Numerical simulations of three-dimensional drop collisions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77346/1/AIAA-13136-185.pd

Numerical Simulations of Drop Collisions

Three-dimensional simulations of the off-axis collisions of two drops are presented. The full Navier-Stokes equations are solved by a Front-Tracking/Finite-Difference method that allows a fully deformable fluid interface and the inclusion of surface tension. The drops are accelerated towards each other by a body force that is turned off before the drops collide. Depending on whether the interface between the drops is ruptured or not, the drops either bounce or coalesce. For drops that coalesce, the impact parameter, which measures how far the drops are off the symmetry line, determines the eventual outcome of the collision. For low impact parameters, the drops coalesce permanently, but for higher impact parameters, a grazing collision, where the drops coalesce and then stretch apart again is observed. The results are in agreement with experimental observations

Numerical simulations of drop collisions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76145/1/AIAA-1994-835-900.pd

Head‐on collision of drops—A numerical investigation

The head‐on collision of equal sized drops is studied by full numerical simulations. The Navier–Stokes equations are solved for the fluid motion both inside and outside the drops using a front tracking/finite difference technique. The drops are accelerated toward each other by a body force that is turned off before the drops collide. When the drops collide, the fluid between them is pushed outward leaving a thin layer bounded by the drop surface. This layer gets progressively thinner as the drops continue to deform, and in several of our calculations we artificially remove this double layer at prescribed times, thus modeling rupture. If no rupture takes place, the drops always rebound, but if the film is ruptured the drops may coalesce permanently or coalesce temporarily and then split again. Although the numerically predicted boundaries between permanent and temporary coalescence are found to be consistent with experimental observations, the exact location of these boundaries in parameter space is found to depend on the time of rupture. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71337/2/PHFLE6-8-1-29-1.pd

Fluid-structure interaction simulation of prosthetic aortic valves : comparison between immersed boundary and arbitrary Lagrangian-Eulerian techniques for the mesh representation

In recent years the role of FSI (fluid-structure interaction) simulations in the analysis of the fluid-mechanics of heart valves is becoming more and more important, being able to capture the interaction between the blood and both the surrounding biological tissues and the valve itself. When setting up an FSI simulation, several choices have to be made to select the most suitable approach for the case of interest: in particular, to simulate flexible leaflet cardiac valves, the type of discretization of the fluid domain is crucial, which can be described with an ALE (Arbitrary Lagrangian-Eulerian) or an Eulerian formulation. The majority of the reported 3D heart valve FSI simulations are performed with the Eulerian formulation, allowing for large deformations of the domains without compromising the quality of the fluid grid. Nevertheless, it is known that the ALE-FSI approach guarantees more accurate results at the interface between the solid and the fluid. The goal of this paper is to describe the same aortic valve model in the two cases, comparing the performances of an ALE-based FSI solution and an Eulerian-based FSI approach. After a first simplified 2D case, the aortic geometry was considered in a full 3D set-up. The model was kept as similar as possible in the two settings, to better compare the simulations' outcomes. Although for the 2D case the differences were unsubstantial, in our experience the performance of a full 3D ALE-FSI simulation was significantly limited by the technical problems and requirements inherent to the ALE formulation, mainly related to the mesh motion and deformation of the fluid domain. As a secondary outcome of this work, it is important to point out that the choice of the solver also influenced the reliability of the final results

Kinematic analysis of asymmetry after strength training session in paralympic powerlifters

Background: Para Powerlifting (PP) is the bench press with a single contest exercise. The rules require symmetry in lifting, but the natural tendency among humans is for asymmetry. Objective: The aim of the present study was to examine the influence of speed, load intensity, and fatigue of a training session on symmetry, and analyze asymmetries of average speeds between the limbs after a training session. Methods: Twelve male PP athletes (age 28.58 ± 5.50 years, experience 4.53 ± 1.27 years, body mass 79.25 ± 18.82 kg, 1RM 150.42 ± 42.07 kg, 1RM/BM 1.94 ± 0.46), had their bench press lifts recorded and downloaded into the Kinovea software. Measures of central tendency, mean ± standard deviation (SD) and the Shapiro–Wilk test were performed. Results: There was a difference in repetition 2, in the dominant limb, between the moment before and after, however, our hypothesis that at higher intensities and in the concentric phase of the exercise it would cause velocity asymmetry between the limbs was not confirmed. Conclusion: It is important to observe the absolute data and carefully evaluate the statistical differences since asymmetries are observed in different sports and are not determinant in sports performance; thus, being acceptable up to a certain level and unfavorable when it exceeds this level, which is individual and intimate to the sports activity