• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.190-197
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• 1998

Equations of motions of a pretwisted rotating blade with a concentrated mass in an arbitrary position are derived. The flapwise and chordwise equations are coupled to each other due to the pretwist angle of the blade. As the angular speed, hub radius ratio, pretwist angle and concentrated mass vary, the vibration characteristics of the blade change. It is found that eigenvalue lociveering phenomena occur between two closing loci due to the pretwist angle. The effect of the pretwist angle on the critical angular speed and location of the concentrated mass on the natural frequencies are also investigated.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.121-126
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• 2007

In this paper the vibration system is consisted of a rotating cantilever pipe conveying fluid and a tip mass. The equation of motion is derived applying a modeling method that employs hybrid deformation variables. 'TI1e influences of the rotating angular velocity, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe are studied by the numerical method. The effect of tip mass on the stability of a rotating cantilever pipe are also studied. The influences of a tip mass, the velocity of fluid the angular velocity of a cantilever pipe and the coupling of these factors on the stability of a cantilever pipe are analytically clarified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.143-147
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• 1998

In this study, nonlinear stiffness characteristics of a discharge valve in a small hermetic compressor was considered. It was approximated, with piecewise-linearity, and cubic or quintic nonlinearity by the static load-displacement experimental results. Based on the fluid-structure interaction effects and mass flow rate, the derived 1-DOF equation of motion for the valve model was analyzed. Finally, the dynamic response of the discharge valve was studied with parameters such as the ratio of the running frequency of the compressor to the linear natural frequency of the valve.

• Wind and Structures
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• v.7 no.4
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• pp.235-250
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• 2004

The current study reports the results of an experimental program conducted on a structure fitted with a liquid damper (TLD) and subjected to harmonic excitation. Screens were placed inside the TLD to achieve the required inherent damping. In the first part of the study, reduced scale models of the building-TLD systems were tested under two levels of excitation. The efficiency of the damper was assessed by evaluating the effective damping provided to the structure and comparing it to the optimum effective damping value, provided by a linear tuned mass damper (TMD). An extensive parametric study was then conducted for one of the three models by varying both the excitation amplitude and the tuning ratio, defined as the ratio of the TLD sloshing frequency to the natural frequency of the structure. The effectiveness and robustness of a TLD with screens were assessed. Results indicate that the TLD can be tuned to achieve a robust performance and that its efficiency is not significantly affected by the level of excitation. Finally, the equivalent amplitude dependent TMD model, developed in the companion paper is validated using the system test results.

• Wind and Structures
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• v.1 no.1
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• pp.43-57
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• 1998

A three-degree-of-freedom base hinged assembly (BHA) for aeroelastic model tests of tall building was developed. The integral parts of a BHA, which consists of two perpendicular plane frames and a flexural pivot, enable this modeling technique to independently simulate building translational and torsional degree-of-freedom. A program of wind tunnel aeroelastic model tests of the CAARC standard tall building was conducted with emphasis on the effect of (a) torsional motion, (b) cross-wind/torsional frequency ratio and (c) the presence of an eccentricity between center of mass and center of stiffness on wind-induced response characteristics. The experimental results highlight the significant effect of coupled translational-torsional motion and the effect of eccentricity between center of mass and center of stiffness on the resultant rms acceleration responses in both along-wind and cross-wind directions especially at operating reduced wind velocities close to a critical value of 10. In addition, it was sound that the vortex shedding process remains the main excitation mechanism in cross-wind direction even in case of tall buildings with coupled translational-torsional motion and with eccentricity.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.43-45
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• 2004

In this paper, new design concept of MEMS gyroscope using multi mass system is proposed. The gyroscope having wide bandwidth was designed utilizing the multi mass system in order to reduce the degradation of the performance by resonance variation. The multi mass system has more than two masses and separates the resonant peak of each mass. Using MATLAB, the variation of bandwidth and driving displacement according to mass ratio of the multi mass system was analyzed. This result was compared with that of current single mass system gyroscope. In the 7 kHz resonant frequency design, the multi mass system has 395.3Hz bandwidth, which is six times larger than single mass system bandwidth, 58.5 Hz.

• Bulletin of the Society of Naval Architects of Korea
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• v.7 no.2
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• pp.3-18
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• 1970

An investigation was made for the added mass moment of inertia induced by the rotational motion of the cylinder with hull section on water in order to obtain the information to estimate the natural frequency of the torsional vibration of ships. The special consideration to the effect of the draught upon the added mass moment of inertia is taken into account in the study. In this paper, the general expression for the added mass coefficients of moment of inertia of arbitary two dimensional forms induced by the torsional vibration, was derived by the author. Hence, the coefficients for these forms are represented as functions of parameters, the section area coefficient and draft beam ratio, from which the added mass coefficients for arbitrary forms can be obtained. The result was shown in a chart for estimation of the added mass moment of inertia induced by the torsional vibration, as first trial, for the convenience of practical use.

• Interaction and multiscale mechanics
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• v.6 no.4
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• pp.339-356
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• 2013

This paper investigates the optimized parameters of Tuned Mass Dampers (TMDs) for vibration control of high-rise structures including Soil Structure Interaction (SSI). The Artificial Bee Colony (ABC) method is employed for optimization. The TMD Mass, damping coefficient and spring stiffness are assumed as the design variables of the controller; and the objective is set as the reduction of both the maximum displacement and acceleration of the building. The time domain analysis based on Newmark method is employed to obtain the displacement, velocity and acceleration of different stories and TMD in response to 6 types of far field earthquakes. The optimized mass, frequency and damping ratio are then formulated for different soil types; and employed for the design of TMD for the 40 and 15 story buildings and 10 different earthquakes, and well results are achieved. This study leads the researchers to the better understanding and designing of TMDs as passive controllers for the mitigation of earthquake oscillations.

• Structural Engineering and Mechanics
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• v.83 no.5
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• pp.655-669
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• 2022

Passive vibration control devices like tuned liquid column dampers (TLCD) not only significantly reduce buildings' vibrations but also can serve as a water storage facility. The recently introduced modified form of TLCD known as tuned liquid column ball damper (TLCBD) suppressed external vibration efficiently compared to traditional TLCD. For excellent performance, the mass ratio of TLCBD should be in the range of 5% to 7%, which does not include the mass of the ball. This additional mass of the ball increases the overall structure mass. Therefore, in this paper, an effort is made to reduce the mass of TLCBD. For this purpose, a new modified version of TLCBD known as tuned liquid column hollow ball damper (TLCHBD) is proposed. The existing mathematical modeling of TLCBD is used for this new damper by updating the numerical values of the mass and mass moment of the ball. Analytically the optimal design parameters are obtained. Numerically the TLCHBD is investigated with a single degree of freedom structure under harmonic and seismic loadings. It is found that TLCHBD performance is similar to TLCBD in both loadings' cases. To validate the numerical results, an experimental study is conducted. The mass of the ball of TLCHBD is reduced by 50% compared to the ball of TLCBD. Both the arrangements are studied with a multi-degree of freedom structure under harmonic and seismic loadings using a shake table. The results of the experimental study confirm the numerical findings. It is found that the performance behavior of both the dampers is almost similar under harmonic and seismic loadings. In short, the TLCHBD is lighter in weight than TLCBD but has a similar vibration suppression ability.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.5
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• pp.30-40
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• 1992

Spark knock obstructs any improvement in the efficiency and performance of an engine. As the knock mechanism of spark ignition engine, the detonation and the autoignition theory have been offered. In this paper, the knock model was established, which was able to predict the onset of knock and knock timing of spark ignition engine by the basis of autoignition theory. This model was a function of engine speed and equivalent air-fuel ratio. When this established knock model was tested from 1000rpm to 3000rpm of engine speed data, maximum error was crank angle 2 degrees between measured and predicted knock time. And the main results were as follows by the experimental analysis of spark knock in spark ignition engine. 1) Knock frequency was increased as engine speed increased. 2) Knock amplitude was increased as mass of end gas increased. 3) Knock frequency was occured above minimum 18% mass fraction of end gas.