The root-mean-square (rms) surface error of a circular and equilateral triangular inflatable element subjected to pressure and isotropic tension in a faceted reflector surface is analyzed. The inflatable elements are assumed to be placed on any place of the reflector surface. Boundaries of the membrane are assumed to coincide with elliptic or hyperbolic paraboloidal surfaces. The deflection of the membrane is calculated based on the linear membrane equation (Poisson's Equation). According to the constraints of parameters which determine the boundary deflection of the membrane element, different kinds of rms error optimizations are carried out, and corresponding optimum membranes are obtained and compared. Effects of pressure/tension ratio, boundary deflection, size, etc. upon surface error of each optimum membrane are examined. The surface error of a circular and equilateral inflatable element whose boundaries coincide with the approximate parabolic surface of the reflector surface is found to be zero, on the assumption that the appropriate pressure/tension ratio is applied. The rms errors of both an optimum circular inflatable element with flat boundary and an optimum equilateral triangular inflatable element whose boundary has an equal optimum radius of curvature, are well below those of mesh elements when the elements are placed near the reflector axis. Comparison of rms error of a circular and triangular inflatable element with the same area is also carried out.
Symmetric laminates exhibit extension-shear or bending-twisting coupling. In a stiffness design of laminates, it is important to make use of coupling terms. The present paper clarifies stiffness characteristics of symmetric laminates using the lamination parameters. The feasible regions of the lamination parameters are examined for several conventional symmetric laminates and stiffness characteristics are represented on the lamination parameter plane. The feasibility and limitation of a stiffness design are discussed for conventional laminates. Based on the fundamental relation of the lamination parameters, a method is developed for determining laminate configurations corresponding to the in-plane or out-of-plane lamination parameters. A genetic algorithm is also applied to the determination of laminate configurations in a stiffness design of laminates.
A simple method to predict the configuration of the bag-type skirt in the static operation is proposed. The weight of the skirt material as well as the pressure distribution in the nozzle flow between the ground and the skirt is considered. Numerical and experimental results are compared. It has been shown that the weight of the skirt material and the pressure distribution in the nozzle region are both important in predicting the bag skirt configuration. The ratio of the pressure in the bag to the cushion pressure is also an important factor.
An experimental study on damping properties of laminated composite beams is reported. Unidirectionally stiffened, angle-plyed, and quasi-isotropic specimens made of T-800/PMR-15 laminates have been exposed to elevated temperature environment up to 300°C. Test specimens have been clampled at one end and electromagnetically excited at free end. Changes in amplitude of beams in damped free vibration have been measured and the logarithmic decrement and damping ratio have been calculated. Some considerations about the experimental results and usability of Adams' approach are given.
The separated boundary layer on an airfoil is highly receptive and unstable to external disturbances and forcings. In the present study, the response of the airfoil boundary layer with separation bubble to acoustic forcing is examined experimentally for NACA0015 airfoil at an angle of attack 10°, at a chord Reynolds number 4.4×104. The results show that when the acoustic forcing is applied, discrete vortices are excited immediately downstream of the separation point and they can govern the flow development upto the station near the trailing edge, through controlling the streamwise and spanwise scales of turbulent vortical structures within the airfoil boundary layer.