Modelling of time-varying dispersion for releases including ... - ukelg
Modelling of time-varying dispersion for releases including ... - ukelg
Modelling of time-varying dispersion for releases including ... - ukelg
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UDM AWD <strong>dispersion</strong> <strong>including</strong> rainout UKELG 2013<br />
Finite-duration release: quasi-instantaneous model (Phast default)<br />
(a) Release just<br />
begun<br />
(b) Release ends<br />
(c) Cloud moves<br />
away from the<br />
release point<br />
<br />
<br />
Continuous/instantaneous transition if<br />
width/length ratio large<br />
disadvantages:<br />
- Abrupt transition<br />
- Less accurate along-wind diffusion<br />
(d) At this point<br />
the release is<br />
quasiinstantaneous<br />
(e) Replaced with<br />
equivalent circular<br />
instantaneous<br />
cloud<br />
(f) The circular<br />
cloud<br />
moves away<br />
© Det Norske Veritas AS. All rights reserved. 8<br />
Finite-duration release: finite-duration correction (FDC) method<br />
(Phast alternative option; improved accuracy <strong>for</strong> validation against Kit Fox experiments)<br />
Steady-state<br />
concentration pr<strong>of</strong>ile<br />
flow rate (kg/s)<br />
Concentration<br />
Actual pr<strong>of</strong>ile<br />
Finite Duration<br />
Correction (FDC)<br />
<strong>time</strong> (s)<br />
Time 1<br />
Current UDM Time 2<br />
Carry out steady-state calculations <strong>for</strong> single segment<br />
Distance<br />
Time 3<br />
Apply along-wind-diffusion by finite-duration correction (accounts <strong>for</strong> wind shear and turbulent spread)<br />
Disadvantage: predicts maximum concentration only (no cloud width/length, dose)<br />
© Det Norske Veritas AS. All rights reserved. 9<br />
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