Actual Shell Research Articles

Buckling performance of inner corrugated pressure shells under external hydrostatic pressure

The most fundamental and central component of submarines and deep-sea space stations is the cylindrical pressure shell. In this paper, a pressure shell with inter corrugated structure was proposed to significantly improve its compression performance. 7 pressure shells including 6 inner corrugated pressure shells and 1 cylindrical pressure shell were fabricated and hydrostatic pressure tested. Geometrical deviations including thickness deviation and out-of-roundness were considered between the actual fabricated pressure shells and the ideal models. 3D scanner was used to measure the 3D contour point cloud data of all shells and the reverse modeling was performed. Nonlinear finite element analysis of reverse modeled shells containing actual geometric imperfections were performed to predict their buckling performance under external hydrostatic pressure. The results show that the corrugated structure can significantly increase the critical buckling load of the pressure shell. The failure positions of most pressure shells in the critical buckling state were mainly located near the middle region of the shell. The numerical calculation results were in good agreement with the experimental results. This research can provide good guidance for the design of pressure structures for large deep-sea equipment such as submarines and deep-sea space station.

Finite element analysis and experimental validation of the failure characteristic of pressurized cylinder

PurposeThe high-pressure accumulator has been widely used in the hydraulic system. Failure pressure prediction is crucial for the safe design and integrity assessment of the accumulators. The purpose of this study is to accurately predict the burst pressure and location for the accumulator shells due to internal pressure.Design/methodology/approachThis study concentrates the non-linear finite element simulation procedure, which allows determination of the burst pressure and crack location using extensive plastic straining criterion. Meanwhile, the full-scale hydraulic burst test and the analytical solution are conducted for comparative analysis.FindingsA good agreement between predicted and measured the burst pressure that was obtained, and the predicted failure point coincided very well with the fracture location of the actual shell very well. Meanwhile, the burst pressure of the shells increases with wall thickness, independent of the length. It can be said that the non-linear finite element method can be employed to predict the failure behavior of a cylindrical shell with sufficient accuracy.Originality/valueThis paper can provide a designer with additional insight into how the pressurized hollow cylinder might fail, and the failure pressure has been predicted accurately with a minimum error below 1%, comparing the numerical results with experimental data.

SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-shell Detonation in a Star-forming Galaxy

The detonation of a thin (≲0.03 M ⊙) helium shell (He-shell) atop a ∼1 M ⊙ white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum brightness, SN 2020jgb is slightly subluminous (ZTF g-band absolute magnitude −18.7 mag ≲ M g ≲ −18.2 mag depending on the amount of host-galaxy extinction) and shows an unusually red color (0.2 mag ≲ g ZTF − r ZTF ≲ 0.4 mag) due to strong line-blanketing blueward of ∼5000 Å. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with an He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb is broadly consistent with a ∼0.95–1.00 M ⊙ (C/O core + He-shell) progenitor ignited by a ≳0.1 M ⊙ He-shell. However, one-dimensional radiative transfer models without non-local-thermodynamic-equilibrium treatment cannot accurately characterize the line-blanketing features, making the actual shell mass uncertain. We detect a prominent absorption feature at ∼1 μm in the near-infrared (NIR) spectrum of SN 2020jgb, which might originate from unburnt helium in the outermost ejecta. While the sample size is limited, we find similar 1 μm features in all the peculiar He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first peculiar He-shell DDet SN discovered in a star-forming dwarf galaxy, indisputably showing that He-shell DDet SNe occur in both star-forming and passive galaxies, consistent with the normal SN Ia population.

Foreword to the special issue on new developments in structural stability.

Foreword to the special issue on new developments in structural stability.

Practical Tutorial on cylindrical structure vibro-acoustics Part 1 - Vibrations

The mathematics which describe the vibroacoustic behavior of cylindrical structures are imposing to say the least. Part 1 of this practical tutorial demystifies cylindrical shell vibration theory by using measured data from actual shells and pipes to explain key concepts. For any shell, you can estimate frequency ranges where shells behave like simple beams and flat plates, greatly simplifying calculations of modes of vibration and mobilities. The key is first calculating the ring frequency - the frequency where membrane waves can propagate fully around the shell circumference. Simple infinite structure theory may then be used to compute mean mobilities for beam, shell, and flat plate behavior. Modes of vibration for a cylinder depend on both longitudinal and circumferential harmonics, or a helical wavenumber. Cremer's simple approximate resonance frequency formula is used to show examples for a large diameter short shell and a small diameter long shell (a pipe). Finally, the measured modal densities of an elbowed pipe are compared to estimates from an empirical expression for modal density of a shell. In all cases in this tutorial, measurements and simple estimates agree well, showing that cylindrical shell vibrations may be estimated without difficult math or complex computer models.

Solution of nonlinear eigenvalues for the viscoelastic damped cylindrical shell considering the frequency dependence of viscoelastic materials

The dynamic model of the cylindrical shell partially attached with a viscoelastic free damping layer is established by a semi-analytical method, and the complex boundary conditions of the cylindrical shell are simulated by using the non-uniform distribution of spring groups. Two new methods for solving nonlinear eigenvalue problems of the viscoelastic damped cylindrical shell are proposed. One method is named as the Vector Iteration method based on Approximate Eigenvalues (VIAE), and the solution process can be described as: the iteration equation is obtained by the characteristic equation; the approximate eigenvalue and the initial eigenvector are used for the iteration calculation; in each iteration, the eigenvectors are normalized and the nonlinear eigenvalues are obtained by using the Rayleigh quotient. Another method is named as the Secant Method of Characteristic Polynomials (SMCP). In this method, the iteration equation of the eigenvalue is derived by the secant method. Furthermore, the approximate eigenvalues of the system are used as the initial iteration eigenvalues and the nonlinear eigenvalues of the system can be approximated through several iteration calculations. Finally, the proposed modeling method and algorithm are verified by the experiment of the actual cylindrical shell attached the ZN-1 viscoelastic material at the free end. The two new methods were also compared with the classical Eigenvector Increment Method (EIM). The comparison results show that the VIAE algorithm has the highest efficiency, and both the VIAE and SMCP algorithms have wider applicability because they do not need to perform eigenvector calculations.

A New Methodology for Predicting Brittle Fracture of Plastically Deformable Materials: Application to a Cold Shell Nosing Process.

The traditional theory of ductile fracture has limitations for predicting crack generation during a cold shell nosing process. Various damage criteria are employed to explain fracture and failure in the nose part of a cold shell. In this study, differences in microstructure among fractured materials and analysis of their surfaces indicated the occurrence of brittle fractures. The degree of “plastic deformation-induced embrittlement” (PDIE) of plastically deformable materials affects the likelihood of brittle fractures; PDIE can also decrease the strength in tension due to the Bauschinger effect. Two indicators of brittle fracture are presented, i.e., the critical value of PDIE and the allowable tensile strength (which in turn depends on the degree of PDIE or embrittlement-effective strain). When the maximum principal stress is greater than the latter and the PDIE is greater than the former, our method determines the likelihood of brittle fracture. This approach was applied to an actual cold shell nosing process, and the predictions were in good quantitative agreement with the experimental results.

Ultimate Strength Assessment of Steel-Welded Hemispheres under External Hydrostatic Pressure

This paper focusses on steel-welded hemispherical shells subjected to external hydrostatic pressure. The experimental and numerical investigations were performed to study their failure behaviour. The model was fabricated from mild steel and made through press forming and welding. We therefore considered the effect of initial shape imperfection, variation of thickness and residual stress obtained from the actual structures. Four hemisphere models designed with R/t from 50 to 130 were tested until failure. Prior to the test, the actual geometric imperfection and shell thickness were carefully measured. The comparisons of available design codes (PD 5500, ABS, DNV-GL) in calculating the collapse pressure were also highlighted against the available published test data on steel-welded hemispheres. Furthermore, the nonlinear FE simulations were also conducted to substantiate the ultimate load capacity and plastic deformation of the models that were tested. Parametric dependence of the level of sphericity, varying thickness and residual welding stresses were also numerically considered in the benchmark studies. The structure behaviour from the experiments was used to verify the numerical analysis. In this work, both collapse pressure and failure mode in the numerical model were consistent with the experimental model.

Influence of Thick Plate Bending Process on Material Strength Distribution in Hydrogenation Reactor Shells

Thick plate bending process (warm bending and tempering) has a profound impact on the material strength distribution (MSD) in hydrogenation reactor shells. To date, few studies have studied the thick plate bending process. In this work, an artificial neural network (ANN) combined with finite element analysis (FEA) was utilized to investigate the impact of thick plate bending on the MSD of reactor shells. First, tensile tests of 0-10% pre-strained 2.25Cr-1Mo-0.25 V specimens were subjected to 390 to 510 °C. The results obtained from this experiment were used to develop ANN with two inputs (temperature and plastic strain) to predict the strength of pre-deformed steel. Subsequently, the plastic strain distribution of reactor shells after warm bending was obtained via FEA. We then inputted the FEA results into well-established ANN to predict the MSD of un-tempered reactor shells. The MSD of an actual tempered reactor shell was measured to study the synergic effect of warm bending and tempering on MSD variation. Results showed that the average absolute relative errors between the proposed ANN and tensile test results were below 4%. The absolute relative errors of the proposed prediction method varied from 0.24 to 7.88%. The proposed method is therefore reliable in the lightweight design of the hydrogenation reactor.

A reappraisal of the type series of the early Cretaceous margaritiferid ‘Unio’ valdensis Mantell, 1844

This study re-examines the type series of the Early Cretaceous freshwater bivalve Unio valdensisMantell, 1844, in relation to the assignment of the species to the genus ParaheudeanaStarobogatov (1970), and the subgenus Pseudunio by Mongin (1961). For the first time, we recognise the type specimens as incomplete lacking critical posterior portions of the shell. We observe that the lectotype, superficially oval in outline, has a shallow, but distinct postero-ventral sinus, seemingly out-grown, the broken ventral margin not preserving actual shell shape or the commissure. Significantly, many other specimens confirm the presence of the postero-ventral sinus and elongate-oval outline. It is unclear why Starobogatov removed Margaritifera (Pseudunio) valdensis but maybe the perceived oval outline was sufficient for separation. Combined with diagnostic characters such as mantle pits, we retain the freshwater mussel Unio valdensis in the genus Margaritifera and refute the validity of the genus ParaheudeanaStarobogatov (1970). Araujo et al. (2016) reviewing the phylogeny of the Margaritiferidae, concluded only the genus Margaritifera was valid, discounting Pseudunio as a valid genus or subgenus, placing further doubt upon the use of the then subgenus, conversely more recent studies have supported the genus Pseudunio promoting it to a genus.

Comparisons of Analytical Approaches for Determining Shell Thicknesses of Core-Shell Nanoparticles by X-ray Photoelectron Spectroscopy.

We assessed two approaches for determining shell thicknesses of core-shell nanoparticles (NPs) by X-ray photoelectron spectroscopy (XPS). These assessments were based on simulations of photoelectron peak intensities for Au-core/C-shell, C-core/Au-shell, Cu-core/Al-shell, and Al-core/Cu-shell NPs with a wide range of core diameters and shell thicknesses. First, we demonstrated the validity of an empirical equation developed by Shard for determinations of shell thicknesses. Values of shell thicknesses from the Shard equation typically agreed with actual shell thicknesses to better than 10 %. Second, we investigated the magnitudes of elastic-scattering effects on photoelectron peak intensities by performing a similar series of simulations with elastic scattering switched off in our simulation software. Our ratios of the C-shell 1s intensity to the Au-core 4f7/2 intensity with elastic scattering switched off were qualitatively similar to those obtained by Torelli et al. from a model that neglected elastic scattering. With elastic scattering switched on, the C 1s/Au 4f7/2 intensity ratios generally changed by less than 10 %, thereby justifying the neglect of elastic scattering in XPS models that are applied to organic ligands on Au-core NPs. Nevertheless, elastic-scattering effects on peak-intensity ratios were generally much stronger for C-core/Au-shell, Al-core/Cu-shell, and Cu-core/Al-shell NPs, and there were second-order dependences on core diameter and shell thickness.

Measurement of inflight shell areal density near peak velocity using a self backlighting technique

The growth of perturbations in inertial confinement fusion (ICF) capsules can lead to significant variation of inflight shell areal density (ρR), ultimately resulting in poor compression and ablator material mixing into the hotspot. As the capsule is accelerated inward, the perturbation growth results from the initial shock-transit through the shell and then amplification by Rayleigh-Taylor as the shell accelerates inwards. Measurements of ρR perturbations near peak implosion velocity (PV) are essential to our understanding of ICF implosions because they reflect the integrity of the capsule, after the inward acceleration growth is complete, of the actual shell perturbations including native capsule surface roughness and “isolated defects”. Quantitative measurements of shell-ρR perturbations in capsules near PV are challenging, requiring a new method with which to radiograph the shell. An innovative method, utilized in this paper, is to use the self-emission from the hotspot to “self- backlight” the shell inflight. However, with nominal capsule fills there is insufficient self-emission for this method until the capsule nears peak compression (PC). We produce a sufficiently bright continuum self-emission backlighter through the addition of a high-Z gas (∼ 1% Ar) to the capsule fill. This provides a significant (∼10x) increase in emission at hυ∼8 keV over nominal fills. “Self backlit” radiographs are obtained for times when the shock is rebounding from the capsule center, expanding out to meet the incoming shell, providing a means to sample the capsule optical density though only one side, as it converges through PV.

음향방출 에너지 파라미터를 이용한 고로 철피균열의 조기 결함탐지 기술

Blast furnaces are crucial equipment for steel production. A typical furnace risks unexpected accidents caused by contraction and expansion of the walls under an environment of high temperature and pressure. In this study, an acoustic emission (AE) monitoring system was tested for evaluating the large-scale structural health of a blast furnace. Based on the growth of shell cracks with the emission of high energy levels, severe damage can be detected by monitoring increases in the AE energy parameter. Using this monitoring system, steel mill operators can establish a maintenance period, in which actual shell cracks can be verified by cross-checking the UT. From this study, we expect that AE systems permit early fault detection for structural health monitoring by establishing evaluation criteria based on the severity of shell cracking.

9. Seashells in the Jordanian Desert: a Cross-Cultural Analysis

The remains of ancient communities have been found at Wadi Ramm and Humayma, Jordan in the midst of what is now the Jordanian desert. In past times these sites were located along caravan routes and were populated by Nabataean, Roman, Byzantine, and early Islamic peoples. Despite the fact that these sites are located tens of kilometers from the seashore, seashells are frequently found in the layers associated with the different population groups. As of yet, shells from the 1996-1997 excavations at Wadi Ramm and from the 2008-2010 excavations at Humayma have not received in depth analyses allowing them to be correctly identified, quantified, and associated with significant archaeological contexts. Archaeomalacology (the study of molluscs in archaeological contexts) is a vital part of deciphering ancient human diet and activity. It is also critical in determining past environments and transportation systems. Clearly these shells came from the sea, but how did they get to these remote desert locales? Based on the preliminary descriptions provided by the field excavators, the photographs of the Wadi Ramm shells, and the actual Humayma shells which are at Queen’s, I am creating a catalogue to identify, describe, and quantify the variety of mollusc species present. This catalogue incorporates all of the significant data in one place, thus allowing me to look for patterns in the frequency, condition, and probable function of the shells. This analysis will lead to a better understanding of the diet and cultural practices of the different ancient inhabitants at Wadi Ramm and Humayma.

Buoyancy of some Palaeozoic ammonoids and their hydrostatic properties based on empirical 3D-models

The interpretation of the function of the ammonoid phragmocone as a buoyancy device is now widely accepted among ammonoid researchers. During the 20th century, several theoretical models were proposed for the role of the chambered shell (phragmocone); accordingly, the phragmocone had hydrostatic properties, which enabled it to attain neutral buoyancy, presuming it was partially filled with gas. With new three-dimensional reconstructions of ammonoid shells, we are now able to test these hypothetical models using empirical volume data of actual ammonoid shells. We investigated three Palaeozoic ammonoids (Devonian and Carboniferous), namely Fidelites clariondi, Diallagites lenticulifer and Goniatites multiliratus, to reconstruct their hydrostatic properties, their syn vivo shell orientation and their buoyancy. According to our models, measurements and calculations, these specimens had aperture orientations of 19°, 64° and 125° during their lives. Although none of our results coincide with the aperture orientation of the living Nautilus, they do verify the predictions for shell orientations based on published theoretical models. Our calculations also show that the shorter the body chamber, the poorer was the hydrodynamic stability of the animal. This finding corroborates the results of theoretical models from the 1990s. With these results, which are based on actual specimens, we favour the rejection of hypotheses suggesting a purely benthonic mode of life of ammonoids. Additionally, it is now possible to assess hydrodynamic properties of the shells through ontogeny and phylogeny, leading to insights to validate theoretical modes of life and habitat through the animal's life.

Microencapsulation of Active Ingredients Using PDMS as Shell Material

We report an efficient and adaptable method for the microencapsulation of active ingredients by a polydimethylsiloxane (PDMS) shell material. The core–shell microcapsules were obtained by phase separation between the core component and the PDMS shell components after repartitioning of the common solvent THF between the PDMS/core material phase and the water phase. For the shell components, two commercially available functional PDMS polymers containing thiol and vinyl side groups were used. Photo-cross-linking in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPA) by thiol–ene radical addition was used to form a PDMS-thioether cross-linked shell. Variation of the PDMS component thiol to ene ratio resulted in different functionalities on the microcapsules surface and in the bulk, which was analyzed by attenuated total-reflection infrared spectroscopy (ATR-IR) and high-resolution magic-angle NMR-spectroscopy (HR-MAS NMR). Organically modified silica particles were mixed into the PDMS shell, resulting in better mechanical properties of the shell and control over the shell permeability, as measured on the one hand by tensile testing of representative PDMS bulk samples of identical composition as the actual shell material and on the other hand by leaching experiments of the core compounds, such as a tetrathiol and the UV-absorber octocrylene, followed by UV–vis.

Design and application of dynamic secondary cooling control based on real time heat transfer model for continuous casting

The control of secondary cooling is extremely important for the quality of billet in the continuous casting. In order to minimise the variation in surface temperature and excessive reheating of billet, which have a considerable influence on the formation of cracks and other defects, a real time heat transfer model that can be used for simulation of varying casting operations was developed. In order to verify the dynamic performance of this model, a charge coupled device temperature measurement system that can eliminate the impact of the scales was presented. The actual shell thickness profile and billet temperature were calculated in real time by this model online and were taken into account to feedback control the casting process based on the desired target cooling pattern to improve the existing cooling system. The dynamic control system based on this model was developed and implemented on some caster, and the billet quality was obviously improved.

Exploring the constancy of the global buckling load after a critical geometric imperfection level in thin-walled cylindrical shells for less conservative knock-down factors

Some of the knock-down factors applied in design of rocket launcher structures are based on design recommendations which rely on lower-bound curves from experimental data. The best known example is the NASA guideline SP 8007, published in 1965 and revised in 1968, which is applied for cylindrical structures in the space industry. This guideline is based on test data, computational methods and resources from the 1930–1960's. At that time the application of less empirical methods for the design of actual cylindrical shells could not count with the current computational power, and the available methods led to quite large discrepancies between experiments and test observations. Significant improvement on the available analyses approaches and manufacturing techniques since 1960's have not been taken into account in design processes using the NASA SP-8007, and many authors have recognized that for the current standards this guideline is leading to conservative structures. Another aspect for attention regarding application of the NASA SP-8007 for composite shells is that it does not consider the laminate stacking sequence. Moreover, physical observations regarding how does the imperfection sensitivity of unstiffened cylindrical shells change with the presence of an induced geometric imperfection have also suggested that the current applied design rules are too conservative. This conservativeness is confirmed by many tests carried out recently. This study presents an overview of the problem and a detailed description of the physical observations regarding the buckling mechanism of the thin shells under consideration. It is discussed how these observations can be used for less conservative, laminate dependent, knock-down factors accounting for geometric imperfections. The single perturbation load approach is studied in detail and a physically based definition for the minimum perturbation load (P1) is given, paving the way for the development of semi-analytical methods to calculate this minimum perturbation load.

Meshless analysis of shear deformable shells: the linear model

This work develops a kinematically linear shell model departing from a consistent nonlinear theory. The initial geometry is mapped from a flat reference configuration by a stress-free finite deformation, after which, the actual shell motion takes place. The model maintains the features of a complete stress-resultant theory with Reissner-Mindlin kinematics based on an inextensible director. A hybrid displacement variational formulation is presented, where the domain displacements and kinematic boundary reactions are independently approximated. The resort to a flat reference configuration allows the discretization using 2-D Multiple Fixed Least-Squares (MFLS) on the domain. The consistent definition of stress resultants and consequent plane stress assumption led to a neat formulation for the analysis of shells. The consistent linear approximation, combined with MFLS, made possible efficient computations with a desired continuity degree, leading to smooth results for the displacement, strain and stress fields, as shown by several numerical examples.

ADAPTATION FROM RESTRICTED GEOMETRIES: THE SHELL INCLINATION OF TERRESTRIAL GASTROPODS

The adaptations that occur for support and protection can be studied with regard to the optimal structure that balances these objectives with any imposed constraints. The shell inclination of terrestrial gastropods is an appropriate model to address this problem. In this study, we examined how gastropods improve shell angles to well-balanced ones from geometrically constrained shapes. Our geometric analysis and physical analysis showed that constantly coiled shells are constrained from adopting a well-balanced angle; the shell angle of such basic shells tends to increase as the spire index (shell height/width) increases, although the optimum angle for stability is 90° for flat shells and 0° for tall shells. Furthermore, we estimated the influences of the geometric rule and the functional demands on actual shells by measuring the shell angles of both resting and active snails. We found that terrestrial gastropods have shell angles that are suited for balance. The growth lines of the shells indicated that this adaptation depends on the deflection of the last whorl: the apertures of flat shells are deflected downward, whereas those of tall shells are deflected upward. Our observations of active snails demonstrated that the animals hold their shells at better balanced angles than inactive snails.