Tottori University Research Result Repository

Adachi, Kazumi

Okamoto, Naoya

Fukuda, Tomomi

SIGNAL : Individual Leaning Material for Extensive Reading at the Jounior High School Level

Macarthur, John

Sheen, Ronald

Perceptions of the JET Programme : Part Three

SAITO, Yuko

TORII, Yoko

Fostering Ability of Management of Dietary Life in Home Economics Education : Survey on the Actual Condition of University Students

Claudia　Isabel, AVilia Zeron

Torii, Yoko

Home Economics Education in Republic of Honduras

Dobashi, Takara

Die Erziehung des hohen Alters : Uber die Erorterungen um die Gerontagogik in NEUE SAMMLUNG

NISHIO, Tatsuo

A Sport Policy in Korea under the Wartime Regime

Jirarote, Buranarote

（様式７） 学 位 論 文 審 査 結 果 の 要 旨   氏       名 JIRAROTE BURANAROTE   (ジラロ ブラナロ)        審 査 委 員          委 員 長              原 豊                     印    委    員              古川 勝                  印      委    員              酒井 武治                 印    委    員              上代 良文                 印     論 文 題 目  Method to Predict Rotor Outputs of VAWT Cluster by Using Wake Model Mimicking the CFD-Created Flow Field (数値流体力学解析(CFD)により生成された流れ場を模擬する後流モデルを用いた垂直軸風車群のロータ出力を予測する方法)                                                                                                                                                                              審 査 結 果 の 要 旨  地球温暖化対策として再生可能エネルギーの大量導入が期待され、水平軸型の大形風力発電機を並べた風車群（ウインドファーム）が世界では主力電源となっている。しかし、後流の影響で風車群の効率が減少する問題があり、風車群の効率を向上させる最適な配置や制御が重要である。そのため、精度の高い後流モデルが必要とされている。  本研究は、単位面積当りの風車群出力が一般的な大形の水平軸風車を並べた風車群よりも大幅に向上する可能性が示されている小形垂直軸風車の風車群の出力予測に関わり、垂直軸風車の後流特性を考慮した独自の後流モデル、およびそれを用いた短時間で風車群の流れ場と出力を予測する手法を提案している。その後流モデルは、従来法と同様にポテンシャル流れに後流の速度欠損を導入するが、先行研究で提案されている水平軸型風車の後流モデルに、垂直軸風車の後流で観測される増速域と後流シフトの効果を追加している。また、従来法では考慮されていない主流に垂直な速度成分も修正し、風車の回転数変化を考慮した二次元数値流体力学解析 (CFD)で予測される流れ場を模倣するように、後流モデルのパラメータを決定している。複数風車間の相互作用による後流のシフトと幅の変化を考慮するため、ビオ・サバールの法則に基づく誘導速度を導入し、速度分布の精度向上を図っている。  任意の風車配置に対する適切な流れ場と出力の予測のために、検査領域における主流方向の運動量保存を用いることを提案している。この手法では初期値として与えた各風車の循環に基づき、流れ場と風車特性を計算するが、運動量保存を満足する適切な循環の組合せを探索する。偽の解を回避するために循環の探索範囲を制限する方法や、後流の重なりに起因する風車間相互作用の圧力損失への影響を考慮する方法などを提案している。校正のため、典型的な４つの風車ペア配置についてのCFD解析を必要とするが、一度、校正パラメータを設定すれば、CFD解析に比べて格段に短い時間で計算は実行可能であり、２～４個からなる風車群を対象としたCFD解析との比較・検証を行い、その有効性を示している。  以上のように、将来の小形垂直軸風車の風車群における最適な風車配置の探索における基礎となる後流モデルおよび予測手法を構築したことは高く評価ができる。よって本論文は、博士（工学）の学位論文として価値あるものと認める。  

English

数値流体力学解析(CFD)により生成された流れ場を模擬する後流モデルを用いた垂直軸風車群のロータ出力を予測する方法

Naito, Hisako

Japanese

L. Janáček, Aesthetics of ‘Realism’ : ‘Nápěvky Mluvy (Speech-melody)’ Theory and His Real Slavic Spirit

Odhiambo, John Otieno

（様式２） 学 位 論 文 の 概 要 及 び 要 旨 氏  名  John Otieno Odhiambo 印 題  目  Processing and Characterization of In-situ Synthesized and Hot-extruded Aluminum Matrix Composites Reinforced with Al2O3-TiB2-TiC Ceramic Particles（In-situ合成と熱間押出しにより合成したセラミック粒子強化アルミニウム基複合材料のプロセッシングと評価に関する研究）  学位論文の概要及び要旨 Aluminum-matrix composites (AMCs) have found widespread applications in various fields including aerospace, automobile and maritime industries due to their high specific strength and modulus, good wear and heat resistance, and low coefficient of thermal expansion.  As a result, there is need to further enhance these properties to meet the increasing demand. However, conventional processing techniques like stir casting and powder metallurgy result in AMCs with large particulates in the order of microns to tens of microns which are usually nonuniformly distributed within the Al matrix. Further, most common AMCs are reinforced with single particulates rather than hybrid reinforcements.  In-situ synthesis of hybrid particle reinforcements followed by hot -extrusion densification process emerges as the best technique of producing AMCs with fine particles which are uniformly distributed within the Al matrix leading to improved microstructure for better mechanical properties resulting from strong bonding and wettability between the matrix and reinforcement phases occasioned by clean and clear interfaces. In this study, AMCs reinforced with submicr on ceramic particles of Al2O3, TiB2 and TiC were in-situ synthesized by reactive sintering of Al/AA6061, TiO 2 and B4C powder mixtures and further densified by a hot-extrusion process. The reaction mechanisms for the formation of reinforcing particles, extrusion behavior, microstructure, hardness, wear behavior, fatigue strength and tensile properties (room and high temp erature) were investigated. To study the reaction mechanisms and reaction path in the Al -TiO2-B4C system, the startingpowders were weighed stoichiometrically to produce AMCs with target reinforcing particula tes at 15 vol%, 20 vol% and 25 vol%. The reactions of TiO2 and B4C with molten Al were a stepwiseprocess, and there were many intermediate phases including oxygen deficient titanium oxides ( Ti3O5, Ti2O3 and TiO ), Al4C3 , AlB2 and Al3Ti , before the expected reinforcing particles of Al2O3 , TiB2 and TiC were formed. Submicron particulates with an average particle size of 0.24 µm were uniformly distributed in the matrix.  The porous reactive-sintered AMCs with 85 - 92% relative density (RD) were successfully densified through hot extrusion in a temperature range of 480°C-550°C to a maximum of 99.8%. Furthermore, the microstructure of the resulting AMCs was characterized by fine reinforcing ceramic phases with an average particle size of 0.24 µm, which were homogeneously distributed in Al matrix. The ceramic particulate content and extrusion temperature have been proved to have small influences on the average particle sizes of the reinforcing phases , but a substantial decrease in Al grain size with increase in ceramic particle contents and decrease in extrusion temperature was observed. The effects of extrusion temperature and ceramic particle contents on mechanical properties including micro-hardness, fatigue strength and wear resistance were also studied. As the ceramic particle contents increased and extrusion temperature decreased, RD, micro -hardness, wear resistance and fatigue strength improved. Maximum micro -hardness of 145.6 HVwas achieved at 25 vol% ceramic particle content and extrusion  temperature of 520°C representing an improvement of 219.1% from the hardness values of pure aluminum (45.6 HV)prepared by powder metallurgy process and extruded at the same temperature.  The tensile strength and yield strength improved with increase in ce ramic particle content and decrease in extrusion temperature. The 25 vol% AMC extruded at 520 °C AMC had the highest average tensile strength of 425.0 MPa which was 9.6% higher for the AMCs with the same ceramic particle content but extruded at a higher temperature of 550 °C (388 MPa). The improved strength was caused by the strengthening mechanisms especially the Orowan and CTE mismatch strengthening which accounted for about 15% and 64% of the estimated theoretical yield strengths respectively. The fracture surface of pure Al extruded at 550 °C exhibited ductile fracture morphology consisting of large dimples and voids. The fracture surfaces of the AMCs were characterized by smaller and shallower equiaxed dimples with tear ridges. Further, high temperature  tensile properties were conducted at 300 °C and 370 °C. Even though precipitation -hardened aluminum alloys AA6061-T6 and AA2024-T3 had 24.2% and 93.5% better tensile strength at 25 °C, 15 vol% AMCs extruded at 550 °C gave a 66.7% and 44.5% better tensile strength at 300 °C and 370 °C respectively. To further enhance the properties of the AMCs, Al matrix was alloyed to the AA6061 standard and the reaction mechanism with TiO2 and B4C studied. The formation of the target reinforcing ceramic particles were completed at 1400 °C without intermediate compounds. Uniformly distributed fine ceramic particles were observed in the AA6061 matrix which appeared larger than those formed in pure Al matrix. The reactive sintered AMCs had several pores (RD ~ 83%) which were positively reduced by hot-extrusion secondary processing to produce composites with improved relative density (about 100%) and microstructures. The microstructure revealed that the ceramic particles of Al 2O3, TiB2 and TiC were uniformly distributed within the alloy matrix. The average particle sizes of 1.03 µm was realized. The dense AA6061 matrix composites exhibited improved micro-hardness which increased with increase in ceramic particle contents and extrusion temperature. A maximum harness of 110.8 HV was realized at an extrusion temperature of 520 °C. The UTS and YS of the AA6061 matrix composites increased with increase in ceramic particle content while ductility decreased. There was little effect of extrusion temperature on mechanical properties. The highest tensile strength of 266.5 MPa was achieved at 20 vol% ceramic particle content and extrusion temperature of 550 °C. The micro-hardness and wear resistance of the AA6061 matrix composites greatly improved with the increase in ceramic particle content.  The AA6061 matrix composites were heat-treated to the T-6 standard and the effect of heat-treatment on microstructure, strength, hardness and wear properties investigated. There was little effect of heat-treatment on the microstructure of the AA6061 matrix composites, however, the presence of ceramic particles leads to further grain refinement. The heat-treated AA6061 matrix composites demonstrated higher hardness than the non-heat-treated alloy composites. The peak-ageing time for the AMCs corresponding to peak-hardness increased with increase in the ceramic particle content. The peak-ageing time for 0 vol%, 15 vol% and 20 vol% AMCs were 4 h, 8 h and 12 h respectively. The UTS and YS improved with increase in ceramic particle contents for the non-heat-treated AMCs. The response to heat treatment was larger for unreinforced AA6061 matrix composites which improved to 322 MPa. The heat treated 15 vol% AMC demonstrated a lower UTS and YS than the heat treated and AA6061 Al alloy with 0 vol% ceramic particle content.  

In-situ合成と熱間押出しにより合成したセラミック粒子強化アルミニウム基複合材料のプロセッシングと評価に関する研究

鳥取大学　博士（工学）　2001年03月24日授与　　甲第92

Ren, Hongwan

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