Multidisciplinary design optimization is one of the modern design methods. It was developed in several different structures and used to solve some of the theoretical and applied problems. Collaborative optimization is one of the structures of bi-level multidisciplinary design optimization. It comprises system level and discipline level, which is used to solve engineering complex problems. Collaborative optimization structure maximizes options of discrete disciplines and provides a mechanism for coordinating design problem at system level. The present research discusses capability of the collaborative optimization method to solve multidisciplinary problems aiming at reducing the weight of a liquid-propellant system. It is realized by implementing a propellant system design comprising an engine and consumption of fuel and oxidizer. To do this, we calculated engine parameters through response surface methodology. The calculation parameters were optimized by applying a response surface and an engine structure design in the collaborative optimization process at the same time in the form of combustion, geometry, and weight (structure) problems with the evolutionary algorithms. Finally, we compared the obtained results with the reference results and specified the optimization rate achieved for the values of variables. The values included pressure increase of combustion, specific impulse, engine mass reduction, rate of fuel and oxidizer consumption with fixed thrust, and burn time.

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The effect of inertial forces on the Structural Dynamics (SD) behaviour of Elastic Flapping Wings (EFWs) is investigated. In this regard, an analytical modal-based SD solution of EFW undergoing a prescribed rigid body motion is initially derived. The formulated initial-value problem is solved analytically to study the EFW structural responses, and sensitivity with respect to EFWs’ key parameters. As a case study, a rectangular wing undergoing a prescribed sinusoidal motion is simulated. The analytical solution is derived for the first time and helps towards a conceptual understanding of the overall EFW's SD behaviour and its analysis required in their designs. Specifically, the EFW transient and steady response in on-off servo condition is also attended.

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A novel integrated aeroelastic model of flapping wings (FWs) undergoing a prescribed rigid body motion is presented. In this respect, the FW nonlinear structural dynamics is enhanced via a newly proposed modification of implicit condensation and expansion (MICE) method that better considers the structural nonlinear effects. In addition, the unsteady aerodynamic model is also an extension of the widely utilized modified strip theory (MST) in which the flexibility effects are accounted for (MST-Flex). The integrated utility of the proposed generalized MICE and MST-Flex is demonstrated to be more realistic for elastic FW flight simulation applications. The prescribed rigid body motion is produced via a servo motor whose dynamics is also considered for the analysis. A special case study is also performed whose combined aeroelastic solution is determined and validated under a sinusoidal flapping motion. To this end, an experimental setup is designed and tested in order to validate the proposed integrated approach for aeroelastic modeling of FWs. There is very good agreement between the numerical and experimental results for elastic FW aerodynamics. It should be noted that the proposed integrated aeroelastic approach is readily adaptable to all kinds of elastic wings with arbitrary geometry and various combination of structural elements.