• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.3
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• pp.44-53
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• 2008

In this paper, we present the design of delta-sigma modulation-based class-D amplifier for driving headphones in portable audio applications. The presented class-D amplifier generates PWM(pulse width modulation) signals using a single-bit fourth-order high-performance delta-sigma modulator. To achieve a high SNR(signal-to-noise ratio) and ensure system stability, the locations of the modulator loop filter poles and zeros are optimized and thoroughly simulated. The test chip is fabricated using a standard $0.18{\mu}m$ CMOS process. The active area of the chip is $1.6mm^2$. It operates for the signal bandwidth from 20Hz to 20kHz. The measured THD+N(total harmonic distortion plus noise) at the $32{\Omega}$ load terminal is less than 0.03% from a 3V power supply.

• PNF and Movement
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• v.7 no.4
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• pp.31-36
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• 2009

Many daily activities require people to complete a motor task while walking. Substantial gait decrements during simultaneous attention to a variety of cognitive tasks have been shown by a group of severely injured neurological patients of mixed etiology. And previous studies have shown that the attentional load of a walking-associated task increased with its level of difficulty. The purpose of this study was to analyze subjects' gait changes are affected by the effects of arithmetic task difficulty and performance level. Participants performed a walking task alone, three different Arithmetic tasks while seated, and among them, two kinds of the simillar Arithmetic tasks in combination with walking. Reaction time and accuracy were recorded for two of the Arithmetic tasks. The mean values of the gait were measured using a Timed Up and Go test among 11 with post-stroke patients while walking with and without forward counting (WFC) and backward counting(WBC).There was significant Arithmetic Task Difficulty level between the 10-forward counting task condition(FC) and the 10-backward counting task condition(BC)(p=0.008). The mean values of T.U.G time were significantly higher under backward counting dual-task condition than during a simple walking task(p=0.009) and WFC(p=0.009). The change in T.U.G time during WFC was higher when compared with the change during a simple walking, but there was no significant difference (p=0.246). This study suggesting that a high interference could be linked with a high level of difficulty, whereas adaptive task enabled participants to perfectly share their attention between two concurrent tasks. Future research should determine whether dual task training can reduce gait decrements in dual task situations in people after stroke. And the dual-task-based exercise program is feasible and beneficial for improving walking ability in subjects with stroke.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.26-33
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• 2001

Thrust vector control system is control device which is mounted exit of the nozzle to generate pitch, yaw and roll directional force by deflecting flow direction of the supersonic jet from the nozzle. By obtaining control force, jetvane which is exposed in jet flow is working thermal and aerodynamic load. Axial thrust loss and side thrust is affected by shock patterns and interactions between jetvanes according to jetvane geometry and turning angle. In this study, we designed 6 types of jetvane to evaluate pitch, yaw and roll characteristics of ietvane in supersonic flow, and perform the cold flow test in range of turning angles of jetvanes between $0^{\cire}$ and $25^{\cire}$ by $5^{\cire}$ respectively. Also, calculation is going side by side to analyse flow interaction. Results show that there is no interactions between jetvanes upto turning angle 20$^{\circ}$, chord and lead length ratio is very important parameter to aerodynamic performance and maximum thrust loss is appeard to 17% of axial thrust in roll directional control.

• Earthquakes and Structures
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• v.8 no.3
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• pp.555-572
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• 2015

This paper presents an experimental study of three two-dimensional (2D/planar) steel reinforced concrete (SRC) T-shaped column-RC beam hybrid joints and six 3D SRC T-shaped column-steel beam hybrid joints under low cyclic reversed loads. Considering different categories of steel configuration types in column cross section and horizontal loading angles for the specimens were selected, and a reliable structural testing system for the spatial loading was employed in the tests. The load-displacement curves, carrying capacity, energy dissipation capacity, ductility and deformation characteristics of the test subassemblies were analyzed. Especially, the seismic performance discrepancies between planar hybrid joints and 3D hybrid joints were intensively compared. The failure modes for planar loading and spatial loading observed in the tests showed that the shear-diagonal compressive failure was the dominating failure mode for all the specimens. In addition, the 3D hybrid joints illustrated plumper hysteretic loops for the columns configured with solid-web steel, but a little more pinched hysteretic loops for the columns configured with T-shaped steel or channel-shaped steel, better energy dissipation capacity & ductility, and larger interlayer deformation capacity than those of the planar hybrid joints. Furthermore, it was revealed that the hysteretic loops for the specimens under $45^{\circ}$ loading angle are generally plumper than those for the specimens under $30^{\circ}$ loading angle. Finally, the effects of steel configuration type and loading angle on the seismic damage for the specimens were analyzed by means of the Park-Ang model.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.562-577
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• 2014

A reliable steady/transient hydro-elastic analysis is developed for flexible (composite) marine propeller blade design which deforms according to its environmental load (ship speed, revolution speed, wake distribution, etc.) Hydro-elastic analysis based on CFD and FEM has been widely used in the engineering field because of its accurate results however it takes large computation time to apply early propeller design stage. Therefore the analysis based on a boundary element method-Finite Element Method (BEM-FEM) Fluid-Structure Interaction (FSI) is introduced for computational efficiency and accuracy. The steady FSI analysis, and its application to reverse engineering, is designed for use regarding optimum geometry and ply stack design. A time domain two-way coupled transient FSI analysis is developed by considering the hydrodynamic damping ffects of added mass due to fluid around the propeller blade. The analysis makes possible to evaluate blade strength and also enable to do risk assessment by estimating the change in performance and the deformation depending on blade position in the ship's wake. To validate this hydro-elastic analysis methodology, published model test results of P5479 and P5475 are applied to verify the steady and the transient FSI analysis, respectively. As the results, the proposed steady and unsteady analysis methodology gives sufficient accuracy to apply flexible marine propeller design.

• Fire Science and Engineering
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• v.34 no.3
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• pp.18-27
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• 2020

An actual fire test was performed on single combustibles placed in a local cinema complex, and quantitative differences in the maximum heat release rate (HRR) and fire growth rate were investigated based on the design fire curve methods (i.e., the general and 2-stage methods). In terms of combustible use and fire load, a total of 12 combustibles were selected, classified into cinema lounge and movie theater. It was found that the maximum HRR and fire growth rate determined using the two-stage method were quantitatively different from those of the general method. The application of the two-stage method, which can be used to determine the fire growth rate of the initial fire stage more precisely, could be useful in accurately predicting the activation time of fire detectors and fire-extinguishing facilities, as well as the available safe egress time (ASET) and required safe egress time (RSET).

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.281-293
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• 2002

Empiricism has characterized the traditional methods of pile design; in essence, pile design recommendations are based on the accumulated knowledge of pile behaviour based on the construction and subsequent load testing of piles in soil and rock. In this paper, the traditional approaches to design of piles in rock will be briefly reviewed. It will be shown that the unrelated empirical relationships developed fur rock lead to considerable uncertainty in the design of piles. A new method for predicting the shaft resistance of piles socketed into rock, and based on fundamental principles is outlined. It is shown that the shaft resistance predictions of this method agree well with the field test data for rock and hard soil. It is demonstrated by way of a limited parametric study that shaft roughness and socket diameter are critical factors in the performance of piles constructed in these materials. The application of the method to piles socketed into the granites and gneisses of Korea is discussed by way of a case study and by reference to recent direct shear tests on these rocks.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.535-542
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• 2005

Two series of experiments on the performance of beam-column joints in High-Strength Reinforced concrete frames were carried out. Main experimental parameters were : concrete strength, column axial load and amount of joint hoop reinforcement. Test result showed that the ultimate shear strength of exterior joints increased of column axial compressive force and the amount of the joint hoop reinforcements. Through the regression analysis on the 24data, the following equation is obtained $jv_u=(2.935{\times}10-3\;{\rho}jw{\cdot}fy\;+\;0.365){\sqrt{f_{ck}}}$

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.707-714
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• 2014

CFT (Concrete-Filled Tube) is a type of steel column comprised of steel tube and concrete. Steel tube holds concrete and the concrete inside tube takes charge of compressive load. This study presents structural performance of the CFT column which has 73~100 MPa high strength concrete inside. Fluidity, mechanical compression, pump pressure test in flexible pipe were conducted for understanding properties of the high strength concrete. Material properties were achieved by various experimental tests, such as slump, slump flow, air content, U-box, O-Lot, L-flow. In addition, mock-up tests were conducted to monitor concrete filling, hydration heat, compressive strength. From construction sites in Sang-am dong and University of Seo-kang, long-term behaviors could be effectively predicted in terms of ACI 209 material model considering elastic deformation, shrinkage and creep.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.16-25
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• 2018

Concrete is a suitable construction material for long-term structure, however, it is needed to understand the calcium leaching damage caused by exposure to underground pure water for a long time. In this paper, it is experimentally investigated that the characteristics of flexural behavior in RC member damaged by calcium leaching degradation. From the test results, when calcium leaching is happened, yielding load and flexural rigidity is reduced, neutral axis depth and displacement is increased. That is, calcium leaching degradation adversely affects RC member performance. And, when the mineral admixture is used in the calcium leaching environment, it is considered that the optimal replacement ratio should be prepared according to the type of mineral admixture.