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1
Content available Development of a machine learning-based design optimization method for crashworthiness analysis
Borse A., Gulakala R., Stoffel M.
Archives of Mechanics
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2024
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Vol. 76, nr 1-2
61--92
EN
This article investigates design optimisation in the automotive field using machine learning (ML). A thin-walled crash box under axial impact is studied and the design parameters are optimised for front-impact crash tests. This study is based on geometrically and physically nonlinear shell theory, finite element analysis (FEA), dynamic buckling analysis and design optimisation using ML. An artificial neural network framework consisting of various ML methods is developed. A generative adversarial network is established for data generation and reinforcement learning is implemented to automate exploration of the design parameter. This ML framework is proven to determine optimal parameters under predefined crashworthiness constraints.
2
Content available remote Stability of feed forward artificial neural networks versus nonlinear structural models in high speed deformations: A critical comparison
Stoffel M., Bamer F., Markert B.
Archives of Mechanics
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2019
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Vol. 71, nr 2
95--111
EN
In recent years, artificial neural networks have been proposed for engineering applications, such as predicting stresses and strains in structural elements. However, the question arises, how many complex influences can be included in an artificial neural network (ANN) and how accurate these predictions are in comparison to classical finite element solutions. A weakness of finite element predictions is that they can behave sensitive and unstable to changes in material parameters. An ANN does not need an underlying model with parameters and uses input variables, only. In the present study the stability of numerical results obtained by ANN and FEM are compared to each other for a problem in structural dynamics. The result gives new insight about the possibilities to predict accurately structural deformations by means of ANNs. As an example for highly complex geometrically and physically nonlinear structural deformations, the response of circular metal plates subjected to shock waves is investigated.
3
Content available remote Changes of flood risk on the northern foothills of the Tatra Mountains
Kundzewicz Z. W., Stoffel M., Ruiz-Villanueva V., Ballesteros-Cánovas J. A., Wyżga B., Niedźwiedź T., Kaczka R., Łupikasza E., Spyt B., Janecka K., Pińskwar I., Choryński A., Zawiejska J., Mikuś P, Hajdukiewicz H.
Acta Geophysica
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2017
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Vol. 65, no. 4
799--807
EN
The present paper reviews selected outcomes of the FLORIST project devoted to flood risk in the region of the northern foothills of the Tatra Mountains in Poland and summarizes novel results. The project encompassed theoretical, field, and modeling work. It was focused around observation-based hydroclimatology; projections for the future; dendrogeomorphology; as well as influence of transport of large wood on fluvial processes. The project improved understanding and interpreting changes in high-flow frequency and magnitude as well as changes in flood risk in the region, related to the presence of large wood in mountain streams. A unique database on past episodes of intense precipitation and flooding was created, harnessing multiple sources. The project showed that the analysis of tree rings and wood logs can offer useful information, complementing and considerably enriching the knowledge of river floods in the region of northern foothills of the Tatra Mountains. Retrospective and scenario-defined modeling of selected past fluvial events in the region was also performed.
4
Content available remote Tree-ring based record of intra-eruptive lahar activity: Axaltzintle valley, Malinche volcano, Mexico
Franco-Ramos O., Stoffel M., Vázquez-Selem L.
Geochronometria
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2016
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Vol. 43, no. 1
74--83
EN
Lahars are a widespread phenomenon in volcanic environments and good knowledge generally exists on contemporary, syn-eruptive lahar activity. Much less data is, by contrast, available on post-eruptive lahars and/or hydrogeomorphic processes out of extinct volcanic complexes. In this study we present a reconstruction of intra-eruptive lahar activity in Axaltzintle valley (Malinche volcano) using growth-ring records of 86 Abies religiosa trees. Based on the identification of 217 growth disturbances, field evidence and hydrological records we reconstruct a total of 19 lahars for the period 1945–2011. The reconstructed lahars were mostly triggered by moderate intensity, but persistent rainfalls with sums of at least ~100 mm. By contrast, the 1998 and 2005 lahars were presumably triggered by hurricane-induced torrential rainfalls with >100 mm in three days.
5
Content available remote Debris-flow activity in five adjacent gullies in a limestone mountain range
Schraml K., Oismüller M., Stoffel M., Hübl J., Kaitna R.
Geochronometria
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2015
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Vol. 42, no.1
60--66
EN
Debris-flows are infrequent geomorphic phenomena that shape steep valleys and can represent a severe hazard for human settlements and infrastructure. In this study, a debris-flow event chronology has been derived at the regional scale within the Gesäuse National Park (Styria, Austria) using dendrogeomorphic techniques. Sediment sources and deposition areas were mapped by combined field investigation and aerial photography using an Unmanned Aerial Vehicle (UAV). Through the analysis of 384 trees, a total of 47 debris-flows occurring in 19 years between AD 1903 and 2008 were identified in five adjacent gullies. Our results highlight the local variability of debris-flow activity as a result of local thunderstorms and the variable availability of sediment sources.
6
Content available remote Floods at the northern foothills of the Tatra Mountains — A Polish-Swiss research project
Kundzewicz Z.W, Pińskwar I., Choryński A., Stoffel M, Ruiz-Villanueva V, Ballesteros-Canovas J.A, Kaczka R.J, Niedźwiedź T, Łupikasza E, Czajka B., Małarzewski Ł., Janecka K, Wyżga B, Mikuś P.
Acta Geophysica
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2014
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Vol. 62, no. 3
620--641
EN
The present paper introduces the topical area of the Polish–Swiss research project FLORIST (Flood risk on the northern foothills of the Tatra Mountains), informs on its objectives, and reports on initial results. The Tatra Mountains are the area of the highest precipitation in Poland and largely contribute to flood generation. The project is focused around four competence clusters: observation-based climatology, model-based climate change projections and impact assessment, dendrogeomorphology, and impact of large wood debris on fluvial processes. The knowledge generated in the FLORIST project is likely to have impact on understanding and interpretation of flood risk on the northern foothills of the Tatra Mountains, in the past, present, and future. It can help solving important practical problems related to flood risk reduction strategies and flood preparedness.
7
Content available remote Modeling of articular cartilage replacement materials
Stoffel M., Weichert D., Muller-Rath R.
Archives of Mechanics
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2009
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Vol. 61, nr 1
69-87
EN
The development of replacement material for human articular cartilage exhibiting similar mechanical properties as the native tissue is a problem of high actuality in biomeclicine. In the present work a new condensed collagen material is investigated. The study aims at developing a mechanical model especially adapted to this particular collagen material. For this purpose, a viscoelastic-diffusion (VED) model is proposed, accounting for two different diffusion evolutions assumed. Moreover, the need for a gradient material description is discussed in order to cover fabrication influences leading to a variable Young's modulus for the material. On this background, a phe-nornenological law is presented to predict deformation-dependent diffusion behavior and internal reaction forces. Furthermore, the present approach allows a practible identification of diffusion parameters. The theoretical model is implemented into a finite element code and parameters are identified by tension tests. The simulation results are validated experimentally.
8
Content available remote Anisotropic damage evolution in shock wave-loaded viscoplastic plates
Stoffel M.
Archives of Mechanics
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2008
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Vol. 60, nr 4
285-301
EN
In the design of structural elements, which are used for protection against explosions, the damage evolution until failure has to be predicted in numerical simulations. However, in the literature a wide variety of damage models is available based on different approaches, e.g. phenomenological and micromechanical theories. Furthermore, the consequences of connections between new damage models and the constitutive equations accounting for elastic-viscoplasticity are unclear. The same problem occurs if structural theories, involving hypotheses, are combined with damage laws. In order to verify the calculated results, experiments with structures subjected to pressure waves are necessary. For this reason, an experimental validation method by means of shock tubes is used in the present study to verify the isotropic and anisotropic damage models. The measured deformations and experimentally observed failure modes can then be compared to the simulated results.
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