Arnout M. P. Boelens

Bio: Arnout M. P. Boelens is an academic researcher from Stanford University. The author has contributed to research in topics: Ambient pressure & Splash. The author has an hindex of 7, co-authored 18 publications receiving 133 citations. Previous affiliations of Arnout M. P. Boelens include University of Chicago & Delft University of Technology.

Drop splashing is independent of substrate wetting

Abstract: A liquid drop impacting a dry solid surface with sufficient kinetic energy will splash, breaking apart into numerous secondary droplets. This phenomenon shows many similarities to forced wetting, including the entrainment of air at the contact line. Because of these similarities and the fact that forced wetting has been shown to depend on the wetting properties of the surface, existing theories predict splashing to depend on wetting properties as well. However, using high-speed interference imaging, we observe that at high capillary numbers wetting properties have no effect on splashing for various liquid-surface combinations. Additionally, by fully resolving the Navier-Stokes equations at length and time scales inaccessible to experiments, we find that the shape and motion of the air-liquid interface at the contact line/edge of the droplet are independent of wettability. We use these findings to evaluate existing theories and to compare splashing with forced wetting.

Generalised Navier boundary condition for a volume of fluid approach using a finite-volume method

Abstract: In this work, an analytical volume of fluid implementation of the generalised Navier boundary condition is presented based on the Brackbill surface tension model. The model is validated by simulations of droplets on a smooth surface in a planar geometry. Looking at the static behavior of the droplets, it is found that there is a good match between the droplet shape resolved in the simulations and the theoretically predicted shape for various values of the Young’s angle. Evaluating the spreading of a droplet on a completely wetting surface, the Voinov-Tanner-Cox law (θ ∝ Ca1/3) can be observed. In addition, the scaling of the droplet radius as a function of time follows r ∝ t1/2, suggesting that spreading is limited by inertia. These observations are made without any fitting parameters except the slip length.In this work, an analytical volume of fluid implementation of the generalised Navier boundary condition is presented based on the Brackbill surface tension model. The model is validated by simulations of droplets on a smooth surface in a planar geometry. Looking at the static behavior of the droplets, it is found that there is a good match between the droplet shape resolved in the simulations and the theoretically predicted shape for various values of the Young’s angle. Evaluating the spreading of a droplet on a completely wetting surface, the Voinov-Tanner-Cox law (θ ∝ Ca1/3) can be observed. In addition, the scaling of the droplet radius as a function of time follows r ∝ t1/2, suggesting that spreading is limited by inertia. These observations are made without any fitting parameters except the slip length.

Simulations of splashing high and low viscosity droplets

Abstract: In this work, simulations are presented for low viscosity ethanol and high viscosity silicone oil droplets impacting on a dry solid surface at atmospheric and reduced ambient pressure. The simulations are able to capture both the effect of the ambient gas pressure and liquid viscosity on the droplet impact and breakup. The results suggest that at early times droplet impact and gas film behavior for both low and high viscosity liquids share the same physics. However, at later times, during liquid sheet formation and breakup, high and low viscosity liquids behave differently. These results explain why for both kinds of liquids the pressure effect can be observed, while at the same time different high and low viscosity splashing regimes have been identified experimentally.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Stochastic Differential Equations

Abstract: We explore in this chapter questions of existence and uniqueness for solutions to stochastic differential equations and offer a study of their properties. This endeavor is really a study of diffusion processes. Loosely speaking, the term diffusion is attributed to a Markov process which has continuous sample paths and can be characterized in terms of its infinitesimal generator.