Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen
OPUS4-3324 Wissenschaftlicher Artikel Nguyen-Xuan, Hung; Nguyen, Hiep Vinh; Bordas, Stéphane Pierre Alain; Rabczuk, Timon; Duflot, Marc A cell-based smoothed finite element method for three dimensional solid structures This paper extends further the strain smoothing technique in finite elements to 8-noded hexahedral elements (CS-FEM-H8). The idea behind the present method is similar to the cell-based smoothed 4-noded quadrilateral finite elements (CS-FEM-Q4). In CSFEM, the smoothing domains are created based on elements, and each element can be further subdivided into 1 or several smoothing cells. It is observed that: 1) The CS-FEM using a single smoothing cell can produce higher stress accuracy, but insufficient rank and poor displacement accuracy; 2) The CS-FEM using several smoothing cells has proper rank, good displacement accuracy, but lower stress accuracy, especially for nearly incompressible and bending dominant problems. We therefore propose 1) an extension of strain smoothing to 8-noded hexahedral elements and 2) an alternative CS-FEM form, which associates the single smoothing cell issue with multi-smoothing cell one via a stabilization technique. Several numerical examples are provided to show the reliability and accuracy of the present formulation. 12 KSCE Journal of Civil Engineering 1230 1242 10.1007/s12205-012-1515-7 Institut für Strukturmechanik
OPUS4-3371 Wissenschaftlicher Artikel Zhao, Jun-Hua; Wang, L.; Jiang, Jin-Wu; Wang, Z.; Guo, Wanlin; Rabczuk, Timon A comparative study of two molecular mechanics models based on harmonic potentials A comparative study of two molecular mechanics models based on harmonic potentials Journal of Applied Physics Institut für Strukturmechanik
OPUS4-3408 Wissenschaftlicher Artikel Bucher, Christian; Most, Thomas A comparison of approximate response functions in structural reliability analysis A comparison of approximate response functions in structural reliability analysis 9 Probabilistic Engineering Mechanics 154 163 Institut für Strukturmechanik
OPUS4-3327 Wissenschaftlicher Artikel Talebi, Hossein; Silani, Mohammad; Bordas, Stéphane Pierre Alain; Kerfriden, Pierre; Rabczuk, Timon A computational library for multiscale modeling of material failure A computational library for multiscale modeling of material failure Computational Mechanics Institut für Strukturmechanik
OPUS4-3348 Wissenschaftlicher Artikel Zhuang, Xiaoying; Huang, Runqiu; Rabczuk, Timon; Liang, C. A coupled thermo-hydro-mechanical model of jointed hard rock for compressed air energy storage A coupled thermo-hydro-mechanical model of jointed hard rock for compressed air energy storage Mathematical Problems in Engineering Institut für Strukturmechanik
OPUS4-3172 Wissenschaftlicher Artikel Zhuang, Xiaoying; Huang, Runqiu; Liang, Chao; Rabczuk, Timon A coupled thermo-hydro-mechanical model of jointed hard rock for compressed air energy storage Renewable energy resources such as wind and solar are intermittent, which causes instability when being connected to utility grid of electricity. Compressed air energy storage (CAES) provides an economic and technical viable solution to this problem by utilizing subsurface rock cavern to store the electricity generated by renewable energy in the form of compressed air. Though CAES has been used for over three decades, it is only restricted to salt rock or aquifers for air tightness reason. In this paper, the technical feasibility of utilizing hard rock for CAES is investigated by using a coupled thermo-hydro-mechanical (THM) modelling of nonisothermal gas flow. Governing equations are derived from the rules of energy balance, mass balance, and static equilibrium. Cyclic volumetric mass source and heat source models are applied to simulate the gas injection and production. Evaluation is carried out for intact rock and rock with discrete crack, respectively. In both cases, the heat and pressure losses using air mass control and supplementary air injection are compared. Mathematical Problems in Engineering urn:nbn:de:gbv:wim2-20170428-31726 10.1155/2014/179169 Institut für Strukturmechanik
OPUS4-3579 Wissenschaftlicher Artikel Zhang, Chao; Wang, Cuixia; Lahmer, Tom; He, Pengfei; Rabczuk, Timon A dynamic XFEM formulation for crack identification A dynamic XFEM formulation for crack identification 21 International Journal of Mechanics and Materials in Design 427 448 Institut für Strukturmechanik
OPUS4-3516 Konferenzveröffentlichung Brehm, Maik; Most, Thomas A four-node plane EAS-element for stochastic nonlinear materials A four-node plane EAS-element for stochastic nonlinear materials Institut für Strukturmechanik
OPUS4-3294 Wissenschaftlicher Artikel Yang, Shih-Wei; Budarapu, Pattabhi Ramaiah; Mahapatra, D.R.; Bordas, Stéphane Pierre Alain; Zi, Goangseup; Rabczuk, Timon A Meshless Adaptive Multiscale Method for Fracture A Meshless Adaptive Multiscale Method for Fracture 13 Computational Materials Science 382 395 Institut für Strukturmechanik
OPUS4-3484 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions 17 Structural Engineering and Mechanics 315 332 Institut für Strukturmechanik
OPUS4-3507 Konferenzveröffentlichung Häfner, Stefan; Könke, Carsten A multigrid finite element method for the mesoscale analysis of concrete A multigrid finite element method for the mesoscale analysis of concrete Institut für Strukturmechanik
OPUS4-2994 Konferenzveröffentlichung Most, Thomas; Bucher, Christian; Macke, M. Gürlebeck, Klaus; Könke, Carsten A NATURAL NEIGHBOR BASED MOVING LEAST SQUARES APPROACH WITH INTERPOLATING WEIGHTING FUNCTION The Element-free Galerkin Method has become a very popular tool for the simulation of mechanical problems with moving boundaries. The internally applied Moving Least Squares approximation uses in general Gaussian or cubic weighting functions and has compact support. Due to the approximative character of this method the obtained shape functions do not fulfill the interpolation condition, which causes additional numerical effort for the imposition of the essential boundary conditions. The application of a singular weighting function, which leads to singular coefficient matrices at the nodes, can solve this problem, but requires a very careful placement of the integration points. Special procedures for the handling of such singular matrices were proposed in literature, which require additional numerical effort. In this paper a non-singular weighting function is presented, which leads to an exact fulfillment of the interpolation condition. This weighting function leads to regular values of the weights and the coefficient matrices in the whole interpolation domain even at the nodes. Furthermore this function gives much more stable results for varying size of the influence radius and for strongly distorted nodal arrangements than classical weighting function types. Nevertheless, for practical applications the results are similar as these obtained with the regularized weighting type presented by the authors in previous publications. Finally a new concept will be presented, which enables an efficient analysis of systems with strongly varying node density. In this concept the nodal influence domains are adapted depending on the nodal configuration by interpolating the influence radius for each direction from the distances to the natural neighbor nodes. This approach requires a Voronoi diagram of the domain, which is available in this study since Delaunay triangles are used as integration background cells. In the numerical examples it will be shown, that this method leads to a more uniform and reduced number of influencing nodes for systems with varying node density than the classical circular influence domains, which means that the small additional numerical effort for interpolating the influence radius leads to remarkable reduction of the total numerical cost in a linear analysis while obtaining similar results. For nonlinear calculations this advantage would be even more significant. 17 urn:nbn:de:gbv:wim2-20170327-29943 10.25643/bauhaus-universitaet.2994 Institut für Strukturmechanik
OPUS4-3443 Wissenschaftlicher Artikel Most, Thomas A natural neighbour-based moving least-squares approach for the element-free Galerkin method A natural neighbour-based moving least-squares approach for the element-free Galerkin method 28 International Journal for Numerical Methods in Engineering 224 252 Institut für Strukturmechanik
OPUS4-3401 Wissenschaftlicher Artikel Nguyen-Xuan, Hung; Rabczuk, Timon; Nguyen-Thanh, Nhon; Nguyen-Thoi, T.; Bordas, Stéphane Pierre Alain A node-based smoothed finite element method (NS-FEM) for analysis of Reissner-Mindlin plates A node-based smoothed finite element method (NS-FEM) for analysis of Reissner-Mindlin plates 22 Computational Mechanics 679 701 Institut für Strukturmechanik
OPUS4-3276 Wissenschaftlicher Artikel Jia, Yue; Zhang, Yongjie; Rabczuk, Timon A Novel Dynamic Multilevel Technique for Image Registration A Novel Dynamic Multilevel Technique for Image Registration Computers and Mathematics with Applications Institut für Strukturmechanik
OPUS4-3577 Wissenschaftlicher Artikel Nguyen-Tuan, Long; Lahmer, Tom; Datcheva, Maria; Stoimenova, Eugenia; Schanz, Tom A novel parameter identification approach for buffer elements involving complex coupled thermo-hydro-mechanical analyses A novel parameter identification approach for buffer elements involving complex coupled thermo-hydro-mechanical analyses 9 Computers and Geotechnics 23 32 Institut für Strukturmechanik
OPUS4-3374 Wissenschaftlicher Artikel Kerfriden, Pierre; Goury, O.; Rabczuk, Timon; Bordas, Stéphane Pierre Alain A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics 19 Computer Methods in Applied Mechanics and Engineering 169 188 Institut für Strukturmechanik
OPUS4-3167 Wissenschaftlicher Artikel Vu-Bac, N.; Nguyen-Xuan, Hung; Chen, Lei; Lee, C.K.; Zi, Goangseup; Zhuang, Xiaoying; Liu, G.R.; Rabczuk, Timon A phantom-node method with edge-based strain smoothing for linear elastic fracture mechanics This paper presents a novel numerical procedure based on the combination of an edge-based smoothed finite element (ES-FEM) with a phantom-node method for 2D linear elastic fracture mechanics. In the standard phantom-node method, the cracks are formulated by adding phantom nodes, and the cracked element is replaced by two new superimposed elements. This approach is quite simple to implement into existing explicit finite element programs. The shape functions associated with discontinuous elements are similar to those of the standard finite elements, which leads to certain simplification with implementing in the existing codes. The phantom-node method allows modeling discontinuities at an arbitrary location in the mesh. The ES-FEM model owns a close-to-exact stiffness that is much softer than lower-order finite element methods (FEM). Taking advantage of both the ES-FEM and the phantom-node method, we introduce an edge-based strain smoothing technique for the phantom-node method. Numerical results show that the proposed method achieves high accuracy compared with the extended finite element method (XFEM) and other reference solutions. Journal of Applied Mathematics urn:nbn:de:gbv:wim2-20170426-31676 10.1155/2013/978026 Institut für Strukturmechanik
OPUS4-3513 Wissenschaftlicher Artikel Döring, R.; Hoffmeyer, J.; Seeger, T.; Vormwald, M. A plasticity model for calculating stress-strain sequences under multiaxial nonproportional cyclic loading A plasticity model for calculating stress-strain sequences under multiaxial nonproportional cyclic loading 9 Computational Materials Science 587 596 Institut für Strukturmechanik
OPUS4-3312 Wissenschaftlicher Artikel Silani, Mohammad; Ziaei-Rad, S.; Talebi, Hossein; Rabczuk, Timon A Semi-Concurrent Multiscale Approach for Modeling Damage in Nanocomposites A Semi-Concurrent Multiscale Approach for Modeling Damage in Nanocomposites Theoretical and Applied Fracture Mechanics Institut für Strukturmechanik
OPUS4-3275 Wissenschaftlicher Artikel Areias, Pedro; Rabczuk, Timon; Cesar de Sa, J.M.; Jorge, R.N. A semi-implicit _nite strain shell algorithm using in-plane strains based on least-squares A semi-implicit _nite strain shell algorithm using in-plane strains based on least-squares Computational Mechanics Institut für Strukturmechanik
OPUS4-3544 Konferenzveröffentlichung Döring, R.; Hoffmeyer, J.; Seeger, T.; Vormwald, M. A Short Crack Growth Model for the Prediction of Fatigue Lives under Multiaxial Nonproportional Loading A Short Crack Growth Model for the Prediction of Fatigue Lives under Multiaxial Nonproportional Loading Institut für Strukturmechanik
OPUS4-3385 Wissenschaftlicher Artikel Talebi, Hossein; Zi, Goangseup; Silani, Mohammad; Samaniego, Esteban; Rabczuk, Timon A simple circular cell method for multilevel finite element analysis A simple multiscale analysis framework for heterogeneous solids based on a computational homogenization technique is presented. The macroscopic strain is linked kinematically to the boundary displacement of a circular or spherical representative volume which contains the microscopic information of the material. The macroscopic stress is obtained from the energy principle between the macroscopic scale and the microscopic scale. This new method is applied to several standard examples to show its accuracy and consistency of the method proposed. Journal of Applied Mathematics 10.1155/2012/526846 Institut für Strukturmechanik
OPUS4-3163 Wissenschaftlicher Artikel Talebi, Hossein; Zi, Goangseup; Silani, Mohammad; Samaniego, Esteban; Rabczuk, Timon A simple circular cell method for multilevel finite element analysis A simple multiscale analysis framework for heterogeneous solids based on a computational homogenization technique is presented. The macroscopic strain is linked kinematically to the boundary displacement of a circular or spherical representative volume which contains the microscopic information of the material. The macroscopic stress is obtained from the energy principle between the macroscopic scale and the microscopic scale. This new method is applied to several standard examples to show its accuracy and consistency of the method proposed. Journal of Applied Mathematics urn:nbn:de:gbv:wim2-20170426-31639 10.1155/2012/526846 Institut für Strukturmechanik
OPUS4-3400 Wissenschaftlicher Artikel Nguyen-Thanh, Nhon; Thai-Hoang, C.; Nguyen-Xuan, Hung; Rabczuk, Timon A smoothed finite element method for the static and free vibration analysis of shells A smoothed finite element method for the static and free vibration analysis of shells 12 Journal of Civil Engineering and Architecture 13 25 Institut für Strukturmechanik
OPUS4-2877 Konferenzveröffentlichung Nguyen-Thanh, Nhon; Rabczuk, Timon Gürlebeck, Klaus; Könke, Carsten A SMOOTHED FINITE ELEMENT METHOD FOR THE STATIC AND FREE VIBRATION ANALYSIS OF SHELLS A four-node quadrilateral shell element with smoothed membrane-bending based on Mindlin-Reissner theory is proposed. The element is a combination of a plate bending and membrane element. It is based on mixed interpolation where the bending and membrane stiffness matrices are calculated on the boundaries of the smoothing cells while the shear terms are approximated by independent interpolation functions in natural coordinates. The proposed element is robust, computationally inexpensive and free of locking. Since the integration is done on the element boundaries for the bending and membrane terms, the element is more accurate than the MITC4 element for distorted meshes. This will be demonstrated for several numerical examples. 24 urn:nbn:de:gbv:wim2-20170314-28777 10.25643/bauhaus-universitaet.2877 Institut für Strukturmechanik
OPUS4-3578 Wissenschaftlicher Artikel Vu-Bac, N.; Lahmer, Tom; Zhuang, Xiaoying; Nguyen-Thoi, T.; Rabczuk, Timon A software framework for probabilistic sensitivity analysis for computationally expensive models A software framework for probabilistic sensitivity analysis for computationally expensive models 12 Advances in Engineering Software 19 31 Institut für Strukturmechanik
OPUS4-3280 Wissenschaftlicher Artikel Jiang, Jin-Wu; Rabczuk, Timon; Park, Harold S. A Stillinger-Weber Potential for Single-Layer Black Phosphorus, and the Importance of Cross-Pucker Interactions for Negative Poisson's Ratio and Edge Stress-Induced Bending The distinguishing structural feature of single-layered black phosphorus is its puckered structure, which leads to many novel physical properties. In this work, we first present a new parameterization of the Stillinger-Weber potential for single-layered black phosphorus. In doing so, we reveal the importance of a cross-pucker interaction term in capturing its unique mechanical properties, such as a negative Poisson's ratio. In particular, we show that the cross-pucker interaction enables the pucker to act as a re-entrant hinge, which expands in the lateral direction when it is stretched in the longitudinal direction. As a consequence, single-layered black phosphorus has a negative Poisson's ratio in the direction perpendicular to the atomic plane. As an additional demonstration of the impact of the cross-pucker interaction, we show that it is also the key factor that enables capturing the edge stress-induced bending of single-layered black phosphorus that has been reported in ab initio calculations. Nanoscale 10.1039/C4NR07341J Institut für Strukturmechanik
OPUS4-3568 Wissenschaftlicher Artikel Ghorashi, Seyed Shahram; Lahmer, Tom; Bagherzadeh, Amir Saboor; Zi, Goangseup; Rabczuk, Timon A stochastic computational method based on goal-oriented error estimation for heterogeneous geological materials A stochastic computational method based on goal-oriented error estimation for heterogeneous geological materials Engineering Geology Institut für Strukturmechanik
OPUS4-3353 Wissenschaftlicher Artikel Jiang, Jin-Wu; Park, Harold S.; Gall, K.; Leach, A.; Rabczuk, Timon A Surface Stacking Fault Energy Approach to Predicting Defect Nucleation in Surface-Dominated Nanostructures A Surface Stacking Fault Energy Approach to Predicting Defect Nucleation in Surface-Dominated Nanostructures Journal of the Mechanics and Physics of Solids Institut für Strukturmechanik
OPUS4-3322 Wissenschaftlicher Artikel Zhao, Jun-Hua; Jiang, Jin-Wu; Jia, Yue; Guo, Wanlin; Rabczuk, Timon A theoretical analysis of cohesive energy between carbon nanotubes, graphene and substrates Explicit solutions for the cohesive energy between carbon nanotubes, graphene and substrates are obtained through continuum modeling of the van der Waals interaction between them. The dependence of the cohesive energy on their size, spacing and crossing angles is analyzed. Checking against full atom molecular dynamics calculations and available experimental results shows that the continuum solution has high accuracy. The equilibrium distances between the nanotubes, graphene and substrates with minimum cohesive energy are also provided explicitly. The obtained analytical solution should be of great help for understanding the interaction between the nanostructures and substrates, and designing composites and nanoelectromechanical systems. 11 Carbon 108 119 10.1016/j.carbon.2013.01.041 Institut für Strukturmechanik
OPUS4-3301 Wissenschaftlicher Artikel Silani, Mohammad; Talebi, Hossein; Ziaei-Rad, S.; Hamouda, A.M.S.; Zi, Goangseup; Rabczuk, Timon A three dimensional Extended Arlequin Method for Dynamic Fracture A three dimensional Extended Arlequin Method for Dynamic Fracture 6 Computational Materials Science 425 431 Institut für Strukturmechanik
OPUS4-3291 Wissenschaftlicher Artikel Vu-Bac, N.; Silani, Mohammad; Lahmer, Tom; Zhuang, Xiaoying; Rabczuk, Timon A unified framework for stochastic predictions of Young's modulus of clay/epoxy nanocomposites (PCNs) A unified framework for stochastic predictions of Young's modulus of clay/epoxy nanocomposites (PCNs) 15 Computational Materials Science 520 535 Institut für Strukturmechanik
OPUS4-3302 Wissenschaftlicher Artikel Msekh, Mohammed Abdulrazzak; Sargado, M.; Jamshidian, M.; Areias, Pedro; Rabczuk, Timon ABAQUS implementation of phase_field model for brittle fracture ABAQUS implementation of phase_field model for brittle fracture 12 Computational Materials Science 472 484 Institut für Strukturmechanik
OPUS4-3386 Wissenschaftlicher Artikel Jiang, Jin-Wu; Wang, Bing-Shen; Rabczuk, Timon Acoustic and breathing phonon modes in bilayer graphene with Moire-acute patterns The lattice dynamics properties are investigated for twisting bilayer graphene. There are big jumps for the inter-layer potential at twisting angle θ=0° and 60°, implying the stability of Bernal-stacking and the instability of AA-stacking structures, while a long platform in [8,55]° indicates the ease of twisting bilayer graphene in this wide angle range. Significant frequency shifts are observed for the z breathing mode around θ=0° and 60°, while the frequency is a constant in a wide range [8,55]°. Using the z breathing mode, a mechanical nanoresonator is proposed to operate on a robust resonant frequency in terahertz range. Applied Physics Letters 10.1063/1.4735246 Institut für Strukturmechanik
OPUS4-1436 Dissertation Luther, Torsten Adaptation of atomistic and continuum methods for multiscale simulation of quasi-brittle intergranular damage The numerical simulation of damage using phenomenological models on the macroscale was state of the art for many decades. However, such models are not able to capture the complex nature of damage, which simultaneously proceeds on multiple length scales. Furthermore, these phenomenological models usually contain damage parameters, which are physically not interpretable. Consequently, a reasonable experimental determination of these parameters is often impossible. In the last twenty years, the ongoing advance in computational capacities provided new opportunities for more and more detailed studies of the microstructural damage behavior. Today, multiphase models with several million degrees of freedom enable for the numerical simulation of micro-damage phenomena in naturally heterogeneous materials. Therewith, the application of multiscale concepts for the numerical investigation of the complex nature of damage can be realized. The presented thesis contributes to a hierarchical multiscale strategy for the simulation of brittle intergranular damage in polycrystalline materials, for example aluminum. The numerical investigation of physical damage phenomena on an atomistic microscale and the integration of these physically based information into damage models on the continuum meso- and macroscale is intended. Therefore, numerical methods for the damage analysis on the micro- and mesoscale including the scale transfer are presented and the transition to the macroscale is discussed. The investigation of brittle intergranular damage on the microscale is realized by the application of the nonlocal Quasicontinuum method, which fully describes the material behavior by atomistic potential functions, but reduces the number of atomic degrees of freedom by introducing kinematic couplings. Since this promising method is applied only by a limited group of researchers for special problems, necessary improvements have been realized in an own parallelized implementation of the 3D nonlocal Quasicontinuum method. The aim of this implementation was to develop and combine robust and efficient algorithms for a general use of the Quasicontinuum method, and therewith to allow for the atomistic damage analysis in arbitrary grain boundary configurations. The implementation is applied in analyses of brittle intergranular damage in ideal and nonideal grain boundary models of FCC aluminum, considering arbitrary misorientations. From the microscale simulations traction separation laws are derived, which describe grain boundary decohesion on the mesoscale. Traction separation laws are part of cohesive zone models to simulate the brittle interface decohesion in heterogeneous polycrystal structures. 2D and 3D mesoscale models are presented, which are able to reproduce crack initiation and propagation along cohesive interfaces in polycrystals. An improved Voronoi algorithm is developed in 2D to generate polycrystal material structures based on arbitrary distribution functions of grain size. The new model is more flexible in representing realistic grain size distributions. Further improvements of the 2D model are realized by the implementation and application of an orthotropic material model with Hill plasticity criterion to grains. The 2D and 3D polycrystal models are applied to analyze crack initiation and propagation in statically loaded samples of aluminum on the mesoscale without the necessity of initial damage definition. 2010 Weiterentwicklung numerischer Methoden der Atomistik und Kontinuumsmechanik zur Multiskalen-Simulation quasi-spröder intergranularer Schädigung urn:nbn:de:gbv:wim2-20101101-15245 10.25643/bauhaus-universitaet.1436 Institut für Strukturmechanik
OPUS4-3511 Konferenzveröffentlichung Unger, Jörg F.; Most, Thomas; Bucher, Christian; Könke, Carsten Adaptation of the natural element method for crack growth simulations Adaptation of the natural element method for crack growth simulations Institut für Strukturmechanik
OPUS4-3409 Wissenschaftlicher Artikel Eckardt, Stefan; Könke, Carsten Adaptive damage simulation of concrete using heterogeneous multiscale models Adaptive damage simulation of concrete using heterogeneous multiscale models 22 Journal of Algorithms & Computational Technology 275 297 Institut für Strukturmechanik
OPUS4-3479 Konferenzveröffentlichung Pham, Hoang Anh Adaptive excitation for selective sensitivity-based structural identification Adaptive excitation for selective sensitivity-based structural identification Institut für Strukturmechanik
OPUS4-3001 Konferenzveröffentlichung Pham, Hoang Anh Gürlebeck, Klaus; Könke, Carsten ADAPTIVE EXCITATION FOR SELECTIVE SENSITIVITY-BASED STRUCTURAL IDENTIFICATION Major problems of applying selective sensitivity to system identification are requirement of precise knowledge about the system parameters and realization of the required system of forces. This work presents a procedure which is able to deriving selectively sensitive excitation by iterative experiments. The first step is to determine the selectively sensitive displacement and selectively sensitive force patterns. These values are obtained by introducing the prior information of system parameters into an optimization which minimizes the sensitivities of the structure response with respect to the unselected parameters while keeping the sensitivities with respect to the selected parameters as a constant. In a second step the force pattern is used to derive dynamic loads on the tested structure and measurements are carried out. An automatic control ensures the required excitation forces. In a third step, measured outputs are employed to update the prior information. The strategy is to minimize the difference between a predicted displacement response, formulated as function of the unknown parameters and the measured displacements, and the selectively sensitive displacement calculated in the first step. With the updated values of the parameters a re-analysis of selective sensitivity is performed and the experiment is repeated until the displacement response of the model and the actual structure are conformed. As an illustration a simply supported beam made of steel, vibrated by harmonic excitation is investigated, thereby demonstrating that the adaptive excitation can be obtained efficiently. 9 urn:nbn:de:gbv:wim2-20170327-30015 10.25643/bauhaus-universitaet.3001 Institut für Strukturmechanik
OPUS4-1416 Dissertation Eckardt, Stefan Adaptive heterogeneous multiscale models for the nonlinear simulation of concrete The nonlinear behavior of concrete can be attributed to the propagation of microcracks within the heterogeneous internal material structure. In this thesis, a mesoscale model is developed which allows for the explicit simulation of these microcracks. Consequently, the actual physical phenomena causing the complex nonlinear macroscopic behavior of concrete can be represented using rather simple material formulations. On the mesoscale, the numerical model explicitly resolves the components of the internal material structure. For concrete, a three-phase model consisting of aggregates, mortar matrix and interfacial transition zone is proposed. Based on prescribed grading curves, an efficient algorithm for the generation of three-dimensional aggregate distributions using ellipsoids is presented. In the numerical model, tensile failure of the mortar matrix is described using a continuum damage approach. In order to reduce spurious mesh sensitivities, introduced by the softening behavior of the matrix material, nonlocal integral-type material formulations are applied. The propagation of cracks at the interface between aggregates and mortar matrix is represented in a discrete way using a cohesive crack approach. The iterative solution procedure is stabilized using a new path following constraint within the framework of load-displacement-constraint methods which allows for an efficient representation of snap-back phenomena. In several examples, the influence of the randomly generated heterogeneous material structure on the stochastic scatter of the results is analyzed. Furthermore, the ability of mesoscale models to represent size effects is investigated. Mesoscale simulations require the discretization of the internal material structure. Compared to simulations on the macroscale, the numerical effort and the memory demand increases dramatically. Due to the complexity of the numerical model, mesoscale simulations are, in general, limited to small specimens. In this thesis, an adaptive heterogeneous multiscale approach is presented which allows for the incorporation of mesoscale models within nonlinear simulations of concrete structures. In heterogeneous multiscale models, only critical regions, i.e. regions in which damage develops, are resolved on the mesoscale, whereas undamaged or sparsely damage regions are modeled on the macroscale. A crucial point in simulations with heterogeneous multiscale models is the coupling of sub-domains discretized on different length scales. The sub-domains differ not only in the size of the finite elements but also in the constitutive description. In this thesis, different methods for the coupling of non-matching discretizations - constraint equations, the mortar method and the arlequin method - are investigated and the application to heterogeneous multiscale models is presented. Another important point is the detection of critical regions. An adaptive solution procedure allowing the transfer of macroscale sub-domains to the mesoscale is proposed. In this context, several indicators which trigger the model adaptation are introduced. Finally, the application of the proposed adaptive heterogeneous multiscale approach in nonlinear simulations of concrete structures is presented. 2009 Adaptive heterogene Mehrskalenmodelle zur nichtlinearen Simulation von Beton urn:nbn:de:gbv:wim2-20100317-15023 10.25643/bauhaus-universitaet.1416 Institut für Strukturmechanik
OPUS4-2391 Dissertation Budarapu, Pattabhi Ramaiah Adaptive multiscale methods for fracture One major research focus in the Material Science and Engineering Community in the past decade has been to obtain a more fundamental understanding on the phenomenon 'material failure'. Such an understanding is critical for engineers and scientists developing new materials with higher strength and toughness, developing robust designs against failure, or for those concerned with an accurate estimate of a component's design life. Defects like cracks and dislocations evolve at nano scales and influence the macroscopic properties such as strength, toughness and ductility of a material. In engineering applications, the global response of the system is often governed by the behaviour at the smaller length scales. Hence, the sub-scale behaviour must be computed accurately for good predictions of the full scale behaviour. Molecular Dynamics (MD) simulations promise to reveal the fundamental mechanics of material failure by modeling the atom to atom interactions. Since the atomistic dimensions are of the order of Angstroms ( A), approximately 85 billion atoms are required to model a 1 micro- m^3 volume of Copper. Therefore, pure atomistic models are prohibitively expensive with everyday engineering computations involving macroscopic cracks and shear bands, which are much larger than the atomistic length and time scales. To reduce the computational effort, multiscale methods are required, which are able to couple a continuum description of the structure with an atomistic description. In such paradigms, cracks and dislocations are explicitly modeled at the atomistic scale, whilst a self-consistent continuum model elsewhere. Many multiscale methods for fracture are developed for "fictitious" materials based on "simple" potentials such as the Lennard-Jones potential. Moreover, multiscale methods for evolving cracks are rare. Efficient methods to coarse grain the fine scale defects are missing. However, the existing multiscale methods for fracture do not adaptively adjust the fine scale domain as the crack propagates. Most methods, therefore only "enlarge" the fine scale domain and therefore drastically increase computational cost. Adaptive adjustment requires the fine scale domain to be refined and coarsened. One of the major difficulties in multiscale methods for fracture is to up-scale fracture related material information from the fine scale to the coarse scale, in particular for complex crack problems. Most of the existing approaches therefore were applied to examples with comparatively few macroscopic cracks. Key contributions The bridging scale method is enhanced using the phantom node method so that cracks can be modeled at the coarse scale. To ensure self-consistency in the bulk, a virtual atom cluster is devised providing the response of the intact material at the coarse scale. A molecular statics model is employed in the fine scale where crack propagation is modeled by naturally breaking the bonds. The fine scale and coarse scale models are coupled by enforcing the displacement boundary conditions on the ghost atoms. An energy criterion is used to detect the crack tip location. Adaptive refinement and coarsening schemes are developed and implemented during the crack propagation. The results were observed to be in excellent agreement with the pure atomistic simulations. The developed multiscale method is one of the first adaptive multiscale method for fracture. A robust and simple three dimensional coarse graining technique to convert a given atomistic region into an equivalent coarse region, in the context of multiscale fracture has been developed. The developed method is the first of its kind. The developed coarse graining technique can be applied to identify and upscale the defects like: cracks, dislocations and shear bands. The current method has been applied to estimate the equivalent coarse scale models of several complex fracture patterns arrived from the pure atomistic simulations. The upscaled fracture pattern agree well with the actual fracture pattern. The error in the potential energy of the pure atomistic and the coarse grained model was observed to be acceptable. A first novel meshless adaptive multiscale method for fracture has been developed. The phantom node method is replaced by a meshless differential reproducing kernel particle method. The differential reproducing kernel particle method is comparatively more expensive but allows for a more "natural" coupling between the two scales due to the meshless interpolation functions. The higher order continuity is also beneficial. The centro symmetry parameter is used to detect the crack tip location. The developed multiscale method is employed to study the complex crack propagation. Results based on the meshless adaptive multiscale method were observed to be in excellent agreement with the pure atomistic simulations. The developed multiscale methods are applied to study the fracture in practical materials like Graphene and Graphene on Silicon surface. The bond stretching and the bond reorientation were observed to be the net mechanisms of the crack growth in Graphene. The influence of time step on the crack propagation was studied using two different time steps. Pure atomistic simulations of fracture in Graphene on Silicon surface are presented. Details of the three dimensional multiscale method to study the fracture in Graphene on Silicon surface are discussed. urn:nbn:de:gbv:wim2-20150507-23918 10.25643/bauhaus-universitaet.2391 Institut für Strukturmechanik
OPUS4-3454 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Adaptive response surface approach for reliability analysis using advanced meta-models Adaptive response surface approach for reliability analysis using advanced meta-models Institut für Strukturmechanik
OPUS4-3476 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Adaptive response surface approach using artificial neural networks and Moving Least Squares Adaptive response surface approach using artificial neural networks and Moving Least Squares Institut für Strukturmechanik
OPUS4-2992 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Gürlebeck, Klaus; Könke, Carsten ADAPTIVE RESPONSE SURFACE APPROACH USING ARTIFICIAL NEURAL NETWORKS AND MOVING LEAST SQUARES In engineering science the modeling and numerical analysis of complex systems and relations plays an important role. In order to realize such an investigation, for example a stochastic analysis, in a reasonable computational time, approximation procedure have been developed. A very famous approach is the response surface method, where the relation between input and output quantities is represented for example by global polynomials or local interpolation schemes as Moving Least Squares (MLS). In recent years artificial neural networks (ANN) have been applied as well for such purposes. Recently an adaptive response surface approach for reliability analyses was proposed, which is very efficient concerning the number of expensive limit state function evaluations. Due to the applied simplex interpolation the procedure is limited to small dimensions. In this paper this approach is extended for larger dimensions using combined ANN and MLS response surfaces for evaluating the adaptation criterion with only one set of joined limit state points. As adaptation criterion a combination by using the maximum difference in the conditional probabilities of failure and the maximum difference in the approximated radii is applied. Compared to response surfaces on directional samples or to plain directional sampling the failure probability can be estimated with a much smaller number of limit state points. 13 urn:nbn:de:gbv:wim2-20170327-29922 10.25643/bauhaus-universitaet.2992 Institut für Strukturmechanik
OPUS4-3524 Konferenzveröffentlichung Roos, Dirk; Bucher, Christian Adaptive Response Surfaces for Structural Reliability of Nonlinear Finite Element Structures Adaptive Response Surfaces for Structural Reliability of Nonlinear Finite Element Structures Institut für Strukturmechanik
OPUS4-2947 Konferenzveröffentlichung Eckardt, Stefan; Könke, Carsten Gürlebeck, Klaus; Könke, Carsten 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. 15 urn:nbn:de:gbv:wim2-20170327-29478 10.25643/bauhaus-universitaet.2947 Institut für Strukturmechanik
OPUS4-3113 Wissenschaftlicher Artikel Rafiee, Roham; Rabczuk, Timon; Milani, Abbas S.; Tserpes, Konstantinos I. Advances in Characterization and Modeling of Nanoreinforced Composites This special issue deals with a range of recently developed characterization and modeling techniques employed to better understand and predict the response of nanoreinforced composites at different scales. JOURNAL OF NANOMATERIALS urn:nbn:de:gbv:wim2-20170411-31134 10.1155/2016/9481053 Institut für Strukturmechanik
OPUS4-3423 Konferenzveröffentlichung De Roeck, G.; Zabel, Volkmar; Brehm, Maik; Liu, K.; Reynders, E. Algorithms for structural identification and damage detection of steel-concrete composite bridges Algorithms for structural identification and damage detection of steel-concrete composite bridges Institut für Strukturmechanik
OPUS4-3420 Konferenzveröffentlichung Zabel, Volkmar; Brehm, Maik Algorithms for vibration-based structural identification and damage detection Algorithms for vibration-based structural identification and damage detection Institut für Strukturmechanik
OPUS4-3439 Konferenzveröffentlichung Cantieni, Reto; Brehm, Maik; Zabel, Volkmar; Rauert, T.; Hoffmeister, B. Ambient modal analysis and model updating of a twin composite filler beam railway bridge for high-speed trains with continuous ballast Ambient modal analysis and model updating of a twin composite filler beam railway bridge for high-speed trains with continuous ballast Institut für Strukturmechanik
OPUS4-3438 Konferenzveröffentlichung Cantieni, Reto; Brehm, Maik; Zabel, Volkmar; Rauert, T.; Hoffmeister, B. Ambient Testing and Model Updating of a Filler Beam Bridge for High-Speed Trains Ambient Testing and Model Updating of a Filler Beam Bridge for High-Speed Trains Institut für Strukturmechanik
OPUS4-3325 Wissenschaftlicher Artikel Budarapu, Pattabhi Ramaiah; Gracie, Robert; Bordas, Stéphane Pierre Alain; Rabczuk, Timon An adaptive multiscale method for quasi-static crack growth This paper proposes an adaptive atomistic- continuum numerical method for quasi-static crack growth. The phantom node method is used to model the crack in the continuum region and a molecular statics model is used near the crack tip. To ensure self-consistency in the bulk, a virtual atom cluster is used to model the material of the coarse scale. The coupling between the coarse scale and fine scale is realized through ghost atoms. The ghost atom positions are interpolated from the coarse scale solution and enforced as boundary conditions on the fine scale. The fine scale region is adaptively enlarged as the crack propagates and the region behind the crack tip is adaptively coarsened. An energy criterion is used to detect the crack tip location. The triangular lattice in the fine scale region corresponds to the lattice structure of the (111) plane of an FCC crystal. The Lennard-Jones potential is used to model the atom-atom interactions. The method is implemented in two dimensions. The results are compared to pure atomistic simulations; they show excellent agreement. 19 Computational Mechanics 1129 1148 10.1007/s00466-013-0952-6 Institut für Strukturmechanik
OPUS4-3437 Konferenzveröffentlichung Most, Thomas An adaptive response surface approach for reliability analyses of high-dimensional problems An adaptive response surface approach for reliability analyses of high-dimensional problems Institut für Strukturmechanik
OPUS4-3453 Konferenzveröffentlichung Most, Thomas An adaptive response surface approach for structural reliability analyses based on support vector machines An adaptive response surface approach for structural reliability analyses based on support vector machines Institut für Strukturmechanik
OPUS4-3378 Wissenschaftlicher Artikel Nguyen-Xuan, Hung; Liu, G.R.; Bordas, Stéphane Pierre Alain; Natarajan, S.; Rabczuk, Timon An adaptive singular ES-FEM for mechanics problems with singular field of arbitrary order An adaptive singular ES-FEM for mechanics problems with singular field of arbitrary order 21 Computer Methods in Applied Mechanics and Engineering 252 273 Institut für Strukturmechanik
OPUS4-3337 Wissenschaftlicher Artikel Nguyen-Thanh, Nhon; Muthu, Jacob; Zhuang, Xiaoying; Rabczuk, Timon An adaptive three-dimensional RHT-splines formulation in linear elasto-statics and elasto-dynamics An adaptive three-dimensional RHT-splines formulation in linear elasto-statics and elasto-dynamics 16 Computational Mechanics 369 385 Institut für Strukturmechanik
OPUS4-3407 Wissenschaftlicher Artikel Nguyen-Thanh, Nhon; Rabczuk, Timon; Nguyen-Xuan, Hung; Bordas, Stéphane Pierre Alain An alternative alpha finite element method (A?FEM) free and forced vibration analysis of solids using triangular meshes An alternative alpha finite element method (A?FEM) free and forced vibration analysis of solids using triangular meshes 23 Journal of Computational and Applied Mathematics 2112 2135 Institut für Strukturmechanik
OPUS4-3396 Wissenschaftlicher Artikel Nguyen-Thanh, Nhon; Rabczuk, Timon; Nguyen-Xuan, Hung; Bordas, Stéphane Pierre Alain An alternative alpha finite element method with stabilized discrete shear gap technique for analysis of Mindlin-Reissner plates An alternative alpha finite element method with stabilized discrete shear gap technique for analysis of Mindlin-Reissner plates 16 Finite Elements in Analysis & Design 519 535 Institut für Strukturmechanik
OPUS4-3329 Wissenschaftlicher Artikel Areias, Pedro; Pinto da Costa, A.; Rabczuk, Timon; Queiros de Melo, F. J. M.; Dias-da-Costa, D. An alternative formulation for quasi-static frictional and cohesive contact problems An alternative formulation for quasi-static frictional and cohesive contact problems 17 Computational Mechanics 807 824 Institut für Strukturmechanik
OPUS4-3381 Wissenschaftlicher Artikel Zhao, Jun-Hua; Guo, Wanlin; Rabczuk, Timon An analytical molecular mechanics model for the elastic properties of crystalline polyethylene We present an analytical model to relate the elastic properties of crystalline polyethylene based on a molecular mechanics approach. Along the polymer chains direction, the united-atom (UA) CH2-CH2 bond stretching, angle bending potentials are replaced with equivalent Euler-Bernoulli beams. Between any two polymer chains, the explicit formulae are derived for the van der Waals interaction represented by the linear springs of different stiffness. Then, the nine independent elastic constants are evaluated systematically using the formulae. The analytical model is finally validated by present united-atom molecular dynamics (MD) simulations and against available all-atom molecular dynamics results in the literature. The established analytical model provides an efficient route for mechanical characterization of crystalline polymers and related materials. Journal of Applied Physics 10.1063/1.4745035 Institut für Strukturmechanik
OPUS4-3352 Wissenschaftlicher Artikel Zhang, Yancheng; Zhao, Jun-Hua; Jia, Yue; Mabrouki, Tarek; Gong, Yadong; Wei, Ning; Rabczuk, Timon An analytical solution on the interface debonding for large diameter carbon nanotube-reinforced composite with functionally graded variation interphase An analytical solution on the interface debonding for large diameter carbon nanotube-reinforced composite with functionally graded variation interphase 8 Composite Structures 261 269 Institut für Strukturmechanik
OPUS4-3486 Wissenschaftlicher Artikel Zabel, Volkmar An application of discrete wavelet analysis and connection coefficients to parametric system identification An application of discrete wavelet analysis and connection coefficients to parametric system identification 13 Structural Health Monitoring 5 18 Institut für Strukturmechanik
OPUS4-3368 Wissenschaftlicher Artikel Nguyen-Thoi, T.; Phung-Van, P.; Rabczuk, Timon; Nguyen-Xuan, Hung; Le-Van, C. An application of the ES-FEM in solid domain for dynamic analysis of 2D fluid-solid interaction problems An application of the ES-FEM in solid domain for dynamic analysis of 2D fluid-solid interaction problems International Journal of Computational Methods Institut für Strukturmechanik
OPUS4-3402 Wissenschaftlicher Artikel Brehm, Maik; Zabel, Volkmar; Bucher, Christian An automatic mode pairing strategy using an enhanced modal assurance citerion based on modal strain energies In the context of finite element model updating using output-only vibration test data, natural frequencies and mode shapes are used as validation criteria. Consequently, the correct pairing of experimentally obtained and numerically derived natural frequencies and mode shapes is important. In many cases, only limited spatial information is available and noise is present in the measurements. Therefore, the automatic selection of the most likely numerical mode shape corresponding to a particular experimentally identified mode shape can be a difficult task. The most common criterion for indicating corresponding mode shapes is the modal assurance criterion. Unfortunately, this criterion fails in certain cases and is not reliable for automatic approaches. In this paper, the purely mathematical modal assurance criterion will be enhanced by additional physical information from the numerical model in terms of modal strain energies. A numerical example and a benchmark study with experimental data are presented to show the advantages of the proposed energy-based criterion in comparison to the traditional modal assurance criterion. 17 Journal of Sound and Vibration 5375 5392 10.1016/j.jsv.2010.07.006 Institut für Strukturmechanik
OPUS4-2833 Konferenzveröffentlichung Brehm, Maik; Zabel, Volkmar; Bucher, Christian; Ribeiro, D. Gürlebeck, Klaus; Könke, Carsten AN AUTOMATIC MODE SELECTION STRATEGY FOR MODEL UPDATING USING THE MODAL ASSURANCE CRITERION AND MODAL STRAIN ENERGIES In the context of finite element model updating using vibration test data, natural frequencies and mode shapes are used as validation criteria. Consequently, the order of natural frequencies and mode shapes is important. As only limited spatial information is available and noise is present in the measurements, the automatic selection of the most likely numerical mode shape corresponding to a measured mode shape is a difficult task. The most common criterion to indicate corresponding mode shapes is the modal assurance criterion. Unfortunately, this criterion fails in certain cases. In this paper, the pure mathematical modal assurance criterion will be enhanced by additional physical information of the numerical model in terms of modal strain energies. A numerical example and a benchmark study with real measured data are presented to show the advantages of the enhanced energy based criterion in comparison to the traditional modal assurance criterion. 18 urn:nbn:de:gbv:wim2-20170314-28330 10.25643/bauhaus-universitaet.2833 Institut für Strukturmechanik
OPUS4-3428 Konferenzveröffentlichung Brehm, Maik; Zabel, Volkmar; Ribeiro, D. An Automatic Mode Tracking Strategy for Model Updating Using the Modal Assurance Criterion and Modal Strain Energies An Automatic Mode Tracking Strategy for Model Updating Using the Modal Assurance Criterion and Modal Strain Energies Institut für Strukturmechanik
OPUS4-3369 Wissenschaftlicher Artikel Phan-Dao, H.; Nguyen-Xuan, Hung; Thai-Hoang, C.; Nguyen-Thoi, T.; Rabczuk, Timon An edge-based smoothed finite element method for analysis of laminated composite plates An edge-based smoothed finite element method for analysis of laminated composite plates International Journal of Computational Methods Institut für Strukturmechanik
OPUS4-3956 Dissertation Alalade, Muyiwa An Enhanced Full Waveform Inversion Method for the Structural Analysis of Dams Since the Industrial Revolution in the 1700s, the high emission of gaseous wastes into the atmosphere from the usage of fossil fuels has caused a general increase in temperatures globally. To combat the environmental imbalance, there is an increase in the demand for renewable energy sources. Dams play a major role in the generation of "green" energy. However, these structures require frequent and strict monitoring to ensure safe and efficient operation. To tackle the challenges faced in the application of convention dam monitoring techniques, this work proposes the inverse analysis of numerical models to identify damaged regions in the dam. Using a dynamic coupled hydro-mechanical Extended Finite Element Method (XFEM) model and a global optimization strategy, damage (crack) in the dam is identified. By employing seismic waves to probe the dam structure, a more detailed information on the distribution of heterogeneous materials and damaged regions are obtained by the application of the Full Waveform Inversion (FWI) method. The FWI is based on a local optimization strategy and thus it is highly dependent on the starting model. A variety of data acquisition setups are investigated, and an optimal setup is proposed. The effect of different starting models and noise in the measured data on the damage identification is considered. Combining the non-dependence of a starting model of the global optimization strategy based dynamic coupled hydro-mechanical XFEM method and the detailed output of the local optimization strategy based FWI method, an enhanced Full Waveform Inversion is proposed for the structural analysis of dams. urn:nbn:de:gbv:wim2-20190813-39566 10.25643/bauhaus-universitaet.3956 Institut für Strukturmechanik
OPUS4-3477 Konferenzveröffentlichung Most, Thomas; Bucher, Christian An enhanced moving least squares interpolation for the element-free Galerkin method An enhanced moving least squares interpolation for the element-free Galerkin method Institut für Strukturmechanik
OPUS4-3296 Wissenschaftlicher Artikel Nguyen-Thanh, Nhon; Valizadeh, N.; Nguyen, Manh Hung; Nguyen-Xuan, Hung; Zhuang, Xiaoying; Areias, Pedro; Zi, Goangseup; Bazilevs, Yuri; De Lorenzis, Laura; Rabczuk, Timon An extended isogeometric thin shell analysis based on Kirchhoff-Love theory An extended isogeometric thin shell analysis based on Kirchho_-Love theory 26 Computer Methods in Applied Mechanics and Engineering 265 291 Institut für Strukturmechanik
OPUS4-3512 Konferenzveröffentlichung Winkel, B. An F-element, composite stress formulation to model muscular tissue in 3D An F-element, composite stress formulation to model muscular tissue in 3D Institut für Strukturmechanik
OPUS4-3478 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan; Schrader, Kai; Deckner, T. An improved cohesive crack model for combined crack opening and sliding under cyclic loading An improved cohesive crack model for combined crack opening and sliding under cyclic loading Institut für Strukturmechanik
OPUS4-2993 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan; Schrader, Kai; Deckner, T. Gürlebeck, Klaus; Könke, Carsten AN IMPROVED COHESIVE CRACK MODEL FOR COMBINED CRACK OPENING AND SLIDING UNDER CYCLIC LOADING The modeling of crack propagation in plain and reinforced concrete structures is still a field for many researchers. If a macroscopic description of the cohesive cracking process of concrete is applied, generally the Fictitious Crack Model is utilized, where a force transmission over micro cracks is assumed. In the most applications of this concept the cohesive model represents the relation between the normal crack opening and the normal stress, which is mostly defined as an exponential softening function, independently from the shear stresses in tangential direction. The cohesive forces are then calculated only from the normal stresses. By Carol et al. 1997 an improved model was developed using a coupled relation between the normal and shear damage based on an elasto-plastic constitutive formulation. This model is based on a hyperbolic yield surface depending on the normal and the shear stresses and on the tensile and shear strength. This model also represents the effect of shear traction induced crack opening. Due to the elasto-plastic formulation, where the inelastic crack opening is represented by plastic strains, this model is limited for applications with monotonic loading. In order to enable the application for cases with un- and reloading the existing model is extended in this study using a combined plastic-damage formulation, which enables the modeling of crack opening and crack closure. Furthermore the corresponding algorithmic implementation using a return mapping approach is presented and the model is verified by means of several numerical examples. Finally an investigation concerning the identification of the model parameters by means of neural networks is presented. In this analysis an inverse approximation of the model parameters is performed by using a given set of points of the load displacement curves as input values and the model parameters as output terms. It will be shown, that the elasto-plastic model parameters could be identified well with this approach, but require a huge number of simulations. 20 urn:nbn:de:gbv:wim2-20170327-29933 10.25643/bauhaus-universitaet.2993 Institut für Strukturmechanik
OPUS4-3746 Wissenschaftlicher Artikel Mosavi, Amir; Najafi, Bahman; Faizollahzadeh Ardabili, Sina; Shamshirband, Shahaboddin; Rabczuk, Timon An Intelligent Artificial Neural Network-Response Surface Methodology Method for Accessing the Optimum Biodiesel and Diesel Fuel Blending Conditions in a Diesel Engine from the Viewpoint of Exergy and Energy Analysis Biodiesel, as the main alternative fuel to diesel fuel which is produced from renewable and available resources, improves the engine emissions during combustion in diesel engines. In this study, the biodiesel is produced initially from waste cooking oil (WCO). The fuel samples are applied in a diesel engine and the engine performance has been considered from the viewpoint of exergy and energy approaches. Engine tests are performed at a constant 1500 rpm speed with various loads and fuel samples. The obtained experimental data are also applied to develop an artificial neural network (ANN) model. Response surface methodology (RSM) is employed to optimize the exergy and energy efficiencies. Based on the results of the energy analysis, optimal engine performance is obtained at 80% of full load in presence of B10 and B20 fuels. However, based on the exergy analysis results, optimal engine performance is obtained at 80% of full load in presence of B90 and B100 fuels. The optimum values of exergy and energy efficiencies are in the range of 25-30% of full load, which is the same as the calculated range obtained from mathematical modeling. Basel MDPI 18 Energies 2018 11, 4 urn:nbn:de:gbv:wim2-20180507-37467 10.3390/en11040860 Institut für Strukturmechanik
OPUS4-3393 Wissenschaftlicher Artikel Simpson, R.; Bordas, Stéphane Pierre Alain; Trevelyan, J.; Kerfriden, Pierre; Rabczuk, Timon An Isogeometric Boundary Element Method for elastostatic analysis The concept of isogeometric analysis, where functions that are used to describe geometry in CAD software are used to approximate the unknown fields in numerical simulations, has received great attention in recent years. The method has the potential to have profound impact on engineering design, since the task of meshing, which in some cases can add significant overhead, has been circumvented. Much of the research effort has been focused on finite element implementations of the isogeometric concept, but at present, little has been seen on the application to the Boundary Element Method. The current paper proposes an Isogeometric Boundary Element Method (BEM), which we term IGABEM, applied to two-dimensional elastostatic problems using Non-Uniform Rational B-Splines (NURBS). We find it is a natural fit with the isogeometric concept since both the NURBS approximation and BEM deal with quantities entirely on the boundary. The method is verified against analytical solutions where it is seen that superior accuracies are achieved over a conventional quadratic isoparametric BEM implementation. Computer Methods in Applied Mechanics and Engineering 10.1016/j.cma.2011.08.008 Institut für Strukturmechanik
OPUS4-3289 Wissenschaftlicher Artikel Anitescu, C.; Jia, Yue; Zhang, Yongjie; Rabczuk, Timon An isogeometric collocation method using superconvergent points An isogeometric collocation method using superconvergent points 24 Computer Methods in Applied Mechanics and Engineer-ing 1073 1097 Institut für Strukturmechanik
OPUS4-3480 Konferenzveröffentlichung Pham, Hoang Anh; Bucher, Christian An iterative procedure for model updating based on selective sensitivity An iterative procedure for model updating based on selective sensitivity Institut für Strukturmechanik
OPUS4-3473 Konferenzveröffentlichung Luther, Torsten; Könke, Carsten Analysis of crack initiation and propagation in polyctystalline meso- and microstructures of metal materials Analysis of crack initiation and propagation in polyctystalline meso- and microstructures of metal materials Institut für Strukturmechanik
OPUS4-3821 unpublished Rezakazemi, Mashallah; Mosavi, Amir; Shirazian, Saeed ANFIS pattern for molecular membranes separation optimization In this work, molecular separation of aqueous-organic was simulated by using combined soft computing-mechanistic approaches. The considered separation system was a microporous membrane contactor for separation of benzoic acid from water by contacting with an organic phase containing extractor molecules. Indeed, extractive separation is carried out using membrane technology where complex of solute-organic is formed at the interface. The main focus was to develop a simulation methodology for prediction of concentration distribution of solute (benzoic acid) in the feed side of the membrane system, as the removal efficiency of the system is determined by concentration distribution of the solute in the feed channel. The pattern of Adaptive Neuro-Fuzzy Inference System (ANFIS) was optimized by finding the optimum membership function, learning percentage, and a number of rules. The ANFIS was trained using the extracted data from the CFD simulation of the membrane system. The comparisons between the predicted concentration distribution by ANFIS and CFD data revealed that the optimized ANFIS pattern can be used as a predictive tool for simulation of the process. The R2 of higher than 0.99 was obtained for the optimized ANFIS model. The main privilege of the developed methodology is its very low computational time for simulation of the system and can be used as a rigorous simulation tool for understanding and design of membrane-based systems. Highlights are, Molecular separation using microporous membranes. Developing hybrid model based on ANFIS-CFD for the separation process, Optimization of ANFIS structure for prediction of separation process 19 2018 1 20 urn:nbn:de:gbv:wim2-20181122-38212 10.25643/BAUHAUS-UNIVERSITAET.3821 Institut für Strukturmechanik
OPUS4-3521 Konferenzveröffentlichung Most, Thomas Anwendung netzfreier Diskretisierungsverfahren zur stochastischen Rissfortschrittsberechnung Anwendung netzfreier Diskretisierungsverfahren zur stochastischen Rissfortschrittsberechnung Institut für Strukturmechanik
OPUS4-3510 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan Application of a hybrid parallelisation technique to accelerate the numerical simulation of nonlinear mechanical problems Application of a hybrid parallelisation technique to accelerate the numerical simulation of nonlinear mechanical problems Institut für Strukturmechanik
OPUS4-3475 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of an adaptive response surface approach for efficient structural reliability analysis Application of an adaptive response surface approach for efficient structural reliability analysis Institut für Strukturmechanik
OPUS4-3436 Konferenzveröffentlichung Luther, Torsten; Könke, Carsten Application of an Atom Continuum Model in Process of Damage Simulation on Multiple Length Scales Application of an Atom Continuum Model in Process of Damage Simulation on Multiple Length Scales Institut für Strukturmechanik
OPUS4-3465 Konferenzveröffentlichung Bucher, Christian; Most, Thomas Application of approximate response functions in structural reliability analysis Application of approximate response functions in structural reliability analysis Institut für Strukturmechanik
OPUS4-3496 Konferenzveröffentlichung Markwardt, Klaus Application of fast wavelet transformation in parametric system identification Application of fast wavelet transformation in parametric system identification Institut für Strukturmechanik
OPUS4-3282 Wissenschaftlicher Artikel Rabizadeh, E.; Saboor Bagherzadeh, Amir; Rabczuk, Timon Application of goal-oriented error estimation and adaptive mesh refinement on thermo-mechanical multifield problems Application of goal-oriented error estimation and adaptive mesh re_nement on thermo-mechanical multi_eld problems 17 Computational Materials Science 27 44 Institut für Strukturmechanik
OPUS4-3522 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of the "Fictitious Crack Model" to meshless crack growth simulations Application of the "Fictitious Crack Model" to meshless crack growth simulations Institut für Strukturmechanik
OPUS4-3503 Konferenzveröffentlichung Brehm, Maik; Zabel, Volkmar; Markwardt, Klaus Applications of biorthogonal wavelets in system identification Applications of biorthogonal wavelets in system identification Institut für Strukturmechanik
OPUS4-3489 Konferenzveröffentlichung Brehm, Maik; Zabel, Volkmar; Markwardt, Klaus Applications of Wavelet Packets in System Identifikation Applications of Wavelet Packets in System Identifikation Institut für Strukturmechanik
OPUS4-3455 Konferenzveröffentlichung Most, Thomas; Hofstetter, G.; Hofmann, Markus; Novák, D.; Lehký, D. Approximation of constitutive parameters for material models using artificial neural networks Approximation of constitutive parameters for material models using artificial neural networks Institut für Strukturmechanik
OPUS4-2174 Masterarbeit / Diplomarbeit Udrea, Mihai-Andrei Assessment of Data from Dynamic Bridge Monitoring The focus of the thesis is to process measurements acquired from a continuous monitoring system at a railway bridge. Temperature, strain and ambient vibration records are analysed and two main directions of investigation are pursued. The first and the most demanding task is to develop processing routines able to extract modal parameters from ambient vibration measurements. For this purpose, reliable experimental models are achieved on the basis of a stochastic system identification(SSI) procedure. A fully automated algorithm based on a three-stage clustering is implemented to perform a modal parameter estimation for every single measurement. After selecting a baseline of modal parameters, the evolution of eigenfrequencies is studied and correlated to environmental and operational factors. The second aspect deals with the structural response to passing trains. Corresponding triggered records of strain and temperature are processed and their assessment is accomplished using the average strains induced by each train as the reference parameter. Three influences due to speed, temperature and loads are distinguished and treated individually. An attempt to estimate the maximum response variation due to each factor is also carried out. urn:nbn:de:gbv:wim2-20140429-21742 10.25643/bauhaus-universitaet.2174 Institut für Strukturmechanik
OPUS4-2716 Dissertation Abbas, Tajammal Assessment of Numerical Prediction Models for Aeroelastic Instabilities of Bridges The phenomenon of aerodynamic instability caused by the wind is usually a major design criterion for long-span cable-supported bridges. If the wind speed exceeds the critical flutter speed of the bridge, this constitutes an Ultimate Limit State. The prediction of the flutter boundary, therefore, requires accurate and robust models. The complexity and uncertainty of models for such engineering problems demand strategies for model assessment. This study is an attempt to use the concepts of sensitivity and uncertainty analyses to assess the aeroelastic instability prediction models for long-span bridges. The state-of-the-art theory concerning the determination of the flutter stability limit is presented. Since flutter is a coupling of aerodynamic forcing with a structural dynamics problem, different types and classes of structural and aerodynamic models can be combined to study the interaction. Here, both numerical approaches and analytical models are utilised and coupled in different ways to assess the prediction quality of the coupled model. Weimar Jonas Verlag 275 urn:nbn:de:gbv:wim2-20180515-27161 10.25643/bauhaus-universitaet.2716 Institut für Strukturmechanik
OPUS4-3376 Wissenschaftlicher Artikel Areias, Pedro; Rabczuk, Timon; Dias-da-Costa, D. Assumed-metric spherically-interpolated quadrilateral shell element Assumed-metric spherically-interpolated quadrilateral shell element 14 Finite Elements in Analysis and Design 53 67 Institut für Strukturmechanik
OPUS4-3357 Wissenschaftlicher Artikel Areias, Pedro; Rabczuk, Timon; Dias-da-Costa, D. Asymmetric Shell Elements Based on a Corrected Updated-Lagrangian Approach Asymmetric Shell Elements Based on a Corrected Updated-Lagrangian Approach CMES: Computer Modeling in Engineering and Sciences Institut für Strukturmechanik
OPUS4-3504 Konferenzveröffentlichung Bucher, Christian; Pham, Hoang Anh Bayesian reliability updating using system identification based on selective sensitivity Bayesian reliability updating using system identification based on selective sensitivity Institut für Strukturmechanik
OPUS4-58 Dissertation Will, Johannes Beitrag zur Standsicherheitsberechnung im geklüfteten Fels in der Kontinuums- und Diskontinuumsmechanik unter Verwendung impliziter und expliziter Berechnungsstrategien 1999 urn:nbn:de:gbv:wim2-20040310-613 10.25643/bauhaus-universitaet.58 Institut für Strukturmechanik
OPUS4-3556 Konferenzveröffentlichung Markwardt, Klaus; Zabel, Volkmar Betrachtungen zur Anwendung der Wavelet- Transformation in der Systemidentifikation Betrachtungen zur Anwendung der Wavelet- Transformation in der Systemidentifikation Institut für Strukturmechanik
OPUS4-3586 Wissenschaftlicher Artikel Lahmer, Tom; Knabe, Tina; Nikulla, Susanne; Reuter, Markus Bewertungsmethoden für Modelle des konstruktiven Ingenieurbaus Bewertungsmethoden für Modelle des konstruktiven Ingenieurbaus 4 Bautechnik 60 64 Institut für Strukturmechanik
OPUS4-3326 Wissenschaftlicher Artikel Zhao, Jun-Hua; Lu, Lixin; Rabczuk, Timon Binding energy and mechanical stability of single- and multi-walled carbon nanotube serpentines Binding energy and mechanical stability of single- and multi-walled carbon nanotube serpentines The Journal of Chemical Physics 10.1063/1.4878115 Institut für Strukturmechanik