Technische Mechanik - European Journal of Engineering Mechanics
https://journals.ub.ovgu.de/index.php/techmech
<p>The journal is edited by <a href="https://www.matem.ovgu.de/">Magdeburger Verein für Technische Mechanik e.V.</a> and <a href="http://www.ovgu.de/">Otto von Guericke University Magdeburg</a><br />Editor-in-chief: Daniel Juhre<br />Assistant editor-in-chief: Elmar Woschke</p> <p>Institute of Mechanics<br />Otto von Guericke University Magdeburg<br />P.O. Box 4120<br />39016 Magdeburg, Germany<br />Telephone: +49 391 67–52 459<br />Fax: +49 391 67–12 439/–12 863<br />E-Mail: <a href="mailto:Technische.Mechanik@ovgu.de">Technische.Mechanik@ovgu.de</a><br />Internet: <a href="http://journals.ub.uni-magdeburg.de/ubjournals/index.php/techmech">www.ovgu.de/techmech</a></p>Magdeburger Verein für Technische Mechanik e.V. & Otto-von-Guericke-Universität Magdeburgen-USTechnische Mechanik - European Journal of Engineering Mechanics0232-3869Convolutional Neural Networks for Time Series Data Processing Applicable to sEMG Controlled Hand Prosthesis
https://journals.ub.ovgu.de/index.php/techmech/article/view/2191
<p>Surface electromyography (sEMG) signals are often used to control prosthetics, but accurately interpreting these stochastic signals remains challenging. Deep learning tools like convolutional neural networks (CNNs) have shown promise for complex classification problems, yet CNN applications for time series data are limited. This work explores adapting CNNs to sEMG time series for improved classification, addressing two questions: 1) Can a CNN trained on cross-subject data generalize without individualization? 2) Can a small individualized dataset sufficiently train an accurate control model? To investigate, sEMG data is formatted into images using handcrafted features, with pixels representing multichannel time series. A ResNet50 architecture is trained on two datasets: individual and cross-subject. Results show cross-subject models fail to provide accurate subject-specific control due to high inter-subject variability of sEMG. However, ResNet50 trained on individual data produces highly accurate offline and near real-time classification. The proposed method is also tested on an external dataset and compared to similar published methods, demonstrating strong performance. In summary, CNNs show promise for prosthetic control from sEMG but require individualized training data. The proposed data formatting and ResNet50 architecture can enable precise control from minimal data, overcoming barriers to clinical implementation. Further research into cross-subject generalizability is warranted to understand the sources of variability and improve model robustness.</p>Golam Gause JamanMarco Schoen
Copyright (c) 2024 Golam Gause Jaman, Marco Schoen
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2024-05-032024-05-03441476010.24352/UB.OVGU-2024-053An efficient mass lumping scheme for isogeometric analysis based on approximate dual basis functions
https://journals.ub.ovgu.de/index.php/techmech/article/view/2192
<p>In this contribution, we propose a new mass lumping scheme for explicit dynamics in isogeometric analysis (IGA). To this end, an element formulation based on the idea of dual functionals is developed. Non-Uniform Rational B-splines (NURBS) are applied as shape functions and their corresponding dual basis functions are applied as test functions in the variational form, where two kinds of dual basis functions are compared. The first type are approximate dual basis functions (AD) with varying degree of reproduction, resulting in banded and diagonally-dominant mass matrices. Dual basis functions derived from the inversion of the Gram matrix (IG) are the second type and already yield diagonal mass matrices. We will show that it is possible to apply the dual scheme as a transformation of the resulting system of equations based on NURBS for both – shape and test functions. Hence, it can be easily implemented into existing IGA routines and it is also promising to retain the accuracy known from similar formulations without mass lumping. Applying additional row-sum lumping to the mass matrices is either not necessary for IG or the caused loss of accuracy is lowered to a reasonable magnitude in the case of AD. Numerical examples show a significantly better approximation of the dynamic behavior for the dual lumping scheme compared to standard NURBS approaches making use of conventional row-sum lumping. In a nutshell, applying IG yields accurate numerical results but fully populated stiffness matrices occur, which are entirely unsuitable for explicit dynamic simulations, while combining AD and row-sum lumping leads to efficient dynamical computations, with respect to effort and accuracy.</p>Susanne HeldSascha EisenträgerWolfgang Dornisch
Copyright (c) 2024 Susanne Held, Sascha Eisenträger, Wolfgang Dornisch
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2024-04-152024-04-15441144610.24352/UB.OVGU-2024-052 On Estimating the Growth Rate of Perturbations in Rivlin-Ericksen Ferromagnetic Convection with Magnetic Field Dependent Viscosity
https://journals.ub.ovgu.de/index.php/techmech/article/view/2190
<p>The unique viscoelastic properties and the consideration of MFD (magnetic field dependent) viscosity in the Viscoelastic ferrofluid model render it highly suitable for the accurate modeling of complex biological fluids, such as blood. The present research comprises the study of perturbation growth rate in a case of Rivlin-Ericksen Ferrofluid layer with viscosity depending on a vertically acting magnetic field. The complex growth rate of an arbitrary oscillatory motion with growing amplitude in Rivlin-Ericksen ferromagnetic convection for free-free boundaries has been analytically proven to be located within a semicircle in the right half of the σiσr-plane and (<em>radius</em>)<sup>2</sup> = [<em>RM</em><sub>1</sub>/<em>P</em><sub>r</sub>(1+2(1+δ<em>M</em><sub>3</sub>)π<sup>2</sup><em>F</em><sub>ν</sub>)]. Bounds are also obtained for situation involving rigid boundaries. For stress-free boundaries, the sufficient condition for PES validity is derived as [<em>RM</em><sub>1</sub><em>P</em><sub>r</sub>/π<sup>4</sup>(1+(1+δ<em>M</em><sub>3</sub>)π<sup>2</sup><em>F</em><sub>ν</sub>)] ≤ 1, where <em>R</em> represents the Rayleigh number, <em>P</em><sub>r</sub> is the Prandtl number, <em>F</em><sub>ν</sub> characterizes viscoelasticity of Rivlin- Ericksen ferrofluid, <em>M</em><sub>3</sub> > 0 is the measure of the nonlinearity of magnetization and <em>M</em><sub>1</sub> is the magnetic number. The mathematical derivation of these results is presented in detail. Thus the analysis presented here reveals that the oscillations in Rivlin-Ericksen ferromagnetic convection can be regulated or halted by taking into account the viscosity dependent on the magnetic field and the viscoelasticity of the fluid.</p>Pankaj KumarMandeep KaurAbhishek ThakurRenu Bala
Copyright (c) 2024 Mandeep Kaur, Pankaj Kumar, Abhishek Thakur, Renu Bala
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2024-04-082024-04-0844111310.24352/UB.OVGU-2024-051