Three-dimensional vibrations of inflatable dams

Inflatable dams are used for various purposes, such as controlling flood-waters, diverting water for irrigation, impounding water for recreation, raising the height of existing spillways, and preventing beach erosion. They are flexible, cylindrical structures attached to a rigid, horizontal base. The vibrations of such dams are investigated in this paper. The dam is modelled as an elastic shell inflated with air and anchored along two of its generators. Both infinitely—long dams and dams of finite length are considered. Previous analyses have only considered two-dimensional vibrations and have assumed that the dam is an inextensible membrane. The finite element method is applied, first to determine the equilibrium shape of the dam and then to analyze small vibrations about that configuration. For the numerical examples, the lowest six vibration frequencies and corresponding mode shapes are obtained. The results are compared to those when no external water is present.     

基于不良地质条件下过坝公路施工技术研究

分析了不良地质的结构特征及形成原因,根据过坝公路的特点及施工程序,对不良地质条件下过坝公路施工技术进行了深入研究,并对过坝公路施工管理程序作了论述,为过坝公路运行提供了保障。     

Collapse of concrete-covered levee under composite effect of overflow and seepage

During the Great East Japan Earthquake and Tsunami of 2011, enormous coastal levees collapsed as a result of tsunami overflows. Concrete-covered levees, where concrete blocks are used to protect levees made of soil, showed a specific failure mode in which back slope blocks and internal soils were dislodged. Although several hydraulic experiments have been conducted in an attempt to understand the failure mechanism, the complexity of the failure requires that both hydro-dynamical and geotechnical points of view be taken into account for a deeper understanding. This study uses a centrifuge to identify the failure behavior of levees from those points of view. The centrifuge can reproduce the stress, water pressure, and overflow velocity of the prototype-scale ground. Overflowing at sufficient time periods was produced in the centrifuge by generating differences in water height for seaside and landside areas. The test results showed that the levees collapsed due to a combination of the effect of water flow on the back slope and seepage inside the levees. In addition, the effectiveness of several proposed countermeasures for preventing collapse was confirmed.     

Axial vibrations of U-shaped bellows with elastically restrained end conditions

Previous work by Li et al. in the area of axial vibrations of bellows dealt with fixed end conditions. However, it is seen on several occasions that bellow ends are welded to a small pipe spool that has a lumped mass such as a valve or an instrument. Hence, the present paper aims at finding out the effect of elastically restrained ends on the axial natural frequencies. The analysis considers finite stiffness axial restraints on the bellows, i.e. solving the set of equations with non-homogeneous boundary conditions. Two bellow specimens are considered for comparison having the same dimensions as taken by Li in his analysis. The transcendental frequency equation deduced is accurate as the first, second and third mode frequencies computed are in close agreement to the ones obtained by Li.     

Mitigation of vortex-induced vibrations in bridges under conflicting objectives

Aerodynamic performance of long-span bridges can be improved by retrofitting cross-sectional shapes or by adding tuned mass dampers. When both the approaches are used simultaneously, the design problem may become too complicated to solve by engineering judgment. The complexity becomes even greater in a real world problem in which both the performance and the cost have to be considered. We propose a multi-objective based approach to obtain optimal solution of the design problem. The approach effectively deals with highly nonlinear design space and the conflicting objectives between the performance and the cost. Due to the conflict of the two objectives, multiple optimal solutions are obtained, which are called Pareto-optimal solutions. The final design is obtained considering the cost and the performance criteria. The proposed method is applied to the mitigation of vortex-induced vibrations, but its general framework is applicable to any other aerodynamic problems.     

Buckling of vibrations of shear-flexible orthotropic plates subjected to mixed boundary conditions

An approximate technique is presented for the analysis of buckling and vibrations of free-form, orthotropic, shear-flexible (‘Mindlin’) plates subject to mixed boundary conditions. The method falls into the category of Rayleigh/ Ritz-techniques; however, by using Lagrangian multipliers to ‘relax’ the geometric boundary conditions, the selection of appropriate trial functions is made considerably simpler. Accuracy and reliability of the proposed technique is demonstrated on the basisof several sample problems.     

不同边界下钢-混凝土组合球面肋壳性能分析

钢-混凝土组合肋壳是一种新型大跨度空间结构,边界约束对结构的极限承载力和稳定性具有很大影响.基于非线性有限元理论,建立了考虑几何非线性和物理非线性的数值计算模型,以40m跨、三种不同截面尺寸、不同矢高下的钢-混凝土组合肋壳为例,分析了包括周边固定、周边铰支、点固定和点铰支在内的四种边界约束对结构极限承载力和结构破坏形态的影响.结果表明,截面尺寸和矢高相同时,边界约束越接近刚性,极限承载力越大;随着截面尺寸增大,不同边界约束下承载力比值增大,但随矢高增大,反而减低;不同边界条件对结构失稳形态影响很小,结构均为极值点失稳,荷载-位移曲线的走势大致相同;随着组合肋截面尺寸增大,组合肋壳在不同约束条件下均表现出越来越高的屈曲后强度.     

Analysis of multi-correlated wind-excited vibrations of structures using the covariance method

Multi-correlated stochastic processes that can be found in nature are described using stochastic differential equations. The power spectral density matrix is evaluated first; then all of the power spectra are approximated by rational functions. By a series of transformations of the power spectral density matrix, a matrix of the transfer functions can be restored. Then by means of minimal realization methods from control theory, the differential equation is evaluated that connects the real excitation process with so-called white noise. The calculation of variances of dynamic responses of structures can be simplified and less calculation time is necessary than with methods using power spectral densities. Simulation techniques can be improved and a better physical insight obtained.     

不同地质条件下后压浆灌注桩承载力分析

通过不同地质条件下采用后压浆工艺的钻孔灌注桩试桩结果的分析，探讨了钻孔灌注桩桩端压力灌浆及桩侧压力灌浆对提高承载力的影响，提出了不同地质条件下呆用后压浆技术的条件。     

上拔条件下扩底基础碎石土地基破坏特征分析

基于弹塑性理论,应用有限差分方法,对碎石土场地扩底基础地基土体在承受上拔荷载作用下的变形破坏进行数值分析,得到碎石土场地扩底基础地基土体在上拔荷载作用下的破坏形态。     

复杂条件下边坡稳定性研究

对青岛市白云寺周边地质特性进行了研究,通过现场勘察和室内试验综合确定岩土物理力学参数.并采用SLIDE软件模拟计算了5种不同工况下边坡的稳定因数和最危险滑动面,对白云寺周边边坡强度稳定性进行分析.通过对不同工况下边坡模型的计算,明确了白云寺周边边坡稳定性的影响因素,研究结论为实际治理提供了理论依据.最后,对白云寺周边岩土体综合治理提出针对性的建议,从而保证白云寺免遭滑坡地质灾害的影响.     

考虑温度与荷载耦合作用的连续配筋混凝土复合式路面损伤分析

连续配筋混凝土路面的裂缝形态和分布模式是影响路面路用性能和寿命周期的重要因素。本文采用通用有限元软件建立了CRCP+AC的复合式路面模型,并用混凝土损伤塑性模型表征CRCP面板的力学特性。通过对路面结构温度场的分析,得到沥青面层与CRCP面板厚度比的临界值为0.15,达到或超过这一临界厚度比值,沥青面层改善CRCP面板温度状况的作用才会发挥明显。在此基础上进一步分析了复合式路面在温度与荷载耦合作用下,CRCP面板结构损伤的演化规律以及裂缝张开闭合的行为特征。研究结果可以为CRCP+AC复合式路面的设计以及施工过程中的裂缝控制提供理论依据与借鉴。     

Options for support tower design of a sensitive equipment under ambient vibrations

This paper describes the options and methodology adopted for the design of an 18‐m high support tower for a vibration sensitive optical telescope. The telescope was to be housed inside an existing building that provided shielding from atmospheric wind and thermal variations. However, proper functioning of the telescope was dependent on the support tower's structural configuration and stiffness to limit angular distortion of the telescope platform to less than 2 µ radians or 0·4 arc‐sec. This level of sensitivity required investigation of support tower response under ambient vibrations resulting from normal operation of the existing facility. The measured peak ambient vibration acceleration ranged from 0·04 m/s/s to 0·27 m/s/s for various recorded events. Two options for the tower were investigated viz. steel braced frame and concrete shaft. The effect of soil structure interaction (SSI) was also examined. It was concluded that the concrete tower option provided the desired performance for both fixed base and SSI cases. On the other hand, the steel tower performed well for the fixed base case but its performance was close to the threshold when SSI was also considered. Effect of soil properties variation on SSI was also examined for both tower options and was found to be relatively insignificant. Copyright © 2008 John Wiley & Sons, Ltd.     

Biotransformation of alkanoylcholines under methanogenic conditions

Ester quaternary ammonium compounds (esterquats), which are mainly used as active ingredients in fabric softeners and personal care products, are beginning to replace traditional quaternary ammonium compounds. As a result of hydrophobicity and increasing use, esterquats reach anaerobic treatment systems. However, little is known about the fate of esterquats under anaerobic conditions. In the present study, the potential inhibitory effect and biotransformation of two alkanoylcholines - acetylcholine chloride (ACh-Cl) and lauroylcholine chloride (LCh-Cl) - which are simple esterquats, under methanogenic conditions were investigated. ACh-Cl up to 300 mg/L was not inhibitory to a mixed methanogenic culture. In contrast, methanogenesis was inhibited by LCh-Cl above 50 mg/L, primarily caused by the accumulation of lauric acid which resulted from the abiotic hydrolysis of LCh. Below inhibitory concentrations, both ACh and LCh were transformed to methane by the mixed methanogenic culture. Mass spectrometric analysis confirmed that both alkanoylcholines were first abiotically hydrolyzed to choline and the corresponding alkanoic acid, which were then biotically transformed to methane, carbon dioxide, and ammonia. Thus, alkanoylcholine-containing waste streams can be bioprocessed to form methane, but hydrolysis products such as long-chain alkanoic acids may adversely impact the anaerobic bioconversion of alkanoylcholines.     

Modelling the advection equation under water hammer conditions

The quality of water delivered by a distribution network may degrade for many reasons. This research considers one of these, focusing attention on the connection between water quality and the hydraulic events in a pipe system. More specifically, pressure and velocity variations associated with hydraulic transients or water hammer conditions, particularly through leaks and rapid device adjustments, have the potential to degrade water quality. In most previous applications, numerical transport schemes have been coupled to quasi-steady hydraulic models. By contrast, the current contribution couples a finite difference solution of the advection-reaction equation to a fully unsteady, method of characteristics (MOC) based, hydraulic solution. Depending on system properties, the effects of advection, compressibility and reaction may be evident in the modelled response. The numerical properties of consistency, stability and convergence of the proposed model are investigated both analytically and numerically. Although some case studies have revealed important water quality implications associated with dynamic conditions, particularly in cases of contaminated water intrusion, it should be admitted that many transient simulations exhibit few differences compared with quasi-steady results.