Due to the great damage to widely utilized flexible structures in ocean engineering, vortex-induced vibration (VIV) of such long flexible marine structures is still a hot issue that needs more theoretical research, and CFD techniques become gradually indispensable to study the VIV problem. In this paper, two-dimensional Reynolds-averaged Navier-Stokes (RANS) equations are adopted to investigate transverse VIV of elastically mounted rigid cylinder with low mass-damping, and two typical turbulent models are applied to solve the RANS equations: RNG k-ε model and SST k-ω model. By comparing the cylinder displacement response and vortex shedding modes of three different response branches, analysis of differences between two turbulence models are presented. The numerical results indicate that SST k-ω model is more appropriate for VIV of the elastically mounted rigid cylinder. Subsequently, other hydrodynamic coefficients obtained by SST k-ω model are discussed and compared with previous research in detail. This investigation provides theoretical evidence for the numerical simulation of VIV of marine riser in engineering application.

In order to evaluate scattering from hypersonic vehicles covered with the plasma efficiently, time domain volume shooting and bouncing rays (TDVSBR) is first introduced in this paper. The new method is applied to solve the transient electromagnetic scattering from complex targets, which combines with non-homogeneous dielectric and perfect electric conducting (PEC) bodies. To simplify the problem, objects are discretized into tetrahedrons with different electromagnetic parameters. Then the reflection and transmission coefficients can be obtained by using theory of electromagnetic waves propagation in lossy medium. After that, we simulate the reflection and transmission of rays in different media. At last, the scattered fields or radiation are solved by the last exiting ray from the target. Compared with frequency-domain methods, time-domain methods can obtain the wideband RCS efficiently. Several numerical results are given to demonstrate the high efficiency and accuracy of this proposed scheme.

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