Prof. Dr. Jörn Behrens

@article{4118ee8b0a0940caaad7191abedafed6,

title = "Bathymetry reconstruction from experimental data using PDE-constrained optimisation",

abstract = "Knowledge of the bottom topography, also called bathymetry, of rivers, seas or the ocean is important for many areas of maritime science and civil engineering. While direct measurements are possible, they are time consuming, expensive and inaccurate. Therefore, many approaches have been proposed how to infer the bathymetry from measurements of surface waves. Mathematically, this is an inverse problem where an unknown system state needs to be reconstructed from observations with a suitable model for the flow as constraint. In many cases, the shallow water equations can be used to describe the flow. While theoretical studies of the efficacy of such a PDE-constrained optimisation approach for bathymetry reconstruction exist, there seem to be few publications that study its application to data obtained from real-world measurements. This paper shows that the approach can, at least qualitatively, reconstruct a Gaussian-shaped bathymetry in a wave flume from measurements of the free surface level at up to three points. Achieved normalised root mean square errors (NRMSE) are in line with other approaches.",

author = "J. Angel and J. Behrens and S. G{\"o}tschel and M. Hollm and D. Ruprecht and R. Seifried",

year = "2024",

month = jun,

day = "1",

doi = "10.1016/j.compfluid.2024.106321",

language = "English",

volume = "278",

journal = "Computers and Fluids",

issn = "0045-7930",

publisher = "Elsevier Ltd",

@article{71c87e9eeaaa40a8b942ec575be91ee7,

title = "A low-rank update for relaxed Schur complement preconditioners in fluid flow problems",

abstract = "The simulation of fluid dynamic problems often involves solving large-scale saddle-point systems. Their numerical solution with iterative solvers requires efficient preconditioners. Low-rank updates can adapt standard preconditioners to accelerate their convergence. We consider a multiplicative low-rank correction for pressure Schur complement preconditioners that is based on a (randomized) low-rank approximation of the error between the identity and the preconditioned Schur complement. We further introduce a relaxation parameter that scales the initial preconditioner. This parameter can improve the initial preconditioner as well as the update scheme. We provide an error analysis for the described update method. Numerical results for the linearized Navier–Stokes equations in a model for atmospheric dynamics on two different geometries illustrate the action of the update scheme. We numerically analyze various parameters of the low-rank update with respect to their influence on convergence and computational time.",

keywords = "Low-rank update, Preconditioner, Saddle-point system, Schur complement",

author = "Beddig, {Rebekka S.} and J{\"o}rn Behrens and Sabine Le Borne",

year = "2023",

month = may,

day = "10",

doi = "10.1007/s11075-023-01548-3",

language = "English",

volume = "94",

pages = "1597--1618",

journal = "Numer. Algorithms",

issn = "1017-1398",

publisher = "Springer Netherlands",

number = "4",

@article{ab0ca8c0d94f415abe9d7c51edde974f,

title = "A linear low effort stabilization method for the Euler equations using discontinuous Galerkin methods",

abstract = "We present a novel and simple yet intuitive approach to the stabilization problem for the numerically solved Euler equations with gravity source term relying on a low-order nodal Discontinuous Galerkin Method (DGM). Instead of assuming isothermal or polytropic solutions, we only take a hydrostatic balance as a given property of the flow and use the hydrostatic equation to calculate a hydrostatic pressure reconstruction that replaces the gravity source term. We compare two environments that both solve the Euler equations using the DGM: deal.II and StormFlash. We utilize StormFlash as it allows for the use of the novel stabilization method. Without stabilization, StormFlash does not yield results that resemble correct physical behavior while the results with stabilization for StormFlash, as well as deal.II model the fluid flow more accurately. Convergence rates for deal.II do not match the expected order while the convergence rates for StormFlash with the stabilization scheme (with the exceptions for the L (Formula presented.) errors for momentum) meet the expectation. The results from StormFlash with stabilization also fit reference solutions from the literature much better than those from deal.II. We conclude that this novel scheme is a low cost approach to stabilize the Euler equations while not limiting the flow in any way other than it being in hydrostatic balance.",

keywords = "general approach, discontinuous Galerkin method, stabilization, Euler equations",

author = "Michel B{\"a}nsch and J{\"o}rn Behrens and Stefan Vater",

year = "2023",

doi = "10.1002/fld.5243",

language = "English",

volume = "96",

pages = "256--276",

journal = "International Journal for Numerical Methods in Fluids",

issn = "0271-2091",

publisher = "John Wiley and Sons Ltd",

number = "3",

@article{ffd5cd847949432e8c825285afc00ce5,

title = "Towards the new Thematic Core Service Tsunami within the EPOS Research Infrastructure",

abstract = "Tsunamis constitute a significant hazard for European coastal populations, and the impact of tsunami events worldwide can extend well beyond the coastal regions directly affected. Understanding the complex mechanisms of tsunami generation, propagation, and inundation, as well as managing the tsunami risk, requires multidisciplinary research and infrastructures that cross national boundaries. Recent decades have seen both great advances in tsunami science and consolidation of the European tsunami research community. A recurring theme has been the need for a sustainable platform for coordinated tsunami community activities and a hub for tsunami services. Following about three years of preparation, in July 2021, the European tsunami community attained the status of Candidate Thematic Core Service (cTCS) within the European Plate Observing System (EPOS) Research Infrastructure. Within a transition period of three years, the Tsunami candidate TCS is anticipated to develop into a fully operational EPOS TCS. We here outline the path taken to reach this point, and the envisaged form of the future EPOS TCS Tsunami. Our cTCS is planned to be organised within four thematic pillars: (1) Support to Tsunami Service Providers, (2) Tsunami Data, (3) Numerical Models, and (4) Hazard and Risk Products. We outline how identified needs in tsunami science and tsunami risk mitigation will be addressed within this structure and how participation within EPOS will become an integration point for community development.",

keywords = "Tsunami, Infrastructures",

author = "Andrey Babeyko and Stefano Lorito and Francisco Hernandez and J{\"o}rn Lauterjung and Finn L{\o}vholt and Alexander Rudloff and Mathilde S{\o}rensen and Alexey Androsov and Inigo Aniel-Quiroga and Alberto Armigliato and Baptista, {Maria Ana} and Enrico Baglione and J{\"o}rn Behrens and Beatriz Brizuela and Sergio Bruni and Didem Cambaz and {Cantavella Nadal}, Juan and Fernando Carillho and Ian Chandler and Denis Chang-Seng and Marinos Charalampakis and Lorenzo Cugliari and Clea Denamiel and Doğan, {G{\"o}zde G{\"u}ney} and Gaetano Festa and David Fuhrman and Alice-Agnes Gabriel and Pauline Galea and Steven Gibbons and Mauricio Gonz{\'a}lez and Laura Graziani and Marc-Andr{\'e} Gutscher and Sven Harig and Helene Hebert and Constantin Ionescu and Fatemeh Jalayer and Nikos Kalligeris and Utku K{\^a}noğlu and Piero Lanucara and {Macias S{\'a}nchez}, Jorge and Shane Murphy and {\"O}cal Necmioğlu and Rachid Omira and Gerassimos Papadopoulos and Rapha{\"e}l Paris and Fabrizio Romano and Tiziana Rossetto and Jacopo Selva and Antonio Scala and Roberto Tonini and Konstantinos Trevlopoulos and Ioanna Triantafyllou and Roger Urgeles and Roberto Vallone and Ivica Vilibi{\'c} and Manuela Volpe and Ahmet Yalciner",

year = "2022",

month = apr,

day = "29",

doi = "10.4401/ag-8762",

language = "English",

volume = "65",

journal = "Annals of Geophysics",

issn = "1593-5213",

publisher = "Istituto Nazionale di Geofisica e Vulcanologia",

number = "2",

@article{9945020b2f94444dab6aacda3a21965f,

title = "Performance Assessment of the Cloud for Prototypical Instant Computing Approaches in Geoscientific Hazard Simulations",

abstract = "Computing forecasts of hazards, such as tsunamis, requires fast reaction times and high precision, which in turn demands for large computing facilities that are needed only in rare occasions. Cloud computing environments allow to configure largely scalable on-demand computing environments. In this study, we tested two of the major cloud computing environments for parallel scalability for relevant prototypical applications. These applications solve stationary and non-stationary partial differential equations by means of finite differences and finite elements. These test cases demonstrate the capacity of cloud computing environments to provide scalable computing power for typical tasks in geophysical applications. As a proof-of-concept example of an instant computing application for geohazards, we propose a workflow and prototypical implementation for tsunami forecasting in the cloud. We demonstrate that minimal on-site computing resources are necessary for such a forecasting environment. We conclude by outlining the additional steps necessary to implement an operational tsunami forecasting cloud service, considering availability and cost. Copyright {\textcopyright} 2022 Behrens, Schulz and Simon.",

keywords = "cloud computing, instant computing, natural hazard, parallel performance, tsunami",

author = "J. Behrens and Arne Schulz and K. Simon",

note = "Export Date: 20 April 2022 Correspondence Address: Behrens, J.; Department of Mathematics/CEN, Germany; email: joern.behrens@uni-hamburg.de Funding details: 603839 Funding details: Deutsche Forschungsgemeinschaft, DFG, 390683824 Funding details: Universit{\"a}t Hamburg, UH Funding text 1: Parts of this research were conducted in the framework of the ASTARTE project with funding from the European Unions Seventh Program for research, technological development and demonstration under grant agreement No. 603839. Additional funding was obtained by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany{\textquoteright}s Excellence Strategy—EXC 2037 {\textquoteright}CLICCS—Climate, Climatic Change, and Society{\textquoteright}—Project Number: 390683824, contribution to the Center for Earth System Research and Sustainability (CEN) of Universit{\"a}t Hamburg.",

year = "2022",

month = mar,

day = "9",

doi = "10.3389/feart.2022.762768",

language = "English",

volume = "10",

journal = "Frontiers in Earth Science",

issn = "2296-6463",

publisher = "Frontiers Media S. A.",

@article{3702b81cd85a406d8d51391df24debe9,

title = "Tsunami risk communication and management: Contemporary gaps and challenges",

abstract = "Very large tsunamis are associated with low probabilities of occurrence. In many parts of the world, these events have usually occurred in a distant time in the past. As a result, there is low risk perception and a lack of collective memories, making tsunami risk communication both challenging and complex. Furthermore, immense challenges lie ahead as population and risk exposure continue to increase in coastal areas. Through the last decades, tsunamis have caught coastal populations off-guard, providing evidence of lack of preparedness. Recent tsunamis, such as the Indian Ocean Tsunami in 2004, 2011 Tohoku and 2018 Palu, have shaped the way tsunami risk is perceived and acted upon. Based on lessons learned from a selection of past tsunami events, this paper aims to review the existing body of knowledge and the current challenges in tsunami risk communication, and to identify the gaps in the tsunami risk management methodologies. The important lessons provided by the past events call for strengthening community resilience and improvement in risk-informed actions and policy measures. This paper shows that research efforts related to tsunami risk communication remain fragmented. The analysis of tsunami risk together with a thorough understanding of risk communication gaps and challenges is indispensable towards developing and deploying comprehensive disaster risk reduction measures. Moving from a broad and interdisciplinary perspective, the paper suggests that probabilistic hazard and risk assessments could potentially contribute towards better science communication and improved planning and implementation of risk mitigation measures.",

keywords = "NEAM Region, Perception, Preparedness, Preventive measures, Tsunami risk, Uncertainties",

author = "Irina Rafliana and Fatemeh Jalayer and Andrea Cerase and Lorenzo Cugliari and Marco Baiguera and Dimitra Salmanidou and {\"O}cal Necmioğlu and Ayerbe, {Ignacio Aguirre} and Stefano Lorito and Stuart Fraser and Finn L{\o}vholt and Andrey Babeyko and Salgado-G{\'a}lvez, {Mario A.} and Jacopo Selva and {De Risi}, Raffaele and S{\o}rensen, {Mathilde B.} and J{\"o}rn Behrens and I{\~n}igo Aniel-Quiroga and {Del Zoppo}, Marta and Stefano Belliazzi and Pranantyo, {Ignatius Ryan} and Alessandro Amato and Ufuk Hancilar",

year = "2022",

month = feb,

day = "15",

doi = "10.1016/j.ijdrr.2021.102771",

language = "English",

volume = "70",

journal = "International Journal of Disaster Risk Reduction",

issn = "2212-4209",

publisher = "Elsevier Limited",

@article{b805bf17001149db848d2b21de524395,

title = "Editorial: From Tsunami Science to Hazard and Risk Assessment: Methods and Models",

keywords = "early warning, hazard, numerical modelling, observations, probabilities, risk, tsunami",

author = "Stefano Lorito and J{\"o}rn Behrens and Finn L{\o}vholt and Tiziana Rossetto and Jacopo Selva",

year = "2021",

month = oct,

day = "8",

doi = "10.3389/feart.2021.764922",

language = "English",

volume = "9",

journal = "Frontiers in Earth Science",

issn = "2296-6463",

publisher = "Frontiers Media S. A.",