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CONTENTS
Volume 6, Number 4, July 2019
 

Abstract
This article is concerned with the investigation of geometrically non-linear vibration response of refined thick porous nanobeams. To this end, non-local theory of elasticity has been adopted to provide the nanobeam formulation. Voids or pores can affect the material characteristics of the nanobeam. So, their effects have been considered in this research and also there are various void distributions. The closed form solution of the non-linear problem has been used that is adopted from previous articles. Then, it is focused on the impacts of non-local field, void distribution, void amount and geometrical properties on non-linear vibrational characteristic of a nano-size beam.

Key Words
non-linear vibration; refined beam theory; metal nanobeam; nonlocal elasticity

Address
Abbas A. Alasadi, Ridha A. Ahmed and Nadhim M. Faleh: Al-Mustansiriah University, Engineering College P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq

Abstract
The influence of different planform parameters on the aerodynamic performance of large-scale subsonic and transonic Blended Wing Body (BWB) aircraft have gained comprehensive research in the recent years, however, it is not the case for small-size low subsonic speed Unmanned Aerial Vehicles (UAVs). The present work numerically investigates aerodynamics governing four different trailing edge geometries characterizing BWB configurations in standard flight conditions at angles of attack from -4o to 22o to provide generic information that can be essential for making well-informed decisions during BWB UAV conceptual design phase. Simulation results are discussed and comparatively analyzed with useful implications for formulation of proper mission profile specific to every BWB configuration.

Key Words
flying wing; BWB; BWB aerodynamic design; low-speed aerodynamics; wing planform

Address
Mohammed A. Ba Zuhair: Department of Aerohydrodynamics, Kazan National Research Technical University - KAI, Kazan,
Karl Marx 10, Russian Federation


Abstract
Dynamic stability of a porous metal foam nano-dimension plate on elastic substrate exposed to bi-axial time-dependent forces has been studied via a novel 3-variable plate theory. Various pore contents based on uniform and non-uniform models have been introduced. The presented plate model contains smaller number of field variables with shear deformation verification. Hamilton\'s principle will be utilized to deduce the governing equations. Next, the equations have been defined in the context of Mathieu–Hill equation. Correctness of presented methodology has been verified by comparison of derived results with previous data. Impacts of static and dynamical force coefficients, non-local coefficient, foundation coefficients, pore distributions and boundary edges on stability regions of metal foam nanoscale plates will be studied.

Key Words
dynamic stability; 3-unkonwn plate theory; porous nanoplate; non-local elasticity; porosities

Address
Raad M. Fenjan, Ridha A. Ahmed and Nadhim M. Faleh: Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq

Abstract
The stiffness degradation of the cross-ply composite laminates containing a transverse cracking and delamination in 90o layer is predicted by using a modified shear-lag model by introducing the stress perturbation function. The prediction shows better agreement with the experimental results published by Ogihara and Takeda 1995, especially for laminates with thicker 90o plies in which extensive delamination occurs. A homogenised analytic model for average transient moisture uptake in composite laminates containing periodically distributed matrix cracks and delamination is presented. It is shown that the model well describes the moisture absorption in a cross-ply composite laminate containing periodically distributed transverse matrix cracks in the 90o plies. The obtained results represent well the dependence of the stiffness degradation on the crack density, thickness ratio and moisture absorption. The present study has proved to be important to the understanding of the degradation of the material properties in the failure process when the laminates in which the delamination grows extensively.

Key Words
delamination; stiffness; hygrothermal effect; absorption; matrix cracks

Address
Mohamed Khodjet Kesba, A. Benkhedda and B. Boukert: Laboratoire des Sciences Aéronautiques, Institut d\'Aéronautique et des études Spatiales, Université de Blida1, Blida, Algérie

E.A. Adda bedia: Laboratoire des Matériaux et Hydrologie, Université de Sidi Bel Abbes, Algérie, Sidi Bel Abbes, Algérie

Abstract
Low fuel regression rate is the main drawback of hybrid rocket which should be overcome. One of the improvement techniques to this problem is usage of a solid fuel grain with a complicated geometry port, which has been promoted owing to the recent development of additive manufacturing technologies. In the design of a hybrid rocket fuel grain with a complicated geometry port, the understanding of fuel regression behavior is very important. Numerical investigations of fuel regression behavior requires a capturing method of solid fuel surface, i.e., gas-solid interface. In this study, level set method is employed as such a method and the preliminary numerical tool for capturing a hybrid rocket solid fuel surface is developed. At first, to test the adequacy of the numerical modeling, the simulation results for circular port are compared to the experimental results in open literature. The regression rates and oxidizer to fuel ratios show good agreements between the simulations and the experiments, after passing enough time. However, during the early period of combustion, there are the discrepancies between the simulations and the experiments, owing to transient phenomena. Second, the simulations of complicated geometry ports are demonstrated. In this preliminary step, a star shape is employed as complicated geometry of port. The slot number effect in star port is investigated. The regression rate decreases with increasing the slot number, except for the star port with many slots (8 slots) in the latter half of combustion. The oxidizer to fuel ratio increases with increasing the slot number.

Key Words
hybrid rocket; fuel surface regression; level set method; numerical simulation

Address
Yuki Funami: Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama-shi, Kanagawa, 221-8686, Japan


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