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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.
Modeling o fRebound Phenomenon between Ball and Racket Rubber with Spinning Effect
Akira Nakashima,Yosuke Kobayashi,YukiOgawa,YoshikazuHayakawa 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
We model the rebound phenomenon between a ping-pong ball and the table/racket rubber. In the model between the ball and racket rubber, it is assumed that the kinetic energy of the contact velocity is stored as the potentialen ergy due to the elasticity of the rubber. This assumption leads to that the impulse in the horizontal direction is propor-tional to the contactve locity. The vertical and horizontal COR in the models of the table and rubber are identified with the measured velocity and spin of the ball by high-speed vision sensors. The models are verified by other experimental data.
Hiroaki Nakashima,Tokumi Kanemura,Kotaro Satake,Yoshimoto Ishikawa,Jun Ouchida,Naoki Segi,Hidetoshi Yamaguchi,Shiro Imagama 대한척추외과학회 2019 Asian Spine Journal Vol.13 No.5
Study Design: Prospective cohort study. Purpose: To identify factors that affect sagittal alignment correction in lateral lumbar interbody fusion (LIF) surgery for adult spinal deformity (ASD) and to investigate the degree of correction in each condition. Overview of Literature: LIF is a useful procedure for ASD, but the degree of correction can be affected by posterior osteotomy, intraoperative endplate injury, or anterior longitudinal ligament (ALL) rupture. Methods: Radiographical data for 30 patients who underwent LIF for ASD were examined prospectively. All underwent two-stage surgery (LIF followed by posterior fixation). Radiographical parameters were measured preoperatively, after LIF, and after posterior fixation; these included the segmental lordotic angle, lumbar lordosis (LL), and other sagittal alignment factors. Results: LL was corrected from 16.5°±16.7° preoperatively to 33.4°±13.8° after LIF (p<0.001) and then to 52.1°±7.9° following posterior fixation (p<0.001). At levels where Schwab grade 2 osteotomy was performed, the acquired segmental lordotic angles from the preoperative value to after posterior fixation and from after LIF to after posterior fixation were 19.5°±9.2° and 9.9°±3.9°, respectively. On average, 12.4° more was added than in cases without osteotomy. Endplate injury was identified at 21 levels (19.4%) after LIF, with a mean loss of 3.4° in the acquired segmental lordotic angle (5.3°±8.4° and 1.9°±5.9° without and with endplate injury, respectively). ALL rupture was identified at seven levels (6.5%), and on average 19.3° more was added in these cases between the preoperative and postoperative values than in cases without ALL rupture. Conclusions: LIF provides adequate sagittal alignment restoration for ASD, but the degree of correction is affected by grade 2 osteotomy, intraoperative endplate injury, and ALL rupture.