Experimental study of strain accumulation of silica sand in a cyclic triaxial test

The experimental and phenomenological investigation of the elasto-plastic long-term behaviour of soils under dynamic loading is important for the development of risk analysis tools and numerical accumulation models for settlement prediction. Soil parameters, test equipment and loading conditions have a significant influence on strain accumulation, therefore a parameterization of the silica sand and a description of the re-engineered cyclic triaxial test device are performed in this paper. Long term cyclic triaxial tests are performed on a silica sand to investigate the influence of the number of cycles, the initial void ratio, the mean pressure and packages of cycles on the accumulation of residual strains. Empirical formulations of existing strain accumulation models are validated with test results on dry test samples

Wind-structure interaction simulations for the prediction of ovalling vibrations in silo groups

Wind-induced ovalling vibrations were observed during a storm in October 2002 on several empty silos of a closely spaced group consisting of 8 by 5 thin-walled silos in the port of Antwerp (Belgium). The purpose of the present research is to investigate if such ovalling vibrations can be predicted by means of numerical simulations. More specifically, the necessity of performing computationally demanding wind-structure interaction (WSI) simulations is assessed. For this purpose, both one-way and two-way coupled simulations are performed. Before considering the entire silo group, a single silo in crosswind is simulated. The simulation results are in reasonably good agreement with observations and WSI simulations seem to be required for a correct prediction of the observed ovalling vibrations

Computational fluid-structure interaction simulations for wind induced vibrations in silo groups

During a storm in October 2002, wind induced ovalling vibrations were observed on several empty silos of a closely spaced group consisting of 8 by 5 silos in the port of Antwerp (Belgium). First, a thorough understanding of the fluid flow around the group is required to clarify the underlying mechanisms for the vibration. Since the configuration and orientation of the group drastically change the pressure distribution on the silos of the group, the flow regime around and within the silo group has been simulated for 7 angles of incidence between 0 and 90, leaving other parameters unchanged (e.g. spacing ratio, Reynolds number,...). The flow regime shows similarities with the flow within tube arrays (e.g. heat exchangers) and the flow around rectangular cylinders. By a ‘one way coupling’ of static (time averaged) and dynamic (fluctuating) pressure loadings on the cylinder surfaces it is examined if the excitation of ovalling vibrations in the silo group is possible. Two probable causes of observable silo vibrations in the group are observed. The first, as a result of large static wind pressures and fluctuating drag and lift coefficients, might lead to rigid body motions of the statically deformed silos. The second, due to higher dynamic pressure oscillations, can excite ovalling oscillations in the third and fourth eigenmodes at the lee side of the group, corresponding with the lowest eigenfrequencies of the silos and the visually detected vibrations in 2002. Although it is shown by this ‘one way coupling’ that ovalling vibrations can be excited in the group, more advanced ‘two way coupled’ fluid-structure interaction simulations are required to determine the underlying mechanism inducing these aeroelastic deformations

A tangential force-displacement model for elastic frictional contact between particles in triaxial test simulations

A tangential contact model for three-dimensional discrete element simulations is proposed and used in the micro-mechanical simulation of a drained triaxial test. In this model, the dependence of the tangential contact force on the contact loading history is accounted for. A representative volume element with spherical discrete elements and periodic boundary conditions is used in the simulations to reduce the computation costs. Numerical results of a triaxial test obtained with a linear and the proposed tangential contact model are compared. The results for both contact models are qualitatively in agreement with theory. The linear contact model needs calibration as the used parameters lack physical meaning, while the proposed contact model only uses physical properties of the particles

Measurements and Numerical Prediction of High Speed Train Vibrations

This paper discusses the experimental validation of a numerical prediction model for train induced vibrations. The model fully accounts for the dynamic interaction between the train, the track and the soil. The track is modelled as a longitudinally invariant system, where two beams represent the rails, while a plate with a rigid cross section represents the subgrade. The track is located at the surface of a horizontally layered elastic halfspace. The translational invariance of the problem geometry enables a solution of the equations of motion in the frequency–wavenumber domain. The model is validated by means of vibration measurements that have been performed at the occasion of the homologation tests of the new HST track on the line L2 between Brussels and K¨oln during the passage of an IC train and a Thalys HST at variable speed

Multi-temporal decomposition for elastoplastic ratcheting solids

This paper presents a multi-temporal formulation for simulating elastoplastic solids under cyclic loading. We leverage the proper generalized decomposition (PGD) to decompose the displacements into multiple time scales, separating the spatial and intra-cyclic dependence from the inter-cyclic variation. In contrast with the standard incremental approach, which solves the (non-linear and computationally intensive) mechanical balance equations at every time step, the proposed PGD approach allows the mechanical balance equations to be solved exclusively for the small-time intra-cyclic response, while the large-time inter-cyclic response is described by simple scalar algebraic equations. Numerical simulations exhibiting complex cyclic responses, including a 2D problem and an application to a monopile foundation, demonstrate that PGD solutions with a limited number of space-time degrees of freedom may be obtained numerically, only requiring a few modes to accurately capture the reference response.Comment: Version accepted for publication in Computer Methods in Applied Mechanics and Engineerin