• The Journal of Natural Sciences
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• v.14 no.2
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• pp.1-14
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• 2004

The observation of the various swing parameters and its effect on golfer swing are tatally analyzed. The golf ball impact and flies away, therefore it must be controlled bofore ball impact. The purpose of this paper is that the cause of hook and slice are found and the posture of swing is corrected. The trajectory after ball impact is on the $\Delta$-plane, which is consisted of the normal vector on club face and the swing velocity vector of club head including the initial celocity and the spin axis after ball imfact. In order to correct the miss shot in golf swing, this paper is is shown that the theoretical review and study is discussed to use the D-plane and $\Delta$-plane.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.102-109
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• 2006

The effects of wind fence on the pressure characteristics around low-rise building model were investigated experimentally. Flow characteristics of turbulences behind wind fence were measured using hot-wire anemometer. The wind fence characterize by varying the porosity of 0 %, 40 % and the distances from the wind fence from 1 H to 6 H with maintaining the uniform flow velocity of 6 m/s. We investigated the overall characterization of the low-rise building by measuring pressure seventy four on model. The effects of porosity fences varied with the porosity of the fence and measurement locations(1H-6H). The 0% porosity proved to be effective for the protection area of 4H to 6H, but the 40% porosity proved to be effective for the protection area of 1H to 6H. The low-rise building of front face was found to be best wind fence for decreasing the mean, maximum and minimum pressure fluctuation.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4
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• pp.105-112
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• 1996

A linear acoustic analysis for baffled rocket combustion chambers has been developed. This study provides the comprehensive theoretical background for the baffle as one of the stabilizing devices in a liquid rocket propulsion system. Several specific effects of baffles are presented as mechanisms by which baffles eliminate instability. Included are longitudinalization of transverse waves inside baffle compartments, severe restriction of velocity fluctuations near the injector face, and decreased normal mode frequency of the chamber.

• Explosives and Blasting
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• v.13 no.1
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• pp.20-31
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• 1995

Many methods and techniques to reduce ground vibrations are well known. Some of them are to adopt electric milisecond detonators with a sequential blasting machine or an initiating system with an adequate number of delay intervals. The types of electric detonators munufactured in Korea include instantaneous, decisecond and milisecond delays byt numbers of delay intervals are only limite from No.1 to No.20 respectively. It is not sufficient to control accurately milisecond time with these detonators in tunnel excavation. Sequential fire time refers to adding an external time delay to a detonators norminal firing time to obtain sequential initiation and it is determined by sequential timer setting. To reduce the vibration level, sequential blasting machine with decisecond detonatore was adopted. A total of 134 blasting was recorded at various sites. Blast-to-structure distances ranged from 20.3 to 42.0 meter, where charge weight varied from 0.25 to 0.75 kg per delay. The results can be summarized as follow : 1. The effects of sequential blasting machine on the vibration level are discussed. The vibration level by S.B.M. are decreased approximately 14.38~18.05 to compare to level of conventional blasting and cycle time per round can be saved. 2. The empirical equations of particle velocity were obtained in S,B.M. and conventional blastin. $V=K(D/W^{1/3})-n$. where the values for n and k are estimated to be 1.665 to 1.710 and 93.59 to 137 respectively. 3. The growth of cracks due to vibrations are found but the level fall to within allowable value.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.519-533
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• 2023

This work focuses on the dynamic analysis of thermal barrier coated straight and curved turbine blades modelled as functionally graded sandwich panel under thermal environment. The pre- twisted straight/curved blade model is considered to be fixed to the hub and, the complete assembly of the hub and blade are assumed to be rotating. The functionally graded sandwich composite blade is comprised of functionally graded face-sheet material and metal alloy core. The constituents' material properties are assumed to be temperature-dependent, however, the overall properties are evaluated using Voigt's micromechanical scheme in conjunction with the modified power-law functions. The blade model kinematics is based on the equivalent single-layer shear deformation theory. The equations of motion are derived using the extended Hamilton's principle by including the effect of centrifugal forces, and further solved via 2D- isoparametric finite element approximations. The mesh refinement and validation tests are performed to illustrate the stability and accurateness of the present model. In addition, frequency characteristics of the pre-twisted rotating sandwich blades are computed under thermal environment at various sets of parametric conditions such as twist angles, thickness ratios, aspect ratios, layer thickness ratios, volume fractions, rotational velocity and blade curvatures which can be further useful for designing the blade type structures under turbine operating conditions.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.31.3-32
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• 2021

We quantify the relative role of galaxy environment and bar presence on AGN triggering in face-on spiral galaxies using a volume-limited sample with 0.02 < z < 0.055, Mr < 19.5, and σ > 70 km s-1 selected from Sloan Digital Sky Survey (SDSS) Data Release 7. To separate their possible entangled effects, we divide the sample into bar and non-bar samples, and each sample is further divided into three environment cases of isolated galaxies, interacting galaxies with a pair, and cluster galaxies. The isolated case is used as a control sample. For these six cases, we measure AGN fractions at a fixed central star formation rate and central velocity dispersion, σ. We demonstrate that the internal process of the bar-induced gas inflow is more efficient in AGN triggering than the external mechanism of the galaxy interactions in groups and cluster outskirts. The significant effects of bar instability and galaxy environments are found in galaxies with a relatively less massive bulge. We conclude that from the perspective of AGN-galaxy coevolution, a massive black hole is one of the key drivers of spiral galaxy evolution. If it is not met, a bar instability helps the evolution, and in the absence of bars, galaxy interactions/mergers become important. In other words, in the presence of a massive central engine, the role of the two gas inflow mechanisms is reduced or almost disappears. We also find that bars in massive galaxies are very decisive in increasing AGN fractions when the host galaxies are inside clusters.

• International Journal of Computer Science & Network Security
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• v.24 no.8
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• pp.145-152
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• 2024

Agile project management is an ongoing method to project completion that actually took place all across length of the project's life cycle. Because loop allows you to adapt as you go rather than maintaining a linear route, iterative methods are mainly applied in software development to ensure velocity and agility. Many pitfalls abound in agile software development adaptations that organizations fail to sidestep. New competitive challenges, fluctuating market dynamics, technological disruption, and the ever-changing demands of empowered customers confront organizations around the world. Organizations are all under tremendous pressure to adapt to change and deliver good products and services to customers more swiftly. Research measured at the challenges that could be encountered and offered advice for how agile development might flourish as it becomes a component of a company's family. Our paper gives a comprehensive review of the most significant obstacles that companies encounter while adopting agile techniques. Adaptability. The agile approach encompasses a variety of techniques, which each have different usage in various sectors. Because certain other standards existing today clash with agile methodology, the adaptation of any of the agile techniques in work environments posed a problem. In this paper, we will cover some of the challenges that firms face in adopting the agile software development life cycle.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• Journal of radiological science and technology
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• v.31 no.3
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• pp.267-276
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• 2008

The 25 healthy male volunteers aged from 20 to 50years old have been employed in this study. 2D-PC MRA was performed to measure the velocity of the blood flow in the internal carotid artery and internal jugular veins using 3.0T MRI Whole body (signa VH/i GE). ECTRICKS-CEMRA was performed to evaluate the pattern of blood circulation from internal carotid artery to internal jugular vein. Using 2D-PC MRA, the cross-section of the 4th and 5th cervical discs was scanned with 24cm FOV. Then the speed of blood flow was measured for internal carotid artery and internal jugular vein when the subject wears a necktie tightly and no tie. The average of maximum velocity of internal carotid arteries without a necktie was 72.13cm/sec in the right side and 74.96cm/sec in the left side(average 73.54cm/sec in both sides) while the average of maximum velocity of internal jugular veins without a necktie was -34.45cm/sec in the right side and -24.99cm/sec in the left side (-29.72cm/sec in both sides). However, when wearing a necktie tightly, the average of maximum velocity of internal carotid arteries was 61.35cm/sec in the right side and 65.19cm/sec in the left side(average 63.27cm/sec in both sides) while the average of maximum velocity of internal jugular veins was -22.14cm/sec in the right side and -17.93cm/sec in the left side(-20.03cm/sec in both sides). With the necktie tightly knotted, the average blood flow speed of both internal carotid arteries slightly decreased to 86% (63.27/73.54cm/sec) compared to no tie case in which both internal jugularveins significantly went down to 67% (-20.03/-29.72 cm/sec). Thus it is suggested that wearing a necktie affects the circulation of internal jugular veins(33% decrease in blood flow speed) more significantly than that of internal carotid artery(14% decrease in blood flow speed). Without a necktie, ECTRICKS-CEMRA showed natural blood circulation patterns of internal carotid arteries and internal jugular veins without any disturbances or compressions. However, when wearing a necktie tightly, ECTRICKS-CEMRA showed severe compression onto both internal jugular veins in all 25 volunteers. In conclusion, the result of the study showed that the tightly worn necktie instantly presses more internal jugular veins than internal carotid arteries, thereby significantly reducing the blood flow speed and leading to the temporary occlusion. Thus, the defecation or washing the face under the tightly tied necktie situations can cause the unexpected and temporary compression or occlusion of the internal jugular veins, subsequently leading to the occurrences of the stroke due to the secondary intracranial venous hypertension.

• Geophysics and Geophysical Exploration
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• v.23 no.4
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• pp.243-252
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• 2020

To share an understanding of trajectory measurement in surveys using borehole, this tutorial summarizes the relevant mathematical principles of the borehole deviation survey based on coordinate transform. For uncased or open holes, calculations of the azimuth-deviation-tool face rotation using three-component accelerometer and magnetometer measurements are summarized. For the steel-cased holes, calculations are based on the time-derivative formula of the coordinate transform matrix; yaw-pitch-roll angles through time are mathematically determined by integrating the threecomponent angular velocity measurements from the gyroscope while also removing the Earth's rotation effect. Sensor and data fusion to increase the accuracy of borehole deviation survey is explained with an example of the method. These principles of borehole deviation surveys can be adapted for attitude estimation in air-borne surveys or for positioning in tunnels where global positioning system (GPS) signals cannot be accessed. Information on the optimization filter that must be incorporated in sensor fusion is introduced to help future research.