水下粉细砂土体在超高频机械振动荷载作用下液化特性的试验研究

为了量化高频机械振动对土壤液化的具体效果,在试验室泥槽中对不同性质的水下粉细砂沉积物开展了诸如不同振动作用时间及不同工况下的液化试验,利用静力触探仪测量了振动作用前后其承载力变化情况,基于试验数据分析讨论了振动作用时间、振动作用距离、振动频率对于液化效果的影响.     

海洋隔水管涡激振动的三维数值模拟研究

流体场采用k-ω湍流模型进行三维CFD数值模拟,固体场采用基于三维实体单元的有限元方法进行模拟,通过一种新的方法实现流-固耦合交界面的无缝数据交换,参考Lehn(2003)长径比为482的模型实验完成隔水管流向与横向涡激振动的三维数值模拟。模拟结果与实验结果吻合良好,都反映了多阶振动模态特性。引入激发速度解释了多阶振动模态的现象。进一步分析表明,大长径比柔性隔水管发生涡激振动时流场尾流区涡的脱落呈现多种涡结构模式,尾涡动力特性在不同截面的变化体现出明显的三维特征。同时隔水管振动时出现非对称弯曲大变形现象,运动轨迹呈现变形的8字形。研究同时表明,顺流向的振动响应不可忽略。     

船舶在迎浪中运动响应和波浪增阻的RANS数值模拟

该文利用naoe-FOAM-SJTU求解器计算分析了Wigley Ⅲ型船模在迎浪中的运动响应.naoe-FOAM-SJTU求解器是基于开源代码OpenFOAM工具箱和数据结构,专门面向船舶与海洋工程复杂水动力学问题而开发的求解器.采用的控制方程为RANS方程,用有限体积法进行离散,采用VOF方法和动网格方法分别处理两相流界面和船体运动,运动响应是通过求解六自由度刚体运动方程得到.计算算例为三个航速和不同波长下Wigley Ⅲ型船模垂荡和纵摇的运动响应,以及波浪增阻,计算结果和试验值吻合较好.此外,还计算了Wigley Ⅲ型船模大幅度运动的算例,用于验证naoe-FOAM-SJTU求解器处理强非线性问题的能力,在该算例中,观察到了明显的非线性特征和严重的甲板上浪现象.     

用MPS方法数值模拟低充水液舱的晃荡

液体晃荡是一种非线性的自由面流动现象.在低充水率下,由于液体具有很大的运动空间,晃荡现象具有强烈的非线性特征,自由面的变形较大,剧烈时甚至会翻卷和破碎,这给数值模拟带来很大挑战.本文基于移动粒子半隐式法(Moving Particle Semi-Implicit,MPS)对低充水率的液舱晃荡问题进行了数值模拟.结果表明:当激励频率等于共振频率时,液体撞击到了液舱的顶板,并出现了飞溅现象,此时液体对侧舱壁产生了较大的抨击压力;在低于共振频率时,自由面出现了破碎波及波前的翻卷和融合等现象,抨击压力相对较小.计算结果表明,MPS方法能够很好地预测晃荡引起的拍击现象,数值计算得到的压力能够与实验结果很好地吻合.在自由面的追踪上,MPS方法具有很大的灵活性,能够很好地处理自由面的破碎、融合及液体的飞溅等流动现象.     

Magnetothermostress Wave Propagation and Perturbation of Magnetic Field Vector in an Orthotropic Laminated Hollow Cylinder

An analytical method is developed to determine the transient response of magneto-thermostress and perturbation of the magnetic field vector produced in orthotropic laminated hollow cylinders subjected to thermal shock, and permeated by a primarily uniform magnetic field. A magnetothermostress equation for each separate hollow cylinder is found by making use of a series of simply mathematical transform. Then, by using the interface continuity conditions between layers and the boundary conditions at the internal and external surfaces of the orthotropic laminated hollow cylinders, the unknown constants involved are determined. Thus, an exact expression for the magnetothermostress wave propagation and the perturbation response of magnetic field vector in the orthotropic laminated hollow cylinders are obtained. From sample numerical calculations, some characters of magnetothermodynamic stresses and perturbation of magnetic field vector in orthotropic laminated hollow cylinders are revealed and discussed.     

Thermal Buckling of Multi-Walled Carbon Nanotubes Based on a Rigorous van der Waals Interaction

This paper reports the result of an investigation on the axially compressed buckling of multi-walled carbon nanotubes under thermal load, based on a rigorous van der Waals interaction which is dependent on the change of interlayer spacing and the radii of tubes. From the point of view of continuum modeling, each of the concentric tubes of multi-walled carbon nanotubes is considered as an individual elastic shell and coupled with any two tubes through a rigorous van der Waals interaction force. Based on this model, some example calculations are carried out to describe the effect of temperature changes and van der Waals interaction models on the axially critical load of multi-walled carbon nanotubes. Some results obtained show that the axial buckling stress of multi-walled carbon nanotubes under thermal environment is dependent on the wave number of axially buckling modes, and the wave numbers corresponding to the minimum axial stress are not unique for the multi-walled carbon nanotubes under thermal environments. On the other hand, a rigorous van der Waals interaction force can make the axially critical load of multi-walled nanotubes under thermal loading increase. The effect of thermal environments on the axially critical stress of multi-walled nanotubes gradually increases as the axial half wavenumber (m) of buckling modes increases.     

MECHANISM OF SOUND GENERATION BY FLOW OVER TWO CAVITIES IN TWO DIMENSIONS

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规则波中弧形返浪墙的非线性水动力载荷数值模拟

运用基于FLUENT软件平台的二维数值波浪水槽,采用流体体积(VOF)方法处理波浪自由面,应用"解析松弛"方法实现了数值造波-消波。模拟规则波下不同返浪墙断面形式情况下的流场和水动力。应用直墙驻波理论解和物理模型试验结果验证了数值波浪水槽的可行性。比较波浪力的数值模拟与物理模型试验结果可以发现,水动力冲量的均方差小于水动力最大值的均方差,且水动力冲量的误差也小于水动力最大值,说明以冲量作为特征量能更好地描述水动力载荷的变化。在给定堤顶超高的条件下,不同堤脚超高和弧形返浪墙高度的组合对越浪量有明显影响:低弧趾超高和大半径弧面组合有利于降低越浪量,但水动力载荷也较大;高弧趾超高和小半径弧面组合越浪量较大。     

A random walk simulation of scalar mixing in flows through submerged vegetations

The scalar transport phenomena in vertical two-dimensional flows are studied using the random walk method. The established Lagrangian model is first applied to study the idealized longitudinal dispersion in open channels, before being used to investigate the scalar mixing characteristics of the flows through submerged vegetations. The longitudinal dispersion coefficients of the fully-developed boundary layer flows, with and without vegetations, are calculated based on the positions of the particles. A convenient way of incorporating the effects of vegetations is proposed, where all the flow parameters are regarded to be continually distributed over the depth. The simulation results show high accuracy of the developed random walk method, and indicate that the new method of accounting for the vegetation effects is appropriate for all the test cases considered. The predicted longitudinal dispersion coefficients agree well with the measurements. The merit of the new method is highlighted by its simplicity and efficiency in comparison with the conventional method that assumes the discontinuous distribution of the flow parameters over the depth.     

Numerical computations of resistance of high speed catamaran in calm water

In this paper, the in-house multifunction solver naoe-FOAM-SJTU is applied to study the resistance and wave-making performance of a high-speed catamaran sailing at different velocity in calm water. The volume of fluid（VOF） method is used to capture the free interface and the finite volume method（FVM） is adopted as the discretization scheme. The hull model is fixed with initial trim and sinkage. The numerical results of the presented paper agree very well with the measurement data of model test. Wave making and vortex field are well simulated to analyze the hydrodynamic performance of a catamaran.