Random vibration analysis of thin-walled elastic rings under multiple moving loads

This paper investigates the random vibration of a thin-walled ring subjected to multiple moving loads from the inside of the ring. A ring gear in a planetary gear train with three equally-spaced planets is taken as an example. The ring is discretized with the finite element method of curved beam elements. The supports of the ring gear are treated as three linear springs to mimic a general bolt connection. The stochastic Newmark algorithm is used to solve the equations and obtain the response's mean and variance. Monte Carlo simulations are also conducted to verify the results from the stochastic Newmark scheme. A parametric study is conducted to examine the effect of design parameters on the responses.

An easily computable error estimator in space and time for the wave equation

We propose a cheaper version of a posteriori error estimator from Gorynina et al. (Numer. Anal. (2017)) for the linear second-order wave equation discretized by the Newmark scheme in time and by the finite element method in space. The new estimator preserves all the properties of the previous one (reliability, optimality on smooth solutions and quasi-uniform meshes) but no longer requires an extra computation of the Laplacian of the discrete solution on each time step.

Time and space adaptivity of the wave equation discretized in time by a second-order scheme

The aim of this paper is to obtain a posteriori error bounds of optimal order in time and space for the linear second-order wave equation discretized by the Newmark scheme in time and the finite element method in space. An error estimate is derived in the $L^{\infty }$-in-time/energy-in-space norm. Numerical experiments are reported for several test cases and confirm equivalence of the proposed estimator and the true error.

An implicit algorithm for the dynamic study of nonlinear vibration of spur gear system with backlash

In this work, we propose some regularization techniques to adapt the implicit high order algorithm based on the coupling of the asymptotic numerical methods (ANM) (Cochelin et al., Méthode Asymptotique Numérique, Hermès-Lavoisier, Paris, 2007; Mottaqui et al., Comput. Methods Appl. Mech. Eng. 199 (2010) 1701–1709; Mottaqui et al., Math. Model. Nat. Phenom. 5 (2010) 16–22) and the implicit Newmark scheme for solving the non-linear problem of dynamic model of a two-stage spur gear system with backlash. The regularization technique is used to overcome the numerical difficulties of singularities existing in the considered problem as in the contact problems (Abichou et al., Comput. Methods Appl. Mech. Eng. 191 (2002) 5795–5810; Aggoune et al., J. Comput. Appl. Math. 168 (2004) 1–9). This algorithm combines a time discretization technique, a homotopy method, Taylor series expansions technique and a continuation method. The performance and effectiveness of this algorithm will be illustrated on two examples of one-stage and two-stage gears with spur teeth. The obtained results are compared with those obtained by the Newton–Raphson method coupled with the implicit Newmark scheme.

Numerical Simulation of the Supersonic Disk-Gap-Band Parachute by Using Implicit Coupling Method

The implicit coupling method is applied to model the 0.8 m disk-band-gap parachute at Mach 2.0. The fluid and structure governing equations are solved by the Lower-Upper Symmetric Gauss-Seidel (LU-SGS) algorithm and Newmark scheme, respectively. By exchanging the numerical results of the coupling surface with Gauss-Seidel algorithm, high accuracy solutions at every physical time step are obtained. The numerical results of the canopy drag coefficient and projected area fit well with the wind tunnel test results. The simulation reproduces the shock oscillation and breathing phenomenon of the canopy that are usually observed in these systems at Mach 2.0. Furthermore, it is found that the unstable saddle point is the main reason for the shock oscillation of the canopy. And the unsynchronized phases of the canopy area and shock oscillation curves lead to the drag of the canopy oscillate in irregular state.

Vibration analysis of an oscillator with non-smooth dry friction constraint

Global vibrational behaviour of a single degree-of-freedom (SDOF) oscillator subjected to Coulomb type of dry frictional constraint and harmonic excitation is investigated in this paper. To obtain a numerical solution to the non-smooth dynamical problem, the equation of motion is discretized in the time domain by means of the implicit Bozzak-Newmark scheme. An algebraic equation governing the current state of the system is obtained in terms of its velocity. Utilizing the fact that the frictional constraint can be completely characterized by two scenarios - (i) forward sliding or stiction with a tendency to move forward, and (ii) backward sliding or stiction with a tendency to move backward, two coupled linear complementary equations are deduced. With the reduction of the non-smooth dynamical problem to a linear complementarity problem (LCP) in terms of supremum velocities and slack forces, the rapid and endless switches from sliding to stiction, and vice versa, in a vibration problem, are automatically detected and handled effectively. This is superior to the event-based methods and analytical methods available in the literature. Numerical results obtained using the proposed method are compared with the analytical solutions for harmonically excited dry-friction oscillator with ordinary behaviour; excellent agreement is observed. The proposed method is then employed for determining the global chaotic and deterministic behaviour of a harmonically excited dry-friction oscillator with system and excitation parameters varying in wide ranges.

A COMPOSITE TIME INTEGRATION SCHEME FOR DYNAMIC ADHESION AND ITS APPLICATION TO GECKO SPATULA PEELING

Simulation of dynamic adhesive peeling problems at small scales has attracted little attention so far. These problems are characterized by a highly nonlinear response. Accurate and stable time integration schemes are required for simulation of dynamic peeling problems. In the present work, a composite time integration scheme is proposed for the simulation of dynamic adhesive peeling problems. It is shown through numerical examples that the proposed scheme remains stable and also has some gain in accuracy. The performance of the scheme is compared with two collocation-based schemes, i.e., Newmark scheme and Bathe composite scheme. It is shown that the proposed scheme and Bathe composite scheme perform equally. However, the proposed scheme adds very little to the computational cost of Newmark scheme. Through a numerical simulation of the peeling of a gecko spatula from a rigid substrate it is shown that the proposed scheme and the Bathe composite scheme are able to simulate the complete peeling process for given time step whereas the Newmark scheme diverges. It is also shown that the maximum pull-off force is within the range reported in the literature.