Abstract Methods of synthesizing discrete torsional vibration systems are developed in this paper. Both minimum weight design (with eigenvalue constraint) and maximum eigenvalue design (with total weight constraint) problems are addressed. Based on the optimality conditions for an optimum design and the equation for the eigenproblem, simple iterative design algorithms are derived. Two numerical examples are included to illustrate the proposed methods.

ABSTRACT One of the major difficulties in structural shape optimal design is to create a design model by parameterizing a geometric model. Shape design parameterization is more complicated and difficult to handle than sizing design parameterization. First, the optimum shape is highly dependent on the design parameterization selected. An inappropriate design parameterization may result in an impractical design. On the other hand, changing the geometric shape of the design model to reflect successive changes in design parameters is a tedious, complicated, and inefficient process. Manual updates of geometric shape and finite element meshes are quite impractical. In this paper, a shape design parameterization method that is built on the geometric modeler PATRAN is presented. Using this method, a number of geometric entities that represent structural design boundaries are parameterized, and a design parameter linking process can be performed to create geometric features from geometric entities. To support the proposed method in structural shape design, a unified velocity computation method using geometric parametric mapping and an elliptic equation solver is developed for shape design sensitivity computation. The design parameterization and associated velocity Held computation methods are general enough to handle a broad range of engineering applications. Finally, automatic finite element mesh and geometric shape update methods are presented, which can be used to easily perform design changes.

Abstract A new explicitly solvable model of a unidirectional composite with nonlinear deformable fibers is introduced in this paper. This model generalizes the shear-lag model by including the nonlinear behavior of fibers. The equations of the model allow a Lax representation. This establishes the existence of an infinite number of invariants. The present theory is unique in that the analytical solution of the boundary value problem for simultaneous nonlinear differential equations is reduced to simultaneous nonlinear equations in terms of the boundary values of unknown functions. The two-dimensional multifilament failure problems of unidirectional fiber composites are analyzed. Example numerical solutions that focus specifically on the stress concentration factors of fibers adjacent to the local imperfections and the cracks are discussed.

Abstract For an arbitrary stress, strain, and displacement functional, second-order sensitivities with respect to varying structural shape are discussed. It is assumed that the external boundary of a structure can undergo shape modification described by a set of shape design parameters. Second derivatives of an arbitrary functional with respect to these parameters are obtained, using the mixed approach in which both the direct and adjoint first-order solutions are used. The general results are particularized for the case of the complementary energy of a structure.

ABSTRACT A new structural model of deformation and fracture of ceramics is presented. The real material is simulated as a periodic grid of hexagonal elastic grains connected with elastic bondings. A method for deformation analysis of such a medium is introduced, and the effective modules of the material are calculated. The solution of the problem of wave propagation gives dispersion correlations. The deformation model introduced and the procedure of Fourier transforms yields a Green function for an infinite periodic grid of nondeformable hexagonal grains that are connected with elastic bondings. The fundamental solution is used to examine the strength of the medium with local defects and to compare it with the strength of a defectless material.

Abstract Major software improvements have been made by the developers of NASTRAN in the area of structural optimization. Grid point sensitivity is available in version 67. This paper tests this capability by comparison with analytical solutions. Suggestions for further improvements are identified as well as recommendations for its use. The new capability has been integrated into an optimization system for component design. Several examples, including a cantilever beam, a simplified engine connecting rod, a cantilever plate, and an upper suspension control arm, are analyzed and optimized using this system.

ABSTRACT An exact method for analysis of the motion of a practical frictional oscillator with velocity-dependent friction is presented. Exact solutions are presented for the cases of free and harmonic forced vibration. It is shown that the oscillator studied exhibits a behavior that, under certain conditions, is significantly different from that of the constant Coulomb oscillator. Under free vibration, the oscillator studied exhibits longer duration of motion and less permanent displacement, whereas under forced vibration it exhibits a much smaller number of stops per cycle and different frequency content. Some of these conclusions appear to be in agreement with experimental results.

ABSTRACT ABSTRACT A new class of methods for solving the equations of motion of constrained mechanical system dynamics is presented. The tangent space local parametrization is used to form an index one system of mixed differential-algebraic equations (DAEs) that describes the constrained motion. Implicit numerical integration formulas are applied to the reduced ordinary differential equations (ODEs) in the tangent space. The resulting system of nonlinear equations is solved by Broyden's method. In the framework presented, the computational complexity of solving the implicit integration equations for the reduced ODE is about same as that of some explicit integration methods for the reduced ODE. In fact, in some cases the implicit method for solving the Euler-Lagrange equations can be implemented more efficiently than the explicit scheme.

ABSTRACT A fully numerical model is presented for simulating the response of slender structures to artificial wind loading. The deterministic method in the time domain is adopted to evaluate the response of very large systems during turbulent gusts lasting 1 to 10 min. Particular attention is devoted to very high-wind-sensitive systems such as guyed masts, as well as television reticulated towers. For this kind of structure, interaction effects between the loading process and the response process cannot be neglected. This causes an adjunctive nonlinearity of the mechanical problem, which is coupled with the so-called geometric nonlinearity that arises from significant displacements occurring during the phenomenon. The wind loading is artificially generated by simulating the time series of the turbulent wind field in the portion of the atmospheric boundary layer that is of interest for real structures (up to about 400 m). The stochastic processes that simulate the wind speed at given points are generated a...

ABSTRACT Structural integrity analyses are often an essential part of the design and fabrication processes. In any structural integrity analysis, an accurate representation of component geometry and material constitutive response is required. Weld geometry and weld inhomogeneity add to the complexity of a structural integrity analysis. The current work consists of a structural integrity analysis of a welded T-frame stiffened panel with a lack of penetration weld defect. Material fracture toughness at the continuum scale is used as the failure criterion. Nonlinear finite elements are used in the computational simulation of the welded T-frame. Complementary global and detailed weld defect region models are used to simulate global and local structural response.Differences in weld and base metal properties are explicitly included in the computational formulation.