打滑地层新型孕镶金刚石钻头

在分析打滑地层特点的基础上,指出了钻进该地层所存在的问题,提出了用于打滑地层钻进的新型孕镶金刚石钻头的设计思路,在钻头工作层中采用主、辅两种磨料,并对这两种磨料的工作机理、处理工艺以及该新型钻头的制造进行了阐述.钻头的室内钻进试验结果表明:在钻进极坚硬致密的锆刚玉时,相对于普通金刚石钻头,新型孕镶金刚石钻头的钻进时效提高1.93倍,平均磨损量增加38%,具有高时效、相对寿命长的优点,是打滑地层钻进的理想钻头.     

变刚度隔震保护装置试验研究

通过在距离隔震层一定位移处设置由弹簧和与其串联的限位挡板组成的变刚度保护装置作为第二道防线,成功地进行了五层框架的变刚度隔震保护模拟地震振动台试验。理论分析和试验结果表明,变刚度隔震保护装置能有效改变结构动力特性,减小隔震层的变形,使之限制在允许的范围内。     

Considering dynamic soil structure interaction (SSI) effects on seismic isolation retrofit efficiency and the importance of natural frequency ratio

This paper utilizes and expands on existing coupled BEM–FEM (finite element method) methods for the investigation of the effects of soil structure interaction (SSI) on both an un-retrofitted and seismically isolated typical bridge structure. A simple numerical model of the bridge and surrounding soil is formulated and excited by an earthquake excitation. Utilizing Newmark's β FEM solution method along with the closed form B-spline BIRF method, the structural damped period, composite damping ratio, pier relative displacement, and base shear demand are monitored. From these results, the effects of SSI on this structure are identified. Additionally, the importance of the relative rigidity between the soil-foundation system and the bridge structure is also investigated. The results of the studies indicate that the response of the complete structure system considered is affected by the inclusion of SSI effects. Furthermore, the efficiency of the isolation measures designed using fixed base conditions is decreased by considering SSI over a certain relative rigidity range that is quantified using the structure to soil-foundation natural frequency ratio.     

动三轴试验机轴向摩擦解决的研究

介绍了20 kN动三轴试验机机械工作原理,分析了该仪器轴向摩擦力的产生原因,提出了解决办法并加以具体实施.     

一种新型双磙子FPS隔振系统的动力学模型

本文基于多体动力学理论建立了一种新型双磙子FPS(Friction Pendu lum System)隔振系统动力学模型。在对该系统进行运动学分析的基础上,可将它归结为一个单自由度系统。应用非惯性系中质点系相对动能定理的微分形式可推导出该系统的运动微分方程,它是一个非线性方程。在小角位移的情形下,可近似得到相应的无阻尼线性系统的固有频率,它与观测结果吻合。这一双磙子FPS隔振系统的动力学方程的建立有助于对该系统动力学行为的研究,对方程的直接求解可提高仿真设计中正问题计算的效率,为设计包含该系统的半主动控制奠定了基础。     

Dynamic loading tests and seismic response analysis of a stud-type damper composed of multiple friction units with disc springs

This paper presents an experimental study on the performance of a shear-sliding stud-type damper composed of multiple friction units with high-tension bolts and disc springs. A numerical evaluation of the response reduction effects achieved by the stud-type damper is also presented. In dynamic loading tests, the behavior of stud-type multiunit friction damper specimens was investigated. Three different full-scale damper specimens, which were composed of five, six, or seven friction units with two or four sliding surfaces, were incorporated into loading devices for testing. The stud-type friction dampers demonstrated stable rigid-plastic hysteresis loops without any remarkable decrease in the sliding force even when subjected to repetitive loading, in addition to showing no unstable behavior such as lateral buckling. The damper produced a total sliding force approximately proportional to the number of sliding surfaces and friction units. The total sliding force of the stud-type damper can thus be estimated by summing the contributions of each friction unit. In an earthquake response simulation, the control effects achieved by stud-type dampers incorporated into an analytical high-rise building model under various input waves, including long-period, long-duration and pulse-like ground motions, were evaluated. A satisfactory response reduction was obtained by installing the developed stud-type dampers into the main frame without negatively impacting usability and convenience in terms of building planning.     

Failure time variation derived from R–S relation: the role of the static stress perturbation

In general, earthquake cycle related to earthquake faulting could include four major processes which could be described by (1) fault locking, (2) self-acceleration or nucleation (possible foreshocks), (3) coseismic slip, and (4) post-stress relaxation and afterslip. A sudden static stress change/perturbation in the surrounding crust can advance/delay the fault instability or failure time and modify earthquake rates. Based on a simple one-dimensional spring-slider block model with the combination of rate-and-state-dependent friction relation, in this study, we have approximately derived the simple analytical solutions of clock advance/delay of fault failures caused by a sudden static Coulomb stress change applied in the different temporal evolution periods during an earthquake faulting. The results have been used in the physics-based explanation of delayed characteristic earthquake in Parkfield region, California, in which the next characteristic earthquake of M 6.0 after 1966 occurred in 2004 instead of around 1988 according to its characteristic return period of 22 years. At the same time, the analytical solutions also indicate that the time advance/delay in Coulomb stress change derived by the dislocation model has a certain limitation and fundamental flaw. Furthermore, we discussed the essential difference between rate- and state-variable constitutive (R–S) model and Coulomb stress model used commonly in current earthquake triggering study, and demonstrated that, in fact, the Coulomb stress model could be involved in the R–S model. The results, we have obtained in this study, could be used in the development of time-dependent fault interaction model and the probability calculation related to the time-dependent and renewal earthquake prediction model.     

一株来源于水库的浮游蓝丝藻SK3株的生长及产毒特性

浮游蓝丝藻是水华蓝藻的常见种属,但对其生长和产毒特性认识不多本文首次对我国水体中的浮游蓝丝藻进行了研究.从广东省一重要供水水库中分离到一株丝状蓝藻,经形态特征鉴定为阿氏浮游蓝丝藻,并在不同的光照和温度下对该藻株进行了培养.结果表明,适合于该藻生长的光强和温度分别为20μmol/(m~2·s)和30℃;该藻株具有mcyE基因,能产生微囊藻毒素MCRR,产量为0.06μg/mg(DW).     

Selective controlled base isolation system with magnetorheological dampers

A base isolation system composed of low‐damping isolation bearings and magnetorheological (MR) fluid dampers is described. The MR fluid changes its properties under the influence of a magnetic field resulting in a damper with characteristics that may be modified in real time. This feature enables optimal control under changing excitations in a stable and cost‐effective manner. The voltage is applied according to a selective control strategy. According to the proposed approach the dampers are activated only within a given range of the base displacements. The selective control improves the efficiency of the system and significantly reduces the control forces required for an optimal structural behaviour. Models of five‐ and eight‐storey buildings are used to study the efficiency of the proposed system. Copyright © 2002 John Wiley & Sons, Ltd.     

Study on effects of damping in laminated rubber bearings on seismic responses for a ⅛ scale isolated test structure

The effects of damping in various laminated rubber bearings (LRB) on the seismic response of a ?‐scale isolated test structure are investigated by shaking table tests and seismic response analyses. A series of shaking table tests of the structure were performed for a fixed base design and for a base isolation design. Two different types of LRB were used: natural rubber bearings (NRB) and lead rubber bearings (LLRB). Three different designs for the LLRB were tested; each design had a different diameter of lead plug, and thus, different damping values. Artificial time histories of peak ground acceleration 0.4g were used in both the tests and the analyses. In both shaking table tests and analyses, as expected, the acceleration responses of the seismically isolated test structure were considerably reduced. However, the shear displacement at the isolators was increased. To reduce the shear displacement in the isolators, the diameter of the lead plug in the LLRB had to be enlarged to increase isolator damping by more than 24%. This caused the isolator stiffness to increase, and resulted in amplifying the floor acceleration response spectra of the isolated test structure in the higher frequency ranges with a monotonic reduction of isolator shear displacement. Copyright © 2002 John Wiley & Sons, Ltd.