The purpose of this investigation is to clarify the form of the vortex street shed from a circular cylinder immersed in a laminar boundary layer. The main technique of this experiments is used the flow visualizations by the smoke-wire method to observe the vortex street behind the cylinder immersed in the boundary layer. The results of the flow visualizations show that there are five different types of the vortex streets depending on the Reynolds numbers as well as the shear parameters. The first pattern which is observed at small Reynolds number is the standing edies. Increasing the Reynolds number the second pattern appears, where the downstream flow of edies becomes unstable similar to that of in the uniform flow. The third is one of the typical case to the wake flow in the boundary layer, that is, the single row vortex street is formed only from the upper edge of the cylinder, and no vortex shedding from the lower edge is observed. In the fourth pattern, the vortex shedding from the lower edge is observed intermittently but does not grow into the street. The fifth pattern is the double row vortex street, but even in this case vortices shed from the lower edge of the cylinder are eliminated at the downstream of the cylinder because of the shear flow in the boundary layer.
Stress analysis around a cylindrical insert embedded in the honeycomb sandwich panel is performed and the solution is derived analytically. As a result, it is found that there is a transition layer in the vicinity of the insert where the stresses in the face sheet and the core vary remarcably. Most of the out-of-plane shear force is mainly supported by the face sheet in the transition layer. The strength tests are performed and their results show that the pull-out strength of the insert is independent of the bonding between the core and the insert. It is proved that the potting compound which is usually used to bond them is not necessary. The weight of the honeycomb sandwich panel can be much reduced without using the potting compound.
High performance spiral water jet cutting system for soft materials such as liver and styrofoam has been developed. With this system, the 7cm-thick liver was cut under the 2.94×106Pa (30kgf/cm2)-4.90×106Pa (50kgf/cm2) water pressure. The kerf was narrower and its surface was smoother than that by conventional system. The motivation behind this study is to clarify water jet cutting performance from the fluid dynamics view point. Alternatively, one would think that materials could be cut by introducing water at high axial velocity. Polymer water jet for converging the jet structure have been trying. But these trials are not satisfactory in its cutting surface condition and its cost performance. The water jet cutting performance is depended on the jet energy transfer efficiency to target material surface. The essential approaches for achieving the high cutting to decrease performance are to increase the water jet momentum and to decrease the chance of collision between the direct and rebounded water jets. These requirement can be responded by spiral system, because the focusing spiral jet with high stability transfers water jet momentum effectively to the materials, and its swirling characteristic decreases the chance of collision of jets. Finally, an approximate solution for normal shear stresses was obtained and the results were compared with the experiments. These superior stress distributions contributed to enhance the performance over a conventional water jet system.
This paper applies an order-n formulation, which efficiently solves dynamic equations of serial rigid body systems, to calculate the deployment process of a folded spacecraft model in space. A spacecraft model is considered to be free in space and has a tree topology with rigid multi-bodies. Discontinuities in velocity and angular velocity occur when a hinge is locked due to a ratchet mechanism during the deployment process. Equations between the velocity jump and the impulsive force are formulated in a recursive manner and are solved by using the order-n formulation. A numerical example demonstrates the validity of the present formulation. A center-arm and six panels of a spacecraft model are deployed due to the force of a shrunk spring.
This paper describes a practical control scheme for autonomous retrieval of tumbling satellite with an onboard manipulator using a CCD camera. In the retrieval of a satellite, a reference trajectory for positioning the end-effector of manipulator is generated with time delay because of processing time for target motion estimator and manipulator controller. Consequently, the end-effector fails to capture the target, and the control system shows poor performance. To solve this problem, a control system is proposed, which utilizes predictive trajectory based on target satellite dynamics. The validity and the usefulness of the proposed control scheme are verified by computer simulations and experiments using 3-D hardware simulator with 9 degrees of freedom.