Changes between Version 8 and Version 9 of palm4u

Timestamp:

Dec 15, 2017 9:51:48 AM (7 years ago)

Author:

maronga

Comment:

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palm4u

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 = PALM-4U components =
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+[[NoteBox(note,This page describes not only the already implemented features, but also to some extent current developments that will be added to PALM-4U within the coming months!)]]
 
 PALM-4U is frequently referred to as a separate model for the simulation of urban atmospheric boundary layers. However, from a technical point of view, PALM-4U are special components that have been developed to suit the needs of modern academic urban boundary layer research and practical city planning related to the urban microclimate and climate change. PALM-4U components are shipped with PALM and are available after installation of PALM. PALM-4U components are thus also available in PALM and might be used without being limited to urban area applications. Per definition, starting from PALM version 5.0, the user runs PALM-4U as soon as buildings are placed within the model domain and at least one of the following PALM-4U components is used:
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 == Radiative transfer in the urban canopy layer ==
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+In addition to the full radiation models in PALM (clear-sky model and RRTMG), a radiative transfer scheme is implemented. It uses the incoming shortwave radiation that is provided by one of the radiation codes used in PALM (i.e. either the clear-sky model or RRTMG) as boundary condition at the top of the urban canopy layer. Direct and diffuse radiation are treated separately. The USM radiation scheme then adds a description of radiation processes within the urban canopy layer, including multiple reflections between buildings. These processes involve the calculation of the incoming shortwave radiation components on each surface element of the grid, based on the position of the sun and shading according to the geometry of the urban canopy; longwave thermal emission based on the surface temperature of each surface element; finitely iterated reflections of shortwave and longwave radiation by all surfaces; absorption of radiation by individual surface elements based on their properties (albedo, emissivity); and partial absorption of shortwave radiation by vegetation. For details, see also Resler et al. (2017). 3D vegetation requires special treatment for both longwave and shortwave radiation, including the thermal capacity of leaves. As this scheme only predicts the radiative fluxes at the surface elements, additional effort is made to provide the necessary radiative quantities for grid volumes not attached to surfaces for photolysis when the chemistry module is used.
 
 == Chemistry ==
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+A fully "online" coupled (Baklanov et al., 2014) chemistry module is implemented into PALM. The chemical species are treated as Eulerian concentration fields that may react with each other, and possibly generate new compounds. For the description of gas-phase chemistry the latest version of Kinetic Preprocessor (KPP 1 ) version 2.3 has been implemented into PALM-4U (see also Damian et al., 2002; Sandu et al., 2003; Sandu and Sander, 2006). It allows to generate Fortran source code directly from a list of chemical rate equations. A further preprocessor (KP4) has been developed that adapts the code to PALM and automatically generates interface routines between the KPP generated modules and PALM. In this way, the chemistry in PALM-4U is fully flexible and easily exchangeable. The PALM chemistry module is implemented in RANS and LES modes. A more complex chemistry module is available for the RANS mode, whereas a strongly simplified chemistry mechanism is available for the LES mode to keep the computational time for chemical transformations and advection of the species at a reasonable level.
 
 == Multi-agent system ==
+The conventional approach to assess biometeorological aspects in urban areas is an Eulerian approach, i.e., the area-wide evaluation of relevant parameters and indices, and subsequent mapping and zoning of these parameters. In this approach, socio-economic aspects of urban residents, such as resident characteristics like age, skin sensitivity, wealth, or population density and the typical behavior and movement patterns of these residents are usually neglected. In order to account for these additional parameters, a multi-agent system is implemented in PALM-4U that allows a new quality of biometeorological assessment studies. The multi-agent system is a Lagrangian approach in which groups (from hundreds to several thousands) of individual agents (i.e., residents) are released at selected locations of interest in the model domain (see e.g. Bruse, 2007; Chen and Ng, 2011; Gross, 2015, for further reading). Each agent can have individual characteristics (age, clothing, speed, starting points, targets, etc.) so that typical population groups can be statistically represented and released in the model. Each agent is able to move according to a path-finding algorithm that takes into account not only the agent’s characteristics, but also the atmospheric conditions in its surroundings, like sun/shaded area, searching for an optimal compromise between the fastest and most convenient path. The path-finding algorithm will be based on a path-load scheme where each accessible surface element is given a specific resistance. The resistance itself can be regarded as the sum of distance from the target area and additional resistances due to sloped terrain, forbidden areas, shaded and non-shaded sites, or the occupation of areas by other agents.
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+The multi-agent system is suited not only for evaluating biometeorological comfort indices and the relevance of the conventional Eulerian approach, but also for investigating escape routes in case of accidents, possibly associated with release of hazardous and toxic sub-