scholarly journals Validation of FIRETEC wind-flows over a canopy and a fuel-break

2009 ◽  
Vol 18 (7) ◽  
pp. 775 ◽  
Author(s):  
François Pimont ◽  
Jean-Luc Dupuy ◽  
Rodman R. Linn ◽  
Sylvain Dupont
Keyword(s):  
Thermal Stratification ◽  
Fire Behavior ◽  
Sensitivity Study ◽  
Uncertain Parameters ◽  
Wind Tunnel Experiments ◽  
Flow Models ◽  
Fire Propagation ◽  
Wind Gusts ◽  
Wind Flows

The wildfire model FIRETEC simulates the large coherent eddies of the wind-flows induced by the canopy. It has been qualitatively validated in its ability to simulate fire behavior, but there is still a need to validate physical submodels separately. In the present study, the dynamics and turbulence of the flow simulated by FIRETEC are validated in a manner similar to other air-flow models without fire, through comparison with measurements associated with flows within continuous and discontinuous forests captured through in situ and wind-tunnel experiments with neutral thermal stratification. The model is shown to be able to reproduce accurately all essential features of turbulent flow over both forests. Moreover, a short sensitivity study shows that the model is not very sensitive to uncertain parameters such as vegetation drag coefficient. Finally, it is shown in the discontinuous forest case that wind gusts on fuel-breaks can be very strong and significantly higher than in surrounding canopies, even if their directions are more stable. These results and others briefly reviewed in the present paper allow better understanding of wind-flow perturbations induced by fuel-breaks. This new validation added to previous ones confirms the ability of FIRETEC for investigating effects of fuel-break design on fire propagation.

Untersuchungen zur Ableitung von Windböen aus Doppler-Lidar-Messungen

2021 ◽  
Author(s):  
Carola Detring ◽  
Eileen Päschke ◽  
Julian Steinheuer ◽  
Ronny Leinweber ◽  
Markus Kayser ◽  
...  
Keyword(s):  
Field Experiment ◽  
Temporal Variability ◽  
Surface Wind ◽  
Doppler Lidar ◽  
Signal To Noise ◽  
Observation Volume ◽  
Wind Gusts ◽  
Die Profile ◽  
Spatio Temporal

<p>Mit Hilfe von Doppler-Lidar-Systemen, lassen sich die Profile von Windgeschwindigkeit und -richtung in der Atmosphärischen Grenzschicht (AGS) auf der Basis klassischer Messstrategien wie einem VAD-24 Scan (Velocity Azimuth Display mit 24 Strahlrichtungen) zuverlässig bestimmen (Päschke et al., 2015). Für praktische Anwendungen von großem Interesse sind jedoch neben dem mittleren Windprofil auch kurzzeitige Fluktuationen des Windes, wie sie zum Beispiel in Verbindung mit Windböen auftreten. Untersuchungen zu Windböen waren ein wesentlicher Aspekt der Messkampagne FESSTVaL (Field Experiment on Sub-Mesoscale Spatio-Temporal Variability in Lindenberg, www.fesstval.de).</p><p>Eine Studie von Suomi et al. (2017) hat gezeigt, dass eine Ableitung von Windböen aus Doppler Lidar Messungen prinzipiell möglich ist. Allerdings wird mit üblichen Messstrategien die hierfür erforderliche hohe zeitliche Auflösung in der Ermittlung des Windvektors nicht erreicht, so dass mit Skalierungsansätzen unter Verwendung von in-situ Windmessungen eine Korrektur der aus den Lidar-Daten abgeleiteten Böenwerte erfolgen muss.</p><p>Im Rahmen der vorliegenden Arbeit wurde eine alternative Messstrategie für Doppler-Lidar-Systeme vom Typ „Streamline“ (Halo Photonics) entwickelt und über mehrere Monate in den Jahren 2020/21 auf dem Grenzschichtmessfeld Falkenberg des DWD erprobt. Die Böenableitung basiert auf einem sog. Continous Scan Mode (CSM); dabei werden die während einer vollständigen Rotation des Lidar-Scan-Kopfes kontinuierlich durchgeführten Messungen 10-11 Strahlrichtungen zugeordnet und die Radialwindgeschwindigkeiten wiederum mit dem VAD-Verfahren ermittelt. Die Dauer eines Scans beträgt etwa 3.4s, damit kann eine Zeitauflösung erreicht werden, die der heute weit verbreiteten Definition einer Windbö entspricht (3s gleitendes Mittel; WMO (2018)).</p><p>Diese neue Konfiguration bringt Herausforderungen an die Datenverarbeitung mit sich. Im CSM muss mit vergleichsweise wenigen Lidar-Pulsen pro Messstrahl gearbeitet werden, so dass klassische Ansätze der Datenfilterung (Signal-to-Noise Schwellwert, Consensus Filterung) nicht verwendet werden können. Es wird ein alternatives Verfahren für die Prozessierung der Lidar-Rohdaten vorgeschlagen. Die Ergebnisse der Ableitung sowohl des mittleren Windvektors als auch der jeweiligen maximalen Windbö in einem 10-Minuten-Mittelungsintervall werden mit Sonic-Messungen in 90m Höhe verglichen. </p><p>Im Rahmen des FESSTVaL Experimentes wurde diese neue Messkonfiguration an drei Standorten, die ein annähernd gleichseitiges Dreieck mit einer Kantenlänge von etwa 5 km bildeten, genutzt. Es werden Fallbeispiele aus der FESSTVaL Kampagne für die Variabilität im Auftreten von Windböen gezeigt.</p><p><strong>Referenzen</strong></p><p>Päschke, E., Leinweber, R., and Lehmann, V. (2015): An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial, Atmos. Meas. Tech., 8, 2251–2266, https://doi.org/10.5194/amt-8-2251-2015</p><p>Suomi, I., Gryning, S.‐E., O'Connor, E.J. and Vihma, T. (2017): Methodology for obtaining wind gusts using Doppler lidar. Q.J.R. Meteorol. Soc., 143: 2061-2072. https://doi.org/10.1002/qj.3059</p><p>World Meteorological Organization (WMO) (2018): Measurement of surface wind. In Guide to Meteorological Instruments and Methods of Observation, Volume I -Measurement of Meteorological Variables, No.8: 196–213, URL: https://library.wmo.int/doc_num.php?explnum_id=10616 (accessed November 2021)</p>

Iron plays a role in nitrate drawdown by phytoplankton in Lake Erie surface waters as observed in lake-wide assessments

2012 ◽  
Vol 69 (2) ◽  
pp. 369-381 ◽  
Author(s):  
Sonya M. Havens ◽  
Christel S. Hassler ◽  
Rebecca L. North ◽  
Stephanie J. Guildford ◽  
Greg Silsbe ◽  
...  
Keyword(s):  
Surface Waters ◽  
Thermal Stratification ◽  
Lake Erie ◽  
Phytoplankton Community ◽  
Sampling Depth ◽  
Phytoplankton Pigment ◽  
Chl A ◽  
Dissolved Iron ◽  
Continuous Surface

Phytoplankton interactions with iron (Fe) were examined in surface waters of Lake Erie during summer thermal stratification. Lake-wide sampling in June and September 2005 was conducted using a continuous surface water sampler (1 m sampling depth) and in July at 18 hydrographic stations (5 m sampling depth). In situ measurements of photosynthetic efficiency (maximum quantum yield of photosystem II) and phytoplankton community composition were measured using fast repetition rate fluorometry and a phytoplankton pigment-specific fluorometer, respectively, during June and September. High ratios (73%–85%) of intracellular Fe to particulate Fe coincident with increases in chlorophyll a (Chl a) concentrations in the western and central basins in June and July imply that the majority of Fe in these regions was associated with intracellular pools. Correlations between intracellular Fe and Chl a were frequently observed when Heterokontophyta and Pyrrophyta dominated the phytoplankton community. Assimilation of Fe by the phytoplankton strongly influenced its partitioning between the dissolved and particulate phase. Dissolved iron (<0.45 µm) concentrations were proportional to Chl a concentrations and both dissolved iron and Chl a were inversely proportional to nitrate concentrations in July and September, suggesting that dissolved iron influenced both nitrate drawdown and Chl a concentrations in Lake Erie surface waters in summer.

scholarly journals Strategies for school buildings refurbishment in Portuguese climate

2020 ◽  
Vol 172 ◽  
pp. 18007
Author(s):  
Francisca Cavaleiro Barbosa ◽  
Vasco Peixoto de Freitas ◽  
Manuela Almeida
Keyword(s):  
Energy Consumption ◽  
Natural Ventilation ◽  
Sensitivity Study ◽  
School Buildings ◽  
Local Climate ◽  
Before And After ◽  
Insulation Thickness ◽  
Free Running ◽  
Near Future

Portuguese school buildings are generally characterized by an in-service thermal discomfort, due to the poor envelope thermal properties and the lack of resources for paying energy consumption. Most Portuguese schools are free-running buildings with a natural ventilation strategy. Hundreds of high and basic schools have not been refurbished and still have problems or anomalies and inadequate in-service conditions and need to be rehabilitated in the near future. There will be, therefore, an opportunity to apply the acquired knowledge of comfort, habits, energy consumption and costs that have been studied since the last refurbishments (2008). This work studies the Portuguese Brandão schools model (from the ’70s), including about 100 non-refurbished basic schools. A prototype classroom was prepared in a Brandão school, in Porto. The in situ experimental campaign consisted of temperature, relative humidity, CO2 concentration and energy consumption measurements. The main tasks of this work are: (1) the validation of an advanced hygrothermal model with experimental measurements before and after the prototype refurbishment; (2) development of a sensitivity study in order to choose the best refurbishment and heating strategies for these buildings, regarding their typology, the local climate features and the actual capacity to support the operating costs; (3) assessment of the roof insulation thickness in Brandão schools; (4) quantification of discomfort indicators.

scholarly journals Seasonal dynamics of Daphnia laevisBirge, 1878 ephippia in a tropical lake with a description of a new methodology for in situ evaluation

2014 ◽  
Vol 74 (3) ◽  
pp. 642-648 ◽  
Author(s):  
LPM Brandão ◽  
DGF Pujoni ◽  
PM Maia-Barbosa
Keyword(s):  
Water Column ◽  
Seasonal Dynamics ◽  
Thermal Stratification ◽  
Core Sample ◽  
Hatching Rate ◽  
The Core ◽  
Significant Difference ◽  
Chi Squared ◽  
Hatching Rates

The effect of dormancy in zooplankton populations is still unknown, largely because of the lack of methods to estimate hatching and production of the dormant stages. This study aimed to compare the production and hatching rates of ephippia of Daphnia laevis between thermal stratification and mixing periods in Jacaré Lake (Middle Rio Doce, Minas Gerais, Brazil). For this, we collected ephippia on the sediment with core sampler and we created a device called the “Ephippial Collector”. There was a significant difference in ephippia hatching in situ between stratification and mixing periods (Pearson's Chi-squared test p <0.001), being higher in the second one. Significant differences in the hatching rates between periods was observed in the laboratory only for ephippia collected with Ephippial Collectors (Pearson's Chi-squared test p <0.001), being higher during the mixing period (∼8%). The core sample allows the collection of a certain fraction of the sediment that may contain a mixture of ephippia produced in different periods, i.e., may contain old and not viable ephippia, which masks the hatching rate. Thus, seasonality in hatching rates of ephippia was reported only by Ephippial Collectors. The higher hatching rate observed during the mixing period in the lake suggests that individuals hatched from ephippia may contribute to the increase in the population of D. laevis in the water column at this time.

scholarly journals Calving cycle of the Brunt Ice Shelf, Antarctica, driven by changes in ice shelf geometry

2019 ◽  
Vol 13 (10) ◽  
pp. 2771-2787 ◽  
Author(s):  
Jan De Rydt ◽  
Gudmundur Hilmar Gudmundsson ◽  
Thomas Nagler ◽  
Jan Wuite
Keyword(s):  
Large Scale ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
Flow Models ◽  
Speed Up ◽  
The Antarctic ◽  
Detrimental Impact ◽  
Natural Laboratory

Abstract. Despite the potentially detrimental impact of large-scale calving events on the geometry and ice flow of the Antarctic Ice Sheet, little is known about the processes that drive rift formation prior to calving, or what controls the timing of these events. The Brunt Ice Shelf in East Antarctica presents a rare natural laboratory to study these processes, following the recent formation of two rifts, each now exceeding 50 km in length. Here we use 2 decades of in situ and remote sensing observations, together with numerical modelling, to reveal how slow changes in ice shelf geometry over time caused build-up of mechanical tension far upstream of the ice front, and culminated in rift formation and a significant speed-up of the ice shelf. These internal feedbacks, whereby ice shelves generate the very conditions that lead to their own (partial) disintegration, are currently missing from ice flow models, which severely limits their ability to accurately predict future sea level rise.

scholarly journals Pyrolysis modeling, sensitivity analysis, and optimization techniques for combustible materials: A review

2019 ◽  
Vol 37 (4-6) ◽  
pp. 377-433
Author(s):  
Tatenda Nyazika ◽  
Maude Jimenez ◽  
Fabienne Samyn ◽  
Serge Bourbigot
Keyword(s):  
Sensitivity Analysis ◽  
Material Properties ◽  
Input Parameter ◽  
Fire Behavior ◽  
Sensitivity Study ◽  
Optimization Techniques ◽  
Decomposition Reactions ◽  
Input Parameters ◽  
Gradient Based ◽  
Complete Set

Over the past years, pyrolysis models have moved from thermal models to comprehensive models with great flexibility including multi-step decomposition reactions. However, the downside is the need for a complete set of input data such as the material properties and the parameters related to the decomposition kinetics. Some of the parameters are not directly measurable or are difficult to determine and they carry a certain degree of uncertainty at high temperatures especially for materials that can melt, shrink, or swell. One can obtain input parameters by searching through the literature; however, certain materials may have the same nomenclature but the material properties may vary depending on the manufacturer, thereby inducing uncertainties in the model. Modelers have resorted to the use of optimization techniques such as gradient-based and direct search methods to estimate input parameters from experimental bench-scale data. As an integral part of the model, a sensitivity study allows to identify the role of each input parameter on the outputs. This work presents an overview of pyrolysis modeling, sensitivity analysis, and optimization techniques used to predict the fire behavior of combustible solids when exposed to an external heat flux.

scholarly journals Sensitivity Study of the 5-station configuration of ARA

2019 ◽  
Vol 216 ◽  
pp. 02009
Author(s):  
Simon Archambault
Keyword(s):  
Phased Array ◽  
Sensitivity Study ◽  
In Situ Calibration ◽  
The Antarctic ◽  
Antenna Model

The Askaryan Radio Array (ARA) is an experiment looking for the Askaryan emission of cosmogenic neutrinos interacting in the Antarctic ice. During the last Antarctic summer, two new stations have been added to the experiment, as well as a prototype version of a phased array, attached to one of the new stations. With these stations, ARA sensitivity should become comparable to IceCube’s from 1018 eV and above. To confirm this, the sensitivity is going to be calculated through new simulations developed in the IceCube framework, with an antenna model built from in-situ calibration measurements.

Sign in / Sign up

Export Citation Format

Share Document