Gernot Boiger

Adaptive time stepping for explicit euler implementation of spherical and non-spherical particle speed up

Numerical implementation schemes of drag force effects on Lagrangian particles can lead to instabilities or inefficiencies if static particle time stepping is used. Despite well known disadvantages, the programming structure of the underlying, C++ based, Lagrangian particle solver led to the choice of an explicit EULER, temporal discretization scheme. To optimize the functionality of the EULER scheme, this paper proposes a method of adaptive time stepping, which adjusts the particle sub time step to the need of the individual particle. A user definable adjustment between numerical stability and calculation efficiency is sought and a simple time stepping rule is presented. Furthermore a method to quantify numerical instability is devised and the importance of the characteristic particle relaxation time as numerical parameter is underlined. All derivations are being conducted for (non-)spherical particles and finally for a generalized drag force implementation. Important differences in spherical and non-sph...

Part 2: LARGE PARTICLE MODELLING Simulation of particle filtration processes in deformable media

In filtration processes it is necessary to consider both, the interaction of the fluid with the solid parts as well as the effect of particles carried in the fluid and accumulated on the solid. While part 1 of this paper deals with the modelling of fluid structure interaction effects, the accumulation of dirt particles will be addressed in this paper. A closer look is taken on the implementation of a spherical, LAGRANGIAN particle model suitable for small and large particles. As dirt accumulates in the fluid stream, it interacts with the surrounding filter fibre structure and over time causes modifications of the filter characteristics. The calculation of particle force interaction effects is necessary for an adequate simulation of this situation. A detailed Discrete Phase Lagrange Model was developed to take into account the two-way coupling of the fluid and accumulated particles. The simulation of large particles and the fluid-structure interaction is realised in a single finite volume flow solver on th...

Part 1: Fluid-Structure Interaction Simulation of particle filtration processes in deformable media

In filtration processes it is necessary to consider both, the interaction of the fluid with the solid parts, as well as the effect of particles carried in the fluid and accumulated on the solid. In this first part a closer look is taken on the influence of the fluid on the solid regions. The required algorithm to couple the governing differential equations is derived on the basis of the equations, governing the solid and fluid regions. For discretization, only one single computational mesh is used and this is adjusted to the deformation at each time-step. The simulation of the fluid-structure interaction is realised in a single finite volume flow solver on the basis of the OpenSource software OpenFoam.

Characterization of Particle Motion and Deposition Behaviour in Electro-Static Fields

As a prerequisite for studying and ultimately improving the powder coating process, particle motion and deposition effects within flow- and electro-static fields need to be thoroughly understood and thus characterized. In this context, a range of dimensionless groups is proposed and new means of characterization are presented. Considering the impact of electro-static, fluid-dynamic and gravity forces on coating particle motion, a triangle chart notation to characterize the state of varying particle size classes, is introduced. Furthermore a derivation of the dimensionless particle momentum equation is shown to lead to a dimensionless chart, representing all possible process states of coating. In combination with a Eulerian-LaGrangian, numerical model, the new means of characterization have led to a far better, over all perspective of occurring phenomena and their causes. Some examples are demonstrated here.

System Dynamic modelling approach for resolving the thermo- chemistry of wood gasification

For Multiphysics problems that require a thorough understanding of multiple, influential, highly transient process parameters, a System Dynamic model can constitute either an alternative option, or a compact prelude to a more expensive 3-D Finite Element or Finite Volume model. As a rather uncommon example for the application of such a modelling method, this work presents a System Dynamic modelling concept, devised for resolving the thermo-chemistry within a wood gasification reactor. It compares the modelling concept as well as its results to a classic, thermo-chemical solution algorithm based on the minimization of LaGrangian Multipliers for resolving the gasification equilibrium equations. In contrast to the latter, the System Dynamic solver can consider the impact of reaction kinetics as well as molecular mass transfer effects on the gasification equilibrium. Thus the transient production rates of methane, hydrogen, carbon (di-) oxide and water, as well as the residual amounts of pyrolysis gas and oxygen, which occur during the gasification of a wood particle, can be predicted.

A thermo fluid dynamic model of wood particle gasification- and combustion processes

In order to qualitatively understand and evaluate the thermo- fluid dynamic situation within a wood gasification reactor, a 1D particle model has been created. The presented tool accounts for the highly in- stationary, kineticand thermo chemical effects, leading to partial gasification and combustion of a wood particle embedded within a packed bed collective. It considers the fluid- dynamic situation within the changing porous bulk structure of the packed bed, its impact on species- and heat transition mechanisms, the energy- and mass balances of wood, coal, pyrolysisgas, wood- gas and off- gas phases, the thermodynamics of locally developing gasification- and combustion reaction equilibria, as well as the presence of the chemical species hydrogen, water, carbon (di-) oxide, methane, oxygen, solid carbon and gaseous, longer chain hydrocarbons from pyrolysis. Model results can be shown to yield very good, qualitative agreement with measurements, found in literature.

Simulation of filtration processes in deformable media Part 3.1: Basic concepts and particle-fluid force implementation of a non-spherical dirt particle solver

A Lagrangian solver to realistically model large, non-spherical dirt particles and their behaviour in the vicinity of deformable filtration fibres has been programmed. While this paper focuses on basic solver concepts as well as drag force implementations, a related article, concerning the realisation of interaction effects and result verification, is forthcoming, [3].Within the framework of a digitally reconstructed, deformable filter fibre geometry, the solver traces the governing multi physics effects down to the occurrence of single force- and torque vectors. In order to go from an initial, spherical particle model [2], to a more sophisticated, non-spherical model, the capabilities of a Six Degrees of Freedom Solver have been included in the programming. A panel model and the concept of satellite help points are used to handle particles that encompass several fluid calculation cells.An innovative drag force implementation allows the consideration of rotational- and shear flow effects on particle motio...

Response of Armour Steel Plates to localised Air Blast Load – A Dimensional Analysis

We report on the results of dimensional analyses on the dynamic plastic response of square armour steel plates due to detonation of proximal cylindrical charges and ensued air blast loading. By assuming a generic function for the blast load, which is multiplicative comprising its spatial and temporal parts, a set of 14 dimensionless parameters, representative of the load and plate deformation, were identified and recast in the form of dimensionless functions of stand-off to charge diameter ratio. Parametric studies were performed using commercial code ABAQUS’s module of Finite Element hydrocode using MMALE and MMAE techniques, and combined with regression analyses to quantify the dimensional parameters and the expressions for dimensionless functions. A few numerical studies with various FE mesh types were also performed to validate the transient deflections against the small-scale experiments. For pulse loading due to proximal charges of small orders of stand-off/charge diameter ratio, the magnitude of the transverse deflection increased abruptly with incremental decrease in stand-off, in contradistinction to the plate deformations at higher stand-offs where variations in displacement are smooth. This confirmed the existence of a stand-off at which a transition in behaviour takes place. For stand-off values less than charge diameter, a dimensionless energy absorbing effectiveness factor was considered to investigate the prediction of rupture in the plate corresponding to different charge masses. This factor is measured as a baseline parameter to predict, using solely numerical means, the blast loads which ensue rupture on full-scale prototypes.

Multi-Parameter Improvement Method for (Micro-) Structural Properties of High Performance Ceramics

Many pH-measurement electrodes rely on porous diaphragms to create a liquid electrolyte junction between reference-electrolyte and the fluid to be measured. In field applications, the diaphragm is required to meet partly contradictory improvement criteria. To minimize measurement errors and to ensure durability of the measurement device, the diaphragm is supposed to maximize electrolyte conductivity and reference-electrolyte outflow velocity, while simultaneously minimizing reference electrolyte flow rate. The task of optimizing the overall performance of this small piece of ceramics has lead to the development of a novel multi-parameter improvement scheme for its (micro-) structural design. The method encompasses the consideration of microscopic material design parameters, such as porosity, poretortuosity and constrictivity, macroscopic material parameters such as diaphragm diameter and length, as well as process parameters like internal electrode pressure or the electrolyte viscosity and specific resistivity. Comprising sets of design parameters to dimensionless groups, concrete design guidelines as well as the introduction of a three-dimensional improvement space concept are proposed. The novel design space concept allows the improvement of each possible diaphragm-based measurement set-up, by considering the simultaneous, dimensionless interaction of all relevant design parameters.

Euler-Lagrangian Model of Particle Motion and Deposition Effects in Electro-Static Fields based on OpenFoam

In order to study the powder coating process of metal substrates, a comprehensive, numerical 3D Eulerian-LaGrangian model, featuring two particle sub-models, has been developed. The model considers the effects of electro-static, fluid-dynamic and gravity forces. The code has been implemented in C++ within the open source CFD platform OpenFoam®, is transient in nature with respect to the applied LaGrangian particle implementation and the electro-static field calculation and is stationary regarding fluid-dynamic phenomena. Qualitative validation of the developed solver has already been achieved by comparison to simple coating experiments and will hereby be presented alongside a thorough description of the model itself. Upon combining knowledge of the relevant dimensionless groups and the numerical model, a dimensionless chart, representing all possible states of coating, was populated with comprehensive, exemplary cases, which are shown here as well.