The study of vibrational properties in engineered periodic structures relies on the early intuitions of Haüy and Boscovich, who regarded crystals as ensembles of periodically arranged point masses interacting via attractive and repulsive forces. Contrary to electromagnetism, where mechanical properties do not couple to the wave propagation mechanism, in elasticity this paradigm inevitably leads to low stiffness and high-density materials. Recent works transcend the Haüy-Boscovich perception, proposing shaped atoms with finite size, which relaxes the link between their mass and inertia, to achieve unusual dynamic behavior at lower frequencies, leaving the stiffness unaltered. Here, we introduce the concept of tacticity in spin-spin-coupled chiral phononic crystals. This additional layer of architecture has a remarkable effect on their dispersive behavior and allows to successfully realize material variants with equal mass density and stiffness but radically different dynamic properties.
We demonstrate the continuous production of liquid-filled polymeric fibers in a stable meltspinning process at the pilot plant scale. Different polymers and liquids could successfully be combined over a wide range of core-sheath dimensions. The ability to produce a continuous liquid-core fiber (LCF) is attractive since post-filling of a hollow fiber with similar dimensions is not practical. We characterized the mechanical properties of the LCF's with particular attention to their damping properties. A LCF can exhibit significantly enhanced
This paper presents a study of the heat transfer influence on the centrifugal compressor performance. The compressor studied in this paper is based on the scale-up of a turbocharger compressor equipped with a shroudless impeller. To account for the heat transfer effect, a conjugate heat transfer analysis is performed with computational fluid dynamics techniques. The heat transfer phenomena not only externally but also internally are investigated at the design point. The grids adopted in the study are verified at the baseline, with an excellent agreement found between numerical simulations and measurements. The results provide an insight into the dependence of the heat transfer influences on the heat flux paths. The path of the external heat flux passing through the impeller shaft is found to have a great impact on the compressor performance. The study of internal heat transfer shows that the shroud surface dominates the internal heat transfer effect on the efficiency loss. Furthermore, the heat transfer influence is also investigated on the compressor performance at other operating points. The results imply a positive potential margin for the improvement of compressor efficiency by means of heat transfer control.
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