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Publication Type: search.filters.UBSTyp.KonferenzbeitragInstitute: search.filters.UBSInstitut.Institut für Wasser- und UmweltsystemmodellierungSubject: search.filters.subject.333.7Start date: 1984End date: 1989

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Now showing 1 - 8 of 8
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    Effects of model configuration, flow conditions and scale in modelling spillway aeration grooves
    (1984) Koschitzky, Hans-Peter; Westrich, Bernhard; Kobus, Helmut
    The hydraulic design of spillways, with high specific discharge usually requires model investigations. Whereas standard small-scale models are sufficient for the assessment of the general flow pattern, studies on cavitation control by means of aeration have to be conducted in detail models at considerably larger scales. Detail models of aeration grooves are studied in order to optimize the geometry and to determine the air entrainment of the grooves. The large model scale necessitates the use of models which represents only a small fraction of the width and length of the spillway. Such sectional models allow only an investigation of a single aeration groove in a given approach flow. This paper presents a hydraulic model study of the spillway of Laiban Dam on the Philippines, which is part of the Manila Water Supply Project III.
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    Hydraulics and design of spillway aerators for cavitation prevention in high speed flows
    (1988) Koschitzky, Hans-Peter; Kobus, Helmut
    The controlling factors for spillway aeration are discussed in view of their relevance to the design of aerators. The air entrainment results from the interaction of the water flow and the air flow in the supply system. An empirical two dimensional air entrainment function for various aerator geometries is presented. The subatmospheric pressure distribution in the aerator is calculated by an iterative method. The combination of both yields the total air entrainment rate. The air entrainment leads to an increase of the water flow velocity.
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    Mass transport in an artificial heterogeneous aquifer : experiments and numerical modelling
    (1989) Schäfer, Gerhard; Kobus, Helmut
    In order to generate a data base for the numerical study of dispersion processes in a well defined heterogeneous porous medium, a laboratory tank of 14 m in length, 0,5 m in height and 0.13 m in width has been constructed, which is composed of 81 different elements of exactly known geometry and hydraulic properties. In dispersion experiments using salt as tracer, breakthrough curves are observed at 80 points in 8 vertical sections. A comparison of three types of numerical models with the experimental data shows how well the models of various complexity describe the advection and dispersion processes and how in these cases the various dispersion parameters depend upon the models used.
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    Nitrat und Biozide im Grundwasser und Konsequenzen für die Trinkwassergewinnung
    (1986) Kobus, Helmut
    Die Bedrohung des Umweltguts Wasser durch die steigenden Belastungen aus der Landwirtschaft stellt eine unmittelbare Gefahr für die Trinkwasserversorgung und langfristig auch für die Qualität unserer Oberflächengewässer dar. Weil Grundwasserschäden Langzeitschäden sind, ist der Grundwasserschutz zum Testfall für die konsequente Anwendung des Vorsorgeprinzips geworden. Die langfristige Sicherung einer qualitativ hochwertigen Trinkwasserversorgung auch für die nächste Generation erfordert gezielte Bemühungen aller Beteiligten - Staat und Gesellschaft, Landwirtschaft, Wasserversorgung, Industrie und Wissenschaft- in der gemeinsamen Verantwortung für die Erhaltung unserer natürlichen Lebensgrundlagen.
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    Das "PWAB-Testfeld Wasser und Boden"
    (1988) Kobus, Helmut
    Der Gedanke, ein Naturmeßfeld für die Boden- und Grundwasserforschung einzurichten, entstand im Jahr 1986 im Projektrat des PWAB. Einerseits kann anwendungsorientierte Forschung nicht auf den gezielten Feldversuch verzichten, welcher die Grundlagenforschung im Labor und am Computer ergänzt und verifiziert; andererseits sind Naturmessungen stets sehr aufwendig und dadurch geprägt, daß stets nur ein Bruchteil der zahlreichen Einflußgrößen und Randbedingungen meßtechnisch erfaßt und berücksichtigt werden kann. Dies legte den Gedanken nahe, die Forschungsinteressen der verschiedenen Disziplinen zu bündeln und ein geeignetes Naturmeßfeld ausfindig zu machen, in dem an ein und demselben Standort unterschiedliche Forschungsvorhaben in gegenseitiger Abstimmung und Ergänzung durchgeführt werden können.
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    Transverse mixing of stratified flows in porous media
    (1985) Kobus, Helmut; Spitz, Karlheinz
    The paper describes a systematic experimental and numerical investigation which explores the transverse vertical mixing across an initially sharp density interface between water containing salt (or high contaminant concentration) and fresh water in a porous medium under nearly horizontal flow conditions. The transversal spreading tendency due to the pore matrix is decreasing with increasing density difference due to gravity action. For a sand of uniform grain size and for a sand with a pronounced grain size distribution, systematic experiments and numerical calculations have been carried out in order to quantify the effects of density differences upon the transverse dispersion coefficient. It was found that in a uniform sand the mixing characteristics are essentially unaffected, whereas the sand mixture exhibits a significant density effect. From an analysis, an approximate relationship for the dispersion coefficient has been derived. The results indicate that density effects on transverse dispersion may be even more pronounced in natural aquifers with smaller velocities and larger inhomogeneities.
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    Research on groundwater flow and transport problems at the Universität Stuttgart
    (1989) Kobus, Helmut
    The groundwater research activities at the Institut für Wasserbau of the Universität Stuttgart are described. Numerical methods as well as laboratory and field measurements are used for the development of transport models and exploration techniques and their applications to problems of groundwater protection.
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    Local air entrainment and detrainment
    (1984) Kobus, Helmut
    Air and water are usually well separated by gravity due to their extreme difference in specific weight. Whenever they are mixed, however, they give rise to a very complex two-phase flow situation. The hydraulic engineer is often faced with the problem of estimating the effects of entrained air upon the flow, because this may be essential for the safe operation of a hydraulic structure.The predominant mechanism in generating airwater mixtures is the inclusion of air at the surface of flowing water. The mechanics of free-surface flow may lead to ambient surface aeration in high-speed flows, or - even at moderate flow velocities - to flow configurations with localized air entrainment, which includes inadvertent self-aeration as well as such specific flow systems in which surface aeration is forced.