This study highlights the effects of a flutter constraint on the multidisciplinary design optimization (MDO) of a truss-braced-wing transport aircraft for both medium-range and long-range missions. Previous MDO studies for both of these missions were performed without considering the effect of flutter. Hence, the flutter constraint has now been added to the other design constraints in this MDO study. Minimizing the takeoff gross weight and the fuel burn are selected as the objective functions. The results show that, for the medium-range mission, the flutter constraint applied at 1.15 times the dive speed imposes a 1.5% penalty on the takeoff weight and a 5% penalty on the fuel consumption while minimizing these two objective functions. The penalties imposed on the minimum-takeoff-grossweight and minimum-fuel-burn designs for the long-range mission due to the similar constraint are 3.5 and 7.5%, respectively. Importantly, the resulting truss-braced-wing designs are still superior to equivalent cantilever designs for both of the missions, as they have both lower takeoff gross weight and fuel burn. However, a relaxed flutter constraint applied at 1.05 times the dive speed can restrict the penalty on the takeoff gross weight to only 0.3%, and that on the fuel burn to 2% for minimizing both the objectives, respectively, for the medium-range mission. For the long-range mission, a similar relaxed constraint can reduce the penalty on fuel burn to 2.9% when that objective function is minimized. These observations suggest the need for a cost-benefit study to determine whether activeflutter-suppression mechanisms with their added weight and complexities can be used for the truss-braced-wing aircraft to further reduce either the takeoff gross weight or the fuel burn.

Response attenuation of seismically excited adjacent buildings connected by a MR damper is studied using semi-active LQR controller design. The modified Bouc-Wen model relating damper force to input voltage/states is considered. Thus, obtaining the input voltage to realize a desired control force is a non-trivial task. The desired control force is obtained using LQR control, and desired voltage predicted based on either a RNN model or a CVL. Results for the 5-storey and 3-storey interconnected buildings (B5-B3) are obtained in terms of peak and RMS responses. These are compared with passive-on control for which a constant saturation voltage is applied to the damper. Percentage reduction in maximum peak [RMS] response, when using LQR-CVL instead of passive on control, is 24[20] for interstorey drift, 18[23] for displacement, and 17[26] for accelerations. Corresponding further percentage reductions of 6[5], 5[5], and À5[4], and reductions in base shear, occur when considering LQR-RNN vis-á-vis LQR-CVL control. Peak accelerations for B5[B3] attenuate [increase] significantly, resulting in a re-distribution and reduction of base shear, when comparing semi-active versus passive-on control. Results show that connection of adjacent buildings using MR damper driven by a LQR-RNN controller provides a promising means of response attenuation.

This study pursues designs for a medium-range, transonic transport aircraft using a multidisciplinary optimization approach which uses the flutter speed as a constraint in addition to the other constraints. The aim is to use the flutter constraint for the study of truss-braced wing aircraft configurations having a cruise Mach of 0.7 and a flight mission that is similar to that of a Boeing 737-800NG. The basic multidisciplinary tools presented here have been used previously to obtain designs for aircraft with a cruise Mach of 0.78 and 0.85; however these designs were not obtained with the current flutter constraint. The objective function considered here is to minimize the take-off gross weight. Results obtained in this study show that the flutter constraint is active for the truss-braced wing configurations, and these aircraft configurations undergo 1% penalty on their takeoff weight to satisfy the flutter constraint. This work is important since it documents the weight penalties associated with satisfying the flutter constraint when the objective is to minimize the take-off gross weight of the aircraft. Thus, the designer can decide if active flutter suppression can be implemented to obtain a lighter aircraft.

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In this study, a multidisciplinary design optimization technique has been used to investigate the potential benefits of truss-braced wing configurations in the design of medium-range subsonic military cargo aircraft. Previous studies of truss braced wing aircraft (both strut-braced wings) and truss-braced wing) at Virginia Tech for both Boeing-777 and Boeing-737 type of missions have shown that such advanced configurations provide both structural and aerodynamic benefits. The objective of this study was to explore the potential benefits of truss-braced wings in minimizing fuel consumption when applied to a subsonic Lockheed Martin C-130J like aircraft with a cruise Mach number of 0.60, 1800 NM range and a maximum payload of 40,000 lbs. The results show a 10.7% reduction in fuel weight with just a 5%increase in TOGW of the aircraft, a 27% increase in lift to drag ratio and 25% increase in wingspan for strutbraced wing aircraft. This study highlights the benefits of the truss-braced wing configurations for cargo aircraft and provides a comparison amongst various trussbraced wing configurations. For this class of aircraft, the strut-braced wing proves more attractive than a truss-braced wing (strut plus one jury) configuration.