• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.361-374
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• 2016

When the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure is generated significantly due to pore volume change associated with rearrangement soil grains. This effect leads a seabed liquefaction around and under structures as a result from decrease in the effective stress, and the possibility of structure failure is increased eventually. These facts shown above have been investigated in the previous studies related to regular and irregular waves. This study suggested a concrete mat for preventing the seabed liquefaction near the submerged breakwater. The concrete mat was mainly used as a countermeasure for scouring protection in riverbed. According to installation of the concrete mattress, the time and spatial series of the deformation of submerged breakwater, the pore water pressure, and the pore water pressure ratio in the seabed were investigated. Their results were also compared with those of the seabed unprotected with the concrete mat. The results presented were confirmed that the liquefaction potential of seabed under the concrete mattress is significantly reduced under regular wave field.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.156-162
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• 1995

A numerical method for a 2-D oil boom model considering the flexibility of skirt has been developed The neater is assumed rigid and the skirt is tensioned membrane having a point mass at its end The fluid motion is potential. The kinematic condition which demands the continuity of the displacement is imposed at the joint between the floater and the skirt. The dynamic condition for the point mass is imposed at the bottom end of the skirt. The numerical method is based on the Green's function method in the frame of linear potential theory. It finds it's solution simultaneously from the total system of three equations, integral equation, the equation of motion of the floater and the equilibrium equation of the deformation of the skirt. Integral equation is derived by applying the Green's theorem to radiation potential and Green's function. Proper descretization of those three equations leads to the system of a linear algebraic equation. Due to the flexibility of skirt the motion of floater can be diminished in some range of wave frequency and furthermore the mechanism of resonance of the oil boom can be changed. The motion responses of various oil booms have been compared varying the length of the skirt and the point mass. The numerical method has been validated indirectly from the good correspondence between the motion responses of the flexible skirt model and the rigid skirt model in low frequency limit.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.87-96
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• 1999

To analyze the dynamic behavior of structure, direct integration and mode superposition may be utilized in time domain analysis. As finite number of frequencies can give relatively exact solutions, mode superposition is preferable in analyzing structural behavior. In non-linear analysis, however, mode superposition is seldom used since time-varying element stiffness changes stiffness matrix, and the change of stiffness matrix leads to the change of essential constants - natural frequencies and mode shapes. In spite of these difficulties, there are some attempts to adopt mode superposition because of low cost compared to direct integration, but the result is not satisfactory. In this paper, a method using mode superposition in non-linear analysis is presented by separating local element stiffness from global stiffness matrix with the difference between linear and non-linear restoring forces to the external force vectors included. Moreover, the hysteresis model changing with the relative deformation in each floor makes it possible to analyze non-linear behavior of structure. The proposed algorithm is applied to shear beam model and the maximum displacement is compared with the result using direct integration method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.415-425
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• 2017

Stresses occur in the spent nuclear fuel disposal canister due to the impulsive forces incurred in the accidental drop and impact event from the transportation vehicle onto the ground during deposition in the repository. In this paper, the comparative study of finite element analysis for stresses occurring in various models of the spent nuclear fuel disposal canister due to these impulsive forces is presented as one of design processes for the structural integrity of the canister. The main content of the study is about the design of the structurally safe canister through this comparative study. The impulsive forces applied to the canister subjected to the accidental drop and impact event from the transportation vehicle onto the ground in the repository are obtained using the commercial rigid body dynamic analysis computer code, RecurDyn. Stresses and deformations occurring due to these impulsive forces are obtained using the commercial finite element analysis computer code, NISA. The study for the structurally safe canister is carried out thru comparing and reviewing these values. The study results show that stresses become larger as the wall encompassing the spent nuclear fuel bundles inside the canister becomes thicker or as the diameter of the canister becomes larger. However, the impulsive force applied to the canister also becomes larger as the canister diameter becomes larger. Nonetheless, the deformation value per unit impulsive force decreases as the canister diameter increases. Therefore, conclusively the canister is structurally safe as the diameter increases.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.4
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• pp.309-314
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• 2002

Rhtological properties of surimi gel from white fishes by acid (acid surimi) and alkali (alkali surmi) process and effect of chemicals on gelation were investigated by punch and dynamic tests. The breaking force and deformation values of heat-induced gel of acid surimi were less than their values of alkali and conventional surimi gel, and whiteness was greatly decreased, Gel point of acid surimi was decreased but it of alkali surimi was increased with increasing moisture content in the range of 80 to $85\%$. Storage modulus of acid surimi was the highest vaule in pH 6.8, but that of alkali surimi showed high value at neutral and slightly alkali pH. Propylene glycol increased storage modulus in $20\~50^{\circ}C$, hut urea and 2-mercaptoethanol suppressed it. Potassium bromide improved storage modulus in $20~80^{\circ}C$, The results suggest that alkai process is used for making surimi instead of conventional method.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.480-490
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• 2016

As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.523-530
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• 2017

In this study, a method of probabilistic evaluation of the performance point of the structure obtained by capacity spectrum method (CSM) is presented. The performance point of the 4-story and 1-bay steel structure was determined by using CSM according to ATC-40. In order to analyze whether the demand spectrums exceed the performance limit of the structure, the limit displacements are derived for the performance limit of the structure defined from the plastic deformation angle of the structural member. In addition, by selecting a total of 30 artificial seismic wave having the response spectrum similar to the design response spectrum, the fragility curves were derived by examining whether the response spectrum obtained from the artificial seismic wave were exceeded each performance limit according to the spectral acceleration. The maximum likelihood method was used to derive the fragility curve using observed excess probabilities. It has been confirmed that there exists a probability that the response acceleration value of the design response spectrum corresponding to each performance limit exceeds the performance limit. This method has a merit that the stochastic evaluation can be performed considering the uncertainty of the seismic waves with respect to the performance point of the structure, and the analysis time can be shortened because the incremental dynamic analysis (IDA) is not necessary.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.489-494
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• 2015

This research focused on minimizing the response of fixed cylindrical offshore structures to a ship impact considering the seawater fluid part. A collision between a ship and offshore structure is generally a complex problem and it is often impractical to perform rigorous finite element analyses to include all the effects and sequences during the collision. The structural behavior of a fixed cylindrical type offshore substructure with a seawater fluid part has a simpler response and small deformation due to the dissipation of impact energy. Upon applying the impact force of a ship to the cylindrical structure, the maximum acceleration, internal energy, and plastic strain are calculated for each load cases using Ls-dyna finite element software. In the maximum cases 2.0 m/s velocity, the response result for the structure was carried out to compare between having a fluid region and no fluid region. Fluid-structure interaction analysis was performed using the ALE method, which make it possible to apply a fluid region on the impact problem. The case of a fixed cylindrical type offshore structure without a seawater fluid part can be a more conservative design.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.177-190
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. Lee et al.(2016) studied for regular waves, and this study considered for irregular waves with the same numerical analysis method used for regular waves. Under the condition of the irregular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated and their results were compared with those of the regular wave field to evaluate the liquefaction potential on the seabed quantitatively. Although present results are based on a limited number of numerical simulations, one of the study's most important findings is that a more safe design can be obtainable when analyzing case with a regular wave condition corresponding to a significant wave of irregular wave.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.87-96
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• 2007

A new Energy-Dissipating Sacrificial Device (EDSD) is developed for steel plate girders, which can effectively dissipate the energy stored in the structures during seismic actions. To verify the performance of the EDSD, various seismic responses of a sample bridge with the EDSD are analyzed in terms of energy, member forces and deformation. The full scale model tests are conducted to certify the performance of the EDSD when it is applied on existing bridges. Using the improved hysteretic model of the sacrificial member, the seismic analysis for an example bridge is performed. The results show that the proposed EDSD under seismic excitations can significantly decrease the energy stored in the bridge structures and reduce the relative displacements of each superstructure to the ground. The EDSD is also found to function as a structural fuse under strong ground motions, sacrificing itself to absorb the excessive energy. Consequently, economical enhancement of the seismic performance of bridges can be achieved by employing the newly developed energy-dissipating sacrificial device.