Development of Prebored Screw Pile Method and Evaluation of Its Bearing Characteristics

The pile-driving method produces considerable noise and vibrations. Hence, an auger-drilled pile method was developed as a low-noise and -vibration substitute. However, this method does not guarantee the bearing capacity of the pile unless some amount of pile-driving is performed. Therefore, the noise and vibration problems cannot be completely solved. In this study, a prebored screw pile method is proposed to solve these problems. In this method, piles are constructed by the rotary penetration of a screw pile into a prebored hole filled with some cement milk and whose diameter is smaller than that of the screw pile. To determine the shape of the screw pile, laboratory tests with model screw piles were conducted. Also, field load tests were conducted on an actual screw pile fabricated based on the laboratory test result and on a smooth-surfaced pile. In addition, the behavior of the screw pile was estimated by using three-dimensional finite element analysis. The results of the field load test and the numerical simulation showed that the ultimate bearing capacity and the unit skin friction of the screw pile are very superior to those of the smooth-surfaced pile and the cement milk is an important factor in the prebored screw pile method.     

海底管道管跨段在内外流体作用下的竖向动力特性研究

根据在复杂的海洋环境条件下,管道的动力特性受到内外流体的综合作用影响,呈现与陆地管道不同的特点。研究了结构受到外界流体所产生的涡激作用,同时考虑管内恒定流的影响,利用有限元方法对海底管道管跨段竖向振动的微分方程进行求解。在此基础上得出了管跨段在不同外流流速情况下,内流流速与结构动力响应幅值的关系及其对管跨段振动频率的影响,并进一步探讨了管跨失稳时的极限管内流速与跨长的关系,这些结论对于海底管道设计具有一定实际指导意义。     

Analysis of Safe Span Length and Fatigue Life of Submarine Pipelines

Owing to the complex environmental conditions, suspension could induce complicated forces on submarine pipelines and even cause vortex-induced vibration, resulting in fatigue damage of pipelines. Through aiming at the 28-inch submarine pipeline in the East China Sea, the pipeline was segmented according to the similarity, considering the factors of pipe assembly, typhoon, current, wave and seabed topography. The effects of span length on natural frequency in each section of submarine pipeline were analyzed by finite element model. The maximum safe span length allowed by each pipeline section was verified by fatigue cumulative damage theory, and the fatigue life of each pipeline section were predicted. The results showed that each order natural frequency of the pipeline decreased with the increase of span length. The calculated results of empirical formulas were much smaller than those of the FEM analysis. The increase of the gap between the suspended pipeline and the seabed was beneficial to enhance the fatigue life of the suspended pipeline.     

均匀流场中并列圆柱涡激振动的现状与预测

并列圆柱体在均匀流场中的涡激振动十分复杂，但又广泛存在于实际工程之中。当两柱在流体激励作用下产生振动时，由于同时存在着流固耦合作用和柱间干扰作用，而使周围流场变得更加复杂。本文对并列刚性和弹性圆柱的流场分类，Ｓｔｒｏｕｈａｌ数及流体载荷等问题进行了综述，在此基础上提出了进一步研究的建议。     

高速摄影对散体振动的研究

以现代高速摄影技术和图像分析以及数据处理方法，针对高效振动磨机中弹性散体工质（如钢棒、球体等）的振动力学进行了深入的探讨和分析，为研究散体动力学和振动超细粉碎过程中的能量分布和传递规律以及能量与物质的相互转换机理奠定了基础，也为相关学科的发展提供了一种可以借鉴的方法。     

Parametric Vibration Analysis of Submerged Floating Tunnel Tension Legs

According to the characteristics of submerged floating tunnel anchored by tension legs,simplifying the tube as point mass and assuming that the tension leg is a nonlinear beam model hinged at both ends,the nonlinear vibration equation of the tension leg is derived.The equation is solved by the Galerkin method and Runge Kutta method.Subsequently,numerical analysis of typical submerged floating tunnel tension leg is carried out.It is shown that,the parametric vibration response of the submerged floating tunnel tension leg is related to the amplitude and frequency of the end excitation.Without considering axial resonance and transverse resonance,it is reasonable that higher order modes are abandoned and only the first three modes are considered.The axial resonance amplitude of the second or third order mode is equivalent to the first order mode axial resonance amplitude,which should not be ignored.     

基于内模原理的汽车主动悬挂系统的减振控制

研究路面粗糙度扰动作用下的汽车主动悬挂系统的减振控制问题。首先简化单自由度四分之一悬挂系统模型,建立路面粗糙度扰动模型。然后基于内模原理设计汽车主动悬挂系统的减振控制结构,并利用线性系统的极点配置方法设计系统的减振控制律。最后利用数字仿真验证了减振控制律的有效性。     

Parametric vibration of submerged floating tunnel tether under random excitation

For the study of the parametric vibration response of submerged floating tunnel tether under random excitation,a nonlinear random parametric vibration equation of coupled tether and tube of submerged floating tunnel is set up.Subsequently,vibration response of tether in the tether-tube system is analyzed by Monte Carlo method.It may be concluded that when the tube is subjected to zero-mean Gaussian white noise random excitation,the displacement and velocity root mean square responses of tether reach the peak if the circular frequency of tube doubles that of tether;the displacement and velocity root mean square responses of tether increase as the random excitation root mean square increases;owing to the damping force of water,the displacement and velocity root mean square responses of tether decrease rapidly compared with tether in air;increasing the damping of the tether or tube reduces the displacement and velocity root mean square responses of tether;the large-amplitude vibration of tether may be avoided by locating dampers on the tether or tube.     

The Effect of Internal Fluid on the Response of Vortex-Induced Vibration of Marine Risers

Based on Iwan‘s wake oseillator model developed with the classical van der Pol equalion, the differential equation for the response of the vortex-induced vihration (VIV) of the riser considering the effect of the internal flowing fluid and the external marine environmental condition is derived. The effect of the intermal flowing fluid on the response of VIV of the riser is studied by means of the Finite Element Method. The results show that the effect of the internal fluid velocity on the VIV of the riser is strong when the natural frequency of the riser is close to the vortex shedding frequency. In addition, the increase of the top tension can decrease the sensitivity of the riser to the internal fluid velocity.     

浅谈挤密碎石桩的施工方法

挤密碎石桩施工法是一种振动成桩法,即先用桩管振动成孔,然后填入足够数量的碎石,最后振动密实成桩体。通过振动、挤密的成桩过程,将原地基土振动夯实,桩体与桩间土形成复合地基,达到既处理可液化地基又增强地基的效果。介绍了挤密碎石柱的施工方法和质量检测方法。