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  • 1
    Electronic Resource
    Electronic Resource
    FINITE ELEMENT SIMULATION OF GUST LOADING (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 1197-1210 
    Details
    ISSN: 0271-2091
    Keywords: finite element method ; gust ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In the structural design of civil aircraft the critical loads are often those encountered in a gust or atmospheric turbulence. The traditional ‘indicial’ solution is restricted to a simple plate. In this paper a finite element formulation is proposed for an aerofoil or arbitrary shape entering a uniform sharp-edged or sinusoidal gust. The thin rotational gust front and wake in an irrotational flow field are successfully modelled by a novel superposition technique. The finite element solutions are compared with the Kussner function and results by other numerical methods. The agreement is good.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Fully discrete arbitrary-order schemes for a model parabolic equation (1994)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 19 (1994), S. 1039-1047 
    Details
    ISSN: 0271-2091
    Keywords: Fully discrete ; High-order ; Conservative ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A fully discrete methodology is investigated from which two-level, explicit, arbitrary-order, conservative numerical schemes for a model parabolic equation can be derived. To illustrate this, fully discrete three-, five-, seven- and nine-point conservative numerical schemes are presented, revealing that a higher-order scheme has a better stability condition. A method from which high-order numerical schemes for a scalar advection-diffusion equation can be developed is discussed. This method is based on high-order schemes of both the advection and diffusion equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650191106
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    FULLY DISCRETE HIGH-ORDER SHOCK-CAPTURING NUMERICAL SCHEMES (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 241-269 
    Details
    ISSN: 0271-2091
    Keywords: fully discrete ; high-order ; conservative ; upwind ; shock-capturing ; TVD ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present paper is a sequel to a previous one by the same authors in which a family of up to fourth-order fully discrete (FD) upwind numerical schemes was presented. In this paper we extend those high-order FD schemes to solutions with discontinuities, e.g. shocks. A rigorous anlaysis of the total variation diminishing (TVD) constraint for the high-order FD schemes is carried out. For non-linear systems the TVD constraint is, as usual, applied empirically. These schemes are validated by solving a test problem for the time-dependent shallow water equations.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    FULLY DISCRETE HIGH-RESOLUTION SCHEMES FOR HYPERBOLIC CONSERVATION LAWS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 309-323 
    Details
    ISSN: 0271-2091
    Keywords: fully discrete ; upwind scheme ; TVD high-order ; hyperbolic ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present paper is a sequel to two previous papers in which rigorous, up to fourth-order, fully discrete (FD) upwind TVD schemes have been presented. In this paper we discuss in detail the extension of these schemes to solutions of non-linear hyperbolic systems. The performance of the schemes is assessed by solving test problems for the time-dependent Euler equations of gas dynamics in one and two space dimensions. We use exact solutions and experimental data to validate the results.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    A co-rotational element/time-integration strategy for non-linear dynamics (1994)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 1897-1913 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: New procedures are proposed for implicit dynamic analysis using the finite element method. The main aim is to give stable solutions with significant rigid-body motions, in particular rotations. In contrast to most conventional approaches, the time-integration strategy is closely linked to the ‘element technologies’ with the latter involving a form of co-rotational procedure. For the undamped situation, one of the solution procedures leads to an algorithm that exactly conserves energy when constant external forces are applied (i.e. with gravity loading).
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620371108
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  • 6
    Electronic Resource
    Electronic Resource
    Combining arc-length control and line searches in path following (1995)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 793-803 
    Details
    ISSN: 1069-8299
    Keywords: arc-length control ; line search ; path-following ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: When solving non-linear algebraic equations resulting from a typical finite element discretization it is quite common that the popular Newton-Raphson iteration fails to converge or requires an excessive number of iterations. To solve this problem, line searches have been proposed in conjunction with load control and quadratic arc-length control, which has proved to be highly successful. In the paper we first review a number of the most popular arc-length controls. Then we highlight the severe drawbacks associated with the coupling of the cylindrical arc-length control and line searches. Next, various other forms of arc-length controls are scrutinized in the light of this coupling. It is shown that for some of the arc-length controls such a combination is extremely simple and straightforward, yet at the same time efficient and effective. For the rest the same complications incurred for the cylindrical arc-length method remain.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640111003
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  • 7
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    Application of SIR-C SAR to Hydrology (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The progress, results and future plans regarding the following objectives are presented: (1) Determine and compare soil moisture patterns within one or more humid watersheds using SAR data, ground-based measurements, and hydrologic modeling; (2) Use radar data to characterize the hydrologic regime within a catchment and to identify the runoff producing characteristics of humid zone watersheds; and (3) Use radar data as the basis for scaling up from small scale, near-point process models to larger scale water balance models necessary to define and quantify the land phase of GCM's (Global Circulation Models).
    Keywords: Earth Resources and Remote Sensing
    Type: Science Results from the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR): Progress Report; 43-47; NASA/CR-97-206707
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    A Comparison of Soil Moisture Retrieval Models Using SIR-C Measurements over the Little Washita River Watershed (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Six SIR-C L-band measurements over the Little Washita River watershed in Chickasha, Oklahoma during 11-17 April 1994 have been analyzed for studying the change of soil moisture in the region. Two algorithms developed recently for estimation of moisture content in bare soil were applied to these measurements and the results were compared with those sampled on the ground. There is a good agreement between the values of soil moisture estimated by either one of the algorithms and those measured from ground sampling for bare or sparsely vegetated fields. The standard error from this comparison is on the order of 0.05-0.06 cu cm/cu cm, which is comparable to that expected from a regression between backscattering coefficients and measured soil moisture. Both algorithms provide a poor estimation of soil moisture or fail to give solutions to areas covered with moderate or dense vegetation. Even for bare soils the number of pixels that bear no numerical solution from the application of either one of the two algorithms to the data is not negligible. Results from using one of these algorithms indicate that the fraction of these pixels becomes larger as the bare soils become drier. The other algorithm generally gives a larger fraction of these pixels when the fields are vegetation-covered. The implication and impact of these features are discussed in this article.
    Keywords: Earth Resources and Remote Sensing
    Type: Laboratory for Hydrospheric Processes Research Publications; 161-162
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Monitoring of Environmental Conditions in Taiga Forests Using ERS-1 SAR Data: Results From the Commissioning Phase (1993)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: This paper describes the results of monitoring environmental conditions in Alaskan Taiga forests using ERS-1 SAR dara.
    Keywords: Earth Resources and Remote Sensing
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    The Hydrosphere State (Hydros) Satellite Mission: An Earth System Pathfinder for Global Mapping of Soil Moisture and Land Freeze/Thaw (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-06
    Description: The Hydrosphere State Mission (Hydros) is a pathfinder mission in the National Aeronautics and Space Administration (NASA) Earth System Science Pathfinder Program (ESSP). The objective of the mission is to provide exploratory global measurements of the earth's soil moisture at 10-km resolution with two- to three-days revisit and land-surface freeze/thaw conditions at 3-km resolution with one- to two-days revisit. The mission builds on the heritage of ground-based and airborne passive and active low-frequency microwave measurements that have demonstrated and validated the effectiveness of the measurements and associated algorithms for estimating the amount and phase (frozen or thawed) of surface soil moisture. The mission data will enable advances in weather and climate prediction and in mapping processes that link the water, energy, and carbon cycles. The Hydros instrument is a combined radar and radiometer system operating at 1.26 GHz (with VV, HH, and HV polarizations) and 1.41 GHz (with H, V, and U polarizations), respectively. The radar and the radiometer share the aperture of a 6-m antenna with a look-angle of 39 with respect to nadir. The lightweight deployable mesh antenna is rotated at 14.6 rpm to provide a constant look-angle scan across a swath width of 1000 km. The wide swath provides global coverage that meet the revisit requirements. The radiometer measurements allow retrieval of soil moisture in diverse (nonforested) landscapes with a resolution of 40 km. The radar measurements allow the retrieval of soil moisture at relatively high resolution (3 km). The mission includes combined radar/radiometer data products that will use the synergy of the two sensors to deliver enhanced-quality 10-km resolution soil moisture estimates. In this paper, the science requirements and their traceability to the instrument design are outlined. A review of the underlying measurement physics and key instrument performance parameters are also presented.
    Keywords: Earth Resources and Remote Sensing
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); Volume 42; No. 10
    Format: text
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    NASA TECHNICAL REPORTS
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