• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.2
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• pp.196-204
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• 1994

Studied was impact assessment of sea dike construction in Saemankeum. To represent complexity of the geometry and topography of the region a flexible finite grid system are adopted. Combined fine and coarse meshes based on automatic mesh generator were applied in pre-processing. A nonlinear periodic finite element model. TEANL, was implied in this analysis, which gave good results compared to the observed data. It was predicted that the front region of dike connecting Shinsi-Karyeok-Daehang-Pyunsan will behave as a closed rectangular bay with wide width, which may affect significantly to the circulation and dispersion mechanism in the region.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.187-190
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• 2008

The water quality at the Dongbin Harbor at Pohang city, is getting worse due to the sewage and the wastewater from communities. In this syudy, RMA2 and RMA4, which is two-dimensional depth-averaged finite element numerical model, were employed to simulate the improvement of water quality from inflowing water through an inland canal to be planned connecting Dongbin Harbor and the Hyeongsan River. For the comparative result of the numerical model, both the present condition and the restoration condition (after construction of an inland canal) is simulated. The results of these conditions reasonably simulate a real situation at the Dongbin Harbor. After construction of an inland canal, the water quality at the Dongbin Harbor will be compared to the fresh water quality of the Hyeongsan River at the steady state. Futhermore, The result of simulation will be used to decide the most effective dimension of the canal.

• Advances in concrete construction
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• v.7 no.3
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• pp.183-189
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• 2019

In this study, it has been tried to prepare an analytical fragility curves for isolated straight continues highway bridges by considering different spectral intensity measures. A three-span concrete isolated bridge has been selected and the seismic performance of the bridge has been improved by Lead Rubber Bearing (LRB). Incremental Dynamic Analysis (IDA) is applied to the bridge in longitudinal direction. A suite of 14 earthquake ground motions from medium to sever motions are scaled and used for nonlinear time history analysis. Fragility function considers the relationship of earthquake intensity measures (IM) and probability of exceeding certain Damage State (DS). A full three dimensional finite element model of the isolated bridge has been developed and analyzed. A wide range of different intensity measures are selected and the optimal intensity measure which has the less dispersion is proposed.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.169-177
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• 2002

We develop the weighted-averaging finite-element method which uses four kinds of element sets. By constructing global stiffness and mass matrices for four kinds of element sets and then averaging them with weighting coefficients, we obtain a new global stiffness and mass matrix. With the optimal weighting coefficients minimizing grid dispersion and grid anisotropy, we can reduce the number of grid points required per wavelength to 4 for a $1\%$ upper limit of error. We confirm the accuracy of our weighted-averaging finite-element method through accuracy analyses for a homogeneous and a horizontal-layer model. By synthetic data example, we reconfirm that our method is more efficient for simulating a geological model than previous finite-element methods.

• Smart Structures and Systems
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• v.10 no.3
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• pp.229-251
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• 2012

Guided waves have shown a great potential for structural health monitoring (SHM) applications. In contrast to traditional non-destructive testing (NDT) methodologies, a key element of SHM approaches is the high process of automation. The monitoring system should decide autonomously whether the host structure is intact or not. A basic requirement for the realization of such a system is that the sensors are permanently installed on the host structure. Thus, baseline measurements become available that can be used for diagnostic purposes, i.e., damage detection, localization, etc. This paper contributes to guided wave-based inspection in anisotropic materials for SHM purposes. Therefore, computational strategies are described for both, the solution of the complex equations for wave propagation analysis in composite materials based on exact elasticity theory and the popular global matrix method, as well as the underlying equations of two active damage localization algorithms for anisotropic structures. The result of the global matrix method is an angular and frequency dependent wave velocity characteristic that is used subsequently in the localization procedures. Numerical simulations and experimental investigations through time-delay measurements are carried out in order to validate the proposed theoretical model. An exemplary case study including the calculation of dispersion curves and damage localization is conducted on an exemplary unidirectional composite structure where the ultrasonic signals processed in the localization step are simulated with the spectral element method. The proposed study demonstrates the capabilities of the proposed algorithms for accurate damage localization in anisotropic structures.

• Economic and Environmental Geology
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• v.52 no.4
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• pp.259-274
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• 2019

Using portable XRF and SWIR analyzer, the characteristics of element dispersion and wallrock alterations induced by interaction between hydrothermal fluids and host rocks were investigated and ore exploration factors were estimated for the orogenic-type Samgwang Au deposits. On this purpose, in-situ measurements were conducted for 804 spots at regular intervals with a total of 4,824 times for host rocks, consisting of schist and gneiss, and altered wallrocks contacted with quartz veins in the Bonhang adit of the deposit, and the results were compared with quantitative data obtained by XRF and ICP analysis. The regression coefficients are 0.88 for major elements and 0.56 for trace elements, excluding V. For polished rock slabs, better results came out for major elements, 0.97 and for trace elements, 0.65. In altered wallrocks contacted with quartz veins, elements such as Fe, Zn, and Rb exhibit positive correlations with As in concentrations, while V forms a negative trend. Contour maps demonstrate that As, Zn, Rb, Fe, Ti, Cr, and Ni are enriched together near quartz veins, showing similar elemental behaviors. In-situ analysis using portable SWIR analyzer represents that schist and gneiss contain mica, illite, chlorite, sericite, amphibole, and epidote, while illite, sericite, gypsum, and mica are present in the altered rocks contacted with quartz veins. In contour maps, chlorite occurs mostly in host rocks, while sericite is concentrated near quartz veins. These results are similar to those of previous studies for element dispersion and hydrothermal alteration, and support the possibility for application of in-situ analysis on the exploration of orogenic gold deposit.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1120-1131
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• 2011

Researches using time reversal acoustics(TRA) for impact localization have been paid attention to recently. Dispersion characteristics of Lamb waves, which restrict the utility of classical nondestructive evaluation based on time-of-flight information, can be compensated through the application of TRA to Lamb waves on a plate. This study investigates the spatial focusing performance of time reversal Lamb waves on a plate using finite element analysis. In particular, the virtual sensor effect caused by multiple wave reflections at the boundaries of a plate is shown to enable the spatial focusing of Lamb waves though a very small number of surface-bonded piezoelectric(PZT) sensors are available. The time window size of forward response signals, are normalized with respect to the number of virtual active sensors. Then their effects on the spatial focusing performance of Lamb waves are investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.439-446
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• 1997

A traditional notion of composites has been composed as a uniform dispersoid, but now it is proposed without regard to such rule with process development. Functionally Graded Material(FGM) consists of a new material design that is to make intentionally irregular dispersion state. In this study, thermal stress analysis of plasma spraying PSZ/NiCrAlY gradient material was conducted theoretically using a finite-element program. A formations of the model are direct bonding material(NFGM) and FGM with PSZ and NiCrAlY component element. The temperature conditions were $700^{\circ}C$ to 1100.deg. C assuming a cooling-down precess up to room temperature. Fracture damage mechanism was analyzed by the parameters of residual stress.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.31.2-31.2
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• 2009

In this research, single walled carbon nano-tube film was manufactured with spray coating method on glass for application as transparent heat element. SWNTs solution to be used for spraying is obtained by dispersion of 0.01 wt% purified SWNTs in dimethylformamide (DMF) solution through ultrasonification and centrifugation. The transmittance and sheet resistance of SWNTs film were determined by the number of spray injection. Manufactured SWNTs film will have sheet resistance range of $200\;\Omega/\square-900\;\Omega/\square$ at transmittance range of 70-90 %. Heat generation characteristic of SWNTs film was measured by applying constant DC voltage of 15V. The result confirmed that SWNTs film with sheet resistance of $200\;\Omega/\square$ reaches surface temperature of $80^{\circ}C$ within several seconds. In addition, PET coating film was coated on top of the SWNTs film by using laminator in order to solve weak adhesive property of the spray coated SWNTs film on the substrate as well as to maintain its electrical and optical properties.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.1
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• pp.1-10
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• 2020

This study deals with the fabrication and thermal characterization of planar heating elements attached to the backside of the reflector used in the electrodeless lamp of a freezer. We tried to solve the problem of the local heat generation of the linear heating element that occurs about 50℃. The homogeneous dispersion and manufacturing excellence of the planar heating element produced were confirmed through SEM and EDS. In addition, the test specimens was prepared according to the change in the ratio of carbon fiber to the basis weight of the planar heating element, and a sample having a basis weight of 50g/㎡ having a content ratio of carbon fiber of 70% was selected. That sample showed low surface resistance of 4.3Ω/sq and high temperature of about 81℃ at 6V. Durability was confirmed by performing repeated bending evaluation of 3000 cycles for the sample. Large area test specimens were prepared to be applied to the actual reflector, insulated by EVA film and analyzed for their thermal characteristics. From 13V application, the temperature of the linear heating element was higher than 50℃ and the average temperature of 68℃ was maximum at 18V.