Horizontal Shear Research Articles

Stress-distribution characteristics of cruise ship based on multiple-beam method

Cruise ship usually has a plump superstructure with multiple decks, and the effective degree of each deck participating in the longitudinal bending is a complicated but unavoidable issue in initial design. This paper proposes one multiple-beam method to examine the stress-distribution characteristics and the bending efficiency of the superstructure. The method assumes that the main hull and each deck of the superstructure can be regarded as thin-walled beams, with vertical forces and horizontal shear forces interacting between adjacent decks. The purpose of the method is to simplify the multiple-beam problem through reasonable assumptions, so as to obtain an approximate solution method with sufficient accuracy. The distribution of longitudinal stress and the bending efficiency of the superstructure of one inland cruise ship is calculated via classical beam theory, two-beam theory, and the multiple-beam method proposed in this paper, and the results are compared with those obtained by the finite-element method. The present research is of reference significance for structural safety and reliability design of cruise ship.

Seismic response of nuclear power station with disconnected pile-raft foundation using dynamic centrifuge tests

The typical foundation type for a nuclear power station is the raft foundation in rock areas. With the power demand, it is possible that a nuclear power station located in soft soil areas. Traditional connected pile raft foundation (CPRF) has been successfully used in soft soil areas. However, under earthquake loads, high horizontal shear stresses and bending moments are generated in the pile head. Accordingly, researchers have sought to develop an innovative disconnected pile raft foundation (DPRF), and the benefits of DPRF have simulated increasing researches on it in the last two decades. In this study, a series of dynamic centrifuge tests were carried out to identify the effect of cushion and its thickness on the dynamic characteristics of the nuclear power station with DPRF. A withe noise excitation and three earthquake waves with different seismic intensities were adopted as ground motion. The seismic responses of soil, structure, and bending moment of piles were analysed. A cushion thickness equal to the diameter of piles is recommended. Comparing with the CPRF, the cushion layer of DPRF has an isolation benefit. With the gravel cushion, attention must be paid to the horizontal displacement, inclination and rocking of the superstructure.

A two‐fluid single‐column model of turbulent shallow convection. Part II: Single‐column model formulation and numerics

AbstractThe two‐fluid single‐column model of Thuburn et al. (Quart. J. R. Meteorol. Soc., 2019, 145, 1535–1550) is extended to include moisture and horizontal wind shear. Turbulent kinetic energy is introduced as a prognostic variable, dependence on a diagnosed boundary‐layer height is removed, and subfilter fluxes are approximated using a two‐fluid version of a Mellor–Yamada scheme. Three mechanisms for entrainment and detrainment processes are introduced, which represent entrainment of unstable air at the surface, forced detrainment of air at the top of the boundary/cloud layers, and turbulent mixing that relaxes the convective fluid to a reference profile. A semi‐implicit Eulerian discretization replaces the semi‐implicit semi‐Lagrangian implementation of Thuburn et al. (Quart. J. R. Meteorol. Soc., 2019, 145, 1535–1550) to improve numerical stability and conservation. The equations for the implicit time step are solved using a quasi‐Newton method, which is shown to perform well in numerical tests for conservation and convergence. The two‐fluid single‐column model presented in this article will be applied to simulations of shallow cumulus convection in Part III.

Acoustic tomography measurement and large-eddy simulation of macroturbulence in high flow tidal channels

Velocity spectra from a pilot tomography experiment in Grand Passage, Nova Scotia, exhibit the structure at 10 m to several 100 m scales similar to that of the spectra of vertically integrated velocity registered by bottom-mounted acoustic Doppler profilers. The experiment was motivated in part by the need for flow and turbulence measurement at sites being targeted for in-stream tidal power development, and by the potential of acoustic tomography for providing this information from shore-based locations in near real time. The measurements were made using a single pair of acoustic transceivers operating at 7 kHz and separated by 1.5 km at an oblique angle to the channel axis. Limited to a single cross-channel path, the experiment provided no information on the spatial structure of the turbulence. In order to investigate this structure, virtual tomographic experiments were carried out by propagating pulses through with meter-scale resolution velocity fields from a non-hydrostatic large-eddy simulation (LES) model of flow in Grand Passage. Results from these virtual experiments are presented, and their implications are discussed in relation to the potential of multi-transceiver tomography for macro-turbulence measurement and the role of horizontal shear in macro-turbulence production in coastal environments.

Cimmerian block detachment from Gondwana: A slab pull origin?

The Cimmerian blocks are ribbons-like micro-continents that detached from the northern margin of Gondwana during the closure of the Paleotethys ocean at the end of the Permian. While it has been hypothesized that slab pull forces induced by subduction of the Paleotethys beneath Eurasia could have driven extension in the lower plate after the Paleotethys mid-oceanic ridge subduction, so far, numerical modeling studies have concluded that these forces alone are not sufficient to drive continental breakup. However, the previous modeling studies neglect olivine phase transitions in the mantle and likely underestimated the slab pull. Here, we present numerical simulations that consider the evolution of the density of the slab associated with metamorphic reactions and analyze carefully when, where, and how the slab pull can lead to the formation of micro-continents. Our results show that the marked increase in slab density related to olivine phase transitions at 410 km discontinuity, in addition to gravitational potential energy, can cause continental rifting of the lower plate. Nonetheless, continental breakup is only achieved in absence of horizontal shear flow at the base of the continental lithosphere. In these successful experiments, the deformation localizes 100-200 km on shore due to bending stress pointing out that this process probably always leads to the formation of small continental ribbons. Our results confirm that the tensional force induced by the Paleotethys subduction dynamics may have caused the detachment of the Cimmerian blocks. Since continental breakup of the lower plate is promoted in the absence of basal shear below Gondwana's lithosphere (with respect to the underlying mantle), we argue that the formation of the Cimmerian blocks provides information on the relative motion between the tectonic plates and the underlying mantle. Our simulations demonstrate that there is a significant time-lag between ridge subduction and continental breakup (i.e. the time needed for the slab to reach the 410 km discontinuity), which is rarely accounted by paleogeographic reconstructions.

Seismic behavior of exterior-diaphragm CFSST connections with or without PBL

The exterior-diaphragm connection to concrete-filled square steel tubular columns with perfobond ribs (i.e., exterior-diaphragm CFSST connection with PBL) is an innovative connection formed by arranging PBL in steel tube of the small-sized-exterior-diaphragm CFSST connection. To explore the seismic behavior of this type of connection, cyclic tests of exterior-diaphragm connections with or without PBL were carried out. The failure modes, P-Δ hysteretic curves, stiffness degradation, energy dissipation capacity, shear deformation of joint region, strain distribution in diaphragm and panel zone of different specimens were compared and analyzed. On this basis, the tensile force transfer paths in different connections were compared by FE numerical simulation quantitatively. It is found that PBL carry a considerable portion of the tensile forces from steel beam flanges and transmit them to core concrete in joint regions, and enable the core concrete to participate in tensile load transferring and then in horizontal shear resisting of the novel connections, which greatly alleviates the stress concentrating at corners of steel tubes and exterior-diaphragm, and decreases the shear deformation and strain in joint regions. So, the stiffness, ductility, load carrying and energy dissipating capacity of exterior-diaphragm connections with PBL are improved a lot. Higher axial load level reduces the shear stiffness and strength of concrete dowels, and then deteriorates the stiffness degradation, energy dissipation capacity and shear deformation of panel zone. Even if the dimension of exterior-diaphragm is much smaller than that specified in codes, the innovative connections under common and high axial load level have good seismic behavior and fail as the yielding of steel beam flanges without obvious damage in exterior-diaphragm and steel tubes.

Seismic performance and fragility analysis of underground subway station with rubber bearings

In this paper, a comparative study of the seismic response and fragility of a station structure before and after being retrofitted with an LNB installed on the top of its columns is conducted to evaluate the effectiveness of retrofitting measures in reducing risk probability employing, for the first time, a probabilistic approach. The Daikai subway station was adopted as a case study, and two-dimensional finite element models of soil-structure system with and without LNB were established. Incremental dynamic analyses (IDA) of original and retrofitted structures were conducted to evaluate their seismic responses under different ground motion intensities and considering the uncertainty of ground motion. Further, the IDA curve cluster and quantile lines of station structure and rubber bearing were constructed. Finally, the seismic fragility curves of structure and LNB were established for the risk assessment under different performance levels based on the structural performance index. The results demonstrated that the horizontal deformation, shear force and bending moment of the central column fitted with rubber bearings are greatly reduced compared with the actual Daikai station structure, which is more pronounced for lower ground motion intensity. In addition, the failure probability of the retrofitted structure corresponding to different damage levels is much lower than that of the original structure under the same ground motion intensity. Meanwhile, the probability of moderate to severe damage for the underground station structure is greatly reduced after retrofitting with the rubber bearings. The overall seismic performance of the structure is significantly improved and post-earthquake repair-demand is greatly decreased.

Snowband Characteristics Associated With Lake‐Effect Misovortices During the OWLeS Project

AbstractVortices of diameters 100 m to 10 km have been observed during lake‐effect snowstorms. Lines of misovortices (diameters = 40–4,000 m) have recently been documented forming over Lake Ontario during long lake‐axis‐parallel (LLAP)‐type lake‐effect storms. Using National Weather Service Weather Surveillance Radar—1988 Doppler (WSR‐88D) and Doppler on Wheels radar data from the Ontario Winter Lake‐effect Systems (OWLeS) project, lines of misovortices (also referred to as “misovortex lines” in this study) were investigated for intensive observation period (IOP)7 (7 January 2014) and IOP9 (9 January 2014). Results revealed that the misovortex lines formed on the southern or northern side of the west‐to‐east‐oriented LLAP band, whichever was closest to a low‐level boundary nearest the corresponding south or north shoreline (northern part in IOP7, southern part in IOP9). Examination of these two IOPs in the context of a total of 23 OWLeS IOPs, 11 of which had predominantly LLAP band morphology, showed that, in 4 of the 11 LLAP IOPs, horizontal shear zones/reflectivity bands formed in preferred regions over Lake Ontario and nearby land areas where low‐level boundaries (e.g., land breeze fronts) have been noted to develop near shoreline irregularities. Horizontal shear zones were predominant in approximately half of the OWLeS LLAP IOPs and were associated with storms having a well‐organized, solid banded reflectivity structure. Misovortices occurred when horizontal shear zones were prevalent, supporting the idea that horizontal shearing instability was important to their formation.

Construction and validation of a novel phased array borehole probe for ultrasonic investigations at sealing structures in radioactive repositories

A new type of ultrasonic borehole probe is developed for the quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The goal is to examine the sealing structures made of salt concrete for possible cracks, delamination, and embedded objects. A prototype probe uses 12 individual dry point contact (DPC) horizontal shear wave transducers separated by equidistant transmitter/receiver arrays, each made up of six individual transducers. It is operated with a commercially available portable ultrasonic flaw detector used in the civil engineering industry. To increase the generated sound pressure of the borehole probe, the number of transducers in the novel probe is increased to 32. In addition, timed excitation of each probe is used to direct a focused sound beam to a specific angle and distance based on calculated time delays. Hence, the sensitive test volume is limited, and the signal-to-noise ratio of the received signals is improved. This paper presents the validation of the newly developed phased array borehole probe by beam computation in CIVA software and experimental investigations on a semi-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction techniques, an optimised radiation pattern of the probe is expected to improve the signal quality and thus increase the reliability of the imaging results. This is of great importance for the construction of safe sealing structures needed for the disposal of radioactive or toxic waste.

Insights into the Mixing Efficiency of Submesoscale Centrifugal–Symmetric Instabilities

Abstract Submesoscale processes provide a pathway for energy to transfer from the balanced circulation to turbulent dissipation. One class of submesoscale phenomena that has been shown to be particularly effective at removing energy from the balanced flow is centrifugal–symmetric instabilities (CSIs), which grow via geostrophic shear production. CSIs have been observed to generate significant mixing in both the surface boundary layer and bottom boundary layer flows along bathymetry, where they have been implicated in the mixing and water mass transformation of Antarctic Bottom Water. However, the mixing efficiency (i.e., the fraction of the energy extracted from the flow used to irreversibly mix the fluid) of these instabilities remains uncertain, making estimates of mixing and energy dissipation due to CSI difficult. In this work we use large-eddy simulations to investigate the mixing efficiency of CSIs in the submesoscale range. We find that centrifugally dominated CSIs (i.e., CSI mostly driven by horizontal shear production) tend to have a higher mixing efficiency than symmetrically dominated ones (i.e., driven by vertical shear production). The mixing efficiency associated with CSIs can therefore alternately be significantly higher or significantly lower than the canonical value used by most studies. These results can be understood in light of recent work on stratified turbulence, whereby CSIs control the background state of the flow in which smaller-scale secondary overturning instabilities develop, thus actively modifying the characteristics of mixing by Kelvin–Helmholtz instabilities. Our results also suggest that it may be possible to predict the mixing efficiency with more readily measurable parameters (viz., the Richardson and Rossby numbers), which would allow for parameterization of this effect.

Effect of the Torsion Box Dimensions on Local Stress Distribution and Fatigue Strength Assessment of a Container Ship

The aim of this paper is to estimate the influence of the dimensions of the torsion box (height and width), of a 2400 TEU feeder-class container ship, on local stress distribution and assessment of local fatigue strength by using a numerical approach based on the fatigue limit-state and ultimate limit-state in the midship region. In terms of the fatigue limit-state, the effect of the dimensions of the torsion box is obtained by geometrical modifications, in the connection between the side shell longitudinal stiffeners with the transverse web frame for nine structural details, referring to different arrangements of strengthening elements (brackets and flat bars). The process of comparing the different elements determines the most effective combination. This structural influence on the local stress distribution is assessed, along the longitudinal plates between ordinary stiffeners bounding the perimeter of the torsion box, by calculating the hull girder stresses, local buckling stresses and shear stress distribution induced by vertical and horizontal shear forces, Saint Venant and warping torques, and finally the shear stresses induced by a warping moment. Scantling criteria are obtained allowing for a better design of this very important region in container ships.

Slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean

Flow in the mantle's bottom boundary layer plays an important role in shaping structures and processes in the deep mantle; however, knowledge of lowermost mantle flow patterns remains elusive. In particular, the influence of remnant slabs on lowermost mantle flow is poorly known, although it is likely that slabs play an important role in driving flow and thus in controlling key aspects of lowermost mantle behavior. Measurements of seismic anisotropy can yield relatively direct constraints on slab-induced lowermost mantle flow; however, such observations are challenging to make. We take advantage of the excellent raypath coverage beneath the northeastern Pacific Ocean provided by the USArray deployment in North America to provide detailed sampling of a region that has a long subduction history, with remnant slabs likely impinging on the core-mantle boundary. We present observations of coherent, strong shear wave splitting of SKKS and Sdiff phases across USArray stations and show through global wavefield modeling that the splitting is due to lowermost mantle anisotropy. A stacking approach enables us to make robust estimates of lowermost mantle splitting parameters, which we model by considering realistic mineral physics scenarios. Under the assumption of simple horizontal shear deformation, our observations are consistent with generally north-south flow directions for either a post-perovskite or a bridgmanite mineralogy; ferropericlase cannot explain observations. We speculate that this flow is driven by subducting slab remnants impinging on the core-mantle boundary.

Seismic Factor of Safety for 3D Reinforced Soil Slope with Piles under Unsaturated Condition

This study investigates the seismic stability of reinforced slope under a three-dimensional (3D) rotational horn-like failure mechanism, using the pseudo-dynamic approach and provides a new procedure to estimate factor of safety (FS) for slope. Such a procedure is able to figure out the influences of the seismic force, the soil property and the reinforcement by piles. Pseudo-dynamic approach is used to describe the seismic force in the time-to-spatial fields in unsaturated soils where matric suction works. Compared to the pseudo-static approach, the current approach considers the effects of time and spatial through the horizontal and vertical shear waves. For the pile driving, different insertion depths can yield various results, whether two work conditions of considering the pile resistance or not are discussed. FS of this study undergoes a decrement as the increase of the pile resistance and seismic force, indicating that the insertion depth affects FS where FS decreases in the early period of pile driving, after that increases and keeps constant in the late of pile driving, showing evident unimodal characteristics during the pile driving. The new expressions for slope reinforced by piles are presented for practical use in unsaturated soil engineering.

Influence of Assimilating Wind Profiling Radar Observations in Distinct Dynamic Instability Regions on the Analysis and Forecast of an Extreme Rainstorm Event in Southern China

This study quantitatively examines the contribution of assimilating observations in the regions with different dynamic instabilities to the analysis and prediction of an extreme rainstorm event in Fujian Province of China. The wind profiling radar (WPR) observations are classified into two groups, i.e., strong and weak instability areas (SIA and WIA), according to their local dynamic instability identified by the ensemble spread. Their performance of assimilation and prediction in terms of the wind and precipitation are evaluated and compared in detail. The results show that the wind analysis error by assimilating all of the WPR observations can be reduced by about 30%. In particular, the wind analysis errors by only assimilating the observations in the SIA are about 12% lower than those in the WIA. They are related to the existence of the low-level horizontal wind shear with strong instability in the SIA. The case study shows that the assimilation of observations in the SIA can effectively correct the wind fields on the two sides of the wind shear line, producing an improved precipitation forecast compared to observation assimilation in the WIA.

A method for calculating lateral response of offshore rigid monopile in sand under slope effect

This paper develops a method for calculating nonlinear lateral response of offshore rigid monopile in sand under slope effect. The method modifies three-dimensional wedge failure model to evaluate the ultimate soil resistance in front of the laterally loaded rigid monopile near sloped ground. The modified model considers the ultimate horizontal frictional resistance, the slope effect, the vertical friction force, the mutual influence of the forces within the wedge. And the base horizontal shear resistance is considered in the method. In addition, the load-displacement curves of the rigid monopile under five different distribution modes of the soil reaction along the pile are calculated by the force and moment equilibrium equations. The method in this paper is verified by comparing its results with those of field test, 3D FE model, 1g laboratory model test and existing analytical methods. Finally, this method is used to study the rotation behavior and lateral response of the offshore rigid monopile.

The Behavior of Interior Beam-Column Joint Models Using Self-Compacting Concrete with Variations of Shear Reinforcement Subjected to Cyclic Lateral Loads

The joint of a beam-column is crucial due to the distribution of cyclic lateral loads. Therefore, the joint detail must meet the design requirements of earthquake-resistant structures. Casting work in joint zones where the steel reinforcement spaces are close requires concrete materials that are easy to flow. An alternative to overcome the difficulty is using Self-Compacting Concrete (SCC) material. However, the properties of SCC for beam-column joint structures under earthquake loads still need to be studied further. This study aimed to analyze the behavior of the Interior Beam-Column (IBC) joint using SCC with variations of shear reinforcement subjected to cyclic lateral loads. Three types of shear reinforcement were modeled using numerical analysis. Variations of horizontal and diagonal shear reinforcements were compared to determine the best performance. The SCC-S3 IBC joint model with horizontal and diagonal shear reinforcements achieved the highest lateral forces and resisted compressive and tensile stresses in the largest stress contour and better stiffness degradation than other models of SCC IBC joints. The results showed that the SCC-S3 IBC joint with a combination of horizontal and diagonal shear reinforcements showed the best performance.

A novel dynamic mechanical analysis device to measure the in-vivo material properties of plantar soft tissue and primary finite elementary analysis results

We have designed a series of dynamic mechanical analysis (DMA)-like device to directly measure the material properties of living human plantar soft tissue. Various mechanical tests of plantar soft tissue such as vertical, horizontal shear and torsion can be carried out on the newly invented instruments, and periodic strain-stress outputs are obtained to analyse the viscoelasticity of the tissue. Pioneering finite element analysis has been done by coupling the machine and human foot FE model from different simulation environments, and the simulation tests show good engineering verification of the device design, and consistent theoretical results of the material properties of plantar soft tissue as expected.

Deep-Current Intraseasonal Variability Interpreted as Topographic Rossby Waves and Deep Eddies in the Xisha Islands of the South China Sea

Abstract Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9–20 and 30–120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and ∼43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being >0.4°C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic–anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.

Elastic Contrast, Rupture Directivity, and Damage Asymmetry in an Anisotropic Bimaterial Strike‐Slip Fault at Middle Crustal Depths

Mature faults with large cumulative slip often separate rocks with dissimilar elastic properties and show asymmetric damage distribution. Elastic contrast across such bimaterial faults can significantly modify various aspects of earthquake rupture dynamics, including normal stress variations, rupture propagation direction, distribution of ground motions, and evolution of off-fault damage. Thus, analyzing elastic contrasts of bimaterial faults is important for understanding earthquake physics and related hazard potential. The effect of elastic contrast between isotropic materials on rupture dynamics is relatively well studied. However, most fault rocks are elastically anisotropic, and little is known about how the anisotropy affects rupture dynamics. We examine microstructures of the Sandhill Corner shear zone, which separates quartzofeldspathic rock and micaceous schist with wider and narrower damage zones, respectively. This shear zone is part of the Norumbega fault system, a Paleozoic, large-displacement, seismogenic, strike-slip fault system exhumed from middle crustal depths. We calculate elastic properties and seismic wave speeds of elastically anisotropic rocks from each unit having different proportions of mica grains aligned sub-parallel to the fault. Our findings show that the horizontally polarized shear wave propagating parallel to the bimaterial fault (with fault-normal particle motion) is the slowest owing to the fault-normal compliance and therefore may be important in determining the elastic contrast that affects rupture dynamics in anisotropic media. Following results from subshear rupture propagation models in isotropic media, our results are consistent with ruptures preferentially propagated in the slip direction of the schist, which has the slower horizontal shear wave and larger fault-normal compliance.

Exploring Jupiter's Polar Deformation Lengths with High-resolution Shallow Water Modeling

The polar regions of Jupiter host a myriad of dynamically interesting phenomena, including vortex configurations, folded-filamentary regions (FFRs), and chaotic flows. Juno observations have provided unprecedented views of the high latitudes, allowing for more constraints to be placed upon the troposphere and the overall atmospheric energy cycle. Moist convective events are believed to be the primary drivers of energetic storm behavior as observed on the planet. Here we introduce a novel single-layer shallow water model to investigate the effects of polar moist convective events at high resolution, the presence of dynamical instabilities over long timescales, and the emergence of FFRs at high latitudes. We use a flexible, highly parallelizable, finite difference hydrodynamic code to explore the parameter space set up by previous models. We study the long-term effects of deformation length (L d ), injected pulse size, and injected geopotential. We find that models with L d beyond 1500 km (planetary Burger number, Bu = 4.4 × 10−4) tend to homogenize their potential vorticity in the form of dominant stable polar cyclones, while lower-L d cases tend to show less stability with regard to Arnol’d-type flows. We also find that large turbulent forcing scales consistently lead to the formation of high-latitude FFRs. Our findings support the idea that moist convection occurring at high latitudes may be sufficient to produce the dynamical variety seen at the Jovian poles. Additionally, derived values of localized horizontal shear and L d may constrain FFR formation and evolution.