GAMM Mitteilungen最新文献

{"title":"Digital image correlation based characterization of rubber material at large shear deformations in an extended temperature range","authors":"Lars Kanzenbach,&nbsp;Thomas Lehmann,&nbsp;Jörn Ihlemann","doi":"10.1002/gamm.202200009","DOIUrl":"10.1002/gamm.202200009","url":null,"abstract":"<p>This contribution deals with a new shear device, which is applied for rubber measurements in simple shear in an extended temperature range. As a special feature for the loading system, no bonding technique, or vulcanization is used, but a form fit connection via pins. The measured stress–shear value curves for different temperature levels are evaluated with a standard method from GOM ARAMIS. In addition, a new approximation based evaluation method is introduced and applied for shear value determination including smoothing of the raw digital image correlation data with consideration of characteristic noise properties. This enables the analysis of noise induced error influences. It was proved by the approximation based method, that the standard ARAMIS evaluation provides shear value results, which are suitable for performed characterization tests. As a consequence, the nearly homogeneous measurement data can be used for parameter fitting of constitutive rubber models.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200009","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78015284","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":"Thickness determination of laminate core layers from microscopy images","authors":"Stefan Hartmann,&nbsp;Pranav Kumar Dileep,&nbsp;Mohamed Harhash,&nbsp;Heinz Palkowski","doi":"10.1002/gamm.202200008","DOIUrl":"10.1002/gamm.202200008","url":null,"abstract":"<p>In sandwich laminates made of metal–polymer–metal (MPM) layers under forming conditions, the thickness changes along the thin-layered specimens are of particular interest. To measure this distribution, it is common to take microscopic images and determine manually the thicknesses at particular discrete points. We compare and provide several methods determining the thickness distribution from microscopic images. First, an interpolation scheme is chosen to obtain a continuous function of the interfaces between the layers instead of the discrete pixel data. Afterwards, the methods—ruled surface approach, orthogonal projection, embedded circle scheme, and a dull but simple method—are applied and compared with each other. For very smooth data, most of the schemes show equivalent results. However, the “brute force”—called the dull approach—turns out to be the most robust scheme, particularly, if noisy data is studied. The Gaussian error propagation concept is applied to study the uncertainties resulting from noisy pixel data. The schemes are adapted to finite element simulation results as well so that a direct comparison of experimental and numerical data would be possible.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200008","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83514915","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 to special issue on direct numerical simulations of turbulent flows—Part I","authors":"Marc Avila,&nbsp;Jörg Schumacher","doi":"10.1002/gamm.202200007","DOIUrl":"10.1002/gamm.202200007","url":null,"abstract":"in rapidly rotating Rayleigh-Bénard convection, in classical horizontal convection, and in an asymptotic suction boundary layer. They found that structures of different temporal and spatial frequencies can be separated and that the most salient features of the dynamics can be generally captured with a small number of dynamic modes, thereby highlighting the capabilities of the method.","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81295031","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":"Coherent structures in turbulent mixed convection flows through channels with differentially heated walls","authors":"Claus Wagner,&nbsp;Tim Wetzel","doi":"10.1002/gamm.202200006","DOIUrl":"10.1002/gamm.202200006","url":null,"abstract":"<p>The occurrence and shape of turbulent structures in mixed convection flows through a differently heated vertical channel are investigated in terms of thermally induced attenuation and amplification of turbulent velocity, pressure, and temperature fluctuations using direct numerical simulations. It is shown that the wall-normal momentum transport is decreased and increased near the heated and cooled wall, respectively, and that this leads to a reduced and elevated production of turbulent velocity fluctuations in the streamwise velocity component in the aiding and opposing flow, respectively. The corresponding flow structures are smoother, faster and warmer in the aiding flow and aligned along the main flow, while the colder structures in the opposing flow are more frayed and less directed. The warmer flow structures in the aiding flow are overall more stable than the colder structures in the opposing flow. Besides, the study reveals that the position of the maximum temperature fluctuations moves toward the heated wall, so that the sweeps produced at the two walls are affected differently by the former. As a consequence, the distance and time period over which the fluctuations develop in the aiding flow are shorter than in the opposing flow. It is further shown that vortex structures oriented in the streamwise direction usually arise with an offset to the right or left above a sweep or an ejection, whereby the decreasing values of the correlation coefficients with increasing Grashof number indicate a weakening of the vortex structures. Since none of the evaluated vortex criteria, that is, the distributions of the vorticity, <math>\u0000 <mrow>\u0000 <msub>\u0000 <mrow>\u0000 <mi>λ</mi>\u0000 </mrow>\u0000 <mrow>\u0000 <mn>2</mn>\u0000 </mrow>\u0000 </msub>\u0000 </mrow></math>- value or Rortex-value correlate well with the evaluated minima of the pressure fluctuations, they do not allow a clear identification of the vortex structures. Finally, analyzing the budget of the turbulent kinetic energy it is confirmed that the velocity fluctuations are only indirectly influenced by the buoyancy force. Thus, the attenuation and amplification of the turbulent velocity fluctuations is reflected in the reduction and exaggeration of the Reynolds shear stresses in the aiding and opposing flow, respectively.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76691744","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":"Turbulent impinging jets on rough surfaces","authors":"Francesco Secchi,&nbsp;Thomas Häber,&nbsp;Davide Gatti,&nbsp;Sebastian Schulz,&nbsp;Dimosthenis Trimis,&nbsp;Rainer Suntz,&nbsp;Bettina Frohnapfel","doi":"10.1002/gamm.202200005","DOIUrl":"10.1002/gamm.202200005","url":null,"abstract":"<p>This work presents direct numerical simulations (DNS) of a circular turbulent jet impinging on rough plates. The roughness is once resolved through an immersed boundary method (IBM) and once modeled through a parametric forcing approach (PFA) which accounts for surface roughness effects by applying a forcing term into the Navier–Stokes equations within a thin layer in the near-wall region. The DNS with the IBM setup is validated using optical flow field measurements over a smooth and a rough plate with similar statistical surface properties. In the study, IBM-resolved cases are used to show that the PFA is capable of reproducing mean flow features well at large wall-normal distances, while less accurate predictions are observed in the near-wall region. The demarcation between these two regions is approximately identified with the mean wall height <math>\u0000 <mrow>\u0000 <msub>\u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow>\u0000 <mrow>\u0000 <mi>m</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow></math> of the surface roughness distribution. Based on the observed differences in the results between IBM- and PFA-resolved cases, plausible future improvements of the PFA are suggested.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88875605","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":"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}