Search

Mechanical response of soils under simple shear conditions has long been a subject of significant interest in the field of geomechanics. When subjected to simple shear loading, soils experience rotations of the principal stress directions. To provide a unified description for the simple shear behavior of clay and sand, this paper proposes a novel critical state model that accounts for the influence of principal stress rotation (PSR), based on the unified critical state model for overconsolidated clay and sand with subloading surface (CASM-S). The novelty of the newly proposed model, which is named as CASM-SP, lies in its ability to consider the influence of direction of the stress increment when establishing the plastic flow rule that is suitable for both clay and sand. Therefore, the model can capture the mechanical response of soils resulting from the PSR loading mechanism, such as noncoaxial behaviors. Then, the newly proposed model is validated through the comparisons with a series of experimental data of clay and sand under both drained and undrained simple shear conditions. Results predicted by the CASM-SP model agree well with those from the experiments, demonstrating that CASM-SP can reasonably describe the simple shear behavior of both clay and sand. [ABSTRACT FROM AUTHOR]

Bi‒Sr‒Ca‒Cu‒O polycrystalline high-temperature superconductors with the 2–2-2–3 structure have been comprehensively studied, their properties have been described, and features of the small magnetic hysteresis in the investigated materials have been established. The small magnetic hysteresis is shown to be caused by the penetration of a magnetic flux into a superconductor and its capture in the region of boundaries between HTS crystallites and by Meissner currents flowing through these boundaries. It has been found that, at a certain magnetic prehistory, the small hysteresis collapses, i.e. its footprints disappear. This has been attributed to the interaction between two superconducting subsystems in the investigated polycrystalline HTS, specifically, the effect of the magnetic moments of HTS crystallites on the effective field in the regions of intercrystalline boundaries. The shape of the small magnetic hysteresis loop has been described within the critical state model. [ABSTRACT FROM AUTHOR]

In order to optimize the efficiency and safety of gas hydrate extraction, it is essential to develop a credible constitutive model for sands containing hydrates. A model incorporating both cementation and damage was constructed to describe the behavior of hydrate-bearing cemented sand. This model is based on the critical state theory and builds upon previous studies. The damage factor Ds is incorporated to consider soil degradation and the reduction in hydrate cementation, as described by plastic shear strain. A computer program was developed to simulate the mechanisms of cementation and damage evolution, as well as the stress-strain curves of hydrate-bearing cemented sand. The results indicate that the model replicates the mechanical behavior of soil cementation and soil deterioration caused by impairment well. By comparing the theoretical curves with the experimental data, the compliance of the model was calculated to be more than 90 percent. The new state-dependent elasto-plastic constitutive model based on cementation and damage of hydrate-bearing cemented sand could provide vital guidance for the construction of deep-buried tunnels, extraction of hydrocarbon compounds, and development of resources. [ABSTRACT FROM AUTHOR]

This article discusses characteristic features of energy dissipation from the eigenfield of transport current upon its stable penetration into a technical superconductor. The regimes of partial and complete penetration are considered. Analysis of dissipative states of a superconductor is compared with the results following from the theory based on the critical state model. It is demonstrated that the critical state model, according to which there is no electric voltage in superconductors at currents lower than critical one, underestimates heat release from the eigenfield of transport current and does not allow calculating correctly the energy losses in superconductors with actual current–voltage characteristics in the range of subcritical currents that can exist upon complete current penetration into superconductor. The error of the critical state model depends on the pattern of increase in current–voltage characteristic, the rate of current input, the transverse size of superconductor, and the critical current density. At the same time the self-similar and the zero-dimensional approximations make it possible to determine the energy losses in superconductors with actual current–voltage characteristic from varying eigenfield of transport current with sufficient accuracy upon both its partial and complete penetration. [ABSTRACT FROM AUTHOR]

A unified critical state model has been developed for both clean sand and silty sand using the modified Cam-clay model (MCC). The main feature of the proposed model is a new critical state line equation in the e-ln(p) plane that is capable of handling both straight and curved test results. With this feature, the error in calculating plastic volumetric strain is, in theory, eliminated. Another crucial feature of the model is the transformed stress tensor based on the SMP (spatially mobilized plane) criterion, which takes into account the proper shear yield and failure of soil under three-dimensional stresses. Additionally, the proposed model applies the intergranular void ratio with the fines influence factor for silty sand. Only eight soil parameters are required for clean sand, and a total number of twelve soil parameters are needed for silty sand. This model not only enhances the predictive accuracy for granular soils but also broadens the applicability of the model to encompass silty sand in both drained and undrained analyses. [ABSTRACT FROM AUTHOR]

Holes drilled in a type-II superconductor trap the magnetic flux. Following Clem's flux pinning model, we consider surface pinning as a mechanism for compressing the magnetic flux in the holes. Estimations of the trapped magnetic flux demonstrate that the holes with the diameter up to 2 mm are advantageous for bulk single-crystal REBCO samples. The REBCO films and tapes can be improved by the holes with diameter smaller than 10 μm. [ABSTRACT FROM AUTHOR]

In a recent paper, Zhang et al. [1] studied the effect of a Pb content on the superconducting properties of Bi-2223. Some earlier, Ramírez et al. [2] explored the effect of compaction pressure on the Bi-2212. In both studies, the critical current densities were estimated and compared for a series of polycrystalline superconducting samples. The synthesis conditions for the highest critical current density were claimed in both works. This comment explains that the average granule size should be used instead of the sample size in the Bean formula for the polycrystalline superconductors synthesized by solid-state, sol–gel, electrospinning, and solution blow spinning methods. The corrected estimations for the commented articles conclude that the synthesis conditions affect both the granule size and the intragranular critical current density. The synthesis parameters for the highest critical current density conditions are clarified. [ABSTRACT FROM AUTHOR]

When modelling the phenomenon of strain localisation in strain-softening soils with the finite element (FE) method, nonlocal approaches have been commonly employed to avoid mesh dependency and numerical instability. This paper first presents the FE formulation of a critical state model for highly overconsolidated clays incorporating a nonlocal method. The performance of the nonlocal strain regularisation is subsequently assessed through a series of coupled hydro-mechanical (HM) analyses of undrained and drained triaxial compression tests on London clay. The mechanism behind the evolution of strain localisation in triaxial tests is investigated and a comparison with equivalent plane strain analyses is discussed. Finally, a comprehensive sensitivity study is presented, investigating the influence of the two nonlocal parameters, in the adopted nonlocal algorithm, on the predicted stress–strain responses. A key outcome is the derived linear relationship between the two parameters, which enables a unique stress–strain response to be achieved in either axisymmetric or plane strain analyses with multiple combinations of the two parameters. Such a modelling capability is essential in applications of the proposed nonlocal strain regularisation in large scale boundary value problems in which restrictions on element size exist. [ABSTRACT FROM AUTHOR]

A unified critical state model has been developed for both clean sand and silty sand using the modified Cam-clay model (MCC). The main feature of the proposed model is a new critical state line equation in the e-ln(p) plane that is capable of handling both straight and curved test results. With this feature, the error in calculating plastic volumetric strain is, in theory, eliminated. Another crucial feature of the model is the transformed stress tensor based on the SMP (spatially mobilized plane) criterion, which takes into account the proper shear yield and failure of soil under three-dimensional stresses. Additionally, the proposed model applies the intergranular void ratio with the fines influence factor for silty sand. Only eight soil parameters are required for clean sand, and a total number of twelve soil parameters are needed for silty sand. This model not only enhances the predictive accuracy for granular soils but also broadens the applicability of the model to encompass silty sand in both drained and undrained analyses.

This paper develops a novel approach for automatic parameter calibration of soil constitutive models by combining Bayesian optimization (BO) and genetic algorithm (GA). The BO method enables locating the possible point over a large multi-parameter search domain quickly, by which the search domain is no longer required to be accurately pre-defined. Thereafter, the GA is employed to find the best solution within the BO-optimized search space. This calibration procedure can quickly give the best-matched model parameters for both sands and clays even with the same large search space. Taking a critical state-based soil model (Clay And Sand Model (CASM)) as an example, the superiority and capability of the proposed calibration method are examined by comparing experimental data with predicted results for both clays and sands. It is shown that the BO-GA-based approach can reduce errors by 46.4% for clays and 41.2% for sands compared with the conventional GA method and outperforms other traditional optimization algorithms. Eventually, the evolution process of BO and GA is visualized to better understand the principles of automatic parameter calibration, which is followed by model uncertainty analyses. [ABSTRACT FROM AUTHOR]

Realistic simulation of cone penetration in soil presents two main challenges: (1) a numerical scheme that is accurate under large deformations and that does not resort to overly simplifying assumptions, and (2) a constitutive model that can accurately predict the stress–strain response of soil under a wide variety of loading conditions. This paper presents a brief overview of the progress made towards realistic cone penetration simulation. The choice of numerical scheme (the material point method) and constitutive models (bounding surface models) used for simulating cone penetration in this study are discussed. For sand, 15 cone penetration simulations are performed at different relative densities subjected to different effective stress values. The simulation results are compared against those from cavity expansion analyses. For clays, cone penetration simulations are performed at different overconsolidation ratios and initial effective stress. Simulation results are then compared against cone penetration tests (CPTs) performed in the field. Based on the simulations, cone factor values are evaluated. The advantages of the current approach and its application to improvement of CPT interpretation are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent phenomena, such as the reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (Tm), highlighting the impact of magnetism on superconductivity. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-criticaltemperature (high-Tc) magnetic superconductor EuRbFe4As4. Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism below Tm, neutron diffraction and magnetization experiments show a ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the direction of the Eu2+ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors. [ABSTRACT FROM AUTHOR]

Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent phenomena, such as the reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (Tm), highlighting the impact of magnetism on superconductivity. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-criticaltemperature (high-Tc) magnetic superconductor EuRbFe4As4. Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism below Tm, neutron diffraction and magnetization experiments show a ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the direction of the Eu2+ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors. [ABSTRACT FROM AUTHOR]

Copyright of Builder (1896-0642) is the property of PWB MEDIA Zdzieblowski sp.j. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, the $H$ formulation of Maxwell's equations has become the de facto standard for simulating the time-dependent electromagnetic behavior of superconducting applications with commercial software. However, there are cases where other formulations are desirable, for example for modeling superconducting turns in electrical machines or situations where the superconductor is better described by the critical state than by a power-law resistivity. In order to accurately and efficiently handle these situations, here we consider two approaches based on the magnetic vector potential: the $T$ - $A$ formulation of Maxwell's equations (with power-law resistivity) and the implementation of a quasi critical state model (QCSM) with a steep $E$ - $J$ relationship limited at $J_{\rm c}$. In this article, we extend the $T$ - $A$ formulation to thick conductors so that large coils with different coupling scenarios between the turns can be considered. We also discuss the QCSM in terms of its ability to calculate ac losses: in particular, we investigate the dependence of the calculated ac losses on the frequency of the ac excitation and the possibility of using quick one-step (instead of full-cycle) simulations to calculate the ac losses. [ABSTRACT FROM AUTHOR]

In this review, we analyze the basic equations and assumptions for the design of critical state models used in the mechanics of non-cohesive media. The relationship of the modified cam clay model with related models of the plasticity theory with isotropic hardening described by closed plasticity surfaces is noted. The state equations of modified cam clay models in the elastic zone are analyzed; the studies, in which the elastic state is described by the hyperelasticity equations with exponential potential, are noted. Generalizations of modified cam clay models to the case of finite deformations are considered. It is important to note that additional research on kinematic combined loading in the spherical and deviatoric regions is needed. [ABSTRACT FROM AUTHOR]

This paper presents a simulation of magnetization process of a high-Tc superconductor (HTS), which is used for undulator magnets of X-ray Fee Electron Laser. The numerical analysis is carried out by a current vector potential method (T-method). In particular, it is discussed to use a power law macro-model for behavior of shielding current in the HTS. It is shown that the power low macro-model provides us better agreement with measurements for the final stage magnetic field distribution compared with conventional simulations based on a critical current macro-model. [ABSTRACT FROM AUTHOR]

Most cyclic soil models which are used to estimate strain and pore pressure accumulations, are soil specific and, often evaluate the accumulation model either as a function of the number of load cycles or they tend to utilize parameters which can only be obtained by using detailed laboratory tests. This paper attempts to enhance the capabilities of a simple plasticity model which can approximate the trend of pore pressure accumulation. This function uses a stress dependent degradation parameter which allows the yield loci to adjust and reduce its size at the end of each load cycle. The cyclic degradation model which was originally developed for clays, was adapted for sands and silts in this work with the use of two new parameters. The model was tested by using the cyclic triaxial data of three non-plastic soils. These samples were subjected to cyclic load amplitudes which are normally used in most seismic studies. The modified degradation model could predict fairly well the pore pressure accumulation in high-load amplitude tests but lead to over-prediction in low-load amplitude tests, unless the function was allowed to taper off at large cycles. Notwithstanding the above, the above cyclic model using the degraded yield surface, was incapable of correctly predicting the stress paths which were close to the sample's ultimate state as it failed to permit phase transformation which is generally observed in sands and silts. [ABSTRACT FROM AUTHOR]

Abstract: Turbidite formation is a common feature of natural hydrate‐bearing sediments that has been observed and reported at several hydrate exploration sites. It is therefore important to incorporate this anisotropic geological feature into the constitutive modeling when evaluating the geomechanical risks involved during hydrate‐based gas production. To date, a number of constitutive models have been proposed to capture the isotropic geomechanical behavior of homogeneous hydrate‐bearing sediments. Since the turbidite formation contains soil layers at a scale much smaller than the size of the numerical element used for reservoir scale simulations, it is necessary to upscale the geomechanical behavior of a layered system to an equivalent anisotropic continuum model by adopting some homogenization techniques. In this study, an anisotropic methane hydrate critical state model is developed by modifying the original isotropic version of Uchida et al. (2012, https://doi.org/10.1029/2011JB008661). The calibration methodology of the anisotropic model parameters for a given set of hydrate heterogeneity and the turbidite formation at the Eastern Nankai Trough is proposed and demonstrated. The upscaled parameters are calibrated by curve fitting the numerically simulated stress‐strain curves of the layered system with the original isotropic constitutive model at the layered scale. Forty‐two sets of model parameters are calibrated from different site element models of this site. They are used to develop empirical correlations between the model parameters and the site input properties within the turbidite formation. This paper presents the details of the new anisotropic constitutive model and the performance of the proposed upscaling procedure for the Eastern Nankai Trough case. [ABSTRACT FROM AUTHOR]

We have studied the thallium fluoride (TlF 3 ) doping and AC field dependence of the weak links behaviour and AC susceptibility of Bi 1.8−x Tl x Pb 0.35 Sr 2 Ca 2 Cu 3 O y F 3x superconductors with range of x = 0, 0.05, 0.10 and 0.15. The estimated value of the peak temperature ( T p ) from the derivative of the resistivity curve ( dρ / dT ) is increased with TlF 3 doping at 0 and 0.5 teslaand attest on both intragranular and weak links transition, while the full width at half maximum ( FWHM ) value is decreased. The susceptibility measurements χ′(χ″) show that as the magnetic field increases the intra and intergranular AC loss peaks shift to lower temperature with broadening. It was found that the onset temperature of diamagnetism T c is increased with TlF 3 doping. However, the intergranular peak temperature T pj decreased with increasing magnetic field and TlF 3 amount. This behaviour was explained by the poor connectivity between the grains caused by the presence of weak links or secondary phases. The calculated volume fraction of the grains ( f g ) was found to improve with increasing TlF 3 doping and AC magnetic field. Furthermore, the estimated values of the maximum of the extracted matrix susceptibility ( χ m , max ″ ) by using a critical state model proved that the intergranular losses are minimized with TlF 3 doping. On the other hand, the obtained results shown that the coupling between the grains is rather weak than the coupling within the grains and attested of the improvement of superconducting parameters in the doped samples. [ABSTRACT FROM AUTHOR]

In a development of the next-generation light source such as X-ray free-electron laser (FEL), it is necessary to achieve very intense undulator magnetic field with compact magnets. For this purpose, the pure-type high-Tc superconductor (HTS) undulator was proposed. In general, it is very difficult to adjust the magnetic field distribution after the HTSs are magnetized all together in a cryostat; therefore, a very careful design of the undulator magnets using a numerical analysis is required. The authors have been working on a development of the numerical simulation code of the magnetization process of the HTS undulator by using the current vector potential method ( $T$ -method). In this paper, the previously developed numerical code is modified to be used for much larger scale simulations by using a method of a multipole expansion for calculations of magnetic field aiming a practical FEL undulator design. [ABSTRACT FROM AUTHOR]

In the present study, we assess the potential for initiating ductile failure in a fractured caprock due to the chemical alteration of its mechanical properties under pressure increase induced by CO leakage and fixed in situ boundary conditions. In this view, 2D numerically coupled reactive-transport simulations were set up by using the Opalinus Clay formation as an analogue for a caprock layer. The fractured system was viewed as a compartmentalised system that consists of a main highly permeable pathway, a moderately permeable damage zone and the intact rock. The outputs of the numerical simulations (mineral fraction, porosity changes, gas saturation, pore-fluid pressure) were converted into parameter changes of the yield surface by viewing the rock material of the three compartments (fault, damage zone and intact rock) as a composite system that consists of a clayey solid material, pores and mineral inclusions (such as carbonate and quartz). Three alteration processes were considered: (1) the effect of the mineral fraction and porosity evolution on the yield surface, (2) changes in the resulting poro-elastic properties and (3) the suction effect, i.e. the bounding effect induced by the presence of two phases, water and CO. Our numerical investigations showed that the decrease in the friction coefficient remained negligible during leakage, while the pre-consolidation stress mainly decreased. Consequently, the damage zone of the fractured system became more collapsible over time, which was driven by low-to-moderate pressure build-up of the fluid penetrating the fault (1 MPa in our case). For the considered case, the initiation of ductile failure is likely under conditions of fixed vertical stress and zero lateral strain. This process could potentially limit the spatial spreading of CO-induced alteration, although this remains very site specific. We recommend that characterisation efforts be intensified to obtain better insight into the properties of fracture systems in caprock-like formations (with special attention to their initial over consolidation ratio). [ABSTRACT FROM AUTHOR]

Various critical state models have been developed to understand the hysteresis loss mechanism of high-temperature superconducting (HTSC) films. The analytic relation between the hysteresis lossx and the remanent field was obtained based on Bean's critical state model for thin films in the full-penetration case. Furthermore, numerical calculation of local hysteresis loops was carried out by Kim's critical state model. In this paper, we investigated local hysteresis losses for a GdBCO coated conductor by using low-temperature scanning Hall probe microscopy and reproduced the experimental results by applying the critical state model. Because of the demagnetizing effect in thin films, analysis of local hysteresis losses can be useful approach to understand of total hysteresis losses. [ABSTRACT FROM PUBLISHER]

Copyright of Metallophysics & Advanced Technologies / Metallofizika i Novejsie Tehnologii is the property of G.V. Kurdyumov Institute for Metal Physics, N.A.S.U and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)