Journal of Aerospace Engineering

The analysis aspects of the 23,000‐line FORTRAN program VICONOPT are described. Overall stiffness matrices assembled from the earlier exact VIPASA flat plate stiffnesses are optionally coupled by Lagrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudinal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in‐plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite‐element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 10⁴ times faster.

A variety of products made from lunar resources will be required for a lunar outpost. These products might be made by adapting existing processing techniques to the lunar environment, or by developing new techniques unique to the moon. In either case, processing techniques used on the moon will have to have a firm basis in basic principles of materials science and engineering, which can be used to understand the relationships between composition, processing, and properties of lunar‐derived materials. These principles can also be used to optimize the properties of a product, once a more detailed knowledge of the lunar regolith is obtained. Using three types of ceramics (monolithic glasses, glass fibers, and glass‐ceramics) produced from lunar simulants, we show that the application of materials science and engineering principles is useful in understanding and optimizing the mechanical properties of ceramics on the moon. We also demonstrate that changes in composition and/or processing can have a significant effect on the strength of these materials.

In a recent article, the writers presented an augmented Lagrangian genetic algorithm for optimization of structures. The optimization of large structures such as high‐rise building structures and space stations with several hundred members by the hybrid genetic algorithm requires the creation of thousands of strings in the population and the corresponding large number of structural analyses. In this paper, the writers extend their previous work by presenting two concurrent augmented Lagrangian genetic algorithms for optimization of large structures utilizing the multiprocessing capabilities of high‐performance computers such as the Cray Y‐MP 8/864 supercomputer. Efficiency of the algorithms has been investigated by applying them to four space structures including two high‐rise building structures. It is observed that the performance of both algorithms improves with the size of the structure, making them particularly suitable for optimization of large structures. A maximum parallel processing speed of 7.7 is achieved for a 35‐story tower (with 1,262 elements and 936 degrees of freedom), using eight processors.

Optimization of combined structural and control systems is a complex problem requiring an inordinate amount of computer‐processing time, especially the solution of the eigenvalue problem of a general unsymmetric square real matrix with complex eigenvalues and eigenvectors, which is frequently used in such problem. The few algorithms presented in the literature thus far have been applied to small structures with a few members and controllers only. Parallel processing on new‐generation multiprocessor computers provides an opportunity to solve large‐scale problems. In this paper, the integrated structural and control optimization problem is formulated by including constraints on displacements, stresses, and closed‐loop eigenvalues and the corresponding damping factors. Then, parallel algorithms are presented for integrated optimization of structures on shared‐memory multiprocessors such as the Cray YMP 8/864 supercomputer. In particular, parallel algorithms are presented for the solution of complex eigenvalue problems encountered in structural control problems using the method of matrix iteration for dominant eigenvalue(s). The solution is divided into two parts. The first part is the iteration for dominant eigenvalue(s) and the corresponding eigenvector(s) and the second part is the reduction of the matrix to obtain the smaller eigenvalue(s) and the corresponding eigenvector(s).

High frequency Space Shuttle liftoff data are treated by autoregressive (AR) and autoregressive‐moving‐average (ARMA) digital algorithms. These algorithms provide useful information on the spectral densities of the data. Further, they yield spectral models, which lend themselves to incorporation into the concept of the random response spectrum. This concept yields a reasonably smooth power spectrum for the design of structural and mechanical systems when the available data bank is limited. Due to the nonstationarity of the liftoff event, the pertinent data are split into three slices. Each of the slices is associated with a rather distinguishable phase of the liftoff event, in which stationarity can be expected. The presented results are preliminary in nature; they aim to call attention to the availability of the discussed concepts and to the need to augment the Space Shuttle data bank as more flights are completed.

The research in this paper is the result of an experimental study regarding a new airfoil‐design concept, which is developed to produce greater lift coefficients over a much broader range of operational angles of attack, to improve or eliminate stall at virtually all operational airspeeds, to increase functional lift‐to‐drag ratios over a greater range of operational angles of attack, and to be adaptable for aircraft of both the fixed‐wing and the rotary‐wing types. The writer has combined his effort with L. L. Smith, and a U.S. Patent, entitled “Airfoil,” Patent No. 4,606,519, was obtained on August 19, 1986. Patents were also obtained or are pending in other countries. The experimental results, obtained by using the new airfoil‐design concept, have been compared with experimental results obtained from a conventional NACA 23012 airfoil. Flight performance tests by using a 2.134‐m (7.0 ft) model and remote‐control devices, as well as flow‐separation studies, were also performed. The results were compared with the ones obtained by using the NACA 23012 airfoil.

A refined higher order shear deformation theory for linear and geometrically nonlinear behavior of fiber‐reinforced angle‐ply composite and sandwich laminates is established. Laminae material is assumed to be linearly elastic, homogeneous and isotropic/orthotropic. The theory accounts for nonlinear quadratic variation of transverse shear strains through the thickness of the laminate and higher order terms in Green's strain vector in the sense of von Karman. A simple $C^0$ finite‐element formulation of this theory is then presented with a total Lagrangian approach, and a nine node Lagrangian quadrilateral element is chosen with nine degrees of freedom per node. Numerical results are presented for linear and geometrically nonlinear analyses of multilayer angle‐ply composite and sandwich laminates. The theory is shown to predict displacements and stresses more accurately than first‐order shear deformation theory. The results are compared with available closed‐form and numerical solutions of plate theories and three‐dimensional finite‐element solutions. New results are also generated for future evaluations.