Partitioned schemes of the finite-element method for dynamic problems of acoustoelectroelasticity

A number of schemes which use partitioned forms of the matrices of the finite-element method are proposed for dynamic problems of acoustoelectric elasticity. The features of the solution, specific for electroelasticity, of generalized eigenvalue problems for large sparse matrices, and also of the realization of the method of expansion in eigenforms in harmonic non-stationary problems are pointed out. An explicit-implicit scheme for the integration with respect to time of the equations of the finite-element method of non-stationary acoustoelectroelasticity is proposed and discussed. Approaches to analysing pyroelectric devices at low modulation frequencies are indicated. The ARPACK software packages for solving eigenvalue problems are integrated into the ACELAN specialized finite-element system, for which corresponding partitioned algorithms are realized. Numerical experiments are presented on determining the first eigenfrequencies and forms of the oscillations of an axisymmetric composite piezoelectric radiator in ACELAN and in the well-known ANSYS finite-element software package. The method of expansion in eigenforms in illustrated by the analysis of a longitudinal-longitudinal piezoelectric transformer

Reliability of 2-out-of-N:G systems with NHPP failure flows and fixed repair times

It is commonplace to replicate critical components in order to increase system lifetimes and reduce failure rates. The case of a general N-plexed system, whose failures are modeled as N identical, independent nonhomogeneous Poisson process (NHPP) flows, each with rocof (rate of occurrence of failure) equal to λ(t), is considered here. Such situations may arise if either there is a time-dependent factor accelerating failures or if minimal repair maintenance is appropriate. We further assume that system logic for the redundant block is 2-out-of-N:G. Reliability measures are obtained as functions of τ which represents a fixed time after which Maintenance Teams must have replaced any failed component. Such measures are determined for small λ(t)τ, which is the parameter range of most interest. The triplex version, which often occurs in practice, is treated in some detail where the system reliability is determined from the solution of a first order differential-delay equation (DDE). This is solved exactly in the case of constant λ(t), but must be solved numerically in general. A general means of numerical solution for the triplex system is given, and an example case is solved for a rocof resembling a bathtub curve