Consequences of Nonlinear Characteristics of a Secondary Suspension in a Three-Piece Freight Car Bogie

Mechanical systems with nonlinear characteristics can show a complex dynamic behavior that should be taken into account when analysing dynamic performance and reliability. The dynamic behavior of the main suspension in a three-piece freight car bogie with constant friction damping is considered in this work. The aim is to investigate the vertical behavior of a specific suspension design due to different driving conditions, weather and wear of the friction wedges. A variation in weather and wear is represented by different friction configurations in the model of the suspension. Models of different levels of detail that are based on experimental data on existing designs are developed. It is found that the suspension performance is very sensitive to variations of the friction configuration and this indicates a possible presence of nonlinear dynamic phenomena at in service like conditions.     

Yaw damper modelling and its influence on railway dynamic stability

This paper deals with the modelling of yaw dampers and determining the influence of the modelling of this component on the results obtained when predicting the dynamic stability of a vehicle. The first part of the work analyses the influence of the yaw damper characteristics on railway dynamic stability. Following this, a physical model of the damper is developed which allows its performance to be reproduced accurately in the whole range of operating conditions the damper is envisaged to operate in. Once obtained, it was found that the computational cost of the model was relatively high. Therefore, a simplified model has been developed. The simplified model allows obtaining accurate results without excessively increasing the time required to perform the simulations. Analysing the results obtained with this model, it has been concluded that with respect to previous model based on conventional approaches, it improves the accuracy of dynamic calculation for the stability assessment. Also, it has been found that the accurate modelling of the yaw damper is critical when dealing with the vehicle's dynamic performance. In the last part of the paper, a special type of yaw damper was studied as well as its effect on the dynamic behaviour of the vehicle.     

Interactions of wind and density driven currents in North Sea ROFIs—a model study

Three different versions of a baroclinic three-dimensional circulation model of the North Sea are used to obtain information on the wind and density interactions in the North Sea ROFIs (Regions Of Freshwater Influence): the standard version with fully prognostic treatment of salinity and temperature is compared to a barotropic model run on the same grid on the one hand and to an also fully prognostic model run on a four times coarser grid on the other hand. In order to gain knowledge on the wind and density interactions, two opposing wind directions are chosen for investigation, namely a time of strong north wind, 21st–28th April 1982, and a time of strong southwest wind, 22nd–24th May 1982. In the April case the effect of the salinity gradients on the border of the ROFIs of Rhine, Weser, Ems and Elbe, i.e. along the continental shore, is shown to lead to a clear enhancement of the mean surface currents. In May this result is partly disguised by the additional effect of the thermocline in the deeper parts of the North Sea, i.e. in the classical shelf sea regime region. Nevertheless, the same pattern of enhanced mean surface currents along the coast is detected and is of the same order of magnitude as in the April case. It is thus concluded that although the circulation in the North Sea is reversed by the wind, the density induced component of the general circulation is modified only slightly.     

Heterogeneous traffic flow modelling for an arterial using grid based approach

A grid based modelling approach akin to cellular automata (CA) is adopted for heterogeneous traffic flow simulation. The road space is divided into a grid of equally sized cells. Moreover, each vehicle type occupies one or more cell as per its size unlike CA traffic flow model where each vehicle is represented by a single cell. Model needs inputs such as vehicle size, its maximum speed, acceleration, deceleration, probability constants, and arrival pattern. The position and speed of the vehicles are assumed to be discrete. The speed of each vehicle changes according to its interactions with other vehicles, following some stochastic rules depending on the circumstances. The model is calibrated and validated using real data and VISSIM. The results indicate that grid based model can reasonably well simulate complex heterogeneous traffic as well as offers higher computational efficiency needed for real time application.     

钦州湾波浪条件数值模拟研究

通过三娘湾海洋站风浪资料得出外海波要素,应用风区推算、抛物型缓坡方程、Boussinesq方程建立数学模型,对钦州湾港区波浪条件进行模拟计算,得出钦州湾波浪的波浪场状况。     

Sequential data assimilation in an upwelling influenced estuary

We have evaluated the impact of assimilating chlorophyll, nitrate, phosphate, silicate and ammonium into a coupled 1D hydrodynamic ecosystem model (GOTM-ERSEM) in an upwelling influenced estuary. The assimilation method chosen is the Ensemble Kalman Filter (EnKF), which has been demonstrated to improve field estimates of key variables (chlorophyll, nutrients) for bulk algal bloom prediction. The 1D model has been set up for a central station inside the Ría de Vigo (Spain). Data from bi-weekly surveys are used to constrain the model. Temperature and salinity profiles are used to ensure the correct representation of the water structure through a relaxation scheme. Chlorophyll extracts and nutrients at three depths are assimilated sequentially during 1 year simulation (1991). The assimilation period includes episodes of active upwelling and downwelling. All five assimilated variables are successfully constrained and represent a large improvement on the reference simulation (without assimilation). Small divergences can be related to poorly resolved physical processes in the model. The assimilation was further evaluated by comparing observed biomass partitioning with model results. Diatoms accounted for the largest biomass update and the largest improvement in terms of percentage of variance explained (R²). This is particularly significant as they represent the 46% of the yearly integrated observed biomass of the planktonic autotrophs. Nonetheless the R² value was low for all phytoplankton groups. Bacteria and nanoflagellates showed an improvement with respect to their yearly Root Mean Square (RMS), while the other functional groups worsen or remained unaffected. Chlorophyll assimilation was responsible for most of the impact on the phytoplankton biomass with small contributions from the silicate. It had minor impact on the updates of nutrients which in turn corrected the state variables related to the detrital pool. In this current setting, combined assimilation of chlorophyll and nutrients is not sufficient to produce a skillful simulation of the phytoplankton succession.     

Development and validation of a Kalman filter-based model for vehicle slip angle estimation

It is well known that vehicle slip angle is one of the most difficult parameters to measure on a vehicle during testing or racing activities. Moreover, the appropriate sensor is very expensive and it is often difficult to fit to a car, especially on race cars. We propose here a strategy to eliminate the need for this sensor by using a mathematical tool which gives a good estimation of the vehicle slip angle. A single-track car model, coupled with an extended Kalman filter, was used in order to achieve the result. Moreover, a tuning procedure is proposed that takes into consideration both nonlinear and saturation characteristics typical of vehicle lateral dynamics. The effectiveness of the proposed algorithm has been proven by both simulation results and real-world data.     

Identifying tyre models directly from vehicle test data using an extended Kalman filter

Individual tyre models are traditionally derived from component tests, with their parameters matched to force and slip measurements. They are imported into vehicle models which should, but do not always properly provide suspension geometry interaction. Recent advances in Global Positioning System (GPS)/inertia vehicle instrumentation now make full state measurement viable in test vehicles, so tyre slip behaviour is directly measurable. This paper uses an extended Kalman filter for system identification, to derive individual load-dependent tyre models directly from these test vehicle state measurements. The resulting model therefore implicitly compensates for suspension geometry and compliance. The paper looks at two variants of the tyre model, and also considers real-time adaptation of the model to road surface friction variations. Test vehicle results are used exclusively, and the results show successful tyre model identification, improved vehicle model state prediction – particularly in lateral velocity reproduction – and an effective real-time solution for road friction estimation.     

Investigating the influence of rail grinding on stability,vibration, and ride comfort of high-speed EMUs using multi-body dynamics modelling

ABSTRACT

High-speed electric multiple units (EMUs) have been popularised rapidly all around the world and have become a major transportation method. Increases in running velocity and wheel-rail deterioration lead to excessive vibration and reduced ride comfort, which are common issues encountered in the operation of high-speed EMUs. While built-in sensors on a car body are able to detect abnormal vibrations in the car body itself, they cannot effectively reflect the ride comfort of passengers. Wheel-rail profile matching can improve the wheel-rail interaction, and rail grinding has thus been introduced as a practical solution to alleviating the aforementioned problems. Nonetheless, the working mechanism of rail grinding has not been investigated theoretically. This study develops flexible car body and human body models based on the rigid-flexible coupled method to systematically study the effects of wheel-rail wear and rail grinding on passenger ride comfort. Case studies show that the proposed models can predict the ride comfort of passengers accurately. It is also demonstrated that rail grinding can significantly alleviate excessive vibration and improve passenger ride comfort in the long term. A long-term investigation reveals that rail grinding can improve the smoothness of the rail surface and reduce the damage to the rail.