Dieter Dinkler

Modelling of the biodegradation of organic matter in municipal landfills

A model is presented to simulate the biodegradation of easily and slowly hydrolyzable organic matter, as well as the generation of biogas and heat release. The model is based on fundamental relationships among physical/ chemical, thermodynamical and microbial processes occurring in municipal landfills. Local, microbially-mediated degradation processes occurring in municipal landfills, are simulated in terms of the hydrolysis of solid organic matter, the formation of glucose and acetate as intermediary carbon substrates and the generation of the biogases CH4 and CO2. Thus, the overall decomposition of the organic matter has been assumed to follow four sequential biochemical reactions: hydrolysis, acidogenesis, acetogenesis and methanogenesis. In order to study the impact of environmental factors on the biological decomposition processes, pH, temperature and hydrogen changes have been integrated into the degradation model as inhibition terms.

Distorted yield surfaces – modelling by higher order anisotropic hardening tensors

Abstract Most of the constitutive models for metallic materials assume yield functions of von Mises or generalized Tsai–Wu type. Isotropic and/or kinematic evolutions are developed for hardening, which correspond to affin expansions or simple shifting of original yield surfaces, whereas experimental results show a distinctive change of the shape of yield surfaces (rotated or dented) depending on loading conditions and load paths. To cover the material behaviour with distorted yield surfaces a hierarchical expansion of yield functions to hardening tensors of the fourth and the sixth order is proposed. Parameters of corresponding evolutionary equations are determined by model parameter optimization. The extended model is investigated comparing numerical results to cyclic experimental data in biaxial σ – τ space.

An energy perturbation applied to nonlinear structural analysis

Abstract A perturbation strategy is outlined, which enables systematic calculation of secondary solution paths in the nonlinear solution manifold of thin-walled imperfection-sensitive structures. The strategy consists of three steps. First, the perturbation pattern is determined, second its critical amplitude is calculated to reach a secondary path and third the iteration to the secondary path itself is performed. The steps are formulated by means of constraints in the solution space. Examples are given for application to arches, plate strips and shells.

Numerical modelling of multiphase flow and transport processes in landfills.

Waste material in municipal landfills can be described as heterogeneous porous media, where flow and transport processes of gases and liquids are combined with local material degradation. This paper deals with the basic formulation of a multiphase flow and transport model applicable to the numerical analysis of coupled transport and reaction processes inside landfills. The transport model treats landfills within the framework of continuum mechanics, where flow and transport processes are described on a macroscopic level. The composition of organic and inorganic matter in the solid phase and its degradation are modelled on a microscopic scale. The degradation model captures the different reaction schemes of various microbial activities. Subsequently, transport and reaction processes have to be coupled, since emissions at the surface and from the drainage layer depend on the flow of leachate and gas, the transport of various substances and heat, and the biodegradation of organic matter. The theoretical considerations presented here are fundamental to the development of numerical models for the simulation of multiphase flow and transport processes inside landfills coupled with biochemical reactions and heat generation. The implicit modelling of leachate and gas flows including growth and decay of micro-organisms are innovative contributions to landfill modelling

Micromechanically based continuum damage mechanics material laws for fiber-reinforced ceramics

Abstract A micromechanically based continuum damage mechanics material law is developed for fiber-reinforced ceramics. Its parameters and internal variables are obtained from micromechanical models rather than from macroscopic experiments. Micromechanical models are derived for the damage and failure mechanisms observed in 2D C/C–SiC composite samples loaded by tension, shear and compression. In specimens subjected to tension, the early stage of damage is characterized by transverse cracking. Further load increase induces fiber failure in the longitudinal plies, what leads to fracture. Shear loading initiates cracks oriented at 0°/90° and 45° to the fiber axes, the latter causing fracture. Specimens loaded in compression exhibit catastrophic failure due to microbuckling of fiber bundles. Simulation results show the ability of the developed model to describe the observed failure mechanism in experiments.

Space-Time Finite Elements for Fluid-Structure Interaction

A numerical method for the analysis of fluid-structure interaction in the areas of building aeroelasticity and building-water interaction is presented. In order to achieve optimal convergence of the solution a consistent space-time discretization and a strong coupling algorithm is applied to the highly nonlinear problem.

Eine Methode zur direkten Berechnung von Gleichgewichtslagen im Nachbeulbereich

ÜbersichtEs wird eine Methode vorgeschlagen, mit der durch Auffassung des Beulens als quasi viskosen Prozeß Gleichgewichtszustände im Nachbeulbereich ohne inkrementelles Vorgehen und unbeeinträchtigt von Durchschlags- oder Verzweigungspunkten berechnet werden können. Für die Anwendung auf Platten und Zylinderschalen werden Beispiele gegebenSummaryThe common incremental procedure is replaced by a quasi viscous method, which allows stable equilibrium states in the post buckling range to be found unaffected by limit points or bifurcations of the solution path. Examples are given for the buckling of plates and shells.ZusammenfassungDas Verfahren der quasi viskosen Dämpfung ermöglicht die direkte Berechnung von Gleichgewichtszuständen im Vor- und Nachbeulbereich von elastischen Konstruktionen.Der Berechnungsprozeß wird von örtlichen Durchschlags- oder Verzweigungspunkten nicht beeinträchtigt. Bei entsprechender Wahl der Dämpfung kann auf das schrittweise Aufbringen der Last, wie in inkrementellen Verfahren üblich, verzichtet werden.

Damage Detection with Piezoceramic Actuators in Thin Steel Structures

This paper deals with an online structural health monitoring (SHM) concept, which enables the detection of damages of structures in civil engineering. Piezoceramic elements are integrated into thin steel plates as actuators and sensors. They excite the structure and measure the dynamic system response. The presented data analysis concept is based on methods of system identification. The model-updating algorithm adapts the finite element model to the measuring data using an output residual, which is minimized using a least-squares method. The application of special indicators enables the localization and quantification of changes in structural behavior.

Investigation of Aeroelastic Effects of a Circulation Controlled Wing

The aeroelastic behavior of the wing of a 100-passenger aircraft under investigation in the Coordinated Research Center SFB 880 is studied. A compressed air jet upstream of the high-lift devices called the Coandă jet enables boundary layer control with delayed flow separation and consequently high lift. Aeroelastic instabilities caused by boundary layer control systems are critical to the aircraft performance. The understanding of cause and effect of these instabilities is of great importance. For analyses, a multilevel approach is pursued using full-scale three-dimensional models and reduced-order models. Both model types use fluid-structure interaction techniques. The full-scale models are used to generate a sized wing structure with realistic mass and stiffness distributions using computational fluid dynamics loads of cruise and landing configuration load cases. A reduced-order model is derived by modal reduction for computationally efficient investigations of multiple flight states. To study local aer...

EVALUATION OF THE PERTURBATION SENSITIVITY OF COMPOSITE LAMINATED SHELLS

Imperfection sensitivity and its influence on the limit loads of shells are widely discussed phenomena. Both phenomena may be classified with respect to the type of imperfection, which may be generalized to a perturbation. As perturbations influence the stability of shells, the identification of unfavorable perturbations is essential for the design of shells. The perturbation energy concept enables one to identify unfavorable perturbations of different kinds and to evaluate the sensitivity of fundamental states against buckling by the perturbation energy. This paper discusses the perturbation sensitivity of unstiffened composite laminated cylindrical shells consisting of unidirectional layers. Moreover, an approach for a load-level-specific modification of the perturbation sensitivity is introduced.