• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3353-3360
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• 2022

Using data from the design earthquake of the Korean standard nuclear power plant, seismic analyses of a fuel assembly are conducted in this study. The modal characteristics are used to develop an input deck for the seismic analysis. With a time history analysis, the responses of the fuel assembly in the event of an earthquake are obtained. In particular, the displacement, velocity, and acceleration responses at the center location of the fuel assembly are obtained in the time domain, with these outcomes then used for a detailed structural analysis of the fuel rods in the ensuing analyses. The response spectra are also generated to determine the response characteristics in the frequency domain. The structural integrity of the fuel assembly can be ensured through this type of time history analysis considering the input excitations of various earthquakes considered in the design.

• International Area Studies Review
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• v.21 no.2
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• pp.3-20
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• 2017

Traditional co-integration analysis method is known to be difficult to clearly determine the relationship between the cointegrated variables. This study utilizes a fractional cointegation method and a causal analysis of time and frequency domain among the exchange rates of Korea, China and Japan. The results show that even though traditional cointegration methods did not clarify the existence of cointegration, exchange rates were fractionally cointegrated. Causal analysis of time domain and frequency domain provided somewhat different results, but the yen/dollar was useful for forecasting won/dollar and yuan/dollar. Proper use of causal analysis of frequency domain and fractional cointegration emthods may provide useful information that can not be explained from the traditional method.

• Journal of Korean Academy of Nursing Administration
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• v.9 no.1
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• pp.5-18
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• 2003

Purpose : For improvement of nursing services in ambulatory unit, ambulatory nursing activity was identified and the required time by nursing activity was measured. Method : The data were collected from 4 tertiary hospitals and 2 secondary hospitals. The method of data collection was used the self-reporting method. The 123 nurse-work days and 137 nurse-aid-work days in 6 hospitals were analyzed. Results : As a result, 11 ambulatory nursing domains and 79 ambulatory nursing activities were confirmed. Above 50% of subjects performed the general outpatient affair domain. The percentage of total time spent in each domain were as follows : general outpatient affair domain, 58.3%, patient education ${\cdot}$ counseling domain, 10.8%, therapeutic care domain, 8.6% and so on. And the average hours were measured by activity and domain. Conclusion : For the improvement of ambulatory nursing care, the strategies that keep the legal standard of number of ambulatory nurse and exchange the nursing-aid for the nurse is needed. And it is also needed to standardize the ambulatory nursing services.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1854-1862
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• 2000

Input shaping method is to convolute input shaper, which is sequence of impulses, with reference input command not to excite the natural frequency of system. To reduce residual vibration for the ch ange of frequency, the number of impulses should be increased. Until now, amplitudes and time interval of those has been searched from the derivative of residual vibration. However, if time interval of impulses is fixed as the half of vibration period of system, input shaper H(z) in z-domain becomes (I-pz-1)n/K in which increasing n is the mean that robustness for change of parameter is improved. Also, design of many types of input shapers in z-domain is very easy because sensitivity curve is displayed with $\mid$H(z)zn$\mid$$\times$100. In the z-domain, EI(Extra-Insensitive) input shaper could be designed without solving nonlinear simultaneous equations as design in continuous time domain. In addition to, the design possibility of input shaper for a damped system was shown.

• Structural Engineering and Mechanics
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• v.31 no.2
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• pp.211-223
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• 2009

Transient response analysis can be conducted either in the time domain, or via the frequency domain. Sometimes a frequency domain method (FDM) has advantages over a time domain method. A practical issue in the FDM is to find out an appropriate extended period, which may be affected by several factors, such as the excitation duration, the system damping, the artificial damping, the period of interest, etc. In this report, the extended period of the FDM based on the Duhamel's integral is investigated. This Duhamel's integral based FDM does not involve the unit impulse response function (UIRF) beyond the period of interest. Due to this fact, the ever-lasting UIRF can be simply set as zero beyond the period of interest to shorten the extended period. As a result, the preferred extended period is the summation of the period of interest and the excitation duration. This conclusion is validated by numerical examples. If the extended period is too short, then the front portion of the period of interest is more prone to errors than the rear portion, but the free vibration segment is free of the wraparound error.

• Smart Structures and Systems
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• v.17 no.5
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• pp.753-771
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• 2016

This paper addresses the free and transient responses of a SDOF linear complex stiffness system by making use of the Hilbert transform and the convolution integral. Because the second-order differential equation of motion having the complex stiffness give rise to the conjugate complex eigen values, its time-domain analysis using the standard time integration scheme suffers from the numerical instability and divergence. In order to overcome this problem, the transient response of the linear complex stiffness system is obtained by the convolution integral of a green function which corresponds to the unit-impulse free vibration response of the complex system. The damped free vibration of the complex system is theoretically derived by making use of the state-space formulation and the Hilbert transform. The convolution integral is implemented by piecewise-linearly interpolating the external force and by superimposing the transient responses of discretized piecewise impulse forces. The numerical experiments are carried out to verify the proposed time-domain analysis method, and the correlation between the real and imaginary parts in the free and transient responses is also investigated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4B
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• pp.379-387
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• 2002

In this paper, we present a procedure to obtain the transient scattering response from three-dimensional arbitrarily shaped and closed conducting bodies using time-domain magnetic field integral equation (TD-MFIE) with triangular patch functions. This approach results in accurate and comparably stable transient responses from conducting scatterers. Detailed mathematical steps are included, and several numerical results are presented and compared with results from a time-domain electric field integral equation (TD-EFIE) and the inverse courier transform solution of the frequency domain results.

• Wind and Structures
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• v.24 no.5
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• pp.481-500
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• 2017

A novel three-degree-of-freedom (DOF) forced vibration system has been developed for identification of aeroelastic (self-excited) load parameters used in time-domain response analysis of wind-excited flexible structures. This system is capable of forcing sinusoidal motions on a section model of a structure that is used in wind tunnel aeroelastic studies along all three degrees of freedom - along-wind, cross-wind, and torsional - simultaneously or in any combination thereof. It utilizes three linear actuators to force vibrations at a consistent frequency but varying amplitudes between the three. This system was designed to identify all the parameters, namely, aeroelastic- damping and stiffness that appear in self-excited (motion-dependent) load formulation either in time-domain (rational functions) or frequency-domain (flutter derivatives). Relatively large displacements (at low frequencies) can be generated by the system, if required. Results from three experiments, airfoil, streamlined bridge deck and a bluff-shaped bridge deck, are presented to demonstrate the functionality and robustness of the system and its applicability to multiple cross-section types. The system will allow routine identification of aeroelastic parameters through wind tunnel tests that can be used to predict response of flexible structures in extreme and transient wind conditions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.12
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• pp.1683-1689
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• 2014

In this paper, we propose an image processing based time-frequency domain reflectometry(TFDR) in order to estimate the fault location of a cable. The Wigner-Ville distribution is used for analysis in both the time domain and the frequency domain when the conventional TFDR estimates the fault location in a cable. However, the Winger-Ville distribution is a bi-linear function, and hence the cross-term is occurred. The conventional TFDR cannot estimate the accurate fault location due to the cross-term in case the fault location is close to the position where the reference signal is applied to the cable. The proposed method can reduce the cross-term effectively using binarization and morphological image processing, and can estimate the fault location more accurately using the template matching based cross correlation compared to the conventional TFDR. To prove the performance of the proposed method, the actual experiments are carried out in some cases.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.79-85
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• 2003

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of defect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode But in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion curves. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.