Unsteady hydrodynamic forces acting on a robotic hand and its flow field
Hideki Takagi1, Motomu Nakashima, Takashi Ozaki
1Faculty of Health and Sport Sciences, University of Tsukuba Tennoudai 1-1-1, Tsukuba 305-8574, Japan. takagi@taiiku.tsukuba.ac.jp
Abstract:
This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force.
Related Concept Videos
Hydrostatic Pressure Force on a Curved Surface
Steady Flow of a Fluid Stream
During this process, the momentum of the fluid within the control volume remains constant over the time interval dt. By applying the...
Pressure Variation in a Fluid at Rest
When measuring pressure at two different levels within the fluid, the difference in pressure...
Hydrostatic Pressure Force on a Plane Surface
Typical Model Studies
Pressure of Fluids


