Sensitivity and Resolution of Controlled-Source Electromagnetic Method for Gas Hydrate Stable Zone

Natural gas hydrate is one of the most important clean energies and part of carbon cycle, due to the least carbon content. Natural gas hydrates depend on high pressure and low temperatures, located under seabed or permafrost. Small changes in temperature and pressure may lead gas hydrates to separate into water and gas, commonly as methane. As a powerful greenhouse gas, methane is much stronger than carbon dioxide. Therefore, it is necessary to detect the gas hydrates stable zone (GHSZ) before the methane gas escapes from GHSZ. Marine controlled source electromagnetic method (CSEM) is a useful tool to detect gas hydrate in offshore. The results from 3D CSEM method are a resistivity cube to describe the distribution of gas hydrates. In order to study the detectability of CSEM method, we simulate the sensitivity and resolution of marine CSEM synthetic data. By using the sensitivity and resolution, a simple statement may be quickly judged on the existence and occurrence range of the natural gas hydrate. In this paper, we compare the resolution of marine CSEM method with various transverse resistance. This information may help researchers find out whether the GHSZ exists or not.

Variation law of water level in water injection drill under the influence of mining in Datong mining area

In view of the variation law of water level in water injection drill between dou?ble-system layers of hard rock strata in Datong mining zone, the failure process and mechanism of boreholes during propulsion are analyzed by the numerical sim?ulation and the test measurement in this paper. After the coal seam is fully mined, it can be divided into the advanced deformation zone, the bending deformation zone and the compaction stable zone. Borehole damage intensifies from top to bottom. The junction of siltstone and sandy mudstone is a high-risk position. The results are verified by the water level measurement and the borehole peeping.

Foundation Failures Mitigation under Expansive Clay by Using Granular Pile Anchor System

Expansive soils are found in typical areas in the world especially in arid and semi-arid regions. The problems associated with this type of soil drive geotechnical engineers to invent new technologies as remediation’s such as physical and chemical treatments. Innovative foundation techniques were also suggested for remedying the swell-shrink problems of the expansive soil. The granular pile anchor (GPA) is relatively a more favorable technique indebted to its cost-effective, easy and fast to assemble and most importantly was found to be more efficient in remedying the expansive soil. Despite the extensive studies on the expansive soil remedies, yet the granular pile anchor system requires more comprehensive and in-depth investigations. This study is aimed at developing a model with granular piles of various length and diameter extended to the stable zone to investigate the heave and uplift pressure in the expansive soil. For this purpose, experimental and numerical analysis were conducted in a small and in a full scale model respectively. A significant improvement was attained in heave reduction and an increment of uplift capacity. The findings also show that heave decreased significantly when the length and diameter of the GPA increases while the uplift capacity increased. However, it was noted that the extension of length to the stable zone resulted in insignificant changes. Therefore, it can be concluded that the maximum length of 6 m is the ideal length for GPA with different diameters according to foundations design requirement for this particular type of soil.

A Robust Nonlinear Control Strategy for Unsupported Paraplegic Standing Using Functional Electrical Stimulation: Controller Synthesis and Simulation

Background: Functional electrical stimulation (FES) applies electrical pulses to paralyzed muscles to restore their function. Closed-loop control of an FES system, incorporating the control strategies, promises to improve the performance of FES systems. Therefore, the purpose of this paper is to design a new control strategy applicable to restoring the upright standing in paraplegic patients through FES. The control strategies proposed in the previous works based on controlling the angular joint position and none of them focused on controlling the center of pressure (CoP) dynamics directly. Since the CoP is representative of posture balance dynamics, in this study, the adopted FES based control strategy designed to control the CoP dynamics directly. Methods: In the proposed control strategy, two controllers determine the stimulation intensity of ankle muscles in a manner to restrict the CoP to a specific zone. According to the proposed strategy, until the CoP confined to the stable zone, an adaptive controller is active. When the CoP goes out of the stable zone, the adaptive controller is deactivated. Then, a sliding mode controller is activated instead of the adaptive controller. In this manner, not only the posture balance can be guaranteed, but also the emerged balance dynamics can be similar to the elicited balance dynamics in the healthy subjects. Results: In this study, extended evaluations carried out through the simulation studies. According to the achieved results, the proposed control strategy is not only robust against the external disturbances, but also insensitive to the initial postural conditions. Conclusion: The achieved results prove the acceptable performance of the proposed control strategy

Water flow in unsaturated soils subjected to multiple infiltration events

In this paper, water flow in a 4 m height column with an unsaturated soil that is subjected to multiple infiltration events for a 62 day period is investigated. One-dimensional (1D) numerical analysis is also undertaken to analyze the flow, extending the seepage theory for unsaturated soils. Results highlight the formation of two wetting fronts; namely, wetting front I and wetting front II that are induced by the first and subsequent infiltration events, respectively. There is a stable zone where the water content is approximately constant; it forms between the two fronts. A conceptual model of the suction profile is proposed for interpreting in situ water flow by dividing the unsaturated zone into four distinct zones; namely, active, steady, transition, and capillary fringe zones. This division is helpful for providing a rational explanation of water flow in different zones. Novel contributions from this study include a relationship between the hydraulic properties in the steady zone and the flow velocity, which is determined by an average influx rate. In addition, the rate of groundwater recharge can also be estimated using the average influx rate. Results of the present study are useful to understand and interpret the relationship between water infiltration and suction or water content profile in the unsaturated zone as well as variation of groundwater table level.