• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.916-921
• /
• 2003

In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method(FVM). This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.132.2-132.2
• /
• 2011

We are developing Adaptive Optics (AO) system for astronomical use. The He-Ne laser works as an artificial light source. The tip-tilt correction servo is added to our AO system. The tip-tilt term, among the Zernike terms, is the biggest contributor of wavefront deformation caused by atmospheric turbulence at small telescopes. The tip-tilt correction servo consists of a Piezo tip-tilt platform with a mirror, a quadrant photodiode as a tip-tilt sensor, and controllers. The Shack-Hartmann wavefront sensor measures the residual wavefront errors and they are corrected by the MEMS (Micro Electro Mechanical System) deformable mirror. The MEMS deformable mirror allows the compact size at low cost compare to adaptive secondary mirror and other deformable mirrors. As the frame rates of the MEMS deformable mirror is about tens of kHz, the frame rates of the detector in wavefront sensor is the bottleneck of the wavefront correction speed. For faster performance, we replaced a CCD which provides frame rates only 70 Hz with a CMOS with frame rates up to 450 Hz.

• Smart Structures and Systems
• /
• v.1 no.4
• /
• pp.369-384
• /
• 2005

The main objectives of this paper are to demonstrate the feasibility of using newly developed smart GFRP reinforcements to effectively monitor reinforced concrete beams subjected to flexural and creep loads, and to develop non-linear numerical models to predict the behavior of these beams. The smart glass fiber-reinforced polymer (GFRP) rebars are fabricated using a modified pultrusion process, which allows the simultaneous embeddement of Fabry-Perot fiber-optic sensors within them. Two beams are subjected to static and repeated loads (until failure), and a third one is under long-term investigation for assessment of its creep behavior. The accuracy and reliability of the strain readings from the embedded sensors are verified by comparison with corresponding readings from surface attached electrical strain gages. Nonlinear finite element modeling of the smart concrete beams is subsequently performed. These models are shown to be effective in predicting various parameters of interest such as crack patterns, failure loads, strains and stresses. The strain values computed by these numerical models agree well with corresponding readings from the embedded fiber-optic sensors.

• Journal of the Korean Geophysical Society
• /
• v.8 no.2
• /
• pp.97-103
• /
• 2005

It is necessary, in the light of the importance of long-term slope stability problem, to develop a simple method or tool which can figure out the possible failure zone resulted from weathering effect and other factors. The FBG sensor system is used to estimate the correlations between the temperature and the slope in Yunhwajae, and to find a failure zone in slopes effectively. This research is to seek for the correlation between the soil temperature distribution and the strain distribution in a active zone by analyzing the data from the in-situ measurement so that the possible failure zone should be well defined based on the correlation. The zone of high temperature fluctuation can be regarded as one of the possible sliding zone due to the weathering effect while the constant temperature depth of the ground, if exists, would not be relatively affected by the weathering process.

• Journal of the Society of Naval Architects of Korea
• /
• v.43 no.2 s.146
• /
• pp.220-227
• /
• 2006

In case of welding, the inherent strains are generated, because a structure experiences the plastic yielding. The inherent strain is defined as the irrecoverable strain after removing structural restraints and loading. For the analysis method of welding distortion, equivalent loading method based on inherent strain is in general use due to its efficiency and effectiveness. However, it is generally difficult to know the final strain of the welded structure if additional loadings were applied after welding. for this reason, this study introduced the concept of the hardening and added the hardening term to the equivalent loading method based on inherent strain. Therefore, the purposes of this study are to develop the inherent strain formula considering the hardening effect and to calculate residual Stresses Using Proposed inherent Strain. Also, this Study Verified the availability Of proposed inherent strain method by loading-unloading experiment on welded plate.

• Journal of ILASS-Korea
• /
• v.22 no.2
• /
• pp.69-79
• /
• 2017

When designing a redox flow battery system, compression of battery stack is required to prevent leakage of electrolyte and to reduce contact resistance between cell components. In addition, stack compression leads to deformation of the porous carbon electrode, which results in lower porosity and smaller cross-sectional area for electrolyte flow. In this paper, we investigate the effects of electrode compression on the cell performance by applying multi-dimensional, transient model of all-vanadium redox flow battery (VRFB). Simulation result reveals that large compression leads to greater pressure drop throughout the electrodes, which requires large pumping power to circulate electrolyte while lowered ohmic resistance results in better power capability of the battery. Also, cell compression results in imbalance between anolyte and catholyte and convective crossover of vanadium ions through the separator due to large pressure difference between negative and positive electrodes. Although it is predicted that the battery power is quickly improved due to the reduced ohmic resistance, the capacity decay of the battery is accelerated in the long term operation when the battery cell is compressed. Therefore, it is important to optimize the battery performance by taking trade-off between power and capacity when designing VRFB system.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2019.05a
• /
• pp.211-212
• /
• 2019

It is possible to realize the concept of long-life housing by utilizing the wall piping infill system. However, when using the wall piping infill system, there is no detailed standard in Korea. Problems may occur in actual use. In this study, we use the results obtained from the performance test method as a basic data. Since the load resistance test of the toilet is not available in Korea, GB 6952 (Sanitary wares) of China is applied. According to the experiment of load resistance of the toilet in this study, the strain recovery ability was good. However, it is not possible to exclude the possibility of permanent deformation of the toilet seat due to long - term repeated loading. Therefore, it is necessary to consider the stiffness enhancement of the wall (steel frame) to the fixing part when installing the toilet in the wall pipe infill system.

• Journal of the Korean Society of Industry Convergence
• /
• v.13 no.3
• /
• pp.125-131
• /
• 2010

This study is to give more accurate information by performing the time depend ent analysis to take into account the long-term losses of precast PSC concrete bridge and analyzing the second stress, final camber and cross section stress of precast PSC caused by creep and drying shrinkage. As time goes by, the stress and deformation in the cross section vary continuously by the influence of creep and drying shrinkage. Due to this, the stress redistribution occurs and the internal force variation also happens along the point on the same cross section and with the passage of time.

• Journal of the Korean GEO-environmental Society
• /
• v.6 no.1
• /
• pp.63-72
• /
• 2005

From the geological and engineering point of view, the limestone is so rigid that it is able to act as a bedrock but if there are some unstable elements which are solubility cavity and cracking zone in the ground, the settlement and bearing capacity of a structure will be required to long-term stability investigations and countermeasures about those problems. When comparing the allowable bearing capacity, the results of Bell's method and the Bowles' method are similar but the results of Hoek-Brown's method are very larger than the others. For weathered limestone, stability is changed by size and depth of the cavity of limestone, but soft and hard rock are stable regardless of size and depth of the cavity.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.6
• /
• pp.1056-1063
• /
• 2015

Waves can be expressed in terms of a spectrum; that is, the energy density distribution of a representative wave can be determined using statistical analysis. The JONSWAP, PM and BM spectra have been widely used for the specific target wave data set during storms. In this case, the extracted wave data are usually discontinuous and independent and cover a very short period of the total data-recording period. Previous studies on the continuous wave spectrum have focused on wave deformation in shallow water conditions and cannot be generalized for deep water conditions. In this study, the Generalized Extreme Value (GEV) function is proposed as a more-optimal function for the fitting of the continuous wave spectral shape based on long-term monitored point wave data in deep waters. The GEV function was found to be able to accurately reproduce the wave spectral shape, except for discontinuous waves of greater than 4 m in height.