alterations for operating reasons. Most of the model updating techniques neglect damping and so these updated models can’t be used for accurate prediction of complex frequency response functions (FRFs) and complex mode shapes. In this paper, a detailed comparison of prediction capabilities of parameter-based and non parameter-based damped updated methods for structural modifications is done. The suitability of paramter-based and non parameter-based damped updated models for predicting the effects of structural modifications is evaluated by laboratory experiment for the case of an F-shape test structure. It is concluded that parameter-based damped updated models are likely to perform better in predicting the effects of structural modifications.

Wavefield simulation and analysis with the finite-element method for acoustic logging while drilling in horizontal and deviated wells

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D525-D543 ◽  
Author(s):  
Hua Wang ◽  
Guo Tao ◽  
Kuo Zhang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Complex Frequency ◽  
The Finite Element Method ◽  
Wavefield Simulation ◽  
Bottom Hole Assembly ◽  
Logging While Drilling ◽  
Assembly Performance ◽  
Element Method ◽  
Deviated Wells

We developed a frequency-domain finite-element method (FFEM) in conjunction with a complex-frequency-shifted perfectly matched layer (CFS-PML) boundary to effectively study the wavefield generated by acoustic multipole logging-while-drilling (LWD) tools in horizontal and highly deviated wells. With such an FFEM, the sources and receivers can be easily set symmetrically in the simulation to model the real tools exactly, while this is very difficult to deal with in the finite-difference method. In addition, the CFS-PML boundaries can be implemented more efficiently in this algorithm. We applied this method to study the effects of tool eccentricity on the measurements in slow formations that most likely need 3D solutions for LWD in horizontal and highly deviated wells. We found that because the tool cannot be centralized in these wells, some nonmonopole modes could appear in monopole measurements and the Stoneley mode could appear in dipole measurements; the flexural collar wave could become increasingly strong with an increase of tool eccentricity, and the Stoneley mode may be the later arriving event, especially in the case of a severely eccentric quadrupole tool. Based on these studies, we introduced a method to quantify the extent and the angle of the tool eccentricity with the phase difference in eccentric dipole measurements. These parameters are very useful for the analysis of the bottom-hole assembly performance in geosteering.

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