Suppression of Vortex-Induced Vibration by Fairings on Marine Risers

Vortex-induced vibration is quite common during the operation of offshore risers or umbilical cables,commonly leading to serious damage to risers and reduced service life.Vortex-induced vibration of the offshore risers could be effectively suppressed by fairing devices.In this paper,a newly developed vortex-induced vibration fairing and large eddy simulation model of the FLUENT software were used for numerical analysis,experimental research and stimulating vortex-induced vibration at 0.1–2 ms^-1.The data of the numerical model with fairing was compared and analyzed to study the vortex shedding frequency at different Reynolds numbers and changes in drag and lift coefficients.The displacement state of 12 in risers with and without fairing was experimentally tested using a five degree-of-freedom balance.The vortex-induced vibration effect of the fairing was tested at different velocities.The result shows the drag reduction effect of the fairing is more obvious when the flow velocity is 0.4–1.2 ms^-1 and the maximum drag reduction reaches 55.6%when the flow velocity is 0.6 ms^-1.Additionally,the drag reduction effect was obvious when the flow velocity was greater than 1.3 ms^-1 and less than 0.3.The result indicates that the developed 12 in fairing,with good potential in engineering applications,has good vortex-induced vibration-suppression effects.     

多功能高速远程滑坡运动堆积过程物理模型试验装置设计与应用

高速远程滑坡运动堆积过程影响因素众多,在物理模型试验装置研发过程中应满足多因素变化需求,从而实现多功能目的.该试验装置初始状态下(垂直角度=20°,水平角度=0°)长3.40m,宽0.56m,高1.35m.设计有滑体体积调节、上滑槽坡度调节和下滑槽水平角度调节三大模块.材料上采用了3mm厚不锈钢钢板与8mm厚钢化玻璃2种材料,使用耐久性较好,并且采用分部件组装形式,安装有万向轮,便于实验仪器的搬运.基于砂子与卵石颗粒材料,应用所研发装置,初步开展了高速远程滑坡运动堆积过程物理模型试验,简要分析了滑体坡度、水平角度、滑体高度及基底材质等参数对滑动距离的影响规律.     

1∶10000数据库快速动态更新方法流程的研究

主要阐述将基于DOM的影像成果对1∶10 000基础地理信息数据库进行快速动态更新工艺流程的研究与分析,并制定了基于重点要素和全要素更新模式技术规程,主要内容有外业数字调绘核查系统、内业基于ArcSDE的分布式生产模式和按区域动态更新模式的技术方案,并对该方案生产出来的数据库进行精度检测,检测结果满足技术设计的要求。     

桩点法在海岛礁测图成果检验中的应用

数学精度的检验是测绘成果质量检验中的重要内容之一。针对在通常采用的野外实地检测模式下,地理空间信息位置数学精度检测工作量大、成本高等问题,该文根据海岛(礁)测图成果特点,提出了桩点法代替野外实地检测的技术方法。通过进行实测试验,解决野外难以获取足够检测点的问题;同时,采用试验结果,对海岛(礁)测图成果数学精度检测进行了验证,结果表明该方法在一定程度上能减少野外工作量,提高工作效率。     

波速测试在岩土工程中的应用

通过波速测试技术进行岩土体弹性波速度原位测试,利用岩土体的纵、横波速度值能够进行场地类别划分,确定场地卓越周期,以及计算地基土的动参数,为岩土工程提供必要的设计参数。通过计算获得了徐州苏宁广场场地土的纵、横波速度以及场地土的动参数,根据《建筑抗震设计规范》确定徐州苏宁广场场地为二类场地,利用波速值计算场地卓越周期为0. 415 s与规范中查表获得的特征周期一致。为该工程场地工程地质评价和抗震设计提供了丰富的参数。     

岩溶地区桩基检测与缺陷处理研究

桩基是岩溶地区建筑基础最常用的形式之一,由于地质条件的复杂性、特殊性和无规律性,岩溶地区的桩基施工质量问题频发。针对岩溶地区桩基施工,采取科学合理的检测手段,形成及时有效的反馈机制,对桩基缺陷采取经济合理的处理措施,是保证岩溶地区建筑物基础质量的重要手段。本文总结了岩溶地区桩基检测的主要方法,提出了针对桩基缺陷的处理措施,并结合深圳市龙岗区一岩溶强发育地区的工程实例,对岩溶地区桩基检测和缺陷处理的技术进行了深入的探讨。岩溶地区基桩的质量问题最常见的就是桩基持力层的缺陷,钻芯法不仅可以探明桩身范围内的缺陷程度和相对位置,更有利于查明桩底持力层范围内是否存在溶洞、破碎带以及软弱夹层。岩溶地区检测出桩基缺陷后,采用高压旋喷注浆的方式对缺陷桩进行加固处理,可使得原本破碎的持力层变得稳固,经再次检测合格后,能够继续满足原有荷载条件下的安全使用要求,可为类似岩溶桩基问题提供借鉴。     

Steady‐state solution for cylindrical penetrometers

This paper suggests a new method for obtaining steady‐state solutions for ‘full‐flow’ penetrometers. The method is based on the numerical solution of the small strain plastic‐flow problem (i.e. rigid plastic material) with an inhomogeneous strength field, which is determined by converting changes of material properties over time in a stationary frame of reference into spatial distribution of strength in a moving frame of reference. Rather than building streamlines from back integration of soil element distortion, as previous methods have suggested, the method treats the domain as continuous with the associated field equations. The method employs an upstream weighting technique for the determination of information flow within the domain. The execution order for the calculation is based on topological ordering. This results in the calculation having a complexity of O(N), as compared with O(N^1.5) for the strain path or streamline methods (N is the number of discretized points), which significantly reduces the calculation time. The formulation is presented for the cylindrical (T‐bar) penetrometer, and includes aspects of soil strength degradation, strain rate effects, strength anisotropy, and interface strength law. Comparison to previously published values, based on large displacement finite element simulations with remeshing, showed good agreement, indicating on the correctness of the suggested approach. Investigation into the soil rigid‐body rotation and the remolding effect on anisotropy characteristics showed an interesting behavior, where the decrease of strength anisotropy due to remolding has a greater influence when the soil strength is higher in the vertical direction. Copyright © 2009 John Wiley & Sons, Ltd.     

Vertical dynamic response of an inhomogeneous viscoelastic pile

The vertical dynamic response of an inhomogeneous viscoelastic pile embedded in layered soil subjected to axial loading has been investigated. The interaction between pile and soil is simulated by a general Voigt model, one that has been demonstrated by earlier investigators to be capable of representing the plane strain case of soil adequately. The analytical solutions of pile responses in the frequency domain are obtained by using the (two-sided) Laplace transform. The corresponding semi-analytical solutions in the time domain for the case of a pile subjected to an instantaneous half-sine exciting force applied at the pile top are obtained via Fourier transform inversion. Using these solutions, a parametric study of the influence of the pile and soil properties on the vertical dynamic responses has been undertaken. It is shown that an abrupt variation of the soil properties with depth cannot yield evident reflection signal that may lead geotechnical engineers to assess the pile integrity wrongly from the velocity curve of the pile top, and the influence of viscosity of the pile material on the response is different from that of the damping of the soil surrounding the pile. The theoretical model developed in the present paper has also been validated in field studies, where it is shown by means of three examples that the solution developed in this study has been adequately verified by comparison of the theoretical pile model and field measurements of the dynamic responses.     

基于自回归滑动平均模型的大口径天线风速预测方法

针对大口径、高性能射电望远镜天线受到的随机及时变风扰的问题, 利用自回归滑动平均模型预测望远镜周围风速, 提前计算风致结构变形量, 同时为望远镜伺服控制系统提供足够执行时间来降低风扰影响. 基于新疆奇台110m口径全向可动射电望远镜(QiTai Telescope, QTT)台址风场数据特征, 通过赤池信息准则和贝叶斯信息准则辨识模型阶次, 利用最大似然法估计模型参数, 分析模型残差特性以检验自回归滑动平均模型的有效性. 通过计算不同季度预测数据与测试数据偏差得到预测模型的精度, 夏季平均绝对误差为0.133mcdots^-1, 秋季平均绝对误差为0.162mcdots^-1, 冬季平均绝对误差为0.287mcdots^-1. 整体来看, 基于QTT台址不同季度风速数据建立的自回归滑动平均模型预测误差较小, 满足射电望远镜风扰控制系统的需求, 能为大口径射电望远镜风扰控制提供必要数据支撑.     

接地电阻测量值的数据处理方法探讨

针对防雷装置接地电阻测量过程中出现的各种误差原因,文章介绍了防雷装置接地电阻测量值数据处理的几种方法,并通过实例进行了验证,以达到让目前的防雷检测工作更加规范和准确的目的.