杆型SFRFQ结构的研究

RFO加速结构是一种非常巧妙的低能强流加速结构,但是它存在能量上限问题.而杆型SFRFQ加速结构是一种改进的无反场的SFRFQ结构.对分离作用杆型RFQ加速结构在能量增益和横向稳定性两个方面进行了研究,最后还和光阑型SFRFQ结构进行了一些简单的比较 关键词： 能量上限问题 RFQ 杆型SFRFQ 反场 光阑型SFRFQ     

On the accumulation of eigenvalues of operator pencils connected with the problem of vibrations in a viscoelastic rod

In this paper, we study the problem of the boundary accumulation of a discrete spectrum, which is essential for a boundary-value problem of fourth order arising in the theory of small transverse vibrations in an inhomogeneous viscoelastic rod (a Kelvin—Voigt body). We establish conditions for such an accumulation and its asymptotics, which are expressed in terms of the coefficients defining the problem posed by the differential expression. The results obtained are illustrated by numerical computation data.     

井眼轨迹控制力学模型

对石油钻井中井眼轨迹控制问题进行了力学分析，给出了底部钻具组合三维受力和变形的控制方程，建立了钻头与正交各向异性地层相互作用模型，阐明了井眼轨迹预测和控制计算方法。     

Experiments on snap buckling, hysteresis and loop formation in twisted rods

We give the results of large deflection experiments involving the bending and twisting of 1 mm diameter nickel-titanium alloy rods, up to 2 m in length. These results are compared to calculations based on the Cosserat theory of rods. We present details of this theory, formulated as a boundary value problem. The mathematical boundary conditions model the experimental setup. The rods are clamped in aligned chucks and the experiments are carried out under rigid loading conditions. An experiment proceeds by either twisting the ends of the rod by a certain amount and then adjusting the slack, or fixing the slack and varying the amount of twist. In this way, commonly encountered phenomena are investigated, such as snap buckling, the formation of loops, and buckling into and out of planar configurations. The effect of gravity is discussed.     

Stability and vibration of a helical rod constrained by a cylinder

The stability and vibration of an elastic rod with a circular cross section under the constraint of a cylinder is discussed. The differential equations of dynamics of the constrained rod are established with Euler’s angles as variables describing the attitude of the cross section. The existence conditions of helical equilibrium under constraint are discussed as a special configuration of the rod. The stability of the helical equilibrium is discussed in the realms of statics and dynamics, respectively. Necessary conditions for the stability of helical rod are derived in space domain and time domain, and the difference and relationship between Lyapunov’s and Euler’s stability concepts are discussed. The free frequency of flexural vibration of the helical rod with cylinder constraint is obtained in analytical form. The project supported by the National Natural Science Foundation of China (10472067). The English text was polished by Yunming Chen.     

Flexural-torsional bifurcations of a cantilever beam under potential and circulatory forces I: Non-linear model and stability analysis

The stability of a cantilever elastic beam with rectangular cross-section under the action of a follower tangential force and a bending conservative couple at the free end is analyzed. The beam is herein modeled as a non-linear Cosserat rod model. Non-linear, partial integro-differential equations of motion are derived expanded up to cubic terms in the transversal displacement and torsional angle of the beam. The linear stability of the trivial equilibrium is studied, revealing the existence of buckling, flutter and double-zero critical points. Interaction between conservative and non-conservative loads with respect to the stability problem is discussed. The critical spectral properties are derived and the corresponding critical eigenspace is evaluated.     

螺旋细杆的均匀扭转振动

讨论螺旋细杆的特殊形式扭转振动，即均匀扭转振动．以非圆截面杆和有原始曲率的圆截面杆为研究对象．杆作均匀扭转振动时各截面有相同的扭角变化规律，且杆中心线的几何形状不受振动过程的影响．研究表明，扭振来源于杆截面的非对称性及杆的原始曲率．杆的扭振规律与单摆运动相似，其动力学方程存在精确解．圆环杆的均匀扭振为螺旋杆的倾角为零时的特例．     

炭纤维增强环氧树脂复合材料/N80钢摩擦学性能研究

利用MG-200型摩擦磨损试验机研究了炭纤维增强环氧树脂复合材料/N80钢的摩擦学性能,考察了介质温度对摩擦学性能的影响;用扫描电子显微镜分析了磨损表面形貌.结果表明:在干摩擦条件下,炭纤维增强环氧树脂复合材料与N80钢对摩时的摩擦系数较低,炭纤维增强环氧树脂复合材料的磨损主要表现为树脂基体脱落碳化和炭纤维的折断剥落,偶件钢环则呈现明显的磨粒磨损特征;在油井产出液润滑下炭纤维增强环氧树脂复合材料的磨损率较低,摩擦系数和磨损率随着润滑介质温度的升高而增大,偶件钢环则呈现明显的磨粒磨损和腐蚀磨损特征.     

Justification of the kinematic assumptions for thin-walled rods with shallow profile

In this Note we present a justification of the kinematic assumptions for thin-walled rods with shallow profile. These assumptions are fundamental to writing the one-dimensional equilibrium equations for such structures. The obtained kinematics are different from the Vlassov case, which is only valid for strongly curved profiles. They are also different from the that classically used in shell theory. The justification given in this Note is based on an asymptotic approach. To cite this article: L. Grillet et al., C. R. Mecanique 333 (2005).     

Nonlinear traveling waves in a compressible Mooney-Rivlin rod I. Long finite-amplitude waves

In literature, nonlinear traveling waves in elastic circular rods have only been studied based on single partial differential equation (pde) models, and here we consider such a problem by using a more accurate coupled-pde model. We derive the Hamiltonian from the model equations for the long finite-amplitude wave approximation, analyze how the number of singular points of the system changes with the parameters, and study the features of these singular points qualitatively. Various physically acceptable nonlinear traveling waves are also discussed, and corresponding examples are given. In particular, we find that certain waves, which cannot be counted by the single-equation model, can arise. The project supported by the Research Grants Council of the HKSAR, China (City U 1107/99P) and the National Natural Science Foundation of China (10372054 and 10171061)