The supersonic flow fields and mixing fields with a perpendicular hydrogen injection from a finite length slit are investigated. The finite length slit means the slit with two ends. The numerical simulations are performed by using three dimensional full Navier-Stokes equations and two conservation equations of the chemical species. The parameter in the calculations is the aspect ratio of the finite length slit. The aspect ratio means the ratio of the lateral length to the streamwise width of the finite length slit. The aspect ratio is changed to keep the area of the injection slit constant. The results show that the total pressure loss is maximum at the aspect ratio of one because the injected hydrogen penetrates deep into the main flow, and the mixing efficiency has the two minima in each region where the aspect ratio is less than one and more than one. It is found that the contact (or mixing) area of the main flow air and the injected hydrogen is important to the mixing in the supersonic flow.
A finite element method is applied to explain significant reduction of compressive properties of composite cross-ply laminates owing to multiple delaminations and the instability of the delamination cracks. Through-width multiple delaminations with equal length are considered. The contact problem is considered by using one-dimensional GAP elements on delaminated surfaces, which can realize piecewise linear force-displacement relation. The postbuckling behavior is numerically obtained and the energy release rates GI and GII at each delamination edge are calculated through virtual crack closure technique at each step. The postbuckling behaviors obtained by the finite element method agree well with those observed in the experiment and obtained by Rayleigh-Ritz approximation technique. The mode I energy release rate GI, however, increases very little as expected from the postbuckling deformation. The mode II energy release rate GII increases proportional to the end-shortening after the buckling. The distributions of total energy release rates G=GI+GII at the delamination edges are discussed.
Basic researches concerning the hub dynamic loads reduction by structural optimization of a rotor blade are conducted. The purpose of this paper is to extend the low vibration blade design methodology proposed in the previous paper so as to be able to consistent with static blade structural optimization. The blade is modeled by a rotating cantilevered beam with a plane tapered cross section and the external load is assumed to be composed by steady and dynamic components with multiple dominant frequencies. Structural optimization is formulated as an optimal control problem to determine the optimum area distribution which contains both static and dynamic blade deformations as a function of radial position. Numerical studies are carried out for various combinations of constraint imposed on the area distribution and natural frequencies with a wide range of the rotor speed. By observing numerical results, influences of constraints on the optimum solution and the physical background for hub load reduction by structural optimization are clearly understood and rationality and usefulness of the proposed optimization procedure are ascertained.
Neal-Smith criteria for evaluating aircraft handling qualities are rewritten in terms of H∞ norms. The mixed sensitivity problem is solved by the Özbay method and the model matching method to show that the obtained H∞ pilot models satisfy the Neal-Smith criteria quite well. H∞ pilot models corresponding to the Neal-Smith flight test configurations are obtained on the Bode diagram. They show that the required pilot compensations exhibited in the H∞ pilot models correlate well with the pilot ratings. A method using the maximum gain gradient and the phase at a particular frequency of the pilot model is proposed to predict the pilot rating for a pitch attitude control task.
As solid Rocket motor cases made of carbon fiber reinforced plastic (CFRP) by the use of inplane filament winding method have nonuniform distributions of thickness and elastic properties, their optimum shapes are far different from spheres and must be determined under the consideration of the stress and/or deformation distributions. A design method, where the shape is determined from the strain ratio between the longitudinal and hoop directions, is proposed first. Then, the deformed shape obtained by a finite element analysis, considering a geometrical nonlinearity, is proposed to be used as the dome shape. Deformation and bending stresses of the rocket motor cases designed by the conventional method based on the netting theory and present methods are calculated by the use of a finite element method (NISA II). The shape derived from the nonlinear analysis is found to be an ideal shape which shows much smaller bending stress than the conventional dome derived from the iso-tensoid shape.