Browsing by Author "Ma, Ming"
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- Elastic and inelastic analysis of panel collapse by stiffener bucklingMa, Ming (Virginia Tech, 1994-08-05)A method is developed for analyzing the flexural-torsional and lateral-torsional buckling ("tripping") behavior of flanged stiffeners subjected to axial force, end moment, lateral pressure and any combination of these. The effects of cross-sectional distortion, postbuckling behavior of the plate (incorporated by considering the plate effective width), initial imperfections and plasticity are included. The method uses the Rayleigh-Ritz approach. Based on an assumed strain distribution, a displacement field is obtained for the tripping model, and the total potential energy functional is then derived. The strain distribution assumptions coincide with van der Neut's assumption. However, unlike the somewhat obscure differential equation approach given by van der Neut, this study provides a simple, clear, energy approach. Also the resulting method is applicable in the inelastic range, which is not possible with van der Neut's approach. Both the rigid web case and the flexible web case are studied. The effect of plate rotational restraint in the elastic range is accounted for. The method requires only four degrees of freedom and therefore the solution process is rapid. In order to verify the method in the elastic range, a number of sample stiffened panels are analyzed using the ABAQUS foote element program; the results are in quite good agreement. An inelastic tripping model is then developed based on the established elastic model, using deformation theory. Results obtained using the inelastic tripping method are shown to be in good agreement with experimental results, and to be more accurate than other methods.
- Mosquito Acetylcholinesterase as a Target for Novel Phenyl-Substituted CarbamatesMutunga, James M.; Ma, Ming; Chen, Qiao-Hong; Hartsel, Joshua A.; Wong, Dawn M.; Ding, Sha; Totrov, Maxim M.; Carlier, Paul R.; Bloomquist, Jeffrey R. (MDPI, 2019-04-28)New insecticides are needed for control of disease-vectoring mosquitoes and this research evaluates the activity of new carbamate acetylcholinesterase (AChE) inhibitors. Biochemical and toxicological characterization of carbamates based on the parent structure of terbam, 3-tert-butylphenyl methylcarbamate, was performed. In vitro enzyme inhibition selectivity (Anopheles gambiae versus human) was assessed by the Ellman assay, as well as the lethality to whole insects by the World Health Organization (WHO) paper contact assay. Bromination at the phenyl C6 position increased inhibitory potency to both AChEs, whereas a 6-iodo substituent led to loss of potency, and both halogenations caused a significant reduction of mosquitocidal activity. Similarly, installation of a hexyl substituent at C6 drastically reduced inhibition of AgAChE, but showed a smaller reduction in the inhibition of hAChE. A series of 4-carboxamido analogs of the parent compound gave reduced activity against AgAChE and generally showed more activity against hAChE than AgAChE. Replacement of the 3-t-buyl group with CF3 resulted in poor anticholinesterase activity, but this compound did have measurable mosquitocidal activity. A series of methyl- and fluoro- analogs of 3-trialkylsilyl compounds were also synthesized, but unfortunately resulted in disappointing activity. Finally, a series of sulfenylated proinsecticides showed poor paper contact toxicity, but one of them had topical activity against adult female Anopheles gambiae. Overall, the analogs prepared here contributed to a better understanding of carbamate structure–activity relationships (SAR), but no new significant leads were generated.
- An Underwater Explosion-Induced Ship Whipping Analysis Method for use in Early-Stage Ship DesignBrainard, Benjamin Chase V. (Virginia Tech, 2016-01-27)This thesis presents an analysis method for determining the whipping response of a hull girder to underwater explosion (UNDEX) bubble pulse loading. A potential flow-based UNDEX bubble model capable of calculating the behavior of a migrating bubble for up to three pulses is developed. An approximate vertical plane ship vibration model is derived using fundamental beam theory by representing the ship as a free-free beam with varying cross-sectional properties along its length. The fluid-structure interaction is approximated using strip theory and the distant flow assumption. The most severe predicted whipping load conditions are applied to a MAESTRO finite element model of the ship as a quasi-static load case to determine the response of the structure to the whipping loads. The calculated hull girder bending moments are compared to the ultimate bending strength of the hull girder to determine if the girder will collapse. The analysis method is found to be a useful method for determining preliminary UNDEX-induced whipping design load cases for early-stage ship design. However, more detailed and accurate data is needed to validate and verify the predicted whipping responses. It is found that the most severe whipping loads occur as the result of an UNDEX event that occurs under the keel near midship and produces a bubble with a pulsation frequency similar to the natural vibration frequency of the ship in its third mode. Significant damage to the ship structure and hull girder collapse is possible as a result of these loads.