• Journal of The Korean Astronomical Society
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• v.48 no.4
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• pp.213-228
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• 2015

The Horizon Run 4 is a cosmological N-body simulation designed for the study of coupled evolution between galaxies and large-scale structures of the Universe, and for the test of galaxy formation models. Using 6300³ gravitating particles in a cubic box of L_box = 3150 h⁻¹Mpc, we build a dense forest of halo merger trees to trace the halo merger history with a halo mass resolution scale down to M_s = 2.7 × 10¹¹h⁻¹M_⊙. We build a set of particle and halo data, which can serve as testbeds for comparison of cosmological models and gravitational theories with observations. We find that the FoF halo mass function shows a substantial deviation from the universal form with tangible redshift evolution of amplitude and shape. At higher redshifts, the amplitude of the mass function is lower, and the functional form is shifted toward larger values of ln(1/σ). We also find that the baryonic acoustic oscillation feature in the two-point correlation function of mock galaxies becomes broader with a peak position moving to smaller scales and the peak amplitude decreasing for increasing directional cosine μ compared to the linear predictions. From the halo merger trees built from halo data at 75 redshifts, we measure the half-mass epoch of halos and find that less massive halos tend to reach half of their current mass at higher redshifts. Simulation outputs including snapshot data, past lightcone space data, and halo merger data are available at http://sdss.kias.re.kr/astro/Horizon-Run4.

• Journal of Environmental Health Sciences
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• v.41 no.2
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• pp.71-81
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• 2015

Objectives: Photochemical ozone pollution is associated with increased mortality risk. This study aims to assess the population exposure to ozone according to population characteristics for high ozone days in the Busan metropolitan region (BMR). Methods: The ozone exposure assessment in this study was performed using the WRF-CMAQ simulated ozone concentrations and the population data in the BMR. The settled and daytime population and their activity were considered to conduct the static and dynamic ozone exposure assessment. Results: Applying a static exposure assessment, in case that high ozone occurred throughout Busan area, the highest exposure levels were evaluated in urban neighborhoods. In case of ozone pollution in outer Busan, because sensitive groups have been relatively higher exposure, this case was also evaluated as part of that should not be overlooked. The dynamic exposure was higher than static exposure because the number of population exposed to ozone of high concentration is increased. This approach is important in a regard consider that daytime population distribution when high ozone occur. Conclusion: This study shows the different population exposure according to various ozone distributions for each episode day. Considering demographic characteristic such as population density and activity should be important to understanding the population exposure assessment when ozone pollution occurs.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.79-86
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• 2015

A blood pump is an important part of a cardiac assist device. Since the shear rate in blood is known to be a primary factor on hemolysis generation, it has been very important to evaluate hemolysis inside blood pumps for understanding performance and reliability of cardiac assist devices. In this study, hemolysis generation inside blood pumps is analyzed using CFD with power-law based models for the blood damage index(BDI), in order to overcome difficulties in measuring hemolysis by experiment. The BDI values in blood pumps can be evaluated using Lagrangian or Eulerian approaches. In this study, several Lagrangian and Eulerian approaches are compared to estimate the efficiency of the numerical methods in a practice sense. It is found that the Eulerian approaches are advantageous in terms of the efficiency and robustness. Two different Eulerian approaches are used to evaluate the BDI values of a few commercial blood pumps. For the conditions of extracorporeal membrane oxygenator(ECMO) and ventricular assist device(VAD), local generation of hemolysis is analyzed using divided regions of blood pumps, in order to investigate the effects of the pump geometry.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.61-68
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• 1988

This study is intended to propose an approach to reliability-based safety evaluation as well as LRFR(Load and Resisitance Factor Rating) type capacity classification of military or civilian bridges based on the limit state models which are delived by incorporating all the uncertainties of resistance and load random variables including deterioration, and are used in a practical AFOSM (Advanced First Order Second Moment) method. The proposed methods for the assement of safety and load carrying capacity are applied for the evaluation of rating and classifications of several practical bridges against the crossing of military vehicles. Based on the observation of the numerical results, it can be concluded that the current NATO classification method which is based on the traditionl allowable stress concept can not provide real load carrying capacity but results in nominal classification, and therefore the reliability-based safety evaluation and LRFR-classification method or the corresponding rational allowable stress method proposed in this paper may have to be introduced into the classification practice.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.51-54
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• 2005

Shape memory alloys (SMAs) find many applications in smart composite structural systems as the active components. Their ability to provide a high force and large displacement makes them an excellent candidate for an actuator for controlling the shape of smart structures. In this paper, using a macroscopic model that captures the thermo-mechanical behaviors and the two-way shape memory effect (TWSME) of SMAs smart morphing polymeric composite shell structures like shape-changeable UAV wings is demonstrated and analyzed numerically and experimentally when subjected to various kinds of pressure loads. The controllable shapes of the morphing shells to that thin SMA strip actuator are attached are investigated depending on various phase transformation temperatures. SMA strips start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the shell structures to deform three dimensionally. The behaviors of composite shells attached with SMA strip actuators are analyzed using the finite element methods and 3-D constitutive equations of SMAs. Several morphing composite shell structures are fabricated and their experimental shape changes depending on temperatures are compared to the numerical results. That two results show good correlations indicates the finite element analysis and 3-D constitutive equations are accurate enough to utilize them for the design of smart composite shell structures for various applications.

• The Journal of Churna Manual Medicine for Spine and Nerves
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• v.10 no.2
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• pp.37-49
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• 2015

Objectives : The purpose of this study is to show the effectiveness of Chuna Cranio-Sacral Therapy for remaining pain and muscle strength decrease after herniated intervertebral disc surgery. Methods : Two patients with Failed Back Surgery Syndrome(FBSS) were hospitalized and treated by Korean medical treatments with Chuna Cranio-Sacral Therapy. The Range of Motion(ROM) of the lumbar spine and Manual Muscle Test(MMT) were adopted to measure the resulting motor recovery after treatment. And the Numerical Rating Scale(NRS) was adopted to measure changes of pain level. Two patients both had Chuna Cranio-Sacral Therapy category III disorder with short right leg. We applied category III blocking technique everyday for 20 minutes with Korean medical treatments. Results : In both cases, the range of motions were improved and the pain level decreased. And in case 1, muscle strength also showed improvements. Conclusions : We suggest Chuna Cranio-Sacral Therapy is effective for pain decrease and motor recovery of FBSS patients. Further studies are needed to set up an Korean medical protocol for FBSS.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.6
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• pp.427-436
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• 2009

In this study, new type of pile foundation was introduced for the better performance of lateral resistance than conventional piles by adopting enlarged upper section, because offshore structure design is subjected to the lateral loading. The numerical simulations were peformed in order to find out the lateral behaviour of the proposed pile. The economical efficiency of new pile system was also analyzed by considering the construction characteristics and material costs as well as the real field condition of harbor sites in Korea. From the study, it was revealed that the lateral resistance of piles with enlarged upper section is increased compared to conventional steel pile, and the construction costs would be reduced to about 62~80% of previous methods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1244-1254
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• 1992

This paper investigates the vibrational damping characteristics of laminated plates composed of elastic, viscoelastic and elastic layers by theoretical and experimental methods. Laminated plates are in cylindrical bending and visco-elastic adhesive layer is assumed as the visco-elastic spring which takes damping effect through both shear and normal deformations. Governing equations oof laminated plates are derived in the form of simultaneous first order differential equations, which account for the longitudinal displacements, rotary inertia and shear deformations of elastic base plate and elastic constraining plate. The numerical calculations of the equations are illustrated by the applications to the cantilever beam in transverse vibration. The results of the solutions agree well with the experimental measurements in general. The damping effects due to the shear and thickness deformations in the adhesives are analyzed and it is shown that for thicker adhesives, the damping effect due to thickness deformation becomes significant and for thinner adhesives, due to shear deformation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.617-622
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• 2012

Structures are often subjected to various types of loading such as static, dynamic, or impact loading. Therefore, experimental and numerical methods have been employed to find adequate material properties according to the conditions. The Split-Hopkinson pressure bar (SHPB) test has frequently been used to test engineering materials, particularly those used under high strain rates. In this study, the compressive deformation behaviors of aluminum alloy under impact conditions have been investigated by means of the SHPB test. The experimental results were then compared with those of finite element analyses. It was shown that reasonably good agreement with the true stress-strain curves was obtained at strain rates ranging from 1000 $s^{-1}$ to 2000 $s^{-1}$. When the strain rate increased by 30%, the peak stress in particular increased by 17%, and the strain also increased by 20%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.437-442
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• 2013

In recent times, surface texturing methods have been widely applied to reduce friction and improve the reliability of machine components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, a numerical analysis is carried out to investigate the effect of uniformly spaced hemispherical dimples on the lubrication characteristics of a slider bearing using a commercial computational fluid dynamics (CFD) code, FLUENT. The pressure distributions, load capacity, leakage flowrate, and friction force are strongly affected by the dimple diameter and the number of dimples. In particular, the load capacity and friction force decrease linearly with the dimple density whereas the leakage increases. These results can be used for designing the optimum dimple characteristics in order to improve the lubrication performance of slider bearings, for which further studies are required.