ALBERT

Description: The possibility of condensation of electron pairs has been established by Yang and Coleman. Recent observations of Bose-Einstein condensate (BEC) of alkali atoms, containing odd number of electrons, require some explanation, which also must be based on a correct permutational symmetry of a system, containing different types of fermions. In the framework of the same reduced density matrix formalism, it is proved that aggregates (atoms), containing even number 2f of fermions, can be condensed only in a mixed quantum state in contrast to elementary bosons because a natural occupation number λ is proved to be strictly smaller than their total sum. If fermions are absent in aggregates the reduction of sum of λ to one term becomes possible. The upper bound λ_{max} for a macroscopic ensemble of n aggregates, built of m different sorts of fermions is shown to be m^1[((2f-1)!!)^3 A/(2f)!!B]^{1/2} where A is the number of all possible aggregates in a system, B is the number of ways to form a given composition of an aggregate from 2f-fermions of m sorts; n is a macroscopic greatest common devisor of fermion numbers of all sorts. The bound λ_{max} increases as n^{f}, while sum of λ grows as n^{2f}. The evenness of the total number of fermions 2f in an aggregate is a necessary and sufficient condition for BEC formation. In particular, the number N of neutrons in neutral atom must be even because of the integrity of f=Z+N/2. The extreme type wave function is built, for which λ is arbitrary close to n^{f} that proves the sufficiency of this criterion. The occupation maximum is achieved when pairs of fermions (identical or different) are condensed independently. The possibility of condensation of bound aggregates only (atoms) is shown arising from nonoverlapping of wave functions of electron relative coordinates of different atoms. This conclusion is based on separation of the centers' of mass motion, which are proved behaving like a bosonic gas. The remaining product of identical atomic wave functions of relative coordinates, which determine main properties of condensate ingredients, is shown not requiring further antisymmetrization that makes condensation possible. Content Type Journal Article Pages 127-142 DOI 10.3233/JCM-2011-0370 Authors M. Mestechkin, 12773 Seabreeze Farms Dr. # 33, San Diego, CA 92130, USA. E-mail: mestechkinmm@gmail.com Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 11 Journal Issue Volume 11, Number 3 / 2011

Description: The present work consists to elaborate a computing program able to generate a Delaunay unstructured triangular meshes around the complex configurations applied in aerodynamics, like airfoil of aircraft, multi-elements airfoils, nacelle, fuselage, etc... While basing on the Delaunay criterion, again called 'in-circle criterion' of the hollow circle that means no point is inside a circle circumscribes a triangle of the mesh. The initial mesh can be set up by joining the trailing-edge point of the airfoil to all the outer boundary points, the surface mesh points for the airfoil are then introduced one at a time, and the internal nodes of the O-mesh generated by using a sequence of conformal transformation of Von Karman Trefftz through the whole domain of the out-flow. Each time a new point is introduced, the triangles failing the 'Delaunay criterion' are located using the tree-search algorithm, forming a convex cavity named 'Delaunay cavity'. These triangles will be broken and will be replaced by new triangles while connecting this new point to each of the points at vertices of this cavity. This generated a new triangulation and the algorithm repeats this process with the next new point until succeed to a Delaunay mesh. A Laplacian filter is used to reposition the mesh points in order to have a regular mesh clever to be exploited by the numerical methods: finite volume method or finite element method. Content Type Journal Article Pages 143-158 DOI 10.3233/JCM-2011-0372 Authors Toufik Zebbiche, University SAAD Dahleb of Blida, BP 270, Blida 09000, Algeria Nasreddine Hamdi, University Amar TELIDJI of Laggouat, BP 37, Lagouat 03000, Algeria Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 11 Journal Issue Volume 11, Number 3 / 2011

Description: The aim of this paper is, in accordance with efficient web search service operation objectives, to propose enhancements to the sophistication of the functionality that can be offered by search engine services. A meta-search third-party result ranking mechanism is proposed, which is capable of adapting over the continuous changes that occur on the web, providing in parallel personalized information acquisition considering the user's navigation behaviour. Transparency is achieved for both personalization and web evolution adaptation mechanisms, requiring virtually none effort from the user's part. In essence, the proposed meta search engine rates, re-organises and combines the results acquired from search services for a specific user information resource request in accordance with a weighted combination of a performance related factor (tightly related to the ranking of the web result as given by the search engine service) and a reliability related factor (corresponding to the user satisfaction stemming from the specific web result that he/she browses), while the performance of each search engine with respect to adequately adapting to the web evolution is taken into account. For the evaluation of the web results reliability, a collaborative reputation mechanism is utilized, which helps estimating their quality and predicting their future usability, taking into account their past performance in consistently satisfying user expectations. A set of results indicative of the efficiency of our proposed scheme is provided. The Internet search services used were Google, MSN and Yahoo! Content Type Journal Article Pages 109-124 DOI 10.3233/JCM-2011-0368 Authors Malamati Louta, University of Western Macedonia, Department of Informatics and Telecommunications Engineering, Kozani, Greece Ioannis Anagnostopoulos, University of Central Greece, Department of Computer Science and Biomedical Informatics, Lamia, Greece Ilias Maglogiannis, University of Central Greece, Department of Computer Science and Biomedical Informatics, Lamia, Greece Angelos Michalas, Technological Educational Institute of Western Macedonia, Department of Informatics and Computer Technology GR-52100, Kastoria, Greece Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 11 Journal Issue Volume 11, Number 3 / 2011

Description: 'Motion' and intention that are involved in the perception of musical structure combined with mirror neuron (MN) system activation are studied in this article. The mechanism of MN involved in the perception of musical structures is seen as a means for cueing the learner on `known' factors that can be used for his/her knowledge scaffolding. To explore such relationships, EEG recordings, and especially the Mu-rhythm in the premotor cortex that relates to the activation of MN, were acquired and explored. Three experiments were designed to provide the auditory and visual stimuli to a group of subjects, including both musicians and non-musicians. The acquired signals, after appropriate averaging in the time domain, were analyzed in frequency and bifrequency domains, using spectral and bispectral analysis, respectively. Experimental results have shown that an intention – related activity shown in musicians could be associated with Mu – rhythm suppression. Moreover, an underlying ongoing function appearing in the transition from heard sound to imagined sound could be revealed in the bispectrum domain. A Mu-rhythm modulation provoked by the MNs could cause bispectral fluctuations, especially when visual stimulation is combined with an auditory one for the case of musicians. These results pave the way for further exploitation of the role of MNs in music and, in general, knowledge perception. Content Type Journal Article Pages 91-107 DOI 10.3233/JCM-2011-0367 Authors Panagiotis Doulgeris, Aristotle University of Thessaloniki, Faculty of Technology, Department of Electrical and Computer Engineering, GR – 541 24, Thessaloniki, Greece Stelios Hadjidimitriou, Aristotle University of Thessaloniki, Faculty of Technology, Department of Electrical and Computer Engineering, GR – 541 24, Thessaloniki, Greece Konstantinos Panoulas, Aristotle University of Thessaloniki, Faculty of Technology, Department of Electrical and Computer Engineering, GR – 541 24, Thessaloniki, Greece Leontios Hadjileontiadis, Aristotle University of Thessaloniki, Faculty of Technology, Department of Electrical and Computer Engineering, GR – 541 24, Thessaloniki, Greece Stavros Panas, Aristotle University of Thessaloniki, Faculty of Technology, Department of Electrical and Computer Engineering, GR – 541 24, Thessaloniki, Greece Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 11 Journal Issue Volume 11, Number 3 / 2011

Description: Content Type Journal Article Category Preface Pages 89-90 DOI 10.3233/JCM-2011-0366 Authors Dimitris Kanellopoulos Sotiris Kotsiantis Panagiotis Pintelas Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 11 Journal Issue Volume 11, Number 3 / 2011

Description: The carbon nanotubes have attracted much interest for their electronic properties which go from metallic to semiconducting behavior, depending both on diameter, number of layers and chirality. The value of their band gap is obviously a crucial point to be addressed because it enters in the nanbotube application as microelectronic devices. This work was developed through an estimate of the behavior of the electronic structure of carbon nanotubes of single walled (8,0) and the assessment of electrical conduction through various methodologies such as LSDA, B3PW91, B3LYP and HF ab initio methods and PM3 and AM1semi-empirical methods. The methods showed similarities with the geometrical parameters reported in the literature. The hybrid methods based on density functional generated a good approximation in the energy gap value of single-walled carbon nanotubes (8,0). Results will be presented. Content Type Journal Article Pages 381-387 DOI 10.3233/JCM-2012-0426 Authors R. López-Planes, Laboratorio De Metales, Departamento de Física, Escuela de Ciencias, Universidad de Oriente, Apartado postal 245, Cumaná, Venezuela S. Dasilva, Laboratorio De Metales, Departamento de Física, Escuela de Ciencias, Universidad de Oriente, Apartado postal 245, Cumaná, Venezuela Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 4-6 / 2012

Description: Quantum chemistry calculations were done, using the ONIOM2 methodology at two different levels of calculation, B3LYP for the high level and UFF for the low level. These calculations were performed on Au_{3}/SAPO-11, Au_{4}/SAPO-11, CO-Au_{3}/SAPO-11 and CO-Au_{4}/SAPO-11 aggregates to analyze the geometries of small clusters of Au_{3} and Au_{4} on SAPO-11 support. Au_{3} cluster present a triangle structure in Au_{3}/SAPO-11. Au_{4 } cluster shows a "Y shaped" structure in Au_{4}/SAPO-11. Au_{4} as a rhombus structure is also studied but it is an unstable intermediate to the "Y shaped" structure. The CO interaction with Au_{3} and Au_{4}/SAPO-11 is studied, this CO adsorption is different from reported in the literature. The formation energy Δ E_{F} of the aggregates and the CO adsorption energy ΔE_{ads} on them are presented. Content Type Journal Article Pages 389-394 DOI 10.3233/JCM-2012-0427 Authors Beulah Griffe, Labs. Química Computacional y Fisicoquímica de Superficies, Centro de Química, Caracas, Venezuela Joaquín L. Brito, Labs. Química Computacional y Fisicoquímica de Superficies, Centro de Química, Caracas, Venezuela Anibal Sierraalta, Labs. Química Computacional y Fisicoquímica de Superficies, Centro de Química, Caracas, Venezuela Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 4-6 / 2012

Description: Common structural optimisation problems consist of problem-specific objective functions which have to be minimised mathematically with respect to design and state variables taking into account particular constraints. In contrast to this, we adopt a conceptually different approach for the design of a structure which is not based on a topology-optimisation technique. Instead, we apply a one-dimensional energy-driven constitutive evolution equation for the referential density–originally proposed for the simulation of remodelling effects in bones–and embed this into the micro-sphere-concept to end up with a three-dimensional anisotropic growth formulation. The objective of this contribution is to investigate this approach with emphasis on its application to structural design problems by means of two three-dimensional benchmark-type boundary value problems. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The present work aims at the modelling and simulation of Internal Traverse Grinding of hardened 100Cr6/AISI 52100 using electro plated cBN grinding wheels. We focus on the thermomechanical behaviour resulting from the interaction of tool and workpiece in the process zone on a mesoscale. Based on topology analyses of the grinding wheel surface, two-dimensional single- and multigrain representative numerical experiments are performed to investigate the resulting load-displacement-behaviour as well as the specific heat generation due to friction and plastic dissipation. A thermoelastic-viscoplastic constitutive model is used to capture thermal softening of the material taken into account. Based on previous work, an adaptive remeshing scheme which uses a combination of error estimation and indicator methods, is applied to overcome mesh dependence. In consequence, the formulation allows to resolve the complex deformation patterns and to predict a realistic thermomechanical state of the resulting workpiece surface. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The fast iterative solution of optimal control problems, and in particular PDE-constrained optimization problems, has become an active area of research in applied mathematics and numerical analysis. In this paper, we consider the solution of a class of time-dependent PDE-constrained optimization problems, specifically the distributed control of the heat equation. We develop a strategy to approximate the (1, 1)-block and Schur complement of the saddle point system that results from solving this problem, and therefore derive a block diagonal preconditioner to be used within the MINRES algorithm. We present numerical results to demonstrate that this approach yields a robust solver with respect to step-size and regularization parameter. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The mechanical behaviour of molecular structures can be described with stiff differential equations, which can not be solved analytically. Several numerical time integration schemes can be found in the literature. The aim of this paper is to present the class of partitioned Runge-Kutta methods applied in molecular dynamics. This class of methods includes a wide range of explicit and implicit, single- and multi-stage, symplectic and non-symplectic, low- and high-order time integration schemes. Also most of the classical methods like explicit and implicit Euler, explicit and implicit midpoint rule, Störmer-Verlet and Newmark are also partitioned Runge-Kutta methods. The schemes are implemented in a finite element code which can serve as a numerical platform for molecular dynamics. This code is used to show the sensitivity of the simulations to the accuracy of the initial values. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: A Discrete Element Model that is capable to describe degradation of ballast tracks in consideration of breakage of the ballast stones is presented. Strong rock is modelled as a granular solid by introduction of breakable bonds with suitable failure criteria between adjacent particles. Irregular angular stones are generated from the granular solid and their crushing strength is evaluated. The degradation process of a ballast bed is assessed and related to the damage occurring to the individual stones. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Natural coordinates have emerged to be well-suited for both rigid and flexible multibody dynamics. Especially the combination of structural elements and energy-momentum consistent time stepping schemes leads to superior numerical stability as well as an automatable assembly, resulting in both excellent run-time behaviour as well as moderate modelling effort (see [1]). Incorporation of modern methods for finite-element simulations, such as mortar methods for contact or domain decomposition both for structural elements as well as continuum elements is straightforward ([2]). Augmentation techniques allow a systematic integration of both mechanical and non-mechanical quantities for simulation (see [3] and [4]), which makes this approach suitable especially for emulation and simulation of mechatronic systems. We will present an approach for evaluating forward control strategies with flexible multibody systems. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this paper, we recall the mutation of the Minkowski spacetime for empty space into the covering isospacetime caused by physical media; we recall its experimental verifications via the isoredshift of laser light in a metal pipe containing air at pressure, as well as additional experimental verifications in other fields; and we present, apparently for the first time, experimental confirmations of Santilli's 1991 prediction of the isoredshift as the primary origin of the redness of direct Sunlight at Sunset and Sunrise without any appreciable relative motion between Earth and Sun, said isoredshift being proportional to the distance traveled by Sunlight in air. Absorption is dismissed as a source of said redness of the Sun because air predominantly absorbs red, as experimentally established, without dismissing minor contributions, e.g., for the shape (but not the shift) of wavelengths. The widely accepted conjecture that scattering is the origin of said redness of the Sun, without dismissing minor contributions, is shown to be inapplicable for direct Sunlight, to have no representational capability for the needed very large shifts (measured up to 200 nm), and to have been dismissed experimentally at the cosmological level with recent measurements via Hubble's telescope, as well as on Earth by recent scattering measurements by some of us. Since intergalactic spaces are far from being empty, and physical laws must be the same throughout the universe, the preceding experimental results are shown to be evidence for the absence of the expansion of the universe, the absence of the acceleration of the expansion, the absence of the big bang, and the elimination of the far reaching conjecture that space itself is expanding as needed, from Hubble's law, to prevent a return to the Middle Ages with Earth at the center of the universe. It is finally shown that the same experimental confirmations of Santilli isoredshift imply the absence of dark matter and dark energy since the universe is nowhere empty, with consequential universal validity of Santilli isospacetime and its Lorentz-Poincaré-Santilli isosymmetry. Content Type Journal Article Pages 141-168 DOI 10.3233/JCM-2012-0409 Authors R.M. Santilli, Magnegas Corporation, Tarpon Springs, FL, USA G. West, Magnegas Corporation, Tarpon Springs, FL, USA G. Amato, Magnegas Corporation, Tarpon Springs, FL, USA Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 3 / 2012

Description: In this publication, we study the supersonic flow around a pointed airfoil in free air. The work is to develop a numerical calculation program using the relations of oblique shock waves; and Prandtl Meyer expansion of constant specific heats around a wedge to determine the characteristics of pointed airfoil in supersonic steady. This regime is characterized by the emergence of a shock wave, usually weak, which will be attached to the leading edge of the airfoil if it has a pointed shape. The airfoil is discretized into flat plate's juxtaposed one to another. It should be noted that the flow is two dimensional. In the place where there is concavity of the wall there will be shock waves and in an other place where there is convexity of the wall there will be an expansion of the flow. The latter type is of Prandtl Meyer. The flow is characterized by increases of entropy seen that there appears a shock wave. The drag is not zero. It is equal to the drag of the shock wave even though the flow is inviscid. We neglect the other components of the drag. Most authors prefer the use of the thin airfoil theory to evaluate the flow around an airfoil. A Comparison is made with this theory for thin thickness to determine a limit of applications of this theory. Applications are made for moderate thickness. The substance chosen is air. Content Type Journal Article Pages 213-233 DOI 10.3233/JCM-2012-0398 Authors Toufik Zebbiche, University SAAD Dahleb of Blida, BP, Blida, Algeria Merouane Salhi, University SAAD Dahleb of Blida, BP, Blida, Algeria Mohamed Boun-djad, University SAAD Dahleb of Blida, BP, Blida, Algeria Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 3 / 2012

Description: This work introduces the third instalment in a series of papers, i.e. the EAS3 multistep approach. In this work we present, for the first time in a journal article, the EAS3 methods, which are part of the explicit advanced step-point (EAS) family of methods. The EAS formulae comprise three distinct schemes: EAS1, EAS2 and EAS3. In this paper we consider the EAS3 methods, which represent a substantial departure compared to EAS1 and EAS2. Here the EAS3 are studied and their superior regions of absolute stability are presented. Content Type Journal Article Pages 201-210 DOI 10.3233/JCM-2012-0399 Authors G. Psihoyios, Laboratory of Computational Science, Department of Computer Science and Technology, University of Peloponnesos, Tripolis, Greece. E-mail: g.psihoyios@gmail.com Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 3 / 2012

Description: While stressing the need for additional independent verifications, in this paper we provide: 1) Confirmatory measurements of Santilli's 1991 hypothesis of the anomalous IsoRedShift (IRS) for the propagation of a blue laser light in a 60 ft ≈ 18 m long steel pipe containing air at a maximum of 70°F ≈ 21°C and at 2,000 psi ≈ 137 bars without any relative motion between the source, the medium and the analyzer; 2) Confirmatory measurements of Santilli's 1991 hypothesis of the anomalous IsoBlueShift (IBS) for a blue laser light in the same conditions as above except for air being at a minimum of 130°F ≈ 54°C; 3) Experimental evidence on the transition from IRS to IBS with the increase of the temperature, thus confirming Santilli's NoIsoShift (NIS); 4) Measurements showing no frequency shift for a blue laser light reflected on a polished metal mirror at temperatures ranging from 70°F ≈ 21°C to 280°F ≈ 137°C, with consequential apparent absence of frequency shift for the scattering of light in a gas, since the Boltzman distribution apparently implies no frequency shift for light scattering in a gas due to relative motions averaged down to zero; and 5) Consequential confirmation of Santilli's 1991 hypothesis that the large difference in cosmological redshift between certain quasars and associated galaxies when physically connected via clear gamma spectroscopic evidence, originates from largely different IRS in the dramatically different quasars chromospheres and innergalactic media. Cosmological and other implications of Santilli IRS, IBS and NIS are discussed by other contributions in these proceedings. Content Type Journal Article Pages 169-188 DOI 10.3233/JCM-2012-0410 Authors Gene West, Magnegas Corporation, Tarpon Springs, FL, USA Gino Amato, Magnegas Corporation, Tarpon Springs, FL, USA Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 3 / 2012

Description: This paper studies the law of the Lie algebras \frak{h}_n associated with a particular type of Lie groups: the Lie groups H_n formed by all the n × n upper-triangular matrices without zeros in their main diagonal. Indeed, these laws are obtained by means of a computational algorithm which we have constructed and particularly implemented by using the symbolic computation package MAPLE. Besides, the complexity of this algorithm is studied by considering the number of computations carried out with this implementation. Content Type Journal Article Pages 189-198 DOI 10.3233/JCM-2012-0397 Authors J.C. Benjumea, Dpto. Geometría y Topología, Facultad de Matemáticas, Universidad de Sevilla, Sevilla, Spain M.D. Morales, Dpto. Geometría y Topología, Facultad de Matemáticas, Universidad de Sevilla, Sevilla, Spain J. Núñez, Dpto. Geometría y Topología, Facultad de Matemáticas, Universidad de Sevilla, Sevilla, Spain A.F. Tenorio, Dpto. Métodos Cuantitativos, Escuela Politécnica Superior, Universidad Pablo de Olavide, Sevilla, Spain Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 3 / 2012

Description: Most optimization problems rely heavily on simulations to evaluate design solutions according to a set of design criteria under stringent constraints. While an inverse problem may also rely on simulation-driven methods, it can sometimes be viewed more properly as a constrained optimization problem because the main aim of inversion is to find the best parameter estimates so as to minimize the differences between predicted results and observations. In this paper, we will take a unified approach to inversion and optimization. We use the latest cuckoo search to solve inverse problems and shape optimization in heat transfer applications. Simulation results show that cuckoo search is also very efficient for inversion. Content Type Journal Article Pages 129-137 DOI 10.3233/JCM-2012-0408 Authors Xin-She Yang, Mathematics and Scientific Computing, National Physical Laboratory, UK. Tel./Fax: +44 208 943 6092; E-mail: xin-she.yang@npl.co.uk Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Public environmental policy formulation can prove complicated when the various system components contain considerable elements of stochastic uncertainty. Invariably, there are unmodelled issues, not captured or apparent at the time a model is constructed, that can greatly impact the acceptability of its solutions. While a mathematically optimal solution may be the best solution to the modelled problem, it is frequently not the best solution for the underlying real problem. Consequently, it is generally preferable to create several good alternatives that provide very different approaches and perspectives to the same problem. This study shows how a computationally efficient simulation-driven optimization (SDO) approach that combines evolutionary optimization with simulation can be used to generate multiple policy alternatives that satisfy required system criteria and are maximally different in decision space. The efficacy of this stochastic modelling-to-generate-alternatives approach is demonstrated on a waste management planning case. Since SDO techniques can be adapted to model a wide variety of problem types in which system components are stochastic, the practicality of this approach can be extended into many other application areas containing significant sources of uncertainty. Content Type Journal Article Pages 111-127 DOI 10.3233/JCM-2012-0407 Authors Julian Scott Yeomans, OMIS Area, Schulich School of Business, York University, Toronto, ON, Canada. Tel.: +1 416 736 5074; Fax: +1 416 736 5687; E-mail: syeomans@schulich.yorku.ca Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Optimization is often used to perform model calibration, the process of inferring the values of model parameters so that the results of the simulations best match observed behavior. It can both improve the predictive capability of the model and curtail the loss of information caused by using a numerical model instead of the actual system. At its heart is the comparison of experimental data and simulation results. Complicating this comparison is the fact that both data sets contain uncertainties which must be quantified in order to make reasonable comparisons. Therefore, uncertainty quantification (UQ) techniques can be applied to identify, characterize, reduce, and, if possible, eliminate uncertainties. Incorporation of UQ into the calibration process can drastically improve the usefulness of computational models. Current approaches are serial approaches in that first, the calibration parameters are identified and then, a series of runs dedicated to UQ analysis is completed. Although this approach can be effective,it can be computationally expensive or produce incomplete results. Model analysis that takes advantage of intermediate optimization iterates can reduce the expense, but the sampling done by the optimization algorithms is not ideal. In this paper, we will review serial approaches and propose a joint calibration and UQ approach that combines Bayesian statistical models and derivative-free optimization in order to monitor sensitivity information throughout the calibration process. Content Type Journal Article Pages 99-110 DOI 10.3233/JCM-2012-0406 Authors Genetha A. Gray, Sandia National Laboratories, Livermore, CA, USA Herbert K.H. Lee, University of California, Santa Cruz, Santa Cruz, CA, USA John Guenther, University of California, Santa Cruz, Santa Cruz, CA, USA Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: The space mapping technique aims at an efficient optimization of complex technical problems. Its success relies on the quality of the coarse model that might be deduced from either physical, algebraic or grid-based hierarchies of models. In this paper we perform a feasibility study for transport processes coming from the fields of fluid dynamics, semiconductors and radiation. We present appropriate model hierarchies and discuss the numerical performance. Space mapping shows to give very convincing suboptimal solutions to the actual fine model optimization regarding the balance of computational effort (speed and memory) and accuracy. Content Type Journal Article Pages 63-74 DOI 10.3233/JCM-2012-0404 Authors Nicole Marheineke, FAU Erlangen-Nürnberg, Lehrstuhl Angewandte Mathematik I, Erlangen, Germany René Pinnau, TU Kaiserslautern, Fachbereich Mathematik, Erwin-Schrödinger, Kaiserslautern, Germany Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Reliable and robust computational fluid dynamics (CFD) solvers are nowadays commonly utilized in the design and analyses of various engineering systems, such as aircraft, turbomachinery, ships, and automotives. Although this has resulted in a drastic decrease of the number of prototype and experimental testing, the use of CFD in the design automation process is still limited. In practice, the geometry parameters that ensure satisfaction of assumed performance requirements are often obtained by repetitive CFD simulations guided by engineering experience. This is a tedious process which does not guarantee optimal results. On the other hand, straightforward automation attempts by employing the CFD solvers directly in the optimization loop are typically impractical, even when using adjoint sensitivity information, because high-fidelity CFD simulations tend to be computationally very expensive. In this paper, we describe a surrogate-based design optimization methodology that shifts the computational burden from the accurate and expensive high-fidelity CFD model to its fast and yet reasonably accurate surrogate. As the surrogate models are computationally much cheaper than the high-fidelity ones, the cost of the design process is greatly reduced. Here, the surrogates are constructed using low-fidelity CFD models and response correction techniques. Application examples, involving the design of axisymmetric hulls in subsonic flow, and airfoils in both subsonic and transonic flows, are presented. Content Type Journal Article Pages 75-98 DOI 10.3233/JCM-2012-0405 Authors Slawomir Koziel, Engineering Optimization and Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland Leifur Leifsson, Engineering Optimization and Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: We present initial steps and first results of a surrogate-based optimization (SBO) approach for parameter optimization in climate models. In SBO, a computationally cheap, but yet reasonably accurate representation of the original high-fidelity (or fine) model, the so-called surrogate, replaces the fine model in the optimization process. We choose two representatives, namely two marine ecosystem models, to verify our approach. We present two ways to obtain a physics-based low-fidelity (or coarse) model, one based on a coarser time discretization, the other on an inaccurate fixed point iteration. Since in both cases, the low-fidelity model is less accurate, we use a multiplicative response correction technique, aligning the low- and the high-fidelity model output to obtain a reliable surrogate at the current iterate in the optimization process. We verify the approach by using model generated target data. We show that the proposed SBO method leads to a very satisfactory solution at the cost of a few evaluations of the high-fidelity model only. Content Type Journal Article Pages 47-62 DOI 10.3233/JCM-2012-0403 Authors M. Prieß, Institute for Computer Science, Cluster The Future Ocean, Christian-Albrechts Universität zu Kiel, Kiel, Germany J. Piwonski, Institute for Computer Science, Cluster The Future Ocean, Christian-Albrechts Universität zu Kiel, Kiel, Germany S. Koziel, Engineering Optimization and Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland T. Slawig, Institute for Computer Science, Cluster The Future Ocean, Christian-Albrechts Universität zu Kiel, Kiel, Germany Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: A popular approach to handling constraints in surrogate-based optimization is through the addition of penalty functions to an infill sampling criterion that seeks objective improvement. Typical sampling metrics, such as expected improvement tend to have multimodal landscapes and can be difficult to search. When the problem is transformed using a penalty approach the search can become riddled with cliffs and further increases the complexity of the landscape. Here we avoid searching this aggregated space by treating objective improvement and constraint satisfaction as separate goals, using multiobjective optimization. This approach is used to enhance the efficiency and reliability of infill sampling and shows some promising results. Further to this, by selecting model update points in close proximity to the constraint boundaries, the regions that are likely to contain the feasible optimum can be better modelled. The resulting enhanced probability of feasibility is used to encourage the exploitation of constraint boundaries. Content Type Journal Article Pages 25-45 DOI 10.3233/JCM-2012-0402 Authors James M. Parr, University of Southampton, Southampton, England, UK Alexander I. J. Forrester, University of Southampton, Southampton, England, UK Andy J. Keane, University of Southampton, Southampton, England, UK Carren M. E. Holden, Airbus Operations Ltd, Bristol, England, UK Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Radial basis functions (RBFs), among other techniques, are used to construct metamodels that approximate multi-objective expensive high-fidelity functions from a finite number of function evaluations (design of experiments, DoE). Radial basis functions can be applied if the DoE covers the parameter space in an arbitrary though uniform manner. Leave-one-out strategies allow for computing tolerance limits. The approximated value and a certain tolerance can be interpreted as expectation and variance of a random experiment. Thus, model improvement as described for Kriging models in the literature can in principal be applied to RBF-based metamodels, too. We describe our adaptive and hierarchical metamodelling approach that deals with the specific problems that such metamodel adaptions pose to RBF-based models. We also briefly discuss implementation details and first industrial test cases. Content Type Journal Article Pages 5-23 DOI 10.3233/JCM-2012-0401 Authors Georg van Bühren, Fraunhofer SCAI, Sankt Augustin, Germany Nils Hornung, Fraunhofer SCAI, Sankt Augustin, Germany Tanja Clees, Fraunhofer SCAI, Sankt Augustin, Germany Lialia Nikitina, Fraunhofer SCAI, Sankt Augustin, Germany Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Content Type Journal Article Category Introduction Pages 1-4 DOI 10.3233/JCM-2012-0400 Authors Slawomir Koziel, Engineering Optimization and Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland Leifur Leifsson, Engineering Optimization and Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland Xin-She Yang, Mathematics and Scientific Computing, National Physical Laboratory, Teddington, UK Journal Journal of Computational Methods in Science and Engineering Online ISSN 1875-8983 Print ISSN 1472-7978 Journal Volume Volume 12 Journal Issue Volume 12, Number 1-2 / 2012

Description: Suitable continuous Sobolev embeddings are applied in order to derive smoothness estimators for adaptive hp -refinements in the context of hp -finite element methods. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper presents mixed finite element methods of higher-order for an idealized frictional contact problem in linear elasticity. The approach relies on a saddle point formulation where the frictional contact condition is captured by a Lagrange multiplier. The convergence of the mixed scheme is proven and some a priori estimates for the h - and p -method are derived. Furthermore, a posteriori error estimates are presented which rely on the estimation of the discretization error of an auxiliary problem and some further terms capturing the error in the friction and complementary conditions. Numerical results confirm the applicability of the a posteriori error estimates within h - and hp -adaptive schemes. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this article we develop the a priori error analysis of so-called two-grid hp -version discontinuous Galerkin finite element methods for the numerical approximation of strongly monotone second-order quasilinear partial differential equations. In this setting, the fully nonlinear problem is first approximated on a coarse finite element space V (𝒯 H , P ). The resulting ‘coarse’ numerical solution is then exploited to provide the necessary data needed to linearize the underlying discretization on the finer space V (𝒯 h , p ); thereby, only a linear system of equations is solved on the richer space V (𝒯 h , p ). Numerical experiments confirming the theoretical results are presented. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Rational Arnoldi is a powerful method for approximating functions of large sparse matrices times a vector. The selection of asymptotically optimal parameters for this method is crucial for its fast convergence. We present a heuristic for the automated pole selection when the function to be approximated is of Markov type, such as the matrix square root. The performance of this approach is demonstrated at several numerical examples. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: We present a model for mechanical activation of the cardiac tissue depending on the evolution of the transmembrane electrical potential and certain gating/ionic variables that are available in most of electrophysiological descriptions of the cardiac membrane. The basic idea consists in adding to the chosen ionic model one ordinary differential equation for the kinetics of the mechanical activation function. A relevant example illustrates the desired properties of the proposed model, such as delayed muscle contraction and correct magnitude of the muscle fibers' shortening. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper introduces, for the first time, a methodology to achieve a forward dynamics simulation of the musculoskeletal system using three-dimensional continuum-mechanical skeletal muscle models. This is achieved by coupling one- and three-dimensional skeletal muscle models. The feasibility of this methodology is demonstrated through a forward dynamics simulation of the upper limb involving the biceps and triceps muscle. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Standard methods for predicting the mechanical response of a human femur bone from quantitative computer-tomography (qCT) scans are classically based on the h -version of the finite element method. These methods are often limited in accuracy and efficiency due to the need for segmentation and the slow convergence rate. With the Finite Cell Method (FCM) a high-order fictitious domain method has been developed that overcomes the aforementioned problems and provides accurate results when compared to high-order finite element methods and experimental results. Herein the FCM applied to the analysis of a patient-specific femur is presented. The femur model is determined based on qCT-scans and the elastic response under compression is presented in terms of strains and displacements. The results are compared with a p -FE analysis and validated by results from an in-vitro test of the modeled femur. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Applanation tonometry estimates intraocular pressure (IOP) by quantifying the force needed to create a defined amount of deformation of the cornea (Goldmann tonometer) or by estimating the diameter of the circular contact area of the cornea and flat tonometer of defined load (Maklakov tonometer). The first simplest models of the applanation method for measurement of the IOP were based on approach, in which an eyeball is modelled as a thin-walled spherical liquid-filled soft shell with corneal biomechanical properties. It was usually supposed that these properties were the same for all patients. In this work numerical simulation have been carried out using finite element code ANSYS. The eye shell is modeled as two joint shells (cornea and sclera) with different mechanical properties. The results are obtained for numerous sets of parameters and were compared to clinical data. For statistics the measurements of IOP for both eyes of 120 patients before and one month after refractive surgery are used. All parameter of refractive surgery (depth, the width and the place of ablation - refractive surgery for myopia or hypermetropia) have effect on IOP reading obtained with both Goldmann and Maklakov tonometry. The results obtained by Goldmann tonometer are significantly more sensitive to all parameters of refractive surgery than those found with Maklakov tonometer with load 10 g. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The aim of this research is to represent, within one modelling framework, selected parts of the musculoskeletal system using principles of continuum mechanics, while other parts are modelled using lumped-parameter models and principles of Multi-Body Dynamics. The most challenging part within such a framework will be to properly model the transition from 3D to 1D models for skeletal muscles as many of the skeletal muscles extend beyond the selected part. Hence, this paper focuses on an interface condition for the 3D-1D transition within a skeletal muscle. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: On daily activity a human operator is exposed to vibration in working environment. So, the human body will react in different way. The problem is how much from the initial signal will be sent to the other parts of the body and how much that motion will be damped along the studied parts. The vibrations in horizontal plane are some unexpected, so the human operator will not take any position to prevent them. In this condition the horizontal vibrations will have the higher effect possible. In this paper, the shoulder, neck and the head are modeled together like a mechanical system with four degree of freedom. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In the present paper, the aim was to develop a numerical method for optimisation an existing mechanical material model [1] including muscle activation concerning the excitation of skeletal muscles. The modelling idea was a weak and non-monolithic coupling of an electric current expressed by Ohm's law with a hyperelastic muscle model with transversal isotropic characteristics, see [2]. We confirmed the ability of the proposed model by applying on real reconstructed complex muscle geometry. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: An essential property of soft biological tissues is the ability to adapt according to respective loading conditions, e.g. by means of fibre reorientation (remodelling). In particular with regard to arterial tissue, an externally unloaded state of the material is generally associated with residual stresses. In this contribution a three-dimensional micro-sphere-based constitutive model for anisotropic soft biological tissue is presented, which includes fibre-reorientation-related remodelling as well as residual stress-effects. As a key aspect of this contribution, time-dependent remodelling effects are incorporated by introducing evolution equations for the integration directions of the micro-sphere scheme, which thereby characterize the material's anisotropic properties. An appropriate remodelling approach for the orthotropic case is discussed, whereas the effect of residual stresses is additionally included in the model by means of a multiplicative decomposition of the deformation gradient tensor. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The material behaviour of skeletal muscles can be decomposed into two parts: an active part, describing the contractile mechanisms, and a passive one, characterising the passive components such as the connective tissue. Computational models are used to support the understanding of complex mechanism inside a muscle. In the present work, we focus on the three-dimensional passive tissue behaviour from the experimental as well as modelling point of view. Therefore, quasi-static experiments have been performed on specimens with regular geometry. By using a three-dimensional optical measurement system the shape of the specimens has been reconstructed at different deformation states. On the modelling side a hyperelastic model with transversal isotropic fibre orientation has been used to describe non-linear stress responses. The model has been validated by performing analyses for different fibre orientations. In summary, it figures out that the proposed modelling approach is able to reflect the experimental results in a satisfying manner. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Numerical simulations of the formation and the characteristic shape of plastic zones at crack tips in rubber-toughened polymers are performed in order to get a better understanding of the underlying micromechanisms. Complementing previous work, the present study focuses on the contribution of distributed crazing. A macroscopic constitutive model therefore has been developed that describes the overall effect of distributed crazing as an anisotropic flow process. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Nondestructive test methods are important for examination of elastic devices regarding existence, position and size of cracks. In the case of hidden cracks (which do not touch the boundary), a simple visual control is not sufficient. The basic idea of this paper is to examine appropriate boundary measurements under certain loads. We focus on a method presented by ANDRIEUX, BEN ABDA and BUI [1] for isotropic linear elasticity, and generalize the crack plane detection to anisotropic linear elastic material. The main idea is the use of the reciprocity principle in order to connect data from the outer boundary with the unknown crack properties. Some 2D numerical examples demonstrate, that the method is working with simulated data. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this paper static Green's functions for functionally graded Euler-Bernoulli and Timoshenko beams are presented. All material properties are arbitrary functions along the beam thickness direction. The closed-form solutions of static Green's functions are derived from a fourth-order partial differential equation presented in [2]. In combination with Betti's reciprocal theorem the Green's functions are applied to calculate internal forces and stress analysis of functionally graded beams (FGBs) under static loadings. For symmetrical material properties along the beam thickness direction and symmetric cross-sections, the resulting stress distributions are also symmetric. For unsymmetrical material properties the neutral axis and the center of gravity axis are located at different positions. Free vibrations of functionally graded Timoshenko beams are also analyzed [3]. Analytical solutions of eigenfunctions and eigenfrequencies in closed-forms are obtained based on reference [2]. Alternatively it is also possible to use static Green's functions and Fredholm's integral equations to obtain approximate eigenfunctions and eigenfrequencies by an iterative procedure as shown in [1]. Applying the Sensitivity Analysis with Green's Functions (SAGF) [1] to derive closed-form analytical solutions of functionally graded beams, it is possible to modify the derived static Green's functions and include terms taking cracks into account, which are modeled by translational or rotational springs. Furthermore the SAGF approach in combination with the superposition principle can be used to take stiffness jumps into account and to extend static Green's functions of simple beams to that of discontinuous beams by adding new supports. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this paper stabilized mixed triangular finite elements are presented in order to avoid volume locking and to damp stress oscillations. Geometrically non-linear elastic problems are addressed. The mixed method of incompatible modes and the mixed method of enhanced strains are considered as special cases. As a key idea, volume and area bubble functions are used for the method of incompatible modes and the enhanced strain method [1], thus giving both the interpretation of a mixed finite element method with stabilization terms. Concerning non-linear problems these are non-linearly dependent on the current deformation state, however, linearly dependent stabilization terms are used [1]. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step is completely avoided. The variational formulation for the standard two-field method, the method of incompatible modes and the enhanced strain method in finite deformation problems is derived for a hyper elastic Neo-Hookean material. In the representative example Cook's membrane problem illustrates the good performance of the presented approaches compared to existing finite element formulations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The scaled boundary finite element method (SBFEM) is extended to the static analysis of thin plates in the framework of Kirchhoff's plate theory. The governing equations are transformed into scaled boundary coordinates. Applying a discrete form of the Kantorovich reduction method results in a set of ordinary differential equations, which can be solved in a closed-form analytical manner. The element stiffness matrices for bounded and unbounded media can be computed, using appropriate subsets of the analytical solution. Examples show the efficiency of the method, applied to plate bending problems. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The contact situation between the brake pad and the disc during the braking process is of particular importance concerning the squeal behavior of brake systems. After the braking process, the surface topography of brake pads can be measured using a confocal microscope. An algorithm to calculate the contact between two surfaces has been developed at the Institute of Dynamics and Vibrations. The algorithm calculates the deflection of asperities under a normal load regarding an elastic material behavior. A normal load is applied to a measured surface topography of the brake pad; the counter body (brake disc) is represented by a flat surface. The potential contact area, the locally distributed forces, deflections and normal stiffness of the pad are computed. Since there is an uncertainty in the relative position between the pad and the disc and hence the real contact situation during the braking process is not known, different contact situations must be considered during the simulations. Concerning various tilt angles of the pad that can arise during the vibrations of the brake system, a sensitivity study has been carried out. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Isogeometric analysis is a high-continuity alternative to the standard finite element method. However, for practical application several issues remain to be addressed. This contribution discusses the imposition of Dirichlet boundary conditions as well as the connection between multiple patches. In particular necessary manipulations of the geometrical input data are provided. Dirichlet boundary conditions can be imposed in weak or in strong form. Due to the non-interpolatory characteristics of NURBS surfaces weak imposition of Dirichlet conditions is a viable option which avoids local transformations. The connection of multiple patches can be realized in a weak manner by adding additional terms to the variational equations, for example by the Lagrange multiplier method or the perturbed Lagrangian method. Both base on the idea of multiplying the mutual deformations with an additional unknown to force the deformations on shared edges to be equal. The numerical treatment leads to different sets of equations. In contrast to strong inter-patch connections, where coinciding control points share the same degrees of freedom, weak imposition allows for hanging nodes and therefore local refinement. The theoretical background and issues of implementation are given. Some numerical examples compare error norms for all mentioned methods and demonstrate that in particular cases a reduction of continuity leads to more accurate results. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: A new soft computing approach is described, which can be applied for the identification of uncertain time-dependent material behaviour. Artificial neural networks are utilized for model-free material formulations. Uncertain stress-strain-time dependencies obtained from uncertain results of experimental investigations are described by recurrent neural networks for fuzzy data. An incremental finite element formulation is presented using neural networks instead of material models. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The present work aims to investigate stable time integrators for large deformation contact problems within the framework of the well known node-to-segment (NTS)-method. For this kind of problem, standard time integrators fail to conserve the total energy of the system. To remedy this drawback, we combine a mixed method with the concept of a discrete gradient applied to the aforementioned NTS-method. In the context of nonlinear elastodynamics stable integrators for ordinary differential equations have been extensively developed and investigated during the last two decades. For contact problems, energy consistent integrators have been developed for the NTS-method (see e.g. Ref. [1]). (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this paper, new solid-shell and solid-beam finite element formulations for finite deformation problems are introduced. One application of interest, concerning these types of elements, can be found in the simulation of stent implementation in the treatment of stenosis. The beam-like structure of the stent and the shell-like structure of the blood vessel can be modelled easily by using these types of elements. Moreover, the modelling of the interaction of the different structural types between each other and with the surounding tissue becomes more simple. A high rate of convergence, by using only one element in thickness direction that is comparable to classical structural elements, can be named as a major requirement for the element formulations. In this regard, different locking effects are cured by a special combination of the assumed natural strain method (ANS) and the enhanced assumed strain method (EAS). In addition a variable number of quadrature points can be used in thickness direction in order to capture nonlinearites. This is combined with the concept of reduced integration for the sake of computational efficiency. An adaptive hourglass stabilization that also accounts for material nonlinearities is a crucial issue in this regard. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this paper a new approach for designing mechatronic vibrating branched structures has been presented. Mechatronic structures have been built from mechanical discrete systems connected to piezoelectric actuator and external L x R x C x network, with different configurations. Modeling simplification has been performed by use of non dimensional transformations and retransformations. In each case reverse task has been solved by distribution into partial fraction method in respect to required dynamic properties in form of frequency spectrum: resonant and anti resonant frequencies. Furthermore, different configurations of final L x R x C x network have been presented. These considerations have been supported by calculation examples, and all results have been presented in the graphical form. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: We will present a comparison between two formulations of the normal vector field for contact algorithms based on the mortar method. First the non steady normal field is discussed. The non steadiness is a result of the C 0 continuity of the boundary discretization. This is the common result if one discretize the domain with classical finite element methods. Second we will present results for a special normal field distribution. We average the nodal normal vector of two ascending edges and interpolate this nodal normal throughout the edges. We have implemented both methods and present comparisons based on numerical experiments. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The numerical simulation of timber structures by means of FEM has been an object of recent research. Most of the material models developed so far are based on idealized assumptions by disregarding inhomogeneities. Here, models to capture structural inhomogeneities in terms of branches and knots and the resulting deviation in grain course in a three-dimensional FE analysis are presented. Besides, naturally varying material properties referred to as material inhomogeneities have to be considered in the structural analysis. Due to the insufficient experimental data, the uncertainty model fuzziness is applied. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The process integrated powder coating by radial axial rolling of rings represents a new hybrid production technique in order to apply the functional layers on ring-shaped work pieces. Since the layer is produced in a powder metallurgical way [1], the ring volume decreases during the compaction of the layer material. In conventional ring rolling processes an isochoric plastic deformation of the ring is exploited in order to control the process. However this is not true any more for a ring exhibiting a compressible layer [2]. Consequently different control mechanisms have to be developed for the new considered process. One major aspect is the stability of the process which is governed by a stable position of the ring as well as the roundness of the ring. Therefore the finite element (FE) model has been coupled with a PID-controller unit and it will be shown that a stable process can be reached in this way. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The problem of the interaction of a finite number of holes in an elastic plane or half-plane is considered. The analysis is based on the complex potential method of Muskhelishvili as well as on the theory of compound asymptotic expansions by Maz'ya. An asymptotic expansion of the complex potentials in terms of relative hole radii is constructed. This expansion is uniformly valid in the whole domain. The method leads to a simple procedure which does not involve any coupled system of linear equations. The successive closed-form approximations can be obtained in an iterative manner to an arbitrary order without any need for numerical approximation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The kinematics and kinetics of a compliant mechanism are analyzed quasi-statically. The mechanism consists of a parallelkinematic (Biglide type) with the particular feature, that its revolute joints are implemented by flexure hinges. In the considered example the flexure hinges are uniform beams similar to leaf springs. The preliminary considerations with a rigid body system and by linear theory of elasticity result in an initial geometry. In order to predict the large displacement behavior more precisely the theory of Elastica is used. An optimization method is applied to solve the mechanism's state of deformation. It was found that some aspects can be approximated by a pseudo rigid body system, while others, namely the rotation, cannot be rendered. The decreased stiffness in the highly deformed operating state appears as key problem. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The main goal of the present work is to develop two structure-preserving time integrators, which are based on the works of Öttinger [1] (GENERIC formalism), Romero [2] (Thermodynamically consistent (TC) algorithm) and Groß [3] (enhanced hybrid Galerkin (ehG) method) and compare them with standard integrators considering a thermoviscoelastic double pendulum. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The Boundary Element Method is quite suitable for solving dynamic semi-infinite or infinite linear problems. In order to establish the boundary integral equations, one crucial condition is the knowledge of corresponding fundamental solutions. For a partially saturated poroelastic continuum, the governing equations in Laplace domain are formulated based on the theory of mixtures, and the related fundamental solutions are derived by using Hörmanders method. The singular behavior of the fundamental solutions are investigated by a series expansion with respect to the variable r. Finally, some exemplary fundamental solutions are calculated to visualize the principal behavior as well, and comparisons with the related results of saturated poroelasticity are given. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: During the production of high-grade wooden components often the conditioning with coated abrasives composes the end of the process train. The chipping process and the resulting wood surface are depending of the scatter pattern parameters (particle size and distribution, …) and their time depending variations. Till now, no models exist concerning the interaction of the scatter pattern with the grinding process, the work piece surface and the clogging. The developed model is based on cooperating cellular automata. One is describing the sandpaper, the other one the work piece. These two automata interacts witch each other. Update rules are designed by physical laws and measurements. The paper shows surprising results with respect of surface structures which are the result of self-organization effects in the boundary layer of wood and sandpaper. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Das Übertragungsverhalten sowie die Eigenfrequenzen und Eigenformen zweier Statorblechpakete wurden experimentell und numerisch, mittels einer Modalanalyse eines homogenen Finite-Elemente Modells, ermittelt. Durch geeignete Abstimmung der Materialparameter des Simulationsmodells wurde die Strukturantwort an die der Messung angepasst. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In linear poroelasticity so far only collocation boundary element methods have been available. However, in some applications, e.g., when coupling with finite elements is desired, a symmetric formulation is preferable. Choosing a Galerkin approach which involves the second boundary integral equation, such a formulation is possible. Here, a previously presented integration by part technique for the regularization of the first boundary integral equation is extended to the second boundary integral equation as well. While the weakly singular representation of the double layer operator has been presented before, the emphasis lies here on the so called hyper-singular boundary integral operator. Due to the regularization, this operator can be evaluated numerically and, hence, be used within a numerical scheme for the first time. Different numerical studies will be presented to show the behavior of the established symmetric Galerkin boundary element method, also comparing it with collocation boundary element methods. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The computation of ropes and cable constructions considering contact as well as friction is often required in engineering practice. That includes mutual frictional contact between two and more ropes and frictional contact between ropes and solid –mostly assumed as rigid– bodies. The latter occurs especially in the mechanical model of a rope wound around a cylinder. So the main topic of this contribution is the development and FE-implementation of a "Segment- To-Analytical-Surface (STAS)"-contact-element which can be used to describe the mechanical model of a rope wound around a cylinder. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Two distinct analytical models are described representing geometrically nonlinear instabilities in layered composites under in-plane compression — kink-banding and delamination buckling. The utilized technique is based on of energy minimization principles in order to examine the underlying mechanics of the systems. It is demonstrated that using this approach enables investigations to be undertaken far into the postbuckling range whilst changing system parameters. Thereby a greater phenomenological understanding of the mechanics of the systems is achieved. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The aim of contribution is to formulate a certain extended version of the tolerance modelling technique for functionally graded composites. For the sake of simplicity, the considerations are restricted to the bidirectionally graded heat conductors. It is shown that the proposed approach enables to determine an entire class of mathematical models for which applications can be found in various specific problems. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Considering a simply supported plate under uni-axial compression it is well-known that after buckling the stress concentrates at the unloaded boundaries as the out-of-plane displacement at the buckle causes an in-plane relaxation, i.e. a decrease of the mid-plane stress. This stress distortion is described by the so-called effective width. The knowledge of the effective width allows the calculation of the stress at the unloaded boundaries, which is usually considered as the highest stress in the plate. However, the out-of-plane displacement also bends the plate, which produces additional stresses. This article analysis the fundamental question, if the total stress at the surface of the buckle is higher than the stress at the unloaded boundaries. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The Finite Cell Method (FCM) combines the fictitious domain approach with high-order finite elements and adaptive integration. For linear elastic problems with smooth solution, FCM has been shown to achieve exponential rates of convergence in energy norm, while its structured cell grid guarantees simple mesh generation irrespective of the geometric complexity involved. In this contribution, the FCM idea is combined with standard finite element technology for the solution of geometrically nonlinear problems. In particular, a modified FCM formulation is introduced, which resets the deformed configuration of the fictitious domain to the deformation-free reference configuration after each Newton iteration. Numerical experiments show that this intervention allows for stable nonlinear FCM analysis with very small values of the penalty parameter, while the accuracy of the geometrically nonlinear solution within the physical domain remains unaffected. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Active control of flexible vibrations by distributed piezoelectric actuators and sensors plays an increasing role in engineering, especially in light-weight structures. Exemplarily, in this contribution a rotating beam is studied which can be found in many practical applications, e.g. as robot arms or flexible manipulators in production processes. It has been intensively shown in the literature that it is possible to completely suppress the flexible vibrations by an appropriate distribution of piezoelectric actuation strains. In order to compensate the inertial forces in the considered rotating beam, a complex distribution is obtained, such that a practical realisation would be very extensive. To overcome the problem, a discrete approximation by piezoelectric patches is applied. In order to find an optimal configuration for an experimental setup, and to investigate several control strategies, a numerical simulation model has been implemented based on Bernoulli-Euler beam theory. The numerical results are verified by an experimental set-up, in which 48 piezoelectric patches have been attached on a beam with rectangular hollow cross-section. Each patch can be used either as an actuator or a sensor. Additionally, strain gauges can be used as sensors. For monitoring, acceleration sensors are used. The control system is implemented within a dSpace environment. The results show a significant reduction of the flexible vibrations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The choice of coordinates for the description of multibody dynamics has a strong impact on the form of the equations of motion. In the talk two alternative formulations are compared: (i) joint coordinates along with Euler angles for the orientation of rigid bodies, and (ii) redundant coordinates where the orientation of rigid bodies is described in terms of direction cosines. In the case of multibody systems with tree structure the use of generalized coordinates yields equations of motion in the form of ordinary differential equations. In contrast to that, the choice of redundant coordinates yields differential-algebraic equations. The two alternative formulations are compared and their influence on the numerical time integration is highlighted. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Mechanical stimuli play a crucial role in the differentiation process of mesenchymal stem cells (MSC). The resulting mechanical signals are important in the regulation of various cell functions and maintenance of many tissues. The underlying molecular and biophysical mechanisms of the differentiation process are poorly understood. Present remodelling and growth models are purely phenomenological without linkage to cell mechanisms. The presented macroscopic model of MSC mechanics is based on a multiphasic-multicomponent formulation within the framework of Theory of Porous Media (TPM), where a single cell is considered as a mixture of interacting constituents. In particular, the constituents are the solid cytoskeleton saturated by a fluid phase (cytoplasm), which itself consists of a liquid solvent and mobile components, e. g., chemical messengers, proteins, etc. To demonstrate the capabilities of the developed model, first qualitative numerical simulations of the impact of external forces on MSC are presented. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The present work deals with the incorporation of residual stresses existing in circumferential direction of arterial walls. For the consideration of the residual stresses a novel model will be presented. This model is based on the assumption that residual stresses decrease the stress gradients through the thickness of the arterial wall. Since arterial walls exhibit a pronounced material behavior in fiber direction, the radial gradients of the fiber stresses are considered for the definition of the residual stresses. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In this contribution a finite element model for the three dimensional investigation of hip joint contact is described. A shell-like interface element with variable thickness is developed for modelling fluid flow in the synovial gap. For this purpose the Taylor-Hood element is extended in order to take a spatial thickness distribution and local thickness changes into account. The interaction between the synovial fluid and the cartilage layers is solved by a staggered iteration using an artificial compressibility method. Cartilage is modelled using the theory of porous media and three dimensional geometries are reconstructed from medical imaging data. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Especially for specific applications, such as contact problems, computer methods for flexible multibody dynamics that are able to treat large deformation phenomena are important. Classical formalisms for multibody dynamics are based on rigid bodies. Their extension to flexible multibody systems is typically restricted to linear elastic material behavior whereas large deformation phenomena are formulated in the framework of the nonlinear finite element method. In the talk we address computer methods that can handle large deformations in the context of multibody systems. In particular, the link between nonlinear continuum mechanics and multibody systems is facilitated by a specific formulation of rigid body dynamics [1]. It makes possible the incorporation of state-of-the-art computer methods for large deformation problems. In the talk we focus on the treatment of large deformation contact whithin flexible multibody dynamics [2]. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The law of bone remodeling, commonly referred to as Wolff's Law, asserts that the internal trabecular bone adapts to external loadings, reorienting with the principal stress trajectories to optimize mechanical efficiency creating a naturally optimum structure. The current study utilized an advanced structural optimization algorithm, called design space toptimization (DSO), to perform a three-dimensional computational bone remodeling simulation on the human proximal femur and analyse the results to determine the validity of Wolff's hypothesis. DSO optimizes the layout of material by iteratively distributing it into the areas of highest loading, while simultaneously changing the design domain to increase computational efficiency. The large-scale simulation utilized a 175 µm mesh resolution with over 23.3 million elements. The resulting anisotropic trabecular architecture was compared to both Wolff's trajectory hypothesis and natural femur samples from literature using radiography. The results qualitatively showed several anisotropic trabecular regions that were comparable to the natural human femur. The realistic simulated trabecular geometry suggests that the DSO method can accurately predict bone adaptation due to mechanical loading and that the proximal femur is an optimum structure as Wolff hypothesized. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This contribution is concerned with mixed finite element formulations for modeling piezoelectric beam and shell structures. Due to the electromechanical coupling, specific deformation modes are joined with electric field components. In bending dominated problems incompatible approximation functions of these fields cause incorrect results. These effects occur in standard finite element formulations, where interpolation functions of lowest order are used. A mixed variational approach is introduced to overcome these problems. The mixed formulation allows for a consistent approximation of the electromechanical coupled problem. It utilizes six independent fields and could be derived from a Hu-Washizu variational principle. Displacements, rotations and the electric potential are employed as nodal degrees of freedom. According to the Timoshenko theory (beam) and the Reissner-Mindlin theory (shell), the formulations account for constant transversal shear strains. To incorporate three dimensional constitutive relations all transversal components of the electric field and the strain field are enriched by mixed finite element interpolations. Thus the complete piezoelectric coupling is appropriately captured. The common assumption of vanishing transversal stress and dielectric displacement components is enforced in an integral sense. Some numerical examples will demonstrate the capability of the presented finite element formulation. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has mainly been applied to fully turbulent flows it is extended here to also cover the laminar flow regime which is relevant for micro systems due to the low Reynolds numbers of these flows. Specific numbers of K can be determined by integration of the entropy generation field (second law analysis) obtained from a numerical simulation. It will be shown that a definition of K based on entropy generation is superior to a widely used definition that refers to a pressure drop caused by the conduit component. With the second law analysis details of the physics become available. For example it can be shown that often the main part of the entropy generation occurs downstream of the component. This aspect becomes important when several conduit components are combined in close proximity, like two 90 degree bends that are close to each other. Often in such situations the combination as a whole has to be looked upon as one new complex component. The general approach is discussed and illustrated for various conduit components and combinations of them. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper reviews the singular perturbation control theory in the context of flexible multibody systems. The theory is motivated and explained by a simple, but sufficiently complex model. It is explained that based on the singular perturbed model an end-effector trajectory tracking can be achieved by an integral manifold controller. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: We consider the use of the Restricted-Denominator (RD) rational Arnoldi method for the computation of the core functions of exponential integrators for parabolic problems. Reliable and easy-to-use a-posteriori error bounds are presented. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The articulated robot ElRob, consisting of flexible links and joints, is considered in several publications. Recent developments are presented in this work. The overall goal of the research is to decrease the effects of structural elasticities in lightweight robots. For this purpose model-based control concepts are investigated and very accurate and efficient kinematic and dynamic models are necessary. The robot is split into groups of bodies, the so called subsystems, with separated describing velocities and coordinate systems. To obtain structured equations of motion the Projection Equation is used. The beams are modelled using the floating frame of reference formulation and a Ritz-approach. Because of its flexibility, the examined robot is an underactuated system leading to special difficulties. As an example is it not possible to compute the desired joint angles with respect to a reference path in task space for the flexible system (inverse kinematic problem). Different methods to solve this drawback and other problems resulting from flexibility are discussed with special focus on feed forward control and different feedback control concepts. The resulting end point error, the necessary control input and other interesting results for the laboratory experiment are presented and compared. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Passively compliant drive concepts are often used in bio-inspired robot designs. Especially fluidic artificial muscles share many characteristics with their natural counterparts. Industrial manipulators can benefit from the increased robustness and safety (in contrast to rigid drives) especially in cooperative human/robot environments. We compare different model-based control concepts for a single rotational joint actuated by two fluidic muscles in combination with proportional valves. While the complete valve and muscle models are already included in this setup, the mechanical model becomes more complex when we extend the control to a full seven axes articulated robot arm with both, electrically and pneumatically actuated joints. In this case the Projection Equation in subsystem description is used for the multibody model, allowing a straight-forward realtime application to different robot kinematics. Remaining model errors and disturbances are handled by observer algorithms. We present measurement results and compare them to simulation outputs. Besides the position control, possible approaches for sensorless external force estimation are discussed. They take advantage of the compliance of the robot and are again based on the actuator and multibody models. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This work discusses two different structure preserving integrators in the framework of optimal control simulations with contact. The first one is a variational integrator, based on the constrained version of the Lagrange-D'Alembert. The resulting scheme preserves the symplecticity and the momentum maps of the simulated multibody dynamics. The second integrator is an energy momentum scheme and it is based on the augmented Hamiltonian equations, which are discretised using the discrete derivative in [2]. Both integrators are applied to simulate the optimal control of compass gait, for which the contact between the foot and the ground is modelled as perfectly plastic contact. The second example represents a monopedal jumper and it is used to examine the dynamical behaviour of the perfectly elastic and perfectly plastic contact formulation. The resulting differential algebraic equations (DAEs) are solved by the aforementioned symplectic momentum method. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Synthesis of adequate mathematical description of the main mechanical line of rolling mill are considered. The four-mass model with weightless elastic connections is chosen as mathematical model of dynamic system of the main mechanical line of the rolling mill. The problem was reduced to solution of integral equation of the first kind (to unsteady problem). The methods of obtaining of the steady solutions are suggested. Synthesis of the adequate mathematical descriptions with unitary model of external load are suggested. The metal rolling was executed with using of real experimental measurements as an example. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In the present paper a three-dimensional beam finite element undergoing large deformations is proposed. Since the definition of the proposed finite element is based on the absolute nodal coordinate formulation (ANCF), no rotational coordinates occur in the formulation. In the current approach, the orientation of the cross section is parameterized by means of slope vectors. Since those are no unit vectors, the cross-section can deform, similar to existing thick beam and shell elements. The nodal displacements and the directional derivatives of the displacements are chosen as nodal coordinates, but in contrast to standard ANCF elements, the proposed formulation is based on the two transversal slope vectors per node only. Different approaches for the virtual work of elastic forces are presented: a continuum mechanics based formulation, as well as a structural mechanics based formulation, which is in accordance with classical nonlinear beam finite elements. Since different interpolation functions as in standard ANCF elements are used, a much better convergence rate (up to order four) can be obtained. Therefore, the present element has high potential for application in geometrically nonlinear problems. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Detailed dynamical modeling is the basis for simulation and model based control. In this contribution the Projection Equation is used for the modeling of a biped walking machine, resulting in the equations of motion which are needed for gait generation and verification of its stability. For biped robots one main issue is the generation of stable trajectories for the center of mass (CoM). Several different approaches based on the Zero Moment Point (ZMP) scheme have been presented in the past. Due to the complex dynamic structure of bipedal robots most of the considered algorithms use a linear inverted pendulum as a simplified model. This results in a decoupling of the ZMP equations in lateral and forward direction, but limits the trajectories to a constant height of the CoM. An extension of the well known LQR theory by future reference values has been proposed. This model based approach seems to perform quite well, but does not allow the consideration of constraints on the position of the ZMP. This limitation is removed by the use of Model Predictive Control (MPC) with inequality constraints. By extending this approach to a time invariant one the restriction to a constant height of the CoM is no longer necessary. Both methods as well as the time invariant approach for variable CoM heights have been evaluated in simulations and will be experimentally verified on a real robot soon. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Mechanical systems with dynamics on varying time scales, in particular those including highly oscillatory motion, impose challenging questions for numerical integration schemes. Tiny step sizes are required to guarantee a stable integration of the fast frequencies. However, for the simulation of the slow dynamics, integration with a larger time step is accurate enough. Small time steps increase integration times unnecessarily, especially for costly function evaluations. For systems comprising fast and slow dynamics, multirate methods integrate the slow part of the system with a relatively large step size while the fast part is integrated with a small time step. Main challenges are the identification of fast and slow parts (e.g. by separating the energy or by distinguishing sets of variables), the synchronisation of their dynamics and in particular the treatment of mixed parts that often appear when fast and slow dynamics are coupled by constraints. In this contribution, a multirate integrator is derived in closed form via a discrete variational principle on a time grid consisting of macro and micro time nodes. Variational integrators (based on a discrete version of Hamilton's principle) lead to symplectic and momentum preserving integration schemes that also exhibit good energy behavior. The resulting multirate variational integrator has the same preservation properties. An example demonstrates the performance of the multirate integrator for constrained multibody dynamics. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper deals with the dynamical modeling and control of modular redundant robots. The robots under consideration consist of modular actuators (brushless DC motors with Harmonic Drive gears) connected by rigid links. Different configurations can be designed by rearranging these subsystems. In order to fulfill the requirement for an efficient dynamical modeling, the Projection Equation in subsystem representation is used. The subsystems are connected via the kinematical chain. The Projection Equation offers the possibility to calculate the minimal accelerations recursively, leading to an O(n) computational effectiveness. To validate the proposed method, the model of an articulated robot arm with seven joints is considered. Simulation results are compared to measurements. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper aims at creating a mathematical model of a bending oscillation rotor system which enables to execute a dynamical analysis of its vibration including the influence of nonlinear bearing characteristics. More specifically, using the finite element method the model of rotating system supported by four hydrodynamic bearings was created. The basic dynamical analysis of the rotor system was performed and the eigenvalues, eigenvectors and stability conditions were evaluated. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Underactuation occurs, when only some generalized coordinates have a control input. For end-effector trajectory tracking a combined feed-forward and feedback control is often a suitable approach. Feed-forward control design based on an inverse model for underactuated multibody systems is presented. The starting point is the transformation of the multibody system into a nonlinear input-output normal-form. The inverse model follows from this and consists of chains of differentiators, driven internal dynamics and an algebraic part. Especially when using the end-effector as system output the internal dynamics is often unbounded. In order to obtain a viable feed-forward control, a bounded solution must be determined. For this task the internal dynamics is solved as a nonlinear optimization problem. Thereby, the coordinates of the internal dynamics define the objective function which is minimized. The equation of the internal dynamics must be fulfilled at each point of a discrete time grid. In addition continuity of the solution is achieved by adding as equality constraint an integration formula, e.g. trapezoidal rule. The optimization problem is then solved by a SQP-method. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The aim of the paper is to investigate the remodeling phenomenon of a cell-seeded material (collagen type-I) due to collagen type-II newly synthesized by the cells. For the experiments, a cell-seeded condensed collagen gel is mechanically stimulated in a bioreactor for four weeks. The remodeled stiffness of the cell-seeded gel is measured by a compression test and is explained with an evolution law. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This article presents the vibration action on the human body found in a tram travel, where made the vibration measurements. Also presented a mathematical model with two degrees of freedom. Finally a comparison was made between the results obtained from measurements and the results of integration. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The present contribution is motivated by the desire to compute physiological loads on the intervertebral discs (IVD) of a human lumbar spine during activities like standing, bending and falling. Following this, a mechanical multi-body system (MBS) is utilised to capture the overall mechanical behaviour of a human, whereas an inhomogeneous, anisotropic, multi-phasic finite-element model (FEM) is applied to resolve the resulting field quantities inside an IVD. In order to couple the FEM of the IVD with the numerically diverse MBS, a homogenisation procedure has to be applied such that field quantities can be converted into discrete quantities. In particular, the MBS captures the mechanical behaviour of an IVD using a bushing element, which provides discrete force-displacement and moment-rotation relations. The goal of this contribution is to present a homogenisation method for the IVD as well as a possibility to include the homogenised results in the MBS without the need for embedded FE computations in the MBS. Instead, certain deformation modes of the IVD are pre-computed and represented using a non-linear constitutive equations. This task becomes even more challenging, as the resulting discrete DOF of a motion segment appear in a coupled fashion due to the structure of the IVD, i. e., a rotation in the sagittal plane triggers a resulting moment and a resulting force. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: This paper presents a hybrid model to describe drill string dynamics for deep hole drilling. Generally, a typical rotary drill string has a length of several kilometers, but the diameter is less than half a meter. Due to the large ratio of length to diameter, a drill string is a very flexible system. Consequently, an operating drill string is always affected by axial, torsional and lateral vibrations, which potentially induce serious failures. In order to avoid fatal defects, simulations to forecast vibrations are necessary. The simulation should be capable to exhibit the complex dynamical phenomena, e.g. sick-slip, forward whirl and backward whirl, and interactions between drill string and borehole. Usually, these simulations are very time-consuming. In this work, a hybrid model consisting of lumped masses connected with weightless beam elements representing the drill string is developed. The interaction between the drill string and the borehole is implemented by unilateral constraints to describe the nonlinear contact behavior. It was shown that accuracy and simulating time were improved by this model with respect to classical finite-element models. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The present work deals with optimal control problems governed by differential-algebraic equations (DAEs). In particular, the control effort, which is necessary for moving a multibody system from one configuration to another, will be minimized. The orientation of the rigid bodies will be described using directors, which facilitates the integration of the equations of motion with an energy-momentum consistent time-stepping scheme [1]. This type of structure-preserving integrators offer outstanding numerical stability and robustness properties in comparison to the often applied generalized coordinates formulation. In the context of optimal control, other kinds of consistent integrators have been applied previously in [2] and [3]. We will test the different formulations with two numerical examples, a 3-link manipulator and a satellite. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Bone tissues are formed by cells, bone matrix and fluids. The bone matrix is a porous structure, which is remodelled by bone-cells. To describe this process, a coupled systems-biological and biomechanical model is presented. The macroscopic mechanical behaviour of bone is specified by a biphasic model embedded in the Theory of Porous Media, where the solid phase represents cells and bone matrix, and the fluid phase summarises the extracellular fluids and its components. In this context, the bone remodelling process is described on the macro-scale by a distinct mass exchange that also results in a change of the constituents'material properties. On the micro-scale, the description of the bone remodelling process stems from a systems-biological cell interaction model. Therein, the bone matrix formation and resorption are a result of the stress-regulated activity of cells. Here, a staggered solutions strategy is presented. Therein, snapshots of the mechanical stress distribution are calculated on the macro-scale by use of the finite element method. The snapshots are locally evaluated on the micro-scale by use of a cell interaction model, which calculates the long term remodelling process. The evaluation results of the micro-scale are then used to update the reference configuration of the mechanical simulation. As an integrative modelling platform scientific workflows and web-service technologies are employed. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Description: In this contribution, a constitutive model adopted from the computational plasticity-models of Drucker-Prager and von Mises is presented. This model captures the material behavior of osseointegration and the curing-process of bone cement. With this basic model, both simulations of bone-ingrowth of uncemented implants and simulations of the curing process of bone cement for cemented implants are carried out in a bone-implant interface. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: In a seated posture into an autovehicle, humans are most sensitive to whole-body vibrations under low-frequency excitation. This research is focused only on the effect of the backrest angle on the biodynamic response functions. In this paper there are present the results of investigations for 10 participants, whose mean body mass was 61.4 kg. For the biodynamic responses of a seated human body subjected to vertical vibrations, three automotive postures was study: without backrest support, with backrest inclined 7° and respectively 15°, by measurement of transmitted vibration in two different situations: with belt and respectively without this. Knowledge of human responses to vibration provides information about the position of backrest support to mitigate vibration transmitted through the body ensuring the health, comfort and performance. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The paper presents a study regarding the linear mechanical models corresponding to hand-arm system. These models was simplified unused the joint in wrist, elbow and shoulder. Also, for these mechanical models effectuated the equations system that would integrate, it obtained the solutions (displacements and velocities) finally. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The interpretation of human knee joint kinematics in terms of displacements is an outcome of the underlying model of the joint and the measurement technique. Measurement errors and noise challenge the development of optimization procedures which, based on a reduction in degrees of freedom, aim for the reproducibility of joint displacements by computational techniques. So far, optimization algorithms have been applied which are based on a kinematic model of the healthy human tibio-femoral joint (TFJ) as a compound hinge with two fixed orthogonal axes. On the other hand, empirical studies find non-orthogonal rotational axes. Therefore, it was the aim of the present study to investigate the implications of a refined kinematic model on the accuracy of computed joint rotation angles. For the purpose of quantitative comparison, kinematic data of a TFJ with two axes intersecting at an arbitrary angle were simulated. The joint rotations were optimized for the assumption of (a) two orthogonal and intersecting axes (model A), and (b) two axes intersecting at an arbitrary angle (model B). Model B recovers the original input data closer in case of low noise level as encountered in invasive measurement techniques. Skin mounted markers tracking involves non-normally distributed noise which is typically larger by on order of magnitude. In this case, model A exhibits a more favorable performance. These observations motivate the search for alternative kinematic descriptions of the TFJ. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: The paper contains the transmitted vibrations produce by shocks to the human bodies into the working space.There are the methods for measuring the vibration experiments transmitted through the shock of the human body by the foundation of forging hammer. There are the results given by the different sorts of accelerations into to special conditions of work in the working space. They are of the vibrometer adding the three directions accelerometer. In this way can be analyze taking into account the vibrations action over the human bodies under the action of the equipment in the working space produced by shocks. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: For surgery training and on-line support during surgeries a method is required which is able to reduce simulation time possibly even to realtime. This contribution compares the effectiveness of three model reduction methods, all of which are widely used for linear problems, in the context of nonlinear structural mechanics. Three reduction methods will be extended to nonlinear elasticity including large deformations. The performance of the extended concepts is investigated for a simplified model of a human inferior turbinate in the context of the functional endoscopic sinus surgery. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)