TY - JOUR A1 - Gravenkamp, Hauke A1 - Birk, C. A1 - Song, C. T1 - Computation of dispersion curves for embedded waveguides using a dashpot boundary condition N2 - In this paper a numerical approach is presented to compute dispersion curves for solid waveguides coupled to an infinite medium. The derivation is based on the scaled boundary finite element method that has been developed previously for waveguides with stress-free surfaces. The effect of the surrounding medium is accounted for by introducing a dashpot boundary condition at the interface between the waveguide and the adjoining medium. The damping coefficients are derived from the acoustic impedances of the surrounding medium. Results are validated using an improved implementation of an absorbing region. Since no discretization of the surrounding medium is required for the dashpot approach, the required number of degrees of freedom is typically 10 to 50 times smaller compared to the absorbing region. When compared to other finite element based results presented in the literature, the number of degrees of freedom can be reduced by as much as a factor of 4000. PY - 2014 DO - https://doi.org/10.1121/1.4864303 SN - 0001-4966 SN - 1520-8524 VL - 135 IS - 3 SP - 1127 EP - 1138 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-30324 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke A1 - Song, C. A1 - Birk, C. T1 - Numerical modeling of waveguides embedded in infinite media N2 - This paper presents recently developed approaches for the numerical simulation of guided elastic waves in structures that are embedded in infinite fluid or solid media. The waveguide is described by the Scaled Boundary Finite Element Method, which is a general semi-analytical method that requires discretization of the boundary only. The influence of the surrounding medium on the wave propagation inside the waveguide is accounted for by appropriate boundary conditions. It is demonstrated that for many practical applications a formulation based on simple dashpot boundary conditions yields sufficiently accurate results. To increase accuracy for fluids, an alternative formulation based on exact boundary conditions and inverse iteration is proposed. This approach is of use particularly if the acoustic properties of the waveguide and surrounding material are similar. T2 - ICSV22 - 22nd International congress on sound and vibration CY - Florence, Italy DA - 12.07.2015 PY - 2015 SN - 978-88-88942-48-3 SN - 2329-3675 SP - 1 EP - 5 AN - OPUS4-33829 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bause, F. A1 - Gravenkamp, Hauke A1 - Rautenberg, J. A1 - Henning, B. T1 - Transient modeling of ultrasonic guided waves in circular viscoelastic waveguides for inverse material characterization N2 - In this contribution, we present an efficient approach for the transient and time-causal modeling of guided waves in viscoelastic cylindrical waveguides in the context of ultrasonic material characterization. We use the scaled boundary finite element method (SBFEM) for efficient computation of the phase velocity dispersion. Regarding the viscoelastic behavior of the materials under consideration, we propose a decomposition approach that considers the real-valued frequency dependence of the (visco-)elastic moduli and, separately, of their attenuation. The modal expansion approach is utilized to take the transmitting and receiving transducers into account and to propagate the excited waveguide modes through a waveguide of finite length. The effectiveness of the proposed simulation model is shown by comparison with a standard transient FEM simulation as well as simulation results based on the exact solution of the complex-valued viscoelastic guided wave problem. Two material models are discussed, namely the fractional Zener model and the anti-Zener model; we re-interpret the latter in terms of the Rayleigh damping model. Measurements are taken on a polypropylene sample and the proposed transient simulation model is used for inverse material characterization. The extracted material properties may then be used in computer-aided design of ultrasonic systems. KW - Viscoelasticity KW - Ultrasonics KW - Guided waves KW - Inverse problem KW - Scaled boundary finite KW - Element method PY - 2015 DO - https://doi.org/10.1088/0957-0233/26/9/095602 SN - 0957-0233 SN - 1361-6501 VL - 26 IS - 9 SP - 095602-1 EP - 095602-17 PB - IOP Publ. Ltd. CY - Bristol AN - OPUS4-33830 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Die Scaled Boundary Finitie Element Method zur Simultaion von Ultraschallwellen T2 - Seminar für Numerische Mathematik und Mechanik, Universität Duisburg-Essen CY - Essen DA - 2015-06-29 PY - 2015 AN - OPUS4-33566 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Modelling ultrasonic waves using the Scaled Boundary Finite Element T2 - Seminar in mechanical engineering, Indian Institute of Technology CY - Chennai (Indien) DA - 2015-04-06 PY - 2015 AN - OPUS4-33567 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gravenkamp, Hauke T1 - A remark on the computation of shear-horizontal and torsional modes in elastic waveguides N2 - When modeling the propagation of elastic guided waves in plates or cylinders, Finite Element based numerical methods such as the Scaled Boundary Finite Element Method (SBFEM) or the Semi-Analytical Finite Element (SAFE) Method lead to an eigenvalue problem to be solved at each frequency. For the particular case of shear horizontal modes in a homogeneous plate or torsional modes in a homogeneous cylinder, the problem can be drastically simplified. The eigenvalues become simple functions of the frequency, while the eigenvectors are constant. The current contribution discusses how this behavior is represented in the numerical formulation and derives the expressions for the eigenvalues and eigenvectors as well as the dynamic stiffness matrix of infinite elastic waveguides. KW - Guided waves KW - Shear-horizontal modes KW - Torsional modes KW - Scaled Boundary Finite Element Method PY - 2016 DO - https://doi.org/10.1016/j.ultras.2016.03.003 SN - 0041-624X VL - 2016/69 SP - 25 EP - 28 PB - Elsevier B.V. CY - Amsterdam, Netherlands AN - OPUS4-36429 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lozano, Daniel A1 - Bulling, Jannis A1 - Gravenkamp, Hauke A1 - Prager, Jens A1 - Birk, Carolin T1 - The SBFEM to simulate the scattering of ultrasonic guided waves interacting with defects in plate structures N2 - In the field of guided waves for non-destructive testing, the interaction of these waves with damages or other discontinuities in a structure is critical. When a guided wave mode travels and hits a defect, it scatters in all directions, converting to other modes and reflecting the existing one. These interactions are captured in scattered far field complex amplitudes. The amplitudes are stored in scattering matrices, which characterise the elastodynamic behaviour of a defect completely. Scattering matrices are also useful to simulate backpropagation from a defect using ray-tracing methods. Simulating these interactions is challenging, and analytical solutions only exist for simple geometries. Still, using general tools like the finite element method results in large, usually costly models. Recently, researchers proposed a method based on a numerical implementation of the Kirchhoff–Helmholtz integral that allows the computation of the scattering matrices using a model containing only the damaged region. However, classical methods to resolve the far field and low-order elements were used, leading to large models yet more efficient than using other techniques. We propose using the SBFEM as an alternative to enhance the computation of the far field scattering. The damaged region is discretised using high-order polyhedral elements, while the far field is constructed using a modified version of the SBFEM. Examples compared to the literature demonstrate the validity of the approach. T2 - Doktorandentreffen CY - Attendorn, Germany DA - 16.10.2023 KW - SBFEM KW - Guided Waves KW - Scattering PY - 2023 AN - OPUS4-59775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lozano, Daniel A1 - Bulling, Jannis A1 - Gravenkamp, Hauke A1 - Birk, Carolin T1 - Domain decoupling implementation for efficient ultrasonic wave simulations using scaled boundary finite elements and the mortar method N2 - We introduce a novel approach that combines the scaled boundary finite element method (SBFEM) with a mortar coupling to enhance the computational modelling of elastic wave propagation and interaction with local features in the ultrasonic range. The key objective is to achieve decoupling between different regions of interest, enabling independent meshes for the zones where waves either propagate or interact with localised discontinuities in the elastic media. This decoupling allows us to exploit the benefits offered by various SBFEM formulations. Thus, we can select the most suitable solution for each specific region. An important concept we emphasise is the differentiation between the near field and far field regions. The near field encompasses zones where the precise representation of small features compared to the wavelength is crucial. At the same time, the far field comprises homogeneous regions where the waves propagate without interactions, eventually radiating towards infinity if the domain is unbounded. By separating these two zones, we can improve the computational performance by employing finer discretisation only where necessary. Furthermore, this decoupling enables the reuse of far field models in parametric analyses, making it highly valuable for scenarios focused particularly on local elastic wave interactions. This approach offers considerable potential in such cases. The modelling technique is validated, and its potential is demonstrated through practical applications. KW - Computer Science Applications KW - General Physics and Astronomy KW - Mechanical Engineering KW - Mechanics of Materials KW - Computational Mechanics PY - 2023 DO - https://doi.org/10.1016/j.cma.2023.116465 SN - 0045-7825 VL - 417 IS - Part A SP - 1 EP - 21 PB - Elsevier BV AN - OPUS4-58478 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krome, Fabian A1 - Gravenkamp, Hauke ED - Every, A. T1 - Analyzing modal behavior of guided waves using high order eigenvalue derivatives N2 - This paper presents a mode-tracing approach for elastic guided waves based on analytically computed derivatives and includes a study of interesting phenomena in the dispersion curve representation. Numerical simulation is done by means of the Scaled Boundary Finite Element Method (SBFEM). Two approaches are used to identify the characteristics of the resulting wave modes: Taylor approximation and Padé approximation. Higher order differentials of the underlying eigenvalue problem are the basis for these approaches. Remarkable phenomena in potentially critical frequency regions are identified and the tracing approach is adapted to these regions. Additionally, a stabilization of the solution process is suggested. KW - Guided waves KW - Mode-tracing KW - Eigenvalue problem derivatives KW - Ultrasound KW - Scaled Boundary Finite Element Method PY - 2016 DO - https://doi.org/10.1016/j.ultras.2016.05.014 SN - 0041-624X VL - 2016 IS - 71 SP - 75 EP - 85 PB - Elsevier B.V. AN - OPUS4-38076 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Krome, Fabian A1 - Gravenkamp, Hauke T1 - 3-D Waveguide modeling and simulation using SBFEM N2 - The modeling of waveguides by means of the Scaled Boundary Finite Element Method (SBFEM) has recently been addressed and is considered an effective procedure for the simulation of ultrasonic guided waves in plates and uniform structures, as well as their interaction with defects. This work presents the extension of the known applications like uniform concrete foundation cylinders to structures with more complex shapes and defects. The main focus is the required modeling of 3-D structures in SBFEM to solve these efficiently. Furthermore the coupling of different models is discussed. This involves models like a mainly uniform foundation cylinder with varying material behavior or geometry in certain areas which has to be modeled in 3-D SBFEM. With the presentation of numerical examples the accuracy and performance of the modeling is discussed and the advantages in improving numerical stability are shown. T2 - ICSV22 CY - Florence, Italy DA - 12.07.2015 KW - Scaled boundary finite element method PY - 2015 SP - 2805 EP - 2810 AN - OPUS4-43416 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhne, Christian A1 - Prager, Jens A1 - Gravenkamp, Hauke T1 - Computation of dispersion relations for axially symmetric guided waves in cylindrical structures by means of a spectral decomposition method N2 - In this paper, a method to determine the complex dispersion relations of axially symmetric guided waves in cylindrical structures is presented as an alternative to the currently established numerical procedures. The method is based on a spectral decomposition into eigenfunctions of the Laplace operator on the cross-section of the waveguide. This translates the calculation of real or complex wave numbers at a given frequency into solving an eigenvalue problem. Cylindrical rods and plates are treated as the asymptotic cases of cylindrical structures and used to generalize the method to the case of hollow cylinders. The presented method is superior to direct root-finding algorithms in the sense that no initial guess values are needed to determine the complex wave numbers and that neither starting at low frequencies nor subsequent mode tracking is required. The results obtained with this method are shown to be reasonably close to those calculated by other means and an estimate for the achievable accuracy is given. KW - Guided waves KW - Numerical method KW - Spectral decomposition KW - Dispersion KW - Cylinders PY - 2015 DO - https://doi.org/10.1016/j.ultras.2015.06.011 SN - 0041-624x VL - 63 SP - 54 EP - 64 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-31946 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bause, F. A1 - Schröder, A. A1 - Rautenberg, J. A1 - Henning, B. A1 - Gravenkamp, Hauke T1 - Time-causal material modeling in the simulation of guided waves in circular viscoelastic waveguides N2 - For the description of linear viscoelasticity, the fractional Zener model may be used. Based on the spectral decomposition of the elasticity matrix as proposed by Theocaris, we generalize the one-dimensional analysis of the material model into three dimensions and discuss appropriate simplifications to reduce the amount of unknowns for the material description. Then, a decomposition approach that considers the real valued frequency dependence of the viscoelastic moduli and the real valued frequency dependence of their attenuation separately is proposed. The Scaled Boundary Finite Element Method is used for the efficient computation of the phase velocity dispersion and the modal wave fields given a frequency dependent but real valued viscoelasticity matrix. Utilizing the modal expansion approach, the transmitting and receiving transducer are taken into account to compute the modal amplitudes. Combining these modal amplitudes, the phase velocity dispersion and re-introducing the viscoelastic attenuation results in a transfer function of the viscoelastic waveguide including excitation and receiving conditions. The performance of the proposed simulation model is shown by comparison to measurements taken on a polypropylene sample. T2 - IUS 2014 - IEEE International ultrasonics symposium CY - Chicago, IL, USA DA - 03.09.2014 PY - 2014 SN - 978-1-4799-7049-0 DO - https://doi.org/10.1109/ULTSYM.2014.0333 SP - 1348 EP - 1351 AN - OPUS4-31869 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Model based sensitivity analysis in the determination of viscoelastic material properties using transmission measurements through circular waveguides T2 - International Congress on Ultrasonics 2015 CY - Metz, Frankreich DA - 2015-05-10 PY - 2015 AN - OPUS4-33196 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Simulation von Ultraschallwellen in ausgedehnten Strukturen T2 - DACH-Jahrestagung Salzburg 2015 CY - Salzburg, Österreich DA - 2015-05-11 PY - 2015 AN - OPUS4-33197 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gravenkamp, Hauke A1 - Birk, C. A1 - Song, C. T1 - Simulation of elastic guided waves interacting with defects in arbitrarily long structures using the scaled boundary finite element method N2 - In this paper, an approach is presented to model the propagation of elastic waves and their interaction with defects in plate structures. The formulation is based on the Scaled Boundary Finite Element Method (SBFEM), a general semi-analytical method requiring the discretization of boundaries only. For a homogeneous finite or infinite plate section, only the through-thickness direction of the plate is discretized. To describe a defect, the full boundary of a short plate section of irregular shape is discretized. High-order spectral elements are employed for the discretization. The formulation for infinite plates can model the transmission into an unbounded domain exactly. Results are compared with conventional Finite Element Analyses in both time domain and frequency domain. The presented approach allows for the simulation of complex reflection and scattering phenomena using a very small number of degrees of freedom while the mesh consists of one-dimensional elements only. KW - Scaled Boundary Finite Element Method KW - Guided waves KW - Unbounded domains KW - Cracks PY - 2015 DO - https://doi.org/10.1016/j.jcp.2015.04.032 SN - 0021-9991 SN - 1090-2716 VL - 295 SP - 438 EP - 455 PB - Elsevier Inc. CY - Amsterdam AN - OPUS4-33207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Novel approaches for the simulation of ultrasonic guided waves T2 - ECNDT 2014 CY - Prag (Tschechien) DA - 2014-10-06 PY - 2014 AN - OPUS4-31979 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Simulation of guided waves in solids using the Scaled Boundary Finite Element Method T2 - Wolrd Congress on Computational Mechanics, WCCM 2014 CY - Barcelona (Spanien) DA - 2014-07-20 PY - 2014 AN - OPUS4-31990 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Time-causal material modeling in the simulation of guided waves in circular viscoelastic waveguides T2 - 2014 IEEE International Ultrasonics Symposium CY - Chicago (USA) DA - 2014-09-03 PY - 2014 AN - OPUS4-31989 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gravenkamp, Hauke A1 - Birk, C. A1 - Van, J. T1 - Modeling ultrasonic waves in elastic waveguides of arbitrary cross-section embedded in infinite solid medium N2 - An approach is presented to model elastic waveguides of arbitrary cross-section coupled to infinite solid media. The formulation is based on the scaled boundary-finite element method. The surrounding medium is approximately accounted for by a dashpot boundary condition derived from the acoustic impedances of the infinite medium. It is discussed under which circumstances this approximation leads to sufficiently accurate results. Computational costs are very low, since the surrounding medium does not require discretization and the number of degrees of freedom on the cross-section is significantly reduced by utilizing higher-order spectral elements. KW - Guided waves KW - Scaled boundary finite element method KW - Leaky waves KW - Ultrasound PY - 2015 DO - https://doi.org/10.1016/j.compstruc.2014.11.007 SN - 0045-7949 SN - 0366-7138 VL - 149 SP - 61 EP - 71 PB - Pergamon Press CY - Oxford AN - OPUS4-32348 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke T1 - Effect of elastic modulus and Poisson´s ratio on guided wave dispersion using transversely isotropic material modelling T2 - SHATIS, International Conference on Structural Health Assessment of Timber Structures CY - Trento, Italy DA - 2013-09-04 PY - 2013 AN - OPUS4-29744 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -