Diakoptic FEM-MoM Analysis Using Explicit Connection between Field and Current Bases

Abstract-A diakoptic technique combining the finite element method (FEM) and the method of moments (MoM), and using dual sets of higher order basis functions is proposed for analysis of 3D electromagnetic radiation and scattering structures. These bases enable efficient modeling and significant reductions in the total number of unknowns, while satisfying the natural relation between curl-conforming and divergence-conforming quantities when closing the FEM domain by a MoM surface. The new diakoptic FEM-MoM technique is validated in an example of an array of 4×4 dielectrically coated spherical metallic scatterers

Accurate characterization of winter precipitation using multi-angle snowflake camera, visual hull, advanced scattering methods and polarimetric radar

Includes bibliographical references (pages 28-31).This article proposes and presents a novel approach to the characterization of winter precipitation and modeling of radar observables through a synergistic use of advanced optical disdrometers for microphysical and geometrical measurements of ice and snow particles (in particular, a multi-angle snowflake camera-MASC), image processing methodology, advanced method-of-moments scattering computations, and state-of-the-art polarimetric radars. The article also describes the newly built and established MASCRAD (MASC + Radar) in-situ measurement site, under the umbrella of CSU-CHILL Radar, as well as the MASCRAD project and 2014/2015 winter campaign. We apply a visual hull method to reconstruct 3D shapes of ice particles based on high-resolution MASC images, and perform "particle-by-particle" scattering computations to obtain polarimetric radar observables. The article also presents and discusses selected illustrative observation data, results, and analyses for three cases with widely-differing meteorological settings that involve contrasting hydrometeor forms. Illustrative results of scattering calculations based on MASC images captured during these events, in comparison with radar data, as well as selected comparative studies of snow habits from MASC, 2D video-disdrometer, and CHILL radar data, are presented, along with the analysis of microphysical characteristics of particles. In the longer term, this work has potential to significantly improve the radar-based quantitative winter-precipitation estimation.Published with support from the Colorado State University Libraries Open Access Research and Scholarship Fund

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Abstract-A novel higher order entire-domain finite element technique is presented for accurate and efficient full-wave three-dimensional (3-D) analysis of electromagnetic structures with continuously inhomogeneous material regions, using large generalized curved hierarchical curl-conforming hexahedral vector finite elements that allow continuous change of medium parameters throughout their volumes. This is the first general 3-D implementation and numerical demonstration of the inherent theoretical ability of the finite element method (FEM) to directly treat arbitrarily (continuously) inhomogeneous materials. The results demonstrate considerable reductions in both number of unknowns and computation time of the entire-domain FEM modeling of continuously inhomogeneous materials over piecewise homogeneous models. They indicate that, in addition to theoretical relevance and interest, large curved higher order continuous-FEM elements also have great potential for practical applications that include structures with pronounced material inhomogeneities and complexities. Index Terms-Computer-aided analysis, electromagnetic analysis, electromagnetic scattering, finite element method, higher order elements, inhomogeneous media, method of moments

Influence of the Accuracy of Geometrical Modeling with Large Curvilinear Elements on FEM Solutions to EM Problems

Abstract — The accuracy of the large, curvilinear, Lagrange-type elements has been analyzed. We have compared the results of the four differently hp-refined models and pointed out the accuracy of our models and the necessity for the large-domain approach in modeling. The influence of geometrical inexactness to the limit of achievable accuracy has been investigated. It has been shown that the elements used here represent a good choice for fast and reliable geometrical modeling of EM structures

Higher Order Geometrical Modeling and Higher Order Field/Current

Higher-order, large-domain electromagnetic simulations are presented based on the finite element method (FEM), method of moments (MoM), and physical optics (PO). The simulations combine higher order geometrical modeling and higher order field/current modeling, which is referred to as double-higher-order modeling. The examples demonstrate that accurate and efficient FEM, MoM, and PO simulations require both higher-order geometrical flexibility for curvature modeling and higher-order basis functions for field/current modeling in the same method. It is optimal to have the geometrical orders and current/field approximation orders of the elements entirely independent from each other, so that the two sets of parameters can be combined independently in a double-higher-order model

Analysis of Electromagnetic Scatterers using Hybrid Higher Order FEM-MoM Technique

Abstract — A higher order large-domain hybrid finite element – method of moments (FEM-MoM) technique is presented. The discretization and solving FEM and MoM parts of the problem and the coupling of the two methods is described. A benchmark example of analysis of a scatterer with pronounced curvature at resonant frequency is given, demonstrating accuracy and robustness of the presented hybrid technique

Variations in Snow Crystal Riming and ZDR: A Case Analysis

A case study in terms of variations in differential reflectivity Z(DR) observed at X band and snow crystal riming is presented for a light-snow event that occurred near Greeley, Colorado, on 26-27 November 2015. In the early portion of the event, Z(DR) values at near-surface levels were low (0-0.25 dB). During a second time period approximately 8 h later, Z(DR) values became distinctly positive (+2-3 dB). Digital photographs of the snow particles were obtained by a Multi-Angle Snowflake Camera (MASC) installed at a range of 13 km from the radar. Image-processing and machine-learning techniques applied to the MASC data showed that the snow particles were more heavily rimed during the low-Z(DR) time period. The aerodynamic effects of these rime deposits promoted a wider distribution of hydrometeor canting angles. The shift toward more random particle orientations underlies the observed reduction in Z(DR) during the period when more heavily rimed particles were observed in the MASC data