High-Speed Generators for Power-Dense, Medium-Power, Gas Turbine Generator Sets

Concepts to improve turbine generator (TG) set power density (PD) are identified, developed, and evaluated. The evaluation focuses on the TG set as a part of overall system optimization, with weight and volume penalties for special auxiliaries. PD is given priority, while other attributes such as efficiency, acoustics, and total system cost are also assessed. The strengths and weaknesses of each concept are assessed based on technical viability, potential for PD improvement, and risk. Sixty-one generator concepts over four generator types—air-cooled wound field, water-cooled wound field, permanent magnet (PM), and high-temperature superconducting (HTS)—are evaluated with three ship-level electrical distribution architectures—high-frequency AC and active- and passive-rectified DC. A prime mover of 14 MW at 7,000 r.p.m. is assumed. The study assesses generator size enabled by directly coupling the generator to the prime mover, eliminating the typical gear required in TG sets with engine speeds greater than 3,600 r.p.m. Technology approaches are described and trends in the design data are identified. Advanced PM and superconducting rotor technologies are evaluated. For the power, speed, and system requirements studied, these technologies do not differ significantly from water-cooled designs in size and weight. A water-cooled generator would be compatible with a range of future power distribution systems such as high-frequency AC, rectified DC, or 60 Hz AC (using a rectifier and an inverter).     

Analyzing pedestrian head injury to design pedestrian-friendly hoods

Head injuries are a major cause of fatalities in pedestrian-car accidents. The HIC (Head Injury Criterion) value, a measure of the fatality risk of a head injury, is calculated from the acceleration of the head’s center of gravity (henceforth, head center) resulting from a head impact. The pedestrian’s head does not impact the hood at a direction normal to the hood’s surface. The direction of motion of the head center may change extremely rapidly upon impact, and normal acceleration may also significantly contribute to the resultant acceleration of the head center. Therefore, pedestrian head protection studies should consider how normal acceleration contributes to the resultant acceleration of the head center. It is necessary to control the resultant acceleration of the head center to produce an optimal characteristic pulse. This study analyzes the composition and variations of the head’s acceleration in head-to-hood impacts, focusing on exactly how the normal and tangential components of the acceleration contribute to the resultant acceleration of the head center. This study also considers how structural design parameters affect each component of the resultant acceleration. Methods to control the resultant acceleration of the head center to produce an optimal characteristic pulse can be proposed based on the results of this study. The analytical models and the results of this study contribute to efforts to design vehicle hoods and pave the way for developing pedestrian protection technologies.     

Inclusion of latent variables in Mixed Logit models: Modelling and forecasting

Travel demand models typically use mainly objective modal attributes as explanatory variables. Nevertheless, it has been well known for many years that attitudes and perceptions also influence users’ behaviour. The use of hybrid discrete choice models constitutes a good alternative to incorporate the effect of subjective factors. We estimated hybrid models in a short-survey panel context for data among many alternatives. The paper analyses the results of applying these models to a real urban case study, and also proposes an approach to forecasting using these models. Our results show that hybrid models are clearly superior to even highly flexible traditional models that ignore the effect of subjective attitudes and perceptions.     

A new shared vehicle system for urban areas

The paper concerns the conceptual design of a transport system for pedestrian areas. The proposed transport system is based on a fleet of eco-sustainable Personal Intelligent City Accessible Vehicles (PICAVs). The vehicles are shared through the day by different users and the following specific services will be provided: instant access, open ended reservation and one way trips. Referring to the proposed transport system, a new methodology to optimise the fleet dimension and its distribution among the stations is proposed in this paper. The problem faced is an optimisation problem where the cost function to be minimised takes into account both the transport system cost and the user costs that depend on the waiting times. A random search algorithm has been adopted. Given a fleet dimension and its distribution among the stations, the waiting times of the users are assessed by a microscopic simulation. The simulation model tracks the second-by-second activity of each PICAV user, as well as the second-by-second activity of each vehicle. The overall methodology has been implemented in an object-oriented simulator. The proposed transport system has been planned and simulated for the historical city centre of Genoa, Italy.     

Effect of Frame Compliance on the Lateral Dynamics of Motorcycles

The lateral dynamics of an uncontrolled motorcycle, running on a straight, level road surface, is investigated in this paper. The structural compliances in the front and the rear frames of the motorcycle are taken into account by introducing additional degrees of freedom in the analysis. The kinematics of the tires is represented by linear differential equations which are based on the taut-string model of pneumatic tires. The linear differential equations of motion are solved to yield the eigensolutions of the system. Numerical results, obtained for parameters corresponding to a Honda CB750 motorcycle, are presented and discussed.     

Hydrodynamic performance of multiple-row slotted breakwaters

This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients (C _R , C _T , and C _E ) for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the C _R increases with increasing wave number, kd, and with a decreasing permeable wall part, dm. The C _T follows the opposite trend. The C _E slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the C _R , while increasing the C _T . At lower values of kd, a decreasing porosity increases the C _E , but for high values of kd, a decreasing porosity reduces the C _E . The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd<0.5. Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd>0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal.     

The numerical friction line

This paper presents a study on the numerical calculation of the friction resistance coefficient of an infinitely thin plate as a function of the Reynolds number. Seven eddy-viscosity models have been selected: the one-equation turbulence models of Menter and Spalart–Allmaras; the k-ω two-equation model proposed by Wilcox and its TNT, BSL and SST variants and the two-equation model. The flow has been computed at 14 Reynolds numbers in sets of seven geometrically similar Cartesian grids to allow a reliable estimation of the numerical uncertainty. The effect of the computational domain size has been reduced to negligible levels (below the numerical uncertainty). And the same holds for the iterative and round-off errors. In the finest grids of each set, the numerical uncertainty of the friction resistance coefficient is always below 1%. Special attention has further been given to the solution behaviour in the laminar-to-turbulent transition region. Curve fits have been applied to the data obtained at the 14 Reynolds numbers and the numerical friction lines are compared with four proposals from the open literature: the 1957 ITTC line, the Schoenherr line and the lines suggested by Grigson and Katsui et al. The differences between the numerical friction lines obtained with the seven turbulence models are smaller than the differences between the four lines proposed in the open literature.     

摩擦楔块几何尺寸对货车转向架性能的影响

分析了俄罗斯18-100型三大件货车转向架摩擦楔块结构的特点,指出改变摩擦楔块形状可以改进转向架的性能.     

Risk factors and theory building: a study to improve passenger vessel safety

Given the inherent complexity of the maritime transportation system, developing effective policy can be challenging. Using risk factors identified by an elicitation and aggregation of expert judgment, a relative-risk rating scheme was developed in the theory-building tradition of the social sciences. The model was empirically evaluated using 18 months of data from the US small passenger vessel sector. The model identified that the top 10% of relatively highest risk vessels accounted for 50% of all marine casualties during the period of examination. A policy for deploying the model nationally is proposed.     

Synoptic transects on the distribution of trace elements (Hg,Pb, Cd,Cu, Ni,Zn, Co,Mn, Fe,and Al) in surface waters of the Northern- and Southern East Atlantic

Surface seawater samples were taken in the framework of the GEOTRACES program on “POLARSTERN” expedition ANT XXIII/1 in the Eastern Atlantic in 2005 to study the distribution of the trace elements Hg (mercury), Pb (lead), Cd (cadmium), Cu (copper), Ni (nickel), Zn (zinc), Co (cobalt), Mn (manganese), Fe (iron), and Al (aluminium). With the exception of Hg, results were compared to earlier datasets from 1989 to 1990. The particulate fraction averaged over the transect was calculated to be 49% for Cd, 23% for Mn and 50% for Fe indicating a release of these TEI's (trace elements and their isotopes) from a leachable SPM fraction in the stored and acidified samples.Total Pb concentrations ranged between 5 and 20 pmol kg^? 1 in 2005 with highest values in the ITCZ (intertropical convergence zone). In 1989 Pb concentrations were twice as high in the region of the ITCZ, while by a factor of 10–15 higher values were obtained in the North Atlantic.Total Cd and Co are dominated, by different seasonal upwelling regimes (Equatorial upwelling, Guinea Dome, Angola Dome).Total Cu, Ni, Fe, Mn and Al show nearly identical concentrations in 1990 and 2005. For total manganese and aluminium strong maxima (3–4 nmol kg^? 1 and 55 nmol kg^? 1 respectively) are observed between 23°N and 0°, while the Fe maximum (6–9 nmol kg^? 1) is located at 7°N. Total Hg concentrations ranged between 0.5 and 4.5 pmol kg^? 1.