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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.
Enhanced electrochemical strain in polypyrrole films
Takaharu Nakashima,Devendra Kumar,Wataru Takashima,Tetsuji Zama,Susumu Hara,Shingo Sewa,Keiich Kaneto 한국물리학회 2005 Current Applied Physics Vol.5 No.2
Electrochemomechanical characteristics of polypyrrole (PPy) lms, electrodeposited from tetra-n-butylammonium triuorometh-ane-sulfonate dissolved in methyl benzoate (PPyFMS), have been investigated using a simultaneous measurement of electrochem-omechanical deformation (ECMD) with cyclic voltammetry (CV) by comparing with PPy lms deposited fromp-phenol sulfonate inaqueous media (PPyPPS). The ECMD magnitude of PPyFMS lm was reached around 9% at 1st cycle and was decreased to beabout 3.2% at 20th cycle with electrochemical cycling in 1 M NaPF6. While in 1 M NaCl solution, the ECMD magnitude was1.9% at 20th cycle in CV measurement. In the case for the PPyPPS lm, ECMD magnitude at 20th cycle was around 0.8% and1.1% in 1 M NaPF 6 and 1 M NaCl solutions, respectively. The results indicate that the combination of electrolytes employed inboth the electrodeposition and the device actuation plays the very important role for achieving the enhancement of ECMD magn-itudes. In the case of ECMD behaviors, it was found that the electrolyte used in the lm actuation determines the ECMD charac-teristics..