Geometrical Distribution Research Articles

Discriminative subspace embedded dynamic geometrical and statistical alignment based on pseudo-label correction for cross-domain bearing fault diagnosis

Many domain adaptation (DA) approaches have been developed to address the challenge of domain divergence in cross-domain fault diagnosis. However, most of them only attempt to align statistical distribution while neglecting geometric alignment between source and target data. Furthermore, the use of some unreliable pseudo-labels may cause geometrical and statistical distributions mismatching and interfere with the DA model generating correct pseudo-labels during the iterative learning. In this paper, we propose a new model called discriminative subspace embedded dynamic geometrical and statistical alignment based on pseudo-label correction (DSDGSA-PC) for bearing fault diagnosis. Firstly, discriminative subspace alignment is proposed to mitigate feature redundancy and divergence by generating aligned subspaces for two domains, while preserving class discriminative information and global structures of data. Then, DSDGSA-PC leverages the representer theorem and the principle of structural risk minimization to learn a domain-invariant classifier in the subspace, while minimizing statistical and geometrical shift by jointly optimizing dynamic graph embedding and dynamic weighted distribution alignment strategies. Finally, a novel pseudo-label correction mechanism is integrated into DSDGSA-PC to evaluate the credibility of pseudo-labels and rectify the unreliable ones during the iterations. The experimental results illustrate that DSDGSA-PC has higher transfer performance compared to several advanced methods on 24 transfer tasks.

Use of peak over threshold data for flood frequency estimation: An application at the UK national scale

This study investigates choices of statistical distributions to represent the threshold exceedance frequency and magnitude of peaks-over-threshold (POT) series from a national dataset of extreme hydrological events from 842 gauging stations in the UK. From the initial POT series, two new series were created, POT1 and POT3, representing POT series with an average of, respectively, one and three exceedances per year. Using a χ2 goodness-of-fit test, the choice of distributions for both the annual exceedance counts and the magnitude of threshold exceedances were explored for both the POT1 and POT3 datasets. The results show that the negative binomial and geometrical distributions provide a better fit to the annual exceedance count than the Poisson distribution typically assumed. These results are particularly pronounced when considering the POT3 dataset and in the South-East of the UK where many river flow series are dominated by slow responding groundwater dominated catchments. Finally, estimates of design floods with a return period of 2 and 100 years were obtained for each POT series and compared to the equivalent estimates obtained from direct at-site analysis of the annual maximum series. The results show a good alignment between the magnitude of the design floods estimated by the two methods, but a generally lower standard deviation of estimates obtained from the POT data, as quantified using a bootstrap procedure. The results presented here show that the POT series could beneficially replace the current operational guidelines based on annual maximum series for design flood estimation in the UK.

Porosity-dependent stability analysis of bio-inspired cellular nanocomposite shells

This paper presents an innovative numerical model to investigate buckling behaviour of bio-inspired continuously graded porous (CGP) nanocomposite cylindrical shells. It is postulated that the shell subjected to combined lateral pressure and axial compressive load is constructed from metal foams with closed-cell structures that possess graded internal pores, which exhibit three types of continuously graded porosity profiles based on a power-law distribution. A scaling relation for the effective Young’s modulus of the cellular structure determined by a variational finite element method (FEM) is used. The effective constitutive law of an elastic isotropic metal matrix containing distributed elastic carbon-nanotubes (CNTs) is estimated in consideration of the impact of CNTs agglomeration using a continuum model based on the Eshelby–Mori–Tanaka (EMT) approach. In contrast to conventional approaches, the study employs Euler–Bernoulli beams to model stiffeners within the CGP shells. This choice allows for a more realistic representation of stiffener effects, as opposed to the prevalent approach of uniform smearing across the shell’s surface. The equilibrium equations of the CGP shell, based on the Reddy higher-order shell theory (RHST), is obtained through the application of the Euler equation. Subsequently, the equations for stability are obtained through the utilization of the variational method. This study emphasizes the effects of geometrical parameters, porosity variability, and distribution of CNTs on the buckling performance of the CGP shells. The intricate interplay between CNTs and porosity distributions critically influences the stability behaviour of CGP shells. CNTs arrangement remarkably impacts buckling behaviour at higher length-to-mean radius ratios, while symmetric porosity near the mid-surface significantly enhances stiffness. These findings provide valuable insights for designing closed-cell cellular stiffened shells with optimal porosity to enhance stability.

A Study on the Effect of Multistage Toolpath in Fabricating a Customized Cranial Implant in Incremental Sheet Metal Forming

Incremental sheet forming (ISF) process offers a high degree of flexibility in the manufacturing of different sheet parts, which makes it an ideal candidate for prototype parts as well as efficient at fabricating various customized products at low production costs compared to traditionally used processes. However, parts produced in this process exhibit notable geometrical inaccuracy and considerable thickness reduction. In this paper, the single point incremental sheet forming variant of the process has been implemented to manufacture a highly customized cranial implant starting from the computed tomography (CT) scan data of the patient's anatomy. A methodology, from the modeling to the realization of the implant, is presented and discussed. The primary aim of the research was to analyze and study the effect of the multistage toolpath strategy compared to the traditional single-stage toolpath in terms of geometrical accuracy and thickness distribution. The final results show that the part formed in the multistage toolpath strategy exhibited a more uniform thickness distribution compared to the single-stage approach. Regarding the geometrical accuracy, the deviation analysis between the nominal and actual data has revealed that the multistage forming has significantly enhanced the final geometrical accuracy of the formed part.

A Computationally Efficient Multiscale, Multi-Phase Modeling Approach Based on CPFEM to Assess the Effect of Second Phase Particles on Mechanical Properties

Crystal plasticity finite element (CPFEM) modeling of metals that can be age hardened consisting of second phase particles is extensively performed based on representative volume element (RVE) models. The RVE model is generated for ferritic low-carbon steel using the data obtained from microstructural observation through optical microscopy (OM) and electron backscatter diffraction (EBSD). The generated RVE is required to statistically represent the original material in terms of grain topology and texture in microscale, as well as the configuration of second phase particles in submicron scale. The multiscale, multi-phase nature of the generated RVE leads to a computationally expensive modeling procedure. To overcome this issue, an alternative multiscale modeling approach based on a homogenization scheme is proposed, in which the effect of second phase particles on deformation behavior is accounted for with no need for the explicit presence of particles in RVE. Lastly, a thorough parametric analysis is performed to investigate the sensitivity of the mechanical properties to the second phase particles in terms of size, volume fraction, geometrical distribution, and deformable or non-deformable properties of precipitates in the investigated material. The results show that the proposed multiscale modeling approach successfully accounts for the effect of second phase particles on deformation behavior, while the computational cost is reduced by more than 99%. In addition, the simulations show that the configuration of second phase particles at a microscale plays an important role in defining the mechanical behavior of the material.

State of the Art in Development of Heat Exchanger Geometry Optimization and Different Storage Bed Designs of a Metal Hydride Reactor.

The efficient operation of a metal hydride reactor depends on the hydrogen sorption and desorption reaction rate. In this regard, special attention is paid to heat management solutions when designing metal hydride hydrogen storage systems. One of the effective solutions for improving the heat and mass transfer effect in metal hydride beds is the use of heat exchangers. The design of modern cylindrical-shaped reactors makes it possible to optimize the number of heat exchange elements, design of fins and cooling tubes, filter arrangement and geometrical distribution of metal hydride bed elements. Thus, the development of a metal hydride reactor design with optimal weight and size characteristics, taking into account the efficiency of heat transfer and metal hydride bed design, is the relevant task. This paper discusses the influence of different configurations of heat exchangers and metal hydride bed for modern solid-state hydrogen storage systems. The main advantages and disadvantages of various configurations are considered in terms of heat transfer as well as weight and size characteristics. A comparative analysis of the heat exchangers, fins and other solutions efficiency has been performed, which makes it possible to summarize and facilitate the choice of the reactor configuration in the future.

Effects of macro-scale heterogeneity on the kinetic interface-sensitive tracer test for measuring the fluid–fluid interfacial area in dynamic two-phase flow in porous media

A novel reactive smart tracer method, termed the kinetic interface-sensitive (KIS) tracer test, has been demonstrated in laboratory column experiments to enable measurement of the specific capillary-associated fluid–fluid interfacial area in dynamic two-phase flow displacement processes in porous media. Development of the tracer method towards effective application in real field conditions requires investigation of the influence of the porous media heterogeneity on the front size and the specific interfacial area, and, consequently, in how far a kinetic interface-sensitive tracer experiment, and the corresponding breakthrough curves, are affected. This study employs a two-dimensional Darcy-scale two-phase flow reactive transport model to investigate numerically the KIS tracer transport in heterogeneous porous media. Simulations were carried out for the primary drainage process in a domain formed of fine and coarse porous media. Various heterogeneity patterns, having different numbers of inclusions and different geometrical distributions, were studied. It is shown that the shape of the breakthrough curves can be used as an indicator for quantifying the displacement front roughness, the specific interfacial area in the domain, and the domain heterogeneity, e.g., the existence of preferential flow pathways inside the porous media. The results indicate that when the displacement front roughness is small, the concentration breakthrough curves exhibit a linear increase. The slopes of the breakthrough curves linearly depend on the fraction of the bulk volume occupied by the low-permeability sand inclusions. The volume-averaged specific interfacial area and the size of the transition zone can be determined from the slopes of the breakthrough curves.

Energy Equivalence Based Estimation of Hybrid Composites Mechanical Properties.

Hybrid composites, usually combining natural and synthetic reinforcing filaments, have gained a lot of attention due to their better properties than traditional two-component materials. For structural applications of hybrid composites, there is a need to precisely determine their mechanical properties on the basis of the mechanical properties, volume fractions, and geometrical distributions of constituent materials. The most common methods, such as the rule of mixture, are inaccurate. More advanced methods, giving better results in the case of classic composites, are difficult to apply in the case of several types of reinforcement. In the present research, a new estimation method is considered, which is simple and accurate. The approach is based on the definition of two configurations: the real, heterogeneous, multi-phase hybrid composite configuration, and the fictitious, quasi-homogeneous one, in which the inclusions are "smeared out" over a representative volume. A hypothesis of the internal strain energy equivalence between the two configurations is formulated. The effect of reinforcing inclusions on the mechanical properties of a matrix material is expressed by functions of constituent properties, their volume fractions, and geometrical distribution. The analytical formulas are derived for an isotropic case of a hybrid composite reinforced with randomly distributed particles. The validation of the proposed approach is performed by comparing the estimated hybrid composite properties with the results of other methods, and with experimental data available in the literature. It is shown that a very good agreement is obtained between experimentally measured hybrid composite properties and their predictions resulting from the proposed estimation method. The estimation errors are much lower than the errors of other methods.

Fabrication and Analysis of Denture Plate Using Single Point Incremental Sheet Forming

Incremental sheet forming (ISF) is a metal forming technology in which small incremental deformations determine the final shape. The sheet is deformed by a hemispherical tool that follows the required shape contour to deform the sheet into the desired geometry. In this study, single point incremental sheet forming (SPIF) has been implemented in dentistry to manufacture a denture plate using two types of stainless steel, 304 and 316L, with an initial thickness of 0.5mm and 0.8mm, respectively. Stainless steel was selected due to its biocompatibility and reasonable cost. A three-dimensional (3D) analysis procedure was conducted to evaluate the manufactured part's geometrical accuracy and thickness distribution. The obtained results confirm the capability of SPIF to produce thin-walled biomedical components with satisfactory dimensional accuracy, as geometrical deviations between the developed and the actual models are predominantly in the range of ±0.25mm.

Uncertainty in the Mobile Observation of Wind

Air quality and greenhouse gas sampling from mobile platforms enables local to regional analyses of pollutant exposure, atmospheric chemistry, and emission sources. Simultaneous meteorological observations, particularly wind speed and direction, are often used to interpret measurements and construct emission fluxes. However, the wind arising from a moving platform contributes to the observed wind speed and direction, and this artifact requires adequate removal to best apply wind observations. Here, we calculate the theoretical limitations to the measurement of wind from a moving vehicle, assess the accompanying uncertainty, and apply these methods to an example transect across a plume of methane. The angle of the wind relative to the moving vehicle is a crucial determinant of the ability to distinguish a true wind and defines its uncertainty. Unlike a stationary wind measurement, the wind speed and direction contain complementary information that broadens the capability of the mobile anemometer. We find that the isolation of a true wind depends on the anemometer wind speed accuracy for true winds moving with or against the vehicle, while the anemometer directional accuracy is more important for crosswinds, such as is experienced when observing across a plume. The uncertainty in estimated wind speed has similar geometry, but the uncertainty in estimating true wind direction is the opposite: the accuracy of measured wind speed most greatly impacts crosswind direction. Exact values are determined by the specific accuracy limitations of the anemometer and vehicle speed, and the geometrical distributions vary. As a result, the characteristics of each mobile lab setup should be assessed individually to best inform meteorological analyses and observation route planning.

Numerical and experimental investigation of high-resolution manipulation of microparticles using a developed two-stage acoustofluidic platform

Acoustophoresis as an emerging label-free, biocompatible, and contactless technique in particle separation has attracted recent interest in the separation of cells and particles from heterogeneous samples. Improving separation resolution in many biological applications in which particles of close sizes must be separated is of great importance. To study the separation of microparticles with similar sizes, a two-stage acoustofluidic platform is developed in this study. The device uses acoustic and hydrodynamic focusing mechanisms to boost alignment efficiency in its first stage. The device's second module separates microparticles using standing acoustic waves. In both numerical and experimental studies, multiple parameters such as geometrical features, pressure distribution, and sheath-flow variation were investigated to optimize separation performance. The experimental results show that particles of sizes 8–10 µm can be separated with a purity of more than 80% and a throughput of 10 µl/min. As a potential application, the separation resolution demonstrated in the study can be applied to the separation of white blood cells, e.g., neutrophils from leukocytes.

A quest for stable phosphonyl radicals: limitations and possibilities of carbocyclic backbones and bulky substituents.

Although phosphonyl radicals play an important role as transient species in many chemical transformations, such as photoinitiated polymerisation reactions, permanently stable phosphonyl radicals are yet to be discovered. In this computational study, we aim at a conceptual understanding of the electronic effects influencing the stabilities of phosphonyl radicals through computing radical stabilisation energies (RSEs) for a large set of phosphonyl radicals with carbocyclic backbones. The studied radicals exhibit ring sizes varying from 3- to 7-membered with full saturation or different grades of unsaturation adjacent to the P-centre in an endo or exocyclic fashion. To gain deeper insight into the stabilisation effects and delocalisation, the geometrical aspects, electronic structures, and spin distributions of the radicals were scrutinised. The five-membered, fully unsaturated ring (phospholyl oxide), which has a planar structure, offers the most substantial electronic stabilisation. By embedding this ring into a more extended π-system, the possibility of gaining further stabilisation was also explored. To screen the effect of steric congestion on the stabilities of previously selected radicals toward dimerisation, a large number of bulky substituents with different sizes and shapes were systematically investigated. Our results outline that stable phosphonyl radicals seem accessible, provided that the electronic stabilisation effects are supplemented by well-designed bulky substituents.

The Use of an Airborne Laser Scanner for Rapid Identification of Invasive Tree Species Acer negundo in Riparian Forests

Invasive species significantly impact ecosystems, which is fostered by global warming. Their removal generates high costs to the greenery managers; therefore, quick and accurate identification methods can allow action to be taken with minimal impact on ecosystems. Remote sensing techniques such as Airborne Laser Scanning (ALS) have been widely applied for this purpose. However, many species of invasive plants, such as Acer negundo L., penetrate the forests under the leaves and thus make recognition difficult. The strongly contaminated riverside forests in the Vistula valley were examined in the gradient of the center of Warsaw and beyond its limits within a Natura 2000 priority habitat (91E0), namely, alluvial and willow forests and poplars. This work aimed to assess the potentiality of a dual-wavelength ALS in identifying the stage of the A. negundo invasion. The research was carried out using over 500 test areas of 4 m diameter within the riparian forests, where the habitats did not show any significant traces of transformation. LiDAR bi-spectral data with a density of 6 points/m2 in both channels were acquired with a Riegl VQ-1560i-DW scanner. The implemented approach is based on crown parameters obtained from point cloud segmentation. The Adaptive Mean Shift 3D algorithm was used to separate individual crowns. This method allows for the delineation of individual dominant trees both in the canopy (horizontal segmentation) and undergrowth (vertical segmentation), taking into account the diversified structure of tree stands. The geometrical features and distribution characteristics of the GNDVI (Green Normalized Vegetation Index) were calculated for all crown segments. These features were found to be essential to distinguish A. negundo from other tree species. The classification was based on the sequential additive modeling algorithm using a multi-class loss function. Results with a high accuracy, exceeding 80%, allowed for identifying and localizing tree crowns belonging to the invasive species. With the presented method, we could determine dendrometric traits such as the age of the tree, its height, and the height of the covering leaves of the trees.

Size-dependent linear and nonlinear vibration of functionally graded CNT reinforced imperfect microplates submerged in fluid medium

The linear and nonlinear vibrations of functionally graded carbon nanotubes reinforced microplate (FGCNTRM) submerged in fluid medium have been studied analytically. The primary novelty of this research is to take into consideration the effects of using carbon nanotubes (CNT) and geometric imperfection on the vibrational behavior of microplates submerged in the fluid. Equations of motion are obtained by first-order shear deformation theory of plates and considering the size effects and large deformations. Effective mechanical properties have been determined using the rule of mixtures for four various types of CNT distributions. The nonlinear equations of motion are discretized using the Galerkin method, and the equation response is acquired applying the method of multiple time scales. After verifying the results, the effect of microplate geometric characteristics, small size parameter, fluid height, geometrical imperfection amplitude, weight fraction, and distribution of CNT on linear and nonlinear frequencies as well as amplitude-frequency curves have been studied. The results demonstrate that an increase in fluid height leads to a decrease in the natural frequency. Also, geometric imperfection causes the stiffening behavior of the softening spring and substantially bends the response curve to the right. This bending can induce jump instabilities as the frequency slowly varies.

Apparatuses for verifying the precision of gravimeters with lifting spherical source masses.

Two apparatuses with lifting spherical source masses are built and used to verify the precision of gravimeters. The 333-kg source mass produces a maximum acceleration of 200 nm/s2 with an uncertainty of 0.31 nm/s2, which corresponds to a relative uncertainty of 0.16%. After evaluating the temperature effect, drift of the gravimeter, the atmospheric effect, and the tidal effect, a combined uncertainty of 1 nm/s2 is obtained. One CG6 gravimeter is tested using two apparatuses, the measured accelerations agree with the theoretical values within the error range. Differential measurement with two CG6 gravimeters on one apparatus is performed, which provides a common-mode rejection of the effects due to ambient noise, such as the gravity tide, atmospheric effect, and drift. The difference in acceleration measured by the two gravimeters is determined to be 199 ± 6 nm/s2, which agrees well with the value 200 ± 1 nm/s2 obtained by using apparatus II. Our apparatuses provide a verification of the precision of gravimeters with an uncertainty of 1 nm/s2, which is one of the lowest uncertainties reached so far. The determination of geometrical metrology and mass distribution and detailed error analysis are presented. The methods on error analysis as well as differential measurement used in our work are helpful for gravity measurement.

Active sloshing control of a circular cylindrical container with FG GPL-RC

The main purpose of the current study is to design a control system for a sloshing system to suppress the vibration of functionally graded graphene platelet-reinforced composite (FG GPL-RC) on the top surface. A set of piezoelectric sensors and actuators are used for active control of fluid-structure coupling in transient seismic analysis of an inviscid liquid sloshing in a cylindrical tank. First, the top surface FG GPL-RC is optimized to satisfy maximum deformation, face failure, mid shear, and face wrinkling by changing the geometrical parameters and weight fraction distribution through the thickness. The nonlinear governing equations of nanocomposite panels with mechanical properties derived from the Halpin–Tsai model are solved by smoothed particle hydrodynamics (SPH) method. A parameter study counting the boundary condition effects, thickness-to-radius ratio, material distribution of the laminates, and dimensions of the sloshing tank on the FG GPL-RC natural frequencies are surveyed and explained in detail. Then, the frequency analysis of the plate with and without sloshing is performed while the inviscid fluid motion is modeled by SPH. The proposed method is validated with available data in the literature. Finally, the active control of the coupled system in response to the external disturbances is completed by a tuned proportional–integral–derivative (PID) controller which used the piezoelectric sheets on the top surface plate. The performance of the proposed control system is illustrated by a comparison of the controlled and uncontrolled transient responses of the coupled hydro-elastic system to the El-Centro seismic load.

Generation expansion planning for Guizhou province based on the complementary characteristics of wind and solar

With the growth of wind power and solar power, power source clean transformation has become a feasible way for achieving the carbon peak target. As a hydropower resource-abundant province, Guizhou has already built Wujiang river cascade hydropower plants. This paper introduces the basic information of the Guizhou provincial power system and geometrical renewable resource distribution characteristics, especially the power source structure. Then, the wind and solar power complementary characteristics are analyzed by different copula conjunction functions. Then, the power structure transformation and generation expansion plan are provided with both carbon peak restriction and curtailment restrictions. At last, the future Guizhou provincial power system in 2029 operation simulation cases are provided, which can reduce the thermal power generation ratio to 42% and increase wind and solar power generation ratio to 8.5% and 13% approximately. The conclusion indicates that coal-fired power plant flexible reform and larger capacity energy storage installation effectively solve the larger power fluctuation and peak regulation demand with more renewable energy integration target.

When stuff gets old: Material surface characteristics and the visual perception of material change over time

Materials’ surfaces change over time due to chemical and physical processes. These processes can significantly alter a material’s visual appearance, yet we can recognise the material as the same. The present study examined the extent of changes the human visual system can detect in specific materials over time. Participants (N = 5) were shown images of different materials (Banana, Copper, Leaf) from an existing calibrated set of photographs. Participants indicated which image pair (of the 2 pairs shown) displayed the largest difference. Estimated perceptual scales showed that observers were able to rank the images of aged materials systematically. Next, we examined the role that global and local changes in material surface colour play in the perception of material change. We altered the information about colour and geometrical distribution in the images used in the first experiment, and participants repeated the task with the altered images. Our results showed significant differences between individual observers. Most importantly, participants’ ability to rank the images varied with material type. The leaf images were particularly affected by our alteration of the geometrical distribution. Together, our findings show the factors contributing to the perception of material change over time.

Microstructure, Mechanical and Electrical Properties of Hybrid Copper Matrix Composites with Fe Microspheres and rGO Nanosheets.

Copper matrix composites have a wide application as magnetic conductive materials, electromagnetic materials, electrical discharge machining materials, etc. Such materials are expected to have a good combination of excellent electrical conductivity and good mechanical strength. In this work, micro/nano hybrid reinforcements with Fe microspheres and reduced graphene oxide (rGO) nanosheets were developed for copper matrix composites. The rGO/Fe/Cu powders were firstly wet-mixed and then densified by the vacuum hot-pressing sintering to obtain the bulk compacts. Microstructure, electrical conductivity and mechanical properties of such compacts were investigated. Microstructural result of as-sintered compacts shows that the Fe microspheres could distribute in the matrix uniformly, and rGO nanosheets exhibit both agglomerated and dispersed states. The grain size of Cu matrix decreased with the increase of the rGO content. Hardness, compression and tensile 0.2% yield strength of the as-sintered compacts were improved evidently by the addition of the hybrid Fe/rGO, comparing with pure Cu and single Fe-added composites. However, a lower electrical conductivity appeared in the more rGO-added composites, but still reached more than 33.0% international annealing copper standard (IACS). These performance change could be sought in the spatially geometrical distribution and characteristics of such micro/nano Fe/rGO hybrid addition, and the relevant mechanisms were discussed.

Uniqueness of the limit cycles for complex differential equations with two monomials

We prove that any complex differential equation with two monomials of the form z˙=azkz¯l+bzmz¯n, with k,l,m,n non-negative integers and a,b∈C, has one limit cycle at most. Moreover, we characterise when such a limit cycle exists and prove that then it is hyperbolic. For an arbitrary equation of the above form, we also solve the centre-focus problem and examine the number, position, and type of its critical points. In particular, we prove a Berlinskiĭ-type result regarding the geometrical distribution of the critical points stabilities.