No abstract

No abstract

Recently, Rim1,2 suggested an exact DtN boundary condition to study the three-dimensional wave diffraction by a floating body or undulated seabed for horizontally-unlimited water domain of finite-depth. This paper focuses on linear wave interaction with a bottom-mounted body in front of a vertical wall. An artificial boundary is chosen as a virtual cylindrical surface so that it can enclose two bodies (one is the original body and another is its imaginary body by the method of mirror image), and the entire water domain is divided into an interior subdomain and an exterior one by the artificial boundary. An exact DtN artificial boundary condition on the artificial boundary is derived from an analytical solution in the exterior subdomain, and it is used as a boundary condition to solve hydrodynamic interaction of the bodies with the interior subdomain numerically using boundary integral equation. The present numerical model is validated by comparison with ANSYS AQWA in case of a bottom-mounted circular cylinder. The effects of heading angle and distance from the wall to the body on exciting forces are considered.

In order for weightlifters to achieve good technical skills in clean & jerk, a study of kinematic analysis and optimization of jerk using elasticity of weightlifting bar in clean & jerk is conducted. First of all, barbell’s trajectory, which leads to derivation of barbell’s velocity and acceleration over time, is tracked from video clip filmed the lifter’s performance by image processing technology including pattern recognition. Since clean lift in clean & jerk is similar to snatch lift in principle, focus is only on jerk just after finish of clean lift. Five kinematic characteristics- “Jerk-Preparing-Time”, “Jerk-Drive-Velocity”, “Jerk-Time”, “Jerk-Offset” and “Jerk-Drop” are newly introduced to evaluate the jerk technique. Then, a kinematic model which is comprised of springs and dashpots is proposed in order to simulate and optimize the jerk using elasticity of weightlifting bar. Spring constant and damping coefficient of the model is estimated by analyzing the barbell’s oscillation on the shoulder. Besides, spring constant is calculated by theory of bending of beam, as well. Finally, an optimal control problem based on the proposed kinematic model is formulated and solved to optimize the jerk. The methodology is illustrated with case study, showing good agreement with actual lifts. It could be useful for optimizing clean & jerk technique.

No abstract