Multiscale modeling of circular and elliptical particles in laminar shear flow

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Progress in particle-based multiscale and hybrid methods for flow applications

This work focuses on the review of particle-based multiscale and hybrid methods that have surfaced in the field of fluid mechanics over the last 20 years. We consider five established particle methods: molecular dynamics, direct simulation Monte Carlo, lattice Boltzmann method, dissipative particle dynamics and smoothed-particle hydrodynamics. A general description is given on each particle method in conjunction with multiscale and hybrid applications. An analysis on the length scale separation revealed that current multiscale methods only bridge across scales which are of the order of O(102)−O(103) and that further work on complex geometries and parallel code optimisation is needed to increase the separation. Similarities between methods are highlighted and combinations discussed. Advantages, disadvantages and applications of each particle method have been tabulated as a reference

Software for evaluating probability-based integrity of reinforced concrete structures

In recent years, much research work has been carried out in order to obtain a more controlled durability and long-term performance of concrete structures in chloride containing environment. In particular, the development of new procedures for probability-based durability design has proved to give a more realistic basis for the analysis. Although there is still a lack of relevant data, this approach has been successfully applied to several new concrete structures, where requirements to a more controlled durability and service life have been specified. A probability-based durability analysis has also become an important and integral part of condition assessment of existing concrete structures in chloride containing environment. In order to facilitate the probability-based durability analysis, a software named DURACON has been developed, where the probabilistic approach is based on a Monte Carlo simulation. In the present paper, the software for the probability-based durability analysis is briefly described and used in order to demonstrate the importance of the various durability parameters affecting the durability of concrete structures in chloride containing environment

Arbitrary slip length for fluid-solid interface of arbitrary geometry in smoothed particle dynamics

We model a slip boundary condition at fluid-solid interface of an arbitrary geometry in smoothed particle hydrodynamics and smoothed dissipative particle dynamics simulations. Under an assumption of linear profile of the tangential velocity at quasi-steady state near the interface, an arbitrary slip length $b$ can be specified and correspondingly, an artificial velocity for every boundary particle can be calculated. Therefore, $b$ as an input parameter affects the calculation of dissipative and random forces near the interface. For $b \to 0$, the no-slip is recovered while for $b \to \infty$, the free-slip is achieved. Technically, we devise two different approaches to calculate the artificial velocity of any boundary particle. The first has a succinct principle and is competent for simple geometries, while the second is subtle and affordable for complex geometries. Slip lengths in simulations for both steady and transient flows coincide with the expected ones. As demonstration, we apply the two approaches extensively to simulate curvy channel flows, dynamics of an ellipsoid in pipe flow and flows within complex microvessels, where desired slip lengths at fluid-solid interfaces are prescribed. The proposed methodology may apply equally well to other particle methods such as dissipative particle dynamics and moving particle semi-implicit methods

Numerical investigation of haemodynamics in spiral-inducing grafts using Eulerian and Lagrangian frameworks

A large range of vascular diseases require the replacement of blood vessels. Bypass grafting is a widely used treatment, in particular for high risk-patients, and consists of the connection of autologous/prosthetic graft and veins/arteries in order to repair the regular blood supply through occluded or damaged vessels. However, the development of stenosis due to thrombosis, atherosclerosis and intimal hyperplasia, linked to unfavourable haemodynamic patterns, reduces the long-term efficiency of the treatment. The identification of the natural blood motion as a swirling flow in the whole arterial system has resulted in new promising lines of research in cardiovascular devices in order to increase the patency rates of graft anastomoses by reproducing this physiological phenomenon. The impact of the proposed research lies in the numerical investigation of the influence of different design parameters of novel spiral-inducing grafts on haemodynamics, with the objective of understanding the physics of the problem and determinating the most relevant geometrical parameters. Conventional Eulerian metrics highlighted the effects of the ridge cross-sectional shape and, particularly, the position of the ridge around the perimeter of the graft on inducing an enhanced swirling blood flow. The Lagrangian approach, which assumes the blood as a heterogeneous solid-liquid suspension, allows to assess the individual behaviour and movement of representative particles travelling in the continuous phase and again highlighted the influence of the ridge orientation from this perspective. The correlation between distributions of friction forces and terminal locations of particles in the wall of the host artery showed a predominant deposition in regions of low wall shear stress, in agreement with those assumptions that were initially considered as optimisation criteria