Pezhman Mardanpour

Engine Placement Effect on Nonlinear Trim and Stability of Flying Wing Aircraft

The effects of engine placement and sweep on the flutter characteristics of an aft-swept flying wing resembling the Horten IV are investigated using the Nonlinear Aeroelastic Trim and Stability of HALE Aircraft. The analysis was validated against the published results for divergence and flutter of swept wings and found to be in excellent agreement. Moreover, the modal frequencies and damping obtained for the Goland wing were found in excellent agreement with published results based on a new continuum-based unsteady aerodynamic formulation. This aircraft exhibits a nonoscillatory yawing instability, expected in aircraft with neither a vertical tail nor yaw control. More important, however, is the presence of a low-frequency “body-freedom flutter” mode. The aircraft center of gravity was held fixed during the study, which allowed the aircraft controls to trim similarly for each engine location and minimized flutter speed variations along the inboard span. The maximum flutter speed occurred for engine placem...

In vitro-derived gametes from stem cells.

Sperm and eggs are essential cells for reproduction and fertility in mammals. Lack of sperm production is one of the leading causes of infertility, a major and growing problem in the developed world affecting 13 to 18% of reproductive-age couples. The birth of the first test tube baby by in vitro fertilization marked an advance in infertility treatment. Later on, several important new techniques called assisted reproductive technologies were developed to help couples who experience infertility. One limiting factor is the requirement of reproductive cells (gametes) for use in in vitro fertilization. For azoospermic men lacking sperm cells, producing gametes in vitro could be a new window to overcome infertility. In the past few years, several reports have been published on generating germ cells from stem cells, one of the epitomes of which was the report on functional in vitro-derived (IVD) germ cells. These mature haploid sperm cells from mouse embryonic stem cells were capable of egg fertilization and producing live offspring. In tandem with previous advancements in germ cell research, development of new technologies based on IVD gametes will change the future of infertility and provide a new basis for the establishment of novel therapeutic approaches to cure more complicated conditions of infertility. In addition, IVD gametogenesis provides an accessible system for studying the specification and differentiation of sperm cells and related processes such as meiosis, morphogenesis, and motility.

Effect of Inertial and Constitutive Properties on Body-Freedom Flutter for Flying Wings

The class of high-altitude long-endurance aircraft often has very slender wings with minimal structure. This leads to large trim deflections and coupling between the vehicle flight dynamics and wing vibrations. When this coupled behavior becomes unstable, it is referred to as body-freedom flutter. Body-freedom flutter behavior is dependent on the inertial and constitutive properties of the wing, as well as the fuselage. This relationship is explored for an aircraft representative of the Horten IV flying wing, using an efficient yet rigorous analysis that relies on geometrically exact, fully intrinsic beam equations and a finite-state induced flow model, which is implemented in the computer code NATASHA (which stands for nonlinear aeroelastic trim and stability of high-altitude long-endurance aircraft). The wing inertial and stiffness properties were calculated using a realistic representative section using the section analysis tool called variational asymptotic beam section analysis. Trade studies on the ...

Dynamic Stability of Pretwisted Cantilever Beams Subjected to Distributed Follower Force

The dynamic stability analysis of a pretwisted cantilever beam subjected to a distributed follower force is investigated. The spatial form of the follower force is chosen to cover a wide range of possible forms of distributed, nonconservative loads acting on a pretwisted cantilever beam such as lateral, axial tangential, or a combination of both types. The effect of the distributed follower force is taken into account by the work and energy terms, and Hamilton’s principle is used to derive the equations of motion. The partial differential equations of motion are transformed into a general eigenvalue problem by using the finite-element method. The effects of several physical parameters, such as the magnitude and setting angles of the follower force, the pretwist angle of the cantilever, geometrical parameters, and the fundamental frequency ratio, are studied. Numerical results show that the pretwist angle and setting angle of the follower force affect the dynamic instability of the cantilever.

Geometrically Exact, Fully Intrinsic Analysis of Pre-Twisted Beams Under Distributed Follower Forces

This paper studied the dynamic behavior of pre-twisted beams subjected to applied, distributed follower forces. The analysis was based on geometrically exact, fully intrinsic nonlinear composite be...

Passive Morphing of Flying Wing Aircraft - Part I: Z Configuration

High Altitude, Long Endurance (HALE) aircraft can achieve sustained, uninterrupted flight time if they use solar power. Wing morphing of solar powered HALE aircraft can significantly increase solar energy absorbency. An example of the kind of morphing considered in this paper requires the wings to fold so as to orient a solar panel to be hit more directly by the sun’s rays at specific times of the day. In this paper solar powered HALE flying wing aircraft are modeled with three beams with lockable hinge connections. Such aircraft are shown to be capable of morphing passively, following the sun by means of aerodynamic forces and engine thrusts. The analysis underlying NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft), a computer program that is based on geometricallyexact, fully intrinsic beam equations and a finite-state induced flow model, was extended to include the ability to simulate morphing of the aircraft into a “Z” configuration. Because of the “long endurance” feature of HALE aircraft, such morphing needs to be done without relying on actuators and at as near zero energy cost as possible. The emphasis of this study is to substantially demonstrate the processes required to passively morph a flying wing into a Z configuration and back again.

Passive Morphing of Solar Powered Flying Wing Aircraft

High Altitude, Long Endurance (HALE) aircraft can achieve sustained uninterrupted flight time if they use solar power. Wing morphing of solar powered HALE aircraft can significantly increase solar energy absorbency. An example of the kind of morphing considered in this paper requires the wings to fold so as to orient a solar panel to be hit more directly by the sun’s rays at specific times of the day. In this paper solar powered HALE flying wing aircraft are modeled with three beams with lockable hinge connections. Such aircraft are shown to be capable of morphing passively, following the sun by means of aerodynamic forces and engine thrusts. The analysis underlying Nonlinear Aeroelastic Trim And Stability of HALE Aircraft (NATASHA), a computer program that benefits from geometrically exact, fully intrinsic beam equations, and a finite-state-induced flow model was extended to include the ability to simulate morphing of the aircraft into a “Z” configuration. Because of the “long endurance” feature of HALE aircraft, such morphing needs to be done without relying on actuators and as near zero energy cost as possible. The emphasis of this study is to substantially demonstrate the processes required to passively morph a flying into a Z- shaped configuration and back again.