• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.10
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• pp.792-798
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• 2002

The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function (FRF) of the structure. However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer are transient and have damping, they are undoubtedly non-periodic. It is inevitable that the signals be acquired for limited recording time, which causes the finite record length error and the leakage error. In this paper, the errors in the frequency response function of multi degree of freedom system are formulated theoretically. And the method to remove these errors is also suggested. This method is based on the optimization technique. A numerical example of 3-dof model shows the validity of the proposed method.

• Korea-Australia Rheology Journal
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• v.20 no.1
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• pp.27-34
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• 2008

Clay suspensions in liquid polymers exhibit a time-dependent behaviour that includes viscoelastic as well as thixotropic features. Because of the presence of interacting clay platelets, particulate networks can develop, which are broken down during flow and rebuild upon cessation of the flow. Here, the use of thixotropic techniques in probing flow-induced structures in nanocomposites is explored with data on a hectorite-poly(isobutylene) model system. By means of fast stress jump measurements the hydrodynamic contributions to the steady state stresses are determined as well as those caused by the stretching of the clay floes. Flow reversal measurements do not provide a clear indication of flow-induced anisotropy in the present case. The recovery of the clay microstructure upon cessation of flow is followed by means of overshoot and dynamic measurements. The development of a particulate network is detected by the appearance and growth of a low frequency plateau of the storage moduli. The modulus-frequency curves after various rest times collapse onto universal master curves, regardless of the pre-shear history or temperature. The scaling factors for this master curve are the crossover parameters. The crossover moduli are nearly a linear function of the crossover frequency, the relation being identical for recovery after shearing at different shear rates. This function depends, however, on temperature.

• Smart Structures and Systems
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• v.31 no.1
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• pp.45-56
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• 2023

Vibration-based structural health monitoring is used to ensure the safety of structures by installing sensors in structures. The peak picking method, one of the applications of vibration-based structural health monitoring, is a method that analyze the dynamic characteristics of a structure using the peaks of the frequency response function. However, the results may vary depending on the person predicting the peak point; further, the method does not predict the exact peak point in the presence of noise. To overcome the limitations of the existing peak picking methods, this study proposes a new method to automate the modal analysis process by utilizing long short-term memory, a type of recurrent neural network. The method proposed in this study uses the time series data of the frequency response function directly as the input of the LSTM network. In addition, the proposed method improved the accuracy by using the phase as well as amplitude information of the frequency response function. Simulation experiments and lab-scale model experiments are performed to verify the performance of the LSTM network developed in this study. The result reported a modal assurance criterion of 0.8107, and it is expected that the dynamic characteristics of a civil structure can be predicted with high accuracy using data without experts.

• The Journal of Korean Physical Therapy
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• v.24 no.1
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• pp.29-34
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• 2012

Purpose: The purpose of this study was to evaluate the difference between respiratory function and speech production, according to the seat surface inclination while in the sitting position. Methods: Respiratory function (FVC, FEV1) and speech production (inspiratory frequency, unit reading time, paragraph reading time) were measured in 3 sitting conditions: horizontal seat surface, seat surface tilted forward 15 degrees, and seat surface tilted backward 15 degrees. Results: We found that the mean values of FVC and FEV1 were statistically significant different according to three types of sitting positions (p<0.05). The following result was observed: forward tilted sitting > horizontal sitting > backward tilted sitting. There was no significant difference in speech production between the different positions. Respiratory function and speech production had a significantly negative correlation in the forward tilted condition and the backward tilted condition. Conclusion: This finding suggests that the seat surface inclination have an effect on respiratory function. Especially, forward tilted sitting may be an effective posture that may help increases the respiratory function.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.269-279
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• 2009

The design flood estimation in a large river basin has a lot of uncertainties in areal reduction factors, time-spatial rainfall distribution, and parameters of rainfall-runoff model. The use of historical concurrent rainfall events for estimating design flood would reduce the uncertainties. This study presents a procedure for estimating design floods using historical rainfall events and storage function model. The design rainfall and time-spatial distribution were determined through analyzing concurrent rainfall events, and the design floods were estimated using storage function model with a non-linear hydrology response. To evaluate the applicability of the procedure of this study, the estimated floods were compared to results of frequency analysis of flood data. Both floods gave very similar results. It shows the applicability of the procedure presented in this study for estimating design floods in practices.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2209-2212
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• 2003

In this paper, we propose the method to extract the important frequency bands from the EMG signal, and for generation of feature vector using the important frequency bands. The EMG signal is measured with 4 sensor and is recorded as 4 channel’s time series data. The same frequency bands from 4 channel’s frequency components are selected as the important frequency bands. The feature vector is calculated by the function formed using the combination of selected same important frequency bands. The EMG signals acquired from seven wrist motion type are recognized by changing into the feature vector formed. Then, the extraction and generation is performed by using the double combination of the genetic algorithm (GA) and the neural network (NN). Finally, in order to illustrate the effectiveness of the proposed method, computer simulations are done.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.6
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• pp.1393-1401
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• 2019

Recently as voice authentication function is installed in the system, it is becoming more important to accurately authenticate speakers. Accordingly, a model for verifying speakers in various ways has been suggested. In this paper, we propose a new method for verifying speaker verification using a Short-time Fourier Transform(STFT). Unlike the existing Mel-Frequency Cepstrum Coefficients(MFCC) extraction method, we used window function with overlap parameter of around 66.1%. In this case, the speech characteristics of the speaker with the temporal characteristics are studied using a deep running model called RNN (Recurrent Neural Network) with LSTM cell. The accuracy of proposed model is around 92.8% and approximately 5.5% higher than that of the existing speaker certification model.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1147-1156
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• 1993

In order to analyze lateral control in the backward maneuver of a tractor -trailer combination , a kinematic vehicle model and a human operator model with time delay were utilized for the operator/vehicle system. The analysis was carried out using the frequency domain approach. The open-loop stability of the vehicle motion was analyzed through the transfer functions. The sensitivity of the stability of the vehicle motion. to a change in the steering angle, was also analyzed. A mathematical model of the closed -loop operator/vehicle system was then formulated. The closed -loop stability of the operator /vehicle system was then analyzed. The effect of the delay time on the system was also analyzed through computer simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.213-219
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• 2004

This paper proposes speaker recognition algorithm which includes the pitch parameter for the peak and valley. The time-frequency hybrid method for pitch extraction is valuable in that it can improve resolution in the time domain and accuracy in the frequency domain at the same time. It makes reference pattern using membership function and performs vocal track recognition of common character using fuzzy pattern matching in order to include time variation width for non-linear utterance for proposed method, speaker recognition experiments are carried out using vowels and number sounds.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.73-82
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• 2005

This paper describes shock waveform synthesis methods for a shock response spectnlm over a short time interval with which intereference between parts within a test item is increased to perform a sufficient shock test for damage or malfunction which may be caused by the interference between parts, and a digital filter for obtaining a shock response history required for the shock waveform synthesis and a digital inverse filter for restoration by inversely using the digital filter. The time at which the maximax value occurs in the response history is detected in order to establish a delay time which is one of the parameters in the wavelet, on the condition that the natural frequency of SDOF system with a Q (quality factor) of 10 equals to the wavelet frequency of the zero delay wavelet input. A shock response spectrum over a short time interval and an abrupt change in the acceleration for an instant are illustrated as features of the synthesized waveform.