In Inkubationsexperimenten wurde die Dynamik der Bodenatmung von 92 Bodenproben aus unterschiedlichen Klimazonen Mittel‐ und Osteuropas unter Laborbedingungen untersucht. Die Ergebnisse verwiesen auf einen differenzierten Anstieg der CO2‐Freisetzung in den ersten zwei Inkubationstagen. Im Unterschied zu allen anderen untersuchten Bodeneigenschaften (Ct, Nt, extrahierbare Kationen und Anionen, einschließlich pH und Nitrat, summare CO2‐Freisetzung nach 35 Inkubationstagen u.a.) zeigte dieser Anfangsanstieg der Bodenatmung eine diskontinuierliche Häufigkeitsverteilung. Ein Glukosezusatz von 7 mg/25 g Boden verstärkte die Unterschiede. Er ermöglichte eine Zuordnung aller Proben zu zwei diskreten Reaktionstypen, die das Adaptionsverhalten der Böden an optimale Umsatzbedingungen nach Lufttrocknung beschreiben. Böden arider Klimate und ackerbaulich genutzte Böden humider Gebiete unterscheiden sich dementsprechend von Boden humider Klimate unter Wald oder Forst durch einen sofortigen Beginn der Bodenatmung und Verstärkung der CO2‐Freisetzung bei Glukoseapplikation. Reversible Veränderungen der mikrobiologischen Verfügbarkeit umsetzbarer Bestandteile im Boden bzw. der Glukose durch Humusstoffe bei der Befeuchtung werden als eine mögliche Ursache des differenzierten Adaptionsverhaltens der Böden vermutet.
In gas and steam turbine applications a common approach to prevent the blades from high cycle fatigue failures due to high vibration amplitudes is the usage of friction damping elements. Besides the intended amplitude reduction this procedure also features some possibly unwanted side effects like a shift in resonance frequencies due to stiffening effects caused by the contact. Thus, as an alternative an eddy current based noncontacting damping concept for the application in turbomachinery is investigated. In this paper two different types of eddy current dampers are considered. Theoretical models for both are established by applying electromagnetic-mechanical theory. The theoretical models are compared with forced response measurements that are performed at a stationary test rig.
An extended water regime model was used for calculating the evapotranspiration, groundwater recharge, and peat mineralization (CO2 and N release) for various fen locations with grassland utilization in dependence on the groundwater level. The results show that an increasing groundwater level leads to a strong decline of the actual evapotranspiration Et. For example, increasing the groundwater level from 30 to 120 cm diminishes the Et by up to 230 mm a—1. A positive groundwater recharge only takes place at groundwater levels of 90 cm and more. At smaller distances the capillary rise into the rooting zone during the summer months is greater than the water seepage during the winter months, so that a negative groundwater recharge-balance is reached in the course of a year. The CO2- and the N-release, as well as the annual decline in peat thickness, increase significantly with rising groundwater levels. The results show, that varying the groundwater level can influence the water regime and the peat mineralization significantly. The lower the groundwater level the less is the peat decomposition. The demand for a groundwater level as small as possible is, however, limited by an agricultural utilization of the fens. Choosing the optimum groundwater level should consider the aims (1) peat mineralization, (2) gas emission (CO2, CH4, N2O), and (3) crop production. If a grassland utilization is supposed to be made possible and all three aims above are given equal importance, the groundwater level should be maintained at 30 cm. At this distance, about 90 % of the optimum plant output can be reached. The peat mineralization can be reduced to 30 to 40 % of the maximum peat mineralization. The gas emission amounts to 50—60 % of the maximum value. Aspekte zum Niedermoorschutz und Wassermanagement Mit Hilfe eines erweiterten Wasserhaushaltsmodells wurden Eva-potranspiration, Grundwasserneubildung und die Torfmineralisation (CO2- und N-Freisetzung) in Abhängigkeit vom Grundwasserflurabstand für verschiedene Niedermoorstandorte unter Grünlandnutzung ermittelt. Die Ergebnisse zeigen, dass mit zunehmendem Grundwasserflurabstand die reale Evapotranspiration Et stark ab-sinkt. So vermindert sich Et bei einem Anstieg des Grundwasserflurabstandes von 30 cm auf 120 cm bis zu 230 mm a—1. Eine positive Grundwasserneubildung findet nur bei Grundwasserflurabständen von 90 cm und mehr statt. Bei geringeren Flurabständen ist der kapillare Aufstieg in den Wurzelraum während des Sommers größer als die Versickerung im Winterhalbjahr, so dass innerhalb eines Jahres negative Grundwasserneubildungsraten auftreten. Mit steigendem Grundwasserflurabstand nehmen die CO2- und N-Freisetzung sowie die jährliche Abnahme der Torfmächtigkeit deutlich zu. Die Ergebnisse zeigen, dass durch Steuerung des Grundwasserflurabstandes der Wasserhaushalt und die Torfmineralisation entscheidend beeinflusst werden können. Je flacher der Grundwasserflurabstand ist, um so geringer ist der Torfabbau. Der Forderung nach möglichst flachen Grundwasserflurabständen sind aber Grenzen gesetzt, wenn die Niedermoore landwirtschaftlich genutzt werden sollen. Für die Wahl des optimalen Grundwasserflurabstandes sind die Zielgrößen (1) Torfmineralisation, (2) Gasemission (CO2, CH4, N2O) und (3) Pflanzenertrag zu be-rücksichtigen. Bei gleichrangiger Berücksichtigung dieser Größen und unter der Voraussetzung, dass eine Grünlandnutzung möglich sein soll, ergibt sich ein einzuhaltender mittlerer Grundwasserflurabstand von 30 cm. Bei diesem Grundwasserflurabstand erreicht man etwa 90 % des optimalen Ertrags. Die Torfmineralisation kann dabei auf 30 bis 40 % der maximalen Torfmineralisation herabgesetzt werden. Die Gasemission liegt bei 50—60 % des maximalen Wertes.
Abstract The presence of a crack in a blade can change the natural frequencies of that blade. It has long been a goal to detect blade cracks by assessing the change in a measured vibration frequency of the blade over time. It has been found that prior frequency assessment methods can be less accurate than is desirable to reliably detect the relatively small frequency changes that are typically associated with blade crack sizes of practical interest. This paper describes a method in which potential temporal changes in the frequencies of individual blades are assessed by periodically analyzing complete rows of blades using mistuning analysis techniques that treat the blade rows as coupled systems, in contrast to other techniques that consider each blade individually in turn. This method, while computationally complicated and challenging, has been found to be capable of detecting blade root cracks that are much smaller than those that can be detected using other techniques. Moreover, this method has been demonstrated to detect cracks that are much smaller than the critical size for mechanical separation of the blade from the rotor. This improved frequency assessment technique has been used to identify more than 30 blades with frequency changes that were considered to be potential indicators of blade cracks. Subsequent inspections verified indications in all of those blades. In addition to providing operational guidance, the frequency change data were used to infer the time periods during which crack growth had occurred.
Abstract Sustainable agricultural land use requires an assessment of degradable soil organic matter (SOM) because of its key function for soil fertility and plant nutrition. Such an assessment for practical land use should consider transformation processes of SOM and its sources of different origin. In this study, we combined a 120‐day incubation experiment with thermal decay dynamics of agricultural soils altered by added organic amendments. The aim was to determine the abilities and limits of thermal analysis as a rapid approach revealing differences in the degradability of SOM. The carried out experiments based on two independent sampling sets. The first sample set consisted of soil samples taken from non‐fertilized plots of three German long‐term agricultural field experiments (LTAEs), then artificially mixed with straw, farmyard manure, sheep faeces, and charcoal equal to 60 Mg ha −1 under laboratory conditions. The second sample set based on soil samples of different treatments ( e.g ., crop type, fertilization, cultivation) in LTAEs at Bad Lauchstädt and Müncheberg, Germany. Before and after the incubation experiment, thermal mass losses (TML) at selected temperatures were determined by thermogravimetry indicating the degradability of organic amendments mixed in soils. The results confirmed different microbial degradability of organic amendments and SOM under laboratory conditions. Thermal decay dynamics revealed incubation‐induced changes in the artificial soil mixtures primarily at TML around 300°C in the case of applied straw and sheep faeces, whereas farmyard manure showed mainly changes in TML around 450°C. Charcoal did not show significant degradation during incubation, which was confirmed by TML. Detailed analyses of the artificial soil mixtures revealed close correlations between CO 2 ‐C evolution during incubation and changes in TML at 300°C with R 2 > 0.96. Results of the soils from LTAEs showed similar incubation‐induced changes in thermal decay dynamics for fresh plant residues and farmyard manure. We conclude that the practical assessment of SOM could be facilitated by thermal decay dynamics if modified sample preparation and evaluation algorithms are used beyond traditional peak analysis.
It is well known that the vibrational behavior of a mistuned bladed disk differs strongly from that of a tuned bladed disk. A large number of publications dealing with the dynamics of mistuned bladed disks are available in the literature. The vibrational phenomena analyzed in these publications are either forced vibrations or self-excited flutter vibrations. Nearly, all published literature on the forced vibrations of mistuned blades disks considers harmonic, i.e., steady-state, vibrations, whereas the self-excited flutter vibrations are analyzed by the evaluation of the margin against instabilities by means of a modal, or rather than eigenvalue, analysis. The transient forced response of mistuned bladed disk is not analyzed in detail so far. In this paper, a computationally efficient mechanical model of a mistuned bladed disk to compute the transient forced response is presented. This model is based on the well-known fundamental model of mistuning (FMM). With this model, the statistics of the transient forced response of a mistuned bladed disk is analyzed and compared to the results of harmonic forced response analysis.
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