• Structural Engineering and Mechanics
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• v.78 no.4
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• pp.425-437
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• 2021

Under foundation shock mats have been used in the current practice in order to reduce/damp vibrations received by buildings through the surrounding environment. Although some investigations have been made on under foundation shock mats performance, their effectiveness in the reduction of railway induced-vibrations has not been fully studied, particularly with the consideration of underneath soil media. In this regard, this research is aimed at investigating performance of shock mat used beneath building foundation for reduction of railway induced-vibrations, taking into account soil-structure interaction. For this purpose, a 2D finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a shock mat, and the building. The model results were validated using an analytical solution reported in the literature. The performance of shock mats was examined by an extensive parametric analysis on the soil type, bedding modulus of shock mat and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, a better performance of shock-mats is observed. A simplified model/method was developed for prediction of shock mat effectiveness in reduction of railway-induced vibrations, making use of the results obtained.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.1-6
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• 2002

A dynamic characteristics of shock absorber in the various excitation is investigated experimentally. Work diagrams and characteristic curves are used as a experimental standard. The various excitation conditions temperature and noise are very important factors in associated with the reduction of damping force. It is found that the heat occurrence from shock absorber, the gas shock absorber is much higher than oil shock absorber and increased in high speed. As to the variation of damping force, there are no change when the speed is low but we fixed amount of variation by increasing speed and change of new and old decrease. The sound pressure of the swash noise from cycle of shock absorber, we compared with theory sound pressure by experiment.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.4
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• pp.380-387
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• 2015

Various forms of passive shock absorber have developed to supplement performance which is poorer than that of active shock absorber. It is called 'Hybrid Conventional Damper (HCD)'. Frequency sensing shock absorber that this study will cover belongs to the HCD. This study aims to demonstrate that performance of frequency sensing shock absorber is superior than that of passive shock absorber. Study process is as follows. Firstly, analysis models for both passive shock absorber and frequency sensing shock absorber are developed to secure reliability. Then, elements which cause difference of ride quality are found out through comparison of hysteresis characteristics. By comparison of frequency characteristic, furthermore, damping principle of frequency sensing shock absorber is understood. Also, it determines if the absorber performs well even though maximum excitation speed is changed. Finally, the study proves that performance of frequency sensing shock absorber is superior than that of passive shock absorber after comparing change of damping power in excitation condition that various frequencies are mixed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.73-80
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• 2014

A camera module that gathers visual information via aerial observation reconnaissance is equipped inside a gimbal structure. This gimbal structure system must reduce dynamic responses in order to obtain clear images under all circumstances. Among many design specifications for this system, there is MIL-STD-810G as a shock standard. This specification indicates a limitation of the acceleration of the camera module under a base shock excitation on the gimbal structure. The satisfaction of this condition can usually be proved by experiment, because it includes bearings and dynamic isolators made of rubber. Numerical analysis must be proposed for design improvement of the gimbal structure. To achieve this goal, transient response analysis for the base shock excitation was performed using the finite element method. Experimental results were compared with numerical solutions and it is shown that the present method is useful.

• Structural Engineering and Mechanics
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• v.19 no.4
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• pp.441-457
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• 2005

An analytical method is presented to solve the problem of transient wave propagation in a transversely isotropic piezoelectric hollow sphere subjected to thermal shock and electric excitation. Exact expressions for the transient responses of displacements, stresses, electric displacement and electric potentials in the piezoelectric hollow sphere are obtained by means of Hankel transform, Laplace transform, and inverse transforms. Using Hermite non-linear interpolation method solves Volterra integral equation of the second kind involved in the exact expression, which is caused by interaction between thermo-elastic field and thermo-electric field. Thus, an analytical solution for the problem of transient wave propagation in a transversely isotropic piezoelectric hollow sphere is obtained. Finally, some numerical results are carried out, and may be used as a reference to solve other transient coupled problems of thermo-electro-elasticity.

• 한국지구과학회:학술대회논문집
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• 2002.09a
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• pp.72-72
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• 2002

• Journal of Biosystems Engineering
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• v.35 no.5
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• pp.323-329
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• 2010

Physical damages on fruits may be caused by shock and vibration inputs that transmitted from the transporting vehicle through the packaging and cushioning materials to the fruit. In this study, both half sine shock test and trapezoidal shock test were performed by MIL-STD-810F specification in order to investigate and represent the shock response properties such as peak acceleration and shock amplification factors of the pear according to packaging and cushioning materials for optimal packaging design during transportation. Shock excitation data that had been measured on the vehicle operating on the real road were used. Shock response properties measured by half sine shock test were smaller than those measured by trapezoidal shock test. Results represent that corrugation shapes and thickness can significantly affect the cushioning performance than the paper configurations of cushioning pad and showed that fruits may be damaged seriously while transported on the unpaved road without the properly cushioned packaging practices.

• Journal of The Korean Astronomical Society
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• v.32 no.1
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• pp.55-63
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• 1999

NGC 6537 is an extremely high excitation bipolar planetary nebula. It exhibits a huge range of excitation from lines of [N I] to [Si VI]or [Fe VII], i.e. from neutral atoms to atoms requiring an ionization potential of $\~$167eV. Its kinematical structures are of special interest. We are here primarily concerned with its high resolution spectrum as revealed by the Hamilton Echelle Spectrograph at Lick Observatory (resolution $\~0.2{\AA}$) and supplemented by UV and near-UV data. Photoionization model reproduces the observed global spectrum of NGC 6537, the absolute H$\beta$ flux, and the observed visual or blue magnitude fairly well. The nebulosity of NGC 6537 is likely to be the result of photo-ionization by a very hot star of $T_{eff} \~ 180,000 K$, although the global nebular morphology and kinematics suggest an effect by strong stellar winds and resulting shock heating. NGC 6537 can be classified as a Peimbert Type I planetary nebula. It is extremely young and it may have originated from a star of about 5 $M_{\bigodot}$.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.3-10
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• 2008

In this paper, the optimal command input is considered in order to minimize the residual vibrations of a flexible cantilever beam when the beam simply changes its position by translation or rotation. Although a cantilever beam has many modes of vibration, it is shown that the consideration of the first mode is sufficient in this case. Thus, the problem becomes a single-degree-of-freedom system subjected to a ground excitation. Two simple methods are proposed to find the optimal command input based on the shock response spectrum (SRS). The first method is the simplest and can be applied to lightly damped cases, and the second method is applicable to more general problems. The second method gives almost the same results as the input shaping method. However the proposed method gives a easier and clearer control strategy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.145-151
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• 2007

Impulsive excitation on vehicle produces shock-type vibration on the seat, which has major frequencies and damping ratios dependent on the characteristics of the suspension, the tire, the seat cushion and so on. The response of single degree of freedom model to a half-sine force input was considered as simple shock-type vibration signal. Quasi-apparent-mass for fifteen subjects was measured with the shock-type vibration generated on a rigid seat mounted on the simulator, so its nonlinearity was apparently found over 6.3 Hz according to the difference of magnitude of the shock.