• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.565-569
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• 2004

Conventional methods for reducing vibration in engineering designs (i.e. by stiffening or detuning) may be undesirable or inadequate in conditions where size or weight must be minimized or where complex vibration spectra exist. Alloys which combine high damping capacity with good mechanical properties can provide attractive technical and economic solutions to problems involving seismic, shock and vibration isolation. To meet these trends, we have developed a new high damping Fe-17%Mn alloys. Also, the alloy has advantages of good mechanical properties and more economical than any other known damping alloys(1/4 times as cost of non-ferrous damping alloy). Thus, the high damping Fe-17%6Mn alloy can be widely applied to household appliances, automobiles, industrial facilities and power plant components with its excellent damping capacity(SDC, 30%) and mechanical property(T.S 700MPa). It is the purpose of this paper to introduce the characterization of the high damping Fe-17%Mn alloy and the results of retrofit several such applications.

• Smart Structures and Systems
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• v.33 no.1
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• pp.27-39
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• 2024

The effectiveness of conventional tuned liquid dampers (TLDs) in controlling the wind-induced response of tall flexible structures has been indicated. However, the impaired control effect in the detuning condition or a considerably high mass cost of liquid may be incurred in ensuring the high-level serviceability. To provide an efficient TLD-based solution for wind-induced vibration control, this study proposes a serviceability-oriented optimal design method for isolated TLDs (ILDs) and derives analytical design formulae. The ILD is implemented by mounting the TLD on the linear isolators. Stochastic response analysis is performed for the ILD-equipped structure subjected to stochastic wind and white noise, and the results are considered to derive the closed-form responses. Correspondingly, an extensive parametric analysis is conducted to clarify a serviceability-oriented optimal design framework by incorporating the comfort demand. The obtained results show that the high-level serviceability demand can be satisfied by the ILD based on the proposed optimal design framework. Analytical design formulae can be preliminarily adopted to ensure the target serviceability demand while enhancing the structural displacement performance to increase the safety level. Compared with conventional TLD systems, the ILD exhibits higher effectiveness and a larger frequency bandwidth for wind-induced vibration control at a small mass ratio.

• Journal of Wind Energy
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• v.13 no.2
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• pp.13-22
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• 2022

In this study, the resonant motion of a floating offshore wind system due to negative damping was mitigated by peak shaving algorithms of the NREL ROSCO controller, and the decreased gains of the blade pitch controller by the gain detuning method for the floating system was increased to the gains of onshore baseline controller to improve the power performance of the turbine. To check the performance of the controller, the dynamic responses between the existing gain-detuned pitch controller and the ROSCO controller with peak shaving control for an OC4 floating offshore wind system were compared. As a result of DLC1.1 at near-rated wind speed, when peak shaving was applied, the average generator power decreased by 1.9%, but it was confirmed that the standard deviation was reduced and stability was improved with fast pitch regulation. In addition, since peak shaving reduces the maximum thrust of the rotor, was confirmed that not only are the loads of the blades and tower reduced, but the surge motion of the floater is also reduced, and the tension of the mooring lines is reduced.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.3
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• pp.75-84
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• 1999

Systematic studies for the effect of the linewidth enhancement factor, the confinement factor, the internal loss and the cavity length on the single mode gain difference and the frequency detuning are performed for $\lambda$/4 phase shifted DFB lasers above threshold. The above threshold characteristics are mainly determined by the linewidth enhancement factor, not by the confinement factor or the parameter defined by the product of the linewidth enhancement factor and the confinement factor. The normalized internal loss defined by the product of the internal loss and the cavity length mainly determines the above threshold characteristics compared to that of the internal loss or the cavity length alone. The effect of the cavity length on threshold characteristics is larger than that of the internal loss in the case of the same normalized internal loss. The above threshold characteristics of quantum well lasers are more resistant to the variations of the confinement factor and the normalized internal loss than those of bulk lasers due to the small linewidth enhancement factor.

• Journal of KSNVE
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• v.9 no.4
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• pp.720-729
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• 1999

Coventional methods for reducing vibration in engineering designs (i.e. by stifferning or detuning) may be undesirable in conditions where size or weight must be minimized, or where complex vibration spectra exist. Some alloys with a combination of high damping capacity and good mechanical properties can provide attractive techanical and economical solutions to problems involving seismic, shock and vibration isolation. Although several non ferrous damping alloys have been developed, none of those materials are applied in any industrial factor due largely to high production cost. To meet these requirement, we have developed a new Fe-Mn high damping alloy. In previous studies, we have reported that an Fe-17%Mn alloy exhibits the highest damping capacity(Specific Damping Capacity:SDC, 30%) among Fe-Mn binary system, and proposed that the boundaries of various types such as $\varepsilon$-martensite variant boundaries, stacking faults in $\varepsilon$-martensite, stacking faults in austenitic and ${\gamma}$$\gamma /\varepsilon$ interfaces give rise to a high damping capacity. The Fe-17%Mn alloy also has advantages of good mechanical properties(T.S. 70 kg/nm$^2$ and low cost over other damping alloys(1/4 times the cost of non-ferrous damping alloy). Thus, the Fe-17%Mn high damping alloy can be widely applied to household appliances, automobiles, industrial facilities and power plant components. In this paper, the overall properties of the Fe-17%Mn high damping alloy is introduced, and its applicability to containment spray pump in the power plant is discussed.

• Tribology and Lubricants
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• v.34 no.5
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• pp.183-190
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• 2018

Tilting pad journal bearing is widely used for steam turbines because of its excellent dynamic stability. As the turbine capacity increases, power loss in the bearings becomes a matter of concern. Power loss in tilting pad journal bearings can be reduced by increasing the bearing clearance and reducing the pad arc length. In this study, the tilting pad journal bearing is tested by changing the seal tooth clearance to verify the static characteristics of the bearing. Bearing power loss and bearing metal temperature are evaluated to compare the bearing's performance and reliability for several test cases. The test bearing is a tilting pad journal bearing with 300.62mm inner diameter and 120.00mm active length. The bearing power loss, its metal temperature, and oil film thickness are measured and evaluated based on the rotor's rotational speed, oil flow rate, and bearing load. Test results show that a tilting pad journal bearing with large seal tooth clearance has 40% lower power loss compared with a bearing with a small seal tooth clearance. As the seal tooth clearance is increased, the power loss of the tilting pad journal bearing decreases. However, with respect to the bearing metal temperatures, a detuning point is observed that makes the minimum bearing metal temperature. Moreover, as the seal tooth clearance is increased, the oil film thickness increases due to high viscosity.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.10
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• pp.59-68
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• 2009

The field oriented control of induction motors is widely used in high performance applications. However, detuning caused by parameter disturbance still limits the performance of these drives. In order to accomplish variable speed operation, conventional PI-like controllers are commonly used. These controllers provide limited good performance over a wide range of operation, even under ideal field oriented conditions. This paper is proposed high performance control of induction motor drive using multi adaptive fuzzy controller. This controller has been performed for speed control with fuzzy adaptation mechanism (FAM)-PI, current control with model reference adaptive fuzzy control(MFC) and estimation of speed using ANN. The proposed control algorithm is applied to induction motor drive system using FAM-PI, MFC and ANN controller. The performance of proposed controller is evaluated by analysis for various operating conditions using parameters of induction motor drive. Also, this paper is proposed the analysis results to verify the effectiveness of this controller.

• Smart Structures and Systems
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• v.19 no.6
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• pp.665-678
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• 2017

In this paper the tuned mass-damper-inerter (TMDI) is considered for passive vibration control and energy harvesting in harmonically excited structures. The TMDI couples the classical tuned mass-damper (TMD) with a grounded inerter: a two-terminal linear device resisting the relative acceleration of its terminals by a constant of proportionality termed inertance. In this manner, the TMD is endowed with additional inertia, beyond the one offered by the attached mass, without any substantial increase to the overall weight. Closed-form analytical expressions for optimal TMDI parameters, stiffness and damping, given attached mass and inertance are derived by application of Den Hartog's tuning approach to suppress the response amplitude of force and base-acceleration excited single-degree-of-freedom structures. It is analytically shown that the TMDI is more effective from a same mass/weight TMD to suppress vibrations close to the natural frequency of the uncontrolled structure, while it is more robust to detuning effects. Moreover, it is shown that the mass amplification effect of the inerter achieves significant weight reduction for a target/predefined level of vibration suppression in a performance-based oriented design approach compared to the classical TMD. Lastly, the potential of using the TMDI for energy harvesting is explored by substituting the dissipative damper with an electromagnetic motor and assuming that the inertance can vary through the use of a flywheel-based inerter device. It is analytically shown that by reducing the inertance, treated as a mass/inertia-related design parameter not considered in conventional TMD-based energy harvesters, the available power for electric generation increases for fixed attached mass/weight, electromechanical damping, and stiffness properties.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1777-1783
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• 2020

As a part of R&D work for the high intensity proton linac of China Accelerator Driven Sub-critical System project, a superconducting half-wave cavity with a frequency of 162.5 MHz and an optimal beta of 0.15 (HWR015) has been developed at Institute of Modern Physics (IMP), Chinese Academy of Sciences. In this paper, the design and test results will be described in detail. We introduced a new stiffening strategy for the HWR cavity, the simulation results show that the cavity has much lower frequency sensitivity coefficient (df/dp), Lorentz force detuning coefficient (KL), and can achieve more stable mechanical properties. The performance of the HWR cavity operated in cryostat will be also reported.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.61-70
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• 1999

An optical switch composed of three-identical, equally-spaced $Ti:LinbO_3$ waveguides and overlaid Al electrodes of CPW structure was designed and fabricated. Patterned Ti was diffused into z-cut $LinbO_3$ substrates at $1025^{\circ}C$ for 6 hours to make a three-waveguide directional coupler. $SiO_2$ buffer layer of $1.2{\mu}m$ was grown by the PECVD to reduce the propagation loss of TM mode, and Al electrodes were built on the layer for switching the guided beam. For an incident beam of ${\lambda}=1.3{\mu}m$, almost perfect optical coupling between two outer waveguides was observed. When an electric field was applied to detune the three waveguides anti-symmetrically, the optical switching phenomenon was successfully confirmed.