Effects of Aspect Ratio and Distance between Two Square Cylinders in a Tandem Arrangement on In-Line Oscillation Characteristics

When multiple structures, such as the main towers for a bridge, heat exchangers and offshore structures, are placed adjacently in fluid, structures placed in the downstream side are exposed to complicated flow regions, because the separated shear layer reattaches to the downstream structures or interferes with the flow. For this reason, the distance between structures greatly influences changes in flow patterns around the downstream cylinder structures, so that the response characteristics of structures can be altered correspondingly. The purpose of this study is to identify the basic in-line oscillation characteristics of two square cylinders in a tandem arrangement. Based on the supposition of actual structures, spring-supported tests, with both square cylinders elastically suspended, were conducted. Not only the distance between the two cylinders but also the aspect ratio, was also chosen as the parameters. Because it was found by past researches that the in-line oscillation characteristics of single cylinder depends on the aspect ratio, it was thought to be important to confirm it by two cylinders. Furthermore, flow visualization tests were performed by forced-oscillating two cylinders for consideration from the results of the spring-supported test.9th International Symposium on Fluid-Structure Interactions, Flow-Sound Interactions, Flow-Induced Vibration & Noise (FIV2018: FSI2 & FIV+N.), July 8-11, 2018, Toronto, Ontario, Canad

Effects of large amounts of hydrogen on the fatigue crack growth behavior of torsional prestrained carbon steel

The effects of large amounts of hydrogen on the fatigue crack growth properties of torsional prestrained ferritic–pearlitic low-carbon steel were investigated. Hydrogen-precharged specimens were produced by conducting cathodic charge to the virgin material and to torsional prestrained JIS-S10C and JISS25C steels (hereafter S10C and S25C steels). Rotating bending fatigue tests were conducted in air at room temperature. Hydrogen content, CH, increased with torsional prestrain for both S10C and S25C steels; the CH of the torsional prestrained S25C steel precharged with hydrogen was lower than that of S10C at the same torsional prestrain. No clear difference between the maximum CH values of the torsional fractured S10C and S25C hydrogen-precharged steel specimens. With respect to crack initiation, there was no obvious difference between the uncharged and precharged specimens in spite of the large amount of CH induced by torsional prestrain. The acceleration of fatigue crack growth by hydrogen was the main cause of the decreased fatigue life. For the virgin material, hydrogen had no obvious effect on the fatigue crack growth rate. In contrast, for the torsional prestrained materials, the acceleration ratios, {(da/dN)H/(da/dN)U}, increased with the torsional prestrain and CH. However, {(da/dN)H/(da/dN)U} did not exceed the value of about 30, even when a large amount of hydrogen was charged (10.0 ? CH ? 30.3 mass ppm). A hydrogen content threshold was found; hydrogen content above this limit enhances the growth of the non-propagated crack, even for metals with lower hardness (HV < 200)

Production of Al-based composite materials including stress-luminescent particles using 3-dimensional penetration casting (3DPC)

A stress-luminescent powder can be applied as sensors because of luminous characteristic under stress. Key point in fabrication is how uniformly to disperse powders in metallic matrix. Three-dimensional penetration casting (3DPC) process is a good application to fabricate the composite materials using stress-luminescent powders and molten Al. A commercial stress-luminescent powder was prepared (a)stress- luminescent powders (Taikourozai Co.) and (b)EZ bright (EZ bright Cooperation). 3DPC process was conducted using a special mould has dimensions of 42mm height and 30mm diameter. Mould was heated up to 750°C before 3DPC. After 3DPC, particles were well dispersed in Al matrix without crack generations with optical microscopy observation. Also, samples were emitted when they were pressed and scratched

Dynamics of light-induced anomalous Hall effect in the three-dimensional Dirac semimetal Cd3_3As2_2

We experimentally study the dynamical behavior of the light-induced anomalous Hall effect in a three-dimensional Dirac semimetal, Cd$_3$As$_2$. An ultrashort, circularly polarized, multi-terahertz pump pulse breaks the time-reversal symmetry of a thin film sample. The resulting anomalous Hall effect is clearly observed through the polarization rotation of a single-cycle terahertz probe pulse. Comparing the experimental result with theory, we find that the field-induced injection current dominates the anomalous Hall effect during pump irradiation, while the Berry curvature of the Floquet-Weyl semimetal state does not appreciably contribute. Remarkably, even after pump irradiation, we observe an anomalous Hall effect that lasts for more than 10 ps. A model fit to the Hall conductivity spectrum reveals a relatively long scattering time over 400 fs. This result shows that circularly polarized light creates a polarization of the isospin degree of freedom in the Dirac semimetal, which labels the crystallographic point group representation of the overlapping Weyl semimetal bands. Our observation paves the way for conversion of a robust isospin flow into an electric current at room temperature, being a new analogue of the inverse spin Hall effect.Comment: 44 pages, 14 figure

Spin fluctuations from Bogoliubov Fermi surfaces in the superconducting state of S-substituted FeSe

The study of the iron-based superconductor, FeSe, has resulted in various topics, such as the interplay among superconductivity, nematicity, and magnetism, Bardeen-Cooper-Schrieffer Bose-Einstein-condensation (BCS-BEC) crossover, and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity. Recently, topologically protected nodal Fermi surfaces, referred to as Bogoliubov Fermi surfaces (BFSs), have garnered much attention. A theoretical model for the S-substituted FeSe system demonstrated that BFSs can manifest under the conditions of spin-orbit coupling, multi-band systems, and superconductivity with time-reversal symmetry breaking. Here we report the observation of spin fluctuations originating from BFSs in the superconducting (SC) state via $^{77}$Se-nuclear magnetic resonance measurements to 100 mK. In a heavily S-substituted FeSe, we found an anomalous enhancement of low-energy spin fluctuations deep in the SC state, which cannot be explained by an impurity effect. Such unusual behavior implies the presence of significant spin fluctuations of Bogoliubov quasiparticles, which are associated with possible nesting properties between BFSs