Local Analysis Method Research Articles

Wavelet-based numerical and semianalytical methods of computational local structural analysis

Numerical or semianalytical solution of problems of structural mechanics of high dimensionality is computationally costly process in many cases. However, structural engineer does not normally face the task of obtaining a solution of the problem with high accuracy at all points of the considered domain occupied by the structure. As a rule, all subdomains that are potentially dangerous in terms of structural strength are well known in advance. Operational and variational formulations of boundary problems of structural mechanics with the use of method of extended domain are presented. After corresponding (finite element or finite difference) discretization and passage to governing equations considering problems are transformed to a multilevel space with the use of multilevel wavelet transform (discrete Haar basis is used). Special algorithms of averaging are presented.

Using Physically Based Synthetic Peak Flows to Assess Local and Regional Flood Frequency Analysis Methods

AbstractAlthough prior studies have evaluated the role of sampling errors associated with local and regional methods to estimate peak flow quantiles, the investigation of epistemic errors is more difficult because the underlying properties of the random variable have been prescribed using ad‐hoc characterizations of the regional distributions of peak flows. This study addresses this challenge using representations of regional peak flow distributions derived from a combined framework of stochastic storm transposition, radar rainfall observations, and distributed hydrologic modeling. The authors evaluated four commonly used peak flow quantile estimation methods using synthetic peak flows at 5,000 sites in the Turkey River watershed in Iowa, USA. They first used at‐site flood frequency analysis using the Pearson Type III distribution with L‐moments. The authors then pooled regional information using (1) the index flood method, (2) the quantile regression technique, and (3) the parameter regression. This approach allowed quantification of error components stemming from epistemic assumptions, parameter estimation method, sample size, and, in the regional approaches, the number of pooled sites. The results demonstrate that the inability to capture the spatial variability of the skewness of the peak flows dominates epistemic error for regional methods. We concluded that, in the study basin, this variability could be partially explained by river network structure and the predominant orientation of the watershed. The general approach used in this study is promising in that it brings new tools and sources of data to the study of the old hydrologic problem of flood frequency analysis.

Distribution of “Invisible” Noble Metals between Pyrite and Arsenopyrite Exemplified by Minerals Coexisting in Orogenic Au Deposits of North-Eastern Russia

The study focused on the forms of occurrence and distribution of hidden (“invisible”) noble metals (NMs = Au, Ag, Pt, Pd, Ru) in the coexisting pyrites and arsenopyrites of four samples of mineral associations from three Au deposits in the north-east of Russia. The unique nature of our approach was the combination of methods of local analysis and statistics of the compositions of individual single crystals of different sizes. This allowed us to take into account the contribution of the surface component to the total NM content and to distinguish the structurally bound form of the elements. The following estimates of the distribution coefficients of the structural (str) and surficial (sur) forms of elements were obtained: D ¯ P y / A s p s t r = 2.7 (Au), 2.5 (Pd), 1.6 (Pt), 1.7 (Ru) and D ¯ P y / A s p s u r = 1.6 (Au), 1.1 (Pd), 1.5 (Pt and Ru). The data on Ag in most cases indicated its fractionation into pyrite ( D ¯ P y / A s p s t r = 17). Surface enrichment was considered as a universal factor in “invisible” NM distribution. A number of elements (i.e., Pt, Ru, Ag) tended to increase their content with a decrease in the crystallite size in pyrite and arsenopyrite. This may be due to both the phase size effect and the intracrystalline adsorption of these elements at the interblock boundaries of a dislocation nature. The excess of metal (or the presence of S vacancies) in pyrite increased Ag and Pt content in its structure and, to a lesser extent, the content of Ru, Pd and Au. Arsenopyrite exhibited a clear tendency to increase the content of Pt, Ru and Pd in samples with excess As over S. Sulphur deficiency was a favourable factor for the incorporation of Ag and platinoids into the structures of the mineral associations studied. Perhaps this was due to the lower sulphur fugacity. Pyrite with excess Fe was associated with higher contents of some NMs. The presence of other impurity elements was not an independent factor in NM concentration.

A Bidirectional Analysis Method for Extracting Glacier Crevasses from Airborne LiDAR Point Clouds

A crevasse is an important surface feature of a glacier. This study aims to detect crevasses from high-density airborne LiDAR point clouds. However, existing methods continue to suffer from the data holes within the crevasse region and the influence of the undulating non-crevasse glacier surfaces. Therefore, a bidirectional analysis method is proposed to robustly extract the crevasses from the point clouds, which utilizes their vertical and horizontal characteristics. First, crevasse points are separated from non-crevasse points using a hybrid-entity method, where the height difference and the nearly vertical characteristic of a crevasse sidewall are considered, to better distinguish the crevasses from the undulating non-crevasse glacier surfaces. Second, the crevasse regions/edges are adaptively delineated by a local statistical analysis method that is based on a novel feature of the Delaunay triangulation mesh of non-crevasse points in the horizontal plane. Last, the pseudo-crevasse points and regions are removed by a cross-analysis method. To test the performance of the proposed method, this study selected airborne LiDAR point clouds from two sites of Alaskan glaciers (i.e., Tyndall Glacier and Seward Glacier) as the experimental datasets. The results were verified by a comparison with the ground truth that was manually delineated. The proposed method achieved acceptable results: the recall, precision, and F 1 scores of both sites exceeded 94.00%. Moreover, a comparative experiment was carried out and the results confirmed that the proposed method achieved superior performance.

Imaging of Lamination Defect in Metallic Plate Based on Local Wavenumber Domain Analysis

In metallic plate structures, a lamination defect is a type of internal defect that is commonly generated in the manufacturing process, which is mostly parallel to the surface of the plate. This study presents a technique of imaging a lamination defect in a metallic plate by using Lamb waves based on the local wavenumber domain analysis method. Owing to the processing technique, an aluminum beam structure is utilized to represent the metallic plate for the detection of the lamination defect. A three-dimensional finite-element model of an aluminum beam with a rectangular lamination defect is constructed with MatLab and ABAQUS commercial software. The propagation characteristics of Lamb waves are discussed by analyzing the simulated wavefield. A complicated wave-propagation phenomenon of multiple reflection and transmission is observed between the interaction of Lamb waves and the lamination. By performing local wavenumber domain analysis on the wavefield, the wavenumber distribution is obtained, from which the location and profile of the lamination defect are identified. An experimental study is carried out to verify the numerical result. A fully non-contact detection system consisting of an electromagnetic acoustic transducer and laser ultrasonic inspection system is established to inspect the artificial machined beam structure. The experimental result is in good agreement with the numerical result.

A stable and effective strategy for angle gather extraction from reverse time migration using traveltime gradient

ABSTRACTThe generation of angle-domain common imaging gathers (ADCIGs) from reverse time migration (RTM) is essential for velocity updates, migration quality control and amplitude variation with angle (AVA) inversion. However, computational stability and efficiency challenges remain with ADCIGs extracted from RTM. Here, we develop a stable and effective strategy to produce ADCIGs during RTM based on the traveltime gradient. The first arrival traveltime is calculated efficiently using the dynamic programming scheme, and the source-side propagating direction of the local plane-wave can be obtained using the traveltime field gradient. Compared with propagation directions calculated using the local slowness analysis method, the traveltime gradient can also provide stable and accurate source-side directions. Benefitting from the migrated images, we can collect normal direction information for the reflector from the stacked images effectively using the omnidirectional plane-wave destruction (OPWD) method. Construction of subsurface scattering angles is straightforward via combination of the source-side propagation and reflector normal directions. Subsequently, we apply an effective imaging condition based on the excitation criterion in the angle domain to generate ADCIGs. Thanks to conversion from a wavefield-based to a traveltime-based calculation, the proposed method provides more stable and reliable wave propagation directions in complicated areas compared with the Poynting vector (PV) method which is based on the full wavefield. Because traveltime can be calculated efficiently beforehand, the proposed method can be adapted economically to the conventional RTM imaging frame, which reveals significant implementation potential for practical seismic exploration. We demonstrate the stability and effectiveness of this approach for both synthetic and field data.

Maximum Loadability of Islanded Microgrids With Renewable Energy Generation

A microgrid (MG) is a small-scale power system which is fed by constrained distributed generation (DG) units and its continuous operation is affected by the variability of available generation resources. In this paper, a global sensitivity analysis (GSA) method is proposed to evaluate the impact of variable energy resources on the maximum loadability of islanded MGs (IMGs). First, a probabilistic optimization problem is formulated to calculate the IMG load margin considering the droop characteristics of DG units and uncertainties of renewable generation, loads and distribution feeder parameters. Next, the global sensitivity (GS) is introduced that can identify the impact of independent and correlated variables on the IMG loadability. Last, the sparse polynomial chaos expansion method is used to obtain the probabilistic models for IMG load margins, and an efficient GSA method is proposed to calculate the GS of IMG loadability to prevailing variables. The probabilistic models are considered for IMG input variables and the impact of variable correlations on IMG loadability is analyzed. The proposed method for calculating the maximum loadability is tested using a 33-bus IMG and the results are compared with those of other GSA and local sensitivity analysis methods.

Altered Spontaneous Brain Activity of Children with Unilateral Amblyopia: A Resting State fMRI Study.

Objective This study is aimed at investigating differences in local brain activity and functional connectivity (FC) between children with unilateral amblyopia and healthy controls (HCs) by using resting state functional magnetic resonance imaging (rs-fMRI). Methods Local activity and FC analysis methods were used to explore the altered spontaneous brain activity of children with unilateral amblyopia. Local brain function analysis methods included the amplitude of low-frequency fluctuation (ALFF). FC analysis methods consisted of the FC between the primary visual cortex (PVC-FC) and other brain regions and the FC network between regions of interest (ROIs-FC) selected by independent component analysis. Results The ALFF in the bilateral frontal, temporal, and occipital lobes in the amblyopia group was lower than that in the HCs. The weakened PVC-FC was mainly concentrated in the frontal lobe and the angular gyrus. The ROIs-FC between the default mode network, salience network, and primary visual cortex network (PVCN) were significantly reduced, whereas the ROIs-FC between the PVCN and the high-level visual cortex network were significantly increased in amblyopia. Conclusions Unilateral amblyopia may reduce local brain activity and FC in the dorsal and ventral visual pathways and affect the top-down attentional control. Amblyopia may also alter FC between brain functional networks. These findings may help understand the pathological mechanisms of children with amblyopia.

ArcFractal: An ArcGIS Add-In for Processing Geoscience Data Using Fractal/Multifractal Models

Fractal and multifractal models, including the concentration-area (C–A) fractal model, spectrum-area (S–A) multifractal model, and local singularity analysis (LSA) method, are widely applied when processing various geoscience datasets. However, there is lack of ArcGIS-based software that contains these popular fractal and multifractal models. Such a situation hinders the popularization and application of fractal and multifractal models. ArcFractal, an easy-to-use ArcGIS add-in for processing geoscience data using fractal and multifractal models, is introduced in this paper. It is developed using C# based on ArcObject for.Net, ArcEngine 10.2, ZedGraph, and Visual Studio 2010. ArcFractal operations require a Windows 7 operating system and ArcGIS Desktop, version 10.2 or higher. The main application of ArcFractal is to determine geochemical threshold/baseline for separating geochemical patterns into anomalous and background components using the C–A, S–A, and LSA techniques. A case study from China Geochemical Baselines Project (CGB) was used to demonstrate the advantage of ArcFractal for processing geochemical exploration data.

RESEARCH OF CORROSIVE DAMAGE TO THE PURPOSE OF FOOD PRODUCTION

Chemical and food processing environments contain chemically active ingredients such as oxygen, carbon dioxide (СО2), carbon monoxide (CO), sulfur, hydrogen, carbon acid ion and sulfuric acid ion, chlorine ions, impurities of calcium carbonate, iron, and hydrochloric acid, etc. All these factors lead to intensive corrosion of the equipment, reducing its reliability and durability. The corrosion-mechanical resistance of metal equipment, such as chemical and sugar plants, is of great importance for environmental and sanitary requirements that make it impossible to contaminate the product with metal ions. First of all, the tubes of evaporation stations, diffusion apparatuses and steam boilers of chemical and agro-processing (sugar) enterprises are exposed to corrosive damage caused by the negative influence of high-temperature and corrosive-active steam under high pressure. Significantly worsens this negative situation and deposition of sediments of salts, carbonates, acids, and others. The analysis of corrosives damages suggests that predominantly point and pitting corrosion predominate, which are exacerbated by internal or external loads. Unlike uniform corrosion, finding and slowing down which is not a particular difficulty, these types of corrosion are usually detected only after they are caused by emergency failures or fractures. Therefore, the main reasons for failures of technical facilities, among which the important placeis the destruction or operation of corrosion and corrosion and mechanical damage, must be carefully investigated and, if possible, eliminated on time. The complex of investigations of the damaged metal of evaporator tubes (steel 20 and 06X1) with a life time (from 0 to 20 years) included, along with standard, also special types of research, in particular: various variants of X-ray spectral analysis using a raster electron microscope "JSM-35CF" (Jeol, Japan),"SEM-515" with Philips microinalyzer "Link" scanning Auger electron spectroscopy (micro-analyzer "AES-2000"). In addition, the content and character of the distribution in the metal of pipes of water heaters of hydrogen, sulfur and oxygen were determined by the method of local mass spectral analysis with a laser microprobe, as well as by the method of melting of metal samples in the flow of carrier gas using the installation of the firm "Leco". With the help of high-precision metallographic experimental equipment, the mechanism of corrosion damage to the surfaces of evaporator tubes and the proposed measures for further research on methods for reducing the corrosion activity of the process environment and the adhesion of salt and carbonate sediments to the surface of the tubes of steam generators of food production is investigated. In particular, it has been shown that in order to eliminate metal corrosion and deposits of salt sediments in the form of scale on the surface of pipes of water heaters, it is necessary simultaneously to reduce the chemical activity of the water-vapor environment using different reagents, and to cover the tube with anticorrosive protective.

Computational simulation of turbulent flows around a marine propeller by solving the partially averaged Navier–Stokes equation

This study concerns the characteristics of the partially averaged Navier–Stokes method for local flow analysis around a rotating propeller. Partially averaged Navier–Stokes, resolving crucial large-scale structures of turbulent flow at a given computational grid resolution, is a bridging turbulence closure model between the Reynolds-averaged Navier–Stokes equation and the direct numerical simulation. A detailed comparison between partially averaged Navier–Stokes and Reynolds-averaged Navier–Stokes models is made to achieve a better understanding of partially averaged Navier–Stokes characteristics for predicting the coherent structures in turbulent flow. The two-equation k-ω shear stress transport model and the seven-equation Reynolds stress model are selected for Reynolds-averaged Navier–Stokes computations. The problem of interest is the flow around a rotating KP505 propeller in open water conditions at an advance ratio of 0.7. Near the leading edge, the partially averaged Navier–Stokes results are similar to those of Reynolds stress model in terms of the vortical structures. Vorticity predicted by different turbulence models, however, shows significant differences. For a more detailed analysis, the velocity gradient constituting the vorticity is identified at the leading edge. It is proven that partially averaged Navier–Stokes is able to capture the anisotropic characteristics of the flow at the leading edge, where both the geometric and flow characteristics change abruptly.

Pressure effects on local atomic structure of Ni15Co15Al70 metallic glasses

Molecular dynamics simulations are used to study the pressure effects on the local atomic structure of Ni15Co15Al70 metallic glasses. Interatomic interactions are modeled by the semi-empirical embedded atom method. The effects of pressure were systematically investigated through a variety of local structural analysis methods, such as bond angle distribution, structure factor, Voronoi tessellation and total and partial coordination numbers. Via the Went-Abraham parameter, our numerical results show an increase of the glass transition temperature Tg with increasing pressure. In the same context, Voronoi tessellation and coordination number analyses indicate that the local structure of glassy Ni15Co15Al70 is obviously influenced by the applied pressure, and the degree of local fivefold symmetry in the quenched systems decreases when the pressure increases. Lastly, we also investigated other parameters of structural disorder in amorphous alloys Ni15Co15Al70, including the concept of free volume and the atomic-level stresses. Implications of these findings are discussed.

Revealing key structural features hidden in liquids and glasses

A great success of solid state physics comes from the characterization of crystal structures in the reciprocal (wave vector) space. The power of structural characterization in Fourier space originates from the breakdown of translational and rotational symmetries. However, unlike crystals, liquids and amorphous solids possess continuous translational and rotational symmetries on a macroscopic scale, which makes Fourier space analysis much less effective. Lately, several studies have revealed local breakdown of translational and rotational symmetries even for liquids and glasses. Here, we review several mathematical methods used to characterize local structural features of apparently disordered liquids and glasses in real space. We distinguish two types of local ordering in liquids and glasses: energy-driven and entropy-driven. The former, which is favoured energetically by symmetry-selective directional bonding, is responsible for anomalous behaviours commonly observed in water-type liquids such as water, silicon, germanium and silica. The latter, which is often favoured entropically, shows connections with the heterogeneous, slow dynamics found in hard-sphere-like glass-forming liquids. We also discuss the relationship between such local ordering and crystalline structures and its impact on glass-forming ability. The knowledge of local structures of non-crystalline materials is of fundamental importance in the understanding of their physical properties. This Review describes recent advances in local structural analysis methods, which shed new light on mysterious phenomena in liquids and glasses.

Local fractional homotopy analysis method for solving non-differentiable problems on Cantor sets

In this paper, we present a semi-analytic method called the local fractional homotopy analysis method (LFHAM) for solving differential equations involving local fractional derivatives based on the local fractional calculus and the homotopy analysis method. The suggested analytical technique always provides a simple way of constructing a series of solutions from the higher-order deformation equation. The LFHAM guarantees the convergence of the series solutions using the nonzero convergence-control parameter. Three examples are provided to illustrate the efficiency and high accuracy of the method.

Local fractional Laplace homotopy analysis method for solving non-differentiable wave equations on Cantor sets

In this paper, we introduce a semi-analytical method called the local fractional Laplace homotopy analysis method (LFLHAM) for solving wave equations with local fractional derivatives. The LFLHAM is based on the homotopy analysis method and the local fractional Laplace transform method, respectively. The proposed analytical method was a modification of the homotopy analysis method and converged rapidly within a few iterations. The nonzero convergence-control parameter was used to adjust the convergence of the series solutions. Three examples of non-differentiable wave equations were provided to demonstrate the efficiency and the high accuracy of the proposed technique. The results obtained were completely in agreement with the results in the existing methods and their qualitative and quantitative comparison of the results.

A Novel Tri-Training Technique for the Semi-Supervised Classification of Hyperspectral Images Based on Regularized Local Discriminant Embedding Feature Extraction

This paper introduces a novel semi-supervised tri-training classification algorithm based on regularized local discriminant embedding (RLDE) for hyperspectral imagery. In this algorithm, the RLDE method is used for optimal feature information extraction, to solve the problems of singular values and over-fitting, which are the main problems in the local discriminant embedding (LDE) and local Fisher discriminant analysis (LFDA) methods. An active learning method is then used to select the most useful and informative samples from the candidate set. In the experiments undertaken in this study, the three base classifiers were multinomial logistic regression (MLR), k-nearest neighbor (KNN), and random forest (RF). To confirm the effectiveness of the proposed RLDE method, experiments were conducted on two real hyperspectral datasets (Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Reflective Optics System Imaging Spectrometer (ROSIS)), and the proposed RLDE tri-training algorithm was compared with its counterparts of tri-training alone, LDE, and LFDA. The experiments confirmed that the proposed approach can effectively improve the classification accuracy for hyperspectral imagery.

Deformation Twinning in Polycrystalline Mg Microstructures at High Strain Rates at the Atomic Scales

Large scale molecular dynamics (MD) simulations are carried out to investigate the twinning behavior as well as the atomic scale micromechanisms of growth of tension and compression twins in polycrystalline Mg microstructures at high strain rates. A new defect characterization algorithm (extended-common neighbor analysis (E-CNA)) is developed that allows for an efficient identification of various types of twins in HCP microstructures. Unlike other local orientation analysis methods, the E-CNA method allows for atomic scale characterization of the structure of different types of twin boundaries in HCP microstructures. The MD simulations suggest that the local orientation of individual grains with the loading axis plays a critical role in determining the ability of grains to nucleate either compression twins or tension twins. The twinning behavior is observed through nucleation of a pair of planar faults and lateral growth of the twins occurs through nucleation of steps along the planar faults. The kinetics of migration of steps that determine the rate of growth of twins are investigated at the atomic scales. The twin tip velocity computed at high strain rates compares well with the experimentally reported values in the literature.

A Screw Approach to the Approximation of the Local Geometry of the Configuration Space and of the Set of Configurations of Certain Rank of Lower Pair Linkages

Abstract A motion of a mechanism is a curve in its configuration space (c-space). Singularities of the c-space are kinematic singularities of the mechanism. Any mobility analysis of a particular mechanism amounts to investigating the c-space geometry at a given configuration. A higher-order analysis is necessary to determine the finite mobility. To this end, past research leads to approaches using higher-order time derivatives of loop closure constraints assuming (implicitly) that all possible motions are smooth. This continuity assumption limits the generality of these methods. In this paper, an approach to the higher-order local mobility analysis of lower pair multiloop linkages is presented. This is based on a higher-order Taylor series expansion of the geometric constraint mapping, for which a recursive algebraic expression in terms of joint screws is presented. An exhaustive local analysis includes analysis of the set of constraint singularities (configurations where the constraint Jacobian has certain corank). A local approximation of the set of configurations with certain rank is presented, along with an explicit expression for the differentials of Jacobian minors in terms of instantaneous joint screws. The c-space and the set of points of certain corank are therewith locally approximated by an algebraic variety determined algebraically from the mechanism's screw system. The results are shown for a simple planar 4-bar linkage, which exhibits a bifurcation singularity and for a planar three-loop linkage exhibiting a cusp in c-space. The latter cannot be treated by the higher-order local analysis methods proposed in the literature.

STRmix™ collaborative exercise on DNA mixture interpretation

An intra and inter-laboratory study using the probabilistic genotyping (PG) software STRmix™ is reported. Two complex mixtures from the PROVEDIt set, analysed on an Applied Biosystems™ 3500 Series Genetic Analyzer, were selected. 174 participants responded.For Sample 1 (low template, in the order of 200 rfu for major contributors) five participants described the comparison as inconclusive with respect to the POI or excluded him. Where LRs were assigned, the point estimates ranging from 2 × 104 to 8 × 106. For Sample 2 (in the order of 2000 rfu for major contributors), LRs ranged from 2 × 1028 to 2 × 1029. Where LRs were calculated, the differences between participants can be attributed to (from largest to smallest impact):•varying number of contributors (NoC),•the exclusion of some loci within the interpretation,•differences in local CE data analysis methods leading to variation in the peaks present and their heights in the input files used,•and run-to-run variation due to the random sampling inherent to all MCMC-based methods.This study demonstrates a high level of repeatability and reproducibility among the participants. For those results that differed from the mode, the differences in LR were almost always minor or conservative.

Stress Response and Damage Characteristics of Local Members of a Structure due to Tunnel Blasting Vibrations Based on the High‐Order Local Modal Analysis

Damage characteristics and dynamic stress response of aging masonry structures for blast‐induced ground motion were performed using high‐order local modal analysis method. A complete investigation of damage types and locations of aging masonry buildings due to tunnel blasting vibration were performed by on‐site survey. A typical 2‐storey aging masonry building located above a tunnel was selected for dynamic response analysis. The experimental dynamic characteristics of the structure were determined by using the operational modal analysis (OMA) method. Finite element models for the masonry structures were updated by modifying material parameters based on OMA results. The first five natural frequencies of the updated finite element models ranged from 8.80–24.99 Hz, and the first five modes were global modes. The sixth to twentieth natural frequencies ranged from 26.10–36.34 Hz, and the sixth to twentieth modes were local modes whose deformation was greater than the global deformation. Since the principal frequencies of the tunnel blast vibration were mostly higher than the natural global modes’ frequencies and were much closer to the natural frequencies of local members, local members experienced more intensive vibrations compared to the main body structure. The principal compressive stress (PCS) and principal tensile stress (PTS) of local members were several times greater than that of the main body structure. Therefore, local members of the masonry building suffered most from the tunnel blasting vibration. Corners due to stress concentration, the contact area between brick and concrete, local members, and precast floor seams are prone to damage during tunnel blasting. With the vibration velocity increasing, the PCS and PTS of local members gradually increase. But, the PTS ratio of local members decreases with the increase of peak particle velocities. The dynamic response analysis result and the damage locations using high‐order local modal analysis method are in accordance with the damage found at the site.