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71.
A fully automated optimization process is provided for the design of ducted propellers under open water conditions, including 3D geometry modeling, meshing, optimization algorithm and CFD analysis techniques. The developed process allows the direct integration of a RANSE solver in the design stage. A practical ducted propeller design case study is carried out for validation. Numerical simulations and open water tests are fulfilled and proved that the optimum ducted propeller improves hydrodynamic performance as predicted. 相似文献
72.
Christian Hirt Martin Schmitz Uwe Feldmann-Westendorff Gerhard Wübbena Cord-Hinrich Jahn Günter Seeber 《GPS Solutions》2011,15(2):149-159
The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation
Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining
conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera
systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km.
This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal
height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed
in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span
of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent
errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement
of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates
the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation
of GNSS height processing strategies. 相似文献
73.
Harm Bartholomeus Lammert Kooistra Antoine Stevens Martin van Leeuwen Bas van Wesemael Eyal Ben-Dor Bernard Tychon 《International Journal of Applied Earth Observation and Geoinformation》2011
Soil Organic Carbon (SOC) is one of the key soil properties, but the large spatial variation makes continuous mapping a complex task. Imaging spectroscopy has proven to be an useful technique for mapping of soil properties, but the applicability decreases rapidly when fields are partially covered with vegetation. In this paper we show that with only a few percent fractional maize cover the accuracy of a Partial Least Square Regression (PLSR) based SOC prediction model drops dramatically. However, this problem can be solved with the use of spectral unmixing techniques. First, the fractional maize cover is determined with linear spectral unmixing, taking the illumination and observation angles into account. In a next step the influence of maize is filtered out from the spectral signal by a new procedure termed Residual Spectral Unmixing (RSU). The residual soil spectra resulting from this procedure are used for mapping of SOC using PLSR, which could be done with accuracies comparable to studies performed on bare soil surfaces (Root Mean Standard Error of Calibration = 1.34 g/kg and Root Mean Standard Error of Prediction = 1.65 g/kg). With the presented RSU approach it is possible to filter out the influence of maize from the mixed spectra, and the residual soil spectra contain enough information for mapping of the SOC distribution within agricultural fields. This can improve the applicability of airborne imaging spectroscopy for soil studies in temperate climates, since the use of the RSU approach can extend the flight-window which is often constrained by the presence of vegetation. 相似文献
74.
Observational and model evidence of global emergence of permanent, unprecedented heat in the 20th and 21st centuries 总被引:2,自引:0,他引:2
Given the severe impacts of extreme heat on natural and human systems, we attempt to quantify the likelihood that rising greenhouse gas concentrations will result in a new, permanent heat regime in which the coolest warm-season of the 21(st) century is hotter than the hottest warm-season of the late 20(th) century. Our analyses of global climate model experiments and observational data reveal that many areas of the globe are likely to permanently move into such a climate space over the next four decades, should greenhouse gas concentrations continue to increase. In contrast to the common perception that high-latitude areas face the most accelerated response to global warming, our results demonstrate that in fact tropical areas exhibit the most immediate and robust emergence of unprecedented heat, with many tropical areas exhibiting a 50% likelihood of permanently moving into a novel seasonal heat regime in the next two decades. We also find that global climate models are able to capture the observed intensification of seasonal hot conditions, increasing confidence in the projection of imminent, permanent emergence of unprecedented heat. 相似文献
75.
Claire Granier Bertrand Bessagnet Tami Bond Ariela D��Angiola Hugo Denier van der Gon Gregory J. Frost Angelika Heil Johannes W. Kaiser Stefan Kinne Zbigniew Klimont Silvia Kloster Jean-Fran?ois Lamarque Catherine Liousse Toshihiko Masui Frederik Meleux Aude Mieville Toshimasa Ohara Jean-Christophe Raut Keywan Riahi Martin G. Schultz Steven J. Smith Allison Thompson John van Aardenne Guido R. van der Werf Detlef P. van Vuuren 《Climatic change》2011,109(1-2):163-190
Several different inventories of global and regional anthropogenic and biomass burning emissions are assessed for the 1980?C2010 period. The species considered in this study are carbon monoxide, nitrogen oxides, sulfur dioxide and black carbon. The inventories considered include the ACCMIP historical emissions developed in support of the simulations for the IPCC AR5 assessment. Emissions for 2005 and 2010 from the Representative Concentration Pathways (RCPs) are also included. Large discrepancies between the global and regional emissions are identified, which shows that there is still no consensus on the best estimates for surface emissions of atmospheric compounds. At the global scale, anthropogenic emissions of CO, NOx and SO2 show the best agreement for most years, although agreement does not necessarily mean that uncertainty is low. The agreement is low for BC emissions, particularly in the period prior to 2000. The best consensus is for NOx emissions for all periods and all regions, except for China, where emissions in 1980 and 1990 need to be better defined. Emissions of CO need better quantification in the USA and India for all periods; in Central Europe, the evolution of emissions during the past two decades needs to be better determined. The agreement between the different SO2 emissions datasets is rather good for the USA, but better quantification is needed elsewhere, particularly for Central Europe, India and China. The comparisons performed in this study show that the use of RCP8.5 for the extension of the ACCMIP inventory beyond 2000 is reasonable, until more global or regional estimates become available. Concerning biomass burning emissions, most inventories agree within 50?C80%, depending on the year and season. The large differences between biomass burning inventories are due to differences in the estimates of burned areas from the different available products, as well as in the amount of biomass burned. 相似文献
76.
Lidia Romero-Viana Ramon Julià Martin Schimmel Antonio Camacho Eduardo Vicente M. Rosa Miracle 《Climatic change》2011,107(3-4):343-361
We present the first winter (December to March) rainfall reconstruction based in a novel proxy, the thickness of annual calcite laminations preserved in Lake La Cruz (central–eastern Spain). A previous calibration analysis between laminae thickness and the instrumental data series (1950 to present) indicated a highly significant correlation with winter rainfall. Therefore this study attempts the winter rainfall reconstruction since the onset of laminations (1579 a.d.) by means of the calibration function previously developed. The verification analysis between inferred annual values and earlier instrumental data (1859–1949) confirms the suitability of this novel proxy and the reliability of the series reconstructed. The reconstructed series show the fluctuating character of winter rainfall in the western Mediterranean area; interdecadal dry periods alternated with wetter periods following, in a board sense, the pattern recorded by documentary sources in other regions of the Iberian Peninsula. At present times regional winter rainfall anomalies are highly correlated with the phase of the North Atlantic Oscillation (NAO). However the time series analysis showed the dominance of nonstationary components at high frequencies of the climate signal over the last four centuries suggesting that the connection between winter rainfall and the NAO has not been stable over time and also other modes of variability, not only NAO, may have conditioned winter rainfall variability. 相似文献
77.
The vital role of forests in limiting the likelihood of dangerous climate change has precipitated renewed interest in debt-for-nature swaps. This article uses evidence on past debt-for-nature deals and similar debt mechanisms to assess a recent second wave of such swaps. It outlines five typical shortcomings of this form of financial transaction: that they often fail to deliver additional resources to the debtor country and/or debtor government budget; often fail to deliver more resources for conservation/climate purposes; often have a negligible effect on overall debt burdens (and, as such, do not generate more ‘indirect’ benefits); and are often in conflict with principles of alignment with government policy and alignment with government systems (these two last shortcomings being important elements within the new aid delivery paradigm). Our analysis is applied to a recent debt-for-nature swap between the United States and Indonesia. We show that this case, which we consider a litmus test for current swap practice, performs unevenly across the five shortcomings. First, although the US-Indonesian swap does increase available resources to Indonesia at the country level, it does not generate extra budgetary room for the Indonesian government. Second, the extent to which the resources provided by the swap are additional to other donor support and reserved domestic budget lines for conservation goals is unclear. Third, the swap is too insignificant to create indirect (positive) economic effects. Regarding alignment issues, fourth, the swap is very much in line with current national policy, but, fifth, appears at odds with the new aid delivery paradigm's insistence on system alignment. We argue that if a second generation of debt-for-nature swaps is to be pursued then they need to avoid the common pitfalls associated with this form of finance. Moreover, there is a need to debate broader ways of linking debt service repayments to climate mitigation and adaptation. 相似文献
78.
Gegar Prasetya John Beavan Xiaoming Wang Martin Reyners William Power Kate Wilson Biljana Lukovic 《Pure and Applied Geophysics》2011,168(11):1973-1987
We undertake detailed near-field numerical modelling of the tsunami generated by the 15 July 2009 earthquake (Mw 7.8) in Fiordland,
New Zealand. High resolution bathymetry and topography data at Breaksea and Dusky Sounds, and Chalky and Preservation Inlets
are derived mostly from digitised New Zealand nautical charts, Shuttle Radar Topographic Mission (SRTM) 3 arc-second data,
and General Bathymetric Chart of the Ocean (GEBCO) 30 s data. A combination of continuous and campaign Global Positioning
System (GPS), satellite radar (ALOS/PALSAR InSAR images) and seismology data are used to constrain the seafloor deformation
for the initial tsunami condition. This source model, derived independently of DART observations, provides an excellent fit
to observed tsunami elevations recorded by DART buoy 55015. The model results in the near field show maximum tsunami elevations
in the range 0.5–2.0 m inside the sounds and inlets with maximum flow speeds of 3.0 m/s. Along the open coast, maximum tsunami
elevations reach 2.0 m. The high flow speeds through the inlets may change the inlet stratifications and water mass inside
the sounds. Media reports and field reconnaissance data show some tsunami evidence at Cormorant Cove, Duck and Goose Coves,
and Passage Point. 相似文献
79.
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