• International Journal of Aeronautical and Space Sciences
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• v.18 no.4
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• pp.797-806
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• 2017

In this study, the reflection coefficient (RC) and the flame transfer function (FTF) were measured by applying acoustic excitation to a duct-type model combustor and were used to predict the frequency of the combustion instability (CI). The RC is a value that varies with the excitation frequency and the geometry of the combustor as well as other factors. Therefore, in this study, an experimentally measured RC was used to improve the accuracy of prediction in the cases of 25% and 75% hydrogen in a mixture of hydrogen and methane as a fuel. When the measured RCs were used, an unstable condition was correctly predicted, which had not been predicted when the RCs had been assumed to be a certain value. The reason why the CI occurred at a specific frequency was also examined by comparing the peak of the FTF with the resonance frequency, which was calculated using Helmholtz's resonator analysis and a resonance frequency equation. As the CI occurred owing to the interaction between the perturbation in the rate of heat release and that in the pressure, the CI was frequent when the peak of the FTF was close to the resonance frequency such that constructive interference could occur.

• Journal of the Korean GEO-environmental Society
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• v.15 no.11
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• pp.43-51
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• 2014

In this study, a series of pullout experiments were conducted on geogrid with attached passive reinforcement with respect to silt containments. Experiments were performed on man-made sand ground containing different silt of 0 %, 17 %, 35 % under various normal stresses 30 kPa, 60 kPa, 120 kPa respectively. The pullout test results showed that passive reinforcement increased the pullout strength over all silt contained condition and showed up to 20 % increases for same soil condition. The test results converted to the coefficient of interaction of pullout test to investigate the effect of reinforcement and the case of passive reinforcement showed 0.7~1.6 distribution depend on a silt contents. Therefore it is concluded that the overall length of geogrid can be reduced under the low vertical stress conditions.