6 research outputs found
Experimental study of air lubrication with fluidic oscillators for flat plate drag reduction
No full textThe frictional drag reduction by air lubrication on a 7 m-long and 1.1 m-wide flat plate was investigated in a towing tank at four towing velocities (3 m/s–8.23 m/s). Air was injected through fluidic oscillators installed on the underside of the plate with air flow rates ranging from 0 L/s to 80 L/s, producing air-layer thicknesses of 0mmto16mm. Maximum drag reduction of 21.2 % was achieved at 3 m/s (10.6 % at 8.23 m/s). Results indicate a drop-off in further drag reduction improvement with air layer thickness beyond 10 mm. Videos of the air topology revealed an initial air layer film immediately downstream of the air injector at low velocities, which transitions to a dispersed bubble layer. The videos also showed side vortices appearing at higher velocities. The oscillator frequency of the fluidic oscillators was shown to increase with air flow rate and with higher towing velocity.</p
Numerical modelling of air-induced drag reduction allowing the transition between bubbly, air layer and mixed regimes
No full textAir lubrication can reduce the frictional resistance of ships, leading to significant fuel cost savings. However, the performance of air lubrication systems varies considerably, depending on the operating conditions. Complex gas morphologies play a crucial role here but are difficult to predict. Such a variety of morphologies (bubbly flow, air layers, or mixed regimes) requires morphology-adaptive methods, such as MultiMorph. This method allows for multiple morphologies of a given phase, including the transfer between them. The injection of gas can result in air bubbles, air layers, or a mixed regime, based on local transfer mechanisms. The ability to predict these morphologies is a distinctive feature of this method. Alternative methods prescribe a specific regime a priori, and do not allow a transition. To assess the suitability of MultiMorph for air lubrication problems, two geometries with different complexities are considered. The first test validates the method against flat plate experiments. Various water velocity and gas flow rate combinations were considered to investigate their influence on gas morphology and the associated drag reduction. The second case features a three-dimensional ship hull geometry with two bubble injectors to test the applicability of the method to a more complex scenario, including a curved geometry. The method performs well in both test cases and qualifies as a useful tool for numerical investigations of air lubrication phenomena
A LANDIS-II extension for simulating forest road networks
No full textForest roads are an important part of forest management, both in terms of cost and impact on surrounding ecosystems. Existing tools to simulate the construction of forest roads have been designed for tactical or operational planning purposes, for relatively small areas (The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Numerical modelling of air-induced drag reduction allowing the transition between bubbly, air layer and mixed regimes
No full textAir lubrication can reduce the frictional resistance of ships, leading to significant fuel cost savings. However, the performance of air lubrication systems varies considerably, depending on the operating conditions. Complex gas morphologies play a crucial role here but are difficult to predict. Such a variety of morphologies (bubbly flow, air layers, or mixed regimes) requires morphology-adaptive methods, such as MultiMorph. This method allows for multiple morphologies of a given phase, including the transfer between them. The injection of gas can result in air bubbles, air layers, or a mixed regime, based on local transfer mechanisms. The ability to predict these morphologies is a distinctive feature of this method. Alternative methods prescribe a specific regime a priori, and do not allow a transition. To assess the suitability of MultiMorph for air lubrication problems, two geometries with different complexities are considered. The first test validates the method against flat plate experiments. Various water velocity and gas flow rate combinations were considered to investigate their influence on gas morphology and the associated drag reduction. The second case features a three-dimensional ship hull geometry with two bubble injectors to test the applicability of the method to a more complex scenario, including a curved geometry. The method performs well in both test cases and qualifies as a useful tool for numerical investigations of air lubrication phenomena.</p
The role of dispersal, selection, and timing of sampling on the false discovery rate of loci under selection during geographic range expansion
No full textIdentifying adaptive loci is important to understand the evolutionary potential of species undergoing range expansion. However, in expanding populations, spatial demographic processes such as allele surfing can create spatial patterns of neutral genetic variation that appear similar to those generated through adaptive processes. As a result, the false discovery rate of adaptive loci may be inflated in landscape genomic analyses. Here, we take a simulation modelling approach to investigate how range expansion affects our ability to correctly distinguish between neutral and adaptive genetic variation, using the mountain pine beetle outbreak system as a motivating example. We simulated the demographic and population genetic dynamics of populations undergoing range expansion using an individual-based genetic model CDMetaPOP. We investigated how the false discovery rate of adaptive loci is affected by (i) dispersal capacity, (ii) timing of sampling, and (iii) the strength of selection on an adaptive reference locus. We found that a combination of weak dispersal, weak selection, and early sampling presents the greatest risk of misidentifying loci under selection. Expanding populations present unique challenges to the reliable identification of adaptive loci. We demonstrate that there is a need for further methodological development to account for directional demographic processes in landscape genomics.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Forecasting wildfire-induced declines in potential forest harvest levels across Québec
No full textWildfires are increasing in importance in many regions of the Canadian boreal forest and are an ongoing risk for forest management activities. We simulated the effects of fires on long-term harvest levels on the 59 forest management units of the province of Québec, Canada, for the 2020-2100 period. Different climate change pathways (stable, RCP 4.5 or 8.5) and salvage logging rates (20% or 70% of mature burned stands) were simulated. Changes in forest flammability due to climate change, species migration and forest management were also considered. Under stable climatic conditions, the decline in potential harvest levels due to fire, based on 50 simulations per scenario, ranged between 3 - 36% (mean = 12%) when high salvage logging rates were simulated, compared to 4 - 59% (mean = 21%) for low salvage rates. Climate change caused increases in burn rates between -3 and 39% for RCP 4.5, and between 33 and 69% for RCP 8.5 at the end of the 21st century. However, the effects of these modified burn rates on harvest levels did not differ substantially from those of baseline burn rates, probably because the projected burn rates were comparatively greater during the later part of the simulations (2070-2100), when their impacts on harvest rate calculations were limited. This study indicates that potential harvest levels calculated without considering wildfires are likely to be non-sustainable.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
