Beitrag zur Verbesserung der Reinigung von Abwasserkanälen

In Germany the cleaning of sewers takes place predominantly with the high pressure cleaning (jetting). Since the beginnings of the jetting 50 years ago the machine and instrument technique of this procedure was improved significantly. On the other hand operating strategies changed hardly until today. Nowadays, jetting is still applied according to the so called system cleaning in most cases. Starting from the initial reaches and ending at the waste water treatment plant this procedure cleans sewer systems gradually in cycles of months or years. A contemporary and area-wide removal of deposits is not possible with that discontinuously and punctually practiced cleaning method.An appreciable reduction or prevention of shocks of pollution load on storm water overflow discharge and waste water treatment in combined sewer systems caused of deposit cannot be achieved, since a reformation of deposit is probable within a few days or weeks by using the conventional cleaning procedure. Also unsoiled reaches are cleaned because neither control of cleaning performance nor an assessment of demand for attend measures is carried through in advance. In addition increasingly damage to fittings and channel walls are deplored due to high compression stresses as well as due to inappropriate application. A proper cleaning of sewer systems cannot be attained therefore with the form of the jetting practiced today any more. On purpose of an effective water pollution control and for the improvement of the operational situation therefore the anyway high financial expenses for sewer cleaning are either to be increased and/or changes of the cleaning strategies and/or the choice of cleaning methods are necessary.In context of the available thesis it was therefore examined whether an improvement of the current situation can be achieved by sewer flushing which is common for a long time and was enhanced during the last years. Following extensive laboratory experiments, field studies and mathematical-numerical simulations were accomplished. The laboratory experiments showed that also small flushing waves cause a significant resuspension of settled particles and can therefore be used successfully in the framework of flushing measures. The results of the field studies clarify that flushing devices can cause both a basic and a preventive cleaning of sewers within certain boundary conditions. Varying hydraulic and structural boundary conditions cleaning performance of flushing waves was determined by one-dimensional flow models. The average bottom shear-stress served as criterion for the determination of flushing lengths. Basing on the results of these investigations a planning procedure for the flushing was developed. It permits a problem-specific planning of flushing measures for successful cleaning of sewers on a long term basis. The economic advantages of the flushing in relation to the jetting became apparent in context of a consideration of costs including the different cleaning qualities of the two methods.Today the flushing is an alternative for cleaning of sewers and sewer systems. Sewers can be kept in durably deposit-free, lasting improvements on water pollution control as well as on operation and maintenance of sewers and treatment plants can be obtained by a quasi-continuous application of flushing devices

Beitrag zur Verbesserung der Reinigung von Abwasserkanälen

In Germany the cleaning of sewers takes place predominantly with the high pressure cleaning (jetting). Since the beginnings of the jetting 50 years ago the machine and instrument technique of this procedure was improved significantly. On the other hand operating strategies changed hardly until today. Nowadays, jetting is still applied according to the so called system cleaning in most cases. Starting from the initial reaches and ending at the waste water treatment plant this procedure cleans sewer systems gradually in cycles of months or years. A contemporary and area-wide removal of deposits is not possible with that discontinuously and punctually practiced cleaning method.An appreciable reduction or prevention of shocks of pollution load on storm water overflow discharge and waste water treatment in combined sewer systems caused of deposit cannot be achieved, since a reformation of deposit is probable within a few days or weeks by using the conventional cleaning procedure. Also unsoiled reaches are cleaned because neither control of cleaning performance nor an assessment of demand for attend measures is carried through in advance. In addition increasingly damage to fittings and channel walls are deplored due to high compression stresses as well as due to inappropriate application. A proper cleaning of sewer systems cannot be attained therefore with the form of the jetting practiced today any more. On purpose of an effective water pollution control and for the improvement of the operational situation therefore the anyway high financial expenses for sewer cleaning are either to be increased and/or changes of the cleaning strategies and/or the choice of cleaning methods are necessary.In context of the available thesis it was therefore examined whether an improvement of the current situation can be achieved by sewer flushing which is common for a long time and was enhanced during the last years. Following extensive laboratory experiments, field studies and mathematical-numerical simulations were accomplished. The laboratory experiments showed that also small flushing waves cause a significant resuspension of settled particles and can therefore be used successfully in the framework of flushing measures. The results of the field studies clarify that flushing devices can cause both a basic and a preventive cleaning of sewers within certain boundary conditions. Varying hydraulic and structural boundary conditions cleaning performance of flushing waves was determined by one-dimensional flow models. The average bottom shear-stress served as criterion for the determination of flushing lengths. Basing on the results of these investigations a planning procedure for the flushing was developed. It permits a problem-specific planning of flushing measures for successful cleaning of sewers on a long term basis. The economic advantages of the flushing in relation to the jetting became apparent in context of a consideration of costs including the different cleaning qualities of the two methods.Today the flushing is an alternative for cleaning of sewers and sewer systems. Sewers can be kept in durably deposit-free, lasting improvements on water pollution control as well as on operation and maintenance of sewers and treatment plants can be obtained by a quasi-continuous application of flushing devices

Statische und dynamische Homogenisierungsanalysen diskreter granularer und atomistischer Strukturen auf verschiedenen Zeit- und Längenskalen

This work deals with scale bridging methods for discrete microscopic granular and nanoscopic atomistic aggregates of particles between different length and time scales. The bridging between the scales is achieved by direct homogenization of micro- and nanoscopic physical quantities. In the first part of the work, static homogenization techniques for granular materials are developed where a distinct definition of a granular microstructure serves as the starting point for the development of homogenization definitions. Three new boundary constraints are consistently derived from classical continuous definitions and implemented in a strain-driven environment. The finite-sized character of the particles is accounted for in the formulation. With regard to stiffness, it is shown that the periodic surface constraints are bounded by the linear deformation- and uniform traction constraints. Additionally, true dual-scale analyses of granular structures at large strains are performed. The continuum approach on the coarse scale employs the finite element method which serves as a numerical tool without any constitutive assumptions as the physical input is solely governed by the granular microstructures. The second part of the work covers dynamic homogenization techniques in connection with the classical molecular dynamics method for atomistic simulations. A uniform traction constraint is developed and it is shown that this formulation is the only suitable choice as it allows for a computational modeling of defects and cracks in a nanosystem. The constraint is implemented in a deformation-controlled environment allowing for computational treatments in coarse scale continuum methods. The dynamic homogenization incorporates the kinetics of all atoms in the aggregate. Several numerical examples in all sections of the thesis round off the discussion of the static and dynamic homogenization techniques for discrete structures.In der vorliegenden Arbeit werden Methoden für Skalenübergänge für diskrete mikroskopisch-granulare sowie nanoskopisch-atomistische Partikelaggregate zwischen verschiedenen Längen- und Zeitskalen entwickelt. Im ersten Teil werden zunächst statische Homogenisierungsmethoden für granulare Materialien behandelt. Beruhend auf einer eindeutigen Definition einer granularen Mikrostruktur werden Formulierungen für drei neue Randbedingungen entwickelt. Die drei diskreten Randbedingungen werden, auf klassischen Kontinuumsformulierungen basierend, konsistent hergeleitet, wobei der diskrete Charakter der Partikel besonders berücksichtigt wird. Es wird gezeigt, dass die Steifigkeit bei periodischen Randbedingungen durch die zwei weiteren Bedingungen beschränkt ist. Zusätzlich werden Mehrskalenanalysen granularer Materialen bei großen Deformationen gezeigt, bei denen die Simulationen auf zwei Skalen simultan durchgeführt werden. Auf der großen Skale wird die Finite-Elemente-Methode als numerisches Werkzeug verwendet. Dabei liefern die granularen Mikrostrukturen den physikalisch-konstitutiven Input. Im zweiten Teil der Arbeit werden dynamische Homogenisierungsmethoden im Rahmen der klassischen Molekulardynamik für atomistische Simulationen diskutiert. Es wird eine diskrete Spannungsrandbedingung entwickelt, mit der Defekt- und Rissbildungen in Nanostrukturen simuliert werden können. Die dynamische Homogenisierung schließt die Kinetik aller Atome im System mit ein. Im Hinblick auf die Nutzung mit Kontinuumsmethoden wird die Einbettung der Randbedingung in deformationsgesteuerte Umgebungen betrachtet. Zahlreiche numerische Beispiele runden die Diskussion statischer und dynamischer Homogenisierungstechniken für diskrete Strukturen ab