• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.443-448
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• 2016

A novel Permanent Magnet based Magneto Rheological (PM-MR) damper is proposed in this paper. The principle of proposed MR damper is achieved by designing a linearly varying magnetization area with-respect to the movable permanent magnetic based piston setup. Nowadays, commercially available MR damper uses electromagnetic coils for generating the variable magnetic fields corresponding to the variable damping force. The amount of magnetic field produced by the electromagnetic coils are depends on the biasing current of voltage source. The key enabling concept of the proposed MR damper is to replace the electromagnetic coils and the voltage sources by utilizing the variable area based permanent magnetic piston setup. The proposed unique design structure of PM-MR damper has an increasing shear mode damping force with the piston movement in both jounce and rebound motion. In this research, analytical model of the proposed structure is derived and the structural design of proposed concept is verified using numerical CAD tool. As a result, the damping force is increase when piston movement in both jounce and rebound motion.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2001.02a
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• pp.292-309
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• 2001

Modulus of elasticity, modulus of rigidity, damping ratio, and natural frequency of three varieties of boxthorn(Lycium chinense Mill) (Cheongyang #2, Cheongyang gugija, and Cheongyang native) branches were analyzed. Modulus of elasticity and modulus of rigidity of the boxthorn branch was determined using standard formula after simple beam bending and torsion test, respectively, using an universal testing machine. Damping ratio and natural frequency of branches were determined using a system consisted of an accelerometer, a PC equipped with A/D converter, and a software for data analysis. Relationship between the elastic modulus and branch diameter in overall varieties and branch types showed a good correlation (r$\cong$-0.81). There was, however, no correlation between torsional rigidity and branch diameter. The internal damping results were highly variable and the overall range of the damping ratio of the boxthorn branch was 0.014 -0.087, which indicated that the branch was a lightly damped structure. The natural frequency of the boxthorn branch was in the range of 89-363 rad/s for the overall varieties and branch types. A good correlation (r$\cong$0.82) existed between the natural frequency and branch diameter in overall varieties and branch type.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.49-64
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• 2022

In this work, the bending and dynamic behaviors of advanced composite plates resting on variable visco-Pasternak foundations are studied using a simple shear deformation integral plate model. The research is carried out with a view to a three-parameter foundation including the influences of the variable Winkler coefficient, the constant Pasternak coefficient and the damping coefficient of the elastic medium. The present theory uses a displacement field with integral terms instead of derivative terms by including also the shear deformation effect without introducing the shear correction factors. The equations of motion for advanced composite plates are obtained using the Hamilton principle. Analytical solutions for the bending and dynamic analysis are deduced for simply supported plates resting on variable visco-Pasternak foundations. Some numerical results are presented to demonstrate the impact of material index, elastic foundation type, and damping coefficient of the foundation, on the bending and dynamic responses of advanced composite plates.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.143-148
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• 2004

The numerical analysis of the hard disk drive slider is presented. The pressure distribution was calculated using the finite element method. The generalized Reynolds equation was applied in order to include the gas rarefaction effect. The balance of the air bearing force and preload force was considered. The characteristics of the small vibrations near the equilibrium were studied using the perturbation method. Triangular mesh with variable element size was employed to model the two-rail slider. The flying height, pitching angle, rolling angle, stiffness and damping of the two-rail slider were calculated for radial position changing from the inner radius to the outer radius and for a wide range of the slider crown values. It was found that the flying height, pitching angle and rolling angle were increased with radial position while the stiffness and damping coefficients were decreased. The higher values of crown resulted in increased flying height, pitching angle and damping and decreased stiffness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.543-546
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• 1997

The purpose of this study is to investigate the ERSU(Electr0-Rheological Suspension IJnit) and some progress of damping force characteristic of a ERSU. This paper describes overall construction of th'e system design and the manufacturing of ERSU. A model of the ERSU is made by using electric field dependent on Bingham properities of ER fluid. In this paper. the ERSU is designed and manufactured for a light ground tracked vehicle. From the results, it is shown that the damping performance of ERSLJ is better than that of a passive suspension unit. This experimental study might be very useful for the simulat~on and the design of semi-active suspension units.

• Journal of Aerospace System Engineering
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• v.8 no.1
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• pp.18-23
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• 2014

This thesis is simulated a aircraft nose landing gear drop-test. flow rate-to-pressure difference characteristics of damping orifices for a nose landing gear is investigated by CFD analyses. Orifice is kind of poppet valve type. it is simulated pressure drop with variable orifice area. it is simulated landing gear model by using ADAMS with CFD result. It's performance evaluated landing gear drop-test and analyzed the results.

• Smart Structures and Systems
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• v.23 no.6
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• pp.627-639
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• 2019

Passive control may not provide enough damping for a stay cable since the control devices are often restricted to a low location level. In order to enhance control performance of conventional passive dampers, a new type of damper integrated with a rotary electromagnetic damper providing variable damping force and a flywheel serving as an inertial mass, called the rotary electromagnetic inertial mass damper (REIMD), is presented for suppressing the cable vibrations in this paper. The mechanical model of the REIMD is theoretically derived according to generation mechanisms of the damping force and the inertial force, and further validated by performance tests. General dynamic characteristics of an idealized taut cable with a REIMD installed close to the cable end are theoretically investigated, and parametric analysis are then conducted to investigate the effects of inertial mass and damping coefficient on vibration control performance. Finally, vibration control tests on a scaled cable model with a REIMD are performed to further verify mitigation performance through the first two modal additional damping ratios of the cable. Both the theoretical and experimental results show that control performance of the cable with the REIMD are much better than those of conventional passive viscous dampers, which mainly attributes to the increment of the damper displacement due to the inertial mass induced negative stiffness effects of the REIMD. Moreover, it is concluded that both inertial mass and damping coefficient of an optimum REIMD will decrease with the increase of the mode order of the cable, and oversize inertial mass may lead to negative effect on the control performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.198-203
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• 2007

The aim of this study is to suppress the high-frequency combustion instability by acoustic absorption through swirl injector with variable air core length. In the previous study, acoustic damping effects on air core (length, shape, volume) and location of the injector in a model chamber were investigated. Through previous results, our study has advanced to the effect of tuned multi-injectors. From the experimental data, it is proved that increasing of numbers of injectors mounted each anti-node point can increase acoustic damping effect. Also, when tuned injectors at 1L, 1T, 1L1T modes simultaneously are installed each anti-node point of model chamber, damping effect of tuned injectors with multi modes is well agreed with it of tuned injectors with single mode.

• Journal of the Society of Disaster Information
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• v.15 no.2
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• pp.292-300
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• 2019

Purpose: To reduce the noise and vibration of reinforced concrete slab structures, the damping performance is to be performed experimentally after installing hollow core or filling it with liquid. Method: Using the hollow rate as an experimental variable, the damping ratio and stiffness of each test specimen at impact load are obtained to determine the difference between the damping ratio and stiffness of the numerical analysis. In addition, the damping effects are reviewed by comparing the difference in the damping ratio and stiffness of a test specimen filled with liquid 50% of the study. Results: Since the difference in resistance between a specimen with or without hollow core is 5%, it is judged that there is no structural problem, and the injection of liquid into the hollow core can increase the damping ratio, which can reduce noise or vibration. Conclusion: At less than 20% of hollow rate, there was little damping effect, and at 30%, damping effect was found. However, if liquid is injected into the hollow core of the specimen, damping rate is shown to increase, and the injection of liquid into the hollow part is believed to reduce noise or vibration.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.4
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• pp.13-21
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• 2001

Electrorheological(ER) fluid is a kind of smart material with variable shear stress and dynamic viscosity under various electric field intensity. Electric field can control the damping characteristics of ER damper. The objective of this study is the analysis of the performance of ER damper and its application to shock absorber. Idealized nonlinear Bingham plastic shear flow model is used to predict the velocity profile between electrodes. Cylindrical dashpot ER damper with moving electrode is constructed and tested under various electric fields. The analytic and experimental results for damping force are compared and discussed. Drop test system using ER damper is prepared to identify transient vibration characteristics. The rebound is eased as the applied electric field increases. When semi-active control algorithm is applied, rebound phenomenon disappears and vibration energy level decays faster than the case of zero electric field.