This paper outlines a methodology for the automatic creation of finite element meshes used for calculating structural dynamic behaviour. Starting from the idealized geometry of the structure, the proposed Intelligent Meshing Tool determines a mesh density that a priori guarantees the resonant frequencies to be calculated within predetermined accuracy limits. Unlike most existing techniques for automatic meshing, this technique is not inherently adaptive, but does not exclude an extra adaptive mesh refinement step, either. Implementation of this methodology is discussed for structures composed of straight uniform, curved and tapered beam-like components. The feasibility of the meshing strategy is illustrated by means of an example.

In the presented paper the response of nonlinear random oscillators is calculated by the numerical solution of the associated Fokker-Planck-Equation. This approach can be used to approximate the invariant probability density of chaotic nonlinear oscillators or to calculate the response of a nonlinear oscillator, driven by additive white noise. A weighted residual approach is proposed to solve the Fokker-Planck-Equations numerically. By this method the partial differential equation is transformed to a coupled set of linear ordinary differential equations. These equations can be derived easily, because the integrals associated to the Galerkin procedure can be solved analytically. Considering stationary densities the solution is given by a generalized Eigenproblem. Utilizing sparse matrix techniques the solution can be calculated very efficiently.

This paper presents an analysis method for reliability measures of a system with step changes in failure and repair rates. Both failure and repair time have exponential function of time. Such a system is called a stepwise exponential distribution system. This kind of failure process can take place in various equipments. This paper deals with the system having components in series arrangement. Bayesian statistics is used in defining prior and posterior probability density functions of failure and repair rates. These functions provide information for the estimation of reliability measures: 1) failure and repair rates, 2) mean time to failure, 3) mean time to repair, 4) reliability function and 5) availability. A sample problem is given to illustrate the methodology. The Bayesian estimation of the stepwise exponential distribution model is useful in the planning of equipment predictive maintenance.

In order to study the behavior of fatigue crack propagation and fatigue reliability of a structural or mechanical component under random loading, a numerical simulation scheme and other analytical prediction models are proposed in this paper. The paper consists of (1) digital generation of random loading from random process theory; (2) numerical simulation of fatigue crack growth based on fracture mechanics concept; (3) a modified rain-flow cycle counting method for the identification of stress cycles and stress amplitudes; (4) Weibull probability density fit and other statistical analyses for the stress amplitudes as well as the crack growth curves; and (5) probabilistic models for the prediction of fatigue crack growth, fatigue life and fatigue reliability. Some conclusions are drawn at the end of this paper which can be used as references in the design of a structural or mechanical component under random loading.

This paper reports on a project in which automatic mesh generation is divided into two phases. In the first phase feature recognition and shape grammar techniques, based on the medial axis of a 2D region, are employed to decompose a complex component into a number of simple subregions. In the second phase the subregions are meshed to a controlled density using conventional mapped mesh methods. The advantage of this approach is that good quality meshes of quadrilateral elements can be generated in 2D and, potentially, meshes of hexahedral elements in 3D. A parallel program of work has concentrated on the analysis of errors: different methods for error estimation and for providing transitions in mesh density have been compared.

The Finite Element Method (FEM) has been recognized as one of the most effective analysis method for complicated domains. Unfortunately, any practical application of FEM requires extensive amount of input data. General pre-processors usually require a large amount of user defined information. Therefore, in some particular applications, where more specific options are needed, a special mesh generator in required. In this paper we present an automatic mesh generator for annular models with inherent geometric constraints, such as fiber orientation in composite-like structures/systems. The developed generator is designed to generate 3-D meshes with minimal users’ input and effort, and it can be used in conjunction with almost any CAD system or FEM software. The code is particularly useful for efficient performance of numerical studies relating mesh density and convergence.

Probabilistic optimization using the moment matching method and the simulation optimization method are discussed and compared to conventional deterministic optimization. A new approach based on successively approximating probability density functions, using recursive quadratic programming for the optimization process, is described. This approach incorporates the speed and robustness of analytical probability density functions and improves accuracy by considering simulation results. Theoretical considerations and an example problem illustrate the features of the approach. The paper closes with a discussion of an objective function formulation which includes the expected cost of design constraint failure.

This paper presents applications of a control-volume finite-difference method to flow problems in cylindrical geometries. The method is an extension of the method known as ETUDE, which is an Euler-explicit in time, transportive-upwind convection, second-order diffusion, finite-difference estimate. The primary purpose of this paper is to present an interesting new method that comes about from control-volume considerations, i.e. , from a proper extension of ETUDE, to solve problems in cylindrical coordinates. One- and two-dimensional test problems are computed to illustrate the properties of this new method. The predicted results of the two-dimensional test problem are compared with similar calculations of the spin-up of homogeneous fluids reported in the literature. With the properties of the method established, it was applied to investigate the spin-up of a two-layered, stably stratified fluid initially at rest in a cylindrical container. The effect of the stable, density structure on spin-up is discussed.

This paper discribes the manufacture of injection mold plastic magnetic gears. The pole of the right tooth face is difficult to that of the left tooth face in one teeth. Those gears mesh with the non-backlash. This paper is primarily to study the principles of plastic magnetic gears regarding the method of injection, mold method of magnetization and measurement of flux density and the results of a dynamic test (the noise test, wear test and measurement of temperature of plastic gears teeth) Regarding preventive gear noise, plastic magnetic gears are superior according to the results of the experiment. Those gears are used with no need for lubrication, but there is some degree of wear when a grease and oil lubrication is used. The shrink fit plastic magnetic gears were made as a non-lubricating type. Those types showed a slight degree of wear. The manufacture of plastic magnetic gears and polyamid coating plastic non-lubricating type. Those types showed a slight degree of wear. The manufacture of plastic magnetic gears (less than module:2) with the establishment of a new method for magnetic york. It was possible to provide a strong magnetic field by improving the magnetic york and this providing practical non-backlash gears.

This paper presents the development of a computational model for the generalized topology optimization problem, using a material distribution approach, of 2-D linear elastic solids subjected to thermal loads, with compliance objective function and an isoperimetric constraint on volume. The model relies on homogenization asymptotic methods to characterize the influence of the material periodic microstructure and a finite element displacement formulation is used to approximate the homogenized equilibrium equations obtained. The computational model developed is tested in several examples considering different finite element approximations and the influence of the design variables (material density and orientation) is analyzed.

An essential part in the genesis of structures or optimal material distribution is the relation between elastic behaviour and material density. This approach makes use of a isotropic material model, which leads to very simple working conditions. The isotropic model is directly formulated and utilized without employing homogenization based on an artificial microstructure. It is shown in theoretical considerations and demonstrated by examples, that this idea works also very easily with plate and shells, even for very general layer structures.

This paper presents an assessment of the suitability of the USA-RG2 (Unified Solution Algorithm for Real Gas in Two Dimensions) computational fluid dynamics code for simulating the flow in a variable-area shock tunnel. A multi-zone gridding technique is used to model the 1:57-Scale Large Blast Simulator test facility at the U.S. Army Research Laboratory. Computations for various grid configurations employing inviscid and viscous solution algorithms with and without turbulence were executed, and the results are compared to experimental data. The need for an adequate mesh density in the grid to obtain a realistic flow simulation and the advantage of solving the full Navier-Stokes equations invoking a two-equation (k-ε) turbulence model are demonstrated for the experiment chosen as a bench mark in the assessment.

Pratt & Whitney Aircraft and NASA Lewis Research Center studied a silicon-carbide-fiber-reinforced, titanium-metal-matrix (MMC) composite designated SiC(SCS-6)/Ti-15V-3Cr-3Al-3Sn. Fracture tests of three nominal 15.24-cm (6-in.) diameter SCS–6/Ti-15-3 rings at 427 °C (800 °F) and room temperature resulted in failure at internal pressures of 0.172 GPa (25 ksi) (average) and 0.235 GPa (34.1 ksi), respectively. Predictions of internal pressure to failure varied from 0.140 to 0.276 GPa (20.3 to 40.1 ksi) at 427 °C (800 °F). Nondestructive evaluation revealed that the rings’ MMC cores had varying density and were not uniformly distributed inside the monolithic casing. Analytical predictions of ring cyclic life at 0.154-GPa (22.4-ksi) internal pressure varied from 1000 to 15 000 cycles. No fatigue life data were obtained with the MMC rings for comparison with theory.

The response of a hysteretic structure under horizontal and vertical random excitations is considered. The excitations are modeled by segments of stationary and nonstationary Gaussian white noise and filtered white noise processes. The linearization technique is used and the moments equations of the responses are evaluated. The transition probability density of the response is described and the associated second moment equations are derived. The transient and nonstationary response statistics for a range of values of parameters are obtained. A Monte-Carlo digital simulation study is performed. The results are compared with the theoretical findings and good agreements is observed. Particular attention is given to the amplification effects of the vertical acceleration. It is shown that the effect of the vertical excitation is usually insignificant, unless the load coefficient is quite large.

The objective of this study was to perform analyses for the static and dynamic mechanical response of a 36 ft fiberglass whip antenna for the purpose of determining survivability under nuclear weapons effects. The static analysis was to obtain the stiffness/deflection characteristics of the antenna using material, wall-thickness, and mechanical loading history provided by the Naval Surface Warfare Center. The results of the static analysis were then to be used in a NASTRAN transient dynamic analysis. The effect of the thermal pulse associated with the blast was not directly considered in these studies. An analytical model of the whip antenna deflected by transverse loading was developed using Castigliano’s Theorem. The resulting integrals were evaluated using Mathematica™. The diameters, wall thicknesses, and mass density resulting from the static response study were then used in the linear, transient dynamic analysis. These studies concluded that the suggested modeling approach is suitable for the static and linear transient dynamic response analysis of a standard 36 foot fiberglass whip antenna to a 4 KT, 7 psi air blast (without thermal effects). The “Basic” model suggests a linear finite element model maximum deformation to be within 10% of the deflection of about 16 feet observed in the test video. Low-to-midrange stresses are expected at this deformation. A 1 MT, 7 psi air blast would probably, but not necessarily, fail the antenna. These studies support the conclusion that the dynamic response of a standard 36 ft whip antenna is “duration-dependent” within the range of overpressures considered.

Random vibration analysis of a nonlinear mass-spring system with a set-up spring type characteristics is considered. This system is a model of a physical device. The motion of the mass is divided into a number of stages. Using the principle of conservation of energy, governing equation of motion for various stages of displacement of the mass are derived. Deterministic free and forced vibration responses are obtained numerically. For the random vibration the excitation at the base of the system is assumed to be Gaussian white noise. Fokker-Planck-Kulmogorov equation is then used to derive the probability density function of the displacement response for this system. Several numerical results with practical engineering applications are presented.

As the quantity of cylindrical components needed for in-space assembly grows to accommodate larger structures, so does the need for compact storage of these components during transportation to the site. Hex-Close-Pack is the ideal configuration for cylindrical parts. It offers a density increased by a factor of 4 compared to existing methods intended for robotic assembly. Usual requirements for objects maneuvered on-orbit include: positive hold-down, positive hand-off, and package strength to withstand launch dynamic loads. The first two issues have been addressed with new manipulation techniques that are compatible with both robotic construction and compact storage. Packaging schemes that improve strength and are consistent with the new techniques are presented. Pallet manipulation and storage are additional issues that are a function of package configuration. Pallet design can greatly reduce time and space required, for these tasks.

These notes are concerned with the optimal design of two dimensional, in-plane loaded structural elements and three dimensional bodies, made of aleotropic materials, with regard to both the elastic and the ultimate behaviour. Sec. 2 is devoted to finding the local orientations of the material symmetry axes in 3D orthotropic solids, corresponding to extreme values of the global elastic stiffness. These orientations are shown to be such that collinearity of principal stress and principal strains is achieved throughout the body. In the particular case of transversely isotropic or cubic materials, optimal orientations are shown to depend both on a material parameter and the strain field. A certain orientation of the material symmetry axes may correspond either to a minimum or to a maximum in the elastic stiffness, depending on whether the material has ‘high’ or ‘low shear modulus’. These results are then specialized to plane orthotropic bodies, in which case the theoretical findings obtained by other authors are recovered. In the plane case, also simultaneous optimization of fiber orientation and density is dealt with. Sec. 3 concerns optimal limit design of plastic 2D in-plane loaded orthotropic structures. Fiber orientation and density are assumed as design variables. Here again, necessary optimality conditions are analytically found and their mechanical interpretation is studied. Analogies with both the numerical results of other authors and the elastic case are observed and discussed as well.

This paper introduces a computational approach to three dimensional component layout that employs simulated annealing to generate optimal solutions. Simulated annealing has been used extensively for two dimensional layout of VLSI circuits; this research extends techniques developed for two dimensional layout optimization to three dimensional problems which are more representative of mechanical engineering applications. In many of these applications, miniaturization trends increase the need to achieve higher packing density and fit components into smaller containers. This research addresses the three dimensional packing problem, which is a subset of the general component layout problem, as a framework in which to solve general layout problems.

Topology optimization is the most complicated problem in structural optimization. One common approach is to utilize the concept of the design domain, such as the homogenization method and the density function approach. In this paper, a new micro-structure based design domain method is proposed. This new method gives simple closed-form expressions for effective Young’s modulus and effective shear modulus in terms of phase properties and volume fractions. Using these simple relations, topology optimization problems can be formulated and solved using mathematical programming algorithms. Results of some design examples obtained from the new method are presented.