Mesh generation is proving to be an important aspect of computational aerodynamics. Over the last few years the topic has received much attention. Methods based on the structured and unstructured philosophies both have their advantages and disadvantages. This paper discusses the possible benefits to be achieved in composite structured-unstructured meshes. An algorithm is described which can solve the Euler equations for inviscid flow on such meshes. Three applications of the composite approach are then described. The first example shows the use of regions of assembled triangles to improve the quality of flow results on a poor quality structured mesh. The second illustrates how geometrically complicated aerodynamic configurations can be treated by utilising local regions of unstructured mesh within a globally structured mesh. Finally, a method of mesh/flow adaptivity is described whereby a structured mesh is enriched in appropriate regions of the domain by the addition of meshes consisting of an assembly of triangles. The results show that distinct benefits can be obtained from this composite approach.

Eigenstructure assignment has been widely used in the past for the synthesis of flight control systems in the time domain. The method, although offering a straightforward way of determining static compensators which satisfy the specifications in terms of desirable time response characteristics, lacks the property of guaranteeing stability margins like the linear quadratic regulator (LQR) methodology. The present paper analyses the performance-robustness properties of eigenstructure assignment against the standard LQR in order to define a loop transfer recovery procedure similar to that of the LQG/LTR. Two applications are described in which helicopter flight controllers are synthesised by eigenstructure assignment and possess robustness properties comparable to those of similar quadratic regulators and yet resulting in a simpler compensator structure. The applications are chosen to correspond to two flight conditions reflecting the aim of generality of the comparison.

Stress intensity factors for centre and edge cracks in finite elastic sheets are calculated from potential energy and complementary energy release rates by dual analysis with simple compatible and equilibrium finite elements. Comparison with very accurate results of other authors who employ special singular functions to model a crack tip provides compelling numerical evidence that the calculated stress intensity factors behave respectively like lower and upper bounds to the exact values. The bound-like character of such results has been reported before in another context, though there are no known bounding principles which strictly apply to finite bodies.