Basal conditions of Kongsvegen at the onset of surge - revealed using seismic vibroseis surveys

<p>Kongsvegen is a well-studied surge-type glacier in the Kongsfjord area of northwest Svalbard. Long-term monitoring has shown that the ice surface velocity has been increasing since around 2014; presenting a unique opportunity to study the internal ice structure, basal conditions and thermal regime, all of which play a crucial role in initiating glacier surges. In April 2019, three-component seismic vibroseis surveys were conducted at two sites on the glacier, using a small Electrodynamic Vibrator source (ElViS). The first site is in the ablation area and the second near the equilibrium line, where the greatest increase in ice-surface velocity has been observed.</p><p>Initial analysis indicates the conditions at the two sites are significantly different. At the ablation area site, the ice is around 220 m thick, and the bed is relatively flat and unvaried, with no clear change in the bed reflection along the profile. The bed appears to comprise a uniform and undisturbed sediment package ~60 m thick, and there are no clear englacial reflections within the ice column. By contrast at the second site, the ice is around 390 m thick, and the internal ice structure is much more complex. Clear internal ice reflections are visible at depths between 150-250 m, and further reflections in the 100 m above the bed indicate there could be shearing or sediment entrainment in this area. Below the bed, cross-cutting layers are clearly visible and the bed reflection itself shows changing reflection polarity – suggesting water or very wet sediment is present in some areas.  The contrast between these two sites at the onset of a surge phase allows us to investigate the physical conditions that are conducive to surge initiation, both at the ice-bed interface and within the ice column.</p>

Subjective Assessment of the Vibration Discomfort Produced by Different Hand Held Machines

A subjective method of paired comparisons was developed to compare the discomfort caused by the vibration from hand-held power tools with the predictions obtained using the procedures recommended by standards for the evaluation of human exposure to hand-transmitted vibration. Fiteen trained subjects were exposed in the laboratory to seven different vibration exposures produced by five hand-held tools (one of the tools was used in two positions) and an electrodynamic vibrator. The good agreement observed between and within subjects shows that they can reliably rank vibration dicomfort produced by different hand-held tools. For five vibration exposures out of seven, the rank deduced from the subjective assessments was in accord with the rank of the predicted evaluations derived from the frequency-weighted acceleration values measured. An exposure with highly impulsive vibration was rated as being much more annoying than it was foreseen by the current procedures of evaluation. The operator's position proved to be an important factor in the perception of the discomfort.

A Technique to Predict the Acoustic Radiation Characteristics of an Automobile Tire

A technique to predict the acoustic radiation characteristics of the predominant structural modes of an automobile tire is presented. A stationary tire is excited by an electrodynamic vibrator and, through conventional modal analysis methods, a description of the surface velocity is obtained. With this information, and a representation of the tire geometry, numerical procedures are used to predict the acoustic surface intensity and field pressure, for a given frequency of interest, based on a Helmholtz integral formulation. Predicted far field sound pressure levels are in close agreement with experimental measurements taken in an anechoic chamber. This provided the necessary validation of the technique.