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排序方式: 共有1038条查询结果,搜索用时 15 毫秒
91.
Daisuke Hiramatsu Yoichi Uemura Shinji Uemoto Junji Okumoto Takehiko Imai Mikio Kakiuchi Ken Nagakura Masafumi Fujita Toru Otaka 《Electrical Engineering in Japan》2011,177(3):17-27
Two‐pole large generators are extensively used in power utilities. Growing demand for electric power in recent years has led to substantial increases in the capacity of generators. In line with this trend, our company has manufactured two‐pole turbine generators in the 900,000‐kVA to 1,200,000‐kVA classes. As the capacity of generators becomes larger, equivalent circuits are increasingly expected to improve their precision in estimating operation characteristics. The Park model has been widely used as an equivalent circuit model. The Park model with quadrature axis transient reactance $x_{q}^{\prime}$ is claimed to be useful for accurately estimating the load rejection characteristics of turbine generators. However, it is difficult to measure $x_{q}^{\prime}$, few studies based on measured data have appeared. As one of the few examples, we have conducted a measured data on a 500,000‐kVA‐class generator. Recently, the authors obtained test data on $x_{q}^{\prime}$ of a 900,000‐kVA‐class generator. In this study, based on these data, we studied the effect of $x_{q}^{\prime}$ using the finite element method and a transient analysis program (EMTP‐ATP). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(3): 17–27, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21099 相似文献
92.
A coalescence-fragmentation model has been developed to predict the behaviors of coal mineral particles during the combustion of pulverized bituminous coals or coal blends. Based on the computer-controlled scanning electron microscope (CCSEM) characterization of coal minerals, the particle size distributions (PSDs) and mineral species of ash particles can be simulated. In particular, the interactions among excluded minerals (mainly referring to the excluded Ca-bearing-species and Fe-bearing-species) and included minerals are accounted for in this model. The PSDs and the mineral species of ash particles are derived from the coalescence and fragmentation of coal mineral particles. Based on this proposed model, both of the predicted PSDs and the mineral species of ash particles are in good agreement with their corresponding experimentally measured values. And the comparisons further demonstrate that the combined effects of coalescence of included minerals and fragmentation of excluded minerals have direct impacts on the ash-forming process. In addition, for the coals rich in excluded Ca- and/or Fe-bearing-species, the interactions among included minerals and excluded minerals are another important mechanism governing ash formation for high-rank coals. 相似文献
93.
Different expressions are used in the literature for the stress intensity factors of interface cracks between anisotropic
material. In particular, two of these approaches will be discussed and compared for orthotropic and monoclinic materials.
Relations between the stress intensity factors will be found. Expressions for the interface energy release rate Gi{\mathcal{G}_i} are presented. Although the expressions appear different, they are shown to be the same by using the relations between the
stress intensity factors. Phase angles are defined which may be used in a fracture criterion. 相似文献
94.
Toru Ohira 《Artificial Life and Robotics》2010,15(4):436-438
A rather peculiar phenomenon has been observed while a human was balancing a stick on a fingertip. The balancing time improved
when the subject moved another object with the other hand. This was particularly so for many subjects with medium stick balancing
skills. On the basis of this example, I consider how this seemingly simple task is composed of intricate mixtures of feedback
delay, fluctuations, and predictions. I present some simple models of dynamics in which these factors lead to complex behaviors.
From these examples, I infer that the concept of “nonlocality” could play an important role in characterizing biological and
physiological systems. 相似文献
95.
Toru Nagaoka Yoshiaki Morisada Masao Fukusumi Tadashi Takemoto 《Metallurgical and Materials Transactions B》2010,41(4):864-871
To obtain sound butt-joints of 5056 aluminum alloy rods, ultrasonic-assisted soldering was conducted using Zn-18Sn and Zn-60Sn
alloys. Each solder foil was inserted between rods of 5056 aluminum alloy. Ultrasonic vibration was propagated to faying surfaces
at soldering temperatures below the liquidus temperature of the solder alloys, and then the samples were air cooled to room
temperature. The optimum vibration time at the soldering temperature must be more than 2 seconds to have complete wetting
and less than 4 seconds to avoid excessive dissolution of the 5056 alloy. The 5056 alloy joints soldered using quasi-melting.
Zn-Sn alloys showed greater strength than the joints soldered at the temperatures over its respective liquidus temperature.
As the soldering temperature was increased, the increased formation of the intermetallic compound Mg2Sn or phases containing Mg generated by dissolution of 5056 into the solder layer decreased the joint strength. Ultrasonic-assisted
soldering at an optimum temperature between solidus and liquidus of the Zn-Sn alloys is an important consideration for producing
sound joints with sufficient strength. 相似文献
96.
97.
Russell G. Keanini Jack L. Ferracane Toru Okabe 《Metallurgical and Materials Transactions B》2001,32(3):409-416
This article reports an experimental and theoretical investigation of mercury dissolution from dental amalgams immersed in
neutral (noncorrosive) and acidic (corrosive) flows. Atomic absorption spectrophotometric measurements of Hg loss indicate
that in neutral flow, surface oxide films formed in air prior to immersion persist and effectively suppress significant mercury
release. In acidic (pH 1) flows, by contrast, oxide films are unstable and dissolve; depending on the amalgam’s material composition,
particularly its copper content, two distinct mercury release mechanisms are initiated. In low copper amalgam, high initial
mercury release rates are observed and appear to reflect preferential mercury dissolution from unstable Sn8Hg (γ
2) grains within the amalgam matrix. In high copper amalgam, mercury release rates are initially low, but increase with time. Microscopic examination suggests that this feature reflects corrosion of copper from grains of Cu6Sn5 (η′) and consequent exposure of Ag2Hg3 (γ
1) grains; the latter serve as internal mercury release sites and become more numerous as corrosion proceeds. Three theoretical
models are proposed in order to explain observed dissolution characteristics. Model I, applicable to high and low copper amalgams
in neutral flow, assumes that mercury dissolution is mediated by solid diffusion within the amalgam, and that a thin oxide
film persists on the amalgam’s surface and lumps diffusive in-film transport into an effective convective boundary condition.
Model II, applicable to low copper amalgam in acidic flow, assumes that the amalgam’s external oxide film dissolves on a short
time scale relative to the experimental observation period; it neglects corrosive suppression of mercury transport. Model
III, applicable to high copper amalgam in acidic flow, assumes that internal mercury release sites are created by corrosion
of copper in η′ grains and that corrosion proceeds via an oxidation-reduction reaction involving bound copper and diffusing hydrogen ions. The models appear to capture the correct
time dependence of each dissolution mechanism and to provide reasonable fits to the experimental data. 相似文献
98.
99.
Osamu Nakagawa Haruo Shimamoto Tetsuya Ueda Kou Shimomura Tsutomu Hata Toru Tachikawa Jiro Fukushima Toshinobu Banjo Isamu Yamamoto 《Journal of Electronic Materials》1989,18(5):633-643
As electronic devices become more highly integrated, the demand for small, high pin count packages has been increasing. We
have developed two new types of IC packages in response to this demand. One is an ultra thin small outline package (TSOP)
which has been reduced in size from the standard SOP and the other, which uses Tape Automated Bonding (TAB) technology, is
a super thin, high pin count TAB in cap (T.I.C.) package. In this paper, we present these packages and their features along
with the technologies used to improve package reliability and TAB. Thin packages are vulnerable to high humidity exposure,
especially after heat shock.1 The following items were therefore investigated in order to improve humidity resistance: (1)
The molding compound thermal stress, (2) Water absorption into the molding compound and its effect on package cracking during
solder dipping, (3) Chip attach pad area and its affect on package cracking, (4) Adhesion between molding resin and chip attach
pad and its affect on humidity resistance. With the improvements made as a result of these investigations, the reliability
of the new thin packages is similar to that of the standard thicker plastic packages. 相似文献
100.