The Effect of Topboxes on Motorcycle Stability

Hot wire anenometry measurements have been made in the wake of a model motorcycle and rider mounted in a windtunnel. Only in tests with a topbox present is there clear evidence of eddy shedding. Calculations have been performed on the corresponding full-scale motorcycle to determine the frequencies of the weave and wobble modes. Comparison with the wake frequencies extrapolated to full size show that at speeds of 31-34 m/s they coincide with those of the wobble mode which is found to be efficiently coupled to the aerodynamic excitation.     

带功率因数补偿的单相半控桥整流器(一)

介绍了绘制正弦线电流的开关模式单相半控桥整流器,用它来获得功率因数补偿并保持直流环节电压的恒定.在该整流器中使用4个有源开关,以便在交流端电压上产生单极脉宽调制(PWM)电压波形.与中性点箝位变流器(NPC)相比,该整流器没有箝位二极管也能实现三点式PWM控制.控制电路采用两个控制回路:外部控制回路用比例积分电压控制器调整直流环节电压,采用相位闭环电路产生与电源电压同相的正弦波形来实现功率因数补偿.在内部控制回路中,用基于载波的电流控制器跟踪线电流信号.为补偿由于负载变化所引起的中点电压,控制电路采用中点电压补偿器.该整流器的交流侧可产生3个电压电平,并用计算机仿真与试验结果验证了控制算法的有效性.     

The shoaling of nutrient-enriched subsurface waters as a mechanism to sustain primary productivity off Central Baja California during El Niño winters

Using CalCOFI data for coastal shallow stations (above 100 m depth), higher than expected nitrate concentrations were detected in near-surface high-temperature waters off of Central Baja California during some El Niño winters. Though recent data are not available for Central Baja California, past El Niño data, though limited, showed nitrate concentrations above 16 μM at temperatures above 16 °C, and nitrate concentrations between 1 and 2 μM at 19 °C, while the previously established relationship of temperature and nitrate for California Current waters predicts nitrate depletion above 14 or 15 °C. The anomalous, high temperature–high nitrate enrichment events documented in Central Baja California were detected as shallow as 9 m and as deep as 73 m, were associated with low-oxygen (between 2 and 4 ml/l) and high-salinity (between 33.8 and 34.3 psu) waters, and occurred during the winter months of an El Niño year. Using recent data for San Diego, CA, similar but weaker enrichment events were detected for the El Niño winter of 1997–1998. The periodic shoaling of a subsurface subtropical water mass of high temperature, high salinity, low oxygen and high nutrients during some El Niño winters is proposed to cause periodic enrichment and to maintain productivity during warming events in this area. Enrichment events were not detected off Ensenada, in Northern Baja California, possibly due to the amplification of the onshore flow during El Niño there, or due to the Ensenada front. The proposed mechanism of periodic enrichment of nutrient-depleted surface waters during some El Niño winters by subsurface waters from the California Undercurrent may explain the following: (1) survival of giant kelp forests at their southern limit in Central Baja California documented during past El Niño events in warm waters, (2) the rapid recovery and high carrying capacity of giant kelp documented after the mass disappearance during El Niño 1997–1998, and (3) the increase in the extent of mesotrophic chlorophyll detected in the area during the 1997–1998 and 1982–1983 El Niño events.     

Shipping and investment incentives: a trilogy Part 3. The effectiveness of investment incentives for shipping—the UK experience 1950-1987

This paper concentrates on the determinants of investment and examines both theoretical and empirical work on the investment function. The major determinants are considered and a case study of the United Kingdom shipping industry in the period 1963-1987 is undertaken. The analysis is unable to find any real link between the value of the investment incentives packages available to the UK shipping industry and the size of the UK fleet during this period. The conclusion follows that while financial factors (e.g. favourable credit arrangements) or individual components (e.g. investment grants) of fiscal packages may influence the decision to invest, the total package has not affected the level of shipping investment in the manner expected.     

Performance estimation model of a torque converter part I: Correlation between the internal flow field and energy loss coefficient

The objective of this paper is to improve the performance estimation model of the internal flow field of a torque converter. Compared with performance experiment results, the converter based on the one-dimensional model does not satisfy the performance requirements demanded in practice. Therefore, we need to develop more predictable and reliable performance estimation models. In order to obtain shape information on three-dimensional blade geometry, a process of reverse engineering conducts a torque converter assembly, impeller, turbine and stator. In addition, a CFD simulation including mesh generation and post-processing was carried out to extract equivalent parameters from the internal flow field. The internal flow field can be explained by analyze the correlation between a performance estimation model and CFD analysis. The equivalent performance model adopts the variation of energy loss coefficients for a given operating condition according to the application of a changing energy loss coefficient by the least mean squares method. The estimated equivalent model improves the agreement in performance between experiments and the theoretical model. This model can reduce the error to within about 3 percent. Furthermore, this procedure for predicted performance achieves eminence in the estimation of the capacity factor.     

Simulation of city bus performance based on actual urban driving cycle in China

This paper establishes the simulation model of a city bus on the basis of the EQ6110 bus prototype and its experimental data. According to the actual urban driving cycle, the fuel economy and the traction performance of the EQ6110 city bus have been simulated, and factors such as the driving cycle, the loss of power to engine accessories, the gear-shifting strategy, the fuel shut-off strategy of the engine, etc., which influence on the bus’s fuel economy, are also quantitatively analyzed. Some conclusions are drawn as follows: (1) driving cycles have a great influence on the fuel economy of a city bus; (2) under the typical urban driving cycle of the public bus in China, the engine fuel shut-off strategy can save about 1 to 1.5 percent of the fuel consumption; and (3) the optimized gear-shifting rules can save 6.7 percent of the fuel consumption. Experimental results verify that the fuel economy for the EQ6110 public bus is improved by 7.2 pecent over the actual Wuhan urban driving cycle of the current public bus in China.     

Lane-following method for high speed autonomous vehicles

This paper presents a steering control method for lane-following in a vehicle using an image sensor. With each image frame acquired from the sensor, the steering control method determines target position and direction, and constructs a travel path from the current position to the target position either as an Arc-path or S-path. The steering angle is calculated from the travel path thus generated, and the vehicle follows the travel path via motor-control. The method was tested using a vehicle dubbed as KAV (Korea Autonomous Vehicle) along an expressway (Seoul Inner Beltway) trajectory with a variety of radii (50 m ∼ 300 m) while traveling at a speed of 60 km/h to 80 km/h. Compared with an experienced human driver, the method showed little much difference in performance in terms of lane-center deviation. The proposed method is currently employed for high speed autonomous driving as well as for stop and go traffic.     

Distributed support modelling for vertical track dynamic analysis

The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pinned–pinned’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.     

垂直及斜出水流场的二维及三维TR-PIV试验

本文对钝头回转体垂直及斜出水流场采用TR-(Time-Resolved)PIV技术进行测量,并对斜出水流场进行3D-Stereo PIV(三维体视 PIV)测量.文中介绍了测试技术及测量结果,揭示了出水过程中流动结构及其演变,展示了TR-PIV技术对具有瞬态历程特征的出水流场研究的适应性.