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1.
The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over-predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non-linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three-step modified grain contact theory model to a two-step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed.  相似文献   
2.
The prerequisite for obtaining variations of terrigenous grain-size of marine sediments is how to effectively remove non-terrigenous matters and preserve terrigenous particles synchronously. Combined with observations under biological microscope and scanning electron microscope, a comparative study of biogenic debris removal effect and terrigenous grain-size analysis under different pretreatment condition was performed on core sediments, which were retrieved in the South China Sea during the MD190 cruise. Our new results showed that the main three biogenic particles, namely, organic matter, carbonate, and opal in marine sediments could be removed effectively by 30% H2O2 in a stirring water bath at 60 ℃ for 3 h, 0.5% HCl for 1 h, and 2 mol/L Na2CO3 in a stirring water bath at 85 ℃ for 5 h, in turn. Such pretreatments achieved the goals of biogenic debris removal efficiency and relatively well-preserved terrigenous particles. Prior to selecting an appropriate pretreatment method, this study suggested that the actual effects of biogenic detritus on grain-size results of diverse marine sediment samples should be taken into account. If the laboratory data are ensured to be closer to the natural grain-size distribution of terrigenous particles, the removals of all biogenic debris are not always needed, and the less pretreatment processes the better. For example, opal particles have little effect on terrigenous grain-size distribution when their percentage is lower than 2%. Thus, there is no use to remove them from marine sediments before laboratory grain-size analysis of terrigenous particles. Additionally, ultrasonic is not suggested through the whole process of terrigenous grain-size analysis because the strong energy of ultrasonic can lead to the fragmentation of some fragile terrigenous particles.  相似文献   
3.
This study presents the results of experimental compaction while measuring ultrasonic velocities of sands with different grain size, shape, sorting and mineralogy. Uniaxial mechanical compaction tests up to a maximum of 50 MPa effective stress were performed on 29 dry sand aggregates derived from eight different sands to measure the rock properties. A good agreement was found between the Gassmann saturated bulk moduli of dry and brine saturated tests of selected sands. Sand samples with poor sorting showed low initial porosity while sands with high grain angularity had high initial porosity. The sand compaction tests showed that at a given stress well‐sorted, coarse‐grained sands were more compressible and had higher velocities (Vp and Vs) than fine‐grained sands when the mineralogy was similar. This can be attributed to grain crushing, where coarser grains lead to high compressibility and large grain‐to‐grain contact areas result in high velocities. At medium to high stresses the angular coarse to medium grained sands (both sorted sands and un‐sorted whole sands) showed high compaction and velocities (Vp and Vs). The small grain‐to‐grain contact areas promote higher deformation at grain contacts, more crushing and increased porosity loss resulting in high velocities. Compaction and velocities (Vp and Vs) increased with decreasing sorting in sands. However, at the same porosity, the velocities in whole sands were slightly lower than in the well‐sorted sands indicating the presence of loose smaller grains in‐between the framework grains. Quartz‐poor sands (containing less than 55% quartz) showed higher velocities (Vp and Vs) compared to that of quartz‐rich sands. This could be the result of sintering and enlargement of grain contacts of ductile mineral grains in the quartz‐poor sands increasing the effective bulk and shear stiffness. Tests both from wet measurements and Gassmann brine substitution showed a decreasing Vp/Vs ratio with increasing effective stress. The quartz‐rich sands separated out towards the higher side of the Vp/Vs range. The Gassmann brine substituted Vp and Vs plotted against effective stress provide a measure of the expected velocity range to be found in these and similar sands during mechanical compaction. Deviations of actual well log data from experimental data may indicate uplift, the presence of hydrocarbon, overpressure and/or cementation. Data from this study may help to model velocity‐depth trends and to improve the characterization of reservoir sands from well log data in a low temperature (<80–100o C) zone where compaction of sands is mostly mechanical.  相似文献   
4.
超声激励低渗煤层甲烷增透机理   总被引:3,自引:0,他引:3       下载免费PDF全文
超声激励增透煤层是一种不受甲烷储层地质条件和气源特性限制,具有普遍应用价值的增采技术.但由于煤岩致密、裂隙发育,煤岩孔隙度存在多尺度效应,受储层介质尺度效应影响的增透促吸机理尚不明确.本文通过CT观测实验和渗透率测定实验,对超声波作用下煤样不同尺度裂隙发展规律进行了分析,对比测定超声作用煤样渗透率变化规律,建立了超声增透煤层甲烷渗透率的修正公式.研究结果表明:CT观测实验很好地证明了超声的机械震碎作用;在声场衰减范围内,煤体损伤和机械震碎作用明显;超声波作用后的煤层渗透率有平均135%~169%的提高.研究工作为超声激励增加煤层的渗透率提供了实验基础.  相似文献   
5.
超声辐射对牟氏角毛藻的生物效应研究   总被引:6,自引:0,他引:6  
设计了一个超声频率,超声功率和辐射时间3因素4水平的正交实验,研究超声辐射对牟氏角毛藻的生物效应。实验结果表明,超声频率对牟氏角毛藻的生物效应显著,而超声功率的辐射时间的影响相对较小,在正交实验所确定的最佳超声辐射条件下,牟氏角毛藻生长速率常数最高可达0.348d^-1,是对照组的1.78倍,并脂肪酸不饱和度最高可达68.4%,比对照组提高5.2%,主要不饱和脂肪酸的百分含量均可得到不同程度的提高。  相似文献   
6.
This numerical investigation was carried out to advance mechanistic understanding of sediment transport under sheet flow conditions. An Euler–Euler coupled two-phase flow model was developed to simulate fluid–sediment oscillatory sheet flow. Since the concentration of sediment particles is high in such flows, the kinematics of the fluid and sediment phases are strongly coupled. This model includes interaction forces, intergranular stresses and turbulent stress closure. Each phase was modeled via the Reynolds-Averaged Navier–Stokes equations, with interphase momentum conservation accounting for the interaction between the phases. The generation and transformation of turbulence was modeled using the two-equation k–εkε turbulence model. Concentration and sediment flux profiles were compared with experimental data for sheet flow conditions considering both symmetric and asymmetric oscillatory flows. Sediment and fluid velocity variations, concentration profiles, sediment flux and turbulence parameters of wave-generated sheet flow were studied numerically with a focus on sediment transport characteristics. In all applications, the model predictions compared well with the experimental data. Unlike previous investigations in which the flow is driven by a horizontal pressure gradient, the present model solves the Navier–Stokes equations under propagating waves. The model’s ability to predict sediment transport under oscillatory sheet flow conditions underscores its potential for understanding the evolution of beach morphology.  相似文献   
7.
为建立超声波法和低应变反射波法检测所得混凝土基桩波速的相互转换关系,本文给出了标准线性固体模型下粘弹性介质的三维和一维纵波速度之比及其实用简化公式,并且通过实验得出,混凝土构件的超声波速与1.054倍低应变动测波速之比处于1.03~1.12,具体数值会随着混凝土龄期、弹性模量和强度等级的增加而有所减小。  相似文献   
8.
埋藏基岩断裂对地震波动影响的超声模拟研究   总被引:4,自引:0,他引:4       下载免费PDF全文
地球表层的地质构造对地震波动有不容忽视的影响,研究其规律,对于探查地壳结构乃至了解地球表层动力学特征具有重要意义。应用超声模拟方法,从基岩断裂对波传播和波场分布的影响以及基岩断裂倾向对地表地震动频率的影响三个方面研究了埋藏基岩断裂对地震波动的影响,揭示了一系列现象和规律。  相似文献   
9.
Summary A method of measuring ultrasonic wave properties in rocks during the complete stress-strain process is described. The relevant experimental laboratory study, to reveal the change of the amplitude spectrum parameters with strain (or stress) has been carried out. A preliminary study was conducted on the application of the ultrasonic measurement technique at a belt conveyor roadway of the north wing in Baodian coal mine, Shandong province. A borehole ultrasonic device with dry coupling was developed to provide better coupling and more accurate measurement data in comparison with those of a water coupled situation. Based on the interrelations between the complete stress-strain properties of specimens and their wave properties, the structural properties of surrounding rocks, the range of yield zones, and the change of stresses within the rocks surrounding a roadway which was subjected to mining influence of upper longwall face were analysed. Amplitude spectrum parameters were used to give a better prediction of the physico-mechanical state of the surrounding rocks.  相似文献   
10.
全波震相分析的应用   总被引:10,自引:0,他引:10  
全波震相分析法是以弹性波传播理论为基础,以现代数字技术为手段,对地震波进行全面综合分析的理论和方法.它既包括对单一分量震波观测记录中的各种震相的识别、确认和分析,又包括对多分量震波记录的合成、分析和图示.全波震相分析法涉及震源、射线路径、初动、走时、振幅、波形、时域和空域的瞬态谱、质点振动矢量等诸多方面,因而能更全面地揭示地震波场与地下介质之间的关系.本文以实例展示在不同领域的研究中全波震相分析的应用情况.全波震相分析法为实现多种波型的联合应用奠定了理论基础,并提供了新的方法.  相似文献   
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