• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.339-339
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• 2006

In this study, the microvoids in glassy polymers were investigated by Xe sorption and $^{129}Xe$ NMR measurements. Xe sorption isotherms of glassy polymers have been successfully interpreted by the dual-mode sorption model. $^{129}Xe$ NMR chemical shift of the $^{129}Xe$ in the samples show nonlinear low-field shift with increasing sorption amount of Xe because of a fast exchange of Xe atoms between Henry and Langmuir sites, whereas it has showed linear shift against sorption amount of Xe into the Langmuir site. From this Xe-density dependence of the $^{129}Xe$ NMR chemical shift, it has been able to estimate mean size of the microvoids in glassy polymer. It is confirmed that there is correlation between ${C_H}'$ and volume or number of microvoids. From these findings, it is demonstrated that $^{129}Xe$ NMR spectroscopy is a powerful technique to determine the mean size and number of microvoids in glassy polymers.

• Journal of Mechanical Science and Technology
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• v.14 no.4
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• pp.380-392
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• 2000

A typical production-distribution system consist of three main echelons representing the retailer, distributors, and a factory each with an on-site warehouse. The system is sufficiently general and realistic to represent many industrial situations. However, decision functions and parameters have been selected to apply particularly to the production and distribution of consumer durables. The flows included in the model are materials, orders, and those information flows needed to support the material and order-rate decisions. In this work, a realistic production-distribution system has been used as a basic model, which consists of three sectors: retailer, distributor, and factory. That system is a nonlinear 25th-order continuous system interconnected between the echelons. Using a modern control algorithm, a typical multi-echelon production-distribution system using a dynamic controller is numerically simulated in the nominal plant and in the perturbed plant when the piecewise constant manufacturing decision is limited by a factory manufacturing upper-limit due to capital equipment, manpower, and factory lotsize.

• Wind and Structures
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• v.27 no.1
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• pp.41-57
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• 2018

Concentrated Solar Photovoltaic (CPV) is a promising alternative to conventional solar structures. These solar tracking structures need to be optimized to be competitive against other types of energy production. In particular, the selection of the structural parameters needs to be optimized with regards to the dynamic wind response. This study aims to evaluate the effect of the main structural parameters, as selected in the preliminary design phase, on the wind response and then on the weight of the steel support structure. A parametric study has been performed where parameters influencing dynamic wind response are varied. The study is performed using a semi-deterministic time-domain wind analysis method. Unsteady aerodynamic model is applied for the shape of the CPV structure collector at different configurations in conjunction with a consistent mass-spring-damper model with the corresponding degrees of freedom to describe the dynamic response of the system. It is shown that, unlike the static response analysis, the variation of the peak wind response with many structural parameters is highly nonlinear because of the dynamic wind action. A steel structural optimization process reveals that close attention to structural and site wind parameters could lead to optimal design of CPV steel support structure.

• Coupled systems mechanics
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• v.9 no.5
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• pp.433-454
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• 2020

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.

• International Journal of High-Rise Buildings
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• v.1 no.3
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• pp.203-209
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• 2012

The purpose of this paper is to present the state of practice being used in the Philippines for the performance-based seismic design of reinforced concrete tall buildings. Initially, the overall methodology follows "An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region, 2008", which was developed by Los Angeles Tall Buildings Structural Design Council. After 2010, the design procedure follows "Tall Buildings Initiative, Guidelines for Performance-Based Seismic Design of Tall Buildings, 2010" developed by Pacific Earthquake Engineering Research Center (PEER). After the completion of preliminary design in accordance with code-based design procedures, the performance of the building is checked for serviceable behaviour for frequent earthquakes (50% probability of exceedance in 30 years, i.e,, with 43-year return period) and very low probability of collapse under extremely rare earthquakes (2% of probability of exceedance in 50 years, i.e., 2475-year return period). In the analysis, finite element models with various complexity and refinements are used in different types of analyses using, linear-static, multi-mode pushover, and nonlinear-dynamic analyses, as appropriate. Site-specific seismic input ground motions are used to check the level of performance under the potential hazard, which is likely to be experienced. Sample project conducted using performance-based seismic design procedures is also briefly presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.120-127
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• 2004

With the proliferation of nonlinear loads such as switching mode power supplies, high neurtral harmonic currents in three-phase four-wire distribution system have been observed. It has been known that the grounded impedance has an effect on the neutral current of a system which operates with harmonics present since the neutral conductor is grounded. On-site measurements of harmonic currents and voltages were made and the corresponding equivalent circuit was developed. The circuit model under study was simulated numerically and graphically through the use of the software MATLAB. Simulation results verifying the relationship between the neutral harmonic current and ground impedance are presented.

• Steel and Composite Structures
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• v.35 no.3
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• pp.353-370
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• 2020

This paper describes a new type of replaceable fuse for moment resisting frames. Column-tree connections with beam splice connections are frequently preferred in the moment resisting frames since they eliminate field welding and provide good quality. In the column-tree connections, a part of the beam is welded to the column in the shop and the rest of the beam is bolted with the splice connection in the field. In this study, a replaceable reduced beam section (R-RBS) connection is proposed in order to eliminate welding process and facilitate assembly at the site. In the proposed R-RBS connection, one end is connected by a beam splice connection to the beam and the other end is connected by a bolted end-plate connection to the column. More importantly is that the proposed R-RBS connection allows the replacement of the damaged R-RBS easily right after an earthquake. Pursuant to this goal, experimental and numerical studies have been undertaken to investigate the performance of the R-RBS connection. An experimental study on the RBS connection was used to substantiate the numerical model using ABAQUS, a commercially available finite element software. Additionally, five different finite element models were developed to conduct a parametric study. The results of the analysis were compared in terms of the moment and energy absorption capacities, PEEQ, rupture and tri-axiality indexes. The design process as well as the optimum dimensions of the R-RBS connections are presented. It was also demonstrated that the proposed R-RBS connection satisfies AISC criteria based on the nonlinear finite element analysis results.

• Ocean and Polar Research
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• v.36 no.3
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• pp.225-234
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• 2014

The 2011 Tohoku earthquake triggered extremely destructive tsunami waves which propagated over the Pacific Ocean, Atlantic Ocean through Drake Passage and Indian Ocean respectively. A total of 10 tide-gauge records collected from the UNESCO/IOC site were analyzed through a band-pass digital filtering device to examine the observed tsunami characteristics. The ray tracing method and finite-difference model with GEBCO 30 arc second bathymetry were also applied to compare the travel times of the Tohoku-originated tsunami, particularly at Rodrigues in the Indian Ocean and King Edward Point in the Atlantic Ocean with observation-based estimates. At both locations the finite-difference model produced the shortest arrival times, while the ray method produced the longest arrival times. Values of the travel time difference however appear to be within tolerable ranges, considering the propagation distance of the tsunami waves. The observed tsunami at Rodrigues, Mauritius in the west of the Madagascar was found to take a clockwise travel path around Australia and New Zealand, while the observed tsunami at King Edward Point in the southern Atlantic Ocean was found to traverse the Pacific Ocean and then passed into the Atlantic Ocean through the Drake Strait. The formation of icebergs captured by satellite images in Sulzberger in the Antarctica also supports the long-range propagation of the Tohoku-originated tsunami.

• Rapid Communication in Photoscience
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• v.4 no.3
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• pp.54-58
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• 2015

Under the condition of femtosecond impulsive nonlinear optical irradiation, the bright and narrowed blue emission of silicon nanocrystal was observed. This synthetic method produced very small (~ 4 nm) oxide-capped silicon nanocrystal having probably ultra small emitting core (~ 1 nm) inferred from luminescence. By controlling the stirring condition, very high efficiencies of luminescence ( 4 fold higher) were obtained compared with the other conventional femtosecond laser fragmentation methods, which was attributed to the differences in hydration shell structure during the femtosecond laser induced irreversible phase transition reaction. When we properly adjusted the irradiation times of the white light continuum and stirring condition, very homogeneous luminescent silicon nanocrystal bands having relatively sharp lineshape were obtained, which can be attributable to the luminescent core site isolated and free from the surface defects.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.88-94
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• 2007

Structures with additional frictional damping system have strong nonlinearity that the dynamic behavior is highly affected by the relative magnitude between frictional force and excitation load. In this study, normalized response spectra of the structures with non-dimensional friction force are obtained through nonlinear time history analyses of the mass-normalized single degree of freedom systems using 20 ground motion data recorded on rock site. The variation of the control performance of frictional damping system is investigated in terms of the dynamic load and the structural natural period, of which effects were not considered in the previous studies. Least square curve fitting equations are presented for describing those normalized response spectrum and optimal non-dimensional friction forces are obtained for controlling the peak displacement and absolute acceleration of the structure based on the derivative of the curve-fitted design spectrum.