A domain method for shape design sensitivity analysis of built-up structures

A numerical method of obtaining accurate shape design sensitivity information for built-up structures is developed and demonstrated through examples. The method utilizes and basic character of the finite element method that gives accurate information not on the boundary, but in the domain. The method is shown to drastically simplify the derivation of shape design sensitivity formulas for complex built-up structures.     

Adaptive finite element methods for shape optimization of linearly elastic structures

Grid adaptive methods combined with means for automatic remeshing are applied to problems in shape optimal design of linearly elastic structures. The quantitative effect of element distortion near the design boundaries is identified in terms of interpolation error associated with the finite element discretization. The grid adaptation is itself formulated as a structural optimization problem, with an objective function that reflects the discretization error. A ‘necessary condition’ from this formulation provides the basis for a computational procedure to predict the modified grid.To avoid the sometimes drastic distortion of the FEM grid that might otherwise occur in conjunction with design change, remeshing must be performed at intermediate stages of the overall solution process. In order to produce results for the optimal shape design without interruption in this process, the computer program combines numerical grid generation and automatic remeshing with the grid adaptation and design change. Results for several shape design problems obtained with the use of grid adaptation are compared to computational results predicted from a fixed grid. Both ‘r-’ and ‘h-adaptation’ are tested.     

Reduction techniques in dynamic substructures for large problems

Dynamic substructuring concepts find increasingly many applications in the solution of large dynamic problems. Substructure synthesis using fixed interface modes is found to be attractive from many angles, but has the major disadvantage in that a large number of interface or boundary degrees of freedom are carried over to system level thus increasing the cost of eigenvalue solution. Reduction of the number of these interface degrees of freedom is very essential for any cost effective solution, and some methods are suggested for this. With free vibration of the Indian Remote Sensing Satellite Structure as the base, reduction of interface degrees of freedom is first attempted by static condensation. It is found to give erroneous results even for frequencies, unlike its use in double Guyan's reduction method, where the results are generally satisfactory except for isolated modes. An alternate approach involving recursive or multilevel substructuring is suggested. The results obtained from the application of recursive substructuring clearly indicate that solution costs can be reduced without affecting the accuracy of results. Moreover, reduction of interface degrees of freedom by recursive substructuring makes it economical to use junction modes. This combination could be very effective in handling large problems.     

Stress analysis of ribbed flanges

In this paper an attempt is made to study the role of stiffening ribs on the behaviour of flanges. Shell theory is resorted to in developing the ribbed shell equations. A shell element with stiffening ribs in the meridional direction is obtained by superposing the stress resultants of a grid shell with the stress resultants of a isotropic shell element. A case of unequal bolt loads is considered by expressing them as Fourier series in the circumferential direction. The effect of varying the rib parameters like rib height, number, etc. is studied. The finite-difference method of solution is adopted. The behaviour of a ribbed flange is found to be similar to that of a taper hub flange.     

Application of folded plate analysis to bending,buckling and vibration of multilayer orthotropic sandwich beams and panels

A unified analysis method based on two-dimensional elasticity theory is outlined for evaluation of bending, buckling and vibration of multilayer orthotropic sandwich beams and panels. The effects of initial geometric imperfections are included. It is shown that beams or panels deforming under conditions of plain stress or plane strain may be treated as special instances of folded-plate structures using computer programs which are now widely available. Examples are given, including evaluation of stress contours in a sandwich panel under patch load and analysis of overall and local (face-wrinkling) buckling modes in sandwich panels with stiff and soft cores.     

Stability of a rotating pretwisted nonuniform cantilever with a tip mass subjected to dissipative and follower forces

The stability of a rotating pretwisted non-uniform viscoelastic cantilever beam subjected to a tangential force applied at its free end is determined by a method of approximation based on an adjoint variational principle. The coupled equations of motion are derived from a conservation law, the adjoint boundary value problem is introduced, and an approximate stability determinant is developed from the variational principle. The stability determinant is solved numerically for a variety of choices of values for the rotary inertia of the beam, transverse and rotary inertia properties of a mass capping the free end, the rotational speed, and the pretwist angle, and several graphs are presented to show the influence of these parameters upon the value of the critical flutter load.     

Some properties of metal/insulator/semiconductor structures with BN and carbon thin layers formed by the reactive pulse plasma method on silicon or SiO2 substrates and annealing effects

Thin layers (100–300 nm) of BN and diamond-like carbon were produced by the reactive pulse plasma method. On the basis of measurements and analysis of electrical properties of metal/insulator/semiconductor (MIS) capacitors, with a BN or carbon layer acting as the dielectric and silicon as the semiconductor, operating parameters were identified for the BN/Si and C/Si structures. A double layer of thermal SiO₂ and either BN or carbon was also used as a dielectric. The structures produced were subjected to annealing at temperatures from 100 to 500°C in N₂ and O₂ atmospheres.Using the spectral investigation method, BN and carbon layers produced on quartz and KBr substrates were examined for their probable composition (IR absorption analysis), absorption coefficient α and refractive index n. After annealing at temperatures of 300–400°C, a marked improvement in the electrical performance of MIS structures was found as well as storage of charge in the double-layer dielectric structures. Hydrogen and oxygen were also found to be present in the test layers. On the basis of the analysis of the electrical characteristics it is assumed that dehydrogenation of the layers during thermal treatment is one of the reasons why their electrical properties tend to vary with time.     

Nucleation and growth of Au-Cu binary alloys from the vapour phase on NaCl single crystals

The nucleation and growth of copper-gold alloys on rock salt surfaces was investigated. The metals were evaporated simultaneously from two different sources in ultrahigh vacuum.During the early stages of condensation the alloy deposits were enriched in gold compared with the ratio of the vapour beam fluxes. The experimental results were interpreted using an extended nucleation model for alloys. This kinetic model allows the determination of the difference between the adsorption energies E_a and between the activation energies E_d for surface diffusion of the two components. Using values for E_a and E_d for gold from previous investigations the corresponding values for copper were determined and found to be E_a = 0.86 eV and E_d = 0.62 eV.Discrepancies between theoretical and experimental results regarding the dependence of the composition of the alloy deposits on deposition time is discussed.     

Sample calculations of flash temperatures at a silver-graphite electric contact sliding on copper

Explicit equations are presented for calculating the flash temperatures at plastically deformed circular contact spots due to friction and/or Joule heat. Numerical examples calculated for a metal-graphite composite in a very wide range of speeds and loads suggest that intuitive estimates of the flash temperatures tend to be too high. On the basis of the figures it should be possible to deduce approximate values for the flash temperature for a great variety of sliding couples and sliding conditions.