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Abstract: Numerical simulation of wave propagation in poroelastic media demands significantly more computational capability compared to elastic media simulation. Use of serial codes in a single scientific workstation limits the size of problem. To overcome this difficulty, a parallel velocity-stress staggered-grid finite-difference method is developed for efficient simulation of wave propagation in 2-D poroelastic media. The finite difference formulation of Biot''s theory has the properties of fourth order accuracy in space and second order accuracy in time. The model is decomposed into small subdomains for each processor. After each processor updates wavefields within its domain, the processors exchange the wavefields via message passing interface (MPI). The parallel implementation reduces the computational time and also allows one to study larger problems. From our numerical experiment, consistent with other 1-D experiments, it is found that the presence of heterogeneity of porous medium can produce significant P-wave attenuation in the seismic frequency range. [Copyright &y& Elsevier]

Abstract: Elemental turnover in porous media depends on substrate concentrations at the pore-scale. In this study, the effect of small scale variability in concentration fields on reaction rate estimates and the validity of the continuum approximation in reactive transport models are investigated via a pore-scale numerical model. Artificial porous media are generated using an identical overlapping sphere algorithm. By comparison between explicit pore-scale simulations and macroscopic continuum approximations, it is shown that inhomogeneous solute distribution within the pores can affect estimates of elemental turnover rates. The error associated with large scale rate estimates depends on the type of reaction, pore geometry, reaction kinetics and macroscopic concentration gradient. A correction term that involves a phenomenological parameter which can be evaluated numerically and macroscopic concentration gradients is introduced to improve the accuracy of upscaled homogeneous reaction rates. Implications for macroscopic descriptions of surface processes and surface attached microbial populations are discussed and it is shown that pore-scale heterogeneity can substantially affect estimates of heterogeneous reactions, while for homogeneous reactions, the error amounts to only a couple of percents. [Copyright &y& Elsevier]

Abstract: We developed a general library for handling a class of objects we call geographical curvilinear grids (GCLgrids). A GCLgrid is a distorted, uniform grid that is georeferenced. The GCLgrid library is implemented in an object oriented system with methods that relate points in the grid to a geographic reference frame. A simple example is a spherical shell divided along latitude, longitude, and depth, but more elaborate shapes can use the same interface. Scalar and vector fields are derived from the base grid through inheritance. Two algorithms are the core of this library. First, we use the Direction Set method to search for a location in space from a starting point. This algorithm converges reasonably fast if the grid is not extremely distorted. Second, we interpolate the grid using methods known from finite element analysis. A Jacobian matrix for an 8-node cube is computed to transform a distorted cube into a unit one. Shape functions for the standard cube are used to compute interpolation coefficients. Once the interpolation coefficients are computed, we can interpolate n-element vectors almost as quickly as scalar data. We show an application of the library to travel time table calculation at regional distances. Our table interpolator was found to be 10 times faster than one based on the tau-p method and is expected to be several orders of magnitude faster than 3D ray-tracing methods. Travel time interpolation errors are reduced significantly by tabulating delay times relative to a homogenous reference model instead of absolute times. This allows much coarser grids to be used at large scales comparing to one using total time. [Copyright &y& Elsevier]

• A novel idea to generate prediction models is proposed. • Failure type and force capacity estimated by Lasso regression. • Evaluation of out-of-plane bending behavior of masonry wallettes. • Non-spatial and spatial stochastic analysis of the brickwork assemblages. • Quantification of the variability in the masonry response. The out-of-plane flexural bending capacity of masonry is a fundamental property for understanding the behavior of masonry structures. This study investigates the behavior of unreinforced masonry wallettes subjected to combined compression-flexural loading using the discrete element method (DEM), and provides a novel framework to estimate the masonry strength. A simplified micro-modeling strategy is utilized to analyze a masonry wallette, including the variation of the mechanical properties in masonry units and joints. Stochastic DEM analyses are performed to simulate brickwork assemblages, assuming a strong unit-weak joint material model typical of most masonry buildings, including historical ones. Once the proposed computational approach is validated against the experimental findings, the effect of spatial and non-spatial variation of mechanical properties is explored. Two failure types are identified: joint failure and brick failure. For each failure mechanism, the variability of the response and the effects of the modeling parameters on the load-carrying capacity is quantified. Afterward, Lasso regression is employed to determine predictive equations in terms of the material properties and vertical pressure on the wallette. The results show that the most important parameters changing the response are the joint tensile strength and the amount of vertical stress for joint failure , whereas the unit tensile strength dominates the response for brick failure. Overall, this research proposes a novel framework adopting validated advanced computational models that feed on simple test results to generate data that is further utilized for training response prediction models for complex structures. [ABSTRACT FROM AUTHOR]

Abstract: A two-dimensional (2D) reactive transport model is used to investigate the controls on nutrient (, , PO4) dynamics in a coastal aquifer. The model couples density-dependent flow to a reaction network which includes oxic degradation of organic matter, denitrification, iron oxide reduction, nitrification, Fe2+ oxidation and sorption of PO4 onto iron oxides. Porewater measurements from a well transect at Waquoit Bay, MA, USA indicate the presence of a reducing plume with high Fe2+, , DOC (dissolved organic carbon) and PO4 concentrations overlying a more oxidizing -rich plume. These two plumes travel nearly conservatively until they start to overlap in the intertidal coastal sediments prior to discharge into the bay. In this zone, the aeration of the surface beach sediments drives nitrification and allows the precipitation of iron oxide, which leads to the removal of PO4 through sorption. Model simulations suggest that removal of through denitrification is inhibited by the limited overlap between the two freshwater plumes, as well as by the refractory nature of terrestrial DOC. Submarine groundwater discharge is a significant source of to the bay. [Copyright &y& Elsevier]

• A two-dimensional mesoscale lattice modeling approach for infill walls is proposed. • Two tests were conducted for aerated autoclaved concrete (AAC) infilled walls with and without openings. • Modeling approach was validated with the test results. • Infill contact length is found to depend on deformation levels. Significant infill wall damage in reinforced concrete frame buildings was observed in the past earthquakes. A vast number of numerical approaches have been proposed to estimate the non-linear behavior of infilled frames at different scales. Mesoscale lattice models were successfully used in the past to simulate the behavior of reinforced concrete member response. In this study, two-dimensional mesoscale lattice approach with an extended calibration technique was consistently applied to simulate the response of unreinforced Aerated Autoclaved Concrete (AAC) masonry infilled reinforced concrete frames. Two AAC infilled walls were tested for the purposes of this study. The objective of the tests were to investigate the effect of infilled wall-frame interaction with and without openings and validate the proposed numerical approach. In addition to the tests conducted, two tests were used from the literature for further validation. The maximum error of load capacity estimation from the simulations was less than 15% for all the examined tests. The proposed lattice model was capable of estimating crack propagation in the infill walls with reasonable accuracy. The frame-infill wall interaction was successfully simulated with providing a realistic representation of strut formation. Finally, a parametric study was conducted to examine contact length and strut width as a function of lateral deformation. The results show that the infill wall-frame contact length is significantly dependent on the lateral deformation demand levels and properties of interaction region. [ABSTRACT FROM AUTHOR]