四川盆地东部垫江盐盆早三叠世嘉陵江组四段杂卤石成因及对成钾的指示

四川盆地三叠纪是主要的成钾期,目前发现的主要含钾矿物为杂卤石,有关早三叠世嘉陵江组四段石盐岩中杂卤石成因一直存在争议.采用薄片鉴定、扫描电镜、稀土元素和锶同位素等手段,分析了四川盆地东部垫江盐盆长寿地区嘉陵江组四段石盐岩中杂卤石矿物形态特征,初步探讨了该杂卤石成因及对寻找海相钾盐的指示意义.扫描电镜下与石盐岩共生的杂卤...     

Coupled analysis of nonlinear sloshing and ship motions

A coupled numerical model considering nonlinear sloshing flows and the linear ship motions has been developed based on a boundary element method. Hydrodynamic performances of a tank containing internal fluid under regular wave excitations in sway are investigated by the present time-domain simulation model and comparative model tests. The numerical model features well the hydrodynamic performance of a tank and its internal sloshing flows obtained from the experiments. In particular, the numerical simulations of the strong nonlinear sloshing flows at the natural frequency have been validated. The influence of the excitation wave height and wave frequency on ship motions and internal sloshing has been investigated. The magnitude of the internal sloshing increases nonlinearly as the wave excitation increases. It is observed that the asymmetry of the internal sloshing relative to still water surface becomes more pronounced at higher wave excitation. The internal sloshing-induced wave elevation is found to be amplitude-modulated. The frequency of the amplitude modulation envelope is determined by the difference between the incident wave frequency and the natural frequency of the internal sloshing. Furthermore, the coupling mechanism between ship motions and internal sloshing is discussed.     

一次典型高压型海雾过程中海上大气波导的数值模拟

2009年4月9—12日黄海海域发生了一次受高压系统影响的海雾过程。利用卫星观测与探空数据、WRF模式(Weather Research and Forecasting Model)对此次海雾过程及相伴的大气波导进行了观测分析与数值模拟。海雾与波导发展可分为3个阶段:(1)大气波导先于海雾存在于黄海海面;受高压下沉影响,黄海上空存在逆温层和较强的湿度梯度,表现为较强的贴海表面波导和非贴海表面波导。(2)海雾始于高压西部,并随高压系统逐渐东移减弱,向黄海北部扩展;辐射冷却虽然使雾顶附近逆温增强,但海雾的机械湍流使其顶部湿度梯度减小,雾顶附近对应弱悬空波导或波导消失。(3)高压系统影响使干空气下沉到雾区导致黄海海雾消散;雾顶附近逆温仍存在,同时湿度梯度增大,黄海上空逐渐变为非贴海表面波导。本研究结果表明:高压系统不仅极易为波导的发生提供有利条件,而且有利于海雾的生成,在海雾演变过程中主要是雾顶水汽梯度的变化导致了波导类型及强度的变化。     

基于ROMS模式利用集合最优插值同化沿轨海表面高度异常数据的研究

The ensemble optimal interpolation （EnOI） is applied to the regional ocean modeling system （ROMS） with the ability to assimilate the along-track sea level anomaly （TSLA）. This system is tested with an eddy-resolving system of the South China Sea （SCS）. Background errors are derived from a running seasonal ensemble to account for the seasonal variability within the SCS. A fifth-order localization function with a 250 km localization radius is chosen to reduce the negative effects of sampling errors. The data assimilation system is tested from January 2004 to December 2006. The results show that the root mean square deviation （RMSD） of the sea level anomaly decreased from 10.57 to 6.70 cm, which represents a 36.6% reduction of error. The data assimilation reduces error for temperature within the upper 800 m and for salinity within the upper 200 m, although error degrades slightly at deeper depths. Surface currents are in better agreement with trajectories of surface drifters after data assimilation. The variance of sea level improves significantly in terms of both the amplitude and position of the strong and weak variance regions after assimilating TSLA. Results with AGE error （AGE） perform better than no AGE error （NoAGE） when considering the improvements of the temperature and the salinity. Furthermore, reasons for the extremely strong variability in the northern SCS in high resolution models are investigated. The results demonstrate that the strong variability of sea level in the high resolution model is caused by an extremely strong Kuroshio intrusion. Therefore, it is demonstrated that it is necessary to assimilate the TSLA in order to better simulate the SCS with high resolution models.     

Amodified discrete element model for sea ice dynamics

Considering the discontinuous characteristics of sea ice on various scales,a modified discrete element model（DEM） for sea ice dynamics is developed based on the granular material rheology.In this modified DEM,a soft sea ice particle element is introduced as a self-adjustive particle size function.Each ice particle can be treated as an assembly of ice floes,with its concentration and thickness changing to variable sizes under the conservation of mass.In this model,the contact forces among ice particles are calculated using a viscous-elastic-plastic model,while the maximum shear forces are described with the Mohr-Coulomb friction law.With this modified DEM,the ice flow dynamics is simulated under the drags of wind and current in a channel of various widths.The thicknesses,concentrations and velocities of ice particles are obtained,and then reasonable dynamic process is analyzed.The sea ice dynamic process is also simulated in a vortex wind field.Taking the influence of thermodynamics into account,this modified DEM will be improved in the future work.     

Origin of the hydrocarbon gases carbon dioxide and hydrogen sulfide in Dodan Field (SE-Turkey)

Gas occurrences consisting of carbon dioxide (CO₂), hydrogen sulfide (H₂S), and hydrocarbon (HC) gases and oil within the Dodan Field in southeastern Turkey are located in Cretaceous carbonate reservoir rocks in the Garzan and Mardin Formations. The aim of this study was to determine gas composition and to define the origin of gases in Dodan Field. For this purpose, gas samples were analyzed for their molecular and isotopic composition. The isotopic composition of CO₂, with values of −1.5‰ and −2.8‰, suggested abiogenic origin from limestone. δ³⁴S values of H₂S ranged from +11.9 to +13.4‰. H₂S is most likely formed from thermochemical sulfate reduction (TSR) and bacterial sulfate reduction (BSR) within the Bakuk Formation. The Bakuk Formation is composed of a dolomite dominated carbonate succession also containing anhydrite. TSR may occur within an evaporitic environment at temperatures of approximately 120–145 °C. Basin modeling revealed that these temperatures were reached within the Bakuk Formation at 10 Ma. Furthermore, sulfate reducing bacteria were found in oil–water phase samples from Dodan Field. As a result, the H₂S in Dodan Field can be considered to have formed by BSR and TSR.As indicated by their isotopic composition, HC gases are of thermogenic origin and were generated within the Upper Permian Kas and Gomaniibrik Formations. As indicated by the heavier isotopic composition of methane and ethane, HC gases were later altered by TSR. Based on our results, the Dodan gas field may have formed as a result of the interaction of the following processes during the last 7–8 Ma: 1) thermogenic gas generation in Permian source rocks, 2) the formation of thrust faults, 3) the lateral-up dip migration of HC-gases due to thrust faults from the Kas Formation into the Bakuk Formation, 4) the formation of H₂S and CO₂ by TSR within the Bakuk Formation, 5) the vertical migration of gases into reservoirs through the thrust fault, and 6) lateral-up dip migration within reservoir rocks toward the Dodan structure.     

Granular experiments of thrust wedges: Insights relevant to methane hydrate exploration at the Nankai accretionary prism

The accumulation mechanism of methane hydrates has been a central issue in previous hydrate research regarding the Nankai accretionary prism, southwest of Japan. Expulsion of formation fluids is significant during the prism accretion process, and the migration of these methane-bearing fluids exerts a strong control on the accumulation of hydrates. Two types of fluid pathways, inter-granular porosity and faults, need to be evaluated to understand hydrate accumulation. Fluid migration along faults can be partly modeled by examining faulting activity. Our study modeled the accretion process by using two granular methods that approximated the geologic body as an assemblage of particles: (1) analog experiments using granular materials, and (2) a numerical simulation based on the distinct element method. The analog experiments closely reproduced the prism geometry observed in seismic profiles across the Nankai accretionary prism. Digital image correlation analysis indicated that the frontal thrust is generally active but older structures are also frequently reactivated. The numerical simulations produced prism geometries similar to those of the analog experiments. The velocity distributions of the particles showed evidence of episodic faulting and reactivation, but the internal stress field exhibited little change in the deeper part of the prism during deformation. The frequent and substantial changes in fault activity displayed by the models indicate episodic fluid flow along fault surfaces. Active frontal thrusting suggests that formation fluids generally migrate from deep within the prism to the deformation front, but may move along reactivated older faults. Inter-granular permeability also fluctuates, as it is controlled by temporal and spatial variations in the internal stress field. However, fluid flow is likely to be relatively stable in the deeper segment of the prism.     

Modeling stress evolution around a rising salt diapir

We model the evolution of a salt diapir during sedimentation and study how deposition and salt movement affect stresses close to the diapir. We model the salt as a solid visco-plastic material and the sediments as a poro-elastoplastic material, using a generalized Modified Cam Clay model. The salt flows because ongoing sedimentation increases the average density within the overburden sediments, pressurizing the salt. Stresses rotate near a salt diapir, such that the maximum principal stress is perpendicular to the contact with the salt. The minimum principal stress is in the circumferential direction, and drops near the salt. The mean stress increases near the upper parts of the diapir, leading to a porosity that is lower than predicted for uniaxial burial at the same depth. We built this axisymmetric model within the large-strain finite-element program Elfen. Our results highlight the fact that forward modeling can provide a detailed understanding of the stress history of mudrocks close to salt diapirs; such an understanding is critical for predicting stress, porosity, and pore pressure in salt systems.     

Delving into three-dimensional structure of the West Luzon Eddy in a regional ocean model

The three-dimensional structure and associated dynamics of the prominent cold (cyclonic) West Luzon Eddy (WLE) were investigated by a high-resolution regional ocean model. The WLE was horizontally and vertically heterogeneous, exhibiting asymmetric structures in the circulation, vorticity, vertical motion and energy distributions within the eddy. The asymmetry was mainly attributed to the existence of an eddy dipole formed by a coexisting warm (anti-cyclonic) eddy to the south of the WLE. Analysis of the momentum balance revealed that the coexistence of two eddies intensified barotropic pressure gradients in the southern WLE to locally enhance the eastward jet. The positive (negative) vorticity of the jet strengthened (weakened) the eddy in the southern sector (periphery), which, together with the formation of a subsurface density front, intensified (suppressed) the corresponding upward motion and cooling. The baroclinic pressure gradients opposed the dominant barotropic components and spun down the eddy at greater depths with stronger weakening in the southern sector near the front. Asymmetric energy distributions showed that larger mean kinetic energy (MKE) and eddy available potential energy (EAPE) were stored in the southern sector of the WLE. While the larger MKE was directly linked with the stronger barotropic currents, the larger EAPE in the southern WLE was formed by baroclinic energy conversions due to a strong density gradient at the front.     

力觉临场感遥操作机器人(3)：环境的动力学描述

力觉临场感遥操作机器人系统是一个典型的人-机-环交互系统.环境是遥操作机器人系统最终的环节,也是操作者感知和作用的对象,环境的动力学特性对整个遥操作机器人系统的控制性能会产生直接的影响.通过分析环境在力觉临场感遥操作机器人系统中的动力学特性,建立了环境在碰撞接触、线性平稳接触和非线性平稳接触3类情况下的动力学模型,并给出了模型的等效阻抗形式,为力觉临场感遥操作机器人系统的分析提供了基础.