Shell Model Research Articles

Indispensability of cross-shell contributions in neutron resonance spacing

Spin- and parity-dependent nuclear level densities (NLDs) are obtained for a configuration interaction shell model using a numerically efficient spectral distribution method. The calculations are performed for 24Na and 25,26,27Mg nuclei using full sd-pf model space that incorporates the cross-shell excitations from the sd to the pf-shell. The obtained NLDs are then employed to determine the s-wave neutron resonance spacing (D0), which is one of the crucial inputs for the predictions of astrophysical reaction rates. Although the considered nuclei are not neutron-rich, the contributions from cross-shell excitations to the pf-shell are indispensable for explaining the experimental data for D0, which otherwise are significantly overestimated.

Multidimensional typologies of faulty medical device events: analysis, risk characterisation, and stakeholder mapping

ABSTRACT This study uses the publicly available International Medical Devices Database in three-phase research to present empirically grounded multi-dimensional typologies of events involving faulty medical devices. In the first phase, considering three major categorical data, i.e. event actions, event types, and countries, and, by employing descriptive analysis, we identify that perhaps ‘Field safety notice’ is the most dominant event type under which 66 event actions exist. In the second phase, employing the two-step clustering analysis technique, we identify that four distinct clusters exist. Finally, in the last phase, employing the focus group-driven content analysis approach using event reason description in conjunction with the SHELL (software-hardware-equipment-liveware) model, we classify the top 10 event actions. We also identify corresponding risk levels considering the top 10 sources of device problems. Further, the focus group employing the interest-influence framework in conjunction with pertinent self-addressed questions ascertained that the greatest number of top 10 event actions lies at the quadrant wherein the major stakeholder has a high degree of interest and influence in mitigating those medical events. Our study bridges the extant research gap about the lack of comprehensive, data-driven, and evidence-based themes around medical device events, the associated risk characteristics, and stakeholder mapping.

Spontaneous Stochasticity Amplifies Even Thermal Noise to the Largest Scales of Turbulence in a Few Eddy Turnover Times.

How predictable are turbulent flows? Here, we use theoretical estimates and shell model simulations to argue that Eulerian spontaneous stochasticity, a manifestation of the nonuniqueness of the solutions to the Euler equation that is conjectured to occur in Navier-Stokes turbulence at high Reynolds numbers, leads to universal statistics at finite times, not just at infinite time as for standard chaos. These universal statistics are predictable, even though individual flow realizations are not. Any small-scale noise vanishing slowly enough with increasing Reynolds number can trigger spontaneous stochasticity, and here we show that thermal noise alone, in the absence of any larger disturbances, would suffice. If confirmed for Navier-Stokes turbulence, our findings would imply that intrinsic stochasticity of turbulent fluid motions at all scales can be triggered even by unavoidable molecular noise, with implications for modeling in engineering, climate, astrophysics, and cosmology.

Nonlinear vibrations analysis of two-directional functionally graded porous cylindrical shells resting on elastic substrates in a thermal environment based on Donnell nonlinear shell theory

The primary objective of this study is to investigate the nonlinear free vibrational characteristics of temperature-dependent two-directional functionally graded porous (TDFGP) cylindrical shells resting on elastic substrates in a thermal environment. To accomplish this, the thermomechanical equations are derived based on the Donnell nonlinear shell theory framework in conjunction with the von Kármán assumption. Two-directional functionally graded porous cylindrical shell models have mechanical properties that can change smoothly and continuously across the length and thickness of the shell. Additionally, it is assumed that the internal porosities in the matrix materials can be dispersed into two independent patterns, either even or uneven porosity distribution. The nonlinearity in free vibration assessed via the nonlinear-to-linear frequency ratio concerning the central deflection amplitude can be gained employing the Galerkin discretization approach and modified Poincare–Lindstedt (P-L) method. The accuracy and effectiveness of the present analytical model are indicated through comparison with existing solutions. Finally, some comprehensive parametric investigations are carried out to gain insight into the impacts of several factors on the nonlinear free vibration characteristics of structures under different conditions. The results of this article demonstrate that parameters such as gradient indices, volume fraction, distribution pattern of porosity, geometric parameters, and ambient temperature rise significantly influence the structure’s nonlinear frequency and free vibration response.

COMPARATIVE STUDY BETWEEN SHELL AND SOLID FINITE ELEMENT MODELS FOR STEEL JOINTS CHARACTERIZATION

AbstractSolid and shell finite element models (FEM) are two commonly used possibilities to analyse the structural behaviour of steel joints. The choice between solid and shell models often comes down to a balance between computational resources and the level of detail required for the study. In this paper, a set of welded beam‐column joints with hot‐rolled open sections is studied using both modelling techniques. The joints' behaviour is assessed in terms of resistance and initial stiffness. An improved shell FEM is proposed. The results indicate that for the studied dataset, both techniques return comparable results. Hence, the use of shell FEM seems to be a possible alternative to solid FEM and can be efficiently used for the joint characterization.

Odd elastic stability of cylindrical shells

Biologically active shells typically exhibit complex mechanical behaviors, with their morphogenesis involving rich symmetry breaking events and non-conservative biological forces. In this article, an accurate buckling solution model of active cylindrical shells is established based on the odd elasticity theory. The tension buckling, non-reciprocal torsional buckling and stress-free active buckling of odd elastic cylindrical shells are reported, which are an anomalous instability caused by odd elastic effects. The result shows that the anomalous buckling of cylindrical shells can only occur in the form of chiral deformation, because the energy required for instability can be obtained based on the odd elastic effects.

STUDY MAGNETIC ELECTRON SCATTERING FORM FACTOR OF 24Mg ISOTOPE

The magnetic form factor of 24Mg isotope under inelastic electron scattering was subjected to computational scrutiny via the utilization of the Oxbash code. The endeavor involved elucidating energy levels intrinsic to this nucleus through the application of the shell model, wherein the model space encompassed zbm, psd, spsdpf, and sd configurations. In the context of the sd model, the investigation harnessed two pioneering USD-type Hamiltonians, denoted as USDC and USDI, in conjunction with tailored amendments to these interaction potentials, referred to as USDCm and USDIm. This study culminated in comprehensively juxtaposing all computational outputs with empirical data sources, including information extracted from the National Nuclear Data Center (NNDC) repository. Significantly, this systematic examination underscored a notable congruence between the derived computational outcomes and the empirical observations. This alignment became conspicuously pronounced subsequent to judicious adjustments made to the g-factors, specifying values of = 1.060 and = -0.060. The profound unity between the findings of this study and experimental data manifests as compelling evidence, substantiating the efficacy and precision of the employed interaction models. It implies a reliable capacity of these models in the precise computation of magnetic form factors M1, M2, and M3

New beam-based models for fire-induced buckling analysis of class 4 steel columns

Steel cross-sections with thin walls are vulnerable to fire-induced buckling instability, which reduces their load-bearing capacity. Eurocode 3 design provisions have been found inadequate, leading to alternative methods such as effective design strategies and advanced structural models built mostly with shell FE, which can be complex. For Class 4 steel beam-columns subjected to fire conditions, beam-type modelling to predict the Flexural-Torsional Buckling (FTB) strength has been proposed as an alternative approach, but it has not yielded satisfactory results for large compressive load eccentricities. This paper presents two new low computational cost modelling strategies based on Timoshenko's beam FE to address this issue: the Single beam-column Model (SbcM) and the Cruciform beam-column Model (CbcM). The first consists of a single line of beam FE, while the second uses a grid of beam FE for more flexibility. Both strategies effectively simulate the FTB behaviour in Class 4 steel beam-column during a fire, offering quicker computations compared to shell models. Still, the single-line model is favoured for its simplicity, making it more efficient in analysing complex fire engineering problems.

PROBING THE NUCLEAR STRUCTURE OF EXOTIC 33Mg ISOTOPE

Research on the nuclear structure of exotic isotopes, such as 33Mg, is an exciting and cuttingedge field of nuclear physics. Exotic isotopes are typically those that are far from the stable region of the nuclear chart and often exhibit unique properties that can help us better understand the fundamental forces and structure of atomic nuclei. In this paper the largescale shell model calculations are performed within the model spaces SDPFMU, to study the positive- and negative-parity energy levels and electromagnetic transitions in the exotic 33Mg isotope. Core-polarization effects on reduced transition probability are introduced through first order perturbation theory, which allows for higher energy configurations through excitations of nucleons from core orbits to that outside model space up to . The corepolarization effects have been improved the agreement of B(E2) with their corresponding experimental data, and have ignorable effect on B(M1)

Study of Nuclear Structure and Elastic Electron Scattering Form Factors for Neutron Halo Nuclei (22N ,23O and 24F) Using Full Correlation Functions with Two Size Parameters

The study of neutron-rich nuclei's form factors, root-mean-square radius (rms), and nuclear density distributions is the focus of this work for the nuclei (22N,23 O and 24F). With the use of a strong short-range effect and a strong tensor force, the nucleons distribution function of the two oscillating harmonic particles in a two-frequency shell model operates with two different parameters: the first (bcore), for the inner (core) orbits, and the second (bvalence) for the outer (halo) orbits. This work demonstrated the existence of neutron halo nuclei for the nuclei (22N, 23O and 24F) in the (2s1/2) shell. The computed density distribution of neutron, proton and matter for these nuclei displayed the long tail performance. Using the Borne approximation of the plane wave, the elastic form factor of the electron scattering from the alien nucleus was calculated, this form factor is independent of the neutrons that make up the halo, but rather it results from a difference in the proton density distribution of the last proton in the nuclei. Fortran 95 power station program was used to the neutron, proton and matter density, elastic electron scattering form factor, and rms radii. The calculated outcomes for these exotic nuclei were in good agreement with the experimental data.

Coronal dimmings as indicators of the direction of early coronal mass ejection propagation

Context. Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun that can cause severe disturbances in space weather. Earth-directed CMEs are responsible for the disruption of technological systems and damaging power grids. However, the early evolution of CMEs, especially Earth-directed ones, is poorly tracked using traditional coronagraphs along the Sun-Earth line. Aims. The most distinct phenomena associated with CMEs in the low corona are coronal dimmings, which are localized regions of reduced emission in the extreme-ultraviolet (EUV) and soft X-rays formed due to mass loss and expansion during a CME. We present a new approach to estimating the early CME propagation direction based on the expansion of coronal dimmings. Methods. We developed the Dimming InfeRred Estimate of CME Direction (DIRECD) method. First, we performed simulations of CMEs in 3D using a geometric CME cone model and varying parameters such as width, height, source location, and deflection from the radial direction to study their influence on the CME projection onto the solar sphere. Second, we estimated the dominant direction of the dimming extent based on the evolution of the dimming area. Third, using the derived dominant direction of the dimming evolution on the solar sphere, we solved an inverse problem to reconstruct an ensemble of CME cones at different heights, widths, and deflections from the radial propagation. Finally, we searched for which CME parameter combinations the CME orthogonal projections onto the solar sphere would match the geometry of the dimming at the end of its impulsive phase best; we did so to derive the CME direction in 3D. We tested our approach on two case studies on 1 October, 2011 and 6 September, 2011. We also validated our results with 3D tie-pointing of the CME bubble in an EUV low corona and with 3D reconstructions by graduated cylindrical shell modeling (GCS) of white-light CMEs higher up in the corona. Results. Using DIRECD, we found that the CME on 1 October, 2011 expanded dominantly toward the south-east, while the CME on 6 September, 2011 was inclined toward the north-west. This is in agreement with the CME direction estimates from previous studies using multi-viewpoint coronagraphic observations. Conclusions. Our study demonstrates that coronal dimming information can be used to estimate the CME’s direction early in its evolution. This allows us to provide information on the CME direction before it is observed in the coronograph’s field of view, which is of practical importance for space weather forecasting and the mitigation of potential adverse impacts on Earth.

Effect of porosity on the nonlinear free vibrational behavior of two-directional functionally graded porous cone-shaped shells resting on elastic substrates

The present article describes an analytical approach to investigate the nonlinear free vibrational behavior of a two-directional functionally graded porous (TDFGP) cone-shaped shell resting on elastic substrates. A mixture model with the power-law distribution functions is utilized to obtain the TDFGP shell’s mechanical properties. In addition, it is assumed that the internal porosities in the matrix materials can be dispersed into two independent patterns, either even or uneven porosity distribution. The field displacement in the TDFGP shell is approximated using first-order shear deformation theory. Hamilton’s principle and von Karman’s large deformation assumptions give a dynamic model for the TDFGP shell. The Galerkin decomposition method is employed to discretize the governing partial differential equations into time-dependent ordinary differential equations. The harmonic balance method is used to analytically solve the final time-dependent equations and acquire the nonlinear frequency response of the TDFGP shell. Research has been conducted on porosity, gradient indexes, elastic substrates, boundary conditions, and geometric ratios through parametric studies to investigate the outcomes and their applicability to real-world issues.

A FE2 shell model with periodic boundary conditions for thin and thick shells

AbstractIn this article a FE2 shell model for thin and thick shells within a first order homogenization scheme is presented. A variational formulation for the two‐scale boundary value problem and the associated finite element formulation is developed. Constraints with 5 or 9 Lagrange parameters are derived which eliminate both rigid body movements and dependencies of the shear stiffness on the size of the representative volume elements (RVEs). At the bottom and top surface of the RVEs which extend through the total thickness of the shell stress boundary conditions are present. The periodic boundary conditions at the lateral surfaces are applied in such a way that particular membrane, bending and shear modes are not restrained. This is shown by means of a homogeneous RVE. The first of all linear formulation is extended to finite strain problems introducing transformation relations for the stress resultants and the material matrix. The transformations are performed at the Gauss points on macro level. Several boundary value problems including large deformations, stability and inelasticity are computed and compared with 3D reference solutions.

Finite-Element Modeling of the Dynamic Behavior of a Crack-like Defect in an Internally Pressurized Thin-Walled Steel Cylinder

This article presents one part of a study on the dynamic deformation and fracture of sections of steel gas pipelines with an external crack-like defect under the action of internal pressure. This work was performed on the basis of finite-element simulations using a cylindrical shell model executed by ANSYS-19.2 on the example of the section of the steel gas pipeline “Beineu–Bozoy–Shymkent” in the Republic of Kazakhstan. The propagation of the incipient crack-like defect along the pipeline and the resulting dynamic fracture in its tip area were investigated. The options of pipeline loading by working and critical internal pressure were both considered. It was found that, within the time of 1.0 ms, the formed crack expanded in the circumferential direction up to the maximum value, which depended on the value of the internal pressure. A further growth of cracks occurred along the longitudinal direction. At the operating pressure, the initial length of the crack increased by a factor of 5.6, while the equivalent stresses increased by a factor of 1.53 within 3.5 ms. Within the time of 3.75 ms, the equivalent stresses stopped growing due to the gas decompression. Specifically, there was a stop to the crack growth along the longitudinal direction. Vice versa, at the maximum pressure, the pipeline fracture did not change qualitatively, while at the time of the process, it decreased up to 3.5 ms. The finite-element results of the stress–strain state and pipeline fracture in the crack tip area at the working pressure showed that, within the time of 1.0 ms, the distance between the crack walls reached 23 mm at the free edge. Conversely, within the time periods of 2.25 and 3.5 ms, it increased two and three times, respectively. The crack elongation in the longitudinal direction occurred 5.8 times with time. Together, within the time of 3.5 ms, the equivalent stresses increased twice, after which the growth of the crack stopped due to the gas decompression. Moreover, studies on the growth of the crack-like defect in its tip area at the maximum pressure showed that additional considerations on the pressure on the crack edges led to an increment of 3.6% of the crack length. The results of this work can be used for the development of measurements for operating gas pipelines in the field of structural reinforcement.

Tarihi Erzincan Çadırcı Hamamı'nın Deprem Davranışının İncelenmesi ve Günümüze Kadar Ulaşmasının Sebepleri

In this study, the earthquake behaviour of the historical Çadırcı Bathhouse in Erzincan, which is located on the North Anatolian Fault, the most active fault line of Turkey, was investigated. This historical masonry structure has preserved its structural integrity despite being exposed to two earthquakes of magnitude 7.8 in 1939 and 6.7 in 1992. In accordance with the architectural survey studies, the historical building was modelled in 3D in two different types according to shell and solid modelling techniques. According to the results of response spectrum analysis, stress and displacement distributions and modal characteristic parameters of the structure were evaluated. When the analysis results of the models created with the solid model technique and the shell model technique are compared, it is concluded that the shell modelling technique is safe in such studies, considering the analysis time and modelling difficulty. According to the results of the analyses, considering the stress distribution in the historical building elements, it is seen that the configuration characteristics of historical masonry structures are important in earthquake resistance like other building systems.

Precast-Monolithic Reinforced Concrete Large-Span Shells of Unique Buildings from Enlarged Elements

The stress-strain state of precast monolithic reinforced concrete shells from enlarged elements taking into account the installation conditions. The results of experimental-theoretical studies of precast monolithic reinforced concrete shells of complex geometry assembled from enlarged elements are given. The studies were carried out on full-scale composite shells 48x48 m and diameter 96m, its enlarged elements 3x18m and 3x24m as well as on the shell model on a scale of 1:10 and 1: 4. The stress-strain state of shells of a similar type was studied with different mounting and splitting designs. Recommendations are given on rational methods for the construction of shells from enlarged elements for public buildings.

Effect of joint stiffness on the load-carrying capacity of single-layer cylindrical reticulated shell with improved bolt-column (IBC) joint

To enlarge the application of single-layer reticulated shells, this study proposes an innovative semi-rigid joint based on the original bolt-column (OBC) joint, referred to as the improved bolt-column (IBC) joint. The mechanical behavior of the IBC joint under the pure load and the coupling effect of bending and axial force is investigated using numerical tests. Then, the practical analytical model of IBC joint is developed based on a three-parameters power model and component method. Subsequently, a mechanical model considering joint stiffness is developed to establish semi-rigidly connected single-layer cylindrical reticulated shell. A total of 456 numerical models of shells are conducted to examine the impact of different kinds of joint stiffness on the load-carrying capacity of shells systematically. The results demonstrate that (i) weak axis bending stiffness and axial stiffness significantly affect the load-carrying capacity of shells by approximately 19 % and 14 % on average respectively; (ii) strong axis bending stiffness and torsional stiffness have relatively minor effects on the critical load of shells, with average decline ratios of only 5 % and 6 % respectively; (iii) out-of-plane shear stiffness and in-plane shear stiffness exhibit negligible impacts on the load-carrying capacity of shells, with an average effect not exceeding 1 %. Finally, the findings of numerical simulation considering all stiffness of IBC joint reveal insights into both varying laws of load-carrying capacity and failure modes for shells. It is observed that the mean critical load can reach up to 59 % of the one of rigidly-connected shells, which is significantly higher than those observed in shells with pinned joints.

First-forbidden transition of nuclear β decay by projected shell model

The first-forbidden transition of nuclear β decay is expected to play crucial roles in many aspects in nuclear physics, nuclear astrophysics and particle physics such as the stellar β-decay rates and the reactor anti-neutrino spectra. In this work we develop the projected shell model (PSM) for description of first-forbidden transition of nuclear β decay for the first time. Detailed theoretical framework and logics are provided, and 35 dominant first-forbidden transitions that are expected to be important for the reactor anti-neutrino spectra problems are calculated and compared systematically with the data to test the new development of the PSM. The corresponding experimental Logf0t values are described reasonably, and the quenching factors of nuclear matrix elements are found to affect the Logf0t values as well as the related shape factors, which may be helpful for better understanding of the reactor anti-neutrino spectra problems.

Nonlinear bending examination of nanocomposite cylindrical shell exposed to mechanical loads using dynamic relaxation method

In the current context, the nonlinear bending examination of a carbon nanotube reinforced composite (CNTRC) shell exposed to mechanical loading using the first-order shear deformation shell model via the dynamic relaxation (DR) procedure, is perused. The composite shell is assumed to be reinforced in the longitudinal axis. The curved morphology distribution of CNTs is considered to be functionally graded (FG) or uniform along the shell thickness. Mechanical properties of the constituents are gathered based on the modified rule of the mixture. For verification, the present numeric outcomes are compared with available references and ABAQUS finite element package. Finally, the roles of effective items including carbon nanotubes (CNTs) distributions, thickness-to-radius and length-to-radius ratios, boundary conditions, and the volume fraction of CNTs are investigated on the maximum non-dimension deflection.

Level structures of 96Tc and their microscopic description

High spin states in the 96Tc nucleus were populated in the 75As(28Si, 4p3n) fusion-evaporation reaction at E lab = 120 MeV and the de-excitations were investigated through in-beam γ-ray spectroscopic techniques using indian national gamma array spectrometer consisting of 18 clover Ge detectors. The present level scheme of the 96Tc nucleus has been extended substantially with the addition of about forty five new γ transitions. The level structures in 96Tc have been established up to excitation energy ∼10 MeV and angular momentum ∼25ℏ. Level structures of 96Tc nucleus are discussed in the framework of triaxial projected shell model calculations.