计算机绘制粒度分布曲线的插值方法

张力样条是在三次样条函数中加入张力系数而构成。根据相同的粒度数据用两种方法在计算机上所作的粒度分布曲线图形的对比,显示出张力样条方法比三次样条方法有明显的优越性,它消除了插值曲线的不必要的摆动,在保持曲线平滑的前提下,能更准确地表达沉积物的粒度特征。用张力样条结合将离散点连成光滑曲线的阿克玛方法进行插值,使复杂的粒度分布曲线的插值同时保持准确性和平滑性,在沉积物粒度的数据的计算机处理方面有明显的意义。     

Modelling of segment structures: Boudins, bone-boudins, mullions and related single- and multiphase deformation features

Finite element modelling has been used to simulate the development of segment structures, deformed layer segments separated by veins, such as boudins, mullions, and bone-boudins. A parameter sensitivity analysis is used to compare the influence of the nature of the flow, the relative viscosities of veins in necks and the host rock, and the initial geometry of the layer segments. Parameter fields have been determined for the relative viscosity of veins and layers, and the kinematic vorticity number of flow. Reworked segment structures can have several shapes such as bone-, bulging, shortened bone-boudins and their asymmetric equivalents such as domino- and shearband-boudin geometry. The model for asymmetric reworked segment structures is applied to such features from the Lower Ugab Metaturbidites in NW Namibia. The model suggests that these structures form where the neck veins are stronger than the boudinaged layer, with a significant simple shear component of the bulk flow. The quartz filled necks in the Lower Ugab are therefore stronger than the quartz-rich wall rock in greenschist facies where the progressive deformation occurred. Bone-boudins are usually interpreted to form in transpressional flow, but simulations of the rotation of tension gashes show that they can also form in simple shear or slightly transtensional shear flow.     

围压条件下岩石的抗拉强度

用水压致裂法对7种岩石的厚壁圆筒试件进行不同围压下的抗拉强度实验,并从试件致裂瞬间的内壁环向应力σt,环向应变εt等五种参数随围压变化的角度,对围压条件下岩石的抗拉强度进行研究。结果表明,若用σt表示岩石的应力抗拉强度,则σt随围压的增加而减少,并由低围压时的拉应力逐渐过渡为高围压时的压应力。高围压时,虽然试件已处于三向受压状态,但其破裂仍表现为典型的张性破裂。从另一意义上讲,处于高围压环境中的岩石,其内部不可能存在拉应力,拉应力只在低围压状态中存在。若岩石的应变抗拉强度由εt表示,即使岩石三向受压,张性破裂的εt始终是拉应变,岩石的抗拉强度由应变来表征似乎更合理。εt先随围压的增大而增大,当围压超过某一特征值后,εt反随围压的增大而有所减少。 将上述结果应用于岩体(或地震)破裂,可以证明,当岩体内存在σ_3<μ(σ_1+σ_2)的应力状态时,即使三向受压,岩体照样会出现张性破裂。由此认为,地震的震源也存在着张性破裂的可能。     

Partitioning of Holocene kinematics and interaction between the Theistareykir Fissure Swarm and the Husavik-Flatey Fault,North Iceland

Our research is aimed at contributing to the general understanding of how transform-rift junctions work, a topic that can be studied in exceptional detail in North Iceland, where the active transform Husavik-Flatey Fault (HFF) connects with the Gudfinnugja Fault (GF), the westernmost structure of the Theistareykir Fissure Swarm (TFS). We studied in the field: i) offsets along the easternmost HFF, ii) the geometry and kinematics of 649 faults and 1208 tension fractures in the TFS, iii) the interactions among all these structures. The HFF transtensional kinematics is compatible with the GF, which shows different offsets north and south of the junction between these two faults. We suggest the possible prolongation of the HFF beyond the junction, based on: i) the change in offsets and strikes of TFS normal faults, ii) the presence of en-échelon, NNW-SSE-striking normal faults and tension fractures with a slight right-lateral component, iii) the transition of some of the faults into tension fractures north of the prolongation of the HFF, and iv) the decrease in the cumulated offset of all the faults north of the HFF prolongation. We interpret these data as field evidence of the first stages of propagation of the HFF upward or across the TFS: This has clear implications for defining the potential rupture length of the HFF and, hence, for seismic hazard assessment.     

Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches

Tension Leg Platform (TLP) is one of the concepts which shows promising results during initial studies to carry floating wind turbines. One of the concerns regarding tension leg platform wind turbines (TLPWTs) is the high natural frequencies of the structure that may be excited by nonlinear waves loads. Since Computational Fluid Dynamics (CFD) models are capable of capturing nonlinear wave loads, they can lead to better insight about this concern. In the current study, a CFD model based on immersed boundary method, in combination with a two-body structural model of TLPWT is developed to study wave induced responses of TLPWT in deep water. The results are compared with the results of a potential flow theory-finite element software, SIMO-RIFLEX (SR). First, the CFD based model is described and the potential flow theory based model is briefly introduced. Then, a grid sensitivity study is performed and free decay tests are simulated to determine the natural frequencies of different motion modes of the TLPWT. The responses of the TLPWT to regular waves are studied, and the effects of wave height are investigated. For the studied wave heights which vary from small to medium amplitude (wave height over wavelength less than 0.071), the results predicted by the CFD based model are generally in good agreement with the potential flow theory based model. The only considerable difference is the TLPWT mean surge motion which is predicted higher by the CFD model, possibly because of considering the nonlinear effects of the waves loads and applying these loads at the TLPWT instantaneous position in the CFD model. This difference does not considerably affect the important TLPWT design driving parameters such as tendons forces and tower base moment, since it only affects the mean dynamic position of TLPWT. In the current study, the incoming wave frequency is set such that third-harmonic wave frequency coincides with the first tower bending mode frequency. However, for the studied wave conditions a significant excitation of tower natural frequency is not observed. The high stiffness of tendons which results in linear pitch motion of TLPWT hull (less than 0.02 degrees) and tower (less than 0.25 degrees) can explain the limited excitement of the tower first bending mode. The good agreement between CFD and potential flow theory based results for small and medium amplitude waves gives confidence to the proposed CFD based model to be further used for hydrodynamic analysis of floating wind turbines in extreme ocean conditions.     

Triangular Configuration Tension Leg Platform behaviour under random sea wave loads

This study investigates the dynamic response of a Triangular Configuration Tension Leg Platform (TLP) under random sea wave loads. The random wave has been generated synthetically using the Monte-Carlo simulation with the Peirson–Moskowitz (P–M) spectrum. Diffraction effects and second-order wave forces have not been considered. The evaluation of hydrodynamic forces is carried out using the modified Morison equation with water particle kinematics evaluated using Airy's linear wave theory. Wave forces are taken to be acting in the surge degree-of-freedom. The effect of coupling of various structural degrees-of-freedom (surge, sway, heave, roll, pitch and yaw) on the dynamic response of the TLP under random wave loads is studied. Parametric studies for random waves with different H_s and T_z under the presence of current have also been carried out. For the orientation of the TLP, surge, heave and pitch degrees-of-freedom responses are influenced significantly. The surge power spectral density function (PSDF) indicates that the mean square response is affected by the amplification at the natural frequency of the surge degree-of-freedom and also at the peak frequency of the wave loading. The PSDF of the heave response shows higher peak values near the surge frequency and near the peak frequency of the wave loading. Surge response, therefore, influences heave response to the maximum. Variable submergence seems to be a major source of nonlinearity and significantly enhances the responses in surge, heave and pitch degrees-of-freedom. In the presence of current, the response behaviour of the TLP is altered significantly introducing a non-zero mean response in all degrees-of-freedom.     

新疆钻孔应变异常与强震活动

在新疆钻孔应变18年的观测期间，发生了6级以上强震17组(次)，其中7级以上地震5次，8级以上地震1次。钻孔应变资料在64％强震前记录到了异常变化。其中属于天山和塔里木地块周边的15例强震中，在儿例地震前钻孔应变资料出现了异常，占全部强震的73％。利用钻孔应变资料正确预报的地震数仅4例，占全部强震的23％，占天山及塔里木地块周边地震数的26％。在这些强震中距离台站250km范围以内发生的地震有7例，正确预报的有4例，占57％。     

Infiltration measurements—a review

Infiltration theory developed from Richards' equation for the movement of water in unsaturated soil is outlined and used as a basis for considering measurements made with ring infiltrometers, rainfall simulators and tension infiltrometers. In particular, the three-dimensional soil-water flow occurring with many of these measurement techniques is considered. Complicating factors of soil heterogeneity, soil swelling and shrinking, and soil aggregation, that limit the interpretation of field measurements using classical theory, are discussed.     

Effect of the development of notches and tension cracks on instability of limestone coastal cliffs in the Ryukyus, Japan

Notches cut by waves are currently developing at the base of vertical coastal limestone cliffs in Okinawa, Japan. The cliff height varies from 3.0–22.1 m, and the maximum notch depth is 8.8 m. Many rectangular or cubic blocks, which appear to have originated from cliff failures, are found on platforms in front of the cliffs. On the flat top surface of the cliff, tension cracks often run parallel to the cliff face. The vertical face of the cliffs displays small undulations but no sliding striation, suggesting that cliff failures have been caused by toppling rather than by shearing or sliding. We use slope stability analysis to determine the critical condition for toppling failure. Physical and mechanical properties of the cliff material were first obtained from laboratory tests. The results indicate that the strength of limestone shows a scale effect, such that the strength decreases with increasing size of the test specimens. Based on this result, we estimated the strength of a rock mass corresponding to the size of the coastal cliff. Cliff stability was then analyzed using a cantilever beam model. Comparison of the stability analysis and the dimension of fallen blocks indicates that toppling failure is strongly associated with the development of notches and tension cracks.     

大射电望远镜索牵引并联机构索力优化分析

为对大射电望远镜馈源支撑系统索牵引并联机构实施控制、获得准确的索长信息,采用精确的悬链线方程建立舱体非线性静平衡方程组来求解索力,进而获得大跨度下刚索索长。提出了线性简化模型——赝曲线模型,该模型保证了解算精度,大大提高了解算效率,为实时控制及进一步大规模计算提供了便利。在给定位置下,利用赝曲线模型对姿态角进行搜索,得到满足索力约束条件的姿态角集合。在此基础上,以索力均匀分布为优化目标对索力进行优化,从而保证系统良好的力特性,避免钢索之间的干扰。数值计算说明了赝曲线模型的精确性和快速性,最后利用赝曲线模型得到了优化后精确的索力、姿态角与索长。