Modeling of a Railway Sanding System Using Vibration Fluidization

The model of the sand distributor of the sand feeding system of traction rolling stock, the operation of which is based on the effect of vibration fluidization of sand, has been considered. A pneumatic pulsator was used as a source of vibration impact. Experimental studies have shown that this design allows for a continuous regulated supply of sand. The power of the sand distributor membrane vibrations at the disturbing frequency can be used as a criterion characterizing the impact of the pulsator on the sand. There is a close to linear dependence of the sand flow rate on the power of vibrations.

Акустические колебания алюминиевых мембран при лазерном возбуждении по термоупругому механизму

A theoretical model of the formation of a photoacoustic signal from metal membranes by laser radiation is proposed taking into account the excitation of defective states in them. The theoretical results obtained are compared for aluminum membranes with a thickness of 197 μm in the frequency range from 20 Hz to 7 kHz when they are excited by laser radiation with a wavelength of 660 nm. It is shown that the proposed theoretical model ensures good agreement between the experimental and theoretical results for membrane vibrations with a purely surface absorption of laser radiation.

High-precision 3D inkjet technology for live cell bioprinting

In recent years, bioprinting has emerged as a promising technology for the construction of three-dimensional (3D) tissues to be used in regenerative medicine or in vitro screening applications. In the present study, we present the development of an inkjet-based bioprinting system to arrange multiple cells and materials precisely into structurally organized constructs. A novel inkjet printhead has been specially designed for live cell ejection. Droplet formation is powered by piezoelectric membrane vibrations coupled with mixing movements to prevent cell sedimentation at the nozzle. Stable drop-on-demand dispensing and cell viability were validated over an adequately long time to allow the fabrication of 3D tissues. Reliable control of cell number and spatial positioning was demonstrated using two separate suspensions with different cell types printed sequentially. Finally, a process for constructing stratified Mille-Feuille-like 3D structures is proposed by alternately superimposing cell suspensions and hydrogel layers with a controlled vertical resolution. The results show that inkjet technology is effective for both two-dimensional patterning and 3D multilayering and has the potential to facilitate the achievement of live cell bioprinting with an unprecedented level of precision.

Fluid–structure coupling mechanism and its aerodynamic effect on membrane aerofoils

Fluid–structure interactions of elastic membrane aerofoils are investigated at Reynolds number $Re=10\,000$ and low angle of attack. The dynamics of the fluid and membrane coupled system are solved using direct numerical simulation (DNS), where the geometry and boundary conditions were applied using a boundary data immersion method. Although membrane aerofoils improve the aerodynamic performance close to stall conditions compared to rigid aerofoils, it has previously been found that membrane aerofoils show lower aerodynamic efficiency at low angles of attack. This study focuses on the coupling mechanism at an angle of attack of 8 degrees, which is below the stall angle. The dynamic behaviour of the coupled system was characterised via spectral analysis in the wavenumber and frequency domain, which allowed the propagating wave nature of the membrane vibrations and their effect on the surrounding pressure field to be clarified. The membrane vibrations are found to introduce upstream-propagating pressure waves that appear to be responsible for a loss in aerodynamic efficiency compared to a rigid aerofoil. Comparison of two- and three-dimensional results reveals that the three-dimensional flow development causes a decrease in the amplitude of the system fluctuations, but the same coupling mechanism is present.