Hydraulic and mechanical properties of wax-coated sands

Wax-coated sands are a new category of synthetic soils, which are gradually becoming a reliable construction material. Because of their valuable drainage ability and mechanical properties, wax coated sandy soils are specifically applicable to pavement construction of horseracing tracks and sport fields. Although the mechanical and hydraulic properties of these synthetic soils are well-proven, there is still a lack of studies on how the soil samples behave differently when mixing with different wax fractions. Adding the wax affects permeability and compressibility of pure sand. Intensity of influences is a function of weight percentage of wax that has been added, and other physical and environmental factors. The effects of wax content on hydraulic properties(permeability), and mechanical properties(stress strain behavior, compressibility) of sandy soils based on a series of experimental efforts were investigated. Obtained experimental results infer that increasing the amount of wax up to 6% causes an about 50% increase in permeability, mainly because of the significant effect of wax in lowering the friction along with covering and filling the angular parts of particles' surfaces and forming rounded particles. In addition, wax-coated sands show a 20% to 60% decrease in confined compression modulus compared to non wax-coated sands.

Analytic wave series solution of out-of-plane(SH) waves diffraction by an almost semi-circular shallow cylindrical hill

A closed-form wave equation analytic solution of two-dimensional scattering and diffraction of outof-plane（SH） waves by an almost semi-circular shallow cylindrical hill on a flat, elastic and homogeneous half space is proposed by applying the discrete Fourier series expansions of sine and cosine functions. The semi-circular hill problem is discussed as a special case for the new formulated equation.Compared with the previous semi-circular cases solutions, the present method can give surface displacement amplitudes which agrees well with previous results. Although the proposed equation can only solve the problem of SH-waves diffracted by almost semi-circular shallow hills, the stress and displacement residual amplitudes are numerical insignificantly everywhere. Moreover, the influences of the depth-towidth ratio（a parameter defined in this paper to evaluate the shallowness of the topography of hills） on ground motions are presented and summarized. The limitations and errors of truncation from Graf’s addition theorem and Fourier series equations in the present paper are also discussed.

Anti-plane (SH) waves diffraction by an underground semi-circular cavity:analytical solution

Diffraction of a two-dimensional （2D） semi-circular cavity in a half-space under incident SH-waves is studied using the classic wave function expansion method with a new de-coupling technique. This so-called ＂improved cosine half- range expansion＂ algorithm exhibits an excellent performance in reducing displacement residual errors at two rim points of concern. The governing equations are developed in a manner that minimizes the residues of the boundary conditions. Detailed derivation and analysis procedures as well as truncation of infinite linear governing equations are presented. The semi-circular cavity model presented in this paper, due to its simple profile, is expected to be used in seismic wave propagation studies as a benchmark for examining the accuracies of various analytical or numerical methods for mixed-boundary wave propagation problems.

An investigation of ballistic response of reinforced and sandwich concrete panels using computational techniques

Structural performance of nuclear containment structures and power plant facilities is of critical importance for public safety. The performance of concrete in a high-speed hard projectile impact is a complex problem due to a combination of multiple failure modes including brittle tensile fracture, crushing, and spalling. In this study, reinforced concrete (RC) and steel-concrete-steel sandwich (SCSS) panels are investigated under high-speed hard projectile impact. Two modeling techniques, smoothed particle hydrodynamics (SPH) and conventional finite element (FE) analysis with element erosion are used. Penetration depth and global deformation are compared between doubly RC and SCSS panels in order to identity the advantages of the presence of steel plates over the reinforcement layers. A parametric analysis of the front and rear plate thicknesses of the SCSS configuration showed that the SCSS panel with a thick front plate has the best performance in controlling the hard projectile. While a thick rear plate is effective in the case of a large and soft projectile as the plate reduces the rear deformation. The effects of the impact angle and impact velocity are also considered. It was observed that the impact angle for the flat nose missile is critical and the front steel plate is effective in minimizing penetration depth.

Molecular simulation-guided and physics-informed mechanistic modeling of multifunctional polymers

Polymeric materials have a broad range of mechanical and physical properties.They have been widely used in material science,biomedical engineering,chemical engineering,and mechanical engineering.The introduction of active elements into the soft matrix of polymers has enabled much more diversified functionalities of polymeric materials,such as self-healing,electroactive,magnetosensitive,pH-responsive,and many others.To further enable applications of these multifunctional polymers,a mechanistic modeling method is required and of great significance,as it can provide links between materials’micro/nano-structures and their macroscopic mechanical behaviors.Towards this goal,molecular simulation plays an important role in understanding the deformation and evolution of polymer networks under external loads and stimuli.These molecular insights provide physical guidance in the formulation of mechanistic-based continuum models for multifunctional polymers.In this perspective,we present a molecular simulation-guided and physics-informed modeling framework for polymeric materials.Firstly,the physical theory for polymer chains and their networks is briefly introduced.It serves as the foundation for mechanistic-models of polymers,linking their chemistry,physics,and mechanics together.Secondly,the deformation of the polymer network is used to derive the strain energy density functions.Thus,the corresponding continuum models can capture the intrinsic deformation mechanisms of polymer networks.We then highlight several representative examples across multiphysics coupling problems to describe in detail for this proposed framework.Last but not least,we discuss potential challenges and opportunities in the modeling of multifunctional polymers for future research directions.

A metadata model for collaborative experiments and simulations in earthquake engineering

Research projects in earthquake engineering yield a very large amount of complex data from experiments and computer simulations.Understanding and exchanging these complicated and voluminous data sets prompted the development of metadata models that document the processes of data generation,and facilitate the collaboration and exchange of information between researchers.The present metadata model was designed to document and exchange a large number of large data files in earthquake engineering,but is applicable to other fields of engineering and science.The model was conceived based on a series of former data models,which were unduly complicated and limited to few types of experiments.Simpler than its predecessors,the present metadata model applies to all kinds of earthquake engineering experiments.It was developed in the object-oriented with examples from centrifuge experiments.

A Comparative Study of Stochastic Collocation Methods for Flow in Spatially Correlated Random Fields

Stochastic collocation methods as a promising approach for solving stochastic partial differential equations have been developed rapidly in recent years.Similar to Monte Carlo methods,the stochastic collocation methods are non-intrusive in that they can be implemented via repetitive execution of an existing deterministic solver without modifying it.The choice of collocation points leads to a variety of stochastic collocation methods including tensor product method,Smolyak method,Stroud 2 or 3 cubature method,and adaptive Stroud method.Another type of collocation method,the probabilistic collocation method(PCM),has also been proposed and applied to flow in porous media.In this paper,we discuss these methods in terms of their accuracy,efficiency,and applicable range for flow in spatially correlated random fields.These methods are compared in details under different conditions of spatial variability and correlation length.This study reveals that the Smolyak method and the PCM outperform other stochastic collocation methods in terms of accuracy and efficiency.The random dimensionality in approximating input random fields plays a crucial role in the performance of the stochastic collocation methods.Our numerical experiments indicate that the required random dimensionality increases slightly with the decrease of correlation scale and moderately from one to multiple physical dimensions.

QUALIFICATION OF UNCERTAINTY FOR SIMULATING SOLUTE TRANSPORT IN THE HETEROGENEOUS MEDIA WITH SPARSE GRID COLLOCATION METHOD

The sparse grid collocation method is discussed to qualify the uncertainty of solute transport. The Karhunen-Loeve （KL） expansion is employed to decompose the log transformed hydraulic conductivity. The head, velocity and concentration fields are represented by the Lagrange polynomial expansion. A sparse grid collocation method is then used to reduce the original stochastic partial differential equations to a set of deterministic equations which is collocated at selected interpolation （collocation） points. The collocation points are constructed by the Smolyak algorithm. The accuracy, efficiency and convergence property of sparse grid collocation method are investigated by numerical experiments. The analysis shows that stochastic collocation strategy helps to decouple stochastic computations, and all the numerical computation is possible to be implemented by existing deterministic finite element codes. The proposed method provides an efficient way to evaluate the uncertainty of the solute transport in the heterogeneous media.

Naval derusting wastewater containing high concentration of iron, treated in UV photo-Fenton-like oxidation

The UV photooxidation with Fe（Ⅲ） and H2O2 was employed to treat a naval derusting wastewater, which contains the high COD （chemical oxygen demand） and various metal concentrations exceptionally with high concentrations of citric acid and iron. Because of its iron containment, the Fenton-like reaction automatically took place with the added amount of H2O2. The decomposition rate was found in a sequence of： UV/HEOE/Fe（Ⅲ） 〉 UV/H2O2 〉 Fe（Ⅱ）/H2O2. Two H2O2 injection methods, single and multiple points, were evaluated. The multiple-point H2O2 injection was more efficient to decompose the citric acid. The decomposition of the synthetic citric acid and the real derusting citric acid wastewater was also compared. The 93% COD reduction of the derusting wastewater was achieved using the UV/HEOE/Fe（Ⅲ） treatment.

Sharkskin-Inspired Magnetoactive Reconfigurable Acoustic Metamaterials

Most of the existing acoustic metamaterials rely on architected structures with fixed configurations,and thus,their properties cannot be modulated once the structures are fabricated.Emerging active acoustic metamaterials highlight a promising opportunity to on-demand switch property states;however,they typically require tethered loads,such as mechanical compression or pneumatic actuation.Using untethered physical stimuli to actively switch property states of acoustic metamaterials remains largely unexplored.Here,inspired by the sharkskin denticles,we present a class of active acoustic metamaterials whose configurations can be on-demand switched via untethered magnetic fields,thus enabling active switching of acoustic transmission,wave guiding,logic operation,and reciprocity.The key mechanism relies on magnetically deformable Mie resonator pillar(MRP)arrays that can be tuned between vertical and bent states corresponding to the acoustic forbidding and conducting,respectively.The MRPs are made of a magnetoactive elastomer and feature wavy air channels to enable an artificial Mie resonance within a designed frequency regime.The Mie resonance induces an acoustic bandgap,which is closed when pillars are selectively bent by a sufficiently large magnetic field.These magnetoactive MRPs are further harnessed to design stimuli-controlled reconfigurable acoustic switches,logic gates,and diodes.Capable of creating the first generation of untethered-stimuli-induced active acoustic metadevices,the present paradigm may find broad engineering applications,ranging from noise control and audio modulation to sonic camouflage.