Presentations

We investigated characteristics of water sloshing in a rotating, laterally oscillating, cylindrical container both theoretically and experimentally. In our experiment, the time-dependent dynamic pressure of the water on the wall rather than the free-surface displacement of the water was measured. We conducted a theoretical analysis to understand the experimental results. The swirling of water in the container had some frequency components; the frequency responses of each frequency component are examined.

We have investigated the free-surface fluctuations of liquid in a rotating, laterally oscillating, cylindrical vessel. We measured the time-dependent fluid-dynamic pressure instead of the free surface luctuations. From an FFT analysis of the dynamic pressure, we obtained two significant frequencies. They are associated, respectively, with waves that rotate in the same direction, and in the opposite direction, relative to the rotation of the vessel. We also examined these results using linearized wave theory.

The resistance force of a magneto-rheological fluid at a cylinder piston with tapered pin in the presence of magnetic field are investigated both experimentally and theoretically. The resistance force at a cylinder piston with tapered pin depends on the strength of magnetic field, tapered pin, etc. It is proved the most dominant effect to the resistance force is magnetic field.

組立式台船の強度は，蟻装に使用された機材の重量とその分布，作業時の負荷等の条件を基に，組立式台船の船体同士を連結する連結継手にかかるモーメントとせん断力を算出して，それらの強度が不足する場合は，H鋼等の汎用の構造部材で補強している。実際に補強した船体の強度の評価手法を新たに提案し，両端分割と中央集中の2つの荷重条件について試算した。

組立式台船は多種多様な作業船の船体として使用され，その浮体としての安定性については，船体の組立形状，鰭装方法，および，施工時の荷重分布の変化を考慮した乾舷の計算や，施工実績・経験を含めて検討している。ここでは，安定性の指標について，推進器を有する自航船と，推進器を持たない非自航船の特徴を把握し，非自航作業船のような矩形船体の指標について提案を行った。

We examined wave phenomena pertinent to water in a rotating, laterally oscillating cylindrical container. The swirling of water in the container had three frequency components; the frequency responses of each frequency component are reported herein. When swirling occurs in a rotating cylindrical container, it was found that the wave rotating in the same direction as the rotation of the cylindrical container and the wave rotating in the opposite direction to the cylindrical container exist at the same time. The swirling direction was determined by the relationship of these magnitude.

Knockdown pontoons with rectangular hulls are often used in work vessels during construction. In this paper, we present a novel method of construction that uses knockdown pontoons. The presented method is a self-dumping pontoon system in which the hull is overturned to unload the earth and sand. We model a series of hull movements as a rigid pendulum, thus developing new model equations and solving them by the Runge-Kutta method. Model experiments were also performed, and the calculation results are in agreement with the experiment results. Lastly, we discuss the criteria for hull overturn in detail.

水平直線方向に振動しながら垂直軸回りを回転する円筒容器内の液体の挙動を調べた。円筒容器内壁に設置した圧力センサで水圧を測定することで，スロッシングが生じた時の液体の自由表面の変位を調べた。スワーリング発生時に圧力センサが測定した水圧変動をFFT解析した。その結果から，容器の回転方向に対して同じ方向と逆方向に回転する２種類の波が同時に存在し，その大小関係によって見かけ上のスワーリングの方向が決まるという事を明らかにした。

MR流体に様々な周波数の振動磁場を印加した時に形成されるクラスタの変化を超音波伝播速度を用いて評価した。振動磁場周波数の2倍の周波数でクラスタの形成崩壊が繰り返されることが確認された。

This study reports magnetic fluid flow in a square duct under DC, AC, and DC+AC magnetic fields. We measured pressure drop with applying different magnetic fields. Under magnetic fields, flow resistance increased by forming a cluster so that pressure drop and friction factor also increased. From FFT analysis of the pressure drop, we obtained different power spectrum for AC and DC+AC magnetic fields.

This study reports the theoretical and experimental resistance force of MR fluid in a pipe that changes depending on a magnetic field. We used Bingham plastic model to represent the dynamic behavior of MR fluid flow in a circular pipe under a magnetic field theoretically. Analytical results indicate that the radius of a pipe has a major effect on the resistance force. We conducted the drop impact test to verify our theoretical approach. The resistance force of MR shock absorber was changed depending on a magnetic field and the radius of the pipe as indicated in theoretical results. We also conducted the flow experiment of MR fluid at a constant flow rate and compared experimental results and analytical results quantitatively.

This paper presented experimental investigation about MR fluid under AC magnetic fields. Clusters in MR fluid are formed along magnetic fields. Clustering structures in MR fluid make ultrasonic propagation velocity change. We investigated clustering structures by measuring ultrasonic propagation velocity. As a result, the clusters in MR fluid have dependence on elapsed time, strength, frequency and angle of AC magnetic fields.

The magnetic particles in an MR fluid form clusters parallel to the direction of the applied magnetic field, and yield stress is generated. As a result, the apparent viscosity of the MR fluid increases. In the present paper, we propose a theoretical approach for obtaining the resistance force controlled by the magnetic field using an MR flow model. We use a mechanical model of an MR fluid pipe flow with a tapered pin. Moreover, we conduct some experiments to test our theoretical approach.

When an external magnetic field is applied to a MR fluid, particles get together and clusters appear along the magnetic fields. These phenomena influence on the velocity of ultrasonic propagation. We changed the frequency and strength of the magnetic field and measured the change of the propagation velocity due to external magnetic fields with several directions. We confirmed the anisotropy of ultrasonic propagation velocity and estimated the structure of cluster formation in a MR Fluids under alternating magnetic fields.

Knockdown pontoons are often used in work vessels during construction. The typical shape of their modules is cuboidal, and these modules are combined into one hull. We proposed a new easy-to-operate technique to calculate the attitude of the floating body with various shapes and/or large inclined angles. The calculated results were compared with the experimental results of this technique.

Free surface movement of water in a rotating, laterally oscillating cylindrical container was qualitatively investigated. Time-dependent dynamic pressure was measured instead of free surface displacement. The swirling direction was determined by forcing the frequency and rotating direction of the cylindrical container. The swirling direction was opposite to that of the rotating cylindrical container when the forcing frequency was less than the resonant frequency, whereas the crest of the free surface swirled in the same direction as that of the rotating cylindrical container when the forcing frequency greatly increased. Unstable swirling occurred at the resonant frequency, but it disappeared as the rotating frequency increased.