Visualization of unsteady fluid flows by using large eddy simulation

Three-dimensional and unsteady flow analysis is a practical target of high performance computation. As recently advances of computers, a numerical prediction by the large eddy simulation (LES) are introduced and evaluated for various engineering problems. Its advanced methods for the complex turbulent flows are discussed by several examples applied for aerodynamic designs, analysis of fluid flow mechanisms and their interaction to complex phenomena. These results of time-dependent and three-dimensional phenomena are visualized by interactive graphics and animations.     

Morphology control technique of ZnO by hydroxide ion supply rate and its effect on the ppt-level gas sensors

The sensitivity of the metal–oxide–semiconductor-type gas sensors has been improved typically using novel metal catalysts, such as Pt, Ru, and Pd. However, the sensing performance could be enhanced by only controlling the nanostructure. Herein, we introduce fabrication methods for ZnO nanobelt by changing the supply rate of hydroxide ions. Hexamethylenetetramine (HMT) and potassium hydroxide were used to generate hydroxide ions, and their rate to reach the maximum pH was different by more than twofold. The supply rate of hydroxide ions caused the different morphology of ZnO nanomaterial due to the change in the seed of material formation. Although both samples could detect acetone gas up to 100 ppt, ZnO nanobelts synthesized by HMT exhibited higher sensitivity. The ZnO morphology influenced the exposed surface area, and a larger specific surface area could facilitate the generation of pre-adsorbed oxygen species that are the main factor for sensitivity.     

Electrochromic thin films prepared by sol–gel process

New methods are shown for lower temperature preparation of amorphous tungsten oxide thin film and preparation of crystalline iridium oxide thin film by sol–gel process using metal chloride as the starting materials and ethanol as a solvent. These electrochromic materials were combined with gel solid electrolyte, and preparation of fully solid-state electrochromic display (ECD) was made. The transmittance of the ECD could be made to change by 35% by applying a voltage of 3 V for 0.2 sec.     

Engineering investigation of hydrogen storage in the form of a clathrate hydrate: Conceptual designs of underground hydrate-storage silos

This paper describes the conceptual designs of a facility for storing, in the form of a clathrate hydrate, hydrogen produced in an industrial complex area. We recently reported the first engineering investigation of hydrate-based hydrogen storage, focusing on the conceptual design of hydrate production plants applicable for the large-scale stationary storage in urban or industrial complex areas (Nakayama et al., Energy Fuels 2010;24:2576−2588). This paper complements the previous study by presenting conceptual designs of underground hydrate-storage silos each to be coupled to a hydrate production plant. Several different types of underground silos each having a 35,000 m³ capacity were planned and designed on a construction-engineering basis, which included (a) a tunnel-type silo consisting of several levels radially arranged around an access shaft, (b) a tunnel-type silo consisting of several levels that branch off from a single access level connected to an access shaft, and (c) a vertically-oriented cylindrical tank-type silo. For each type of silo, we have specified the hydrate loading and unloading equipment as well as the cooling system, and have estimated the construction cost.     

Flame acceleration and blast wave of H2–O2–N2–Ar mixtures in unconfined areas

In the present study, the flame acceleration and blast wave of H₂-air and H₂–O₂–N₂–Ar mixtures in nearly unconfined conditions were investigated conducting laboratory-scale and large-scale experiments. In particular, the effect of the volumetric expansion ratio on the flame acceleration examined, because Darrieus-Landau instability is essentially caused by a volumetric expansion of burned gas at flame front. Results demonstrated that the critical Péclet number Pe_c for the onset of flame acceleration decreased with the decrease in the equivalence ratio and the increase in the expansion ratio diluted with Ar. The dimensionless burning velocity increased as the flame radius became larger. The acceleration exponent for H₂-air and H₂–O₂–N₂–Ar mixtures was evaluated. The saturation of the exponent corresponding to the fractal dimension for only very lean H₂-air flame is observed, notwithstanding the value for other mixtures still existed in the transition regime. The blast wave intensity of H₂-air and H₂–O₂–N₂–Ar explosion discussed by the acoustic theory. From the analysis, it is clear the blast wave intensity depends on the expansion ratio, laminar burning velocity and flame acceleration.     

智能滑雪板训练指导系统的研究

为解决冰雪爱好者对滑雪教练的需求，设计出一种基于STM32为核心控制的智能滑雪教练系统。采用零力矩点判定平衡方法来评价用户实时的滑雪状态，决策生成相适应的滑雪指导。经过模拟实验表明，该系统可实现实时姿态采集、动态评价、预先决策，为使用者提供稳定可靠的滑雪指导。     

Effect of Cold Working and Long-Term Heating in Air on the Stress Corrosion Cracking Growth Rate in Commercial TT Alloy 690 Exposed to Simulated PWR Primary Water

The authors have previously reported that the number of cavities at or near grain boundary (GB) carbides in commercial thermally treated (TT) Alloy 690 increases with increasing cold work reduction ratio and with heating temperature in air. In the present work after very long-term heating in air, the number of cavities at or near GB carbides in cold worked commercial TT Alloy 690 was observed to saturate, and the shape and size of the cavities changed. The shape and size of cavities and cracks were categorized, and a GB defect index number was defined as a function of their number, shape and size. Stress corrosion cracking growth rates in a commercial TT Alloy 690 with various levels of cold work exposed to simulated PWR primary water at 633 K (360 °C) have been measured and correlated with the defined GB defect index number. Cavities and cracks in the same materials before and after long-term heating in air have also been correlated with the defined GB defect index number. For the heavily cold worked (≥ 15 pct) commercial TT Alloy 690, a good correlation has been observed between the PWSCCGR and the GB defect index number. By contrast, for lightly cold worked (≤ 10 pct) commercial TT Alloy 690, the SCCGR in the simulated PWR primary water was very low and the GB defect index number was usually zero, regardless of cold working reduction ratio ≤ 10 pct. It is concluded that the mechanism of SCCGR for lightly cold worked TT Alloy 690 in PWR primary water is likely to be different from that for heavily cold worked TT Alloy 690.

     

Levee damage and revetment erosion by the 2019 Typhoon Hagibis in the Chikuma River,Japan

Due to Typhoon Hagibis (Typhoon No. 19) in October 2019, also known as the Reiwa 1 East Japan Typhoon, many parts of the Chikuma River’s levee in Nagano Prefecture were damaged. There were instances of levee collapse due to overtopping, and an electric railway bridge also collapsed when an eroded revetment broke. In the present study, these disasters were investigated.The investigation considered both the geology - geomechanics and the hydraulics of the levee collapse due to overtopping. The results suggest that the most significant factor in the collapse of the levee was structural weakness. There were cases in which the tenacity of a levee was improved by taking simple measures against seepage. It was found that the bridge abutments washed away mainly because the river levee became a water-colliding front due to changes in the water route following the erosion of a sandbar in the process of river level decline after the peak.     

Immobilization of MacMillan Imidazolidinone as Mac‐SILC and its Catalytic Performance on Sustainable Enantioselective Diels–Alder Cycloaddition

MacMillan’s imidazolidinone catalyst was immobilized as a supported ionic liquid catalyst (Mac‐SILC) in the pores of silica gel with the aid of an ionic liquid – 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide. The heterogenized organocatalyst was utilized for the enantioselective Diels–Alder reaction of cyclopentadiene and cinnamaldehyde, recovered by simple filtration and subsequent evacuation, and repeatedly used up to six times in 81% average chemical yield, 87% ee for endo‐ and 80% ee for exo‐products. The Mac‐SILC was effective for a variety of substrates.     

Analysis of disulfoton sulfoxide in chingentsuai by pulsed splitless mass spectrometry using programmed temperature vaporization (PTV) inlet

A peak considered to be due to disulfoton sulfoxide as a metabolite of disulfoton was detected in the analysis of the chingentsuai extraction solution of vegetables by GC-FPD. In the analysis by GC/MS for identification, though the retention time and the mass spectrum were the same as those of the standard, the spectrum was different from MS library data. It appeared that decomposition of disulfoton sulfoxide occurred at the inlet. Therefore, we used a programmed temperature vaporization (PTV) inlet in the pulsed splitless mode to achieve a low inlet temperature and high injection pressure. As a result, the expected mass spectrum of disulfoton sulfoxide was obtained. Under this condition, the peak obtained from chingentsuai was identified as disulfoton sulfoxide. Disulfoton sulfoxide was detected from 2 of 25 chingentsuai samples, at concentrations of 0.66 microg/g and 0.14 microg/g.