Natural frequencies of vibration of a class of solids composed of layers of isotropic materials

In a recent paper, the Ritz method with simple algebraic polynomials as trial functions was used to obtain an eigenvalue equation for the free vibration of a class of homogeneous solids with cavities. The method presented is here extended to the study of a class of non-homogeneous solids, in which each solid is composed of a number of isotropic layers with different material properties. The Cartesian coordinate system is used to describe the geometry of the solid which is modelled by means of a segment bounded by the yz, zx and xy orthogonal coordinate planes and by two curved surfaces which are defined by fairly general polynomial expressions in the coordinates x, y and z. The surface representing the interface between two material layers in the solid is also described by a polynomial expression in the coordinates x, y and z. In order to demonstrate the accuracy of the approach, natural frequencies are given for both a two- and three-layered spherical shell and for a homogeneous hollow cylinder, as computed using the present approach, and are compared with those obtained using an exact solution. Results are then given for a number of two- and three-layered cylinders and, to demonstrate the versatility of the approach, natural frequencies are given for a five-layered cantilevered beam with a central circular hole as well as for a number of composite solids of more general shape.     

Possibilities of Using Sources of Neutron Radiation for Radiation Testing of Dikes of Trunk Pipelines

Methodical aspects of in-tube testing of the media surrounding a trunk pipeline are considered. The method is based on radiating media with a source of fast neutrons and the subsequent measurement of the albedo of thermal neutrons and neutron-capture gamma rays. On the basis of a laboratory model of a pipeline segment, a set of model experiments was conducted to assess the information content of radiation signals for different types of media surrounding pipes.     

磨削螺旋刀具刀尖圆角的研究

通过对大螺旋角刀具刀尖圆角所形成的空间曲线进行分析,找到形成该空间曲线的方法,给出一种支片工装的结构,从而实现大螺旋角刀具刀尖圆角的磨削。     

Effect of Impregnation of Iodine Complex on Friction of Anodic Oxide of Aluminum

Polyvinyl pyrrolidone-Iodine complex (PVP-I) molecules were impregnated into the anodic oxide of an aluminum disk specimen. It was rubbed against a silicon nitride ball specimen using a ball-on-disk type friction test rig. Over the limited range of parameters studied (load: 0.2-1.0 N, sliding velocity: 0.6 mm/s, and sliding distance: 1-7 m), the coefficient of friction decreased to a value as low as 0.01 from values of 0.3 to 0.7 for the anodic oxide surface. Single-crystal iodine rubbed against silicon nitride showed a coefficient of friction of 0.1. The low coefficient of friction is attributed to the thin PVP-I film on the relatively hard anodic oxide. The mechanism of coefficient of friction reduction is the same as that of a thin soft film on a hard substrate.     

水冷式冷渣机单根管路冷却性能分析

冷渣机主筒结构的整体分析比较复杂,为此提出对冷渣机单根管路的冷却性能进行分析,运用ANSYS-FLOTRAN对其进行流体热分析,从而得到管内渣体的温度数据,为冷渣机主筒结构和热分析提供参考依据.     

On the problem of reconstruction of defects of complex shapes

The paper considers reconstruction of a defect of an arbitrary shape in a solid on the basis of changes in the characteristics of a back-scattered ultrasonic wave. Typical dimensions of the defect are assumed to be larger than the wavelength, and the defect is assumed to be in the far-field zone, which allows us to operate in the plane-wave approximation. An algorithm for constructing a convex shell for a non-convex defect using the return time of the back-scattered wave measured by scanning the angles around the tested object is described. The method is illustrated on examples of convex shells of two-dimensional defects of different shapes.     

Studies of the radiation resistance of active elements of calorimeters

The measurement results of the radiation resistance of materials of a thick-layer gas electron multiplier (TGEM), which is considered as a candidate for active elements of calorimeters operating under high radiation loadings, are presented. The radiation resistance of the active element of an organic-scintillator-based hadronic calorimeter and light collection by a reemitting fiber, is measured for comparison. The obtained data, i.e., invariability of the signal from the TGEM up to 5 Mrad with an almost triple reduction of the signal from the scintillator, can be considered as a qualitative indicator of possible use of the TGEM as a detector operating at high radiation loads.     

Calculation of the Reluctance of a Wedge-Like Air Gap of a Magnetic System

A method for the calculation of the reluctance of a wedge-like air gap between the face surface of the core of a magnetizing device and the surface of a magnetizing article is considered. A method for the transformation of a wedge-like air gap under a pole is described. The transformation is performed in a complex space by constructing an equivalent plane-parallel gap.     

Model of a single-row flow of cars: Derivation and integration of equations

A chain of cars moving one after another in a single traffic lane is considered. It is assumed that the cars are point particles and these particles interact with adjacent ones according to the safe distance law. The differential functional equations of the particle flow are derived, and their solution is obtained. Boundary conditions at sections of particle input and output from a piece of a traffic lane are added to the equations. It is shown that models of a single-row flow of particles can be constructed as a chain of a finite number of mass points in a friction-free channel with pulse control as well as a finite-state automation model.     

Monitoring of the course of fixation of plant cells

The fixation of cells of petiolar hairs of tomato was monitored by phase contrast and Nomarski interference contrast microscopy. Because the cuticle covering these hairs is relatively impermeable some fixatives enter only the base of the hair so that a ‘fixation front’ can be followed through a single cell. The basal end of such a cell may be immobilized by the fixative while the apical end is still streaming. A variety of fixatives were tested at room temperature and at 273–278 K. All procedures tested failed to stabilize a pleomorphic canalicular system that is a dominant feature of these cells so that no clue to the presence of this system can be seen in sectioned material. It is therefore very desirable that images of fixed cells be compared to the structure of similar cells which are still alive.     

基于CT图像的侧凸脊柱胸腰段及骶骨整体三维有限元模型的建立

探讨AIS患者的胸椎T1-T12、腰椎L1-L5及骶骨整体三维有限元模型建立方法,建立侧凸脊柱胸腰段及骶骨整体三维有限元模型.对患者进行螺旋CT扫描,获得特发性脊柱侧凸患者T1至骶骨整段DICOM格式的CT数据文件.通过图像、图形处理软件从CT数据中提取脊柱组织的轮廓信息,构建侧凸脊柱胸腰段及骶骨整体的三维几何模型,并与现有文献中的模型进行对比分析.所建模型包括皮质骨、松质骨、椎间盘、韧带等组织,共102371单元、132877节点.对比分析结果表明,同等边界条件下,利用该模型计算得到的脊柱各部位的应力和位移分布与文献中的结果基本吻合.所建立的胸腰骶整体脊柱的三维有限元模型是有效、可靠的,为特发性侧凸脊柱的生物力学特性研究及临床矫形治疗仿真提供数值分析平台,同时为患者个性化矫形支具设计的理论研究提供支持.     

Analysis of similarity of physical processes during simulation of cooling of machine crystallizers

Similarity criteria describing physical the processes of boiling and condensation of a heat carrier were determined with a model and natural experiments based on the analysis of dimensions of parameters in the heat exchange problem during cooling of a crystallizer by heat pipes. Relationships of the geometrical sizes of heat pipes (diameter, length) were estimated. The novelty of the results is confirmed by patents of invention of catalyst cooling by heat pipes.     

Image-based measurement of the dimensions and of the axis straightness of hot forgings

Non-contact measurement of shapes and dimensions is currently quite a common issue. A lot of systems with different speeds and accuracies are in the market. Measurement of high temperature objects is, however, a very special task which ensures a specific solution. This paper presents a measurement system composed of two high resolution single-lens reflex cameras and a software application, which is designed for the fast measurement of shapes and dimensions of rotationally symmetric forgings. The software computes the length, diameter, and straightness of the axis, based on a 3D model constructed from four boundary curves of the forging captured in two images. Experimental measurements have shown an error of up to 2% for the length measurement and 1% for the diameter measurement. Results are available in a few seconds. The proposed measurement approach based on boundary curves shows a great potential for practical use in forging plants.     

Digitization of electron micrographs: A comparison of three different types of scanners

Some aspects of digitization of electron micrographs have been investigated. The performances of a flat-bed, a rotating drum, and a diode array scanner have been evaluated. Estimates have been achieved for resolution, mechanical and optical stability, and optical density response. It is concluded that for routine transmission electron microscopy of, for example, negatively stained biologic specimens, a diode array scanner produces data good enough to obtain resolutions at a level normally expected. High speed is the major advantage with this type of equipment. However, for high-resolution work it is necessary to use a conventional scanner with a relatively slow scan speed.     

Accurate alignment of sets of images

Two modifications to the conventional procedure of cross-correlation are described, widely used for establishing the relative alignment of the members of a set of images from which a higher resolution or more interpretable restoration is sought. Both achieve a high and sharp peak in circumstances where the conventional peak is too ill defined to be recognizable; neither involves significant additional computation time. The more general method requires rough knowledge of the imaging conditions, but a variant applicable to images with axial resolution has no such requirement. In addition, a least-squares procedure is presented for achieving an optimum compromise between many pair-wise displacement measurements, preventing the accumulation of alignment errors across a set of images.     

Determination of spectral densities of dynamic characteristics of a nonlinear model of structure

A stochastic problem of the dynamics of a nonlinear model of structure is considered. The problem is solved with the use of an expansion of the solution in the truncated orthogonal basis of eigenvectors of the linear model. It is assumed that nonlinearities of the system do not result in a fundamental change in its dynamical behavior, but contribute a significant quantitative correction relative to the linear model. The nonlinear characteristics are statistically linearized. The coefficients of statistical linearization are formally interpreted as some variations in the corresponding elements of the stiffness matrix of the linear model. Spectral densities, displacement variances of the linearized system, as well as its eigenvalues and eigenvectors, are represented as a power series expansion in the above variations considering linear or square approximations. To find the coefficients in the expansion, the sensitivity theory is used. This allows one to form a set of algebraic transcendental equations in displacement variances, which is solved by the method of successive approximations. Then all the target spectral densities are found. The results are illustrated by examples.     

直升机复合材料传动轴的主共振分岔分析

传动轴主共振分岔时,振幅突变,有可能运动失稳。在根据质心定理和Galerk in法求得非惯性移动系下直升机的倾斜两端支承纤维增强复合材料传动轴的弯曲运动方程基础上,用多尺度法求得稳态下主共振的分岔方程,再分析了运动稳定性、幅频响应曲线的拓扑结构等主共振分岔问题。得到了复合材料传动轴比钢、铝合金传动轴运动稳定性好等结论。提出通过加大阻尼使传动轴主共振不分岔。在挠度大的轴段上增加阻尼能使传动轴主共振不分岔,并能充分发挥阻尼的作用,优化轴的重量。     

提高枪钻孔加工直线度的方法

从枪钻的导向条布局出发,分析影响被加工孔直线度的因素。由于枪钻加工是在密闭环境下进行的,因此加工过程很不稳定,而枪钻走偏现象直接影响被加工孔的直线度,甚至造成工件报废。通过对加工过程中枪钻导向条进行受力分析,计算其在加工过程中的稳定度,建立Pro/E三维模型并进行ANSYS分析,得出在加工过程中稳定度最高的枪钻导向条布局参数,进行打孔试验并得到很好的效果。本文对提高小直径、大长径比的深孔直线度有实际意义。     

Effect of the difference of materials of the fastening and abutting members of shearing joint on the distribution of contact pressure

The solution obtained for the distribution of a long contact load with the bolt pressure on the wall of a hole in abutting members of a shearing joint is corrected and extended to the more general case where all members of a joint are made from materials differing in their mechanical characteristics. It is shown that the difference in the elastic modulus of materials of the fastening and abutting members affects the distribution of contact pressure significantly less than the ratio of their diameter and thickness.     

Restoration of the Magnetic Field of a Cluster of Discontinuity Flaws in a Ferromagnetic Product on the Basis of Minimization of a Smothering Functional

A technique of restoring the magnetic field of a flaw cluster in a tested object is proposed. The possibility of restoring the magnetic field strength and estimating the number and the depth of flaws is demonstrated on the basis of the results of measuring the magnetic field of a flaw cluster in a steel plate.