Nonlinear dynamic analysis of deep water risers

The paper presents a theoretical and numerical approach to the dynamical behaviour of risers in deep water which takes into account two types of nonlinearity; that due to viscous drag forces and that due to the large displacements of the riser when submitted to strong axial loads. As the second nonlinearity may have a significant influence upon the behaviour of risers in deep water, a method for automatically updating the structural geometry during the dynamic analysis is given. A computer programme has been written for this purpose.     

1998年长江巨洪与厄尔尼诺事件

1997～ 1 998年出现了 2 0世纪中最强的一次厄尔尼诺事件。根据长江洪水与厄尔尼诺事件的实测资料 ,指出 1 998年的长江巨洪与这次厄尔尼诺事件具有较密切的关系。同时讨论了厄尔尼诺事件影响长江洪水的物理途径 ,这对长江巨洪的长期及超长期预报具有较重要的指示作用     

杭州湾海域水体悬沙粒度统计分析

利用2000年9月在杭州湾进行的原型水文泥沙测验所获取的648个悬沙粒度样品,进行了样品粒度统计分析,结果表明:在杭州湾测验区域,粒径为4.00～20.20μm的悬沙出现频率最高;悬沙的中值粒径值自东向西迅速增大;北岸海域悬沙的中值粒径值大于南岸海域悬沙的中值粒径值。     

Experimental studies on the slowly varying drift motion of a berthed container ship model

The effects of free-surface waves on the floating structures are of great importance in the offshore industry. Among the six degrees of motions of a surface ship the absence of restoring forces in surge, sway and yaw led to critical situations for moored ships in the recent times. The order of forces in horizontal plane and their exciting frequencies are matters of interest. The resonance with the presence of moored chains led to many accidents in the recent past. The lines in dry conditions may not give good damping and in wet condition they may trigger the system to chaotic motions and jumps. Two different loading conditions of a container ship model are tested with waves in laboratory conditions in two different drafts. The mooring lines are chosen as per scale law and the energy under the response spectrum is determined from the plots. The results give new insights into the movement of a berthed ships subjected to waves. Response of the moored ship to different loading conditions in different water depths are discussed in this paper. The paper gives the order of energy due to first-order and slowly varying movement of a berthed container model in a towing tank.     

Growth and reproduction of the bivalve Spisula subtruncata (da Costa) in Dutch coastal waters

The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm³. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns.     

Variations of the Kuroshio Axis South of Kyushu in Relation to the Large Meander of the Kuroshio

The characteristics of the Kuroshio axis south of Kyushu, which meanders almost sinusoidally, are clarified in relation to the large meander of the Kuroshio by analyzing water temperature data during 1961–95 and sea level during 1984–95. The shape of the Kuroshio axis south of Kyushu is classified into three categories of small, medium, and large amplitude of meander. The small amplitude category occupies more than a half of the large-meander (LM) period, while the medium amplitude category takes up more than a half of the non-large-meander (NLM) period. Therefore, the amplitude and, in turn, the curvature of the Kuroshio axis is smaller on average during the LM period than the NLM period. The mean Kuroshio axis during the LM period is located farther north at every longitude south of Kyushu than during the NLM period, with a slight difference west of the Tokara Islands and a large difference to the east. A northward shift of the Kuroshio axis in particular east of the Tokara Islands induces small amplitude and curvature of the meandering shape during the LM period. During the NLM period, the meandering shape and position south of Kyushu change little with Kuroshio volume transport. In the LM formation stage, the variation of the Kuroshio axis is small west of the Tokara Islands but large to the east due to a small meander of the Kuroshio. In the LM decay stage, the Kuroshio meanders greatly south of Kyushu and is located stably near the coast southeast of Kyushu. This revised version was published online in July 2006 with corrections to the Cover Date.     

地形因素对航空面阵CCD影像的影响分析与评价

地形因素,包括地面起伏和地球曲率,是造成航空数字遥感影像变形的主要原因之一.本文以中国科学院遥感所自行研发的多模态航空CCD相机系统为对象,结合其成像模式和几何形态,分析了地形因素给影像带来的变形,推导出航空面阵CCD影像变形的一般公式,并通过概算进行了定量评价,得出了对于航空面阵CCD影像,要想得到高精度的几何处理,必须改正地球曲率影响的结论.     

Large eddy simulation of hydrocyclone—prediction of air-core diameter and shape

Hydrocyclones are widely used in the mining and chemical industries. An attempt has been made in this study, to develop a CFD (computational fluid dynamics) model, which is capable of predicting the flow patterns inside the hydrocyclone, including accurate prediction of flow split as well as the size of the air-core. The flow velocities and air-core diameters are predicted by DRSM (differential Reynolds stress model) and LES (large eddy simulations) models were compared to experimental results. The predicted water splits and air-core diameter with LES and RSM turbulence models along with VOF (volume of fluid) model for the air phase, through the outlets for various inlet pressures were also analyzed. The LES turbulence model led to an improved turbulence field prediction and thereby to more accurate prediction of pressure and velocity fields. This improvement was distinctive for the axial profile of pressure, indicating that air-core development is principally a transport effect rather than a pressure effect.