Reinhard Hinkelmann

Numerische Modellrechnungen zur Darß-Zingster Boddenkette

Die Dars-Zingster Boddenkette ist ein sehr flaches deutsches Astuar mit einer schmalen Verbindung zur Ostsee. Im Rahmen der hydrodynamisch-numerischen Modellierungen wurde ein zweidimensionales, tiefengemitteltes Modell fur die Simulation von Wasserstanden, Stromungen und Salztransportporzessen entwickelt und anhand von speziell durchgefuhrten Naturmessungen und amtlichen Pegelregistrierungen verifiziert. Das HN-Modell zeigt gute Ubereinstimmungen zwischen gemessenen und numerisch berechneten Wasserstands- und Salzgehaltsverteilungen. Bei der Reproduktion der sehr unregelmasigen Stromungsmuster sind einige offene Fragen verblieben. Das HN-Modell wurde danach fur zahlreiche ingenieurpraktische Fragestellungen eingesetzt, deren Schwerpunkte die Dimensionierung von Deichen, die Bestimmung von Wasserstandsanderungen infolge kunstlicher Verbindungen zur Ostsee und Auswirkungen von Fliesquerschnittserweiterungen an Engstellen bilden.

Water management and aquatic ecosystem services of a tropical reservoir (Itaparica, São Francisco, Brazil)

Reservoirs have a wide variety of uses that have led to frequent conflicts over ecological conservation and contamination, especially as land management has intensified. Oligotrophication must be implemented in numerous tropical reservoirs that experience advanced eutrophication to maintain aquatic ecosystem functions. To quantify impacts on ecosystem functions and to develop an adaptive management policy, multiple studies have been conducted on the Itaparica Reservoir, São Francisco River, in the semi-arid north-eastern region of Brazil. Here, we add to that existing body of knowledge through investigating how nutrient accumulation is affected by water exchange between the main river flow and Icó-Mandantes Bay. Operational water-level fluctuations in the reservoir create large desiccated littoral areas that release high amounts of nutrients when they are rewetted. In particular, water-level variation promotes proliferation of Egeria densa, a noxious weed, thus elevating trophic levels of the Itaparica Reservoir and Icó-Mandantes Bay. Analysis with a P efficiency model determined 25xa0μgxa0Pxa0L−1 to be the critical concentration and further indicated that the critical load in both bodies of water have been exceeded. Moreover, intensive fish aquaculture using net cages has led to further overtaxing of the reservoir. We conclude that an effective ecological reservoir management policy must involve oligotrophication, harvesting of noxious water weeds for use as soil amendment in agriculture or biogas production, “blue” aquaculture, and limiting hydroelectric power production based on current water availability.

Multiphase Modeling of Hydrosystems Using OpenFOAM

This paper presents three computational fluid dynamics applications regarding multiphase modeling of hydro systems with the open source software OpenFOAM. The first model investigates flow processes of groundwater and surface water using an integral approach which solves the three-dimensional Navier–Stokes equations, extended by the consideration of porosities. For the validation, seepages through homogeneous dams with impervious foundations were compared with analytical and numerical solutions. A further application examines the water–air interface in sewer systems.The focus of the model lies on the description of in-sewer water–air flow and transformation processes, reaeration and hydrogen sulfide emission which highly depend on the three-dimensionality of the hydraulic behavior in the closed duct. A test case analyzing the hydraulic behavior in a sewer stretch showed a good agreement of the numerical results with measured water levels. In the third model, fluid–structure interaction is investigated applying FOAM Extend Project. Calculations of the fluid phase are linked with the solid phase via a coupling algorithm to achieve an equilibrium state. To describe the time-varying position of the fluid boundary, caused by the structural response, dynamic meshes are considered. A technical case, consisting of the air flow around a thin tower as well as a natural case, describing the water flow around aquatic vegetation and its response, were examined.

A Parallel 2D Operator Splitting Method for the Navier-Stokes and Transport Equations

A 2D algorithm for free surface flow and salinity transport in coastal areas on a ‘multiple instruction multiple data’ (MIMD) parallel computer with 128 processors is presented. Operator splitting in the basic equations leads to a separated treatment of the hyperbolic and parabolic terms, which are then combined by coupling the Method of Characteristics with the Finite Element technique. Different iterative solvers based on conjugate gradient methods and different preconditioners are used for solving the two sets of linear equations. The data of the unstructured grids are distributed among the processors with Recursive Spectral Bisection in combination with the Kernighan-Lin heuristic. The performance of the implemented algorithm is demonstrated using a field case study of the German estuary ‘Dars-Zingster Boddenkette’.