• Wind and Structures
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• v.35 no.1
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• pp.1-20
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• 2022

This research work presents an experimental study's outcomes to reveal the impact of an O-ring on the flow control over a sphere placed in a turbulent boundary layer. The investigation is performed quantitatively and qualitatively using particle image velocimetry (PIV) and dye visualization. The sphere model having a diamater of 42.5 mm is located in a turbulent boundary layer flow over a smooth plate for gap ratios of 0≤G/D≤1.5 at Reynolds number of 5 × 10³. Flow characteristics, including patterns of instantaneous vorticity, streaklines, time-averaged streamlines, velocity vectors, velocity fluctuations, Reynolds stress correlations, and turbulence kinetic energy (), are compared and discussed for a naked sphere and spheres having O-rings. The boundary layer velocity gradient and proximity of the sphere to the flat plate profoundly influence the flow dynamics. At proximity ratios of G/D=0.1 and 0.25, a wall jet is formed between lower side of the sphere and flat plate, and velocity fluctuations increase in regions close to the wall. At G/D=0.25, the jet flow also induces local flow separations on the flat plate. At higher proximity ratios, the velocity gradient of the boundary layer causes asymmetries in the mean flow characteristics and turbulence values in the wake region. It is observed that the O-ring with various placement angles (𝜃) on the sphere has a considerable alteration in the flow structure and turbulence statistics on the wake. At lower placement angles, where the O-ring is closer to the forward stagnation point of the sphere, the flow control performance of the O-ring is limited; however, its impact on the flow separation becomes pronounced as it is moved away from the forward stagnation point. At G/D=1.50 for O-ring diameters of 4.7 (2 mm) and 7 (3 mm) percent of the sphere diameter, the -ring exhibits remarkable flow control at 𝜃=50° and 𝜃=55° before laminar flow separation occurrence on the sphere surface, respectively. This conclusion is yielded from narrowed wakes and reductions in turbulence statistics compared to the naked sphere model. The O-ring with a diameter of 3 mm and placement angle of 50° exhibits the most effective flow control. It decreases, in sequence, streamwise velocity fluctuations and length of wake recovery region by 45% and 40%, respectively, which can be evaluated as source of decrement in drag force.

• Journal of the Korea Furniture Society
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• v.10 no.1
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• pp.57-63
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• 1999

This study was carried out to analyze the relationship between basic physical properties and acoustical characteristics of imported violin wood and to offer the information on raw material procurement and incoming-material quality control to domestic violin makers which have purchased most raw materials from European exporting countries at high expense. Equilibrium moisture content of European spruce with lower specific gravity after the prolonged storage was rather higher than that of European maple with higher specific gravity. The specific gravity of spruce increased with decreasing annual ring width, however, that of narrower annual ring. Increasement in specific gravity enhanced the dynamic Young's modulus of both wood species, but influenced the vibration energy loss by internal friction differently between two species. For dynamic MOE, qurater-sawn spruce was higher than the flat-sawn, but maple showed the reverse directional characteristics. Consequently, it would be well for violin makers to establish the standard for materials and quality control system to assure the quality of their violin products.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.120-126
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• 2013

This paper proposes a novel scheme of fault detection and self-recovery for space-borne dual ring counters subject to transient faults. The considered ring counter is equipped with hardware redundancy, but it has a limited output domain where direct access to the current state is unavailable. We employ the theory of corrective control to detect any transient fault occurring to the counter bits and to realize immediate self-recovery of the ring counter back to the normal state. The structure of the fault-tolerant controller is designed to be minimal regardless of the counter size. To validate the applicability, we implement the proposed system on a commercial FGPA board.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.319-323
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• 2000

A method for miniaturization of microstrip patch antenna without degrading its radiation characteristics is investigated. The ring geometry introduces additional parameters to the antenna that can be used to control its resonance frequency and bandwidth. For a single square ring increasing the size of patch decreases the resonance frequency and bandwidth. To match the antenna to a transmission line and also enhance its bandwidth. the square ring patch is stacked by a square ring patch. The computed results are compared with experiment and good agreement is obtained.

• Journal of Institute of Convergence Technology
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• v.7 no.2
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• pp.13-16
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• 2017

The design of sealing mechanisms of a manual pressure valve was analyzed with FE analysis for a hydrogen fuels charge and discharge system of FCEV. The damage prediction of the O-ring with respect to the material models of rubbers was calculated by the gap analysis of the backup ring and O-ring according to the internal pressure. Two kinds of the rubber material characteristic models were adopted to the O-ring. One was the linear elastic and the other was hyperelastic of Ogden $3^{rd}$ order model. The experimental data of urethane of Shore hardness 90 was utilized to the curve fitting of hyperelastic properties. It was found that the contact pattern of the backup ring was different in two models and the sealing mechanism was better in the case of the hyperelastic characteristic model.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.436-442
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• 2009

This paper describes a study on the design of compact polymer bushing with inner control shield. In the bushing, a high electric stress occurred between field shaper and central conductor by the closely space. Also coaxial cylindrical shield has a great height along the axis to control an electric field. Consequently, all the potentials are raised axially along the field shaper and electric stress is concentrated on a part of the surface of the FRP tube near the upper end of the field shaper. In accordance, the field control can be achieved by means of the designs of such inner control shields. The floating and ring shield designs was decreased electric field concentration at critical parts of the bushing. The shield gaps is formed between field shaper and ring shield. Accordance equipotential lines extend through gaps. As a result, the resulting electrical stress are thus reduced in the range $17{\sim}23%$ in the bushing with floating and ring shield designs. Maxwell 2D simulator based on the boundary element method was also introduced in order to verify the reliability of the polymer bushing. The optimized design uses internal elements for electric stress grading at critical parts of the bushing.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.212-215
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• 2016

In this paper, a 5.08 GHz Ring Voltage Controlled Oscillator(Ring VCO) was implemented using $0.18{\mu}m$ standard CMOS technology. The proposal Ring VCO is 3-stage structure. This research confirmed that the each stage's different transistor size ratio influence the current change and alter power consumption consequentially. This circuit is formed to control the current thereby adding the Current Mirror and to tune the frequency by supplying control voltage. It has an 65.5 %(1.88~5.45 GHz) tuning range. The measured output power is -0.30 dBm. The phase noise is -87.50 dBc/Hz @1 MHz offset with operating frequency of 5.08 GHz fundamental frequency. The total power consumption of Ring VCO is 31.2 mW with 2.4 V supply voltage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.271-272
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.183-184
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• 2011

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.534-539
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• 1986

This paper considers the ring rolling process contorl and treats the problem of controlling the pressure roll and conical roll motion which critically affects final quality of the rolled products. Since the process dynamics reveals nonlinear characteristics and parameter uncertainty, an adaptive control scheme was applied. The results show that this proposed adaptive control scheme can produce rolled rings of closer dimensional tolerances as compared with nonadaptive control system.