Pedestrian Bridge Evaluation and Modelling Subjected to Running Load Cases

<p>This paper presents the dynamic measurements performed at two pedestrian bridges in Sweden subjected to different loading scenarios. Using accelerometers, the natural frequencies, the experimental mode shapes, and damping properties were determined for each bridge. Analysis were performed using the generalized single degree of freedom theory, the finite element method and the coupled system approach taking into account the flying phase of the running load. Additionaly, a simplified sensitivity analysis is presented in terms of accelerations due to the pedestrian transient event of a running load case. Results indicate that there is an excellent agreement between the aforementioned modelling strategies and, that it is possible to have human structure interaction under running load scenarios.</p>

Experimental study and numerical simulation of inerter-based systems

Based on a single degree of freedom system, the inerter principles of an inertial mass damper and clutch inerter damper are introduced. The motion equations of the systems are derived, and the rotational speed and damping are considered. In addition, a reducer is innovatively combined with clutch inerter damper to significantly improve the inertance. Accordingly, an innovative reducer clutch inerter damper is proposed. Shaking table experiments are carried out on the uncontrolled inertial mass damper, clutch inerter damper, and reducer clutch inerter damper structures under the inputs of harmonic and seismic waves. Simulation models of the four types of structures are developed, and the validity of the theoretical models is verified by a comparison between the simulation and experiment. Moreover, the nonlinear models of clutch inerter damper and reducer clutch inerter damper are discussed. Finally, according to the test results, the vibration reduction effects of the three inerters are analyzed, and the reasons why they are different from the ideal clutch inerter damper are also explained. The results show that clutch inerter damper, especially reducer clutch inerter damper, has a good vibration damping performance.

Energy harvesting from railway slab-tracks with continuous slabs

This paper contributes to the literature and development of knowledge in the topic of energy harvesting by presenting the modelling and calculations of energy from vibration of railway tracks due to moving trains on floating-slab tracks with continuous slabs, considering both the quasi-static and dynamic effects. The floating-slab track is modelled as a double Euler–Bernoulli beam connected by continuous spring and damper elements. The dynamic excitation is accounted for by considering the un-sprung axles of a passing train with a number of coaches. The dynamic excitation is simulated using randomly generated unevenness from standard functions of power spectral density . The responses of rails’ beam and slab are calculated for different unevenness realizations, and then used as inputs for a base-excited single-degree-of-freedom system that models the harvester. The change in the harvested energy is investigated due to the change of natural frequency of the harvester, the change of condition of track and change of train’s velocity. The parameters used in this paper correspond to tracks and trains for Doha metro and unevenness information from the literature. The results show that more energy can be harvested by tuning the harvester’s natural frequency to the frequency of axle-track resonance. It is found that a maximum mean-energy can be harvested from the rails of 0.35 J/kg for a train moving at 100 km/h for a track with poor condition and this is obtained at the axle-track resonance frequency. For the same track condition, a reduction of about 55% and 61% is observed for train’s velocities of 70 km/h and 40 km/h, respectively. Using a track with medium and good conditions resulted in reduction of the mean harvested energy at the axle-track resonance by 73.5% and 99.9%, respectively.

A minimum transmitted load control method for shock isolation mounts with magnetorheological energy absorbers

This paper proposed a minimum transmitted load (MTL) control method for drop-induced shock isolation mounts (SIM) with magnetorheological energy absorbers (MREAs). MTL control method consists of two parts of maximum damping force (MDF) control and one part of constant acceleration (CA) control, which can make the payload stop after fully utilize MREA stroke (soft landing) with minimum transmitted load. The control algorithm of MTL control method is derived in a single-degree-of-freedom (SDOF) system. The relationship between the controllable velocity range of MTL control method and parameters of shock isolation mounts is also derived. An optimal control method selection criterion between Bingham number (BN) control method and MTL control method is developed. The performance of MTL control method and selection criterion are shown by applying to the SIM system with variable drop velocities and system parameters. Results shows that MTL control method has the minimum transmitted load and the selection criterion is feasible.

Study on Dynamic Characteristics and Parameter Influence of a Kind of Bilateral Restraint Impact Vibration System

In this paper, the hinge in the articulated structure is studied, the gap hinge is described as a nonlinear bilateral constraint, and the equivalent modeling and analysis of the hinge connection collision vibration are carried out based on the Lankarani–Nikravesh nonlinear contact force model. With the help of the method of nonlinear system dynamics analysis research, the Poincaré mapping of hinge joint collision vibration is constructed, the bifurcation diagram of the system with different parameters is solved, and the variation law of the system motion and the influence of parameters are analyzed by combining the time response diagram, phase diagram, Poincaré cross section diagram, and spectrum diagram of the typical motion of the system. The simulation results show that the system moves in a single degree of freedom and varies with parameters with multiplicative period bifurcation and rubbing edge bifurcation leading to chaos; the system’s periodic motion has shock state mutation and mirror jump transformation.

A novel electro-hydraulic servo steering system for Ackermann steering of heavy multi-axle vehicle

Ackermann steering is important for the steering performance of heavy multi-axle vehicle. When Ackermann steering condition is not satisfied, it will lead to abnormal tire wear. Traditional trapezoidal mechanism of heavy multi-axle vehicle is a single degree of freedom (DOF) mechanism, which is difficult to completely realize Ackermann steering. In this paper, a new two DOF electro-hydraulic servo steering system (TDEHSSS) by using a variable length tie rod is proposed for solving the issue. First, a complex nonlinear dynamic model of TDEHSSS is established. This model includes the two DOF mechanical model based on a Lagrange equation, the valve-controlled double steering power cylinders model and the valve-controlled tie rod cylinder model. Then, a simulation model is built through MATLAB/Simulink and the simulation results show that TDEHSSS can realize the proposed requirement. At last, a test bench is founded to verify model. It is indicated that the simulation and experimental curves are consistent, showing that mathematical model is in accordance with the experimental system. This research is valuable for analyzing TDEHSSS, designing advanced controllers, and finally realizing Ackermann steering for heavy multi-axle vehicles.

Vibrations in Single-Degrees-of-Freedom Sampled-Data Linear Mechanical Systems

This paper aims to present that the effect of sampling can result in multi-frequency vibration even in the case of a single-degree-of-freedom linear mechanical model. Even though the sampled-data systems have an infinite number of characteristic exponents due to sampling, the vibrations of these systems can still be characterized by an effective system model with a single dominant frequency. However, as this paper shows, additional harmonics become relevant, resulting in multi-frequency vibrations depending on the magnitude of applied control parameters. The vibrations presented by the time histories of vibration and their spectra resulted in numerical simulation of the sampled-data system.