• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.73-86
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• 1995

The transducer section of the forward-looking ultrasound imaging catheter (FLUIC) consists of a circular piezoelectric element as a vibrator and a conical acoustic mirror as a perfect reflector. A small diameter piezoelectric transducer element is mounted on the side of a catheter's rotating shaft. The unique design of FLUIC provides the capability to form a two-dimensional image of a cross-section of vessel in front of the catheter, which is lacking in the present generation of intravascular ultrasound (IVUS) transducers, as well as a conventional side view image. The mirror configuration for the transducer section of the FLUIC is designed using an approximated ray tracing techniques. The diffraction transfer function approach [1] developed for the field prediction from primary sources is generalized and extended to predict the secondary diffraction characterstics from an acoustic mirror. The extended model is verified by simulation and experiment through a simple plane reflector and employed to analyzed the field characteristics of a FLUIC.

• Journal of Magnetics
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• v.22 no.2
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• pp.299-305
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• 2017

Magnetic fluid, a new type of magnetic material, is a colloidal liquid constituted of nano-scale ferromagnetic particles suspended in carrier fluid. Magnetic fluid sealing is one of the most successful applications of magnetic fluid. As a new type of seal offering the advantages of no leakage, long life and high reliability, the magnetic fluid seal has been widely utilized under vacuum- and low-pressure-differential conditions. In practical applications, for improved pressure capacity, a multistage sealing structure is always used. However, in engineering applications, a uniform distribution of magnetic fluid under each tooth often cannot be achieved, which problem weakens the overall pressure capacity of the seals. In order to improve the pressure capacity of magnetic fluid seals and broaden their applications, the present study theoretically and experimentally analyzed the degree of non-uniform distribution of multistage magnetic fluid seals. A mathematical model reflecting the relationship between the pressure capacity and the distribution of magnetic fluid under a single tooth was constructed, and a formula showing the relationship between the volume of magnetic fluid and its contact width with the shaft was derived. Furthermore, the relationship of magnetic fluid volume to capacity was analyzed. Thereby, the causes of non-uniform distribution could be verified: injection of magnetic fluid; the assembly of magnetic fluid seals; the change of magnetic fluid silhouette under pressure loading; the magnetic fluid sealing mechanism of pressure transmission, and seal failure. In consideration of these causes, methods to improve the pressure capacity of magnetic fluid seals was devised (and is herein proposed).

• Journal of the Korean Geotechnical Society
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• v.28 no.12
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• pp.87-98
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• 2012

A sonar sensor system of a new socket roughness profiling system (SRPS) which can measure the socket roughness of the large-diameter drilled shafts under the in-situ condition was developed and verified. In model tests, the salinity, temperature, and high-turbidity have been changed for simulating the in-situ borehole water conditions. From the test results, it was found that the sonar sensor can measure the distance within an accuracy of 1mm. Because of the wave form characteristics of sonar sensor, the relative error exists in case of the inclined and curved surface, however, the shape of specimen was confirmed relatively exactly using the developed sonar sensor. Moreover, the salinity, temperature, and high-turbidity did not affect the measured data of socket roughness.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.224-234
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• 2008

Multi-phase machines can be used in variable speed drives. Their applications include electric ship propulsion, 'more-electric aircraft' and traction applications, electric vehicles, and hybrid electric vehicles. Multi-phase machines enable independent control of a few numbers of machines that are connected in series in a particular manner with their supply being fed from a single voltage source inverter(VSI). The idea was first implemented for a five-phase series-connected two-motor drive system, but is now applicable to any number of phases more than or equal to five-phase. The number of series-connected machines is a function of the phase number of VSI. Theoretical and simulation studies have already been reported for number of multi-phase multi-motor drive configurations of series-connection type. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information concerning the rotor speed is extracted from measured stator currents and voltages at motor terminals. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an MRAS estimator based sensorless control of a vector controlled series-connected two-motor five-phase drive system with current control in the stationary reference frame. Results, obtained with fixed-voltage, fixed-frequency supply, and hysteresis current control are presented for various operating conditions on the basis of simulation results. The purpose of this paper is to report the first ever simulation results on a sensorless control of a five-phase two-motor series-connected drive system. The operating principle is given followed by a description of the sensorless technique.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.643-651
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• 2001

Paddlewheel-driven circulation in a culture pond has been simulated based on the depth integrated 2 dimensional hydrodynamic model. Acceleration by paddlewheel is expressed as shaft force divided by water mass discharged by paddlewheel blades. The model has been calibrated and applied to culture ponds as following steps:- i) The model predicted velocities at every 10 m along longitudinal direction from the paddlewheel. The model was calibrated comparing the results with the measured values at mass correction factor $\alpha$ and dimensionless eddy viscosity constant $\gamma$, respectively, in a range $15\~20$ and 6. ii) Wind shear stress was simulated under conditions of direction $0^{\circ}C,\;90^{\circ}C\;and\;180^{\circ}C$ and speed 0.0, 2.5, 5.0 and 7.5 m/s. Change rate of current speed was <$1\%$ at wind in parallel or opposite direction to the paddlewheel-driven jet flow, while $4\%$ at orthogonal angle. iii) The model was then applied to 2 culture ponds located at the Western coast of Korea. The measured and predicted currents for the ponds were compared using the regression analysis. Analysis of flow direction and speed showed correlation coefficients 0.8928 and 0.6782 in pond A, 0.8539 and 0.7071 in pond B, respectively. Hence, the model is concluded to accurately predict circulation driven by paddlewheel such that it can be a useful tool to provide pond management strategy relating to paddlewheel operation and water quality.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.459-465
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• 2011

It has been reported that the femoral morphology has a major correlation to femoral neck fractures(FNF). Previous studies to analyze these correlations have relied on mechanical testing and finite element methods. However, these methods have not been widely applied to various femur samples and models. It is because of the availability of the samples from both patients and cadavers, and also of the geometric limitations in changing the shape of the models. In this study we analyzed femoral neck fractures using a parameterized femoral model that could provide flexibility in changing the geometry of the model for the wide applications of FNF analysis. With the parameterization a variety of models could be generated by changing four major dimensions: femoral head diameter(FHD), femoral neck diameter(FND), femoral neck length(FNL), and neck-shaft angle(NSA). We have performed FEA on the models to compute the stress distributions and reaction forces, and compare them with the data previously generated from mechanical testing. The analysis results indicate that the FND is significantly related with the FNF and the FHD is not significantly related with the FNF.

• Steel and Composite Structures
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• v.34 no.5
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• pp.681-698
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• 2020

The paper addresses contribution to the modeling and optimization of major machinability parameters (cutting force, surface roughness, and tool wear) in finish dry hard turning (FDHT) for machinability evaluation of hardened AISI grade die steel D₃ with PVD-TiN coated (Al₂O₃-TiCN) mixed ceramic tool insert. The turning trials are performed based on Taguchi's L₁₈ orthogonal array design of experiments for the development of regression model as well as adequate model prediction by considering tool approach angle, nose radius, cutting speed, feed rate, and depth of cut as major machining parameters. The models or correlations are developed by employing multiple regression analysis (MRA). In addition, statistical technique (response surface methodology) followed by computational approaches (genetic algorithm and particle swarm optimization) have been employed for multiple response optimization. Thereafter, the effectiveness of proposed three (RSM, GA, PSO) optimization techniques are evaluated by confirmation test and subsequently the best optimization results have been used for estimation of energy consumption which includes savings of carbon footprint towards green machining and for tool life estimation followed by cost analysis to justify the economic feasibility of PVD-TiN coated Al₂O₃+TiCN mixed ceramic tool in FDHT operation. Finally, estimation of energy savings, economic analysis, and sustainability assessment are performed by employing carbon footprint analysis, Gilbert approach, and Pugh matrix, respectively. Novelty aspects, the present work: (i) contributes to practical industrial application of finish hard turning for the shaft and die makers to select the optimum cutting conditions in a range of hardness of 45-60 HRC, (ii) demonstrates the replacement of expensive, time-consuming conventional cylindrical grinding process and proposes the alternative of costlier CBN tool by utilizing ceramic tool in hard turning processes considering technological, economical and ecological aspects, which are helpful and efficient from industrial point of view, (iii) provides environment friendliness, cleaner production for machining of hardened steels, (iv) helps to improve the desirable machinability characteristics, and (v) serves as a knowledge for the development of a common language for sustainable manufacturing in both research field and industrial practice.

• Smart Structures and Systems
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• v.4 no.2
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• pp.221-232
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• 2008

This paper represents the final results of a research program sponsored by the European Commission through project WIND-CHIME ($\underline{W}$ide Range Non-$\underline{IN}$trusive $\underline{D}$evices toward $\underline{C}$onservation of $\underline{HI}$storical Monuments in the $\underline{ME}$diterranean Area), in which the possibility of using advanced seismic protection technologies to preserve historical monuments in the Mediterranean area is investigated. In the current research, the dynamic characteristics of two outstanding Mamluk-Style minarets, which similar minarets were reported to experience extensive damage during Dahshur 1992 earthquake, are investigated. The first minaret is the Qusun minaret (1337 A.D, 736 Hijri Date (H.D)) located in El-Suyuti cemetery on the southern side of the Salah El-Din citadel. The minaret is currently separated from the surrounding building and is directly resting on the ground (no vaults underneath). The total height of the minaret is 40.28 meters with a base rectangular shaft of about 5.42 ${\times}$ 5.20 m. The second minaret is the southern minaret of Al-Sultaniya (1340 A.D, 739 H.D). It is located about 30.0 meters from Qusun minaret, and it is now standing alone but it seems that it used to be attached to a huge unidentified structure. The style of the minaret and its size attribute it to the first half of the fourteenth century. The minaret total height is 36.69 meters and has a 4.48 ${\times}$ 4.48 m rectangular base. Field investigations were conducted to obtain: (a) geometrical description of the minarets, (b) material properties of the minarets' stones, and (c) soil conditions at the minarets' location. Ambient vibration tests were performed to determine the modal parameters of the minarets such as natural frequencies and mode shapes. A $1/16^{th}$ scale model of Qusun minaret was constructed at Cairo University Concrete Research Laboratory and tested under free vibration with and without SMA wire dampers. The contribution of SMA wire dampers to the structural damping coefficient was evaluated under different vertical loads and vibration amplitudes. Experimental results were used along with the field investigation data to develop a realistic 3-D finite element model that can be used for seismic risk evaluation of the minarets. Examining the updated finite element models under different seismic excitations indicated the vulnerability of such structures to earthquakes with medium to high a/v ratio. The use of SMA wire dampers was found feasible for reducing the seismic risk for this type of structures.

• Publications of The Korean Astronomical Society
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• v.36 no.3
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• pp.79-95
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• 2021

This study aims to develop a restoration model of an armillary sphere of Tongcheon-ui (Pan-celestial Armillary Sphere) by referring to the records of Damheonseo (Hong Dae-Yong Anthology) and the artifact of an armillary sphere in the Korean Christian Museum of Soongsil University. Between 1760 and 1762, Hong, Dae-Yong (1731-1783) built Tongcheon-ui, with Na, Kyung-Jeok (1690-1762) designing the basic structure and Ann, Cheo-In (1710-1787) completing the assembly. The model in this study is a spherical body with a diameter of 510 mm. Tongcheon-ui operates the armillary sphere by transmitting the rotational power from the lantern clock. The armillary sphere is constructed in the fashion of a two-layer sphere: the outer one is Yukhab-ui that is fixed; and the inner one, Samsin-ui, is rotated around the polar axis. In the equatorial ring possessed by Samsin-ui, an ecliptic ring and a lunar-path ring are successively fixed and are tilted by 23.5° and 28.5° over the equatorial ring, respectively. A solar miniature attached to a 365-toothed inner gear on the ecliptic ring reproduces the annual motion of the Sun. A lunar miniature installed on a 114-toothed inner gear of the lunar-path ring can also replay the moon's orbital motion and phase change. By the set of 'a ratchet gear, a shaft and a spur gear' installed in the solstice-colure double-ring, the inner gears in the ecliptic ring and lunar-path ring can be rotated in the opposite direction to the rotation of Samsin-ui and then the solar and lunar miniatures can simulate their revolution over the period of a year and a month, respectively. In order to indicate the change of the moon phases, 27 pins were arranged in a uniform circle around the lunar-path ring, and the 29-toothed wheel is fixed under the solar miniature. At the center of the armillary sphere, an earth plate representing a world map is fixed horizontally. Tongcheon-ui is the armillary sphere clock developed by Confucian scholars in the late Joseon Dynasty, and the technical level at which astronomical clocks could be produced at the time is of a high standard.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.37-51
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• 2007

In this study, pile load tests have been carried out to develop new P-y curves and then, to investigate the effects of pile rigidities on laterally loaded offshore drilled shafts in Incheon marine clay. This paper consists mainly of two parts: the first part, performance of a series of lateral load tests on small- and full-scale piles under one- and two-way loadings and the second part, comparison between the measured and predicted results by using O'Neill's and Matlock's clay models. Based on the results obtained, it is shown that relatively good agreements in bending moments and lateral displacements were obtained between the measured results using calculated P-y curves and predicted ones by O'Neill's and Matlock's clay models. The cases were considered with varying rigidity factors based on pile diameter, length and subgrade soil reaction. Through comparisons, it is found that soil P-y curve influences highly the behavior of flexible pile rather than that of rigid pile.