Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 5 Articles
This paper is devoted to introduce a novel method of the operational matrix of integration for Legendre wavelets in order to predict\nthe thermal behavior of stratospheric balloons on float at high altitude in the stratosphere. Radiative and convective heat transfer\nmodels are also developed to calculate absorption and emission heat of the balloon film and lifting gas within the balloon. Thermal\nequilibrium equations (TEE) for the balloon system at daytime and nighttime are shown to predict the thermal behavior of\nstratospheric balloons. The properties of Legendre wavelets are used to reduce the TEE to a nonlinear system of algebraic\nequations which is solved by using a suitable numerical method. The approximations of the thermal behavior of the balloon film\nand lifting gas within the balloon are derived. The diurnal variations of the film and lifting gas temperature at float conditions\nare investigated, and the efficiency of the proposed method is also confirmed....
A cyclic cohesive zone model is applied to characterize the fatigue crack growth behavior of a IN718 superalloy which is frequently\nused in aerospace components. In order to improve the limitation of fracture mechanics-based models, besides the predictions of\nthe moderate fatigue crack growth rates at the Parisââ?¬â?¢ regime and the high fatigue crack growth rates at the high stress intensity factor\nÃ?â?K levels, the present work is also aimed at simulating the material damage uniformly and examining the influence of the cohesive\nmodel parameters on fatigue crack growth systematically. The gradual loss of the stress-bearing ability of the material is considered\nthrough the degradation of a novel cohesive envelope. The experimental data of cracked specimens are used to validate the\nsimulation result. Based on the reasonable estimation for the model parameters, the fatigue crack growth from moderate to high\nÃ?â?K levels can be reproduced under the small-scale yielding condition, which is in fair agreement with the experimental results....
The study and analysis of human physiology during short- and long-duration space flights are the most valuable approach in order\nto evaluate the effect of microgravity on the human body and to develop possible countermeasures in prevision of future\nexploratory missions and Mars expeditions. Hand performances such as force output and manipulation capacity are\nfundamental for astronautsââ?¬â?¢ intra- and extravehicular activities. Previous studies on upper limb conducted on astronauts during\nshort-term missions (10 days) indicated a temporary partial reduction in the handgrip maximum voluntary contraction (MVC)\nfollowed by a prompt recovery and adaptation to weightlessness during the last days of the mission. In the present study, we\nreport on the ââ?¬Å?Crewââ?¬â?¢s Health: Investigation on Reduced Operabilityââ?¬Â (CHIRO) protocol, developed for handgrip and pinch\nforce investigations, performed during the six months increment 7 and increment 8 (2003-2004) onboard International Space\nStation (ISS). We found that handgrip and pinch force performance are reduced during long-term increments in space and are\nnot followed by adaptation during the mission, as conversely reported during short-term increment experiments. The\napplication of protocols developed in space will be eligible to astronauts during long-term space missions and to patients\naffected by muscle atrophy diseases or nervous system injury on Earth....
In this paper, a new adaptive sliding mode control method is presented for the longitudinal model of a generic hypersonic vehicle\nsubject to uncertainties and external disturbance. Firstly, an oriented-control model with mismatched uncertainties is built for a\ngeneric hypersonic vehicle. Secondly, the back-stepping technique is introduced to design a sliding mode controller with an\nadaptive law to adapt to the disturbance and uncertainty. Thirdly, a set of nonlinear disturbance observers are designed to\nestimate the lumped disturbance and compensate the sliding mode controller, and the stability of the proposed controller is\nanalyzed by utilizing Lyapunov stability theory. Finally, simulation results show that the effectiveness of the proposed controller\nis validated by the nonlinear model and the proposed method exhibits promising robustness to mismatched uncertainties....
During countersunk hole machining, defects like geometrical deviation of the chamfer angle and delamination are easily introduced\ninto the structure. To investigate the influences of geometrical deviation on delamination propagation around the countersunk hole\nduring assembly, a progressive damage model (PDM) combining cohesive element was proposed and validated. Numerical analyses\nwere then carried out to study delamination propagation behavior under the influences of geometrical parameters including\ndelamination factor, chamfer angle, and location of delamination. The results show that when delamination appears at the\ntransition area of the countersunk hole, the load causing the delamination evolution is much smaller than other cases....
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