This paper concerns with numerical evaluation of a new computation method for unsteady subsonic lifting surfaces, BIS (Box-In-Strip), the formulation of which was reported minutely in our previous paper. The numerical results of BIS-QS, a refined version, are compared with those of DLM (DoubletLattice Method) and DPM (Doublet-Point Method). Three kinds of wing planform, designated as Wing R, H, and E are used for evaluating these schemes. A new criterion is used on Wing R (rectangular planform); comparison is made between the pressure distribution at the root chord of a high aspect ratio wing and that of 2-dimensional airfoils, besides the "Error-Index" is used which has been developed by our laboratory previously. The Wing H has leading and trailing edges of a smooth hyperbolic curve, while the Wing E has a swept-tapered planform and so a kink at the midspan. It is found that the convergence and accuracy of BIS-QS are superior to DLM significantly and to DPM remarkably, without increasing computation cost, even for high frequency and high subsonic Mach number.
The stress concentration around a hole in CFRP laminates is numerically studied by using the finite element method. The classical lamination theory is used for the plane stress problem, namely the effect of interlaminar stress is not included. The lamination constitutions studied are [0°, 90°, 45°, -45°; each 25%], [45°, -45°; each 50%], [0°; 75% and 90°; 25%], [0°, 90°; each 50%] and [0°; 25% and 90°; 75%]. Two types of load, i. e. uniform tension or bolt load, are applied. The eight points quadrilateral isoparametric elements are used. The mainpurpose of the present study is not to disclose the thickness-wise mean stress but the stresses in each layer and the principal strains and the maximum shearing strain. The stress concentration factor in each layer is much higher than that of the isotropic one, Furthermore the so-called initial failure stress is calculated by applying the maximum stress theory or Tsai-Wu theory for failure to the normal stresses in the fiber and transverse directions and the shearing stress in each layer. The influence of lamination constitution on the initial failure stress and the failure mode is disclosed.
The effect of RDX addition on the combustion wave structure of double-base propellants has been examined in order to understand the burning rate characteristics of RDX-CMDB (composite modified double-base) propellants and to extend the burning rate domain of double-base propellants, RDX was used in this study as the energetic material and also the agent to decrease the burning rate of doublebase propellants. Experiments were conducted to determine the temperature profile in the combustion waves by means of fine thermocouples, It was found that the reaction rate in the fizz zone is decreased by the addition of RDX. This is caused by the equivalence ratio in the fizz zone becoming fuel rich when RDX is added. The reduction of the reaction rate in the fizz zone decreases the heat feedback from the gas phase to the burning surface. Thus, the burning rate of RDX-CMDB propellants decreases when RDX is added to double-base propellants.
This note investigates the characteristic of a coefficient matrix, which is derived from governing equations used in a discrete vortex method. When singular points on a body are arranged symmetrically, the rank of the coefficient matrix is reduced. Namely, the matrix is singular. When Kelvin's theorem is introduced in order to avoid the reduction of rank, that becomes regular. Then, governing equations can be solved by using a suitable method. When those are arranged asymmetrically, another unknown parameter should be introduced.