• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.835-841
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• 2013

Modern solid-state gyroscopes (HRG) with hemispherical resonators from high-purity quartz glass and special surface superfinishing and ultrathin gold coating become the best instruments for precise-grade inertial reference units (IRU) targeting long-term space missions. Designing of these sensors could be a notable contribution into development of Korea as a space nation. In participial, 40mm diameter thin-shell resonator from high-purity fused quartz, fabricated as a single-piece with its supporting stem has been designed, machined, etched, tuned, tested, and delivered by STM Co. (ATS of Ukraine) several years ago; an extremely-high Q-factor (upto 10~20 millions) has been shown. Understanding of the best way how to match such a unique sensor with inner glass assembly of the gyro means how to use the high potential in a maximal extent; and this has become the urgent task. Inner quartz glass assembly has a very thin indium (In) layer soldered the resonator and its silica base (case), but effects of internal resonances between operational modal pair of the shell-cup and its side (parasitic) modes can notable degrade the potential of the sensor as a whole, instead of so low level of resonator's intrinsic losses. Unfortunately, there are special combinations of dimensions of the parts (so-called, "resonant sizes"), when intensive losses of energy occurs. The authors proposed to use the length of stem's fixture as an additional design parameter to avoid such cases. So-called, a cyclic scheme of finite element method (FEM) and ANSYS software were employed to estimate different combinations of gyro assembly parameters. This variant has no mismatches of numerical origin due to FEM's discrete mesh. The optimum length and dangerous "resonant lengths" have been found. The special attention has been paid to analyses of 3D effects in a cup-stem transient zone, including determination of a difference between the positions of geometrical Pole of the resonant hemisphere and of its "dynamical Pole", i.e., its real zone of oscillation node. Boundary effects between the shell (cup) and 3D short "beams" (inner and outer stems) have been ranged. The results of the numerical experiments have been compared with the classic model of a quasi-hemispherical shell band with inextensional midsurface, and the solution using Rayleigh's functions of the $1^{st}$ and $2^{nd}$ kinds. To guarantee the truth of the recommended sizes to a designer of the real device, the analytical and FEM results have been compared with experimental data for a party of real resonators. The consistency of the results obtained by different means has been shown with errors less than 5%. The results notably differ from the data published earlier by different researchers.

• Ocean and Polar Research
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• v.30 no.3
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• pp.361-372
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• 2008

A satellite tracked drifter experiment was conducted to observe thermal structure and surface circulation in the northeastern East China Sea. For this experiment, four ADOS buoys, assembled with surface float and thermister chain, were deployed on August 2007 in southern Jeju-do, where the Kuroshio Branch Current is separated from the main stream. Thermal structure in the upper layer of the northeastern East China Sea was successfully observed during the following $1{\sim}3$ months. Strong thermo-haline front in a northeast-southwest direction was observed. In the frontal zone, warm and saline Kuroshio origin water intermixes with fresher coastal water and flows toward the Korean Strait. Typhoon Nari, which passed over the East China Sea 20 days after commencement of study, caused distinct signals in the thermal structure and trajectory of buoys. During the typhoon, surface temperature abruptly dropped to about $4^{\circ}C$, while the thermocline formed at $30{\sim}50$ m depth vanished due to strong vertical mixing. Internal inertial oscillation occurred several days after the typhoon. The fortuitous occurrence of typhoon Nari showed that ADOS buoys can provide useful and accurate air-sea interaction data during typhoons.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.573-580
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• 2021

Paraffin wax is attracting many attentions for promising solid fuel of hybrid rocket because of its higher regression than other fuels. However, even with paraffin fuel combustion, unsteady low-frequency oscillation of combustion pressure is still observed. And, this is related to the formation of liquid layer and the entrainment of fuel droplets entering the axial combustion gas flow. This study investigates the effect of additional combustion of fuel droplets on the occurrence of low-frequency combustion instability. On the other hand, the formation of fuel droplets depends on Weber Number (the ratio of the inertial force to the surface tension of the liquid) and Reynolds Number of the oxidizer flow. Therefore, a laboratory-scale hybrid rocket was used to monitor the occurrence of combustion instability while changing We number. A series of combustion tests were conducted to control We number by changing the oxidizer flow rate or adding LDPE (low density polyethylene) to base fuel. In the results, it was confirmed that there is a critical We number above which the low-frequency combustion instability occurs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.380-388
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• 2016

Using the magnet gear, it is possible to transmit power without mechanical contact. As the drive shaft in a magnet gear-based speed reducer system is isolated from the drive shaft, the system is a two-inertia resonance system that should cope with an external load with the limited air-gap stiffness. On the other hand, the drive shaft or low-speed side is controlled only by the torque of the drive shaft through an air-gap, and the excessive oscillation or the slip can then be generated because of an abrupt disturbance that is different from the general mechanical gear system. Therefore, the disturbance loaded at the low speed side should be measured or estimated, and considered in the control of the driving shaft. This paper proposes a novel full-state feedback controller with a reduced-order observer for the speed reducer system using a magnet gear with a unified harmonic modulator. The control method was verified by simulation and experiment. To estimate the load at the low speed side, a novel observer was designed, in which the new state variable is introduced and the new state equation is formulated. Using a full-state feedback controller including the observer, the test result against disturbance was compared with two D.O.F PI speed controllers. The pole slip was compensated within relatively a short time, and the simulation result about the estimated variable shows a similar tendency to the test result. The test results showed that the magnet gear-based reducer can be applied to an accurate servo system.