• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.435-449
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• 2014

The effects of the gravity field and the free surface on the cavity shape and the drag are investigated through a numerical analysis for the steady supercavitating flow past a simple two-dimensional body underneath the free surface. The continuity and the RANS equations are numerically solved for an incompressible fluid using a $k-{\epsilon}$ turbulence model and a mixture fluid model has been applied for calculating the multiphase flow of air, water and vapor using the method of volume of fluid and the Schnerr-Sauer cavitation model. Numerical solutions have been obtained for the supercavitating flow about a two-dimensional $30^{\circ}$ wedge in wide range of depths of submergence and inflow velocities. The results are presented for the cavity shape, especially the length and the width, and the drag of the wedge in comparison with those of the case for the infinite fluid flow neglecting the gravity and the free surface. The influences of the gravity field and the free surface on the aforementioned quantities are discussed. The length and the width of the supercavity are reduced and the centerline of the cavity rises toward the free surface due to the effects of the gravity field and the free surface. The drag coefficient of the wedge, however, is about the same except for shallow depths of submergence. As the supercavitating wedge is approaching very close to the free surface, it is found the length and the width of a cavity are shorten even though the cavitation number is reduced. Also the present result suggests that, under the influence of the gravity field and the free surface, the length of the supercavity for a certain cavitation number varies and moreover is proportional to the inverse of the submergence depth Froude number.

• Journal of Distribution Science
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• v.10 no.12
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• pp.13-17
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• 2012

Purpose - The Asia-Pacific Economic Cooperation (APEC) forum has evolved and is actively facilitating free and open trade. It is debated whether APEC has effectively reduced trade barriers in a preferential manner to encourage liberalized trade and whether increased trade between member countries has reduced trade with nonmember countries. Research designs, data, methodology -This paper empirically tests whether APEC creates or diverts trade, using an extended gravity model with tariff rates, exchange rates, and dummy variables to analyze how APEC affects intra-trade between members.The model utilizes the annual panel data between 1990 and 2007 of 16 selected APEC members and nonmembers. Results - Results reveal the changing role of APEC only between 2002 and 2007 has it created trade, fostering increased trade among trading partners and between members and nonmembers. Conclusion - APEC can be expected to demonstrate a stronger trade creating effect once its advanced and developing members complete tariff reductions by 2010 and 2020, respectively.

• IEMEK Journal of Embedded Systems and Applications
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• v.12 no.5
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• pp.311-318
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• 2017

A reduced order observer is developed for depth control of a hybrid underwater glider which combines the good aspects of a conventional autonomous underwater vehicle and a underwater glider. State variables include the center of gravity of the robot and the weight of the buoyancy bag, which can not be directly measured. By using the mathematical model and available information such as directional velocities, accelerations, and attitudes, we developed a Luenberger's reduced order observer to estimate the center of gravity and the buoyancy weight. By simulations using Matlab/Simulink, the efficiency of the proposed observer is shown, where a LQR controller using full state variables is adopted as a depth controller.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.74.1-74.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the regulation of star ormation rates in turbulent, multiphase, galactic gaseous disks. Our simulation domain is xisymmetric, and local in the radial direction and global in the vertical direction. Our models nclude galactic rotation, vertical stratification, self-gravity, heating and cooling, and thermal onduction. Turbulence in our models is driven by momentum feedback from supernova events ccurring in localized dense regions formed by thermal and gravitational instabilities. Self-onsistent radiative heating, representing enhanced/reduced FUV photons from the star formation, s also taken into account. Evolution of our model disks is highly dynamic, but reaches a quasi-teady state. The disks are overall in effective hydrostatic equilibrium with the midplane thermal ressure set by the vertical gravity. The star formation rate is found to be proportional pproximately linearly to the midplane thermal pressure. These results are in good agreement with the predictions of a recent theory by Ostriker, McKee, and Leroy (2010) for the thermal/dynamic equilibrium model of star formation regulation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1075-1088
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• 1992

This paper presents techniques used to model a two arm experimental robot. Both arms are compliant and the robot operates in a vertical plane and is therefore influenced by gravity. The robot is being built to study different control strategies for robots containing compliant members. The system is built with extremely flexible members. This limits the required bandwidth of the control electronics, and mimics the flexible motions that are observed for stiffer faster robots. The objective of this paper is to develop a reduced order model of the robot system and to experimentally validate the model. Validation requires that the model includes gravitational effects. Therefore, an assumed modes model is developed which facilitates modeling of gravitational effects. In order to select the order and mode shapes for the model, an analytical solution is derived for a linearized continuous model. This is compared to the assumed modes model to determine the number of mode shapes needed to model the system. The final model, which includes shortening effects, correlates very well with experimental results.

• Structural Monitoring and Maintenance
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• v.11 no.3
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• pp.235-246
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• 2024

Structural seismic tests usually need to simulate the gravity load borne by the structure, the gravity load application devices should keep the force value and direction unchanged, and can adapt to the structural deformation. At present, there are two main ways to simulate gravity load in laboratory: roller group and prestress. However, there are few differential analysis between these two ways in the existing experimental studies. In this paper, the simulation software ABAQUS is used to simulate the static pushover analysis of reinforced concrete column and frame, which are the most common models in structural seismic tests. The results show that the horizontal restoring force of the model using prestressed loading method is significantly greater than roller group, and the difference between the two will increase with the increase of the horizontal deformation. The reason for the difference is that the prestressed loading method does not take the adverse effects of gravity second-order effect (P-Delta effect) into account. Therefore, the restoring force obtained under prestressed loading method should be corrected and the additional shear force caused by P-Delta effect should be deducted. After correction, the difference of restoring force between the two gravity load application methods is significantly reduced (when storey-drift is 1/550, the relative error is within 1%; and when storey-drift is 1/50, the relative error is about 3%). The research results of this research can provide reference for the selection and data processing of gravity load simulation devices in structural seismic tests.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.3
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• pp.257-264
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• 2012

Objectives: This study's aims were to evaluate the effects of load center of gravity within an object lifted and feet placements on peak EMG amplitude acting on bilateral low back muscle groups, and to suggest adequate foot strategies with an aim to reducing low back pain incidence while lifting asymmetric load. Methods: The hypotheses that asymmetric load imposes more peak EMG amplitude on low back muscles contralateral to load center of gravity than symmetric load and maximum peak EMG amplitude out of bilateral ones can be relieved by locating one foot close to load center of gravity in front of the other were established based on biomechanics including safety margin model and previous researches. 11 male subjects were required to lift symmetrically a 15.8kg object during 2sec according to each conditions; symmetric load-parallel feet (SP), asymmetric load-parallel feet (AP), asymmetric load-one foot contralateral to load center of gravity in front of the other (AL), and asymmetric load-one foot ipsilateral to load center of gravity in front of the other (AR). Bilateral longissimus, iliocostalis, and multifidus on right and left low back area were selected as target muscles, and asymmetric load had load center of gravity 10cm deviated to the right from the center in the frontal plane. Results: Greater peak EMG amplitude in left muscle group than in right one was observed due to the effect of load center of gravity, and mean peak EMG amplitudes on both sides was not affected by load center of gravity because of EMG balancing effect. However, the difference of peak EMG amplitudes between both sides was significantly affected by it. Maximum peak EMG amplitude out of both sides and the difference of peak EMG amplitude between both sides could be reduced with keeping one foot ipsilateral to load center of gravity in front of the other while lifting asymmetric load. Conclusions: It was likely that asymmetric load lead to the elevated incidence of low back pain in comparison with symmetric load based on maximum peak EMG amplitude occurrence and greater imbalanced peak EMG amplitude between both sides. Changing feet positions according to the location of load center of gravity was suggested as one intervention able to reduce the low back pain incidence.

• Economic and Environmental Geology
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• v.48 no.6
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• pp.451-465
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• 2015

The free-air anomalies are computed using a data set from various types of gravity measurements in the Korean Peninsula area. The gravity values extracted from the Earth Gravitational Model 2008 are used in the surrounding region. The upward continuation technique suggested by Dragomir is used in the computation of the external free-air anomalies at various altitudes. The integration radius 10 times the altitude is used in order to keep the accuracy of results and computational resources. The direct geodesic formula developed by Bowring is employed in integration. At the 1-km altitude, the free-air anomalies vary from -41.315 to 189.327 mgal with the standard deviation of 22.612 mgal. At the 3-km altitude, they vary from -36.478 to 156.209 mgal with the standard deviation of 20.641 mgal. At the 1,000-km altitude, they vary from 3.170 to 5.864 mgal with the standard deviation of 0.670 mgal. The predicted free-air anomalies at 3-km altitude are compared to the published free-air anomalies reduced from the airborne gravity measurements at the same altitude. The rms difference is 3.88 mgal. Considering the reported 2.21-mgal airborne gravity cross-over accuracy, this rms difference is not serious. Possible causes in the difference appear to be external free-air anomaly simulation errors in this work and/or the gravity reduction errors of the other. The external gravity field is predicted by adding the external free-air anomaly to the normal gravity computed using the closed form formula for the gravity above and below the surface of the ellipsoid. The predicted external gravity field in this work is expected to reasonably present the real external gravity field. This work seems to be the first structured research on the external free-air anomaly in the Korean Peninsula area, and the external gravity field can be used to improve the accuracy of the inertial navigation system.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1996.10a
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• pp.7-9
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• 1996

A simple two-and -half-layer model is used to study the circulation of South China Sea( SCS ). The model is coming from the reduced gravity model of Hurbult and Thompson, with the assumption of rigid surface. It shows there is no distinct branch of the Kuroshio into the SCS. Both the upper and lower pycnocline height anomaly show that the main feature of the circulation of SCS is a cyclone, which is generated by the transportion of the vorticity from the Kuroshio. Aftr generated, the cyclone moves westward due to the beta effect, then dissipates near the west boundary due to the viscosity. After an old one dissipates, a new one appears again. The life cycle of the cyclone is about 160 days.

• Journal of muscle and joint health
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• v.5 no.1
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• pp.83-109
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• 1998

This study was carried out to identify the Important modifiable risk factors for reduced bone mass and to construct prediction model which can classify women with either low or high bone mass. Through the literature review, individual characteristics such as age, body weight, height, education level, family history, age of menarche, postmenopausal period, gravity, parity, menopausal status, and breast feeding period were identified and factors of life style such as past milk consumption, past physical activity, present daily activity, present calcium intake, alcohol intake, cigarette smoking, coffee consumption were identified as influencing factors of reduced bone mass in women. Four hundred and eighty women aged between 28 and 76 who had given measurement bone mineral density by dual energy x-ray absortiometry in lumbar vertebrae and femur from July to October, 1997 at 4 general hospitals in Seoul and Pusan were selected for this study. Women were excluded if they had a history of any chronic illness such as rheumatoid arthritis, diabetes mellitus, hyperthroidism, & gastrointestinal disorder and any medication such as calcium supplements, calcitonin, estrogen, thyroxine, antacids, & corticosteroids known affect bone. As a result of these exclusion criteria, four hundred and seventeen women were used for analysis. Multiple logistic regression model was developed for estimating the likelihood of the presence or absence of reduced bone mass. A SAS procedure was used to estimate risk factor coefficient. The results are as follows For lumbar spine, the variables significant were age, body weight, menopause status, daily activity, past milk consumption, and past physical activity(p<0.01), while for femoral Ward's triangle, age, body weight, level of education, past milk consumption, past physical activity(p<0.001). Past physical activity, present daily activity and past milk consumption are the most powerful modifiable predictors in vertebrae and femur among the predictors. When the model performance was evaluated by comparing the observed outcome with predicted outcome, the model correctly identified 74.1% of persons with reduced bone mass and 84.5% of persons with normal bone mass in the lumbar vertebrae and 82.9% of persons with reduced bone mass and 75.0% of persons with normal bone mass in the femoral Ward's triangle. On the basis of these results, a number of recommendations for the management of reduced bone mass may be made : First, those woman who are classified as high risk group of the reduced bone mass in the prediction model should examine the bone mineral density to further examine the usefulness of this model. Second, the optimal amount of milk consumption and a regular weight bearing exercise in childhood, adolescence, and early adult should be ensured.