• 한국군사과학기술학회지
• /
• 제13권6호
• /
• pp.1026-1033
• /
• 2010

The analysis of water-entry impact forces acting on the fin shaft of high speed water-entry body is described. During the entry of high speed body into water, the physical phenomenon and flow properties are analyzed. A proper analysis model is established and the method to estimate the flow force which causes impact torque at the fin shaft is described. It is assumed that the fin shaft is damaged by the force which is induced by contacting with cavity wall. The pressure distribution of fin and the maximum torque are estimated and compared with breaking force. Conclusively, it is hard to resist water-entry impact force in terms of the reinforcement of fin shaft. Additionally safe equipment is essentially required.

• 한국전산유체공학회지
• /
• 제4권1호
• /
• pp.1-7
• /
• 1999

The numerical methodology for computing tile impact forces and water entry behaviors of high speed water entry bodies was been developed. Since the present method assumed the impact occurs within a very short time interval. the viscous effects do not have enough time to play a significant role in the impact forces, that is, the flow around a water-entry object was assumed as an incompressible potential flow and is solved by the source panel method. The elements fully submerged into the water are routinely treated, but the elements intersected by the effective planar free surface are redefined and reorganized to be amenable to the source panel method. To validate the present code, it was applied to disk, cone and ogive model and compared with experimental data. Good agreement was obtained. The water entry behavior such as the bouncing phenomena from the free surface was also simulated using the impact forces and two degree of freedom dynamic equation. Physically acceptable results were obtained.

• Ocean Systems Engineering
• /
• 제8권2호
• /
• pp.223-246
• /
• 2018

In this paper the results of CFD simulations, that were carried out to study the impact pressures acting on a symmetric wedge during water entry under the influence of gravity, are presented. The simulations were done using a solver implementing finite volume discretization and using the VOF scheme to keep track of the free surface during water entry. The parameters such as pressure on impact, displacement, velocity, acceleration and net hydrodynamic forces, etc., which govern the water entry process are monitored during the initial stage of water entry. In addition, the results of the complete water entry process of wedges covering the initial stage where the impact pressure reaches its maximum as well as the late stage that covers the rebound process of the buoyant wedge are presented. The study was conducted for a few touchdown velocities to understand its influence on the water entry phenomenon. The simulation results are compared with the experimental measurements available in the literature with good accuracy. The various computational parameters (e.g., mesh size, time step, solver, etc.) that are necessary for accurate prediction of impact pressures, as well as the entry-exit trajectory, are discussed.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제11권1호
• /
• pp.482-494
• /
• 2019

In this paper, the oblique water-entry impact of a vehicle with a disk cavitator is studied experimentally and numerically. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments in this paper and the data available in the literature. Then, the numerical model is used to simulate the hydrodynamic characteristics and flow patterns of the vehicle under different entry conditions, and the axial force is found to be an important parameter. The influences of entry angle, entry speed and cavitator area on the axial force are studied. The variation law of the force coefficient and the dimensionless penetration distance at the peak of the axial force are revealed. The research conclusions are beneficial to engineering calculations on the impact force of a vehicle with a disk cavitator over a wide range of water-entry parameters.

• 한국컴퓨터정보학회논문지
• /
• 제29권4호
• /
• pp.125-134
• /
• 2024

본 연구는 빈곤 장애 여성의 사회자본이 노동시장 진입에 미치는 영향을 검증하여 그 관계를 밝히기 위해 수행되었다. 빈곤 장애 여성의 경우 경제활동을 위해 장애 여성들이 보유하거나 관계하고 있는 사회자본 수준과 유형에 따라 노동시장 진입에 미치는 영향에 대한 연구는 매우 부족한 것이 현실이다. 따라서 본 연구에서는 빈곤 장애 여성이 보유하고 있는 사회자본 수준과 유형이 노동시장 진입에 어떠한 영향을 미치는지에 대해 살펴보았으며, 연구결과 빈곤 장애 여성의 사회자본 수준에서는 규모가 크고, 밀도가 강할수록 노동시장 진입에 매우 주요한 영향을 미치는 것으로 나타났으며, 사회자본 유형에서는 신뢰와 참여가 클수록 노동시장 진입에 매우 유의미한 영향을 미치는 것으로 나타났다. 이러한 연구결과를 근거로 빈곤 장애 여성의 사회자본 수준과 유형이 노동시장 진입에 미치는 주요한 정책적 시사점을 제언하였다.

• 경영과정보연구
• /
• 제5권
• /
• pp.185-209
• /
• 2000

A review of shows that past research has focused predominately on foreign market entry strategy issues in relatively well-established firms. These studies have either ignored venture firms or have failed to treat these firms separately. Only recently, researchers have broadened their search to include aspects of the foreign market investment of the venture. The purposes of this study are to identify and explain the impact factors such as ownership specific advantage, transaction cost, and location specific advantage on the choice of foreign market entry strategy for venture firms. To find the perceived the foreign market entry strategy and determinant factors, 130 venture CEOs from the computer and communications equipment industries were asked to describe their venture's foreign market entry strategy through 17 questionnaire items on competitive method. Using factor analysis, the six determinant factors were categorized. To test the relationships between the foreign market entry strategy and factors such as ownership specific advantage, transaction cost, and location specific advantage, the data collected by questionnaire from 92 ventures. The main results of this research are as follows. First, the factors of ownership specific advantage have partially significant impact on the foreign market entry strategy of venture firms, Second, the factors of transaction cost have significant impact on their foreign market entry strategy. Third, the factors of location specific advantage have significant impact on their foreign market entry strategy. This study has produced evidence to demonstrate that the foreign market entry strategy profile of venture firms can be distinguished from those of relatively well-established firms. An expanded study would allow for stronger conclusions regarding the relative explanatory power of individual variables in the method. Additional research is also needed to examine other determinant variables connecting foreign market entry strategy.

• 한국항공운항학회지
• /
• 제21권4호
• /
• pp.71-76
• /
• 2013

This paper seeks to investigate the effect of technology readiness on the usage of smart entry service. The questionnaires were distributed to passengers who were experience with smart entry service and structural equation modeling was utilized to analyze the data. The results revealed that optimism had a positive impact on perceived usefulness and insecurity had a negative effect on perceived enjoyment. Perceived ease of use had a positive impact on perceived enjoyment, perceived usefulness and intention to use. In addition, perceived usefulness had a positive impact on intention to use. The results from this paper can be used as basic knowledge for developing the smart entry service activation plan.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 춘계학술대회논문집
• /
• pp.191-195
• /
• 2009

A parametric study for for the water entry of a two dimensional symmetric wedge with deadrise angle of 10 degrees was carried out to find out the most dominant parameter. Water entry problem with constant velocity is simplified as the stationary wedge in the way of the upcoming water surface. The calculated impact loads showed that the effect of the viscosity was not so important in this problem. For a given grid system a suitable time step size can be found. The most sensitive parameter was found to be the grid size.

• 한국군사과학기술학회지
• /
• 제20권4호
• /
• pp.467-473
• /
• 2017

In this paper, impact characteristics of a water entry gliding vehicle were analyzed using a finite element method. To guarantee the validity of analysis results, a convergence test was performed for several ratios of Euler and Largrange mesh sizes. The impact coefficient was calculated with respect to entry angles and angle of attacks. It can be observed that the impact coefficient was large at a high cross-section gradient and was also affected by cavitation. This study could be useful in the preliminary design stage of a water entry bomb development.

• 한국전산구조공학회논문집
• /
• 제15권1호
• /
• pp.1-8
• /
• 2002

물체가 수중에 입수할 때, 원래의 운동에너지는 물체와 그 주위의 물에 부가질량 형태로 분배된다. 이러한 에너지 혹은 운동량의 전달에 기인하여 물체는 유체동력학적 충격력과 가속도를 받는다. 이러한 충격거동은 수중운동체의 공중 발사에 중요한 고려 요인이 된다. 본 논문에서는 구명정 모델을 바탕으로 원통형 물체의 입수에 대한 충격거동을 해석하는 근사기법을 제안하였다. 충격력은 von Karman의 운동량 이론으로 계산하고, 운동, 특히 가속도는 유체동력학적 힘의 평형에 의하여 유도된 운동방정식의 수치 적분으로 계산하였다. 제안된 방법은 입수충격을 받는 물체의 초기설계나 운동 해석을 위한 단순하면서도 효과적인 방안이 될 수 있을 것으로 기대된다.