It is an important subject to solve the problem of Elastodynamics numerically.In this paper,a calculation formula to compute singular intergral for elastodynamics under Fourier transform using Boundary Element Methods is discussed. 相似文献
A Lagrangian experiment was conducted over Iowa during the daytime (9:00–17:30 LT) on June 19, 2007 as part of the North American Carbon Program's Mid-Continent Intensive using a light-weight and operationally flexible aircraft to measure a net drawdown of CO2 concentration within the boundary layer. The drawdown can be related to net ecosystem exchange when anthropogenic emissions are estimated using a combination of the Vulcan fossil fuel emissions inventory coupled with a source contribution analysis using HYSPLIT. Results show a temporally and spatially averaged net CO2 flux of −9.0 ± 2.4 μmol m−2 s−1 measured from the aircraft data. The average flux from anthropogenic emissions over the measurement area was 0.3 ± 0.1 μmol CO2 m−2 s−1. Large-scale subsidence occurred during the experiment, entraining 1.0 ± 0.2 μmol CO2 m−2 s−1 into the boundary layer. Thus, the CO2 flux attributable to the vegetation and soils is −10.3 ± 2.4 μmol m−2 s−1. The magnitude of the calculated daytime biospheric flux is consistent with tower-based eddy covariance fluxes over corn and soybeans given existing land-use estimates for this agricultural region. Flux values are relatively insensitive to the choice of integration height above the boundary layer and emission footprint area. Flux uncertainties are relatively small compared to the biospheric fluxes, though the measurements were conducted at the height of the growing season. 相似文献
Availability of water and nitrogen are key constraints to primary productivity in arid and semiarid ecosystems. Theoretically, plant growth is maximised when all resources are equally limiting. This paper tested the hypothesis that for a given amount of available water, the gap between actual and attainable yield of dryland crops in semiarid southern Australia is inversely proportional to the degree of nitrogen and water co-limitation.
Field and simulation experiments were combined in an analysis involving three steps. Step 1 assessed the capacity of a crop simulation model to estimate yield and its responses to water and nitrogen inputs in the semiarid Mallee region. Step 2 derived a boundary function relating grain yield and water availability using simulations with long-term weather records. Step 3 explored the link between degree of co-limitation and deviations between actual yield and the boundary function. Degree of co-limitation (CWN) was calculated as a function of model-derived nitrogen (NSI) and water stress indices (WSI), i.e. CWN = 1 − |NSI − WSI|. Stress indices range from zero (no stress) to 1 (maximum stress), and CWN tends to 1 when both resources impose constraints of similar magnitude to crop growth.
The field experiment combining locations, seasons and management practices generated a range of grain yield from 0.6 to 3.8 t ha−1. Water availability, i.e. seasonal rainfall plus change in soil water content from sowing to harvest, ranged from 127 to 370 mm. Nitrogen fertiliser varied from nil to 36 kg N ha−1 and inorganic nitrogen in the soil profile at sowing ranged from 29 to 497 kg ha−1. For these ranges of conditions, the relationship between simulated and measured yield was statistically undistinguishable from the y = x function.
A factorial modelling experiment combining sites, seasons, initial soil water content and dose of nitrogen fertiliser was used to derive a boundary function which provided an objective and independent upper limit for the field data. Actual yield was below the boundary function in most cases. The difference between actual and attainable yield was inversely proportional to CWN. This study thus supported the hypothesis that yield and water-use efficiency of water- and nitrogen-stressed crops increase with increasing degree of co-limitation. 相似文献
