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- Svensson, Gunilla, et al.
(författare)
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Evaluation of the Diurnal Cycle in the Atmospheric Boundary Layer Over Land as Represented by a Variety of Single-Column Models : The Second GABLS Experiment
- 2011
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Ingår i: Boundary-layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 140:2, s. 177-206
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Tidskriftsartikel (refereegranskat)abstract
- We present the main results from the second model intercomparison within the GEWEX (Global Energy and Water cycle EXperiment) Atmospheric Boundary Layer Study (GABLS). The target is to examine the diurnal cycle over land in today's numerical weather prediction and climate models for operational and research purposes. The set-up of the case is based on observations taken during the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99), which was held in Kansas, USA in the early autumn with a strong diurnal cycle with no clouds present. The models are forced with a constant geostrophic wind, prescribed surface temperature and large-scale divergence. Results from 30 different model simulations and one large-eddy simulation (LES) are analyzed and compared with observations. Even though the surface temperature is prescribed, the models give variable near-surface air temperatures. This, in turn, gives rise to differences in low-level stability affecting the turbulence and the turbulent heat fluxes. The increase in modelled upward sensible heat flux during the morning transition is typically too weak and the growth of the convective boundary layer before noon is too slow. This is related to weak modelled near-surface winds during the morning hours. The agreement between the models, the LES and observations is the best during the late afternoon. From this intercomparison study, we find that modelling the diurnal cycle is still a big challenge. For the convective part of the diurnal cycle, some of the first-order schemes perform somewhat better while the turbulent kinetic energy (TKE) schemes tend to be slightly better during nighttime conditions. Finer vertical resolution tends to improve results to some extent, but is certainly not the solution to all the deficiencies identified.
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| 2. |
- Wijns, W, et al.
(författare)
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Myocardial revascularization
- 2011
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Ingår i: REVISTA PORTUGUESA DE CARDIOLOGIA. - : Elsevier BV. - 0870-2551 .- 2174-2049. ; 30:12, s. 951-1005
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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- Buelow, P. V., et al.
(författare)
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Optimization of structural form using a genetic algorithm to search associative parametric geometry
- 2010
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Ingår i: Structures and Architecture - Proceedings of the 1st International Conference on Structures and Architecture, ICSA 2010. - : CRC Press. - 9780415492492 ; , s. 715-722
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Konferensbidrag (refereegranskat)abstract
- Different methods using evolutionary computation (EC) have been successfully applied to structural form optimization for many years. A well known limitation of these methods is the computational effort required to analyze significantly large and complex systems. As a result most examples have been limited to simple truss forms or smaller aspects of overall structural systems. This is because the number of variables used to describe the structural geometry limits the size and complexity of problems that can be explored using EC methods. One solution to this limitation is the use of associative parametric models. In recent years use of parametric modeling software has become more widespread in architectural design. Parametric approaches to geometric modeling have the advantage that they are able to describe large, complex systems with very few variables. The reduced number of variables needed to describe geometric systems makes parametric models ideal for use with EC to explore optimal forms. This paper shows examples of how large, complex structural systems can be optimized for basic parameters like weight and number of components by combining a genetic algorithm with a finite element analysis and parametric modeling software. The procedure is outlined with specific applications. Examples show the use of this technique used to explore complex spatial structures. Results are shown with specific documentation of computational effort required.
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