@unpublished{AbbasKavrakovMorgenthaletal.,
  author    = {Abbas, Tajammal and Kavrakov, Igor and Morgenthal, Guido and Lahmer, Tom},
  title     = {Prediction of aeroelastic response of bridge decks using artificial neural networks},
  doi       = {10.25643/bauhaus-universitaet.4097},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200225-40974},
  abstract  = {The assessment of wind-induced vibrations is considered vital for the design of long-span bridges. The aim of this research is to develop a methodological framework for robust and efficient prediction strategies for complex aerodynamic phenomena using hybrid models that employ numerical analyses as well as meta-models. Here, an approach to predict motion-induced aerodynamic forces is developed using artificial neural network (ANN). The ANN is implemented in the classical formulation and trained with a comprehensive dataset which is obtained from computational fluid dynamics forced vibration simulations. The input to the ANN is the response time histories of a bridge section, whereas the output is the motion-induced forces. The developed ANN has been tested for training and test data of different cross section geometries which provide promising predictions. The prediction is also performed for an ambient response input with multiple frequencies. Moreover, the trained ANN for aerodynamic forcing is coupled with the structural model to perform fully-coupled fluid--structure interaction analysis to determine the aeroelastic instability limit. The sensitivity of the ANN parameters to the model prediction quality and the efficiency has also been highlighted. The proposed methodology has wide application in the analysis and design of long-span bridges.},
  subject      = {Aerodynamik},
  language  = {en}
}
@unpublished{BodeMarxVogeletal.,
  author    = {Bode, Matthias and Marx, Steffen and Vogel, Albert and V{\"o}lker, Conrad},
  title     = {Dissipationsenergie bei Erm{\"u}dungsversuchen an Betonprobek{\"o}rpern},
  volume    = {2019},
  doi       = {10.25643/bauhaus-universitaet.4493},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211012-44938},
  pages     = {9},
  abstract  = {Aufgrund des visko-elastoplastischen Materialverhaltens von Beton wird Probek{\"o}rpern und Bauteilen infolge zyklischer Beanspruchungen Energie zugef{\"u}hrt. Die entsprechenden Energiegr{\"o}ßen werden durch Hysteresefl{\"a}chen der Spannungs-Dehnungslinien beschrieben. In der Literatur finden sich dabei unterschiedliche Ans{\"a}tze, wof{\"u}r diese Energie verwendet wird. Erste Untersuchungen zeigen, dass zumindest ein Teil dieser dissipierten Energie in thermische Energie umgewandelt wird. Mithilfe der in diesem Beitrag beschriebenen Methodik lassen sich diese Energiegr{\"o}ßen f{\"u}r jeden Lastwechsel eines Erm{\"u}dungsversuches schnell und zuverl{\"a}ssig bestimmen. Anschließend wurden mit dem implementierten Algorithmus die dissipierten Energien von insgesamt 27 zyklischen Versuchen ausgewertet. Analog zu der Dehnungsentwicklung und der Steifigkeitsdegradation weisen auch die Verl{\"a}ufe der dissipierten Energie {\"u}ber die Lastwechselzahl einen dreiphasigen Verlauf auf. Die Auswertung zeigt außerdem eine Korrelation zwischen der Bruchlastwechselzahl und der dissipierten Energie. Auch der Zusammenhang zwischen Probek{\"o}rpererw{\"a}rmung und dissipierter Energie konnte best{\"a}tigt werden.},
  subject      = {Erm{\"u}dung},
  language  = {de}
}
@unpublished{EngelmannSchwendnerSeim,
  author    = {Engelmann, Iris and Schwendner, Sascha and Seim, Werner},
  title     = {Materialsparende Nagelbinder - Aspekte der Konstruktionsgeschichte von 1930 bis 1990},
  doi       = {10.25643/bauhaus-universitaet.4888},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230112-48882},
  pages     = {33},
  abstract  = {Materialsparende Holzkonstruktionen, die insbesondere w{\"a}hrend der Kriegs- und Nachkriegszeit im 20. Jahrhundert entwickelt und optimiert wurden, erlangen aktuell aus konstruktionshistorischer Sicht, aber auch aus {\"o}konomischer Sicht erneut Interesse. Der vorliegende Beitrag gibt einen {\"U}berblick angefangen von den ersten Konstruktionen Ende der 1920er Jahre bis hin zu Typenbindern der DDR, die noch bis 1990 {\"u}ber Landwirtschaftsbauten errichtet wurden und heute oft als Tragkonstruktionen f{\"u}r Photovoltaikanlagen weiterverwendet werden. Der Fokus liegt auf der chronologischen Vorstellung ausgew{\"a}hlter Konstruktionsweisen f{\"u}r Hallen- und Hausd{\"a}cher unterschieden nach Fachwerk- und Vollwandbindern. Sowohl die verantwortlichen Ingenieure und deren Herkunft, sowie wesentliche Anwendungsfelder und Beispielbauten kommen in der {\"U}berblicksdarstellung zur Sprache. Eine wesentliche Erkenntnis ist die im Betrachtungszeitraum 1930 bis 1990 zu verzeichnende Reduzierung einer Vielzahl genagelter Spar- hin zu Typenkonstruktionen, die im wesentlichen {\"a}ußerst materialeffiziente Fachwerkbinder f{\"u}r Satteld{\"a}cher hervorbrachte.},
  subject      = {Ingenieurholzbau},
  language  = {de}
}
@unpublished{FischerSchwendnerSeimetal.,
  author    = {Fischer, Jens and Schwendner, Sascha and Seim, Werner and Engelmann, Iris},
  title     = {Verbindungen mit N{\"a}geln im Holzbau - Die Erforschung und Entwicklung von Konstruktionsregeln},
  doi       = {10.25643/bauhaus-universitaet.4889},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230112-48893},
  pages     = {25},
  abstract  = {Der Nagel als tragendes Holzverbindungsmittel ist heute gut bekannt. Doch noch vor 100 Jahren war das anders: sein statisch konstruktiver Gebrauch war verboten. Das {\"a}nderte sich mit Beginn dessen Erforschung Ende der 1920er Jahre. Seit 1933 ist der Nagel Bestandteil der deutschen Regelwerke und findet seitdem breite Verwendung. {\"U}ber weite Teile des 20. Jahrhunderts diente er in Not- und Sparkonstruktionen wie Brett- und Bohlenbindern als hocheffizientes Verbindungsmittel der Wahl. Diese materialsparenden Tragwerke waren bei der periodisch im-mer wiederkehrenden Ressourcenknappheit sehr gefragt und sind ein wichtiger Bestandteil der Konstruktionsgeschichte des Holzbaus. In dem folgenden Beitrag wird die Erforschung des Na-geltragverhaltens und die einhergehende fortlaufende Normierung behandelt. Die Errungen-schaften einzelner Forschungsvorhaben werden vorgestellt. Anhand eines Zeitstrahls werden Zusammenh{\"a}nge zwischen Forschung und Normung gezeigt. Tabellen und Grafiken verdeutli-chen die {\"A}nderungen innerhalb der Normen von der ersten DIN 1052 im Jahr 1933 {\"u}ber die erste eigenst{\"a}ndige Holzbaunorm in der DDR, der TGL 112-0730, aus 1963 bis zur DIN 1052- 1988. Dabei wird immer Bezug zum derzeitigen Entwurf des Eurocode 5 genommen. Allgemein zeigt sich, dass ein Großteil der heutigen Kenntnisse immer noch auf die Grundlagenforschung der 1930er Jahre zur{\"u}ckgeht.},
  subject      = {Ingenieurholzbau},
  language  = {de}
}
@unpublished{GrundhoeferBimber2006,
  author    = {Grundh{\"o}fer, Anselm and Bimber, Oliver},
  title     = {Real-Time Adaptive Radiometric Compensation},
  doi       = {10.25643/bauhaus-universitaet.784},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-7848},
  year      = {2006},
  abstract  = {Recent radiometric compensation techniques make it possible to project images onto colored and textured surfaces. This is realized with projector-camera systems by scanning the projection surface on a per-pixel basis. With the captured information, a compensation image is calculated that neutralizes geometric distortions and color blending caused by the underlying surface. As a result, the brightness and the contrast of the input image is reduced compared to a conventional projection onto a white canvas. If the input image is not manipulated in its intensities, the compensation image can contain values that are outside the dynamic range of the projector. They will lead to clipping errors and to visible artifacts on the surface. In this article, we present a novel algorithm that dynamically adjusts the content of the input images before radiometric compensation is carried out. This reduces the perceived visual artifacts while simultaneously preserving a maximum of luminance and contrast. The algorithm is implemented entirely on the GPU and is the first of its kind to run in real-time.},
  subject      = {Maschinelles Sehen},
  language  = {en}
}
@unpublished{KavrakovArgentiniOmarinietal.,
  author    = {Kavrakov, Igor and Argentini, Tommaso and Omarini, Simone and Rocchi, Daniele and Morgenthal, Guido},
  title     = {Determination of complex aerodynamic admittance of bridge decks under deterministic gusts using the Vortex Particle Method},
  doi       = {10.25643/bauhaus-universitaet.4088},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200206-40883},
  abstract  = {Long-span bridges are prone to wind-induced vibrations. Therefore, a reliable representation of the aerodynamic forces acting on a bridge deck is of a major significance for the design of such structures. This paper presents a systematic study of the two-dimensional (2D) fluid-structure interaction of a bridge deck under smooth and turbulent wind conditions. Aerodynamic forces are modeled by two approaches: a computational fluid dynamics (CFD) model and six semi-analytical models. The vortex particle method is utilized for the CFD model and the free-stream turbulence is introduced by seeding vortex particles upstream of the deck with prescribed spectral characteristics. The employed semi-analytical models are based on the quasi-steady and linear unsteady assumptions and aerodynamic coefficients obtained from CFD analyses. The underlying assumptions of the semi-analytical aerodynamic models are used to interpret the results of buffeting forces and aeroelastic response due to a free-stream turbulence in comparison with the CFD model. Extensive discussions are provided to analyze the effect of linear fluid memory and quasi-steady nonlinearity from a CFD perspective. The outcome of the analyses indicates that the fluid memory is a governing effect in the buffeting forces and aeroelastic response, while the effect of the nonlinearity is overestimated by the quasi-steady models. Finally, flutter analyses are performed and the obtained critical velocities are further compared with wind tunnel results, followed by a brief examination of the post-flutter behavior. The results of this study provide a deeper understanding of the extent of which the applied models are able to replicate the physical processes for fluid-structure interaction phenomena in bridge aerodynamics and aeroelasticity.},
  subject      = {Bridge},
  language  = {en}
}
@unpublished{KavrakovMorgenthal,
  author    = {Kavrakov, Igor and Morgenthal, Guido},
  title     = {A synergistic study of a CFD and semi-analytical models for aeroelastic analysis of bridges in turbulent wind conditions},
  doi       = {10.25643/bauhaus-universitaet.4087},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200206-40873},
  abstract  = {Long-span bridges are prone to wind-induced vibrations. Therefore, a reliable representation of the aerodynamic forces acting on a bridge deck is of a major significance for the design of such structures. This paper presents a systematic study of the two-dimensional (2D) fluid-structure interaction of a bridge deck under smooth and turbulent wind conditions. Aerodynamic forces are modeled by two approaches: a computational fluid dynamics (CFD) model and six semi-analytical models. The vortex particle method is utilized for the CFD model and the free-stream turbulence is introduced by seeding vortex particles upstream of the deck with prescribed spectral characteristics. The employed semi-analytical models are based on the quasi-steady and linear unsteady assumptions and aerodynamic coefficients obtained from CFD analyses. The underlying assumptions of the semi-analytical aerodynamic models are used to interpret the results of buffeting forces and aeroelastic response due to a free-stream turbulence in comparison with the CFD model. Extensive discussions are provided to analyze the effect of linear fluid memory and quasi-steady nonlinearity from a CFD perspective. The outcome of the analyses indicates that the fluid memory is a governing effect in the buffeting forces and aeroelastic response, while the effect of the nonlinearity is overestimated by the quasi-steady models. Finally, flutter analyses are performed and the obtained critical velocities are further compared with wind tunnel results, followed by a brief examination of the post-flutter behavior. The results of this study provide a deeper understanding of the extent of which the applied models are able to replicate the physical processes for fluid-structure interaction phenomena in bridge aerodynamics and aeroelasticity.},
  subject      = {Ingenieurwissenschaften},
  language  = {en}
}
@unpublished{KavrakovMorgenthal,
  author    = {Kavrakov, Igor and Morgenthal, Guido},
  title     = {Aeroelastic analyses of bridges using a Pseudo-3D vortex method and velocity-based synthetic turbulence generation},
  doi       = {10.25643/bauhaus-universitaet.4086},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200206-40864},
  abstract  = {The accurate representation of aerodynamic forces is essential for a safe, yet reasonable design of long-span bridges subjected to wind effects. In this paper, a novel extension of the Pseudo-three-dimensional Vortex Particle Method (Pseudo-3D VPM) is presented for Computational Fluid Dynamics (CFD) buffeting analysis of line-like structures. This extension entails an introduction of free-stream turbulent fluctuations, based on the velocity-based turbulence generation. The aerodynamic response of a long-span bridge is obtained by subjecting the 3D dynamic representation of the structure to correlated free-stream turbulence in two-dimensional (2D) fluid planes, which are positioned along the bridge deck. The span-wise correlation of the free-stream turbulence between the 2D fluid planes is established based on Taylor's hypothesis of frozen turbulence. Moreover, the application of the laminar Pseudo-3D VPM is extended to a multimode flutter analysis. Finally, the structural response from the Pseudo-3D flutter and buffeting analyses is verified with the response, computed using the semi-analytical linear unsteady model in the time-domain. Meaningful merits of the turbulent Pseudo-3D VPM with respect to the linear unsteady model are the consideration of the 2D aerodynamic nonlinearity, nonlinear fluid memory, vortex shedding and local non-stationary turbulence effects in the aerodynamic forces. The good agreement of the responses for the two models in the 3D analyses demonstrates the applicability of the Pseudo-3D VPM for aeroelastic analyses of line-like structures under turbulent and laminar free-stream conditions.},
  subject      = {Bridge},
  language  = {en}
}
@unpublished{KhosraviSheikhKhozaniCooper,
  author    = {Khosravi, Khabat and Sheikh Khozani, Zohreh and Cooper, James R.},
  title     = {Predicting stable gravel-bed river hydraulic geometry: A test of novel, advanced, hybrid data mining algorithms},
  volume    = {2021},
  doi       = {10.25643/bauhaus-universitaet.4499},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211004-44998},
  abstract  = {Accurate prediction of stable alluvial hydraulic geometry, in which erosion and sedimentation are in equilibrium, is one of the most difficult but critical topics in the field of river engineering. Data mining algorithms have been gaining more attention in this field due to their high performance and flexibility. However, an understanding of the potential for these algorithms to provide fast, cheap, and accurate predictions of hydraulic geometry is lacking. This study provides the first quantification of this potential. Using at-a-station field data, predictions of flow depth, water-surface width and longitudinal water surface slope are made using three standalone data mining techniques -, Instance-based Learning (IBK), KStar, Locally Weighted Learning (LWL) - along with four types of novel hybrid algorithms in which the standalone models are trained with Vote, Attribute Selected Classifier (ASC), Regression by Discretization (RBD), and Cross-validation Parameter Selection (CVPS) algorithms (Vote-IBK, Vote-Kstar, Vote-LWL, ASC-IBK, ASC-Kstar, ASC-LWL, RBD-IBK, RBD-Kstar, RBD-LWL, CVPSIBK, CVPS-Kstar, CVPS-LWL). Through a comparison of their predictive performance and a sensitivity analysis of the driving variables, the results reveal: (1) Shield stress was the most effective parameter in the prediction of all geometry dimensions; (2) hybrid models had a higher prediction power than standalone data mining models, empirical equations and traditional machine learning algorithms; (3) Vote-Kstar model had the highest performance in predicting depth and width, and ASC-Kstar in estimating slope, each providing very good prediction performance. Through these algorithms, the hydraulic geometry of any river can potentially be predicted accurately and with ease using just a few, readily available flow and channel parameters. Thus, the results reveal that these models have great potential for use in stable channel design in data poor catchments, especially in developing nations where technical modelling skills and understanding of the hydraulic and sediment processes occurring in the river system may be lacking.},
  subject      = {Maschinelles Lernen},
  language  = {en}
}
@unpublished{KhosraviSheikhKhozaniMao,
  author    = {Khosravi, Khabat and Sheikh Khozani, Zohreh and Mao, Luka},
  title     = {A comparison between advanced hybrid machine learning algorithms and empirical equations applied to abutment scour depth prediction},
  doi       = {10.25643/bauhaus-universitaet.4388},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210311-43889},
  pages     = {43},
  abstract  = {Complex vortex flow patterns around bridge piers, especially during floods, cause scour process that can result in the failure of foundations. Abutment scour is a complex three-dimensional phenomenon that is difficult to predict especially with traditional formulas obtained using empirical approaches such as regressions. This paper presents a test of a standalone Kstar model with five novel hybrid algorithm of bagging (BA-Kstar), dagging (DA-Kstar), random committee (RC-Kstar), random subspace (RS-Kstar), and weighted instance handler wrapper (WIHWKstar) to predict scour depth (ds) for clear water condition. The dataset consists of 99 scour depth data from flume experiments (Dey and Barbhuiya, 2005) using abutment shapes such as vertical, semicircular and 45◦ wing. Four dimensionless parameter of relative flow depth (h/l), excess abutment Froude number (Fe), relative sediment size (d50/l) and relative submergence (d50/h) were considered for the prediction of relative scour depth (ds/l). A portion of the dataset was used for the calibration (70\%), and the remaining used for model validation. Pearson correlation coefficients helped deciding relevance of the input parameters combination and finally four different combinations of input parameters were used. The performance of the models was assessed visually and with quantitative metrics. Overall, the best input combination for vertical abutment shape is the combination of Fe, d50/l and h/l, while for semicircular and 45◦ wing the combination of the Fe and d50/l is the most effective input parameter combination. Our results show that incorporating Fe, d50/l and h/l lead to higher performance while involving d50/h reduced the models prediction power for vertical abutment shape and for semicircular and 45◦ wing involving h/l and d50/h lead to more error. The WIHW-Kstar provided the highest performance in scour depth prediction around vertical abutment shape while RC-Kstar model outperform of other models for scour depth prediction around semicircular and 45◦ wing.},
  subject      = {maschinelles Lernen},
  language  = {en}
}