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EVOLUTION OF A MASS ACCRETING PROTOSTAR OF ONE SOLAR MASS UNDER QUASI-HYDROSTATIC EQUILIBRIUM
HONG SIK YUN 한국천문학회 1978 天文學會報 Vol.3 No.-
The evolutionary tracks of a protostar of one solar mass under quasi-hydrostatic equilibrium are computed with mass-accretion time scales of 10^3,10^4,10^5 and 10^6 years, and their resulting behaviors in the H-R diagram are discussed. It is found that there exists a critical time scale of mass accretion, which reverses the course of their evolutionary tracks. A value of the critical time scale appears to lie between 10^3 and 10^4 years. The physical cause for the presence of the critical time scale is discussed. Finally, it is proposed that star formation requires at least several 10^3 years before any star is born out of dark dense interstellar clouds.
Analysis on Torque, Flowrate, and Volumetric Displacement of Gerotor Pump/Motor
Hongsik Yun,Young-Bog Ham,Sungdong Kim 유공압건설기계학회 2020 드라이브·컨트롤 Vol.17 No.2
It is difficult to analytically derive the relationship among volumetric displacement, flowrate, torque, and rotation speed regarding an instantaneous position of gerotor hydraulic pumps/motors. This can be explained by the geometric shape of the rotors, which is highly complicated. Herein, an analytical method for the instantaneous torque, rotation speed, flowrate, and volumetric displacement of a pump/motor is proposed. The method is based on two physical concepts: energy conservation and torque equilibrium. The instantaneous torque of a pump/motor shaft is determined for the posture of rotors from the torque equilibrium. If the torque equilibrium is combined with the energy conservation between the hydraulic energy of the pump/motor and the mechanical input/output energy, the formula for determining the instantaneous volumetric displacement and flowrate is derived. The numerical values of the instantaneous volumetric displacement, torque, rotation speed, and flowrate are calculated via the MATLAB software programs, and they are illustrated for the case in which inner and outer rotors rotate with respect to fixed axes. The degrees of torque fluctuation, speed fluctuation, and flowrate fluctuation can be observed from their instantaneous values. The proposed formula may provide a better understanding of the design or analysis process of gerotor pumps/motors.