When did the Falklands rotate?

Similarities in the styles and relative timings of tectonic events in the Outeniqua Basin, South Africa and the North Falkland Basin suggest that basin formation in both regions may have preceded rotation of the Falklands microplate. Contrary to previous models for the break-up of Gondwana, which suggest Jurassic rotation, the data implies Valanginian rotation, contemporaneous with the first recorded motion on the Agulhas Falkland Fracture Zone and South Atlantic rifting. The data also suggests that the formation of the Falkland Plateau Basin may also be a Cretaceous event as opposed to the previously assumed Jurassic age. Such a model is consistent with new offshore seismic evidence while the inconclusive nature of the supportive evidence for Jurassic rotation does not exclude later rotation as a possibility.     

南海中尺度涡的形转、内转及平移运动研究

中尺度涡旋的运动整体可分为两部分：平移及转动。平移指涡旋在整个生命周期内的水平移动，而转动除了包括内转 （海表地转流引起的涡旋自身水体转动） 外，还包括形转 （涡旋实际边界最佳拟合椭圆的转动）。本文基于 1993—2018 年共计 26 年间的卫星高度计涡旋识别与追踪数据，首次对南海中尺度涡旋的完整运动形式，即形转、内转、平移展开了系统的研究。其中，对内转及平移的分析，可通过涡旋的识别追踪数据集直接进行；为研究涡旋形转，提出了一种基于涡旋识别追踪数据自动提取涡旋形转信息的算法，以此得到涡旋形转方向、每天形转的角度以及形转圈数等信息，获得涡旋形转数据集。通过对涡旋识别追踪数据以及形转数据集的统计分析发现：南海涡旋的平移方向多为西向，且其速率呈偏态分布，主要以南海南部偏高。同样，涡旋的内转速率也呈偏态分布，高速率内转的涡旋主要分布在吕宋海峡附近。涡旋的形转主要以南海南部速率偏高，且与涡旋的寿命及长轴有一定的关系，倾向于随着涡旋寿命的增长、涡旋长轴的增大而变慢。同时南海涡旋的这三种不同运动形式之间也存在一定的相关性。     

Phase and doppler errors in a spaceborne synthetic aperture radar imaging the ocean surface

Data processing in a spaceborne synthetic aperture radar (SAR) imaging the ocean surface is affected by earth rotation, orbit eccentricity, and wave motion. Without compensation these sources will cause the images to shift in range and in-track positions and also cause defocusing. Ionospheric granularities may degrade image quality. Calculations of the magnitudes of these effects are presented.     

台风对海上风电单桩基础累积变形影响试验研究

文中主要采用小比尺模型试验,研究了台风对海上风电单桩基础累积变形的影响。通过在模型槽中进行桩的水平静力和循环加载试验,得到了不同工况下桩的累积转角与循环加载次数之间的关系曲线。随后对曲线进行分析,拟合出无台风工况下累积转角的计算公式,然后运用叠加法,得出了有台风工况下累积转角的计算公式。试验结果表明,单独作用一种循环荷载时,桩的累积转角是循环次数的幂函数。台风引起的大幅值循环荷载会导致转角的陡升,且增加幅度与小幅值循环荷载的幅值负相关。当将台风荷载设置在加载过程的开头时,对于疲劳设计工况,台风荷载产生的累积转角占总的累积转角的99%以上,因而可以忽略小幅值循环荷载产生的累积转角,直接用台风荷载产生的累积转角代表桩的长期累积转角,实现简化设计。     

地磁感应线圈在投弃式探头水下转速测量中的应用

介绍了地磁感应线圈的工作原理,针对投弃式探头水下转速测量需要,设计专用线圈传感器及测量电路,并搭建专用试验台进行室内试验。试验结果表明,采用地磁感应线圈可以准确地得到旋转体转速信息,可应用于投弃式探头水下转速测量。     

考虑平台转动的等效水深截断系泊系统优化设计

等效水深截断是混合模型试验中非常重要的一步,合理的截断方案是模型试验成功的前提。现有的研究大多忽略对平台转动的考虑,该文在静态相似准则的基础上增加对平台转动的考虑,推导了系泊系统回复力和转矩的计算公式,建立了满足静态一致性的目标函数,进而采用粒子群算法进行等效水深截断优化设计。以某深水半潜式平台为例,首先在不考虑转动的情况下对其系泊系统进行等效截断,研究发现截断水深的变化对转矩的优化结果影响较大,从而证明了平台转动是应该考虑的。其次在考虑转动的情况下对系泊系统进行等效截断,通过水动力软件验证所优化的结果,证明该方法的可行性,为后续的等效水深截断优化设计的研究提供参考。     

若干海洋状况与地球运动参数

月球运动参数对海洋潮汐的影响,早就为人们所关注,并从理论研究到实际应用方面作了不少工作;可是地球参数在若干海洋状况上的反应却很少引起人们的注意.近十年来,国外这方面的工作有所加强[1],但大多偏重大西洋的研究,联系与我国直接有关的太平洋状况较少,而联系我国近海状况的则更少.本文试图阐明地球运动参数影响若干海洋状况可能的物理原因,并根据世界和我国海平面高度的若干观测资料,海洋上大气动活中心的资料,以及北太平洋6个点的海温资料,进行数理统计,然后与地球参数的相应统计进行综合分析,从而讨论它们之间的规律性的联系.     

The rôle of the complete Coriolis force in cross-equatorial flow of abyssal ocean currents

Ocean currents flowing close to or across the equator are strongly constrained by the change in sign of f, the locally vertical component of the Earth’s rotation vector, across the equator. We investigate these currents using a shallow water model that includes both the locally vertical and locally horizontal components of the Earth’s rotation vector, thus accounting for the complete Coriolis force. We therefore avoid making the so-called “traditional approximation” that retains only the part of the Coriolis force associated with the locally vertical component of the rotation vector. Including the complete Coriolis force contributes an additional term to the fluid’s potential vorticity, which may partially balance the change in sign of f as fluid crosses the equator over suitably shaped bathymetry.We focus on the Antarctic Bottom Water, which crosses the equator northwards in the western Atlantic ocean where the local bathymetry forms an almost-zonal channel. We show that this bathymetry facilitates the current’s equatorial crossing via the action of the “non-traditional” component of the Coriolis force. We illustrate this process using both analytical and numerical solutions for flow of an abyssal current over idealised equatorial topography. We also consider the one-dimensional geostrophic adjustment of a body of fluid across the equator, and show that the “non-traditional” contribution to the fluid’s angular momentum permits a larger cross-equatorial transport. These results underline the importance of including the complete Coriolis force in studies of the equatorial ocean, particularly in the weakly-stratified abyssal ocean where the non-traditional component is most pronounced.     

Evidence for the Trapping and Amplification of Near-Inertial Motions in a Large Anticyclonic Ring in the Oyashio

Three ARGOS drift buoys were deployed in the Oyashio Current off the Kuril Islands near 45°N in fall, 1990, during a joint Russia/Canada study of western boundary current dynamics in the Subarctic Pacific Ocean. We here report on one buoy deployed within an anticyclonic warm core ring (WCR86B) which shows evidence of large amplitude inertial motions of near-diurnal frequency. During its first week within the ring the buoy drifted with a mean azimuthal current speed of 0.40–0.45 m s⁻¹ and a radius of rotation of 15–20 km. However, superimposed on the mean rotation of the ring at this time were “loops” of near-diurnal period, radius 7–8 km and speeds exceeding 1 m s⁻¹. During successive rotations the buoy spiraled outward, its mean period of rotation increased and the amplitude of the near-diurnal motions decreased. The large motions are explained by inertial wave trapping and amplification within the extremely large and weakly stratified eddy, wherein the negative vorticity of the eddy reduces the local inertial frequency to near-diurnal frequency. We here suggest that either tidal or wind forcing may generate these high-amplitude “loop” motions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preliminary attempt to characterize the rotation of seafloor in the Pito Deep area of the Easter Microplate using a submersible magnetometer

Several mechanisms have been proposed to account for the rotation of the nearly north-south abyssal hill fabric formed on the East Pacific Rise north of the Easter Microplate to the nearly east-west trends in the northern microplate interior. Proposed mechanisms include rigid microplate rotation, transform fault – parallel shear, and bookshelf faulting during the transfer of lithosphere from the Nazca Plate to the microplate. We used a submersible magnetometer on a NAUTILE dive program to measure the magnetic vector rotation of a pillow basalt and dike spur near Pito Deep, the present location of the tip of the propagating rift system that created the microplate. Our results, although too limited to draw strong conclusions from, suggest clockwise rotations of the seafloor magnetic vectors inconsistent with the transform-parallel shear model, and larger than can be explained solely by rigid microplate rotation.     

地球赤道上空地月距离的4.425a周期与厄尔尼诺、地球自转、海面变化及地裂缝的关系

文中论述了在地球赤道上空,地月距离存在4.425a 的变化周期,是由于月近地点在8.85a的周期性运移中,每到黄径0°和180°(赤道线上)在地球自转的背景下使地月距效果相同所致。而每年的地近日点(1月3日或4日)正置圣诞节过后几天,因此,日、月、地相对运动每隔4.425a 在圣诞节前后三者距离总会达到最近。本文计算了1910～1991年圣诞节前后赤道上空地月距离的变化,发现日、月、地最近时与厄尔尼诺、地球自转、海平面变化,地裂缝等自然现象的发生存在着统计上可以认可的相关性。     

广东三水盆地晚自垩世—始新世古地磁研究及构造意义

对广东三水盆地上白垩统三水组、大　山组、古新统莘庄组及始新统　心组、宝月组的系统的古地磁研究结果表明：（１）旋转运动是该区构造运动的主要形式，顺时针旋转盆地拉张发育，这时针旋转盆地挤压衰亡，发育的程度与旋转角度有关；（２）始新世该区旋转方向由顺时针旋转变为道时针旋转，对应于太平洋－库拉板块对欧亚板块作用方向的改变，说明三水盆地的形成发育与太平洋－库拉板块对欧亚板块的作用密切相关；（３）三水盆地所在的华南地块从晚白垩世至始新世在纬向上不存在明显的运动，一直停留在略低于现今纬度的位置上。     

Accumulated Rotation of A Modified Suction Caisson and Soil Deformation Induced by Cyclic Loading

Modified suction caissons (MSCs) acting as offshore wind turbine foundations will generate the accumulated rotation under cyclic loading resulted from waves. The accumulated rotation and the range of soil deformation around the MSC under long-term cyclic wave loading were studied using 3-D numerical simulations. The Morison equation was adopted to calculate the wave loadings. It was found that the MSC accumulated rotation increases linearly with the increase of the logarithm of cyclic number. The normalized expression was proposed to reflect the relationship between the accumulated rotation and cyclic number. The soil deformation range around the MSC increases when increasing the cyclic number and loading amplitude. It can also be concluded that the accumulated rotation increases rapidly with this change of excess pore pressure in the first 4000 cycles. The responses of the MSC to wave and wind loads were also investigated. Results show that the accumulated rotation of the MSC under both wave and wind loadings is larger than that under the wave loading only.     

Numerical Investigation on Vortex-Induced Rotations of A Triangular Cylinder Using An Immersed Boundary Method

A numerical study of vortex-induced rotations(VIRs) of an equivalent triangular cylinder, which is free to rotate in the azimuthal direction in a uniform flow, is presented. Based on an immersed boundary method, the numerical model is established, and is verified through the benchmark problem of flow past a freely rotating rectangular body.The computation is performed for a fixed reduced mass of m~*=2.0 and the structural stiffness and damping ratio are set to zero. The effects of Reynolds number(Re=25-180) on the characteristics of VIR are studied. It is found that the dynamic response of the triangular cylinder exhibits four distinct modes with increasing Re: a rest position,periodic rotational oscillation, random rotation and autorotation. For the rotational oscillation mode, the cylinder undergoes a periodic vibration around an equilibrium position with one side facing the incoming flow. Since the rotation effect, the outset of vortex shedding from cylinder shifts to a much lower Reynolds number. Further increase in Re leads to 2 P and P+S vortex shedding modes besides the typical 2 S pattern. Our simulation results also elucidate that the free rotation significantly changes the drag and lift forces. Inspired by these facts, the effect of free rotation on flow-induced vibration of a triangular cylinder in the in-line and transverse directions is investigated. The results show that when the translational vibration is coupled with rotation, the triangular cylinder presents a galloping response instead of vortex-induced vibration(VIV).     

Experimental investigation on cyclic deformation behavior of soft marine clay involved principal stress rotation

To investigate cyclic deformation behavior of natural soft marine clay-involved principal stress rotation, a series of undrained tests were conducted by using GDS hollow cylinder apparatus. The principal stress rotates 5000 cycles while the deviator stress was kept at a constant level. The tests results show that the deformation behavior of the tested samples are significantly dependent on cyclic stress ratio (CSR). Furthermore, different type of generation of axial strains occur under different CSRs. With the same CSR, the type of axial strain is different between that considering and ignoring principal stress rotation. When CSR is larger than CSR = 0.42 under principal stress rotation, the axial strain grows rapidly after a few cycles. Compared with the results conducted by cyclic triaxial results, the effect of principal stress rotation on the axial strain is significant.     

Rotation Center and Horizontal Bearing Capacity of the Bucket Foundation in Soft Ground

In the last 20 years, the bucket foundation has been developed as a new type of offshore platform structure. Because of its short period of application to engineering practices, the theoretical decision on the rotation center and horizontal bearing capacity of the bucket foundation has yet to be agreed. A limit analysis method is used to determine the updated rotation center position and horizontal bearing capacity to evaluate the failure mechanisms of the bucket foundations. The results are compared with numerical simulation and experiments, and also with other theoretical methods. The proposed method can satisfactorily consider the engineering conditions and the result is accurate in determining the rotation center and horizontal bearing capacity.     

Reflection and diffraction of internal solitary waves by a circular island

We have investigated the reflection and diffraction of first-mode and second-mode solitary waves by an island, using a three-dimensional nonhydrostatic numerical model. The model domain consists of a circular island 15 km in diameter in an ocean 300 m deep. We use prescribed density anomalies in an initially motionless ocean to produce highly energetic internal solitary waves; their subsequent propagation is subject to island perturbations with and without the effect of earth’s rotation. In addition to reflected waves, two wave branches pass around the island and reconnect behind it. Island perturbations to the first-mode and second-mode waves are qualitatively similar, but the latter is more profound because of the longer contact time and, in the presence of earth’s rotation, the scale compatibility between Rossby radius of the second baroclinic mode and the island diameter. Without earth’s rotation, reflected and diffracted waves are symmetrical relative to the longitudinal axis passing through the island center. With earth’s rotation, the current following the wave front veers to the right due to Coriolis deflection. For a westward propagating incoming wave, the deflection favors northward wave propagation in the region between the crossover point and the island, shifting the wave reconnection point behind the island northward. It also displaces the most visible part of the reflected waves to the southeast. In the presence of earth’s rotation, a second-mode incoming wave produces island-trapped internal Kelvin waves, which are visible after the passage of the wave front.     

Double diffusive convection in a rotating system

Linear instability theory of double diffusive convection is generalized to a rotating system. For sufficiently large rotation, rotation has a stabilizing effect, and viscosity stabilizes most of oscillatory modes but destabilizes direct modes. The following behavior is found in oscillatory modes in the case of destabilizing temperature distribution and stabilizing solute distribution. With the fixed destabilizing temperature distribution (1) the system is stable when the stabilizing solute gradient is large, (2) it becomes unstable with respect to oscillatory modes when the gradient is less than a certain value. (3) When the gradient is reduced further, the system becomes stable again. This anomalous phenomenon happens only when the Prandtle number is less than unity and larger than the ratio of the diffusivity of solute and that of temperature, under the existence of rotation.     

海洋测绘中船体姿态改正的误差分析

船体姿态变化是海洋测绘中重要的误差来源,需要进行修正。姿态改正实际上是进行坐标系变换,存在着不同的坐标轴旋转顺序,对应的旋转矩阵形式也不一样。实际应用中发现不同的旋转矩阵导致不同的姿态改正结果,甚至出现错误的改正。仔细分析了姿态改正中的三种旋转方式,重点讨论了两种常用模型简化后的误差量级。研究后发现,坐标系变换中的旋转角并非姿态角,并由此导出了两种常用旋转方式对应的旋转角,它是纵摇角和横摇角的函数。采用正确的旋转角,不同的旋转方式能够得到一致的姿态改正结果。另外,在姿态改正精度要求不高于0.2m的前提下,第一种旋转方式可以采用简化模型。     

苏北东部海域辐射沙洲研究的新思路

苏北东部海域辐射沙洲以往仅侧重于外动力方面的研究，这里提出开展内动力与外动力同步研究的新思路，指出两者的结合点是旋扭运动，要在以往外动力研究的基础上，加强地震震中研究、地形变监测、地应力实测等方面内容，以确定该区不同层圈、不同介质条件下是否存在同一的旋扭运动。上述思路的实施，有利于地理学与地质学研究的沟通和溶合，同时提出地震往往伴随旋扭现象的事实，丰富了地震学的研究内容，其研究成果将为多方面的开发辐射沙洲提供基础资料。