Silica fume stabilization of an expansive clay subgrade and the effect of silica fume-stabilised soil cushion on its CBR

ABSTRACT

Expansive soil subgrades, which are subjected to dual swell-shrink problem consequent upon absorption and evaporation of water, need to be improved by chemical stabilization or compacted cushion or geosynthetic reinforcement in order that pavements constructed over them are even, stable and safe. This paper presents extensive experimental data on plasticity, free swell index (FSI) and compaction characteristics of a highly swelling expansive clay stabilized with varying silica fume contents. In another series of tests on a laterite soil to be used as a cushion over the expansive clay subgrade, plasticity properties, compaction characteristics and strength characteristics were determined at varied silica fume contents. Further, CBR of the expansive clay subgrade was determined in the laboratory stabilizing it with varied silica fume contents and providing a cushion of 50 mm thickness of silica fume-stabilized lateritic soil. Liquid limit (LL), plasticity index (PI) and free swell index (FSI) of the expansive clay decreased with increasing silica fume contents. The compaction and strength characteristics of both the soils improved with silica fume stabilization. The CBR of the expansive clay provided with silica fume-stabilized cushion improved significantly.     

Numerical investigation on the suppression of VIV for a circular cylinder by three small control rods

Laminar flow past a circular cylinder with 3 small control rods is investigated by numerical simulation. This study is concerned with the suppression efficacy of vortex induced vibration by small control rods located around a main cylinder. The effects of the attack angle and rod-to-cylinder gap ratio on the hydrodynamics and vibration responses of the main cylinder are investigated. The attack angle of α = 45° is performed as the critical angle for VIV suppression of 3 control rods. The 3 control rods have no effect on VIV suppression when the attack angle is less than the critical angle. The 3 control rods have an excellent VIV suppression efficacy when the attack angle is larger than the critical angle. The transverse vibration frequency of the cylinder with 3 control rods is less than that for an isolated cylinder for all the configurations. The numerical results for the configurations of α = 45° & 60°, G/D = 0.6–1.2 show excellent suppression efficient among the cases investigated in this study. The best suppression efficient is found at α = 45°, G/D = 0.9 for 3 control rods. 2 rods in behind of the main cylinder perform more efficient than that of 1 rod in front for VIV suppression as the gap ratio of G/D less than 1.0.     

脉动激励下的浅埋管道轴向应力分析

考虑土体-结构-流体耦合作用,研究流体脉动对浅埋输液管道轴向应力的影响.基于流固耦合、管-土耦合理论,建立了浅埋管道动力学分析模型,应用力平衡条件,推导了浅埋管道的静力及动力方程,并利用行波方法求取了动力方程的解析解.在此基础上,研究了管道应力特性.结果表明:流固耦合对浅埋管道应力有较大影响,较小幅值的压力脉动可使管道应力大幅增加.同时,讨论了管道埋深、土质条件及管道半径对管道应力的影响.在相同流体脉动激励下,管道应力随覆盖层厚度、土体刚度、管道半径增加而减小.     

垂直轴潮流能水轮机直叶片流固耦合分析

在开放海域运行的潮流能水轮机需要应对复杂多变的海洋环境,要有较好的刚度、强度和抗疲劳性能。这对水轮机结构,尤其是为其运行提供动力的叶片结构的设计提出了较高要求。文中建立了垂直轴潮流能水轮机叶片及流场的三维数值计算模型,基于ANSYS商业软件提供的CFX与瞬时结构模块的双向流固耦合分析功能,分析了叶片在不同流速下的流体力学性能,分析了流场的三维效应及其引起叶片升力损失的原因,研究了其结构的刚度和强度特性。还对比分析了使用铝合金和钢材作为水轮机叶片材料的优劣。     

Distributed TLDs in RC floors and their vibration reduction efficiency

A novel distributed tuned liquid damper （DTLD） for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete （RC） floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluid- structure conpling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.     

A novel approach to eliminate error induced by cell to node projections

In engineering practices, different numerical methods for fluid flow simulation and solid deformation/stress simulation are adopted to model fluid–structure interaction problems in porous media. Cell‐centered finite volume method is widely used in fluid flow simulation, while the solid deformation/stress simulation is usually accomplished by using the Galerkin vertex‐centered finite element method, which leads to the incompatibility between cell variables with nodal variables. Therefore, the data transfer between cell variables and nodal variables is inevitable. Consequently, this kind of transfer will lead to extra artificial error. Hence, the major concern is how to minimize the error due to cell to node projections. In this paper, a problem of pore pressure diffusion within a one‐dimensional heterogeneous porous medium is investigated. We present a new projection scheme and corresponding error formula, where the error control factor is introduced. The new projection scheme is based on piecewise linear interpolations. Results demonstrate that if the error control factor is chosen properly, the error due to the projection from cell to node can be controlled effectively, and the most desired zero error can be achieved. Finally, we analyze some practical cases in consideration of permeability contrast and mesh uniformity. Copyright © 2015 John Wiley & Sons, Ltd.     

大型三维矩形、U形渡槽地震响应对比分析

本文应用任意拉格朗日-欧拉(ALE)有限元方法对比分析大型三维排架支撑矩形、U形渡槽结构地震响应,以获得渡槽中动水压力资料。研究表明,渡槽中水体的晃动幅度十分显著,水体的大幅晃动显著地改变两种截面形式渡槽中水压力、槽体应力值及U形渡槽动水压力和应力分布,对矩形渡槽动水压力和应力分布规律影响不大。动应力分布的改变直接影响到大型预应力U形截面渡槽结构中预应力钢筋的有效性。在渡槽的抗震设计中,应充分考虑U形截面渡槽动水压力和动应力分布变化问题,动水压力应该作为一项主要的外荷载予以考虑。     

Review on Tidal Energy Technologies and Research Subjects

Tidal current power is one of the promising and reliable renewable energies with the advantage of continuous and predictable resource. It can make stable electricity regardless of weather conditions or seasons all year around. The required technologies for tidal current power in the ocean have been developed for years and now recognized that it could be commercialized after intensive field tests and successful demonstrations. There are several tidal farm development projects in the world, such as the MeyGen project in UK with its commercialization at hand. However, various research subjects in the tidal current energy field are seeking improvements and industrialization of tidal current power in terms of economy and technical reliability. This paper introduces the resource assessment procedure of tidal energy that has been applied in Korea coastal regions. The key research subjects for tidal current power together with the interaction effect of multi-arrangement is described. Also, this paper is to introduce the research output of each subject such as turbine design, experimental validation, turbine interaction and wake, multi-array module, FSI (fluid-structure interaction), and duct application.     

Numerical simulation of a short flexible pipe subject to forced motion and vortex-induced vibration

A series of numerical simulations about a small scale(aspect ratio:63.2) flexible pipe undergoing forced harmonious oscillation and vortex-induced vibration(VIV) have been taken into account.The wake hydrodynamics and pipe deformation were accomplished by ANSYS MFX solution strategy designed for fluid-structure interaction(FSI) problem with well-performed LES model.The configuration of structured mesh,multi-domain design,different mesh stiffness admeasured by User Fortran ensured that the numerical task was competent to deal with large deformation related to this case.The introduction of instantaneous amplitude definition and modeless component decomposition method(Chen and Kim,2008) was helpful to reveal much more information from modal analysis.Most results from numerical simulation are generally consistent with those from model test(Choi and Hong,2000) via the comparison between them.As supplementary to model test,visualization of the vortex wake was also provided.It has been proved that the forced oscillation doesn't only excite a complicated dumbbell-like wake pattern around the outer thimble,but also results in inner flow inside the PVC pipe.The velocity of the inner flow increases with the frequency of forced oscillation.     

大型矩形渡槽-水耦合体系的动力性能分析

本文把任意拉格朗日-欧拉(ALE)方法用于分析大型矩形渡槽结构-水耦合体动力性能,并针对不同的水位、不同截面深宽比,研究渡槽结构在谐波激励、地震激励下的振动反应。研究表明,渡槽结构中水体的泼溅具有明显的非线性特征;渡槽中水位对耦合体动力特性影响极具规律性,但是随截面深宽比减小,水体振荡的非线性明显增强;渡槽结构截面深宽比选择合理,水体泼溅作用产生的倾覆力矩不会使槽体发生倾覆失稳,但是水体的大幅晃动产生的动水压力对渡槽槽身应力有显著的影响,在渡槽抗震设计中应给予足够重视。