Numerical investigation of auto-pitch wing-in-ground effect oscillating foil propulsor

The propulsive characteristics of auto-pitch wing-in-ground effect oscillating foil propulsors (APWIGs) were numerically investigated through an unsteady Reynolds Averaged Navier-Stokes solver. The kinematics of such a biplane configuration is characterized by the prescribed heave motion and flow-induced pitch motion restrained by a torsional spring for each foil. Based on the validated numerical model, the comparison of propulsive performance between APWIGs and single auto-pitch oscillating foil, as well as dual-foil heave-only configuration, was conducted at different advance speeds. Results show that APWIGs is advantageous in both thrust production and efficiency enhancement over other two configurations due to the resulting wing-in-ground effect and substantial reduction of flow separation by the flow-regulated pitch motion. Furthermore, the effect of torsional spring stiffness on the propulsion of APWIGs was studied under different loaded conditions. It was found that both the maximum pitching angle and phase difference of pitch with heave are dramatically affected by the spring stiffness, which has major contribution to the hydrodynamic behaviours of the foils. Under a certain operating speed, an optimal torsional spring stiffness that produces the best propulsive performance can be found. With respect to the parametric space in the current study, the APWIGs can achieve a constant high efficiency over 70% by employing an appropriate spring stiffness.     

The effect of temporal sampling intervals on typical human mobility indicators obtained from mobile phone location data

Mobile phone location data have been extensively used to understand human mobility patterns through the employment of mobility indicators. The temporal sampling interval (TSI), which is measured by the temporal interval between consecutive records, determines how well such data can describe human activities and influence the values of human mobility indicators. However, systematic investigations of how the TSI affects human mobility indicators remain scarce, and characterizing those relationships is a fundamental research question for many related studies. This study uses a mobile phone location dataset containing 19,370 intensively sampled individual trajectories (TSI < 5 minutes) to systematically assess the impacts of the TSI on four typical mobility indicators that describe human mobility patterns from different aspects, which are movement entropy, radius of gyration, eccentricity, and daily travel frequency. We find that different TSIs have complex impacts on the values of different mobility indicators. Specifically, (1) coarser TSIs tend to underestimate the values of the four selected indicators with different degrees; (2) the degrees of underestimation vary significantly among users for eccentricity and daily travel frequency but exhibit high inter-user consistency for radius of gyration and movement entropy. The above findings can help better understand the variations among human mobility studies.     

Evaluating sampling efficiency when estimating sediment source contributions to suspended sediment in rivers by fingerprinting

A general method is proposed which measures the increase in uncertainty when sampling effort is reduced in sediment fingerprinting. The method gives quantitative measures of how reduced sampling of material in one of the source areas, and/or of suspended sediment in streams, increases the uncertainties in the proportions of sediment contributed from the sources. Because the proportions of sediment contributed by the source areas must add to one, standard errors of the estimated proportions cannot be used as the usual measures of uncertainty: the paper uses instead the volume of the joint 95% confidence region for the estimated proportions. The paper shows how the uncertainty in this volume changes as numbers of suspended sediment samples, and the numbers of samples collected from cropped fields, are reduced by successive steps from 24 (20, in the case of cropped fields) to 16, 12, 8, 4 and 2 samples. As expected, uncertainty increases rapidly as the number of samples – whether of suspended sediment or from cropped fields – is reduced drastically. The pattern of increasing uncertainty is similar both for reductions in suspended sediment sampling, and for reduced sampling from cropped areas. When the number of suspended sediment samples, and the number of samples from cropped fields, are reduced to the same values, the increase in uncertainty from fewer suspended sediment samples was always slightly greater than the increased uncertainty from the reduced sampling of cropped areas, although this finding took no account of differences in the costs of field sampling and laboratory analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Micro‐sampling Lu–Hf geochronology reveals episodic garnet growth and multiple high‐P metamorphic events

We present Lu–Hf dates from multiple growth zones within two large garnet porphyroblasts by a micro‐sampling method. A single eclogite sample, taken from the Huwan shear zone in the Hong'an orogen, was investigated with Lu–Hf geochronology by micro‐sampling and traditional bulk separation methods. The sample contains a few large garnet porphyroblasts up to several centimetres in diameter and a second major population of smaller (0.1–2.0 mm) garnet porphyroblasts, comprised of dark cores and pale rims. Elemental compositions and mineral inclusions in the garnet appear consistent with two garnet generations. Lu–Hf dates (c. 400–264 Ma) were determined from twelve micro‐sawed garnet sections from two large garnet porphyroblasts. These Lu–Hf dates overlap with age peaks defined by 115 SIMS zircon U–Pb analyses from the same eclogite sample. Bulk analyses of smaller garnet separates define a minimum date of c. 306 Ma and a maximum date of c. 252 Ma for the dark cores and pale rims respectively. These Lu–Hf dates were interpreted to bracket the period of garnet growth and the broad interval from c. 400 to 264 Ma is best explained by protracted and episodic garnet growth, which may require that these rocks experienced two subduction cycles that were initiated during the Devonian and terminated in the Triassic.     

锂电池电动冲击取样钻机及其配套工具的研制

冲击钻进取样是支撑生态地质调查中松散地层优质高效、原状无污染取样的有效手段,但目前常见的便携式冲击取样钻机采用汽油机驱动,不能较好地适应安全生产与绿色勘查的发展要求。鉴于此,本文研制了一种以锂电池作为动力源的便携式电动冲击取样钻机及配套工具,详细介绍了钻机的电动冲击器、控制器、锂电池动力源及配套的取样器、锂电池液压起拔器的设计选型过程,并开展了钻机取样试验。实践证明该钻机及配套工具轻便可靠,可以实现5 m以浅松散地层的安全、高效、零碳排取样,是践行绿色勘查理念、推动浅层钻探装备电动化升级的有益尝试。     

地表基质钻探取样技术方法与应用研究

地表基质取样是开展地表基质层调查必不可少的工作环节,笔者等在浅地表层钻探技术的基础上,结合浅覆盖区矿产勘查、地球化学勘查、区域地质填图、环境调查、工程勘查、考古调查等领域钻探技术应用现状,根据不同地表景观及基质类型条件下的钻探取样需求,梳理了岩石、砾质、土质、泥质等地表基质钻探取样技术要点,研发了电动背包式钻机、Ф60/40mm单管冲击钻进、Ф50mm双管冲击钻进、Ф208mm中空螺旋钻进等取样器具及配套钻进工艺,在北京、内蒙古巴彦淖尔、浙江宁波、西藏那曲等地区开展了野外试验应用,通过获取满足要求的样品,很好的揭示了地层信息及物质组成,进一步在实践中提出了不同种类地表基质钻探取样技术方法,为建立自然资源调查监测体系及地表基质层调查工作提供钻探技术支撑。     

羌塘盆地天然气水合物钻探试验井取样技术与施工实践

羌塘盆地天然气水合物钻探试验井工程位于羌塘盆地西北部,海拔4998～5100 m。羌塘盆地是青藏高原年平均地温最低、冻土层相对较厚的地区,所处的水文地质及工程地质环境极其复杂,多年冻土层经反复冻胀融沉,地层破碎。另外,该处地层节理、裂隙、小断层和地下水极其发育,施工条件十分恶劣和困难。从取心钻具结构改进、钻头设计、冲洗液配方以及钻孔结构等方面总结了近年在羌塘盆地实施天然气水合物钻探试验井工程的实践和经验,为未来高海拔地区天然气水合物及其他矿产资源勘探提供参考。     

考虑地形遮蔽影响的电磁传播算法与可视化研究

采用规则格网数据(DEM)建立虚拟地理环境,并设定研究平面和电磁设备的空间位置,通过三角图元求交算法确定电磁波与地形是否存在遮蔽情况,从而计算得到受地形遮蔽影响的电磁场数据;采用颜色混合技术和优化处理的体绘制技术,将抽象的电磁场数据映射到可见的不同颜色值,形成直观、形象的可视化效果。     

光释光测年法——综述及进展

光释光(OSL)测年是对沉积物最后一次曝光(或热)事件年代的测定,其测试对象主要为石英和长石。自20世纪80年代该方法提出以来,在国内外得到了广泛的应用。但国内不少地学工作者对该技术的原理与测年方式了解十分有限,为了使应用者能更好、更全面地了解和使用这一方法,对OSL测年法及其近年来的国内外主要研究进展进行了回顾,重点对OSL测年法的基本原理、样品采集及实验室前处理过程、等效剂量(De)值的测定方式、环境剂量率的计算,以及影响测年结果可靠性的重要因素等进行了全面介绍、分析和探讨。同时,对近年来国内外关于De值测定方法与技术上的进展及已经获得较可信年龄的相关方法等进行了总结分析,并对OSL可能测年的范围和影响结果可靠性的一些潜在因素,以及对获得100ka~1Ma间的年龄新的释光信号研究方法等进行了介绍和探讨。     

熔融制样-X射线荧光光谱法测定重晶石中主次量元素

准确测定重晶石中硫酸钡及锶等组分的含量,对于评价矿石的质量品级十分重要。文章应用X射线荧光光谱法测定重晶石中BaO、Al2O3、Fe、CaO、MgO、SiO2、Na2O、K2O、Sr等9种主、次量组分。采用熔融片制样,消除了矿物结构效应,降低基体效应的影响,研究了熔样的条件,确定仪器测量的最佳参数。各元素相对标准偏差(RSD,n=10)≤10%,测定结果与化学法测定值相符,同时满足了ISO 9507对各元素分析结果准确度≤0.5%的要求。方法快速、准确,方便快捷,具有良好的精密度和准确度,可用于重晶石矿选矿样品尾矿、中矿、精矿中钡、锶、铁、钙、镁、铝、硅、钾、钠的同时测定,也可代替传统的化学法用于选冶实验分析。