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Liming Song,Jun Li,Kesong Wen 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.1
Aerodynamic performance of partial admission dual row control stage at the rated and off-designed operating conditions was numericallyinvestigated using three-dimensional Reynolds-averaged Navier-Stokes (RANS) and k -e turbulence model. The full scale computationalmodel includes the four nozzle boxes, full first and second row rotor blade, as well as two admission guided vanes with considerationof the rotor tip clearance and stator diaphragm gland. The numerical results of the mass flow rate, power output and aerodynamicefficiency of the dual row control stage at the rated and off-designed conditions are well in agreement with the experimental data. The obtained results at rated condition show that the blocking segmental arc of guided vane increased the exit pressure of the upstreamnozzle, which reduced the mass flow rate and changed the aerodynamic performance of the nozzle. The circumferential non-uniformityof aerodynamic parameters and partial admission losses increases with the decrease in the admission degree for the computed three operatingconditions. The analysis of axial steam velocity shows that the trailing shedding vortex and the complex flow vortex in flow passageshave a significant impact on the magnitude and direction of the axial steam velocity. Furthermore, the partial admission degreechanged the proportions of the power output of two rotor blade rows. The lower partial admission degree leads to a larger proportion ofthe power output of the first rotating blade row. The detailed flow pattern in the partial admissions dual row control stage at differentoperating conditions is also illustrated.
Vulnerable Path Attack and its Detection
( Chuyu She ),( Wushao Wen ),( Quanqi Ye ),( Kesong Zheng ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.4
Application-layer Distributed Denial-of-Service (DDoS) attack is one of the leading security problems in the Internet. In recent years, the attack strategies of application-layer DDoS have rapidly developed. This paper introduces a new attack strategy named Path Vulnerabilities-Based (PVB) attack. In this attack strategy, an attacker first analyzes the contents of web pages and subsequently measures the actual response time of each webpage to build a web-resource-weighted-directed graph. The attacker uses a Top M Longest Path algorithm to find M DDoS vulnerable paths that consume considerable resources when sequentially accessing the pages following any of those paths. A detection mechanism for such attack is also proposed and discussed. A finite-state machine is used to model the dynamical processes for the state of the user`s session and monitor the PVB attacks. Numerical results based on real-traffic simulations reveal the efficiency of the attack strategy and the detection mechanism.