Comparative nonlinear seismic analysis of an existing RC bridge designed with obsolete codes

The evolution of seismic design and calculation criteria for highway bridges has a direct influence on their structural behavior. This paper presents a nonlinear dynamic analysis using a detailed 3D finite element model of an existing bridge, with different design criteria for the column transverse reinforcement, according to code requirements of different times. The numerical model is able to simulate both the collapse of the structure and the generation of damage in its elements when subjected to extreme seismic actions. Through the numerical model, it is possible to represent the cyclic behavior of the concrete, and to evaluate the influence of the transverse reinforcement assigned to the column on the overall response of the bridge. The formation of plastic hinges is verified, as well as the identification of different collapse mechanisms.

Numerical and Experimental Investigations on a Friction Ring Damper for a Flywheel

A damping strategy using a friction ring damper for an industrial flywheel was numerically and experimentally investigated. The friction ring damper, located on the arms of the flywheel, was experimentally found to effectively reduce the vibration amplitude of the flywheel. The vibration energy is dissipated when relative motions occur at the friction contact interfaces. Nonlinear dynamic analysis based on a lumped-parameter model of a flywheel equipped with a friction ring damper was conducted. A dimensionless parameter, κ, defined as the ratio of the critical friction force to the amplitude of harmonic force, was used to evaluate the damping performance. For several values of κ, steady-state responses under harmonic excitation and nonlinear modes were obtained using the harmonic balance method (HBM) combined with the alternating frequency–time domain method (AFT). The forced response analysis proved the existence of an optimal value of κ, which can minimize the vibration amplitude of the flywheel. The nonlinear modal analysis showed that all the damping ratio–frequency curves are completely coincident even for different κ, and the frequency corresponding to the maximum damping ratio is equal to the frequency at the intersection of the forced response curves under the fully slip and the fully stick states of the friction contact interface. By analyzing the behaviors of the friction contact interface, it is shown that the friction contact interface provides damping in the combined stick–slip state. The forced response under random excitation was calculated using the Runge–Kutta method and the friction interface behaviors were analyzed. Finally, spectral testing was conducted to verify the numerical results.

An Efficient and Robust Nonlinear Dynamic Analysis Method for Framed Structures Using the Rigid Body Rule

In this paper, by implanting the rigid body rule (RBR)-based strategy for static nonlinear problems into the implicit direct integration procedure, an efficient and robustness nonlinear dynamic analysis method for the response of framed structures with large deflections and rotations is proposed. The implicit integration method proposed by Newmark is improved by inserting an intermediate time into the time step and by adding the 3-point backward difference in the second substep so as to preserve the momentum conservation and to maintain the stability of the direct integration method. To solve the equivalent incremental equations of motion, the RBR is built in to deal with the rigid rotations and the resulting additional nodal forces of element. During the increment-iterative procedure, the use of RBR-qualified geometric stiffness in the predictor reduces the numbers of iterations, while the elastic stiffness alone in the corrector to update the element nodal forces makes the computation efficiency and convergence with no virtual forces caused by the ill geometric stiffness. The proposed algorithm is advanced in the applications of several framed structures with highly nonlinear behavior in the dynamic response by its simplicity, efficient and robustness.

Nonlinear dynamic analysis of multiple grooved water-lubricated journal bearings using attenuation rate interpolation method

Purpose The stringent requirements for environmental protection have induced the extensive applications of water-lubricated journal bearings in marine propulsion. The nonlinear dynamic analysis of multiple grooved water-lubricated bearings (MGWJBs) has not been fully covered so far in the literature. This study aims to conduct the nonlinear dynamic analysis of the instability for MGWJBs. Design/methodology/approach An attenuation rate interpolation method is proposed for the determination of the critical instability speed. Based on a structured mesh movement algorithm, the transient hydrodynamic force model of MGWJBs is set up. Furthermore, the parameters’ analysis of nonlinear instability for MGWJBs is conducted. The minimum water film thickness, side leakage, friction torque and power loss of friction are fully analyzed. Findings With the increase of speed, the journal orbits come across the steady state equilibrium motion, sub-harmonic motion and limit circle motion successively. At the limit circle motion stage, the orbits are much larger than that of steady state equilibrium and sub-harmonic motion. The critical instability speed increases when the spiral angle decreases or the groove angle increases. The minimum water film thickness peak is at the rotor speed of 4,000 r/min for the MGWJB with Sa = 0°. As rotor speed increases, the side leakage decreases slightly while the friction torque and the power loss of friction increase gradually. Originality/value Present research provides a beneficial reference for the dynamic mechanism analysis and design of MGWJBs.