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Browsing by Author "Adjerid, Khaled"

Now showing 1 - 3 of 3
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    The Biomechanics of Tracheal Compression in the Darkling Beetle, Zophobas morio
    Adjerid, Khaled (Virginia Tech, 2019-11-05)
    In this dissertation, we examine mechanics of rhythmic tracheal compression (RTC) in the darkling beetle, Zophobas morio. In Chapter 2, we studied the relationship between hemolymph pressure and tracheal collapse to test the hypothesis that pressure is a driving mechanism for RTC. We found that tracheae collapse as pressure increases, but other physiological factors in the body may be affecting tracheal compression in live beetles. Additionally, as the tracheae compress, they do so in varying spatial patterns across the insect body. In chapter 3, we examined spatial variations in the taenidial spacing, stiffness, and tracheal thickness along the length of the tracheae. We related variations in Young's modulus and taenidial spacing with measurements of collapse dimples and found that spatial patterns of Young's modulus correlate with dimensions of collapse dimples. This correlation suggests an intuitive link between tracheal stiffness variations and the unique patterns observed in compressing tracheae. Lastly, in chapter 4, we studied the non-uniform collapse patterns in 3-D. By manually pressurizing the hemocoel and imaging using synchrotron microcomputed tomography (SR-µCT), we reconstructed the tracheal system in its compressed state. While previous studies used 2-D x-ray images to examine collapse morphology, ours is the first to quantify collapse patterns in 3-D and compare with previous 2-D quantification methods. Our method is also the first to make a direct measure of tracheal volume as the tracheal system compresses, similar to the phenomenon that occurs during rhythmic tracheal compression.
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    Functional compartmentalization in the hemocoel of insects
    Pendar, Hodjat; Aviles, Jessica; Adjerid, Khaled; Schoenewald, Caroline; Socha, John J. (Springer Nature, 2019-04-15)
    The insect circulatory system contains an open hemocoel, in which the mechanism of hemolymph flow control is ambiguous. As a continuous fluidic structure, this cavity should exhibit pressure changes that propagate quickly. Narrow-waisted insects create sustained pressure differences across segments, but their constricted waist provides an evident mechanism for compartmentalization. Insects with no obvious constrictions between segments may be capable of functionally compartmentalizing the body, which could explain complex hemolymph flows. Here, we test the hypothesis of functional compartmentalization by measuring pressures in a beetle and recording abdominal movements. We found that the pressure is indeed uniform within the abdomen and thorax, congruent with the predicted behavior of an open system. However, during some abdominal movements, pressures were on average 62% higher in the abdomen than in the thorax, suggesting that functional compartmentalization creates a gradient within the hemocoel. Synchrotron tomography and dissection show that the arthrodial membrane and thoracic muscles may contribute to this dynamic pressurization. Analysis of volume change suggests that the gut may play an important role in regulating pressure by translating between body segments. Overall, this study suggests that functional compartmentalization may provide an explanation for how fluid flows are managed in an open circulatory system.
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    A Study on the Dynamic Characterization of a Tunable Magneto-Rheological Fluid-Elastic Mount in Squeeze Mode Vibration
    Adjerid, Khaled (Virginia Tech, 2011-06-09)
    This research undertakes the task of static and dynamic characterization for a squeeze mode Magneto-Rheological (MR) Fluid-Elastic mount. MR fluid's variable viscosity rate is advantageously used to develop a mount capable of mitigating input vibrations of varying magnitudes and frequencies depending on electromagnetic flux. Various mechanical components are synthesized into a dynamic testing rig in order to extract vibrational characteristics of the mount and to compare it with existing mount technologies. This project focuses on a mount design that was proposed and improved upon by previous researchers at the Center for Vehicle Systems and Safety (CVeSS). Using a previously designed electromagnet and test rig, the MR mounts are characterized using a quasi-static test. From this test we extract the stiffness and damping characteristics of the MR mount. A set of upper and lower limit baseline mounts made with rubber and steel inserts are also tested simultaneously with the MR mount. Their isolation improvements are compared with conventional passive mounts. After acquiring the stiffness and damping characteristics of the mount, a model is used to simulate a response to input vibrations in the frequency domain. A dynamic test is run on both the baseline testers as well as the MR mount. Having the frequency-magnitude response allows us to determine a usable resonance range and magnitude of vibration mitigation. The results of this study indicate that the mounts tested here are an effective means of suppressing start-up vibrations within mechanical systems and show promise for further development and application. Future studies of these systems can include tests of MR metal-elastic mount designs for durability as well as parametric studies based on MR fluid type and other factors.