Discussion on Cathodic Protection of HZ 21-1 Platform

The environmental conditions around the first offshore HZ 21- 1 steel wellhead platform in the South China Sea are characterized by deep water, frequent typhoons, rough waves, high water temperature, severely corrosive seawater, and thick fouling organism attachments. The design and effectiveness of galvanic anode protection system are presented, and several methods are described, which are the calculation method of the protective current density considering the variation of water depth, the method of determining protection parameters considering various factors, the arrangement of anodes based on potential distribution and current requirements at different water depths, and the method of anode installation. Finally the effect of the accuracy of selected cathodic protection parameters on the economic benefits of offshore projects is also discussed..     

不同温度下铝牺牲阳极合金元素对工作电位影响的灰箱分析

目前，城市用水中约80%是工业用水，而工业用水中约80%是工业冷却水。为节约淡水，人们试图利用海水代替淡水做工业冷却水。但在海水冷却系统中，换热器的出口及其后续部分的钢铁设施由于海水温度较高(一般在50℃左右，有的还大于55℃)，腐蚀现象相当严重，解决该部位的腐蚀防护问题是直接利用海水代替淡水做工业冷却水中不可缺少的一个环节。牺牲阳极是防止海水中钢铁设备腐蚀的一种行之有效的方法，但常用的几种牺牲阳极在该温度下不能适用。因此，找出牺牲阳极性能在不同温度下的变化规律，对研制能在高温下使用的牺牲阳极有着重要的理论和实际意义。 工作电位是牺牲阳极一项重要的性能指标。牺牲阳极只有具备了足够负的工作电位，才能在实际应用中保持足够的驱动电压(朱相荣等，1999；火时中，1988)，达到长期使用的目的。有关文献报道了牺牲阳极添加元素对工作电位的影响(朱承德等，1997；Gurrappa1997；张信义等，1996)，但哪些元素对阳极工作电位的影响更大些，元素对工作电位的影响是否有一定的规律，却均无报道。本文作者根据以上文献选择元素，自制了28种铝基牺牲阳极，并按国标GB4948-85的方法进行实验，用灰箱分析的数学方法对得到的数据进行分析，所得结果对研制高温海水中如何应用牺牲阳极有一定的指导作用。     

Toppling and stabilization of the intake slope for the Fengtan Hydropower Station enlargement project, Mid-South China

The intake slope for the Fengtan Hydropower Station enlargement project is composed of thickly bedded sedimentary rock. During excavation of the intake slope and tunnels, toppling was observed in the rock masses of the intake slope. Research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation. The in situ monitoring data and possible causes for toppling were analyzed. A method for analyzing monitoring data was proposed, which can be used to calculate the depth and rotation angle of block toppling. The monitoring results showed that toppling occurred only at a shallow depth, and induced local instability of the slope. Deformation had been controlled and the slope tended to be stable after reinforcement. Through this case study, it can be seen that the stability of the slope and underground openings during and after excavation is variable, especially when the loading conditions and topography are changed. A proper construction sequence is essential, i.e., excavation from the inside toward the free slope surface; excavating the slope above the tunnel after the tunnel lining is in place. This is particularly important for the excavation of multiple tunnels at the slope toe.     

Implementation of Particle-scale Rotation in the 3-D Lattice Solid Model

In this study, 3-D Lattice Solid Model (LSMearth or LSM) was extended by introducing particle-scale rotation. In the new model, for each 3-D particle, we introduce six degrees of freedom: Three for translational motion, and three for orientation. Six kinds of relative motions are permitted between two neighboring particles, and six interactions are transferred, i.e., radial, two shearing forces, twisting and two bending torques. By using quaternion algebra, relative rotation between two particles is decomposed into two sequence-independent rotations such that all interactions due to the relative motions between interactive rigid bodies can be uniquely decided. After incorporating this mechanism and introducing bond breaking under torsion and bending into the LSM, several tests on 2-D and 3-D rock failure under uni-axial compression are carried out. Compared with the simulations without the single particle rotational mechanism, the new simulation results match more closely experimental results of rock fracture and hence, are encouraging. Since more parameters are introduced, an approach for choosing the new parameters is presented.     

Reference frame, angular momentum, and porphyroblast rotation

Rotation of small rigid objects in a deforming ductile matrix can produce two different types of microstructure: a shape fabric due to alignment of the principal axes of a population of elongate objects and the inclusion trail microstructure preserved in syntectonic porphyroblasts. We use numerical modeling to show that inclusion trails of elongate porphyroblasts are expected to be extremely complex. In contrast, snowball garnets are readily interpretable. But misuse of reference frame and kinematic misconceptions have obfuscated the discussion on the formation of porphyroblast inclusion trails in general and snowball garnet inclusion trails in particular. We clarify this point. Models for snowball garnet formation that are based on the notion of garnets being irrotational with respect to the earth can be rejected on a geometrical and kinematic basis. Further, the notion that rigid objects embedded in a deforming ductile matrix generally do not rotate is unsound—it violates the fundamental physical law of balance of angular momentum.     

Tertiary paleomagnetic results and structural analysis from the Transdanubian Range (Hungary): rotational disintegration of the Alcapa unit

We carried out an integrated paleomagnetic and structural study in the Transdanubian Range, western and central Hungary. As a result, the Tertiary tectonic history of this area can be characterized by three events of counterclockwise (CCW) rotation and four or five phases of brittle deformation. The change of the orientation of stress axes between phases is mainly apparent and reflects the rotation of the faults predating a particular rotation event. The first two rotation events (R1 and R2) were probably governed by the rollback mechanism of the subducting European plate. We suggest that these rotations were taking place from 18–17 and 16–14.5 Ma, respectively, i.e. simultaneously with the rotations of the North Hungarian Paleogene Basin and the main part of the Western Carpathians. However, the angle of both rotations was less in the Transdanubian Range due to increasing distance from the subduction front. The differential rotation was accommodated by extensional faulting by formation of a graben system. On the other hand, the youngest rotation event R3 seems to be connected to the renewed rotation of the Adriatic plate around 5 Ma. Our combined data set strongly supports earlier conclusions, namely, that the different subunits of the Eastern Alpine–Western Carpathian–Northern Pannonian unit (Alcapa) did not form a rigid unit, although they moved in similar manner.     

On long-period polar motion

 Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions: retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy, demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years. The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period variations in published polar motion time series. Received: 27 March 2001 / Accepted: 15 October 2001     

IERS1996规范在参考系方面的改进

对ＩＥＲＳ１９９６规范中有关参考系方面作了简单而系统的介绍，重点叙述了与ＩＥＲＳ１９９２标准相比ＩＥＲＳ１９９６规范在参考系方面的主要改进：天球参考架中的基本源从５７颗增加到２３６颗；动力学参考架采用ＪＰＬ ＤＥ４０３／ＬＥ４０３历表代替ＤＥ２００／ＬＥ２００历表；采用ＮＵＶＥＬ ＮＮＲ－１Ａ板块运动模型代替ＮＵＶＥＬ ＮＮＲ－１模型；变更了９个基本常数值；给出了天极坐标的观测和理论间差的经验模型     

On the inclination functions and a rapid stable procedure for their evaluation together with derivatives

The authors’ individual work on the inclination functions over a period of more than 30 years has led to the need for a joint paper. Intervening papers by other authors have demonstrated misunderstandings needing to be corrected, in particular concerning the key recurrence relation published by the present first author in 1971. This relation is remarkably stable, though this has not always been recognized. The real source of error with the specific functions that are involved in the recurrence relation arises from the possibilities for underflow (as well as overflow) in the computation. The problem exists even with normalized versions of the functions, and is carefully addressed. Very important, for both academic and practical reasons, is a general invariance relation that had been found earlier by the second author, for which a proof is given here for the first time. Some numerical results from our new (and highly efficient) procedure for computing the inclination functions are tabulated, and comparisons made with the results of other authors. Finally, Fortran code for an optimized implementation of this procedure is in supplementary material. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.