IBJdis assumes that the values xmin/ymin refer, for area and volume means (entry in vldf is V), to the
left/lower edge of the area i=1/j=1 and, for point values (entry in vldf is P), to the point i=0/j=0.
this guarantees that the values of xmin/ymin can be maintained if an index subrange is taken. For example,
if for a DMNA file with volume means and index range i=1..5 the data row i=1 is removed and the index range
is changed accordingly to i=2..5 (parameters lowb, hghb), IBdis displays the areas still at the correct locations.
- In emissions.def the parameter Emisfac must be defined as time
dependent (Emisfac = ?).
Take care that the parameter is defined in a continuation line or separated from the point (.) that starts the assignment line by at least one blank (this applies in general; without blank the parameter is ignored and the calculation gives a wrong result).
- The files meteo.def and variable.def must be created with the program Lpraks from the provided dispersion class statistics (AKS).
- Set parameter Interval to 1.00:00:00 in param.def and adjust parameters End and Average according to the AKS (see log output of Lpraks and further information in the reference book).
- According to the draft TA Luft (2018/2019), wet deposition cannot be accounted for when applying an AKS.
- Check the project with the LASAT tool DefCheck.
- (18) What are
the main differences between the boundary layer versions 2.1 and2.6?
- Version 2.1 applies a slightly different assignment of Monin-Obukhov lengths to Klug/Manier stability classes as compared to Version 2.6 (see the reference book).
- Version 2.1 does not consider a turn of wind direction with height, in contrast to Version 2.6.
- Version 2.1 yields for emission at larger heights larger more realistic plume widths as compared to Version 2.6.
- In the displacement layer close to the ground, Version 2.1 applies a linear decrease of the turbulence profiles whereas Version 2.6 keeps them constant.
- For small roughness lengths (approx. smaller 0.1m) the horizontal exchange coefficient in Version 2.1 shows a strong gradient close to the ground and requires for sources close to the ground (approx. below 10m) with a small spatial extent for the calculation of short time values a finer vertical resolution than provided by the default raster (0m, 3m etc.), which would yield in this case plumes that are too small.
- (17) What
should be considered if spatially varying deposition velocities are
applied?
For some or all of the substances applied in a LASAT calculation, spatially (and temporally) varying deposition velocities can be applied. For further information see the reference book. The following points should be considered:
- If the calculation is carried out for several substances, a
separate register can be applied for each of them and transferred
into an input file for LASAT using the LASAT tool Lprgrd. The LASAT
tool Lprgrd appends with each call the deposition velocities of the
specified substance in form of a value matrix to file vdp*.dmna. See
example DEMO-2D in the working book. For substances not encountered
in file vdp*.dmna, the usual deposition velocity in file
substances.def is applied, see Section 3.5.1 of the reference book.
- If a data matrix is applied for the deposition velocities of a
substance, the usual deposition velocity in file substances.def for
this substance should be set to 0. The value in substances.def is
applied if no value matrix for this substance is specified or found
by the program. A value 0 thus helps cross-checking the results.
- In file param.def, the parameters DepoBase and Depo must be set.
Parameter Depo must be set to a value larger 0 (either explicitly
or, if defined in form of a time series, within the time series).
With Depo = 0 (this is the default) no deposition files are applied.
- The register applied with the LASAT tool Lprgrd must cover at
least the calculation area. If not, Lprgrd sets the value for grid
cells not covered by the register to -1. This leads to an error
message in the subsequent dispersion calculation. Beside this, the
cell size and position of the applied register is not restricted and
must not coincide with the settings of file grid.def.
- If the calculation is carried out for several substances, a
separate register can be applied for each of them and transferred
into an input file for LASAT using the LASAT tool Lprgrd. The LASAT
tool Lprgrd appends with each call the deposition velocities of the
specified substance in form of a value matrix to file vdp*.dmna. See
example DEMO-2D in the working book. For substances not encountered
in file vdp*.dmna, the usual deposition velocity in file
substances.def is applied, see Section 3.5.1 of the reference book.
- (16) How
should calms be defined in a AKTerm?
According to the specification of the German Weather Service DWD, calms (hours with no wind) are encoded in a AKTerm file by wind direction 0 (wind from north is defined by 360 deg). In addition, the wind speed should be set to 0: first for obvious plausibility, second to allow a consistent treatment of the wind direction redistribution according to paragraph 8.2 of TA Luft, Annex 3. Thus, a wind direction 0 should only occur together with wind speed 0 and vice versa. This is also the convention followed by the DWD. The programs Lprakt and Austal2000 detect calms at hand of wind speed 0.
- (15) What
must be considered for a spatial average of odor hour frequencies?
The existance of an odor hour is detected by internal comparison of the hourly mean concentration in a given grid cell with the threshold value. For this purpose the concentration must be spatially resolved with a sufficient accuracy. For hourly means, in general a finer spatial resolution is required than for long time means. This aspect can be of particular importance at small distances to near-ground point sources. As a rule of thumb for such a case, at least 5 grid meshes should be between the source and the point of interest. If the grid meshes are too large, the hourly concentration plume is not well resolved and the resulting odor hour frequency may be under- or overestimated, depending on the emission rate.
Based on the results of a sufficiently resolved dispersion calculation, larger spatial averages can be derived. For example the auxiliary program A2KArea.jar can be used for this purpose. It is provided on www.austal2000g.de and requires the output files that are created by the LASAT tool LTlopxtr. This distinctive feature of spatially averaging odor hour frequencies is due to the non-linear relationship between odor hour and concentration (yes/no decision: concentration above or below a threshold). For the spatial average of concentration in contrast, the values provided by the dispersion program on a coarse calculation grid can be directly used.
- (14) What
meaning has a concentration time series in the context of a
dispersion class statistics (AKS)?
No direct one, because the concentration values contain the statistical weight and cannot be directly interpreted (see also FAQ 11). Therefore, for calculations with an AKS, flag MNT in param.def should not be used..
- (13) Why is
Rate=8 (equivalent to AUSTAL2000 quality level 2) in some
situations not sufficient to faithfully calculate the frequency of
odor hours?
A sufficiently large number of simulation particles is required to avoid systematic effects in the calculation of odor hour frequencies (see the discussion in the annex of the program manuals of AUSTAL2000 and LASAT). Usually (one or several sources near ground and close together) Rate=8 (AUSTAL2000 quality level 2) is sufficient for time series calculations. However, if the sources are far apart or if a source, which is dominant with respect to the emission, has almost no contribution to the total concentration near ground due to its construction height and/or plume rise (but nevertheless takes most of particles, which are assigned to the sources according to their emissions), a considerably larger rate may be required. This is also the case if the counting volume (averaging volume) is strongly reduced by a small horizontal or vertical mesh width. Once the systematic effect is avoided, the listed (absolute) statistical uncertainty is a faithful measure also for odor hours.
- (12) Why are
some non AUSTAL2000 substances not evaluated by the LTool Lopxtr?
Avoid using a minus sign ("-") in the name of the substance. It is interpreted by LTools as the marker for a subsequent diameter fraction according to TA Luft. Use an underscore ("_") instead.
- (11) What is
the meaning of the total emission that is written out by LASAT
(since 3.1) to lasat.log in a calculation for a dispersion class
statistics (AKS)?
The total emission has no direct meaning as such a calculation refers to a weighted average over stationary situations without time reference (an assignment of one hour to a single meteorological situation and of one year to the statistics in total is a matter of interpretation).
In the calculation, each meteorological situation is formally run over one day (in a way that yields a result corresponding to a stationary situation). At the beginning of the day, the emission takes place over a time interval proportional to the statistical weight of the situation. The sum of emission times over all situations is one day. In addition, the constant emission rate q provided by the user is multiplied with the number of situations N, so that the average over all N days corresponds to the average over all stationary situations.
The formal total emission is therefore q*24h*N. For comparison: The total emission in a true time series calculation over one year is (for constant q) is q*24h*365. The total emission in a calculation for a dispersion class statistics is thus by a factor N/365 heigher than the total emission of a corresponding time series calculation, where N is the number of situations that is provided in file param.def as parameter Average.
Note that parameter Emisfac in file emissions.def must be declared as time-dependent. The time series is set by Lprtaks in file variable.def. It controls the turn on and off of the emission and the multiplication by N.
- (10) Which precausions must be considered on
applying DEF files from the temporary AUSTAL2000 directory
WORK for a calculation with LASAT?
This must be done, if at all, with special care because the DEF files do not necessarily obey the LASAT conventions. For example, for rated odorants the Flag RATEDODOR must be inserted by hand in param.def (before AUSTAL2000 2.5).
Also files meteo.def and metlib.def require care: The value of the roughness length and the version of the boundary layer model may not be modified as this would result in incorrect values of the Monin-Obukhov length listed in these files (the value depends on the roughness length and the boundary layer model - 2.1 and 2.6 apply different classifications).
- (9) Why are the values Ua and Ra specified in
meteo.def for more than one anemometer height (Ha = { ...
}) not used?
Specification of more than one anemometer height is not allowed with the TA Luft profile version 2.6. Use the default version 2.1 instead.
- (8)
What must be considered when applying externally generated wind
fields?
- The wind fields must be defined on the Arakawa-C net.
- Before the actual dispersion calculation, any divergence in the
provided wind field is internally removed by a simple adjustment
of the z-components. To keep this modification at a minimum, the
provided wind fields should be already sufficiently free of
divergence.
- For an application of the wind fields without scaling, file
meteo.def must still contain an explicit value for Ua and the
stability class (class Km or Obukhov length Lm) ) as these values are
required by LASAT to determine the friction velocity and the
(plain) turbulence profiles.
The stability class (or Obukhov length) is also required internally to set the plume rise according to VDI 3782/3 or VDI 3784/2. If plume rise is calculated with PLURIS, PLURIS requires the friction velocity; it can be explicitly specified, otherwise it is calculated internally from the theoretical wind profile; in the latter case, specification of Km/Lm, Ua, Ha, Z0, D0 are required, even if all fields are otherwise specified externally.
Without plume rise and with provision of all wind and turbulence fields, a formal stability class (or Obukhov length) is required to mark the time interval as valid.
- The meteorological fields actually applied by LASAT can be
inspected with the help of the program Lprprf. It
writes out for a specified time to file prfa0li.dmna the
model fields as they are applied in the actual disperrsion
calculation. This is an important tool to check whether the fields
have been created as required by LASAT. Before carring out the
dispersion calculation, the files prfa0li.dmna should be
deleted, otherwise Lasat takes the fields directly from these
files and changes in meteo.def or the external wind fields would
not be accounted for.
- Buildings: Buildings
are resolved on the calculation grid. A cell is interpreted as
building cell if the vertical component Vs of the wind vector at
the bottom of the cell is equal -99 m/s. If the wind field is
modified (e.g. by adding topographic effects), care must be taken
that this value is not changed. Below a building cell there may be
no free cell (this would result either in an error message or in
incorrect concentration values).
- Terrain profile
and nested grids: LASAT
adjusts the z-values specified in files srfa0li.dmna
for the two boundary stripes of inner grids at hand of the values
of the next coarser grid. This "tuning" guarantees a smooth
transition between the grids. The resulting values are written to
the wind fields generated by LASAT. If external fields are
provided, they must contain these tuned z-values. In default mode
(index Wind not set),
LASAT checks the z-values of the wind field files with the
internally created ones and aborts with an according error message
if they do not agree.
- Incorporation in a wind field library: If external wind fields are added to a standard wind field library in order to directly access them by a value larger 0 for index "Wind" (for example for modelling a time dependent drain of cold air), care must be taken that these fields are not applied for the usual superposition of base fields for situations with index "Wind" being equal 0. This can be avoided by setting the dispersion class index "akl" in the file header to for example 7. The field is then included in the list of base fields but never accessed as such, as for the superposition only indices 1 to 6 are addressed. The list of base fields and their class attribution can be printed to the screen and the log file lasat.log with the Lasat program call option -p. It should be carefully checked at hand of the messages in lasat.log for each interval of the dispersion calculation whether the fields are super-imposed or not super-imposed as desired.
- The wind fields must be defined on the Arakawa-C net.
- (7) In stark
gegliedertem Gelände erhalte ich Konzentrationsverteilungen, die
ich so nicht erwarten würde (z.B. Ansammlung von Schadstoffen in
einer Talebene).
Prüfen Sie, ob die Restdivergenz des Windfeldes hinreichend klein ist. Bei starken Geländeunebenheiten (Steigungen von mehr als 1/4) konvergiert das Iterationsverfahren bei der Beseitigung der Divergenz nur langsam, 100 Iterationsschritte (Standard) sind hier eventuell nicht ausreichend (Parameter Im in grid.def). Als Faustregel sollte die Restdivergenz (Dimension Geschwindigkeit/Länge, siehe Lprwnd.log) deutlich kleiner sein als die typische Anströmgeschwindigkeit geteilt durch die typische Hindernisabmessung.
- (6) Was muß ich bei der
Definition von Gebäuden beachten?
- Gebäude werden auf dem Rechengitter aufgerastert und in dieser Form berücksichtigt. Die Aufrasterung wird standardmäßig in der Datei volout00.dmna ausgegeben und kann hier überprüft werden.
- Die Unterkante eines Gebäudes liegt immer auf dem Erdboden.
- Die Dachneigung verläuft immer parallel zum Erdboden.
- (5) Warum werden Änderungen in
manchen Eingabedateien (zum Beispiel Gebäudedefinitionen oder
meteorologische Parameter) nicht erkannt?
Vor einer Rechnung schauen Programme wie Lprwnd oder Lprgrd nach, ob schon binäre Parameterdateien vorhanden sind (zum Beispiel grdaxxx.arr, sldaxxx.arr, srfa100.arr). Sind diese vorhanden, werden sie nicht neu erzeugt. Löschen Sie vor dem Programmstart diese Dateien, damit Ihre Parameteränderungen auch wirklich berücksichtigt werden.
- (4) Was ist bei der Berechnung
von Windfeldern in komplexem Gelände zu beachten?
Der an der Anemometerposition vorgegebene Windvektor wird zur Erzeugung des freien Anströmfeldes verwendet, welches dann an das Gelände angeglichen und divergenzfrei gemacht wird. Bei diesem Vorgang kann sich auch der Windvektor an der Anemometerposition ändern. Damit das endgültige Windfeld am Anemometerort exakt die vorgegebenen Werte besitzt, müssen zuerst zwei Basisfelder erzeugt werden (zum Beispiel Anströmung aus Süden und aus Westen), aus denen durch Linearkombination das endgültige Windfeld gebildet wird (Windfeldbibliothek). Dieses Verfahren ist vor allem dann vorzuziehen, wenn das Anemometer nicht in freiem Gelände, sondern zum Beispiel in der Nähe eines Berghangs liegt. Die Verwendung von (eventuell intern erzeugten) Basisfeldern ist daher die Standardeinstellung.
Beachten Sie, daß für sehr ungünstige Anemometerpositionen die Basisfelder am Anemometerort aufgrund von zum Beispiel Kanalisierungseffekten bei stabiler Schichtung fast parallel verlaufen können. In diesem Fall ergeben sich meist sehr hohe Werte für die Faktoren, die zur Linearkombination verwendet werden (siehe lprwnd.log) und es treten im endgültigen Windfeld unerwünschte Effekte auf. Es ist daher wichtig, die Anemometerposition in komplexem Gelände sorgfältig zu wählen.
Bei der Überlagerung von Basis-Windfeldern für komplexes Gelände und Netzschachtelung kann es für Netze, die nicht die Anemometerposition enthalten, passieren, daß die Basisfelder nicht korrekt überlagert werden. In der Regel liegt das Anemometer im feinsten Netz, so daß dieses Problem nicht auftritt. Bei der Verwendung eines Geländeprofils wird empfohlen, das feinste Netz immer so zu wählen, daß es die Anemometerposition enthält, da die Überlagerung der Basisfelder sonst als Notbehelf anhand der Windwerte eines gröberen Netzes erfolgen muß.
Wird in grid.def der Netztyp (Ntype) mit 2 bzw. FLAT3D vorgegeben, dann müssen keine Oberflächendateien srfa*.dmna vorgegeben werden. Es sollten auch keine vorgegeben werden, da sie sonst eingelesen und verwendet, aber verschiedene interne Tests übergangen werden. Mit Oberflächendateien sollte grundsätzlich der Netztyp 3 bzw. COMPLEX verwendet werden.
- (3) Warum konvergiert die
Berechnung des Windfeldes mit Lprwnd für stabile Schichtung für ein
von mir gewähltes Gelände mit großen Höhenunterschieden nicht?
Das diagnostische Windfeldmodell Lprwnd verwendet zur Berechnung des Windfeldes in komplexem Gelände die
Gewichtungsfaktoren av und ah. Ist av>1, so wird ein Hindernis eher umströmt als überströmt. Die resultierende Strömung entspricht einer Potentialströmung (av=1), die sich ergeben würde, wenn das Hindernis um den Faktor av erhöht wäre. Der Faktor av wird aus einer charakteristischen Geschwindigkeit, vc, und einer charakteristischen Längenskala der Geländeunebenheiten berechnet. Bei Gelände mit starken Höhenunterschieden kann es vorkommen, daß das so berechnete av zu groß ist. Für diesen Fall ist bekannt, daß Konvergenzprobleme auftreten können. Erfahrungsgemäß sollte av den Wert 5 nicht überschreiten. Über die Aufrufoption -m<AvMax> von Lprwnd kann ein reduzierter Maximalwert für av vorgegeben werden (Standard ist 10).
- (2) Warum ergeben sich in
meiner Rechnung in komplexem, stark erhöhtem Gelände mit Lprwnd für
labile Schichtungen unsinnige meteorologische Profile?
Beachten Sie, daß in LASAT die Mischungsschichthöhe für negative Monin-Obukhov-Längen (labile bis neutrale Schichtungen, Klassen III/2, IV, V) über NN gerechnet wird. Hat das Gelände einen globalen Höhen-Offset (beispielsweise ein Hügel auf einem Plateau), so sollte dieser Offset zu der Mischungsschichthöhe dazuaddiert werden. Dies geschieht über die Angabe von HmMean in der Datei wetter.def (zum Beispiel HmMean = { 0 0 0 1500.0 1800.0 1800.0 } für einen Offset von 700 m; bei der Angabe 0 wird der Standardwert übernommen).
- (1) Wenn ich die Quellstärke um
einen Faktor 1000 erhöhe, so ergeben sich nicht um genau einen
Faktor 1000 erhöhte Konzentrationen - warum?
Im ersten Moment würde man erwarten, daß sich in diesem Fall exakt um einen Faktor 1000 erhöhte Konzentrationen ergeben, da die Trajektorien der Simulationsteilchen unverändert bleiben und sich nur die Masse, die von jedem Simulationsteilchen repräsentiert wird, erhöht. Bei der Berechnung der Gesamtteilchenzahl, die von der Quellstärke abhängt, können jedoch Rundungsfehler auftreten (die Teilchenzahl muß ganzzahlig sein!), so daß bei Vorgabe einer anderen Quellstärke auf einmal mit einem Teilchen mehr oder weniger gerechnet wird. Damit teilt sich auch die Folge von Zufallszahlen, die zur Berechnung der Teilchentrajektorien benötigt werden, anders auf die Teilchen auf und es entstehen entsprechend andere statistische Fluktuationen in der Konzentrationsverteilung.