Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling

We study evolution of various statistical quantities of smoothed cosmic density and velocity fields using N-body simulations. The parameter $C\equiv /( )$ characterizes nonlinear coupling of these two fields and determines behavior of bulk velocity dispersion as a function of local density contrast. It is found that this parameter depends strongly on the smoothing scale even in quasi-linear regimes where the skewness parameter $S_3$ is nearly constant and close to the predicted value by the second-order perturbation theory. We also analyze weakly nonlinear effects caused by an adaptive smoothing known as the gather approach.Comment: 22 pages, 4 figures, to appear in ApJ (558, Sep 10

Dissipative behaviour of reinforced-earth retaining structures under severe ground motion

This paper focuses on the seismic performance of geosynthetic-reinforced retaining walls (GRWs) that several evidences have shown to be generally adequate. This can be attributed to the dissipation of energy produced by the internal plastic mechanisms activated during the seismic shaking, and to an overall ductile behaviour related to the large deformation that can be accommodated by the soil-reinforcement system. Using a number of numerical computations, this work compares the behaviour of three idealized structures that were conceived in order to have a similar seismic resistance, that however is activated through different plastic mechanisms. The analyses include numerical pseudo-static computations, carried out iteratively to failure, and time-domain nonlinear dynamic analyses, in which acceleration time-histories were applied to the bottom boundary of the same numerical models used for the pseudo-static analyses. The results of the dynamic analyses were interpreted in the light of the plastic mechanisms obtained with the pseudo-static procedure, confirming that GRWs develop local plastic mechanisms during strong motion resulting in a significant improvement of their seismic performance

Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues

State of the art research and treatment of biological tissues require accurate and efficient methods for describing their mechanical properties. Indeed, micromechanics motivated approaches provide a systematic method for elevating relevant data from the microscopic level to the macroscopic one. In this work the mechanical responses of hyperelastic tissues with one and two families of collagen fibers are analyzed by application of a new variational estimate accounting for their histology and the behaviors of their constituents. The resulting, close form expressions, are used to determine the overall response of the wall of a healthy human coronary artery. To demonstrate the accuracy of the proposed method these predictions are compared with corresponding 3-D finite element simulations of a periodic unit cell of the tissue with two families of fibers. Throughout, the analytical predictions for the highly nonlinear and anisotropic tissue are in agreement with the numerical simulations

Effect of moisture on mechanical behavior of granular material in initial laboratory and mechanical tests

In this article authors present results of initial laboratory tests and further numerical analyses using finite element method (FEM) and back - calculation method. Laboratory tests are based on trial loadings of granular material in different moisture conditions. Numerical analyses were obtained in FEM software using Coulomb - Mohr model of tested material. Presented results are the part of wider research program in which the main aim is to evaluate the influence of variable moisture content of granular materials used in road pavement structures on their fatigue life and in Life Cycle Assessment (LCA)

Modeling of ductile damage using numerical analyses on the micro-scale

The presentation deals with a continuum damage model which has been generalized to take into account the effect of stress state on damage criteria as well as on evolution equations of damage strains. It is based on the introduction of damaged and corresponding undamaged configurations. Plastic behavior is modeled by a yield criterion and a flow rule formulated in the effective stress space (undamaged configurations). In a similar way, damage behavior is governed by a damage criterion and a damage rule considering the damaged configurations. Different branches of the damage criterion are considered corresponding to various damage mechanisms depending on stress intensity, stress triaxiality and the Lode parameter. Experiments with carefully designed specimens are performed and the test results are used to identify basic material parameters. However, it is not possible to determine all parameters based on these tension and shear tests. To be able to get more insight in the complex damage behavior under different loading conditions, additional series of micro-mechanical numerical analyses of void containing unit cells have been performed. These finite element calculations on the micro-level cover a wide range of stress triaxialities and Lode parameters in the tension, shear and compression domain. The numerical results are used to show general trends, to develop equations for the stress-statedependent damage criteria, to propose evolution equations of damage strains, and to identify parameters of the continuum model

Three-dimensional advanced numerical approaches to the seismic soil and structural response analyses

A 3D non-linear finite element approach is developed to study the free-field seismic ground response and the soil-structure interaction (SSI) phenomena at the Lotung site (Taiwan) during the earthquake event occurred on May 20 1986. The site was extensively instrumented with down-hole and surface ac- celerometers, these latter located also on a 1/4–scale nuclear power plant containment structure. An advanced constitutive model is adopt- ed for simulating the soil behaviour, while a linear visco-elastic be- haviour is assumed for the structural model. The free-field and SSI analyses are carried out applying both the NS and EW horizontal components of the acceleration time history as recorded at the depth of 47 m b.g.l. The predicted ground response re- sults are in fair agreement with the recorded motion at depth and at the surface. The dynamic response of structure is well captured for this specific seismic event, thus confirming the validity of the numerical approach

Self-force with (3+1) codes: a primer for numerical relativists

Prescriptions for numerical self-force calculations have traditionally been designed for frequency-domain or (1+1) time-domain codes which employ a mode decomposition to facilitate in carrying out a delicate regularization scheme. This has prevented self-force analyses from benefiting from the powerful suite of tools developed and used by numerical relativists for simulations of the evolution of comparable-mass black hole binaries. In this work, we revisit a previously-introduced (3+1) method for self-force calculations, and demonstrate its viability by applying it to the test case of a scalar charge moving in a circular orbit around a Schwarzschild black hole. Two (3+1) codes originally developed for numerical relativity applications were independently employed, and in each we were able to compute the two independent components of the self-force and the energy flux correctly to within $< 1$. We also demonstrate consistency between $t$-component of the self-force and the scalar energy flux. Our results constitute the first successful calculation of a self-force in a (3+1) framework, and thus open opportunities for the numerical relativity community in self-force analyses and the perturbative modeling of extreme-mass-ratio inspirals.Comment: 23 pages, 13 figure