Robust multi-steps input command for liquid sloshing control

A robust input command based on multiple steps for eliminating the residual vibrations of a multimode linear system is proposed. Only the system resonant frequencies are needed to determine the step magnitudes in the shaped command. The command duration is selectable to help in designing an optimum command that compensates between the reduction in the transient vibration, the enhancement in the command robustness, and the increase in the total maneuver time. The induced transient and residual sloshing oscillations of a suspended water-filled container are suppressed using the proposed command. The dynamics of the sloshing is numerically simulated using finite element method that accommodates the interactions between the fluid, structural, and multi-body dynamics. A short move time penalty is incurred with the price of significant reduction in the liquid sloshing. The performance of the shaped command to the system parameters and the robustness to their uncertainty are investigated. An improved robust input command in the presence of uncertainties in the cable length and water depth is also introduced. The effectiveness and excellence of the proposed command is demonstrated through a comparison with multimode zero-vibration input shaper and time-optimal flexible-body control.

Learning Body Techniques: Dance and Body Flexibility among Gay Black Teens in Salvador de Bahia, Brazil

This article is the result of ethnographic fieldwork among amateur dancers, mainly among gay adolescents from the outskirts of Salvador de Bahia (Brazil), who label themselves as “flexible”. This self-definition arises out of bodily flexibility techniques, cultivated through intense physical work. By focusing on specific training situations, such as stretching exercises, I trace understand how the “flexible” body is built. I propose that the language mobilized by these young people offer an important guide to understanding the distinctive elements of this practice. The practitioners’ accounts and my own observations of the practice indicate that the embodiment of acrobatic skills occurs in a process that weaves body and environment. Following Ingold, I argue that an ecological approach help us to comprehend this kinesthetic practice as spatial realization, as well as providing useful insights into its learning practices exploring the richly sensory dimension of learning practices and development of motor sensibilities, such as the sound and the imperative pain experience. Furthermore, I analyze how my interlocutors’ concept of body fits the theoretical idea of how bodies should not be defined by what they are, but rather by what they are able to do.