Pin Yan

Application of AVO analysis to gas hydrates identification in the northern slope of the South China Sea

Amplitude versus offset (AVO) analysis is a conventional seismic exploration technique in geophysical and lithological interpretation and has been widely used in onshore and offshore exploration. Its use in marine gas hydrate research, however, is still in initial stages. In this study, AVO analysis is applied to seismic profiles at drilling sites where hydrate samples have been recovered. The AVO responses of free gas, bottom simulating reflector (BSRs), and gas hydrates are discussed, and the AVO attributes in relation to gas hydrates are summarized. The results show that changes in intercept, gradient, fluid factor and Poisson’s ratio clearly reflect: (i) location of free gas and the BSR, and (ii) spatial relations between blank zone, BSR, gas hydrate, and free gas.

An Anomalous Seamount on the Southwestern Mid-Ridge of the South China Sea

The development of continental rifting and seafloor spreading can be predominated by magmatic upwelling (magma-rich) or tectonic stretching (magma-poor). Located in the terminal portion of propagating seafloor spreading of the South China Sea (SCS), the southwestern mid-ridge of the southwest sub-basin (SWSB) of the SCS was found with much thin crust and numerous faulted blocks coupling with magma-poor continental margins along its flanks. Therefore, the southwestern part of the SWSB is most likely to be a tectonic-dominated basin. To justify the hypothesis with further evidence, we investigated the nature of seamounts on the southwestern mid-ridge of the SWSB which may inherit seafloor spreading.

A simple model of high-power thyristor and its application in EML transient analysis

High-power solid-state devices are introduced to electromagnetic launchers (EML) as leading switch technology, which make the systems superior of improved energy efficiency and reduced volume. The semiconductor device models available in most circuit simulation software packages do not accurately characterize high-power thyristors for thermal management and snubber design. A simple PSpice model for high-power thyristor is proposed, which is based on the device behavior rather than on the physical structure. The model is used to analyze capacitor-based pulsed power circuits for experimental railgun system. Extensive simulations have been performed to examine the model characteristics. Also, the factors influencing waveform of discharging current and system efficiency are discussed

Experiment and computation on the initial contact force of the rails and C-shaped solid armature interface

The contact condition of the armature-rail interface (ARI) is analyzed by building a two-dimensional (2-D) model and a three-dimensional (3-D) model, and a small experimental electromagnetic launcher (EML) and a C-shaped solid armature are designed and used to verify the simulation results. Simulated by the finite element software ANSYS, the distributions of the contact pressure, contact area (or contact length) and the von mises stress (VMS) are shown in the 2-D and 3-D models, and the simulation results of two models are analyzed by processing the data. The simulation and experimental results are carefully compared by observing the distribution of the melted object remaining on the surface of rails at the initial position after launch, and the variation of contact condition with the sliding of the armature can also be found. The results show that the contact pressure and contact area distributions of the ARI are not only non-uniform along the armature arm length, but also non uniform along the thickness, and it is nearly impossible to make the armature arm completely contact with the rail. The results also tell us that the satisfactory contact force and contact area can be gotten by properly designing the armature structure.

Modeling seismic waves in transversely isotropic media

Seismic waves in anisotropic media are more complex than in isotropic media. Here we derive the propagating matrices for seismic waves in 2-D transversely isotropic medium (TIM). With eigen‐decomposition, eigenvalues and eigenvectors are given in analytical forms, therefore, calculation of propagators are simple and accurate. For a 2-D model of layered media, we compute the seismic responses to an impulse in the f-k domain, and then do a 2-D inverse Fourier transformation. Clear qP and qSV waves can be recognized from the resultant sections.