Synchrosqueezing is a procedure for improving the frequency localization of a continuous wavelet transform. This research focuses on using a synchrosqueezed wavelet transform (SWT) to determine the damping ratios of a vibrating system using a free-response signal. While synchrosqueezing is advantageous due to its localisation in the frequency, damping identification with the original SWT is not sufficiently accurate. Here, the synchrosqueezing was researched in detail, and it was found that an error in the frequency occurs as a result of the numerical calculation of the preliminary frequencies. If this error were to be compensated, a better damping identification would be expected. To minimize the frequency-shift error, three different strategies are investigated: the scale-dependent coefficient method, the shifted-coefficient method and the autocorrelated-frequency method. Furthermore, to improve the SWT, two synchrosqueezing criteria are introduced: the average SWT and the proportional SWT. Finally, the proposed modifications are tested against close modes and the noise in the signals. It was numerically and experimentally confirmed that the SWT with the proportional criterion offers better frequency localization and performs better than the continuous wavelet transform when tested against noisy signals.
COBISS.SI-ID: 14633755
We present a combined analytical approach and numerical study on the stability of a ring bound to an annular elastic substrate, which contains a circular cavity. The system is loaded by depressurizing the inner cavity. The ring is modeled as an Euler%Bernoulli beam and its equilibrium equations are derived from the mechanical energy which takes into account both stretching and bending contributions. The curvature of the substrate is considered explicitly to model the work done by its reaction force on the ring. We distinguish two different instabilities: periodic wrinkling of the ring or global buckling of the structure. Our model provides an expression for the critical pressure, as well as a phase diagram that rationalizes the transition between instability modes. Towards assessing the role of curvature, we compare our results for the critical stress and the wrinkling wavelength to their planar counterparts. We show that the critical stress is insensitive to the curvature of the substrate, while the wavelength is only affected due to the permissible discrete values of the azimuthal wavenumber imposed by the geometry of the problem. Throughout, we contrast our analytical predictions against finite element simulations.
COBISS.SI-ID: 14610203
To obtain the initial conditions for ejection analysis of an injection molded part, a numerical simulation of the stress evolution in the material during injection molding is required. This topic, described in the literature only modestly for the full three-dimensional geometry, is addressed here by proposing an approach simple enough to be implemented in a general purpose solid mechanics simulation code. This feature makes it especially suitable with respect to the analysis of ejection, where custom code development might present hindering amount of additional work. As temperature and pressure field evolutions are obtainable through a computational fluid dynamics analysis, they are taken as input data in the stress analysis. The novelty of the approach is in the treatment of the melt region, where explicit tracking of the melt-solid interface is substituted by imposing the known pressure field in the melt region. The validity of the approach is experimentally tested by analyzing shrinkage and mass of moldings, as well as partial cavity pressure evolution at different packing pressure settings.
COBISS.SI-ID: 14956571
The numerical modeling of joints with a certain amount of clearance and a subsequent validation of the model are important for accurate multibody simulations. For such validated modeling, not only the kinematic constraints, but also the contact models, are important. If a joint has no clearance, it is assumed to be ideal. However, in real applications, there is frequently some clearance in the joints. Adding clearance and kinematic conditions to a pin-slot joint significantly increases the number of kinematic and contact parameters. Consequently, the resulting kinematics and the contact forces can vary significantly with regard to the selection of those parameters. This research covers the development of a validated model for a pin-slot clearance joint. Different kinematic constraints and contact models are discussed. The presented model is an experimentally validated one for a pin-slot clearance joint that is commonly used in safety-critical applications like electrical circuit breakers. Special attention is given to the Hertz, Kelvin-Voigt, Johnson, and Lankarani-Nikravesh contact models. When comparing different contact models within numerical approaches and comparing the results with experimental data, significant differences in the results were observed. With a validated model of a pin-slot clearance joint, a physically consistent numerical simulation was obtained.
COBISS.SI-ID: 15116059
Laser Shock Peening (LSP) can be used to improve the surface properties of metallic materials. During the LSP process, martensitic phase transformation can take place in austenitic steels under certain processing conditions in addition to plastic deformation. In this study, the plastic strains and the amount of martensite in 304 austenitic stainless steel after LSP is numerically predicted. In order to simulate the response, an existing elasto-plastic model that includes phase transformation is extended to capture the rate dependency of plastic deformation during LSP. The influence of temperature, laser pulse duration and laser intensity on the residual state is studied. It is, for example, found that martensite formation is accelerated by lowering the processing temperature, increasing the peening pressure as well as extending the laser pulse duration.
COBISS.SI-ID: 14602779