• Journal of KSNVE
• /
• v.6 no.1
• /
• pp.107-114
• /
• 1996

The damping characteristics of a cylindrical structure containing oil and bearing balls is investigated for external bending forces. The experimental data obtained through the use of bearing balls with viscous oil in a column is given and analyzed. The viscous action of the oil and inertia effects of the balls on the inside of column create a drag force. The drag force dampens the vibration of the column. This study aims to search for an optimum combination of oil and balls which would produce maximum damping. Machining oils of various viscosities along with ball bearings of various sizes place inside cantilevered aluminium tubes of various diameters to create a rig on which the damping properties of the oil and balls can be studied. The contileved tubes are studied in both horizontal and vertical positions in order to gauge the effect of gravity on the system. The actions of the ball in the column and damping characteristics are investigated according to the dimensionless terms. The Buckingham theorem is used to reduce the variables and to predict the damping of an oil ball column. Though the damping ratio remains fairly constant in the horizontal position of column, the damping ratio begins to increase as the ratio of the number of balls and column length rise above 0.28 in the vertical position of oil ball column. The ratio of the ball diameter to column diameter influences the damping ratio with an optimum diameter ratio. Slenderness ratio and gravity effects on the damping ratio ane investigated.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.6
• /
• pp.147-154
• /
• 2014

The cable damages of the bridge structures induce very important impact on the structural safety, which implies the close monitoring of the cable damage is required to secure sustained safety of the bridges. Most usual available maintenance techniques are based on the monitoring the change of the natural frequency of the structures by damages. However, existing method are based on vibration method to calculate lateral vibration and system identification can calculate the axial stiffness using sensitivity equation by trial error method. But the frequency study by the longitudinal movement need because of the sag effect in system identification. This study proposes a new method to investigate the damage magnitudes and status. The method improves the accuracies in the magnitudes and status of damages by adopting the natural frequency of longitudinal movement. The study results have been validated by comparing them with the approximate solution of FEM. Thus, the relationship of cable damage and frequency appear with relation that the severe damage has the little frequency. If we know the real frequency we can estimate the cable damage severity using this relationship. This method can be possible the efficient management of the cable damage.

• Earthquakes and Structures
• /
• v.13 no.1
• /
• pp.59-66
• /
• 2017

Modern seismic codes rely on performance-based seismic design methodology which requires that the structures withstand inelastic deformation. Many studies have focused on the inelastic deformation ratio evaluation (ratio between the inelastic and elastic maximum lateral displacement demands) for various inelastic spectra. This paper investigates the inelastic response spectra through the ductility demand ${\mu}$, the yield strength reduction factor $R_y$, and the inelastic deformation ratio. They depend on the vibration period T, the post-to-preyield stiffness ratio ${\alpha}$, the peak ground acceleration (PGA), and the normalized yield strength coefficient ${\eta}$ (ratio of yield strength coefficient divided by the PGA). A new inelastic deformation ratio $C_{\eta}$ is defined; it is related to the capacity curve (pushover curve) through the coefficient (${\eta}$) and the ratio (${\alpha}$) that are used as control parameters. A set of 140 real ground motions is selected. The structures are bilinear inelastic single degree of freedom systems (SDOF). The sensitivity of the resulting inelastic deformation ratio mean values is discussed for different levels of normalized yield strength coefficient. The influence of vibration period T, post-to-preyield stiffness ratio ${\alpha}$, normalized yield strength coefficient ${\eta}$, earthquake magnitude, ruptures distance (i.e., to fault rupture) and site conditions is also investigated. A regression analysis leads to simplified expressions of this inelastic deformation ratio. These simplified equations estimate the inelastic deformation ratio for structures, which is a key parameter for design or evaluation. The results show that, for a given level of normalized yield strength coefficient, these inelastic displacement ratios become non sensitive to none of the rupture distance, the earthquake magnitude or the site class. Furthermore, they show that the post-to-preyield stiffness has a negligible effect on the inelastic deformation ratio if the normalized yield strength coefficient is greater than unity.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.13 no.3
• /
• pp.212-218
• /
• 2020

When Radiofrequency energy is applied to the human body, the vibration width is very short. Therefore, the electrolyte burn generated when using the direct current does not occur. Ion molecules, polarized molecules, etc., vibrate more than 40,000 times per second, converting them into frictional heat to generate deep heat. The blood flow of capillaries increases 4-5 times more than at rest, increasing the supply of oxygen, nutrients, antibodies, and white blood cells. In addition, the electrochemical reaction does not occur because the vibration width and the pulsation period are very short. It is a physical factor treatment method that does not stimulate the sensory nerves and motor nerves. In this study, an isotonic exercise is performed in a young normal adult using a Radiofrequency pain treatment device. The purpose of this study is to integrate rehabilitation therapy by measuring electromyography data during isotonic exercise and confirming the effect on changes in motor neuron response. The EMG data generated when isotonic exercise of the forearm biceps muscle and the EMG data measured after the use of a Radiofrequency pain treatment device after exercise were RMS, respectively, and verified through t-test. It was confirmed that there was a significant difference in both men and women because the t-value was smaller than the significance level p (<.05).

• Journal of the Society of Naval Architects of Korea
• /
• v.30 no.3
• /
• pp.116-126
• /
• 1993

The finite element method(FEM) has been commonly used for structural dynamic analysis. However, the direct global application of FEM to large complex structures such as ships and offshore structures requires considerable computational efforts, and remarkably more in structural dynamic optimization problems. Adoption of the component-mode synthesis method is an efficient means to overcome the above difficulty. Among three classes of the component-mode synthesis method, the free-interface mode method is recognized to have the advantages of better computational efficiency and easier implementation of substructures' experimental results, but the disadvantage of lower accuracy in analytical results. In this paper, an advanced method to improve the accuracy in the application of the free-interface mode method for the vibration analysis of large complex structures is presented. In order to compensate the truncation effect of the higher modes of substructures in the synthesis process, both residual inertia and stiffness effects are taken into account and a frequency shifting technique is introduced in the formulation of the residual compliance of substructures. The introduction of the frequency shrift ins not only excludes cumbersome manipulation of singular matrices for semi-definite substructural systems but gives more accurate results around the specified shifting frequency. Numerical examples of typical structural models including a ship-like two dimensional finite element model show that the analysis results based on the presented method are well competitive in accuracy with those obtained by the direst global FEM analysis for the frequencies which are lower than the highest one employed in the synthesis with remarkably higher computational efficiency and that the presented method is more efficient and accurate than the fixed-interface mode method.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.5
• /
• pp.609-616
• /
• 2019

When the fouling of a vessel occurs, its resistance at sea increases and there is a corresponding increase in fuel consumption. The maintenance cost of the vessel also increases because it is time-consuming to remove the fouling. To solve this problem and minimize environmental contamination of sea-water, there have been recent developments in anti-fouling paints as self-polishing copolymers that not include toxic elements such as tin. When these conventional techniques are applied to vessels, polishing is promoted during the operation whereby friction or vibration with seawater occurs. This leads to enhanced anti-fouling performance. However, when fouling is intensified such as during an anchorage, there is no flow of seawater and polishing is suppressed. This leads to a deterioration of the performance of anti-fouling. To solve these problems, we developed a system that induces vibration in a vessel during anchorage. As such, the deterioration of polishing due to insuf icient flow of seawater is inhibited. The reliability of the ultrasonic antifouling system was evaluated by calculating its repeatability. The removal efficiency of fouling of the proposed system was qualitatively evaluated using test specimens. The test revealed that the value of the coefficient of variation for the reproducibility of the frequency and amplitude was 0.2 % and 4.0 % on average. The degree of fouling of the specimens was the highest at 73.3 g in the No.5 sepcimen. Moreover, efficiency of fouling removal was 93.2 % on average compared to the specimens without the proposed system.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.1
• /
• pp.141-152
• /
• 2022

As interest increases related to the development of eco-friendly energy, the offshore wind turbine market is growing at an increasing rate every year. In line with this, the demand for an installation vessel with large scaled capacity is also increasing rapidly. The wind turbine installation vessel (WTIV) is a fixed penetration of the spudcan in the sea-bed to install the wind turbine. At this time, a review of the spudcan is an important issue regarding structural safety in the entire structure system. In the study, we analyzed the current procedure suggested by classification of societies and new procedures reflect the new loading scenarios based on reasonable operating conditions; which is also verified through FE-analysis. The current procedure shows that the maximum stress is less than the allowable criteria because it does not consider the effect of the sea-bed slope, the leg bending moment, and the spudcan shape. However, results of some load conditions as defined by the new procedure confirm that it is necessary to reinforce the structure to required levels under actual pre-load conditions. Therefore, the new procedure considers additional actual operating conditions and the possible problems were verified through detailed FE-analysis.

• Journal of Navigation and Port Research
• /
• v.46 no.4
• /
• pp.367-374
• /
• 2022

The purpose of this study was to propose a deep learning algorithm that applies to the fault diagnosis of fuel pumps and purifiers of autonomous ships. A deep learning algorithm reflecting the time dependence of the measured signal was configured, and the failure pattern was trained using the vibration signal, measured in the equipment's regular operation and failure state. Considering the sequential time-dependence of deterioration implied in the vibration signal, this study adopts Conv1D with sliding window computation for fault detection. The time dependence was also reflected, by transferring the measured signal from two-dimensional to three-dimensional. Additionally, the optimal values of the hyper-parameters of the Conv1D model were determined, using the grid search technique. Finally, the results show that the proposed data preprocessing method as well as the Conv1D model, can reflect the sequential dependency between the fault and its effect on the measured signal, and appropriately perform anomaly as well as failure detection, of the equipment chosen for application.

• Journal of the Korean GEO-environmental Society
• /
• v.24 no.2
• /
• pp.31-40
• /
• 2023

We installed temporary strong motion seismometers at the ground surface, 1 m, 2 m, and 9 m at an existing seismic station that houses permanent seismometers installed at 20 m and 100 m, to investigate the influence of installation depth on the recorded ambient and anthropogenic noise level and the characteristics of earthquake signals. Analysis of the ambient noise shows that anthropogenic noise dominates where vibration period T < 1 s at the studied site, whereas wind speed appears to be strongly correlated with the noise level at T > 1 s. Frequency-wavenumber analysis of 2D seismometer array suggests that ambient noise in short periods are predominantly body waves, rather than surface waves. The level of ambient noise was low at 9 m and 20 m, but strong amplification of noise level at T < 0.1 s was observed at the shallow seismometers. Both the active-source test result and the recorded earthquake data demonstrated that the signal level is decreased with the increase of depth. Our result also shows that recorded motions at the ground and 1 m are strongly amplified at 20 Hz (T = 0.05 s), likely due to the resonance of the 3 m thick soil layer. This study demonstrates that analysis of ambient and active-source vibration may help find optimal installation depth of strong motion seismometers. We expect that further research considering various noise environments and geological conditions will be helpful in establishing a guideline for optimal installation of strong motion seismometers.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
• /
• v.21 no.2
• /
• pp.55-60
• /
• 2015

Packaging of export cut lilies reduces physical damage during distribution like dropping, shock, vibration, compression and serves to protect from necrosis, microbial contamination and decomposition. Study on which packaging materials must be selected is necessary because it serves to direct effect maintaining quality and the degree of freshness. newspaper, perforated OPP film, Oriented Nylon film (ON), punched OPP film, OPP films are used in this study. Plant senescence of lilies was happened rapidly during storage at $25^{\circ}C$ rather than at $5^{\circ}C$. Also, water absorption, fresh weight at during storage $25^{\circ}C$ rather than at $5^{\circ}C$ In addition, fresh weight of lilies storage at $25^{\circ}C$ appears higher than at $5^{\circ}C$ all of the packaging materials except OPP because water absorption of lily storage at $5^{\circ}C$ appears higher than at $25^{\circ}C$, thereby suppressing the fresh weight reducing Also, effect on biological activity of lilies from shape of packaging material appears higher during storage at $5^{\circ}C$ than at $25^{\circ}C$. Compared with each packaging materials, newspaper packaging is the smallest effect on changes in biological activity of cut lilies during storage. Thus, the results demonstrate that flowering date are affected mainly by the storage temperature rather than packaging materials.