Hoop Force Research Articles

Roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST

The safe operation of most tokamaks, especially the large ones, relies on the feedback control of vertical displacement events (VDEs). However, most of these feedback control systems are based on axisymmetric VDE models. In this study, we use NIMROD simulations to study the role of non-axisymmetric perturbations in free drift vertical displacement events on EAST. The high-n modes in the non-axisymmetric VDE grow first, which drives the formation of high-n magnetic island chains. Subsequently, the magnetic island chains grow and overlap with each other, leading to the destruction of the magnetic flux surface, which induces a minor disruption and accelerates the start of the following major disruption. The magnetic island and the stochastic magnetic field allow the toroidally non-axisymmetric poloidal plasma current to jet towards the hoop force direction, forming finger-like and filamentary structures. Such a plasma current non-axisymmetry strongly depends on the anisotropy in the thermal transport coefficients.

Design, construction, and monitored behavior of two large-diameter cylindrical diaphragm walls on an offshore reclamation island

Two semi-underground liquefied natural gas (LNG) storage tanks with an excavation depth of 25.6 m were constructed on an offshore reclamation island in Dapeng Bay, Shenzhen, China. Two cylindrical retaining diaphragm walls with a diameter of 100 m were adopted for the deep excavation. This paperpresents detailed information on the design and construction of these two cylindrical retaining diaphragm walls. As the elevation changes in the soil and rock layers were very severe, the non-axisymmetric distribution of the lateral pressure was significant. Diaphragm walls with different embedded depths were designed to cut off the seepage paths inside and outside the retaining structure. The strength of the rock was extremely high; therefore, a combination of predrilling using a rotary excavator and grooving using a milling machine was adopted in the trenching construction of the diaphragm wall. The monitored soil and rock pressures acting on the diaphragm wall are discussed. The lateral deformation of the diaphragm wall was described, and the hoop force and vertical bending moment of the retaining diaphragm wall were analyzed, which could be a reference for similar projects.

Use of Sutureless Valve in Aortic Root Enlargement

The small aortic annulus is a surgical challenge in patients undergoing aortic valve replacement which may lead to patient prosthesis mismatch. Management options include aortic root enlargement, aortic root replacement, and the use of sutureless valves. In this case series, we report our results with aortic root enlargement, sutureless valve implantation, and benchtop modelling of the radial forces exerted. Five patients underwent aortic root enlargement and insertion of the Perceval valve as part of the management strategy to enlarge their effective orifice area. We further investigate this strategy with a benchtop model to quantify the radial forces exerted by the Perceval valve on the aortic annulus. Radial and hoop forces on the aortic annulus and inner ring of the Perceval valve were recorded using a Mylar force tester. Five female patients with native annulus between 18mm-20mm underwent root enlargement and insertion of a Perceval S valve. The postoperative course was uncomplicated for all patients except for one who required a permanent pacemaker insertion. Transvalvular pressure gradients remained low at up to 4 years of follow-up (12 mmHg-21 mmHg), with no evidence of paravalvular leak. Benchtop testing demonstrated radial forces exerted at the annulus in all-size Perceval S valves to be within physiological variables, whereas compressive forces required to deform the valves were supraphysiological. The deployment of a sutureless valve within a surgical enlarged aortic root is a feasible solution in patients with a small aortic root.

A Titov–Démoulin Type Eruptive Event Generator for β > 0 Plasmas

We provide exact analytical solutions for the magnetic field produced by prescribed current distributions located inside a toroidal filament of finite thickness. The solutions are expressed in terms of toroidal functions, which are modifications of the Legendre functions. In application to the MHD equilibrium of a twisted toroidal current loop in the solar corona, the Grad–Shafranov equation is decomposed into an analytic solution describing an equilibrium configuration against the pinch-effect from its own current and an approximate solution for an external strapping field to balance the hoop force. Our solutions can be employed in numerical simulations of coronal mass ejections (CMEs). When superimposed on the background solar coronal magnetic field, the excess magnetic energy of the twisted current loop configuration can be made unstable by applying flux cancellation to reduce the strapping field. Such loss of stability accompanied by the formation of an expanding flux rope is typical for the Titov & Démoulin eruptive event generator. The main new features of the proposed model are as follows: the filament is filled with finite β plasma with finite mass and energy, the model describes an equilibrium solution that will spontaneously erupt due to magnetic reconnection of the strapping magnetic field arcade, and there are analytic expressions connecting the model parameters to the asymptotic velocity and total mass of the resulting CME, providing a way to connect the simulated CME properties to multipoint coronograph observations.

Experimental and numerical investigation into locally corroded circular concrete-filled steel tubular stub columns strengthened by CFRP

Concrete-filled steel tube (CFST) is vulnerable to corrosion in service, especially local corrosion. Nevertheless, limited work has been conducted on the behaviors and strengthening methods of locally corroded CFSTs. This paper presents experimental and numerical investigations into the behavior of locally corroded CFST stub columns and locally corroded CFST stub columns strengthened by carbon fiber reinforced polymer (CFRP). Tests were conducted on thirteen specimens with local corrosion of steel tubes simulated by means of artificial notches, and the notch length and number of CFRP layers were chosen as test parameters. The test results revealed that the performance of the specimens strengthened by CFRP was significantly improved, compared with that of the unstrengthened specimens. The maximum compression resistance increment of the CFRP-strengthened specimens was up to 58.8%. Subsequently, finite element (FE) models were developed and verified by the experimental results. Based on the FE models, parametric analyzes were conducted to investigate the axial behavior of locally corroded circular CFST stub columns strengthened by CFRP. The parametric analysis results indicated that CFRP can compensate for the loss of confinement effect of steel tube caused by local corrosion. In addition, when the hoop force provided by CFRP is equal to that provided by the yield stress of steel tube, the compression resistance of locally corroded CFST stub columns strengthened by CFRP is even slightly higher than that of CFST stub columns without corrosion.

A Model for Confined Solar Eruptions Including External Reconnection

The violent disruption of the coronal magnetic field is often observed to be restricted to the low corona, appearing as a confined eruption. The possible causes of the confinement remain elusive. Here, we model the eruption of a magnetic flux rope in a quadrupolar active region, with the parameters set such that magnetic X-lines exist both below and above the rope. This facilitates the onset of magnetic reconnection in either place but with partly opposing effects on the eruption. The lower reconnection initially adds poloidal flux to the rope, increasing the upward hoop force and supporting the rise of the rope. However, when the flux of the magnetic side lobes enters the lower reconnection, the flux rope is found to separate from the reconnection site and the flux accumulation ceases. At the same time, the upper reconnection begins to reduce the poloidal flux of the rope, decreasing its hoop force; eventually this cuts the rope completely. The relative weight of the two reconnection processes is varied in the model, and it is found that their combined effect and the tension force of the overlying field confine the eruption if the flux ratio of the outer to the inner polarities exceeds a threshold, which is ∼1.3 for our Cartesian box and chosen parameters. We hence propose that external reconnection between an erupting flux rope and overlying flux can play a vital role in confining eruptions.

Analytical model for the nonlinear buckling responses of the confined polyhedral FGP-GPLs lining subjected to crown point loading

This paper focuses on the nonlinear buckling responses of the confined functionally graded porous (FGP) lining with polyhedral shapes reinforced by graphene platelets (GPLs). The FGP-GPLs polyhedral lining is surrounded tightly and rigidly by a medium. It is assumed that the interface is smooth between the lining and pipeline. The deformation of the lining may be represented by an admissible displacement expression when a point load is applied at the crown position. Afterward, the nonlinear governing equilibrium equations are obtained explicitly by combining the thin-walled shell theory and the principle of minimum potential energy. Solving the nonlinear governing equilibrium equations yields the critical buckling load. A comparison study is strictly completed with the other closed-form solutions when the polyhedral lining reduces to a circular one. In addition, an improvement factor is quantified to understand the effect of polyhedral shapes on the bending stiffness. Finally, the effects of polyhedral shapes, porosity coefficient, weight fraction, and geometric parameters of the GPLs are explored in terms of buckling load, hoop force, and bending moment.

Lining forces in tunnel interaction problems

In big cities the construction of new tunnels in close proximity to existing ones is unavoidable given the densely and growing occupation of the subsoil. The interaction between tunnels in such conditions is well identified in the literature and has been thoroughly investigated in the past. However, most of those studies are focused on the effect of the ground conditions and relative position between tunnels on the ground movements and often disregard the impact induced by the second excavation on the lining forces of both tunnels. To provide further insight into this subject a numerical study of the sequential excavation of side-by-side twin tunnels is presented in this paper. The study also assesses the influence of parameters that have not been covered in the previous studies, namely the stiffness of the lining and the initial stress conditions. The results confirm that significant interaction occurs when the tunnels are spaced less than one diameter, where a considerable increase on both hoop forces and bending moments, particularly on the lining of the existing tunnel, is observed after the second excavation. For a spacing higher than two diameters the interaction between tunnels is almost negligible. The magnitude of the lining forces and of the interaction effects are also dependent of the stiffness of the linings and of the initial stress conditions.

Seismic resilience of extra-large LNG tank built on liquefiable soil deposit capturing soil-pile-structure interaction

Assessment of seismic resilience of critical infrastructure such as liquefied natural gas (LNG) storage tanks, is essential to ensure availability and security of services during and after occurrence of large earthquakes. In many projects, it is preferred to build energy storage facilities in coastal areas for the ease of sea transportation, where weak soils such as soft clay and loose sand with liquefaction potential may be present. In this study, three-dimensional finite element model is implemented to examine the seismic response of a 160,000 m3 full containment LNG tank supported by 289 reinforced concrete piles constructed on liquefiable soil overlaying the soft clay deposit. The seismic soil-structure interaction analysis was conducted through direct method in the time domain subjected to the 1999 Chi-Chi and the 1968 Hachinohe earthquakes, scaled to Safe Shutdown Earthquake hazard level for design of LNG tanks. The analyses considered different thicknesses of the liquified soil deposit varying from zero (no liquefaction) to 15 m measured from the ground surface. The key design parameters inspected for the LNG tank include the acceleration profile for both inner and outer tanks, the axial, hoop and shear forces as well as the von Mises stresses in the inner tank wall containing the LNG, in addition to the pile response in terms of lateral displacements, shear forces and bending moments. The results show that the seismic forces generated in the superstructure decreased with increasing the liquefied soil depth. In particular, the von Mises stresses in the inner steel tank exceeded the yield stress for non-liquefied soil deposit, and the elastic–plastic buckling was initiated in the upper section of the tank where plastic deformations were detected as a result of excessive von Mises stresses. However, when soil liquefaction occurred, although von Mises stresses in the inner tank shell remained below the yield limit, localised stress concentrations were observed in the lower section of the tank near the base, increasing the risk of the elephant foot buckling. The lateral displacements, shear forces and bending moments in the piles increased with increasing depth of the liquefied soil. Indeed, increasing the pile lateral displacement amplified the bending moment at the pile head, thus resulting in increases in the pile bending moments especially when the liquefied soil depth exceeded one third of the entire soil deposit. In particular, the bending moment at the pile head exceeded the yield moment capacity of the pile and subsequent plastic hinges were formed. Moreover, when the thickness of the liquefied soil was more than half of the entire soil depth, the mobilised bending moments in the piles exceed the ultimate moment capacity of the pile and thus total failure of the piles were observed. In addition, in the absence of liquefied soil layer, the inertial interaction had a dominant impact on the pile response in this study. However, with increasing the thickness of the liquefied layer, further loads were developed in the piles due to amplified kinematic interaction, while the inertial interaction-induced loads decreased.

Effects of the skew angle of new tunneling on an existing tunnel: three-dimensional centrifuge and numerical modeling

Tunneling results in stress relief and arching in the ground. New tunnel excavation beneath an existing tunnel but at different angles can lead to different patterns of stress redistribution. Studies on multitunnel interaction have mainly focused on perpendicular tunnels, and the effects of tunneling skew angle remain poorly understood. Three-dimensional centrifuge modeling and numerical back-analyses were conducted to investigate the effects of twin-tunnel interaction at three skew angles (30°, 60°, and 90°). The effects of new tunnel excavation on an existing tunnel were simulated by controlling tunnel volume and weight losses in-flight. A hypoplastic soil model capable of simulating path-dependent and strain-dependent soil stiffness was adopted for the numerical back-analyses. Distinct load redistribution patterns were identified to explain deformations of the existing tunnel at different skew angles due to the advancement of the new tunnel. For 90° tunneling, hoop force increased at the crown and decreased at the left springline of the existing tunnel. The opposite responses were identified at 30° tunneling. A critical skew angle of 30° tunneling led to the maximum invert settlement and tunnel deformation of the existing tunnel. At 30° tunneling, the induced strain in the tunnel lining was 2.3 times larger than that of tunneling at 90°, exceeding the cracking limit suggested by the American Concrete Institute.

Data-constrained Magnetohydrodynamic Simulation of a Long-duration Eruptive Flare

Abstract We perform a zero-β magnetohydrodynamic simulation for the C7.7 class flare initiated at 01:18 UT on 2011 June 21 using the Message Passing Interface Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC). The initial condition for the simulation involves a flux rope, which we realize through the regularized Biot–Savart laws, whose parameters are constrained by observations from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) and the Extreme Ultraviolet Imager (EUVI) on the twin Solar Terrestrial Relations Observatory (STEREO). This data-constrained initial state is then relaxed to a force-free state by the magnetofrictional module in MPI-AMRVAC. The further time-evolving simulation results reproduce the eruption characteristics obtained by SDO/AIA 94 Å, 304 Å, and STEREO/EUVI 304 Å observations fairly well. The simulated flux rope possesses similar eruption direction, height range, and velocity to the observations. In particular, the two phases of slow evolution and fast eruption are reproduced by varying the density distribution in the light of the draining process of the filament material. Our data-constrained simulations also show other advantages, such as a large field of view (about 0.76 R ⊙). We study the twist of the magnetic flux rope and the decay index of the overlying field, and find that in this event, both the magnetic strapping force and the magnetic tension force are sufficiently weaker than the magnetic hoop force, thus allowing the successful eruption of the flux rope. We also find that the anomalous resistivity is necessary to keep the correct morphology of the erupting flux rope.

Graphical Modelling of Hoop Force Distribution for Equilibrium Analysis of Masonry Domes

The behaviour of axisymmetric masonry shells can be simulated by a system of forces constituted by meridian forces acting in the vertical planes, and by hoop forces acting circumferentially. A crucial component for the assessment of these structures using the Modified Thrust Line Method (MTLM) is the determination of hoop forces, whose computation is strenuous, limiting the practical application of MTLM. Working around this limitation, the current research introduces a strategy to manipulate the hoop forces by graphically implementing a function describing their distribution. The adaptiveness of this distribution function not only allows the application of MTLM for the analysis of a range of geometries, but also enables the simulation of membrane behaviour, arch behaviour and their combination, for considering partially cracked structures. Taking this into account, the approach is applied in the case studies illustrated within the current research.

Dynamic response of cylindrical water storage tanks made byECC compared to normal concrete

In this paper, the dynamic behaviour and seismic damages of concrete cylindrical water storage tanks are investigated. Furthermore, by modeling the reservoirs, using normal concrete and engineered cementitious composite (ECC), the effects of ECC on reducing the seismic damages of reservoirs are investigated. For this purpose, ANSYS software is used to perform the nonlinear dynamic analysis of the tanks and different parameters including the hoop force and bending moment of the wall and cracking or crushing of the concrete were examined. According to the results, the relationships and criteria provided in the ACI standard for design of tanks are recommended to be revised in certain parts. Unlike the normal concrete tanks, in those made of ECC, concrete fracture is not observed and the crack width remains very small at a level that is not problematic. Finally, the use of ECC in cylindrical water storage tanks is suggested as a strategy for reducing the seismic vulnerability of this type of hydraulic structures.

Computational and experimental mechanical performance of a new everolimus-eluting stent purpose-built for left main interventions

Left main (LM) coronary artery bifurcation stenting is a challenging topic due to the distinct anatomy and wall structure of LM. In this work, we investigated computationally and experimentally the mechanical performance of a novel everolimus-eluting stent (SYNERGY MEGATRON) purpose-built for interventions to large proximal coronary segments, including LM. MEGATRON stent has been purposefully designed to sustain its structural integrity at higher expansion diameters and to provide optimal lumen coverage. Four patient-specific LM geometries were 3D reconstructed and stented computationally with finite element analysis in a well-validated computational stent simulation platform under different homogeneous and heterogeneous plaque conditions. Four different everolimus-eluting stent designs (9-peak prototype MEGATRON, 10-peak prototype MEGATRON, 12-peak MEGATRON, and SYNERGY) were deployed computationally in all bifurcation geometries at three different diameters (i.e., 3.5, 4.5, and 5.0 mm). The stent designs were also expanded experimentally from 3.5 to 5.0 mm (blind analysis). Stent morphometric and biomechanical indices were calculated in the computational and experimental studies. In the computational studies the 12-peak MEGATRON exhibited significantly greater expansion, better scaffolding, smaller vessel prolapse, and greater radial strength (expressed as normalized hoop force) than the 9-peak MEGATRON, 10-peak MEGATRON, or SYNERGY (p < 0.05). Larger stent expansion diameters had significantly better radial strength and worse scaffolding than smaller stent diameters (p < 0.001). Computational stenting showed comparable scaffolding and radial strength with experimental stenting. 12-peak MEGATRON exhibited better mechanical performance than the 9-peak MEGATRON, 10-peak MEGATRON, or SYNERGY. Patient-specific computational LM stenting simulations can accurately reproduce experimental stent testing, providing an attractive framework for cost- and time-effective stent research and development.

Creep of CFRP confined reinforced concrete members under large eccentric compression

Based on the multiaxial stress statetheory of concrete under and B3 model for calculating concrete creep, combined with the mechanical characteristics of reinforced concrete members under large eccentric compression, considering the influence of member deflection, reinforcement configuration and hoop force, the creep model of CFRP confined reinforced concrete members under long-term load is established. Compared with the experimental results, the theoretical calculation results are in good agreement with the experimental values. It has a certain guiding significance to the actual engineering structure.

Creep behavior of steel bonded reinforced concrete members under small eccentric compression

In this paper, the creep behavior of steel bonded reinforced concrete members under small eccentric compression is studied. Firstly, based on the existing mechanical characteristics of concrete under multi axial stress state, the stress-strain relationship of steel bonded small eccentric concrete is theoretically deduced and analyzed by considering the reduction coefficient of hoop force. Secondly, according to the creep characteristics of confined core concrete, combined with the existing concrete creep model and the analysis of its influencing factors, the influence of sticking steel on the creep of small eccentric reinforced concrete compression members is discussed. The corresponding creep calculation formula is established. Finally, the existing experimental data are used to verify the proposed formula, and its applicability is analyzed.

Structural Design of Close-Fit Liners in Fractured Rigid Circular or Non-Circular Gravity Pipes

The French standard for the design of liners for gravity pipe application offers a fully analytical approach for the design of circular and noncircular liners under groundwater pressure. Liners’ geometrical imperfections, which dramatically decrease the resistance of the lining to groundwater pressure, are treated using single or combined analytical correction factors that apply to quantities (buckling pressure, deflection, hoop force, and bending moment) calculated based on the perfect profile. This paper presents analytical calculations that establish correction factors for close-fit liners encased in fractured rigid circular and noncircular host pipes. An approximate solution is generated by assuming an allowable displacement function and minimizing the potential energy. It is shown that the effect of fractures on liners’ resistance to buckling is governed by the rotation angle of the hinge formed by the fracture, which imposes an angular step to the liner. Finite-element simulations of liners encased in fractured rigid circular, elliptical, and egg-shaped pipes are presented, and showed good agreement with the analytical solution.

Wall-Bottom Joint Rotation of Cylindrical Concrete Water Tank

AbstractCylindrical concrete water tanks resting on the ground are widely used in water and wastewater treatment plants. The hoop force in the cylindrical wall is a critical design force. Rotation ...

Magnetic Rayleigh–Taylor Instability in an Experiment Simulating a Solar Loop

Abstract A hoop force driven magnetic Rayleigh–Taylor instability (MRTI) is observed in a laboratory experiment that simulates a solar coronal loop. Increase of the axial wavelength λ is observed when the axial magnetic field increases. This scaling is consistent with the theoretical MRTI growth rate , which implies that if is parallel to (i.e., undular mode), the fastest-growing mode has .

Exploration of the encased nanocomposites functionally graded porous arches: Nonlinear analysis and stability behavior

This paper explores the nonlinear stability mechanism of the functionally graded porous (FGP) arch reinforced by graphene nanocomposites. Both the pores and the nanocomposites are distributed symmetrically to the mid-surface of the arch but not uniformly in the cross-section so that the bending stiffness can be best improved. The arch is confined in an elastic medium with a radially-pointed concentrated load at the crown position. The confinement of the medium results in a symmetrical deformed shape of the arch, which can be described by an admissible displacement function. Associated with the thin-walled arch theory and the principle of minimum potential energy, analytical predictions are obtained to express the critical buckling load, as well as the hoop force and bending moment. Subsequently, a numerical model is developed to simulate the medium and the arch in ABAQUS software. By introducing the modified arc-length method, the equilibrium paths of the encased arch are traced. After comparison in terms of the critical buckling load and the equilibrium paths, it is found the numerical results are in good accordance with the analytical solutions. Finally, particular attention is paid to the parameters that may impact the buckling load, such as the porosity coefficient, the weight fraction, the central angle, the geometry of the Graphene platelets (GPLs) et al.