著者

菊地 謙次 今野 友博 市川 誠司 窪田 佳寛 望月 修

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.798, pp.151-163, 2013 (Released:2013-02-25)

参考文献数

29

被引用文献数

2

---

The purpose of this study is to know differences between steady and unsteady drag coefficients of a sphere. Though we often have to estimate unsteady drag-forces acting on a moving obstacle, we are obliged to use the well-known steady drag coefficient for the first estimation because of lack of information about effects of unsteadiness on the drag coefficient. The usual way to take account of unsteadiness is an added mass. However, its application is restricted within the simple shape of an obstacle. We propose a way based on the equation of motion to obtain the unsteady drag coefficient. To confirm validity of the way, we measured and analyzed the motion of the falling sphere in water by using a high-speed camera and a motion capture method. The drag coefficients as a function of time were obtained by substituting measured values of velocity and acceleration into the equation of motion. The drag coefficient was 0.52 when the sphere attains the terminal velocity, being quite large at the beginning of motion. Comparing with the values obtained by the other previous studies, our result is reasonable.

著者

佐藤 慧拓 窪田 佳寛 望月 修

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.82, no.833, pp.15-00386, 2016 (Released:2016-01-25)

参考文献数

11

---

Many features of organisms have the possibility that can be applied to the infrastructure and network system for the communication. From the previous studies, the network system of the venation is known as the strong network on the damage. This relates the structure of leaf vein. In this study, we are focusing on the network of leaf vein to understand the strong network system. First, we study the network structure to know the relation between damage on leaf and the strong network. Then, the influence of damage on leaf vein for the water absorption on the leaf was studied with the dye flow visualization. The result shows that the network type of vein on real leaf is the mesh type network. The mesh type network has the benefit to make a bypath when the vein has the damage. The result of dye flow visualization shows that the real leaf requires the single vein to make a bypath for damage region. The increasing of area on water absorbed relates the distance of water absorption. This means that number of vein is not dominant for the speed of water absorption. Therefore, the network of leaf vein has a high robustness from the damage of vein by the mesh type network.

著者

松本 浩乃 窪田 佳寛 大石 正行 望月 修

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.82, no.833, pp.15-00389-15-00389, 2016 (Released:2016-01-25)

参考文献数

13

---

The typhoon often causes a serious damage of the apple before harvest. Many apples fall from trees by the strong wind. These apples are bagged to protect them from insects and control sun light for the apples coloring while they are ripening on the tree. We conceive that the wind-force acting on the bagging apple exceeds one without bag. Thus, we investigate the drag coefficient CD of the bagging apple by measuring drag force acting on an apple model experimentally. The shear stress on a stem under the typhoon is estimated for understanding one of mechanism for dropping apple due to the strong wind. The shear stress of a stem whose apple encounters the maximum velocity recorded at the past typhoon is estimated by the obtained CD. The drag force of the bagging apple becomes bigger than that of the apple without the bag. The bagging apple is not a rotational symmetry so that the CD is different with the different wind direction. The angle against the flow of model with the bag is changed from 0 deg. to 90 deg. to understand the influence of shape, since CD depends on the geometry. The shear force acting on the stem depends on the drag. Thus, the shear stress is larger if the drag is larger. The obtained shear stress is compared with allowable shear stress of a real tree. We suggest that there is possibility to decrease damage if we can decrease the drag of the bagging.

著者

村上 優依 窪田 佳寛 望月 修

出版者

日本流体力学会

雑誌

ながれ : 日本流体力学会誌 = Nagare : journal of Japan Society of Fluid Mechanics (ISSN:02863154)

巻号頁・発行日

vol.36, no.6, pp.417-420, 2017-12