Offshore Turbine Arrays: Numerical Modeling and Experimental Validation

The interaction between wind turbines in a large wind farm needs to be better understood to reduce array losses and improve energy production. A numerical test bed for an array of offshore wind turbines was developed in the open-source computational fluid dynamics (CFD) framework OpenFOAM. It provides a computational tool which can be used in combination with physical model turbine array studies in the Flow Physics Facility (FPF) at UNH as well as other test facilities. Turbines were modeled as actuator disks with turbulence sources to reduce computational cost. Both k-ϵ and k-ω SST turbulence models were utilized to capture the flow in the near-wall, wake, and free stream regions. Experimental studies were performed in the FPF to validate the numerical results and to provide realistic initial and boundary conditions, for example turbulent boundary layer inlet velocity profiles. Mesh refinement and boundary condition studies were performed. Numerical simulations were executed on a custom-built server, designed to be the head node of a future CFD cluster. The entire project was built on open-source software to facilitate replication and expansion. The numerical model provides building blocks for simulations of large wind turbine arrays, computational resources permitting. The numerical model currently replicates a three by one array of wind turbines in the FPF, and provides detailed insight into the array fluid dynamics

Trends in the Dates of Ice Freeze-up and Breakup over Hudson Bay, Canada

Hudson Bay experiences a complete cryogenic cycle each year. Sea ice begins to form in late October, and the Bay is usually ice-free in early August. This seasonally varying ice cover plays an important role in the regional climate. To identify secular trends in the cryogenic cycle, we examined variability in the timing of sea-ice formation and retreat during the period 1971– 2003. The dates of ice freeze-up and breakup at 36 locations across Hudson Bay were catalogued for each year from weekly ice charts provided by the Canadian Ice Service. We used the nonparametric Mann-Kendall test to determine the statistical significance of the trends and the Theil-Sen approach to estimate their magnitude. Our results indicate statistically significant trends toward earlier breakup in James Bay, along the southern shore of Hudson Bay, and in the western half of Hudson Bay, and toward later freeze-up in the northern and northeastern regions of Hudson Bay. These trends in the annual ice cycle of Hudson Bay coincide with both the regional temperature record and the projections from general circulation models. If this trend toward a longer ice-free season continues, Hudson Bay will soon face important environmental challenges.Chaque année, la Baie d’Hudson connaît un cycle cryogénique complet. La formation de la glace marine commence en fin d’octobre et la baie est habituellement exempte de glace en début d’août. La présence saisonnière du couvert de la glace de la Baie d’Hudson revêt une importance primordiale sur le climat régional. Dans cet article, on étudie la variabilité des dates de formation et de retrait de la glace marine de la Baie d’Hudson dans le but d’identifier des tendances séculaires durant la période 1971 à 2003. Les dates de formation et de retrait de la glace marine ont été cataloguées pour tous les ans dans le cas de 36 endroits à travers la Baie d’Hudson et la Baie James en utilisant des images hebdomadaires publiées par le Service canadien des glaces. Le test non paramétrique Mann Kendall a été utilisé pour déterminer la signification statistique des tendances alors que la méthode de Theil Sen nous a fourni un estimé de l’ampleur de ces mêmes tendances. Notre analyse statistique nous indique qu’il existe des tendances significatives vers une date de déglacement plus avancée dans la Baie James, le long de la côte sud de la Baie d’Hudson, et dans la partie ouest de la Baie d’Hudson. De plus, des tendances significatives vers un gel plus tardif ont été observées dans les régions du nord et du nord-est de la Baie d’Hudson. Ces tendances dans le cycle annuel de glace de la Baie d’Hudson coïncident avec les tendances des températures de la région de même qu’avec les projections des modèles de circulation générale. Si cette tendance vers une durée plus courte du couvert de glace continue, la région de la Baie d’Hudson relèvera des défis environnementaux importants dans un proche avenir

La potentialité subversive du langage dans la pratique des arts vivants - é(cri)re le corps-déchet

Mon corps d’artiste-chercheur en art vivant, qui se sent enfermé dans la conception d’un monde-machine régi par le marché et la publicité, une société « de la consommation de soi » comme le dit Quessada (1999), tente de trouver des possibilités d’évasion de ce monde-prison, des possibilités de renverser son ordre marchand par la conscience des structures profondes du langage telle qu’elles s’articulent au sein de ma pratique des arts du vivant. J’ai choisi d’abord d’explorer mon champ d’action sur mon corps-déchet au coeur de ma biographie, que j’ai voulu penser à la croisée d’auteurs qui me traversent et m’influencent. À travers l’écriture d’un journal d’alternance et l’élaboration d’un texte pour la scène qui s’intitule Oh Happy Days, j’ai tenté de trouver des façons singulières de bouleverser ma perception de la réalité et celle du public, par la mise en place d’une dramaturgie de l’expérience de la crise, afin d’interroger les potentialités subversives du langage, telle une sorte de « peste purificatrice » comme le souhaitait Artaud (1978) pour son théâtre de la cruauté

L'adaptation des stations de ski face aux changements climatiques

L’objectif est de quantifier les changements climatiques hivernaux du Mont Sutton, du Mont Orford, du Massif de Charlevoix et du Mont-Vidéo, quatre stations de ski québécoises. Par le fait même, évaluer les impacts sur ces stations et tenter de prévoir leurs conditions dans un avenir rapproché. C’est notamment en réponse à ces objectifs qu’il importe de comprendre l’adaptation des stations de ski face aux changements climatiques. Pour ce faire, la situation précaire des stations de ski du Québec et d’ailleurs a été démontrée. Il apparait clair que celle-ci ne fait que s’envenimer. En effet, les données provenant du North American Regional Reanalisys ont été analysées de manière à étudier la situation des quatre stations. En plus de cela, des questionnaires ont permis de rendre compte de la réalité sur le terrain de deux de ces stations. Les températures augmentent, les précipitations augmentent et les vents changent. De manière générale, c’est le Mont-Vidéo, en Abitibi-Témiscamingue, qui est le plus assujetti aux changements climatiques. Le Massif de Charlevoix écope moins des effets de ces derniers alors que les deux stations du sud du Québec sont pourtant celles où les conditions de ski changent le plus drastiquement. Si les tendances observées se maintiennent, l’état de la situation des stations de ski pourrait devenir catastrophique. Afin de remédier à la situation et de s’y adapter, les stations de ski ont accès à de nombreuses solutions. Dans une optique de développement durable, il est toutefois possible qu’advienne une restructuration du rôle premier de la station de ski, plutôt vers une station de villégiature multi saisons. Il existe donc des méthodes d’adaptation intéressantes, notamment par l’incorporation de l’évènementiel, l’augmentation et la diversification d’installations sportives ainsi que des services. Il est aussi envisageable de mitiger les effets des changements climatiques, par de nouvelles techniques ou l’amélioration des systèmes d’enneigements artificiels actuels par exemple, ou en offrant des passes de saisons multi stations. Enfin, dans une optique de constante amélioration, les stations de ski peuvent réduire leurs empreintes écologiques et devenir plus durables. Il est certain que les changements climatiques affectent les stations de ski, et ce, tant au Québec qu’ailleurs dans le monde, notamment dans le reste de l’Amérique du Nord, en Bolivie, en Europe et en Océanie. Les gouvernements, les entreprises énergétiques, ainsi que les stations de ski, devront agir à l’unisson. D’importantes démarches doivent être prises afin que les stations de ski s’adaptent à ces changements.

Response of a native bamboo [Arundinaria gigantea (Walt.) Muhl.] in a wind-disturbed forest

Numerous bamboos are known to form extensive single-species stands, including species in the United States. Formerly prominent in the southeastern US, canebrakes are dense stands of the bamboos collectively called cane [Arundinaria (Michx)]. Canebrakes are now a critically endangered component of the bottomland hardwood forest ecosystem. Cane still occurs in its historic range, primarily in small remnant patches. A poor understanding of the ecological processes that generated large canebrakes limits their restoration and management. We hypothesize that cane\u27s spreading clonal structure enables these bamboos to persist beneath a forest canopy and then respond rapidly to large-scale wind disturbances. We quantified patterns of clonal growth in one cane species, giant cane [Arundinaria gigantea (Walt.) Muhl.], in a very large tornado-generated canopy gap and in surrounding bottomland hardwood forest in Louisiana. We tested these four hypotheses over a 12-month study period in the large canopy gap: (1) production of new culms should be greater, (2) clonal expansion should be greater, (3) culm damage rate should be reduced, and (4) culm size should be reduced compared to giant cane stands under forest canopy. We found that new culm production in tornado-blowdown plots was twice that in forest plots. Accordingly, culms were younger on average in the tornado blowdown than under forest. Rate of clonal expansion was similar between the two environments, suggesting clonal spread was not disturbance-dependent. With fewer branch-fall impacts, culms in the tornado blowdown were less often damaged. Culms were smaller in tornado-blowdown plots than in forest plots. Giant cane\u27s clonal plasticity should enable it to persist in old-growth bottomland forests by responding to local light conditions. Genets should increase culm production in small gaps and senesce as gaps fill in. Giant cane stands could thereby shift location over time. Wind disturbance that opens forest canopy should trigger redevelopment of denser stands that could merge with other expanding stands into expansive canebrakes. Giant cane\u27s clonal ecology may be a useful model for understanding spreading bamboos and other forest-growing clonal perennials. © 2007 Elsevier B.V. All rights reserved

Multi-year salutary effects of windstorm and fire on river cane

Canebrakes are monodominant stands of cane (Arundinaria gigantea [Walter] Muhl.), a bamboo native to and once prominent in the southeastern USA. Canebrakes were important wildlife habitat within the bottomland hardwood forest ecosystem. They have been reduced in areal coverage by an estimated 98% since European settlement due to land conversion and the drastic alteration of disturbance regimes in their floodplain habitat. Ongoing canebrake restoration efforts are hampered by incomplete understanding of the role of natural disturbance in cane ecology. We used a large tornado blow down and multiple prescribed fires to quantify the response of cane to the sequential disturbances of windstorm and fire in the Tensas Watershed of northeastern Louisiana using number and condition of bamboo stems (culms) as response variables. We hypothesized that culms would be more abundant in burned than in unburned stands and that culm populations in burned stands would be younger than in unburned stands. In this study, conducted four years post fire, effects of both windstorm and burning were additive and beneficial. Results indicate that periodic aboveground disturbance has three salutary effects on cane ramet demography: 1) clonal growth following disturbances more than compensates for any culms killed; 2) the cohort of new culms is younger than the culms they replace; and 3) disturbance appears to inoculate some cane stands for several years against local die-offs. Fire is a valuable tool for canebrake management. By periodically resetting cane stands, fires and other disturbances may have played a key role in canebrake formation and persistence over time

Understanding the empirical literature on purchasing power parity: the post-Bretton Woods era

Foreign exchange ; Purchasing power

Data Validation of the NASA Time-Resolved Observations of Precipitation Structure and Storm Intensity with a Constellation of Smallsats (TROPICS) Pathfinder Microwave Radiometer

Launched in June 2021, the TROPICS Pathfinder CubeSat has a microwave radiometer payload sensitive to the frequencies for observing precipitation, humidity, temperature, and cloud ice. The observed brightness temperatures must be compared to a data set of ‘known’ quality to validate the measured data across all channels of the microwave radiometer. This research explores validating TROPICS Pathfinder data against reanalysis data to determine the quality of the provisional TROPICS Pathfinder data product, with an eye for the future of comparing against other microwave radiometer measurements. Validation involves comparing Pathfinder data to ERA5 reanalysis data by using the Community Radiative Transfer Model (CRTM) to calculate simulated radiances. The simulated radiances are then compared to the on-orbit Pathfinder data to determine biases, in a method known as single-differencing. The Pathfinder data presented here is at the provisional data maturity level and should be considered preliminary. This effort will be repeated when the TROPICS Pathfinder Level-1 radiances reach the validated data product maturity level late in the summer of 2022. To effectively validate the Pathfinder mission, we have developed a process using MATLAB to read and match the TROPICS Pathfinder data for latitudes between -40° – 40° with desired data for comparison, which is ERA5 in this research. These latitude-longitude data match-ups are then filtered for data points without clouds, using cloud cover data from the GOES-16 satellite. Using data that is cloud-free and overocean ensures that single-differencing comparisons are made using like-data sets and will result in minimal error introduced by the reanalysis and radiative transfer models. After filtering the data, this validation process generates the input files required by CRTM to simulate the model, simulates these observations using the unique Pathfinder CRTM coefficients resulting in the most accurate data, and performs the necessary difference calculations. The end result is an automated process that performs data comparisons for researchers, and we present them as a summary for analysis. The provisional Level-1 radiances show good agreement with combined ERA5 and CRTM simulated radiances, and we expect even better agreement with the upcoming validated Level-1 radiances

Groundcover community assembly in high-diversity pine savannas: seed arrival and fire-generated environmental filtering

Environmental filtering—abiotic and biotic constraints on the demographic performance of individual organisms—is a widespread mechanism of selection in communities. A given individual is “filtered out” (i.e., selectively removed) when environmental conditions or disturbances like fires preclude its survival and reproduction. Although interactions between these filters and dispersal from the regional species pool are thought to determine much about species composition locally, there have been relatively few studies of dispersal × filtering interactions in species-rich communities and fewer still where fire is also a primary selective agent. We experimentally manipulated dispersal and filtering by fire (pre-fire fuel loads and post-fire ash) in species-rich groundcover communities of the longleaf pine ecosystem. We tested four predictions: (1) That species richness would increase with biologically realistic dispersal (seed addition); (2) that the immediate effect of increased fuels in burned communities would be to decrease species richness, whereas the longer-term effects of increased fuels would be to open recruitment opportunities in the groundcover, increase species richness, and increase individual performance (growth) of immigrating species; (3) that adding ash would increase species richness; and (4) that increased dispersal would generate larger increases in species richness in plots with increased fuels compared to plots with decreased fuels. We found that dispersal interacted with complex fire-generated filtering during and after fires. Dispersal increased species richness more in burned communities with increased and decreased fuels compared to burned controls. Moreover, individuals of immigrating species generally grew to larger sizes in burned communities with increased fuels compared to burned controls. In contrast to dispersal and fuels, ash had no effect on species richness directly or in combination with other treatments. We conclude that filtering occurs both during fires and in the post-fire environment and that these influences interact with dispersal such that the consequences are only fully revealed when all are considered in combination. Our experiment highlights the importance of considering the dynamic interplay of dispersal and selection in the assembly of species-rich communities