• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.67-75
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• 1986

This paper introduces the nonlinear Stream Function Wave Theory for design waves efficiently to compute the wave energy and energy transport quantities and to analyze the effects of nonlinearities on them. The Stream Function Wave Theory was developed by Dean for case of the observed waves with assymmetric wave profiles and of the design waves with symmetric theoretical wave profiles. Dalrymple later improved the computational procedure by adding two Lagrangian constraints so that more efficient convergence of the iterative numerical method to a specified wave height and to a zero mean free surface displacement resulted. And the Stream Function coefficients are computed numerically by the improved Marquardt algorithm developed for this study. As the result of this study the effects of nonlinearities on the wave quantities of the average potential energy density, the average kinetic energy density result in overestimation by linear wave theory compared to the Stream Function Wave Theory and increase monotonically with decreasing $L^*/L_O$ and with increasing $H/H_B$. The effects of nonlinearities on the group velocity and the wavelength quantities result in underestimation by linear wave theory and increase monotonically with increasing $H/H_B$. Finally the effect of nonlinearity on the average total energy flux results in overestimation for shallow water waves and underestimation for deep water waves by linear wave theory.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.12
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• pp.1217-1222
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• 2010

This paper describes the Model-Based Development(MBD) process behind the flight control software of a close-range unmanned aerial vehicle(KUS-9). An integrated development environment was created using a commercial tool(MATLAB $Simulink^{(R)}$), which was utilized to design models for linear/nonlinear simulation, flight control law, operational logic and HILS(Hardware In the Loop Simulation) system. Software requirements were validated through flight simulations and peer reviews during the design process, whereas the models were verified through the application of a DO-178B verification tool. The integrity of automatically generated C code was verified by using a separate S/W testing tool. The finished software product was embedded on two different types of hardware and real-time operating system(uC/OS-II, VxWorks) to perform HILS and flight tests. The key findings of this study are that MBD Technology enables the development of a reusable and an extensible software product and auto-code generation technology allows the production of a highly reliable flight control software under a compressed time schedule.

• Journal of Korean Society of Steel Construction
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• v.23 no.6
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• pp.669-677
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• 2011

The multi-span suspension bridge generally has more than three towers and two main spans. To economically and effectively design a multi-span suspension bridge, the proper stiffness ratio of the center tower to the side tower must be determined. This study was conducted to propose a method of figuring out briefly the structural behavior of the towers in a multi-span suspension bridge. In the equivalent suspension bridge model, the main cable of the multi-span suspension bridge is idealized as an equivalent cable spring, and the external loads of horizontal and vertical forces that were calculated using the tensile forces of the main cable were applied on top of the towers. The equilibrium equations of the equivalent multi-span suspension bridge model were derived and the equations were solved via nonlinear analysis. To verify the proposed method, a sample four-span suspension bridge with a main span length of 3,000 m was analyzed using thefinite element method. The displacements and moment reactions of each tower in the proposed method were compared with the FEM analysis results. Consequently, the results of the analysis of the equivalent suspension bridge model tended to be consistent with the results of the FEM analysis.

• Land and Housing Review
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• v.2 no.2
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• pp.195-204
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• 2011

During mechanical demolition of RC structures, weights of dismantling equipment and demolition waste of building are applied to unexpected load which did not be considered during the design of structural member. Nevertheless, the loading of dismantling equipment and dismantling process are mainly dependent on field managers' field workers' or experiences without considering safety of structural member by a structural engineer. It is urgently required that reflecting actual circumstance of mechanical demolition, safety evaluation method to evaluate the safety and the guideline for appropriate capacity of structural member to support dismantling equipment weight, be provided. Through site investigation and questionnaire on field workers, this paper proposed demolition waste load, load factor, strength reduction factor, and so on. These are essential to safe evaluation of a building, ready to demolition. Considering actual circumstance of mechanical demolition, safety evaluation method of building and design method of slab and beam was suggested to a dilapidated building. An capability to loading of dismantling equipment was proposed, applied to RC slab and RC beam. Therefore, the suggested safety evaluation method and the guideline for an capability to loading of dismantling equipment weight can reasonably evaluate the capacity of structural member in demolition and use effectively as increasing efficiency and improving safety of demolition through proper management of dismantling equipments.

• Composites Research
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• v.28 no.4
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• pp.212-218
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• 2015

A large composite spar was manufactured using an automatic fiber placement (AFP) machine. To verify its structural performance, the weakest part of the structure, which is called 'corner radius', was tested under bending and examined by finite element analysis. Since the application of AFP machine to composite structure fabrication is still in early stage in Korea, this paper presents the summary of whole process for manufacturing composite spar using AFP machine from mandrel design and analysis to verification test. The deflection and stress by mandrel weight and AFP machine force, thermal deformation and natural frequency were all examined for mandrel design. The target structure was composite C-spar and cured in an autoclave. Test results were compared with nonlinear finite element analysis results to show that the structure has the strength close to the theoretical value. It was confirmed that the corner radius of the spar manufactured by AFP process showed deviation less than 20% compared with first ply failure strength. The results indicate that the AFP technology could be used for large scale composite structure production in the near future.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.301-304
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• 2008

The stair joints constructed with prefabricated system are general method doing structure design at hinge. If you regarded joints to come in contact with a flight of stairs and a slope of stairs as hinge, the moment performance of joints is not in the least moment, so as the bending moment of the stair case is increased, the reinforcement increase. Also the use is decreased because increasing the joint damage of the vibration & fatigue load. No less the reason constructed with pin the stair joints because the construction efficiency of field work is useable. Recently, they are considering the construction efficiency, while the semi-rigid detail for bending performance of joints is proposed, but for now they don't reflect the detail. Therefore, we proposed that reflecting the method at design semi-rigid joints. We compared the moment performance with the stair joints designed at the rigid joints, semi-rigid joints and pin joints. The nonlinear behavior of staircase core statically indeterminate structure. The result of research is that a bending stiffness modulus bring to reflect the semi-rigid performance, the performance of the semi-rigid joint is better than pin joints, and that is judged the system better seismic and vibration performance because have excellent ductility more than rigid joint.

• Elastomers and Composites
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• v.44 no.3
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• pp.196-208
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• 2009

Sophisticated polymeric materials with 'responsive' properties are beginning to reach the market. The use of reversible, noncovalent interactions is a recurring design principle for responsive materials. Recently developed hydrogen-bonding units allow this design principle to be taken to its extreme. Supramolecular polymers, where hydrogen bonds are the only force keeping the monomers together, form materials whose (mechanical) properties respond strongly to a change in temperature or solvent. In this review, we describe some examples of hydrogen-bonded supramolecular polymers that can be utilized for self-healing materials. Synthesis of a rubber-like material that can be recycled might not seem exciting. But one that can also repeatedly repair itself at room temperature, without adhesives, really stretches the imagination. Autonomic healing materials respond without external intervention to environmental stimuli in a nonlinear and productive fashion, and have great potential for advanced engineering systems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.333-340
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• 2019

Tests using a middle velocity propulsion impact machine (MVPIM) were performed to verify the impact resistance capability of sandwich concrete panels (SCP) in a modular liquefied natural gas (LNG) outer tank, and numerical models were constructed and analyzed. $2{\times}2m$ specimens with plain sectional characteristics and specimens including a joint section were used. A 51 kg missile was accelerated above 45 m/s and impacted to have the design code kinetic energy. Impact tests were performed twice according to the design code and once for the doubled impact speed. The numerical models for simulating impact behaviors were created by LS-DYNA. The external steel plate and filled concrete of the panel were modeled as solid elements, the studs as beam elements, and the steel plates as elasto-plastic material with fractures; the CSCM material model was used for concrete. The front plate deformations demonstrated good agreement with those of other tests. However the rear plate deformations were less. In the doubled speed test for the plain section specimen, the missile punctured both plates; however, the front plate was only fractured in the numerical analysis. The impact energy of the missile was transferred to the filled concrete in the numerical analysis.

• Structural Engineering and Mechanics
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• v.72 no.1
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• pp.99-111
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• 2019

To investigate the seismic performance of long-span partially earth-anchored cable-stayed bridge, a super long-span partially earth-anchored cable-stayed bridge scheme with main span of 1400m is taken as example, structural response of the bridge under E1 seismic action is investigated numerically by the multimode seismic response spectrum and time-history analysis, seismic behavior and also the effect of structural geometric nonlinearity on the seismic responses of super long-span partially earth-anchored cable-stayed bridges are revealed. The seismic responses are also compared to those of a fully self-anchored cable-stayed bridge with the same main span. The effects of structural parameters including the earth-anchored girder length, the girder width, the girder depth, the tower height to span ratio, the inclination of earth-anchored cables, the installation of auxiliary piers in the side spans and the connection between tower and girder on the seismic responses of partially ground-anchored cable-stayed bridges are investigated, and their reasonable values are also discussed in combination with static performance and structural stability. The results show that the horizontal seismic excitation produces significant seismic responses of the girder and tower, the seismic responses of the towers are greater than those of the girder, and thus the tower becomes the key structural member of seismic design, and more attentions should be paid to seismic design of these sections including the tower bottom, the tower and girder at the junction of tower and girder, the girder at the auxiliary piers in side spans; structural geometric nonlinearity has significant influence on the seismic responses of the bridge, and thus the nonlinear time history analysis is proposed to predict the seismic responses of super long-span partially earth-anchored cable-stayed bridges; as compared to the fully self-anchored cable-stayed bridge with the same main span, several stay cables in the side spans are changed to be earth-anchored, structural stiffness and natural frequency are both increased, the seismic responses of the towers and the longitudinal displacement of the girder are significantly reduced, structural seismic performance is improved, and therefore the partially earth-anchored cable-stayed bridge provides an ideal structural solution for super long-span cable-stayed bridges with kilometer-scale main span; under the case that the ratio of earth-anchored girder length to span is about 0.3, the wider and higher girder is employed, the tower height-to-span ratio is about 0.2, the larger inclination is set for the earth-anchored cables, 1 to 2 auxiliary piers are installed in each of the side spans and the fully floating system is employed, better overall structural performance is achieved for long-span partially earth-anchored cable-stayed bridges.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.125-132
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• 2019

This paper presents a seismic reliability analysis method for an offshore wind turbine with a twisted tripod support structure under earthquake loading. A three dimensional dynamic finite element model is proposed to consider the nonlinearity of the ground-pile interactions and the geometrical characteristics of the twisted tripod support structure where out-of-plane displacement occurs even under in-plane lateral loadings. For the evaluation of seismic reliability, the failure probability was calculated for the maximum horizontal displacement of the pile head, which is calculated from time history analysis using artificial earthquakes for the design return periods. The application of the subset simulation method using the Markov Chain Monte Carlo(MCMC) sampling is proposed for efficient reliability analysis considering the limit state equation evaluation by the nonlinear time history analysis. The proposed method can be applied to the reliability evaluation and design criteria development of the offshore wind turbine with twisted tripod support structure in which two dimensional models and static analysis can not produce accurate results.