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SUMMARYAn innovative method of analysis was developed to simulate the non-linear seismic finite-amplitude liquid sloshing in two-dimensional containers. In view of the irregular and time-varying liquid surface, the method employed a curvilinear mesh system to transform the non-linear sloshing problem from the physical domain with an irregular free-surface boundary into a computational domain in which rectangular grids can be analysed by the finite difference method. Non-linearities associated with both the unknown location of the free surface and the high-order differential terms were considered. The Crank-Nicolson time marching scheme was employed and the resulting finite difference algorithm is unconditionally stable and very lightly damped with respect to the temporal co-ordinate. In order to minimize numerical instability caused by the computational dispersion in spatially discretized surface wave, a second-order dissipation term was added to the system to filter out the spurious high-frequency waves. Sloshing effects and structural response were measured in terms of sloshing amplitude, base shear and overturning moment generated by the hydrodynamic pressure of the liquid exerted on the container walls. Simulation results of liquid sloshing induced by earthquake and harmonic base excitations were compared with those of the linear wave theory and the limitations of the latter in assessing the response of seismically excited liquids were addressed.KEY WORDS: liquid sloshing; nonlinear large-amplitude waves; hydrodynamic pressure; seismic response; numerical stability and dissipation; physical and computational domains

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In a conventional turbojet and turbofan engine, fuel is burned in the main combustor before the heated highpressure gas expands through the turbine. A turbine-burner concept was proposed in a previous paper in which combustion is continued inside the turbine to increase the ef ciency and speci c thrust of the turbojet engine. This concept is extended to include not only continuous burning in the turbine but also "discrete" interstage turbine burners as an intermediate option. A thermodynamic cycle analysis is performed to compare the relative performances of the conventional engine and the turbine-burner engine with different combustion options for both turbojet and turbofan con gurations. Turbine-burner engines are shown to provide signi cantly higher speci c thrust with no or only small increases in thrust speci c fuel consumption compared to conventional engines. Turbine-burner engines also widen the operational range of ight Mach number and compressor pressure ratio. The performance gain of turbine-burner engines over conventional engines increases with compressor pressure ratio, fan bypass ratio, and ight Mach number.

The morphing of an air vehicle is to change its shape and size substantially during flight. Thus, the morphing vehicle is to achieve a broader range of operational modes, all of which will maximize the vehicle performance throughout its mission profile. The dream of human flight has been to mimic birds or insect flights in similar manner since the days of Leonardo da Vinci. Our current aeronautical technology brings us closer to such a feat by vehicle morphing. This is evidenced by the ongoing DARPA contracts on designs of a Sliding-skin concept (in-plane morph) and a Folding wing concept (out-of-plane morph). [1][2][3][4]. However, the R&D of its engineering design/analysis methodology appears to be lagging behind. One such important methodology is the computational capability to assess the flight dynamics and aeroelastic instability, or stability, of a morphing vehicle during the course of its morphing motion.

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A Cartesian grid approach for the solution of the Euler equations within the framework of a patched, embedded Cartesian field mesh is described. As Cartesian grids are not necessarily body-aligned, an accurate representation for the surface boundary is important. In this paper a gridless boundary treatment using a cloud of nodes in the vicinity of the body combined with the multiquadric radial basis function (RBF) for the conserved flux variables for boundary implementation is proposed. In the present work, the RBF is applied only at the boundary interface, while a standard structured Cartesian grid approach is used everywhere else. Flow variables for solid cell centers for boundary condition implementation are determined via the use of reflected node involving a local RBF fit for a cloud of grid points. RBF is well suited to approximate multidimensional scattered data without any mesh accurately. Compared to the least-square method, RBF offers greater flexibility in regions where point selection may be very limited since the resulting matrix will be non-singular regardless of the sampling point's location. This is particularly important in the context of computations involving complex geometries where eligible points selected may be very close to one another. It is also shown that it provides similar accuracy with less cloud of points. The use of a Cartesian field mesh for the non boundary regions allows for effective implementation of multigrid methods, and issues associated with global conservation are greatly mitigated. Several two and three-dimensional problems are presented to show the efficiency and robustness of the method.