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機能創成セミナー Seminar on Mechanical Science and Bioengineering
第120回 | 2016年12月22日 17:30-18:30 基礎工学C棟4階 C棟共用セミナー室 |
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| 非一様性による乱流統計量の初期値鋭敏性 Long-range memory and therefore inhomogeneity in periodic turbulence | |
| 伝統的な乱流の統計理論は，一様性・等方性といった概念の導入により発展してき ．例えば，一様等方乱流に対する縦速度相関関数の時間発展方程式 [1] から，Kolmogorovの5分の4乗則が導き出されている．しかしながら，実際の多くの乱流の流れ場（少なくとも，瞬間場）は非一様・非等方であることから，より深く正しい理解に辿り着くために，一様性・等方性の概念を用いずに乱流の現象解明を試みる必要がある．近年の研究者らの精力的な研究により，ひとつの仮定も用いない最も一般的な2次速度構造関数の時間発展方程式 [2] が導出された．本研究では，直交する3方向に流れ場が周期的である乱流（周期箱乱流）の数値計算を行い，上記方程式を用いて2点統計解析を行った．それにより，われわれは非一様性に起因する乱流統計量の初期値鋭敏性の存在を明らかにした．この発見は，「ある一定の境界条件の下では，いかなる乱流も生み出された詳細に依らず，漸近的にひとつの乱流状態に発達していく」（Narasimha, 1989）という，経験に基づいた初期条件に対する認識に反するものである． 【参考文献】 [1] Karman, T. von & Howarth, L. (1938). Proc. Roy. Soc. A, 164, 192-215. [2] Hill, R. J. (2002). J. Fluid Mech., 468, 317-326. | |
| 安田 達哉 氏 インペリアル・カレッジ・ロンドン，博士研究員 Dr. Tatsuya Yasuda (Imperial College London, Research Associate) | |
| 世話人：河原 源太 / 参加者：未定 | |
第119回 | 2016年12月21日 16:30-17:30 基礎工学研究科B棟 B401講義室 |
| Rehabilitation Robotics: Translating Neuroscience Motor Control into Practice | |
| The demand for rehabilitation services is growing apace with the graying of the population. This situation creates both a need and an opportunity to deploy technologies such as rehabilitation robotics, and in the last decade and half several research groups have deployed variations of this technology. Results so far are mixed with the available evidence demonstrating unequivocally that some forms of robotic therapy can be highly effective,even for patients many years post-stroke, while other forms of robotic therapy have been singularly ineffective. The contrast is starkest when we contrast upper-extremity and lower-extremity therapy. In fact, the 2010 and 2016 Stroke Care Guidelines of the American Heart Association (AHA) and of the Veterans Administration/Department of Defense (VA/DoD) endorsed the use of the rehabilitation robotics for upper extremity post-stroke care, but concluded that lower extremity robotic therapy is much less effective as compared to usual care practices in the US. We submit that the contrasting effectiveness of upper- and lower-extremity therapies arises from neural factors, not technological factors. Though, no doubt, it might be improved, the technology deployed to date for locomotor therapy is elegant and sophisticated. Unfortunately, it may be misguided, providing highly repeatable control of rhythmic movement but ultimately doing the wrong thing. The technology we have deployed to date for upper-extremity therapy is firmly based on an understanding of how upper extremity behavior is neurally controlled and derived from decades of neuroscience research. The limitations of lower-extremity robotic therapy lie not in the robotic technology but in its incompatibility with human motor neuroscience. Here I will briefly review the evidence supporting such negative views, and based on our experience with upper extremity robotic therapy, we describe what we are presently investigating to revert and work towards a future endorsement of the AHA and VA/DoD for rehabilitation robotics for lower extremity post-stroke care. | |
| Hermano Igo Krebs Department of Mechanical Engineering, Massachusetts Institute of Technology | |
| 世話人：平井 宏明 / 参加者：未定 | |
第118回 | 2016年11月16日 (1)15:00-15:45 (2)15:45-16:30 基礎工学国際棟1Fセミナー室 |
| (1)Airflow in relation to human speech sound production (2)Mechanical replicas for studying the physics of the vocal tract | |
| (1) Despite the obvious crucial role of airflow to drive human speech sound production, traditionally, researchers studying the mechanisms underlying speech soundproduction considered extremely simple flow models in order to describe flow through the human upper airways. Whereas such a crude description might be sufficient to understand basic mechanisms for normal vowel sound production, it might be questioned for instance in the case of pathologies or when considering the production of non-vowel speech sounds. Indeed, moderate Reynolds numbers are associated with upper airway flow so that it is reasonable to assume that complex flow phenomena associated with the transition of laminar to turbulent flow can occur. In addition, geometrical asymmetries are likely to affect the flow during sound production. In this talk, experimental evidence will be presented illustrating the occurrence of complex flow phenomena related to the upper airway geometry. The shown studies aim to increase our understanding of the described phenomena as well as to comprehend their role in normal or pathological human speech sound production. (2) Making measurements on the human voice organ in vivo is invasive and difficult. Reproducibility and accuracy is usually hard to achieve with living or excised tissue. For studying fundamental phenomena of the physics of voice production, it is often more convenient to use mechanical replicas of the various parts of the voice organ. In comparison to computer simulations, the physicality of replicas can impart a more immediate and intuitive appreciation of the structural dimensions and the mechanical and/or aeroacoustical aspects of voice production. In some cases, a highly simplified geometry for the vocal folds or the vocal tract is useful; it facilitates the specification of parameters, and the validation by measurement of numerical simulations of the corresponding geometries. In other cases, a more realistic 3-D geometry is needed to answer the research questions; such as for the study of the influence of particular pathologies or the cause of particular voice features. Modern 3-D printers have opened up the possibility to recreate complex shapes from MRI data, recently even in soft materials. In this talk, we first present a brief historical review of past or present work dealing with mechanical replicas and then illustrate some applications of these replicas in voice research. | |
| (1)Annemie Van Hirtum (CNRS researcher, GIPSA-lab; and Specially Appointed Professor, Osaka Univ.) (2)Prof. Xavier Pelorson (CNRS Director of Research, Gipsa-lab, France) | |
| 世話人：和田 成生 / 参加者：未定 | |
第117回 | 2016年11月4日 15:00-16:30 基礎工学B棟2階 B205講義室 |
| ヘリカル管内流の層流・乱流遷移と完全発達乱流への移行 | |
| ヘリカル管内の流れは、曲率とねじり率の影響を同時に受け、非常に興味深い動を示す。岡山大学では以前から本問題の実験的、理論的研究を進めてきたが、今回の報告は、これらの研究に基づき、層流解の不安定と、その結果発生する乱流の、完全発達乱流への移行を数値計算により調べたものである。主な結果としては、一つは、層流解の不安定が、あるパラメータ領域では強い3次元不安定を伴い、その場合、臨界レイノルズ数が極めて低い値（100程度）となることを見出したことである。もう一つは、実験結果と乱流モデルを利用した数値計算結果を比較することによって、乱流が完全発達状態へ移行するレイノルズ数を推定することができた点である。同時に、いくつかの非等方性を許容する乱流モデルがこの乱流に対して、非常に高い予測性能を持つことを示すことができた。さらに、層流の渦構造と乱流状態の秩序渦構造の相違点を明らかにする。 | |
| 柳瀬 眞一郎 教授 岡山大学大学院自然科学研究科産業創成工学専攻先端機械学 教授 | |
| 世話人：河原 源太 / 参加者：未定 | |
第116回 | 2016年11月1日 13:00-13:40 D棟セミナー室 (D404) |
| 鉄道総合技術研究所での列車まわりとトンネル内における空力現象に関する研究内容 | |
| 鉄道総合技術研究所（鉄道総研）は，公益財団法人として，鉄道に関する技術研究を行っている．本講演では，鉄道総研で行っている列車まわりおよびトンネル内における空力現象に関する研究内容を紹介する．鉄道の空力現象には，新幹線車両の空気抵抗以外にも，列車の横風問題，トンネル突入・通過によるトンネル内外での波動現象，パンタグラフなどから生じる空力騒音，地下トンネル内での温熱環境などがある．これらの現象は列車の速度向上や安全・安定性向上のため，常に技術向上する必要がある．鉄道総研では，現地試験や理論解析のみならず，さらなる現象解明や低減対策開発のため，大型実験装置や数値シミュレーション手法の開発も行っている．本講演では，これらの研究内容に関する取り組みに加え，その成果を世界へ発信するための海外研究機関との連携や，近年取り組み始めている新しい課題もあわせてご紹介する． | |
| 宮地徳蔵 鉄道総合技術研究所 環境工学研究部 熱・空気流動 主任研究員 | |
| 世話人：杉山 和靖 / 参加者：未定 | |
第115回 | 2016年10月24日 16:20-17:20 基礎工国際棟1Fセミナー室 |
| Changes in the mechanical properties of the cell nucleus with implications in cardiovascular disease and aging | |
| The sequencing of the human genome has provided a wealth of scientific information, but this information is limited by the poor understanding of the mechanisms which control gene expression. In addition to containing the code for the cell and beyond, the genome within the nucleus is a self-assembled polymeric structure with unique mechanical properties. Using spectrocopy, imaging, micromanipulation and computational techniques, we measure the mechanics of the nucleus at various length scales. We are particularly interested in the role that force and cytokine treatment play in altering nuclear mechanics and gene expression in primary human endothelial cells that line blood vessels. We examine the role of fluid shear stress and endothelial-specific growth factors on the reorganization of the nucleus and changes in nuclear mechanics. We find both a shear-dependent and time-dependent influence on nuclear mechanics. However, expression of proteins related to premature aging reduce or eliminate the ability of the nucleus to respond appropriately to applied force. Thus, there appears to be a balanced stiffness maintained throughout the cell including in the nucleus that can be modulated by external force; if this balance is altered by the accumulation of aging-specific proteins and the nucleus is stiffened pathology arises. | |
| Prof. Kris Noel Dahl Chemical Engineering and BioMedical Engineering, Carnegie Mellon University | |
| 世話人：出口 真次 / 参加者：未定 | |
第114回 | 2016年9月16日 16:00-17:30 基礎工学C棟セミナー室 |
| 発電用ガスタービンのタービン冷却翼の変遷と将来展望 | |
| 産業用ガスタービンはコンバインドサイクルの主機として発展し、現在タービン入り口温度は1600℃級J形ガスタービンが開発され、これを用いたコンバインドプラントの熱出力は約491MW、熱効率は約62％（LHV)に達している。また1700℃級のガスタービンの研究開発が国家プロジェクトで進められている。これらの高温ガスタービンに用いられるタービン動静翼の冷却技術を概説し、今後の動向を紹介する。 | |
| 武石 賢一郎 招聘教授 大阪大学招聘教授/徳島文理大学理工学部教授 | |
| 世話人：河原 源太 / 参加者：未定 | |
第113回 | 2016年8月3日 14:40-16:10 基礎工学Ｄ棟４階 Ｄ棟共用セミナー室 |
| EXTREME VORTEX STATES AND THE HYDRODYNAMIC BLOW-UP PROBLEM | |
| In the presentation we will discuss our research program concerning the study of extreme vortex events in viscous incompressible flows. These vortex states arise as the flows saturating certain fundamental mathematical estimates, such as the bounds on the maximum enstrophy growth in 3D (Lu & Doering, 2008). They are therefore intimately related to the question of singularity formation in the 3D Navier-Stokes system, known as the hydrodynamic blow-up problem. We demonstrate how new insights concerning such questions can be obtained by formulating them as variational PDE optimization problems which can be solved computationally using suitable discrete gradient flows. In offering a systematic approach to finding flow solutions which may saturate known estimates, the proposed paradigm provides a bridge between mathematical analysis and scientific computation. In particular, it allows one to determine whether or not certain mathematical estimates are "sharp", in the sense that they can be realized by actual vector fields, or if these estimates may still be improved. In the
presentation we will review a number of new results concerning 2D and 3D flows characterized by the maximum possible growth of, respectively, palinstrophy and enstrophy. It will be shown that certain types of initial data, such as the Taylor-Green vortex, which have been used in numerous computational studies of the blow-up problem are in fact a particular instance (corresponding to an asymptotic limit) of our family of extreme vortex states. We will present results comparing the growth of relevant quantities in high-resolution direct numerical simulations of the Navier-Stokes system obtained using our extreme vortex states and different initial data employed in earlier studies. [Joint work with Diego Ayala] | |
| Prof. Bartosz Protas Department of Mathematics and Statistics, McMaster University | |
| 世話人：河原 源太 / 参加者：未定 | |
第112回 | 2016年7月29日 13:00-15:00 基礎工学Ａ棟１階 A145室 |
| (1)Deviation from High-Entropy Configurations in the Al1.3CoCrCuFeNi Alloy (2)Study of Serrated Flows in Bulk Metallic Glasses and High Entropy Alloys | |
| (1)The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as “high-entropy alloys”. Understanding the elemental distributions, and, thus, the evolution of the configurational entropy during solidification, are the goal of the present research. The case of the Al1.3CoCrCuFeNi model alloy is examined, using integrated theoretical and experimental techniques, such as ab initio molecular-dynamics simulations, neutron scattering, synchrotron X-ray diffraction, high-resolution electron microscopy, and atom-probe tomography. It is shown that even when the material undergoes elemental segregation, precipitation, chemical ordering, and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. The results suggest that the high-entropy-alloy-design strategy may be used to develop a wide range of complex materials, which are not limited to single-phase solid solutions. The integrated experimental and theoretical techniques, discussed here, are particularly well-suited to studying partially-ordered materials, produced using the high-entropy-alloy design strategy. (2)Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) attract more and more attention for their unique mechanical properties. Recent work suggests that BMGs and HEAs show serrated flows at certain temperatures and strain rates, which is similar to the Portevin-Le Chatelier effect (PLC) in traditional alloys. Therefore, the study of serration behavior could provide a unique way to investigate the deformation dynamics of BMGs and HEAs, and, consequently, to endow us with the fundamental understanding of deformation mechanisms for BMGs and HEAs. In this study, compressive behavior of BMGs and HEAs are characterized statistically, and a new model developed from the mean-field theory is utilized to describe the serrated flows in BMGs and HEAs. | |
| Prof. Peter K. Liaw Department of Materials Science and Engineering, University of Tennessee | |
| 世話人：尾方 成信 / 参加者：未定 | |
第111回 | 2016年7月8日 11:00～12:00 D棟セミナー室 |
| 雲の放射特性およびレーダ反射特性に及ぼす乱流クラスタリングの影響 | |
| 計算機性能の高度化に伴って気象シミュレーションの高解像度化が進んでいる．高解像度の気象シミュレーション（ラージ・エディ・シミュレーション）を精度よく行うためには，要素物理モデルの精緻化が必要不可欠である．本研究では，特に，雲の発達において重要となる乱流・放射モデルに着目し，乱流中における雲粒の不均一分布（乱流クラスタリング）が雲の放射特性に及ぼす影響やレーダ反射強度に及ぼす影響，およびそのモデル化に関する研究を行ってきた．今回は，これまでの取組みにおいて，粒子の分散を伴う乱流場の直接数値シミュレーションや放射伝達シミュレーションを用いて得られた成果について紹介する． | |
| 海洋研究開発機構 地球情報基盤センター 松田 景吾 | |
| 世話人：後藤 晋 / 参加者：未定 |
