珊瑚岛礁环境噪声成像

珊瑚岛作为海洋中宝贵的土地,不仅是开发利用海洋资源和保护海洋权益的重要基地,也是地球科学许多领域突破性研究的重要场所。因此,经济高效地确定珊瑚岛地下结构已成为珊瑚岛工程地质研究的重要内容,但传统的海洋地球物理勘探和钻探方法仍面临挑战。虽然密集阵列环境噪声层析成像技术已广泛应用于大陆地区,但其在珊瑚岛的适用性尚未确定。本文以南海某孤立珊瑚岛密集阵列观测数据为基础,分析了该珊瑚岛的环境噪声特征,利用环境噪声层析成像技术获得了该珊瑚岛的三维地下结构。结果表明:①环境噪声频率大致可分为<1,1-5 Hz和bbb5hz三个等级。5 Hz以下的噪声在不同台站的频谱特征基本一致,而5 Hz以上的噪声特征差异显著。②对于5 Hz以下的环境噪声,仅需24h的波形数据即可获得高质量的互相关函数。然而,对于高于5 Hz的环境噪声,很难提取有意义的互相关函数。③岛内横波速度向海方向高,向礁湖方向低,这与向海侧外礁平面地层胶结程度高一致。④25~75 m和200~300 m两个低速层位与岩心样品显示的高孔隙度层位吻合较好,反映了礁体的风化历史。我们的研究表明,环境噪声层析成像是一种潜在的经济、高效、环保的珊瑚礁地质勘探方法。

Three-dimensional S-wave velocity structure of the upper crust in the Guangdong-Hong Kong-Macao Greater Bay Area:insights into the basins structure and genesis of hot springs

As one of the four largest bay areas with strong economic activities in the world,the Guangdong-Hong Kong-Macao Greater Bay Area(GHMGBA)is located in the zone of interaction between the South China Block(SCB)and the South China Sea(SCS).Under the influence of complex geologic evolution,basin-range structures,fault systems and hot springs are well developed here.However,the characteristics of geological structures and the genetic mechanism of these geological phenomena are still unclear.Therefore,we performed ambient noise tomography to obtain 3-D upper crust(0-7.5 km)S-wave velocity structures of the GHMGBA by using 40-day continuous waveform data from 130 seismic stations in the GHMGBA.Our results show that sedimentary basins in the GHMGBA are mainly characterized by low-velocity anomalies.S-wave velocities of sediment formation in basins are about 2.8-3.1 km/s.Rapid changes in velocity appear at the edges of the basins,which correspond to the NE-,NEE-,and NW-trending faults,indicating prominent basin-controlling effects of the faults.The Sanshui Basin(SSB),the largest in the GHMGBA,has a developmental depth of about 4 km,and there is a significant difference in velocity gradient between the east and west sides of the basin,indicating that SSB has experienced east-west asymmetric expansion.Moreover,there are prominent low-velocity anomalies at a depth of about 4.5 km beneath the hot springs at the west of the Zhujiang(Pearl)River estuary(ZRE).We infer that the low-velocity anomalies are fluid reservoirs of the hot springs,which lead to the development of the hot springs on the surface.In addition,the distribution of main cities in the GHMGBA shows a spatial correlation with low-velocity areas at shallow depths(<3 km).The population development trend in the GHMGBA in the past 20 years is also mainly concentrated in the structural province of relatively low-velocity.In combination with the GHMGBA basin structures and drainage distribution characteristics,we suggest that the basic geological environment to some extent affects the habitability of the human settlement and thus determines the distribution and development trend of the main urban context.We believe that the 3-D S-wave velocity structure of the upper crust of the GHMGBA obtained in this study,as well as the deep structural characteristics of the basins and hot springs,will provide support to urban construction planning and geological hazards research of the GHMGBA.

Geometrically Nonlinear Flutter Analysis Based on CFD/CSD Methods and Wind Tunnel Experimental Verification

This study presents a high-speed geometrically nonlinear flutter analysis calculation method based on the highprecision computational fluid dynamics/computational structural dynamics methods.In the proposed method,the aerodynamic simulation was conducted based on computational fluid dynamics,and the structural model was established using the nonlinear finite element model and tangential stiffness matrix.First,the equilibrium position was obtained using the nonlinear static aeroelastic iteration.Second,the structural modal under a steady aerodynamic load was extracted.Finally,the generalized displacement time curve was obtained by coupling the unsteady aerodynamics and linearized structure motion equations.Moreover,if the flutter is not at a critical state,the incoming flow dynamic pressure needs to be changed,and the above steps must be repeated until the vibration amplitude are equal.Furthermore,the high-speed geometrically nonlinear flutter of the wing-body assemblymodel with a high-aspect ratio was investigated,and the correctness of the method was verified using high-speed wind tunnel experiments.The results showed that the geometric nonlinearity of the large deformation of the wing caused in-plane bending to become a key factor in flutter characteristics and significantly decreased the dynamic pressure and frequency of the nonlinear flutter compared to those of the linear flutter.

Numerical Simulation Research on Static Aeroelastic Effect of the Transonic Aileron of a High Aspect Ratio Aircraf

The static aeroelastic effect of aircraft ailerons with high aspect ratio at transonic velocity is investigated in this paper by the CFD/CSD fluid-structure coupling numerical simulation.The influences of wing static aeroelasticity and the‘scissor opening’gap width between aileron control surface and the main wing surface on aileron efficiency are mainly explored.The main purpose of this paper is to provide technical support for the wind tunnel experimental model of aileron static aeroelasticity.The results indicate that the flight dynamic pressure has a great influence on the static aeroelastic effect of ailerons,and the greater the dynamic pressure,the lower the aileron efficiency.Aileron deflection causes asymmetric elastic deformation of the main wing surfaces of the left and right wings.The torque difference caused by the load distribution on the main wing surface offsets the rolling torque generated by the aileron.This results in a significant reduction in aileron efficiency,and it is noticeable that it is not the elastic deformation of the aileron itself or the reduction in effective deflection that leads to the reduction in rolling control efficiency.Under typical transonic conditions,the rolling control torque of the aileron can be reduced by more than 25%,in the range of 2.5–10 mm,and the‘scissor opening’gap width of the aileron has almost no influence on its static aeroelastic effect.