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How to model the contractive behavior of soil in a heating test

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Underground Space 2016年第1期1卷 30-43页

作者： Feng Zhang yuhei Kurimoto Nagoya Institute of Technology Japan Graduate School of Engineering Nagoya Institute of TechnologyJapan

In this paper,the thermodynamic behavior of soil was observed in well-known heating tests via a simulation,which included THMcoupled finite element analysis as the boundary value problem(BVP).The primary purpose of the paper was to identify the necessity to model a phenomenon called‘the volumetric contraction of soft clay due to heating’by introducing some extra parameters in the thermoelastoplastic model in which the THM analyses were *** on the simulation,it was determined that the heating test is only a BVP,and the phenomenon is simply an average behavior of the BVP,not an inherent property of *** on the universal rule that any material will expand when heated,it is not necessary to introduce an extra parameter into a properly organized thermo-elastoplastic model to describe the *** results may provide a useful insight for researchers who are interested in modeling the thermodynamic behavior of soils.

关键词： THM analysis Thermo-elasto-viscoplastic model Heating test Normal and over-consolidated clay

Simultaneous Oxidization of NO_x and SO_2 by a New Non-thermal Plasma Reactor Enhanced by Catalyst and Additive

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Plasma Science and Technology 2008年第1期10卷 53-56页

作者： Heejoon KIM 韩军 yuhei SAKAGUCHI Wataru MINAMI Department of Ecological Engineering Toyohashi University of Technology Hnbei Province Key Laboratory of Coal Conversion and New Carbon Materials Wuhan University of Science and Technology

The non-thermal plasma as one of the most promising technologies for removing NOx and SO2 has attrm^ted much attention. In this study, a new plasma reactor combined with catalyst and additive was developed to effectively oxidize and remove NOx and SO2 in the flue gas. The experimental results showed that TiO2 could improve the oxidation efficiency of SO2 in the case of applying plasma while having a negative effect on the oxidation process of NO and NOx. With the addition of NH3, the oxidation rates of NOx, NO and SO2 were slightly increased. However, the effect of adding NH3 on NOx oxidation was negative when the temperature was above 200℃.

关键词： additive catalyst NOx SO2 oxidation rate plasma

Unsteady Behavior and Control of Vortices in Centrifugal Compressor

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Journal of Thermal Science 2014年第5期23卷 401-411页

作者： Yutaka ohta Nobumichi Fujisawa Department of Applied Mechanics and Aerospace Engineering Waseda University3-4-1OkuboShinjukuTokyo169-8555Japan Graduate School of Fundamental Science and Engineering Waseda University3-4-1OkuboShinjukuTokyo169-8555Japan

Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this *** the case of high-flow operation of a centrifugal compressor with a vaned diffuser,a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane,which appears most notably in the power spectra of the radiated noise,can be reduced using a tapered diffuser vane(TDV) without affecting the performance of the *** longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the *** use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise *** the case of low-flow operation,a leading-edge vortex(LEV) that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser *** formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to *** a one-side tapered diffuser vane to suppress the evolution of an LEV,the stable operating range of the compressor can be increased by more than 12 percent,and the pressure-rise characteristics of the compressor can be *** results of a supplementary examination of the structure and unsteady behavior of LEVs,conducted by means of detailed numerical simulations,are also presented.

关键词： centrifugal compressor vortex control interaction tone noise noise reduction CFD DES analysis stability enhancement leading-edge vortex.

Coexisting State of Surge and Rotating Stall in a Two-Stage Axial Flow Com-pressor using a Double-Phase-Locked Averaging Technique

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Journal of Thermal Science 2017年第1期26卷 38-46页

作者： Yuu SAKATA Yutaka ohta Graduate school of Fundamental Science and Engineering Waseda University 3-4-10kuboShinjuku Tokyo 169-8555 Japan. Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-10kubo Shinjuku Tokyo169-8555 Japan.

The interaction between surge and rotating stall in an axial flow compressor was investigated from the viewpoint of an unsteady inner flow structure. The aim of this study was to identify the key factor that determines the switching phenomenon of a surge cycle. The main feature of the tested compressor is a shock tube connected in series to the compressor outlet through a diaphragm, slits, and a concentric duplex pipe: this system allows surge and rotating stall to be generated by connecting the shock tube with the compressor, or enables the compression plane wave injection. The unsteady characteristics and the internal flow velocity fluctuations were measured in detail, and the stall cell structure was averaged and visualized along the movement of the operation point under a coexisting state of surge. A coefficient of the cell scale fluctuation was calculated using the result of the averaging, and it confirmed that the processes of inner flow structure change differed from each other according to the next cycle of the surge. The result suggests that the key factor that determines the next cycle is the transformation of the internal flow structure, particularly between the stall cell and the entire circumferential stall, in both the recovering and stalling processes.

关键词： Axial flow compressor, Rotating stall, Surge, Double-phase-locked measurement, Compression wave.

Effect of hydraulic retention time on the hydrogen yield and population of Clostridium in hydrogen fermentation of glucose

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Journal of Environmental Sciences 2009年第4期21卷 424-428页

作者： CHU Chunfeng EBIE Yoshitaka INAMORI yuhei KONG Hainan School of Environmental Science and Engineering Shanghai Jiao Tong University Shanghai 200240 China National Institute for Environmental Studies Tsukuba 305-8506 Japan Faculty of Symbiotic Systems Science Fukushima University Fukushima 960-1296 Japan

The conversion of glucose to hydrogen was evaluated using continuous stirred tank reactor at pH 5.5 with various hydraulic retention times （HRT） at 30℃. Furthermore, the population dynamics of hydrogen-producing bacteria was surveyed by fluorescence in-situ hybridization using probe Clost IV targeting the genus Clostridium based on 16S rRNA. It was clear that positive correlation was observed between the cells quantified with probe Clost IV and hydrogen yield of the respective sludge. The numbers of hydrogen- producing bacteria were decreased gradually with increasing HRT, were 9.2 × 10^8, 8.2 × 10^8, 2.8 × 10^8, and 6.2 × 10^7 cell/mL at HRT 6, 8, 12, and 14 h, respectively. The hydrogen yield was 1.4-1.5 mol H2/mol glucose at the optimum HRT range 6-8 h. It is considered that the percentage of the hydrogen-producing bacteria to total bacteria is useful parameter for evaluation of hydrogen production process.

关键词： bio-hydrogen fluorescence in-situ hybridization genus Clostridium

The thermal conductivity of the Earth's core and implications for its thermal and compositional evolution

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National Science Review 2021年第4期8卷 18-20页

作者： Kenji ohta Kei Hirose Department of Earth and Planetary Sciences Tokyo Institute of Technology Earth-Life Science Institute Tokyo Institute of Technology Department of Earth and Planetary Science The University of Tokyo

The thermal conductivity of iron alloys is a key to understanding the mechanism of convection in the Earth’s liquid core and its thermal history. The Earth’s magnetic field is formed by a dynamo action that requires...

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Coexisting Phenomena of Surge and Rotating Stall in an Axial Flow Compressor

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Journal of Thermal Science 2013年第6期22卷 547-554页

作者： Takuya ABE Hiroaki MITSUI Yutaka ohta Graduate Student Graduate School of Science and EngineeringWaseda University Department of Applied Mechanics and Aerospace Engineering Waseda University

The unsteady inner flow structure of a single-stage axial flow compressor under the coexisting conditions of surge and rotating stall was experimentally investigated via detailed measurements of the unsteady characteristics and the internal flow velocity fluctuations. The main relevant feature of the tested compressor is a shock tube with a capacity tank connected in series to the compressor outlet through slits and a concentric duplex pipe: surge and rotating stall can both be generated by connecting the shock tube. Research attention is focused on the unsteady behavior of a rotating stall during the surge cycle. The size of the rotating stall cell during the recovery process of an irregular surge cycle was experimentally determined by the circumferential flow velocity fluctuations ahead of the rotor blade. The results suggested that the size of the rotating stall cell at the switching point of the performance curve between large and small cycles is considered to be the key parameter in determining the following surge cycle. In addition, the surge cycle is largely influenced by the unsteady behavior of the rotating stall cell.

关键词： Axial flow compressor Surge Rotating stall Coexisting state of surge and rotating stall

Unsteady Behavior of Leading-edge Vortex and Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

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Journal of Thermal Science 2016年第1期25卷 13-21页

作者： Nobumichi FUJISAWA Shotaro HARA Yutaka ohta Graduate Student Graduate School of Fundamental Science and EngineeringWaseda University 3-4-10kuboShinjukuTokyo 169-8555Japan Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-1 OkuboShinjukuTokyo 169-8555Japan

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.

关键词： Centrifugal Compressor Vaned Diffuser Rotating Stall Leading-edge Vortex CFD DES

Unsteady Behavior of Surge and Rotating Stall in an Axial Flow Compressor

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Journal of Thermal Science 2012年第4期21卷 302-310页

作者： Yutaka ohta Yutaka FUJITA Daisuke MORITA Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-1 Okubo Shinjuku Graduate Student Graduate School of Science and Engineering Waseda University 3-4-1 Okubo Shinjuku

Unsteady behaviors as well as unsteady cascade flow fields of a single-stage axial flow compressor were experi- mentally investigated by detail measurements of unsteady performance characteristics and casing wall pressure and internal flow velocity fluctuations. The main feature of the test compressor is a capacity tank connected di- rectly to the compressor outlet in series through slits and a concentric duplex pipe, and also jet nozzles in order to inject compressed air toward the rotor tip region. Research attention is focused on the post-stall characteristics of surge and rotating stall which occur simultaneously. When the compressor was connected to the capacity tank, surge was generated with rotating stall in accordance with the capacitance increment of whole compressor system The surge behavior changed irregularly with throttling valve installed behind the compressor, and several types of surge cycles were observed. In addition, the surge cycle changed by jet injection to the rotor tip region. The re- suits suggested that the blockages of the cascade flow which were generated by a stall cell play an important role in deciding the surge behaviors.

关键词： Axial flow compressor Surge Rotating stall Stall cell Jet injection