| Summary: | 碩士 === 國立臺灣大學 === 生物產業機電工程學研究所 === 97 === Since harvested fruit easily softens and loses its market value at room temperature, a low-temperature environment is required to preserve the fruit’s firmness if a longer shelf life is desired. Thus using elastic property to establish a nondestructive quality evaluation index is one of the important research issues of biological engineering. This study aims at investigating the variations of the elastic properties of stored “Jen-Ju Bar” a most popular variety of guava in Taiwan. The ASABE standard parallel plate compression test and the impulse response test were used to measure the variation of impulse vibrating resonant frequencies, vibrating damping ratios and elastic moduli of the fruit stored at 5°C, 10°C, 15°C and room temperature. Besides, COMSOL Multiphysics was used to simulate the fruit’s vibration modes and resonant frequencies during resonating. Nested experimental design was adopted to analyze the effects of storage duration and temperature on the above elastic properties. Model geometries of fruits for finite elements simulation were constructed using surface topology scanning. Then, the elastic moduli measured in the impulse response test were taken for the material properties. The 3-D structural mode was then used to calculate the samples’ vibrating eigenfrequencies, and the resonant frequencies were determined based on the vibration modes of elastic sphere in literature. The results of the simulation showed that the resonant frequencies of S20 mode resembled the values measured by impulse response test; in addition, the resonant frequencies of S30 mode and S40 mode, rarely observed in experiments, were found. The results of the experiments showed that the impulse vibrating resonant frequencies and the elastic moduli measured by parallel plate compression test and the impulse response test decreased as the storage duration lengthened, and these three showed a similar trend. Vibrating damping ratios measured by impulse response test increased as the storage duration lengthened, with a slower rate of rising at a low storage temperature than at a high storage temperature. The nested experimental design analyses of vibrating damping ratios showed significant effects of both storage temperature and duration. Compared with impulse vibrating resonant frequency, the variation of vibrating damping ratio was less affected by individual sample differences, thus more appropriate for a nondestructive index to evaluate the physical properties of “Jen-Ju Bar”.
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