Recent zbMATH articles in MSC 74J99 https://www.zbmath.org/atom/cc/74J99 2021-04-16T16:22:00+00:00 Werkzeug Wave modelling in predictive vibro-acoustics: applications to rail vehicles and aircraft. https://www.zbmath.org/1456.74003 2021-04-16T16:22:00+00:00 "Orrenius, Ulf" https://www.zbmath.org/authors/?q=ai:orrenius.ulf "Liu, Hao" https://www.zbmath.org/authors/?q=ai:liu.hao.1|liu.hao|liu.hao.2 "Wareing, Andrew" https://www.zbmath.org/authors/?q=ai:wareing.andrew "Finnveden, Svante" https://www.zbmath.org/authors/?q=ai:finnveden.svante "Cotoni, Vincent" https://www.zbmath.org/authors/?q=ai:cotoni.vincent Summary: Three different predictive methods based on wave descriptions of the acoustic field are presented and used to calculate transmission and radiation properties of typical rail and aerospace structures. First, a transfer matrix method assesses the sound transmission and wavenumbers of composite sandwich fuselage structures in a wide frequency range. The method is computationally effective and can be used for numerical optimization of sandwich lay-ups common in rail and aerospace engineering. Further, an approach for which a small finite element model of a periodic cell is applied to create a statistical model of a near periodic structure is shown to determine transmission and radiation properties of stiffened fuselage structures and an extruded train floor structure. Finally, a novel combination of the waveguide FE method with the Rayleigh-Ritz method is applied to: (i) calculate the transmission through a double wall structure; (ii) again assess the sound transmission of an extruded floor structure and also (iii) determine the sound pressure inside a large section of a rail car excited by external sound sources. All three methods presented can be used to effectively support decision making in the design process of trains and aircraft. Extraction of bulk wave characteristics from a pulsed ultrasonic polar scan. https://www.zbmath.org/1456.74102 2021-04-16T16:22:00+00:00 "Kersemans, Mathias" https://www.zbmath.org/authors/?q=ai:kersemans.mathias "Lammens, Nicolas" https://www.zbmath.org/authors/?q=ai:lammens.nicolas "Degrieck, Joris" https://www.zbmath.org/authors/?q=ai:degrieck.joris "Van Den Abeele, Koen" https://www.zbmath.org/authors/?q=ai:van-den-abeele.koen "Pyl, Lincy" https://www.zbmath.org/authors/?q=ai:pyl.lincy "Zastavnik, Filip" https://www.zbmath.org/authors/?q=ai:zastavnik.filip "Sol, Hugo" https://www.zbmath.org/authors/?q=ai:sol.hugo "Van Paepegem, Wim" https://www.zbmath.org/authors/?q=ai:van-paepegem.wim Summary: The pulsed ultrasonic polar scan (P-UPS) technique provides a map with characteristic contours reflecting the critical bulk wave angles, which directly relate to the in-plane elastic properties of the insonified material spot. Besides these contours, additional information is captured in a P-UPS experiment which has particular importance for the inspection of anisotropic materials. By extensive post-processing on a single P-UPS experiment, we successfully extracted the local directional (i) critical bulk wave angles, (ii) phase velocity profiles, (iii) slowness curves, (iv) walk-off angles and (v) energy velocity profiles, for the three different polarization states of bulk waves. The procedure is demonstrated and discussed for an isotropic aluminum sample as well as an autoclave manufactured orthotropic $$_8$$ carbon/epoxy laminate. In addition, a numerical and experimental investigation of the role of the immersion liquid as a lens for the P-UPS result is performed. This lensing effect permits to zoom in/out on the P-UPS fingerprint, hence broadening the class of materials which can be inspected by the P-UPS technique. Temporal behavior of laser induced elastic plate resonances. https://www.zbmath.org/1456.74103 2021-04-16T16:22:00+00:00 "Laurent, Jérôme" https://www.zbmath.org/authors/?q=ai:laurent.jerome "Royer, Daniel" https://www.zbmath.org/authors/?q=ai:royer.daniel "Prada, Claire" https://www.zbmath.org/authors/?q=ai:prada.claire Summary: This paper investigates the dependence on Poisson's ratio of local plate resonances in low attenuating materials. In our experiments, these resonances are generated by a pulse laser source and detected with a heterodyne interferometer measuring surface displacement normal to the plate. The laser impact induces a set of resonances that are dominated by Zero Group Velocity (ZGV) Lamb modes. For some Poisson's ratio, thickness-shear resonances are also detected. These experiments confirm that the temporal decay of ZGV modes follows a $$t^{- 0.5}$$ law and show that the temporal decay of the thickness resonances is much faster. Similar decays are obtained by numerical simulations achieved with a finite difference code. A simple model is proposed to describe the thickness resonances. It predicts that a thickness mode decays as $$t^{- 1.5}$$ for large times and that the resonance amplitude is proportional to $$D^{- 1.5}$$ where $$D$$ is the curvature of the dispersion curve $$\omega(k)$$ at $$k = 0$$. This curvature depends on the order of the mode and on the Poisson's ratio, and it explains why some thickness resonances are well detected while others are not. Continuous dependence on the coefficients for a class of non-autonomous evolutionary equations. https://www.zbmath.org/1456.35194 2021-04-16T16:22:00+00:00 "Waurick, Marcus" https://www.zbmath.org/authors/?q=ai:waurick.marcus Summary: The continuous dependence of solutions to certain equations on the coefficients is addressed. The class of equations under consideration has only recently be shown to be well posed. We give criteria that guarantee that convergence of the coefficients in the weak operator topology implies weak convergence of the respective solutions. We discuss three examples: A homogenization problem for a Kelvin-Voigt model for elasticity, the discussion of continuous dependence of the coefficients for acoustic waves with impedance type boundary conditions and a singular perturbation problem for a mixed type equation. By means of counterexamples, we show optimality of the results obtained. For the entire collection see [Zbl 1420.78002]. Complex wavenumber Fourier analysis of the B-spline based finite element method. https://www.zbmath.org/1456.74149 2021-04-16T16:22:00+00:00 "Kolman, R." https://www.zbmath.org/authors/?q=ai:kolman.radek "Plešek, J." https://www.zbmath.org/authors/?q=ai:plesek.jiri "Okrouhlík, M." https://www.zbmath.org/authors/?q=ai:okrouhlik.miloslav Summary: We present the results of one-dimensional complex wavenumber Fourier analysis of the B-spline variant of Finite Element Method (FEM). Generally, numerical results of elastic wave propagation in solids obtained by FEM are polluted by dispersion and attenuation. It was shown for the higher-order B-spline based FEM, that the optical modes did not occur in the case of infinite domains, unlike the higher-order Lagrangian and Hermitian finite elements, and also the dispersion errors are smaller. The paper's main focus is on the wave propagation through B-spline multi-patch/segment discretization with the $$C0$$ connection of B-spline segments and, chiefly, to the determining of dispersion and attenuation dependences. The numerical approach employed leads to substantial minimization of dispersion errors. Furthermore, the errors decrease in line with the increasing order of the B-spline elements/segments, with the local refinement, and also by the particular choice of the positions of control points through the optimizing procedure. Lamb wave mode decomposition for structural health monitoring. https://www.zbmath.org/1456.74104 2021-04-16T16:22:00+00:00 "Park, Ilwook" https://www.zbmath.org/authors/?q=ai:park.ilwook "Jun, Yongju" https://www.zbmath.org/authors/?q=ai:jun.yongju "Lee, Usik" https://www.zbmath.org/authors/?q=ai:lee.usik Summary: Lamb waves propagate over large distances in plate-like thin structures and they have received great attention in the structural health monitoring (SHM) field as an efficient means to inspect a large area of a structure by using only a small number of sensors. The times-of-flight of the Lamb wave modes are useful for detecting damage generated in a structure. However, due to the dispersive and multi-mode nature of Lamb waves, it is very challenging to decompose Lamb wave modes into symmetric and anti-symmetric modes for potential applications to structural health monitoring. Thus, we propose an efficient Lamb wave mode decomposition method based on two fundamental rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of $$A_0$$ and $$S_0$$ modes must be constant. The mode amplitude ratio rule means that the ratio of the magnitudes of $$A_0$$ and $$S_0$$ modes in a measured response signal must be always greater than one once the center frequency of the input signal is determined, such that the magnitude of the $$A_0$$ mode in the excited signal is larger than that of the $$S_0$$ mode, and \textit{vice versa}. The proposed method is verified through experiments conducted for a plate specimen.