混相流
Online ISSN : 1881-5790
Print ISSN : 0914-2843
ISSN-L : 0914-2843
最新号
選択された号の論文の6件中1~6を表示しています
【特集】気候変動と混相流
  • 水田 亮
    原稿種別: 特集
    2023 年 37 巻 4 号 p. 368-375
    発行日: 2023/12/15
    公開日: 2024/01/14
    ジャーナル フリー

    High-resolution atmospheric, climate large-ensemble simulations are used to assess future changes in heavy rainfall events. In most parts of the world, the rate of increase in precipitation is noticeably larger for events occurring once in 100 years than those occurring once every year. The increase can be decomposed into two contributions. One is that from water vapor in the atmosphere that increases ~7% per 1-K temperature rise. The other is that from upward motion that lifts up near-surface water vapor to condensate into rainfall. The simulation results show that the upward motion in the middle and upper troposphere conspicuously increases for the events occurring once in 100 years.

  • 山野井 一輝, 藤田 正治
    原稿種別: 特集
    2023 年 37 巻 4 号 p. 376-383
    発行日: 2023/12/15
    公開日: 2024/01/14
    ジャーナル フリー

    Under the background of enrichment of the precipitation database, which is based on the climate change projection, future-change projection of flood risk is already developing. However, when we focus on the sediment-related hazard on a watershed scale, sediment production and transport in the catchment should be carefully treated. In this description paper, firstly, we introduce the structure of the simulation model SiMHiS, composed of a sediment production and supply model based on landslide prediction, rainfall infiltration and runoff, and sediment transport in the channel system. Secondly, we introduce a future-projection result in the Akatani River watershed in Northern Kyushu Island, Japan, damaged by heavy rainfall in 2017. Maximum water discharge, total volume of sediment discharge, maximum water level, and maximum riverbed level at specific locations are selected as indicators for the assessment. For the rainfall data, local extreme values of heavy rainfall data that occurs in northern Kyushu during the rainy season were given to the simulation to evaluate the future change of the extreme event by using the limited period of the dataset. The results showed a clear increasing trend for all indexes, indicating that phenomena of a scale that does not occur in the current climate might occur. We also discussed the possibility of statistical and quantitative evaluation in future studies using our method with the precipitation dataset, which has finer spatiotemporal resolution and a more extended period.

  • 伴野 雅之
    原稿種別: 特集
    2023 年 37 巻 4 号 p. 384-391
    発行日: 2023/12/15
    公開日: 2024/01/14
    ジャーナル フリー

    Sea level rise is expected to cause significant normal-state shoreline retreat and higher waves due to changes in wave climate are expected to cause significant temporary shoreline retreat. The shoreline changes will increase the risk of coastal disasters. The Bruun rule is currently widely used to predict shoreline retreat due to sea level rise, although its reliability should be improved. The effective use of long-term beach monitoring data with deep neural networks can lead to a better understanding of the processes of beach response to sea level rise.

【論文】
  • 村瀬 道雄, 西田 浩二, 高木 俊弥, 喜多 新一郎, 栗本 遼, 林 公祐, 冨山 明男
    原稿種別: 研究論文
    2023 年 37 巻 4 号 p. 392-400
    発行日: 2023/10/30
    公開日: 2024/01/14
    [早期公開] 公開日: 2023/10/30
    ジャーナル フリー

    The wall friction term in a one-dimensional model vanishes under the stagnant liquid conditions (i.e. the liquid volume flux JL = 0). Hence void fraction αG(ΔP) in rod bundles have been evaluated using measured pressure gradients dP/dz. However, effects of the wall friction term on αG(ΔP) have not been quantitatively evaluated. In this study, we therefore carried out air-water experiments using a 3×3 rod bundle under the conditions of JL = 0, and measured dP/dz and αG,exp with the closing valve method. We obtained the dimensionless wall friction force Fw* (= αG(ΔP)-αG,exp) from the measured dP/dz and αG,exp. The Fw* values were expressed by using the gas volume flux JG, because the liquid flow field was induced by the gas flow (i.e. JG). The difference between αG,exp and αG(ΔP) was reduced by half after αG(ΔP) was corrected using the obtained correlation for Fw*. The Fw* correlation was applied to existing αG(ΔP) data for 4×4 and 8×8 bundles, and effects of Fw* on the αG(ΔP) values were confirmed to be small in a large rod bundle due to the small wall area per unit fluid volume.

  • Toshiya TAKAKI, Masaki YAMASHITA, Ryo KURIMOTO, Kosuke HAYASHI, Mi ...
    原稿種別: research-article
    2023 年 37 巻 4 号 p. 401-411
    発行日: 2023/11/24
    公開日: 2024/01/14
    [早期公開] 公開日: 2023/11/24
    ジャーナル フリー

    In our previous studies, we carried out air-water counter-current flow experiments under flooding conditions in vertical pipes of 40 mm diameter with combinations of sharp-edged or rounded top and bottom ends to measure counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction αG. We obtained the wall and interfacial friction factors, fw and fi, and proposed a correlation of fw. In the present study, we carried out similar experiments with sharp-edged top and bottom ends, and obtained fw and fi. We proposed a correlation of fi for all flow patterns including smooth film (SF) and rough film (RF) due to flooding at the top and bottom ends, respectively. By using the one-dimensional annular flow model and the proposed fw and fi correlations, we computed the liquid volume fraction αL,cal and compared it with the experimental data αL,exp. The computation gave two solutions of αL,cal for SF and RF, which agreed relatively well with the αL,exp values for SF and RF in the regions of low gas superficial velocity JG and high JG, respectively.

  • 富岡 薫平, 奥山 邦人
    原稿種別: 研究論文
    2023 年 37 巻 4 号 p. 412-420
    発行日: 2023/11/30
    公開日: 2024/01/14
    [早期公開] 公開日: 2023/11/30
    ジャーナル フリー

    Passive production of synthesis gas from liquid methanol using a packed bed of porous particles supporting a catalyst is investigated. Heating of an upper side of the packed tube the bottom of which is immersed in liquid methanol causes upward flow by the capillary action enhanced by evaporation and syn-gas is produced in temperature increased dried region. The extension of the dried region toward the wetted region reduces considerably the responsiveness in the productions of the reactant vapor and syn-gas due to the high flow resistance of the bed. Utilization of a combined particle bed, which consists of two different size particles geometrically arranged and separates the dried and wetted regions to the prescribed ranges, allows low flow resistance and, as a result, causes significant increases in the mass flow rate and the responsiveness.

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