Dynamics of Normal and Superfluid Fogs Using Diffusing-Wave Spectroscopy

The dynamics of normal and superfluid fogs are studied using the technique of diffusing-wave spectroscopy. For a water fog generated with a 1.75 MHz piezoelectric driver below the liquid surface, the 7 μm diameter droplets are found to have diffusive dynamics for correlation times long compared to the viscous time. For a fog of 10 μm diameter superfluid helium droplets in helium vapor at 1.5 K the motion appears to be ballistic for correlation times short compared to the viscous time. The velocity correlations between the helium droplets are found to depend on the initial velocity with which the droplets are injected from the helium surface into the fog

QRA Considering Multi-Vessel Failure Scenarios due to a Natural Disaster – Lessons from Fukushima

PresentationThe Fukushima accident is the largest nuclear power plant accident caused by a natural disaster, which shut off the cooling system. In this accident, an initiating event from a single unit was propagated to other units at the site. Prior to the Fukushima accident, scenarios for multi-unit failures had been screened out, so that only single unit failure scenarios were taken into account in the nuclear industry. Since that accident, the nuclear industry in South Korea is now more concerned with multi-unit Probabilistic Safety Assessment (PSA) and is attempting to develop a new methodology since there are generally more than four units on one site in the country The chemical and petrochemical industries have experienced a number of incidents/accidents related to multi-units such as vessels and tanks because many of these units are usually installed on a site. The chemical industry has a wide range of experience, but most scenarios have involved domino effects, while the study of multi-vessel accidents caused by natural disasters (i.e., earthquakes) is lacking. The purpose of this paper is to review past experiences in the chemical industry and adapt appropriate process safety applications using risk analysis related to multiple vessels (tanks) at a site. Several QRA approaches have been searched and employed to compare the risks of some chemical plant complexes in South Korea regarding multi-vessel (unit) failure scenarios due to natural disasters

Exciting and Harvesting Vibrational States in Harmonically Driven Granular Chains

This article explores the excitation of different vibrational states in a spatially extended dynamical system through theory and experiment. As a prototypical example, we consider a one-dimensional packing of spherical particles (a so-called granular chain) that is subject to harmonic boundary excitation. The combination of the multi-modal nature of the system and the strong coupling between the particles due to the nonlinear Hertzian contact force leads to broad regions in frequency where different vibrational states are possible. In certain parametric regions, we demonstrate that the Nonlinear Schr¨odinger (NLS) equation predicts the corresponding modes fairly well. We propose that nonlinear multi-modal systems can be useful in vibration energy harvesting and discuss a prototypical framework for its realization. The electromechanical model we derive predicts accurately the conversion from mechanical to electrical energy observed in the experiments