圆锥浮环动静压轴承动态特性理论研究

对一种新型结构的滑动轴承——圆锥浮环动静压轴承的动态特性进行理论分析和数值计算。首先给出内、外膜的动态雷诺方程和边界条件,应用有限元得到内外膜36个刚度系数和阻尼系数,在此基础上分析该轴承的稳定性,计算其稳定性参数。结果表明该轴承具有稳定性好,易于实现主动控制的优点,在高速旋转机械领域有广泛的应用前景。     

Thermal effect on free vibration of ring-stiffened rotating functionally graded conical shell with clamped ends

An approximate solution is presented to investigate the effects of thermal load on the frequency of ring-stiffened rotating functionally graded conical shell. Material properties and the temperature field are assumed to be graded and varied in the thickness direction. The shell is reinforced by equal interval rings. The equations of motion are derived by the Hamilton's principle. Approximate analytical solutions are assumed to satisfy clamped boundary conditions, and then Fourier decomposition and Galerkin method are applied to achieve relations of frequencies. To validate, the comparisons are made with a number of particular cases in literature and with the FEM solutions.     

Multiobjective crashworthiness optimization of hollow and conical tubes for multiple load cases

Much attention of current design analysis and optimization of crashworthy structures have been largely paid to the scenarios with single load case in literature. Nevertheless the designed structures may often have to be operated in other load conditions, thus raising a critical issue of optimality. This paper aims to understand and optimize the dynamic responses and energy absorption of foam-filled conical thin-walled tubes under oblique impact loading conditions by using multiobjective optimization method. The crashworthiness criteria, namely specific energy absorption (SEA) and crushing force efficiency (CFE), are related to loading parameters and design variables by using D-optimal design of experiments (DoE) and Kriging model. To obtain the optimal Pareto solutions of hollow and foam-filled conical tubes, design optimization is first performed under different loading case (DLC) using multiobjective particle swarm optimization (MOPSO) algorithm separately. The optimal designs indicate that hollow tube has better crashing performance than the foam-filled tube under relatively high impacting velocity and great loading angle. To combine multiple load cases (MLC) for multiobjective optimization, a double weight factor technique is then adopted. It is found that the optimal foam-filled tube has better crashing performance than empty conical tube under any of overall oblique loading cases concerned. The study gains insights in deriving multiobjective optimization for multiple load cases, providing a guideline for design of energy absorber under multiple oblique loading.     

Minimum Spouting Velocity of Draft Tube Conical Spouted Beds Using the Neural Network Approach

A multilayer perceptron with back‐propagation learning algorithm is developed to predict the minimum spouting velocity (u_ms) in draft tube conical spouted beds. Six dimensionless variables involving ten essential geometric and operating parameters of the beds were taken as model inputs. To compare the model results with both experimental data and those predicted by the limited existing empirical equations, the root mean square error and the mean relative error are utilized. Although there is a complex relationship between the input variables and u_ms, and despite the huge number of data available, the steps of training and testing show good agreement with the corresponding experimental values. This demonstrates that an artificial neural network is a useful approach to predict u_ms, especially when the relationship between the geometric and operating parameters and u_ms is complex and difficult to define.     

Re-interpreting simultaneous buckling modes of axially compressed isotropic conical shells

Elastic stability of shell structures under certain loading conditions is characterized by a dramatically unstable postbuckling behavior. The presence of simultaneous ‘competing’ buckling modes (corresponding to the same critical buckling load) is understood to be largely responsible for such behavior. In this paper, within the framework of linear bifurcation eigenvalue analysis and Donnell shallow shell theory, the presence of simultaneous buckling modes in axially compressed isotropic cones is determined using the semi-analytical method of Galerkin. The results are presented in the plane of the dimensionless reciprocal meridional and circumferential buckling half wavelengths, and are compared with the locus of simultaneous buckling modes of axially compressed cylinders, described by the so-called Koiter circle. By using an optimizing procedure, it is shown that the cluster of simultaneous buckling modes in cones is well described by the Koiter circle of an equivalent cylinder with appropriate length and radius. Such optimizing values of length and radius allow us to gain some insight into the simplifying treatment of the buckling of cones through the concept of equivalent cylinder.     

On elastic–plastic buckling of cones

The paper considers the buckling of short, and relatively thick, mild steel conical shells subjected to the combined action of external pressure and axial compression. Past results on axially compressed cones and on cones subjected to hydrostatic external pressure are compared with fresh test results on equivalent, axially compressed cylinder and with the equivalent cylinder subjected to external hydrostatic pressure.     

锥形套注塑模具设计与制造

锥形套制品为深腔类产品,其模具设计与制造从产品工艺分析、模具结构等方面提出合理的解决方案,实践证明,模具结构合理、操作方便。     

The Nine Lives of Buildings

Like cats being gifted with a new life every time they just miss their demise, buildings are constantly propelled towards change and reinvention in order to sustain their existence. Here Jill Stoner , Director of the Azrieli School of Architecture and Urbanism at Carleton University in Ottawa, and Professor of Architecture at the University of California, Berkeley, for 28 years, identifies and reflects upon nine possible future lives for buildings.     

Vibration of twisted laminated composite conical shells

A methodology for free vibration of a laminated composite conical shell with twist is proposed, in which a strain–displacement relationship of a twisted conical shell is given by considering the Green strain tensor on the general thin shell theory, the principle of virtual work is utilized, and the governing equation is formulated by the Rayleigh–Ritz procedure with algebraic polynomials in two elements as admissible displacement functions. The convergence, the accuracy and the validity of the methodology are verified by comparisons. As a result of the vibration frequencies and mode shapes, the effects of the laminated constructional and the geometric parameters, such as the number of laminae, the fiber orientation angles, the twist angle, the subtended angle and the taper ratio, on the vibration characteristics are studied by the present methodology.