Selected methods for validating computational electromagnetic modeling techniques

The authors' teaching experiences with numerical techniques in computational electromagnetics are described. Course descriptions and objectives are discussed, as well as their relationship to engineering practice.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents the author's teaching experiences on Numerical Techniques in Computational Electromagnetics for years, which includes course descriptions and objectives as well as the relation with engineering practice, etc.

This paper identifies several important aspects of current Feature Selective Validation (FSV) methodologies that are embodied in IEEE Standard 1597.1 for the Validation of CEM Computer Modeling and Simulations. The FSV method facilitates comparisons of sets of electromagnetic (EM) observable data for a given problem to determine “levels of agreement” across amplitude and feature variables. Areas of future revision to this standard are presented that will further enhance the standard's utility for performing Computational Electromagnetic (CEM) technique validation for a wide range of problems. In particular, we consider the utility of the N-dimensional FSV and revisit applications of the Amplitude Difference Measure (ADM), Feature Difference Measure (FDM) and the Global Difference Measure (GDM). This is discussed within the context of large complex system problems that present interesting challenges to the FSV method due to the potentially wide dynamic range of the data. Certain use cases for scattering cross section, system-level coupling, and large system-level EMC problems require a somewhat modified approach in computing the GDM based on how the FDM and ADM are weighted. For the current 1-D FSV, unweighted or incorrectly weighted amplitude and feature measures can potentially lead to inconclusive or even misleading results. These issues are addressed and future revisions to the IEEE Standard 1597.1 are highlighted.

Spatial Sampling and Interpolation Techniques in Computational Electromagnetics and Beyond

Recently, the authors have developed a number of new hierarchical and singular basis functions for field representation in two- and three-dimensional cells. Scalar and vector basis functions of both interpolatory and hierarchical kind together with some singular functions of the additive kind are discussed in detail, with several results, in a recent SciTech-IET book (R.D. Graglia and A.F. Peterson: Higher-order Techniques in Computational Electromagnetics), as well as in several other publications (for example, Graglia et al., IEEE TAP, vol. 61, pp. 3674–3692, Jul. 2013; IEEE TAP, vol. 62, pp 3632–3644, Jul. 2014; IEEE AWPL, vol. 13, pp 1701–1704, 2014, and in the special issue on "Finite Elements for Microwave Engineering," Electromagnetics, vol. 34, pp. 171–198, 2014).

Integrated electromagnetic (EM) and Electrical Resistivity Tomography (ERT) geophysical studies of environmental impact of Awotan dumpsite in Ibadan, southwestern Nigeria

The most common lateral load is a wind load. The wind speed profile considers as an effective parameter to find the wind load. Topographic features such as escarpments and hills in flat area can significantly amplify wind speeds near the ground. The main aim of this study is to investigate the effects of the escarpment characteristics on the velocity profile and speed-up using the numerical model. At the first, the numerical model validated with the experimental results obtained through the wind tunnel of Texas University. Then, three kinds of escarpments with different slopes simulated and speed-ups obtained from the numerical model, wind tunnel, ASCE and Iran codes compared. The results of numerical model at the smaller slope showed better accordance with wind tunnel results. The effect of inlet velocity profile on the speed-up was numerically studied. Comparison of the results showed that the maximum speed-up using the velocity profile of Iran code is greater than using ASCE code. Finally, the effect of the escarpment height and width with the same slope on speed-up was investigated. The results showed that speed-up grows as the width and height increase; however, the effect of increasing the height is less.

We show in this paper how a system of equations of motion, diffusion and continuity that present the effects of vorticity through a vorticity transfer length scale may be used to model 2D-3D vorticity behaviour. The local turbulent vorticity is separated from the large-scale flow following the Reynolds decomposition (Reynolds 1894, Taylor 1931)—∇ × v + ∇ × v —similar to the technique used for velocity. The system of equations extended through the terms ∇ × v and ∇ × v is solved numerically using a purely statistical local method that details the role of vorticity transport in the turbulence behaviour of the flow. Moreover, this numerical model that shows the temporal evolution of both fields, 3D velocity and 3D vorticity is used to investigate the propagation of turbulent perturbations that arise from the development of a vortex placed in the centre of the numerical domain. Even with a small mesh (60 × 60 × 120), the results show the propagation of vorticity-related waves both in the plane and in the vertical. The numerical results are compared with experiments performed in a stratified flow, where velocity and vorticity are measured with PIV as turbulence behind a grid decay, these experiments have been performed both in a rotating frame of reference and with no rotation and show features also detected in the numerical simulations when the assumption of a quasi– two-dimensional flow is used.

Progressive collapse is defined as the spread of an initial local failure of a critical load bearing structural element to the remaining structure, ultimately leading to the collapse of the entire building or of a large portion of it. After the partial collapse of the Ronan Point apartment tower in 1968, when a localised gas explosion ultimately led to the collapse of the whole corner of the building, progressive collapse firstly drew public attention due to its catastrophic consequences on human casualties and economic losses. Other recent collapse events, such as those of the Murrah Federal Building in 1995, Sampoong department store in 1995 and World Trade Centre towers in 2001, have further highlighted the importance of this topic and made engineering communities aware of the necessity to prevent the occurrence of progressive collapse in building structures. In the past decades, considerable research has been devoted to investigate progressive collapse of building structures. These research typically followed an alternate load path approach. This approach allows an initial failure to occur, while the remaining structure needs to seek alternate load paths to dissipate damage and prevent progressive collapse. In practice, the progressive collapse resistance of building structures is generally evaluated by notionally removing one or more load bearing structural elements, representing the initial failure. Despite all research efforts made, they have predominately focused on frame systems. Relevant investigations on reinforced concrete (RC) flat plate structures, a commonly used structural system, are still scarce. The flat plate system contains slabs, of uniform thickness, directly supported by columns without using beams, drop panels and column capitals. This provides structures with increased storey height, architectural convenience and significant savings in construction costs. Nevertheless, the slab-column connection is prone to punching shear failure, which may propagate to the vicinity of connections, potentially leading to progressive collapse. The present study aims at filling some of the current knowledge gap with comprehensive experimental, analytical and numerical investigations on RC flat plate structures. The experimental program consists of four quasi-static large-deformation tests performed on three 1/3-scale, 2×2-bay RC flat plate substructures subjected to critical column removal scenarios. The test specimens included one specimen tested under two consecutive corner column removal scenarios, one specimen under an edge column removal and one specimen under the scenario of concurrently removing both an edge and an interior column. For the loading scheme, a multi-point loading system was specially designed to simulate an increasing uniformly distributed load (UDL). The loading points of this system were equally positioned on the bays adjacent to the removed column(s) to apply the load until failure of the slab. Throughout each test, the structural behaviour of the slab was monitored by extensive apparatuses mounted to the slab both internally and externally. Failure and post-failure behaviours, failure modes, and collapse resisting mechanisms were observed and analysed. Additionally, a complement of analytical studies to the experimental tests, based on the observed yield lines, was carried out to estimate the flexural capacity of the test specimens. To numerically investigate the progressive collapse behaviour of RC flat plate structures, a set of 3D nonlinear finite element modelling approaches, using LS-DYNA software, was established. A total of five numerical models were explicitly created based on the four experimental tests in present research and one from the literature. The proposed modelling approach was basically composed of appropriate definitions of element types, bond-slip relationships, loadings and boundary conditions, and more importantly development of the material models for concrete and reinforcements and calibration of failure criteria for element erosion. A quasi-static loading scheme in displacement control in the numerical models was adopted, the same as that in the conducted tests, through explicitly modelling the multi-point loading system in order to replicate the true test conditions. The numerical models were respectively validated by comparing the load displacement responses, failure modes, crack patterns, and displacement and strain results against the experimental ones, which confirmed the appropriateness and reliability of the proposed models. The validated modelling techniques could be applied to further perform parametric studies of the progressive collapse resistance of RC flat plate substructures and prototype structures. In summary, the significant and original contribution of this research is to (1) obtain a solid understanding of the collapse behaviour of RC flat plate structures under critical column removal scenarios, (2) examine the analytical solution using the yield line theory to predict the flexural capacity of RC flat plate structures, (3) establish a set of numerical modelling techniques which can reasonably replicate the experimental process and provide valuable references of numerically analysing progressive collapse of RC flat plate structures, and (4) give design insights into Australian and international Standards in mitigating progressive collapse of RC flat plate structures.

According to the transformation relationships between the Cartesian coordinates and the general curvilinear coordinates, the governing equations of the model are derived as the forms in the general curvilinear coordinates from those in the Cartesian coordinates. In the model, the contravariant velocities are adopted as the independent variables in non-orthogonal grids. The momentum equations keep strongly conservative forms and the boundary conditions can be given easily. The model used a staggered grid arrangement. The discrete equations are solved using the SIMPLIC algorithms. The numerical model has been validated against the bifurcated flow of which the diversion angle is 30 degree. Compared with the measured values, the numerical shallow water model is shown to be capable of simulating the water domains with irregular boundaries.

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

In the present study, the local scour and topographical change in open channels of a tideland dike are studied numerically. A 2D numerical model was presented for the simulation of scour depth in open channels of the tideland dike in the west of the DPR Korea. Because the computation using a 3D numerical model is time-consuming, the depth-averaged 2D numerical model is applied in the calculation of the scour depth. The numerical model is implemented by the method coupled finite element method with finite difference method. Generally, scour depth depends on flow velocity, bed material composition, and suspended sediment concentration. In the present study, as the width of open channel between tideland dikes decreased, the scoured depth dramatically increased due to increased flow velocity. For all the scenarios of damming up, however, the scoured depth increased very slightly in open channels with the width of 50 m. The numerical results showed that when damming up according to Scenario 1, the flow velocity and scoured depth are smallest.

This thesis focuses on the numerical modeling of co-reactant electrogenerated chemiluminescence (ECL) systems that have been recently proposed for analytical applications. Co-reactant ECL is light emission triggered by an electrochemical reaction of a luminophore with a co-reactant. Many researchers are trying to expand its application in the analytical field with carrying out various experiments. However, recent reports on the co-reactant ECL have revealed several phenomena that are not yet fully understood from theoretical viewpoint. Better understanding of the reaction mechanism for ECL generation is necessary for further improvement of the co-reactant ECL. In this context, three kinds of recently-proposed co-reactant ECL systems were numerically modeled in this study to analyze the reaction mechanism. The numerical modeling in this study mainly deals with dynamic ECL behavior while the potential of a working electrode changes with time. The modeling of this kind of dynamic ECL behavior provides us more information than that of static ECL behavior because very precise analysis can be carried out by the consideration of dynamic changes in the modeling parameters. In conclusion, the numerical modeling in this study contributed to the better understanding of the reaction mechanism for ECL generation, which can support further improvement of co-reactant ECL systems. Analysis for the reaction mechanism from theoretical viewpoint should be adequately considered in future experimental studies.

An advanced analysis code, ARKAS_cellule, has been developed to determine the core distortion and the mechanical behavior of fast reactors. In this code, each hexagonal subassembly duct is represented by a folded thin plate structure divided into a user-specified number of shell elements so that the interduct contact forms and the cross-sectional distortion effect of each duct are properly taken into account. In this paper, the numerical model of the ARKAS_cellule code is introduced, and the analytical results for two validation problems are presented. From a single duct compaction analysis, the first validation problem, it is clarified that the new analytical model is applicable to simulating the change of duct compaction stiffness that depends on the loading conditions such as the loading pad forms and the number of contact faces. The second validation analysis has been conducted by comparison with the experimental values obtained by the National Nuclear Corporation Limited in the United Kingdom using the core restraint uniplanar experimental rig (CRUPER), an ex-reactor rig in which a cluster of 91 short ducts is compressed by 30 movable peripheral rams toward the center of the cluster in seven stages. The analysis clarified that the predictions obtained using ARKAS_cellule agree well with the measured ram loads and interwrapper gap widths during the compaction sequence. One may conclude that ARKAS_cellule is valid for quantitative analysis of the core mechanical behavior and will be particularly useful for the evaluation of transient deformation of core assemblies during accidents in which the distortion of loading pads have important effects on obtaining favorable reactivity feedback.

Computer modelling techniques were employed to investigate the adsorption of a selection of organic surfactant molecules to a range of fluorapatite surfaces, and new interatomic potential models for the apatite/ adsorbate interactions are presented. The adsorbates coordinate mainly to the surfaces through interaction between their oxygen (or nitrogen) atoms to surface calcium ions, followed by hydrogen-bonded interactions to surface oxygen ions and, to a much lesser extent, surface fluorides. Bridging between two surface calcium ions is the preferred mode of adsorption, when the geometry of the adsorbates allows it, and multiple interactions between surfaces and adsorbate molecules lead to the largest adsorption energies. All adsorbates containing carbonyl and hydroxy groups interact strongly with the surfaces, releasin energies between approximately 100 and 215 kJ mol(-1) but methylamine containing only the -NH2 functional group adsorbs to the surfaces to a much lesser extent (25-95 kJ mol(-1)). Both hydroxy methanamide and hydroxy ethanal prefer to adsorb to some surfaces in an eclipsed conformation, which is a requisite for these functional groups. Sorption of the organic material by replacement of pre-adsorbed water at different surface features is calculated to be mainly exothermic for methanoic acid, hydroxy methanamide and hydroxy ethanal molecules, whereas methyl amine would not replace pre-adsorbed water at the fluorapatite surfaces. The efficacy of the surfactant molecules is calculated to be hydroxy aldehydes > alkyl hydroxamates > carboxylic acids >> alkyl amines. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic surfactants for use in mineral separation by flotation.