• Journal of Korea Multimedia Society
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• v.16 no.10
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• pp.1147-1155
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• 2013

In this study, we designed and implemented a step detection analyzer that can compare and analyze the step detection rates and results among the step detection algorithms. The step detection analyzer converts 3-axes accelerometer data into continuous energy stream through SVM operation, shows the horizontal comparison among the step detection results for each step detection algorithms, and can make elemental detection analyses. For these processes, the step detection analyzer presents the continuous energy stream as energy waveform, checks the peak values and time location of the detected steps with step detection algorithms, and gives visual interface to get some possible causes in cases of step detection miss. It can also give the threshold graph for each algorithm to check the threshold value on missed cases directly and can help to get more appropriate threshold values or other adjustable parameters in step detection algorithm. This step detection analyzer can be applied efficiently on performance enhancement of step detection algorithm, on deciding an appropriate algorithm for a specific step counter system in the various step counter filed operations.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.32-39
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• 2013

The next generation high-speed train(HEMU-430X) is Korea's first electric multiple unit type, high speed vehicle resulting from a national R&D project. Tests have been conducted on the Kyungbu High Speed Line running at speeds up to 354.64km/h, and analysis of the dynamic behavior of the train was carried out to evaluate its safety. In this study, a simplified method using an accelerometer(the method specified in UIC 518 OR) was chosen to analyze the safety of the train's dynamic behavior. The section chosen for analysis section was ${\pm}10{\sim}20km/h$ with respect to the maximum speed point. In addition, we analyzed the trend of this dynamic behavior with increasing speed by comparing the analyzed values with those of UIC 518 OR. The dynamic behavior results met the limit values of UIC 518 OR and the study indicates that this trend is predicted to continue at speeds above 354km/h.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.414-419
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• 2020

An artificial intelligence-based cable tension estimation model was developed to expand the utilization of data obtained from cable accelerometers of cable-stayed bridges. The model was based on an algorithm for selecting the natural frequency in the tension estimation process based on the vibration method and an applied artificial neural network (ANN). The training data of the ANN was composed after converting the cable acceleration data into the frequency, and machine learning was carried out using the characteristics with a pattern on the natural frequency. When developing the training data, the frequencies with various amplitudes can be used to represent the frequencies of multiple shapes to improve the selection performance for natural frequencies. The performance of the model was estimated by comparing it with the control criteria of the tension estimated by an expert. As a result of the verification using 139 frequencies obtained from the cable accelerometer as the input, the natural frequency was determined to be similar to the real criteria and the estimated tension of the cable by the natural frequency was 96.4% of the criteria.

• Journal of Digital Convergence
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• v.14 no.8
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• pp.253-259
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• 2016

Regarding the research on lane recognition, continuous studies have been in progress for vehicles to navigate autonomously and to prevent traffic accidents, and lane recognition and detection have remarkably developed as different algorithms have appeared recently. Those studies were based on vision system and the recognition rate was improved. However, in case of driving at night or in rain, the recognition rate has not met the level at which it is satisfactory. Improving the weakness of the vision system-based lane recognition and detection, applying sensor convergence technology for the response after accident happened, among studies on lane detection, the study on the curve road detection was conducted. It proceeded to study on the curve road detection among studies on the lane recognition. In terms of the road detection, not only a straight road but also a curve road should be detected and it can be used in investigation on traffic accidents. Setting the threshold value of curvature from 0.001 to 0.06 showing the degree of the curve, it presented that it is able to compute the curve road.

• Geotechnical Engineering
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• v.11 no.4
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• pp.37-48
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• 1995

The dynamic behavior of dry sand under different vibration conditions is studied through laboratory experiments. Sinusoidal and random vibration experiments of sand are carried out in vertical direction under various surcharge loads. Five different sand samples are selected for the azperiment. They are composed of four different -size samples of particles and one sample which is simulated the field condition. In case of sinusoidal vibration, the change in relative density is measured with acceleration levels. To produce an acceleration, the vibration amplitude is maintained within the range of 0.4mm~0.6mm and the vibration frequency is changed within the range of 3Hz~40Hz. In case of random vibration, the combined sinusoidal acceleration is produced by a random vibration generator and the change in relative density is measured by an accelerometer. Based on the experimental results, it is found that the sandy soil is compacted to 94%~99% of relative density by vertical acceleration and the peak acceleration producing the maximum relative density is proportional to the difference between maximum and minimum void ratios. It is also found that the effect of surcharge loading : the greater the surcharge loading, the larger the change in relative density and the greater the acceleration required to change the relative density.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.46-54
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• 2021

In this paper, active noise control was performed to reduce radiated noise in the low frequency band of dishwashers. First, through an analysis of the noise environment of the dishwasher, it was confirmed that the pump noise contributed the most to the radiated noise in the low frequency band, From the result of the noise environment analysis, the reference signal was selected to be the vibration signal of the pump body. The reference signal was obtained by using the accelerometer on the pump body, which can prevent acoustic feedback. The error signal sensor was selected as a microphone located at 1 m in front of the dishwasher and 0.5 m in height. And to design the controller, the error signal and the reference signal were measured at the operational rpms of the dishwasher at 2,500 rpm, 2,600 rpm and 2,800 rpm, and the secondary path transfer function was measured. The designed controller was mounted on Digital Signal Processor (DSP) equipment, and the control performance was verified experimentally. As a result of the measurement at the 3 operational rpms, the 7th multiple component of pump operating frequency decreased by 1.93 dB, 4.43 dB, 5.15 dB per rpm, and the 12th multiple component decreased by 6.67 dB, 2.34 dB, 4.28 dB per rpm. And overall Sound Pressure Level (SPL) decreased by 0.84 dB, 2.58 dB, 1.48 dB by rpm.

• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.167-174
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• 2016

Objective: The purpose of this study was to determine the interrelationship between ranges of motion of the knee and ankle joints on the sagittal plane and the attenuation magnitude of impact shock at high frequency (9~20 Hz) in the support phase during downhill running. Method: Fifteen male heel-toe runners with no history of lower extremity injuries were recruited for this study (age, $25.07{\pm}5.35years$; height, $175.4{\pm}4.6cm$; mass, $75.8{\pm}.70kg$). Two uniaxial accelerometers were mounted to the tuberosity of tibia and sacrum, respectively, to measure acceleration signals. The participants were asked to run at their preferred running speed on a treadmill set at $0^{\circ}$, $7^{\circ}$, and $15^{\circ}$ downhill. Six optical cameras were placed around the treadmill to capture the coordinates of the joints of the lower extremities. The power spectrum densities of the two acceleration signals were analyzed and used in the transfer function describing the gain and attenuation of impact shock between the tibia and the sacrum. Angles of the knee and ankle joints on the sagittal plane and their angle ranges were calculated. The Pearson correlation coefficient was used to test the relationship between two variables, the magnitude of impact shock, and the range of joint angle under three downhill conditions. The alpha level was set at .05. Results: Close correlations were observed between the knee joint range of motion and the attenuation magnitude of impact shock regardless of running slopes (p<.05), and positive correlations were found between the ranges of motion of the knee and ankle joints and the attenuation magnitude of impact shock in $15^{\circ}$ downhill running (p<.05). Conclusion: In conclusion, increased knee flexion might be required to attenuate impact shock during downhill and level running through change in stride or cadence while maintaining stability, and strong and flexible ankle joints are also needed in steeper downhill running.

• The Journal of the Acoustical Society of Korea
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• v.33 no.1
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• pp.31-39
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• 2014

In this paper, two calibration methods for angular vibration pickups using a precision rotary encoder are proposed. The KRISS (Korea Research Institute of Standards and Science) primary angular vibration calibration system and the calibration procedures are briefly explained. The rotary encoder is shown to be calibrated in two methods: The one is to use the laser interferometer to calibrate the rotary encoder under test and the other is to exploit the certificate of the encoder supplied. Complex sensitivities measured from the first are shown to be less than 0.1 % difference in magnitude and $0.01^{\circ}$ difference in phase shift in reference to those of the primary calibration system. Their expanded uncertainties were observed to be less than 0.6 % in magnitude and $0.4^{\circ}$ in phase shift over the range of 0.4 to 200 Hz. Under the same calibration conditions, complex sensitivities evaluated by the second method are shown be 0.1 % difference in magnitude and $0.6^{\circ}$ difference in phase shift in reference to those of the primary calibration system. Their expanded uncertainties were seen to be less than 4.8 % in magnitude and $2.8^{\circ}$ in phase shift.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.1
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• pp.53-62
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• 2017

In this paper, we present the score classification accuracy of BBS(Berg Balance Scale) which is the most commonly used balance evaluation tool using machine learning. Data acquisition was performed using the Noraxon system and an inertial sensor of Noraxon system was attached to the body in 8 locations (left and right ankle, left and right upper buttocks, left and right wrists, back, forehead). Based on the 3-axis accelerometer of the inertial sensor, the feature vector STFT(Short Time Fourier Transform) and SAM(Signal Area Magnitude) were extracted. Then, the items of the BBS were divided into static movement and dynamic movement depending on the operation characteristics, and the feature vectors were selected according to the sensor attachment positions which affect the score for each item of the BBS. Feature vectors selected for each item of BBS were classified using GMM(Gaussian Mixture Model). As a result of the accuracy calculation for 40 subjects, 55.5%, 72.2%, 87.5%, 50%, 35.1%, 62.5%, 43.3%, 58.6%, 60.7%, 33.3%, 44.8%, 89.2%, 51.8%, 85.1%, respectively.

• Journal of the Korean Wood Science and Technology
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• v.16 no.3
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• pp.48-64
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• 1988

This study was carried out to investigate the free vibrational properties of traditional and replaceable species for sounding board, using piezoelectrical accelerometer and signal analyzer. In the study, the frequency equations of free-free beam carrying a concentrated mass in the transverse vibration and of free-mass beam in the longitudinal vibration were used. The results obtained were as follows. 1. Average values of dynamic modulus of rigidity of Korean commercial species measured were as follows. Paulownia tomatosa (Thunb.) Steudel: $5.590\times10^9\;dyne/cm^2$ Tilia amurensis Rupr.: $5.414\times10^9\;dyne/cm^2$ Macckia amurensis Rupr.: $10.044\times10^9\;dyne/cm^2$ Fraxinus mandshurica Rupr.: $8.876\times10^9\;dyne/cm^2$ Ulmus davidiana var.japonica Nakai: $8.677\times10^9\;dyne/cm^2$ Pinus rigida Miller: $6.33\times10^9\;dyne/cm^2$ Fraxinus rhynchophylla Hance: $4.666\times10^9\;dyne/cm^2$ 2. The ratio of dynamic transverse Young's modulus to dynamic modulus of rigidity, $E_T/G_{LT}$, was 24.922 for Fraxinus rhynchophylla Hance, which was the highest, 7.317 for Paulownia tomentosa (Thunb.) Steudel, which was the lowest among Korean commercial species measured. 3. The value of longitudinal dynamic Young's modulus was about 3.7% and 19.8%, respectively, higher than those of transverse dynamic and static Young's modulus. The value of transverse dynamic Young's modulus was about 15.5% higher than that of static Young's modulus. 4. Predicted value of MOR in terms of correlation coefficient by transverse dynamic Young's modulus was slightly higher than that of static Young's modulus, but no significance was found out. 5. Transverse dynamic Youne's modulus was $(2.002\pm0.288)\times10^{11}\;dyne/cm^2$ for Fraxinus mandshurlca Rupr., which was the highest, $(0.601\pm0.100)\times10^{11}\;dyne/cm^2$ for Paulownia tomentosa (Thunb.) Steudel, which was the lowest among Korean commercial species measured. The sound velocity of sitka spruce was 5,685 m/sec, which was the highest. 6. Internal friction of Paulownia tomentosa (Thunb.) Steudel was shown the lowest value among Korean commercial species, $(8.795\pm1.795)\times10^{-3}$, but was higher than that of sitka spruce, $(7.331\pm0.991)\times10^{-3}$. Internal friction was shown negative correlation with density and dynamic Young's modulus, respectively. 7. K value was affected largely by internal friction and was the highest, $2.225\times10^8$ for Paulownia tomentosa (Thunb.) Steudel and was the lowest, $0.550\times10^8$ for Fraxinus rhynchophylla Hance. K value of Paulownia tomentosa (Thunb.) Steudel was higher than that of sitka spruce and K values of melapi and cottonwood, which have been considered to be replaceable species with sitka spruce in the piano industry, were lower than those of Paulownia tomentosa (Thunb.) Steudel and mill amurensis Rupr.