Experimental investigation on a cabin-suspended catamaran in terms of motion reduction and wave energy harvesting by means of a semi-active motion control system

A novel concept catamaran equipped with a suspended cabin, named Wave Harmonizer Type 4 (WHzer-4), is proposed and evaluated. The mass-spring-mass system is constructed by mounting four sets of suspensions in-between the cabin and the twin-hull. Two sets of dual motor/generators (M/Gs) are attached on the center beam of the cabin's deck fore and aft. Each shaft-end of the dual M/Gs is connected to the twin-hull through a rack-pinion gear unit. In this way the vertical relative motion between the cabin and the twin-hull can be transferred into the rotational motion of the M/Gs, and vice versa. A semi-active motion control system, which contains a proportional-integral (PI) controller, is designed and applied to each of the dual M/Gs for the aim of absorbing wave energy under the condition of suppressing the local vertical velocity of the cabin as much as possible. A 1/5 scale model ship with a length of 1.6 m is built, and a forced-oscillation bench test is implemented to validate the performance of the control system. Then, a series of towing tank tests is carried out in regular head waves. The heave and pitch responses of the cabin, those of the twin-hull and the corresponding wave energy capture width ratio (CWR) at five control scenarios and two reference scenarios are investigated. Discussion on the results of the tank test shows that the motion reduction of the cabin and the wave energy harvesting can be achieved simultaneously at a few wave conditions. However, at other conditions, although noticeable amount of wave energy is harvested, motion reduction of the heave and pitch of the cabin could not be obtained at the same time. It is suggested that varying the gain settings of the PI controllers according to the location of the controllers may improve the effectiveness of the proposed control system.     

2015年台风“彩虹”过境后下山冷急流引起的南海北部海域异常海面降温

This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18,2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7d of the typhoon passage, and lasted for 5d from October 10 to 15. The maximum SST cooling was –4℃ and occurred after 12d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau(YGP), Typhoon Mujigea(2015) met the westerly wind front on October 5. The lowpressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough,thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau(QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4d later after the maximum air temperature drop of –9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.     

虚拟地理环境中基于多模式的多人动作捕捉方法

虚拟地理环境对人类理解、探索地理现象以及发现地理现象之间的联系起到很重要的作用。在基于VR技术的虚拟地理环境中更高效,更自然的交互对虚拟地理环境系统的可用性以及理解、探索地理现象的效率至关重要。当前,人机交互中更自然便捷的交互依赖于动作捕捉技术,而现有的基于单种捕捉模式的动作捕捉方式,易受到遮挡、定位漂移等的影响,捕捉精度受到限制,并只能捕捉单个人的动作,不能满足虚拟地理环境对动作捕捉技术提出的特殊需求。针对单种模式的动作捕捉设备应用于虚拟地理环境受到的限制,本文分析了虚拟地理环境系统中的交互需求以及其对动作捕捉技术提出的特殊需求,创新性的提出了一种基于多种动作捕捉模式以捕捉多人动作的方法。本文方法集中于如何融合基于多种模式的多台设备的动作数据,描述了多人动作捕捉框架及其涉及到的技术,在动作捕捉效果上具有明显提升,能够捕捉多人动作,并开发了原型系统对此方法进行了验证。     

利用跨断层形变资料研究天山中段断层现今活动特征

利用2001年以来天山中段多个跨断层形变场地的测量资料,从断层运动方向和断层平均速率2个方面分析天山中段3条断层现今活动特征。结果表明,霍玛吐断裂呼图壁段断层的活动性质为正、逆断和左、右旋交替活动;北轮台-辛格尔断裂库尔勒段断层表现为右旋运动特征,活动性质为逆断性;妖魔山F2断裂乌鲁木齐段的断层活动性质以逆断为主。妖魔山F2断裂乌鲁木齐段断层的活动程度最高,霍玛吐断裂呼图壁段最低。霍玛吐断裂、北轮台-辛格尔断裂、妖魔山F2断裂垂直方向上基本均处于张性变化,前两者水平向处于挤压状态;断层活动速率的时间进程具有阶段性特征,各个时间段转折点有较好的匹配性。     

Truss Spar平台在波流联合作用下运动响应预报方法比较

基于细长体水动力模型比较了Truss Spar平台在波流联合作用下运动响应预报的三种方法。分别采用波流耦合、速度叠加及力叠加计算Truss Spar平台在波流联合作用下的水动力载荷,根据流场水质点运动规律和Truss Spar外部形状特点,分段高效计算水动力载荷。利用Runge-Kutta-Fehlberg方法求解刚体非线性运动方程得Truss Spar在波流场中的运动响应。研究结果表明力叠加法所预报的Truss Spar纵荡和纵摇运动明显大于其他两种方法的相应运动响应预报结果,而波流耦合法与速度叠加法所预报的纵荡与纵摇运动响应幅值相当,三种方法所预报的垂荡运动响应的大小取决于具体波流参数。     

半潜式浮式风机支撑平台首摇运动特性分析

借助FAST软件对OC4半潜式浮式风机平台进行数值计算,分析了影响海上浮式风机平台首摇运动的一系列重要因素及其变化规律(如风向变化、浪向变化、陀螺力矩等)。研究了平台首摇运动所诱导的风机系统动力响应,发现浮式风机首摇运动不仅会加剧平台耦合运动响应,而且还会影响风机的气动性能和加剧锚泊张力波动。提出并探讨了几种减小海上浮式风机支撑平台首摇运动的方法。     

Towards new applications of underwater photogrammetry for investigating coral reef morphology and habitat complexity in the Myeik Archipelago,Myanmar

Photogrammetry represents a non-destructive, cost-effective tool for coral reef monitoring, able to integrate traditional remote sensing techniques and support researchers’ work. However, its application to submerged habitats is still in early stage. We present new ways to employ Structure from Motion techniques to infer properties of reef habitats. In particular, we propose the use of Digital Surface Models and Digital Terrain Models for assessing coral colonies extension and height and discriminating between seabed and coral cover. Such information can be coupled with digital rugosity estimates to improve habitat characterization. DTM, DSM and orthophotos were derived and used to compute a series of metrics like coral morphologies, reef topography, coral cover and structural complexity. We show the potentialities offered by underwater photogrammetry and derived products to provide useful basic information for marine habitat mapping, opening the possibility to extend these methods for large-scale assessment and monitoring of coral reefs.     

现今绝对板块运动

根据热点假设,热点对于中间层是固定的.相对热点的板块运动叫做绝对板块运动.绝对板块运动模型可以通过反演火山链传播的速率和走向数据以确定相对板块运动在角速度空间的原点来得到.利用一组近来(0～7.8 Ma)全球分布的热点的迁移速率和走向数据,结合板块运动模型NNR-NUVEL1A,已研制出一个叫做APM2的现今绝对板块运动模型.按照该模型,太平洋板块围绕60.063°S、102.210°E处的极以(0.833 0°±0.013 3°)/Ma的速率运动,非洲板块围绕46.849°N、44.372°W的极以(0.101 5°±0.013 4°)/Ma的速率运动,南极板块的运动则以46.871°N、146.942°E为极,速率为(0.084 6°±0.017 7°)/Ma,欧亚板块的运动更慢,极为27.291°N、171.925°W,速率为(0.065 5°±0.020 6°)/Ma.这一模型表明,岩石圈相对深部地幔有一个以49.423°S、90.625°E为极,速率为(0.198 3°±0.013 5°)/Ma的净旋转.表明太平洋热点同印度-大西洋热点不一致,显示太平洋热点的运动也不一致.为了分析和比较,还给出了仅用全球分布的热点的走向数据和仅用印度-大西洋热点的走向数据得到的板块绝对运动的角速度.     

Floating and fixed artificial habitats: Spatial and temporal patterns of benthic communities in a coral reef environment

While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column.     

Analysis of threshold and incipient conditions for sediment movement

Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data.