• Journal of the Korean Vacuum Society
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• v.12 no.2
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• pp.93-104
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• 2003

For evaluation of durability of low vacuum pumps, it is required to examine the performance and degradation of low vacuum pumps. Pump degradation may result from abnormalities associated with the performance in many areas of pump operation. The diagnostics method can be used to monitor the pump performance in the semi-conductor process line. Based on the mechanical defect of the pump, the dynamic response and reliability of the system for performance test, and the dynamic characteristics of the pump were experimentally assessed. The theoretical work rate for the compression process in the pump was calculated, and then the efficiency of the pump associated with the power consumption was evaluated. This analysis will be useful in detecting pump degradation with increasing the power consumption. To determine the predominant factors of pump degradation, it is important to evaluate the entire pumping system. We studied vibration, dynamic pressure, pumping speed, and power consumption of low vacuum pumps. Our results can be utilized for the future research on the evaluating technology of durability of low vacuum pumps.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.48-55
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• 2018

The purpose of the present study is to compare the reduction rate of natural frequency and the increase rate of damping parameter with structural damage in system. For this purpose, experiment and numerical simulation analysis are performed for the 2-span H-Beam with lower natural frequency and higher damping parameter from free vibration in structure. The response signal by impact load before and after damage is analyzed at 14 locations. The response signals for all locations are performed fast fourier transform to estimate the natural frequency reduction rate and wavelet transform to estimate the damping parameter increase rate. The time domain function corresponding to each scale(frequency) is separated from the response signal by wavelet parameter. The estimation of damping parameter increase rate using wavelet transform is more sensitive than the estimation of natural frequency reduction rate in structure.

• Wind and Structures
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• v.20 no.5
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• pp.701-718
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• 2015

The joint distribution of wind speed and wind direction at a bridge site is vital to the estimation of the basic wind speed, and hence to the wind-induced vibration analysis of long-span bridges. Instead of the conventional way relying on the weather stations, this study proposed an alternate approach to obtain the original records of wind speed and the corresponding directions based on field measurement supported by the Structural Health Monitoring System (SHMS). Specifically, SHMS of Sutong Cable-stayed Bridge (SCB) is utilized to study the basic wind speed with directional information. Four anemometers are installed in the SHMS of SCB: upstream and downstream of the main deck center, top of the north and south tower respectively. Using the recorded wind data from SHMS, the joint distribution of wind speed and direction is investigated based on statistical methods, and then the basic wind speeds in 10-year and 100-year recurrence intervals at these four key positions are calculated. Analytical results verify the reliability of the recorded wind data from SHMS, and indicate that the joint probability model for the extreme wind speed at SCB site fits well with the Weibull model. It is shown that the calculated basic wind speed is reduced by considering the influence of wind direction. Compared to the design basic wind speed in the Specification of China, basic wind speed considering the influence of direction or not is much smaller, indicating a high safety coefficient in the design of SCB. The results obtained in this study can provide not only references for further wind-resistance research of SCB, but also improve the understanding of the safety coefficient for wind-resistance design of other engineering structures in the similar area.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.319-327
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• 2017

In this study, characteristics of seismic behaviors of offshore wind turbine systems using concrete-suction-type supporting structures are investigated. Applying hydrodynamic pressure from the surrounding sea water and interaction forces from the underlying soil to the structural system which is composed of RNA, the tower, and the supporting structure, a governing equation of the system is derived and its earthquake responses are obtained. It can be observed from the analysis results that the responses are significantly influenced by soil-structure interaction because dynamic responses for higher natural vibration modes are increased due to the flexibility of soil. Therefore, the soil-structure interaction must be taken into consideration for accurate assessment of dynamic behaviors of offshore wind turbine systems using concrete-suction-type supporting structures.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.95-102
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• 2004

For the simultaneous measurement of strain and damage signal, a fiber Bragg grating sensor system with a dual demodulator was proposed. One demodulator using a tunable Fabry-Perot filter can measure low-frequency signal such as strain and the other demodulator using a passive Mach-Zehnder interferometer can detect high-frequency signal such as damage signal or impact signal. Using a proposed fiber Bragg grating sensor system, both the strain and damage signal of a cross-ply laminated composite beam under tensile loading were simultaneously measured. Analysis of the strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were induced due to transverse crack propagation in the 90 degree layer of composite beam and vibration with a maximum frequency of several hundreds of kilohertz was generated.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.46-58
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• 2018

A two-axis gimbal-type X-band antenna is widely used to transmit bulk image data from high-resolution observation satellites. However, undesirable microvibrations induced by driving the antenna should be attenuated, because they are a main cause of image-quality degradation of the observation satellite. In this study, a pseudoelastic memory alloy (SMA) gear was proposed to attenuate the microvibrations by driving the antenna in an azimuth angle. In addition, the proposed gear can overcome the limitations of the conventional titanium blade gear, which is not still enough and is vulnerable to plastic deformations under excessive torque. To investigate the basic characteristics of the proposed SMA mesh washer gear, a static load test was performed on the thickness of the SMA mesh washer and the rotation of the gear. Moreover, The microvibration measurement test demonstrated that the SMA mesh washer gear proposed in this study is effective for microvibration attenuation.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.821-831
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• 2006

There are 5 railway bridges in a Seoul metro network; Jamsil, Dangsan(line 2), Dongho(line 3), Dongjak(line 4) and Chungdam(line 7). Because there are strong wind and vibration in the bridges, uplift of a contact wire caused by pantographs in the bridge section is higher than in a normal section. If the uplift at the support point exceed 10 cm, an interference between pantographs and catenary system happens. Estimated maximum uplift is obtained by applying safety factor 2 to the simulation results. The application of the safety factor is needed for taking into account of the effect of the wind, etc. Previously, we can not check whether or not the safety factor is proper. Recently, we can measure the uplift during the train operation, as a telemetry system which can measure dynamic behavior of the contact wire has been developed. The aim of this research is to review how proper the safety factor related to the uplift is, based on the measurement. We performed simulations and experiments for the uplift at the Jamsil railway bridge. The simulations were performed for the every kind of the train passing the Jamsil bridge. In order to compare the analysis results with the measurement results, we measured the uplifts at the support when the trains passed the measuring point. Finally, we proposed adequate safety factor with the uplift for the bridge section.

• Fire Science and Engineering
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• v.29 no.1
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• pp.53-59
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• 2015

Water hammering created by an unsteady flow in pipeline systems can cause excessive change in pressure, vibration, and noise. So, water hammer analysis is very important for limiting the damage caused to pipeline, pump and valve systems by operation conditions. On the other hand, water hammer arrester has been manufactured and used in order to minimize the damage caused by water hammering phenomenon in domestic, and it has been produced and installed as the low cost-oriented because of being no separate standard in the meanwhile. Therefore, our research team investigated about the standardization of water hammer arrester performance through the various methods, such as test methods for verification of one pipe, assuming the occurrence of water hammer in a water-based fire extinguishing system, separated for opening impact pressure and shut off impact pressure and for a branch pipe in order to make guideline for water hammer arrester performance. And finally, verified the performance of the water hammer pressure as the simple mechanical way using the U-shaped pipe and a test weight, so KFI standards for the water hammer arrester could be established.

• Earthquakes and Structures
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• v.13 no.4
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• pp.377-386
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• 2017

Earthquake-induced pounding damages to building structures were repeatedly observed in many previous major earthquakes. Extensive researches have been carried out in this field. Previous studies mainly focused on the regular shaped buildings and each building was normally simplified as a single-degree-of-freedom (SDOF) system or a multi-degree-of-freedom (MDOF) system by assuming the masses of the building lumped at the floor levels. The researches on the pounding responses between irregular asymmetric buildings are rare. For the asymmetric buildings subjected to earthquake loading, torsional vibration modes of the structures are excited, which in turn may significantly change the structural responses. Moreover, contact element was normally used to consider the pounding phenomenon in previous studies, which may result in inaccurate estimations of the structural responses since this method is based on the point-to-point pounding assumption with the predetermined pounding locations. In reality, poundings may take place between any locations. In other words, the pounding locations cannot be predefined. To more realistically consider the arbitrary poundings between asymmetric structures, detailed three-dimensional (3D) finite element models (FEM) and arbitrary pounding algorithm are necessary. This paper carries out numerical simulations on the pounding responses between a symmetric rectangular-shaped building and an asymmetric L-shaped building by using the explicit finite element code LS-DYNA. The detailed 3D FEMs are developed and arbitrary 3D pounding locations between these two buildings under bi-directional earthquake ground motions are investigated. Special attention is paid to the relative locations of two adjacent buildings. The influences of the left-and-right, fore-and-aft relative locations and separation gap between the two buildings on the pounding responses are systematically investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.296-302
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• 2019

In this study, a basic durability assessment was performed by selecting the main part of a trial product of a shale shaker, which is one of components for a mud circular system. For a preliminary durability assessment, it was assumed that the lifetime of the bearing for the vibrator motor and the stiffness of the support spring are affected by the vibration when the motor operates continuously. In the case of the motor, the initial p-p level was 0.72 g, but after 100 hours of operation, the p-p level was rapidly increased to 1.26 g. Bearing defects could be estimated through ball defect frequency analysis. In the case of the spring, the stiffness of the spring was reduced by approximately 3.78% at the end of 2,000 hours of the fatigue-durability test by applying excitation conditions to shale shaker body. In the future, we will analyze the influence of the particle removal efficiency of the shale shaker.