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Teaching De-Anglo-Americanized English for International Communication
( Nobuyuki Hino ) 한국영어영문학회 2014 영어 영문학 Vol.60 No.1
In the age of globalization, languages leave the hands of their native speakers. This trend is especially conspicuous with English today, sometimes referred to as “Englishes,” symbolizing the linguistic and cultural diversity in the three circles of English.the Inner Circle (e.g. British English), the Outer Circle (e.g. Indian English), and the Expanding Circle (e.g. Korean English). While the traditional teaching of English based on Anglo-American values should certainly continue in its own right, substantial changes are required when the purpose of English language education is focused on international communication. This paper discusses how English may be taught as a lingua franca beyond the linguistic and cultural framework of native speakers, as to the issues of materials, methodologies, and models. In short, the content of teaching materials needs to reflect the diversity of English including non-native varieties. Methodologies for teaching English should also be accommodated in accordance with local sociocultural factors. Most significantly, models of English will be liberated from native speaker norms for free expression of indigenous values. As concrete examples of such pedagogical practice, the author`s efforts to teach de-Anglo-Americanized English are presented. They include a weekly radio talk-show program between non-native speakers of English for which he served as the host, as well as his current university classes where real-time news across the world are used as authentic materials to enable the students to participate in the community of users of English as an international language.
Effects of Pressure Ratios of Axial Flow Compressors on the Deep Surge Frequencies
Nobuyuki Yamaguchi 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.4
Effects of compressor pressure ratios and flowpath geometries on the frequencies of deep-surges in multi-stage axial flow compressors are studied on the basis of numerical experiments. The frequencies tend generally to lower in a complicated manner toward higher rpms and higher pressure ratios of the compressors. The general behaviors of the frequencies are found to be described in large in terms of an effective reduced surge frequency numerical-experimentally searched for. The parameter tends to keep a nearly constant level of values for a wide range of stalling pressure ratios, rpms, and number of stages of compressors. For multi-stage compressors, however, at slightly below the design speed, the parameter values tend to drop rather steeply, and above the speed, they tend to keep again a new constant level of values at the lowered level. The transition of the behavior is more significant for the conditions of compressors designed for higher pressure ratios and in shorter delivery flow-paths. It could be attributed to the effect of a relocation of surge-triggering stages in the local zone of the surge flow mode with the amplitude varying much in the axial direction. The detailed phenomena involved in the behaviors will be clarified in Part 2.
Nobuyuki Yamaguchi 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4
Macroscopic behaviors of the frequencies of deep-surges in systems of multi-stage compressors and flowpaths could be evaluated very roughly by a constant value of an effective reduced surge frequency fRsmeff, as described in Part I ofthe present study. However, some deviations from the rough average value could often appear, depending on the situations of the concerned systems. In the present study, the causes of the deviations are made clear by examinations on the numerical results. The deviations are concerned with the following three conditions; (1) a multi-stage compressor having a sufficiently high design pressure-ratio, (2) changes in the compressor speeds through near the design speed, and (3) a sufficiently short delivery plenum. In the situations affected by combined effects of the above three, the compressor could be located in a zone of the surge flow mode where the amplitude could vary noticeably in the axial direction. When the stall-responsible stages relocate from the front stages to the rear ones within the zone during the speed increase through near the design speed, the small difference in the relative location of the stall-responsible stages in the surge mode could sensitively affect the surge behaviors and lower the surge frequency. In the situations, incomplete stall recoveries, and sometimes subharmonic surges, tend to occur additionally, elongating the deep-surge periods and lowering the surge frequencies. It should be emphasized from the aspects of numerical-experimental observations that very local events as such could happen to have significant effects on the surge phenomena.
A Comprehensive View to Surge Frequencies and Stall Stagnations in Axial Flow Compressor Systems
Nobuyuki Yamaguchi 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2
Essential features of compressor surge phenomena are found to be described by the following two non-dimensional parameters; a resonance excitation frequency and a surge frequency parameter. The former is the number of times of excitations by the system resonance frequency given to the fluid particle in the time required for the particle to pass through the whole flowpath, or, in short, the resonance frequency multiplied by the passing time. The latter is the number of surge cycles repeated in the particle passing time. When multiplied by corresponding Mach number of the compressor tip speed, both parameters become nearly independent of the compressor speeds. Both parameters construct numerical-experimentally a whole picture of the surge behaviors on the basis of simulation results. It shows the behaviors of surge frequencies and the stall stagnation limits affected by the resonance excitation frequency under the influence of various factors, such as flowpath configurations, relative locations of the compressor in the flowpath, numbers of compressor stages, compressor speeds and operating conditions, pressure ratios, etc. The growth or decay of surge actions and the stagnation occurrences are found to be controlled essentially by the resonance excitation frequency. For less than some specified value of the resonance excitation frequency, stall stagnations will occur. On the other hand, sufficient magnitude of the parameter value will develop deep surges. It could be employed also as a relatively simple and reasonable criterion for the stall-stagnation boundary.
Macroscopic Features of Surge Behaviors in Axial Flow Compressors
Nobuyuki Yamaguchi 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2
An essential parameter governing the surge behaviors in compressor systems was found on the basis of numerical-experimental results by surge simulations. It is named “flowpath-average reduced resonance frequency”, consisted of the resonance frequency, the total flowpath length and the average velocity. The reduced frequency normalized by the compressor tip Mach number tends to be basically about 1.5 at the stall stagnation boundaries for compressors having few stages and low pressure-ratios, although the value could vary to some extent affected by various circumstantial factors. It means that the stall stagnations could be caused by insufficient number of times of excitations by the resonant frequency on the fluid particles in passing through the whole flowpath. Deep surges tend to occur for the parameter values greater than around 1.5. On the foundation of the normalized flowpath-average reduced resonance frequency can be formed a basic framework for the surge behaviors in terms of non-dimensional surge frequencies and stall-stagnation points. In reference to the framework, several general features of the surge behaviors are described in a relatively unified manner, including the behaviors of surge frequencies and stall stagnation boundaries, which are affected in a complicated manner by compressor conditions of speeds, pressure ratios, and number of stages, and flowpath geometries, relative compressor locations in the flowpath, etc. The framework contributes much to clarification of the characteristic behaviors in surges hitherto unexplained and could provide keys to further surge studies. It could also be useful to devise countermeasures against stall stagnation problems.