Experimental Study of a Command Governor Adaptive Depth Controller for an Unmanned Underwater Vehicle     

《Applied Ocean Research》2019

Unmanned Underwater Vehicles (UUVs) are increasingly being used in advanced applications that require them to operate in tandem with human divers and around underwater infrastructure and other vehicles. These applications require precise control of the UUVs which is challenging due to the non-linear and time varying nature of the hydrodynamic forces, presence of external disturbances, uncertainties and unexpected changes that can occur within the UUV’s operating environment. Adaptive control has been identified as a promising solution to achieve desired control within such dynamic environments. Nevertheless, adaptive control in its basic form, such as Model Reference Adaptive Control (MRAC) has a trade-off between the adaptation rate and transient performance. Even though, higher adaptation rates produce better performance they can lead to instabilities and actuator fatigue due to high frequency oscillations in the control signal. Command Governor Adaptive Control (CGAC) is a possible solution to achieve better transient performance at low adaptation rates. In this study CGAC has been experimentally validated for depth control of a UUV, which is a unique challenge due to the unavailability of full state measurement and a greater thrust requirement. These in turn leads to additional noise from state estimation, time-delays from input noise filters, higher energy expenditure and susceptibility to saturation. Experimental results show that CGAC is more robust against noise and time-delays and has lower energy expenditure and thruster saturation. In addition, CGAC offers better tracking, disturbance rejection and tolerance to partial thruster failure compared to the MRAC.  相似文献   

Soil water dynamics under different forest vegetation cover: Implications for hillslope stability   总被引：1，自引：0，他引：1       下载免费PDF全文

Elyas Hayati  Ehsan Abdi  Mohsen Mohseni Saravi  John L. Nieber  Baris Majnounian  Giovanni B. Chirico  Bruce Wilson  Moharramali Nazarirad 《地球表面变化过程与地形》2018,43(10):2106-2120

Though it is well known that vegetation affects the water balance of soils through canopy interception and evapotranspiration, its hydrological contribution to soil hydrology and stability is yet to be fully quantified. To improve understanding of this hydrological process, soil water dynamics have been monitored at three adjacent hillslopes with different vegetation covers (deciduous tree cover, coniferous tree cover, and grass cover), for nine months from December 2014 to September 2015. The monitored soil moisture values were translated into soil matric suction (SMS) values to facilitate the analysis of hillslope stability. Our observations showed significant seasonal variations in SMS for each vegetation cover condition. However, a significant difference between different vegetation covers was only evident during the winter season where the mean SMS under coniferous tree cover (83.6 kPa) was significantly greater than that under grass cover (41 kPa). The hydrological reinforcing contribution due to matric suction was highest for the hillslope with coniferous tree cover, while the hillslope with deciduous tree cover was second and the hillslope with grass cover was third. The greatest contributions for all cover types were during the summer season. During the winter season, the wettest period of the monitoring study, the additional hydrological reinforcing contributions provided by the deciduous tree cover (1.5 to 6.5 kPa) or the grass cover (0.9 to 5.4 kPa) were insufficient to avoid potential slope failure conditions. However, the additional hydrological reinforcing contribution from the coniferous tree cover (5.8 to 10.4 kPa) was sufficient to provide potentially stable hillslope conditions during the winter season. Our study clearly suggests that during the winter season the hydrological effects from both deciduous tree and grass covers are insufficient to promote slope stability, while the hydrological reinforcing effects from the coniferous tree cover are sufficient even during the winter season. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

RESEARCH ON PASSIVE SERVO SEISMIC ROTATIONAL ACCELERATION SENSOR WITH LARGE DAMPING     

QU Ming-zhe  GAO Feng  YANG Xue-shan  YANG Dong-xia 《地震地质》2018,40(5):1170-1178

Many strong motion records show that under the strong seismic vibration of, the torsional disfigurement of building structures is a common and serious damage. At present, there are no special sensors for measuring seismic rotation in the world. Most of the experts obtain rotational components through observing deformation, theoretical analysis and calculation. The theory of elastic wave and source dynamics also prove the conclusion that the surface of the earth will rotate when an earthquake occurs. Based on a large number of investigations and experiments, a rotational acceleration sensor was developed for the observation of the rotational component of strong ground motions. This acceleration sensor is a double-pendulum passive servo large-damped seismic rotational acceleration sensor with the moving coil transducer. When an earthquake occurs, the seismic rotational acceleration acts on the bottom plate at the same time. The magnetic circuit system and the middle shaft fixedly connected to the bottom plate follow the bottom plate synchronous vibration, and the moving part composed of the mass ring, the swing frame and the moving ring produces relative corners to the central axis. The two working coils mounted on the two pendulums produce the same relative motion with respect to the magnetic gaps of the two magnetic circuits. Both working coils at this time generate an induced electromotive force by cutting magnetic lines of force in the respective magnetic gaps. The generated electromotive forces are respectively input to respective passive servo large damper dynamic ring transducer circuits and angular acceleration adjusting circuits, and the signals are simultaneously input to the synthesizing circuit after conditioning. Finally, the composite circuit outputs a voltage signal proportional to the seismic rotational acceleration to form a seismic rotational acceleration sensor. The paper presents the basic principles of the rotational acceleration sensor, including its mechanical structure diagram, circuit schematic diagram and mathematical models. The differential equation of motion and its circuit equation are derived to obtain the expressions of the main technical specifications, such as the damping ratio and sensitivity. The calculation shows that when the damping ratio is much larger than 1, the output voltage of the passive servo large damping dynamic coil transducer circuit is proportional to the ground rotation acceleration, and the frequency characteristic of bandpass is wider when the damping ratio is larger. Based on the calibration test, the dynamic range is greater than or equal to 100dB and the linearity error is less than 0.05%. The amplitude-frequency characteristics, the phase-frequency characteristics and their corresponding curves of the passive servo rotational acceleration sensor are acquired through the calculations. Based on the accurate measurement of the micro-vibration of the precision rotating vibration equipment, the desired result is obtained. The measured data are presented in the paper, which verify the correctness of the calculation result. The passive servo large damping rotational acceleration sensor has simple circuit design, convenient operation and high resolution, and can be widely applied to seismic acceleration measurement of earthquake or structure.  相似文献   

Intermediate to Long-term Estimation of Strong Earthquake Risk Areas in the Chinese Mainland Based on Geodesic Measurements     

Zhang Jing  Zhu Yiqing  Wu Yanqiang  Zhang Xi  Yang Guohua 《中国地震研究》2018,32(2):153-172

Based on previous research results, present-day crustal deformation and gravity fields in the Chinese mainland are analyzed using the GPS data, leveling, gravity and cross-fault deformations. We analyzed strain accumulation of the major faults, and identified locked or high strain accumulation segments. Combining the effects of large earthquakes in the study area, the long-term (decade) probability of large earthquakes in the Chinese mainland is estimated.  相似文献   

蒙自喀斯特断陷盆地边坡与盆缘的露石差异性     

蒋若涵  沈有信  赵志猛 《山地学报》2020,38(1):42-49

喀斯特露石常常占据一定比例的地表面积,且具有许多已知或未知的水文—生态功能,对于喀斯特地区的植被恢复和环境改善发挥着重要的作用。本实验运用样线法和拍照法识别喀斯特断陷盆地不同位置(盆缘和盆地边坡)露石的数量特征和外部形态特征,同时比较了两种方法测量样地岩石裸露率的精准度。结果发现:盆地边坡与盆缘的露石数量和外部特征存在显著差异,盆缘露石分布密度(0.54个·m-2)>盆地边坡(0.39个·m-2);但盆地边坡露石的长宽比大于盆缘,单体占地面积为盆缘露石的两倍,接近40%的盆地边坡露石与山体等高线平行。样线法和拍照法测量样地岩石裸露率的结果存有差异,但并不显著,且这种差异呈现出随着岩石裸露率的增加而逐渐增加的趋势,拍照测量结果具有较小的变异系数。这些结果说明了研究区露石具有较强的空间异质性,对解释地表水土运移规律和植物分布提供重要参考。拍照法能准确地测量岩石裸露率,并提供露石外部形态特征的精准数据,可以作为喀斯特样地露石调查的新方法加以推广。  相似文献   

区域创新政策评价的框架、测度与检验     

俞立平 《地理科学》2020,40(10):1610-1617

构建区域创新政策评价的理论框架，在宏观知识生产函数中引入信息化作为创新技术进步的替代变量，基于DEA与Malmquist指数，用全要素生产率指数存量来衡量区域创新政策。并以省际高技术产业为例进行了实证，研究结果表明：区域创新政策的特征和评价维度决定评价的多样性，基于政策效果与政策交互作用的区域创新政策评价具有重要意义；区域创新政策总体上处于稳步提高阶段，较低地区以西部中部地区为主；区域创新政策测度模型系统性较好，其检验方法有待进一步深化；采用政府研发经费投入作为区域创新政策的替代变量值得商榷。  相似文献   

A note on the lake level variations of Nam Co,south-central Tibetan Plateau from 2005 to 2019     

ShiQiao Zhou 《寒旱区科学》2020,12(6):430-435

Tibetan lake levels are sensitive to global change, and their variations have a large impact on the environment, local agriculture and animal husbandry practices. While many remote sensing data of Tibetan lake level changes have been reported, few are from in-situ measurements. This note presents the first in-situ lake level time series of the central Tibetan Plateau. Since 2005, daily lake level observations have been performed at Lake Nam Co, one of the largest on the Tibetan Plateau. The interannual lake level variations show an overall increasing trend from 2006 to 2014, a rapid decrease from 2014 to 2017, and a surge from 2017 to 2018. The annual average lake level of the hydrological year (May-April) rose 66 cm from 2006 to 2014, dropped 59 cm from 2014 to 2017, and increased 20 cm from 2017 to 2018, resulting in a net rise of 27 cm or an average rate of about 2 cm per year. Compared to the annual average lake level based on the calendar year, it is better to use the annual average lake level based on the hydrological year to determine the interannual lake level changes. As the lake level was stable in May, it is appropriate to compare May lake levels when examining interannual lake level changes with fewer data. Overall, remote sensing results agree well with the in-situ lake level observations; however, some significant deviations exist. In the comparable 2006-2009 period, the calendar-year average lake level observed in-situ rose by 10-11 cm per year, which is lower than the ICESat result of 18 cm per year.  相似文献   

湖南省似大地水准面2017模型及精度分析     

董明旭  李建成  华亮春  姜卫平  尹昊华  敖敏思  曾翔强 《大地测量与地球动力学》2019,39(1):66-71

利用近7万个湖南及邻近省份重力观测数据、502个GNSS/水准控制点及数字高程模型，以EIGEN-6C4全球重力场模型作参考重力场，采用顾及地球曲率影响的各类地形质量位及引力的第二类Helmert凝集法严密算法，利用高分辨率地形数据恢复甚短波扰动重力场，确定空间分辨率2′×2′的高精度湖南省似大地水准面模型（HNGG2017）。经外部检核，模型整体精度均优于±0.022 m。与历史模型相比，新模型在湖南北部常德汉寿、西南部永州江永等地区精度得到显著改善。  相似文献   

九寨沟M_S7.0地震地电阻率变化时空演化分析          下载免费PDF全文

王同利  崔博闻  叶青  李菊珍  王丽红  童琼 《地球物理学报》2020,63(6):2345-2356

本文应用归一化变化速率(NVRM)方法,研究了2017年九寨沟M_S7.0地震周边800km范围内25个地电阻率台站2012—2018年的连续观测数据,分析了震中区周围的地电阻率时、空演化过程.结果显示:(1)25个台站中共有14个台站在震前出现了地电阻率变化,结合本次地震震源机制等分析其时空变化,认为邻近地震破裂带的临夏、通渭、武都和宝鸡台地电阻率在震前出现了下降—折返回升型的变化,符合前人已总结的强地震前地电阻率的变化过程.(2)地震发生前震中区周围大区域内出现了地电阻率负异常变化,且以震中区为中心呈条带分布,异常区的长轴方向与地震断裂带走向或地震烈度分布的长轴方向几乎垂直,与地震主压应力轴方向吻合.本文认为九寨沟M_S7.0强震发生之前,震中区周围出现的区域性地电阻率异常空间丛集现象是很好的中期和短临前兆;地电阻率震前异常动态演化、各向异性等特征对认识本次强震发震断层活动以及震源区应力场分布有启示意义.  相似文献   

海底底质声学原位测量电路控制系统研究     

吕斌  祁国梁  李官保  王景强  刘杰 《海洋科学》2018,42(5):32-39

介绍了一种液压驱动贯入式海底沉积声学原位测量系统的电路控制单元的研究实现过程,以及该控制单元在南海北部海底沉积声学调查中的应用。该电路控制单元以Cortex-A8处理器为核心,集成大容量FLASH存储器,与单片机接口控制板进行串口通讯,实现对声学发射采集单元和机械液压贯入单元的可视化控制和监测。基于该电路控制单元,海底底质声学原位测量系统兼具自容式和在线式两种工作模式,可自容记录或实时采集声学原位测量单元在海底的工作状态数据、海底沉积物声速和声衰减系数等声学特性数据。该声学原位测量系统的实验室联调及南海海试结果表明,使用该电路控制单元对海底底质声学测量过程的监测与控制是有效的,对精确获取海底底质的原位声学特性有重要作用,可以促进海底底质声学原位测量系统的产品化。  相似文献