192 research outputs found
Finite difference modelling of the temperature rise in non-linear medical ultrasound fields
No full textNon-linear propagation of ultrasound can lead to increased heat generation in medical diagnostic imaging due to the preferential absorption of harmonics of the original frequency. A numerical model has been developed and tested that is capable of predicting the temperature rise due to a high amplitude ultrasound field. The acoustic field is modelled using a numerical solution to the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation, known as the Bergen Code, which is implemented in cylindrical symmetric form. A finite difference representation of the thermal equations is used to calculate the resulting temperature rises. The model allows for the inclusion of a number of layers of tissue with different acoustic and thermal properties and accounts for the effects of non-linear propagation, direct heating by the transducer, thermal diffusion and perfusion in different tissues. The effect of temperature-dependent skin perfusion and variation in background temperature between the skin and deeper layers of the body are included. The model has been tested against analytic solutions for simple configurations and then used to estimate temperature rises in realistic obstetric situations. A pulsed 3 MHz transducer operating with an average acoustic power of 200 mW leads to a maximum steady state temperature rise inside the foetus of 1.25°C compared with a 0.6°C rise for the same transmitted power under linear propagation conditions. The largest temperature rise occurs at the skin surface, with the temperature rise at the foetus limited to less than 2°C for the range of conditions considered
Development of layered models for geotechnical centrifuge tests
No full textCentrifuge modelling is an established technique for investigating the ground response to complex and non-standard geotechnical events. These models are usually made from re-formed soil, allowing for comparisons with naturally occurring soil deposits. Clay models are formed by mixing clay powder and water into a slurry. This slurry is placed within a container and loaded to create a uniform stiff clay model. However, there is a fundamental disparity between this process and the deposition of natural soils, because natural soil is deposited in layers creating a unique structure. This structure is important for modelling true soil behaviour because some essential soil properties (such as permeability, stiffness and strength) are not identical in all directions. Currently, there are limited methods for creating layered soil samples. This paper describes the development of a new procedure for creating layered centrifuge models with structure – leading to potentially more representative models of naturally occurring ground
A new test setup for studying sand behaviour inside an immersed tunnel joint gap
No full textDuring inspections of several immersed tunnels in the Netherlands, damage of immersion joints has been observed. In some cases the Gina seal has moved inwards from its original location, and in other cases a permanent elongation of the entire tunnel structure has been measured. For both cases it has been hypothesised that a seasonal expansion and contraction of the tunnel elements allows sand to enter the joint gap between elements during winter, where it is compacted during summer, leading to an increasing amount of sand in the joint gap over the years. In order to study this mechanism and assess its impact, a 1:3 scale model joint gap has been designed and constructed. This setup can simulate expansion and contraction cycles of the joint and measure stresses in the joint gap and deformations of the Gina seal. First test results are presented here and show that compaction of the sand entering the joint gap indeed occurs and leads to the observed large inwardsdeformations of the Gina seals.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete StructuresGeo-engineerin
Modelling tunnel behaviour under seismic actions: An integrated approach
No full textThis paper intends to describe the integration of physical and numerical modelling, focusing on tunnels under seismic actions. It shows how numerical calculations can be used in association with centrifuge testing to model different aspects of tunnel behaviour during earthquakes. The scope of the paper has been limited to a few aspects, mainly concerning the change of internal forces in the tunnel lining during shaking and the effect of soil liquefaction. The interaction between a tunnel and a building in a soil layer undergoing liquefaction has also been taken into account
Mrs. Arthur E. Jackson House, 415 Alta Avenue, Santa Monica, Calif.
No full textSanta Monica Public Library Image Archives.
A675
Digital object 3594 img0017
City of Santa Monica Historic Resources Inventory
Period Revival style built 1922-23 by Edward Divall
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