An experimental study on microscopic characteristics of gas-bearing sediments under different gas reservoir pressures     

Zhenqi Guo  Tao Liu  Lei Guo  Xiuting Su  Yan Zhang  Sanpeng Li 《海洋学报(英文版)》2021,40(10):144-151

Gas-bearing sediments are widely distributed in five continents all over the world. Most of the gases exist in the soil skeleton in the form of discrete large bubbles. The existence of gas-phase may increase or decrease the strength of the soil skeleton. So far, bubbles’ structural morphology and evolution characteristics in soil skeleton lack research, and the influence of different gas reservoir pressures on bubbles are still unclear. The micro characteristics of bubbles in the same sediment sample were studied using an industrial CT scanning test system to solve these problems. Using the image processing software, the micro variation characteristics of gas-bearing sediments in gas reservoir pressure change are obtained. The results show that the number and volume of bubbles in different equivalent radius ranges will change regularly under different gas reservoir pressure. With the increase of gas reservoir pressure, the number and volume of tiny bubbles decrease. In contrast, the number and volume of large bubbles increase, and the gas content in different positions increases and occupies a dominant position, driving the reduction of pore water and soil skeleton movement.  相似文献   

DEM simulation of granular media—structure interface: effects of surface roughness and particle shape     

Richard P. Jensen  Peter J. Bosscher  Michael E. Plesha  Tuncer B. Edil 《国际地质力学数值与分析法杂志》1999,23(6):531-547

  相似文献   

Segmentation of soil roughness profiles     

Lorenzo Borselli 《地球表面变化过程与地形》1999,24(1):71-90

A robust and flexible algorithm to study spatial series like soil roughness profile has been introduced. It avoids using classic spectral analysis, considers the profile first and foremost as non-stationary and makes it possible to identify the separate domains inside the profile where chosen statistical parameters and roughness indexes have their own value. The method analyses a roughness profile considering it as an assemblage of several entities that may differ in terms of statistical properties and length, without establishing constraints as to number and extension. The method derives the variability of statistical and roughness properties along the profile and extracts the possible components - random and oriented - detectable inside the sample. Some examples of application illustrate the possibility offered by the method to study real roughness profiles recorded in the field by a portable laser microprofilometer. The procedure proposed allows the investigation of local roughness properties with varying degrees of accuracy and should be useful to monitor the differential evolution of roughness on patterned soil surface, increasing the overall information content. A general definition of ‘ordered roughness’ is introduced. The definition proposed seems more suited to current techniques for the numerical treatment of digital profiles and for the existing physical relationships between the scale of observation of roughness and the scale of the process investigated (hydraulic resistance, water storage in depressions). Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The asymmetric elastic wavefields in a model comprising a liquid layer overlying an anisotropic solid seabed due to an arbitrary source within the solid     

《Applied Ocean Research》2017

The asymmetric three-dimensional radiation pattern and resultant elastodynamic response of stress waves in a model comprising a compressible water column overlying a transversely isotropic seabed in which a time-harmonic source acts is theoretically investigated. The use of potential functions, the Hankel transform, and a Fourier series expansion are adopted to deal with the equations of motion for both media. Closed-form integral expressions are developed for the potentials and the stress/displacement components. The expressions and introduced procedure are sufficiently flexible to incorporate various types of source loads. To evaluate the field quantities, the residue method and a robust integration scheme are utilized to handle the poles and branch points within the integrand. Any possible number of dispersive propagation modes are taken into account in the integral evaluation. The deduced velocity dispersion curves depict the characteristics of the various modes. They also indicate the existing singular points (poles) for a specific dimensionless frequency and the surface wave type associated with each pole. Numerical results are presented for the hydrodynamic pressure and displacement in the liquid layer and stress and displacement components in the solid seabed due to distributed and concentrated source excitations. The formulation and the numerical scheme are valid for calculating the wavefield anywhere within the model including both far- and near-field effects. The sensitivity of the results to different parameters is also analyzed. Both analytical and numerical comparisons with existing solutions for simpler cases are made to confirm the validity of the results. The results are especially useful in seismic hazard assessment of submarine earthquakes, landslides, and tsunamis. They can also be extended to deal with the fluid-solid-structure interaction problems.  相似文献   

Predicting the effect of biofouling on ship resistance using CFD     

《Applied Ocean Research》2017

This paper proposes a Computational Fluid Dynamics (CFD) based unsteady RANS model which enables the prediction of the effect of marine coatings and biofouling on ship resistance and presents CFD simulations of the roughness effects on the resistance and effective power of the full-scale 3D KRISO Container Ship (KCS) hull.Initially, a roughness function model representing a typical coating and different fouling conditions was developed by using the roughness functions given in the literature. This model then was employed in the wall-function of the CFD software and the effects of a typical as applied coating and different fouling conditions on the frictional resistance of flat plates representing the KCS were predicted for a design speed of 24 knots and a slow steaming speed of 19 knots using the proposed CFD model. The roughness effects of such conditions on the resistance components and effective power of the full-scale 3D KCS model were then predicted at the same speeds. The resulting frictional resistance values of the present study were then compared with each other and with results obtained using the similarity law analysis. The increase in the effective power of the full-scale KCS hull was predicted to be 18.1% for a deteriorated coating or light slime whereas that due to heavy slime was predicted to be 38% at a ship speed of 24 knots. In addition, it was observed that the wave resistance and wave systems are significantly affected by the hull roughness and hence viscosity.  相似文献   

沙漠下垫面地面温度及能量收支的BATS模式参数化改进     

马迪  吕世华  鲍艳  奥银焕  韩博  赵林 《中国沙漠》2017,37(4):749-754

利用陆面过程模式BATS,引入地表发射率及两种大气发射率参数化方案,同时引入不同的地表粗糙度参数化方案,对比各种参数化方案对沙漠下垫面地面温度及能量收支的模拟状况。结果表明：采用Van Bavel等发展的地表发射率及Chung等发展的大气发射率方案可以明显改进地面温度及向上长波辐射的模拟,Chung等方案在夜间与正午的模拟效果更好,减小了1 ℃左右的地面温度模拟偏差,减小了10 W·m^-2左右的向上长波辐射模拟偏差。晴天地面温度及向上长波辐射的模拟结果优于阴天。利用Zhang等发展的裸土粗糙度参数化方案也会提高模式对地表感热通量模拟的准确性。  相似文献   

波浪导致黄河口海床沉积物超孔压响应现场试验研究     

刘晓磊  贾永刚  郑杰文 《岩土力学》2015,36(11):3055-3062

黄河口海床特殊的工程地质性质与复杂的工程动力稳定性问题,均与海床沉积物在波浪荷载作用下的孔压动力响应密切相关。在现代黄河水下三角洲潮间带岸滩选择4个典型研究点,现场模拟波浪作用对原状海床沉积物实施循环加载,利用孔隙水压力观测、沉积物强度测试、样品采集与实验室土工测试等方法手段,测定黄河口原状海床沉积物在循环荷载作用不同阶段的孔压响应与强度变化。研究发现,黄河口原状海床沉积物在经历循环加载过程中,典型的超孔压响应可分为逐渐累积、部分消散、快速累积、累积液化和完全消散5个阶段,分别对应沉积物强度的衰减、增大、衰减、丧失和恢复过程,沉积物的粒度组成与结构性强弱决定了超孔压的具体响应模式。波浪导致原状海床液化深度受沉积物的干密度、孔隙比、饱和度等初始物理性质影响显著,细颗粒组分的相对含量高低也在很大程度上控制着沉积物的液化特性。  相似文献   

近海欠密实砂质海床内波致渐进液化特征研究     

王良民  叶剑红  朱长歧 《岩土力学》2015,36(12):3583-3588

利用一个经过广泛验证的数值模型FSSI-CAS 2D为计算工具,采用砂土的高级本构模型Pastor-Zienkiewicz-Mark III (PZIII) 描述海床砂土的动态力学行为,定量研究松散海床地基土在波浪作用下,其内部的液化过程和特征,以加深对波致海床液化特征、性质的认识。计算结果分析表明,开发的耦合数值模型FSSI-CAS 2D能够很好地捕捉到波浪作用下欠密实海床的动力响应特征,以及海床内的累积液化过程等一些列的非线性物理现象。研究表明,波浪导致的松砂海床液化是一个渐进过程,海床表面首先液化,并逐渐向下扩展。  相似文献   

Numerical modelling of aeolian erosion over a surface with non‐uniformly distributed roughness elements          下载免费PDF全文

B. Furieri  J. L. Harion  M. Milliez  S. Russeil  J. M. Santos 《地球表面变化过程与地形》2014,39(2):156-166

The present study is focused on the analysis of the mean wall friction velocity on a surface including roughness elements exposed to a turbulent boundary layer. These roughness elements represent non‐erodible particles over an erodible surface of an agglomeration of granular material on industrial sites. A first study has proposed a formulation that describes the evolution of the friction velocity as a function of geometrical parameters and cover rate with different uniform roughness distributions. The present simulations deal with non‐uniform distributions of particles with a random sampling of diameters, heights, positions and arrangements. The evolution (relative to geometrical parameters of the roughness elements) of the friction velocity for several non‐uniform distributions of roughness elements was analysed by the equation proposed in the literature and compared to the results obtained with the numerical simulations. This comparison showed very good agreement. Thus, the formulation developed for uniform particles was found also to be valid for a larger spectrum of particles noted on industrial sites. The present work aims also to investigate in detail the fluid mechanics over several roughness particles. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Sensitivity of interfacial hydraulics to the microtopographic roughness of water‐lain gravels          下载免费PDF全文

Stephen P. Rice  Thomas Buffin‐Bélanger  Ian Reid 《地球表面变化过程与地形》2014,39(2):184-199

Flow within the interfacial layer of gravel‐bed rivers is poorly understood, but this zone is important because the hydraulics here transport sediment, generate flow structures and interact with benthic organisms. We hypothesized that different gravel‐bed microtopographies generate measurable differences in hydraulic characteristics within the interfacial layer. This was tested using a high density of spatially and vertically distributed, velocity time series measured in the interfacial layers above three surfaces of contrasting microtopography. These surfaces had natural water‐worked textures, captured in the field using a casting procedure. Analysis was repeated for three discharges, with Reynolds numbers between 165000 and 287000, to evaluate whether discharge affected the impact of microtopography on interfacial flows. Relative submergence varied over a small range (3.5 to 8.1) characteristic of upland gravel‐bed rivers. Between‐surface differences in the median and variance of several time‐averaged and turbulent flow parameters were tested using non‐parametric statistics. Across all discharges, microtopographic differences did not affect spatially averaged (median) values of streamwise velocity, but were associated with significant differences in its spatial variance, and did affect spatially averaged (median) turbulent kinetic energy. Sweep and ejection events dominated the interfacial region above all surfaces at all flows, but there was a microtopographic effect, with Q2 and Q4 events less dominant and structures less persistent above the surface with the widest relief distribution, especially at the highest Reynolds number flow. Results are broadly consistent with earlier work, although this analysis is unique because of the focus on interfacial hydraulics, spatially averaged ‘patch scale’ metrics and a statistical approach to data analysis. An important implication is that observable differences in microtopography do not necessarily produce differences in interfacial hydraulics. An important observation is that appropriate roughness parameterizations for gravel‐bed rivers remain elusive, partly because the relative contributions to flow resistance of different aspects of bed microtopography are poorly constrained. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.  相似文献