High speed visualizations of the cavitating vortices of 2D mixing layer

The present study investigates experimentally vortex dynamics of a cavitating two-dimensional mixing layer at a high Reynolds number in order to determine the effect of growth and collapse of cavitation. The dynamics and the topology of the vorticity regions corresponding to the low pressure area where cavitation effects take place are studied from the single phase state to highly cavitating conditions. LDV techniques are used in order to characterize the pattern of the turbulent single phase flow. Highspeed visualizations have been performed using a specific image processing of time series to highlight the behaviour and dynamics of the vapour phase. Visualizations, image processing and statistical analysis enable the estimation of the convective velocity and the shedding frequency of the cavitating Kelvin–Helmholtz vortices. The measured visual vapour thickness grows linearly as the Kelvin–Helmholtz instability develops and its expansion rate stays constant for the range of cavitation levels studied. The vortex pairing phenomenon is also analysed. Results show that the spatial development of the mixing area is slightly affected by the vapour phase allowing a self-similar behaviour of the mean motion

SBIR Phase II Final Report for Scalable Grid Technologies for Visualization Services

This project developed software tools for the automation of grid computing. In particular, the project focused in visualization and imaging tools (VTK, ParaView and ITK); i.e., we developed tools to automatically create Grid services from C++ programs implemented using the open-source VTK visualization and ITK segmentation and registration systems. This approach helps non-Grid experts to create applications using tools with which they are familiar, ultimately producing Grid services for visualization and image analysis by invocation of an automatic process

Data Center Networking with Multipath TCP

Recently new data center topologies have been proposed that offer higher aggregate bandwidth and location independence by creating multiple paths in the core of the network. To effectively use this bandwidth requires ensuring different flows take different paths, which poses a challenge. Plainly put, there is a mismatch between single-path transport and the multitude of available network paths. We propose a natural evolution of data center transport from TCP to multipath TCP. We show that multipath TCP can effectively and seamlessly use available bandwidth, providing improved throughput and better fairness in these new topologies when compared to single path TCP and randomized flow-level load balancing. We also show that multipath TCP outperforms laggy centralized flow scheduling without needing centralized control or additional infrastructure

Improving datacenter performance and robustness with multipath TCP

The latest large-scale data centers offer higher aggregate bandwidth and robustness by creating multiple paths in the core of the network. To utilize this bandwidth requires different flows take different paths, which poses a challenge. In short, a single-path transport seems ill-suited to such networks. We propose using Multipath TCP as a replacement for TCP in such data centers, as it can effectively and seamlessly use available bandwidth, giving improved throughput and better fairness on many topologies. We investigate what causes these benefits, teasing apart the contribution of each of the mechanisms used by MPTCP. Using MPTCP lets us rethink data center networks, with a different mindset as to the relationship between transport protocols, routing and topology. MPTCP enables topologies that single path TCP cannot utilize. As a proof-of-concept, we present a dual-homed variant of the FatTree topology. With MPTCP, this outperforms FatTree for a wide range of workloads, but costs the same. In existing data centers, MPTCP is readily deployable leveraging widely deployed technologies such as ECMP. We have run MPTCP on Amazon EC2 and found that it outperforms TCP by a factor of three when there is path diversity. But the biggest benefits will come when data centers are designed for multipath transports