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
OPUS4-3557 Konferenzveröffentlichung Roos, Dirk; Bucher, Christian; Bayer, Veit Polyhedral response surfaces for structural reliability assessment Polyhedral response surfaces for structural reliability assessment Institut für Strukturmechanik
OPUS4-3445 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization 20 International Journal for Numerical and Analytical Methods in Geomechanics 285 305 Institut für Strukturmechanik
OPUS4-3499 Konferenzveröffentlichung Most, Thomas; Unger, Jörg F.; Bucher, Christian Stochastic crack growth simulation in R/C structures by means of meshless methods Stochastic crack growth simulation in R/C structures by means of meshless methods Institut für Strukturmechanik
OPUS4-3464 Konferenzveröffentlichung Brehm, Maik; Bucher, Christian Wavelet packet system identification Wavelet packet system identification Institut für Strukturmechanik
OPUS4-495 Wissenschaftlicher Artikel Bucher, Christian; Schorling, York SLang - the Structural Language : Solving Nonlinear and Stochastic Problems in Structural Mechanics Recent developments in structural mechanics indicate an increasing need of numerical methods to deal with stochasticity. This process started with the modeling of loading uncertainties. More recently, also system uncertainty, such as physical or geometrical imperfections are modeled in probabilistic terms. Clearly, this task requires close connenction of structural modeling with probabilistic modeling. Nonlinear effects are essential for a realistic description of the structural behavior. Since modern structural analysis relies quite heavily on the Finite Element Method, it seems to be quite reasonable to base stochastic structural analysis on this method. Commercially available software packages can cover deterministic structural analysis in a very wide range. However, the applicability of these packages to stochastic problems is rather limited. On the other hand, there is a number of highly specialized programs for probabilistic or reliability problems which can be used only in connection with rather simplistic structural models. In principle, there is the possibility to combine both kinds of software in order to achieve the goal. The major difficulty which then arises in practical computation is to define the most suitable way of transferring data between the programs. In order to circumvent these problems, the software package SLang (Structural Language) has been developed. SLang is a command interpreter which acts on a set of relatively complex commands. Each command takes input from and gives output to simple data structures (data objects), such as vectors and matrices. All commands communicate via these data objects which are stored in memory or on disk. The paper will show applications to structural engineering problems, in particular failure analysis of frames and shell structures with random loads and random imperfections. Both geometrical and physical nonlinearities are taken into account. 1997 urn:nbn:de:gbv:wim2-20111215-4957 10.25643/bauhaus-universitaet.495 Professur Informatik im Bauwesen
OPUS4-3398 Wissenschaftlicher Artikel Brehm, Maik; Zabel, Volkmar; Bucher, Christian Optimal reference sensor positions for applications in model updating using output-only vibration test data based on random excitation: Part 2 - improved search strategy and experimental case study Optimal reference sensor positions for applications in model updating using output-only vibration test data based on random excitation: Part 2 - improved search strategy and experimental case study Mechanical Systems and Signal Processing 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
OPUS4-3483 Wissenschaftlicher Artikel Bucher, Christian; Pham, Hoang Anh On model updating of existing structures utilizing measured dynamic responses On model updating of existing structures utilizing measured dynamic responses 8 Structure and Infrastructure Engineering 135 143 Institut für Strukturmechanik
OPUS4-3543 Konferenzveröffentlichung Ebert, Matthias; Bucher, Christian Stochastic finite element modeling of damage evolutions of R/C beams Stochastic finite element modeling of damage evolutions of R/C beams Institut für Strukturmechanik
OPUS4-3535 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic dynamic stability analysis for nonlinear structures Stochastic dynamic stability analysis for nonlinear structures Institut für Strukturmechanik
OPUS4-3561 Konferenzveröffentlichung Zabel, Volkmar; Bucher, Christian; Riedel, J. The dynamic behaviour of a historical bell tower - in- situ tests and numerical investigations The dynamic behaviour of a historical bell tower - in- situ tests and numerical investigations 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
OPUS4-3559 Konferenzveröffentlichung Schorling, York; Bucher, Christian; Purkert, G. Stability analysis for randomly imperfect structures Stability analysis for randomly imperfect structures 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
OPUS4-3508 Konferenzveröffentlichung Most, Thomas; Unger, Jörg F.; Bucher, Christian Stochastic modeling of cohesive crack propagation using meshless discretization techniques Stochastic modeling of cohesive crack propagation using meshless discretization techniques Institut für Strukturmechanik
OPUS4-3509 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic modeling of cohesive crack evolution in concrete using meshless interpolation techniques Stochastic modeling of cohesive crack evolution in concrete using meshless interpolation techniques Institut für Strukturmechanik
OPUS4-3490 Konferenzveröffentlichung Bucher, Christian; Zabel, Volkmar Experiences with detection of damage in bridge structures using dynamics tests Experiences with detection of damage in bridge structures using dynamics tests Institut für Strukturmechanik
OPUS4-3462 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Stochastic simulation of cracking in concrete structures using multi-parameter random fields Stochastic simulation of cracking in concrete structures using multi-parameter random fields 19 International Journal of Reliability and Safety 168 187 Institut für Strukturmechanik
OPUS4-3444 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Probabilistic analysis of concrete cracking using neural networks and random fields Probabilistic analysis of concrete cracking using neural networks and random fields 10 Probabilistic Engineering Mechanics 219 229 Institut für Strukturmechanik
OPUS4-3514 Wissenschaftlicher Artikel Kirichuk, A.; Most, Thomas; Bucher, Christian Numerical nonlinear analysis of kinematically excited shells Numerical nonlinear analysis of kinematically excited shells 13 International Journal for Computational Civil and Structural Engineering 61 74 Institut für Strukturmechanik
OPUS4-3549 Konferenzveröffentlichung Schorling, York; Most, Thomas; Bucher, Christian Stability Analysis for Imperfect Systems with Random Loading Stability Analysis for Imperfect Systems with Random Loading 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
OPUS4-3502 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian; Schorling, York Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading 19 Journal of Sound and Vibration 381 400 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
OPUS4-3480 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
OPUS4-3408 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
OPUS4-3517 Konferenzveröffentlichung Bucher, Christian Structural Reliability and Stochastic Finite Elements Structural Reliability and Stochastic Finite Elements Institut für Strukturmechanik
OPUS4-3498 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Mixed mode crack simulation using Virtual Crack Extension and a normal/shear cohesive crack model within a meshless discretization Mixed mode crack simulation using Virtual Crack Extension and a normal/shear cohesive crack model within a meshless discretization 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
OPUS4-3526 Wissenschaftlicher Artikel Bucher, Christian; Ebert, Matthias Nichtlineare Berechnung von Stahlflanschverbindungen mit gemessenen Imperfektionen Nichtlineare Berechnung von Stahlflanschverbindungen mit gemessenen Imperfektionen 6 Stahlbau 516 522 Institut für Strukturmechanik
OPUS4-3459 Wissenschaftlicher Artikel Bucher, Christian; Frangopol, D.M. Optimization of lifetime maintenance strategies for deteriorting structures considering probabilities of violating safety, condition, and cost thresholds Optimization of lifetime maintenance strategies for deteriorting structures considering probabilities of violating safety, condition, and cost thresholds 7 Probabilistic Engineering Mechanics 1 8 Institut für Strukturmechanik
OPUS4-3523 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Moving Least Squares-elements for stochastic crack propagation simulations coupled with stochastic finite elements Moving Least Squares-elements for stochastic crack propagation simulations coupled with stochastic finite elements Institut für Strukturmechanik
OPUS4-3533 Konferenzveröffentlichung Ebert, Matthias; Bucher, Christian Damage Effects on the Dynamic Properties of R/C Beams- Experimental and Numerical Investigations Damage Effects on the Dynamic Properties of R/C Beams- Experimental and Numerical Investigations Institut für Strukturmechanik
OPUS4-3525 Konferenzveröffentlichung Zabel, Volkmar; Bucher, Christian Experiment und Analyse - erweiterte Konzepte für Nachweis und Bemessung - Schwingungsmessungen Experiment und Analyse - erweiterte Konzepte für Nachweis und Bemessung - Schwingungsmessungen Institut für Strukturmechanik
OPUS4-3539 Konferenzveröffentlichung Zabel, Volkmar; Bucher, Christian Experiences with dynamic investigations of historical bell towers and belfriens Experiences with dynamic investigations of historical bell towers and belfriens Institut für Strukturmechanik
OPUS4-3540 Konferenzveröffentlichung Zabel, Volkmar; Bucher, Christian Parametric system identification by means of the wavelet transformation Parametric system identification by means of the wavelet transformation Bauhaus-Institut für zukunftsweisende Infrastruktursysteme
OPUS4-3560 Konferenzveröffentlichung Zabel, Volkmar; Bucher, Christian The utilization of a visualisation tool in system identification The utilization of a visualisation tool in system identification Institut für Strukturmechanik
OPUS4-582 Konferenzveröffentlichung Ebert, Matthias; Bucher, Christian Modelling of changing of dynamic and static parameters of damaged R/C Dynamic testing for damage assessment as non-destructive method has attracted growing in-terest for systematic inspections and maintenance of civil engineering structures. In this con-text the paper presents the Stochastic Finite Element (SFE) Modeling of the static and dy-namic results of own four point bending experiments with R/C beams. The beams are dam-aged by an increasing load. Between the load levels the dynamic properties are determined. Calculated stiffness loss factors for the displacements and the natural frequencies show differ-ent histories. A FE Model for the beams is developed with a discrete crack formulation. Cor-related random fields are used for structural parameters stiffness and tension strength. The idea is to simulate different crack evolutions. The beams have the same design parameters, but because of the stochastic material properties their undamaged state isn't yet the same. As the structure is loaded a stochastic first crack occurs on the weakest place of the structure. The further crack evolution is also stochastic. These is a great advantage compared with de-terministic formulations. To reduce the computational effort of the Monte Carlo simulation of this nonlinear problem the Latin-Hypercube sampling technique is applied. From the results functions of mean value and standard deviation of displacements and frequencies are calcu-lated. Compared with the experimental results some qualitative phenomena are good de-scribed by the model. Differences occurs especially in the dynamic behavior of the higher load levels. Aim of the investigations is to assess the possibilities of dynamic testing under consideration of effects from stochastic material properties 2000 urn:nbn:de:gbv:wim2-20111215-5825 10.25643/bauhaus-universitaet.582 Professur Informatik im Bauwesen
OPUS4-3458 Konferenzveröffentlichung Zabel, Volkmar; Brehm, Maik; Bucher, Christian Climatic influences on the dynamics of railway bridges with steel girders embedded in concrete Climatic influences on the dynamics of railway bridges with steel girders embedded in concrete Institut für Strukturmechanik
OPUS4-3553 Konferenzveröffentlichung Bucher, Christian; Ebert, Matthias Load Carrying Behavior of Prestressed Bolted Steel Flanges Considering Random Geometrical Imperfections Load Carrying Behavior of Prestressed Bolted Steel Flanges Considering Random Geometrical Imperfections Institut für Strukturmechanik
OPUS4-3555 Konferenzveröffentlichung Ebert, Matthias; Bucher, Christian SFE- Modelling of dynamic and static properties of R/C Beams in progressive damage SFE- Modelling of dynamic and static properties of R/C Beams in progressive damage Institut für Strukturmechanik
OPUS4-3418 Konferenzveröffentlichung Brehm, Maik; Zabel, Volkmar; Bucher, Christian Optimal reference sensor placement within roving setup configurations Optimal reference sensor placement within roving setup configurations Institut für Strukturmechanik
OPUS4-335 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of the "fictious crack model" to meshless crack growth simulations In this paper a meshless component is presented, which internally uses the common meshless interpolation technique >Moving Least Squares<. In contrast to usual meshless integration schemes like the cell quadrature and the nodal integration in this study integration zones with triangular geometry spanned by three nodes are used for 2D analysis. The boundary of the structure is defined by boundary nodes, which are similar to finite element nodes. By using the neighborhood relations of the integration zones an efficient search algorithm to detected the nodes in the influence of the integration points was developed. The components are directly coupled with finite elements by using a penalty method. An widely accepted model to describe the fracture behavior of concrete is the >Fictitious Crack Model< which is applied in this study, which differentiates between micro cracks and macro cracks, with and without force transmission over the crack surface, respectively. In this study the crack surface is discretized by node pairs in form of a polygon, which is part of the boundary. To apply the >Fictitious Crack Model< finite interface elements are included between the crack surface nodes. The determination of the maximum principal strain at the crack tip is done by introducing an influence area around the singularity. On a practical example it is shown that the included elements improve the model by the transmission of the surface forces during monotonic loading and by the representation of the contact forces of closed cracks during reverse loading. 2003 urn:nbn:de:gbv:wim2-20111215-3359 10.25643/bauhaus-universitaet.335 Professur Informatik im Bauwesen
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
OPUS4-2833 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
OPUS4-3475 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
OPUS4-3465 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
OPUS4-3497 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic dynamic stability analysis of shell structures Stochastic dynamic stability analysis of shell structures Institut für Strukturmechanik
OPUS4-2831 Konferenzveröffentlichung Bombasaro, Emanuel; Bucher, Christian Gürlebeck, Klaus; Könke, Carsten INVESTIGATION OF MODELING ERRORS OF DIFFERENT RANDOM FIELD BASED WIND LOAD FORMULATIONS In this paper the influence of changes in the mean wind velocity, the wind profile power-law coefficient, the drag coefficient of the terrain and the structural stiffness are investigated on different complex structural models. This paper gives a short introduction to wind profile models and to the approach by Davenport A. G. to compute the structural reaction of wind induced vibrations. Firstly with help of a simple example (a skyscraper) this approach is shown. Using this simple example gives the reader the possibility to study the variance differences when changing one of the above mentioned parameters on this very easy example and see the influence of different complex structural models on the result. Furthermore an approach for estimation of the needed discretization level is given. With the help of this knowledge the structural model design methodology can be base on deeper understanding of the different behavior of the single models. 11 urn:nbn:de:gbv:wim2-20170314-28318 10.25643/bauhaus-universitaet.2831 Graduiertenkolleg 1462
OPUS4-3411 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares 9 Engineering Analysis with Boundary Elements 461 470 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
OPUS4-3522 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
OPUS4-3511 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
OPUS4-3454 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
OPUS4-3529 Konferenzveröffentlichung Bucher, Christian Numerical Solution of the First-Passage Problem by FORM and Importance Sampling Numerical Solution of the First-Passage Problem by FORM and Importance Sampling Institut für Strukturmechanik