An Implicit Multistage Integration Method Including Projection for the Numerical Simulation of Constrained Multibody Systems

To be efficient, the simulation of multibody system dynamics requires fast and robust numerical algorithms for the time integration of the motion equations usually described by Differential Algebraic Equations (DAEs). Firstly, multistep schemes especially built up for second-order differential equations are developed. Some of them exhibit superior accuracy and stability properties than standard schemes for first-order equations. However, if unconditional stability is required, one must be satisfied with second-order accurate methods, like one-step schemes from the Newmark family.Multistage methods for which high accuracy is not contradictory with stringent stability requirements are then addressed. More precisely, a two-stage, third-order accurate Implicit Runge–Kutta (IRK) method which possesses the desirable properties of unconditional stability combined with high-frequency dissipation is proposed.Projection methods which correct the integrated estimates of positions, velocities and accelerations are suggested to keep the constraint equations satisfied during the numerical integration. The resulting time integration algorithm can be easily implemented in existing incremental/iterative codes. Numerical results indicate that this approach compares favourably with classical methods.     

3D projection of the LuGre friction model adapted to varying normal forces

Multibody System Dynamics - In this paper, we develop an adaptation of the LuGre friction model so as to allow the development of the friction force and its application in any directions on systems...     

A new formulation for the direct dynamic simulation of flexible mechanisms based on the Newton–Euler inverse method

This paper is concerned with the direct dynamic analysis of mechanisms comprising flexible members. It is first recalled how the time integration of the dynamic equations governing the motion of a flexible mechanism is conditioned by the availability of the so-called iteration matrix. The latter is obtained not only from the mass matrix, which is sufficient in the rigid case, but also from the stiffness and damping tangent matrices. Hence, in a context based upon relative co-ordinates where the deformation of the flexible bodies is described by component modes, two formulations, a classical one and a new one, which permit the determination of this iteration matrix are presented. The classical formulation is based upon the Lagrange's theorem. The new one consists in a direct calculation of the residues of the dynamic equations by using the inverse method of Newton–Euler. In this case, the iteration matrix is obtained by a numerical derivation technique which proves well-conditioned. A first simple example is treated in order to compare the two formulations. A more complex one illustrates the real capabilities of the new formulation.     

An adaptive degradation‐based maintenance model taking into account both imperfect adjustments and AGAN replacements

This paper presents an adaptive maintenance model for equipment that can be adjusted (minor preventive maintenance, imperfect state) or replaced (major preventive maintenance, as good as new) at specific scheduled times based on degradation measurements. An initial reliability law that uses a degradation‐based model is built from the collection of hitting times of a failure threshold. Inspections are performed to update the reliability, the remaining useful life, and the optimum time for preventive maintenance. The case of both as good as new replacements and imperfect adjustments is considered. The proposed maintenance model is based on the optimization of the long‐term expected cost per unit of time. The model is then tested on a numerical case study to assess its effectiveness. This results in an improvement for the occurrences of maintenance tasks that minimizes the mean cost per unit of time as well as an optimized number of adjustments that can be considered before replacing an item. The practical application is a decision aid support to answer the 2 following questions: Should we intervene now or wait for the next inspection? For each intervention, should we adjust or replace the item of equipment? The originality is the presence of 2 criteria that help the maintainer to decide to postpone or not the preventive replacement time depending on the measured degradation and to decide whether the item should be adjusted or replaced.     

Cutting tools reliability and residual life prediction from degradation indicators in turning process

In the field of cutting tool reliability, an investigation based on four complementary approaches for tool wear assessment is proposed: the approach 1 is a general failure times approach (statistical reliability based on flank wear threshold hitting times), the approach 2 is based on power consumption monitoring (statistical reliability based on power threshold hitting times), the approach 3 is based on vibration signal analysis (statistical reliability based on vibration threshold hitting times), and the approach 4 is based on the evolution of flank wear for each insert (statistical reliability based on predicted failure times). For this study, 30 identical inserts from a same batch were studied with a CNC lathe in identical turning conditions. As the remaining useful life assessment is the final goal, this study highlight four approaches in order to find out the safest one. The results obtained showed that the approach 1 has too many uncertainties, whereas the approach 2 provides more specific and safer replacement times. The approach 3, in the first hand, highlights the fact that cutting conditions are not exactly identical and, in the second hand, leads to a safe conditional replacement of an insert. Finally, it appeared that the approach 4 allows applying a predictive maintenance strategy.