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Altitude has a significant effect on combustion of heavy-duty diesel engines, especially during cold start. An experimental study on a heavy-duty diesel engine operating at different altitudes was conducted. Tests were based on a direct injection (DI) turbocharged diesel engine with intake and exhaust pressure controlled by the plateau simulation test system to stimulate altitude conditions including 0 m, 1000 m, 2000 m, 3000 m and 4000 m. Results indicated that the compression and expansion resistance moment reduced and the speed increased during the cranking period. The peak pressure of several cycles was increased during the start-up period; however, the expansion pressure dropped more and the indicated mean effective pressure (IMEP) reduced as the altitude rose. While at an altitude of over 2000 m, the peak pressure fluctuated obviously during the start-up period. The higher the altitude was, the more the fluctuation amplitude and cycle number increased and combustion instability enhanced, which resulted the start-up period time increasing at high altitude. When the altitude rose, the cycle-to-cycle variation of the peak pressure and speed fluctuation increased during the idle, the ignition and CA50 were delayed and the combustion duration was shortened. The effect of altitude on combustion characteristics of the diesel engine was more significant during the start-up period than during its idle period.
Recently, there is a strong demand for high power conversion system in power electronics area especially in photovoltaic (PV) power conditioning system (PCS), wind power generation, and fuel cell power generation system. However, there is a limit in increasing power level mainly due to the limitations in switching device's voltage and current rating. One way to solve this problem is to connect power converters in parallel. Parallel operation of inverter has many advantages such as modularity, ease of maintenance, (n+1) redundancy, high reliability, etc. This paper presents parallel operation of voltage-fed-trans-Z-source inverter. A 2.6 ㎾ prototype inverter is built and tested to verify performances of the proposed inverter.
One solution to the low specific power of hybrid electric vehicular batteries is a hybrid energy storage system (HESS) that takes advantage of the high specific power performance of ultra-capacitors. The design of a type of zero current transition (ZCT) soft switching bidirectional direct current-direct current (DC-DC) power converter that can be used as an ultra-capacitor-battery interface in an active parallel schema of a HESS is described. The circuit operation of the ZCT DC-DC power converter is depicted in detail. The HESS controller is designed as a two-layered hierarchical control structure: the first layer is responsible for working mode control of the HESS, and the second layer is responsible for DC-DC power converter control in which a fuzzy logic PID algorithmis employed. Simulation results indicate that this design is a potential solution to the problem of the low specific power of batteries, especially for regenerative braking and electric motor assist. The proposed active parallel schema with ZCT exhibits a significant advantage in power and energy decoupling. HESS with ZCT achieves better efficiency compared to the battery only operation. The experimental results validates the idea that the ultra-capacitor cooperates with the battery in acceleration mode.
This paper develops a two-stage method for structural damage identification by using modal data. First, the Residual Force Vector (RFV) is introduced to detect any potentially damaged elements of structures. Second, data of the frequency domain are used to build up the objective function, and then the Imperialist Competitive Algorithm (ICA) is utilized to estimate damaged extents. ICA is a heuristic algorithm with simple structure, which is easy to be implemented and it is effective to deal with high-dimension nonlinear optimization problem. The advantages of this present method are: (1) Calculation complexity can be decreased greatly after eliminating many intact elements in the first step. (2) Robustness, ICA ensures the robustness of the proposed method. Various damaged cases and different structures are investigated in numerical simulations. From these results, anyone can point out that the present algorithm is effective and robust for structural damage identification and is also better than many other heuristic algorithms.