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31.
The Stirling engine is an environmentally friendly external combustion heat engine and reduces the complexities of the combustion process, and indirectly helps in reduction of CO2 emission. Modelling based on cyclic analysis is performed for a Beta configuration Stirling engine of 1.5?kWe capacity using a rhombic drive for the solar-dish-supported Stirling engine. The analysis helps in estimating the overall efficiency of the system using the experimental correlation of the solar concentrator ARUN160 at the engine operating temperature. The analysis shows that the system will have overall efficiency around 25% in the range of 750–1050?K at the expansion space. The degradation of performance compared to that at an operating temperature of 1025?K is only marginal and makes 750?K a more preferred temperature. The present study evaluates a range of possible design goals and provides suitable alternatives and thus provides a clear understanding of the system design considerations. 相似文献
32.
Current EU regulation restricts continuously reviewing X-ray images of passenger baggage to 20-min duration as a precautionary measure to prevent performance decrements in airport security officers (screeners). However, this 20-min limit is not based on clear empirical evidence on how well screeners can sustain their performance over time. Our study tested screeners in a 60-min simulated X-ray cabin baggage screening task. One group took 10-min breaks after 20 min of screening; the other group worked without breaks. We found no decrease in performance over 60 min in either group. Breaks did not affect performance, but they did reduce the amount of subjective distress. By varying target prevalence, we found that da with a slope of about 0.6 is a more valid measure of detection performance than d'. Target prevalence caused a criterion shift. Our results provide a basis for conducting field studies of prolonged screening durations, and open the discussion on whether more flexible break policies and work schedules should be considered. 相似文献
33.
This article presents an improved cuckoo search (ICS) algorithm based on the parametric adaptation mechanism and non-uniform mutation. In the ICS algorithm, the biased random walk operator is modified to take advantage of the neighbourhood information of the current solution, and then the control parameters of step size, discovery probability and scaling factor are directly integrated into the optimized problems. Meanwhile, the non-uniform mutation operation is used to adaptively tune the search step of the current optimal solution. To evaluate the feasibility and efficiency of the presented algorithm, three groups of benchmark test functions are employed to perform the validation analysis. Subsequently, to diagnose the vibration fault of a hydroelectric generating unit, a combinational model is built, which combines ICS with a back-propagation neural network (ICSBP). The experimental results indicate that ICS is competitive on the optimization problems, and the ICSBP approach can effectively improve the accuracy of vibration fault diagnosis for a hydroelectric generating unit. 相似文献
34.
M. Sanchiz F. Amadieu P.-V. Paubel A. Chevalier 《Behaviour & Information Technology》2020,39(10):1094-1109
ABSTRACT This study investigates how a search interface that displays users’ ultimate query (i.e. users’ current search goal) can cope with the age-related decrease of fluid abilities and support older users’ search behaviours. 30 young and 18 older adults completed 9 search problems with a regular web browser or with the experimental search interface. Results showed that older adults spent longer time on the search engine result pages, they needed more time to reformulate, and they had more difficulties exploring the search paths elaborated. Age-differences also appeared as soon as the beginning of the search. The support tool helped older users reformulate their queries more rapidly and elaborate more flexible search strategies at the beginning of the activity. Indeed, older adults who interacted with the support tool switched to the processing of a new search path more rapidly instead of exploiting their initial query (i.e. they visited fewer websites for the initial query produced and reformulated a query instead of keeping on conducting a deeper investigation of the search results provided in the search engine result page). Implications of these findings for the design of effective support tools for older users are discussed. 相似文献
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37.
基于AVL-EXCITE软件搭建了YC12VC发电用高速柴油机轴系动力学模型,其模拟值与试验值吻合性较好,验证了该模型可以较好地模拟不同工况条件下轴系的运动情况。基于平衡性和均匀发火等原则,设计了8种不同的发火顺序,并针对轴承受力、轴承润滑、轴系扭振和转速不均匀性开展影响规律研究。结果表明:通过发火顺序的优化,在保证最大主轴承负荷和最小油膜厚度满足设计要求的前提下,标定工况下的曲轴扭振总振幅从0.465°降低到0.259°,转速不均匀系数从0.018降低到0.009。 相似文献
38.
基于典型故障案例的阐述和故障原因分析,归纳总结了船舶柴油机燃油系统在日常使用和管理中应注意的问题,可为船舶操作人员和管理人员提供参考。 相似文献
39.
G.M. Kosmadakis D.C. Rakopoulos C.D. Rakopoulos 《International Journal of Hydrogen Energy》2021,46(34):17955-17968
The cyclic variability in a spark-ignition (SI) engine is examined fueled with methane/hydrogen blends with the use of an in-house computational fluid dynamics (CFD) code. A recent methodology is followed, which has been developed with the main aim at providing accurate predictions of the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) in a fraction of time. Instead of simulating several tens of engine cycles, the methodology is based on the numerical results obtained from just 5 cycles, which are then processed for developing suitable fitted correlations of the main parameters as a function of a normalized distance. The latter expresses the distance of the spheres of the initial flame within the computational cell at the spark-plug region with the local turbulent eddy, and provides a smooth transition from the laminar burning regime to the fully turbulent one. This sub-model is included in the ignition numerical approach and is applied here in a SI engine with 3 different hydrogen contents, 10%, 30% and 50%, and three equivalence ratios, 1, 0.8 and 0.7, showing that the COV of IMEP is well predicted compared to the available measured data. Other parameters of engine cycle variations are also examined, such as the distribution of the IMEP. The variability of NO (nitric oxide) emissions is also examined, showing that for the stoichiometric cases it follows a distribution similar to a normal (Gaussian) one, while for lower ratios it is positively skewed. Overall, the methodology seems to provide reliable results for the whole range of the operating conditions examined, while the next steps of this activity will focus on similar cases for engine with variable speed and load, with the final goal to include additional mechanisms that contribute to the engine cycle variations. 相似文献
40.
Makoto Koike Tetsunori Suzuoki Tadashi Takeuchi Takayuki Homma Satoshi Hariu Yoshitaka Takeuchi 《International Journal of Hydrogen Energy》2021,46(50):25689-25698
This work demonstrated the first-ever cold-start operation of an ammonia (NH3)-fueled four-cylinder spark ignition engine with an on-board fuel reformer, applying autothermal reforming. In this system, an electrically heated NH3-air mixture was provided to a reforming catalyst and approximately 3 s was found to elapse between the start of engine rotation and the onset of combustion. Stable fast idle operation in conjunction with a cold start was realized with a H2-to-NH3 molar ratio of 2:1. Nearly zero NH3 emissions were achieved during cold start and fast idle until the engine warmed up, by adsorbing unburned NH3 passing through a three-way catalyst before the catalyst was sufficiently warmed up. The NH3 adsorption capacity of this system could be regenerated during the engine warm-up when the engine was running under lean conditions. 相似文献