Artigos - Engenharia de Telecomunicações - São João da Boa Vista
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ItemArtigo Vortex induced vibration in a single degree of freedom cylinder with structural nonlinearities(ABCM, 2019-10-25) Bastos, Sérvio Túlio Suenai Haramura [UNESP]; Vasconcellos, Rui Marcos Grombone de [UNESP]; Marques, Flávio DonizetiIn this research project, it is proposed the investigation of the effects of hardening structural nonlinearity in a single degree of freedom cylinder exposed to a transverse flow, presenting the vortex induced vibration effect. To check the validity of the implemented phenomenological model, numerical simulations have been performed and the results have been compared with experiments. Simulations showed that the presence of this type of nonlinearity extends the lock-in region by changing the structural natural frequency as the amplitude of oscillations increases with the freestream speed and the vortex shedding frequency. Besides, other parameters, such as the mass and the diameter of the cylinder, affect the synchronization region. A wind tunnel test validated of the obtained simulated results. The contributions of this research can be helpful in order to prevent vortex induced vibrations in realistic nonlinear structures.ItemArtigo Design antena de microfita com alto ganho deslocando a frequência de ressonância com pinos em curto-circuito para aplicações no 5G(Sociedade Brasileira de Telecomunicações, 2023-10-12) Santos, Renan Alves dos; Bernardo, Helton Silva [UNESP]; Almeida, Milene Rodrigues; Penchel, Rafael Abrantes [UNESP]; Universidade Federal de UberlândiaEste artigo apresenta a aplicação de uma técnica de aumento de ganho em antenas de microfita para uso em redes celulares de quinta geração (5G), operando na faixa de frequência de 3,5 GHz. O método consiste em inserir quatro pinos metálicos de forma simétrica no elemento ressonante de uma antena de microfita quadrada, estabelecendo um curto-circuito com o plano de terra. Esta modificação introduz um feito indutivo na impedância de entrada que desloca frequência de ressonância 1,86 vezes, aumentando a área efetiva do ressonador. Resultados obtidos por meio de simulações demonstram que as antenas modificadas apresentam uma largura de banda semelhante à de uma antena convencional, porém com um ganho aumentado de 2,47 dB, alcançando um ganho de 10,14 dBi na direção de máxima irradiação.ItemArtigo A study of the errors of the averaged models in the restricted three-body problem in a short time scale(Springer, 2015-07-01) Domingos, Rita de Cássia [UNESP]; Prado, Antonio Fernando Bertachini de Almeida; Moraes, Rodolpho Vilhena de; Universidade Estadual Paulista (Unesp); Instituto Nacional de Pesquisas Espaciais (INPE); Universidade Federal de São Paulo (UNIFESP)The objective of the present research is to study the accuracy of the double- and single-averaged models that are usually considered to predict the motion of spacecrafts or celestial bodies that have their motion perturbed by a third-body. Those two models are compared with each other and then validated against the complete elliptic restricted three-body problem. Those models are developed to give a faster but general behaviour of the motion of the perturbed body in a medium or longer time scale. The researches performed here verify the accuracy of those methods for shorter time scales by showing the differences in terms of the values of the inclination and eccentricity of the perturbed body predicted by those models. Those differences are calculated both at every instant of time and as an integral over the time. The use of the integral along the time for the errors is a new form to study those differences and show a more complete comparison of the accuracy of those approximations, completing the instantaneous picture given by the usual approach of looking at the instantaneous measurement. If the value of the integral is divided by the time integration, the mean error is obtained. The results show that the single-averaged model is better in the short time scale and the difference among those models is smaller when predicting the eccentricity than the inclination. The effects of the time scale is verified by varying the study to values from 2 days up to 50 revolutions of the Moon (1,366 days). Another important point found in the present paper is the range of the eccentricities of the perturbing body that accelerates the dynamics.