Experiment and numerical simulation on the characteristics of fluid–structure interactions of non-rigid airships

Fluid-structure interaction is an important issue for non-rigid airships with inflated envelopes. In this study, a wind tunnel test is conducted, and a loosely coupled procedure is correspondingly established for numerical simulation based on computational fluid dynamics and nonlinear finite element analysis methods. The typical results of the numerical simulation and wind tunnel experiment, including the overall lift and deformation, are in good agreement with each other. The results obtained indicate that the effect of fluid-structure interaction is noticeable and should be considered for non-rigid airships. Flow- induced deformation can further intensify the upward lift force and pitching moment, which can lead to a large deformation. Under a wind speed of 15 m/s, the lift force of the non-rigid model is increased to approximatelv 60% compared with that of the rigid model under a high angle of attack.

Continued Increases of Gross Primary Production in Urban Areas during 2000-2016

Urbanization affects vegetation within city administrative boundary and nearby rural areas.Gross primary production(GPP)of vegetation in global urban areas is one of important metrics for assessing the impacts of urbanization on terrestrial ecosystems.To date,very limited data and information on the spatial-temporal dynamics of GPP in the global urban areas are available.In this study,we reported the spatial distribution and temporal dynamics of annual GPP during 2000–2016 from 8,182 gridcells(0.5°by 0.5°latitude and longitude)that have various proportion of urban areas.Approximately 79.3%of these urban gridcells had increasing trends of annual GPP during 2000-2016.As urban area proportion(%)within individual urban gridcells increased,the means of annual GPP trends also increased.Our results suggested that for those urban gridcells,the negative effect of urban expansion(often measured by impervious surfaces)on GPP was to large degree compensated by increased vegetation within the gridcells,mostly driven by urban management and local climate and environment.Our findings on the continued increases of annual GPP in most of urban gridcells shed new insight on the importance of urban areas on terrestrial carbon cycle and the potential of urban management and local climate and environment on improving vegetation in urban areas.

Annual Maps of Forests in Australia from Analyses of Microwave and Optical Images with FAO Forest Definition

The Australian governmental agencies reported a total of 149 million ha forest in the Food and Agriculture Organization of the United Nations(FAO)in 2010,ranking sixth in the world,which is based on a forest definition with tree height>2 meters.Here,we report a new forest cover data product that used the FAO forest definition(tree cover>10%and tree height>5 meters at observation time or mature)and was derived from microwave(Phased Array type L-band Synthetic Aperture Radar,PALSAR)and optical(Moderate Resolution Imaging Spectroradiometer,MODIS)images and validated with very high spatial resolution images,Light Detection and Ranging(LiDAR)data from the Ice,Cloud,and land Elevation Satellite(ICESat),and in situ field survey sites.The new PALSAR/MODIS forest map estimates 32 million ha of forest in 2010 over Australia.PALSAR/MODIS forest map has an overall accuracy of~95%based on the reference data derived from visual interpretation of very high spatial resolution images for forest and nonforest cover types.Compared with the canopy height and canopy coverage data derived from ICESat LiDAR strips,PALSAR/MODIS forest map has 73%of forest pixels meeting the FAO forest definition,much higher than the other four widely used forest maps(ranging from 36%to 52%).PALSAR/MODIS forest map also has a reasonable spatial consistency with the forest map from the National Vegetation Information System.This new annual map of forests in Australia could support cross-country comparison when using data from the FAO Forest Resource Assessment Reports.