Entity

Time filter

Source Type

San Diego, CA, United States

Oktay T.,Erciyes University | Sultan C.,Virginia Polytechnic Institute and State University | Sultan C.,Ocean Aero
Journal of Aircraft | Year: 2013

This article proposes simultaneous helicopter and control system design and illustrates its advantages. First, the traditional, sequential approach in which a satisfactory control system is designed for a given helicopter is applied. Then, a novel approach, in which the helicopter and control system are simultaneously designed, is applied to redesign the entire system. This redesign process involves selecting certain helicopter parameters as well as control system parameters. For both design procedures the key objectives are to minimize control energy and satisfy prescribed variance constraints on specific outputs. In order to solve the complex optimization problem corresponding to the simultaneous design approach, an efficient solution algorithm is developed by modifying the simultaneous perturbation stochastic approximation method to account for limits on optimization parameters. The algorithm is applied to redesign helicopters using models generated in straight level as well as maneuvering flight conditions. The performance of the designs obtained using the sequential and simultaneous design approaches is compared and the redesign process is thoroughly investigated. Finally, the robustness of the redesigned systems is also studied. © 2012 by Ernesto Benini. Source


Tamijani A.Y.,Virginia Polytechnic Institute and State University | Kapania R.K.,Virginia Polytechnic Institute and State University | Kapania R.K.,Ocean Aero
AIAA Journal | Year: 2010

The element-free Galerkin method, which is based on the moving-least-squares approximation, is developed for vibration analysis of unitized structures (e.g., a plate with curvilinear stiffeners). The plate and stiffeners are modeled using the first-order shear deformation theory and Timoshenko beam theory, respectively. The moving-leastsquares approximation does not satisfy the delta function property. Consequently, an approximation method (e.g., the well-known penalty method) must be used for imposing essential boundary conditions. A key benefit of using element-free Galerkin for the vibration analysis of a stiffened panel is that the locations and curvatures of the stiffeners can be changed without modifying the plate nodes. Numerical results for different stiffeners, configurations, and boundary conditions are presented. All results are verified using the commercial finite-element software ANSYS. Excellent agreement is seen in all cases. A comparison of the present formulations with other available results for stiffened plates is also made. The mesh-free approach yields highly accurate results for the plates with curvilinear stiffeners. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Source


Zhang G.,Harbin Institute of Technology | Zhou D.,Harbin Institute of Technology | Mortari D.,Texas A&M University | Henderson T.A.,Virginia Polytechnic Institute and State University | Henderson T.A.,Ocean Aero
Journal of Guidance, Control, and Dynamics | Year: 2012

This paper presents an analytical study of the two-body tangent orbit technique by providing solution-existence conditions. The flight-direction angle is used to describe and solve this problem. Closed-form solutions are obtained for three classic problems: specified arrival flight-direction angle, specified departure flight-direction angle, and cotangent transfers. Not all of the problems admit solutions; thus, closed-form conditions for solution existence are provided by imposing a positive semilatus rectum constraint and a negative transfer-orbit energy (elliptic orbit transfer) constraint. The final solution-existence condition is then provided in terms of the true anomaly range for initial or final orbit. The singularity problem of 180 deg orbit transfer is also analyzed. Several examples are provided to verify the proposed analytical methods. Copyright © 2011 by Gang Zhang, Di Zhou, Daniele Mortari, and Troy A. Henderson. Published by the American Institute of Aeronautics and Astronautics, Inc. Source


Sunny M.R.,Aliah University | Kapania R.K.,Ocean Aero
International Journal of Computational Methods in Engineering Science and Mechanics | Year: 2014

We have developed an artificial-neural-network-based identification scheme for a modified version of the Preisach model for the hysteresis and relaxation observed in the variation of electrical resistance with strain in conductive polymer nanocomposites. This modeling approach models hysteresis and relaxation as two independent phenomenons. At first, the effects of the relaxation and static hysteresis have been decoupled from the total value of the resistance at different time steps. Unknown parameters in the relaxation model have been identified using a global optimization scheme. Identification of the static hysteresis has been done using an artificial neural network. © 2014 Copyright Taylor and Francis Group, LLC. Source


A submersible vessel having wing and keel assemblies that are extendable for wind-powered surface operation and retractable to reduce drag for submerged operation or to place the vessel in a more compact configuration. A deployment mechanism including an actuator and linkage pivots the wing and keel assemblies simultaneously between the deployed and retracted configuration. The vessel may have first and second pressure hulls flanking the wing and keel assemblies. A drive mechanism including a motor and a gear train employing pulley-and-cable assemblies rotates either the wing and flap together such that the flap angle relative to the wing is constant, or to change the flap angle relative to the wing with the wing angle of incidence held constant. The invention also provides a retractable wind-powered propulsion apparatus that is mountable to the hull assembly of a submersible or non-submersible vessel.

Discover hidden collaborations