GAMM Mitteilungen最新文献

{"title":"Data-driven identification of the spatiotemporal structure of turbulent flows by streaming dynamic mode decomposition","authors":"Rui Yang,&nbsp;Xuan Zhang,&nbsp;Philipp Reiter,&nbsp;Detlef Lohse,&nbsp;Olga Shishkina,&nbsp;Moritz Linkmann","doi":"10.1002/gamm.202200003","DOIUrl":"10.1002/gamm.202200003","url":null,"abstract":"<p>Streaming Dynamic Mode Decomposition (sDMD) is a low-storage version of dynamic mode decomposition (DMD), a data-driven method to extract spatiotemporal flow patterns. Streaming DMD avoids storing the entire data sequence in memory by approximating the dynamic modes through incremental updates with new available data. In this paper, we use sDMD to identify and extract dominant spatiotemporal structures of different turbulent flows, requiring the analysis of large datasets. First, the efficiency and accuracy of sDMD are compared to the classical DMD, using a publicly available test dataset that consists of velocity field snapshots obtained by direct numerical simulation of a wake flow behind a cylinder. Streaming DMD not only reliably reproduces the most important dynamical features of the flow; our calculations also highlight its advantage in terms of the required computational resources. We subsequently use sDMD to analyse three different turbulent flows that all show some degree of large-scale coherence: rapidly rotating Rayleigh–Bénard convection, horizontal convection and the asymptotic suction boundary layer (ASBL). Structures of different frequencies and spatial extent can be clearly separated, and the prominent features of the dynamics are captured with just a few dynamic modes. In summary, we demonstrate that sDMD is a powerful tool for the identification of spatiotemporal structures in a wide range of turbulent flows.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85732843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Active control of compressible channel flow up to \u0000 \u0000 M\u0000 \u0000 \u0000 a\u0000 \u0000 \u0000 b\u0000 \u0000 \u0000 =\u0000 3\u0000 using direct numerical simulations with spanwise velocity modulation at the walls","authors":"Marius Ruby,&nbsp;Holger Foysi","doi":"10.1002/gamm.202200004","DOIUrl":"10.1002/gamm.202200004","url":null,"abstract":"<p>Active turbulence control has been pursued continuously for the last decades, striving for an altered, energetically more favorable flow. In this article, our focus is on a promising method inducing a spanwise wall movement in order to reduce turbulence intensity and hence friction drag, investigated by means of direct numerical simulation. This approach transforms a previously time dependent oscillatory wall motion into a static spatial modulation with prescribed wavelength in the streamwise direction [48]. Most procedures related to turbulence control including the present one have been overwhelmingly applied to incompressible flow. This work is different and novel to the effect, that this control method is applied to compressible, supersonic channel flow up to a bulk Mach number of <math>\u0000 <mrow>\u0000 <mi>M</mi>\u0000 <mi>a</mi>\u0000 <mo>=</mo>\u0000 <mn>3</mn>\u0000 </mrow></math>. Due to substantial variations of viscosity, density, and temperature within the near-wall region in supersonic flow, the impact of the control method is altered compared to solenoidal flow conditions. By creating a data set of different Mach-/Reynolds numbers and control parameters, knowledge is gained in which way the effectiveness of oscillatory techniques and physical mechanisms change under the influence of compressibility. It is shown that the control method is able to effectively reduce turbulence levels and lead to large drag reduction levels in compressible supersonic flow. Variable property effects even enhance this behavior for the whole set of investigated parameters. Overall, the higher Mach number cases show a larger net power saving compared to the incompressible ones. Furthermore, we observe an increase of the optimum wavelength with increasing Mach number, which helps in guiding optimal implementations of such a control method.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76022973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the incorporation of a micromechanical material model into the inherent strain method—Application to the modeling of selective laser melting","authors":"","doi":"10.1002/gamm.202200002","DOIUrl":"10.1002/gamm.202200002","url":null,"abstract":"<p>In Noll et al.,<span>¹</span> an error was published in the Acknowledgement section. The name “Lena Koppka” was misspelled in the original publication.</p><p>The correct Acknowledgement section is presented below:</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84676021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of the sound sources of lean premixed methane–air flames","authors":"Sohel Herff,&nbsp;Konrad Pausch,&nbsp;Matthias Meinke,&nbsp;Wolfgang Schröder","doi":"10.1002/gamm.202200001","DOIUrl":"10.1002/gamm.202200001","url":null,"abstract":"<p>Two investigations on the sound generation mechanisms of lean methane–air flames are reviewed and linked. A two-step approach is used for the analysis. First, the compressible conservation equations are solved in a large-eddy simulation formulation to compute the acoustic source terms of the reacting fluid. Second, the acoustic source terms are used in computational aeroacoustics simulations to determine the acoustic field by solving the acoustic perturbation equations. To identify the contributions of the different source terms to the overall sound emission of the flames different source term formulations are considered in the computational aeroacoustics simulations. The results of various flames of increasing complexity are shown: harmonically excited laminar flames, a turbulent jet flame, and an unconfined and a confined swirl flame. The results show that in general the heat release source alone does not determine the acoustic emission of the flame. Only the acoustic emission of the unconfined swirl flame could be computed by the heat release source. To accurately predict the phase and the amplitude of the sound emission of the other flames the acceleration of density gradients occurring at the flame front must be included in the considered set of source terms.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79666593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Simulation-supported characterization of 3D-printed biodegradable structures","authors":"Richard Wolfgang Schirmer,&nbsp;Martin Abendroth,&nbsp;Stephan Roth,&nbsp;Lisa Kühnel,&nbsp;Henning Zeidler,&nbsp;Bjoern Kiefer","doi":"10.1002/gamm.202100018","DOIUrl":"10.1002/gamm.202100018","url":null,"abstract":"<p>In this article, a proof-of-concept study is presented, in which in-situ full-field deformation measurements via digital image correlation, finite element analysis, and nonlinear optimization techniques are combined to characterize the heterogeneous structural behavior of a bio-based material 3D-printed via binder jetting. The special features of this composite material are its biodegradability and its easy manufacturability using conventional 3D printers. The binder-jetting process enables innovative applications such as additively manufactured, highly customized, recyclable, or compostable packaging solutions. Compared to other 3D printing techniques, it is relatively fast and inexpensive and can make use of raw material powders that are by-products of the food or other industries. As an initial step towards gaining a simulation-supported understanding of the complex process-structure-property relations, a first quantitative assessment of the effective behavior of a bio-based binder-jetted material is conducted under the following operating assumptions: (i) Its mechanical response can be described by means of a nonlinear elasto-plastic constitutive law, enriched by a cohesive damage model capturing failure on the structural level, (ii) established mechanical tests on a 3D-printed component, involving standardized sample geometries, and optical measurements, should yield sufficient information to allow the identification of the corresponding material parameters. First, experimental results of optically monitored four-point bending tests, with varying alignments of loading axes and printing directions, are presented in detail. Then the proposed parameter identification strategy is explained and its capabilities and limitations, as made evident from quantitative case studies based on the measured structural response data, are thoroughly discussed.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202100018","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78821850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On accurate time integration for temperature evolutions in additive manufacturing","authors":"Stefan Kollmannsberger,&nbsp;Philipp Kopp","doi":"10.1002/gamm.202100019","DOIUrl":"10.1002/gamm.202100019","url":null,"abstract":"<p>We investigate two numerical challenges in thermal finite element simulations of laser powder bed fusion (LPBF) processes. First, we compare the behavior of first- and second-order implicit time-stepping schemes on a fixed domain. While both methods yield comparable accuracies in the pre-asymptotic regime, the second-order method eventually outperforms the first-order method. However, the oscillations present in the pre-asymptotic range of the second-order method can render it less suitable for simulating LPBF processes. Then, we consider sudden domain extensions resulting from subsequently adding new layers of material with ambient temperature. We model this extension on the continuous level in an energy conservative manner. The discontinuities introduced here reduce the convergence order for both time-stepping schemes to 0.75. First and second order accuracy could only be achieved by strongly grading the time-steps towards the domain expansion.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202100019","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84276742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preface on mechanics of additive manufacturing—Part II","authors":"Thorsten Bartel,&nbsp;Markus Kästner,&nbsp;Björn Kiefer,&nbsp;Andreas Menzel","doi":"10.1002/gamm.202100020","DOIUrl":"10.1002/gamm.202100020","url":null,"abstract":"In the first part of this two-part special issue, the focus is on the modeling and simulation of elementary processes within various materials that can be used for additive manufacturing. It comprises selective laser sintering of polymers, topology optimization in the context of additively manufactured structures, a general overview on the challenges related to the modeling and simulation of powder bed fusion additive manufacturing as well as the modeling of phase changes during Selective Laser Melting and the related analysis of process-induced inherent strains. As sophisticated as these models may be, they also require experimental data for verification and validation. The more complex the modeled and simulated processes, as well as the material models themselves, become the more important becomes the sound and comprehensive experimental characterization and experimental investigation of the effective material behavior. Even with accurate and experimentally verified material and process models successfully developed and established the general challenge of their algorithmic implementation remains. In this context, it is essential to establish efficient and robust numerical methods, some of which have to be newly developed due to the high numerical complexity. The contributions of this Part II of the Special Issue of the Surveys for Applied Mathematics and Mechanics (GAMM-Mitteilungen) mainly focus on these above-mentioned aspects: The paper referenced by Kollmannsberger and Kopp [1] elaborates advanced modeling and simulation approaches with emphasis on different time scales. This includes, among other topics, the investigation and comparison of different time-stepping schemes with special focus on robustness, prevention of oscillating solutions and general applicability. In Zhou et al. [2], a multilayer phase-field simulation of selective sintering process and the calculation of effective mechanical properties and residual stresses is proposed. In this regard, quantitative relations between the process parameters and the microstructure and its properties are established. The contribution of Schirmer et al. [3] addresses the additive manufacturing of a novel class of bio-based materials via binder-jetting. The highly customizable printed structures are recyclable and use renewable raw materials that are often industrial by-products. The article presents a proof-of-concept study, in which digital image correlation, finite element analysis and optimization techniques are combined to characterize the heterogeneous structural behavior of such 3D-printed biodegradable materials. The work presented in Raßloff et al. [4] aims at the prediction of structure–property linkages for additively manufactured materials with a particular focus on process-induced imperfections like pores. It uses light microscopy and X-ray computed tomography to determine microstructure characteristics of Ti–6Al–4V in combination with microscale simulations to assess the influe","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74709886","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3D-multilayer simulation of microstructure and mechanical properties of porous materials by selective sintering","authors":"Xiandong Zhou,&nbsp;Yangyiwei Yang,&nbsp;Somnath Bharech,&nbsp;Binbin Lin,&nbsp;Jörg Schröder,&nbsp;Bai-Xiang Xu","doi":"10.1002/gamm.202100017","DOIUrl":"10.1002/gamm.202100017","url":null,"abstract":"<p>This work presents multilayer phase-field simulation of selective sintering process and the calculation of effective mechanical properties and residual stress of the microstructure using the finite element method. The dependence of the effective properties and residual stress on the process parameters, such as beam power and scan speed, are analyzed. Significant partial melting of powders is observed for large beam power and low scan speed, which results in low porosity of the microstructure. Nonlinear relationship between the effective mechanical properties and process parameters is observed. The increasing rate of effective mechanical properties decreases with increasing beam power, while increases with decreasing scan speed. The dependence of effective Young's modulus and Poisson's ratio on porosity are well established using power law models. Stress concentrations are found at the necking region of powders and the intensity increases with the level of partial melting, which results in increasing residual stress in the microstructure. The numerical results reveal quantitatively the process-microstructure-property relation, which implies the feasibility of the subsequent data-driven approach.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202100017","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83728199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preface on mechanics of additive manufacturing—Part I","authors":"Thorsten Bartel,&nbsp;Markus Kästner,&nbsp;Björn Kiefer,&nbsp;Andreas Menzel","doi":"10.1002/gamm.202100016","DOIUrl":"10.1002/gamm.202100016","url":null,"abstract":"Additive manufacturing processes—often referred to as 3D printing—have developed since the 1980s into a promising and groundbreaking way of producing components and workpieces with geometries of almost any complexity. And the developments continue to advance! In the meantime, various methods that can be divided into different categories have been introduced. To cover just a few of the most common methods, inkjet technologies, material extrusion, powder bed fusion, direct energy deposition, and stereolithography shall be mentioned here. The latter is considered in some sources to be virtually the starting point of additive manufacturing. The category “powder bed fusion” includes processes such as selective laser sintering, selective laser melting, and electron beam melting. Laser cladding is an example of direct energy deposition. In conventional subtractive manufacturing processes, the final contour of the component is achieved by material removal. In contrast, additive manufacturing processes are characterized by the targeted addition of the respective material to the component layer by layer. The great potential of these processes is evident in the aerospace and automotive industries as well as in biomedical technology, and especially in the manufacturing of custom-made products and lightweight constructions. Developments have even gone so far that local material properties can be specifically adjusted by, for example, adapting the material feed. Moreover, no tools or joining processes are in principle required for direct manufacturing. Additive manufacturing processes can thus be initiated and adapted in a much faster and straight-forward way. For applied mathematics and mechanics, additive manufacturing opens up numerous new perspectives and opportunities, but also major challenges. Particularly in the field of topology optimization, additive manufacturing seems to overcome a previously existing and seemingly insurmountable limitation, namely that of realizability. Until recently, the mathematically optimal structure, for example, in the sense of an optimum density distribution within a given design space, was always subjected to the constraint that the structure must also be manufacturable via conventional methods. Among other things, voids were not allowed to become too small and the density distribution had to be binary—either “no material” or “full material”. Nowadays, additive manufacturing processes indeed enable the production of the mathematically/physically optimal structures. With regard to the modeling of the material and structural behavior of additively manufactured components, numerous new challenges arise. In order to be able to perform load-bearing capacity verifications, the constitutive behavior of the material finally obtained must be modeled and predicted as accurately as possible. In this context, the manufacturing process results in specific and spatially highly inhomogeneously distributed residual stresses, which can ha","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/gamm.202100016","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89566691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the incorporation of a micromechanical material model into the inherent strain method—Application to the modeling of selective laser melting","authors":"Isabelle Noll,&nbsp;Thorsten Bartel,&nbsp;Andreas Menzel","doi":"10.1002/gamm.202100015","DOIUrl":"10.1002/gamm.202100015","url":null,"abstract":"<p>When developing reliable and useful models for selective laser melting processes of large parts, various simplifications are necessary to achieve computationally efficient simulations. Due to the complex processes taking place during the manufacturing of such parts, especially the material and heat source models influence the simulation results. If accurate predictions of residual stresses and deformation are desired, both complete temperature history and mechanical behavior have to be included in a thermomechanical model. In this article, we combine a multiscale approach using the inherent strain method with a newly developed phase transformation model. With the help of this model, which is based on energy densities and energy minimization, the three states of the material, namely, powder, molten, and resolidified material, are explicitly incorporated into the thermomechanically fully coupled finite-element-based process model of the micromechanically motivated laser heat source model and the simplified layer hatch model.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"44 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/gamm.202100015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87328232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}