| Autor(en) | Blech, Christopher | Appel, Christina K. | Ewert, Roland | Delfs, Jan W. | Langer, Sabine |
|---|---|
| Titel | Numerical prediction of passenger cabin noise due to jet noise by an ultra-high-bypass ratio engine |
| Herausgeber | Journal of Sound and Vibration, 464 (2020): 114960 |
| Erscheinungsjahr | 2019 |
| Abstract | Within the framework of the Collaborative Research Center 880, future civil transportation aircraft are investigated. One major aim is a drastic reduction of the noise emission to the ground and an appropriate noise immission into the passenger cabin. The latter forms the focus of this contributionwith the aim to ensure an equal or lower noise level in the cabin for new aircraft configurations. Numerical methods are applied to establish a multidisciplinary modeling chain resulting in a prediction of cabin noise due to jet noise by two different engine configurations. An ultra–high–bypass ratio engine is compared to a conventional engine on the basis of a preliminary aircraft design used for both configurations. On the basis of flow calculations in cruise flight as operation point, the hybrid Computational Aeroacoustics solver PIANO combined with the Fast RandomParticleMeshmethod is applied to compute the pressure fluctuations due to jet noise on the outer skin of the fuselage. These loads are applied to a finite elementmodel considering the structure and the fluid of the aircraft cabin. The acoustic model resolving the structure-borne and airborne sound waves is derived from the design data. The results show a lower sound pressure level induced by the ultra–high–bypass ratio engine in the entire frequency range on the outer skin. Within the cabin, the modern engine is still much quieter, though this fact is not generally valid for the entire frequency range as transmission effects of the double wall occur. |
| Autor(en) | Langer, Sabine C. | Blech, Christopher |
|---|---|
| Titel | Cabin noise prediction using wave-resolving aircraft models |
| Herausgeber | PAMM 19.1 (2019): e201900388 |
| Erscheinungsjahr | 2019 |
| Abstract | Within the Coordinated Research Center (CRC) 880, future civil aircraft with short take-off and landing capabilities are investigated. A main motivation are efficient point-to-point connections within Europe. Environmental friendliness is a key factor in the development of such aircraft systems in order to ensure the acceptance of new technologies. Therefore, the sound immission at the ground and in the passenger cabin is a major focus in the project. In this paper, wave-resolving models of complex aircraft fuselage structures and solution strategies of these large systems in frequency domain are presented. On the basis of preliminary aircraft design data available in the project, a mechanical model of all fluid and structural parts is developed. The model comprises the back partition starting from the wing-box and assumes a linear behavior in deflection, strain and material. The thickness distribution on the outer surface, the stiffeners, the floor, the bulk heads and the inner panels are considered concerning the structural domain. The insulation is modeled by an equivalent fluid approach. The cabin fluid, the structural domain, and the insulation are fully coupled. All domains are discretized automatically applying coincident nodes at the coupling interfaces. Frequency-dependent pressure fluctuations distributed on the outer surface as a result of Computational Aeroacoustic (CAA) simulations of jet noise are applied to the model. A realistic consideration of such characteristic noise footprints is only possible due to the wave-resolving approach. The direct result of the aircraft model is the cabin's pressure field in frequency domain. The finite element discretization leads to a system of equations with 1-3 mio degrees of freedom to be solved in frequency domain. As one solver run is easily realized, many solutions in the frame of uncertainty analyses or sensitivity studies require a highly efficient solution process. Different strategies applying direct solvers, iterative solvers or its combination are discussed within this contribution as well. |
| Autor(en) | Delfs, Jan | Bertsch, Lothar | Zellman, Christoph | Rossian, Lennart | Far, Ehsan Kian | Ring, Tobias | Langer, Sabine C. | Rossian, Lennart | Rossian, Lennart |
|---|---|
| Titel | Aircraft Noise Assessment - From Single Components to Large Scenarios |
| Herausgeber | Energies 2018, 11(2), 429, doi:10.3390/en11020429 |
| Erscheinungsjahr | 2018 |
| Abstract | The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “. . . The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000. . . ”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels. |
| Autor(en) | Guruprasad, Shreyas M. | Blech, Christopher | Römer, Ulrich | Matthies, Hermann G. | Langer, Sabine C. |
|---|---|
| Titel | Uncertainty Quantification of numerical transmission loss calculations of an aircraft fuselage section |
| Herausgeber | Proceedings of DAGA |
| Erscheinungsjahr | 2018 |
| Abstract | The prediction of aircraft cabin noise is important in preliminary design stages as potential acoustic problems can be detected in these stages to consider damping measures as early as possible. In these early design stages a final design is not yet given and design parameters are uncertain. Especially for the cabin noise assessment concerning new technologies, the predicted behavior is crucially sensitive to chosen deterministic design parameters. Hence, the combination of an uncertainty quantification with a deterministic acoustic model is a promising approach. In this contribution, a finite element model of an aircraft fuselage section is used to predict the transmission loss. The finite element model is treated as black box with certain input parameters on which basis a statistical analysis and a global sensitivity analysis is conducted. A non-intrusive surrogate modeling technique is applied in frequency domain to reduce the computational costs significantly. The results show a reliable fit of the transmission loss curve by the polynomial surrogate model. However, a limit of the polynomial surrogate model is indicated by a convergence study (polynomial order and numbers of samples) as problems in the strongly non-monotonic resonances occur. |
| Autor(en) | Uphoff, Sonja | Krafczyk, Manfred | Kutscher, Konstantin | Rurkowska, Katherina | Langer, Sabine | Lippitz, Nicolas | Faßmann, Benjamin |
|---|---|
| Titel | A HIERARCHICAL APPROACH TO DETERMINING ACOUSTIC ABSORPTION PROPERTIES OF POROUS MEDIA COMBINING PORE-RESOLVED AND MACROSCOPIC MODELS |
| Herausgeber | Journal of Porous Media, Volume 21, Begell House, 83-100, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | Acoustic properties of porous media are very important for numerous industrial applications, the typical goal being to maximize broadband absorption to decrease the sound pressure level of the engineering system under consideration. Up to now acoustic absorption for porous media with complex inner geometry is determined experimentally, as acoustic simulations on the pore scale are computationally challenging due to the tedious geometric reconstruction of computer tomography (CT) data and the corresponding mesh generation as well as substantial computational requirements for the corresponding transient 3D solvers. The lattice Boltzmann method (LBM), which is an established computational approach to simulate pore-resolved porous media transport problems, has been used successfully for aeroacoustic setups and is utilized in this work to fill this gap. This paper presents a comparison of different experimental and numerical approaches to determine the acoustic absorption of different porous media. Experimental work with an impedance tube was carried out for comparison and CT scans were conducted to supply the detailed numerical simulation with geometry data of the porous samples. Results of LB simulations for the acoustic impedance of a microperforated plate and a felt are shown. Finally we demonstrate how microscopic parameters determined by a pore scale approach can be used to feed homogenized models to bridge the gap towards simulations of components where acoustic absorbers are applied to, e.g., wing flaps of airplanes. |
| Autor(en) | Blech, Christopher | Appel, Christina K. | Langer, Sabine C. | Delfs, Jan W. |
|---|---|
| Titel | Numerical prediction of cabin noise due to jet noise excitation of two different engine configurations |
| Herausgeber | Proceedings of ICSV |
| Erscheinungsjahr | 2017 |
| Abstract | The development of environmental friendly aircraft requires, inter alia, a drastic reduction of aircraft noise. In the framework of the Collaborative Research Centre (CRC) 880, an aircraft with innovative high-lift systems is investigated. In comparison to a conventional engine on underwing position, an Ultra High Bypass Ratio (UHBR) engine on over-wing position is expected to reduce the sound radiation towards the ground. To ensure the acceptance of this configuration, a potential negative impact on the cabin noise must be excluded. As the UHBR engine is installed closer to the passenger cabin and as the engine generates sound at lower frequencies due to its larger dimensions, a more effective sound transmission into the cabin is expected. Apart from that, less sound is radiated due to a reduced rotational speed of the UHBR engine. In this contribution, the hybrid computational aeroacoustic (CAA) solver PIANO combined with the FRPM method is applied to compute the pressure fluctuations due to jet noise on the outer surface of the fuselage. This approach uses the turbulence statistics from an underlying RANS computation to model the fluctuating sound sources and involves the mean flow data for the sound propagation. In a second step, the pressure fluctuations are applied to a generic mechanical model of the fuselage which is solved in frequency domain by the in-house code ELPASO using the Finite Elements Method (FEM). The model includes the double wall structure, insulating material and the enclosed fluid cavities. The approach results in the differences of the cabin’s mean pressure of both engine configurations. |
| Autor(en) | Blech, Christopher | Langer, Sabine C. |
|---|---|
| Titel | Systematische Untersuchung mathematischer Korrelationskriterien im Frequenzbereich |
| Herausgeber | Proceeding of DAGA |
| Erscheinungsjahr | 2017 |
| Abstract | Die mechanische Modellbildung komplexer Strukturen sowie die Lösung dieser mit Hilfe numerischer Verfahren bedarf stets einer Validierung. Um die Validität eines mechanischen Ersatzmodells zu zeigen, muss eine Zieldefinition sowie ein standardisierter Vergleich mit einem Experiment oder einem höherwertigen Modell erfolgen. Dafür werden neben einfachen optischen Abgleichen oft mathematische Korrelationskriterien wie FDAC (Frequency Domain Assurance Criterion) oder FRAC (Frequency Response Assurance Criterion) herangezogen. Es ergeben sich reelle Werte zwischen 0 (keine Korrelation) und 1 (ideale Korrelation), um beispielsweise ein automatisiertes model parameter updating zu erlauben. Um mathematische Korrelationskriterien im Rahmen einer Validierung zu nutzen, müsste ein Zielwert defniert werden, ab welchem das untersuchte Modell als valide angenommen werden kann. Dieser Beitrag untersucht mit Hilfe systematischer Anwendungen der genannten Kriterien an Fallbeispielen von Strukturantworten im Frequenzbereich, ob eine Zieldefiniton auf Basis solcher mathematisch geprägter Kriterien möglich ist. Es werden Anforderungen an ein Korrelationskriterium in der Akustik formuliert, anhand welcher die Anwendbarkeit eingeschätzt werden kann. Abschließend werden Verbesserungsvorschläge und der Ansatz für ein neues Kriterium aufgezeigt. |
| Autor(en) | Blech, Christopher | Langer, Sabine C. |
|---|---|
| Titel | Aircraft cabin noise reduction by means of acoustic black holes |
| Herausgeber | Proceedings of internoise |
| Erscheinungsjahr | 2017 |
| Abstract | Regarding the aims of Flightpath 2050, aircraft noise in general must be reduced drastically during the next three decades. An acceptable or even comfortable cabin noise is one aspect of this challenge and a crucial factor for the introduction of new technologies in aircraft. One promising possibility is the use of highly innovative damping technologies in combination with drastic design changes. During the past decades, acoustic black holes have been introduced as highly efficient vibration damping systems. The vibration amplitudes, the radiation coefficient and the weight of plate structures can be reduced in parallel. Both, the acoustic performance gain and the weight reduction are excellent characteristics for passive vibration damping of aircraft structures. Acoustic black holes have mainly been investigated in simple structures to clarify a lot of basic research questions concerning positioning, shaping and damping application. This contribution illustrates the possibility of introducing acoustic black holes into the inner cabin linings of a research aircraft developed within the Coordinated Research Centre 88o. A generic mechanical model of the aircraft is used to predict the cabin noise. The model includes the primary and secondary structure, the insulation and the passenger cavity. It is numerically solved using the Finite Element Method (FEM). In a second calculation, acoustic black holes are considered in the cabin linings. The results show a comparison of the transmission loss with and without acoustic black holes. The potential reduction of cabin noise due to acoustic black holes in cabin linings is assessed. |
| Autor(en) | Blech, Christopher | Langer, Sabine C. |
|---|---|
| Titel | Systematische Untersuchung mathematischer Korrelationskriterien im Frequenzbereich |
| Herausgeber | Proceedings of DAGA |
| Erscheinungsjahr | 2017 |
| Abstract | Die mechanische Modellbildung komplexer Strukturen sowie die Lösung dieser mit Hilfe numerischer Verfahren bedarf stets einer Validierung. Um die Validität eines mechanischen Ersatzmodells zu zeigen, muss eine Zieldefinition sowie ein standardisierter Vergleich mit einem Experiment oder einem höherwertigen Modell erfolgen. Dafür werden neben einfachen optischen Abgleichen oft mathematische Korrelationskriterien wie FDAC (Frequency Domain Assurance Criterion) oder FRAC (Frequency Response Assurance Criterion) herangezogen. Es ergeben sich reelle Werte zwischen 0 (keine Korrelation) und 1 (ideale Korrelation), um beispielsweise ein automatisiertes model parameter updating zu erlauben. Um mathematische Korrelationskriterien im Rahmen einer Validierung zu nutzen, müsste ein Zielwert defniert werden, ab welchem das untersuchte Modell als valide angenommen werden kann. Dieser Beitrag untersucht mit Hilfe systematischer Anwendungen der genannten Kriterien an Fallbeispielen von Strukturantworten im Frequenzbereich, ob eine Zieldefiniton auf Basis solcher mathematisch geprägter Kriterien möglich ist. Es werden Anforderungen an ein Korrelationskriterium in der Akustik formuliert, anhand welcher die Anwendbarkeit eingeschätzt werden kann. Abschließend werden Verbesserungsvorschläge und der Ansatz für ein neues Kriterium aufgezeigt. |
| Autor(en) | Delfs, Jan W. | Appel, Christina | Bernicke, Paul | Blech, Christopher | Blinstrub, Jason | Heykena, Constance | Kumar, Pradeep | Kutscher, Konstantin | Lippitz, Nicolas | Lummer, Markus | Rossian, Lennart | Savoni, Luciana | Delfs, Jan |
|---|---|
| Titel | Aircraft and technology for low noise short take-off and landing |
| Herausgeber | 35th AIAA Applied Aerodynamics Conference |
| Erscheinungsjahr | 2017 |
| Abstract | This paper discusses characteristic multi-disciplinary issues related to quiet short take-off and landing for civil transport aircraft with a typical short to medium range mission. The work reported here is focussing on the noise aspects and is embedded in the collaborative research centre CRC880 in Braunschweig, Germany. This long term aircraft research initiative focusses on a new transport aircraft segment for operation on airports with shorter runway length in commercial air transport. This calls for a community-friendly aircraft designed for operations much closer to the home of its passengers than today. This scenario sets challenging, seemingly contradictory aircraft technology requirements, namely those for extreme lift augmentation at low noise. The Research Centre CRC880 has therefore devised a range of technology projects that aim at significant noise reductions and at the generation of efficient and flexible high lift. The research also addresses flight dynamics of aircraft at takeoff and landing. Two companion papers, reporting about the research in the field of ”Efficient high lift” 1 and ”Flight dynamics” 2 complete the presentation of the CRC880. It is envisaged that in general significant noise reduction -compared to a reference turbofan driven aircraft of year 2000 technology- necessarily requires component noise reduction in combination with a low noise a/c concept. Results are presented from all the acoustics related projects of CRC880 which cover the aeroacoustic simulation of the source noise reduction by flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new UHBR turbofan arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of jet noise vibration excitation of cabin noise by UHBR engines compared to conventional turbofans at cruise. |
| Autor(en) | Beck, Silja C. | Müller, Lars | Langer, Sabine C. |
|---|---|
| Titel | Numerical assessment of the vibration control effects of porous liners on an over-the-wing propeller configuration |
| Herausgeber | CEAS Aeronaut J 7:275–286 |
| Erscheinungsjahr | 2016 |
| Abstract | An over-the-wing position of propellers comes with noise shielding and significantly reduced sound emission to the ground. A drawback of this configuration may be the additional impact due to the passing propeller blades on the airfoil’s surface inducing structure-borne sound in the wing. This structural sound propagates within the wing and the fuselage and can radiate further into the cabin as airborne sound. In order not to trade the advantage of reduced noise transmission to the ground with higher sound pressure levels within the cabin, a remedy is proposed, which consists in placing a poroelastic liner on the wing’s surface below the rotor where the blade tips move closely to the airfoil’s skin. In this work, a numerical approach to assess the effects of porous liners for an over-the-wing propeller configuration is presented. A simplified generic channelwing structure is exposed to pressure fluctuations on its surface which are caused by an over-the-wing propeller. Porous liners are applied to the wing’s surface where the blade tips pass in close proximity. Structural vibrations are determined using the finite element method in frequency domain. Surface data is obtained from CFD computations. The porous material is represented by Biot’s theory. |
| Autor(en) | Blech, Christopher | Shi, Xiaojun | Langer, Sabine Christine |
|---|---|
| Titel | Überdie Sensitivität des FRAC für eine objektive Validierung mechanischer Modelle |
| Herausgeber | Fortschritte der Akustik - DAGA 2016, ISBN 978-3-939296-10-2, 42, 859ff, DAGA, Aachen, Deutschland, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | Die Validierung von mechanischen Ersatzmodellen ist heute und in den nächsten Jahrzehnten trotz zunehmender Genauigkeit und Akzeptanz der Modelle essentiell. Beschränkt man sich auf die direkte Strukturantwort eines Systems im Frequenzbereich, so finden sich in der Literatur häufig rein optische Vergleiche von Frequenzgängen einzelner Freiheitsgrade oder Durchschnittsgrößen aus Versuch und Berechnung. Der optische Vergleich, beispielsweise zweier Eingangsadmittanzen, bestätigt jedoch aufgrund des subjektiven Einflusses keinesfalls die Validität eines gesamten mechanischen Ersatzmodells. Besser wäre die Anwendung einer objektiven Größe wie das FRAC (Frequency Response Assurance Criterion). FRAC nutzt das normierte Skalarprodukt der Vektoren zweier Frequenzgänge und erlaubt somit einen Vergleich dieser auf einer Skala von Null bis Eins für jeden definierten Freiheitsgrad des betrachteten Systems. Eine Eins stellt dabei ein identisches Systemverhalten dar. Die Interpretierbarkeit des FRAC-Wertes abseits der Extremwerte wurde bis heute in der Literatur kaum untersucht. Entsprechend beschäftigt sich dieser Beitrag mit der Sensitivität des FRAC auf Steifigkeit, Dämpfung und Masse einfacher beispielhafter Strukturen. Während die Massenverteilung hinreichend genau definiert werden kann, sind Steifigkeit und vor allem Dämpfungen meist schwerer zu bestimmen. Als Beispiel dient hier die Modellierung elastischer Randbedingungen mit Federn (anstelle zwischen einer festen Einspannung oder einer gelenkigen Lagerung zu entscheiden). Der Beitrag ermöglicht zukünftig objektive Vergleiche von Frequenzgängen und eine bessere Einschätzung eines Modells auf Basis des FRAC. |
| Autor(en) | Blech, Christopher | Shi, Xiaojun | Langer, Sabine Christine |
|---|---|
| Titel | Über die Sensitivität des FRAC für eine objektive Validierung mechanischer Modelle |
| Herausgeber | Fortschritte der Akustik - DAGA 2016, ISBN 978-3-939296-10-2, 42, 859ff, DAGA, Aachen, Deutschland, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | Die Validierung von mechanischen Ersatzmodellen ist heute und in den nächsten Jahrzehnten trotz zunehmender Genauigkeit und Akzeptanz der Modelle essentiell. Beschränkt man sich auf die direkte Strukturantwort eines Systems im Frequenzbereich, so finden sich in der Literatur häufig rein optische Vergleiche von Frequenzgängen einzelner Freiheitsgrade oder Durchschnittsgrößen aus Versuch und Berechnung. Der optische Vergleich, beispielsweise zweier Eingangsadmittanzen, bestätigt jedoch aufgrund des subjektiven Einflusses keinesfalls die Validität eines gesamten mechanischen Ersatzmodells. Besser wäre die Anwendung einer objektiven Größe wie das FRAC (Frequency Response Assurance Criterion). FRAC nutzt das normierte Skalarprodukt der Vektoren zweier Frequenzgänge und erlaubt somit einen Vergleich dieser auf einer Skala von Null bis Eins für jeden definierten Freiheitsgrad des betrachteten Systems. Eine Eins stellt dabei ein identisches Systemverhalten dar. Die Interpretierbarkeit des FRAC-Wertes abseits der Extremwerte wurde bis heute in der Literatur kaum untersucht. Entsprechend beschäftigt sich dieser Beitrag mit der Sensitivität des FRAC auf Steifigkeit, Dämpfung und Masse einfacher beispielhafter Strukturen. Während die Massenverteilung hinreichend genau definiert werden kann, sind Steifigkeit und vor allem Dämpfungen meist schwerer zu bestimmen. Als Beispiel dient hier die Modellierung elastischer Randbedingungen mit Federn (anstelle zwischen einer festen Einspannung oder einer gelenkigen Lagerung zu entscheiden). Der Beitrag ermöglicht zukünftig objektive Vergleiche von Frequenzgängen und eine bessere Einschätzung eines Modells auf Basis des FRAC. |
| Autor(en) | Lippitz, Nicolas | Blech, Christopher | Rösler, Joachim | Langer, Sabine |
|---|---|
| Titel | Identification of Material Parameters for the Simulation of Acoustic Absorption of Fouled Sintered Fiber Felts |
| Herausgeber | Materials, ISSN 1996-1944, 9(8), 709, MDPI |
| Erscheinungsjahr | 2016 |
| Abstract | As a reaction to the increasing noise pollution, caused by the expansion of airports close to residential areas, porous trailing edges are investigated to reduce the aeroacoustic noise produced by flow around the airframe. Besides mechanical and acoustical investigations of porous materials, the fouling behavior of promising materials is an important aspect to estimate the performance in long-term use. For this study, two intered fiber felts were selected for a long-term fouling experiment where the development of the flow resistivity and accumulation of dirt was observed. Based on 3D structural characterizations obtained from X-ray tomography of the initial materials, acoustic models (Biot and Johnson–Champoux–Allard) in the frame of the transfer matrix method were applied to the sintered fiber felts. Flow resistivity measurements and the measurements of the absorption coefficient in an impedance tube are the basis for a fouling model for sintered fiber felts. The contribution will conclude with recommendations concerning the modeling of pollution processes of porous materials. |
| Autor(en) | Ring, Tobias | Blech, Christopher | Langer, Sabine Christine |
|---|---|
| Titel | An approach to evaluate the model quality using model updating Techniques |
| Herausgeber | ICSV, 23, 2016, Athens, Greece |
| Erscheinungsjahr | 2016 |
| Abstract | The understanding of physical processes in engineering as well as in most scientific fields is based on models which are built in order to answer specific questions. The design of models for specific questions results in a limited applicability and a limited prediction accuracy. For example, if the deflection shape of a plate-like structure shall be computed, the applied plate theory limits the accuracy of the obtained results. Giving another example, the static bending shape of a beam can be computed with a low number of elements with reasonable accuracy. The same model may be used in order to study the dynamic behavior of the beam. Then the ratio of wavelength and element size limits the applicability of the model. Both examples show that the accuracy of results always depends on the model, its properties and the assumptions made during the model design process. In this paper a method is proposed, which uses a model updating technique in order to measure the quality of different models for structural dynamics. Therefore, a simple structure is modeled using approaches of different complexity. The dynamic response is compared to measurement results and the models are being updated. Different measures concerning the updating process are identified in order to evaluate the model quality. The obtained knowledge about model quality measures can be used to design models which enable higher accuracy and less necessary iterations during the model updating process a priori. |
| Autor(en) | Rothe, Sebastian | Blech, Christopher | Langer, Sabine Christine |
|---|---|
| Titel | Model Updating Strategies in Frequency Domain For Different Use Cases |
| Herausgeber | ICSV, 23, Athens, Greece, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | In acoustics, finite element models are frequently used to simulate the dynamic response of structures. The validation of finite element models is indispensable and often supported by model updating techniques. Furthermore, the computation of structures with high modal densities or non-linearities is nearly impossible in modal space. Hence, the simulation in frequency domain is preferred. In literature, many correlation criteria and updating techniques are available for the application in frequency domain. The main purpose of model updating is to find suitable modeling parameters in order to achieve a good agreement between the model and reality. Since reality is not known, often experimental data is taken as reference for the applied correlation criteria. Besides classical model updating, a lot more use cases as inverse material parameter identification, model assessment, topology optimization and shape optimization may be pursued for parameterized finite element models. It is assumed that specific adaptations of the correlation criterion and the updating technique can improve the outcome for each use case. In this contribution, strategies to combine the frequency response assurance criteria (FRAC) and an optimization algorithm are applied to different use cases. As an application example a plate structure is selected. The computational costs, the convergence behavior and the final results are evaluated for each pursued use case (e.g. model assessment). Modifications of the setup (correlation criteria or optimization algorithm) are discussed and tested for each use case to improve efficiency, robustness and the quality of results. |
| Autor(en) | Blech, Christopher | Falkenberg, Paul | Langer, Sabine Christine | Vietor, Thomas |
|---|---|
| Titel | A geometrical approach to remove stress singularities in continuum models of multi-material structures |
| Herausgeber | Proc. Appl. Math. Mech., DOI 10.1002/pamm.201510130, 15, Wiley-VCH Verlag GmbH, 279 – 280, GAMM, Lecce, Italy, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | In the frame of stress based topology optimisation multi-material structures are investigated. At the interface of dissimilar materials an adhesive joint shall be considered. Selecting a continuum approach to model the two adherends and the adhesive, stress singularities occur at the material-interfaces due to the difference in the impedance [1]. This contribution investigates a geometrical opportunity to remove singularities at the interface of two different linear elastic structures. Sensitivities of important parameters are qualitatively shown by a simple example consisting of two cubes under tension. |
| Autor(en) | Unruh, Oliver | Blech, Christopher | Monner, Hans Peter |
|---|---|
| Titel | Numerical and Experimental Study of Sound Power Reduction Performance of Acoustic Black Holes in Rectangular Plates |
| Herausgeber | SAE Int. J. Passeng. Cars - Mech. Syst., doi:10.4271/2015-01-2270, 8(3), SAE International, SAE, Detroit, Michigan, USA, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | Global attenuation of structural velocities is one of the most effective approaches in order to reduce noise emitted by shell structures such as a car roof or aircraft fuselage panels. This global reduction can be achieved by the application of passive damping treatments like constraint layer damping on large fractions of the vibrating surface. The main disadvantage of this approach arises from the fact that it leads to increasing total cost and weight of the structure. To overcome this problem, acoustic black holes can be used to create locations with high vibration amplitudes and low bending waves velocity in order to dissipate the energy of structure borne sound by very limited application of damping treatments. Acoustic black holes are funnel shaped thickness reductions that attract sound radiating bending waves and allow a global vibration reduction by an acceptable use of additional damping. This paper presents the results of a numerical and experimental study of acoustic black holes located on a rectangular plate. The presented work is focused on the influence of size, position and number of acoustic black holes on the acoustic performance. A large number of different configurations of these parameters is studied by finite-element-analysis and evaluated in terms of vibration amplitude and sound power level. In order to confirm simulation results the most efficient configuration is implemented in laboratory setup and characterized in terms of vibrational and acoustic performance. |
| Autor(en) | Beck, Silja | Langer, Sabine |
|---|---|
| Titel | Flow-Induced sound of structures with porous layer (title in publication changed to: Modeling of flow-induced sound in porous materials) |
| Herausgeber | Int. J. Numer. Meth. Engng 2014, 98:44–58 |
| Erscheinungsjahr | 2014 |
| Abstract | The impact of flow on a structure plays a crucial part when considering structural behavior, for example, in aviation. As structural vibrations (also denominated as structural sound) propagate within a structure, sound radiation is a likely consequence. To reduce the emission of noise, the use of poroelastic material is investigated. The approach consists in applying a poroelastic layer on the surface submitted to flow, as such utilizing the damping properties of poroelastic material. To predict flow-induced sound, a computational model has been developed to account for (1) flow-induced sound immission into a structure, (2) sound propagation, and (3) possible resulting sound radiation. Con- sistent formulation of the interactions between the components—that is, flow, poroelastic material, elastic structure, and acoustic fluid—allows to apply different simulation techniques for each component and thus to exploit each method’s advantages. The key aspect of this work is the formulation of the interface con- ditions to couple flow with poroelastic material. The proposed and implemented coupling conditions are studied. The given example shows a possible application and demonstrates the effectiveness of poroelastic material to reduce flow-induced sound emission. |
| Autor(en) | Beck, Silja | Uphoff, Sonja | Langer, Sabine | Krafczyk, Manfred |
|---|---|
| Titel | Sensitivity of the slip rate coefficient in fluid flow – poroelastic coupling conditions |
| Herausgeber | Proceedings in Applied Mathematics and Mechanics, 85th Annual Meeting of the International Association of Applied Mathematics and Mechanics, Erlangen |
| Erscheinungsjahr | 2014 |
| Abstract | To model flow-induced structural vibrations, an interface to couple fluid flow and poroelastic material in a finite element formulation has been developed. One parameter of this interface condition is the slip rate coefficient, resulting from the so- called Beavers-Joseph-Saffman condition. This condition states that the jump in tangential velocity at a fluid flow – porous interface is proportional to the shear stress. Up to now no a priori determination of this parameter exists, and the known parameter range has been deducted from measurements, i. e., in our case from the results of the pore-resolving simulations. When modeling realistic problems assuming incompressible fluids, vectorial flow velocity and scalar pressure interact with the poroelastic material. As the slip rate coefficient only influences the tangential contributions, its overall influence is not clear. In this work, the sensitivity of the slip rate coefficient regarding the interface’s coupling conditions is evaluated. |
| Autor(en) | Delfs, Jan | Faßmann, Benjamin | Lippitz, Nicolas | Mößner, Michael | Müller, Lars | Rurkowska, Katherina |
|---|---|
| Titel | SFB 880 – AEROACOUSTIC RESEARCH FOR LOW NOISE TAKE-OFF AND LANDING |
| Herausgeber | CEAS Aeronautical Journal |
| Erscheinungsjahr | 2014 |
| Abstract | This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short take-off and landing capabilities. The work is embedded in the collaborative research centre SFB880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials. |
| Autor(en) | Rurkowska, Katherina | Beck, Silja | Langer, Sabine |
|---|---|
| Titel | Influence of porous materials on structure-borne sound in aircraft application |
| Herausgeber | Proceedings of DAGA 2014, Deutsche Gesellschaft für Akustik e. V. (DEGA) |
| Erscheinungsjahr | 2014 |
| Abstract | Porous surfaces are used to influence the flow noise and the excitation of the structure-borne noise. Within the project Sonderforschungsbereich 880 Fundamentals of High Lift for Future Civil Aircraft, the aim is to reduce sound produced by aircraft propeller drives and trailing edges. The influence of porous layer on the surface of airfoil is evaluated, specifically on the upper surface of a channel wing. A sensitivity analysis is carried out in or- der to study the behaviour of the structure-borne sound with the implementation of porous material layers. Mi- croperforated plates, sintered fibre felts and metal foam materials are considered. To perform this study a simple structure representing an airfoil segment is used. Some results showing the influence of a porous layer applied on a generic channel wing geometry are presented as well. |
| Autor(en) | Rurkowska, Katherina | Langer, Sabine |
|---|---|
| Titel | Coupling elastic-poroelastic material in structure-borne sound modelling |
| Herausgeber | Acoustical Society of America, Proceedings of Meetings on Acoustics, Vol. 19, 030073 (2013) |
| Erscheinungsjahr | 2013 |
| Abstract | Porous materials are widely used in noise reduction applications. To minimize the external noise produced by aicraft propeller drives, porous materials are implemented. As a part of the project Sonderforschungsbereich 880 "Fundamentals of High Lift for Future Civil Aircraft", porous surfaces are used in the High-lift configuration to mitigate the flow noise and to influence the structure-borne sound. In order to model the performance of the applied poroelastic material, an approach coupling a poroelastic material with an elastic structure using Finite Element Method is presented. The Biot's theory is used to model the poroelastic material. The aim of this work is to simulate the effect of the entry and transmission of the structure-borne sound into the poroelastic medium. An example of the implemented model shows the plausibility of presented approach. |
| Autor(en) | Rurkowska, Katherina | Sabine, Langer |
|---|---|
| Titel | Prediction of acoustic behaviour of microperforated plates in High-lift configuration |
| Herausgeber | AIA-DAGA, Meran |
| Erscheinungsjahr | 2013 |
| Abstract | Porous materials are widely used in noise reduction applications. To minimize the external noise produced by aicraft propeller drives, microperforated plates are implemented. As a part of the project Sonderforschungsbereich 880 "Fundamentals of High Lift for Future Civil Aircraft", porous surfaces are used in the High-lift configuration to mitigate the flow noise and influence the structure-borne sound. In order to model the performance of the these microperforated plates, an approach based in the Johson-Allard for ridig frame porous media proposed by Atalla and Sgard is used. In this model an equivalent tortuosity is used and Biots parameters for cylindrical pores are assumed. The aim of this work is to predict the behavior and acoustic effect of the used microperforated plates during its operation lifetime. The sound absorption of the porous materials is carried on with our in-house Code using the transfermatrix method. |
| Autor(en) | Zahid, Muhammad | Beck, Silja | Langer, Sabine |
|---|---|
| Titel | Modeling of flow-induced sound in poroelastic materials |
| Herausgeber | 5th Biot Conference on Poromechanics (BIOT-5), pp. 882--890, Vienna - Austria, July 10-12, 2013 |
| Erscheinungsjahr | 2013 |
| Abstract | The use of poroelastic materials on the surfaces under flows–part of the Collaborative Research SFB 880, “Fundamentals of high-lift for future commercial aircrafts”– is investigated. Besides the positive influence that porous surfaces have on aeroacoustics, a poroelastic layer may also help reduce the impact sound. An approach to model the interface between a flow and a poroelastic material, which tracks the propagation of flow-induced structure-borne sound into the poroelastic medium, is illustrated. Firstly, the overall simulation approach and the selected material model is presented, followed by an explanation of the coupling conditions for the interface between the fluid and the poroelastic material. To illustrate the plausibility of this coupling, flow-induced structure-borne sound entry into an airfoil-like structure, layered with a porous material, is examined. The analysis is carried out on a finite element method-based in-house code. |
| Autor(en) | Klesa, Jan | Langer, Sabine |
|---|---|
| Titel | Einfluss von Verschmutzung auf die Absorptionswirkung von porösen Materialien |
| Herausgeber | Proceedings of DAGA 2012, Deutsche Gesellschaft für Akustik e. V. (DEGA) |
| Erscheinungsjahr | 2012 |
| Abstract | Poröse Oberflächen haben positive akustische Eigenschaften und werden in verschiedenen technischen Anwendungen verwendet. Im Zuge des Gebrauchs bzw. des technischen Einsatzes und im Laufe ihrer Lebensdauer werden diese Materialien häufig verschmutzt, was sich auch nachteilig auf die akustischen Eigenschaften auswirken kann. |