• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.6
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• pp.83-95
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• 1996

The normal cement concrete is widely used material to build the construction recently, but it has a fault to increase the dead load on account of its unit weight is large compared with strength. So, main purpose of this study was to establish the physical and mechanical properties of lightweight concrete using expanded polystyrene bead on fine aggregate and natural gravel, expanded clay and pumice stone on coarse aggregate. The test rusults of this study are summarized as follows; 1. The water-cement ratio of concrete using pumice stone was larger than that of the concrete using natural gravel and expanded clay. 2. The unit weights of concrete using pumice stone and expanded caly were shown less than 1,000g/$m^3$. 3. The compressive strengths of all types were shown less than 60kg/$cm^2$, tensile and bending strengths were shown less than l3kg/$cm^2$ and 3lkg/$cm^2$$^2$, respectively. 4. The pulse velocity of concrete was shown similar with using natural gravel and pumice stone, and shown the lowest using pumice stone. 5. The dynamic modulus of elasticity of concrete was shown considerably smaller, and shown the lowest using pumice stone. 6. The static modulus of elasticity of concrete using expanded clay and pumice stone were shown considerably smaller, and shown 22% ~29% as compared with the dynamic modulus of elasticity. 7. The stress-strain curves of concrete were shown similar, generally. And the curves were repeated at short intervals increase and decreased irregularly.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.968-980
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• 2023

The dynamic structural responses are sensitive to the time-frequency content of seismic waves, and seismic input motions in time-history analysis are usually required to be compatible with design response spectra according to nuclear codes. In order to generate spectra-compatible input motions while maintaining the intrinsic non-stationarity of seismic waves, an improved time-domain approach is proposed in this paper. To maintain the nonstationary characteristics of the given seismic waves, a new time-frequency envelope function is constructed using the Hilbert amplitude spectrum. Based on the intrinsic mode functions (IMFs) obtained from given seismic waves through variational mode decomposition, a new corrective time history is constructed to locally modify the given seismic waves. The proposed corrective time history and time-frequency envelope function are unique for each earthquake records as they are extracted from the given seismic waves. In addition, a dimension reduction iterative technique is presented herein to simultaneously superimpose corrective time histories of all the damping ratios at a specific frequency in the time domain according to optimal weights, which are found by the genetic algorithm (GA). Examples are presented to show the capability of the proposed approach in generating spectra-compatible time histories, especially in maintaining the nonstationary characteristics of seismic records. And numerical results reveal that the modified time histories generated by the proposed method can obtain similar dynamic behaviors of AP1000 nuclear power plant with the natural seismic records. Thus, the proposed method can be efficiently used in the design practices.

• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.487-495
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• 2017

Recently rapid-transit railway systems have been constructed in many developing countries due to its advantages in congestions and environmental problems. Railway bridges show many different aspects compared to road bridges and passenger comfort and traffic safety are one of them. In particular, deflection and acceleration due to repeated vibration characteristics have a structural weakness that can cause undesirable response. Especially steel railway bridges have been known to have weaknesses due to its relatively light weights compared to concrete bridges. The purpose of this study is to analyze the dynamic response of steel box girder bridges due to passing trains then propose the appropriate method to mitigate the level of vibration in terms of accelerations. Three steel railway bridges are tested and the numerical model to analyze the dynamic response of the bridge by passing train are developed. For the verification of the model, the natural frequency extracted using the acceleration data measured in the bridge is compared with the natural frequency of the numerical model. To mitigate the acceleration level of the bridge, parametric studies are performed to find the effectiveness of the method. Based on the analysis, the appropriate method is proposed for decreasing the acceleration of the bridge for passenger comfort and traffic safety.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.1
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• pp.71-78
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• 2005

Rescaled Simulated Annealing(RSA) has been devised for improving the disadvantage of Simulated Annealing(SA) which requires tremendous amount of computation time. RSA and SA have been for optimization of truss and satellite structures and for comparison of results from two algorithms. Ten bar truss structure which has continuous design variables are optimized.. As a practical application, a satellite structure is optimized by the two algorithms. Weights of satellite upper platform and propulsion module are minimized. MSC/NASTRAN is used for the static and dynamic analysis. The optimization results of the RSA are compared with results of the classical SA. The numbers of optimization iterations could be effectively reduced by the RSA.

• Water for future
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• v.25 no.3
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• pp.105-113
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• 1992

The purpose of this paper is to introduce and to apply the artificial neural network theory to real hydrologic system for forecasting daily streamflows during flood periods. The hydrologic dynamic process of rainfall-runoff is identified by the iterated estimation of system parameters that are determined by adjusting the weights of the network according to the non-linear response characteristics which is formed the model. Back propagation algorithm of neural network model is applied for the estimation of system parameters with past daily rainfall and runoff series data, and streamflows are forecasted using the parameters. The forecasted results are analyzed by statistical methods for the comparison with the observed.

• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.897-919
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• 2015

In this study, the effects of ground shocks due to explosive loads on the dynamic response of historical masonry bridges are investigated by using the multi-point shock response spectrum method. With this purpose, different charge weights and distances from the charge center are considered for the analyses of a masonry bridge and depending on these parameters frequency-varying shock spectra are determined and applied to each support of the two-span masonry bridge. The net blast induced ground motion consists of air-induced and direct-induced ground motions. Acceleration time histories of blast induced ground motions are obtained depending on a deterministic shape function and a stationary process. Shock response spectrums determined from the ground shock time histories are simulated using BlastGM software. The results obtained from uniform and multi-point response spectrum analyses cases show that significant differences take place between the uniform and multi-point blast-induced ground motions.

• Journal of Korean Biological Nursing Science
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• v.13 no.3
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• pp.291-297
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• 2011

Purpose: The research was to investigate the effect of stepbox exercise program on both male and female elderly' physiological index such as cardiovascular and to improve exercise efficacy. Methods: The research design was a non-equivalent control group, quasiexperimental study. From 2011-05-10 to 2011-07-26, 3 times a week for 12 weeks, the 43 elderly of health center of D district in G city who participated in the program and pre and post test at the same time were investigated. Results: Statistical significant differences had not been detected in systolic blood pressure and diastolic blood pressure, pulse showed a statistical significant differences. After test of physiological index, weights of participants showed decreasing tendency. body fat mass, skeletal muscle mass, BMI, body fat rate and waist-hip-ratio had also showed statistically significant differences. Conclusion: In conclusion, stepbox exercise program has positive effects on physiological index, blood pressure and pulse. Therefore, dynamic stepbox exercise program is considered to be a helpful intervention to improve comprehensive health conditions by giving the elderly both easy and less-pain exercise and the opportunity to manage their own health.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.4
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• pp.396-401
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• 2006

It is well-known that a neural network with cyclic connections generates plural limit cycles, thus, being used as a memory system for storing large number of dynamic information. In this paper, a continuous-time cyclic connection neural network was built so that each neuron is connected only to its nearest neurons with binary synaptic weights of ${\pm}1$. The type and the number of limit cycles generated by such network has also been demonstrated through simulation. In particular, the effect of chaos signal for transition between limit cycles has been tested. Furthermore, it is evaluated whether the chaotic noise is more effective than random noise in the process of the dynamical neural networks.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.48-56
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• 2003

This paper investigates the collapse characteristics of CF/Epoxy composite tubes subjected to axial loads as changing interlaminar number and outer ply orientation angle. The tubes are aften used for automobiles, aerospace vehicles, trains, ships, and elevators. We have performed static and dynamic impact collapse tests by a way of building impact test machine with vertical air compression. It is fanad that CF/Epoxy tube of the 6 interlaminar number (C-type) with 90$^{\circ}$ outer orientation angle and trigger absorbed more energy than the other tubes (A. B and D-types). Also collapse mode depended upon outer orientation angle of CF/Epoxy tubes and loading type as well； typical collapse modes of CF/Epoxy tubes are wedged, splayed and fragmentcl.

• Journal of Ocean Engineering and Technology
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• v.16 no.1
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• pp.8-15
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• 2002

This paper presents a neural net based nonlinear adaptive controller for an autonomous underwater vehicle (AUV). AUV's dynamics are highly nonlinear and their hydrodynamic coefficients vary with different operational conditions, so it is necessary for the high performance control system of an AUV to have the capacities of learning and adapting to the change of the AUV's dynamics. In this paper a linearly parameterized neural network is used to approximate the uncertainties of the AUV's dynamic, and the basis function vector of network is constructed according to th AUV's physical properties. A sliding mode control scheme is introduced to attenuate the effect of the neural network's reconstruction errors and the disturbances in AUV's dynamics. Using Lyapunov theory, the stability of the presented control system is guaranteed as well as the uniformly boundedness of tracking errors and neural network's weights estimation errors. Finally, numerical simulations for motion control of an AUV are performed to illustrate the effectiveness of the proposed techniques.