Procedia IUTAM最新文献

Strain gradients at domain walls in polydomain ferroelectric thin films generally are huge, reaching a value of 10⁷-10⁸ m^-1, appears at domain walls. These huge strain gradients always play a considerable impact on polarization distribution via flexoelectricity. However, the ability of the flexoelectricity to tune the leakage current in ferroelectric nanofilms is untouched to date. By combining the phase field model and diffusion equations for an electron/electron hole, a self-consistent model is established to investigate the influence of flexoelectric effect on the current-voltage characteristic of Pt/Pb(Zr_0.1Ti_0.9)O₃/Pt capacitor. It is shown that the longitudinal flexoelectric coefficient related coupling type would reduce the electric potential, and thus, increase the electron hole concentration and cause leakage current increasing in thin films. In contrast, the transverse flexoelectric coefficient related coupling type would raise the electric potential, decrease the electron hole concentration and cause leakage current decreasing in thin films.

An application of X-ray topography methods allowed us to construct a two-dimensional map of the impurity distribution in a GaSb:Te crystal grown under microgravity conditions. This map served as a framework for the analysis of crystal growth features and of the impurity inhomogeneity in the crystal. The data on the impurity distribution in the sample became an experimental basis for the analysis of the crystallization parameters (the crystal growth rate and the maximum convection velocity) and an adequate application of theoretical models (analytical and numerical) to explaining the mechanisms of onset of impurity inhomogeneities in the crystal.

This study investigates energy absorption of thermally loaded composites and nanocomposites laminates during impact loading. The laminates are prepared by glass fiber/epoxy with and without nano particles in the matrix system. Nano clay and carbon nano tube are used as filliers in the epoxy matrix. The composites specimens are subjected to impact loading at 0° C, 30° C and 60° C temperature environments. A gas gun impact testing facility is used for propelling the projectile of mass 7.6 g and diameter 9.5 mm with hemi spherical nose. The initial and residual velocities of projectile are predicted to find the energy absorbing capacity of laminates. The energy absorption and delamination area of the specimens are analyzed and discussed for the laminates with and without clay. Also, the ballistic limit is predicted for the specimens of nanocomposites made with glass fibers and epoxy matrix, and the effect of temperature on impact resistance is discussed. Analytical model is developed and the energy absorption characteristics are also studied.

Propagation of a plane longitudinal acoustic wave in a solid with dislocations is theoretically studied. The effect of dislocations on the phase velocity dispersion and the character and degree of wave damping is analyzed. The following results are obtained. The phase velocity exhibits infinite growth at zero frequency and asymptotically approaches the tabulated value for the longitudinal wave velocity in solids as the frequency tends to infinity. The frequency dependence of the wave damping coefficient has a peak whose position depends on the characteristics of the solid. The results are compared with experimental data for the dislocation relaxation process in lead and are found to be in good agreement with these.

The influence of the dislocation structure on the character of the dependencies obtained for wave damping and phase velocity dispersion is analyzed. The results are compared with experimental data for the dislocation damping during plastic deformation and cycling loading of polycrystalline copper and aluminum.

We derive the dynamic equations of solid media with dislocations containing geometrical and physical nonlinearity. The evolution of nonlinear acoustical waves under the influence of a dislocation field is studied. The development of modulation instability quasiharmonic longitudinal waves is shown to be possible.

We have reviewed the development and the analysis of the coupled two degrees-of-freedom model of drill-string vibration, which assumes a state-dependent time delay and a viscous damping for both the axial and torsional vibration. This model corrects the instability deficiencies of the previous models but it is still based on a uniform angular distribution of blades on a drill-bit, which can lead to unrealistic regenerative types of instability. However, the model sheds some lights on the origin and the interplay between stick-slip and bit-bounce, the dangerous dynamic phenomena encountered during rotary drilling. The experimental rig developed by the Centre of Applied Dynamics Research at the University of Aberdeen is used to show some shortcomings of this model and to develop a new more realistic one. The new model assuming a non-uniform distribution of blades for drag type drill-bits is proposed.

To identify unknown parameters from the noise-polluted measurement in time-delayed systems, this paper proposes the incremental harmonic balance based approach. By assuming that the steady response is periodic and the noise pollution does not change the periodicity of the measured response, this approach expands the ideal and measured response into the form of Fourier series. With this process, the noise correction can be parameterized as the harmonic increments of the measured response so that the noise correction can be determined by the same process of the identification of the unknown parameters. Numerical examples are given to verify the efficiency of the proposed approach. In comparison with the identified parameters without noise correction, the results show that the accuracy of the ones with noise correction is significantly improved. This achievement also implies that the proposed approach is reliable in similar cases of engineering applications.

During the last years, the round window (RW) has become a well established application position for active middle ear implants¹. The coupling condition between actuator and round window membrane (RWM) is the critical point regarding the lasting function of the reconstruction. A preload force is needed to maintain sound transmission dealing with an unilateral contact. In this work, the RW stimulation is examined from the mechanical point of view. Based on laboratory experiments and computational simulations, the effects of parameter variations on the dynamical behaviour of the reconstructed ear are revealed in sensitivity analyses and case studies.

Force-displacement measurements are carried out in order to capture the nonlinear stiffening and the relaxation behaviour of the RWM. Its characteristics are quantifed by mechanical parameters based on visco-elastic models². A simplified mechanical multibody model is used to simulate the transfer of sound in the natural ear. Hereby, the transmission ratio between oval window and RW has to be taken into account. In case of otosclerosis, stiffening of the annular ring leads to alterations in the transfer behaviour. A hearing loss is observed mainly in the low frequency range, whereas increased hearing sensation may occur in the higher frequency range.

With free floating actuators, vibration is transmitted via the actuator housing. The working principle is based on the inertia effect of an internal seismic mass. As an example, the Floating Mass Transducer (FMT) is presented, which is acting as a force transducer. In the not implanted case, the actuator exhibits freqency dependent spatial motions. For assessing the dynamics of the reconstructed ear, the natural structure and the actuator have to be considered as a whole. Based on a multibody model, various influences are investigated by means of virtual experiments, e.g. the preload force, the actuator suspension and the intermediate layer in the contact area. The preload force leads to stiffening of the natural system due to its nonlinear behaviour. As a consequence, resonances are shifted to higher frequencies and low frequency amplitudes are reduced. With increasing preload force, the dynamic force amplitude transmittable without lift-off in the contact area is increased. The corresponding maximum level of equivalent sound pressure is determined by the mechanical properties of the natural structure, but not by not the actuator. The suspension of the actuator housing should be designed to be as compliant as possible in order to maintain the mobility of the actuator during stimulation and to preserve the preload force during large quasistatic deformations of the RWM. Increased motion transfer is observed in the higher frequency range in case of additional damping in the intermediate layer.

Long waves approaching a cliff are significantly affected by a variable bathymetry. Wave breaking is observed, and determined by both the bathymetry and nonlinear interactions of the waves with the cliff and other waves. Geometric and kinematic measures are applied to determine a breaking criteria, however there are inconsistencies in both when the wave parameters are close to breaking/non-breaking interface values. Wave crest-cliff interaction is discussed in terms of its effect on the phase and fluid velocities. Runup amplification increases with the number of waves in the approaching wavepacket, their amplitude, and the bathymetry slope, but is approximately independent of the wave period. Runup amplifications approaching a factor of 12 are observed for a bathymetry approximating that of the Aran Islands, Ireland.

The coastal regions in Eastern Asia are under the potential threat of storm surges, especially the surge inundation caused by typhoons. In this study, the COMCOT (COrnell Multi-grid Coupled Tsunami Model) storm surge model has been developed for the approach of operational process and successfully coupled with dynamic atmospheric WRF model and global tidal TPXO 7.1 model. The large-scale and near-shore storm surge propagation could be simulated simultaneously with nested-grid scheme, and high-resolution inundated areas could also be calculated from the wet-dry-cell method. The destructive storm surge event induced by 2013 Typhoon Haiyan is chosen as the case study in this research, and the non-symmetric WRF fields and TPXO tidal effect are both considered in this case. From simulated results, the storm surges are concentric before Typhoon Haiyan landing off the Philippines because the pressure gradient was significant at that time, and then storm surges are concentrated at near-shore regions when wind shear stress turn to be the main force after landing off. The relationship between maximum storm surges and typhoon crack is also found in this study. More details would be presented at 2016 IUTAM Symposium.

Excessive typhoon design is an interesting topic in coastal engineering. To design an excessive typhoon, the most popular method is typhoon path translation, but it may cause unreasonable results sometimes. In this paper, a correction method is introduced by using statistical air pressure map and wind speed map. Longquangang area along the north bank of Hangzhou Bay is taken as the research area here. The designed typhoon path is translated from Typhoon Khanun (2005). After typhoon strength correction and time translation, the result of wind speed and typhoon-induced storm surge seems more reasonable and can be used in coastal engineering, such as dike design and dike risk assessment.