• Earthquakes and Structures
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• v.23 no.2
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• pp.115-128
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• 2022

One common method to select input ground motions to predict dynamic behavior of structures subjected to seismic excitation requires spectral acceleration (S_a) match target mean response spectrum. However, dispersion of ground motions, which explicitly affects the structural response, is rarely discussed in this method. Generally, selecting ground motions matching target mean and variance has been utilized as an appropriate method to predict reliable seismic response. The goal of this paper is to investigate the impact of target spectra variance of ground motions on structural seismic response. Two sets of ground motions with different target variances (zero variance and minimum variance larger than inherent variance of the target spectrum) are selected as input to two different structures. Structural responses at different heights are compared, in terms of peak, mean and dispersion. Results show that increase of target spectra variance tends to increase peak floor acceleration, peak deformation and dispersions of response of interest remarkably. To short-period structures, dispersion increase ratios of seismic response are close to that of S_a of input ground motions at the first period. To long-period structures, dispersions of floor acceleration and floor response spectra increase more significantly at the bottom, while dispersion increase ratios of IDR and deformation are close to that of S_a of input ground motions at the first period. This study could further provide useful information on selecting appropriate ground motion to predict seismic behavior of different types of structures.

• Korean Journal of Applied Biomechanics
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• v.12 no.1
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• pp.193-204
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• 2002

The purpose of this study was to investigate the effect of martial art type and target height on the ground reaction force factors during Dollyuchagi motion. Data were collected using force plate. Five Taekwondo players and five Hapkido players were tested during Dollyuchagi motion to three different target heights(0.8, 1.2, 1.6 m). After analysis of kinetics using force plate data, maximum vertical ground reaction force was 1.62~2.44 BW, and impulse was $0.66\sim1.01 BW{\cdot}s$. Even though there was no difference for maximum ground reaction forces and impulse between Hapkido and Taekwondo, as target height was higher, impulse increased. Anterior-posterior and vertical ground reaction forces at kicking foot take-off were greater with target height, although there was no difference for medio-lateral force with target height. At impact there was significant difference for anterior-posterior ground reaction force between Hapkido and Taekwondo players. Taekwondo players' force (range, -0.23~-0.26 BW) was greater than Hapkido players's force (range, -0.08~-0.14 BW).

• International Journal of Contents
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• v.15 no.1
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• pp.32-38
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• 2019

In an environment where a large number of weapons are operated compared to a large number of ground targets, it is important to monitor and manage the targets to set up a fire plan, and through their multilateral analysis, to equip them with a priority order process for targets having a high threat level through the quantitative calculation of the threat level. Existing studies consider the anti-aircraft and anti-ship targets only, hence, it is impossible to apply the existing algorithm to ground weapon system development. Therefore, we proposed an effective threat evaluation algorithm for multiple ground targets in multi-target and multi-weapon environments. Our algorithm optimizes to multiple ground targets by use of unique ground target features such as proximity degree, sorts of weapons and protected assets, target types, relative importance of the weapons and protected assets, etc. Therefore, it is possible to maximize an engagement effect by deducing an effective threat evaluation model by considering the characteristics of ground targets comprehensively. We carried out performance evaluation and verification through simulations and visualizations, and confirmed high utility and effect of our algorithm.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.5
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• pp.1-10
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• 2011

This paper proposes an efficient method for selecting ground motions with the mean response spectrum matching a target spectrum. Since former studies reported that the shape and amplitude of the response spectra can be treated independently for selecting ground motions, this study first selects ground motions such that the shape of their mean response spectrum matches that of the target spectrum, then scales the ground motions. To select the ground motions best matching the shape of the target response spectrum, the standard deviation of the difference between the target response spectrum and the mean response spectrum of the selected ground motions needs to be minimized. Unlike the existing procedure, the scaling factor can be computed without iteration. Based on the selection results of 7 ground motions from a library of 40 ground motions, the proposed method is verified as an accurate and efficient method.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.2
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• pp.155-160
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• 2012

In this paper, a strip modeling method is developed for the acquisition of target positions in remote area and validated using the imagery of SPOT satellite. This method utilizes the parameters given in header files and constructs a camera model without ground control points. In most cases, the root mean squared error of check points is less than pixel size with one ground control point. The model error of reference image is evaluated using ground control points and used to remove the model error of target images acquired along the same satellite orbit, which enables one to calculate target positions in remote area where no ground control points are available.

• Earthquakes and Structures
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• v.16 no.5
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• pp.563-573
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• 2019

When generating spectrum-compatible artificial ground motion in engineering practices, the effect of the variation in fitting parameters on the distribution of the peak ground displacement (PGD) has not yet drawn enough attention. In this study, a method for simulating ground motion matching for multiple targets is developed. In this method, a frequency-dependent amplitude envelope function with statistical parameters is introduced to simulate the nonstationarity of the frequency in earthquake ground motion. Then, several groups of time-history acceleration with different temporal and spectral nonstationarities were generated to analyze the effect of nonstationary parameter variations on the distribution of PGD. The following conclusions are drawn from the results: (1) In the simulation of spectrum-compatible artificial ground motion, if the acceleration time-history is generated with random initial phases, the corresponding PGD distribution is quite discrete and an uncertain number of PGD values lower than the limit value are observed. Nevertheless, the mean values of PGD always meet the requirement in every group. (2) If the nonstationary frequencies of the ground motion are taken into account when fitting the target spectrum, the corresponding PGD values will increase. A correlation analysis shows that the change in the mean and the dispersion values, from before the frequencies are controlled to after, correlates with the modal parameters of the predominant frequencies. (3) Extending the maximum period of the target spectrum will increase the corresponding PGD value and, simultaneously, decrease the PGD dispersion. Finally, in order to control the PGD effectively, the ground motion simulation method suggested in this study was revised to target a specified PGD. This novel method can generate ground motion that satisfies not only the required precision of the target spectrum, peak ground acceleration (PGA), and nonstationarity characteristics of the ground motion but also meets the required limit of the PGD, improving engineering practices.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.3 s.18
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• pp.93-100
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• 2004

In this paper, we describe the design, fabrication, and test results of a W-band FMCW radar for the metal target detection under the ground clutter environment. In order to detect metal targets on the ground, we used a single cassegrain antenna with the beamwidth of $1.45^{\circ}$ which forms pencil-beam footprint on the ground. A log envelope detector was applied to improve radar performance in the severe ground clutter known as Weibull and log normal clutter. The designed FMCW radar can acquire altitude information from the ground clutter with $\sigma_0=-23dB$ at the height of 160m. The fabricated W-band FMCW radar transmits 11 dBm power and the dynamic range of the receiver is from -106dBm to -30dBm. The performances of the fabricated sensors were tested out in the fields and detected a car target of 200m apart on the grass.

• Journal of the Korea Society of Computer and Information
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• v.16 no.3
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• pp.1-7
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• 2011

An attack aircraft such as a fighter needs an accurate location information of a target for the exact air-to-air or air-to-ground attack. In this paper a method is proposed that generates a location information of an air-to-ground target just in use of HMD without the target tracking sensors such as the radar and the FLIR. HMD is an embedded device to induce the seeker header to indicate the direction of a pilot's head. As a simulation result, it is founded that the target location information is able to be generated with a high degree of precision by using of HMD as a passive sensor.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.4
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• pp.11-21
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• 2015

In order to achieve success in ground operations, searching for moving targets is one of critical factors. Usually, the system of searching for adversary ground moving targets has complex properties which includes target's moving characteristics, camouflage level, terrain, weather, available search time window, distance between target and searcher, moving speed, target's tactics, etc. The purpose of this paper is to present a practical quantitative method for effectively searching for infiltrated moving targets considering aforementioned complex properties. Based upon search theories, this paper consists of two parts. One is infiltration route analysis, through terrain and mobility analysis. The other is building dynamic probability maps through Monte Carlo simulation to determine the prioritized searching area for moving targets. This study primarily considers ground moving targets' moving pattern. These move by foot and because terrain has a great effect on the target's movement, they generally travel along a constrained path. With the ideas based on the terrain's effect, this study deliberately performed terrain and mobility analysis and built a constrained path. In addition, dynamic probability maps taking terrain condition and a target's moving speed into consideration is proposed. This analysis is considerably distinct from other existing studies using supposed transition probability for searching moving targets. A case study is performed to validate the effectiveness and usefulness of our methodology. Also, this study suggests that the proposed approach can be used for searching for infiltrated ground moving target within critical time window. The proposed method could be used not only to assist a searcher's mission planning, but also to support the tactical commander's timely decision making ability and ensure the operations' success.

• Korean Journal of Remote Sensing
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• v.36 no.3
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• pp.441-448
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• 2020

GMTI (Ground Moving Target Indication) radar system can detect ground moving targets and can provide position and velocity information of each target. However, the azimuth position of target has some offset because of the hardware errors such as mechanical tolerances. In this case, an error occurs no matter how accurate the monopulse ratio is. In this paper, target position correction method in azimuth direction has been proposed. The received sum and difference signals of monopulse GMTI system are post-processed to correct the target azimuth angle error. This method is simple and adaptive for nonhomogeneous area because it can be implemented by using only software without any hardware modification or addition.