研究者業績

高垣 直尚

タカガキ ナオヒサ  (Naohisa Takagaki)

基本情報

所属
兵庫県立大学 工学研究科 機械工学専攻 教授
学位
博士(工学)(2009年3月 京都大学)

連絡先
takagakieng.u-hyogo.ac.jp
研究者番号
00554221
ORCID ID
 https://orcid.org/0000-0002-9672-0920
J-GLOBAL ID
201401024740331854
researchmap会員ID
7000008779

外部リンク

論文

 46
  • Shunsuke Matsushima, Hironori Matsuhisa, Kohki Wakita, Takanori Tsujimoto, Naohisa Takagaki, Itsuro Honda, Yoshihiro Oshima, Osamu Kawanami, Kenji Okada
    The Journal of Thoracic and Cardiovascular Surgery 167(2) 439-449.e6 2024年2月  査読有り
    Objective: This study reviewed the application of curved and bileaflet designs to pulmonary expanded polytetrafluoroethylene conduits with diameters of 10 to 16 mm and characterized this conduit on in vitro experiment, including particle image velocimetry. Methods: All patients who received this conduit between 2010 and 2022 were evaluated. Three 16-mm conduits were tested in a circulatory simulator at different cardiac outputs (1.5-3.6 L/minute) and bending angles (130°-150°). Results: Fifty consecutive patients were included. The median operative body weight was 8.4 kg (range, 2.6-12 kg); 10-, 12-, 14-, and 16-mm conduits were used in 1, 4, 6, and 39 patients, respectively. In 34 patients, the conduit was implanted in a heterotopic position. The overall survival rate was 89% at 8 years with 3 nonvalve-related deaths. There were 10 conduit replacements; 5 16-mm conduits (after 8 years) and 1 12-mm conduit (after 6 years) due to conduit stenosis, and the remaining 4 for reasons other than conduit failure. Freedom from conduit replacement was 89% and 82% at 5 and 8 years, respectively. Linear mixed-effects models with echocardiographic data implied that 16-mm conduits were durable with a peak velocity <3.5 m/second and without moderate/severe regurgitation until the patient's weight reached 25 kg. In experiments, peak transvalvular pressure gradients were 11.5 to 25.5 mm Hg, regurgitant fractions were 8.0% to 14.4%, and peak Reynolds shear stress in midsystolic phase was 29 to 318 Pa. Conclusions: Our conduits with curved and bileaflet designs have acceptable clinical durability and proven hydrodynamic profiles, which eliminate valve regurgitation and serve as a reliable bridge to subsequent conduit replacement.
  • Naohisa Takagaki, Naoya Suzuki, Koji Iwano, Kazuki Nishiumi, Ryota Hayashi, Naoki Kurihara, Kosuke Nishitani, Takumi Hamaguchi
    Coastal Engineering Journal 66(1) 1-14 2023年8月10日  査読有り筆頭著者責任著者
    Accurate estimates of momentum flux through the air-sea interface at very high wind speeds are important for predicting tropical cyclone intensities. To estimate the air-sea momentum flux under the long-fetch condition (20 m fetch) at very high wind speeds using a laboratory tank, a simple momentum flux measurement method using only four water-level gauges is conducted based on the momentum budget method. The air-water momentum flux under long-fetch conditions at very high wind speeds was measured in a typhoon simulation tank at the Research Institute of Applied Mechanics, Kyushu University. The verification was performed using previous values estimated by the eddy correlation method in a typhoon simulation tank at Kyoto University, Japan. The results showed good correlation between the values of momentum flux measured by the present momentum budget method and the other methods. The drag coefficient at very high wind speeds (41 m/s) under long-fetch conditions leveled off, as well as under the short-fetch condition (4.5 m and 6.5 m fetch). Moreover, a very weak relationship was found between the drag coefficient and the fetch. Since the maximum fetch in the present laboratory experiments is 20 m, the future field observation with the longer fetch condition will be needed for applying the results to oceans.
  • Keigo Matsuda, Satoru Komori, Naohisa Takagaki, Ryo Onishi
    Journal of Fluid Mechanics 960 2023年4月  査読有り
    Effects of surface tension reduction on wind-wave growth are investigated using direct numerical simulations of air-water two-phase turbulent flows. The incompressible Navier-Stokes equations for air and water sides are solved using an arbitrary Lagrangian-Eulerian method with boundary-fitted moving grids. The wave growth of finite-amplitude and non-breaking gravity-capillary waves, whose wavelength is less than 0.07 m, is simulated for two cases of different surface tensions under a low-wind-speed condition of several metres per second. The results show that significant wave height for the smaller surface tension case increases faster than that for the larger surface tension case. Energy fluxes for gravity and capillary wave scales reveal that when the surface tension is reduced, the energy transfer from the significant gravity waves to capillary waves decreases, and the significant waves accumulate more energy supplied by wind. This results in faster wave growth for the smaller surface tension case. The effect on the scalar transfer across the air-water interface is also investigated. The results show that the scalar transfer coefficient on the water side decreases due to the surface tension reduction. The decrease is caused by suppression of turbulence in the water side. In order to support the conjecture, the surface tension effect is compared with laboratory experiments in a small wind-wave tank.
  • Takagaki Naohisa, Sasaki Santa, Suzuki Naoya, Goda Soichiro, Troitskaya Yuliya, Komori Satoru
    Journal of Advanced Marine Science and Technology Society 27(1) 63-72 2022年7月30日  査読有り筆頭著者責任著者
  • Suzuki Naoya, Ueda Yohei, Takagaki Naohisa, Ueki Iwao, Ikeda Atsutoshi
    Journal of Advanced Marine Science and Technology Society 27(1) 73-79 2022年7月30日  査読有り

MISC

 19

講演・口頭発表等

 154

担当経験のある科目(授業)

 19

所属学協会

 7

共同研究・競争的資金等の研究課題

 25

産業財産権

 1

社会貢献活動

 7