A combined finite-discrete element model for reinforced concrete under seismic load

In this work a numerical model for analysis of reinforced concrete structures under seismic load is presented. The model uses the combined finite-discrete element method; thus taking into account the discontinuous nature of the reinforced concrete at the failure stages. The application of the combined finite-discrete element method includes a number of deformable discrete elements that interact with each other, fracture, fragmentation and disjoint during the seismic load. To these a robust model for reinforcement bars has been added. Interaction solutions between bars and concrete have also been developed and implemented into the open source Y2D combined finite-discrete element code. This way it is possible to describe initiation of the cracks, crack propagation and fracture which are important mechanisms in the analysis of reinforced concrete structures under seismic load. Through numerical examples these have been demonstrated and tested using reinforced concrete structure under an experimentally recorded earthquake accelelogram

An investigation on the rheodynamics of human red blood cells using high performance computations

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Studies on the haemodynamics of human circulation are clinically and scientifically important. The flow of human blood is extremely complex due to the existence of the highly deformable red blood cells (RBCs), which are able to pass through capillaries smaller than their size. To investigate the effect of deformation and aggregation in blood flow, a computational technique has been developed by coupling the interaction between the fluid and the deformable solids. The flow of 49,512 RBCs at 45% concentration and under the influence of aggregating forces was examined to improve the existing knowledge on how to simulate and study the blood flow and its structural characteristics of blood at a large scale. The simulation was carried out with full parallelization of the coupled fluid-solid code using spatial decomposition and high performance supercomputers. The large scale feature of the simulation has enabled a macroscale verification and investigation of the overall characteristics of RBC aggregations to be carried out. The results are in excellent agreement with experimental studies and, more specifically, both the experimental and the simulation results show uniform RBC distributions under high shear rates (60-100/s) whereas large aggregations were observed under a lower shear rate of 10/s. The statistical analysis of the simulation data also shows that the shear rate has significant influence on both the flow velocity profiles and the frequency distribution of the RBC orientation angles. The flow under the low shear rate also tended to have bi-phasic velocity profile which is mainly due to the formation of large scale aggregation clusters

Saltation of particles in turbulent channel flow.

This paper numerically investigates particle saltation in a turbulent channel flow having a rough bed consisting of two to three layers of densely packed spheres. The Shields function is 0.065 which is just above the sediment entrainment threshold to give a bed-load regime. The applied methodology is a combination of three technologies, i.e., the direct numerical simulation of turbulent flow; the combined finite-discrete element modeling of the deformation, movement, and collision of the particles; and the immersed boundary method for the fluid-solid interaction. It is shown that the presence of entrained particles significantly modifies the flow profiles of velocity, turbulent intensities, and shear stresses in the vicinity of a rough bed. The quasi-streamwise-aligned streaky structures are not observed in the near-wall region and the particles scatter on the rough bed owing to their large size. However, in the outer flow region, the turbulent coherent structures recover due to the weakening rough-bed effects and particle interferences. First- and second-order statistical features of particle translational and angular velocities, together with sediment concentration and volumetric flux density profiles, are presented. Several key parameters of the particle saltation trajectory are calculated and agree closely with published experimental data. Time histories of the hydrodynamic forces exerted upon a typical saltating particle, together with those of the particle's coordinates and velocities, are presented. A strong correlation is shown between the abruptly decreasing streamwise velocity and increasing vertical velocity at collision which indicates that the continuous saltation of large-grain-size particles is controlled by collision parameters such as particle incident angle, local bed packing arrangement, and particle density, etc.This work was supported by a Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme (Grant No. PIIF-GA-2009-236457). The first author acknowledges the financial support of the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No. 51321065), National Natural Science Foundation of China (Grants No. 50809047, No. 51109157, and No. 51009105), and Natural Science Foundation of Tianjin (Grants No. 12JCQNJC02600, No. 12JCQNJC04900, and No. 12JCQNJC05600

Direct numerical simulation of sediment entrainment in turbulent channel flow

This research was supported by a Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme (Grant No. PIIF-GA-2009-236457). The first author acknowledges the financial support of the Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No. 51021004), National Natural Science Foundation of China (Grant Nos. 50809047 and 51009105), and Natural Science Foundation of Tianjin (Grant No. 12JCQNJC02600)

An Investigation on the Aggregation and Rheodynamics of Human Red Blood Cells Using High Performance Computations.

Studies on the haemodynamics of human circulation are clinically and scientifically important. In order to investigate the effect of deformation and aggregation of red blood cells (RBCs) in blood flow, a computational technique has been developed by coupling the interaction between the fluid and the deformable RBCs. Parallelization was carried out for the coupled code and a high speedup was achieved based on a spatial decomposition. In order to verify the code's capability of simulating RBC deformation and transport, simulations were carried out for a spherical capsule in a microchannel and multiple RBC transport in a Poiseuille flow. RBC transport in a confined tube was also carried out to simulate the peristaltic effects of microvessels. Relatively large-scale simulations were carried out of the motion of 49,512 RBCs in shear flows, which yielded a hematocrit of 45%. The large-scale feature of the simulation has enabled a macroscale verification and investigation of the overall characteristics of RBC aggregations to be carried out. The results are in excellent agreement with experimental studies and, more specifically, both the experimental and simulation results show uniform RBC distributions under high shear rates (60-100/s) whereas large aggregations were observed under a lower shear rate of 10/s

Image based simulation of one-dimensional compression tests on carbonate sand

High factors of safety and conservative methods are commonly used on foundation design on shelly carbonate soils. A better understanding of the behavior of this material is, thus, critical for more sustainable approaches for the design of a number of offshore structures and submarine pipelines. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods. In this study, a one-dimensional compression test was performed inside an X-ray scanner to obtain 3D images of the evolving internal structure of a shelly carbonate sand. A preliminary inspection of the images through five loading increments has shown that the grains rearrange under loading and in some cases cracks develop at the contacts. In order to replicate of the experiments in the numerical domain, the 3D image of the soil prior to loading was imported into a micro Finite Element (µFE) framework. This image-based modelling tool enables measurements of the contact force and stress map inside the grains while making use of the real microstructure of the soil. The potential of the µFE model to contribute insights into yield initiation within the grain is demonstrated here. This is of particular interest to better understand the breakage of shelly grains underpinning their highly compressive behavior