• Ocean Systems Engineering
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• v.10 no.3
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• pp.243-266
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• 2020

In-place analysis for offshore platforms is required to make proper design for new structures and true assessment for existing structures. In addition, ensure the structural integrity of platforms components under the maximum and minimum operating loads and environmental conditions. In-place analysis was carried out to verify the robustness and capability of structural members with all appurtenances to support the applied loads in either operating condition or storm conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have an important effect on the results of the in-place analysis behavior. The influence of the soil-structure interaction on the response of the jacket foundation predicts is necessary to estimate the loads of the offshore platform well and real simulation of offshore foundation for the in-place analysis. The result of the study shows that the in-place response investigation is quite crucial for safe design and operation of offshore platform against the variation of environmental loads.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.1
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• pp.87-94
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• 1986

Under natural condition, many rivers had shallow and gently curved shape in plane. A two dimensional mathematical model of the flow was a very attractive one. The flow characteristics in bended open channels were analyzed. The mathematical model based on the mass and the momentum equation of the two-dimensional unsteady flow was developed by introducing finite difference method and the double sweep algorithm. For the purpose of the verification of this model, the modeling results were applied to the L.F.M flume and the I.I.H.R flume. The results had a good agreement with the experimental data of the flumes. The results could be more close to the experimental data by controlling Chezy Coefficients in order to reduce the effect of friction around side wall, and be studied the importance of the convective term. The water surface profile, the direction and scale of depth average mean velocity and the path of the thread of maximum velocity in bended open channels could be computed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.2
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• pp.151-160
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• 2002

A modeling system for three-dimensional flow (FEMOS) has been developed and applied to simulate the tidal currents of Asan Bay. The system can consider tidal flats changing with time and uses a finite element method that can adapt coastline change effectively. The simulation results for Asan Bay with large tidal flats, shallow water depth and high tidal range showed good agreements with the observed currents of long-term variations at the medium layer and short-term variations of vertical profiles. Based on the simulated tidal currents, the horizontal distributions of bottom shear stress were calculated and showed close relation with the change of bottom topography. The system can be used widely to study coastal circulation in the coastal region with complex geography.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.16-25
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• 2005

The effect of vertical riser support system on the dynamic behaviour of a classical spar platform is investigated. Spar platform generally uses buoyancy-can riser support system, but as water depth gets deeper the alternative riser support system is required due to safety and cost issues. The alternative riser support system is to hang risers off the spar platform using pneumatic cylinders rather than the buoyancy-can. The existing numerical model for hull/mooring/riser coupled dynamics analysis treats riser as an elastic rod truncated at the keel (truncated riser model), thus, in this model, the effect of riser support system can not be modeled correctly. Due to this reason, the truncated riser model tends to overestimate the spar pitch and heave motion. To evaluate more realistic global spar motion, mechanical coupling among risers, guide frames and support cylinders inside of spar moon-pool should be modeled. In the newly developed model, the risers are extended through the moon-pool by using nonlinear finite element methods with realistic boundary condition at multiple guide frames. In the simulation, the vertical tension from pneumatic cylinders is modeled by using ideal-gas equation and the vertical tension from buoyancy-cans is modeled as constant top tension. The different dynamic characteristics between buoyancy-can riser support system and pneumatic riser support system are extensively studied. The alternative riser support system tends to increase spar heave motion and needs damper system to reduce the spar heave motion.

• Journal of the Korean Society for Railway
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• v.16 no.3
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• pp.202-206
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• 2013

A submerged floating railway is an innovative tunnel infrastructure passing through the deep sea independent of wave and wind so that high speed trains can run on it. It doesn't depend on water depth and is cost effective due to modular construction on land. The construction period can be reduced drastically. This paper introduces the concept design of a submerged floating railway, and for securing safety, proposes a method to analyze the structural behavior of the body in case of collision with a submarine. The theory of a beam with an elastic foundation was used to calculate the equivalent mass of the body so that the perfect elastic collision could be applied to calculate the collision velocity. The maximum deformation and bending moment was analyzed based on energy conservation. To verify the results, a collision analysis using a finite element analysis code was made. Comparing the results confirmed that this simplified collision analysis method gives enough accurate deformation and bending moment to be used for actual estimation in the initial design stage.

• Economic and Environmental Geology
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• v.43 no.3
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• pp.259-267
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• 2010

Resistivity logging instruments were designed to measure electrical resistivity of formation, which can be directly interpreted to provide water-saturation profile. Short and long normal logging measurements are made under groundwater level. In some investigation sites, groundwater level reaches to a depth of a few meters. It has come to attention that the proximity of groundwater level might distort short and long normal logging readings, when the measurements are made near groundwater level, owing to the proximity of an insulating air. This study investigates the effects of the proximity of groundwater level (and also the proximity of earth surface) on the normal by simulating normal logging measurements near groundwater level. In the simulation, we consider all the details of real logging situation, i.e., the presence of wellbore, the tool mandrel with current and potential electrodes, and currentreturn and reference-potential electrodes. We also model the air to include the earth’'s surface in the simulation rather than the customary choice of imposing a boundary condition. To obtain apparent resistivity, we compute the voltage, i.e., potential difference between monitoring and reference electrodes. For the simulation, we use a twodimensional, goal-oriented and high-order self-adaptive hp finite element refinement strategy (h denotes the element size and p the polynomial order of approximation within each element) to obtain accurate simulation results. Numerical results indicate that distortion on the normal logging is greater when the reference potential electrode is closer to the borehole and distortions on long normal logging are larger than those on short normal logging.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.2
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• pp.118-134
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• 2015

An analytical solution of dynamic responses for seabed in shallow, finite and infinite thicknesses has been developed under flow and standing wave coexisting field at a constant water depth condition. To do this, based on the Biot's consolidation theory, the seabed is assumed as a porous elastic media with the assumptions that pore fluid is compressible and Darcy law governs the flow. The developed analytical solution is compared with the previous results and is verified. Using the analytical solution the deformation, pore pressure, effective and shear stresses of seabed are examined under various given values of flow velocity, incident wave period and seabed thickness. From this study, it is confirmed that the seabed response is quite different depending on consideration of flow, which causes changing period and length of incident and reflection waves.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.294-302
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• 2018

To analyze the behavior of a soil beam under pore water pressure, the results of analytical solutions and finite element analysis (FEM) were compared quantitatively. In contrast to the results of the analytical solution, the horizontal stress obtained from the FEM did not show a symmetrical distribution. On the other hand, the horizontal stress became closer to symmetrical distribution as the number of elements of the soil beam were increased. A comparison of the horizontal stresses from the analytic solution with those obtained from Gaussian points of FEM showed that the magnitude of the tensile stress from the FEM using 3 elements was 6% of the maximum value of the analytical solution and the compressive stress from the FEM using the same elements was 37% of the maximum value of the analytical solution. The magnitude of the tensile stress from the FEM using 6 elements was 61% of the maximum value of the analytical solution and the magnitude of the compressive stress from the FEM using the elements was 83% of the maximum value of the analytical solution. Vertical stresses, which were obtained from the analytical solution, showed a continuous distribution with the depth of the soil beam, whereas the vertical stresses from the FEM showed a discrete distribution corresponding to each element. The results also showed that the average value of the vertical stresses of each element was close to that of the pore water pressure. A comparison of the vertical displacements computed at the near vertical center line of the soil beam from the FEM with those of the analytical solution showed that the magnitude of the vertical displacement from FEM using 3 elements was 35% of the value of the analytical solution and the magnitude of the vertical displacement from FEM using 6 elements was 57% of the value of the analytical solution.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.4
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• pp.433-453
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• 1999

There are a lot of elements affecting the success of implant prosthesis. The quality of surgical procedure is considered as one of the key factors. To avoid the excess heat generation is an important element of successful osseointegration and it can be achieved by using a gentle surgical technique with a sharp instrument in bone drilling. This study was performed to measure and analyze comparatively the heat transmitted to sur-rounding bone at a distance of 0.5mm from the periphery of the drill hole in each drilling stage. The results were as follows. In standard system, the temperature of surrounding bone tissue ranged from $29.2^{\circ}C\;to\;48.3^{\circ}C$ with irrigation and from $34.6^{\circ}C\;to\;84.3^{\circ}C$ without irrigation. And in wide system, the temperature of surrounding bone tissue ranged from $29.5^{\circ}C\;to\;52.5^{\circ}C$ with irrigation and from $34.8^{\circ}C\;to\;87.8^{\circ}C$ without irrigation. And the temperature ranges exceeded the threshold without irrigation, while showing less than the threshold by the cooling effect of irrigation. In comparing standard system with wide system, although there was no significant difference, ${\phi}4.3mm$ pilot and ${\phi}4.3mm$ twist drill of wide system showed high value and wide system showed slightly high elevation of temperature in all depth in fixture installation. In the finite element analysis, the calculated value by the Fourier's cooling law were applied to the bone drilling surface. And through analysis using different irrigation temperatures at $28^{\circ}C,\;15^{\circ}C\;and\;5^{\circ}C$, and according to the time. The result was that the cooling water at least below $15^{\circ}C$ was required to maintain the temperature of surrounding bone less than threshold in bone drilling, the cooling water below $5^{\circ}C$ was required to gain more sufficient cooling effect, and cooling over 5 seconds was needed after bone drilling for sufficient effect.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.82-89
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• 2016

In this study, we proposed a pier of pontoon-type, "Very Large Floating Structure" (VLFS), with the length of 500m, breadth of 200 m and height of 2 m in Yeosu domestic port. Since this structure ought to endure wave loads for long periods at sea, it is essential to analyze the wave response characteristics. Direct-method is used to analyze the fluid-structure problem and the coupled motion of equation is used to obtain response results. The structural part is calculated by using finite element method (FEM) and the fluid part is analyzed by using boundary element method (BEM). Dynamic responses caused by the elastic deformation and rigid motion of structure are analyzed by numerical calculation. To investigate response characteristics of the pier in regular waves, several factors such as the wavelength, water depth, wave direction and flexural rigidity of structure are considered. As a result, wave response of pier changed at the point of $L/{\lambda}$ 1.5 and represented the torsional phenomenon according to the various incident waves. And the responses showed increasing tendency as the water depths increase at the incident point in case of $L/{\lambda}=8.0$ and peak point of vertical displacement amplitude moved from side to side as the flexural rigidity of structure changes.