RESUMO
Vortex-sheet (V-S) models of jets are widely used to describe the dynamics of modes, such as the Kelvin-Helmholtz instability and guided acoustic waves. However, the absence of the free-stream acoustic modes in the V-S eigenspectrum is seldom pointed out in the literature. This family of modes is important if, for example, one is interested into the problems of sound emission or flow-acoustic interactions. In this work, it is shown how a distantly confined jet may be used as a surrogate problem for the free jet, in which the free-stream acoustic waves appear as a set of discrete modes. Comparing the modes observed in the free jet with those of the distantly confined jet, we show that other than the free-stream acoustic modes, the eigenvectors and eigenvalues converge exponentially with the wall distance. The proposed surrogate problem, thus, efficiently reproduces the dynamics of the original problem while accounting for the dynamics of the free-stream acoustic eigenmodes.
RESUMO
O arremesso no handebol é um gesto complexo e rápido podendo ser realizado com um salto prévio ou com os pés em contacto com o solo (arremesso em apoio). A fim de tentar compreender as variáveis envolvidas no arremesso com apoio no handebol. O presente trabalho teve como objetivo principal analisar as componentes críticas envolvidas na face de aceleração do braço. Os Dados foram coletados perante um atleta de handebol do sexo masculino, 27 anos, 94Kg e 190 cm de altura. Os resultados foram obtidos através de análise tridimensional (3D), sendo utilizadas 6 câmeras de vídeo com ritmo de amostragem de 200 imagens por segundo. Para análise das variáveis cinemáticas foi usado um software ?C-Motion INC - Visual 3D Professional?. A posição angular e velocidade de rotação interna do ombro no momento do lançamento da bola foi de 58º graus e 1159 º/s, respectivamente. O cotovelo apresentou 56º de flexão e 907 º/s de velocidade no momento de liberação da bola. A velocidade linear da bola foi de 22 m/s. Levando em consideração o fato de que a rotação interna do ombro juntamente com a extensão do cotovelo correspondem a 73% da velocidade da bola podemos concluir que é necessário analisar outras componentes críticas para melhor compreensão do gesto.
The shot in handball is a complex and fast gesture that can be performed prior to a jump or with feet in contact with the ground (supported shot). In order to try to understand the variables involved in handball supported shot, this study aimed to analyze the critical components involved in the arm acceleration face. Data were collected from a male handball athlete, 27 years old, 94 kg, and 190 cm tall. The results were obtained though three-dimensional analysis (3D), which required 6 video cameras with sampling rate of 200 frames per second. In order to analyze kinematic variables, a ?C-Motion Inc ? Professional Visual 3D? software was used. The angular position and speed of internal rotation of the shoulder at the moment of the shot were 58 degrees and 1159 º/s, respectively. The elbow presented a 56º flexion and 907º/s speed at the time of the ball release. The linear speed of the ball was 22 m/s. Taking into account the fact that the internal rotation of the shoulder along with the elbow extension corresponds to 73% of the ball speed, we can conclude that it is necessary to analyze other critical components to better comprehension the gesture.
