• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.593-599
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• 2016

Incheon Bridge is 13.38 km long with an 800 m span, connecting Incheon International Airport and Songdo International City, Per hour 73.8 vessels navigate this space. The purpose of this study was to suggest a safe passing speed based on the displacement of a vessel based on the safety criteria of Incheon Bridge's anti-collision fence, which was designed during its initial construction. As AASHTO LRFD suggested, vessel collision energy, vessel collision velocity, and the hydrodynamic mass coefficient were considered to derive a safe vessel traffic speed. Incheon Bridge's anti-collision fence was designed so that 100,000 DWT vessels can navigate at a speed of 10 knot. This research suggests a safe speed for vessel traffic through a comparative analysis of an experimental ship's (300,000 DWT) speed and cargo conditions, regulation speed has been calculated according to the collision energy under each set of conditions. Additionally, safe traffic vessel's safe speed was analyzed with reference to tidal levels. Results from the experimental ship showed that a vessel of maximum 150,000 DWT is able to pass Incheon Bridge at a maximum of 7 knots with an above average water level, and is able to pass the bridge with a maximum of 8 knots under ballast conditions.

• Journal of the Korean Institute of Intelligent Systems
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• v.13 no.2
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• pp.247-258
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• 2003

In this paper, we present a pen-shaped input device equipped with accelerometers and gyroscopes that measure inertial movements when a user writes on 2 or 3 dimensional space with the pen. The measurements from gyroscope are integrated once to find the attitude of the system and are used to compensate gravitational effect in the accelerations. Further, the compensated accelerations are integrated twice to yield the position of the system, whose basic concept stems from the field of inertial navigation. However, the accuracy of the position measurement significantly deteriorates with time due to the integrations involved in recovering the handwriting trajectory This problem is common in the inertial navigation system and is usually solved by the periodic or aperiodic calibration of the system with external reference sources or other information in the filed of inertial navigation. In the presented paper, the calibration of the position or velocity is performed on-line and off-line. In the on-line calibration stage, the complementary filter technique is used, where a Kalman filter plays an important role. In the off-line calibration stage, the constant component of the resultant navigational error of the system is removed using the velocity information and motion detection algorithm. The effectiveness and feasibility of the presented system is shown through the experimental results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.2
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• pp.105-112
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• 2007

Sediment transport model based on the Lagrangian concept considering the grain size distribution(GSD) was setup and the change of the sediment diffusion range was analysed in the condition of considering and not considering the GSD. The GSD curve is assumed as the Log-normal distribution function in order to consider the GSD with respect to the Lagrangian concept and the random numbers, i.e. sediment particles, are generated based on the distribution function. The sediment particles is assumed as the spherical type and the random numbers based on the sediment weight is converted to the sediment diameters. Sediment transport patterns are analysed by the settling simulation, in which the settling velocity is computed by the van Rijn formulae and the horizontal diffusion coefficient is used as the constant parameter. The diffusion patterns are very similar to the patterns with GSD condition. The diffusion range defined as the range including 90%, 99% sediment weight of the total sediment weight, however, is larger than without considering GSD condition in 90%-option and shorter than with considering GSD condition in 99-option, respectively. The diffusion range is defined as tile p-percentage of the cumulative sediment weight region with reference to the 50% region, 90%- option, 99%-option, respectively.

• Korean Journal of Applied Biomechanics
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• v.15 no.3
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• pp.143-152
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• 2005

The purpose of this study was to predict the failure or success of the Snatch-lifting trial as a consequence of the stand-up phase simulated in Kane's equation of motion that was effective for the dynamic analysis of multi-segment. This experiment was a case study in which one male athlete (age: 23yrs, height: 154.4cm, weight: 64.5kg) from K University was selected The system of a simulation included a multi-segment system that had one degree of freedom and one generalized coordinate for the shank segment angle. The reference frame was fixed by the Nonlinear Trans formation (NLT) method in order to set up a fixed Cartesian coordinate system in space. A weightlifter lifted a 90kg-barbell that was 75% of subject's maximum lifting capability (120kg). For this study, six cameras (Qualisys Proreflex MCU240s) and two force-plates (Kistler 9286AAs) were used for collecting data. The motion tracks of 11 land markers were attached on the major joints of the body and barbell. The sampling rates of cameras and force-plates were set up 100Hz and 1000Hz, respectively. Data were processed via the Qualisys Track manager (QTM) software. Landmark positions and force-plate amplitudes were simultaneously integrated by Qualisys system The coordinate data were filtered using a fourth-order Butterworth low pass filtering with an estimated optimum cut-off frequency of 9Hz calculated with Andrew & Yu's formula. The input data of the model were derived from experimental data processed in Matlab6.5 and the solution of a model made in Kane's method was solved in Matematica5.0. The conclusions were as follows; 1. The torque motor of the shank with 246Nm from this experiment could lift a maximum barbell weight (158.98kg) which was about 246 times as much as subject's body weight (64.5kg). 2. The torque motor with 166.5 Nm, simulated by angular displacement of the shank matched to the experimental result, could lift a maximum barbell weight (90kg) which was about 1.4 times as much as subject's body weight (64.5kg). 3. Comparing subject's maximum barbell weight (120kg) with a modeling maximum barbell weight (155.51kg) and with an experimental maximum barbell weight (90kg), the differences between these were about +35.7kg and -30kg. These results strongly suggest that if the maximum barbell weight is decided, coaches will be able to provide further knowledge and information to weightlifters for the performance improvement and then prevent injuries from training of weightlifters. It hopes to apply Kane's method to other sports skill as well as weightlifting to simulate its motion in the future study.

• Geophysics and Geophysical Exploration
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• v.23 no.1
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• pp.1-12
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• 2020

In the development of geodynamic structures such as subduction and rift zones, a weakening mechanism is essential for localized weak zone formation in the lithosphere. Shear heating, a weakening mechanism, generates short-wavelength temperature elevation in the lithosphere; the increased temperature can reduce lithospheric strength and promote its breakup. A two-dimensional elastoplastic extensional basin model was used to conduct benchmarking based on previous numerical simulation studies to quantitatively analyze shear heating. The amount of shear heating was investigated by controlling the yield strength, extensional velocity, and strain- and temperature-dependent weakening. In the absence of the weakening mechanism, the higher yield strength and extensional velocity led to more vigorous shear heating. The reference model with a 100-MPa yield strength and 2-cm/year extension showed a temperature increase of ~ 50 K when the bulk extension was 20 km (i.e., 0.025 strain). However, in the yield-strength weakening mechanism, depending on the plastic strain and temperature, more efficient weakening induced stronger shear heating, which indicates positive feedback between the weakening mechanism and the shear heating. The rate of shear heating rapidly increased at the initial stage of deformation, and the rate decreased by 80% as the lithosphere weakened. This suggests that shear heating with the weakening mechanism can significantly influence the strength of relatively undamaged lithosphere.

• Atmosphere
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• v.29 no.1
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• pp.105-112
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• 2019

Measurements of vertical air motion and microphysics are essential for improving our understanding of convective clouds. In this paper, the author reviews the current research on the retrieval of vertical air motions using the cloud radar. At radar wavelengths of 3 mm (W-band radar; 94-GHz radar; cloud radar), the raindrop backscattering cross-section (${\sigma}b$) varies between successive maxima and minima as a function of the raindrop diameter (D) that are well described by Mie theory. The first Mie minimum in the backscattering cross-section occurs at D~1.68 mm, which translates to a raindrop terminal fall velocity of ${\sim}5.85m\;s^{-1}$ based on the Gunn and Kinzer relationship. Since raindrop diameters often exceed this size, the signal is captured in the radar Doppler spectrum, and thus, the location of the first Mie minimum can be used as a reference for retrieving the vertical air motion. The Mie technique is applied to radar Doppler spectra from the surface-based and airborne, upward pointing W-band radars. The contributions of aircraft motion to the vertical air motion are also described and further the first-order aircraft motion corrected equation is presented. The review also shows that the separate spectral peaks due to the cloud droplets can provide independent validation of the Mie technique retrieved vertical air motion using the cloud droplets as a tracer of vertical air motion.

• Journal of Korea Water Resources Association
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• v.47 no.5
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• pp.459-468
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• 2014

Groyne to control the direction and velocity of flow in rivers is generally installed for the purpose of protecting riverbanks or embankments from erosion caused by running water. In particular, as interest in river restoration and natural river improvement increases, groynes are proposed as a key hydraulic structure for local flow control and riparian habitat establishment. Groynes are installed mainly in groups rather than as individual structures. In case of groynes installed as a group, flow around the groynes change according to spacing in between the groynes. Therefore, groyne spacing is regarded as the most important factor in groyne design. This study aimed at examining changes of flows around and within the area of groynes that take place according to the spacing of groynes installed in order to propose the optimal spacing for upward groynes. To examine flow characteristics around groynes, this study looked at flows in main flow area and recirculation flow area separately. In main flow area, it examined the impact of flow velocity increasing as a result of conveyance reduction that is exerted on river bed stability in relation to changes in the maximum flow velocity according to installation spacing. As a factor causing impacts on scouring and sedimentation within the area of groynes, recirculation flow in the groyne area can lead problems concerning flow within the area and stability of embankment. As for recirculation area, an analysis was conducted on the scale of rotational flow and the flow around embankment that exerts impacts on stability of the embankment. In addition, a comparative analysis was carried with reference to changes of the central point of rotational flow that occur within the area of groynes. As a result of compositely examining the results, the appropriate installation spacing is proposed as min. four times-max. six times considering a decrease in flow velocity according to the installation of upward groynes, river bed stability and stability of embankments against counterflow within the area of groynes.

• Polymer(Korea)
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• v.29 no.6
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• pp.536-542
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• 2005

The effect of lime-related parameters such as loading velocity, load application time, gauge reading time on Rockwell hardness measurement was investigated for PE, PP PVC, and PMMA. It was found that keeping the specific requirements in the same condition is very important to obtain reliable and repeatable darn in polymer hardness measurement. The optimum condition for hardness measurement was 4 sec for load application time,15 sec for test load application net time, and 15 sec for gauge reading time after unloading. Using thess conditions, round robin test was carried out for 6 laboratories and it was shown that the testing machine should be one in which time-related variables are controllable. Indirect verification of hardness tester using brass reference block was not enough to guarantee the test results for polymer.

• Smart Structures and Systems
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• v.15 no.2
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• pp.335-353
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• 2015

Previous long-term measurements of the Uldolmok tidal current power plant showed that the structure's natural frequencies fluctuate with a constant cycle-i.e., twice a day with changes in tidal height and tidal current velocity. This study aims to improve structural health monitoring (SHM) techniques for offshore structures under a harsh tidal environment like the Uldolmok Strait. In this study, lab-scale experiments on a simplified offshore structure as a lab-scale test structure were conducted in a circulating water channel to thoroughly investigate the causes of fluctuation of the natural frequencies and to validate the displacement estimation method using multimetric data fusion. To this end, the numerical study was additionally carried out on the simplified offshore structure with damage scenarios, and the corresponding change in the natural frequency was analyzed to support the experimental results. In conclusion, (1) the damage that occurred at the foundation resulted in a more significant change in natural frequencies compared with the effect of added mass; moreover, the structural system became nonlinear when the damage was severe; (2) the proposed damage index was able to indicate an approximate level of damage and the nonlinearity of the lab-scale test structure; (3) displacement estimation using data fusion was valid compared with the reference displacement using the vision-based method.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.35-40
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• 2015

Centrifugal pumps consume considerable amounts of energy in various industrial applications. Therefore, improving the efficiency of pumps machine is a crucial challenge in industrial world. This paper presents numerical investigation of flow characteristics in volutes of centrifugal pumps in order to compare the energy consumption. A wide range of volumetric flow rate has been investigated for each case. The standard k-${\varepsilon}$ is adopted as the turbulence model. The impeller rotation is simulated employing the Multi Reference Frames(MRF) method. First, two different conventional design methods, i.e., the constant angular momentum(CAM) and the constant mean velocity (CMV) are studied and compared to a baseline volute model. The CAM volute profile is a logarithmic spiral. The CMV volute profile shape is an Archimedes spiral curve. The modified volute models show lower head value than baseline volute model, but in case of efficiency graph, CAM curve has higher values than others. Finally for this part, CAM curve is selected to be used in the simulation of different cross-section shape. Two different types of cross-section are generated. One is a simple rectangular shape, and the other one is fan shape. In terms of different cross-section shape, simple rectangular geometry generated higher head and efficiency. Overall, simulation results showed that the volute designed using constant angular momentum(CAM) method has higher characteristic performances than one by CMV volute.