• Journal of KSNVE
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• v.9 no.1
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• pp.206-213
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• 1999

In the beam-like ship vibration analysis. three-dimensional correction factor(J-factor) can be calculated by considering the three-dimensional effect of the two-dimensional added mass. However, existing method is time-consuming with low accuracy in respect of global vibration analyses for vessels with large breadth. In this paper, to improve the demerit of the previous method, a new method of the beam-like ship vibration analysis is introduced In this method. the three-dimensional fluid added mass of surrounding water is calculated directly by solving the velocity potential problem using the Boundary Element Method (BEM). Then the three-dimensional added mass is evaluated as the lumped mass for each strip. Also, the beam-like ship vibration analysis for the structural beam model if performed with the lumped mass considered. It was verified that this new method is useful for the beam-like ship vibration analysis by comparing results obtained from both the existing method and the new method with experimental measurements for the open top container model.

• KIPS Transactions on Software and Data Engineering
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• v.9 no.2
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• pp.69-76
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• 2020

In this paper, we introduce a method to visualize the contrast diffusion patterns and the dynamic vascular patterns in a contrast-enhanced ultrasound image sequence. We present an imaging technique to visualize parameters such as contrast arrival time, peak intensity time, and contrast decay time in contrast-enhanced ultrasound data. The contrast flow pattern and its velocity are important for characterizing focal liver lesions. We propose a method for representing the contrast diffusion patterns as an image. In the methods, respiratory motion may degrade the accuracy of the parametric images. Therefore, we present a respiratory motion tracking technique that uses dynamic weights and a momentum factor with respect to the respiration cycle. Through the experiment using 72 CEUS data sets, we show that the proposed method makes it possible to overcome the limitation of analysis by the naked eye and improves the reliability of the parametric images by compensating for respiratory motion in contrast-enhanced ultrasonography.

• Journal of The Korean Society of Integrative Medicine
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• v.4 no.4
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• pp.21-32
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• 2016

Purpose: The purpose of this study was to identify whether task-related circuit exercise program combined with sensorimotor training for 4 weeks could improve the balance and gait in stroke patients. Method: Fifteen stroke patients who had agreed with the study were randomly divided into 3 groups categorized as task-related circuit exercise program combined with sensorimotor training group (experimental group 1, n=5), task-related circuit exercise program group (experimental group 2, n=5), and control subjects performed conventional physical therapy (control group, n=5). The balance and gait were assessed by BT-4 force platform system, Berg Balance Scale, 10meter Walk Test and Smart Step at before training and after training. Wilcoxon signed rank test was used to analyze change before and after intervention in intra-group. Kruskal Wallis H test, Mann-Whitney U test and Bonfferoni correction were used to analyze changes of all variables in inter-groups. Result: The experimental group 1 showed significant improvements in postural sway area, BBS scores, walking velocity and plantar pressures of affected foot, whereas the experimental group 2 showed significant improvements in BBS scores, and the control group were no significantly different in all variables following training. The changes of postural sway area and BBS scores in the experimental group 1 were significantly greater than them of the control group. The changes of postural sway area in the experimental group 1 was significantly greater than that of the experimental group 2. Conclusion: The result of this study suggest the task-related circuit exercise program combined with sensorimotor training is an effective intervention to improve balance and gait in stoke patients.

• 한국지구물리탐사학회:학술대회논문집
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• 2000.09a
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• pp.158-172
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• 2000

In order to visualize mine cavities, 3D seismic reflection data were acquired at the ground subsidence sites near Nampung coal mine area, Neukguri, Dogye, Samchuck. Full range 3D array with complete range of azimuths on the bins was considered in the data acquisition design. Because of poor S/N data, we estimated the stacking velocities by CVS method, and we estimated the shot and receiver statics on the shot and receiver stack data. We could confirm that features of ground collapse that were expected from the subsidence. In order to visualize the cavities, we need to apply more sophisticated processing schemes, such as velocity analysis, residual statics correction.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.66-74
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• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.323-333
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• 2016

In this study, the uncertainty requirements for orbit, attitude, and burn performance were estimated and analyzed for the execution of the $1^{st}$ lunar orbit insertion (LOI) maneuver of the Korea Pathfinder Lunar Orbiter (KPLO) mission. During the early design phase of the system, associate analysis is an essential design factor as the $1^{st}$ LOI maneuver is the largest burn that utilizes the onboard propulsion system; the success of the lunar capture is directly affected by the performance achieved. For the analysis, the spacecraft is assumed to have already approached the periselene with a hyperbolic arrival trajectory around the moon. In addition, diverse arrival conditions and mission constraints were considered, such as varying periselene approach velocity, altitude, and orbital period of the capture orbit after execution of the $1^{st}$ LOI maneuver. The current analysis assumed an impulsive LOI maneuver, and two-body equations of motion were adapted to simplify the problem for a preliminary analysis. Monte Carlo simulations were performed for the statistical analysis to analyze diverse uncertainties that might arise at the moment when the maneuver is executed. As a result, three major requirements were analyzed and estimated for the early design phase. First, the minimum requirements were estimated for the burn performance to be captured around the moon. Second, the requirements for orbit, attitude, and maneuver burn performances were simultaneously estimated and analyzed to maintain the $1^{st}$ elliptical orbit achieved around the moon within the specified orbital period. Finally, the dispersion requirements on the B-plane aiming at target points to meet the target insertion goal were analyzed and can be utilized as reference target guidelines for a mid-course correction (MCC) maneuver during the transfer. More detailed system requirements for the KPLO mission, particularly for the spacecraft bus itself and for the flight dynamics subsystem at the ground control center, are expected to be prepared and established based on the current results, including a contingency trajectory design plan.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4664-4670
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• 2010

Comparison of the classical mobile-immobile zone (MIM) model to the derived model led to several conclusions. If the MIM model is to be applied, the initial concentration in the immobile zone has to be down-scaled by a correction factor that is a function of pore geometry. The MIM model was valid only after sufficiently long time has passed, i.e., only after the diffusion front reaches the deepest pore wall in the immobile zone. The MIM mass-transfer coefficient $\alpha$, was inversely proportional to the square of the pore depth. Also it did not depend on the mobile-zone flow velocity, contrary to the number of laboratory and field observations. The classical MIM model displayed a rapid exponential decay of immobile-zone concentration. Meanwhile at large times, the newly derived model displayed similar exponential decay. This was contrary to the mounting evidence of power-law BTC tails observed in laboratory and field settings.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.19-24
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• 1998

This paper deals with tomographic travel time inversion of three dimensional seismic refraction survey conducted over a dipping interface. The slowness, and thus velocity as its reciprocal, distribution on the subsurface interface is to be determined applying an ART with under-relaxtion parameter. The models chosen are realistic, i.e., most likely to be met in engineering seismics, and the interface includes anomalous zones. It is found that, generally speaking, the inversion could be misleading or meaningless without the correction of the dip of the interface. This is rather surprising when we recall that usual assumption for the interpretation of refraction seismics data is the horizontal attitude of structures within the limit of $15^{\circ}$ dip or so. To make the present method tenable for a new means of routine seismics, some practical ways of identifying head wave arrivals are to be devised.

• Journal of Ship and Ocean Technology
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• v.10 no.4
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.157-163
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• 2011

In this study, after the target basin was divided into both overland and channel grids, the travel time from center of each grid cell to watershed's outlet was calculated based on the manning equation. Through this process, volumetric discharge was calculated according to the isochrones and finally, the direct runoff hydrograph was estimated considering watershed's hydrodynamic characteristics. Sanseong subwatershed located in main stream of Bocheong basin was selected as a target basin. The model parameters are only two: area threshold and channel velocity correction factor; the optimized values were estimated at 3,800 and 3.3, respectively. The developed model based on the tuned parameters led to well-matching results between observed and calculated hydrographs (mean of absolute error of peak discharge: 3.41%, mean of absolute error of peak time: 0.67 hr). Moreover, the analysis results regarding histogram of travel time-contribution area demonstrates that the proposed model characterizes relatively well hydrodynamic characteristics of the catchment due to effective rainfall.