Passive Control of Tall Buildings Using Distributed Multiple Tuned Mass Dampers

The vibration control of the tall building during earthquake excitations is a challenging task due to their complex seismic behavior. This paper investigates the optimum placement and properties of the Tuned Mass Dampers (TMDs) in tall buildings, which are employed to control the vibrations during earthquakes. An algorithm was developed to spend a limited mass either in a single TMD or in multiple TMDs and distribute them optimally over the height of the building. The Non-dominated Sorting Genetic Algorithm (NSGA – II) method was improved by adding multi-variant genetic operators and utilized to simultaneously study the optimum design parameters of the TMDs and the optimum placement. The results showed that under earthquake excitations with noticeable amplitude in higher modes, distributing TMDs over the height of the building is more effective in mitigating the vibrations compared to the use of a single TMD system. From the optimization, it was observed that the locations of the TMDs were related to the stories corresponding to the maximum modal displacements in the lower modes and the stories corresponding to the maximum modal displacements in the modes which were highly activated by the earthquake excitations. It was also noted that the frequency content of the earthquake has significant influence on the optimum location of the TMDs

A geometrical inclusion-matrix model for the finite element analysis of concrete at multiple scales

This paper introduces a method to generate adequate inclusion-matrix geometries of concrete in two and three dimensions, which are independent of any specific numerical discretization. The article starts with an analysis on shapes of natural aggregates and discusses corresponding mathematical realizations. As a first prototype a two-dimensional generation of a mesoscale model is introduced. Particle size distribution functions are analysed and prepared for simulating an adequate three-dimensional representation of the aggregates within a concrete structure. A sample geometry of a three-dimensional test cube is generated and the finite element analysis of its heterogeneous geometry by a uniform mesh is presented. Concluding, aspects of a multiscale analysis are discussed and possible enhancements are proposed

Damping in Bolted Joints

With the help of modern CAE-based simulation processes, it is possible to predict the dynamic behavior of fatigue strength problems in order to improve products of many industries, e.g. the building, the machine construction or the automotive industry. Amongst others, it can be used to improve the acoustic design of automobiles in an early development stage. Nowadays, the acoustics of automobiles plays a crucial role in the process of vehicle development. Because of the advanced demand of comfort and due to statutory rules the manufacturers are faced with the challenge of optimizing their car’s sound emissions. The optimization includes not only the reduction of noises. Lately with the trend to hybrid and electric cars, it has been shown that vehicles can become too quiet. Thus, the prediction of structural and acoustic properties based on FE-simulations is becoming increasingly important before any experimental prototype is examined. With the state of the art, qualitative comparisons between different implementations are possible. However, an accurate and reliable quantitative prediction is still a challenge. One aspect in the context of increasing the prediction quality of acoustic (or general oscillating) problems - especially in power-trains of automobiles - is the more accurate implementation of damping in joint structures. While material damping occurs globally and homogenous in a structural system, the damping due to joints is a very local problem, since energy is especially dissipated in the vicinity of joints. This paper focusses on experimental and numerical studies performed on a single (extracted) screw connection. Starting with experimental studies that are used to identify the underlying physical model of the energy loss, the locally influencing parameters (e.g. the damping factor) should be identified. In contrast to similar research projects, the approach tends to a more local consideration within the joint interface. Tangential stiffness and energy loss within the interface are spatially distributed and interactions between the influencing parameters are regarded. As a result, the damping matrix is no longer proportional to mass or stiffness matrix, since it is composed of the global material damping and the local joint damping. With this new approach, the prediction quality can be increased, since the local distribution of the physical parameters within the joint interface corresponds much closer to the reality

Funktionsanalyse einer interdisziplinären Datenbank zu Optimierungszwecken

Tinnitus ist ein weit verbreitetes, aber noch wenig erforschtes Krankheitsbild. Tinnitus eingehender zu erforschen und Daten über verschiedene Formen des Tinnitus zu sammeln, ist eines der Ziele der COST Action TINNET. Dabei fallen große Datenmengen an, die in einer webbasierten Datenbank gespeichert werden. Die Struktur dieser Datenbank soll überprüft und ihre Funktionalität, die sich momentan auf die grundlegenden Dinge beschränkt, erweitert werden. Diese Arbeit analysiert die Struktur der Datenbank auf ihre Konsistenz hin. Es werden einige mögliche Änderungen erläutert. Ein in vorgeschlagenes Validierungssystem wird umgesetzt. FOREIGN KEY Constraints ermöglichen eine effizientere Datenhaltung in der Datenbank. Mittels MySQL-Triggern werden E-Mail-Benachrichtigungen für Benutzerinnen und Benutzer des Systems ermöglicht, wenn Änderungen der Datensätze erfolgen

Weight reduction in lightweight structures of dynamically loaded systems by new energy dissipative elements in bolted joints

In order to reduce vibration amplitudes, joint damping is being investigated at the MFPA Weimar and Fraunhofer IWM. It is intended to replace damping, often done by a frequency shift of naturals frequencies via added masses, and thus contribute to lightweight construction. To characterise the energy dissipation ability of joints, fretting wear tests with various parameter settings have been performed. In fretting wear tests, two material samples are set in relative motion with a constant normal force. Friction in the joint creates a friction-force-hysteresis, the area of which reflects the energy dissipation. The larger the hysteresis area, the greater the energy dissipation. Based on the experimental observations, a new material model is formulated to capture energy dissipation starting form micro slipping up to macro-slip situations in joints. Input parameters for the constitutive law are material pairing, the contact force, the frequency spectrum and the surface roughness. The constitutive law is defined in a finite element method (FEM) in intermediate elements between two friction bodies, where energy dissipation can be simulated for complex geometries. The numerical calculations are compared with validation experiments. Bolted joints are investigated as an application. The pressure distribution in the connection depends on the distance of the considered point to the bolt. According to distance, the constitutive law is variously implemented in the joint. Bolted joints exhibit both micro-slip (near the bolt shank) and macro-slip as relative motions, resulting in different friction states in the joint. Despite the displacement, the function must be maintained, which is why materials with low fretting wear are used. Figure 1 illustrates the relationship

Эмманюэль Левинас: "лицо" как абсолютное выражение

Проводится анализ ключевой для метафизики современного французского мыслителя Эмманюэля Левинаса категории "лица" как своего рода "истока" всякого смысла. Анализ направляется вопросом о соотношении онтологического и этического регистров смысла, в свете которого рассматривается также возможная аналогия лица и (эстетического) образа, в частности - в его трактовке у Мориса Бланшо

DAMAGE SIMULATION OF HETEROGENEOUS SOLIDS BY NONLOCAL FORMULATIONS ON ORTHOGONAL GRIDS

The present paper is part of a comprehensive approach of grid-based modelling. This approach includes geometrical modelling by pixel or voxel models, advanced multiphase B-spline finite elements of variable order and fast iterative solver methods based on the multigrid method. So far, we have only presented these grid-based methods in connection with linear elastic analysis of heterogeneous materials. Damage simulation demands further considerations. The direct stress solution of standard bilinear finite elements is severly defective, especially along material interfaces. Besides achieving objective constitutive modelling, various nonlocal formulations are applied to improve the stress solution. Such a corrective data processing can either refer to input data in terms of Young's modulus or to the attained finite element stress solution, as well as to a combination of both. A damage-controlled sequentially linear analysis is applied in connection with an isotropic damage law. Essentially by a high resolution of the heterogeneous solid, local isotropic damage on the material subscale allows to simulate complex damage topologies such as cracks. Therefore anisotropic degradation of a material sample can be simulated. Based on an effectively secantial global stiffness the analysis is numerically stable. The iteration step size is controlled for an adequate simulation of the damage path. This requires many steps, but in the iterative solution process each new step starts with the solution of the prior step. Therefore this method is quite effective. The present paper provides an introduction of the proposed concept for a stable simulation of damage in heterogeneous solids

Feasibility study of using integrated fiber optical sensors to monitor laser-assisted metal-polymer joining

The possibilities and challenges of using fiber optical sensors to monitor the laser-assisted joining of metal-polymer joints have been described in this article. Fundamental investigation proves the basic suitability of the measuring method for this application and studies the effect of essential influencing variables of the joining process - e.g., the clamping force - on the resulting sensor signals. In addition, the strain state (because of the process temperature and shrinkage of the polymer) of the parts to be joined can be traced as a function of the joining partners, the process parameters, and the material thicknesses. It is shown that the fiber optical method is suitable for process monitoring directly in the joining zone of metal-polymer hybrids and providing a tool for detailed strain measurements in the joint zone during subsequent component testing

ADAPTIVE SIMULATION OF THE DAMAGE BEHAVIOR OF CONCRETE USING HETEROGENEOUS MULTISCALE MODELS

In this paper an adaptive heterogeneous multiscale model, which couples two substructures with different length scales into one numerical model is introduced for the simulation of damage in concrete. In the presented approach the initiation, propagation and coalescence of microcracks is simulated using a mesoscale model, which explicitly represents the heterogeneous material structure of concrete. The mesoscale model is restricted to the damaged parts of the structure, whereas the undamaged regions are simulated on the macroscale. As a result an adaptive enlargement of the mesoscale model during the simulation is necessary. In the first part of the paper the generation of the heterogeneous mesoscopic structure of concrete, the finite element discretization of the mesoscale model, the applied isotropic damage model and the cohesive zone model are briefly introduced. Furthermore the mesoscale simulation of a uniaxial tension test of a concrete prism is presented and own obtained numerical results are compared to experimental results. The second part is focused on the adaptive heterogeneous multiscale approach. Indicators for the model adaptation and for the coupling between the different numerical models will be introduced. The transfer from the macroscale to the mesoscale and the adaptive enlargement of the mesoscale substructure will be presented in detail. A nonlinear simulation of a realistic structure using an adaptive heterogeneous multiscale model is presented at the end of the paper to show the applicability of the proposed approach to large-scale structures