Cavitation Inception in Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves

Cavitation Inception in Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under non-cavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to non-cavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves

Entwicklung und Etablierung eines Benchmarking zur Optimierung des heimischen Bio-Kartoffelbaues

Zusammenfassung Während die Nachfrage nach ökologisch erzeugten Nahrungsmitteln stetig zunimmt, erwartet der Verbraucher zusehends mehr innere, äußere und sensorische Qualität sowie produktionsspezifische Prozessqualität. Speziell die ökologische Kartoffelproduktion bedarf eines Qualitätsmanagementsystems, welches die Landwirte bei der Erreichung einer ganzen Reihe von Qualitätsparametern unterstützt. Das Kartoffel-Qualitätsmanagement (QM) wurde entwickelt, um dieses Ziel durch direkt aus der Praxis gewonnene Daten zu erreichen. So werden jährlich von allen beteiligten Landwirten Kartoffelproben bonitiert und die Produktionsdaten detailliert dokumentiert. Einmal jährlich besucht der Kartoffelbauberater die Landwirte für ein "Audit", welches für die korrekte Datenerfassung und die gemeinsame Reflexion der aktuellen Anbauperiode wichtig ist. Alle Daten werden in einer Internetdatenbank verwaltet, auf welche jeder beteiligte Landwirt mit einem eigenen “Account“ zugreifen kann. Im Auswertungsteil des Programms kann der Landwirt eigene Qualitätsdaten mit den anonymisierten Daten aller Teilnehmer vergleichen. Somit kann er Stärken und Schwächen seiner eigenen Produktionsmethodik herausarbeiten. Zusätzlich werden die gesamten Daten durch die Fachberatung analysiert und wichtige Ergebnisse an die Landwirte weitergereicht. Erste Auswertungen zeigten, dass interessante Zusammenhänge zwischen bestimmten Produktionsdaten und Qualitätsergebnissen bereits bei einem kleinen Datenumfang abgeleitet werden können. Es ist anzunehmen, dass Aussagekraft und Repräsentativität dieser Ergebnisse mit wachsendem Datenumfang zunehmen

The Sensitivity of the Southwest Monsoon Phytoplankton Bloom to Variations in Aeolian Iron Deposition over the Arabian Sea

[1] A coupled, 3-D biophysical ocean general circulation model is used to investigate how aeolian iron deposition affects the Arabian Sea ecosystem. Two separate aeolian iron deposition fields, derived from the GISS and GOCART atmospheric transport models, have been applied as surface boundary conditions. The model results exhibit widespread biogeochemical sensitivity to the choice of deposition field. With GOCART deposition, SW Monsoon phytoplankton blooms in the western and central Arabian Sea are enhanced and exhibit greater realism. The central Arabian Sea bloom is supported by supplemental input of horizontally advected iron from a pool that undergoes a yearlong progression that begins in the Gulf of Oman, where the difference in aeolian iron enrichment between the two deposition fields is most prevalent. The GOCART-enhanced blooms result in a more pronounced shift toward netplankton, an increase in euphotic zone export flux of up to a 20% during the SW Monsoon and an additional annual biogenic export of 3.5 TgC. The potential ramifications of regional N-cycle alteration through stimulation of N2-fixation that is promoted by significant aeolian mineral flux needs to be explored. The canonical thinking that the northern Arabian Sea is invariably iron replete is now being challenged by both our model results and recent observational studies. As well, our results indicate that Arabian Sea iron concentrations are strongly modulated by the specific nature of aeolian mineral deposition. Thus climate or land use influences on dust mobilization could exercise leading-order controls on regional biogeochemical variability, metabolic status and air-sea exchanges of CO2

Safe Connectivity Maintenance in Underactuated Multi-Agent Networks for Dynamic Oceanic Environments

Autonomous Multi-Agent Systems are increasingly being deployed in environments where winds and ocean currents can exert a significant influence on their dynamics. Recent work has developed powerful control policies for single agents that can leverage flows to achieve their objectives in dynamic environments. However, in the context of multi-agent systems, these flows can cause agents to collide or drift apart and lose direct inter-agent communications, especially when agents have low propulsion capabilities. To address these challenges, we propose a Hierarchical Multi-Agent Control approach that allows arbitrary single agent performance policies that are unaware of other agents to be used in multi-agent systems, while ensuring safe operation. We first develop a safety controller solely dedicated to avoiding collisions and maintaining inter-agent communication. Subsequently, we design a low-interference safe interaction (LISIC) policy that trades-off the performance policy and the safety controller to ensure safe and optimal operation. Specifically, when the agents are at an appropriate distance, LISIC prioritizes the performance policy, while smoothly increasing the safety controller when necessary. We prove that under mild assumptions on the flows experienced by the agents our approach can guarantee safety. Additionally, we demonstrate the effectiveness of our method in realistic settings through an extensive empirical analysis with underactuated Autonomous Surface Vehicles (ASV) operating in dynamical ocean currents where the assumptions do not always hold.Comment: 8 pages, submitted to 2023 IEEE 62th Annual Conference on Decision and Control (CDC) Nicolas Hoischen and Marius Wiggert contributed equally to this wor

The social construction of human-robot co-work by means of prototype work settings

Whether we look at Europe, the USA or Japan, in many areas in the world new possibilities of employing robotic systems in work settings essentially rely on direct collaborative interaction be-tween human workers and collaborative robots leading to new distributions of agency between them and making available robotic operations as resources for performing different forms of work, work which otherwise would remain out of reach for robotic automation for the time being. In this paper we introduce our concepts of studying the social construction of these collaborative work settings and the distribution of agency, accordingly. Referring to the basic idea of actor-network theory that technology in use should be analysed in a symmetrical manner, treating all the human and nonhuman entities involved as actors, our concept of distributed agency goes beyond actor-network theory in that it introduces the notion of gradualised action, which allows distinguishing between different levels of distributed agency. Therefore, we can precisely describe, in which way and to what extent activities and actor positions are delegated to robot co-workers or remain with its human counterpart. For analysing how the distribution of agency between human and robot co-workers is socially constructed in different stages, first in laboratory settings and then in increas-ingly realistic real-world settings, we interpret the spectrum of manifestations of human-robot col-laboration as prototypically realised scenarios at different stages of elaboration. In doing so we introduce the current state of collaborative robots in the areas of industrial production and care work as they represent contrastive cases: In industrial production collaborative robots are the next step in a long-standing history of robotic automation whereas in care work the new robots are also the first robots to be employed there. We believe that in both fields a perspective on collaborative work between humans and robots as a socio-technical constellation is helpful in order to be able to identify new distributions of work tasks

A Modelling Study of Developmental Stage and Environmental Variability Effects on Copepod Foraging

We used a stochastic Lagrangian model to study how behaviour contributes to copepod grazing success. The model simulates distinct foraging behaviours of Clausocalanus furcatus, Paracalanus aculeatus, and Oithona plumifera. Three sets of simulations were performed to investigate the effects of (a) prey-size preference; (b) variation in prey-size spectra; and (c) turbulence intensity on these species’ grazing rates. The size preference simulations demonstrate that, compared with copepodites, mature females have cell ingestion rates that are an order of magnitude lower, while carbon uptake is reduced by 35%. A prey spectrum that is skewed towards cells ,\u3c6 μm promotes copepodite success because the basal metabolic needs of the adult females require a prey concentration of 850–1000 cells ml-1. Variations in turbulence intensity reveal distinct ecological niches, with stronger mixing favouring O. plumifera and stable conditions favouring C. furcatus. Differences in theoretically derived and simulated prey-encounter rates demonstrate that the hopping behaviour of O. plumifera provides an order of magnitude increase in prey encounter, whereas the feeding behaviour of C. furcatus can result in localized depletion of prey. These simulations highlight the importance of species-specific feeding behaviour in defining oceanic copepod distributions

Monsoon-driven biogeochemical processes in the Arabian Sea

Although it is nominally a tropical locale, the semiannual wind reversals associated with the Monsoon system of the Arabian Sea result annually in two distinct periods of elevated biological activity. While in both cases monsoonal forcing drives surface layer nutrient enrichment that supports increased rates of primary productivity, fundamentally different entrainment mechanisms are operating in summer (Southwest) and winter (Northeast) Monsoons. Moreover, the intervening intermonsoon periods, during which the region relaxes toward oligotrophic conditions more typical of tropical environments, provide a stark contrast to the dynamic biogeochemical activity of the monsoons. The resulting spatial and temporal variability is great and provides a significant challenge for ship-based surveys attempting to characterize the physical and biogeochemical environments of the region. This was especially true for expeditions in the pre-satellite era. Here, we present an overview of the dynamical response to seasonal monsoonal forcing and the characteristics of the physical environment that fundamentally drive regional biogeochemical variability. We then review past observations of the biological distributions that provided our initial insights into the pelagic system of the Arabian Sea. These evolved through the 1980s as additional methodologies, in particular the first synoptic ocean color distributions gathered by the Coastal Zone Color Scanner, became available. Through analyses of these observations and the first largescale physical–biogeochemical modeling attempts, a pre-JGOFS understanding of the Arabian Sea emerged. During the 1990s, the in situ and remotely sensed observational databases were significantly extended by regional JGOFS activities and the onset of Sea-viewing Wide Field-of-View Sensor ocean color measurements. Analyses of these new data and coupled physical–biogeochemical models have already advanced our understanding and have led to either an amplification or revision of the pre-JGOFS paradigms. Our understanding of this complex and variable ocean region is still evolving. Nonetheless, we have a much better understanding of time–space variability of biogeochemical properties in the Arabian Sea and much deeper insights about the physical and biological factors that drive them, as well as a number of challenging new directions to pursue