Gunter Knoll

Inverse localization of electric dipole current sources in finite element models of the human head

The paper describes finite element related procedures for inverse localization of multiple sources in realistically shaped head models. Dipole sources are modeled by placing proper monopole sources on neighboring nodes. Lead field operators are established for dipole sources. Two different strategies for the solution of inverse problems, namely combinatorial optimization techniques and regularization methods are discussed and applied to visually evoked potentials, for which exemplary results are shown. Most of the procedures described are fully automatic and require only proper input preparation. The overall work for the example presented (from EEG recording to visual inspection of the results) can be performed in roughly a week, most of which is waiting time for the computation of the lead field matrix or inverse calculations on a standard and affordable engineering workstation.

The influence of skull-conductivity misspecification on inverse source localization in realistically shaped finite element head models

SummaryThe electric conductivities of different tissues are important parameters of the head model and their precise knowledge appears to be a prerequisite for the localization of electric sources within the brain. To estimate the error in source localization due to errors in assumed conductivity values, parameter variations on skull conductivities are examined. The skull conductivity was varied in a wide range and, in a second part of this paper, the effect of a nonhomogeneous skull conductivity was examined. An error in conductivity of lower than 20% appears to be acceptable for fine finite element head models with average discretization errors down to 3mm. Nonhomogeneous skull conductivities, e.g., sutures, yield important mislocalizations especially in the vincinty of electrodes and should be modeled.

Spatio-Temporal Current Density Reconstruction (stCDR) from EEG/MEG-Data

Among the different approaches to the bioelectromagnetic inverse problem, the current-density reconstruction methods (CDR) provide the most general solutions. Since the inverse problem does not have a unique solution, model assumptions have to be taken into account. Multi-channel measurements contain not only spatial, but also temporal information about the sources, so a naturally extension to existing methods leads to spatio-temporal model constraints. Spatio-temporal CDRs (stCDR) have been tested in simplified volume conductor models, assuming different spatial model constraints and a smooth temporal activation model. Comparison to existing spatial model constraints showed a significant improvement of spatial and temporal resolution of the reconstructed sources for the spatio-temporal models especial in noisy data.

Auswirkung von Ethanol E85 auf Schmierstoffalterung und Verschleiss im Ottomotor

Die Auswirkung von ethanolhaltigem Kraftstoff auf die Schmierolalterung in Ottomotoren ist bisher kaum untersucht. Das FVV-Forschungsprojekt 930 von TU Clausthal, Universitat Kassel und IFOS Kaiserslautern zeigt auf, dass der Betrieb mit E85 die Lebensdauer des Motors verkurzt. Fur die Steuerkette als Triboleitsystem erhoht sich die Verschleisrate um 20 %.

Run-up of turbocharger rotors in nonlinearly modelled floating bush bearings

With small-sized high-speed rotors, such as exhaust turbochargers in cars and trucks, floating bush bearings are used. The multi-body simulation of the run-up of exhaust gas turbocharger rotors with nonlinearly modelled floating bush bearings represents a great challenge for hydrodynamics and rotor dynamics. The development of computer time-efficient methods and modelling techniques as well as the explanation of the various instability phenomena were the major objectives of the FVV project “Run-up Simulation” (No. 912). The task was given by Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) and was solved at Karlsruhe Institute of Technology (KIT) and University of Kassel.

Ölalterung und Verschleiß im Ottomotor

Aus Grunden des Umweltschutzes und der Servicefreundlichkeit ist die Automobilindustrie bestrebt, die Olwechsel-intervalle zu optimieren. Im Auftrag der Forschungsvereinigung Verbrennungskraftmaschinen e. V. (FVV) haben drei Forschungspartner in einem gemeinsamen Forschungsprojekt die Schmierstoffalterung und deren Einfluss auf das Verschleisverhalten der Tribosysteme im Ottomotor untersucht. Die Partner sind das Institut fur Tribologie und Energiewandlungsmaschinen der Technischen Universitat Clausthal, das Institut fur Maschinenelemente und Konstruktionstechnik der Universitat Kassel und das Institut fur Oberflachen- und Schichtanalytik GmbH der Technischen Universitat Kaiserslautern.

Berechnung von Motoren-Gleitlagern unter Berücksichtigung der Deformation

Dieser Beitrag gibt einen Uberblick uber den Leistungsumfang der am Institut fur Maschinenelemente und Konstruktionstechnik der Universitat Gh Kassel eingesetzten Gleitlager-Berechnungsprogramme [1, 2]. Auserdem wird an Fallstudien exemplarisch der Einflus der berucksichtigten physikalischen Effekte sowie konstruktiver Parameter aufgezeigt.

Application of FDEM on the Numerical Simulation of Journal Bearings with Turbulence and Inertia Effects

For the numerical simulation of journal bearings, current software solutions use the Reynolds differential equation where inertia terms are not included. The Finite Difference Element Method (FDEM) is a black-box solver for nonlinear systems of elliptic and parabolic partial differential equations (PDEs). Based on the general black-box we implement the Reynolds equation with inertia terms for the simulation of a journal bearing. We can easily implement different models for the turbulence factors and the dynamic viscosity, and we also consider cavitation. We give results for different Reynolds numbers, and we also give a global error estimate for each of the cases. This shows the quality of the numerical solution and is a unique feature of FDEM.

Piston pin in mixed friction contact

Within the framework of the research project No. 868 of the FVV research association Verbrennungskraft maschinen e. V. (Combustion Vehicles Reg.) a user-friendly numerically stable simulation tool was developed by Stuttgart University and Kassel University. The tool was validated by experiments, and offers designers and developers the possibility of system analysis and optimization of piston pin bearings. Non-linear elasto-hydrodynamic processes were included at the same time in the dynamically loaded bearing contacts of piston/piston pin and piston pin/connecting rod, with the reciprocal effects.

Lubricant degradation and wear behaviour in a spark-ignition engine

For protecting the environment and increasing convenience in service, the automotive industry is endeavouring to optimise the oil-change intervals. On behalf of the German Research Association for Combustion Engines (FVV), three research partners have investigated the degradation of lubricants and its effect on the wear behaviour of the tribo-systems in a spark-ignition engine in the course of a joint research project. The partners are the Institute of Tribology and Energy Conversion Machinery at Clausthal University of Technology, the Institute of Machine Elements and Design Engineering at University of Technology Kassel, and the Institute of Surface and Coating Analysis at University of Technology Kaiserslautern.