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A new formulation for the prediction of free surface dynamics related to the turbulence occurring nearby is proposed. This formulation, altogether with a breakup criterion, can be used to compute the inception of self-aeration in high velocity flows like those occurring in hydraulic structures. Assuming a simple perturbation geometry, a kinematic and a non-linear momentum-based dynamic equation are formulated and forces acting on a control volume are approximated. Limiting steepness is proposed as an adequate breakup criterion. Role of the velocity fluctuations normal to the free surface is shown to be the main turbulence quantity related to self-aeration and the role of the scales contained in the turbulence spectrum are depicted. Surface tension force is integrated accounting for large displacements by using differential geometry for the curvature estimation. Gravity and pressure effects are also contemplated in the proposed formulation. The obtained equations can be numerically integrated for each wavelength, hence resulting in different growth rates and allowing computation of the free surface roughness wavelength distribution. Application to a prototype scale spillway (at the Aviemore dam) revealed that most unstable wavelength was close to the Taylor lengthscale. Amplitude distributions have been also obtained observing different scaling for perturbations stabilized by gravity or surface tension. The proposed theoretical framework represents a new conceptualization of self-aeration which explains the characteristic rough surface at the non-aerated region as well as other previous experimental observations which remained unresolved for several decades.
Vectrino profiler spatial filtering for shear flows based on the mean velocity gradient equation
(2018)
A new methodology is proposed to spatially filter acoustic Doppler velocimetry data from a Vectrino profiler based on the differential mean velocity equation. Lower and upper bounds are formulated in terms of physically based flow constraints. Practical implementation is discussed, and its application is tested against data gathered from an open-channel flow over a stepped macroroughness surface. The method has proven to detect outliers occurring all over the distance range sampled by the Vectrino profiler and has shown to remain applicable out of the region of validity of the velocity gradient equation. Finally, a statistical analysis suggests that physically obtained bounds are asymptotically representative.
Air-water flows can be found in different engineering applications: from nuclear engineering to huge hydraulic structures. In this paper, a single tip fibre optical probe has been used to record high frequency (over 1 MHz) phase functions at different locations of a stepped spillway. These phase functions have been related to the interfacial velocities by means of Artificial Neural Networks (ANN) and the measurements of a classical double tip conductivity probe. Special attention has been put to the input selection and the ANN dimensions. Finally, ANN have shown to be able to link the signal rising times and plateau shapes to the air-water interfacial velocity.
Sensitivity of turbulent Schmidt number and turbulence model to simulations of jets in crossflow
(2016)
Environmental discharges have been traditionally designed by means of cost-intensive and time-consuming experimental studies. Some extensively validated models based on an integral approach have been often employed for water quality problems, as recommended by USEPA (i.e.: CORMIX). In this study, FLOW-3D is employed for a full 3D RANS modelling of two turbulent jet-to-crossflow cases, including free surface jet impingement. Results are compared to both physical modelling and CORMIX to better assess model performance. Turbulence measurements have been collected for a better understanding of turbulent diffusion's parameter sensitivity. Although both studied models are generally able to reproduce jet trajectory, jet separation downstream of the impingement has been reproduced only by RANS modelling. Additionally, concentrations are better reproduced by FLOW-3D when the proper turbulent Schmidt number is used. This study provides a recommendation on the selection of the turbulence model and the turbulent Schmidt number for future outfall structures design studies.
Bauwirtschaft
(2024)
Die Leistungen der Bauwirtschaft und deren wirtschaftliche Bedeutung in Deutschland werden anhand einer Vielzahl statistischer Daten verdeutlicht. Die im Vergleich zu anderen Wirtschaftsbereichen auftretenden branchenspezifischen Besonderheiten der Bauwirtschaft werden anhand von verschiedenen Kriterien herausgearbeitet. Das Zusammenspiel der einzelnen Akteure des Sektors und die dabei sich ergebenden bzw. zu beachtenden Rechts- und Vertragsgrundlagen werden dargestellt. Aufgrund der meist erheblichen Höhe des eingesetzten Kapitals werden auch notwendige Formen der Risikoabsicherungen und der in der Branche üblichen und teilweise vorgeschriebenen Versicherungsmöglichkeiten angesprochen.
Boden, Baugrube, Verbau
(2016)
Die Lösung den Baugrund betreffender Fragestellungen beginnen i. d. R. mit der Durchführung von Baugrunderkundungen, um alle notwendigen Parameter zu erhalten, die für die Planung und Durchführung von Bauvorhaben notwendig sind. Im Folgenden werden die wichtigsten Erkundungen in Abhängigkeit der erforderlichen Güteklasse der Proben beschrieben und vorgestellt.
Der baurechtliche Vertrag
(2019)
Anhand von kurzen theoretischen Einführungen werden anhand von Beispielen die wesentlichen Aspekte des baurechtlichen Vertrages erläutert. Nach einer Einführung über das Zustandekommen von (Bau-) Verträgen wird die für Streitfälle unerlässliche Dokumentation auf Baustellen erläutert. Hierbei werden Hinweise zur Erstellung von Protokollen, zum E-Mail bei Großprojekten und zur Dokumentation von Stundenlohnarbeiten gegeben. Des Weiteren wird eine Schriftverkehrsliste vorgestellt, die zur Nachverfolgung des Schriftverkehrs bei Großprojekten unerlässlich ist.
Anschließend werden die typischen Vertragsarten vorgestellt, die bei der Abwicklung von Großprojekten zu beachten sind und die Unterschiede werden durch Fallbeispiele erläutert.
Einen Schwerpunkt des Kapitels bilden auftragsnehmerseitige Verzüge sowie mangelbehaftete Leistungen. Hier werden Hinweise gegeben, wie in den entsprechenden Situationen zu reagieren ist.