Joe Petrolito

A simple model for estimating shocks in unrestrained building contents in an earthquake

Building contents that include cabinets housing electronic equipment are typically not rigidly secured to the floor, nor to the adjacent wall except in regions of high seismic activities. The behavior of unrestrained building contents in an earthquake is a cause of concern because of the consequence of damage to certain equipment or other forms of fragile items. Much of the research reported in the literature has been devoted to studying the rocking and sliding motion behavior of base-excited rigid objects and their risks of overturning. In contrast, this paper is concerned with estimating the impact acceleration that can be generated by the pounding of the rocking object onto the floor. Algebraic expressions for predicting the acceleration level, which can be translated into dynamic force values, are derived and illustrated by case studies. Importantly, the proposed expressions have been verified by comparisons with results from both simulated and physical experiments. In illustrating the use of the proposed analytical procedure, a parametric experimental study has been undertaken on a cushion material to study the sensitivity of its static and dynamic stiffness to changes in the boundary conditions of the cushion. The proposed calculation procedure, while simple to apply, can be used as a means of predicting shock and the dynamic forces that can be generated in an object in the course of the response to an earthquake.

Employing numerical techniques in the analysis and design of musical instruments

In the simplest of terms, a musical instrument consists of a source of oscillation coupled to a resonating body. The exception to this is an idiophone such as a triangle or gong, where the vibrating source is able to be its own radiator of sound. Whatever the configuration, the radiating structure is generally not a simple shape easily represented by a mathematical formulation, and analytical solutions to the governing equations of even a simplified model are often not obtainable. Working with Neville Fletcher in the 1980’s a personal computer was employed to undertake a time-stepping routine through the equations of a simplified model of a kinked metal bar, to depict nonlinear coupling of its modes of vibration. Similar analysis of a gong modelled by a spherical shell with a kinked edge was well beyond the available computing power. In this paper we illustrate how the development of computers and numerical techniques over the intervening thirty years means that we are now able to describe and analyse com...