Dynamics of the Rolling Stock and the Choice of Parameters of Vibration Dampers

Modern railway rolling stock should meet requirements regarding comfort (maximum travel speed with minimum vibrations of wagons, noiselessness of movement, etc.).To eliminate the influence of dynamic loads, rolling stock is equipped with vibration dampers. The objective of the work is to select the parameters of the vibration dampers of rolling stock, depending on its characteristics, to ensure the due indicators of comfort and safety of transportation of passengers and goods by rail. To achieve this objective, applied methods of mathematical modelling were based on numerical programming of operation of dynamic systems. The indicators of vibration dampers are evaluated according to the results of studies of the dynamics of the rolling stock (in particular, of vibration protection rates).Assessment of dynamic state of the rolling stock implies application of methods of mathematical and physical modelling, which include the development of a physical and mathematical model, a calculation algorithm, and computer programming. The study of the mathematical model by numerical methods makes it possible to carry out a multifactorial experiment using a large number of input parameters (factors) and to select the characteristics of vibration dampers that are optimal for the conditions under consideration.To solve dynamic problems, the harmonic perturbation model, which is the most widespread, was specified in the form of a sinusoid with a period corresponding to the rail length.A quantitative assessment of the vibration process (frequency, amplitude) makes it possible to identify the main processes occurring in the system under consideration under various types of external load. The introduced assumptions related to rigidity, mobility and geometric immutability of the system allow determining the methods for obtaining a mathematical model and considering the vibrations as flat ones.The equations were solved in MathCad Prime 4.0 package using the Runge–Kutta method with automatic step selection. The subsequent study of the properties of the dynamic system was carried out by changing the resistance parameter of dampers of the first stage of spring suspension, while recording the values of the amplitude of the vibrations of the system and the period.The analysis of the results has shown that the vibration period of the body and bogies under any changes in the resistance parameter of the damper remains unchanged, while rational parameters of resistance of axle box dampers have been revealed for specified indicators. Hydraulic vibration dampers with the revealed parameters used on rolling stock help to reduce wear and damageability of running gears, improve ride comfort and traffic safety, as well as to reduce repair and maintenance costs.

Numerical Simulation of Dynamic Response of Submerged Floating Tunnel under Regular Wave Conditions

A submerged floating tunnel (SFT) is considered an innovative alternative to conventional bridges and underground or immersed tunnels for passing through deep water. Assessment of hydrodynamic performance of SFT under regular wave loading is one of the important factors in the design of SFT structure. In this paper, a theoretical hydrodynamic model is developed to describe the coupled dynamic response of an SFT and mooring lines under regular waves. In this model, wave-induced hydrodynamic loads are estimated by the Morison equation for a moving object, and the simplified governing differential equation of the tunnel with mooring cables is solved using the fourth-order Runge–Kutta and Adams numerical method. The numerical results are successfully validated by direct comparison against published experimental data. On this basis, the effects of the parameters such as the cable length, buoyancy-weight ratio, wave period, wave steepness, and water/submergence depth on the dynamic response of the SFT under wave loading are studied. The results show that tunnel motions and cable tensions grow with wave height and period and decrease with submergence depth. The resonance of the tunnel will be triggered when the wave period is close to its natural vibration period, and the estimation formula of wave period corresponding to tunnel resonance is proposed in this paper.

Shear Characteristic Changes in Blended Rubber of Elastomeric Bearings due to Aging

Rubber bearings are widely used for seismic retrofit of bridges because they reduce the seismic force by making the vibration period of the bridge longer and distributing the seismic force to all the piers. However, they have the disadvantage of being easily aged compared to steel bearings as well as having variations in the shear stiffness. The shear characteristic changes in the blended rubber for the rubber bearings were analyzed, specifically, the aging accelerated by heat. The higher the aging temperature and longer the exposure time, the greater is the maximum stress and strain at that time, and the greater is the shear stiffness. This implies that the seismic performance gradually deteriorates due to aging as the service period becomes longer. This can provide the basis for the mechanical model of the aging bearing.

Field Test for a Base Isolation Structure on Condition of Horizontal and Initial Displacement

There are a few isolated structures that have been subjected to seismic testing. An isolated structure is incapable of tracking, adjusting, and controlling its dynamic characteristics. As a result, field evaluations of solitary structures’ dynamic characteristics are important. The horizontal initial displacement of a base isolation kindergarten made of 46 isolation bearings is 75 mm. The method for creating the horizontal initial displacement condition is illustrated, as are the primary test findings. Horizontal initial displacement is accomplished with the assistance of a reaction wall, rods, and hydraulic pump system. To begin, we removed the building using hydraulic jacks to produce horizontal displacement of the isolation layer and then attached rods to support the building. The rods were then shot and unloaded, causing the building to shake freely, and its dynamic response and other parameters were tested. The results indicate that the natural vibration period of an isolated structure is much greater than the natural vibration period of a seismic structure. The isolation layer’s hysteretic curve as completely filled; upon unloading, the isolation layer as promptly reset; the dynamic response control effect of each was visible, but the top floor’s acceleration was magnified by approximately 1.27 times.

Influence of near-fault characteristics on inelastic response of multi-storey building with intensity measurement analysis

This study is presented to achieve three objectives: (1) to compare between the inelastic responses of buildings under near and far fault excitations, (2) to investigate the effect of the pulse to structural period ratio, and (3) to evaluate a set of intensity measurements (IMs) in terms of near fault (NF) earthquakes. A real reinforced concrete building with 35 storeys is analysed in the scope of the first and second objectives, whereas the third objective involves three general-frame buildings consisting of 6, 13, and 20 storeys. Results show that the NF excitation can drive the building to exceed its life safety performance level. Furthermore, the accuracy of the IM highly depends on the vibration period of the building and the function used to calculate the IM.

Strategic alterations of posture are delayed in Parkinson’s disease patients during deep brain stimulation

Parkinson’s disease (PD) is characterized by rigidity, akinesia, postural instability and tremor. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) reduces tremor but the effects on postural instability are inconsistent. Another component of postural control is the postural strategy, traditionally referred to as the ankle or hip strategy, which is determined by the coupling between the joint motions of the body. We aimed to determine whether DBS STN and vision (eyes open vs. eyes closed) affect the postural strategy in PD in quiet stance or during balance perturbations. Linear motion was recorded from the knee, hip, shoulder and head in 10 patients with idiopathic PD with DBS STN (after withdrawal of other anti-PD medication), 25 younger adult controls and 17 older adult controls. Correlation analyses were performed on anterior–posterior linear motion data to determine the coupling between the four positions measured. All participants were asked to stand for a 30 s period of quiet stance and a 200 s period of calf vibration. The 200 s vibration period was subdivided into four 50 s periods to study adaptation between the first vibration period (30–80 s) and the last vibration period (180–230 s). Movement was recorded in patients with PD with DBS ON and DBS OFF, and all participants were investigated with eyes closed and eyes open. DBS settings were randomized and double-blindly programmed. Patients with PD had greater coupling of the body compared to old and young controls during balance perturbations (p ≤ 0.046). Controls adopted a strategy with greater flexibility, particularly using the knee as a point of pivot, whereas patients with PD adopted an ankle strategy, i.e., they used the ankle as the point of pivot. There was higher flexibility in patients with PD with DBS ON and eyes open compared to DBS OFF and eyes closed (p ≤ 0.011). During balance perturbations, controls quickly adopted a new strategy that they retained throughout the test, but patients with PD were slower to adapt. Patients with PD further increased the coupling between segmental movement during balance perturbations with DBS ON but retained a high level of coupling with DBS OFF throughout balance perturbations. The ankle strategy during balance perturbations in patients with PD was most evident with DBS OFF and eyes closed. The increased coupling with balance perturbations implies a mechanism to reduce complexity at a cost of exerting more energy. Strategic alterations of posture were altered by DBS in patients with PD and were delayed. Our findings therefore show that DBS does not fully compensate for disease-related effects on posture.

Electrical Efficiency of SECE-based Interfaces for Piezoelectric Vibration Energy Harvesting

Piezoelectric energy harvesting (PEH) interfaces have been widely investigated during the last decades in order to maximize the harvested power. Among the energy extraction circuits proposed in the literature, some of the most effective ones consist of extracting the electric charges from the piezoelectric elements in a synchronous way with the vibrations and within a very short portion of the vibration period (SECE, SECPE, FTSECE, etc.). For these strategies, most previous studies take the electrical efficiency (i.e., the electrical losses between the energy extracted from the piezoelectric element and the energy which is finally transferred in a storage element) into account in an ad-hoc and case-by-case manner. In this brief, we propose a unified analysis that applies to model the electrical efficiency of these SECE-based strategies taking into account losses introduced by the electrical interface. We identify the main loss mechanisms by demonstrating that the electrical efficiency mainly varies with two parameters: the quality factor of the electrical interface and the voltage inversion ratio of the considered strategy. Measurements on the FTSECE strategy show that our model predicts the stored power with a good accuracy and allows a better optimization of the harvesting interface (up to 5.4 times more stored power at off-resonance frequencies, and 30% larger harvesting bandwidth).

The Effect of Atmospheric Corrosion on Steel Structures: A State-of-the-Art and Case-Study

Atmospheric corrosion can seriously affect the performance of steel structures over long periods of time; thus, it is essential to evaluate the rate of corrosion and subsequent modification of dynamic properties of a structure over different time periods. Standards and codes represent the general guidelines and suggest general protection techniques to prevent structures from corrosion damage. The available models in the literature propose the thickness reduction method that accounts for the exposure time of structures in corrosive environments. The purpose of this study is to review the existing corrosion models in the literature and report as well as compare their effectiveness in low (C2 level), medium (C3 level) and high (C4 level) corrosivity class in accordance with the ISO standard. Furthermore, the influence of corrosion loss during the lifetime of a structure is studied through a realistic case study model using FEM (finite element method) in both linear and nonlinear regions. The results showed that the corrosion can considerably affect the dynamic characteristics of the structure. For instance, the vibration period rose up to 15% for the C4 class and 100-year lifespan. Additionally, the corroded structure presented higher acceleration and drift demand, and the base reaction forces were reduced up to 60% for the same class and time period.

Ecological Efficiency of Life Cycle of Concrete Fabricated Composite Slab in Earthquake Area

With the development of prefabricated buildings, the construction mode of buildings has changed greatly. Infilled wall is an important part of architecture. The traditional manual masonry method is not suitable for the construction of prefabricated buildings. Precast concrete infilled wall, as a form of infilled wall suitable for the construction of prefabricated buildings, came into being. Infilled wall has a great influence on the performance of frame structure. Compared with the traditional masonry infilled wall, the concrete infilled wall has greater stiffness, better integrity and stronger bearing capacity. Based on the existing research, this paper analyzes the influence of the height width ratio of the concrete infilled wall, the wall thickness, and the tie mode with the frame on the structural performance through the finite element software Atena. Combined with the results of practical engineering modal analysis, this paper evaluates the value method of natural vibration period of concrete frame infilled wall structure, and puts forward some suggestions for Chinese codes.

Predicting the peak structural displacement preventing pounding of buildings during earthquakes

The aim of the present paper is to verify the effectiveness of the artificial neural network (ANN) in predicting the peak lateral displacement of multi-story building during earthquakes, based on the peak ground acceleration (PGA) and building parameters. For the purpose of the study, the lumped-mass multi-degree-of-freedom structural model and different earthquake records have been considered. Firstly, values of stories mass and stories stiffness have been selected and building vibration period has been automatically calculated. The ANN algorithm has been used to determine the limitation of the peak lateral displacement of the multi-story building with different properties (height of stories, number of stories, mass of stories, stiffness of stories and building vibration period) exposed to earthquakes with various PGA. Then, the investigation has been focused on critical distance between two adjacent buildings so as to prevent their pounding during earthquakes. The proposed ANN has logically predicted the limitation of the peak lateral displacement for the five-story building with different properties. The results of the study clearly indicate that the algorithm is also capable to properly predict the peak lateral dis-placements for two buildings so as to prevent their pounding under different earthquakes. Subsequently, calculation of critical distance can also be optimized to save the land and provide the safety space between two adjacent buildings prone to seismic excitations.