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A Study on the Fundamental Surge Frequencies in Multi-Stage Axial Flow Compressor Systems
Nobuyuki Yamaguchi 한국유체기계학회 2014 International journal of fluid machinery and syste Vol. No.
Surge phenomena in multi-stage axial flow compressors were studied with attention to the frequency behaviors. A new parameter “volume-modified reduced surge frequency” was introduced, which took into consideration the essential surge process, i.e., emptying and filling of the working gas in the delivery plenum. The behaviors of the relative surge frequencies at the stall stagnation boundaries, compared with the corresponding duct resonance frequencies, have demonstrated the existence of two types of surges; i.e., a near-resonant surge and a subharmonic surge. The former, which has fundamentally a near-resonance frequency, occurs predominantly at the stall stagnation boundary for the short-and-fat plenum delivery flow-path and the long-and-narrow delivery duct flow-path, and possibly in the intermediate conditions. The latter, which has a subharmonic frequency of the fundamental near-resonant one and occurs mainly in the inter-mediate zone, is considered to be caused by the reduced frequency restricted to a limited range. In relation with those dimensionless frequencies at the stall stagnation boundary, the surge frequency behaviors in more general situations away from the boundaries could be estimated, though very roughly.
Fertility-preserving hormonal therapy in young patients with early-stage endometrial cancer
( Nobuyuki Susumu ) 대한산부인과학회 2017 대한산부인과학회 학술대회 Vol.103 No.-
Endometrial cancer (EC) is the most common gynecological cancer in developed countries, and it’s incidence is constantly increasing. Atypical endometrial hyperplasia (AEH) is the precursor of type 1 EC. EC and AEH sometimes occur before the age of 40. Risk factors for endometrial carcinoma include a history of nulliparity or infertility including polycystic ovarian syndrome (PCOS), irregular menstrual cycles, obesity, diabetes mellitus, and hypertension, and so on. Standard treatment for EC and AEH is total hysterectomy and bilateral salpingo-oophorectomy, however, young patients with early-stage EC and AEH in reproductive age often hope to preserve their fertility. Criteria for conservative treatment include well-differentiated (grade1) endometrioid adenocarcinoma, or AEH, no myometrial invasion, no extra-uterine involvement, no contraindications for medical management, and strong desire for preservation of fertility. However, the data of long-term and pregnancy-related outcomes are limited for fertility- preserving therapy for EC and AEH. Medroxyprogesterone acetate (MPA), megestrol acetate (MA), and intrauterine system-levonorgestrel (IUS-LNG) are often used for fertility-preserving therapy. KGOG2002 study retrospectively analyzed the long-term oncologic outcomes of a fertility-sparing management using oral progestin MPA or MA in 148 patients of presumed stage IA, grade 1, with no myometrial invasion, and showed 78% as complete response (CR) rate, 68% as 5-year recurrence- free survival (RFS) rate. A multicenter prospective phase II study in Japan enrolled 28 patients having EC at presumed stage IA and 17 patients with AEH, and revealed that CR rate was 55% in EC and 82% in AEH, and 47% recurred between 7 and 36 months. In Keio University hospital, we retrospectively reviewed the long-term outcomes of fertility-preserving hormonal therapy using MPA for 142 grade 1 EC patients, 4 grade 2 EC patients, and 102 AEH patients. Median follow-up period was 38 months. In initial MPA therapy, pathological CR rate was 97% in AEH, 90% in G1/G2. After MPA therapy, we experienced 116 times pregnancies in 84 patients, and got 84 alive children. The pregnancy rate was 34% in AEH, 32% in G1/G2. 5 year-RFS rate was 45% in AEH, 17% in G1/G2, and after delivery or abortion, 5 year-RFS rate was 65% in AEH, 38% in G1/G2. We experienced 15 double cancers, including 11 patients with ovarian cancers. Fertility-preserving hormonal therapy in young patients with early-stage endometrial cancer is highly effective and safe, however, careful management is needed during and after hormonal therapy, and even after successful pregnancy.
Nobuyuki Yamaguchi 한국유체기계학회 2014 International journal of fluid machinery and syste Vol. No.
Surge phenomena in the zone of reduced speeds in a system of a nine-stage axial flow compressor coupled with ducts were studied analytically by use of a surge transient simulation code. Main results are as follows. (1) Expansion of apparently stable, non-surge working area of the pressure vs. flow field beyond the initial stage-stall line was predicted by the code in the lower speed region. The area proved analytically to be caused by significantly mismatched stage- working conditions, particularly with the front stages deep in the rotating stall branch of the characteristics, as was already known in situ and in steady-state calculations also. (2) Surge frequencies were found to increase for decreasing compressor speeds as far as the particular compressor system was concerned. (3) The tendency was found to be explained by a newly introduced volumemodified reduced surge frequency. It suggests that the surge frequency is related intimately with the process of emptying and filling of air into the delivery volume. (4) The upstream range of movement of the fluid mass having once passed through the compressor in surge was found to reduce toward the lower speeds, which could have caused additionally the increase in surge frequency. (5) The concept of the volume- modified reduced surge frequency was able to explain, though qualitatively at present, the behaviors of the area- pressure ratio parameter for the stall stagnation boundary proposed earlier by the author.
Nobuyuki Kasa,Takahiko Iida 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
This paper presents a newly developed transformer-less single phase inverter for a photovoltaic (PV) power system In the proposed system, there is no earth-leakage current at all in the theoretical base, and the main circuit of this system is rather simple and it is expected the higher efficiency will be teahzed The system is operated by a digital signal processor (DSP) which makes it more flexible in the control. From the experimental results, it is found that this new inverter supplies the AC power to utility grid line with the power factor of nearly unity.<br/>
Analytical Study on Stall Stagnation Boundaries in Axial-Flow Compressor and Duct Systems
Nobuyuki Yamaguchi 한국유체기계학회 2013 International journal of fluid machinery and syste Vol.6 No.2
Stall stagnations in the system of axial-flow compressors and ducts occur in transition from deep surge conditions to decayed or converged stall conditions. The present study is concerned with the boundaries between the deep surges and the stagnation stalls on the basis of analytical results by a code on surge transients analysis and simulation. The fundamental acoustical-geometrical stagnation boundaries were made clear from examinations of the results on a variety of duct configurations coupled with a nine-stage compressor and a single stage fan. The boundary was found to be formed by three parts, i.e., B- and A-boundaries, and an intermediate zone. The B-boundary occurs for the suction-duct having a length of about a quarter of the wave-length of the first resonance in the case of very short and fat plenum-type delivery duct. On the other hand, the A-boundary occurs for the long and narrow duct- type delivery flow-path having a length about a fifth of the wavelength and relatively small sectional area in the case of short and narrow suction ducts. In addition to this, the reduced surge-cycle frequencies with respect to the duct lengths are observed to have respective limiting values at the stagnation boundaries. The reduced frequency for the B-boundary is related with a limiting value of the Greitzer's B parameter. The tendency and the characteristic features of the related flow behaviors in the neighborhood of the boundaries were also made clearer.