GAMM Mitteilungen最新文献

{"title":"Nonlinear vibration phenomena in hydrodynamically supported rotor systems","authors":"Steffen Nitzschke,&nbsp;Elmar Woschke,&nbsp;Cornelius Strackeljan","doi":"10.1002/gamm.202300003","DOIUrl":"https://doi.org/10.1002/gamm.202300003","url":null,"abstract":"<p>It is a well-known fact, that hydrodynamically supported systems are prone to nonlinear vibrations. Their exact simulative prediction with respect to frequency and amplitude is complicated by the fact that different system properties interact. The paper at hand outlines an approach that takes all relevant influences like rigid body motions, elastic deformations, nonlinear relation between fluid film pressure and bearing kinematics as well as temperature increase due to power loss or adjacent heat sources into account as detailed as necessary. Both journal and thrust bearings are considered as they contribute to the system's stiffness and damping capabilities. The approach is applied to self-excited pad vibrations of tilting pad thrust bearings as well as the run-up simulation of a turbocharger rotor under different axial loads. Both models are validated against measurements.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202300003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50137406","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":"A minimal model for the influence of equilibrium positions on brake squeal","authors":"Sebastian Koch,&nbsp;Nils Gräbner,&nbsp;Utz von Wagner","doi":"10.1002/gamm.202300001","DOIUrl":"https://doi.org/10.1002/gamm.202300001","url":null,"abstract":"<p>The phenomenon brake squeal has been an ongoing topic for decades, both in the automotive industry and in science. Although there is agreement on the excitation mechanism of brake squeal, namely self-excitation due to frictional forces between the disk and the pad, in the subject of squeal it is very complex to discover all relevant effects and to take them into account. Several of these problems are related to nonlinearities, for example, in the contact between pad and disk or drum or in the behavior of the brake pad material. One of these nonlinear effects, which has been almost completely neglected so far, is that the brake can engage, mainly due to the bushing and joint elements within the brake, different equilibrium positions. This in fact has serious influence on the noise behavior as shown in experimental studies. For example, it is observed in experiments that, despite identical operating parameters, squeal sometimes occurs and sometimes not. In initial experimental studies, this could be related to the engaged equilibrium position. Following these experimental studies, the present paper introduces a minimal model by extending the well-known minimal model by Hoffmann et al. by corresponding elements and nonlinearities allowing the system to engage different equilibrium positions. As will be presented, the stability behavior strongly depends on the engaged equilibrium position. Therefore, the minimal model represents the key experimentally observed issues. Additionally, a limit cycle behavior can also be observed.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202300001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50116537","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":"Application of stable inversion to flexible manipulators modeled by the absolute nodal coordinate formulation","authors":"Svenja Drücker,&nbsp;Robert Seifried","doi":"10.1002/gamm.202300004","DOIUrl":"https://doi.org/10.1002/gamm.202300004","url":null,"abstract":"<p>Compared to conventional robots, flexible manipulators offer many advantages, such as faster end-effector velocities and less energy consumption. However, their flexible structure can lead to undesired oscillations. Therefore, the applied control strategy should account for these elasticities. A feedforward controller based on an inverse model of the system is an efficient way to improve the performance. However, unstable internal dynamics arise for many common flexible robots and stable inversion must be applied. In this contribution, an approximation of the original stable inversion approach is proposed. The approximation simplifies the problem setup, since the internal dynamics do not need to be derived explicitly for the definition of the boundary conditions. From a practical point of view, this makes the method applicable to more complex systems with many unactuated degrees of freedom. Flexible manipulators modeled by the absolute nodal coordinate formulation (ANCF) are considered as an application example.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202300004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50116534","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":"Interpolation-based parametric model order reduction of automotive brake systems for frequency-domain analyses","authors":"Fabian Matter,&nbsp;Igor Iroz,&nbsp;Peter Eberhard","doi":"10.1002/gamm.202300002","DOIUrl":"https://doi.org/10.1002/gamm.202300002","url":null,"abstract":"<p>Brake squeal describes noise with different frequencies that can be emitted during the braking process. Typically, the frequencies are in the range of 1 to 16 kHz. Although the noise has virtually no effect on braking performance, strong attempts are made to identify and eliminate the noise as it can be very unpleasant and annoying. In the field of numerical simulation, the brake is typically modeled using the Finite Element method, and this results in a high-dimensional equation of motion. For the analysis of brake squeal, gyroscopic and circulatory effects, as well as damping and friction, must be considered correctly. For the subsequent analysis, the high-dimensional damped nonlinear equation system is linearized. This results in terms that are non-symmetric and dependent on the rotational frequency of the brake rotor. Many parameter points to be evaluated implies many evaluations to determine the relevant parameters of the unstable system. In order to increase the efficiency of the process, the system is typically reduced with a truncated modal transformation. However, with this method the damping and the velocity-dependent terms, which have a significant influence on the system, are neglected for the calculation of the eigenmodes, and this can lead to inaccurate reduced models. In this paper, we present results of other methods of model order reduction applied on an industrial high-dimensional brake model. Using moment matching methods combined with parametric model order reduction, both the damping and the various parameter-dependent terms of the brake model can be taken into account in the reduction step. Thus, better results in the frequency domain can be obtained. On the one hand, as usual in brake analysis, the complex eigenvalues are evaluated, but on the other hand also the transfer behavior in terms of the frequency response. In each case, the classical and the new reduction method are compared with each other.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202300002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50146353","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":"Special Issue on Experimental Solid Mechanics","authors":"Stefan Hartmann,&nbsp;Stefan Diebels","doi":"10.1002/gamm.202200019","DOIUrl":"10.1002/gamm.202200019","url":null,"abstract":"<p>In the present special volume, the German Association of Applied Mathematics and Mechanics (GAMM) Expert Committee “Experimental Solid Mechanics” was again given the opportunity to summarize the current scientific activities of individual participating working groups in Germany. Both optical measurement methods from surface information as well as radiation-based methods for detecting the internal states present in material bodies are receiving increasing interest. Nowadays, the required measurement systems can simply be purchased, or they can be developed in-house. In addition, there are still many scientific questions left open in the evaluation of the found measurement data. In the meantime, image correlation methods are often used to determine the surface deformation of components, the discrete data of which are now evaluated using proprietary software tools, or are coupled with infrared thermography systems, in particular to determine the dissipating energy of mechanically loaded components.</p><p>In the first issue of this special volume, four contributions are compiled proposing (1) a shear evaluation tool using digital image correlation (DIC) for plane problems [<span>5</span>], the coupling of infrared thermography (IRT) and 3D DIC for both (2) identifying material parameters in metal plasticity [<span>6</span>] as well as (3) applicability studies of foams and auxetic materials [<span>3</span>], and, finally, (4) identifying the heat conductivity parameters in transversal isotropy using IRT [<span>8</span>].</p><p>The second issue treats distance measurements of laminate layers using microscopical images [<span>4</span>], and three further contributions on <i>μ</i>-CT measurements. First, new in-situ measurements in granular media using <i>μ</i>-X-ray computer tomography (CT) combined with ultrasonic wave propagation is investigated [<span>7</span>]. A further contribution treats the influence of the pores on the fatigue properties of particular additively manufactured parts [<span>2</span>], and, finally, a study on the micro-structural characterization and stochastic modeling of open-cell foam using <i>μ</i>-CT image analysis [<span>1</span>]. All articles contribute to contact-less measurement sensing and evaluation in the field of solid mechanics.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200019","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82316468","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":"Microstructure characterization and stochastic modeling of open-cell foam based on μCT-image analysis","authors":"Lukas Bogunia,&nbsp;Stefan Buchen,&nbsp;Kerstin Weinberg","doi":"10.1002/gamm.202200018","DOIUrl":"10.1002/gamm.202200018","url":null,"abstract":"<p>Foam is a cellular material whose mechanical properties are strongly determined by its complex microstructure. To study the microstructure, at first a foam characterization based on <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>μ</mi>\u0000 </mrow>\u0000 <annotation>$$ upmu $$</annotation>\u0000 </semantics></math>CT image processing is required. Here we present an image segmentation procedure and determine the foam's characteristics using the lattice cell-based concept of intrinsic volumes. Information like porosity, pore size distribution, and ligament shape are derived. These data are then employed as input for the generation of stochastic foam volume elements with the corresponding morphology. The introduced microstructural characterization and foam generation procedures are validated by an inverse analysis, that is, by a <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>μ</mi>\u0000 </mrow>\u0000 <annotation>$$ upmu $$</annotation>\u0000 </semantics></math>CT image analysis of the stochastic foam volume element. Additionally, an example investigation of industrial polyurethane foam proves the concepts.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200018","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72398799","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":"Influence of CT image processing on the predicted impact of pores on fatigue of additively manufactured Ti6Al4V and AlSi10Mg","authors":"Ulrike Gebhardt,&nbsp;Paul Schulz,&nbsp;Alexander Raßloff,&nbsp;Ilja Koch,&nbsp;Maik Gude,&nbsp;Markus Kästner","doi":"10.1002/gamm.202200017","DOIUrl":"10.1002/gamm.202200017","url":null,"abstract":"<p>Pores are inherent to additively manufactured components and critical especially in technical components. Since they reduce the component's fatigue life, a reliable identification and description of pores is vital to ensure the component's performance. X-ray computed tomography (CT) is an established and non-destructive testing method to investigate internal defects. The CT scan process can induce noise and artefacts in the resulting images which afterwards have to be reduced through image processing. To reconstruct the internal defects of a component, the images need to be segmented in defect region and bulk material by applying a threshold. The application of the threshold as well as the previous image processing alter the geometry and size of the identified defects. This contribution aims to quantify the influence of selected commercial image processing and segmentation methods on identified pores in several additively manufactured components made of AlSi10Mg and Ti6Al4V as well as in an artificial CT scan. To that aim, gray value histograms and characteristic parameters thereof are compared for different image processing tools. After the segmentation of the processed images, particle characteristics are compared. The influence of image processing and segmentation on the predicted fatigue life of the material is evaluated through the change of the largest pore in each set of data applying Murakami's empirical <math>\u0000 <semantics>\u0000 <mrow>\u0000 <msqrt>\u0000 <mrow>\u0000 <mtext>area</mtext>\u0000 </mrow>\u0000 </msqrt>\u0000 </mrow>\u0000 <annotation>$$ sqrt{mathrm{area}} $$</annotation>\u0000 </semantics></math>-parameter model.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200017","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91089861","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":"Phase-resolving direct numerical simulations of particle transport in liquids—From microfluidics to sediment","authors":"Jochen Fröhlich,&nbsp;Thomas E. Hafemann,&nbsp;Ramandeep Jain","doi":"10.1002/gamm.202200016","DOIUrl":"10.1002/gamm.202200016","url":null,"abstract":"<p>The article describes direct numerical simulations using an Euler–Lagrange approach with an immersed-boundary method to resolve the geometry and trajectory of particles moving in a flow. The presentation focuses on own work of the authors and discusses elements of physical and numerical modeling in some detail, together with three areas of application: microfluidic transport of spherical and nonspherical particles in curved ducts, flows with bubbles at different void fraction ranging from single bubbles to dense particle clusters, some also subjected to electro-magnetic forces, and bedload sediment transport with spherical and nonspherical particles. These applications with their specific requirements for numerical modeling illustrate the versatility of the approach and provide condensed information about main findings.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200016","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89591953","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":"Applicability of correlated digital image correlation and infrared thermography for measuring mesomechanical deformation in foams and auxetics","authors":"Sergej Grednev,&nbsp;Stefan Bronder,&nbsp;Francesco Kunz,&nbsp;Martin Reis,&nbsp;Susanne-Marie Kirsch,&nbsp;Felix Welsch,&nbsp;Stefan Seelecke,&nbsp;Stefan Diebels,&nbsp;Anne Jung","doi":"10.1002/gamm.202200014","DOIUrl":"10.1002/gamm.202200014","url":null,"abstract":"<p>Cellular materials such as metal foams or auxetic metamaterials are interesting microheterogeneous materials used for lightweight construction and as energy absorbers. Their macroscopic behavior is related to their specific mesoscopic deformation by a strong structure-property-relationship. Digital image correlation and infrared thermography are two methods to visualize and study the local deformation behavior in materials. The present study deals with the full-field thermomechanical analysis of the mesomechanical deformation in Ni/PU hybrid foams and Ni/polymer hybrid auxetic structures performing a correlative digital image correlation and infrared thermography. Instead of comparing and correlating only the primary output variables of both methods, strain and temperature, also strain rates and temperature rates occurring during deformation were compared. These allow for a better correlation and more conclusive results than obtained using only the primary output variables.</p>","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 3-4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/gamm.202200014","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88662221","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 II","authors":"Marc Avila,&nbsp;Jörg Schumacher","doi":"10.1002/gamm.202200015","DOIUrl":"10.1002/gamm.202200015","url":null,"abstract":"This issue and its preceding twin issue are devoted to the simulation of turbulent fluid flows. The focus is on numerical solutions of the governing Navier–Stokes equations, in which all temporal and spatial scales are resolved and which are known as direct numerical simulations (DNS) [8]. For a brief introduction to DNS, the reader is referred to the preface of the preceding issue [1], and references therein. The two issues contain a broad spectrum of topics which includes the study of sound generation mechanisms in combustion [4], the extraction of dominant spatiotemporal patterns and coherent structures in several canonical flows [12,14], the active control of turbulence in compressible fluid flows [9], the modeling of jets impinging on rough surfaces [10], the high-order, low-dissipation modeling of compressible multi-phase flows [2] and the accurate simulation of particleand bubble-laden fluid flows [3]. In what follows, we briefly summarize the three contributions to the second issue. Flows driven by pressure gradients and by temperature-induced buoyancy forces are referred to as mixed convection flows and are common in nature and in engineering, for example, in heat exchangers, cooling systems, and air-conditioned rooms and spaces, such as an airplane cabin. Wagner and Wetzel [12] discuss results of recent DNS of a pressure-driven flow in a differentially heated, vertical channel [13]. They demonstrate that differential heating induces a strong asymmetry in the turbulent flow, when compared to an isothermal fluid. Specifically near the cooled wall, turbulence is enhanced, whereas it is damped in the heated wall. This effect, which is quantified with a thorough analysis of the coherent structures in the flow, becomes more pronounced as the thermal driving is increased. Compressible, multiphase flows exhibit very complex dynamics acting in a wide range of scales, ranging from molecular (shock waves, fluid–fluid interfaces) up to the largest coherent structures in the flow, dictated by the geometry and the driving. On the one hand, the experimental measurement of such flows is very difficult and limited to gross features. On the other hand, their simulation is particularly challenging, as numerical diffusion (dissipation) must be introduced to stabilize the numerical solutions against unphysical oscillations. As a consequence, compressible multiphase flows remain poorly understood. Fleischmann et al. [2] present an overview of recent improvements in high-order, low-dissipation schemes for compressible multi-phase flows. Level sets are employed to model discontinuous phase-interface interactions. The very good accuracy of the implementation in the code ALPACA [5,6] is demonstrated for several paradigmatic examples of considerable difficulty. Overall, the paper provides an introduction to several advanced techniques, such as multiresolution data compression, and includes detailed elaborations of the treatment of floating-point induced disturban","PeriodicalId":53634,"journal":{"name":"GAMM Mitteilungen","volume":"45 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75249826","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}