• Structural Engineering and Mechanics
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• v.15 no.4
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• pp.381-394
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• 2003

While constructing multistorey buildings with reinforced concrete framed structures it is a common practice to provide parking space for vehicles at the ground floor level. This floor will generally consist of open frames without any infilled walls and is called an open-storey. From a post disaster damage survey carried out, it was noticed that during the January 26, 2001 Bhuj (Gujarat, India) earthquake, a large number of reinforced concrete framed buildings with open-storey at ground floor level, suffered extensive damage and in some cases catastrophic collapse. This has brought into sharp focus the need to carry out systematic studies on the seismic vulnerability of such buildings. Determination of vulnerability requires realistic structural response estimations taking into account the stochasticity in the loading and the system parameters. The stochastic finite element method can be effectively used to model the random fields while carrying out such studies. This paper presents the details of stochastic finite element analysis of a five-storey three-bay reinforced concrete framed structure with open-storey subjected to standard seismic excitation. In the present study, only the stochasticity in the system parameters is considered. The stochastic finite element method used for carrying out the analysis is based on perturbation technique. Each random field representing the stochastic geometry/material property is discretised into correlated random variables using spatial averaging technique. The uncertainties in geometry and material properties are modelled using the first two moments of the corresponding parameters. In evaluating the stochastic response, the cross-sectional area and Young' modulus are considered as independent random fields. To study the influence of correlation length of random fields, different correlation lengths are considered for random field discretisation. The spatial expectations and covariances for displacement response at any time instant are obtained as the output. The effect of open-storey is modelled by suitably considering the stiffness of infilled walls in the upper storey using cross bracing. In order to account for changes in soil conditions during strong motion earthquakes, both fixed and hinged supports are considered. The results of the stochastic finite element based seismic analysis of reinforced concrete framed structures reported in this paper demonstrate the importance of considering the effect of open-storey with appropriate support conditions to estimate the realistic response of buildings subjected to earthquakes.

• Journal of Korea Water Resources Association
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• v.44 no.2
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• pp.157-167
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• 2011

A numerical model was developed to predict the stage-discharge curve and lateral distribution of unit discharge in open channels with nonuniform cross section or compound open-channels. The governing equation is the one-dimensional momentum equation based on assumptions of the steady and uniform flow conditions in the longitudinal direction and the uniform water surface elevation in a cross section. Vegetative drag force term was included in governing equation in order to reflect the effect of floodplain vegetation on the flow characteristics. Finite element method was applied to obtain the numerical solution of the governing equation. Stage-discharge curve and lateral distribution of unit discharge for a given water surface are calculated based on input data, such as the cross sectional geometry, Manning's roughness coefficient, vegetative information and longitudinal slope of channel bed. The developed model was verified by comparing the calculated results with the observed data and the results of Darby and Thorne's(1996) model and the nonlinear k-$\epsilon$ model. The verified model was applied to estimate the upstream boundary conditions in two-dimensional flow model. The numerical results using laterally distributed unit discharge were compared with those obtained using uniformly distributed unit discharge in two-dimensional flow model.

• Restorative Dentistry and Endodontics
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• v.33 no.4
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• pp.323-331
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• 2008

Flexibility and fracture properties determine the performance of NiTi rotary instruments. The purpose of this study was to evaluate how geometrical differences between three NiTi instruments affect the deformation and stress distributions under bending and torsional conditions using finite element analysis. Three NiTi files (ProFile .06 / #30, F3 of ProTaper and ProTaper Universal) were scanned using a Micro-CT. The obtained structural geometries were meshed with linear, eight-noded hexahedral elements. The mechanical behavior (deformation and von Mises equivalent stress) of the three endodontic instruments were analyzed under four bending and rotational conditions using ABAQUS finite element analysis software. The nonlinear mechanical behavior of the NiTi was taken into account. The U-shaped cross sectional geometry of ProFile showed the highest flexibility of the three file models. The ProTaper, which has a convex triangular cross-section, was the most stiff file model. For the same deflection, the ProTaper required more force to reach the same deflection as the other models, and needed more torque than other models for the same amount of rotation. The highest von Mises stress value was found at the groove area in the cross-section of the ProTaper Universal. Under torsion, all files showed highest stresses at their groove area. The ProFile showed highest von Mises stress value under the same torsional moment while the ProTaper Universal showed the highest value under same rotational angle.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.12 no.1
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• pp.34-38
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• 2001

Background and Objectives : With the development of computerized systems, an objective evaluation methods of nasal speech and nasal geometry have become readily available by means of a simple, noninvasive technique. In this study, we assessed the nasality, nasal formant, nasal volume and nasal area in patients with hypertrophic rhinitis before and after turbinate surgery. Material and Method : With the nasometer, we measured nasalance, which reflects the ratio of acoustic energy output of nasal sounds from the nasal and oral cavities. With CSL 4300B, we measured nasal formants. We used acoustic rhinometer to measure nasal area and nasal volume. Postoperative changes of above factors were compared with preoperative values. Paired t-test and Pearson's correlation were used for statistical analysis. Results : The first nasal formant frequency, nasalance scores of three passages(baby, mamma and rabbit passages), minimal cross sectional area(MCA) of narrow side, nasal volume of narrow side and nasal volume of wide side had increased significantly after turbinate surgery (p <0.05). The MCA and nasal volume of narrow side and MCA of wide side showed significant correlation with nasalance score of rabbit passage and baby passage showed significant correlation with nasal volume of narrow side(p<0.05). Conclusion : There were significant increases in nasalance scores, first nasal formant frequency, MCA and nasal volume after turbinate surgery. Thus, we must consider the possibility of voice changes postoperatively in professional voice users.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.3
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• pp.285-294
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• 2000

In this paper, a practical procedure for the design optimization of tubular-steel-pile-type substructure in a mooring dolphin is investigated and numerically evaluated. In the finite-dimensional optimum design formulation, geometry and cross-sectional shapes of classified group of piles are identified as design variables. The design objective is the total weight of piles, and the design constraints on stresses, penetration depth, and size limits are imposed. Several classes of practical design alternatives are sought through the linking and fixing of design variables. Among the available numerical optimization codes, both PLBA program and DNCONF subroutine in IMSL library are used. They are based on SQP algorithm and relatively easy to get. A dolphin of numerical example has 20 tubular steel piles, 4 vertical and 16 inclined. Optimum designs for different cases are successfully obtained for the practical purpose.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.96-105
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• 1995

A modified method for the analysis of short fatigue crack growth has been presented, and calculations based upon the modified method are compared with experimental results for S45C carbon steel. It is also shown that the modified method is in good agreement with experimental data. The proposed equation for the fatigue crack growth rates includes a material constant which relates the threshold level to the endurance limit, a correction for elastic-plastic behaviour and a means for dealing with the effects of crack closure. In this study one of the modifications is to substitute the Forman' s elastic expression of the stress intensity factor range into the geometrical factor The other is a consideration of the bending effect which is developed from the moment caused by the eccentric cross sectional geometry as the crack grows. Thus, this method is useful for residual life prediction of the mechanical structures as well as the welding structures.

• Journal of the korean society of oceanography
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• v.39 no.1
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• pp.72-95
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• 2004

The Yellow Sea is characterized by relatively shallow water depth, varying range of tidal action and very complex coastal geometry such as islands, bays, peninsulas, tidal flats, shoals etc. The dynamic system is controlled by tides, regional winds, river discharge, and interaction with the Kuroshio. The circulation, water mass properties and their variability in the Yellow Sea are very complicated and still far from clear understanding. In this study, an effort to improve our understanding the dynamic feature of the Yellow Sea system was conducted using numerical simulation with the ROMS model, applying climatologic forcing such as winds, heat flux and fresh water precipitation. The inter-annual variability of general circulation and thermohaline structure throughout the year has been obtained, which has been compared with observational data sets. The simulated horizontal distribution and vertical cross-sectional structures of temperature and salinity show a good agreement with the observational data indicating significantly the water masses such as Yellow Sea Warm Water, Yellow Sea Bottom Cold Water, Changjiang River Diluted Water and other sporadically observed coastal waters around the Yellow Sea. The tidal effects on circulation and dynamic features such as coastal tidal fronts and coastal mixing are predominant in the Yellow Sea. Hence the tidal effects on those dynamic features are dealt in the accompanying paper (Kim et at., 2004). The ROMS model adopts curvilinear grid with horizontal resolution of 35 km and 20 vertical grid spacing confirming to relatively realistic bottom topography. The model was initialized with the LEVITUS climatologic data and forced by the monthly mean air-sea fluxes of momentum, heat and fresh water derived from COADS. On the open boundaries, climatological temperature and salinity are nudged every 20 days for data assimilation to stabilize the modeling implementation. This study demonstrates a Yellow Sea version of Atlantic Basin experiment conducted by Haidvogel et al. (2000) experiment that the ROMS simulates the dynamic variability of temperature, salinity, and velocity fields in the ocean. However the present study has been improved to deal with the large river system, open boundary nudging process and further with combination of the tidal forcing that is a significant feature in the Yellow Sea.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.156-162
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• 2008

The static aeroelastic analysis of composite hingeless rotor blades in hover was performed using free-wake method. Large deflection beam theory was applied to analyze blade motions as a one-dimension beam. Anisotropic beam theory was applied to perform a cross-sectional analysis for composite rotor blades. Aerodynamic loads were calculated through a three-dimensional aerodynamic model which is based on the unsteady vortex lattice method. The wake geometry in hover was described using a time-marching free-wake method. Numerical results of the steady-state deflections for the composite hingeless rotor blades were presented and compared with those results based on two-dimensional quasi-steady strip theory and prescribed wake method. It was shown that wakes affect the steady-state deflections.

• Journal of Biomedical Engineering Research
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• v.14 no.1
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• pp.89-96
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• 1993

During high frequency ventilation (HFV), mean alveolar pressure has been measured to increase with mean airway opening pressure controlled at a constant level in both humans and experimental animals. Since this phenomenon could potentiate barotrauma limiting advantages of HFV, the present study theoretically predicted the difference between menu alveolar and airway opening pressures ($MP_{alv}$). In a Weibel's trumpet airway model, approximated formula for $MP_{alv}$ was derived based on momentum conservation assuming a uniform velocity profile. The prediction, equation was a func pion of gas density($\rho$), mean flow rate(Q), and diameter of the airway opening where the pressure measurement was made($D_0$) : $MP_{alv}=4{\rho}(Q/D_0^{2})^2$. This was a result of the difference in crosssectional area between the alveoli and the airway opening. A simple aireway model experiment was performed and the results well fitted to the prediction, which demonstrated the validity of the present analysis. Previously reported $MP_{alv}$ data from anesthetized dogs in supine position were comparable to the predicted values, indicating that the observed dissociation between mean alveolar and airway opening pressures during HFV can be explained by this innate geometric (or cross-sectional area) asymmetry of the airways. In lateral position, however, the prediction substantially underestimated the measurements suggesting involvement of other important physiological mechanisms.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.735-744
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• 2012

In order to quantify the flow distribution characteristics of APR+ reactor, a test was performed on a test facility, ACOP ($\underline{A}$PR+ $\underline{C}$ore Flow & $\underline{P}$ressure Test Facility), having a length scale of 1/5 referring to the prototype plant. The major parameters are core inlet flow and outlet pressure distribution and sectional pressure drops along the major flow path inside reactor vessel. To preserve the flow characteristics of prototype plant, the test facility was designed based on a preservation of major flow path geometry. An Euler number is considered as primary dimensionless parameter, which is conserved with a 1/40.9 of Reynolds number scaling ratio. ACOP simplifies each fuel assembly into a hydraulic simulator having the same axial flow resistance and lateral cross flow characteristics. In order to supply boundary condition to estimate thermal margins of the reactor, the distribution of inlet core flow and core exit pressure were measured in each of 257 fuel assembly simulators. In total, 584 points of static pressure and differential pressures were measured with a limited number of differential pressure transmitters by developing a sequential operation system of valves. In the current study, reactor flow characteristics under the balanced four-cold leg flow conditions at each of the cold legs were quantified, which is a part of the test matrix composing the APR+ flow distribution test program. The final identification of the reactor flow distribution was obtained by ensemble averaging 15 independent test data. The details of the design of the test facility, experiment, and data analysis are included in the current paper.