• 설비공학논문집
• /
• 제2권4호
• /
• pp.279-287
• /
• 1990

An experimental study of the heat transfer characteristics between circular water jet and cylindrical inner surface is presented. The ratios of the semi-cylinder's inner diameter and the nozzle outlet diameter were varied parametrically, as were the Reynolds number and the supplementary water heights. The measurements showed that cirucmferential distribution of the heat transfer coefficient peaked at the stagnation point and, there occurred a kind of a secondary maximum of heat transfer that moved toward to stagnation point as the ratio d/D increased. The local heat transfer coefficient increases as the Reynolds number becomes larger, and the rate of increase is subjected to the influence of d/D & position of angle. Also, optimum heights of supplementary water which brings about the augmentation of heat transfer are S/D=1 for the stagnation point, the position of $15^{\circ}$ & $30^{\circ}$ angle, but for the positions of $45^{\circ}$ angle (d/D=10~11.67), $60^{\circ}$ & $75^{\circ}$ angle, the heat transfer coefficients in the case of using supplementary water are smaller than simple jet (S/D=0).

• 한국정밀공학회지
• /
• 제17권8호
• /
• pp.113-119
• /
• 2000

There are two major factors which affect the cam design : the pressure angle and the radius of curvature, Cam shape will have an instantaneous radius of curvature at every point. Even though the design constraint of the pressure angle has been satisfied the follower may still not complete the desired contact motion. If the radius of the follower roller is larger than the concave(negative) radius on the cam it occurs the gap between the cam and the follower roller at the contact point. And also if the curvature of the pitch curve of the cam is too sharp the cam profile may be undercut. This paper proposes a new approach which uses the relative velocity of the follower roller parallel to the tangent line at the contact point on the cam surface for determining the pressure angle and the relative acceeration for determining the radius of curvature.

• Structural Engineering and Mechanics
• /
• 제68권5호
• /
• pp.633-638
• /
• 2018

One of the important problems in the vehicle design is vehicle handling and stability. Effective parameters which should be considered in the vehicle handling and stability are roll angle, camber angle and scrub radius. In this paper, a planar vehicle model is considered that two right and left suspensions are double wishbone suspension system. For a better analysis of the suspension geometry, a kinestatic model of vehicle is considered which instantaneous kinematic and statics relations are analyzed simultaneously. In this model, suspension geometry is considered completely. In order to optimum design of double wishbones suspension system, a multi-objective genetic algorithm is applied. Three important parameters of suspension including roll angle, camber angle and scrub radius are taken into account as objective functions. Coordinates of suspension hard points are design variables of optimization which optimum values of them, corresponding to each optimum point, are obtained in the optimization process. Pareto solutions for three objective functions are derived. There are important optimum points in these Pareto solutions which each point represents an optimum status in the model. In other words, corresponding to any optimal point, a specific geometric position is determined for the suspension hard points. Each of the obtained points in the Pareto optimization can be selected for a special design purpose by designer to create an optimum condition in the vehicle handling and stability.

• 한국정밀공학회지
• /
• 제4권1호
• /
• pp.42-52
• /
• 1987

Experimental investigation on the characteristics of the air flow around a square prism located in a uniform flow with various angles of attack was carried out. Experimental results were obtained for the angle of attack from 0 .deg. to 45 .deg. and for Reynolds No. from $2.6{\times}^4$to $12.8^4$. Seperation and reattachment was occurred on the forward face (face AB). Reattachment phenomenon was not developed in the range of attack angle lower 13 .deg. . But, for the range, 13 .deg. .approx. 35 .deg. , the reattachment developed and its position was moved forward the angle of attack increases. Pressure distributions on the reattachment face has a maxium at the reattachment point and a minimum at the separation point. Pressurea on two back faces are nearly symmetric in spite of the changes of the angle of attack and are influenced by the turbulence in rearward flow field.

• 한국유체기계학회 논문집
• /
• 제13권3호
• /
• pp.37-42
• /
• 2010

This study investigated on details of flow characteristics of a multi-blade fan for domestic ventilation. Experiments and analysis were carried out to describe on flow pattern with variations of cut-off angle near the scroll housing throat, which were performed by PIV measurement for the flow field and by total pressure probes. The stagnation point at cut-off region of the fan moves to the exit of the scroll housing as the cut-off angle increases. The movement of stagnation point and the variation of throat area of the scroll housing influence to the distribution of velocity magnitude at the exit of the fan. Furthermore, a large distortion of the velocity distribution at the scroll exit causes to increase mixing loss along the flow path.

• 대한기계학회논문집B
• /
• 제30권12호
• /
• pp.1164-1172
• /
• 2006

Measurements of the local heat transfer coefficients on hemispherical convex and concave surfaces with a turbulent impinging jet were made. The Reynolds number used was 11000, 23000, 50000 and the nozzle- to- surface distance was L/d=2, 4, 6, 8, and 10 and the jet angle was a = $0^{\circ}$, $15^{\circ}$, $30^{\circ}$ and $40^{\circ}$. In case of concave surface, the Nusselt number at the stagnation point decreases as the jet angle increases and has the maximum value for L/d=6. The X-axis Nusselt number distributions exhibit secondary maxima at $0^{\circ}$ $\leq$ a $\leq$ $15^{\circ}$, L/d $\leq$ 4 for X/d<0(upstream) and at $0^{\circ}$ $\leq$ a $\leq$ $40^{\circ}$, L/d $\leq$ 4 and at $30^{\circ}$ $\leq$ a $\leq$ $40^{\circ}$, 4 < L/d $\leq$ 6 for X/d<0(downstream). The secondary maximum occurs at long distance from the stagnation point as the jet angle increases or the nozzle-to-surface distance decreases. In case of convex, correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are presented. In the stagnation point, in term of Ren, n ranges from 0.43 in case of 2 $\leq$ L/d $\leq$ 6 to 0.45 in case of 6 < L/d $\leq$ 10, there agrees roughly appears to be laminar boundary layer result. The maximum Nusselt number, in this experiment, occurred in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. On this condition about surface curvature D/d=10, the maximum displacement is about 0.7 times of the jet nozzle diameter. The ratio of the maximum Nusselt number to the stagnation Nusselt number increases as the jet angle increases.

• 대한방사선기술학회지:방사선기술과학
• /
• 제42권3호
• /
• pp.167-173
• /
• 2019

The Cobey method and the modified Cobey method are most commonly used in clinical practice. Therefore, the purpose of this study was to investigate the radiological differences between Cobey and modified Cobey and provide radiographic information about changes of hindfoot image with X-ray entrance center and tube angle change in modified Cobey. This study was performed on foot and ankle phantom. First, for image comparison of Cobey and modified Cobey, the images obtained by applying the same X-ray entrance center to the ankle joint were compared and analyzed. Second, in the modified Cobey, the X-ray entrance center is set as ankle joint and lateral malleolus. The X-ray tube angle was varied from $10^{\circ}$ to $40^{\circ}$ at $5^{\circ}$ intervals for each X-ray entrance center. The images obtained by varying the X-ray tube angle from $10^{\circ}$ to $40^{\circ}$ at intervals of $5^{\circ}$ for each X-ray entrance center were compared and analyzed. The irradiation conditions were the same with 110 kVp, 200 mA, 10 ms, and 110 cm of source - image receptor distance (SID). Image evaluation was performed by two radiologists. Measurements were made on the lateral point, middle point, and calcaneus width based on a hypothetical line parallel to the calcaneal tuberosity. Data were analyzed by using descriptive statistics as the mean of the distance to each measurement location. The modified Cobey was longer than the Cobey by an average of 3 to 4 mm lateral and medial points, and the calcaneus width was similar (ICC = 0.939). In modified Cobey method, when the X-ray entrance center is ankle joint, the lateral point is about 3 mm and the medial point is about 4.3 mm longer than lateral malleolus. Also, when the X-ray tube angle is more than $20^{\circ}$, the degree of distortion is large. The ICCs for the lateral, medial point, and calcaneus width were 0.998, 0.961, and 0.997, respectively, as the X-ray entrance center and tube angle were changed. There was no significant difference between Modified Cobey and Cobey. Modified Cobey showed no need to compensate the $20^{\circ}$ detector angle of the Cobey. In addition, we suggest that tube angle should be limited within $20^{\circ}$ when modified Cobey is performed.

• 대한조선학회논문집
• /
• 제61권2호
• /
• pp.98-105
• /
• 2024

Due to the low accuracy of measured data obtained from low-cost GNSS and IMU devices, it was hard to secure the required accuracy of the measured position and heading angle for autonomous navigation which was conducted by a model-scale marine mobility. In this paper, a localization technique using the Extended Kalman Filter (EKF) is proposed for coping with the issue. First of all, a position and heading angle estimator is developed using EKF with the assumption of a point mass model. Second, the measured data from GNSS and IMU, including position, heading angle, and velocity are used for the estimator. In addition, the heading angle is additionally obtained by comparing the LiDAR point cloud with map information for a temporal water tank. The newly acquired heading angle is integrated into the estimator as an additional measurement to correct the inaccuracy in the heading angle measured from the IMU. The effectiveness of the proposed approach is investigated using data acquired from preliminary tests of the model-scale autonomous marine mobility.

• 대한기계학회논문집B
• /
• 제30권7호
• /
• pp.656-662
• /
• 2006

The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

• 한국정보처리학회논문지
• /
• 제5권3호
• /
• pp.824-832
• /
• 1998

본 논문에서는 영상의 코너점을 추출하기 위한 방법을 제안한다. 먼저 윤곽선을 따라 경계화소의 방향각을 lookup table의 참조에 의해 구하고, 기준치 이상의 화소를 후보점으로 선정한 뒤, 면적편차를 이용하여 코너점을 추출한다. 본 방법은 실시간 처리를 위해 처리시간을 줄이는 동시에 디지털 영상을 표현하는데 있어 라운드 오프 오차에 의해 발생되는 한 화소차를 극복하는 장점을 가진다. 제안된 방법의 검증을 위해 각종 실험 패턴을 이용하여 기존의 방법과 비교분석을 하였다.