• 한국해양공학회지
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• 제23권6호
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• pp.117-123
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• 2009

This paper presents a numerical simulation of guided ultrasonic waves propagating in aluminum-epoxy-aluminum adhesive plates. In particular, this study investigated the effect of the epoxy thickness on the dispersive patterns, such as the phase velocity and group velocity of guided ultrasonic waves. In addition to investigating the dispersive curves, a numerical simulation using the pulse-echo method was carried out. This simulation showed that the degree of sensitivity of the epoxy thickness is dependent on the curvature of the phase and group dispersion curves, the maximum amplitude of the received time signals, and the peak frequency of the real components of the Fourier transform. Then, the linear relations between the epoxy thickness and the received and transformed signals were constructed to estimate the epoxy thickness.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.80-83
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• 1999

Rigid Plasticity Finite Element Analysis is developed for the shapes of dead metal zone and the curving velocity distribution in the eccentric square dies extrusion. The shape of dead metal zone is defined as the boundary surface with the maximum friction constant between the deformable zone and the rigid zone. The curving phenomenon in the eccentric square dies is caused by the eccentricity of square dies. The deviated velocity is changed with the distance form the center of cross-section of the workpiece. The results show that the curving of products and the shapes of the dead metal zone are determined by Rigid Plasticity Finite Element Analysis and that the curvature of the extruded products increases with the eccentricity.

• 한국유체기계학회 논문집
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• 제11권1호
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• pp.9-17
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• 2008

A numerical study for three-dimensional laminar flow in the entrance region of helical tubes connected with straight ones is carried out to investigate the effects of Reynolds number, pitch and curvature ratio on the oscillation periods of the flow. The fully elliptic governing equations were solved by means of a finite volume method. The fully developed laminar flow boundary condition was applied at the straight tube inlet. This results cover a curvature ratio range of 1/10${\sim}$1/320, a pitch range of 0.0${\sim}$3.2, and a Reynolds number range of 62.5${\sim}$2000. A comparison is made with previous experimental correlations and numerical data. The developments of velocity, local and average friction factors are discussed. The average friction factors are oscillatory in the entrance region of helical pipes. It has been found that the angle required for the flow to be similarly developed is most affected by the curvature ratio. The pitch and Reynolds number do not have any significant effect on the angle. The characteristic angle ${\phi}_c(={\phi}/sqrt{\delta})$, or the characteristic length to diameter ratio $s_c(=l\sqrt{\delta} cos(atan{\lambda})/d)$, can be useful to represent the development of flow in helical tubes. As the pitch increases and as the curvature ratio and Reynolds number decrease, the amplitude and the number of flow oscillations along the main streamwise direction decrease.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.120.4-120
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• 2001

In this paper, a method of generating trajectories in real time for a mobile robot in a dynamic environment is proposed. Specifically, this method is focused on soccer-playing robots that need to calculate trajectories in real time, which are constantly subject to rapidly change as targets and obstacles move. The robots also should move at the fastest available speed, while tracking the generated trajectories. The method proposed in this paper solves the geometric problem of finding a smooth curve that joins two endpoints. To have this solved, we assign five constraints to each endpoint, which are the usual x, y, theta, and curvature as well as the influence of the initial robot velocity on the path. With these five constraints, the path generated can always be physically followed by robot. Through this method, the travel time of the robot over the entire path can b optimized. Therefore it can ...

• 대한기계학회논문집A
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• 제30권9호
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• pp.1049-1061
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• 2006

In the study, the flow stress of material and friction condition were determined by using the cylinder compression test and numerical method. We proposed the flow stress equation including the initial yield strength to predict it from the upper bound method. The upper bound technique uses the velocity field which includes two unknowns to effectively express bulging. Also, inverse engineering technique uses the object function to minimize area enclosed by load-stroke curve. The friction factor is determined from the radius of curvature of the barrel by cylinder compression test. Flow stress and initial yield strength predicted from the above techniques are verified through the finite element simulation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.502-507
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• 2003

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.111-115
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• 2002

The objective of this work is to develop improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan by investigating the validity of various slip factor models. Both steady and unsteady three-dimensional CFD analyses were performed with a commercial code tn validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the presented model takes into account the effect of blade curvature. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peaktotal pressure coefficient.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.575-586
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• 2008

The main objective of this paper is to develop an improved model for the analysis of liquefaction potential and to predict excess pore pressure (EPP) using the proposed model that can simulate behavior of saturated sand under earthquake loading conditions. The damage concept is adopted for the development of the proposed model. For the development of the model, a general formulation based on experimental results and damage potential using cumulative absolute velocity (CAV) is proposed for a more realistic description of dynamic responses of saturated sand. Undrained dynamic triaxial tests are conducted using earthquake loading conditions. Based on test results, the NCER-NCW function in terms of $w_d$ and CAV is developed. Procedure for the evaluation of EPP and determination of model parameters for the proposed model is presented as well. For the determination of initial liquefaction, the minimum curvature method using the NCS-NCW curve is proposed. It is observed that predicted initial liquefaction using the proposed method agrees well with measured initial liquefaction. From results of additional undrained dynamic triaxial tests, it is seen that predicted EPP generation using the proposed model agrees well with measured results for earthquake loading cases.

• Clinical and Experimental Pediatrics
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• 제58권6호
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• pp.218-223
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• 2015

Purpose: Idiopathic scoliosis is a structural lateral curvature of the spine of unknown etiology. The relationship between degree of spine curvature and cardiopulmonary function has not yet been investigated. The purpose of this study was to determine the association between scoliosis and cardiopulmonary characteristics. Methods: Ninety children who underwent preoperative pulmonary or cardiac evaluation at a single spine institution over 41 months were included. They were divided into the thoracic-dominant scoliosis (group A, n=78) and lumbar-dominant scoliosis (group B, n=12) groups. Scoliosis severity was evaluated using the Cobb method. In each group, relationships between Cobb angles and cardiopulmonary markers such as forced vital capacity (FVC), forced expiratory volume in one second ($FEV_1$), $FEV_1$/FVC, left ventricular ejection fraction, pulmonary artery flow velocity, and tissue Doppler velocities (E/E', E'/A') were analyzed by correlation analysis linear regression. Results: In group A, 72 patients (92.3%) underwent pulmonary function tests (PFTs), and 41 (52.6%) underwent echocardiography. In group B, 9 patients (75.0%) underwent PFT and 8 (66.7%) underwent echocardiography. Cobb angles showed a significant negative correlation with FVC and $FEV_1$ in group A (both P<0.05), but no such correlation in group B, and a significant negative correlation with mitral E/A ratio (P<0.05) and tissue Doppler E'/A' (P<0.05) in group A, with a positive correlation with mitral E/A ratio (P<0.05) in group B. Conclusion: Pulmonary and cardiac function was significantly correlated with the degree of scoliosis in patients with thoracic-dominant scoliosis. Myocardial diastolic function might be impaired in patients with the most severe scoliosis.

• 대한기계학회논문집A
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• 제34권7호
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• pp.891-896
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• 2010

제로터는 유압모터나 펌프뿐만 아니라 조향장치인 파워 스티어링 유닛(PSU)에도 사용된다. 제로터의 내치차는 일상적인 경우 단일 원호형상의 외치차에 의하여 생성된다. 본 논문에서 PSU의 특성 개선을 위하여 보다 일반화 된 외치차의 형상으로부터 내치차를 생성하는 방법을 해석하였다. 해석의 결과로서, 외치차의 형상곡선이 특별한 2중곡률을 갖는 원호인 경우에 대하여, 내치차의 형상과 곡률, 제로터의 유량 및 접촉점의 위치와 슬립속도 등의 설계자료를 구하여 제시하였다. 이러한 해석은 새로운 PSU의 개발과 소형화를 가능케 한다.