Markku Kataja

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Papers by Markku Kataja

Floc Rupture and Re-Flocculation in Turbulent Shear

Permeability and effective porosity of porous media

Physical Review E, 1997

The concept of permeability of porous media is discussed, and a modification of Kozeny's permeabi... more The concept of permeability of porous media is discussed, and a modification of Kozeny's permeability equation to include the effect of effective porosity is introduced. An analytical expression for the specific surface area of a system constructed of randomly placed identical obstacles with unrestricted overlap is derived, and a lattice-gas cellular automaton method is then used to simulate the dependence on porosity of permeability, tortuosity, and effective porosity for a flow of Newtonian uncompressible fluid in this twodimensional porous substance. The simulated permeabilities can well be explained by the concept of effective porosity, and the exact form of the specific surface area. The critical exponent of the permeability near the percolation threshold is also determined from the simulations.

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Tortuous flow in porous media

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996

The concept of tortuosity of fluid flow in porous media is discussed. A lattice-gas cellular auto... more The concept of tortuosity of fluid flow in porous media is discussed. A lattice-gas cellular automaton method is applied to solve the flow of a Newtonian uncompressible fluid in a two-dimensional porous substance constructed by randomly placed rectangles of equal size and with unrestricted overlap. A clear correlation between the average tortuosity of the flow paths and the porosity of

Simulations of Single-Fluid Flow in Porous Media

International Journal of Modern Physics C, 1998

Several results of lattice-gas and lattice-Boltzmann simulations of single-fluid flow in 2D and 3... more Several results of lattice-gas and lattice-Boltzmann simulations of single-fluid flow in 2D and 3D porous media are discussed. Simulation results for the tortuosity, effective porosity and permeability of a 2D random porous medium are reported. A modified Kozeny-Carman law is suggested, which includes the concept of effective porosity. This law is found to fit well the simulated 2D permeabilities. The results for fluid flow through large 3D random fibre webs are also presented. The simulated permeabilities of these webs are found to be in good agreement with experimental data. The simulations also confirm that, for this kind of materials, permeability depends exponentially on porosity over a large porosity range.

A method for measuring Darcian flow permeability of thin compressed fibre mats

Nordic Pulp and Paper Research Journal, 2009

ABSTRACT A method for measuring the Darcian permeability coefficient of thin samples of soft poro... more

Three dimensional hydrodynamics of ultrarelativistic heavy ion collisions

Zeitschrift für Physik C Particles and Fields, 1988

We have utilized a 2 + i dimensional numerical code based on Flux Corrected Transport method to f... more We have utilized a 2 + i dimensional numerical code based on Flux Corrected Transport method to find a solution for 3 + 1 dimensional cylindrically symmetric hydrodynamic flow of hadronic matter which is assumed to be formed in extremely high energy heavy ion collisions. The hydrodynamics is supplemented with a decoupling calculation in order to produce measurable particle distributions. This numerical procedure is applied here to Landau type initial conditions which have been fixed using a simple geometrical picture for a central O+Pb collision at 200 GeV/nucleon. The bag equation of state for nonbaryonic matter is used to simulate the deconfinement phase transition to quark gluon plasma. The resulting pseudorapidity distributions of transverse energy for the final massless pions are calculated.

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A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites

by Markku Kataja and Cris L Luengo Hendriks

Composites Science and Technology, 2012

An improved method based on X-ray microtomography is developed for estimating fibre length distri... more An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting the biasing effects caused by the finite sample size as defined by the limited field of view of the tomographic devices. The method is first tested for computer generated fibre data and then applied in analyzing the fibre length distribution in three different types of wood fibre reinforced composite materials. The results were compared with those obtained by an independent method based on manual registration of fibres in images from a light microscope. The method can be applied in quality control and in verifying the effects of processing parameters on the fibre length and on the relevant mechanical properties of short fibre composite materials, e.g. stiffness, strength and fracture toughness.

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Lattice-Boltzmann hydrodynamics on parallel systems

Computer Physics Communications, 1998

Realistic lattice-Boltzmann simulations often require large amounts of computational resources an... more Realistic lattice-Boltzmann simulations often require large amounts of computational resources and are therefore executed on parallel systems. Generally, parallelization is based on one-and two-dimensional decomposition of the computational grid in equal subvolumes, and load balancing is completely ignored for simplicity. Besides reviewing the existing parallelization strategies we report here a new approach based on the Orthogonal Recursive Bisection (ORB) method. To illustrate the different decomposition methods, two realistic applications were simulated, namely fluid flow in random fibre networks and flow in a centrifugal elutriation chamber. For heterogeneously distributed workloads, the ORB method is found to be 12 to 60% more efficient compared to traditional parallelization strategies. It is shown that high parallel efficiencies can be obtained for both homogeneously and heterogeneously distributed workloads, thus supporting efficient simulations of a variety of realistic systems.

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Implementation Aspects of 3D Lattice-BGK: Boundaries, Accuracy, and a New Fast Relaxation Method

Journal of Computational Physics, 1999

In many realistic fluid-dynamical simulations the specification of the boundary conditions, the e... more In many realistic fluid-dynamical simulations the specification of the boundary conditions, the error sources, and the number of time steps to reach a steady state are important practical considerations. In this paper we study these issues in the case of the lattice-BGK model. The objective is to present a comprehensive overview of some pitfalls and shortcomings of the lattice-BGK method and to introduce some new ideas useful in practical simulations. We begin with an evaluation of the widely used bounce-back boundary condition in staircase geometries by simulating flow in an inclined tube. It is shown that the bounce-back scheme is first-order accurate in space when the location of the non-slip wall is assumed to be at the boundary nodes. Moreover, for a specific inclination angle of 45 degrees, the scheme is found to be second-order accurate when the location of the non-slip velocity is fitted halfway between the last fluid nodes and the first solid nodes. The error as a function of the relaxation parameter is in that case qualitatively similar to that of flat walls. Next, a comparison of simulations of fluid flow by means of pressure boundaries and by means of body force is presented. A good agreement between these two boundary conditions has been found in the creeping-flow regime. For higher Reynolds numbers differences have been found that are probably caused by problems associated with the pressure boundaries. Furthermore, two widely used 3D models, namely D 3 Q 15 and D 3 Q 19 , are analysed. It is shown that the D 3 Q 15 model may induce artificial checkerboard invariants due to the connectivity of the lattice. Finally, a new iterative method, which significantly reduces the saturation time, is presented and validated on different benchmark problems.

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X-ray tomographic method for measuring three-dimensional deformation and water content distribution in swelling clays

by Markku Kataja and Jarno Alaraudanjoki

Applied Clay Science, 2015

ABSTRACT

X-ray micro-computed tomography investigation of agglomeration and fibre length degradation through the processing chain of wood fibre composite

by Markku Kataja and Thomas Joffre

Method for Controlling the Amount of Treating Agent in the Manufacture of a Paper or Board

Effect of refining on bleached and unbleached Kraft furnish rheology

by Markku Kataja and Pasi Raiskinmäki

ABSTRACT

Non-destructive automatic determination of aspect ratio and cross-sectional properties of fibres

by Markku Kataja and Lisa Wikström

Composites Part A: Applied Science and Manufacturing, 2015

ABSTRACT

Quantitative analysis of length-diameter distribution and cross-sectional properties of fibers from three-dimensional tomographic images

by Markku Kataja and Roberts Joffe

Measuring intrinsic thickness of rough membranes: application to nanofibrillated cellulose films

Journal of Materials Science, 2015

Structural Characterisation of Kraft Pulp Fibres and Their Nanofibrillated Materials for Biodegradable Composite Applications

by Markku Kataja and Cris L Luengo Hendriks

Nanocomposites and Polymers with Analytical Methods, 2011

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Multiscale flow modeling - MASIT19

The objective of Multi-scale flow modeling (MUSCA) consortium project is to develop verified nume... more The objective of Multi-scale flow modeling (MUSCA) consortium project is to develop verified numerical tools in order to model complex fluid flows in selected industrial applications. Research is accomplished in a close collaboration between the participating institutes. In the following, results achieved in thisfar from the different subprojects are briefly described. 1) The 2D Fibre Orientation Probability Distribution (FOPD) model has been validated and the dependence of fibre orientation on turbulence is studied in the headbox slice channel by using experimental data provided by TUT. In addition, a model based on population bal- ance method is used for modelling of fibre flocculation phenomenon. 2) New method is being developed for measuring 3D velocity fields in opaque suspensions at VTT. The measurements are based on Pulsed Ultra- sound Doppler Velocimeter (PUDV) equipped with a submersible probe. Experimental results obtained for a solid-liquid stirred tank have been used to ...

Hydrodynamical description of 200A GeV/c S+Au collisions: Hadron and electromagnetic spectra

Physical Review C, 1997

We study relativistic S+Au collisions at 200A GeV/c using a hydrodynamical approach. We test vari... more We study relativistic S+Au collisions at 200A GeV/c using a hydrodynamical approach. We test various equations of state (EOSs), which are used to describe the strongly interacting matter at densities attainable in the CERN-SPS heavy ion experiments. For each EOS, suitable initial conditions can be determined to reproduce the experimental hadron spectra; this emphasizes the ambiguity between the initial conditions and the EOS in such an approach. Simultaneously, we calculate the resulting thermal photon and dielectron spectra, and compare with experiments. If one allows the excitation of resonance states with increasing temperature, the electro-magnetic signals from scenarios with and without phase transition are very similar and are not resolvable within the current experimental resolution. Only EOSs with a few degrees of freedom up to very high temperatures can be ruled out presently.

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Coupling of longitudinal and transverse flows in the hydrodynamics of ultrarelativistic nuclear collisions

Nuclear Physics A, 1994