290 research outputs found
Nonlinear disturbance observer based spacecraft attitude control subject to disturbances and actuator faults
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Study on array laterolog response simulation and mud-filtrate invasion correction
No full textIt is a complicated task to evaluate the reservoirs influenced by mud-filtrate invasion. This paper presents the numerical simulation results of array laterolog response and the approach for mud-filtrate invasion correction. Based on the differential equations and boundary conditions of the steady current field in the rock medium, the finite element method (FEM) is applied to solve the Laplace equation, then computing the potential value at each node and calculating the apparent resistivity of six measuring modes of array laterolog. Based on the numerical results, the array laterolog response is affected by many parameters including borehole radius, mud-filtrate resistivity, mud-filtrate invasion radius and invaded area resistivity. Correction charts for borehole and mud-filtrate invasion were made to quickly and accurately obtain the mud-filtrate invasion depth and the true resistivity of the uninvaded formation, which can be used to qualitatively estimate the oiliness and permeability characteristics of the formation.Cited as: Zhao, P., Qin, R., Pan, H., Ostadhassan, M., Wu, Y. Study on array laterolog response simulation and mud-filtrate invasion correction. Advances in Geo-Energy Research, 2019, 3(2): 175-186, doi: 10.26804/ager.2019.02.0
Finite-Time Attitude Stabilization of Flexible Spacecrafts via Reduced-Order SMDO and NTSMC
No full textExperimental Study on the Concrete with Compound Admixture of Iron Tailings and Slag Powder under Low Cement Clinker System
No full textIn order to study the performance of concrete with compound admixture of iron tailings and slag powder under low cement clinker system, the mixture ratio of different iron tailings powder and slag powder was designed to prepare C30 and C50 concrete. The workability, strength, carbonation depth, chloride diffusion coefficient, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) of concrete were measured, respectively. The test results show that iron tailings powder is beneficial to improve the workability, and the strength of concrete decreases with the increase of iron tailings powder content, while the carbonation depth and chloride diffusion coefficient increase with the increase of iron tailings powder content. Under low cement clinker system, the iron tailings powder should not be used alone (below 70% of mineral admixture). When the ratio of iron tailings to slag powder is 1 : 1, the strength, carbonation depth, chloride ion permeation coefficient, and the microstructure of concrete are roughly the same to that of concrete with single slag powder. So, the iron tailings powder can replace S95 grade slag powder in the same quantity. Iron tailings powder does not take part in hydration reaction, but it can improve particle gradation, reach close accumulation, and increase the quantity of central grains
Disturbance observer-based attitude control of spacecraft with single-gimbal control moment gyros
No full textSuper-twisting disturbance observer-based finite- time attitude stabilization of flexible spacecraft subject to complex disturbances
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The creep behavior of semicrystalline carbon nanotube/polypropylene nanocomposite: a coarse-grained molecular study
No full textPolypropylene (PP) is vulnerable to creep under constant loads, which is a serious problem for PP-based applications. By incorporating carbon nanotubes (CNTs), the CNT/PP composite exhibits improved creep resistance, while the CNT aggregation with high contents could limit the improvement. In order to ensure the long-term durability, the creep response of CNT/PP composite with different CNT contents should be carefully characterized. In this paper, the coarse-grained models of CNT/PP nanocomposite with various CNT contents are constructed, which are subjected to constant loads at various levels. It is found that the threshold stress and energy barrier for the initiation of fracture show an initial increase and a subsequent decrease, with the transition at 3 wt%. The decline of creep properties with high CNT contents is related to the limited CNT restriction effect on the PP chain behaviors, which is resulted from the sliding between CNT chains and the accelerated interfacial sliding between CNT and PP due to increased interfacial voids, as observed from the behaviors and interactions of investigated molecules and chains during creep. This study provides insights into the molecular creep behavior of CNT/PP nanocomposite, which contributes to the understanding of degradation of composite materials under constant loads
Coarse-grained molecular simulation of the effects of carbon nanotube dispersion on the mechanics of semicrystalline polymer nanocomposites
No full textWith the incorporation of carbon nanotubes (CNTs), CNT/polypropylene (PP) nanocomposites are found to possess enhanced mechanical properties, but the reinforcing effect is reduced at large added CNT weight percentages due to CNT aggregation. Optimizing the properties of a nanocomposite requires a fundamental understanding of the effects of CNT dispersion on the nanocomposite. In this work, coarse-grained molecular models of CNT/PP nanocomposites are constructed, which consist of randomly dispersed or aggregated CNT bundles. Our simulation results reveal that with randomly dispersed CNT bundles, the nanocomposite shows properties that continuously improve with increasing CNT contents due to the effective CNT/PP interface and the reinforcing effect of CNTs. By comparison, the nanocomposite with aggregated CNT clusters exhibits a decline in yield strength at CNT contents over 3 wt%, which results from a reduced CNT load-carrying capacity due to the formation of structural voids in the interfacial region. This study achieves an in situ observation of the structural void evolution of loaded nanocomposites, provides valuable insights into the effects of CNT dispersion on the mechanics of CNT/PP nanocomposites, and paves the way for optimizing the design of nanocomposites with superior mechanical properties by designing the CNT dispersion in the structure
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