Analytical Solution for Vibrations of a Modified Timoshenko Beam on Visco-Pasternak Foundation Under Arbitrary Excitations

An analytical solution is derived for dynamic response of a modified Timoshenko beam with an infinite length resting on visco-Pasternak foundation subjected to arbitrary excitations. The modified Timoshenko beam model is employed to further consider the rotary inertia caused by the shear deformation of a beam, which is usually neglected by the traditional Timoshenko beam model. By using Fourier and Laplace transforms, the governing equations of motion are transformed from partial differential forms into algebraic forms in the Laplace domain. The analytical solution is then converted into the time domain by applying inverse transforms and convolution theorem. Some widely used loading cases, including moving line loads for nondestructive testing, travelling loads for seismic wave passage, and impulsive load for impact vibration, are also discussed in this paper. The proposed generic solutions are verified by comparing their degraded results to the known solutions in other literature. Several examples are performed to further investigate the differences of the beam responses obtained from the modified and the traditional Timoshenko beam models. Results show that the modified Timoshenko beam simulates the beam responses more accurately than the traditional model, especially under the dynamic loads with a high frequency. The analytical solutions proposed in this paper can be conveniently used for design and applied as an effective tool for practitioners.

Distinguishing friction- from shock-generated melt products in hypervelocity impact structures

ABSTRACT Field, microtextural, and geochemical evidence from impact-related melt rocks at the Manicouagan structure, Québec, Canada, allows the distinction to be made between friction-generated (pseudotachylite) and shock-generated melts. Making this distinction is aided by the observation that a significant portion of the impact structure’s central peak is composed of anorthosite that was not substantially involved in the production of impact melt. The anorthosite contrasts with the ultrabasic, basic, intermediate, and acidic gneisses that were consumed by decompression melting of the >60 GPa portion of the target volume to form the main impact melt body. The anorthosite was located below this melted volume at the time of shock loading and decompression, and it was subsequently brought to the surface from 7–10 km depth during the modification stage. Slip systems (faults) within the anorthosite that facilitated its elevation and collapse are occupied by pseudotachylites possessing anorthositic compositions. The Manicouagan pseudotachylites were not shock generated; however, precursor fracture-fault systems may have been initiated or reactivated by shock wave passage, with subsequent tectonic displacement and associated frictional melting occurring after shock loading and rarefaction. Pseudotachylites may inject off their generation planes to form complex intrusive systems that are connected to, but are spatially separated from, their source horizons. Comparisons are made between friction and shock melts from Manicouagan with those developed in the Vredefort and Sudbury impact structures, both of which show similar characteristics. Overall, pseudotachylite has compositions that are more locally derived. Impact melts have compositions reflective of a much larger source volume (and typically more varied source lithology inputs). For the Manicouagan, Vredefort, and Sudbury impact structures, multiple target lithologies were involved in generating their respective main impact melt bodies. Consequently, impact melt and pseudotachylite can be discriminated on compositional grounds, with assistance from field and textural observations. Pseudotachylite and shock-generated impact melt are not the same products, and it is important not to conflate them; each provides valuable insight into different stages of the hypervelocity impact process.

Impact of Local Site Conditions on Simulation of Non-stationary Spatial Variable Seismic Motions

It is commonly accepted that multi-scale structures are subject to spatially variable seismic motions. This spatial variability of seismic motions is described by different intensities at different locations due to the coherency loss effect, wave passage effect and local site conditions. For multi-scale structures, the estimation of seismic excitations must consider these factors. Often, the influence of the spatial variability of seismic motion on the dynamic response of structures is performed by neglecting the site effect. In several cases, it has been observed that the high intensities of seismic motion are caused by the site amplification besides coherency loss and wave passage effects. This study aims to analyze the impact of local site conditions on seismic motions. For this purpose, a method of simulation of spatially variable seismic motions is performed. The seismic signals on the bedrock are defined by considering a target power spectral density and a coherency loss model. According to the seismic wave propagation theory, the projection of these seismic motions on the surface is realized. The results of this study show that neglecting the local site conditions induces an undervaluation of spatially variable seismic excitations.

Structural Identification and Damage Detection in Bridges using Wave Method and Uniform Shear Beam Models: A Feasibility Study

This report presents a wave method to be used for the structural identification and damage detection of structural components in bridges, e.g., bridge piers. This method has proven to be promising when applied to real structures and large amplitude responses in buildings (e.g., mid-rise and high-rise buildings). This study is the first application of the method to damaged bridge structures. The bridge identification was performed using wave propagation in a simple uniform shear beam model. The method identifies a wave velocity for the structure by fitting an equivalent uniform shear beam model to the impulse response functions of the recorded earthquake response. The structural damage is detected by measuring changes in the identified velocities from one damaging event to another. The method uses the acceleration response recorded in the structure to detect damage. In this study, the acceleration response from a shake-table four-span bridge tested to failure was used. Pairs of sensors were identified to represent a specific wave passage in the bridge. Wave velocities were identified for several sensor pairs and various shaking intensities are reported; further, actual observed damage in the bridge was compared with the detected reductions in the identified velocities. The results show that the identified shear wave velocities presented a decreasing trend as the shaking intensity was increased, and the average percentage reduction in the velocities was consistent with the overall observed damage in the bridge. However, there was no clear correlation between a specific wave passage and the observed reduction in the velocities. This indicates that the uniform shear beam model was too simple to localize the damage in the bridge. Instead, it provides a proxy for the overall extent of change in the response due to damage.

Low-temperature separation of helium-helion mixture

The research is devoted to the problem of designing materials with an adjustable property of permeability. The obtained tool for property regulation allows achieving hyper-selectivity in relation to separation of helium isotope mixtures, as well as some other gas mixtures. The reasearch is theoretical in nature; however, it suggests a clear direction of activity for experimenters. The result obtained is valid for ultrathin barriers of any form. As a result, a new exact solution of the Schrödinger equation of wave dynamics, which is valid for the case of two-barrier systems, is found. This solution allows for comprehensive consideration of the process of wave passage through a barrier and identification of the causes leading to super-permeability of individual components.

A New Radio-Frequency Acoustic Method for Remote Study of Liquids

In the present work, a novel conductive liquids method of study has been proposed. It is based on the phenomenon of radiofrequency anisotropy of electrolyte solution discovered by us. It arises in response to mechanical or acoustic excitation of the solution. We have observed the phenomenon during the development of an RF polarimetric contactless cardiograph. The electric field vector of the transmitted 433.82 MHz signal rotated after its transition through the pericardial region. That rotation depends on the change of blood acceleration when passing through the chambers of the heart and large vessels. It has also been revealed that rotation occurs after RF wave passage through the physiological saline (0.9% NaCl) subjected to any mechanical excitation inside it like a jet appearing or soundwave passing. No significant difference was detected experimentally between NaCl and KCl solutions behavior. It means that the mechanism of hydrodynamic separation of ions is apparently not suitable to explain the phenomenon. The response we have registered resembles the magnetization process of spin glasses. From the nature of the observed response, we have concluded that a fundamentally new physical effect is discovered. It may provide wide opportunities for remote measurement of the electrolyte solution parameters with polarized radio-frequency signals.