On the Design and Development of a Magneto-Rheological Mount

This paper evaluates the performance of a Magneto-Rheological (MR) mount. The mount incorporates MR fluid in a conventional fluid mount to open and close an inertia track between the fluid chambers of the mount. It is shown that such switching of the inertia track improves the mount's isolation effect by eliminating the large transmissibility peak that commonly exists at frequencies larger than the notch frequency for conventional fluid mounts. The switching frequencies of the MR mount are evaluated based on the parameters of the mount. A simple control scheme for switching the mount between the open and closed states is proposed, and the performance of the controlled mount is compared with conventional mounts. A sensitivity analysis is conducted to evaluate the effect of parameter errors in estimating the switching frequencies and mount performance. The results show that the switching frequencies can be accurately determined from mount parameters that are easily measured or estimated.     

Magneto-rheological suspensions for improving ground vehicle’s ride comfort,stability, and handling

ABSTRACT

A state-of-the-art discussion on the applications of magneto-rheological (MR) suspensions for improving ride comfort, handling, and stability in ground vehicles is discussed for both road and rail applications. A historical perspective on the discovery and engineering development of MR fluids is presented, followed by some of the common methods for modelling their non-Newtonian behaviour. The common modes of the MR fluids are discussed, along with the application of the fluid in valve mode for ground vehicles’ dampers (or shock absorbers). The applications span across nearly all road vehicles, including automobiles, trains, semi-trucks, motorcycles, and even bicycles. For each type of vehicle, the results of some of the past studies is presented briefly, with reference to the originating study. It is discussed that Past experimental and modelling studies have indicated that MR suspensions provide clear advantages for ground vehicles that far surpasses the performance of passive suspension. For rail vehicles, the primary advantage is in terms of increasing the speed at which the onset of hunting occurs, whereas for road vehicles – mainly automobiles – the performance improvements are in terms of a better balance between vehicle ride, handling, and stability. To further elaborate on this point, a single-suspension model is used to develop an index-based approach for studying the compromise that is offered by vehicle suspensions, using the H₂ optimisation approach. Evaluating three indices based on the sprung-mass acceleration, suspension rattlespace, and tyre deflection, it is clearly demonstrated that MR suspensions significantly improve road vehicle’s ride comfort, stability, and handling in comparison with passive suspensions. For rail vehicles, the simulation results indicate that using MR suspensions with an on-off switching control can increase the speed at which the on-set of hunting occurs by as much as 50% to more than 300%.     

Improving the coexistence of offshore wind farms and shipping: an international comparison of navigational risk assessment processes

The continued growth and evolution of the offshore wind industry, and the emergence of other novel marine uses such as wave and tidal generators, have upped the ante for spatial planners, as well as consenting and approval authorities in various coastal states. These stakeholders rely on processes such as navigational risk assessments (NRAs) to balance safety and efficiency requirements and to make optimal decisions over use of space. Given the increasingly complex and crowded seascape, however, there are some apprehensions about potential shortcomings in these NRA processes. There is also some concern that these inadequacies may lead to unsafe or inefficient marine spatial use. To understand how NRA processes can be improved further, a literature review is conducted, followed by a survey of respondents who are involved in the planning, consenting and/or approval of offshore wind farms across seven different countries. A summary of the NRA processes in these seven countries is presented, and several shortcomings are identified. Based on the findings of the survey, a list of recommendations is presented to enhance existing NRA processes—and to improve the coexistence of shipping and offshore wind farms (OWFs).     

The relationship between urban street networks and private motorized trips at the city level

There are factors that impact car usage in urban areas, such as density, diversity and design, but there have been few studies that examine the relationship between street network factors and car usage at the city level (macro level). This paper focuses on this relationship by introducing urban street network variables, such as blocks per area, nodes per block and length of roads and motorways, as independent variables and the percentage of daily trips by private motorized modes as the dependent variable. The street network in this study includes interconnecting lines and points that present streets, roads, motorways, intersections and blocks. The strength of the relationship in this study is found using multiple linear regression. The findings of this research indicate that an increase in car usage is correlated with an increasing number of blocks per area, number of nodes per block and length of motorways. In addition, because the urban street network is the result of macro-scale planning decisions, considering this relationship can lead to better planning decisions.     

A performance evaluation model for supply chain of shipping company in Iran: an application of the relational network DEA

Shipping business is capital intensive and highly competitive. It necessitates for the shipping companies to constantly monitor their performance and measure relative efficiencies of their supply chains. Despite such importance, the studies devoted to this field have been surprisingly limited. This paper reviews the involved factors and proposes a relational network data envelopment analysis (DEA) model for measuring the efficiency of supply chain of an international shipping company in Iran with relevant sub-processes in the period 2008–2011. First, the supply chain network of the company is illustrated and then the input and output variables associated to each member are determined. The proposed model is suitable for shipping companies which usually use similar pattern in this business. Finally based on the results, recommendations are made for improvements and a new field of business is also proposed.     

Exploiting the fundamental diagram of urban networks for feedback-based gating

Traffic signal control for urban road networks has been an area of intensive research efforts for several decades, and various algorithms and tools have been developed and implemented to increase the network traffic flow efficiency. Despite the continuous advances in the field of traffic control under saturated conditions, novel and promising developments of simple concepts in this area remains a significant objective, because some proposed approaches that are based on various meta-heuristic optimization algorithms can hardly be used in a real-time environment. To address this problem, the recently developed notion of network fundamental diagram for urban networks is exploited to improve mobility in saturated traffic conditions via application of gating measures, based on an appropriate simple feedback control structure. As a case study, the proposed methodology is applied to the urban network of Chania, Greece, using microscopic simulation. The results show that the total delay in the network decreases significantly and the mean speed increases accordingly.     

A new method for calibration of unidirectional double-peak spectra

This study aims at presenting a new approach in calibrating standard two-peak design spectra for specific regions in absence of wind data. The main principle in these kinds of fitting for a new area is to minimize the least square error between measured and fitted spectra and there has been less attention to double-peak spectra individual characteristic as co-existence of wind-sea and swell parts in one spectrum. Here, separation frequency, approximately dividing such parts, is implemented to virtually extract wind-sea and swell components of a measured spectrum considering their intrinsic overlap near the separation frequency. Then, they have been easily utilized to calibrate two parts of standard double-peak spectrum in a revisory manner. To verify benefits of this new methodology, it has been applied on Ochi-Hubble as well as Torsethaugen spectra regarding field measurements in a coastal region at Gulf of Oman, Chabahar bay. Results obviously show a better adjustment of formula to field spectrum using this simple approach when compared with output of calibration on integrated field spectrum irrespective of its main characteristic such as availability of two-wave systems.     

Non-motorised Level of Service: Addressing Challenges in Pedestrian and Bicycle Level of Service

Motorised vehicle conditions have been evaluated by many researchers. In contrast, there are very limited studies on vulnerable and non-motorised users, such as cyclists and pedestrians, specifically children, the elderly and the disabled. Thus, this paper reviews prominent studies on street evaluations to identify effective indicators for non-motorised trips. The street condition for these trips is measured by the bicycle level of service (BLOS) and the pedestrian level of service (PLOS). In previous studies, different methods have been introduced for PLOS and BLOS. However, these methods have several major shortcomings. First, pedestrians and cyclists are assumed to be users who can share street facilities with motorised vehicles and thus are considered equivalent to cars. Second, the majority of these methods are complicated and time-consuming, and it is difficult to connect them to a design process. Furthermore, these methods support only a limited number of walking and cycling facilities; therefore, they may not be valid for a wide range of pedestrians and cyclists with a diverse variety of abilities and ages. This study discusses the challenges in the BLOS and PLOS research and attempts to introduce new objectives for further studies in this field to eliminate the aforementioned shortcomings.     

Effect of System Nonlinearities on Locomotive Bogie Hunting Stability

This paper presents the effect of system parameters on hunting of a rail vehicle with nonlinear yaw dampers and wheel-rail interface. This study is intended to complement earlier studies by True et al. where they investigated the effect of nonlinearities stemming from creep-creep force saturation and wheel/rail contact forces. The rail vehicle is represented by a two-axle truck (bogie) that includes the dynamics of the wheelsets and the truck frame. The numerical simulation results show that yaw damping can have a mixed effect on the hunting critical speed. In some ranges, increasing damping can actually lower the critical speed, unlike the results commonly obtained from a linear model. Flange contact nonlinearities can also have a significant effect on the hunting behavior. Large lateral stiffness of the rail can increase lateral force to vertical force (L/V) ratio during hunting. Increasing the gauge clearance, however, can have an opposite effect. The effect of a variety of other parameters, such as the primary suspension yaw and lateral stiffness, primary suspension lateral damping, wheelset mass, and truck frame mass, are summarized in a table.