Implementation of an efficient coupled fem-sbfem approach for soil-structure-interaction analysis

Buildings are grounded in the surrounding soil, so that soil and structure interact with each other. Consequently in the soil induced vibrations are transmitted to the structures. Neighbouring buildings and structures interact with each other, as they are connected by the soil. Nowadays numerical simulation of soil structure interaction is of great interest and is applied to very different problems. These include for example the construction of reliable earthquake-resistant structures in seismic active areas, and also the increase of comfort of buildings by decouple them form surrounding emissions like vibrations induced by traffic of machine foundations. This work shows that the simulation of soil-structure-interaction taking unbounded domains into account, which fulfils the Sommerfeld radiation condition exactly, is not only possible for academic examples, but for large scale real life problems as well. Therefore two numerical methods where coupled to create an efficient coupled method, which can be used to simulate soil-structure-interaction in time domain. The numerical implementation of this coupled approach bases on a combination of finite element method [1] and scaled boundary finite element method [2]. The finite element method is used to discretise the near-field, containing structures and its surrounding soil. The coupled infinite half-space, the far-field is realised by the scaled boundary finite element method. A contemporary parallel implementation of the coupling algorithms is done, since the simulation of soil structure interaction in time domain is very time and memory consuming [3]. Subsequent the numerical performance of the implemented software is discussed in terms of speed-up and efficiency. Different geotechnical applications are illustrated and the applicability of the coupled method is shown and discussed on chosen examples

Soil-Structure Interaction Simulations Taking into Account the Transient Propagation of Seismic Waves

In this contribution we present a strategy to investigate the vibrations of build­ ings subjected to a transient seismic excitation, including the soil-structure inte ract ion . The proposed simulation method can be helpful during the design of earthquake-resistant structures in seismic active areas as well as for the design of vibration reduction measures for buildings subjected to surrounding emissions like vibrations induced by traffic or ma­ chine foundations. The structures and their foundation as well as parts of the soil arc modeled by Finite Element Method (FEM). The far field is idealized as an infinite half­ space and modeled with the Scaled Boundary Finite Element Method (SBFEM). Both methods arc coupled at the common inter face. This approach fulfills exactly the Sommer­ feld radiation condition. The seismic excitation is idealized as a plane wave propagating toward the structure with an arbitrary angle with respect to the soil surface. The 3D seismic wave field, caused by the wave passage at the near field boundary, is transformed into boundary tractions , which arc then applied at the interface between the near and far fields. We present an application of the proposed method for a group of three buildings, which interact with each other through the soil during the propagation of the transient seismic waves. Although not shown here, the proposed method can handle nonlinear material properties assigned to any clement of FEM part

An Efficient Coupled FEM-SBFEM Approach to Analyse Soil-Structure-Interaction in Time Domain

Bauwerke sind auf den umgebenden Baugrund gegründet, sodass Baugrund und Bauwerk miteinander interagieren können. Dabei können in den Baugrund eingeleitete Erschütterungen in die angrenzenden Gebäude übertragen werden. Zusätzlich interagieren benachbarte Bauwerke, wenn diese über den Baugrund miteinander verbunden sind. Heute ist die erdbebensichere Auslegung von Strukturen in seismisch aktiven Regionen oder auch die Komfortsteigerung von Gebäuden, indem diese von umgebenen Emissionen wie z.B. eingebrachten Vibrationen durch Verkehr oder Maschinenfundamente entkoppelt werden, von großem Interesse. Bei der Bearbeitung dieser sehr unterschiedlichen Fragestellungen wird immer häufiger auf numerische Simulationen zurückgegriffen, um die Boden-Bauwerk-Interaktion (BBI) zu untersuchen. In dieser Arbeit wird gezeigt, dass die Simulation der BBI unter Berücksichtigung randloser Gebiete, die die Sommerfeld'sche Abstrahlbedingung exakt erfüllen auch für großskalige realitätsnahe Modelle, wie sie in der Praxis benötigt werden, möglich ist. Dafür wird mit zwei numerischen Methoden ein effizientes gekoppeltes Verfahren zur Simulation der BBI im Zeitbereich vorgeschlagen. Die numerische Umsetzung beruht auf einer Kombination von FEM und SBFEM. Die FEM bildet dabei das Nahfeld ab, in dem die zu untersuchende Struktur samt anstehenden Baugrund enthalten ist. Der angekoppelte unendliche Halbraum wird als Fernfeld mit der SBFEM diskretisiert. Weil die Simulation der BBI im Zeitbereich mit einem großen Rechenaufwand und Speicherbedarf einhergeht, werden unterschiedliche Methoden eingesetzt um eine numerische Simulation in angemessener Zeit durchführen zu können. Es wird gezeigt, dass bei entsprechender Diskretisierung des Fernfeldes realitätsnahe Fragestellungen der BBI untersucht werden können. Verschiedene Ansätze werden für die Reduktion des Berechnungsaufwands verfolgt und miteinander kombiniert. Nach Einführung in die theoretischen Grundlagen der Modellbildung und einer Diskussion der numerischen Verfahren wird auf die Validierung des hier gewählten Kopplungsansatzes eingegangen. Dies erfolgt anhand ausgewählter Beispiele, für die analytische bzw. semi-analytische Lösungen bekannt sind. Es werden mögliche Anwendungen aus dem Bereich der Geotechnik vorgestellt und die Anwendbarkeit des hier entwickelten Verfahrens an Modellbeispielen gezeigt.Buildings are directly in contact with surrounding, such that the soil and the structure interact with one other. Consequently, soil induced vibrations are transmitted to the structures. Additionally nearby structures interact with one another as they are connected by the soil. Nowadays numerical simulation of soil-structure-interaction (SSI) is of great interest, and is applied to a wide range of different problems. These include the analysis and design of reliable earthquake-resistant structures in seismic active areas, and also design to the increase the comfort of buildings by decoupling them from surrounding emissions such as vibrations induced by traffic of machine foundations. The present work shows the simulation of SSI which takes unbounded domains into account. This work fulfils the Sommerfeld radiation condition exactly, and shows that it is not only applicable for academic examples, but for large scale real life problems as well. Two numerical methods are coupled to create an efficient coupled method which can be used to simulate soil-structure-interaction in the time domain. The numerical implementation of this coupled approach is based on a combination of the FEM and the SBFEM. The FEM is used to discretise the near field, containing structures and its surrounding soil. The coupled infinite half-space the so called far field is realised by the SBFEM. The simulation of SSI in the time domain is computationally very time and memory intensive. Different methods are used to perform numerical simulations in the appropriate time. It is shown that using a suitable optimisation of the far field, realistic problem analysis of the SSI can be realised, therefore various optimisation approaches are used and combined with each other. Additionally a contemporary parallel implementation of the algorithms is done. After introducing the theoretical background and discussing the chosen numerical approach, a validation of the used coupling scheme is done. This validation is carried out by comparison of numerical and analytic solutions for defined test cases. Subsequently the numerical performance of the implemented software is tested in terms of speed-up and efficiency. Finally, different geotechnical applications are illustrated and the applicability of the coupled method is shown and discussed using examples

Coupling Concept of two Parallel Research Codesfor Two and Three Dimensional Fluid Structure Interaction Analysis

This paper discuss a coupling strategy of two different software packages to provide fluid structure interaction (FSI) analysis. The basic idea is to combine the advantages of the two codes to create a powerful FSI solver for two and three dimensional analysis. The fluid part is computed by a program called PETSc-FEM a software developed at Centro de Investigacion de Metodos Computacionales CIMEC. The structural part of the coupled process is computed by the research code elementary Parallel Solver (ELPASO) of the Technische Universitat Braunschweig, Institut fur Konstruktionstechnik (IK).Fil: Garelli, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones En Metodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones En Metodos Computacionales; ArgentinaFil: Schauer, Marco. Technische Universität Braunschweig; AlemaniaFil: D'elia, Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones En Metodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones En Metodos Computacionales; ArgentinaFil: Storti, Mario Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones En Metodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones En Metodos Computacionales; ArgentinaFil: Langer, Sabine C.. Technische Universität Braunschweig; Alemani

Feedback control of arm movements using Neuro-Muscular Electrical Stimulation (NMES) combined with a lockable, passive exoskeleton for gravity compensation

Within the European project MUNDUS, an assistive framework was developed for the support of arm and hand functions during daily life activities in severely impaired people. This contribution aims at designing a feedback control system for Neuro-Muscular Electrical Stimulation (NMES) to enable reaching functions in people with no residual voluntary control of the arm and shoulder due to high level spinal cord injury. NMES is applied to the deltoids and the biceps muscles and integrated with a three degrees of freedom (DoFs) passive exoskeleton, which partially compensates gravitational forces and allows to lock each DOF. The user is able to choose the target hand position and to trigger actions using an eyetracker system. The target position is selected by using the eyetracker and determined by a marker-based tracking system using Microsoft Kinect. A central controller, i.e., a finite state machine, issues a sequence of basic movement commands to the real-time arm controller. The NMES control algorithm sequentially controls each joint angle while locking the other DoFs. Daily activities, such as drinking, brushing hair, pushing an alarm button, etc., can be supported by the system. The robust and easily tunable control approach was evaluated with five healthy subjects during a drinking task. Subjects were asked to remain passive and to allow NMES to induce the movements. In all of them, the controller was able to perform the task, and a mean hand positioning error of less than five centimeters was achieved. The average total time duration for moving the hand from a rest position to a drinking cup, for moving the cup to the mouth and back, and for finally returning the arm to the rest position was 71 s.EC/FP7/248326/EU/MUltimodal Neuroprostesis for Daily Upper limb Support/MUNDU

Parallel computation of 3-D soil-structure interaction in time domain with a coupled FEM/SBFEM approach

The final publication is available at Springer via http://dx.doi.org/10.1007/s10915-011-9551-xThis paper introduces a parallel algorithm for the scaled boundary finite element method (SBFEM). The application code is designed to run on clusters of computers, and it enables the analysis of large-scale soil-structure-interaction problems, where an unbounded domain has to fulfill the radiation condition for wave propagation to infinity. The main focus of the paper is on the mathematical description and numerical implementation of the SBFEM. In particular, we describe in detail the algorithm to compute the acceleration unit impulse response matrices used in the SBFEM as well as the solvers for the Riccati and Lyapunov equations. Finally, two test cases validate the new code, illustrating the numerical accuracy of the results and the parallel performances. © Springer Science+Business Media, LLC 2011.Jose E. Roman and Enrique S. Quintana-Orti were partially supported by the Spanish Ministerio de Ciencia e Innovacion under grants TIN2009-07519, and TIN2008-06570-C04-01, respectively.Schauer, M.; Román Moltó, JE.; Quintana Orti, ES.; Langer, S. (2012). Parallel computation of 3-D soil-structure interaction in time domain with a coupled FEM/SBFEM approach. Journal of Scientific Computing. 52(2):446-467. doi:10.1007/s10915-011-9551-xS446467522Anderson, E., Bai, Z., Bischof, C., Demmel, J., Dongarra, J., Croz, J.D., Greenbaum, A., Hammarling, S., McKenney, A., Sorensen, D.: LAPACK User’s Guide. Society for Industrial and Applied Mathematics, Philadelphia (1992)Antes, H., Spyrakos, C.: Soil-structure interaction. In: Beskos, D., Anagnotopoulos, S. (eds.) Computer Analysis and Design of Earthquake Resistant Structures, p. 271. Computational Mechanics Publications, Southampton (1997)Appelö, D., Colonius, T.: A high-order super-grid-scale absorbing layer and its application to linear hyperbolic systems. J. Comput. 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MUNDUS project : MUltimodal neuroprosthesis for daily upper limb support

Background: MUNDUS is an assistive framework for recovering direct interaction capability of severely motor impaired people based on arm reaching and hand functions. It aims at achieving personalization, modularity and maximization of the user’s direct involvement in assistive systems. To this, MUNDUS exploits any residual control of the end-user and can be adapted to the level of severity or to the progression of the disease allowing the user to voluntarily interact with the environment. MUNDUS target pathologies are high-level spinal cord injury (SCI) and neurodegenerative and genetic neuromuscular diseases, such as amyotrophic lateral sclerosis, Friedreich ataxia, and multiple sclerosis (MS). The system can be alternatively driven by residual voluntary muscular activation, head/eye motion, and brain signals. MUNDUS modularly combines an antigravity lightweight and non-cumbersome exoskeleton, closed-loop controlled Neuromuscular Electrical Stimulation for arm and hand motion, and potentially a motorized hand orthosis, for grasping interactive objects. Methods: The definition of the requirements and of the interaction tasks were designed by a focus group with experts and a questionnaire with 36 potential end-users. Five end-users (3 SCI and 2 MS) tested the system in the configuration suitable to their specific level of impairment. They performed two exemplary tasks: reaching different points in the working volume and drinking. Three experts evaluated over a 3-level score (from 0, unsuccessful, to 2, completely functional) the execution of each assisted sub-action. Results: The functionality of all modules has been successfully demonstrated. User’s intention was detected with a 100% success. Averaging all subjects and tasks, the minimum evaluation score obtained was 1.13 ± 0.99 for the release of the handle during the drinking task, whilst all the other sub-actions achieved a mean value above 1.6. All users, but one, subjectively perceived the usefulness of the assistance and could easily control the system. Donning time ranged from 6 to 65 minutes, scaled on the configuration complexity. Conclusions: The MUNDUS platform provides functional assistance to daily life activities; the modules integration depends on the user’s need, the functionality of the system have been demonstrated for all the possible configurations, and preliminary assessment of usability and acceptance is promising

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO