Meridional Direction Research Articles

Modeling Toroidal Currents in the Ionospheric Electrojet Regions

AbstractNew basis functions, suitable for fitting magnetic field observations of the auroral and equatorial electrojets, are constructed by applying principal components analysis (PCA) to a set of rotated current loops in the ionospheric E‐layer. The current loops, which are defined with respect to quasi‐dipole coordinates, are placed in the electrojet regions (northern polar, equatorial, and southern polar) and are then rotated and tilted to capture both zonal and meridional flow directions, enabling a fully 2D representation of the toroidal flow in the E‐layer. We consider four possible covariance functions that define correlation between individual loops, and use PCA to derive a set of modes representing toroidal electrojet current flow. These modes can be fitted to magnetic field observations recorded in space and/or on ground in order to reconstruct an equivalent height‐integrated current system in the E‐layer which best describes the measurements. We present an application of this new technique, which we call LoopPCA, to model quasi‐steady ionospheric current systems, by fitting mean ionospheric magnetic fields recorded by the Swarm satellite mission over a 6 year time period.

The free vibration analysis of ring-stiffened FG conical sandwich shells with auxetic and non-auxetic honeycomb cores

In this paper, the natural frequencies of a ring-stiffened conical sandwich shell with a functionally graded (FG) honeycomb core are calculated. The core can be either a non-auxetic honeycomb (NAH) or an auxetic honeycomb (AH). The honeycomb core and face layers are fabricated from metal-ceramic functionally graded material (FGM) in which the volume fraction of the ceramic increases from zero at the inner surface of the shell to one at its outer surface based on either power-law function (P-FGM), sigmoid function (S-FGM), or exponential function (E-FGM). The sandwich shell is modeled based on Murakami’s zig-zag theory and the intermediate ring support is modeled as a rigid structure. Hamilton’s principle is employed to derive the governing equations, compatibility conditions, and boundary conditions. A semi-analytical solution is presented which includes an exact solution in the circumferential direction followed by an approximate numerical solution via the differential quadrature method (DQM) in the meridional direction. It is concluded that for each vibrational mode, optimal values can be found for the inclined angle, core-to-shell thickness ratio, and location of the ring support which bring about the highest natural frequency. The presented work is the first theoretical work associated with the free vibration analysis of a ring-stiffened FG conical sandwich shell with a honeycomb core which provides a reduction in the mass and improvement in the thermo-mechanical characteristics, simultaneously. Such properties make such a structure widely used in the aerospace industry. Considering the importance of the dynamic characteristics of aerospace structures, the results of this research can be used by these industries in the analysis and optimal design of the main body of airplanes and missiles.

Study of the influence of physical nonlinearities of spherical caps made by Elastomeric Materials

The analysis of the behavior of structural elements in terms of variations in physical and geometric influences has been the subject of study since the early days of mechanical and structural engineering research. When it comes to shells, especially those composed of hyperelastic materials, many researchers have carried out work evaluating both the influences of the type of curvature of these elements and the type of deformation expected due to hyperelasticity. This work will investigate the behavior of a spherical cap with a boundary condition established by the locking of the circumference that makes up its base and subjected to uniformly distributed loading on its surface. Two different types of material were considered, one elastic following Hooke's Law and the other hyperelastic represented by elastomeric constitutives models. The Novozhilov and Donnell-Mushtari-Vlasov (DMV) shell theories together with the Rayleigh-Ritz method are used to obtain the governing equations of the problem. The displacements will be approximated using trigonometric functions in the circumferential direction and the Legendre polynomial of the first type in the meridional direction. Linear results are obtained, such as natural frequencies, and non-linear results, such as frequency-displacement and load-displacement relationships.

Complex Ionospheric Fluctuations Over East and Southeast Asia During the May 2024 Super Geomagnetic Storm

AbstractThe May 2024 super storm is one of the strongest geomagnetic storms during the past 20 years. One of the most remarkable ionospheric responses to this event over East and Southeast Asia is the complex ionospheric fluctuations following the storm commencement. The fluctuations created multiple oscillations of total electron content (TEC) embedded in the diurnal variation, with amplitudes up to 10 TECu. Along the same latitude, the fluctuations were nearly synchronized over a wide longitude span up to 35°. In the meridional direction, the fluctuations over low latitudes were the most significant and complex, which contained two main components, the poleward extending oscillations originated from the magnetic equator, and the equatorward propagating traveling ionospheric disturbances (TIDs) from high latitudes. The TIDs likely occurred around the globe. The storm‐time interplanetary electric fields penetrating into equatorial latitudes of the ionosphere and the auroral energy input were suggested to drive the poleward extending oscillations and the equatorward TIDs, respectively.

Process Evaluation of Subseasonal North Atlantic Oscillation Prediction in the ECMWF Ensemble Forecast System

AbstractThis study evaluates the prediction skill of the North Atlantic Oscillation (NAO) pattern and its associated energy budget as simulated by the European Center for Medium‐Range Weather Forecasts ensemble forecast system. By classifying NAO events into high‐ and low‐skill cases, we analyzed the stationarity of NAO patterns and the role of baroclinic energy conversion in NAO prediction. In both positive and negative NAO phases, high‐skill cases exhibited more stationary NAO patterns than low‐skill cases. The analysis of processes indicates that high‐skill NAO cases are due to stronger baroclinic maintenance of NAO, with its initial position at the climatological thermal trough, whereas low‐skill NAO cases result from forecast biases in wave propagation from the North Pacific. Specifically, biases in baroclinic energy conversion in the meridional direction from week 2 lead to weak advection of the eddy available potential energy (EAPE), resulting in lower prediction skill.

Static analysis of masonry polygonal domes with membrane forces

Masonry polygonal domes are parts of several historic monuments and masonry buildings. The analysis of polygonal domes with a static approach is here presented, considering the structure made of vault cells and ribs. The vaults are portions of a cylindrical surface with single curvature in the meridian direction, and translation of the generatrix curve in the direction of the cylinder axis. The system is divided into rigid elements with interfaces. The first part of the work regards the geometry of the rigid elements, in particular the angles that characterize the shape of these. Then the equilibrium equations applied to every element are presented, with a procedure to calculate the membrane response for the self-weight in a non-redundant system, under symmetry conditions. The sum of the solution for the vaults is combined with effects of the weight of ribs and radial walls. The use of the equilibrium solution for pointed domes, domes with a lantern and oculus or additional load to the dome self-weight is shown. A limit analysis static approach is formulated calculating the maximum load relative to the equilibrium of the rigid elements considering the interfaces tensile strength and limited cohesion and friction for the shear resistance.

A Statistical Examination of the Spatial Correlations of HF Ionospheric Absorption Signatures Using the GO‐Canada Riometer Network

AbstractA network of 30‐MHz riometers distributed across Canada have been monitoring auroral absorption for decades. Electron precipitation can cause enhanced densities to develop below ∼100 km where the higher neutral density can cause absorption of High Frequency (HF) signals. Modeling D‐region absorption accurately can be challenging due to the large distances between riometer monitoring sites. It is of interest to develop an understanding of the typical scale sizes of these regions for assimilation in ionospheric models. Using the entire network of GO‐Canada riometers, auroral absorption events may be monitored as they develop through a wide MLT sector. By examining correlations between sites, proxies for the scale sizes of absorption regions may be estimated. It was found that the sizes of the absorbing regions in the zonal direction are on the order of 900 km. Conversely, the characteristic scale sizes of the regions in the meridional direction were ∼700 km. These results are consistent with the general magnetospheric structure which sees higher energy electrons primarily present in the nightside transition region, and ring current. This creates a natural limit in latitudinal correlations, while the spread in longitude is likely connected to the size of precipitation regions in MLT. Our results also show significant spread in scale sizes in both directions from a few hundred to several thousand km. In this paper, we summarize these results in terms of the observed trends in high energy electron precipitation spatial and temporal scales and discuss future work to connect these scales to magnetospheric drivers.

Nonlinear finite element formulation for thin-walled conical shells

This study presents a novel finite element formulation to predict the geometrically nonlinear response of conical shells under a wide range of practical loading conditions. The formulation expresses the discretized equilibrium equations in terms of the first Piola-Kirchhoff stress tensor and its conjugate gradient of the virtual displacements, is based on the kinematics of Love-Kirchhoff thin shell theory and the Saint-Venant-Kirchhoff constitutive model, and captures the follower effect of pressure loading. The formulation takes advantage of the axisymmetric nature of the shell geometries by adopting a Fourier series to characterize the displacement distributions along the circumferential direction while using Hermitian interpolation along the meridional direction. Comparisons with general shell models show the accuracy of the formulation under various loading conditions with a minimal number of degrees of freedom, resulting in a significant computational efficiency compared to conventional general-purpose shell solutions.

აჭარა-გურიის გეოლოგიური აგებულება მიღებული მაღლივი-კოსმოსური მასალების დეშიფრირებით

The geological structure of the Adjara-Guria region is defined by the fault zones of the orthgonal-diagonal system, which are the constituent parts (segments) of the transregional lineaments, and are well interpreted on high-space images.The block structure of the regionis determined by fault zones. Nine tectonic blocks of different configurations and geological structures are separated. There are deciphered 11 and 12 km wide tectonic zones with meridian direction, compiled,replaced by a large number of faults and related dykes. The gold occurencesin the region are associated with meridian structures, that’s why the identified tectonic zones are promising spaces for gold.

Thermal analysis of a reflection mirror by fluid and solid heat transfer method.

High-repetition-rate free-electron lasers impose stringent requirements on the thermal deformation of beamline optics. The Shanghai HIgh-repetition-rate XFEL aNd Extreme light facility (SHINE) experiences high average thermal power and demands wavefront preservation. To deeply study the thermal field of the first reflection mirror M1 at the FEL-II beamline of SHINE, thermal analysis under a photon energy of 400 eV was executed by fluid and solid heat transfer method. According to the thermal analysis results and the reference cooling water temperature of 30 °C, the temperature of the cooling water at the flow outlet is raised by 0.15 °C, and the wall temperature of the cooling tube increases by a maximum of 0.5 °C. The maximum temperature position of the footprint centerline in the meridian direction deviates away from the central position, and this asymmetrical temperature distribution will directly affect the thermal deformation of the mirror and indirectly affect the focus spot of the beam at the sample.

Analytical calculation approach for rocket nose cone structure with orthotropic material

The Authors of this research developed an analytical calculation method to estimate the strength of nose cone structures made of orthotropic materials, which were crucial components in aircraft and spacecraft. Strength analysis of nose cones had been comprehensively addressed for isotropic materials; however, the lack of efficient approaches for orthotropic materials presented a challenge. In this research, a new analytical method was proposed, combining membrane stress theory for isotropic materials with classical laminate theory for orthotropic materials. This approach enabled the determination of stresses on the nose cone shell structure in both meridional and circumferential directions in an efficient and straightforward manner. The analysis results indicated that the developed analytical method exhibited stress distribution trends similar to those obtained using the Finite Element Method. Stresses in the +45° and –45° direction, as well as in-plane shear stress and Tsai-Wu failure indices, showed trend similarity between the two methods. Despite specific numerical differences in the calculation results, these consistent trends suggested that the analytical method could serve as a tool for the preliminary design of a nose cone structure with a similar configuration analyzed in this study.

Impacts of Local Circulations on Ozone Pollution in the New York Metropolitan Area: Evidence From Three Summers of Observations

AbstractElevated surface ozone levels are often detected in the New York metropolitan area during summertime. Moreover, surface ozone in this region exhibits sharp spatial gradients and distinctive diurnal cycles under the influence of complex boundary layer circulations induced by the intricate coastal geometry. This study examines how surface ozone is impacted by local circulations spatially and temporally under different temperature scenarios (all summer days, hot summer days, and extreme heat days) with the help of cluster‐based meteorological conditions during the summertime of 2017–2019. The most polluted days are found to be highly associated with hot sea breeze days with weak background flow. When sea breeze development in the New York Bight is delayed and its penetration north is intercepted by the dominant westerlies during hot summer days, daily maximum 8‐hr average ozone (DMA8) in some ozone hot spots of New York City (NYC) and the south shore of Connecticut (CT) typically drops 9–10 ppb under comparable temperature levels. The average regional decrease of DMA8 for NYC and coastal CT is 6.7 and 8.3 ppb, respectively. Furthermore, we conclude that a change in early morning meridional wind direction is the most critical meteorological characteristic in controlling sea breeze onset type and helping modulate ozone exceedances in the region during extreme hot days when ozone exceedances are expected to be very common. The conclusion is further demonstrated with two case studies during the Long Island Sound Tropospheric Ozone Study 2018 field campaign.

The aeroelastic stability characteristics of a ring-stiffened conical three-layered sandwich shell with an FG auxetic honeycomb core utilizing zig-zag shell theory

This paper is devoted to the supersonic flutter analysis of a ring-stiffened conical three-layered sandwich shell consisting of an auxetic honeycomb (AH) core fabricated from functionally graded material (FGM). The face sheets are manufactured of FGM as well in which the volume fraction of the ceramic increases from zero at the inner surface to one at the outer surface based on a power-law function. The sandwich shell is mathematically modeled based on the Murakami's zig-zag shell theory and the aerodynamic pressure is modeled utilizing piston theory. The derivation of governing equations along with compatibility and boundary conditions are performed using Hamilton's principle and are solved through a semi-analytical solution consisting of an exact solution in the circumferential direction followed by an approximate solution in the meridional direction. The flutter boundaries are attained to investigate the variations of the natural frequencies and damping ratios to find the critical aerodynamic pressure (CAP). The impacts of several factors on the CAP are examined such as the power-law index, geometric characteristics of the cells in the FGAH, thickness of the honeycomb core, location of the ring, and boundary conditions. It is observed that an optimal location can be found for the ring support somewhere between the middle length and large radius of a conical shell that provides the best aeroelastic stability.

Discrete differential geometry-based model for nonlinear analysis of axisymmetric shells

In this paper, we propose a novel one-dimensional (1D) discrete differential geometry (DDG)-based numerical method for geometrically nonlinear mechanics analysis (e.g., buckling and snapping) of axisymmetric shell structures. Our numerical model leverages differential geometry principles to accurately capture the complex nonlinear deformation patterns exhibited by axisymmetric shells. By discretizing the axisymmetric shell into interconnected 1D elements along the meridional direction, the in-plane stretching and out-of-bending potentials are formulated based on the geometric principles of 1D nodes and edges under the Kirchhoff–Love hypothesis, and elastic force vector and associated Hessian matrix required by equations of motion are later derived based on symbolic calculation. Through extensive validation with available theoretical solutions and finite element method (FEM) simulations in literature, our model demonstrates high accuracy in predicting the nonlinear behavior of axisymmetric shells. Importantly, compared to the classical theoretical model and three-dimensional (3D) FEM simulation, our model is highly computationally efficient, making it suitable for large-scale real-time simulations of nonlinear problems of shell structures such as instability and snap-through phenomena. Moreover, our framework can easily incorporate complex loading conditions, e.g., boundary nonlinear contact and multi-physics actuation, which play an essential role in the use of engineering applications, such as soft robots and flexible devices. This study demonstrates that the simplicity and effectiveness of the 1D discrete differential geometry-based approach render it a powerful tool for engineers and researchers interested in nonlinear mechanics analysis of axisymmetric shells, with potential applications in various engineering fields.

Thermal optimization of a high heat load liquid-metal-bath cooled mirror at the Hefei Advanced Light Facility.

Within the beamlines of diffraction-limited storage rings, the liquid-metal-bath cooling scheme is a prevalent choice for the cooling of high-heat load mirrors. This study employs the finite element analysis method to evaluate the thermal deformations of liquid-metal-bath horizontally deflecting mirrors in the Hefei Advanced Light Facility. In particular, we introduce a novel optimization strategy to obtain the optimal thermal deformation scenario, which also satisfies mechanical design requirements. Moreover, a concurrent optimization approach across multiple structural parameters of mirrors is adopted to attain globally optimal thermal deformation. Following the optimization of the mirror's structural parameters, the curvature radius increases to 227 km, while the residual slope error decreases to 36.3 nrad at 6eV in the meridian direction. The ray tracing analysis of the beam demonstrates a considerable reduction in the influence of thermal deformation on the beam's focal point. This work proposes an optimization method for designing cooling schemes under mechanical constraints.

Diversity of the tropical easterly jet’s core location

The upper-tropospheric tropical easterly jet (TEJ) is one of the most important systems in modulating the Asian summer monsoon rainfall. In addition to the intensity variability that has been extensively studied, the TEJ’s core experiences remarkable changes in the zonal and meridional directions. The TEJ can be identified as three locational patterns using the cluster analysis: the east, northwest, and southwest modes. The frequencies of the three locational modes exhibit discernable changes on the monthly and the interannual-decadal time scales. While the anomalous zonal divergent circulation with the convergent/divergent center over the tropical Indian Ocean (IO) determines the zonal location of the TEJ’s core, the meridional temperature gradient between the Eurasian continent and the tropical IO distinguishes the meridional location of the TEJ’s core. It reflects the fundamental role of the large-scale east-west and north-south thermal contrasts in the movement of the TEJ’s core location. The variability of the TEJ’s core location has distinct impacts on the summer monsoon precipitation via redistributing the upper-level divergence and modulating the monsoon meridional circulation, especially in South, Southeast, and East Asia. In conjunction with the thermal effect of the Tibetan Plateau, the meridional shift of the TEJ’s core can affect the precipitation along the south slope of the Tibetan Plateau. These findings highlight the cause of the diversified TEJ’s core location and the significant impacts on the summer monsoon rainfall.

Deformation behavior and failure mechanism of AA7075 alloy during the cryogenic temperature-assisted incremental sheet forming process

High-strength aluminum alloys are potential structural materials for thin-walled aerospace and automotive components. However, the limited formability at room temperature (RT) hinders their wide industrial application. In this study, a cryogenic temperature-assisted incremental sheet forming (CT-ISF) process for manufacturing 3D curved thin-walled structures was proposed. An experimental platform for CT-ISF was established to form AA7075 alloys. We found that the formability of the solution-treated AA7075 alloy sheet was greatly improved under the cryogenic environment without sacrificing its strength. In combination with double pass forming process, the formability of the sheet can be further improved. The stable deformation of the sheet is promoted due to the suppression of the Portevin-Le Chatelier (PLC) effect at CT, which reduces axial force fluctuations during the forming process. The line roughness value of the meridional direction was reduced by 36.8% at CT due to the enhanced work-hardening and the utilization of MoS2 lubricant. In terms of microstructural evolution, we found that the fracture morphology of the formed parts changed from tensile fracture at RT to shear fracture at CT. The improved formability was attributed to increased Goss and E texture contents, delay in dislocation evolution, and suppression of the PLC effect. This work introduces a novel CT-ISF process that significantly enhances the formability of high-strength Al alloy. In particular, it unravels the enhancement mechanism of formability in the CT-ISF process, providing theoretical support for further research.

Statistical evaluation of measured biomechanical properties of human brain aneurysm samples.

<p>Human brain aneurysms may often prove fatal if not re&shy;cognized in time and treated accordingly. The understanding of development and rupture of aneurysms can significantly be improved by the application of numerical modelling, which in turn, requires the knowledge of mechanical properties of vessel wall. This study aims to identify assumed differences with respect to age, sex, spatial orientation, and rupture by utilizing detailed statistical analysis of uniaxial tensile measurements of human brain aneurysm samples, performed by the authors in a previous project.</p>. <p>At surgery of 42 patients, aneu&shy;rysm fundi were cut distally to the clip. In each case, depending on size, varying number of stripes (altogether 88) were prepared and uniaxial stress-strain measurements were performed. Quantities related to the capacity, energy absorption or stiffness were determined and statistically analysed.</p>. <p>The number of specimens in the aneurysm sample was sufficient to establish statistical differences with respect to sex and rupture (p&lt;0.05). No significant differences were detected in orientation, though higher values of stresses and deformations were ob&shy;tained in the circumferential direction com&shy;pared to the meridional direction.&nbsp;</p>. <p>Significant differences bet&shy;ween sexes with respect to ultimate deformations were demonstrated according to expectation, and the hypothesis on equality of energy capacity could be supported. Similarity of curves with respect to specimen orientation was also observed and ruptured aneurysm sacs tended to be smaller in size. It seems that differences and trends described in this paper are realistic and need to be applied in numerical modelling.</p>.

Effect of pulsation elongational stress on the structure and properties of preparing self-reinforced sheets

A vane-type melt pulsation pumping device induces molecular chain orientation in HDPE melts via pulsating stretch-compression, enabling self-reinforced sheet extrusion. Experiments assess the impact of varying device temperature and rotational speed on the mechanical properties and microstructure of extruded sheets. The results show that the orientation of the samples can be preliminarily verified by heating test. SEM analysis reveals closely aligned HDPE crystal regions along the extrusion direction following pulsating elongational stress. 2D-WAXD analysis demonstrates a shift in diffraction intensity where it diminishes in the meridional direction and intensifies in the equatorial plane, resulting in a maximum orientation index of 0.683, an increase of 16.6% compared to direct extrusion. When the temperature of the melt pulsation pumping device is set to 180°C and the shaft speed is set to 30 rpm, the tensile strength of the sheets in the extrusion direction reached a maximum value of 66.37 MPa, surpassing that of directly extruded samples by 42.7% and that of compression-molded samples by 90%. In summary, this research realizes the self-reinforced and efficient continuous extrusion of single-component HDPE sheets through a simple device and process, which is of great significance for convenient recycling and environmental protection.

Free vibration analysis of a sandwich conical shell with a magnetorheological elastomer core, enriched with carbone nanotubes and functionally graded porous face layers

In this paper, the free vibration behaviors of a sandwich conical shell with a magnetorheological elastomer (MRE) core enriched with carbon nanotubes (CNTs) and two functionally graded (FG) porous face layers are investigated. The mathematical modeling of the shell is performed via the first-order shear deformation theory (FSDT) incorporating the continuity conditions between the face layers and the core. The porosity parameters are adjusted to provide the same mass for all porosity dispersion patterns. The governing equations and boundary conditions are derived via Hamilton’s principle and are solved through a semi-analytical solution to attain the natural frequencies and the loss factors for various boundary conditions. First, appropriate triangular functions are utilized to provide an exact solution in the circumferential direction. Then, a numerical solution is presented in the meridional direction utilizing the differential quadrature method (DQM). The influences of various factors on the natural frequencies and loss factors are investigated including intensity of the applied magnetic field, mass fraction of the CNTs subjoined to the core, thickness of the CNT-reinforced MRE core, thickness of the FG porous face layers, porosity parameter and dispersion pattern of the pores in the FG porous face layers, and the boundary conditions. Numerical results show that although subjoining CNTs to the MRE core and applying magnetic field have weak effects on the natural frequencies of the shell, increases in the mass fraction of the CNTs and intensity of the applied magnetic field result in remarkable increases in the loss factors, and provide stronger vibration suppression.