A Mathematical Model for Driver Steering Control, with Design, Tuning and Performance Results

A mathematical model for the steering control of an automobile is described. The structure of the model derives from linear optimal discrete time preview control theory but it is non-linear. Its parameter values are obtained by heuristic methods, using insight gained from the linear optimal control theory. The driver model is joined to a vehicle dynamics model and the path tracking performance is demonstrated, using moderate manoeuvring and racing speeds. The model is shown to be capable of excellent path following and to be robust against changes in the vehicle dynamics. Application to the simulation of manoeuvres specified by an ideal vehicle path and further development of the model to formalise the derivation of its parameter values and to put it to other uses are discussed.     

Technical Note: RMS Values for Control Force, Suspension Stroke and Tyre Deflection in an Active Suspension

Expressions are derived for the numerical computation of rms values for control force, suspension stroke and dynamic tyre deflection in a quarter-car vehicle model on a random road of given roughness. A quadratic performance index is employed and the effects of the assumed weighting factors on the rms values and overall static stiffness determined.     

Lateral dynamics of motorcycles towing single-wheeled trailers

A motorcycle towing a single-wheel trailer may provide useful transport for light cargo on narrow tracks and off-road use, particularly in rural areas of developing countries. Four designs of such trailers are described. Linear models are derived for the lateral dynamics of an off-road motorcycle towing this type of trailer straight ahead at constant speed. The trailers were tested behind an instrumented motorcycle. Linear autoregressive models were fitted to the experimental data using system identification techniques. Analytical and experimentally derived models largely agreed on frequency, damping and shape of the weave, wobble and trailer sway normal modes. The trailers made the motorcycle's steering heavier but the analytical models did not predict this. The location of the articulation axes between the motorcycle and the trailer were found to be critical for stability. The best trailer design handled well with loads up to 200 kg and speeds up to 70 km/h.     

MTU396系列柴油机在铁路上的应用

德国ＭＴＵ公司生产的３９６系列柴油机广泛应用于铁路电传动和液力传动内燃机车，内燃动车以及用于列车供电的发电车，至今已售出１６００多台，其中累计工作时间最长的已超过９００００ｈ。文中介绍了该系列柴油机的主要设计特点以及最近所作的技术改进，列举了若干该系列发动机的典型应用实例。     

Evaluation of two atmospheric models for wind–wave modelling in the NW Mediterranean

The NW Mediterranean experiences, as illustrated by the last decade, strong and rapidly varying storms with severe waves and winds. This has motivated a continuous validation of models and the efforts to improve wave and wind predictions. In this paper we use two atmospherics models, MASS (from SMC-Meteorological Office of Catalunya) and ARPEGE (from Météo-France), to force two third generation wave models: WAM and SWAN. The evaluation and comparison has been carried out for two severe storms registered in November 2001 and March–April 2002.The ARPEGE and MASS models predicted higher 10 m wind speeds than coastal meteorological stations, a fact attributed to local land influences. Regarding the 10 m wind direction, models do not present large differences, although considerable deviations from recorded data were found during some dates. ARPEGE presents less scatter and lower errors than MASS when compared with QuikSCAT data.The 10m wind fields from both atmospheric models were used to force the two selected wave models and analyse the errors and sensitivities when predicting severe wave storms. The wave model simulations show some interesting results; during the storm, the spatial wave pattern using ARPEGE showed a higher maximum, although the values of significant wave height at the buoys were lower than the ones forced by MASS (with both WAM and SWAN). The SWAN simulations show a better agreement in predicting the growing and waning of the storm peaks. The prediction of mean period was improved when using the ARPEGE wind field. However the underestimation by SWAN due to the large energy at high frequencies was evident. Validation of spectral shape predictions showed that it still has considerable error when predicting the full frequency spectra. The storms showed bimodal spectral features which were not always reproduced by wave models and are likely to be responsible for part of the discrepancies.     

Experimental study of controlling tip clearance flow in a pump-jet propulsor北大核心CSCD

[Objective]This paper aims to suppress the adverse effects of tip clearance flow on the hydrodynamic performance and unsteady excitation force of a pump-jet propulsor. [Method]As for the pre-swirl stator pump-jet propulsor, an annular flexible seal structure closely matched with a rotor tip ring is used to study the validity of suppressing the clearance flow on the rotor tip. The rotor thrust and torque of the propulsor are measured by keeping the shroud approximately rigidly fixed, enabling the rotor open water efficiency to be obtained. In addition, the point of cavitation inception at each design condition is observed and recorded carefully with the help of a high-power stroboscope, and the cavitation inception curves of the propulsor with/without tip clearance are obtained through calculation. Finally, tests of shaft vibration acceleration on the pump-jet propulsor with/without tip clearance are conducted under conditions of cavitation and non-cavitation in order to evaluate the effects of diminishing tip clearance. [Results]The results show that the thrust and torque of the rotor of the pump-jet propulsor with a flexible seal structure are significantly increased, which in turn renders open water efficiency significantly increased at low and medium advance coefficients, unchanged near the design point and slightly decreased at the high advance coefficient. Moreover, the cavitation performance of the pump-jet propulsor without clearance is better at a wide range of advance coefficient, 0.85 相似文献   

Integrating natural and socio-economic science in coastal management

The future more sustainable management of coastal resources is an important policy goal for all governments of countries with coastlines. Coastal areas are under intense environmental change pressure with extensive feedback effects between the natural systems and the human systems. It could be argued that there is just one jointly determined and coevolving system that needs to be studied and managed. Understanding the interactions between the coastal zone and environmental change cannot be achieved by observational studies alone. Modelling of key environmental and socio-economic processes is a vital tool, required to buttress coastal management institutions and practice. Three overlapping procedural stages can be identified in the coastal resource assessment process. The scoping and auditing stage, implemented via a ‘pressure–state–impact–response’ framework, details, among other thing, problems, system boundaries and value conflicts. The framework is itself based on a conceptual model, which lays stress on functional value diversity and the links between ecosystem processes, functions and outputs of goods and services which are deemed ‘valuable’ by society. The two subsequent stages are integrated modelling, combining natural and social science methodologies, and evaluation of management options and related gains and losses. An overview of a research project, which utilised the pressure–state–impacts–response (P–S–I–R) framework and supporting concepts and methods, is presented in the last section of the paper, together with some generic ‘lessons’ for interdisciplinary research.     

合拢弯矩作用下复合材料曲梁突变屈曲的研究

研究了复合材料曲梁在受到合拢弯矩作用下发生的屈曲情况,并给出一种理论解析方法来分析这种很可能发生在复合材料弯曲结构中的脱层耦合屈曲问题.该方法是基于曲梁大变形理论及断裂力学而提出来的.文中并用该解析方法分析了一个特定的常见的情况,在该题例中脱层发生在非常靠近内表面处并且突变屈曲就发生在该薄脱层.在文中也对脱层裂纹的弧角对极限载荷的影响进行了研究.     

Time series for sea water and seaweed of Tc and Sb originating from releases at La Hague

⁹⁹Tc and ¹²⁵Sb have been released in low level liquid waste at the reprocessing plant at La Hague (Fr). Over a number of years data have been obtained on the concentration of ⁹⁹Tc in sea water and in seaweed from sampling locations close to and at increasing distances north and east of the point of release into the English Channel.In addition such data have been obtained on ¹²⁵Sb for a small number of sampling points. These time series, and the information derived from their intercomparison and from comparison with the release data, are presented in this paper.Time series on ⁹⁹Tc as well as ¹²⁵Sb in sea water and seaweed clearly confirm a considerable decrease in release rates at La Hague over the years 1986–1993. Transit times and transfer factors derived from the series are generally in good agreement with the results of modelling efforts. The data do not provide evidence for a time lag between levels of the radionuclides in sea water and those in seaweed longer than a few months.The very high concentration factors for ⁹⁹Tc in brown seaweeds make these seaweeds very useful for environmental monitoring the radionuclide at low release rates and to trace releases in areas remote from the point of release.     

瑞士和其他国家人口稠密城市的无轨电车的现状和未来

瑞士和其他国家正致力于发展现代化的地区和城市公共交通系统.日益增长的交通需要,要求继续在技术、政治、经济和环境等方面对各种有轨和其他交通工具进行试验评价.此外,还对无轨电车的使用条件及今后的发展轨迹进行了分析.