• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.940-948
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• 2012

In Korea, researches on the exposure assessment of the hand-transmitted vibration started from the mid-90, however, they were performed in the limited industries such as auto-assembly plants and the evaluation of the vibration was mostly conducted by ISO 5349(1986). Therefore, it was necessary to assess hand-transmitted vibration levels of workplace such as ship building/repairing industry or mining industry where occupational injuries are largely occurred and to evaluate the vibration levels using revised ISO 5349(2001). The SVAN 948 Four Channels Sound & Vibration Analyser was used for the measurement. The workers using a chain saw were exposed to 1.7~2.8 $m/s^2$ of daily vibration level. Workers using a rock drill in a coal mining were exposed to the highest vibration acceleration among workers and the levels were 7.1~10.8 $m/s^2$. Vibration levels of grinders were different according to the types of grinders. The hand-transmitted vibration of 3 types of grinders were measured and the levels were 3.3~11.1 $m/s^2$. Workers using a impact wrench were exposed to 1.5~1.6 $m/s^2$ of vibration. Out of 20 kinds of machines, only 4 tools provided the information of vibration acceleration on the instructions. In addition, the current condition of workplace to control vibration was not much different from the past because there are no vibration exposure limit.

• Structural Engineering and Mechanics
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• v.15 no.3
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• pp.299-314
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• 2003

This investigation presents an efficient method for identifying modal characteristics from the measured displacement, velocity and acceleration signals of multiple channels on structural systems. A Vector Backward Auto-Regressive model (VBAR) that describes the relationship between the output information in different time steps is used to establish a backward state equation. Generally, the accuracy of the identified dynamic characteristics can be improved by increasing the order of the Auto-Regressive model (AR) in cases of measurement of data under noisy circumstances. However, a higher-order AR model also induces more numerical modes, only some of which are the system modes. The proposed VBAR model provides a clear characteristic boundary to separate the system modes from the spurious modes. A numerical example of a lumped-mass model with three DOFs was established to verify the applicability and effectiveness of the proposed method. Finally, an offshore platform model was experimentally employed as an application case to confirm the proposed VBAR method can be applied to real-world structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.541-545
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• 1996

In this paper, The performance and functions of automatic flatness control system installed on the 4 hi-reversing mill and has been investigated under actualconditions. A new automatic flatness control system incorporates a measuring roll for measurement and correction calculations, hydraulic roll benders, selective roll cooling, and a programmable controller for interface and data logging. The test results are as following. The more the exit steel strip thickness is thick, the smaller the I value, and the more it is thin, the larger the I value. And, a complex distribution of strip tension was controlled, for example, not only a quarter buckle but also a simple center wave and edge wave. Because the tension deviation is larger at acceleration speed and deceleration speed than steady speed, so automatic flatness control system of contact type is better to adopt over 450 m/min, automatic flatness control system reduces rapidly large flatness deviation. The maximum I value of strip has been decreased to 13 I, and defects caused by poor flatness have been drastically decreased. And coolant temperature for work roll cooling system on the automatic flatness control system is better to adopt about 50-55 .deg. C.

• Smart Structures and Systems
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• v.26 no.5
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• pp.667-680
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• 2020

This study aims at reporting a systematic procedure for evaluating the static and dynamic structural performance of steel bridges based on a short-period structural health monitoring measurement. Sungsu bridge located in Korea is considered as a case study presenting the most recent tests carried out to examine the bridge condition. Short-period measurements of Structural Health Monitoring (SHM) system were used during the bridge testing phase. A novel symmetry index is introduced using statistical analyses of deflection and strain measurements. Frequency Domain Decomposition (FDD) is implemented to the strain measurements to estimate the bridge mode shapes and damping ratios. Furthermore, Markov Chain Monte Carlo (MCMC) is also implemented to examine the reliability of bridge performance while ambient design trucks are in static or moving at different speeds. Strain, displacement and acceleration were measured at selected locations on the bridge. The results show that the symmetry index can be an efficient and useful measure in assessing the steel bridge performance. The results from the used method reveal that the performance of the Sungsu bridge is safe under operational conditions.

• Journal of Astronomy and Space Sciences
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• v.32 no.3
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• pp.189-200
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• 2015

In this study, we present the results of orbit determination (OD) using satellite laser ranging (SLR) data for the Science and Technology Satellite (STSAT)-2C by a short-arc analysis. For SLR data processing, the NASA/GSFC GEODYN II software with one year (2013/04 - 2014/04) of normal point observations is used. As there is only an extremely small quantity of SLR observations of STSAT-2C and they are sparsely distribution, the selection of the arc length and the estimation intervals for the atmospheric drag coefficients and the empirical acceleration parameters was made on an arc-to-arc basis. For orbit quality assessment, the post-fit residuals of each short-arc and orbit overlaps of arcs are investigated. The OD results show that the weighted root mean square post-fit residuals of short-arcs are less than 1 cm, and the average 1-day orbit overlaps are superior to 50/600/900 m for the radial/cross-track/along-track components. These results demonstrate that OD for STSAT-2C was successfully achieved with cm-level range precision. However its orbit quality did not reach the same level due to the availability of few and sparse measurement conditions. From a mission analysis viewpoint, obtaining the results of OD for STSAT-2C is significant for generating enhanced orbit predictions for more frequent tracking.

• Structural Engineering and Mechanics
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• v.78 no.3
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• pp.333-350
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• 2021

Motivated by the demand of seismic protection of museum collections and development of performance-based seismic design guidelines, this paper investigates the seismic fragility of sliding artifacts based on incremental dynamic analysis and three-dimensional finite element model of the artifact-showcase-museum system considering nonlinear behavior of the structure and contact interfaces. Different intensity measures (IMs) for seismic fragility assessment of sliding artifacts are compared. The fragility curves of the sliding artifacts in both freestanding and restrained showcases placed on different floors of a four-story reinforced concrete frame structure are developed. The seismic sliding fragility of the artifacts within a real-world museum subjected to bi-directional horizontal ground motions is also assessed using the proposed IM and engineering demand parameter. Results show that the peak floor acceleration including only values initiating sliding is an efficient IM. Moreover, the sliding fragility estimate for the artifact in the restrained showcase increases as the floor level goes higher, while it may not be true in the freestanding showcase. Furthermore, the artifact is more prone to sliding failure in the restrained showcase than the freestanding showcase. In addition, the artifact has slightly worse sliding performance subjected to bi-directional motions than major-component motions.

• The Journal of Korea Robotics Society
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• v.18 no.4
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• pp.427-435
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• 2023

This paper proposes a method of estimating the pose of a mobile robot by using a learning model. When estimating the pose of a mobile robot, wheel encoder and inertial measurement unit (IMU) data are generally utilized. However, depending on the condition of the ground surface, slip occurs due to interaction between the wheel and the floor. In this case, it is hard to predict pose accurately by using only encoder and IMU. Thus, in order to reduce pose error even in such conditions, this paper introduces a pose estimation method based on a learning model using data of the wheel encoder and IMU. As the learning model, long short-term memory (LSTM) network is adopted. The inputs to LSTM are velocity and acceleration data from the wheel encoder and IMU. Outputs from network are corrected linear and angular velocity. Estimated pose is calculated through numerically integrating output velocities. Dataset used as ground truth of learning model is collected in various ground conditions. Experimental results demonstrate that proposed learning model has higher accuracy of pose estimation than extended Kalman filter (EKF) and other learning models using the same data under various ground conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.233-238
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• 2016

The purpose of this study is to investigate the reliability of static balance measurements using a smartphone. Thirty subjects were selected among university students who had no fractures, history of operation, or inflammatory arthritis, and they had not started regular exercise during the past three months. The smartphone used in this study was a Galaxy S5LTE (SM-G900F, Samsung, Korea, 2014), and the application was a Sensor Kinetics Pro (Ver. 2.1.2, INNOVENTIONS Inc., US, 2015). Static balance ability was measured three times at one-day intervals between tests and retests. The first and second measurements used the same process. Analysis was done using the Wilcoxon signed rank test and intraclass correlation coefficient (ICC (2,1)). The results were as follows. With eyes opened, there was no significant difference (p>0.05), a high volume of correlation (r>0.75, p<0.05), and very high reliability (ICC>0.80) between the first measurement and second measurement. With eyes closed, there was also no significant difference (p>0.05), a high volume of correlation (r>0.75, p<0.05), and very high reliability (ICC>0.80) between the measurements. The results show that the smartphone is likely accurate for measuring static balance. This study will look forward to being the only basis for measuring future application development and the ability to balance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5C
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• pp.355-364
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• 2012

Target processing mechanisms are necessary to collect target information, real-time data fusion, and tactical environment recognition for cooperative engagement ability. Among these mechanisms, the target tracking starts from predicting state of speed, acceleration, and location by using sensors' measurements. However, it can be a problem to give the reliability because the measurements have a certain uncertainty. Thus, a technique which uses multiple sensors is needed to detect the target and increase the reliability. Also, data fusion technique is necessary to process the data which is provided from heterogeneous sensors for target tracking. In this paper, a target tracking algorithm is proposed based on probabilistic data association(PDA) by fusing radar and ESM sensor measurements. The radar sensor's azimuth and range measurements and the ESM sensor's bearing-only measurement are associated by the measurement fusion method. After gating associated measurements, state estimation of the target is performed by PDA filter. The simulation results show that the proposed algorithm provides improved estimation under linear and circular target motions.

• Journal of the Korean Magnetics Society
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• v.24 no.1
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• pp.22-27
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• 2014

North indicating azimuth angle sensors have been used in airplanes, ships traditionally and nowadays employed in smart phones. For the azimuth and roll angle measurement of the sensor, 3-axis acceleration sensor was added to the 3-axis magnetic field sensor. In this work, we have constructed a measuring system for the measurement of the magnetic field and the angle uncertainty of the magnetic field sensors. Measuring system could be useful not only in non-magnetic laboratory but also in normal laboratory, we constructed small size of 3-axis Helmholtz coils for the compensation environment magnetic field (Earth magnetic field and magnetic field from building) and the generation of magnetic field for the test of magnetic field sensor. The constructed measuring system could compensate environment magnetic field below 10 nT level and generate 3-dimensional magnetic field with magnitude uncertainty of 0.2 % and angle error of $0.2^{\circ}$ within the volume of ${\pm}30mm$ diameter at center of Helmholtz coils. For the conformation of developed measuring system, We tested commercially available 3-axis magnetometer and heading sensor.