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장지욱(Jee-Uk Chang),안형준(Hyeong-Joon Ahn),이길용(Gil-Yong Lee),한동철(Dong-Chul Han) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
A negative-stiffness mechanism (NSM), which varies the stiffness of spring by adjusting compression force to column or leaf spring, offers an advantage for the passive isolation system. This paper presents optimal design of the NSM for a passive vibration isolator. The optimal shape of the spring is determined through solving several governing formula that are specified by material strength, buckling, target natural frequency. Thickness, minimum length and compression force of the notched column or leaf spring are expressed explicitly by key design parameters like spring width, material strength, maximum displacement, etc. Using this method, we can design a desired NSM systematically.
이길용(Gil-Yong Lee),장희도(Hee-Doh Jang),장지욱(Jee-Uk Chang),한동철(Dong-Chul Han) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The vibration isolator using negative stiffness mechanism(NSM) which shows very low natural frequency could be designed by applying axial compressive forces to the beam-column springs. In this paper the design specifications of NSM passive vibration isolator are investigated. A commercial NSM vibration isolator has little damping, so the constrained layer damping(CLD) with viscoelastic materials which could give effective damping characteristic to the system is suggested. The beam-column springs show structural damping characteristics depending on the mechanical properties and the geometries of the added viscoelastic materials. The design specifications of the beam-column springs with built-in viscoelastic materials are considered by analytical and experimental approaches. And then also its validity is considered by applying it to the 1 DOF passive vibration isolator.
김성학(Sheng-He Jin),차재은(Jae-Eun Cha),장지욱(Jee-Uk Chang),최상현(Sang-Hyun Choi),안형준(Hyeong-Joon Ahn) Korean Society for Precision Engineering 2020 한국정밀공학회지 Vol.37 No.10
Since sCO₂ (Supercritical Carbon Dioxide) turbomachinery are generally small and operate at high rotational speed, the bearings remain a significant challenge to the design of the turbomachinery for the sCO₂ power cycles. However, a fluid induced instability similar to the oil whirl may occur even with the magnetic bearing under high pressure and high speed conditions of the sCO₂ turbomachinery. This paper presents experimental investigation on the instability of a sCO₂ compressor supported by the magnetic bearing. First, we introduce the sCO₂ compressor supported by the magnetic bearing. The procedure to guarantee the rotordynamic performance of the sCO₂ compressor supported by the magnetic bearing is provided. Then, the effects of the working condition such as the pressure and rotating speed on the fluid induced instability are investigated experimentally. Finally, a strategy to resolve the fluid-induced instability with conventional PID control is proposed and experimentally verified.