Aeroelastic stability analysis using reduced order aerodynamic models

The stability of linear systems defined by ordinary differential equations with constant or periodic coefficients can be assessed from the spectral radius of their transition matrix. In classical applications of this theory, the transition matrix is explicitly computed first, then its eigenvalues are evaluated; if the norm of the largest eigenvalue is larger than unity, the system is unstable. The proposed implicit transition matrix approach extracts the dominant eigenvalues of the transition matrix using the Arnoldi algorithm, without the explicit computation of this matrix. As a result, the proposed implicit method yields stability information at a far lower computational cost than that of the classical approach, and is ideally suited for stability computations of systems involving a large number of degrees of freedom. Examples of application of the proposed methodology are presented that demonstrate its accuracy and computational efficiency

Implicit Floquet analysis for rotorcraft stability evaluation

Floquet theory has been extensively used for assessing stability of periodic systems. In the classical application of the theory, the transition matrix of the system is explicitly computed first, then its eigenvalues are evaluated. The stability of the system depends on the dominant eigenvalue: if this eigenvalue is larger than unity, the system is unstable. The proposed implicit Floquet analysis extracts the dominant eigenvalues of the transition matrix using the Arnoldi algorithm, without the explicit computation of this matrix. As a result, the proposed method yields stability information at a far lower computational cost than that of the classical Floquet analysis. The proposed implicit Floquet analysis is ideally suited for stability computations of systems involving a large number of degrees of freedom. Examples of application of the proposed methodology are presented that demonstrate its accuracy and computational efficiency

Prediction of Cleavage Probability Using Higher Order Terms of the Crack Tip Field

The dependence of the Weibull stress is investigated on the parameters of the elasticplastic crack tip field. The general form of the Weibull stress is given for a three-parameter approximation of the elasto-plastic crack tip field. This is the basis to define a constraint correction of the critical value of the J-integral for cleavage fracture

Static-explicit FE modeling of 3-d large deformation multibody contact problems on parallel computer

A static-explicit method is employed to simulate static or quasi-static multi-deformation-body contact problems with friction. Based on the characteristics of the explicit time integration algorithm, a reliable and efficient contact element strategy is developed to handle the multi-deformation-body contact with friction. The friction behaviour is governed by the Coulomb friction model with an additional limit on the allowable shear stress, which is treated as a flow plasticity rule. The penalty method is adopted to impose the normal and the sticking contact. Meanwhile, with choosing contact interfaces as sub-domain boundaries, a parallel algorithm for contact is proposed based on domain decomposition method and implemented for the large scale computation. In addition, a contact searching algorithm is also introduced. Finally, numerical examples of contact between finite deformation bodies are presented to show the efficiency and stability of this algorithm

The influence of the HAZ softening on the mechanical behaviour of welded joints containing cracks in the weld metal

The mechanical behaviour of welds containing cracks was analysed through the numerical simulation of the three-point bending tests of welded specimens. This paper presents the mechanical model and the methodology used for the numerical simulation of the tests. The variation in crack driving force of cracked welds is studied as a function of the strength mismatch in the heat affected zone and of the crack position relative to the weld metal/heat affected zone interface. This analysis was performed with recourse to the numerical calculation of the J integral.http://www.sciencedirect.com/science/article/B6V2R-4B0X38N-6/1/7027467d6e068a7f5c062427de733a1