Trailing vortices in a free-surface flow

The free-surface effect on two-dimensional flow structures, especially on the trailing vortices, is investigated numerically in this paper. The solution procedure employs a higher-order semi-implicit projection method. The numerical results have been compared with experimental data on wave elevation disturbed by a submerged translating hydrofoil with a positive angle of attack. The schematic computations reveal some interesting and unique characteristics of the trailing-vortex development in a laminar flow beneath a free surface. Based on the computational data, an empirical Strouhal–Reynolds–Froude number relationship is proposed for the purely laminar vortex shedding in a free-surface flow. Moreover, the numerical findings also indicate that the presence of a free surface accelerates the Strouhal vortex frequency, yet delays not only the onset of a large-scale Kármán instability but also the occurrence of transitional behaviors. The shedding frequency downshifts drastically or even becomes discontinuous when the secondary vortex grows on the suction side. A metastable transition frequency emerges at the same time and becomes distinct with increasing Reynolds number. The variation of the vortex-shedding Strouhal number with respect to both Reynolds and Froude numbers is obtained. The power spectra of the trailing wake consist of harmonics of the vortex-shedding and transition frequencies (mfs,nft), as well as their combinations (mfs±nft). © 2002 American Institute of Physics.published_or_final_versio

ICNavS: A tool for reliable dynamic route guidance

The aim of this paper is to devise a new reliable dynamic route guidance approach by integrating the A* algorithm, the concept of reliability and an existing route guidance method into a single package. A new purpose-developed software tool, the Imperial College Navigation Software (ICNavS), is presented, so as to implement and demonstrate the new approach on a real road network, using simulated data. A summary of the background of the program is given, followed by a procedure developed in order to model the features of real road networks, as well as missing data. Then, a imulation experiment on a part of West London’s road network is carried out and the results are presented

User equilibrium traffic network assignment with stochastic travel times and late arrival penalty

The classical Wardrop user equilibrium (UE) assignment model assumes traveller choices are based on fixed, known travel times, yet these times are known to be rather variable between trips, both within and between days; typically, then, only mean travel times are represented. Classical stochastic user equilibrium (SUE) methods allow the mean travel times to be differentially perceived across the population, yet in a conventional application neither the UE or SUE approach recognises the travel times to be inherently variable. That is to say, there is no recognition that drivers risk arriving late at their destinations, and that this risk may vary across different paths of the network and according to the arrival time flexibility of the traveller. Recent work on incorporating risky elements into the choice process is seen either to neglect the link to the arrival constraints of the traveller, or to apply only to restricted problems with parallel alternatives and inflexible travel time distributions. In the paper, an alternative approach is described based on the ‘schedule delay’ paradigm, penalising late arrival under fixed departure times. The approach allows flexible travel time densities, which can be fitted to actual surveillance data, to be incorporated. A generalised formulation of UE is proposed, termed a Late Arrival Penalised UE (LAPUE). Conditions for the existence and uniqueness of LAPUE solutions are considered, as well as methods for their computation. Two specific travel time models are then considered, one based on multivariate Normal arc travel times, and an extended model to represent arc incidents, based on mixture distributions of multivariate Normals. Several illustrative examples are used to examine the sensitivity of LAPUE solutions to various input parameters, and in particular its comparison with UE predictions. Finally, paths for further research are discussed, including the extension of the model to include elements such as distributed arrival time constraints and penalties

Testing a reliable in-vehicle navigation algorithm in the field

The results of a field experiment carried out to assess the accuracy and efficiency of a new in-vehicle navigation algorithm, whose aim is to incorporate and consider travel time reliability and route the guided vehicle along uncongested roads, in the absence of real-time traffic information are presented. Using historical travel time profiles deduced from floating vehicle data, the algorithm is implemented in a purpose-developed software tool and tested in the London Congestion Charging Zone. The experiment consists of driving a vehicle along routes computed by the algorithm and comparing the outcome with that of a conventional navigation system installed in a second vehicle. The results indicate that the new algorithm outperforms the conventional system in most cases, thus suggesting that it is a step forward towards a more intelligent navigation system

Mobile Web applications

This document presents the work that was elaborated at the company Present Technologies as part of the academic discipline Internship/Industrial Project for the Master’s degree in Informatics and Systems, Software Development branch, at Instituto Superior de Engenharia de Coimbra. The area of the mobile web applications has grown exponentially over the last few years turning it into a very dynamic field where new development platforms and frameworks are constantly emerging. Thus, the internship consisted in the study of two new mobile operating systems, Tizen and Firefox OS, as well as two frameworks for packaging of mobile web applications – Adobe PhoneGap and Appcelerator Titanium. These platforms are in the direct interest of Present Technology since it pretends to use them in its future projects in general and in the Phune Gaming project in particular. Since Television is one of the Present Technologies’ business areas, during the course of the internship it was decided to perform additionally a study of two Smart TV platforms, namely Samsung Smart TV and Opera TV, which was considered as a valuable knowledge for the company. For each of the platforms was performed a study about its architecture, supported standards and the development tools that are provided, nevertheless the focus was on the applications and for this reason a practical case study was conducted. The case studies consisted in the creation of a prototype or packaging of an application, for the case of the packaging tools, in order to prove the feasibility of the applications for the Present Technologies’ needs. The outcome of the work performed during the internship is that it raised the awareness of Present Technology of the studied platforms, providing it with prototypes and written documentation for the platforms’ successful usage in future projects

An approach to time dependence and reliability in dynamic route guidance

This paper presents a methodology, in order to increase the reliability of the route suggestions in route guidance systems. Based on the A* path finding algorithm and Chen’s link penalty method, the procedure involves penalising links with a high risk of being congested and obtaining a set of reliable route suggestions. Time-dependence of travel times is considered by adapting the Flow Speed Model technique accordingly. Modifications to the structure of the path finding algorithms are also made, so as to account for real road network features. Finally, experiments using simulated travel time and reliability data are carried out on a road network and the results are discussed

A Proposed ANN-Based Acceleration Control Scheme for Soft Starting Induction Motor

In this article, a new soft starting control scheme based on an artificial neural network (ANN) is presented for a three-phase induction motor (IM) drive system. The main task of the control scheme is to keep the accelerating torque constant at a level based on the value of reference acceleration. This is accomplished by the proper choice of the firing angles of thyristors in the soft starter. Using the ANN approach, the complexity of the online determination of the thyristors firing angles is resolved. The IM torque-speed characteristic curves are firstly used to train the ANN model. Secondly, the IM- soft starter system is modeled using MATLAB/SIMULINK. To prove the effectiveness of the proposed ANN-based acceleration control scheme, different reference accelerations and loading conditions are applied and investigated. Finally, a laboratory prototype of 3 kW soft starter is implemented. The proposed control scheme is executed in a real-time environment using a digital signal processor (Model: TMS320F28335). The simulation and real-time results significantly confirm that the proposed controller can efficiently reduce the IM starting current and torque pulsations. This in turn ensures a smooth acceleration of the IM during the starting process. Moreover, the proposed control scheme has the superiority over several soft starting control schemes since it has a simple control circuit configuration, less required sensors, and low computational burden of the control algorithm. © 2021 Institute of Electrical and Electronics Engineers Inc.. All rights reserved

Association of plasma GFAP with elevated brain amyloid is dependent on severity of white matter lesions in an Asian cognitively impaired cohort

INTRODUCTION: While elevated blood glial fibrillary acidic protein (GFAP) has been associated with brain amyloid pathology, whether this association occurs in populations with high cerebral small vessel disease (CSVD) concomitance remains unclear. METHODS: Using a Singapore-based cohort of cognitively impaired subjects, we assessed associations between plasma GFAP and neuroimaging measures of brain amyloid and CSVD, including white matter hyperintensities (WMH). We also examined the diagnostic performance of plasma GFAP in detecting brain amyloid beta positivity (Aβ+). RESULTS: When stratified by WMH status, elevated brain amyloid was associated with higher plasma GFAP only in the WMH– group (β = 0.383; P < 0.001). The diagnostic performance of plasma GFAP in identifying Aβ+ was significantly higher in the WMH– group (area under the curve [AUC] = 0.896) than in the WMH+ group (AUC = 0.712, P = 0.008). DISCUSSION: The biomarker utility of plasma GFAP in detecting brain amyloid pathology is dependent on the severity of concomitant WMH. Highlight: Glial fibrillary acidic protein (GFAP)’s association with brain amyloid is unclear in populations with high cerebral small vessel disease (CSVD). Plasma GFAP was measured in a cohort with CSVD and brain amyloid. Plasma GFAP was better in detecting amyloid in patients with low CSVD versus high CSVD. Biomarker utility of GFAP in detecting brain amyloid depends on the severity of CSVD