Published papers

It is of great importance for universities to introduce internal regulations which allow flexible student mobility when the promotion of internationalization is considered. Through the activity of EBA Consortium, a new status for international student has been settled, so that students can come and leave at any time regardless of the academic calendar. For Japanese students to leave during the study at the university, the problems due to discrepancy in academic calendar could be partially resolved by introducing four-term system. The appropriate design of such regulation should be conducted in accordance with the global picture of the academic activities in consortium to avoid local optimization.

Following on the 2008-2012 OECD Assessment of Higher Education Learning Outcomes (AHELO) feasibility study of civil engineering, in Japan a mechanical engineering learning outcomes assessment working group was established within the National Institute of Education Research (NIER), which became the Tuning National Center for Japan. The purpose of the project is to develop among engineering faculty members, common understandings of engineering learning outcomes, through the collaborative process of test item development, scoring, and sharing of results. By substantiating abstract level learning outcomes into concrete level learning outcomes that are attainable and assessable, and through measuring and comparing the students’ achievement of learning outcomes, it is anticipated that faculty members will be able to draw practical implications for educational improvement at the program and course levels. The development of a mechanical engineering test item bank began with testscale test implementation in 2016 of 348 first semester master’s students in 9 institutions in Japan, using both multiple choice questions designed to measure the mastery of basic and engineering sciences, and a constructive response task designed to measure “how well students can think like an engineer.” The same set of test items were translated from Japanese into to English and Indonesian, and used to measure achievement of learning outcomes at Indonesia’s Institut Teknologi Bandung (ITB) on 37 rising fourth year undergraduate students. This paper highlights how learning outcomes assessment can effectively facilitate learning outcomes-based education, by documenting the experience of Japanese and Indonesian mechanical engineering faculty members engaged in the NIER Test Item Bank project.

Simultaneous measurements of fluctuating velocity and pressure were performed in various turbulent free shear flows including a turbulent mixing layer and the wing-tip vortex trailing from a NACA0012 half-wing. Two different methods for fluctuating static pressure measurement were considered: a direct method using a miniature Pitot tube and an indirect method where static pressure was calculated from total pressure. The pressure obtained by either of these methods was correlated with the velocity measured by an X-type hot-wire probe. The results from these two techniques agreed with each other in the turbulent mixing layer. In the wing-tip vortex case, however, some discrepancies were found, although overall characteristics of the pressure-related statistics were adequately captured by both methods.

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, the time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of the vortex is evident from both velocity and pressure measurements: The power spectral density (PSD) of the transverse velocity fluctuation increases in the lower frequency range, and the distribution of the pressure fluctuation exhibits an elongated shape in the z direction as well as two peaks slightly off from the vortex center. The distribution of the measured velocity-pressure correlation varies significantly near the center of the vortex especially in downstream locations.

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of vortex is evident from both velocity and pressure measurements: The PSD of transverse velocity fluctuation increases in lower frequency range, and the distribution of pressure fluctuation exhibit elongated shape in z-direction and two peaks slightly off from the vortex center. The measured velocity-pressure correlation shows significant gradient near the center of the vortex especially in a downstream location.

Flow visualization and velocity measurements with particle image velocimetry (PIV) have been conducted in the near field of the tip of a sinusoidally flapping plate with the initial condition of fluid at rest. Experiments were conducted at Reynolds number of 1580 and 3160. We visualized the evolution of vortices and performed force calculation based on stereo PIV velocity field data. Three planes near the wing tip were measured with PIV and we found that several features of the flow from PIV measurements are similar with flow visualization.

The present study attempts to characterize the fluctuating pressure field in turbulent flow associated with strong streamwise vortex. The instantaneous velocity distribution is measured by a stereoscopic PIV and the corresponding pressure field is obtained as a solution of discrete Poisson equation. The results are presented for the statistics of turbulence containing the pressure velocity correlation. It is indicated that the distribution of normal components of Reynolds stress are attributable to the magnitude of velocity pressure-gradient correlation terms in the corresponding transport equations.

Passive flow control around circular cylinder using porous media is studied by means of two-dimensional numerical simulation. Brinkman-Navier-Stokes equation is used to simulate flow in the porous media. The simulation is performed at the Reynolds number of Re = 100 and 1000. Both the drag and lift forces are found to be modified due to the presence of porous media. Especially, the fluctuation of lift force is suppressed at Re = 1000 with an intermediate value of porosity. The case of minimum lift force fluctuation is investigated in detail by examining the statistics and flow visualization.

We perform direct numerical simulation (DNS) of a plane mixing layer under a predetermined control. The inlet velocity is given as the sum of a hyperbolic-tangent base flow and random disturbances. The base flow is periodically excited to mimic the actuation in the experiment. The Reynolds number (Re) based on the velocity difference and the vorticity thickness is 400. The effects of excitation amplitude and frequency are systematically investigated and it is found that the mixing is enhanced for lower frequency, while suppressed for higher frequency. Through the examination of flow statistics, we clarify the mechanisms of mixing enhancement/suppression due to the control input.

固気昆相流中の球形粒子の振る舞いを解明する目的でLESによる数値シミュレーションを行なった。主流の速度分布が一様な場合とせん断がある場合について、円柱に作用する抗力に発生する変化を詳細に調べ、レイノルズ応力の発生機構との関連で論じた。

The weak-equilibrium condition, which is the basis in the development of algebraic Reynolds stress models is assessed in the prediction of fully developed turbulent channel flow under the influence of system rotation. The budget of the various terms of the exact transport equation for the anisotropy tensor is evaluated by using a DNS database. Two diffusive transport constraints are evaluated by using the DNS data. The results show that neither of them can hold for the nearwall region. An asymptotic analysis of the near-wall behavior is performed and an alternative form of the diffusive transport constraint is proposed. The analysis shows that the proposed alternative diffusive transport constraint has the potential to improve the predictive ability of the resultant ARSM.

乱流せん断層において変動圧力速度相関を計測する新しい手法を開発しその性能評価を行なった。従来のミニチュアピトー管ではマルチセンサー型熱線風速計との併用において空間解像度に制限があったが、新しくミニチュア全圧プローブを併用する手法を開発し、基本性能の評価と旋回乱流への適用を通じて妥当性を示した。

レイノルズ応力の圧力拡散モデルについて、楕円型緩和方程式を用いたモデルの援用を提唱し、乱流クウェット流れへの適用を通じてその妥当性を示した。また、DNSデータによるアプリオリテストを行い、従来言われていた斉次モデルの選択方法に対して壁面近傍の漸近挙動を満たすモデルを採用しなければならないことを指摘した。

分子動力学専用計算機MDGRAPE3を渦法による流体の数値シミュレーションに応用し、FMMとの組み合わせにより計算速度の加速を試みた。汎用計算機の場合と異なり、FMMにおける最適化に際して直接計算の比重を考慮した結果、100倍以上の加速性能を得ることができた。

ハードディスクドライブを模した容器内積層円盤系における空力特性と円盤振動の関係について実験的研究を行なった。PIVにより円盤表面に複数個の大規模渦構造が発生すること、それにより周期的な速度・圧力変動が発生することを見出し、円盤の固有振動とこの圧力変動の関係について論じた。

円柱が、一様流中に置かれた場合と、一様せん断流中に置かれた場合で、流れとの力学的な相互作用にどのような変化が生れるかをLESにより詳細に調べた。従来、混相流中での粒子の運動を議論する際に焦点とされた浮力項が主流のせん断によって発生する機構を明らかにすることができた。

乱流中で変動する速度と圧力を同時に計測し、速度－圧力相関項を評価する目的で、超ミニチュア圧力プローブを開発した。X型熱線風速計プローブとの組み合わせにより、従来の方法に比べて空間解像度を格段に改良した。ノイズ除去方法について系統的な検討を加えた。