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.844 北京科技大学学报 第29卷 2005,15:2083 with self-test.Sens Actuators A.2001.92:161 [13]Aikele M.Bauer K.Ficker W.et al.Resonant accelerometer Air damping in micro beam resonators FENG Chuang2,ZHAO Yapu,LIU Dongqing2) 1)State Key Laboratory of Nonlinear Mechanics (LNM).Institute of Mechanics.Chinese Academy of Sciences,Beijing 100080.China 2)Applied Science School.University of Science and Technology Beijing Beijing 100083.China ABSTRACI To research the effect of air damping on resonators,based on the Euler Bernoulli assumption, beam vibration mechanism and air damping theory,a vibration equation was established and its solution was ob- tained according to corresponding boundary conditions.The air damping influences on the resonant frequency and quality factor of a micro-beam resonator were obtained under two different conditions.By analyzing air damping in two different ways,it is found that a critical squeeze film thickness exists under the condition that the aspect ratio of the beam is constant,and the obtained expression of critical thickness can give some sugges- tions to devices designing. KEY WORDS micro-beam resonator;air damping:resonant frequency quality factor (上接第821页) Effect of nozzle outlet angle on the fluid flow and level fluctuation in a bloom casting mould WANG Weiwei),ZHANG Jiaquan,CHEN Suqiong?,DONG Jinming2) 1)Metallurgical and Ecological Engineering School,University of Science and Technology Beijing.Beijing 100083.China 2)Jianlong Iron and Steel Holding Company.Beijing 100070.China ABSTRACI Based on the coupled model of turbulence and multiphase fluid flow,the flow behavior with free surface fluctuation in a bloom casting mould was numerically simulated.The influence of nozzle outlet angle on the fluid flow and free surface oscillation in the mould was analyzed.The results show that when the dow nw ard nozzle outlet angle increase by 5,the impinging spots descend by 13mm and 10mm at the wide faces and nar- row faces respectively.At a given submergence depth of 100 mm,outlet angle show limited influence on the fluctuation within 3mm.The fluid close to mould wall is more active than that close to nozzle.The nozzle outlet angle of 20is recommended to use. KEY WORDS mould;bloom;fluid flow free surface fluctuation200515：2083 ［13］ Aikele MBauer KFicker Wet al．Resonant accelerometer with self-test．Sens Actuators A200192：161 Air damping in micro-beam resonators FENG Chuang 12）ZHAO Y apu 1）LIU Dongqing 2） 1） State Key Laboratory of Nonlinear Mechanics （LNM）Institute of MechanicsChinese Academy of SciencesBeijing100080China 2） Applied Science SchoolUniversity of Science and Technology BeijingBeijing100083China ABSTRACT To research the effect of air damping on resonatorsbased on the Euler－Bernoulli assumption beam vibration mechanism and air damping theorya vibration equation was established and its solution was obtained according to corresponding boundary conditions．The air damping influences on the resonant frequency and quality factor of a micro-beam resonator were obtained under two different conditions．By analyzing air damping in two different waysit is found that a critical squeeze-film thickness exists under the condition that the aspect ratio of the beam is constantand the obtained expression of critical thickness can give some suggestions to devices designing． KEY WORDS micro-beam resonator；air damping；resonant frequency；quality factor （上接第821页） Effect of nozzle outlet angle on the fluid flow and level fluctuation in a bloom casting mould WA NG Weiwei 12）ZHA NG Jiaquan 1）CHEN Suqiong 2）DONG Jinming 2） 1） Metallurgical and Ecological Engineering SchoolUniversity of Science and Technology BeijingBeijing100083China 2） Jianlong Iron and Steel Holding CompanyBeijing100070China ABSTRACT Based on the coupled model of turbulence and multiphase fluid flowthe flow behavior with free surface fluctuation in a bloom casting mould was numerically simulated．The influence of nozzle outlet angle on the fluid flow and free surface oscillation in the mould was analyzed．The results show that when the downward nozzle outlet angle increase by5°the impinging spots descend by13mm and10mm at the wide faces and narrow faces respectively．At a given submergence depth of 100mmoutlet angle show limited influence on the fluctuation within3mm．The fluid close to mould wall is more active than that close to nozzle．The nozzle outlet angle of 20°is recommended to use． KEY WORDS mould；bloom；fluid flow；free surface fluctuation ·844· 北 京 科 技 大 学 学 报 第29卷