• Smart Structures and Systems
• /
• v.13 no.2
• /
• pp.281-303
• /
• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• Earthquakes and Structures
• /
• v.26 no.3
• /
• pp.239-249
• /
• 2024

A new layered shear continuum model box was developed to address the dynamic response issues of buried oil and gas pipelines under multi-point excitation. Vibration table tests were conducted to investigate the seismic response of buried pipelines and the surrounding soil under longitudinal multi-point excitation. A nonlinear model of the pipeline-soil interaction was established using ABAQUS finite element software for simulation and analysis. The seismic response characteristics of the pipeline and soil under longitudinal multi-point excitation were clarified through vibration table tests and simulation. The results showed good consistency between the simulation and tests. The acceleration of the soil and pipeline exhibited amplification effects at loading levels of 0.1 g and 0.2 g, which significantly reduced at loading levels of 0.4 g and 0.62 g. The peak acceleration increased with increasing loading levels, and the peak frequency was in the low-frequency range of 0 Hz to 10 Hz. The amplitude in the frequency range of 10 Hz to 50 Hz showed a significant decreasing trend. The displacement peak curve of the soil increased with the loading level, and the nonlinearity of the soil resulted in a slower growth rate of displacement. The strain curve of the pipeline exhibited a parabolic shape, with the strain in the middle of the pipeline about 3 to 3.5 times larger than that on both sides. This study provides an effective theoretical basis and test basis for improving the seismic resistance of buried oil and gas pipelines.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.1330-1336
• /
• 2007

The purpose of the study was to verify deduction of each coefficient necessary to analysis on micro-pressure waves and reliability of the analysis result. The tunnel running train model testing device used in the test was manufactured by scale of 1:60 and the study used a train model with ten cars long according to specifications of KTX model. The study applied tunnels with cross sections of $107.9m^3\;and\;95.1m^3$ and applied tunnel extensions with 1km, 0.75km and 0.5km. Also, the study tested train speed by changing it into 275, 300, 325 and 350km/h. The test device was a hydraulic launch system composed of a train model, a hydraulic launcher, a tunnel model and a brake. The study measured speed of a model trainby a speed sensor installed in the point of each 1.2m from the front of tunnel entrance and a pithead of tunnel exit and measured pressure change of internal tunnel continuously by installing pressure sensors in the entrance part of tunnel, in the middle part of tunnel and in the exit part of tunnel. As the result of the measurement, it was known that pressure slope of pressure wave happened in the entrance part of tunnel was increased by a nonlinear effect while spreading the tunnel or its pressure slope was reduced by diffusion. Also, the study compared and analyzed micro-pressure waves happened in the exit part of the tunnel by installing each kind of hoods in the entrance part of the tunnel to prevent reduction of micro-pressure waves.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.18 no.2
• /
• pp.154-165
• /
• 2006

In the present study, a numerical model using Boussinesq equation is set up to predict the interacted equilibrium between waves and their induced currents in the occurrence of breaking waves over an underwater shoal, and the numerical results are compared with results of existing hydraulic experiments. A sensitivity analysis has been done to find out appropriate values of breaking wave parameters with the result (regular wave case) of Vincent and Briggs (1989)’ experiment. Then the numerical model is applied to the irregular wave cases of the experiment and the hydraulic model test of Ieodo which is a natural undersea shoal. The results show that a strong current forms in the wave direction at the downstream side of the shoals, causing the attenuation of wave heights there. The calculated wave heights generally show a similar pattern with the measured data.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.12 no.3
• /
• pp.211-217
• /
• 2019

In this study, we compare and analyze the attributes of the software development cost model according to the shape parameters change of the Type-2 Gumbel lifetime distribution using the NHPP model. In order to analyze the software failure phenomena, the parametric estimation is applied to the maximum likelihood estimation method, and the nonlinear equations are calculated using the bisection method. As a result, when the attributes of the cost curves according to the change of shape parameters are compared, it is found that the larger the number of shape parameters, the lower the software development cost and the faster the release time. Through this study, it is expected that it will be helpful for the software developers to search for the development cost according to the software shape parameters change, and also to provide the necessary information for the attributes of the software development cost.

• Journal of the Korean Society of Visualization
• /
• v.20 no.3
• /
• pp.94-101
• /
• 2022

The evaluation of the drag and lift as the aerodynamic performance of airfoils is essential. In addition, the analysis of the velocity and pressure fields is needed to support the physical mechanism of the force coefficients of the airfoil. Thus, the present study aims at establishing two different deep learning models to predict force coefficients and flow fields of the airfoil. One is the convolutional neural network (CNN) model to predict drag and lift coefficients of airfoil. Another is the Encoder-Decoder (ED) model to predict pressure distribution and velocity vector field. The images of airfoil section are applied as the input data of both models. Thus, the computational fluid dynamics (CFD) is adopted to form the dataset to training and test of both CNN models. The models are established by the convergence performance for the various hyperparameters. The prediction capability of the established CNN model and ED model is evaluated for the various NACA sections by comparing the true results obtained by the CFD, resulting in the high accurate prediction. It is noted that the predicted results near the leading edge, where the velocity has sharp gradient, reveal relatively lower accuracies. Therefore, the more and high resolved dataset are required to improve the highly nonlinear flow fields.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.6B
• /
• pp.543-550
• /
• 2009

The traditional simple extrapolation type short term quantitative rainfall forecast can not realize the evolution of rainfall generating weather system. To overcome the drawback of the linear extrapolation type rainfall forecasting model, the history of a weather system from sequential weather radar information and a polynomial regression technique were used to generate forecast fileds of x-directional, y-directional velocities and radar reflectivity which considered the nonlinear behavior related to the evolution of weather systems. Results demonstrated that test statistics of forecasts using the developed model is better than that of 2-CAPPI forecast. However there is still a large room to improve the forecast of spatial and temporal evolution of local storms since the model is not based on a fully physical approach but a statistical approach.

• KEPCO Journal on Electric Power and Energy
• /
• v.2 no.3
• /
• pp.469-475
• /
• 2016

As we are facing the shortage of oil energy, studies on renewable energy, wind energy research has been naturally getting attention. Among wind energies, ocean wind energy is relatively abundant compared to land wind energy and therefore, is getting much attention in terms of its efficiency. However, the problem is the cost. Generally, the cost ratio of the supporting structure is over 25% of the total installation cost of a offshore wind turbine system. Thus, it is very important to reduce the total installation cost of the offshore wind turbine and develop accurate analysis methodology for various offshore wind turbine foundations. In this study, nonlinear structure-soil interaction analyses have been proposed and conducted for the typical suction bucket model of an offshore wind turbine foundation, and the results were compared with experimental test data for numerical validations.

• Steel and Composite Structures
• /
• v.27 no.1
• /
• pp.75-87
• /
• 2018

This paper presents a new method to compute the shear strength of composited structural B-C-W members. These B-C-W members, defined as concrete-filled steel box beams, columns and shear walls, consist of a slender rectangular steel plate box filled with concrete and inserted steel plates connecting the two long-side steel plates. These structural elements are intended to be used in structural members of super-tall buildings and nuclear safety-related structures. The concrete confined by the steel plate acts to be in a multi-axial stressed state: therefore, its shear strength was calculated on the basis of a concrete's failure criterion model. The shear strength of the steel plates on the long sides of the structural element was computed using the von Mises plastic strength theory without taking into account the buckling of the steel plate. The spacing and strength of the inserted plates to induce plate yielding before buckling was determined using elastic plate theory. Therefore, a predictive method to compute the shear strength of composited structural B-C-W members without considering the shear span ratio was obtained. A coefficient considering the influence of the shear span ratio was introduced into the formula to compute the anti-lateral bearing capacity of composited structural B-C-W members. Comparisons were made between the numerical results and the test results along with this method to predict the anti-lateral bearing capacity of concrete-filled steel box walls. Nonlinear static analysis of concrete-filled steel box walls was also conducted by using ABAQUS and the results agreed well with the experimental data.

• Journal of the Korea Concrete Institute
• /
• v.22 no.4
• /
• pp.511-517
• /
• 2010

The purpose of this study is to investigate the shear behavior of prestressed concrete deep beams and to provide the data for development of improved design criteria. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. Hence, in this study, the computer program, named RCAHEST (reinforced concrete analysis in higher evaluation system technology), was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. A bonded or unbonded tendon element based on the finite element method, that can represent the interaction between tendon and concrete of prestressed concrete member, is used. The proposed numerical method for the shear behavior of prestressed concrete deep beams is verified by comparing the analytical results with test data by others.