Modeling Riverbank Slope Reinforcement Using Anti-Slide Piles with Geocells

Geocells are increasingly used in engineering applications, but the design of riverbank slope reinforcements that use only geocells limits reinforcement performance. Moreover, the design and use of anti-slide piles with geocells are mainly based on experiences that are unsupported by theoretical models. In this paper, by combining the confinement effect and vertical action mechanism of geocells, the horizontal friction mechanism of the geocell layer and the vertical support mechanism of piles, a theoretical model of riverbank slope reinforced by anti-slide piles with geocells was constructed. In addition, to describe the mechanical behavior of a riverbank slope reinforced by anti-slide piles with geocells, the slip-resisting mechanism of the anti-slide pile with interaction between geocells and their internal filler is considered in the model. Furthermore, to investigate the influence of changes in water level on riverbank slope stability, the developed model takes into account settlement, lateral displacement, pile bending moment and pile axial force. The model predications were validated by the field measurement data. The results from a series of parametric studies show that the use of anti-slide pile and geocells can effectively reduce the settlement and the lateral displacement of a riverbank slope. The developed model could contribute to an optimal design of anti-slide pile with geocells for enhancing the stability of a riverbank slope.

Identifying resonances of the Galactic bar in Gaia DR2: I. Clues from action space

ABSTRACT Action space synthesizes the orbital information of stars and is well suited to analyse the rich kinematic substructure of the disc in the second Gaia data release's radial velocity sample. We revisit the strong perturbation induced in the Milky Way disc by an m = 2 bar, using test particle simulations and the actions (JR, Lz, Jz) estimated in an axisymmetric potential. These make three useful diagnostics cleanly visible. (1) We use the well-known characteristic flip from outward to inward motion at the outer Lindblad resonance (OLR; l = +1, m = 2), which occurs along the axisymmetric resonance line (ARL) in (Lz, JR), to identify in the Gaia action data three candidates for the bar’s OLR and pattern speed Ωbar: 1.85Ω0, 1.20Ω0, and 1.63Ω0 (with ∼0.1Ω0 systematic uncertainty). The Gaia data is therefore consistent with both slow and fast bar models in the literature, but disagrees with recent measurements of ∼1.45Ω0. (2) For the first time, we demonstrate that bar resonances – especially the OLR – cause a gradient in vertical action 〈Jz〉 with Lz around the ARL via ‘Jz-sorting’ of stars. This could contribute to the observed coupling of 〈vR〉 and 〈|vz|〉 in the Galactic disc. (3) We confirm prior results that the behaviour of resonant orbits is well approximated by scattering and oscillation in (Lz, JR) along a slope ΔJR/ΔLz = l/m centred on the l:m ARL. Overall, we demonstrate that axisymmetrically estimated actions are a powerful diagnostic tool even in non-axisymmetric systems.

Radial migration and vertical action in N-body simulations

ABSTRACT We study the radial migration of stars as a function of orbital action as well as the structural properties of a large suite of N-body simulations of isolated disc galaxies. Our goal is to establish a relationship between the radial migration efficiency of stars and their vertical action. We aim to describe how that relationship depends on the relative gravitational dominance between the disc and the dark matter halo. By changing the mass ratio of our disc and dark matter halo, we find a relationship between disc dominance, number, and strength of spiral arms, and the ensuing radial migration as a function of the vertical action. We conclude that the importance of migration at large vertical action depends on the strength of the spiral arms and therefore the dominance of the disc. Populations with more radial action undergo less radial migration, independently of disc dominance. Our results are important for the future of analytical modelling of radial migration in galaxies and further the understanding of radial migration that is a key component of the restructuring of galaxies, including the Milky Way.

A Suggestion to the Vertical Earthquake Action Stipulated in Seismic Design Specification

In order to further regulate the vertical earthquake action in seismic design specification, to overcome the unreasonable and inconvenient flaws in certain conditions by using vertical to horizontal spectra ratio function, the feasibility of stipulating vertical design response spectrum with the same way of horizontal one is deal with in this paper. 1513 sets of three component records during 64 earthquakes from NGA-west1 database are selected and grouped by magnitude, distance and site conditions. Average acceleration response spectrum of each group is generalized to get the corresponding mean maximum amplitude and effective peak acceleration EPA. Furthermore, some groups with EPA in an interval are merged into one. Once again, the parameters, such as maximum amplitude and characteristic periods of each final grouping are acquired by the same way. The former is divided by the corresponding horizontal value for site category, to obtain the site coefficient for vertical action. Finally a preliminary suggestion of vertical site coefficient and characteristic period are presented. Comparison of observed data with results from the new suggestion and those from spectral ratio shows that the improvement of this study is obvious.

A Mechanistic Multibody Model for Simulating the Dynamics of a Vertical Piano Action

The theoretical framework for constructing a fully mechanistic multibody dynamic model of a vertical piano action is described, and its general validity is established. Equations of motion are derived symbolically using a graph-theoretic formulation. Model fidelity is increased by introducing several novel features: (i) a new contact model for representing the compression of the felt-lined interfaces between interacting parts, capable of capturing the intermittent loading and unloading of these contacts occurring through the key stroke, as well as providing smooth transitions between these states; (ii) models for two important components that are unique to the vertical action, the bridle strap and the butt spring; (iii) a sophisticated key pivot model that captures both the rotational motion and the vertical translation of the key as it can lift off the balance rail under some conditions; (iv) flexible beam models for backcheck wire and hammer shank so as to predict observed vibrations in the response accurately; and (v) coupling of the mechanism model to a flexible stiff string model for realistic hammer impact. For simulation, parameters were obtained by experimental testing and measurement of a physical prototype vertical action. Techniques are described for the virtual regulation of the model to ensure that initial conditions and pseudostatic response accurately represent the precise configuration and desired relationships between the parts during the key stroke. Two input force profiles were used for simulations, a forte pressed (hard) and piano pressed touch (soft), typical of those measured at the key surface when activated by a pianist. Simulated response to these quite different inputs is described, and compared to experimental observations obtained from a physical prototype.

Vertical Action of a Concentric Multi-Annular Punch on a Transversely Isotropic Elastic Half-Space

In this paper, the response of a transversely isotropic half-space under the punch action of a set of rigid concentric annuli frictionless contacts is considered. By virtue of a compact potential representation and Hankel transforms, a set of ring-load Green’s functions for the axisymmetric equations of equilibrium are derived and shown to be expressible in terms of standard elliptic integrals. With the aid of a rigorous yet highly efficient numerical method, the integral equation is solved for the multi-interval singular mixed boundary value problem. Detailed solutions to illustrate the performance of the computational approach and the influence of the degree of anisotropy and contact conditions on the mechanics problem are presented.