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Study on Flow Instability and Countermeasure in a Draft tube with Swirling flow
Nakashima, Takahiro,Matsuzaka, Ryo,Miyagawa, Kazuyoshi,Yonezawa, Koichi,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.4
The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.
Nakashima Hiroaki,Kanemura Tokumi,Satake Kotaro,Ito Kenyu,Ishikawa Yoshimoto,Ouchida Jun,Segi Naoki,Yamaguchi Hidetoshi,Imagama Shiro 대한척추외과학회 2020 Asian Spine Journal Vol.14 No.3
Study Design: Retrospective comparative study.Purpose: We compared clinical and radiographical outcomes after lumbar decompression revision surgery for restenosis by lateral lumbar interbody fusion (LLIF) and posterior lumbar interbody fusion (PLIF).Overview of Literature: Indirect lumbar decompression with LLIF was used to treat degenerative lumbar diseases requiring neural decompression. However, only a few studies have focused on the effectiveness of this technique for restenosis after lumbar decompression.Methods: We retrospectively investigated 52 cases involving lumbar interbody fusions for restenosis with spondylolisthesis after lumbar decompressions; these cases consisted of 15 patients who underwent indirect decompression with LLIF and posterior fixation and 37 patients who underwent the same procedure with PLIF. We compared Japanese Orthopaedic Association (JOA) scores and perioperative complications between groups. The cross-sectional areas of the thecal sac on magnetic resonance imaging were measured before, immediately after, and 2 years after surgery. We conducted statistical analyses using unpaired t -test and Fisher’s exact tests, and a <i>p</i> -value <0.05 was considered statistically significant.Results: The operative time was significantly shorter in the LLIF group than in the PLIF group (115.3±33.6 min vs. 186.2±34.2 min, respectively; <i>p</i> <0.001). In addition, the intraoperative blood loss was significantly lower in the LLIF group than in the PLIF group (58.2±32.7 mL vs. 303.2±140.1 mL, respectively; <i>p</i> <0.001). We found two cases of transient lateral thigh weakness (13.3%) in the LLIF group and five cases of incidental durotomy, one case of deep infection, and one case of neurological deterioration in the PLIF group—resulting in a higher complication incidence (18.9%), although it did not reach (<i>p</i> =0.63). The JOA scores improved significantly in both groups.Conclusions: Indirect decompression using LLIF provided acceptable clinical and radiographical outcomes in patients with restenosis with spondylolisthesis after lumbar decompression; no revision-surgery-specific complications were found. Our results suggest that LLIF is a safe and minimally invasive procedure for revision surgery.
Ferroelectric and Magnetoelectric Properties of BiFeO3 Thin Films Prepared on a Membrane Structure
Seiji Nakashima,Kwi-Young Yun,Masanori Okuyama,Yoshitaka Nakamura 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Multiferroic BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2 membrane and Pt/TiO2/SiO2/Si plate structures by using pulsed laser deposition. The X-ray diffraction pattern of the BFO thin film on the membrane structure slightly shifted to lower angle compared to that of the film on the Pt/TiO2/SiO2/Si substrate. Ferroelectric hysteresis loops were also obtained successfully at a measurement temperature of 150 K. The BiFeO3 thin film on the membrane structure showed a remanent polarization (Pr) of 91 μC/cm2 for a maximum applied voltage of 20 V, which was larger than that of the film on the Pt/TiO2/SiO2/Si plate structure at the same measurement conditions (Pr: 54 μC/cm2). Under a magnetic field perpendicular to the film plane, the remanent polarization (Pr) of the BiFeO3 thin film on the membrane structure at 150 K increased from 91 μC/cm2 (0 T) to 97 μC/cm2 (1.1 T).
Maximum-Efficiency Tracking Scheme for Piezoelectric-Transformer Inverter with Dimming Control
Satoshi Nakashima,Hiroshi Ogasawara,Hidenori Kakehashi,Tamotsu Ninomiya 전력전자학회 2001 ICPE(ISPE)논문집 Vol.2001 No.10
This paper provides a solution for the problem of efficiency decrease caused by load variation. A novel control scheme of tracking the PT's operation frequency for the maximum efficiency is proposed. As a result, a high efficiency over 80% has been achieved even under the output-current decrease down to 10% of the full load current.